Calcrete Field Trip 2021 - Overview
Materials from my September 2021 "Geology Field Trip Guide to the Rain Shadow Calcretes near Othello, WA" with Northwest Geological Society (Seattle/UW). Your comments are welcome. Email is the best way to reach me.
WC = Warden Canal, LR = Liesle Rd, LCF = Lind Coulee Fault, SG = Stokrose Gravel, HRC = Herman Railcut, RTH = Red Tank Hike, TP = Taunton Powerhouse, OFF = Offramp, BRC = Booker Rd at Canal, HL = Hatton Rd-Lemaster Rd Intersection, CR = Coyan Rd, HX = Hendricks Rd, WBO = White Bluffs Overlook
Field trip stops. Black circles are stops described in the field guide, most of which we plan to visit. Open circles are other sites I've described. Black squares are the sites of others.
Timeline compilation. I've compiled information constraining the timing of Cascade Range uplift and arrival of a rain shadow in Eastern Washington from 40+ sources. Gray band brackets black bars, which are unconformities or other firm sidebars on rock uplift, topographic rise, and onset of dryland conditions east of the divide. Older studies tend to push the date back, while newer studies argue for a younger rise. This compilation is not exhaustive.
Calcrete-armored paleosurface. Stops in this field guide highlight sedimentary evidence of a relict Plio-Pleistocene landscape. Stacked calcretes, calcrete gravels, alluvial fan-loess complexes, and cemented silt diamicts delineate a dissected and deformed paleosurface located at the transition between the flood-dominated Channeled Scabland, loess-dominated Palouse Slope, and alluvial fan-dominated Yakima Fold Belt. The paleosurface may extend southwest to Eureka Flat and northern Walla Walla Valley (i.e, Rulo site), but we lose the calcrete as moisture and elevation increases.
White circles are my study sites, a selection of which are in this field guide. Black circles are sites in Baker et al., (2001), Bjornstad et al. (2001), Medley (2012), Bader et al. (2016), or unpublished locations from my field notes. Bold white line loosely delineates Pasco Basin, the colloquial name for the local portion of a once larger Neogene basin that was segmented by N-S and E-W faults and folds (see Eric Cheney's eggcrate model in Cheney, 2016).
BB = South Bombing Range Rd, BR = Booker Road at Canal, RR = Site 21-04, C = Connell, CB = Cummins Bridge, CCB = Cold Creek Bar, CR = Coyan Rd, EC = East Connell, FMEF = Fuels Materials and Examination Facility, FR = Field Rd, GL = George Landfill, GWB = Ringold Rd Bluffs, HL = Hatton-Lemaster Intersection, HO = Houghton Rd, HRC = Herman Railcut, HX = Hendricks Rd, LCF = Lind Coulee Fault, LF = Liesle Rd, LR = Lind Rd, LS = Leslie Rd, OFF = Offramp, OMC = Old Maid Coulee, PP = Potholes Park, PH = Poplar Heights Rd, RC = Reese Coulee, RT = Red Tank Hike, RULO = Rulo Site, Overlook, SB = Smyrna Bench, SP = Stokrose Pit, SR = Scooteney Rd, SS = Silicard Site, TPS = Taunton Power Station, WBO = White Bluffs Overlook, WC = Warden Canal, YB = Yakima Bluffs.
** See separate posts for selected photos for each individual stop. **
Directions - Offramp stop is located just east of the Hwy 26-Hwy 17 interchange SE of Othello. There are two ways to access it depending on how many vehicles you have. If your group is small, drive south from Othello on Hwy 17. Take offramp to Hwy 26 toward Pullman. Before the overpass, pull into gravel lot on left (north side). Walk beneath overpass and local a dusty two-track between the offramp road and the hay storage area. Walk a few hundred meters south, cross the wire fence, and drop down below the rim to canal level and the cutbank exposure. Footing can be loose, brushy, and seasonally wet.
If your group is large with several vehicles, access is better via a short track accessible from the northbound lane of Hwy 17 south of the interchange. From Othello, drive S on Reynolds Rd to Bench Rd and turn L (north) onto Hwy 17. Before reaching the northbound offramp onto Hwy 26, look for an unmarked spur road on the right just past the white "Othello Truck Route" sign and before the green "Othello/Vantage" sign. Beware of fast-moving traffic behind you. Move to shoulder and carefully pull off highway. Drive the grassy access road N, paralleling the highway for a few hundred meters to its end near Potholes Canal. Follow a messy, informal trail north a few hundred meters through sagebrush to the outcrop near a hay storage lot, crossing a wire fence (5 min hike). Drop down to outcrop at its north end.
GPS: 46.809707, 119.132850
Outcrop Summary - Two thick calcrete ledges are exposed beneath irregular lenses of reddish, fine grained sediment containing abundant soil features and trace fossils between. The red beds are in part water lain and wind deposited, resembling units in Palouse loess. The sediment was colonized by plants, insects, and rodents. Flat-lying Savage Island lake beds are present at the base of the exposure.
Medley (2012) visited and sampled this same location (her "Othello Canal" site),
A calcrete paleosol that is two meters thick in places overlies a slackwater deposit at the outcrop...Sample OC3 was collected from the massive calcrete paleosol and measures 38.3% ± 4.79 CaCO3, Stage III+ calcrete development (Figure 96). However, based on the massive and platy morphology and thickness of the paleosol, it qualifies for Stage V soil development.
