Belknap Crater and Little Belknap Crater Trail (Tr 4A.1)

This exceptional day hiking opportunity begins at the Pacific Crest Trail parking area at mile 15.8 (Map 4A.13).  The trail ascends the southern flank of the Belknap Crater shield volcano complex over stark terrain; raw, blocky, mafic lavas recently poured onto its slopes from Little Belknap Crater.  Much of it is on the well-maintained Pacific Crest Trail, although it’s out and back traverse over Little Belknap’s aa lavas does demand a good footing and attention to detail. It can be shortened or lengthened depending whether or not you include the summit cones of both Belknap Crater and Little Belknap Crater in your hike’s itinerary; a plan this author highly recommends, as few other locations in central Oregon offer as much unusual scenery or as many opportunities for geological observation for the effort.  In this one day hike, you can witness a fascinating variety of volcanic features close at hand, as well as take in superb panoramic views in all directions.  The excursion to the summit of Belknap Crater is a cross-country route that requires some map-reading and route-finding skill.  The round-trip distance of the hike is about six and a half miles if you climb both Belknap and Little Belknap summit cones.

Begin at the trailhead sign immediately to the northeast end of the parking area; the trail gets underway at the base of the southwesterly of two small, vegetated, Pleistocene cinder cones that form kipuka in lava flows from Little Belknap Crater just west of McKenzie Pass (Map 4A.13).  It climbs around the southeastern side of the cone, and at just over three tenths of a mile, quickly crosses an aa lava flow from Little Belknap Crater where it oozed downslope through a swale between the older cinder cones (Figure 4A.17).  You ascend rapidly around the western and northern base of the northeasterly kipuka, and at a little over seven tenths of a mile, climb onto the rough wilderness of lava flows from Little Belknap Crater near the position where lavas split and flowed around either flank of the cinder cone (Map 4A.14).

Figure 4A.17 - Little Belknap's lava flow copyrighted

Figure 4A.17.  The eastern margin of an aa lava flow from Little Belknap Crater, frozen in time where it flowed downslope through the small valley between two older cinder cones.  Belknap Crater and Little Belknap Crater form the highpoints to the left and right, respectively.

The surface of the lava is comprised of loose heaps of jagged-edged blocks, the characteristic trait of an aa flow.  These flows typically form when mafic lava with a slightly higher than average silica content and a slightly lower than average water (gas) content is extruded at the surface.  Cooling and congealing of the flow surface insulates the flow’s interior which continues to move; the viscous liquid lava then drags pieces of overlying solidified crust around with it, buckling it into pressure ridges here, tearing it apart and rafting along pieces there, eventually constructing the jumble of chunky plates you see today.  In about one tenth of a mile, you pass the first of several large “armored lava balls” perched among the blocky material at the surface of the lava flow to the right of the trail.  These probably formed in a snowball-like fashion as chunks of still hot, semi-solid lava broke loose from the flow and were rafted along at the surface.  As these blocks were rolled and tumbled within the flow, they accumulated mass as more lava and semi-solidified blocks were plastered to their exteriors in irregular layers.  Look for more as you climb.  At just short of one mile, the trail crosses a short section of slabby flow surface; careful observation reveals more slabs nearby.

After ascending through these flows for some distance (a total of one and a quarter miles from the trailhead), you encounter the first of several dead limber pine snags, this one growing up through a fracture in the lava to the right of the trail (Map 4A.14).  Walk the short distance over to it (watch your step) for a good look at a typical lava flow pressure ridge and squeeze-up (Figure 4A.18).  The pressure ridges form as the congealing surface of the lava flow cracks and buckles due to movement beneath within the still-hot, molten interior of the flow.  Squeeze-ups may occur where lava oozes upward through these cooling fractures and pours out onto the flow surface to solidify as tongue-like features.

Figure 4A.18 - Lava Squeeze Ups

Figure 4A.18.  Typical lava flow pressure ridges (A) and squeeze-ups (B) formed on the surface of the Little Belknap Crater Flow.

From this point, the trail continues its gradual climb upward through the aa lavas from Little Belknap Crater.  Look for several small, partially collapsed lava tubes at about one and seven-tenths and one and nine-tenths miles, as well as a prominent squeeze-up (on the right) and pressure ridge (on the left) at just over two miles.  At nearly two and two-tenths of a mile, a spur trail on the right leads to the summit cone of Little Belknap Crater and a well-preserved lava tube on its western flank (Map 4A.14).  Take the spur trail, this is a round-trip excursion of about half a mile that is well worth the effort, and it serves as a good turn-around point for your outing.

Shortly, to the left of the trail, you begin to encounter several intact segments of the lava tube that originates from a vent at the northwest base of Little Belknap’s summit cone (Figure 4A.19).  This lava tube likely formed during the final eruptive stage from Little Belknap because it was not subsequently buried by younger flows.  Refer to Field Trip 1C for a discussion of the basics of lava tube formation.  Take time to examine the smooth-walled interior of the second, larger section of tube, then continue toward the summit of Little Belknap Crater.  In about 150 feet, another section of tube occurs on the left; this section of tube can be walked into, but be observant, the tube ends abruptly at a 40 foot deep vertical shaft, the vent source for the lava tube, the preverbal throat of the dragon (Figure 4A.20).  Preservation of the tube and vent are superb, even a portion of the tube ceiling that was not quite roofed over (you can see the sides of the tube tilting inward and becoming thinner, then open air).  Now climb several hundred feet further to the top of Little Belknap’s summit cone.  Note the reddish lava bombs and agglutinate that form the volcanic breccia of the cone’s upper flanks, a result of oxidation from gases escaping during eruption of the lavas.  The summit affords excellent views highlighting High Cascades volcanism, including: 1) the cinder cones of Yapoah Crater on the ridge between North Sister and Black Crater to the southeast, Collier Cone further south on the same ridge, Four-in-One Cone in between and downslope to the west, and their lava flows and associated kipuka; 2) the composite volcanoes of North and Middle Sister, nicely framing Collier Glacier in their center; 3) the large cinder cones of Black Crater to the east and Black Butte to the northeast; 4) the highly glaciated remnants of the Mt. Washington composite volcano in the near distance to the north and the Three Fingered Jack  composite volcano further north, with the more youthful and much larger composite volcano of Mt. Jefferson still further north; and 5) Belknap Crater’s summit cone looms larger than life immediately to the west.

Figure 4A.19 - Little Belknap's Lava Tube copyrighted

Figure 4A.19.  Remnants of a lava tube formed on the northwest flank of Little Belknap Crater’s summit cone.

Figure 4A.20 - Little Belknap's vent copyrighted

Figure 4A.20.  The vent source for the lava tube formed on the northwest side of Little Belknap’s summit cone.

Return to the junction with the main trail.  Limited for time?  Turn left and return to the trailhead.  However, if time permits and you have the inclination, head right which takes you over more of Little Belknap’s lava flows and to the foot of Belknap Crater’s southern and largest cone (Map 4A.14).  Pressure ridges occur on the right side of the trail about 200 feet north of the junction, just past a rock cairn to the left side of the trail.  Observe these ridges upslope toward Little Belknap, and note the nice example of a large lava squeeze-up feature.  Continuing another two-tenths of a mile, the trail leaves the western edge of the Little Belknap Lava Flow and almost immediately to your left is a poorly defined trail that leads to Belknap Crater.  Remain on the main trail for now, you’ll return on this fainter spur trail after climbing Belknap Crater’s summit cone from a northwest approach.  The climb to the summit requires about a two mile hike cross-country over an often indistinct trail that eventually loops back to this location.

Shortly you’ll reach a point where the summit cone of Belknap Crater lies to the west at 9:00; turn left and head off-trail, walking upslope through patchy forest and cinder-covered ground (Map 4A.14).  The Pacific Crest Trail continues onward, but don’t follow it.  Head for the east face of Belknap’s summit cone; you will cross through a swale, and then break out of the patchy forest at the northwestern base of the main cone.   You should see trails curving southwestward up the steep southern flank of the summit cone, but ignore these for now (you will descend one of these on your way down from the top).

Belknap Crater is best ascended from its northeast flank; your trail (there really isn’t one at this point, but its fairly obvious where you’re going) winds its way around and up this side of Belknap Crater, this is a more gentle climb than those trails to the southwest, and there’s more to see.  Make for the dark basaltic ridge on the north flank of the volcano (Map 4A.14); once you reach the ridgeline, you should see a small spatter cone at the north end of the ridge with good examples of agglutinate lava “cow-pats” and lava blocks and bombs.  Scrambling around a bit, you can locate the nicely developed lava channel that poured down the southeast side of the spatter cone (Figure 4A.21), and climbing up onto the cone itself provides a nice view of Mt. Washington’s dissected form off to the northeast (Figure 4A.22). The forest fire scars on the slopes of Mt. Washington are part of the 90,000+ acre B & B Complex forest fire burned in the summer of 2003.  Looking south, North and Middle Sister can be seen in the distance  Nearer your position, you should recognize a distinctive divot carved into the east flank of Belknap Crater’s summit cone (Figure 3.4A.23).  This is an incipient cirque excavated by neoglacial activity since the summit cone formed, likely during the Little Ice Age.

Figure 4A.21 -  Belknap Crater lava flow copyrighted

Figure 4A.21.  A lava channel spills from the southeast side of a spatter cone perched on the northern flank of Belknap Crater’s summit cone in the foreground; while in the background, the haggard remnants of Mount Washington’s glaciated edifice perched on the Cascade Crest contrasts nicely with the nearly pristine, unglaciated symmetry of Black Butte.

Figure 4A.22 - Mt. Washington copyrighted

Figure 4A.22.  Much sculpted by glacial erosion, Mt. Washington’s summit cone is easily observed from a spatter cone on the north flank of Belknap Crater.

Figure 4A.23 - Incipient cirque on Belknap Crater copyrighted

Figure 4A.23.  Belknap Crater’s Little Ice Age incipient cirque

Now walk along the ridge to the southwest; several trails wind their way up the north flank of Belknap Crater to the lip of another, somewhat larger crater (Map 4A.14).  Once you reach this crater’s northern rim, hike around to the west and climb to the northwest rim of Belknap’s largest, southern crater.  As you can see, eruptions in the summit area were complex, resulting in at least three overlapping craters, each presumably associated with separate outpourings of lava now comprising the shield volcano’s flanks.  From here, you can readily ascend to the high point on Belknap Crater’s summit cone along a ridge separating its two main craters; a location just over four-tenths of a mile from the first spatter cone you encountered.  For expanded views, the summit ridge can be walked several hundred feet to a rock shelter at its northwest end.

The views from the summit of Belknap Crater are as fabulous as those from Little Belknap Crater, and are different enough to make the climb well worth your while.  From here, you can observe the landscape on the west side of the Cascade Crest much better.  Due north, Mt. Washington is in the foreground, Three Fingered Jack north of that, and Mt. Jefferson still further north and slightly to the east.  All three are typical Pleistocene stratovolcanoes of the High Cascades, although based on its size and preservation, Mt. Jefferson’s eruptions clearly occurred more recently and/or endured much longer.  Slightly to the northwest of Mt. Washington are Hayrick Butte and Hog Rock, distinctive, glaciated, flat-topped andesite domes.  Hoodoo Butte sits just west of Hayrick Butte.  This is a Pleistocene cinder cone with a summit crater showing limited signs of glaciation, so either it was protected from the brunt of glacial erosion by Hayrick Butte, or it erupted in the late Pleistocene and was affected only by the last major episode of glaciation.  Looking west and northwest to the lower slopes of Belknap Crater, an extensive cover of youthful lava flows can be seen flanking the volcano and spreading downslope, in some places reaching all the way to the upper McKenzie River valley.  Further to the northwest, Sand Mountain is visible as the tallest member of a chain of cinder cones that produced copious flows of basaltic lava that also reached into the upper McKenzie drainage (Figure 4A.11).

Although the broad shield of Belknap Volcano did not exist during Pleistocene glaciation, from its summit, one can see several prominent glaciated arms of the upper watershed of the McKenzie River that originate on the western slope of the Cascade Crest in the area.  Research by this author (Bevis et al., 2008) shows that these U-shaped valleys were occupied by major ice lobes that descended from Pleistocene ice caps that periodically covered the Cascade Crest (Figure 4A.7).  The long reach of the upper McKenzie itself can be seen trending south in the background beyond Sand Mountain and Scott Mountain before it swings almost due west.  On the south side of Scott Mountain, the valley of the White Branch of the McKenzie River can be observed to flow westward and join the upper McKenzie just beyond its right-hand bend.  Further to the southwest, the valley of Horse Creek cuts westward from the flanks of the Three Sisters, then bends sharply north before turning westward again along Foley Ridge, finally joining the McKenzie just west of the White Branch.  Foley Ridge is a classic example of inverted topography, formed where lava flows from the early development of the High Cascades occupied an ancestral drainage system only to become a resistant ridge as the younger McKenzie watershed became superimposed on the landscape (Taylor, 1981 and Priest et al., 1983).

The roughly straight-line path of the upper McKenzie is not purely by chance, instead its valley is controlled by a normal fault that forms the western edge of the High Cascades graben (Priest, 1983; Priest et at., 1983; Priest, 1990; and Taylor, 1990) (Figure 4.2 and Figure 4.3).  This fault continues under Foley Ridge to control the orientation of the north-trending middle section of Horse Creek’s valley.  Beyond the valleys of the upper McKenzie and Horse Creek, the highly crenulated fault escarpment is punctuated by several significant peaks from Echo Mountain to the northwest to Horsepasture Mountain in the southwest.  This ridgeline and the faulted river valleys mark the boundary between the High Cascades geologic providence of late Pliocene to Holocene volcanics, best exemplified by its youthful stratovolcanoes, and the Western Cascades geologic providence of Tertiary volcanics, well known for its deeply dissected terrain (Figure 4.1).

