Road Log

0.0 (0.0)       Refer to Map 1E.1.  Intersection of Franklin Avenue and U.S. Hwy 97 Bend, OR.  Drive in west on Franklin Avenue.  Remain on Franklin Avenue through the downtown business district.

0.2 (0.2)       Underpass beneath the Burlington Northern – Santa Fe Railroad.  Road cuts on either side of Franklin Avenue are in the Basalt of Bend (Sherrod et al., 2004).

0.6 (0.4)       Intersection of Franklin Avenue and NW Bond Street.  Continue west through two traffic lights; Franklin Avenue becomes NW Riverside Boulevard after the second traffic light.  NW Riverside Boulevard curves gently to the south along the river.

1.1 (0.5)       Junction of NW Riverside Boulevard and NW Tumalo Avenue.  Turn right (west) onto NW Tumalo Avenue.

1.2 (0.1)       Cross the Deschutes River.  NW Tumalo Avenue becomes NW Galveston Avenue after crossing the river here.

1.5 (0.3)       Intersection of Galveston Avenue and NW 14th Street.  Remain on Galveston Avenue through the roundabout.

1.8 (0.3)       Bend city limits; Galveston Avenue becomes Skyliners Rd.  The road lies in a valley between two small, early Pleistocene basaltic shield volcanoes (Awbrey Butte to the north and Overturf Butte to the south) that rest on tuffaceous sediments and lava flows of the upper part of the Teritary Deschutes Formation (not exposed here).  The valley acted as a conduit through which four major pyroclastic flows passed from west to east, erupted from the silicic Tumalo volcanic center (Taylor, 1978 and 1981; Hill and Taylor, 1989; and Hill and Scott, 1990).  These and other pyroclastic rock units are explored in detail on Field Trip 1D.

2.8 (1.0)       Intersection of Skyliners Rd and Mt. Washington Drive.  Remain on Skyliners Rd through the roundabout.

4.2 (1.4)       Refer to Map 1E.2.  Deschutes National Forest Boundary.  Skyliners Rd becomes FS Rd 4601, gradually climbing an apron of glacial outwash related to late Pleistocene glaciation on the Tumalo Creek drainage.

8.1 (3.9)       This location marks the approximate extent of glacial till related to late Pleistocene glaciation of the Tumalo Creek watershed (the lateral moraines of this glacial advance are prominently displayed on Map 1E.2 just above this point); the terminal position of the valley glacier occupying Tumalo Creek about 20,000 years ago.  Bevis and Moreland (2013) correlate these moraines with the Suttle Lake advance of the Cabot Creek glaciation (Scott, 1977).  Figure 1E.1 displays the extent of the Suttle Lake advance in the combined upper Deschutes River-Tumalo Creek watersheds; while Figure 1E.2 offers a reconstruction of the Suttle Lake glacier system itself (Bevis and Moreland, 2013). The Suttle Lake advance was particularly extensive in the Tumalo Creek drainage and any evidence of the Jack Creek glaciation or older glacial periods is buried by these younger deposits.

Figure 1E.1.  The extent of the late Pleistocene Suttle Lake advance of the Cabot Creek glaciation in the upper Deschutes River and Tumalo Creek watersheds.

Figure 1E.2.  A reconstruction of the Suttle Lake glacier system in the greater upper Deschutes River-Tumalo Creek drainages.

9.3 (1.2)       A good example of the platy jointing that often develops in basaltic-andesite lavas is exposed in the road cut to the right.

10.0 (0.7)     Nicely columnar-jointed High Cascades basaltic lava flows exposed in a road cut to the left here.

11.6 (1.6)     Refer to Map 1E.3.  Cross Tumalo Creek here to an immediate junction of FS Rd 4601 and 4603.  Turn left onto FS Rd 4603.  FS Rd 4601 bends to your right and climbs the inner slope of the left-lateral, terminal moraine of the Suttle Lake glacial advance.  If you desire to see good road cut exposures of youthful till of late Pleistocene age and an aerial view of the valley of Tumalo Creek, follow this road to the first major switchback on FS Rd 4601, then return to this road junction and continue up FS Rd 4603.