Early work on old soils - Numerous researchers have described the ambiguous package of carbonate-cemented sediments sandwiched between Ringold Fm and Missoula flood deposits, but few in detail. The Plio-Pleistocene package has gone by various names, including "early Palouse soil", "pre-Missoula gravels", "Plio- Pliestocene unit", "stratified fines", and a "locally derived subunit" (Merriam and Buwalda, 1917; Bryan, 1927; Beck, 1936; Culver, 1937; Bretz and Horberg, 1949; Bretz et al., 1956; Newcomb, 1958; Brown, 1959, 1960, 1970; Tallman et al., 1979; DOE, 1988, Bjornstad 1990; Delaney et al., 1991; Lindsey et al., 1992; Lindsey et al, 1994; Slate, 1996, 2000; Lindsey et al., 2000; Wood et al., 2000; Wood et al., 2001). A notable early effort to map and characterize the unit was by Grolier and Bingham (1971, 1978). Since then, there has been considerable naming, renaming, lumping, and splitting of the deposits at the Hanford Site based on information from wet borehole cuttings (i.e., Bjornstad et al., 2010).
Hanford's Cold Creek Unit - Geologists at the Hanford Site call their Plio-Pleistocene strata the "Cold Creek unit (CCU)" and divide it into upper and lower units. "Calcrete and sidestream deposits" of the lower unit (late Pliocene) are differentiated from the "eolian and alluvial silt-dominated facies" of the upper unit (early-middle Pleistocene) by a sharp, distinct contact (Reidel and Chamness, 2007).
The lower CCU consists of basaltic to quartzitic gravels, sands, silt, and clay cemented by multiple layers of secondary calcium carbonate interpreted to be pedogenic locally influenced by the paleo-water table. The lower unit includes a variety of relict soil structures, cemented root casts, and burrows by insects and animals.
The upper CCU consists of generally massive, unconsolidated, brown-red-yellow silt and sand of fluvial and eolian origin. It is typically loose, friable, and includes the "early Palouse soil" and other pre- Missoula Pleistocene sediments believed correlative. The upper unit includes relict soil structures, root casts, and burrows. The contact between the upper unit and overlying megaflood deposits is indistinct and possibly gradational. It is unclear whether pre-Missoula flood deposits overlie or interfinger with the CCU.
Slate (1996, 2000), employing a soil-stratigraphic approach to cores from a Hanford study site, recognized the lateral continuity, low permeability, and variable thickness of Plio-Pleistocene carbonates. She found evidence of superimposed carbonate development (welding), modification by groundwater, and an enigmatic absence of soil horizons that typically overlie pedogenic carbonates (cambic horizon, etc.). Of particular interest is her recognition of carbonate morphologies unlike those described at classic localities in the U.S. Southwest (i.e., Gile et al., 1966).
Refs for Offramp: Medley (2012), Book M, p. 132, Book N, p. 53
Directions to Outcrop - From the Cunningham Rd-Hwy 17 intersection at Othello, drive 4.5 miles north on Hwy 17. Turn L (west) onto Herman Rd if traffic is light. There is no left turn lane here. The safer choice for a string of vehicles is to turn R onto Herman and make a U-turn in the Yancey Pallet parking lot, then cross Hwy 17 orthogonally. Drive a mile west on Herman Rd and park in small pullouts on both sides of road right next to RR tracks (2-4 vehicles) or proceed to the bottom of hill below tracks where a wide pullout can accommodate many vehicles. Hike the tracks to the north cut. For the south cut, make a gently rising traverse up the sagebrush slope, behind the stack of ties, toward a small tree in the distance. Stay above the wet ditch that parallels the tracks. The outcrop south of the road can get weedy and buggy in late summer. Better to go north after mid-July. Pray the mid-summer wind is not from the west (feed lots).
Outcrop Summary - The railcuts are located along the east bank (an outer bend) of Crab Creek Coulee just south of the Othello Channels constriction. To the northwest and across the valley is the butte-and-basin scabland of Drumheller Channels. The railway runs along the flood-cut escarpment. We are marginal to high energy, erosive flows rushed down the coulee. We are far removed from alluvial fans spilling from Saddle Mountains and Frenchman Hills uplifts. The coarse gravels here are flood-laid. Savage Island lakebeds underlie a boulder gravel and are accompanied by cemented water-worked pebbly silt diamict and nodular loess beneath a thick armor of calcrete.
Do carbonate fronts advance up or down in soils? - The world literature on pedogenic carbonate is clear on the direction of water movement in soils. Soil water, which transports carbonate, moves in various directions (Zamanian et al., 2016). Water percolation from the surface moves dissolved ions downward. Evapotranspiration moves only water upward. Throughflow moves both water and ions subhorizontally. Capillary rise moves water and a certain amount of carbonate in any direction. The movement of dissolved carbonate is therefore restricted. Dissolved ions move almost entirely downward and sideways with soil water, not upward. For Ca2+ ions and dissolved inorganic carbon species, its a one-way ratchet. Apparent upward growth (thickening) of Bk horizons occurs primarily with the addition of new sediment to the surface (new parent material) followed by calcic soil development.
In the windy Palouse, for example, surface burial by silt raises the ground surface. With burial, the Bk horizon shifts upward and thickens. The A-horizon is mostly preserved and the lower B-horizon may become inactive (too deep). Peroclation, evapotranspiration, throughflow, and capillary rise at work.
