Calcrete Growth in Alluvial Lowlands - New Findings in Eastern Washington State

I can't get any lower.

Still I feel I'm sinking.

-Soundgarden

Calcrete is not a caprock. Thick pedogenic calcrete is intrinsically related to valleys. Calcrete forms in stable, lowland settings where vigorous evapotranspiration occurs. Resistant calcretes, once formed, persist and often define remnant geomorphic surfaces that are later incised and dissected. Calcrete that today occupies an elevated position in the landscape (caprock) formed as a lowland soil - a crust on alluvial sediments of a floodplain or gently-sloping fan.

Abstract

This article explores the spectacular calcretes of south-central Washington. The thick, bright white CaCO3-rich paleosols overprint the Pliocene Ringold Fm, Plio-Pleistocene fanglomerates, pre-Wisconsin flood gravels, and early Palouse loess. The blanket-like hardpans formed in alluvial sediments low in the landscape where strong evapotranspiration moved large volumes of water through the soil column via vegetation rooted near the water table. The aridity necessary to precipitate CaCO3 arrived to Eastern Washington no earlier than 7 Ma, during the very latest Miocene. The shift to a cooler, drier climate was driven in part by the rise of the Cascade Range and in part due to changes in ocean circulation (i.e., Isthmus of Panama). While calcretes predate the Pleistocene, they thickened considerably during the Pleistocene (~2 Ma to ~50 ka) with accelerated development during interglacials. Calcretes described in this field guide span three important geomorphic domains: Palouse Hills (loess deposition), Channeled Scablands (cataclysmic flooding), and Yakima Fold Belt (young tectonism). They cement sediments of each and are interwoven into their geologic histories. Calcretes described here are confined to a relatively brief period of time and occupy a thin slice of Washington's stratigraphic column; they form excellent marker horizons. Because they formed in valley settings, they provide paleotopographic control on the Yakima Fold Belt deformation.

Field Guide Materials for FOP PNW Cell - September 8-10, 2023 - Handouts provided to attendees w/ some minor edits.

Western calcrete region. Dryland soils and sediments cemented by calcite occur primarily west of the 'calcium line' of Jenny (1941). Yellow areas correspond with semi-arid climates and alluvial valley fills containing varying amounts of CaCO3. Blue area is a broad alluvial fan apron composed of cemented gravels and sands. The Columbia Basin, an improbable northern outlier, is home to a set of thick, stacked calcretes developed in alluvium, loess, and fan gravels on par with those in the desert southwest (i.e., Gile et al. 1966). Jenny's eastern limit closely matches the 'Eastern Boundary of Arid Region' shown on an 1891 USGS map titled Arid Region of the United States (USGS, 1891, Part II, Plate LXVIII). Map modified from Soil Conservation Service (1970) and Machette (1985).

My calcrete study sites in south-central Washington. Calcretes grew thick in an ancient structurally-controlled alluvial low spot centered approximately on Othello, WA.

Study area. My fieldwork focuses on the Othello-Saddle Mountains area, from Quincy Basin to White Bluffs.

Topographic profile across 3 geomorphic domains. Calcrete spans three geomorphic domains in Eastern Washington: Yakima Fold Belt (active tectonism), Channeled Scabland (catastrophic flooding), and Palouse Hills (loess-dominated landscape).

Geomorphic domains overlap. Yakima Fold Belt, Channeled Scablands, and Palouse Hills converge near Othello, WA. Calcrete-bearing strata interfinger with sediments of each domain and cementation is interwoven into the geologic histories of each.

Warped by faulting, incised by megafloods, buried by loess. Calcrete-armored surfaces (heavy black lines) are deformed across Yakima Fold Belt ridge-anticlines and stripped from coulees cut by Ice Age floods. In places, the armored surface was able to resist erosional stripping by overland floods, especially near trimlines, where the flow energy was lower. The level of maximum flooding in the N-S transects above is approximated by the Lake Lewis shoreline (366m). Black dots are my study locations. Thrust belt anticlines between Moses Coulee and Cold Creek Valley (top profile) include Badger Mountain, Frenchman Hills, Saddle Mountains, and Umtanum Ridge. Figure from Cooley (2022), Tobacco Root Geological Society Guidebook Vol. 51, 'Wenatchee Area Geology'. Purchase volume from www.trgs.org or MBMG publications office in Butte, MT.