The western flanks of the Three Sisters volcanic platform are revealed to the south and southeast (Figure 4.2).  The massive composite volcanoes of North, Middle, and South Sister are on the skyline.  These peaks formed during the middle to late Pleistocene, and display a trend of decreasing age toward South Sister volcano.  They are comprised chiefly of basaltic andesite and basaltic lava flows, lesser pyroclastic deposits of the same composition, and scattered concentrations consisting of more intermediate andesitic and more silicic dacitic, rhyodacitic, and rhyolitic lavas and tephras (Taylor, 1968, 1981, and 1990).  North Sister was constructed on an older basaltic shield volcano base, beginning roughly 170,000 years ago.  Both Middle Sister and South Sister lack this foundation and are younger, volcanic eruptions at South Sister having begun as little as 93,000 years ago (Hill, 1992).  Each stratovolcano has been sculpted during several periods of Pleistocene and Holocene glaciation, this high elevation platform probably serving as the regional locus for development of the Cascade Crest ice cap at least twice during the late middle to late Pleistocene.  Today, Oregon’s largest surviving glacier, Collier Glacier, lies tucked in the saddle between North and Middle Sister and is the site of well-developed, Holocene, neoglacial moraines.

In the middle distance, on the northwest flank of the Three Sisters volcanic platform, multiple youthful lava flows can be observed, cinder cones marking their source vents.  A long ridge connects between North Sister and Black Crater Volcanoes.  This is a glaciated ridge of late Pleistocene basaltic andesite lavas consisting of multiple, small cinder cones comprised of cinders, scoria, and lava bombs formed along a 5-mile-long chain (Taylor, 1968 and 1981).  Two large Holocene cinder cones are superimposed on this ridge (Figure 4A.1); Yapoah Crater formed about 2,600 years ago, the closer of the two and lying slightly to the left (east), and Collier Cone formed about 1,500 years ago, more distant and nearer the base of North Sister volcano.  Vents at each location produced tremendous outpourings of basaltic andesite lavas; the Yapoah Crater lavas moved down the northwest flank of the ridge in several lobes which coalesced near McKenzie Pass and flowed northeast downslope adjacent to the route of Oregon Hwy 242, ultimately traveling for more the eight miles from the vent.  The lavas from Collier Cone spread outward in two lobes, one that flowed northwest from the ridge to pool and stall out in a large area near the cone of relatively low gradient, the other lobe poured off the ridge to the west and down the glaciated trough of the White Branch of the McKenzie River, reaching a distance over seven miles from the vent source.  Another interesting cinder cone complex, Four-in-One Cone, lies below and to the west of the ridge (Figure 4A.1), sandwiched between the lava flows from Yapoah Crater and Collier Cone.  This unique ridge cone, part of a north-south alignment of nineteen vents, is breached in four locations on its northwest, downslope-facing flank.  The composite cone erupted andesitic lavas about 1,900 years ago (Sherrod et al., 2004), generating two flow lobes that generally wrap around the northeast and southwest sides of a ridge punctuated by Condon Butte.  The southwestern lobe is in contact with Collier Cone’s more northerly lava flow.

Finally, look to the east.  In the foreground, on the southeast flank of Belknap Crater lies Little Belknap Crater, marking a major subsidiary vent of the Belknap Crater complex that generated substantial lava flows and built its own shield (Figure 4A.1 and Figure 4A.24).  Careful observation reveals a ribbon-like trail descending westward from Little Belknap’s summit cone, the lava tube you visited earlier.  In the middle distance, Black Crater lies nearer your position and slightly to the southeast, while Black Butte lies further away to the northeast.  Both volcanoes are atypically large cinder cones (or small, steep shield volcanoes) erupted during the Pleistocene (Figure 4.2).  Black Crater is generally composed of basaltic andesite tephra and near-vent scoria and lava blocks and bombs, whereas Black Butte is built of similar material, but is of more basaltic composition.  Black Crater rests nearer the Cascade Crest and was subjected to more substantial glacial erosion as evidenced by the well-developed cirques on its east and northeast flanks.  Black Butte cinder cone was erupted at the southern end of Green Ridge, along a normal fault that bounds the eastern edge of the central Oregon High Cascades graben (Smith and Priest; 1983; Taylor, 1990; and Smith, 1991) (Figure 4.2 and 4.3).  Green Ridge’s steep west-facing, north-south trending fault escarpment can be seen behind and to the north of Black Butte.  The well-defined symmetry of this volcano is related to its youthful age and its position off the Cascade Crest where it was not influenced by glaciation as most other large volcanoes in the Cascade Range.  Cache Mountain lies to the northeast between Black Butte and Mt. Washington.  This prominent ridge is a remnant of the early Pleistocene High Cascades basaltic andesite platform.  Lateral moraines wrapping around its flanks show that it formed a divide between ice lobes emanating from the ice cap covering the Cascade Crest to the west, but the eastern portion of the ridge was itself not glaciated.

Figure 4A.24 - Black Crater & Little Belknap  copyrighted

Figure 4A.24.  Little Belknap Crater marks a major subsidiary vent of the Belknap Crater volcanic complex that generated substantial lava flows and built its own shield; Black Crater’s massive cinder cone lies in the background.

When you feel that you have absorbed as much as you are able of this boundless volcanic display, walk the eastern rim of Belknap Crater’s main vent around to its southern side (Map 4A.14).  Before descending, take in a good view of inner walls of the vent where an interesting stratigraphy of pyroclastic materials is exposed (Figure 4A.25).  Now descend the obvious trail down the steep southern flank of Belknap Crater’s cone; it’s a short distance of a bit over half a mile back to the main trail from whence you left it.  When you reach the cone’s base, head due east.  If you happen to hit the edge of the lava flow before you cross the trail, head east along the flow margin until you find the trail.  If you cross the trail upslope to the north of the lava flow, head back southward on the trail until you find the lava flow.  From here, follow the trail roughly three miles back to the trailhead and your vehicle.

Figure 4A.25 -Belknap Crater summit vent copyrighted

Figure 4A.25.  Alternating layers of agglutinate spatter (more indurated cliff-forming layers) and scoriaceous cinders exposed on the inner walls of Belknap Crater’s main vent; Scott Mountain lies in the background to the left.

Black Crater Trail (Tr 4A.2)

This day hike is a personal favorite and begins at a parking area at mile 12.4 (Map 4A.13).  Begin at the trailhead sign immediately to your right at the upslope end of the parking area.  The Black Crater Trail is steep and fairly relentless, gaining 2500 feet in elevation, but it is relatively short (about seven miles round-trip), and does offer wonderful views of many of central Oregon’s volcanic landforms.  If you had to choose between Black Butte’s shorter, more gradual hike, but arduous drive to reach the trailhead, and Black Crater’s longer, steeper trail, but very accessible trailhead, this author would have you come here.  The views from the summit are better (and closer to the volcanic action).  In fact, the Three Sisters stratovolcanoes, the Belknap Crater shield volcano complex, as well as Yapoah Crater and Collier Cone seem almost close enough to touch.  Bring a lunch to enjoy at the top while you bask in the stupendous views.

The trail heads upslope through a diseased and dying stand of lodgepole pine, not very sightly.  Shortly, the trail passes a frost-shattered, bouldery slope of basaltic andesite on the right, the upslope extension of the rib of rock exposed at Windy Point.  After numerous switchbacks and an uphill climb, you cross a low ridge and into a small basin at about two miles (Map 4A.15), a left-lateral moraine on the lower northeast side of the late Pleistocene cirque carved into Black Crater’s northeast flank.  Not much of the terrain is visible, however, due to the tree covered slopes.  In about four tenths of a mile, you cross out of the cirque by first ascending a right-lateral moraine crest and then up a steep slope above the moraine.  The moraines you just crossed terminate just beyond the cirque and are likely recessional in nature, associated with a short still-stand of ice under overall late Pleistocene deglaciation.

At roughly two and three-quarters miles, the trees thin out and at a switchback in the trail you can peer to the left into the upper part of the cirque cut deeply into Black Crater’s eastern slope (Map 4A.15).  Sisters, OR and Black Butte come into view to the east as you ascend this more open slope covered in gnarled krummholz (German for “crooked wood”) trees.  These are mostly whitebark pine which grow only at higher elevations, generally above 6000 feet, and seem to have occupied a weather-blasted nitch that no other “sane” trees would want.  Unfortunately, the ravages of climate change are making their mark, as many of the whitebark pine in the Cascades is succumbing to disease and pest species that the warming temperatures bring.  Another four tenths of a mile the slope levels out substantially and you walk onto the outer crest of Black Crater’s summit cone.  Walk to the right across this broad, cinder-strewn area and to the edge of a steep slope that drops into the upper end of the cirque basin you passed through on the climb up, a wonderful array of volcanic peaks is displayed to the north.  The late Holocene vents and lava flows erupted just north of McKenzie Pass (Figure 4A.1) are outstandingly displayed.  Keep heading west on the trail, the summit is only about 600 feet away and the views just get better (Map 4A.15).

When you reach the summit of Black Crater, find a convenient perch on the highpoint of the crater’s rim and take in the stellar views.  There are few places more ideally situated and with such easy access to observe the plethora of volcanic features that the McKenzie Pass area has to offer.  Let’s begin the tour to the north and work our way around, briefly examining many of the more prominent volcanic and glacial landforms seen from here.  Try to imagine Mauna Loa Volcano in the Hawaiian Islands, its massive, broadly shield-like shape and layer-cake of mafic lava flows, a textbook example of a shield volcano.  Here too, we have Belknap Crater and its subsidiary cone Little Belknap Crater just to the northwest that provide good examples of a shield volcano, albeit a small one (Figure 4A.26).  In the distance, almost due north of your position is Mt. Jefferson.  Mt. Jefferson is a classic Pleistocene composite or stratovolcano of the Oregon High Cascades.  Composite volcanoes are volumetrically smaller than shield volcanoes, with generally cylindrical shapes and steep slopes, and comprised of interlayered intermediate lava flows and pyroclastic deposits.  Northwest of Mt. Jefferson, in the nearer distance lies Three Fingered Jack and to the fore of that peak lies Mt. Washington (Figure 4A.26).  Both are highly glaciated remnants of substantial, basaltic andesite stratovolcanoes erupted in the Pleistocene.  The exposed central volcanic neck and flanking dike swarms are exposed in their summit cones, each peak having endured considerable glacial sculpting related to their older age and position on the periodically ice-cap-covered Cascade Crest.  Slightly northeast of here in the middle distance is Suttle Lake, dammed by an end moraine complex of the late Pleistocene glacial maximum.  These moraines are the type locality of the Suttle Lake advance of the Cabot Creek glaciation (Scott, 1977) which produced an ice cap covering much of the Cascade Crest visible from here about 20,000 years ago.  Cache Mountain lies just west of Suttle Lake.  This prominent ridge is a remnant of the early Pleistocene High Cascades basaltic andesite platform that served as a divide between ice lobes emanating from the ice cap covering the Cascade Crest to the west, but the eastern portion of the ridge itself was not glaciated.

Figure 4A.26 - View northwest from Black Crater copyrighted

Figure 4A.26.  A view to the northwest from Black Crater’s northern rim; there is no better location to observe the major late Holocene vents of Belknap Crater and Little Belknap Crater and their associated lava flows.  The highly dissected summit cones of Mt. Washington and Three Fingered Jack form the peaks in the middle and further distances.

In the foreground to the west lies the massive compound shield volcano of Belknap Crater (Figure 4A.1 and Figure 4A.26).  The summit cone of Little Belknap Crater’s subsidiary shield is just downslope to the east, and South Belknap Cone, a small, breached cinder cone lies surrounded by younger lavas mid-way up Belknap Crater’s southern flank.  This area was the nexus for a long, complex period of Holocene basaltic andesite and basaltic volcanism that erupted nearly continuously from about 3,000 to 1,500 years ago, building a voluminous complex shield volcano on the Cascade Crest (Taylor, 1968 and 1981).  Initially, basaltic lavas flowed from Belknap Crater’s main vent downslope nearly seven miles to the east.  About 1,800 years ago, South Belknap Cone formed; and later, about 1,500 years ago, a major pulse of volcanism produced basaltic andesite that issued from vents on the north and south flanks of Belknap Crater, near the base of the summit cone.  These lavas flowed mainly downslope to the northwest as much as twelve miles from their source, even reaching the glaciated valley of the upper McKenzie River and disrupting its drainage.  A smaller flow lobe moved southwest into the upper end of Lake Valley on the west side of Scott Mountain, surrounding South Belknap Cone in the process.  Belknap Crater’s summit actually contains two main vent craters and a third small crater.  The northeast face of the largest, southern cone shows signs of an incipient glacially-carved cirque, a product of late Holocene neoglaciation, perhaps even the Little Ice Age.  Little Belknap Crater erupted about 2,900 years ago over a major subsidiary vent on Belknap Crater’s southeast flank, extruding substantial overlapping flow lobes of basaltic andesite that resulted in the formation of a shield volcano.

Slightly to the southwest of Belknap lies Scott Mountain, a small late Pleistocene summit cone perched on a somewhat older, broad shield volcano base.  The more subdued Condon Butte lies due south of Belknap Crater, a cinder cone formed on the back of a glaciated ridge of early Pleistocene basaltic andesite.  Sims Butte, a late Pleistocene to early Holocene cinder cone breached on the west side, occurs just beyond Condon Butte.  Finally, several kipuka can be observed near McKenzie Pass where young lava flows have surrounded high ground related to slightly older volcanic vents.  Three small islands occur just north of Hwy 242, where younger lavas from Little Belknap Crater flowed around small, basaltic andesite volcanoes; and several small to large islands occur within the Yapoah Lava Flow south of the highway under similar circumstances.

