Road Log

0.0 (0.0)       Refer to Map 1C.1.  Intersection of Franklin Avenue and U.S. Hwy 97 (3rd Street) in Bend, OR.  Drive south, remaining on Hwy 97 (3rd Street) through town.

0.3 (0.3)       Underpass beneath the Burlington Northern Santa Fe Railroad.  Road cuts on either side of the road expose typical basalts from Newberry Volcano’s lower flanks (Sherrod et al., 2004).  These basaltic lava flows have been offset by NW-SE trending faults along the Tumalo Fault Zone which extend through the Bend area (Jensen, 2006) and are highlighted in Field Trip 1C.

1.6 (1.3)       The highway passes over the Central Oregon Canal which diverts water from the Deschutes River for irrigation.

2.9 (1.3)       Hwy 97 (3rd Street) crosses a major northwest trending fault trace associated with the Tumalo Fault Zone.  The fault block to the northeast has been dropped downward.  Look carefully, another fault scarp of the Tumalo Fault Zone is clearly visible on Map 1A.1 north of Pilot Butte.

3.0 (0.1)       Junction of U.S. Hwy 97 (3rd Street) and the Bend Parkway.  Turn left (south) and remain on Hwy 97.

4.6 (0.9)       Refer to Map 1C.2.  Southbound off ramp to Baker Rd and Knott Rd, remain on Hwy 97. Almost immediately, the highway crosses the Arnold Canal and another northwest trending fault trace here, with the northeast block dropped downward.

5.1 (0.5)       Northbound off ramp to Baker Rd and Knott Rd lies on the opposite side of the highway here.  The return route for Field Trip 1C will diverge here, but for now continue straight ahead.

5.9 (0.8)       Good view of Lava Butte at 12:00; notice Lava Butte’s relatively small size and conical shape; geologist’s refer to this type of volcano as a cinder (or scoria) cone); U.S. Hwy 97 passes around the eastern side of this cinder cone.  This volcano and its associated lava flows form part of a northwest trending linament of cones and flows on Newberry Volcano’s lower northwest flank (Figure 1A.1).  They erupted along the Northwest Rift Zone (Jensen, 2006), a system of youthful normal faults that cut across Green Mountain northwest of Lava Butte and continues southeast to the East Lake Fissure above East Lake in Newberry Volcano’s caldera rim.

9.4 (3.5)       Intermittent road cuts on both sides of the highway for about the next half mile reveal a thickening and then thinning blanket of dark tephra erupted from Lava Butte as the highway traverses across the NE trending axis of the cinder cone’s ash plume (Figure 1A.2).  Charcoal obtained from the base of the deposit indicates the tephra erupted about 7,000 years ago (Jensen, 2006).  A well-preserved section of Mazama ash occurs beneath the Lava Butte tephra.  Several cylindrical columns of reworked Lava Butte tephra were excavated here into the top of the Mazama ash during highway expansion in 1988 and Jensen (2006) indicates that these features represent the molds of trees rooted in the underlying Mazama ash.  The tephra buried the trees deeply enough to kill them, and as they subsequently rotted, volcanic cinders from the surrounding tephra filled the void to form the tree molds.

9.8 (0.4)       FS Rd 9710 lies on the opposite side of the highway here.  Field Trip 1B merges with the route at this point.

10.0 (0.2)     The basaltic aa lava flow margin from Lava Butte lies on the right side of the highway (Figure 1A.2); Lava Butte is in the background.  The highway continues around the eastern margin of the flow for about the next mile.

10.4 (0.4)     The Northwest Rift Zone of Newberry Volcano is expressed by a shallow fault scarp to the left side of the road here.

10.5 (0.1)     Gas-Line lava flows occur to the left and Lava Butte flows are to the right (Figure 1A.2).  The Gas-Line flows are also dated at about 7,000 years, but underlie the Lava Butte flows.  Jensen (2006) suggests eruptive activity along this portion of the Northwest Rift Zone began with vents near the Gas-Line flows and finally coalesced at a vent now under Lava Butte.