At Herman Railcut, secondary carbonate clearly overprints the tops of the boulder gravel; the CaCO3 front moved downward. Horizontal stringers and vertical seams of caliche in finer grained diamict also attest to vertical and horizontal flow. Little evidence of organic matter (A-horizon) is present at Herman Railcut or elsewhere in the Othello area. B-horizons dominate (i.e., pedogenic carbonate, cemented root casts, burrows, horizontal stringers, vertical seams).
Springs - Springs at the south end of the south cut emerge at the top of the low-permeability Savage Island. The clayey unit restricts infiltration of water supplied by irrigation. Perched water zones associated with pedogenic carbonates can impact crop productivity, slope stability, groundwater movement, and contaminant migration (i.e., Reidel and Chamness, 2007).
Refs for Herman Railcut: Baker (1973), Book N, p. 83, Book M, p. 127-129, Book O, p. 28
HATTON-LEMASTER ROAD INTERSECTION
Directions - From the Cunninghan Rd-Hwy 17 intersection at Othello, drive 4 miles S on Hwy 17. Turn L (east) onto Hatton Rd. Continue 2 miles E to the outcrop, located near the canal bridge. Shoulder pullouts are narrow. Watch for traffic. Instead park out of the way at top of hill on quieter Lemaster Rd.
GPS: 46.766520, 119.091857
Outcrop Summary - We are located in the eastern portion of the former Ringold lake basin, where loess-dominated hills begin to overtake the flood-sculpted landscape (Palouse Slope-Channeled Scabland transition). The focus of this brief stop is the Savage Island Member of the Ringold Fm. Here, we get a good look at undeformed, green-white-gray-black-tan laminated siltstones and a few thin, gray interfingering sand lenses. A serviceable type section for the Paradise Flats area.
BOOKER ROAD AT CANAL
Directions - Located along Booker Rd near the bridge over Potholes Canal 1 mile south of Hwy 26. Booker Rd (called Road U SE to the north) is a busy haul truck route where traffic moves fast, so visits are best done from a distance. Shoulder pullouts are unsafe. Instead, park on gravel farm-access driveways north of the canal. Park out of the way of farm equipment. Walk to the top of the west side bluff to view the east side exposure. Best light during afternoon hours.
Driving Directions - Starting from Moses Lake at the Kittleson Rd-Starbucks-McDonalds parking lot, head south to the left turn lane to eastbound I-90 towards Spokane. Drive 9.7 miles on I-90 to Exit 188 "Warden/Road U SE". Proceed south on Road U SE for 3 miles. Turn L (east) onto Road 3 SE and drive another 3 miles across low-relief, undulating farmland to the intersection of Leisle Rd, Fox Rd, and Road X SE. Turn R (south) and park in the WDFW lot. Walk back to roadcut located just east of intersection on Leisle Rd. This is typically a low-traffic roadcut.
GPS: 47.042750, 118.979940
Outcrop Summary - The Liesle Rd outcrop is a long ways from Othello, near the NE limit of Ringold sedimentation (Pasco Basin) and the farthest north and east of our stops. This is the western Palouse Slope, but we've not yet made it to the thick loess hills of the Palouse. Evidence of scabland flooding here is subtle and roadcuts sparse. Deep coulees so common to the west are missing from the landscape here. This was a depositional setting for broad, shallow Ice Age floods carrying sand, possibly reworked from local dune fields. The reason we stop here is to put flood deposits and caliche ledges in context of one another.
Stratigraphy. At the base of the exposure, a moderately cemented reddish, silt-sand bed crops out. Look to the opposite side of the road for better exposure (south side). The bed is >50cm thick with fine horizontal parting. Quiet water deposition, probably an overbank deposit. A lowland setting. Cemented red beds similar to this occur in the upper Ringold and lower Palouse loess, often with colorful paleosols.
Above this is a reddish, silty, nodular unit some 20-30cm thick. Cicada burrows create the nodules. This is old loess that may have been partially reworked by water. Horizontal stringers and vertical seams of CaCO3 are cemented cracks (macropores). An upland deposit.
Next is a 40cm-thick Stage III caliche ledge with a strong horizontal fabric so as to appear bedded. Cementation follows bedding in the parent material (silty red unit below) or was influenced by water moving through it. Voids are not completely plugged by CaCO3 - caliche, not calcrete.
Flood deposits are next in the stack. The first glacial outburst floods to sweep across this area encountered a loess-blanketed landscape and armoring calcretes. Three different flood-laid deposits overlie the caliche ledge. The lowest flood-laid bed is composed of silt and fine sand, and contains abundant rip-up clasts of carbonate. The unit thickens from 10-50cm as you move east across the outcrop.
The middle bed is an 80cm-thick silty, gray silt-sand bed that also contains pebble-sized rip-ups, but fewer of them. Its thickness and high silt content suggests it is reworked loess, rinsed from hillslopes. Cementation is weak, consistent with the Missoula flood cycle (18-14 ka).
The lower and middle beds may be two parts of the same unit; a dashed line separates the two. The first floods to reach here might not be the oldest in the scablands.
Above lie about 10 thin Touchet Bed rhythmites with a pinkish hue, each 10-15cm thick. Sheeted clastic dikes, sourced in these beds, taper downward and pinch out in the caliche ledge below. Their tops fade into the base of the modern soil.
The modern soil is thin (20cm) and shows evidence of disturbance. The bright white 1980 Mount St. Helens ash is visible just below the ground surface.