Remnant surface. A hasty map of the pre-glacial 'remnant' surface (white areas) in south-central WA. Calcrete is found at or near the ground surface nearly everywhere shown in white. Ringold Fm and Plio-Pleistocene sediments typically lie beneath. The surface is elevated above bedrock-floored scabland coulees (purple areas). Green areas at Saddle Mountains and Frenchman Hills are recently uplifted bedrock ridges and young, proximal alluvial fans draping their flanks. Dark blue areas are portions of the Ice Age floodway mostly covered by flood sediment. Orange areas are the Palouse Hills. The white snake-looking things are box-floored coulees and dendritic drainages incised into the remnant surface. White stars are diatomite deposits and the dashed white line loosely defines the Miocene diatomite lake basin, which pre-dates the calcrete. A few interesting things to note: a.) A connection between Drumheller Channels and Othello Channels is clear. Othello Channels may have been the original route to the Columbia taken by floods, abandoned during later floods as fill in the Crab Creek Valley was excavated and flushed west. b.) Scabland floodways breach anticlines. Major floodways widened older (pre-glacial) fluvial channels across fold crests. c.) This map differs from traditional surficial geologic maps. It doesn't follow the rules, yet captures a lot of what geologists find important. It ignores the thin, incidental veneer of Holocene loess, highlighting instead the more consequential sedimentary units below. Rule-breaking maps like this help us visualize and reconstruct paleolandscapes. I drafted this in one day using Adobe Illustrator, field notes, and the lidar hillshade. No GIS needed.

Offramp Site at Othello. Stacked calcretes with loess/silt-pebble diamicts over Ringold Fm.

Herman Railcut site. Stacked calcretes with loess and silt-pebble diamicts over an ancient flood gravel atop Ringold Fm.

Columbia Basin calcrete

In Eastern Washington, a robust association exists between thick pedogenic calcretes (petrocalcic horizons) and lowland alluvial deposits. That's a key finding of my work since 2019 on Pliocene-Pleistocene geology in the Saddle Mountains-Othello-White Bluffs area. Meter-thick (Stage III-V) calcretes here post-date sediments of the uppermost Ringold Formation and have pedogenic (soil-formed) and shallow groundwater morphologies (throughflow in soils and seasonal residence in capillary fringe). Puzzling why this lowland association goes unmentioned in previous articles on Washington calcretes, especially when numerous studies from other calcrete provinces demonstrate a clear association with alluvial fills on low-gradient valley bottoms (i.e., Machette 1985, Othberg et al. 1997, Chen et al. 2002, Sofoulis 1963, Budd et al. 1977).

One reason for the oversight might be the Palouse. Numerous articles on the Palouse loess and its "caliche" horizons have been published over the past century (Bryan 1927, McDonald and Busacca 1988, McDonald et al. 2012). Many geologists were first introduced to caliche on field trips to the Palouse. In fact, many of us equate caliche with the Palouse, though its expression there is just one of many variants. Caliche in Palouse soils is generally weakly developed (< Stage III), laterally discontinuous, and unquestionably formed by soil processes on upland hillslopes. The landscape never permitted calcrete ledges to growth very thick. Meter-thick, multi-story calcretes (> Stage IV) are found west of the Palouse in the lower, drier Pasco Basin. Pasco Basin calcretes are as old or older than the loess hills. Some appear to pre-date the oldest dated loess (1.15 Ma). The region's thickest calcretes developed in lowland sediments of a long-lived alluvial plain that has since been deformed by YFB tectonism, today occupied by the Saddle Mountains, Smryna Bench, Wahluke Slope, and Paradise Flats.

A second reason might be linguistics, specifically the term "caprock". Calcrete in the Pasco Basin has for decades been described as the "calcareous cap on the Ringold Formation" and typically viewed in outrops at White Bluffs or along the crest of the Saddle Mountains (looking up from Crab Creek). The word "caprock" is succinct and kind of fun to say, but the concept remains problematic. Caprock occupies a high position in the landscape, commonly a plateau or bluff. At the time they formed, however, they were soils in lowland settings probably quite near the water table. Later they were elevated by tectonism and fluvial incision.