12.3 (0.7)     Notice the large cliff, in part smoothly polished, exposed to your right at 2:00.  This cliff represents the right side of Tumalo Creek’s U-shaped valley cross-section; similar cliffs occur on the left side of the valley in places.  The distinctive U-shape of the valley is due to glacial erosion.  The once V-shaped drainage, the typical cross-sectional shape of a stream-carved valley, was transformed to the current U-shape by a succession of valley glaciers.

14.1 (1.8)     Cross Tumalo Creek and enter the parking area for the Tumalo Falls Trailhead.  Park here and walk to the overlook of Tumalo Falls (Figure 1E.3).  After taking in this amazing vista, hike upvalley to see two other spectacular waterfalls (see the Tumalo Falls Trail, under Optional Hiking Trails at the end of this road log for a complete description of this hike); this is a wonderful fall-weather hike.

Figure 1E.3 - Tumalo Falls copyrighted

Figure 1E.3.  Tumalo Falls and its valley; note the layer of resistant lavas resting on less resistant pyroclastic deposits.

Everyone enjoys seeing a waterfall, but why do they occur?  Tumalo Falls, and its smaller partners higher in the Tumalo Creek drainage, provide excellent examples of these common geologic features and a perfect opportunity to discuss their origins.  If the earth’s crust were composed of homogenous material, a stream’s erosive ability would depend primarily on the channel gradient and the stream’s average discharge.  Where stream gradients are relatively steep, channels tend to incise into the material underlying the bed, forming a fairly straight pattern in a generally narrow, V-shaped valley.  Where stream gradients are gentle, channels tend to wonder laterally, cutting into their bank on one side while simultaneously depositing sediment on their opposite bank, forming a meandering pattern on a floodplain in a generally wide, flat valley.  Over time, the stream’s valley would broaden and its channel gradient would decrease at the downstream end, while maintaining a narrow, V-shaped valley and steeper gradient upstream.  The stream’s channel would lengthen in the upstream direction by a process called headward erosion because the maximum erosive ability would remain concentrated higher in the watershed.  However, the earth’s crust is rarely uniform, especially over the distance of a gradually deepening and lengthening stream valley.  Instead, the stream would encounter multiple rock and/or sediment types with variable resistance to erosion by running water.  Eventually, at some location along the stream’s channel, flowing water may begin to incise into a relatively resistant material.  Where the channel first succeeds in eroding through the resistant bed material and into a weaker substance below, erosion would continue more slowly upstream and more rapidly downstream.  This process creates a short steep segment of stream channel, what a geologist calls a “nick point” in the stream and a waterfall begins to develop (Figure 1E.4).  Over time, the downstream segment of the stream overlying the weaker material would erode more deeply (especially at the base of the waterfall) and begin to undercut the resistant material above, causing it to break loose, only to be carried away in the flowing water.  Waterfalls are self-perpetuating, once the process has begun, they may back-waste upstream at the nick point by differential erosion for considerable distances.

Figure 1E.4.  Development of a nickpoint and waterfall on a stream system.

Notice the stratigraphy at the falls; a thick dense basalt forms the cap rock which is underlain by less indurated pyroclastic deposits, oxidized a reddish color by paleosol development.  Undercutting of the weaker pyroclastics by the rushing water of the falls causes calving of basalt blocks above and overall backwasting of the valley and headward erosion.  Incision of Tumalo Creek and generation of the nick-point and waterfall that is Tumalo Falls was aided by glacial erosion.  The waterfall has probably cut headward by several hundred feet since deglaciation of the drainage roughly 18,000 years ago.  Nick points and waterfalls can be generated in other ways, such as where faulting has steepened a segment of the stream channel, or as seen in Field Trip 1A, where a stream channel’s gradient has been steepened by blockage from a lava flow or other natural obstruction.

Return to your vehicle (but take the hike first!).

14.2 (0.1)     Recross Tumalo Creek and begin your drive back into Bend, OR along the same route you followed getting to Tumalo Falls.