Refs for Liesle Rd: Book O, p. 27, Book M, p. 118
Directions - From the Cunningham Rd-Hwy 17 intersection at Othello, drive south 10.4 miles toward Scooteney Reservoir. Turn L (east) onto Coyan Rd. Continue past a house with large green barn, through an uphill bend, and past the roadcut to the top of the hill. Park along shoulder or in the private farm pullout. Get permission from the farmer at the house with green barn. Alternatively, park vehicles along highway at a wide pullout and walk to the roadcut. Roadcut is located below the crest of the hill. Farm trucks move fast here. Stay completely off roadway. Set out cones above crest of hill to alert traffic.
GPS: 46.72312, 119.016711
Outcrop Summary - The outcrop is located at an outer bend in Koontz Coulee, which merges with larger Ringold-Eagle Lakes Coulee farther downstream before emptying to the Columbia Valley. The broad terrace-like surface extending to the east is Paradise Flats (~330m elevation), a flood-beveled plain. Floodwater mainly from the Telford-Crab Creek tract and Grand Coulee arrived here after flowing through Othello Channels. The nose of the Saddle Mountains anticline points right at us. The fold terminates just east of the highway. The Koontz Coulee scabland surface floors the valley east of the highway and is partially filled by a shallow lake (Scooteney Reservoir). Camping and recreation there are managed by the Bureau of Reclamation.
Laminated silty lacustrine deposits exposed low in the roadcut are the Savage Island Member. The lakebeds appear white, gray, and tan on fresh surfaces. Horizontal bedding at road level becomes deformed and obscured just above. Soft sediment deformation structures consisting of ascending tongues (green) and downward-sagging load casts (white) comprise a zone some 40cm thick and laterally continuous across the exposure (25m). Horizontal spacing between lobes and tongues is fairly regular, varying between 16" and 36". The upward tongues, composed of Savage Island material, lean both uphill and downhill. Look for rectangular, pebble-sized laths of siltstone oriented with the folds. Descending lobes are composed of white "nodules" in a silty, light-colored matrix. The nodules are subangular, pebble to cobble sized rip up clasts of Stage III-III+ calcrete. The matrix appears to be a mixture of disaggregated and reworked lakebeds, loess, and overbank mud. The clasts were liberated from a calcrete ledge older than the one exposed here. The older calcrete was stripped away by floodwaters moving across Paradise Flats. An identical diamict unconformably overlies deformed Savage Island siltstone at Ringold, White Bluff Overlook, and elsewhere in the area.
Above the nodular unit is a prominent calcrete ledge I interpret as loess overprinted by calcic soil. An erosional surface necessarily separates the two. Savage Island and rip ups are water-laid units, above is dry, upland sediment. A subtle change occurs within the ledge. Its morphology goes from blocky to platy. The blocky lower portion is a Stage IV-V calcrete. Above is a silcrete with wavy parting and a platy, laminar cap. Silica cement was confirmed in the upper by soaking samples in HCl (thanks to Keith Harrington of NRCS). Locally thickened portions of the ledge are interpreted as shallow upland channels (swales) overprinted by the calcrete-silcrete.
Top of the section is Holocene loess disturbed by farming. Modern soils here are mapped as Sagemoor Series and Sagemoor-Kennewick-Shano Complex, common on gently-sloping and dissected "terraces" between 120-400 m elevation (NRCS, 2006). The Sagemoor Series is formed in loess over laminated lacustrine siltstone. Kennewick in lakebed sediments. Shano in loess.
Less Erosion in Koontz Coulee - Koontz Coulee contains a jumble of low hills that border the Scooteney Reservoir scabland - a knick zone. The hills are underlain by weak Ringold sediments, which was not completely scoured away as it was in portions of Ringold and Eagle Lakes Coulees (scablands). Remnant Ringold sediments remain in Koontz Coulee because after its partial incision, floodwaters diverted to those deeper, more direct routes to the Columbia Valley. Other shallow coulees along the western Palouse Slope appear to have been cut by early floods, then abandoned as the floodway evolved, left to accumulate loess and thick paleosols.
The perched outlet of Koontz Coulee, barely visible on the western horizon, was of interest to Bretz (1923, p. 646),
Koontz Coulee, 20 miles north of Pasco, is cut in the weak Ringold formation. It is 250 feet deep and a mile wide. It is floored with basaltic stream gravel from the scablands farther upstream. Though the Ringold silts extend down to the level of the Columbia...the mouth of the glacial river channel hangs 200 feet above [the Columbia Valley flood surface]. No cataract could have been maintained here, as was done at The Potholes and Frenchman Springs...
Streamlined Hill Across the Valley - Ringold sediments compose the hill dividing Koontz and Ringold Coulees (Scooteney-Hogback-Ridge Rd area) visible across the highway to the SW. The hill, now covered by orchards, was streamlined by Pleistocene floods, but not overtopped. A trimline at ~330m elevation is visible in aerial photos (Bjornstad, 2006, p. 101). The same calcretes and lake beds we see at Coyan Rd occur with basaltic fan gravels near the top of the hill, at 330m near the Mastre Farm (Scootenay-Horseshoe Rd area).
Directions: Drive 7.5 miles west on Hendricks Road from the Hwy 17-Hwy 260/Hendricks Road intersection. Roadcuts are located a short walk downhill from the kiosk/public parking area for Bailie Memorial Youth Ranch and Wildlife Area, where Bailie Creek crosses the road. An unnamed pond to the west fills a scabland basin. Do not block gated driveways near roadcuts. Road shoulders are narrow.