10.9 (0.4)     Junction of U.S. Highway 97 and FS Rd 9702 to Lava Lands Visitor Center and Lava Butte (these sites are described in Field Trip 1A).  Continue south on Hwy 97.

11.9 (1.0)     The highway passes over Lava River Cave near here.  Not to worry though, the lava tube’s roof is at least 50 feet thick.

12.0 (0.1)     Road cuts for about the next 0.3 miles expose the basalts of the Lava River Cave Flow, believed to be the equivalent of the middle to late Pleistocene Basalt of Bend.  The vent for this extensive flow occurred upslope from here, but is now buried by younger lavas.

13.4 (1.3)     Refer to Map 1C.3.  The highway passes over younger basaltic lava flows here, erupted from a chain of cinder cones to the left (east), the largest of which occurs at the site of the Camp Abbot cinder pit (visited just ahead).

14.1 (0.7)     Refer to Map 1C.4.  Sunriver Junction highway interchange.  Take Exit 153 which provides access to FS Rd 9720 and a continuation of Field Trip 1B on the left (east), or FS Rd 40 and a divergence to Field Trip 1A to the right (west).

14.4 (0.3)     Junction of Hwy 97 off-ramp and FS Rd 40 (right)/FS 9720 (left).  Turn right (east) onto FS Rd 9720 toward Lava Cast Forest to remain on Field Trip 1C.

14.8 (0.4)     Junction of FS Rd 9720 and Cottonwood Drive.  Turn left (north) onto Cottonwood Drive toward Lava River Cave of Newberry Volcanic National Monument to remain on Field Trip 1C; continuing straight ahead would diverge onto Field Trip 1B.

17.2 (2.4)     North entrance to the Lava River Cave parking area.  Turn in here and park; then walk to the cave entrance.  Access to the cave requires the purchase of a day-use pass (obtained here or at the Lava Lands Visitor Center).  Propane lanterns can be rented here, but bring your own headlamp if possible.

Lava River Cave was discovered by Leander Dillman in 1889 (Larson and Larson, 1987b).  It was known as Dillman’s Cave until 1921.  The Shevlin-Hixon Lumber Company deeded 22.5 acres of land surrounding the lava tube entrance to the state of Oregon in 1926 and the area became a state park.  In 1981, the area was acquired by the Deschutes National Forest in a land exchange with the state and it became part of Newberry National Volcanic Monument in 1994.  There are two portions to the cave, both entered from the same section of collapsed tube (Figure 1C.1).  The southeastern, upslope section is about 1600 feet long, but is closed to the public.  The more spectacular, northwestern, downslope, and accessible section is 6,180 feet long and drops 170 feet in elevation over its length.  This is the longest lava tube in Oregon.

Figure 1C.1 - Lava River Cave

Figure 1C.1.  Map and cross-section of Lava River Cave (modified from Larson and Larson, 1987b).

The walk through Lava River Cave is well worth your time.  This is not a cave in the same sense of the word that conjures up images of great limestone halls with drapes of flowstone, stalactites hanging from the ceilings, and stalagmites growing upward from the floors.  This cave is instead, a fine example of a lava tube, formed in the Lava River Cave Flow erupted from the lower northern flank of Newberry Volcano.  This flow is considered the equivalent of the Basalt of Bend (Sherrod et al., 2004) that extends around Pilot Butte in Bend, OR, which has been dated at about 188,000 years old (providing a minimum age for the flow and cave).

Lava tube formation is unique, but vital to the process of removing lava from the near vent area during relatively fluid, mafic, volcanic eruptions.  Active tube formation has been described in detail by Peterson et al. (1994).  The most significant factor in the formation of lava tubes is the viscosity of the extruded lava.  More fluid lavas are less viscous.  In general, lower viscosity lava occurs with greater heat content (higher temperature), greater gas content, and lower silica content.  Lower temperatures, lower gas content, and higher silica promotes mineral crystallization within the lava, and the lava solidifies too quickly and too thoroughly for tube formation.   Another important factor in lava tube formation is the rate-volume relationship of the flowing lava.  Low to moderate rates of lava production from the vent, sustained for long periods of time, work best to develop extensive tube systems.