Looking to the west into the McKenzie Pass area, one can only be awed by the copious, recent outpourings of lava that literally cascade down North Sister’s northern flank (Figure 4A.1).  You have only to look at the many kipuka on the slopes west of Black Crater to imagine the hot, sticky stuff oozing from multiple vents, seeking the paths of least resistance in older stream valleys, and surrounding intervening ridge tops.  Immediately to the southwest, you can observe a long ridge running slightly southwest that connects Black Crater to North Sister (Figure 4A.27).  This glaciated ridge of late Pleistocene basaltic andesite lavas consists of multiple, small cinder cones formed along a 5-mile-long chain (Taylor, 1968 and 1981).  These cones are comprised of cinders, scoria, and unusually large and abundant lava blocks and bombs.  Two large Holocene cinder cones are superimposed on this ridge (Figure 4A.27); Yapoah Crater lies slightly to the right (northwest) and is nearer to this position, while Collier Cone is more to the left (southeast) nearer the base of North Sister.  Vents at each location produced incredible outpourings of basaltic andesite lavas.  The Yapoah Crater lavas erupted between 2,900 and 2,600 years ago (Taylor, 1968 and 1981) and moved down the northwest flank of the ridge in several lobes which coalesced at McKenzie Pass and flowed northeast down the glaciated trench that wraps around the western base of Black Crater, adjacent to the route of Oregon Hwy 242, reaching more the eight miles from the vent.  The lavas from Collier Cone, erupted about 1,500 years ago (Sherrod et al., 2004) are less visible from here, but spread outward in two lobes, one that flowed northwest from the ridge to pool and stall out in a large area near the cone of relatively low gradient, the other lobe poured off the ridge to the west and down the glaciated trough of the White Branch of the McKenzie River, reaching a distance over seven miles from the vent source.  Four-in-One Cone, part of a north-south alignment of nineteen vents, lies below and to the west of the ridge and is sandwiched between the lava flows from Yapoah Crater and Collier Cone.  This is a unique ridge cone, breached in four locations on its northwest, downslope-facing flank.  The cone complex erupted andesitic lavas about 1,900 years ago (Sherrod et al., 2004), generating two flow lobes that generally wrap around the northeast and southwest sides of a ridge punctuated by Condon Butte.  The southwestern lobe is in contact with Collier Cone’s more northerly lava flow.

Figure 4A.27 - North Sister and late Holocene volcanics copyrighted

Figure 4A.27.  The looming mass of North Sister Volcano seems to lie a mere stone’s throw from Black Crater’s summit, its northern flank coated in ribbons of basaltic lava originating from several major late Holocene vents, Collier Cone Four-In-One Cone, and Yapoah Crater.

Immediately in the foreground, you can see the well-developed cirque gouged into Black Crater’s northeast face; although not so easy to see from here is the cirque carved at a lower position on its east flank.  Just to the southeast of Black Crater is Trout Creek Butte, an older Pleistocene, basaltic-andesite shield volcano.  In the distance to the south and southwest, lie the Whychus Creek watershed and the major stratovolcanoes of the Three Sisters and Broken Top.    These peaks formed during the Pleistocene, and display a trend of decreasing age from north to south and east to west toward South Sister volcano; eruptions may have begun about 170,000 years ago and 93,000 years ago at North Sister and South Sister, respectively (Hill, 1992; and Taylor, 1968, 1981, and 1990).  They are comprised chiefly of basaltic andesite and basaltic lava flows, lesser pyroclastic deposits of the same composition, and scattered concentrations consisting of more intermediate andesitic and more silicic dacitic, rhyodacitic, and rhyolitic lavas and tephras.  Each has been sculpted during several periods of Pleistocene and Holocene glaciation, readily exhibited by the large, compound cirque basin at the head of the Whychus Creek drainage and the multitude of smaller, accentuated cirques higher on the flanks of the mountains.  The entire basin from the southern flank of Black Crater to Tam McArthur Rim east of Broken Top was occupied by an ice lobe the flowed northeast from the ice cap that covered much of the Cascade Crest during the late Pleistocene last glacial maximum, the Suttle Lake advance of the Cabot Creek glaciation (Bevis, et al., 2011).  The ice lobe retreated slightly to stabilize as separate lobes in the valleys of Trout Creek and Whychus Creek.  The glaciated valley of Trout Creek heads on North Sister and the ridge connecting to Black Crater and cuts between Black Crater and Trout Creek Butte; a well-developed end moraine complex is visible on the southeast side of the valley wrapping around the western flank of Trout Creek Butte.  The major U-shaped valley of Whychus Creek coalesces from several tributaries draining the compound cirque from North Sister all the way around to Tam McArthur Rim and is enclosed by impressive lateral moraines southeast of Trout Creek Butte.

      After you have sufficiently enjoyed your eagle’s Eyre, return the way you came to the Black Crater Trailhead and parking area.

Lava River Trail (Tr 4A.3)

This brief excursion can be found at mile 15.3 (Map 4A.13), adjacent to the Dee Wright Observatory near McKenzie Pass.  The trail leads across the main channel of the Yapoah Crater Flow just east of the observatory and presents the visitor with good opportunities to observe flow features related to an aa lava flow.  This flow was erupted from Yapoah Crater about 2600 years ago (Taylor, 1968 and 1981).  The trail is short, paved, family-friendly, and has interpretive signage to serve as a guide to some of the more significant features.

Begin at the trailhead sign at the east end of the Dee Wright Observatory parking area at the edge of the Yapoah Lava Flow.  Notice the angular blocks that make up the rubbly surface of this basaltic andesite aa lava flow.  The trail leads across the main channel of the lava flow and an elongated section of collapsed lava tube to the imposing levee on its eastern side (Figure 4A.28). As the supply of lava to the gutter system diminished, the molten interior drained away and the channel surface subsided.  Large segments of the levee tipped toward the central gutter because they lacked the support of the once lava-filled channel, opening deep, irregular tension fractures parallel to the crest of the levee.  When the channel was filled, lava occasionally poured over and/or breached the levee to form tongues against its eastern base.  The trail climbs to a high point on the levee where just such a breach and outpouring occurred, with excellent views of the congealed lavas that once flowed as glowing rivers down from fiery vents at Yapoah Crater and Little Belknap Crater.  Then it proceeds through the cracked levee showing internal cooling fractures and columnar jointing.  As you walk, try to imagine the channel in the full fury of a lava flood, roaring along and randomly splashing against and spilling over the gutter’s levees; eventually the lava subsides, congeals, and contracts to leave flow features much as you see them today.

Figure 4A.28 - Lava River Trail copyrighted

Figure 4A.28.  The massive inner wall of the lava levee formed on the east side of the main gutter system feeding the Yapoah Crater Flow.

Obsidian and Scott Loop Trail (Tr 4A.4)

      This superlative loop hike begins at the north end of the parking area at the end of the access road for old Frog Camp Campground at mile 21.8 (Map 4A.16), now the Obsidian Trailhead.  This combination of the Obsidian, Scott, and part of the Pacific Crest trails is over 15 miles in length and provides access to some of the most exceptional country in the Oregon High Cascades.  The main backpacking loop is on well-maintained trails, but additional day-hiking treks require some off-the-established-trails route finding and glacier climbing, portions of which are rather strenuous and potentially dangerous, and advised against for those not in good physical condition or poorly skilled in backcountry hiking and camping.  The loop hike could be done as a no-frills, somewhat grueling, one-day stomp, but if your intent is to see and enjoy the geological features of this marvelous area, take more time.  The primary goal of the loop hike described here is to experience the immensely diverse geology in the vicinity of North and Middle Sister stratovolcanoes first hand; including ample opportunities to explore recent and ongoing glaciation, youthful basaltic cinder cones and lava flows, and the anatomy of a stratovolcano as exposed on its glaciated flanks.  To complete all of the connected day-hiking options, a multi-day backpacking trip is in order, and thus, the description offered here is written as a four day excursion.  As a note of precaution, the Glacier Creek area, a base of operations central to this trip, is extremely popular and heavily utilized by day- hikers, backpackers, and climbers, so try to avoid this area on weekends in mid-summer to early fall, and please follow leave-no-trace camping etiquette.  Be aware that the Willamette National Forest requires that anyone camping in this area carry a backcountry permit (which can be obtained free of charge at the McKenzie Bridge Ranger Station in McKenzie Bridge, OR).

Day One

Head north from the trailhead, a brief walk brings you to a “T” intersection (Map 4A.16).  Turn right onto the Obsidian Trail (the left fork is a connector trail to the Scott Trail which you’ll return on in a few days).  The trail rapidly climbs out of Lake Valley and onto the glaciated Three Sisters volcanic platform.  Occasional rock outcrops, some striated by passage of glaciers, are in older Pleistocene basaltic andesite, part of the mafic shield volcano that forms the foundation for North Sister’s younger composite volcano (Taylor, 1968 and 1981; Taylor et al., 1987).  At about eight-tenths of a mile, a faint spur trail on the right descends to Spring Lake, nestled between the margin of the late Holocene Collier Cone Lava Flow and Sims Butte, a late Pleistocene to early Holocene cinder cone.

After about one and three-quarter miles (Map 4A.16), all of it steady uphill hiking, the trail begins to skirt the northern edge of the basaltic andesite aa lava flow from Collier Cone, erupted about 1,500 years ago (Sherrod et al., 2004).  The flow followed the older glaciated stream valley of the White Branch of the McKenzie River and fills it nearly rim to rim.  In another mile, following a brief jog away from the Collier Cone lavas, the trail abruptly swings back and then crosses the rubbly flow at a narrow constriction in the valley (Map 4A.17).  As you traverse the flow, note the steep-sided lava levees that have formed along the lava flow’s margins, the deflated interior of the flow, and jagged nature of the flow surface.  Great views of North and Middle Sister Volcanoes briefly open up from the crest of the left-lateral flow levee, and the older silicic volcanic rock of the Obsidian Cliffs can be seen exposed in the north wall of White Branch’s valley just to the south of the flow.

Once across the Collier Cone Lava Flow, roughly half a mile beyond your initial climb onto its bouldery margin, the trail quickly crosses the White Branch of the McKenzie River just below its confluence with Glacier Creek.  Look downstream, the margin of the basaltic Collier Cone Flow contrasts nicely with the rhyolitic Obsidian Cliffs in the background to the left (Figure 4A.29).  Above the confluence, the White Branch is usually dry except during spring snowmelt.  The source of this stream was originally meltwater from Collier Glacier.  A recent glacial outburst flood poured down this drainage, released when the small proglacial lake trapped within a bowl formed by its Little Ice Age end moraine overtopped the moraine and caused rapid downcutting of the unconsolidated material.  The stream channel is littered with coarse, bouldery debris from this flood.  A trail junction appears just beyond the White Branch crossing (Map 4A.17).  The right fork continues to follow the Obsidian Trail, but for now, take the Glacier Way Trail to the left.  This trail ascends perennial Glacier Creek (a sweaty, uphill climb with a backpack) for a bit over half a mile to an intersection with the Pacific Crest Trail (PCT) and faster access to good camping.

Figure 4A.29 - Glacier Creek copyrighted

Figure 4A.29.  A view down the valley of White Branch Creek at its confluence with Glacier Creek; notice the light-colored, rhyolitic Obsidian Cliffs in the background to the left and the darker, valley filling basaltic lavas of the Collier Cone Flow in the foreground to the right.

If you plan to stay in the Glacier Creek area to enjoy some day-hiking options, you’ll want to find a campsite; otherwise head east on the PCT to continue hiking the Obsidian and Scott Loop Trail.  Note this junction, because you’ll return this way more than once; but for now, follow the well-established climber’s route from the junction as it continues upstream along the valley of Glacier Creek (Map 4A.17 and Map 4A.18).  The fine meadows in this area provide popular camping sites, so claim yours early.  A hike up this stream valley should provide several good options within half a mile, and since it parallels the PCT on the ridge just to the west, it’s a relatively simple matter to reconnect with that trail at the valley’s upper end for more camping options on the ridge above Obsidian Falls.

When you are settled in, leave your packs behind for an afternoon day-hike to the Obsidian Cliffs and Obsidian Falls.  First, reconnect with the Glacier Way Trail at its junction with the PCT.  Head back downstream on the Glacier Way Trail, and at the intersection near White Branch Creek, take the Obsidian Trail to the left (Map 4A.17).  In half a mile, the trail climbs to the top of a broad, table-like ridge comprised of resistant, Pleistocene rhyolitic lavas; look for outcrops of obsidian near the trail for the next several hundred feet.  This area is comprised of normally polarized, rhyodacite and dacite lavas erupted less than 700,000 years ago from vents scattered around Middle Sister, South Sister, and Broken Top volcanoes (Taylor et al., 1987). Continue on the Obsidian Trail for about three-tenths of a mile; you’ll pass a clearing with a gorgeous view of Middle Sister, another short stretch of trees, and then enter a larger clearing strewn with obsidian fragments.  Leave the trail here and head west-northwest, remaining upslope of a shallow, usually dry drainage on your left (Map 4A.17).  You should pass a small pond (dry in some years) on your left in roughly half a mile, then turn right and continue almost due north, remaining out of the trees as much as possible.  In a little over two-tenths of a mile, after crossing a low ridge and a swale, you arrive at the edge of the Obsidian Cliffs (Map 4A.17).  Continue walking west-southwest near the cliffs; the views of the White Branch drainage and the Collier Cone Lava Flow are excellent (Figure 4A.30).  The lava flow’s main gutter system can be seen directly below, with its rubbly surface, dual levees, and a deflated interior which exhibits wave-like ridges that curve downstream in the direction that the lava flowed.