GPS: 46.674414, 119.151598
Outcrop Summary - Three roadcuts at Bailie Creek expose old sediments deposited atop the Eagle Lakes scabland surface. Five nondescript, gray-brown mudstone beds composed of locally-derived sediment contain weathered basalt cobbles, fossil cicada burrows, and Bk soil profiles (Stage I-II caliche). A yellow-green zone of weathered basalt (20 cm-thick) occurs below the beds and atop unweathered basalt. The weathered zone either began to form immediately after coulee cutting (i.e., the loose material was not stripped away by floodwaters) or formed more recently beneath a pothole lake (Holocene). The mudstone beds appear to lie unconformably atop the weathered zone. Three beds have Bk soil profiles, suggesting time passed between deposition of each. The top bed has the most prominent Bk horizon. Are they backflood rhythmites? The fact that these fine-grained sediments exist here in a flood-scoured scabland is amazing. Floodwaters rushed across this location during initial cutting of the coulee (Time 2) and during later flood events (Time 4). Columnar basalts form walls of a dry cataract now filled by an unnamed pond, the southernmost of the Eagle Lakes.
Refs for Hendricks Rd: Book 0, p. 29-30, 62; Baker et al. (2016, p. 49) describes overlook of Othello Channels scabland nearby.
LIND COULEE FAULT
Directions: From the Cunningham Rd-Hwy 17 intersection at Othello, drive north on Hwy 17 for 11.4 miles. Turn L (west) on Hwy 262 and follow it for 4 miles to the intersection with Road M SE. Turn R (north) onto Road M SE and soon pull off into a dusty fisherman's parking area at the south end of the bridge over Lind Coulee Wasteway. No parking permit required here. Hike an informal footpath west for a few hundred meters along top of the bluff through cheatgrass and sage to outcrops exposing the Lind Coulee Fault. If you have a Discover Pass, park instead at the WDFW fishing/hunting area off Hwy 262 to the west and hike the short distance east to shoreline bluff exposures. A large parking lot with a pit toilet is just north of the bridge. Gaiters, boots, long pants, and bug spray recommended. Explore other outcrops located east of the bridge and the roadcut along Hwy 262.
GPS: 46.988960, 119.216728
Outcrop Summary - Shoreline bluffs along the Lind Coulee Wasteway, an arm of Potholes Reservoir, expose faulted Miocene basalt, an interesting gouge zone, and Pliocene-Pleistocene sediments including loess and calcrete.
Lind Coulee Fault - The north-vergent thrust shoves Wanapum Roza basalt over brown alluvium and cemented, buff-colored Palouse loess. A meter of brecciated Roza basalt atop the fault plane grades upward into competent, spheroidally weathered basalt. The fault itself is highlighted by a white rubbly gouge zone 5cm thick. Footwall exposures contain a variety of sedimentary units and basalt. Loess appears to stand on end beneath the fault in one location, but the same loess lies flat a few meters to the east. Quaternary movement and basalt-over-loess relationships were established here and elsewhere along the fault by mapping parties decades ago (Grolier and Bingham, 1971, 1978 Figs. 14, 23; Reidel and Fecht, 1994).
The dip on the fault changes from east to west along the bluff. Dips between 10° to 60° are reported for this site and others in the vicinity (Grolier and Bingham, 1978; Lefevre and McConnell, 1987; Geomatrix, 1990; Galster, 1987). Lind Coulee Fault (No. 561b) is a strand of the larger Frenchman Hills system (Lidke and Haller, 2016) trenched in three locations by Michael W. West/GEI for the U.S. Bureau of Reclamation in the 1980s (Lefevre and O'Connell, 1987; Galster, 1987; West and Shaffer/ GEI, 1988; Shaffer and West, 1989; Geomatrix, 1990). Faulted loess exposed in the outcrops described here was not found in the trenches. A pedogenic carbonate in the trench (footwall) was assigned an age of 40-50 ka by the consultant. Alluvium locally buries strands of the fault.
Megaflood evidence - Flood deposits are not well exposed in the shoreline bluffs, but evidence of flooding is abundant in the surrounding landscape. Lind Coulee and the bench-like surface above are flood-formed. Low hills to the north, across the channel are partly underlain by high energy megaflood gravels. Flood-transported boulders are strewn across the undulating bluff to the south. Deeply scoured scabland of Othello Channels is found just across Hwy 262.
Sedimentary record of seismicity. I have found no sedimentary evidence of strong shaking (clastic dikes, liquefaction, or soft sediment deformation structures) in the brown alluvium that lies in direct contact with the fault or in other sediments at the site. Clastic dikes, so common in flood deposits of the region (Cooley, 2020), are absent here.
What is all this alluvium doing here? - The thick body of fine grained material preserved here, at the upper end of the Othello Channels scabland is curious. If this segment of the Lind Coulee thrust is ~13,000 years old, as paleoseismic studies and faulted footwall loess suggest, then the sliver of Roza and its tidy stack of sediments were uplifted at the tail end of the Missoula cycle floods. They would seem at high risk of removal by floodwaters. Was faulting too late? What provided the protection?