During a prolonged eruption, lava initially spills out from a fissure, crater, or lava lake over a broad area as a thin sheet, each cooling and solidifying at relatively short distances from the vent.  As flow continues, lava becomes channelized in the depressions between previously formed sheets and begins to flow progressively greater distances from the vent.  Channelized flow and channel formation is a critical first step in lava tube development, but flow from the vent must be sustained for hours to days for one or more of four significant processes to begin actively forming tubes.

The formation of a lava tube may result from the growth of a surface crust rooted to the banks of a lava stream.  If a lava stream flows at a nearly constant rate, volume, and height within the channel for a considerable period of time, lava will cool and solidify at the surface, adhering in thin layers to the banks.  As flow is maintained, lava will continue to accrete to these outwardly growing margins, gradually forming a crust over the entire surface and an incipient lava tube.  If the surface level of the lava stream remains relatively constant, the roof of the lava tube will thicken and grow in the downstream direction.  If the height of lava in the stream abruptly decreases, the fragile roof of the tube will collapse; and if the height abruptly increases, the roof will be torn loose from the lava stream’s banks and carried away in the flow.  Eventually, the roof becomes strong and extensive enough to suspend itself without the support of the underlying flow, and the lava tube is firmly established.

Lava tube formation may also result from the accretion of stream bank levees when flow in the channel fluctuates significantly in rate, volume, and height.  During successive fluctuations, lava is accreted to the upper and inner edges of levees perched on the channel banks and the levees gradually arch toward each other over the lava stream.  Eventually, the slot between approaching levees grows narrow enough, so that the next surge of lava in the stream squeezes into the gap and solidifies, forming a seal over the channel and an incipient lava tube.  This process of tube formation may occur to a limited extent nearer to the vent, where splashing and spattering of lava is enhanced by the vigorous pulsating of gas-rich lava.

Formation of a lava tube may result from the accumulation of rafted slabs of chilled, semi-solid lava at channel bends and/or constrictions in conjunction with other processes.  In this process, a skin of congealed lava forms on the surface of the lava stream where flow is nonturbulent (flow that is not mixing).  Initially, these skins are thin and flexible, able to deform, bending through curves and/or squeezing through constrictions in the channel.  As the raft thickens and becomes more rigid, it will eventually get stuck at a particularly sharp bend or in a narrow constriction, becoming the roof of an incipient lava tube.  Flow of lava in the stream continues to jam additional rafts behind the new roof, thickening it, and extending it upstream.  Individual slabs gradually lose their distinctiveness as the rafts are contorted and fused together.

Where topographic gradient decreases, lava emerges at the lower end of a tube to produce laterally spreading fields of pahoehoe not confined in well-defined channels.  The surface of the spreading lava cools and solidifies to form a crust.  Molten lava beneath this crust continues to move outward and the overlying crust bulges upward.  In this way, small, distributary lava tubes may form.  Some of these tubes stagnate and congeal; others remain active, conducting lava to the flow perimeter and forming new flow lobes, incorporated into and extending the lava tube system.  Molten lava may split the overlying crust and pour out to form new flow lobes that crust over and branch again.  Younger flows are often stacked upon older flows and sometimes develop their own lava tubes fed by those below.  This process is continually repeated at the expanding flow front, creating an extremely complex system of relatively small, short distributary tubes.