Sidebar: J Harlan Bretz's Field Notes on Calcrete in the 1920s

Whatever aspect of Scabland geology interests you, J Harlan Bretz probably noted it in his field book 100 years ago. Calcrete is no different. Here's a few examples from his original field notes recently unearthed by Professor Nick Zentner of CWU (www.geology.cwu.edu/facstaff/nick/gFLOODS/).

A well 2-1/2 miles west of Connell, on the brink of [a high gravel bar], penetrated 35 of limestone gravel, 100 ft of yellow clay, and 100 ft of dark colored sticky clay before finding the basalt...The limestone gravel is exposed near the well in a road cut. It is dense and firm but rubs like chalk and is pure white in color. Secondary deposition has partially indurated it and growth of fragments with tuffaceous accretions, particulary on their lower sides, it part obliterates the appearance of a gravel conglmerate. But it is such. Plenty of rounded pebbles can be collected. Reported that by analysis, the deposit is 96% CaCO3.

- July 25, 1923: Pasco to Connell

An area of scabland on south side of Washtucna a mile west of Sulphur [railway Station]. It is a rock terrace above the coulee walls. Altitude between 1100 and 1150. Road skirts south edge of it. Typical Spokane [age] talus. Upland to south descends to it by the old river channel bluffs of pronounced development, 50 ft high and 30 degree slopes. Road cut in base of one of these steep slopes shows loess with much calcareous deposition, in tubules and especilally along stratification planes. This material is probably that which constitutes the upland rolling toopgraphy tho it may be possible that it is a later deposit at the foot of the old bluff.

- July 27, 1923: Connell to Kahlotus

Here the glacial stream which cut [Devils Canyon] made a steep scarp in the loess and the road grading has exposed material which originally was at the base in the center of the hill. It is loess, and full of secondary lime in seams and rootlet casts. These root casts are indisputable. Some are shells deposited around sage roots, 2-3 inches in diameter, identical with those seen in present soils at Cold Springs Resevoir [in Umatilla Basin, OR].

- July 27, 1923: Connell to Kahlotus

A splendid section in a Palouse hill 1-1/2 miles north of Harrington...The loess is stratified throughout...a number of different reddened zones were easily visible. These are taken to be old surfaces, oxidized during the accumulation of the loess. Rootlet marks, fine enough and abundant enough to have been grass roots, are common. Indeed, the material is full of them. Not a square foot that doesn't show from several to perhaps a hundred. Markings are recorded in CaCO3. Much lime deposited also in stratification planes. Some horizons partially indurated because of the abundance of the lime.

- August 9, 1923: Davenport to Harrington to Odessa to Wilbur

A third reason might be the dire warnings from so-called experts, who perhaps inadvertently discourage new work with their 'Here be dragons' comments,

The dating of land surfaces presents difficult and exasperating problems for geomorphologists...fraught with problems...in many instances the essential evidence has been eliminated, so that some surfaces are...undateable.

- Twidale and Bourne (1998)

Caution is advised in...attempts to correlate duricrust types on the basis of valley exposures...only duricrust host material characteristics and not cementing materials should be considered...there is no evidence for correlation of duricrust cements between exposures. - Nash et al. (1994)

A fourth might be oversimplified figures in Soil Science and Geomorphology textbooks. For example, Figure A below shows a slope profile where evaporation decreases downslope. In general the concept works fine, but when applied to pedogenic calcrete, it fails. The figure implies a Bk horizon will form on the drier summit. The second (B) questions this concept. What if the summit is rocky and soil-free, the toeslope heavily vegetated, and a water table present only in valley alluvium? Calcrete will form there instead.