Once you exit the parking area, observe the valley of Tumalo Creek more closely.  Notice that the stream channel itself is wide, gentle, and braided in this area (unusual for a typical, fast-flowing mountain stream).  This is a product of two events, separated by some 20,000 years.  First, the valley has been widened and deepened into a U-shape by repeated glacial erosion, and its channel gradient reduced by deposition of glacial outwash during final retreat of the Suttle Lake age valley glacier here.  Secondly, you are witnessing the affects of the 1979 Bridge Creek fire and subsequent salvage logging of burned, standing and fallen trees.  The fire burned 4,300 acres of original pine-spruce forest.  The removal of vegetation from steep slopes and stream banks by these natural and human events enhanced soil erosion.  The eroded soils caused excessive sedimentation in the stream channel, resulting in a reduced channel gradient and braiding of the stream channel, and overall flattening of the valley floor.  Unfortunately, this redistribution of floodplain materials led to damaging impacts on the stream ecosystem, including degraded water quality, wetlands, and both aquatic and terrestrial wildlife.  In 2004, a coalition between the City of Bend, Deschutes National Forest, and the Upper Deschutes Watershed Council, initiated a stream restoration program in this area.  This principally involved returning downed timber (referred to as large woody debris) to the stream banks and channels to simulate a more natural stream environment.  Over time, the affects of the fire and human misunderstanding will disappear.

28.3 (14.1)     Refer to Map 1E.1.  Intersection of Franklin Avenue and Oregon Highway 97 (3rd Street).  This ends Field Trip 1E.

Road Route Maps

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

Map 1E.2.  Color shaded-relief map of the Shevlin Park 7.5” Quadrangle containing segments of Field Trip 1A, 1D, and 1E, as well as Field Trip 2A.

Map 1E.3.  Color shaded-relief map of the Tumalo Falls 7.5” Quadrangle containing segments of Field Trip 1D and Field Trip 4B.

Optional Hiking Trail

Tumalo Falls Trail (Tr 1E.1)

This trail, aside from being a scenic hike along upper Tumalo Creek within easy reach of Bend, OR, also illustrates the geologic origins of the waterfalls described in Field Trip 1E.  The trail ascends fairly steadily to the uppermost of three waterfalls (Map 1E.1.1), an easy round-trip day-hike of a little over three miles in length that is suitable for families, and a great opportunity to learn about the formation of waterfalls.  Each waterfall on this hike formed where the stream channel “stair steps” downward over volcanic rocks of differential resistance to erosion, the more resistant unit forming the step over which the water tumbles.

The trail begins immediately beyond the information kiosk near the parking area.  Walk to the lower overlook of Tumalo Falls first.  While enjoying the view (Figure 1E.1.1), observe the surrounding bedrock exposed in the valley walls.  The falls have developed where a thick, dense, basaltic lava flow forms a resistant cap over a weaker pyroclastic deposit (Figure 1E.2).  Undermining of the less resistant rock at the base of the falls weakens the overlying basalt; it breaks up along joints into large blocks that are gradually broken up and swept away in the rushing water.  Tumalo Falls has probably back-wasted upstream several hundred feet since late Pleistocene glaciers last occupied the valley.

From the lower overlook, hike upslope to the left.  The trail splits in several hundred yards; take the right fork to the viewpoint at the top of Tumalo Falls.  The left fork bypasses the overlook altogether, but the birds-eye view down onto the water as it rushes over the falls is well worth the detour of about 500 feet.  Above the falls, Tumalo Creek has managed to cut several tens of feet into the resistant lava flow (although some of the incision may be due to glacial erosion concentrated along joints in the basalt.  Continue along the stream until the side trail to the upper viewpoint rejoins the main trail.

Hike upstream on the main trail, the valley of Tumalo Creek is quite pretty; in about six-tenths of a mile you reach another viewpoint, this time of Double Falls.  Two sets of double falls separated by a few hundred feet give this falls its name; Lower Double Falls is the more impressive of the two (Figure 1E.5).  Notice the platy jointing in the basaltic andesite lava flow here.  Both sets of Double Falls seem to have formed in a well-jointed basaltic andesite.  Zones of concentrated platy jointing within the lava flow may have caused the differential erosion necessary for the falls to develop.  Continue upvalley another three-quarters of a mile to a viewpoint of Upper Falls.  This falls has formed where a zone of weakness occurs between separate lava flows. 

Turn around and return to the parking area, it’s an easy (and pleasant) saunter of one and half miles downslope to your vehicle.

Figure 1E.1.1.  Lower Double Falls on upper Tumalo Creek; the set of falls here forming at zones of weakness in the basaltic andesite bedrock.

Hiking Trail Map

Map 1E.1.1.  Color shaded-relief map of a portion of the Tumalo Falls 7.5” Quadrangle showing the Tumalo Falls Trail (Tr3.1E.1).