This tendency for lava streams to encase themselves in tubes enables the molten lava to retain heat content and remain fluid because the congealed crust acts as an insulator.  Insulation, heat retention, and fluidity allow copious volumes of lava extruded at low to moderate rates to flow great distances and cover large areas.  In contrast, lava of greater viscosity or erupted too rapidly tends to solidify, reducing its ability to spread.  The molten lava in large, long-lived lava tubes will gradual decline in volume and height as the vent extrusion rate decreases.  The upper portion of the tube system often drains to preserve an empty lava tube, but the lower portion may not drain at all.  The lava stops moving, solidifying to become the floor of the tube.  Occasionally, lava tubes may become reoccupied by flows from subsequent eruptive periods.

Many fascinating late stage flow features can be preserved in lava tubes associated with the waning stages of an eruption or with reoccupation by subsequent, lesser volume, eruptive periods (Larson, 1993).  Numerous wonderful examples of these lava flow features are found in Lava River Cave.  Lava levees have formed along the tube walls in some places.  Careful observation of these levees indicates that they gradually descend downtube, indicating the variable flow levels related to temporary stabilization of flow volume in the tube.  Drip marks on the tube walls (Figure 1C.2a) and lavacicles hanging from the tube ceiling (Figure 1C.2b) have formed at various locations.  These features formed in the evacuated portion of the tube, either by semi-congealed lava oozing down the walls and from the ceiling as the lava level dropped or by the reheating and melting of lava on the walls subsequent to evacuation, possibly during reoccupation of the lower part of the tube by a low volume flow.  One portion of the cave preserves stacked tubes (Figure 1C.3); indicating either partial capping of a subsequent flow of lesser volume by congealed lava during reoccupation of the older tube or possibly melting of the older tube floor by a subsequent flow followed by capping of that flow.

Figure 1C.2 - Lava Formations

Figure 1C.2.  Drip marks on the tube walls (A) and lavacicles hanging from the tube ceiling (B) of Lava River Cave; arrows indicate orientation of the features.

Figure 1C.3 - Double Tube copyrighted

Figure 1C.3.  A smaller lava tube inset within the main tube indicates reoccupation of the cave by a subsequent lava flow.

One unique feature of Lava River Cave is the partial filling of its lower portion by sediment washed in along overhead fractures long after the cave had formed.  Excavations into the sediment by earlier explorers of the cave reveal alternating bands of “varved” coarse and fine material (Figure 1C.4).  The thicker layers of sand may be related to periods of sediment influx and cave flooding under higher energy conditions, while the thinner layers of silt and clay are probably due to gradual settling of the finer grains from quiet water as it slowly drained from the cave.  Sediment accumulation (varved and non-varved) is not uncommon in lava tubes.  Water continuing to drip from the ceiling today, has carved weird, castle-like forms into the sediment.  For more information on Lava River Cave or lava tubes of central Oregon, this author suggests Greely (1971), Larson (1982) or Larson and Larson (1987a and 1987b).

Figure 1C.4 - Sediments in Lava River Cave

Figure 1C.4.  The main photograph shows varved sediment filling the lower end of Lava River Cave, one of the author’s boys (7-years-old) for scale; the inset photo provides a more detailed view of the finer sediment.

17.4 (0.2)     Drive to the south exit from the Lava River Cave parking area back onto Cottonwood Drive.  Turn right (south) onto Cottonwood Drive and return to its junction with FS Rd 9720.

19.7 (2.3)     Junction of Cottonwood Drive and FS Rd 9720.  Turn right (west).

19.9 (0.2)     Northbound entrance ramp to Hwy 97 is on the right (north); take it to remain on Field Trip 1C.  Continuing straight would diverge onto Field Trip 1A.

29.3 (9.4)     Northbound off-ramp to Baker Rd and Knott Rd.  Field Trip 1C leaves Hwy 97 here; exit right (east) off of the highway.

29.5 (0.2)     Junction of exit ramp from U.S. Hwy 97 and Knott Rd.  Turn right (east) onto Knott Rd.  The road junction here is on the Basalt of Bend.