Refs for Lind Coulee Fault: Grolier and Bingham (1971, 978), Galster/USBOR memo (1987, "Area No. 2"); Levfevre and McConnell memo (1987), West and Shaffer (1988), Shaffer and West (1989), Reidel and Campbell (1989, "Stop 21-A", Fig. 14), Geomatrix Consultants Inc. (1990, "East Fault Exposure"), Reidel and Fecht (1994), Schuster et al. (1997), Lidke and Haller (2016)
WHITE BLUFFS OVERLOOK
General Directions - Hwy 24, Hwy 26, and 1st Avenue all meet in south Othello at the Chevron station. Head north and the sign for "Hwy 24 West/Yakima" and Broadway. Proceed south under overpass and through roundabout where Broadway becomes Hwy 24. About 17 miles farther, turn L (south) through the gate to White Bluffs Area. Proceed another 8 miles to the White Bluffs Overlook at road's end. Outcrop is through gate along the Old Ringold Road (Wahluke Walking Trail). The quality of this outcrop changes over time. In some years it will be nicely weathered with clean, vertical steps. At other times it can be collapsed to rubble.
Outcrop Description - The exposure begins a short walk from the vehicles along the Old Ringold Road. The focus here is on a.) upper Ringold Fm (Savage Island Member lake beds, colorful paleosols, thinner sands), b.) multi-story calcretes and interbedded sediments, and c.) megaflood deposits. Sediments of the Ringold basin comprise a "complex floodplain", including both lake system deposits and channel-overbank deposits. Colorful paleosols are consistent with a wetland environment. Above the paleo- shoreline we find alluvial fans, loess, and calcretes, which indicate hillslopes nearby had some topographic relief and steepness to them.
Savage Island siltstones - Laminated lacustrine siltstones comprise the uppermost portion of the Ringold Fm. The Savage Island Member, or "buff laminated clay" of Grolier and Bingham (1978), is thin-bedded, white-gray-tan on fresh surfaces, weathering to green. Fracture pattern changes moving down the hill. Diagonal fractures in the buff colored beds and vertical fractures in the laminated beds.
Gray fluvial sand beds - Gray-brown-tan rippled sand beds interrupt lake bottom deposits. Sands vary from unconsolidated to thoroughly-cemented. Soft sediment deformation (swirling and convoluted bedding, flame structures, pseudonodules) commonly occurs in the sands themselves and in lacustrine deposits sediment they override. Deformation appears to result from rapid sand deposition atop the soupy bottom sediment. Also, when the outcrop is in good condition (not freshly collapsed), curious massive beds 20-80 cm thick and composed of medium to fine sand can be found near road level.
Deformed zones - Soft sediment deformation occurs in three places, a.) base of calcrete gravel, b.) inside and beneath gray rippled sands, c.) inside "massive" sand beds. An early mention of deformed Ringold Fm comes from a 1934 field notebook of
M.A. Search titled "Field notes on Ringold Formation and other alluvium, central Washington, 1934" (Washington Geological Survey Archives, Book ID #68, p. 25),
Ringold 3-1/2 miles N of Warden. Dry creek (Lind Coulee). Bedded sandstone and clays. Mostly horizontal. Beds near bottom of coulee are wrinkled. This looks more like warping than ripple marked sediments, they are so irregular. The bank exposes about 8'. The upper 3' is topsoil - breaks off in vertical faces.
Search mentions calcrete,
...the section [is]...interrupted by 3+ ft of calcareous material. This appears to have broken the upper part of the last bed, destroying the bedding. This horizon forms a prominent ledge in places. Thickness is not certain since windblown material covers the highest part back of bluff.
And notes large concretions in sandstone,
Large concretions. The concretions are formed in a single horizon. The weathering of the bluffs has caused them to work down the hill. They are rod-shaped and elliptical in x-sec to nearly round. The bedding of the medium to coarse, x-bedded sand runs parallel to the longest dimension, clearly indicating that the columns were formed in horizontal position. The sand is about a coarse sand, of arkosic nature. There is dark mineral present. The concretionary zone lies just below a cliff of horizontally bedded volcanic dust. The elevation is about 650'. Indications are this zone overlies fossil horizon [by] about 50'.
Homogenized sand beds - Two conspicuously thick and massive beds of silty sand are found in the upper 10m of section. A good view of them is near the lower end of the first yellow guardrail. It is difficult to generate a whole lot of energy in a lake basin; flatlying strata suggests little local topography. But these homogenized beds came from somewhere. Perhaps they are the distal toes of subaqueous alluvial fans spilled from a distant ridge across the lake bottom.
Diatomite Layers - Diatomite occurs as thin, resistant beds up to 20cm thick interbedded with lacustrine Savage Island siltstones. Layers typically pinch laterally over tens of meters. Some are deformed by compaction into boudins. Freshwater diatomites in the western U.S. are white, very fined grained sedimentary rocks formed in shallow, warm, eutrophic lakes during the Miocene-Pliocene (24-2 Ma) (Wallace et al., 2006). Diatomite forms by the accumulation of silica-rich skeletons of diatoms, a type of single-celled algae. Basaltic rocks provided abundant dissolved phosphorus necessary for algal growth. When fresh, diatomite is soft with a chalk-like appearance. When cemented, it can achieve a chert-like hardness. Conditions that favored thick accumulation of the commercially-mined Quincy Diatomite that rest atop ~15 Ma Wanapum Roza flows near George, WA (Silica Rd), appear to have diminished during late Ringold time (after ~4 Ma), at least at White Bluffs. Increased evaporation during the Pliocene and the felsic, low-P content of Ringold lake sediments may have played a role.