Figure 4A.30 - Collier Cone lava flow

Figure 4A.30.  Views to the northeast (A) and west (B) from the Obsidian Cliffs; (A) shows 1,500 year old Collier Cone in the background on the right, with its aa lava flow snaking to the left and down slope into the foreground as it follows the course of the White Branch; while (B) shows the Collier Cone Flow as in pours westward down the White Branch and past Sims Butte.

From this general location, simply keep the cliffs on your right as you circumnavigate the outer rim of the tableland and take in more superlative views (Map 4A.17).  Be on the lookout for telltail outcrops of obsidian, the namesake of these cliffs (Figure 4A.31).  The south side of the ridge offers scenic vistas of Middle and South Sister, as well as glacially striated outcrops of obsidian near at hand.  In about one and two-tenths of a mile, you should see that small pond off to your left (you are on its opposite side now), and from here it’s a simple matter to head east and reconnect with the Obsidian Trail.  Eventually, with nearly two miles of travel under your belt, you will have completed your circuit of the table-like ridge and arrived back at the Obsidian Trail in nearly the same place you left it.

Figure 4A.31 - Obsidian outcrop along Obsidian Cliffs copyrighted

Figure 4A.31.  The western edge of the Obsidian Cliffs; an outcrop of obsidian lies at the base of the photograph, the namesake silicic rock type exposed along these cliffs (that’s Mt. Washington in the distance at the top of the photo).

Now continue to the right (south) on the Obsidian Trail, there is certainly more to see.  The trail crosses a low, resistant ridge of silicic rock bordering the southern edge of the tableland and drops into a beautiful meadow harboring Obsidian Creek.  The Obsidian Trail then climbs a glacially sculpted ridge and in about half a mile, it reaches the Richard Ward Montague Memorial just off to the right.  An unusually smooth outcrop of volcanic breccia and excellent glacial striations preserved on basaltic andesite can be found near the memorial.

Another half mile brings you to the end of the Obsidian Trail at a juncture with the PCT (Map 4A.17).  Turn left here, in about 600 feet, a short spur trail on the left takes you to a view of pretty Obsidian Falls which cascades downward across an outcrop of rock by the same name (Figure 4A.32).  A short climb of about two-tenths of a mile from the trail junction brings you to the top of the ridge overlooking Obsidian Falls; and in several hundred feet, you pass Sister Spring (the source of Obsidian Creek’s perennial flow) issuing from the base of a sheer cliff of dacite.  Presumably, the spring formed at the contact between the dacitic and rhyolitic lava flows.  About three-quarters of a mile from the trail junction brings you to a climber’s trail on the right side of the PCT.  Take this spur trail back into the upper valley of Glacier Creek and to your campsite.  If you miss the climber’s trail, don’t be alarmed, as you will shortly find yourself at the familiar junction of the PCT and Glacier Way Trail; from there, you can connect with the climber’s trail at its lower end.  On your return downvalley, note the dark gray silicic volcanic rock outcropping in the cliff near the valley’s upper end (Figure 4A.33); Middle Sister lurks just to the right in the distance.

Figure 4A.32 - Obsidian Falls copyrighted

Figure 4A.32.  Obsidian Falls rushes over an outcrop of resistant, silicic bedrock.

Figure 4A.33 - Glacier Creek copyrighted

Figure 4A.33.  The upper end of the valley of Glacier Creek.  The glacially sculpted cliff on the right is a dacitic lava flow passed on your hikes to and from your campsite (the summit of Middle Sister Volcano lies veiled by clouds in this photo).

Day Two

Remain camping along Glacier Creek, today is your day to climb to the summit of Middle Sister Volcano, an arduous hike that requires more than 3000 feet of elevation gain over steep terrain that is often rocky, and sometimes snow or ice covered.  No technical gear is required, but do watch your footing.  Begin by hiking up the climber’s trail toward the head of Glacier Creek.  To begin your ascent, cross Glacier Creek at an obvious ford used by climbers (Map 4A.18); then head straight up the narrow valley on a well-used climber’s route that keeps the ice-sculpted, dacitic cliff first seen yesterday to your right.  Eventually, the valley broadens out onto a northwest-facing slope; continue upward toward the perennial snowfields ahead.  In about three-quarters of a mile from the stream crossing, the trail begins climbing in earnest after passing a boulder-choked dry snowmelt channel recently occupied by a debris-flow.  Notice the well-preserved bouldery debris-flow levees to either side of the channel (Figure 4A.34).

Figure 4A.34 - Debris Flow copyrighted

Figure 4A.34.  A small snowmelt channel above Glacier Creek recently occupied by a debris flow; note the well-preserved debris-flow levees to either side of the channel.

As you climb, navigate around the snowfields as best you can, in certain places they really can’t be avoided so be careful of firm footing as you go (crampons and an ice axe would help, but are not necessary and even burdensome if you simply practice patience and care as you step).  At about one and three-quarters of a mile, you arrive at a low point in a ridge that serves as a wonderful vantage point to survey your progress (Map 4A.18).  Black Finn, comprised of resistant Pleistocene dacite recently polished by glaciation forms the end of the ridge.  Just to the right of the ridge is a perennial snowbank, once part of Collier Glacier, from which a marvelous view to the north unfolds (Figure 4A.35).  Displayed in the middleground is the recently deglaciated valley below Collier Glacier, both well-preserved lateral moraines can be clearly observed, as well as a small proglacial lake at its northern end resting against the base of Collier Cone.  Collier Cone occupies the far end of the valley beyond the lake; and the reddish peak to the far left is Little Brother, while Black Crater and Black Butte occur to the far right.  In the background, the stratovolcanoes of Mount Washington, Three Fingered Jack, Mount Jefferson, and Mount Hood march to the north, forming the backbone of the Oregon High Cascades.   Looking west, the characteristically U-shaped glacial trough of the White Branch can be followed to its confluence with the McKenzie River, the highly dissected Western Cascades beyond; and the landmarks along the route taken to reach this perch, Sims Butte, the Collier Cone Lava Flow, and Glacier Creek’s valley, can all be readily observed.  Take time to enjoy this spot; it is truly one of the greats in all of the Oregon Cascades and it makes for a pleasant day-hiking goal if you’re unsure of the multiple snowfield crossings ahead.

Figure 4A.35 - Collier Glacier copyrighted

Figure 4A.35.  The view northward from a bedrock ridge on Middle Sisters’ northwest flank; Collier Cone and the recently deglaciated valley below the remnants of Collier Glacier are spectacularly displayed in the middle distance below the snow field, and beyond, several major stratovolcanoes of the Oregon High Cascades.

Climb southwest, up a perennial snowbank west of the bedrock ridge, and when the gradient lessens, cross to the left and onto the ridge, keeping the western margin of Collier Glacier on your immediate left (Map 4A.18).  You’ll cross a snowfield and then onto a second rocky ridge.  The bedrock exposed along the ridgeline exhibits very fresh glacial polish and striations, owing to its recent deglaciation (Figure 4A.36).  North Sister’s highly eroded western flank lies beyond Collier Glacier to the east of your position; note the mafic dikes criss-crossing through brecciated vent deposits and pyroclastic material exposed to view (Figure 4A.37).  When you reach a second snowfield (actually a remnant of glacial ice) in about seven-tenths of a mile from the first Collier Glacier viewpoint, begin traversing to the right across snow-covered glacier as you continue to ascend (thus avoiding the frost-shattered bedrock exposed to the left – tough climbing).  Don’t go too far to the right, too quickly, where the slope is steep; in about six-tenths of a mile you cross onto solid ground (well, at least volcanic debris) for the duration of the climb.  Eventually, you reach a platform just above a distinctive saddle between Middle Sister’s summit cone before you, and Prouty Point’s rocky knob off to your left.  This is a col; the ridgeline here forms a nexus of headward erosion between Collier Glacier (to the north), Hayden Glacier (to the east), and Renfrew Glacier (to the west).  These glaciers have suffered substantial retreat in recent decades as a result of global warming.  Renfrew Glacier, with its greater exposure to the sun, may be little more than glorified perennial snowfields at this time.

Figure 4A.36 - Glacial Striations copyrighted

Figure 4A.36.  Basaltic andesite striated and polished by the passage of glacial ice on a recently deglaciated bedrock ridge along the western margin of Collier Glacier.  The pencil indicates ice flow direction.

Figure 4A.37 - North Sister's west face copyrighted

Figure 4A.37.  Basaltic dikes intruding pyroclastic material exposed in North Sister’s glacially eroded western flank; Collier Glacier lies to the lower left edge of the photograph.

Before your final ascent, consider heading east the short distance to Prouty Point (Map 4A.18).  From there, the extra effort is paid off with a fabulous view to the east and southeast of the glaciated headwaters of Whychus Creek, with Hayden and Diller Glaciers clinging to the upper slopes of Middle Sister.  To the south, the eastern face of Middle Sister, sheared-off by glacial erosion is spectacularly exposed.  Mafic dikes injected upward through thin lavas, near vent volcanic breccias, and pyroclastic deposits are well expressed (Figure 4A.38).  The interlayered volcanic deposits can be seen to slope back and away from the central axis of the volcano’s summit cone vent, indicating the depth of glacial gouging.  The exceptional view of Hayden Glacier from here offers a great opportunity to observe crevasses in the central portion of the ice mass where the ice surface slope is fairly steep.  These curvilinear fractures develop in the upper layer of ice, which is generally under less pressure and is therefore more brittle.  As the glacier moves downslope, the surface layer breaks up, forming deep cracks perpendicular to ice flow.  If you examine the glacier’s surface from terminus to headwall carefully, you may notice that the lower part of the glacier is generally bare and dirty ice, while the upper glacier is still covered in snow.  Your view has passed the glacier’s equilibrium-line altitude (ELA), the elevation on the glacier’s surface where the amount of summer melting (of snow and ice) is equal to the amount of winter accumulation (snowfall, wind-drifted snow, and avalanched snow).  On healthy, mid-latitude glaciers, roughly 35% of the glacier’s surface lies below the ELA, and 65% lies above.  Therefore, the position of the ELA at the end of the summer melt season can be used as a proxy for measuring the glacier’s health, higher ELA’s (roughly more than 35% of the glacier’s surface) translate into unhealthy glaciers; many of the ELAs on glaciers in the Oregon Cascades have been above that position for much of the last 25 years, hence they are in retreat.

Figure 4A.38 - Middle Sister's east face copyrighted

Figure 4A.38.  The eastern face of Middle Sister Volcano, severely eroded by the Hayden Glacier, exposes vertically oriented mafic dikes intruding westward sloping, interlayered thin lava flows, near vent breccias, and pyroclastic material.

Return to the saddle between the Hayden and Renfrew Glaciers.  Continue ascending the steep ridge ahead and all the way to Middle Sister’s spectacular top; it’s roughly half a mile of slow-going ascent on the scree-covered upper slopes of the summit cone; however, once achieved, breathtaking views surround you.  Take a few moments to explore; there are few places more rewarding than this.  A multitude of volcanically- and glacially-derived landmarks are discernable from here, but let’s focus on just a few prominent features.  In the immediate foreground, Middle Sister hosts the remnants of several large glaciers, each of which has carved deeply into her slopes; Collier Glacier to the north, Renfrew Glacier to the northwest, and Hayden and Diller Glaciers to the east and southeast.  Nested sets of Holocene neoglacial and Little Ice Age moraines encircle each glacier and mark their most recent advances.

In the middle distance, at opposite ends of the compass, are Middle Sister’s marvelous siblings, North Sister and South Sister.  The three composite volcanoes (Figure 4.1 and Figure 4.2) exhibit a decrease in age and increase in the content of silicic volcanic materials from north to south.  North Sister is comprised of basaltic andesite and andesite lavas and pyroclastic deposits constructed on a more mafic shield volcano base that is believed to have begun erupting as much as 300,000 years ago (Taylor, 1968, 1981, and 1990).  Its flanks have been considerably eroded by ice masses of two glaciations and expose the central volcanic plug, dike systems, and near-vent volcanic breccias.  Middle and South Sisters are primarily comprised basalt porphyry lava flows and lesser amounts of basaltic andesite, andesite, dacite, and rhyodacite lavas and pyroclastic deposits.  Middle and South Sister probably formed concurrently, eruptions beginning roughly 93,000 years ago (Hill, 1992).  Middle Sister’s summit cone must be somewhat older than her southern sibling, a suggestion strongly supported by its significant degree of erosion (as witnessed earlier on this hike).  South Sister’s more youthful edifice nevertheless displays many fine examples of glacial activity (Figure 4A.39), including a well-preserved record of late Holocene neoglaciation on its northern and eastern flanks (a subject described under Field Trip 4B’s Camp Lake Trail).  To the southeast, beyond South Sister, lies Broken Top (Figure 4A.39), an older Pleistocene composite volcano that has clearly seen its share of glacial abrasion; compare Broken Top to each of the Three Sisters, it’s not difficult to see the affects of time and erosion.

Figure 4A.39 - South Sister and Broken Top copyrighted

Figure 4A.39.  Broken Top and South Sister Volcanoes as seen from the summit of Middle Sister.  Notice the not-so-subtle differences in glacial erosion affecting these two stratovolcanoes.

Now look further afield along the Cascade Crest; on a clear day, in the distance beyond South Sister and Broken Top, Oregon’s youngest stratovolcano, Mount Bachelor can be seen (Figure 4A.39).  Eruptions building Mount Bachelor began at the close of the late Pleistocene and continued well into the Holocene (Scott, 1989 and 1990).  Beyond the Three Sisters to the north, several High Cascades stratovolcanoes from Mount Washington to Mount Adams can often be observed, indicating other centers of intermediate volcanism during the Pleistocene.