30.8 (1.3)     Intersection of Knott Rd  and FS Rd 18 (China Hat Rd).  Turn right on FS Rd 18 for now to visit Boyd Cave, a short but interesting lava tube (and one of the few “wild” caves on the Deschutes National Forest still open to the public).  Alternatively, remain on Knott Rd to continue with Field Trip 1C at mileage 38.2 if you do not want to visit the cave.

Unlike Lava River Cave, Boyd Cave is a “wild” lava tube and exploring it requires additional care.  Bring a light source (and a back up) and proceed slowly when climbing around in the cave.  China Hat Rd provides access to a number of other lava tubes on the northern flank of Newberry Volcano, but the Deschutes National Forest has closed many of them due to vandalism and threat to bats living in the caves from the spread of whitenose disease.  Wanderlust Tours offers a tour of Skeleton Cave and possibly others, but check their website for details (www.wanderlusttours.com).

Always inquire at the Lava Lands Visitor Center for the most recent information on access to any caves in the area.

31.8 (1.0)     Deschutes National Forest Boundary.  Almost immediately, the road begins following the margin of the 39,000 year old Klawhop Lava Flow on the left (Jensen, 2006).  This basaltic-andesite flow originated from Klawhop Butte about seven miles to the south; visited on Field Trip 1B.

33.0 (1.2)     After making a gentle left-hand 90° turn, FS Rd 18 leaves the Basalt of Bend here and climbs onto the margin of the Klawhop Lava Flow.

33.7 (0.7)     The road crosses a small draw at this location that is related to a NW-SE trending fault that cuts the Klawhop Lava Flow here.  Based on the age of the lava flow, this fault (and others you’ll soon pass) must be younger than 39,000 years old (Jensen, 2006), making it one of the youngest documented faulting events in the Bend area.

34.7 (1.0)     The road leaves the Klawhop Lava Flow here and crosses onto a basaltic lava flow from a low, unnamed vent two miles to the south.  This small vent produced a major lava flow that extends more than ten miles downslope to the north and northeast (Jensen, 2006), typical of the vents on Newberry’s lower northern flank that supplied lava to the Bend-Redmond area.  Many of these vents were relatively small and/or topographically low because the basaltic lava they extruded was very fluid.  They became buried by younger flows from upslope, making the sources of the Bend-Redmond flows difficult to locate.  Shortly, the road affords a view of Bessie Butte straight ahead; an older Pleistocene cinder cone surrounded on the west side by the younger Klawhop Butte Lava Flow, and on the east side by the unnamed flow you are now driving on.

36.2 (1.5)     Refer to Map 1C.5.  The road now leaves the unnamed lava flow first mentioned at mile 25.3.

37.1 (0.9)     FS Rd 18 makes a 45° bend to the left and climbs onto the margin of a lava flow from Kelsey Butte dated at about 284,000 years old (Jensen, 2006).  The low scarp running NW-SE here likely indicates a fault with displacement down to the southwest that accentuates the lava flow margin.  As you climb the fault scarp, look south for a good view of Kelsey Butte.

38.7 (1.6)     The road leaves the flow from Kelsey Butte and passes onto the Skeleton Flow.  Boyd Cave is one of several lava tubes formed in the Skeleton Flow.

38.9 (0.2)     Junction of FS Rd 18 and FS Rd 1819-242.  Turn left onto FS Rd 1819-242 to Boyd Cave.  A fence line and cattlegaurd lie just ahead on FS Rd 18 and the pavement ends at this point; if you pass these human-made landmarks and find yourself on gravel road, turn around.

39.2 (0.3)     Parking area for Boyd Cave.  Figure 1C.5 presents a map and cross- section of the cave.  This cave is a well-preserved lava tube with very little of its roof collapsed (Figure 1C.6).  Its ceiling, walls, and floor exhibit textbook flow structures, and several small feeder tubes extend as much as 10 feet from the main tube but are plugged.  Gorgeous flow levees can be observed along the margins of the lava tube indicating its last occupation by a lava flow (Figure 1C.7).  The total length of the cave is 1880 feet.  You will need your own headlamp or lantern to visit this cave.