Post-Ringold unconformity - The top of the Ringold is truncated by a prominent erosional surface. The post-Ringold unconformity may appear as a clear, flat, abrupt contact in some places and highly irregular, diffuse contact elsewhere. It represents the draining of Pasco Basin and the end of Ringold deposition at ~3.2 Ma.
Capping calcretes - Two thick calcretes are present. The lower calcrete is 20-40 cm thick with blocky morphology. It is partially disaggregated; look for large rip-ups. Above is a reddish, massive to stratified, water-lain silty unit that contains cobble- to boulder-sized rip-up clasts of calcrete and stratified laths of siltstone. The unit exhibits considerable variation in thickness and grainsize. A thin, cemented, semi- continuous conglomerate occurs near the base of the unit in places (more to north, less to south). The upper calcrete is a ~3m-thick, stage IV-V, ledge-former with blocky to platy-laminar morphologies. It is probably a stack of welded calcretes, but the ledge is too broken up along the rim to tell. The contact with the underlying unit is well defined and fairly flat.
Calcrete gravels contain exotic clasts - Access the ledge by walking S a few hundred meters along the top of the bluff before dropping a short ways down below the ledge. The unit is a conglomerate more than a meter thick with south-dipping foresets and subangular to rounded, pebble- to cobble-sized clasts of calcrete (rip ups) and clasts of exotic lithologies (volcanic, granitic, metamorphic) and some weathered basalt. Exotics comprise only a small fraction of gravel, so look close. Mafics will disintegrate when excavated.
Paleosols - A colorful paleosol interval is exposed a few hundred meters down the Old Ringold Road. The soils mark a shoaling of the lake and separate two packages of Savage Island siltstones.
White Bluffs Overlook Refs: Bjornstad (2006), Baker et al. (2016), Lindsey (1996), Reidel et al. (1992)
RED TANK HIKE
Directions - Same as Corfu Landslide Overlook. From the 4-way intersection at saddle crest, follow the curving road leading west, then north and downhill for 0.8 miles to the red metal tank. The road is rough and rocky, go slow. Appropriate for high-ish clearance vehicles. Park off the road to the left on a reasonably flat spot just past the tank. There is not a lot of room for vehicles. Don't block Corfu Road. Hike NW for 1/4 mile downhill to join trail leading along scarp through the "summit graben" toward a conspicuous knob of basalt. Just past the knob a wire fence leads north. Follow it to fence corner, then to outcrops beyond. Other hiking and game trails exist nearby.
GPS: 46.802445, 119.465330
CORFU LANDSLIDE COMPLEX
Directions - From Othello, drive Hwy 26 west to the White Bluffs Area gate. Do not turn. Instead, continue west on the highway 2.8 miles farther. Turn R (north) onto the gravel road (Corfu Rd) and locate the sign "Saddle Mountains Overlook 5 miles". Drive north up the south flank of Saddle Mountains. At 4.9 miles cross the canal, after which potholes and washboard increase. At 7.1 miles reach the saddle crest and 4-way intersection (565m elevation). Turn R (east) at the sign to "Saddle Mts Overlook 1 Mile". Continue up the easy incline to concrete slabs and road's end. Park and walk to the head scarp of the Corfu Landslide Complex.
Overlook: 46.791953, 119.446162
Saddle Crest 4-way Intersection: 46.793399, 119.470546
Red Tank: 46.802443, 119.465334
Return route and other stops - Return to the 4-way intersection at the saddle crest. Choose one of three options: a.) Stay L to return to Hwy 26. b.) Stay R for Red Tank Hike. The north half of Corfu Road is a rough, high-clearance route that descends through dusty, loose switchbacks to Crab Creek Valley. c.) The middle route leads to Wahatis Peak summit and radio towers. Gravel road that roughens near the top.
Corfu Landslide Complex - The shear cliff below your feet is the head scarp of the Corfu Landslide Complex. The complex consists of more than two dozen distinct slides covering some 20 km2 and a volume of ~1km3 (Lewis, 1985). Sliding occurred during the Late Pleistocene probably along a weak, clay-rich interbed within the basalt. Slide debris includes boulder-sized clasts of broken basalt, Ringold, and loess. Sliding may have initiated when the slope was undercut by the Missoula floods. Failure of thick, saturated loess (Hart et al., 2012) and ground vibrations generated by cataclysmic floods might also have played a role. Outburst floods post-date some lobes of the slide complex; flood-beveled benches in slide debris are visible at low elevations. Higher benches are truncated by the slide. Failures of mid-level benches creates a blocky pattern on lidar imagery and hints at more recent instability. Crab Creek has completely reworked slide debris spilled onto the valley floor. Both MSH Set S and Mazama ash are found in loess overlying slide deposits.
No soft sediment deformation - There is a distinct lack of soft sediment deformation in this 3m-high section despite its proximity to the Saddle Mountains Fault and a major league landslide. Evidence of shaking should be here. A thin interval of mildly contorted bedding occurs in places, but its quite unremarkable.