Middle Sister offers unparalleled observation of the landscape to the west comprising the High Cascades-Western Cascades transition.  Below Middle Sister’s western slopes lies a gently westward dipping, glacially dissected, volcanic platform consisting mainly of mafic lava flows with patches of more silicic volcanics (Figure 4.1 and Figure 4.2) representing early High Cascades, graben-filling shield volcanoes and lava domes.  Look to the southwest, a prominent crag juts above the rolling topography of the western High Cascades volcanic platform called The Husband, a much eroded early Pleistocene shield volcano now reduced to a mafic volcanic plug and vent breccias.  Similarly, to the northwest, near Collier Cone at the base of North Sister, Little Brother forms a promontory on a ridge of Pleistocene basalt, the remnants of the basaltic shield volcano on which the more intermediate volcanics of North Sister’s composite cone was constructed.  Beyond the platform lies the Western Cascades geological province, essentially where the multiple smaller, U-shaped, tributary valleys draining the High Cascades converge to form a main glacial trunk stream, the McKenzie River valley.  The Western Cascades are comprised of more mafic, Tertiary, arc-related volcanics that have undergone considerably greater erosion.  The transition to Western Cascades volcanics is made more abrupt by the presence of a north-south trending normal fault which bounds the western edge of the High Cascades graben.  Look west and north, the central Oregon High Cascades graben and the prominent volcanic platform on which the Three Sisters stratovolcanoes and their northern partners rest is readily discerned.  Notice that the terrain slopes gently westward from the foot of the stratovolcanoes and is relatively flat, except where it is bisected by a few large glacial troughs; however, there is a distinctive break in the middle distance where drainages are kinked and the terrain becomes much more heavily dissected.  This marks the edge of the graben and volcanic platform and a rapid transition into the older Western Cascades.

      Take a last good look around.  Now it is time to return to your campsite along the same path you ascended.

Day Three

If you have the time and inclination for another day-hike, you may wish to climb Little Brother, a considerably easier ascent than Middle Sister, and a wonderful roost from which you get close-up views of North Sister, Collier Glacier, Collier Cone, and the Collier Cone Lava Flow.  To begin, return to the stream crossing at the upper end of Glacier Creek’s valley (as if you were heading to the summit of Middle Sister again).  Cross the stream, but this time head cross-country in a northeasterly direction away from the climber’s route (Map 4A.18).  You are making for a small hanging valley, tributary to Glacier Creek’s larger glacial trough, on Little Brother’s western slope, visible from here.

After climbing a steep, forested slope at the tributary valley’s mouth, the small valley opens up into a pleasant, meadow-filled basin beneath Little Brother.  In about four-tenths of a mile from the stream crossing, you’ll want to begin traversing to the right onto the valley’s southern slope in order to navigate around the cliffs on Little Brother’s southwest flank (Map 4A.18).  As you climb, make note of the bedrock exposed here; much of it is platy-jointed basalt, interlayered with a more massive variety of basalt.  The platy nature of the basalt makes it particularly vulnerable to frost action, a periglacial process in which water seeps into the fractures, expands and contracts through multiple freeze-thaw cycles, and acts like a natural jack-hammer to break the rock apart (Figure 4A.40).  This process is typical of alpine environments where there is ample water and an average spring through fall air temperature near freezing.

Figure 4A.40 - Frost shattered rock copyrighted

Figure 4A.40.  The basaltic andesite bedrock exposed in outcrops near Little Brother exhibits platy-jointed and massive varieties in gradational contact; the more platy variety displays strong evidence of periglacial frost shattering (such as that shown here) in this cool, moist environment.

Little Brother and its immediate vicinity is a remnant of the older Pleistocene shield volcano foundation on which the more youthful stratovolcano of North Sister was built.  The wall of massive basalt to your left that forms Little Brother’s southwest face is a volcanic plug, a resistant remnant of the vent source for the basalt near here.  Continue climbing toward the low point in the saddle between Little Brother and Black Finn, a location just over a mile from your starting point.  Once in the saddle, the route to the summit of Little Brother on your left becomes obvious.  Notice the variety of rock types exposed here (Figure 4A.41).  Little Brother’s summit is comprised of massive basalts and near vent volcanic breccias, oxidized by escaping gases during eruptions.  This is in sharp contrast to the rounded, bouldery debris in the saddle itself, a product of glacial meltwater spillover from the valley to the east that contained a much more massive Collier Glacier during the Little Ice Age.  In fact, this position is near the upper end of a textbook left-lateral moraine resulting from that glaciation (Map 4A.18).

Figure 4A.41 - Little Brother copyrighted

Figure 4A.41.  Sharply contrasting rock types exposed in the saddle between Little Brother and Black Finn;  Little Brother’s summit is comprised of massive basalts and oxidized near vent volcanic breccias, while the saddle itself contains rounded, bouldery debris of glacial origin.

Little Brother’s summit is a long ridge with isolated, jagged rock outcrops.  Previous climbers have made an easy-to-follow, albeit rough trail that winds along the length of the ridge (Map 4A.18); it’s about four-tenths of a mile to the end where great views abound, so make for that spot as you won’t be disappointed.  The view of Collier Cone and its associated lava flow, juxtaposed against Collier Glacier’s Little Ice Age terminal moraine is breaktakingly intimate (Figure 4A.42).  Lavas breached the cinder cone’s western flank and poured downslope, one lobe following the natural drainage of the White Branch of the McKenzie River, the other lobe ponding on the plateau to the northwest.  Collier Glacier once extended down the valley on North Sister’s western flank all the way to Collier Cone, ice piling up against the cinder cone’s southern side and leaving a coating of glacial till and outwash on its rim.  A small proglacial lake is retained behind the terminal moraine and cinder cone (Figure 4A.42), the remnant of a much larger lake that recently breached the moraine’s northwest rampart, releasing an outburst flood down the White Branch.  Look to the east and southeast for wonderful views of North Sister’s eroded western face and the now much depleted, but still viable Collier Glacier sandwiched in the valley between it and Middle Sister.  The valley below Collier Glacier contains beautifully preserved Little Ice Age lateral moraines and the bouldery ground moraine on the valley floor still retains lineated debris, grooved by the passage of overriding ice.  Examine Collier Glacier itself, can you locate the current position of the ELA, and is the glacier doing well?  To the west in the near distance is the now familiar watershed of Glacier Creek; to the southwest in the middle distance is The Husband, and similar to Little Brother, another mafic volcanic plug juts from its center.  Looking beyond your immediate surroundings, Little Brother also offers superb views of much of Oregon’s High Cascades to the north, and Western Cascades to the west.

Figure 4A.42 - Collier Cone and Flow copyrighted

Figure 4A.42.  The summit of Little Brother offers a bird’s eye view of Collier Cone and Lava Flow with a spectacular vista of the High Cascades beyond.  Take note of the breach in Collier Cone’s western flank, the source of the Collier Cone lavas; as well as the position of Collier Glacier’s Little Ice Age terminal moraine, some of its debris forming a veneer on Collier Cone’s southern rim.

      Stay for lunch, then make your way back to your campsite along the same the same route you ascended.

When you return to camp, pack up and make ready to move on; your destination is an excellent campsite near Minnie Scott Spring on the Pacific Crest Trail.  Return to the junction of the PCT and Glacier Way Trail and turn right. Hike the PCT as it traverses a spur ridge on the western flank of Little Brother  (Map 4A.18 and Map 4A.19).  In a little over one mile, the trail begins paralleling the southern edge of the Collier Cone Lava Flow.  At just over one and a half miles, you reach a great view overlooking Sawyer Bar on the White Branch of the McKenzie with Collier Cone and its breaching lavas straight ahead.  The trail soon descends into the valley of the White Branch; you cross its normally dry stream bed, and soon reach the margin of the Collier Cone lavas in about a quarter mile.  Before you leave the White Branch, take note of the bouldery debris around you (Figure 4A.43) and recall that this material was carried here by a glacial outburst flood that poured downvalley from an earlier version of the proglacial lake now filling the lower end of the glacial trough below Collier Glacier.  The size of the boulders indicates the power of the rushing meltwater.  The threat of another flood is not imminent, as the lake is now much smaller.

Figure 4A.43 - Outwash channel below Collier Cone copyrighted

Figure 4A.43.  Bouldery debris deposited by the glacial outburst flood on the White Branch of the McKenzie River at Sawyer Bar.  Note the person for scale; Collier Cone and its lava flows lie in the background.

If you have the time and inclination, you can gain access to the valley below Collier Glacier by following this dry water course upstream.  As you walk, look for marvelous examples of interbedded lava flows and pyroclastic material exposed in the walls of the channel, as well as evidence of the glacial outburst flood from the proglacial lake upvalley; young lavas from Collier Cone are on your left.  Eventually, you pass through a substantial breach in Little Ice Age left-lateral moraine deposited by Collier Glacier and into the lower end of the valley; to the left, Collier Cone lavas transition into scoriaceous deposits of Collier Cone itself.   Continuing upvalley within the glacial trough requires a good deal more time, but if you’re looking for a “textbook” exercise in glacial geology, it’s worth it.  Within the valley are many fine examples of glacial sediments that can be interpreted as to their glacial-depositional environments, such as fine-grained lakebed sediment of former proglacial lakes, lodgment till containing aligned bullet stones deposited at the base of flowing ice, and hummocky melt-out till comprised of material haphazardly deposited from stagnant ice.  Should you make your way to the glacier’s modern terminus, turn around, and consider for a moment that the distance you have just walked upvalley from the base of Collier Cone was filled with ice from moraine crest to moraine crest less than100 years ago; the melting is primarily the affect of a rise in air temperature related to global warming, at least some of which was human-induced.

Continue on the PCT across the Collier Cone Lava Flow, providing more opportunities to observe aa lava flow features (Map 4A.19).  It soon becomes apparent that the trail climbs right into the breach on Collier Cone’s western flank (Figure 4A.44).  This is the very source of the lavas that began pouring across the Three Sisters platform to the northwest about 1,500 years ago, stacking up and diverting lavas to the west and eventually finding the path of least resistance down the valley of the White Branch of the McKenzie!  The trail passes through the breach, then along the inner edge of the flow’s massive right-lateral lava levee; observe the smooth inner walls of the breach, plastered with successive layers of basaltic lava.  This is actually the younger of at least two recognizable breaches and associated gutter systems you’ll traverse.  In six-tenths of a mile from Sawyer Bar, the PCT reaches Opie Dilldock Pass within the cinder cone’s crater; the trail soon crosses into the other, larger and older breach and gutter system, and in a quarter mile, passes from the inside to the outside of a prominent right-lateral lava flow levee associated with this second gutter system.  Another four-tenths of a mile brings you to perennial Minnie Scott Spring; your campsite lies just to the left on an obvious campers trail.

Figure 4A.44 - Breach in Collier Cone copyrighted

Figure 4A.44.  Collier Cone’s western flank was breached at least twice during eruptions that built the cinder cone; here, the PCT (seen in the right foreground) passes upwards through the younger breach.

After passing a restful afternoon in camp, make an early dinner and then walk back along the PCT to the foot of the northern flank of Collier Cone.  Bring a headlamp for the return trip to camp and keep track of the time, you’re about to enjoy one of the prettiest (and most geologically interesting) sunset hikes in the Oregon Cascades.  You probably noticed several spur trails leading to the summit of Collier Cone when you passed by this area earlier in the day, now climb to the cone’s rim on the first available climber’s route for marvelous views north and northwest toward Yapoah Crater and Four-in-One-Cone and their associated lava flows, south toward Collier Glacier and Middle Sister and North Sister, and west down the lava-filled trough of the White Branch.  As you circumnavigate the cone’s rim from north to south, note the layering of tephra deposits exposed on Collier Cone’s rim, and be sure to look northeastward at the immense, nearly treeless, cinder field spewed downwind of Collier Cone (Figure 4A.45); can you guess the prevailing wind direction during those eruptions 1,500 years ago?  A cinder cone’s asymmetry, tephra fallout pattern, and breaching can be used to indicate this.  If windy conditions prevail during an eruption, they cause cinders large and small to stack preferentially in the direction they are blowing, creating a distinctive downwind tephra pattern and a lopsided cone.  Lesser accumulation of cinders on the upwind side of the cone leaves it weak and more vulnerable to breaching by lavas temporarily filling the cone’s interior during an eruption.  Figure 4A.45 also displays the wonderful view northward toward McKenzie Pass from your location and the now familiar volcanic landmarks of Belknap Crater, Black Butte, Black Crater, Mt. Washington, Three Fingered Jack, and Mt. Jefferson.

Figure 4A.45 - Collier Cone and Tephra Plume copyrighted

Figure 4A.45.  The Ahalapam Cinder Field lies northeast and downwind of Collier Cone, a product of tephra fallout from the volcanic eruptions that built the cone 1,500 years ago.  Black Crater lies in the middle distance, while Black Butte lies to its right and the trebled points of Mt. Washington, Three Fingered Jack, and Mt. Jefferson march into the distance on its left.

Great views of North Sister’s intensely glaciated northern flank open up as you go; the remnants of Linn Glacier lie in a steep-walled cirque gouged into its summit cone (Figure 4A.46).  When you reach the cinder cone rim’s southeast side, look into the valley wedged between North Sister and Collier Cone; a classic set of nested moraines and hummocky topography associated with Collier Glacier’s recent Little Ice Age advance lies below (Figure 4A.46).  Hummocky terrain such as this often forms when stagnant ice, buried by till, melts out slowly over many years.  Now find a good perch on the cone’s southern rim and watch the light of the setting sun on Collier Glacier, North Sister, Middle Sister, and Little Brother serving as a perfect backdrop (Figure 4A.47).  The view up Collier Glacier’s recently vacated glacial trough is intense, its fresh, sharp-crested, Little Ice Age right- and left-lateral moraines are spectacularly displayed.  Your own resting place may well be on glacial till and outwash, a thin veneer of it was deposited on the cinder cone’s southern rim during the maximum Little Ice Age advance of Collier Glacier.  After this recommended diversion, return to your campsite for a good night’s rest. Make sure you have a headlamp and that its working properly, otherwise the walk back to camp could be a bit tricky.