Figure 1C.5

Figure 1C.5.  Map and cross-section of Boyd Cave (modified from Larson and Larson, 1987a).

Figure 1C.6 - Arched Ceiling copyrighted

Figure 1C.6.  One of the many nicely preserved sections of Boyd Cave’s lava tube; note the smaller, plugged, side branch from the main tube across from where the person is standing.

Figure 1C.7 - Lava Levees copyrighted

Figure 1C.7.  Well-preserved flow levees along the margins of  Boyd Cave indicate the last time the lava tube was occupied by a lava flow.

39.5 (0.3)     Junction of FS Rd 1819-242 and FS Rd 18.  Turn right onto FS Rd 18 and return to the intersection of Knott Rd and FS Rd 18.

As you drive, FS Rd 18 travels downslope toward the northwest and affords some nice views of the lower Crooked River valley and Smith Rock (to the north), Pilot Butte and the Bend, OR area (to the northwest), and the stratovolcanoes of the Cascade Crest (to the northwest and west).

47.6 (8.1)     Refer to Map 1C.2.  Intersection of FS Rd 18 (China Hat Rd) and Knott Rd; turn right onto Knott Rd.  If you did not choose to visit Boyd Cave, this is the mileage point where you want to pick up the route description from mile 21.4.

This segment of the trip explores faulting associated with the northwest trending Tumalo Fault Zone, a belt of en echelon normal faults that extend from near Sisters, OR southeastward, only to disappear beneath young lava flows of Newberry Volcano (Figure 1C.8).  Displacements on the nearly vertical faults rarely exceed 100 feet, although part of the fault scarp relief is obscured by sediment accumulation on the downthrown fault block.  Much of Bend, OR is underlain by two extensive lava flows of similar age which are cut by the faults of the Tumalo Fault Zone; the Basalt of Bend, originating from a now buried vent about mid-way up the northern flank of Newberry Volcano that extends to the southern edge of Redmond, and the western lobe of the Basalt of the Badlands erupted from a chain of spatter cones southeast of Bend.  Discussion in Field Trip 1A suggests that these lava flows are no older than 188,000 years, the age of the Pilot Butte cinder cone and its associated andesitic lavas which form a kipuka surrounded by these flows.   The 39,000 year old Klawhop Lava Flow on the lower northern flank of Newberry Volcano is also cut by these faults.  Geologists have yet to identify any evidence of Holocene displacement on the faults of the Tumalo Fault Zone, so apparently secession of faulting occurred during late Pleistocene time.

Figure 1C.8 - Normal Faults near Bend

Figure 1C.8.  Normal faults and grabens of the Bend area related to the Tumalo Fault Zone (modified from Jensen, 2006).

47.9 (0.3)     Refer to Map 1C.1.  Knott Rd crosses a northwest trending fault scarp here, with displacement down to the southwest.  Crossing this fault is not obvious to the casual observer, the road simply climbs over a subdued ridge.  This fault displaces the Basalt of Bend in this location as well as the Klawhop Flow further to the southeast.

48.2 (0.3)     Pass over the Arnold Canal and almost immediately cross another northwest trending fault, with 60-80 feet of displacement down to the northeast.  The Basalt of Bend is only marginally offset by this fault (about 10 feet of relief) and the Klawhop Flow to the southeast is not offset.  Apparently this fault has not moved as recently as some of those previously crossed.

49.7 (1.5)     The road leaves the Basalt of Bend and climbs onto the western lobe of the Basalt of the Badlands (recall this flow has a different vent source but is similar in age).

49.9 (0.2)     The road now climbs onto the Klawhop Butte Lava Flow.

50.4 (0.5)     Knott Rd crosses a buried fault trace here that apparently does not cut the Klawhop Butte Lava Flow.  Displacement on this fault is down to the northeast, forming the western bounding fault of a small graben.  The Klawhop Butte Flow spilled over the fault scarp and into the graben. The road shortly descends the fault scarp and leaves the Klawhop Butte Lava  Flow to begin traversing sedimentary fill within the graben.