Fishy people - The nearby Taunton Bench site is an important fossil locality. Taunton is stratigraphically the highest of three Blancan faunas in the Ringold and appears to span the Plio-Pleistocene boundary (2.8–3.0 Ma). The three local faunas are the White Bluffs (~4.5 Ma), the Blufftop (~3.7 Ma), and the Taunton (2.8-3.0 Ma). Blufftop equates to our field stop at White Bluffs Overlook. Fish fossils excavated at Taunton indicate that the eastern Pasco Basin was connected to the Pacific via the ancestral Columbia- Salmon-Clearwater River through the Dalles-Umatilla syncline (Columbia Trans-arc Low) in the late Miocene, but isolated from the Pacific Ocean in the Pliocene, likely by waterfalls and water temperature (Smith et al., 2000).
Thick loess on Smyrna Bench - When we think of thick loess in eastern Washington, the Palouse comes to mind. Palouse loess was derived from outburst flood deposits, piled to a depth of 75m in places. Repeated episodes of watery southbound transport alternated with northbound recycling by wind. The oldest Palouse loess dates to 1.15 Ma (Sweeney et al. 2017). Smyrna Bench also hosts impressively thick loess, which farmers take advantage of with the help of center pivot irrigation. 3-4m of loess were exposed in a paleoseismic trench excavated by M.W. West/GEI off Road 17 SW near the base of Smyrna Bench (Section 36, T16N, R26E). Holocene loess 2m thick is exposed in roadcuts of Corfu Road below the mythical Red Tank. Dust accumulation continues today with Pasco storms thickening Palouse soils and Palouse storms thickening Okanogan soils.
Refs for Corfu Landslide: Sweeney et al. (2017), Baker et al. (2016, Stop 10, p. 42-43), King et al. (2016), McDonald et al. (2012), Hart et al. (2012), Sweeney et al., (2007), Sweeney et al. (2004), Bjornstad (2006), Richardson et al. (1997), West et al. (1996), Busacca and McDonald (1994), Busacca (1989), McDonald and Busacca (1988), Galster (1987), Lewis (1985), Reidel (1984), Bingham (1970).
Directions - From Othello, drive north on Hwy 17 and turn R (east) on Hwy 170/Rd 8 SE at the '76 gas station toward Warden. Follow for 0.5 miles, turn L (north) onto Rd S SE and follow for ~6 miles, passing by the Bassett Junction trestle at a sweeping curve. Feedlots owned by El Oro Cattle Feeders on right. Continue for another 1.3 miles, crossing the canal bridge, and turn L (southwest) onto Rd 3 SE. In a hundred meters, pull off on the wide shoulder near a guardrail. Do not block gates. The the canal spillway crosses below the road. The cutbank exposure is near the spillway outlet. Walk across the top of the bluff, then drop below the lip at some scruffy trees to inspect. Location is in Weber Coulee, a feature within larger Lind Coulee. Additional outcrops along canal are shown on map.
GPS: 47.043027, 119.110941
Touchet Beds - Missoula flood rhythmites comprise the 7m-thick section, perhaps a dozen. A prominent color change - from orange to gray - occurs about 2/3 of the way up. The orange tint may be from oxidation (orange = older floods), a changing sediment source, or accelerated weathering due to a high local water table. A thin, but conspicuous light gray mud line marks an unconformity that truncates sheeted clastic dikes. I've documented dikes identical to these from Hunters, WA to The Dalles to Salem, OR.
Load casts & large sags - Soft sediment deformation is abundant, repetitive, and takes different forms. The lower 8 rhythmites have load casts at their bases, where plane bedded sand contacts finer sediment of the rhythmite beneath. Load casts also occur within rhythmites, where the sand transitions to siltier stuff (flood-backflood transition or backflood-slackwater transition). Large sags in at least 2 beds (possibly as many as 4), initiated in the finer grained upper portions of rhythmites. Sags appear directly related to rapid deposition. Contorted bedding also occurs high in the section.
Clastic dikes - A sizable sheeted clastic dike cuts the exposure and is truncated by the light gray mud. It is filled with sand and silt like many others in the region. It measures ~30 cm wide and contains about half that many fill bands. Two additional sets of very thin, short dikes descend from the sandy bases of beds low in the stack. Clastic dikes are typically considered to be soft sediment deformation structures formed by liquefaction and fluid escape during seismic shaking. But some are not. In fact, these are not. The sheeted dikes in the Touchet Beds formed by hydrofracture in response to loading by floodwater and slackwater lakes. Pressurized fluid entered and expanded cracks in the flooded substrate, possibly involving some vadose zone shenanigans. See my article in Northwest Geology, the annual publication of the Tobacco Root Geological Society (Cooley, 2020), for the details.
Burrowed by rodents - A bed containing backfilled rodent burrows lies just below the dike-truncating unconformity. Burrowing rodents need time to recolonize the landscape between floods. Their presence indicates a years-long period of dry, upland surface stability. Oxidized concretions (root casts), slightly higher in the stack, mark another long pause between floods.
Dish structures & T-shaped mud squirts - Dish structures completely obscure a sandy bed located above the light gray mud/color change/unconformity. These are sedimentary structures formed by liquefaction/fluidization/water escape either during deposition or immediately after. They imply rapid deposition of wet sediment. The dishy layer also contains t-shaped mud squirts that rise from a muddy bed. The skinny, irregular structures are 10-20cm tall. Such structures are common in rapidly-deposited sediments where strong grainsize contrasts occur (sand piled quickly atop mud). Identical features are found in shoreline bluffs of the Sanpoil Arm, Rufus Woods Lake, and Banks Lake (Glacial Lake Columbia-Missoula flood deposits).
Refs for Warden Canal: Book O, p. 22-24