Figure 4A.46 - Hummocky moraines of Collier Glacier copyright

Figure 4A.46.  Glacially sculpted North Sister Volcano as seen from Collier Cone; at the volcano’s feet lays a complex of nested right-lateral and terminal moraines, as well as hummocky morainal deposits associated with the Little Ice Age advance of Collier Glacier.

Figure 4A.47 - Sunset on Collier Glacier copyright

Figure 4A.47.  A marvelous sunset on Collier Glacier, North and Middle Sister, and Little Brother awaits your viewing pleasure from the summit rim of Collier Cone.

Day Four

In the morning, begin your hike back to the Obsidian Trailhead.  In about a half mile, you enter the upper end of a small valley southwest of the large, late Holocene cinder cone of Yapoah Crater with good views of its summit.  It is slightly more than a mile north on the Pacific Crest Trail from Minnie Scott Spring to its junction with the Scott Trail (Map 4A.19).  It is a relatively short hike of about six-tenths of a mile on the PCT to the foot of Yapoah Crater.  If you feel so inclined, find a good place to stow your pack and make the brief excursion to Yapoah Crater’s summit; however, this destination is described as a separate trek elsewhere in this guidebook.  The meadow you are standing in offers a last look at the impressive twin peaks of North and Middle Sister Volcanoes.  At the junction, make a left onto the Scott Trail and head over a low ridge and downslope to the west.  After about a mile, the trail breaks from the trees onto a cinder-strewn plain for a good view of the eastern side of the long summit ridge of Four-in-One-Cone, the source of the dark tephra blanket you are crossing.  A large rock cairn stands in the middle of the plain at precisely one mile from the last trail junction (Map 4A.19); this is a convenient location near the southern base of the cone complex where you can stow your pack and make the brief climb to the top of the summit ridge (about four-tenths of a mile round-trip to the high point on the summit ridge).  An obvious path leads up onto the ridge and can be followed nearly to its end.  As you walk the ridge line to the north, you quickly realize the significance of this cinder cone’s name.  Four-in-One Cone is actually four separate, overlapping cones, each breached on its western flank (Figure 4A.48).  Notice the eastward-skewed asymmetry of the cone complex and the distribution of its tephra, clearly the prevailing winds blew west to east during the Four-in-One Cone eruptions, much as they do today.  This asymmetry caused a weaker perimeter on the downslope side of the cinder cones, this and gravity caused preferential breaching on the west flank of the cones.  Lava flows issuing from these breaches poured downslope in one short flow lobe to the west and another, much longer flow lobe to the northwest.  Four-in-One Cone also affords a great view northward to Belknap Crater, Mount Washington, and other prominent landmarks.

Figure 4A.48 - Four-in-One-Cone copyrighted

Figure 4A.48.  The view northeast from the high point on the summit ridge of Four-in-One Cone.  This cinder cone complex and its associated lava flows formed as a series of lava fountains issued from a fissure vent system about 2700 years ago.  In the central  background,  the rounded summit cone of youthful Belknap Crater contrasts nicely with the jagged spire of Mount Washignton’s much older glaciated peak.

Return to Scott Trail and make your way downslope along the northern edge of a flow lobe from Collier Cone (Map 4A.16).  Just over a mile from the rock cairn near Four-in-One Cone, Scott Trail traverses through a section of aa lavas separated briefly by a kipuka.  The kipuka formed on a topographic high that wasn’t inundated by the lava flows from either Collier Cone or Four-in-One Cone.  Where the trail crosses lava flows proper, the slightly reddish-gray basaltic andesite lavas on the left are from Collier Cone, while the slightly darker, more vesicular lavas on the right are from Four-in-One Cone.  From here it is about three miles down hill to a trail junction; the Scott Trail head right.  Take the spur trail to the left; it connects with the Obsidian Trailhead in just over half a mile.  You’re home free.

Proxy Falls Trail (Tr 4A.5)

The trail to upper and lower Proxy Falls is found at mile 28.5 (Map 4A.20); this is an easy, family-friendly, one and a half mile “loop” hike traversing the lower end of basaltic andesite aa lavas from Collier Cone (Figure 4A.1) with short spur trails that provide access to Upper Proxy Falls and its more impressive twin, Lower Proxy Falls (Figure 4A.49).  These waterfalls occur where small glaciated tributary valleys join the main glacial valley of the White Branch of the McKenzie River.  The larger glaciers periodically occupying the main stem valley were considerably more erosive than their tributary counterparts, and so they eventually carved a much deeper U-shaped trough, the difference in net erosion having left the floor of the tributary streams high on the canyon walls of the White Branch as hanging valleys.  Open views from the top of the lava flow of the northern slope of White Branch’s canyon reveal Deer Butte, a volcanic plug and associated cinder cone enclosed in younger, intracanyon lava flows literally cut in half and exposed in cross-section by glacial erosion (Figure 4A.50).

Figure 4A.49 - Lower Proxy Falls copyrighted

Figure 4A.49.  Lower Proxy Falls; this waterfall and its partner, Upper Proxy Falls, formed where small, less deeply carved hanging valleys join the main glacial trough of the White Branch of the McKenzie River.

Figure 4A.50 - Deer Butte copyrighted

Figure 4A.50.  The Collier Cone Lava Flow’s rubbly surface offers a great view of Deer Butte, a volcanic plug with its flanking cinder cone deposits enclosed in younger, intracanyon lava flows lies perched and literally cut in half by glacial erosion on the cliff face along the north side of White Branch canyon.

From the trailhead, hike counterclockwise around the loop (Map 4A.20).  It is about four-tenths of a mile to the first spur trail on your right to Lower Proxy Falls, just over one-tenth of a mile further around the loop to the second spur trail on your right for Upper Proxy Falls, and about one quarter mile back to the trailhead and parking area from there.  Each spur trail adds another quarter mile out and back from the main trail.

Sand Mountain Trail (Tr 4A.6)

This trail is found by following FS Rd 2960 and 2690-810 once leaving Hwy 20/126 at mile 63.7.  This is a relatively short day-hiking opportunity of about four miles round-trip and 800 feet of elevation gain, with a fairly gradual grade, much of it on an old access road for the Sand Mountain fire lookout.  Most of the work was accomplished in the drive getting to the trailhead.  To begin, hike south on the fire tower access road (Map 4A.21); in about one third of a mile you’ll arrive at the old trailhead and parking area (please respect the signage at the new trailhead and do not drive to this location).  As you ascend Sand Mountain, a late Pleistocene cinder cone at the nexus of the Sand Mountain chain of volcanoes, views open up to the north.  At a little over one and a half miles, the trail (access road) leads to the original parking area below the fire tower; the trail continues upward from its southern side.  You reach the summit and fire tower at just under two miles from your starting point.  The lookout is usually staffed in the summer and if the gate at the entry stairway is open, feel free to climb up.  However, if the gate is barred, please respect the signage and privacy of the attendant.

Look around, expansive views open up in all directions; sometimes the easy hikes do provide the most stunning vistas.  To the north and somewhat east, the glacially scared southern flanks of the Mount Jefferson stratovolcano can be seen in the distance.  Nearer, along the same line of sight, great views of Three Fingered Jack and Maxwell Butte are available.  Three Fingered Jack is a highly dissected, oft-glaciated, composite volcano chiefly composed of basaltic andesite lava flows, with a smaller component of indurated, near-vent mafic breccias comprised of cinders and lava bombs and blocks at the summit.  Maxwell Butte is a smaller, somewhat younger basaltic andesite shield volcano exhibiting its own signs of glaciation.  Both volcanoes are perched on volcanic and volcaniclastic rocks of the early High Cascades platform.  Immediately to the northeast are the glacially sculpted, Pleistocene andesite domes of Hogg Butte and Hayrick Butte, their flat tops suggesting that formative eruptions occurred while an ice cap occupied this area.  In the same vicinity, the younger, better preserved, basaltic cinder cone of Hoodoo Butte can be seen oxidized to a slightly reddish color; and to the north and northwest are the Holocene cinders cones of the Lost Lake volcanic chain, as well as Nash Crater, and Little Nash Crater and their associated basaltic lava flows filling the glacial trough that wraps around the southern flank of Maxwell Butte.

Looking to the west, one gets a Birdseye view of the glaciated upper McKenzie River valley and the eroded Western Cascades escarpment displaying the much-modified trace of the normal fault that bounds the western side of the High Cascades graben (Figure 4A.51).  In the foreground, lava flows associated with the 22 aligned cinder cones and 41 vents of the Holocene Sand Mountain volcanic chain are readily observed.  These basaltic lavas poured westward into the McKenzie valley about 3000 years ago, blocking and reshaping its drainage since deglaciation (Figure 4A.11).  Further to the southwest, similar lava flows from Belknap Crater can also be seen.  Almost due south of here, Scott Mountain, a glacially sculpted Pleistocene cinder cone lies on the skyline.  To the southeast, the northern flanks of Mt. Washington and Belknap Crater form a classic contrast between old and new.  Mt. Washington is a highly glaciated remnant of a once substantial, basaltic andesite stratovolcano erupted in the Pleistocene.  The exposed central volcanic neck and flanking dike swarms are exposed in its summit cone, the peak having endured considerable glacial sculpting related to its greater age and position on the Cascade Crest.  Belknap Crater on the other hand is a Holocene shield volcano complex constructed of basalt and basaltic andesite lavas that fills the formerly glaciated terrain between Mt. Washington and Black Crater.

Figure 4A.51 - View from Sand Mountain copyrighted

Figure 4A.51.  The view westward from the top of Sand Mountain; the cinder cone’s summit crater lies in the foreground, the upper watershed of the McKenzie River in the middleground, with the Western Cascades beyond.  The western escarpment of the Central Oregon High Cascades graben is defined by the transitional boundary between the upper McKenzie River valley and immediate line of peaks in the Western Cascades.

Finally, in the distance to the east is Black Butte.  This volcano’s near perfect symmetry, its steep slopes, and the mafic composition of its mostly pyroclastic cinders and lava blocks and bombs, provides a textbook example of a cinder cone volcano.  Just to the forefront of Black Butte are the glaciated, U-shaped valleys of Lake Creek and Cache Creek.  Cache Mountain lies in the foreground.  This prominent ridge is a remnant of the early Pleistocene High Cascades basaltic andesite platform that divides the valleys of Lake Creek to the north from Cache Creek to the south.  Ice lobes emanating from the ice cap covering the Cascade Crest to the west wrapped around the ridge, but the eastern portion of the ridge itself was not glaciated.  Well-developed end moraine complexes occupy the Lake Creek and Cache Creek valleys to either side of Cache Mountain.  Northeast of Cache Mountain is Suttle Lake, dammed by the terminal moraines of the late Pleistocene glacial maximum on Lake Creek.  These moraines are the type locality of the Suttle Lake advance of the Cabot Creek glaciation (Scott, 1977) which produced an ice cap covering much of the Cascade Crest visible from here about 20,000 years ago.

After you have had enough of the distant sites, be sure to make some observations of Sand Mountain itself.  Signs discourage cross-country exploration here, so please stay on existing trails.  This and its many nearby siblings is a “textbook” basaltic cinder cone comprised of small lava blocks and bombs as well as a prodigious amount of scoriaceous cinders.  Outcrops of tuffaceous material are exposed near the fire tower; if you make careful observation, you may notice that layers of tuff along the rim dip inward, toward the crater to the right of the trail and outward, away from the crater to the left of the trail.

Return to the trailhead along the same path you followed to the summit.  

Scott Mountain and Hand Lake Loop Trail (Tr 4A.7)

This trail is found by following FS Rd 2400-260 to its end after turn off  Hwy 242 at mile 21.3.  Scott Mountain is a Pleistocene shield volcano, its eastern flanks exhibiting signs of glacial erosion, located just west of the Cascade Crest near McKenzie Pass.  Its meadow-filled summit provides excellent opportunities to view the Pleistocene Three Sisters stratovolcanoes to the southeast, as well as the immense outpourings of Holocene volcanics associated with the late Holocene Belknap Crater shield volcano complex near McKenzie Pass.  The round-trip hike is fairly long, a little over eight miles to the top and back being the shortest option, with a 1300 foot elevation gain in the bargain; an excursion this author still recommends, especially if you like to avoid the more popular, but often dusty and crowded trails in the area.  Extending the hike to include a trek past the Twin Craters Lava Flow and Hand Lake is well worth the extra several miles of exertion; if you make it to Scott Mountain’s summit, you have to come back, so it might as well be over a different (and more scenic) trail.

Begin at the Benson Lake Trailhead at the end of the Scott Lake Road at an old cinder pit and parking area (Map 4A.22).  Climb steadily for about one and three-tenths miles to a ridge and a short spur trail to the left.  Take this brief side-trip to the rock-lined shore of Benson Lake; notice the glacially scoured bedrock outcrops along the lake sides.  After returning to the main trail, continue hiking upslope another mile and a quarter to another spur trail on the left to the Tenas Lakes.  It’s about two-tenths of a mile round-trip to the first and largest of several small, rock-rimmed lakes (the others require bushwhacking to reach).  The far shore of this lake hosts beautifully glacially-sculpted bedrock outcrops; and the lake itself offers a swim that is quite refreshing in August.  Return to the main trail; hike about a quarter mile to a trail junction just beyond a small lake on your left.  The left fork continues as the Benson Lake Trail to “The Knobs”; the right fork, the Hand Lake Trail, and more heavily utilized of the two is the one you want (Map 4A.22).   In nearly nine-tenths of a mile, you reach a not-so-obvious “T” intersection; the main trail continues upslope to the summit of Scott Mountain, but the Hand Lake Trail veers off to your right.  The trail sign was knocked over the last time I hiked this trail in August, 2009, so be on the lookout for it if you plan to return to the trailhead on the Hand Lake Trail.