50.6 (0.2)     Junction of Knott Rd and Rickard Rd.  Turn right (east) onto Rickard Rd and cross the floor of the graben.

51.3 (0.7)     Refer to Map 1C.6.  Junction of Rickard Rd and Arnold Market Rd.   Turn right (south) onto Arnold Market Rd.  The eastern bounding fault of the graben is clearly visible to the left of the road; its orientation is NW-SE with displacement down to the southwest.  Notice the houses perched on the edge of the fault scarp on the upthrown block, and houses at the base of the fault scarp on the downthrown block (Figure 1C.9).

Figure 1C.9 - Pleistocene Faulting near Bend copyrighted

Figure 1C.9.  A normal fault scarp near Arnold Market Rd in the southeast suburbs of Bend, OR.  Notice the two, more distant houses atop the scarp and another, closer house at its base.  This fault forms the northeast bounding fault of a small graben partially filled with sediment.

52.0 (0.7)     Refer to Map 1C.5.  Arnold Market Rd makes three sharp, right-angle bends beginning with this one.  Drive carefully.

52.9 (0.9)     The road crosses a northwest-trending fault with displacement down to the southwest.  This is the same eastern bounding fault of the graben you have been driving through (first viewed at mile 41.9).  Look to the southeast as you cross the fault scarp, the offset on this fault is as obvious as Mother Nature makes them (a better example of a normal fault does not exist in this guidebook).

53.2 (0.3)     Intersection of Arnold Market Rd and Billadeau Rd.  Turn left (north) onto Billadeau Rd.

53.8 (0.6)     Refer to Map 1C.6.  Billadeau Rd climbs a hill here.  This is a northwest-trending fault with displacement down to the southwest.  The field trip route zigzags across this fault several more times.

54.2 (0.4)     Intersection of Billadeau Rd and Rickard Rd.  Turn left (west) onto Rickard Rd.

54.5 (0.3)     Rickard Rd recrosses the same subtle fault as at mile 44.4.

54.7 (0.2)     Junction of Rickard Rd and Larsen Rd.  Turn right (north) onto Larsen Rd.

55.2 (0.5)     Larsen Rd climbs a long, fairly gentle slope here which is the same fault first crossed at mile 44.4 of the trip route.  The fault scarp is still fairly subtle here, although it becomes quite pronounced just to the northwest (Map 1C.2).

56.2 (1.0)     “T” junction of Larsen Rd and Ward Rd.  Larsen Rd ends here, continue straight (north) on Ward Rd.

56.7 (0.5)     Ward Rd curves sharply to the left (west); continue on Ward Rd.

57.2 (0.5)     Junction of Ward Rd and Stevens Rd.  Ward Rd curves sharply to the right here; continue straight (west) on Stevens Rd.  Just west of the junction, the road descends a slope representing another fault scarp (the same fault originally crossed at mile 44.4).  At this location, the fault scarp forms the eastern margin of the western lobe of the Basalt of the Badlands, although about half a mile northwest of this location the fault scarp is buried by the lava flow (Map 1C.2).  Displacement on the fault had apparently already occurred prior to emplacement of the Basalt of the Badlands.

58.2 (1.0)     Refer to Map 1C.1.  Junction of Stevens Rd and 27th Street (Arnold Market Rd.).  Turn right (north) onto 27th Street and cross the Central Oregon Canal.  Almost immediately after crossing the canal, the road leaves the western lobe of the Basalt of the Badlands and passes onto the Basalt of Bend.

59.6 (1.4)     Intersection of 27th Street and U.S. Hwy 20.  Turn left (west) onto Hwy 20.  Hwy 20 is called Greenwood Avenue within the city of Bend.

59.7 (0.1)     Hwy 20 (Greenwood Avenue) crosses a NW-SE trending fault scarp here with displacement down to the northeast.