Is the standard slope-accumulation model relevant to pedogenic calcrete? A.) Generalized evaporation-erosion-deposition model shows how soil moisture, sediment type, and thickness varies along a slope (i.e., McCraw 1967). This figure is found in all soil science, pedology, and soil geomorphology textbooks. The model predicts soil moisture will increase downslope and that greater evaporation, thus more CaCO3 preciptiated in soils, will occur higher on the hillslope. Bk horizons will form up there, not down here. B.) Real-world examples contradict the model (i.e., Foley et al. 2006). Bk horizons form at various landscape positions due to a variety of factors, but thick petrocalcic horizons (Bkk) tend to form at lower positions where strong evapotranspiration moves large volumes of water through the soil column via vegetation rooted near the water table. Alluvial fans, fluvial terraces, dusty and sluggish alluvial plains, and the floors of flood coulees. At high, dry positions moisture is limited, thus the supply of dissolved constituents is limited. More water, not less, seems to create thicker pedogenic calcretes in a semi-arid region like Columbia Basin. Mountainous terrain tends to thwart soil science concepts developed in flat farmlands of middle America. Out west, the geology and terrain dominate; soils take a back seat. Never heard a grizzled old geologist advise a promising, career-seeking youngster to "Go Midwest, young man." If you're career is in soils, you must.

Relative topographic position. Relative topographic position is the vertical location of any element in the landscape relative to other elements nearby, independent of elevation above sea level. For example, the summit of Little Tahoma (11,138'), a satellite peak of Mt. Rainier (14,417'), occupies a high topographic position, though it is >3200' lower than nearby Mt. Rainier. Likewise, a cirque valley occupies a relatively low position even though it may be perched high above the valley of the river drains the mountain range.

Landscape position of calcrete. Do meter-thick, advanced-stage calcretes form high or low in the landscape? Relative topographic position seems to provide some answers. Floodplains are low elements. Alluvial fans emerging from mountain fronts are low elements. Scabland coulees are low elements. Abandoned fluvial terraces occupy middle positions. Loess hills of the Palouse occupy medium to high positions, though their elevations are quite modest. Windblown silt of the Palouse, like that in other loess regions, hosts multiple stacked layers of caliche, commonly Carbonate Stage III or less. Most Palouse loess is less than 1 million years old. Caliche in the Palouse appears far less developed, thinner, laterally discontinous, but the think layers are more numerous with respect to the Pasco Basin. Argillic horizons, perched water tables, and lateral throughflow in deep loess may enhance calcrete growth, but to my eye the thickest accumulations of CaCO3 have noting to do with wet, concave hollows between convex hills; different soils developed there. The Palouse's high sedimentation rate alone doesn't completely explain more numerous thinner Bk horizons to the east and fewer, thicker Bkk horizons to the west. Landscape position and age do a better job. The oldest unit of Palouse loess, identified as 'L3' by Busacca and McDonald, is better expressed in Pasco Basin. I interpret L3 loess in the Palouse as the eastern fringe of a unit deposited in both Pasco Basin and Palouse beginning in the Pliocene or even latest Miocene (~7 Ma) - long before Ice Age floods showed up. Cicada-burrowed L3 loess spans the Pliocene-Pleistocene boundary and is a constituent of the a.) lowest part of the Palouse Fm, b.) 'Plio-Pleistocene unit/Cold Creek unit' of the Hanford literature, and c.) upper half of the Ringold Fm. The source of L3 silt is both Ringold-age alluvial fans, the abandoned Lake Ringold surface, post-Ringold alluvial fans, overbank and bar sediments of the ancestral Columbia-Snake River floodplain, and wind-recycled Ice Age flood deposits (<1.8 Ma).

Thick calcrete over time. Geologic timescale showing common subdivisions relevant to Pliocene-Pleistocene events in the PNW. CaCO3 cements occur in sediments older than 1.8 Ma, both with pedogenic and groundwater-influenced morphologies. For example, Pliocene-age cicada-burrowed loess paleosols in the upper Ringold Fm are carbonate cemented, suggesting a rain shadow was established prior to 4 Ma Pliocene (i.e., Chaney, 1959).

Richmond holds up. With a few caveats, Richmond's timeline of events in Eastern Washington holds up surprisingly well (Richmond et al., 1965). The sweeping article cataloging Quaternary deposits of the western U.S. was early and remarkable. I've redrawn and slightly revised (clarified?) the relevant portion of their 'Table 1: Correlation of deposits and events of the Cordilleran Region and Columbia Plateau'.