However, first complete the one and a quarter miles round-trip to Scott Mountain’s broad summit cone (Map 4A.22).  At the top, you can obtain exceptional views of many of the Cascade Crest’s finer volcanic features from northeast to southeast, as well as the glaciated upper McKenzie River drainage and western escarpment of the High Cascades graben to the south and west (Figure 4.1).  Looking immediately to the northeast, one is almost overwhelmed by the massive basaltic shield volcano complex of Belknap Crater (Figure 4A.52).  This area was the nexus for a long, complex period of Holocene basaltic and basaltic andesite volcanism that erupted nearly continuously from about 3,000 to 1,500 years ago, building a compound shield volcano on the Cascade Crest as much as 1700 feet thick and 1.3 cubic miles in volume (Taylor, 1968 and 1981) (Figure 4A.1).  On Belknap’s southern flank, just poking above the level of the general slope, one can see Little Belknap Crater which erupted over a major vent about 3,000 years ago, extruding substantial overlapping flow lobes of basaltic andesite that resulted in the formation of a significant subsidiary shield volcano.  South Belknap Cone, a small, breached cinder cone, visible as a brownish smudge mid-way up Belknap Crater’s southwestern flank, formed about 2,600 years ago. The last major pulse of volcanism about 1,500 years ago produced basaltic andesite lava flows that cover much of Belknap Crater’s western flanks.  These lavas issued from vents on the north and south flanks of Belknap Crater near the base of the summit cone and mainly moved downslope to the northwest; some flows reaching as far as the glaciated valley of the upper McKenzie River, disrupting its drainage.  A smaller flow lobe moved southwest into the upper end of Lake Valley on the west side of Scott Mountain, surrounding South Belknap Cone in the process.

Figure 4A.52 - Belknap Crater from Scott Mtn copyrighted

Figure 4A.52.  The view eastward from the summit of Scott Mountain.  Belknap Crater’s massive shield occupies much of the image, flanked in the background by Mt. Washington to the north and Black Crater to the southeast.  Little Belknap Crater is the promontory just right of Belknap’s summit cone, with South Belknap Cone barely discernable below and to the right of it. Twin Craters, source of the Hand Lake Lava Flow, lies in the foreground at the base of Belknap’s western slope.

Looking in the same direction, Scott Mountain also offers a good view of Twin Craters cinder cone (Figure 4A.52), the source of the Hand Lake Lava Flow which lies below you at the western base of Scott Mountain (Figure 4A.1).  Volcanic eruptions that generated these lavas which terminate on the shores of Hand Lake, and indeed form the dam that produced the lake, erupted between 2,900 and about 2,700 years ago (Sherrod et al., 2004).  Looking in the same direction, to the northeast beyond Belknap Crater’s summit cone, you can see Mount Washington Volcano’s highly dissected form (Figure 4A.52).  The similarly preserved remnants of the Three Fingered Jack stratovolcano are somewhat further to the north, with Mt. Jefferson in the background.

Almost due north of your position, the cinder cones of the Sand Mountain volcanic chain march toward you in a line, multiple basaltic lava flows from these vents having poured westward into the McKenzie valley several thousand years ago, blocking and reshaping its post-glacial drainage (Taylor, 1968 and 1981) (Figure 4A.11).  Slightly northwest and a little more distant, Nash Crater, Little Nash Crater, the cinder cones of the Lost Lake volcanic chain, and their associated basaltic lava flows can be discerned west of Santiam Pass.  The andesitic domes of Hayrick Butte and Hogg Rock, and the nearby basaltic cinder cone of Hoodoo Butte can be seen at a similar distance just to the northeast of Sand Mountain, closer to Santiam Pass.

To the southeast, lies Black Crater Volcano just beyond McKenzie Pass (Figure 4A.52), a large late Pleistocene cinder cone formed over a slightly older shield volcano base (Taylor, 1968 and 1981).  Looking slightly southeast, you can observe a long ridge running between North Sister Volcano to Black Crater.  This glaciated ridge of late Pleistocene basaltic andesite lavas consists of multiple, small cinder cones formed along a 5-mile-long chain (Taylor, 1968 and 1981).  Two large Holocene cinder cones are superimposed on the ridgeline (Figure 4A.1); Yapoah Crater lies slightly to the left (north), while Collier Cone is more directly to the south nearer the base of North Sister.  Vents at each location produced voluminous outpourings of basaltic andesite lavas.  As observed, the Yapoah Crater lavas, erupted between 2,900 and 2,600 years ago (Taylor, 1968 and 1981), moved down the northwest flank of the ridge in several lobes which coalesced near McKenzie Pass and flowed downslope to the northeast.  The lavas from Collier Cone spread outward in two lobes associated with volcanic eruptions roughly 1,500 years ago, one that flowed northwest from the ridge to pool and stall out in a large area of relatively low gradient near the cone, the other lobe poured off the ridge to the west and down the glaciated trough of the White Branch of the McKenzie River.  Four-in-One Cone, lying below the ridge, occurs as a complex of coalescent basaltic cinder cones sandwiched between the lava flows from Yapoah Crater and Collier Cone (Figure 4A.1).  This unique ridge cone is breached in four locations on its northwest, downslope-facing flank, having erupted andesitic lavas about 2,600 years ago along a series of fissure fountains to generate two flow lobes that generally wrap around the northeast and southwest sides of a ridge punctuated by Condon Butte.  The southwestern lobe is in contact with Collier Cone’s more northerly lava flow.

Southeast of this center of late Holocene volcanic activity lies the trebled edifice comprised of the Three Sisters stratovolcanoes (Figure 4A.53).  North Sister is the oldest of the three siblings, a basaltic andesite composite volcano constructed on an older basaltic shield volcano base roughly 300,000 years ago (Taylor, 1968 and 1981; Taylor et al., 1987).  Middle Sister is younger, while South Sister is the youngest of the three, eruptions there beginning as early as 93,000 years ago (Hill, 1992); both of these volcanoes share much greater compositional variation than their eldest sibling, and both lack a shield volcano base.

Figure 4A.53 - Three Sisters from Scott Mtn copyrighted

Figure 4A.53.  The Three Sisters stratovolcanoes (with The Husband’s prominent volcanic plug to the right) seen from Scott Mountain’s summit cone.

Last, but not least, the glaciated, U-shaped troughs of the upper McKenzie basin are plainly visible toward the setting sun.  Fault-controlled Horse Creek oriented north, separated from the westward flowing White Branch of the McKenzie by Foley Ridge, both lie southwest of Scott Mountain; while the main branch of the McKenzie is due west.  Prominent Foley Ridge forms a classic example of what geologists refer to as inverted topography, that is, early High Cascades lava flows poured down a pre-existing drainage, presumably a tributary of the ancestral McKenzie River, only to become a resistant ridge of intracanyon volcanics today as younger streams cut through older, more weathered, and less resistant material around the perimeter of the intracanyon basalts (Taylor, 1981 and Priest et al., 1983). indicate that it is comprised of intracanyon basaltic lava flows of origin.  The eroded escarpment beyond the main branch of the upper McKenzie is comprised of Pliocene volcanics of the Western Cascades – High Cascades transition and forms the western margin of the central High Cascades graben (the wide avenue of the McKenzie itself is carved along the fault trace).

Seen all there is to see?  Not by a long shot.  Now return to the Hand Lake trail junction you passed on the way to Scott Mountain’s summit, about six-tenths of a mile back downslope.  You can continue on to the Scott Lake trailhead, back the way you came, or if you’re feeling up to adding a mile and a quarter to your return route, make a left instead (Map 4A.22).  Hike downward through Douglas-fir dominated slopes about one and three-quarters miles to another trail junction, passing several glacially-striated bedrock outcrops along the way; then make a right (a left here takes you to Robinson Lake), and continue about three-tenths of a mile to where the trail encounters the fresh-looking basaltic andesite lavas from Twin Craters.  The trail parallels this lava flow for roughly one mile to the western edge of Hand Lake; as you saunter along, note that some portions of the lava flow margin are clearly higher than the flow’s interior.  This is a product of deflation, where the still-molten lava beneath a congealed flow top evacuates from within to pile up along the flow’s outer edge.  Look for alternating smooth, ropy plates of cracked and buckled pahoehoe lavas and irregular, blocky aa lavas.  When you reach about seven-tenths of a mile downtrail from its last junction, begin looking for a high point along the flow margin just upslope from a steep, narrow constriction in the valley (presumably the lava was temporarily backed up here as it flowed downslope).  The old wagon road first observed near the Dee Wright Observatory crosses the Hand Lake Lava Flow just below the constriction.  In a little over three-tenths of a mile you can view Hand Lakes’ northeast shoreline through the trees on the left side of the trail.

The official trail follows Hand Lake on the forested slope above the shoreline, but since the lake is nearly desiccated, drop down to its shore for a close-up view of the lava flow’s terminus (Figure 4A.54), then follow the old shoreline down the length of the lake basin and pick up the trail at the other end (Map 4A.22).  You’ll encounter a spur trail that crosses the grassy meadow over to the historic Hand Lake Shelter.  Check out this old structure built by the CCC, but don’t follow the spur trail around the building to the left (the trail pads off to a small trailhead along Hwy 242).  Instead, return to the north side of the clearing on the spur trail and hike upslope until you merge with the Hand Lake Trail again (Map 4A.22).  Head left for Scott Lake; in about one mile you’ll encounter a (usually) dry stream bed, look carefully for the trail emerging from the opposite side (don’t follow the channel – an easy mistake).  Shortly, you should see the north end of Scott Lake on your left as you traverse through a lakeshore meadow.  The trail merges with the shoreline of Scott Lake in about three-tenths of a mile; follow the lake shore until you encounter an old road on your right (now used as a walk-in trail for several nearby campsites).  Take the road back to the Benson Lake Trailhead and your vehicle.

Figure 4A.54 - Hand Lake & Lava Flow copyrighted

Figure 4A.54.  A now much-desiccated Hand Lake, formed where lavas form Twin Craters dammed the former drainage to the north.

Tamolitch Falls Trail (Tr 4A.8)

This trail, an easy stroll along the McKenzie River suitable for families, can be reached from FS Rd 2600-730  and 2600-655 after leaving Hwy 126 at mile 46.3.  The trail provides nice views of the upper McKenzie on a peaceful stretch of the river and brings you to a unique location where the McKenzie seeming appears from nowhere as a full-blown river.  Tamolitch Pool occurs at the base of the dry Tamolitch Falls, a large plunge-pool basin from which springs emerge beneath late Holocene intracanyon lava flows to form an instant river.  Although today at this location, all of the McKenzie’s water issues from these springs, the empty river bed above the dry falls tells a different story.  In fact, until the recent construction of the reservoir-siphon tunnel-powerhouse system (discussed at mile 46.3 of Field Trip 4A), water did seasonally occupy the channel above the falls, plunging into Tamolitch Pool over Tamolitch Falls (at least after wet winters).  However, now that much of the water is shunted around this section of the river, the McKenzie no longer flows there and the springs and pool form an idyllic setting, albeit an artificially enhanced one.  The trail winds through an old growth temperate rainforest of conifers and traverses a youthful intracanyon lava flow that has come all the way from Belknap Crater, features adding to its charm and uniqueness.

Begin at the Upper McKenzie Trail sign on the right-hand side of the road next to the parking area (Map 4A.23).  In about two-tenths of a mile, the trail descends steeply from the top of an older stream terrace here to the modern floodplain of the McKenzie River.  Note the multitude of rounded cobbles in the cut bank to the left.  A stream terrace marks the former position of a river’s floodplain, in part determined by the passage of time (as streams flow, they erode into their beds and lower themselves into the landscape) and by a former stream flow regime that accommodated substantially greater volumes of water and sediment.  This latter factor is often the result of former cool, moist glacial climatic regimes, a scenario that likely explains the existence of this terrace.

The trail meanders along the river’s floodplain through beautiful old-growth western red cedar and Douglas fir forest, and at about a mile begins crossing jumbled piles of blocky basaltic rubble indicative of an aa lava flow; this flow is from Belknap Crater.  Two cylindrical holes (one quite large, the other smaller) occur in the lava flow surface to the left of the trail about one-tenth of a mile further upvalley of the lava flow margin (Figure 4A.55).  These are tree molds, formed when trees growing on the valley floor (much like the ones you see around you here) were inundated by the lava flow, the trunks either burned as they were enveloped or rotted away subsequently.  They are often preserved near flow margins where the lava is relatively thin and cool, and when they preserve charcoal, the organic material can be useful for radiocarbon dating of the lava flow and the volcanic eruption which caused it.

Figure 4A.55 - Tree Molds  copyrighted

Figure 4A.55.  The larger of two tree molds formed when trees growing on the valley floor were inundated by Belknap Crater lavas.

When you reach about one and seven-tenths of a mile from the trailhead, you get your first good look at Tamolitch Pool and the steep-walled basin behind that forms the cliff over which (the now dry) Tamolitch Falls once poured.  In another 500 feet you reach the official Tamolitch Falls (and Pool) overlook (Figure 4A.56).  The McKenzie River seems to appear from nowhere, but in fact it is issuing from springs in the lava flows beneath the pool.  Lava flows are inherently porous for several reasons; individual lava flows may contain coarse crystals and or vesicles, lava flows may be well-jointed and/or fractured, and sequences of lava flows often contain interlayered porous units formed in association with rubbly flow tops and bases or weathered zones.  In this case, groundwater seeps downslope along the McKenzie River corridor through porous lavas and rises in the bed of the channel at an artesian spring where hydrostatic pressure from the weight of water upslope literally pushes the water to the surface.

Figure 4A.56 - Tamolitch Falls (Pool) copyrighted

Figure 4A.56.  Dry Tamolitch Falls (and Pool), where the McKenzie River emerges from large springs in the porous lava flows along its former channel.