60.3 (0.6)     The entrance for the Pilot Butte Trailhead parking area is on the right. Pilot Butte is an Oregon State Park and use of trailhead parking requires a fee.  There are two hiking trails to the butte’s summit.  The author has not hiked either trail, but the longer and more gentle one follows the road that coils upward to top, while the other trail is somewhat shorter, but steeper.  The views of the city of Bend are excellent, as are more distant views of the Cascade Range and other prominent peaks of central Oregon.

60.4 (0.1)     The highway leaves the Basalt of Bend and climbs onto the lower southeast flank of Pilot Butte.

60.9 (0.5)     The entrance road to Pilot Butte State Park is to the right here.  This road leads to the summit of Pilot Butte and is 2.2 miles round-trip.  Entrance to the park requires a day use fee.  Turn right onto Pilot Butte Road and drive to the summit.

62.0 (1.1)     Park in the summit parking area and explore.  Pilot Butte offers great views of the Cascade Range to the west, Newberry Volcano to the south, and the westernmost Ochoco Mountains to the northeast.  On a clear day, the view of the Cascade Range north to south includes the major strato-volcanoes: Mt. Adams, Mt. Hood, Mt. Jefferson, Three Fingered Jack, Mt. Washington, the Three Sisters and Broken Top, and Mt. Bachelor.  Notice the multitude of cinder cones perched on the flanks of Newberry Volcano.  Smith Rock, on the Crooked River, can be observed at the western foot of the Ochoco Mountains.

Pilot Butte is a late Pleistocene cinder cone about 188,000 years old (Sherrod et al., 2004).  Considerable erosion of the scoriaceous material comprising the cone has obscured the summit crater.  A vent on the northern side of the cinder cone at its base produced a small andesitic lava flow.  This flow is cut by faults of the Tumalo Fault Zone and forms a kipuka surrounded by the Basalt of Bend.

63.1 (1.1)     Junction of the Pilot Butte Rd and U.S. Highway 20 (Greenwood Avenue).  Turn right onto Hwy 20 (Greenwood Avenue).

63.3 (0.2)     The highway crosses back onto the Basalt of Bend.

63.7 (0.4)     Hwy 20 (Greenwood Avenue) crosses a NW-SE trend fault here, down to the northeast.  This fault is buried for much of its nearly 10-mile length by the Basalt of Bend.

63.8 (0.1)     Intersection of U.S. Hwy 20 (Greenwood Avenue) and U.S. Highway 97 (3rd Street). Turn left (south) on Hwy 97 (3rd Street).

64.1 (0.3)     Intersection of U.S. Hwy 97 (3rd Street) and Franklin Avenue.  This ends Field Trip 1C.

Road Route Maps

Map 1C.1 - Bend, OR

Map 1C.1.  Color shaded-relief map of the Bend 7.5” Quadrangle containing segments of Field Trip 1A-F and Field Trip 2.

Map 1C.2 - Lava Butte

Map 1C.2.  Color shaded-relief map of the Lava Butte 7.5” Quadrangle containing segments of Field Trip 1A, 1B, and 1C, as well as Field Trip 2A.

Map 1C.3 - Benham Falls

Map 1C.3.  Color shaded-relief map of the Benham Falls 7.5” Quadrangle containing segments of Field Trip 1A, 1B, and Field Trip 2A.

Map 1C.4 - Anns Butte

Map 1C.4.  Color shaded-relief map of the Anns Butte 7.5” Quadrangle containing segments of Field Trip 1A-1C,  Field Trip 2A, and Field Trip 3A.

Map 1C.5 - Kelsey Butte

Map 1C.5.  Color shaded-relief map of the Kelsey Butte 7.5” Quadrangle containing segments of Field Trip 1C.

Map 1C.6 - Bend Airport

Map 1C.6.  Color shaded-relief map of the Bend Airport 7.5” Quadrangle containing segments of Field Trip 1C.