Calcrete Field Trip - Coyan Rd
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.
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).
Soft sed def - Ascending tongues of green lakebeds alternate with descending lobes of calcrete gravel.
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 Medley (2012), Bjornstad et al. (2001), Bader et al. (2016), or unpublished locations from my field notes. Bold white line delineates Pasco Basin. 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.
Not frost churn - When I discovered this outcrop in 2017, I suspected the deformation structures might be products of frost churn formed in a periglacial climate. But I kept finding this same deformed zone in less ambiguous exposures, which, along with a field visit with a the local NRCS soil scientist and a some back and forth with a periglacial geologist, changed my thinking. Ground ice features here, at ~46 degN, are more than 100 km south of the former ice margin (Withrow moraine). Too far south to feel periglacial influence. Loess hills, mima mounds, and nivation hollows are not distinctive enough to call periglacial; you need soil wedges or similarly definitive structures that say ground ice formed here (French, 2017). Relict cryoturbation features, indeed clear evidence of frozen ground in any form, is all but non-existent in eastern Washington - even on the Waterville Plateau.
Coyan Road is located 100km south of the former ice margin.
Alternative (Bad?) Ideas - When I discovered Coyan Rd in 2017, I struggled to explain the subtle unconformity on the Savage Island. It is smooth and gradational. I didn't recognize the calcrete gravel for what it was, instead interpreting it as nodular caliche, a product of soil processes. That line of reasoning sent me down a creative path toward explaining the sub-unconformity deformation. The figure at right is a simple stepwise growth model for a carbonate front descending through cracked material. Horizontal and vertical advance at 140% an 115%, respectively, generated features that closely resembled the drooping load casts and ascending tongues I saw in the outcrop. It mostly made sense until I discovered calcrete gravels with identically-deformed stuff below. My model might be correct, but the many analogs suggest otherwise. The structures are evidence of mechanical deformation, not soil process, though the "clasts" in the descending lobes at Coyan Road deserve a closer look.
Soft sediment deformation. Ascending tongues of green, deformed lacustrine mudstone alternate with descending lobes of white, fine grained sediment containing calcrete clasts beneath a thick calcrete- silcrete ledge. The deformed zone is ~40cm thick, subhorizontal, and continuous across the exposure (20m).
Topographic profiles - Remnants of the Plio-Pleistocene pedocomplex are preserved in scabland channels cut long before Missoula cycle floods. South-moving floods that cut them likely flowed at lower elevations than the Lake Lewis maximum. That sediments and paleosols are preserved inside old coulees argues for an evolving scabland channel network, one that simplified and incised over time. Ancient floods moved in part through virgin loess hills and encountered few deep canyons.
Huge water volume in Columbia Valley - There is a difference between broad-spreading overland floods and floods confined by the Columbia Valley. Which would arrive in Pasco Basin first? The Columbia Valley could accommodate huge volumes of flood water and flows that rose to a considerable height, possibly preventing overland floods entering the valley from forming cataracts at White Bluffs. The cutting of Koontz Coulee, Ringold Coulee, and Paradise Flats provides clues to flood routing, flow confluence, and the evolution of the flood-channel network.
Analogous deformed lakebeds beneath calcrete gravel at Ringold Road, White Bluffs.
Waterline trench - Calcrete-bearing gravel and sand exposed in trench walls.
Waterline Trench - In March, 2020, I inspected a 300m-long trench opened for a new waterline installed parallel to Hwy 17 near Othello. The 1.5m-high walls exposed high energy flood gravels and south-dipping foresets. The gravel was composed of calcrete rip-ups and stratified chunks of Savage Island siltstone in a sandy, "salt and pepper" mixture of calcrete, mudstone chips, and basalt. Similar calcrete-bearing gravels are found at Coyan Road, Ringold Road, White Bluffs Overlook, and elsewhere in the Othello area. Paradise Flats, into which the trench was dug, was beveled smooth by outburst floods and generations of farm equipment. The continuous, gently southwestward-sloping surface stretches between Othello and Scooteney Reservoir, armored here (Herman Road), dissected there (Koontz Coulee). The Flats otherwise provide few clues to the geology beneath. The open trench was a lucky find; it existed for just two weeks and the friendly crew tolerated my entry.
Analogous bedded calcrete gravel (not a mass wasting deposit) containing exotic clasts cuts upper Ringold Savage Island at WBO. Deformed lakebeds are present at the contact a few meters away.
Foresets in flood-laid calcrete gravel at WBO overlie a calcrete developed in lakebeds and underlie a >1.5m thick Stage V blocky calcrete.
Analogous deformed Savage Island beneath calcrete gravel at Ringold Rd, White Bluffs.
Analogous deformed Savage Island beneath calcrete gravel at White Bluffs Overlook.
Analogous deformed Savage Island beneath calcrete gravel at White Bluffs Overlook.
Analogous deformed lakebeds near top of Ringold near Greenacres Farm, White Bluffs. Note the deformation occurs near the top of the Ringold, but does not post-date lake deposition. Lake deposits overlie the deformed zone. Calcrete gravel absent, but stratigraphic position is identical to other sites.