If you continue upvalley beyond the overlook, you quickly reach a location where you can observe the bed of the dry river channel to your right.  A walk of a less than 50 feet lets you clamber onto the channel floor where the presence of rounded stream cobbles and polished rock attests to the fact that water once flowed vigorously through here.

Turn around here and make your way back to the trailhead and parking area.  No need to hurry.

Yapoah Crater Trail (Tr 4A.9)

The Yapoah Crater Trail begins at the Pacific Crest Trail parking area near Lava Camp Lake Campground and is accessed via FS Rd 900 at mile 14.9 on Hwy 242 (Map 4A.13).  The trail highlights the Yapoah Crater cinder cone and its associated lava flows, as well as North and South Matthieu Lakes, pleasant little lakes with quite different origins.  Yapoah Crater erupted during an early phase of Holocene volcanic activity in the McKenzie Pass area that lasted from about 2,900 to 2,600 years ago (Taylor, 1968 and 1981).  Flow lobes of Yapoah lava poured downslope to the northwest from their vent source on a ridgeline between Black Crater and North Sister (Figure 4A.1).  When they reached McKenzie Pass, each was diverted eastward by slightly older lava flows of Belknap Crater Volcano, down a Pleistocene carved glacial trough along the north flank of Black Crater.  The PCT parallels the edge of the easternmost Yapoah flow all the way to the cinder cone and beyond.  This day-hike follows one branch of the PCT past North and South Matthieu Lakes to the base of the cone, ascends to its summit for spectacular views of the entire McKenzie Pass area, then returns on the PCT via another branch.

The trailhead for the PCT connector trail leaves the southwest end of the parking area and reaches a “T” intersection with the actual PCT in about one third of a mile.  Take the left-hand trail; the lava flow from Yapoah Crater lies to your right as you ascend.  Map 4A.13 displays the crenulated surface and lobate nature of the lava flow; particularly noticeable is the right-hand bend in the flow where it encountered the base of Little Belknap Crater and its slightly older lavas (the Yapoah Crater Lava Flow eventually flows off the map to the northeast).

Continue on the PCT, in about one mile, you’ll arrive at a branching in the trail (Map 4A.13); either direction can be followed to the same destination, but take the right fork.  As you climb, this segment of the PCT wraps around the edge of a small, fan-shaped flow lobe from the right margin of the Yapoah Crater Flow.  In roughly six-tenths of a mile, the trail passes a pond on the left (Map 4A.19) where basaltic andesite bedrock outcrops have been glacially smoothed and striated, in sharp contrast to the angular, blocky nature of Yapoah Crater’s more youthful lavas of similar composition that occur on the right.  Ascend a brief, switch-backed section of steep trail for another six-tenths of a mile to a bedrock ledge and enjoy your first view of North Matthieu Lake.  This lake owes its origins to the damming of water normally draining downslope to the west by the Yapoah Crater Flow from a shallow basin carved into the bedrock by the passage of glaciers.

The trail traverses around the eastern end of North Matthieu Lake and gradually ascends the western flank of a cinder cone comprised of near-vent pyroclastic lava blocks, bombs, and scoria with a thin veneer of patchy glacial till (Map 4A.19).  Looking toward the south and southeast, you can observe a long ridge running slightly northeast toward you, seemingly connecting North Sister Volcano to Black Crater Volcano.  This cone is part of a glaciated ridge of late Pleistocene basaltic andesite lavas consisting of multiple, small cinder cones formed along a 5-mile-long chain (Taylor, 1968 and 1981).  These cones are comprised of cinders, scoria, and unusually large and abundant lava blocks and bombs likely spewed from an array of lava fountains associated with a series of fissure eruptions.  Two much larger, younger Holocene cinder cones are superimposed on this same ridgeline to the southeast; Yapoah Crater , nearer to your current position and the goal of this hike, and Collier Cone further to the south nearer the base of North Sister.

In about three-quarters of a mile, the right branch of the PCT rejoins its left branch; make note of this juncture, you may want to take this slightly shorter, but less scenic way back to your vehicle upon your return.  Just beyond the trail junction, you arrive at South Matthieu Lake (Figure 4A.57).  This lake lies in a small basin tucked between Yapoah Crater’s lavas to the west and two cinder cones forming the immediate part of the ridge just described (Map 4A.19).  North Sister looms prominently to the south, while Yapoah Crater appears for the first time to the southwest, lower on the horizon.  After swinging around the east side of South Matthieu Lake, the PCT is joined by a trail from the left, but ignore this trail and continue south on the PCT (this trail is another branch of the PCT that heads over the Cascade Crest, drops into the Whychus Creek drainage, and eventually passes the Green Lakes to reconnect with the PCT near Devils Lake, south of South Sister Volcano).  Just over a half mile from here, the trail reaches the western edge of the Yapoah Crater Lava Flow; another glacially polished bedrock outcrop occurs  next the trail on the left here.  Now traverse the jagged aa lava flows; first crossing several pressure ridges that lie parallel to the axis of the flow, and then running between two such ridges along the length of the flow.  Yapoah Crater begins to crowd the view on the southwestern skyline.  A careful observer will notice that the lavas become increasingly buried in coarsening cinders on the uphill traverse; this tephra produced by a northeasterly wind drift during latter-stage eruptions of Yapoah Crater.  Eventually, a buff-colored ridge can be observed to the right of the trail, a kipuka of older tephra probably related to early- stage eruptions from Yapoah capping a small cinder cone, later partially buried by lavas issuing from the Yapoah Crater’s northwest breach.

Figure 4A.57 - South Mathieu Lake copyrighted

Figure 4A.57.  South Matthieu Lake on the Pacific Crest Trail; from the shore North Sister Volcano rises in the background to the south, while Yapoah Crater conical summit rises to the southeast.

The trail eventually breaks free of the rough-surfaced lavas (about eight-tenths of a mile from where it initially climbed onto the flow), veers west, and begins crossing a cinderfield at the northern base of Yapoah’s cone (Map 4A.19).  Tephra here essentially buries the flow where it poured eastward over the southern end of the kipuka ridge, and here the trail abruptly climbs counterclockwise upward around the base of the Yapoah Crater cone.  In about a quarter mile, the trail reaches the crest of a low ridge running northward from beneath Yapoah Crater’s cone.  Now it can be observed that the eastern flank of a small cinder cone perched on this ridge forms the buff-colored kipuka indicated earlier. Apparently, Yapoah’s lavas initially poured northeasterly from the cone’s breach across the saddle to the fore of this cinder cone and around its eastern side, but later flowed northwesterly around the cones’ opposite flank after the gap in the ridge filled with congealed lavas (Figure 4A.58).

Figure 4A.58 - Congealed lavas near Yapoah Crater copyrighted

Figure 4A.58.  A saddle in a ridge projecting northward from the base of Yapoah Crater, formed between Yapoah’s cone and an older cinder cone capping the ridge, allowed lavas initially pouring from Yapoah Crater’s breach to flow northeast.  Eventually this gap was choked with congealed lavas, forcing flows to the northwest around the cinder cone-capped ridge and leaving it as a kipuka.

Continue about two-tenths of a mile around the cinder cone, the rough mound of lava protruding from Yapoah Crater’s western flank here probably marks the location of the breach although it is blanketed with tephra.  Look for a faint trail on the left which switchbacks up the side of the cinder cone; follow it to the crater rim (Map 4A.19).  When you reach the summit, look to the northwest toward McKenzie Pass, more-or-less down the axis of the Yapoah Crater Lava Flow (Figure 4A.59).  Note the rubbly, aa-textured surface of the lava flow.  Despite its appearance, the lavas producing this flow were quite fluid, reaching all the way to the base of Little Belknap Crater (lying on Belknap Crater’s southeastern flank), making a right-angle bend, and continuing downslope several more miles to the east.  In the foreground to the left, pressure ridges buckle the lava flow’s surface where still-fluid lava pushed from upslope nearer the breach, warping the already congealed surface of the flow.  In the background, several prominent volcanic peaks can be seen; from left to right these include Scott Mountain, Belknap Crater, Mount Washington, and Three-Fingered Jack, they’re “sharpness” related to age and degree of sculpting by glacial activity.  The Western Cascades can be observed on the skyline.

Figure 4A.59 - View northwest from Yapoah Crater copyrighted

Figure 4A.59.  The view to the northwest from Yapoah Crater’s summit rim.  The near vent portion of the Yapoah Crater Lava Flow is spectacularly displayed.

As you walk clockwise around the rim to take in more spectacular views, you should be able to make out Mount Jefferson and Mount Hood well to the north.  Nearer Yapoah Crater, a glaciated ridge consisting of late Pleistocene basaltic andesite lavas runs northeasterly toward prominent Black Crater, a 5-mile-long chain of multiple buff-to-reddish colored cinder cones peppering its back, their cinders oxidized by escaping gases during a series of closely timed fissure eruptions (Taylor, 1968 and 1981).  The cinders comprising Yapoah Crater are similarly oxidized in places.  This cone, as well as Collier Cone to the southwest, erupted more recently, but probably along the same NE-SW fracture system.

Continue walking; North and Middle Sister Volcanoes lie south of Yapoah Crater, although the view is partially obscured by a southwest continuation of the same glaciated ridge and more cinder cones associated with the late Quaternary fissure system just described.  After traversing half way around the cinder cone’s rim, make your way to the saddle between Yapoah Crater and the next cinder cone lying the south.  From this point, ascend several hundred feet along the red cindered slope south of the saddle for a wonderful profile view back to the north of Yapoah Crater (Figure 4A.60).  Yapoah Crater’s steep flanks and treeless summit belay its youth and lie in sharp contrast to the more subdued and forested late Pleistocene cinder cones in the area.  Return to the saddle and descend the prominent deer trail (probably groomed and expanded by hikers) that slopes downward on your right into the small valley on Yapoah Crater’s southeast side (Map 4A.19).  Once in this valley, simply walk around the cinder cone’s base to the northwest until you intersect the PCT.  At this point, you have hiked about six miles with almost four and half yet to go in order to reach the PCT trailhead near Lava Camp Lake.

Figure 4A.60 - Yapoah Crater copyrighted

Figure 4A.60.  Yapoah Crater’s late Holocene cinder cone (left) protrudes from the flank of an adjacent, older cinder cone.  This cone, Yapoah Crater, and other nearby cinder cones (such as those erupted between here and Black Crater) form a 5-mile long chain of cinder cones active since the late Pleistocene.

Return to the parking area and your vehicle, but try the alternate section of the PCT just below South Matthieu Lake.  No trail description of the alternate branch of the PCT is provided here; its most interesting feature occurs at the beginning where it traverses scoria and lava blocks and bombs of a late Pleistocene cinder cone.

Hiking Trail Maps

Map 4A.13 - Belknap Crater Trail A web version

Map 4A.13.  Color shaded-relief map of the southeast quarter of the Mount Washington 7.5” Quadrangle showing portions of the Belknap Crater and Little Belknap Crater Trail (Tr 4A.1), Black Crater Trail (Tr 4A.2), Lava River Trail (Tr 4A.3), and Yapoah Crater Trail (Tr 4A.9).

Map 4A.14 - Belknap Crater Trail B

Map 4A.14.  Color shaded-relief map of the southwest quarter of the Mount Washington 7.5” Quadrangle showing a portion of the Belknap Crater and Little Belknap Crater Trail (Tr 4A.1).

Map 4A.15 - Black Crater Trail

Map 4A.15.  Color shaded-relief map of the southwest quarter of the Black Crater 7.5” Quadrangle showing a portion of the Black Crater Trail (Tr 4A.2).

Map 4A.16 - Obsidian & Scott Loop Trail A web version

Map 4A.16.  Color shaded-relief map of the northwest quarter of the North Sister 7.5” Quadrangle showing a portion of the Obsidian and Scott Loop Trail (Tr 4A.4).

Map 4A.17 - Obsidian & Scott Loop Trail B

Map 4A.17.  Color shaded-relief map of the southwest quarter of the North Sister 7.5” Quadrangle showing a portion of the Obsidian and Scott Loop Trail (purple), as well as a hiking route to the Obsidian Cliffs and Obsidian Falls (orange).

Map 4A.18 - Obsidian & Scott Loop Trail C, Camp Lake Trail B

Map 4A.18.  Color shaded-relief map of the southeast quarter of the North Sister 7.5” Quadrangle showing a portion of the Camp Lake Trail (purple), as well as hiking routes to Carver Lake, and to the summits of South Sister Volcano and Little Brother (orange).

Map 4A.19 - Obsidian & Scott Loop Trail D

Map 4A.19.  Color shaded-relief map of the southeast quarter of the North Sister 7.5” Quadrangle showing a portion of the Obsidian and Scott Loop Trail and Yapoah Crater Trail (purple), as well as hiking routes linking these two main trails, and to the summits of Collier Cone and Four-in-One Cone (orange).

Map 4A.20 - Proxy Falls Trail web version

Map 4A.20.  Color shaded-relief map of a portion of the Linton Lake 7.5” Quadrangle showing the Proxy Falls Trail (Tr 4A.5).

Map 4A.21 - Sand Mountain Trail web version

Map 4A.21.  Color shaded-relief map of a portion of the Santiam Junction 7.5” Quadrangle showing the Sand Mountain Trail (Tr 4A.6).

Map 4A.22 - Scott Mountain & Hand Lake Trail web version

Map 4A.22.  Color shaded-relief map of the northeast quarter of the Linton Lake 7.5” Quadrangle showing the Scott Mountain and Hand Lake Loop Trail (Tr 4A.7).

Map 4A.23 - Tamolitch Falls Trail web version

Map 4A.23.  Color shaded-relief map of a portion of the Tamolitch Falls 7.5” Quadrangle showing the Tamolith Falls Trail (Tr 4A.8).