Neogene lowlands of south-central Washington. Visualize the Eastern Washington landscape during the Pliocene like this. The tan areas, identified as "overburden" for purposes of this water resources map, provide a big picture perspective on what was formerly a more contiguous inland basin prior to rise of the Yakima Folds. Today's basins are small fragments of an older region-scale lowland, where sediments accumulated and major rivers conflued. While the geographic terms "Pasco Basin" and "Columbia Trans-arc Lowland" are useful, recognize that certain valleys that today stand apart from one another were previously connected to one degree or another. Correct-thinking geologists have made several attempts to produce a more unified basin model for Pliocene basin fills: Farooqui et al. (1981) correlated post-CRBG sediments across several Neogene basins in WA and OR; Tolan et al. (2002) recognized a region of interconnected lakes during 'pre-Rosalia time' (~14.5 Ma); Staisch and Sadowski (2021) confirmed the Kittitas Valley was isolated from the Pasco-Crab Creek-Quincy Basin by the rise of the Hog Ranch-Naneum anticline after 10 Ma. Some have proposed older valley connections between south-central Washington and the Puget Lowland existed prior to the rise of the Cascade divide. Post-basalt depocenters east of the mountains collected a wide variety of sediments from the surrounding highlands. The basin fill sediments often contrast with those of large through-flowing rivers (i.e., Ellensburg Fm). Calcretes are thickest near the center of this ancient basin - the Pasco Basin between Othello and Kennewick, Ritzville and Vantage (portions of Grant, Franklin, and Adams Counties). Calcrete, like the sediments and basalts below, thins with distance away from Othello. Map by USGS/Snyder and Haynes (2010, Plate 1).

Calcrete over basalt over diatomite. All three units occupied a lowland position in the landscape when formed. Miocene Quincy diatomite beds were deposits of shallow, warm, isolated lakes atop flat-lying basalt flows; diatomite lakes on the developing lava field, but isolated from muddy streams. Miocene flood basalts flowed along and partially filled valleys. Plio-Pleistocene calcrete caps alluvial surfaces and sediments. Erosional contacts separate the units, but bedding is parallel between all three (no tilting). WGS archives photo #3529 from 1947 photo of diatomite mining operation near George, WA.

Lower Lind Coulee. A 2m-thick blocky calcrete developed in loess overlies mixed alluvium north of Othello, WA. The alluvium consists of wetland muck and thin channel sands with abundant soil features. It represents an overbank and sidesteam setting (ancestral Crab Creek/Columbia River floodplain) that transitions upward to a slightly drier, loess-blanketed hillslope. The water table is nearby throughout, suppling water for evapotranspiration that helped thicken the calcrete. The entire section unquestionably lies in a valley. The calcrete's caprock position and association with loess suggests it could be Pleistocene in age. Its considerable thickness and the fact that loess paleosols occur in the upper Ringold, however, indicates its Plio-Pleistocene age perhaps equivalent to shoaling sediments in the Ringold's uppermost lacustrine member, the Savage Island. Nearby, the top of the calcrete is reworked and overlain by younger Missoula flood rhythmites. A few thin clastic dikes descend from them through the ledge. Exposures nearby also reveal a crossbedded basaltic channel gravel beneath the overbank deposits. Hwy 17 bridge over Lind Coulee.

A line across the mountain. Elevation profile of the calcrete-bearing unit (red line) along Saddle Mountains uplift as seen from Royal Slope. The conspicuous white unit follows a mostly unbroken line for tens of kilometers atop footwall benches (Taunton Bench, Smyrna Bench), gently rising as it approches Sentinel Gap. I have not yet investigated areas east of the river (Yakima Training Center and Firing Range). The calcrete unit continues beyond the edges of the figure: To the east it armors Paradise Flats-Othello Benches. To the north it armors large portions of Royal Slope. To the south, it caps White Bluffs. Profile is ~75 km long.

Capping calcretes formed low. View looking east along the crest of the Saddle Mountains anticline. The ridge today stands some 600m above Crab Creek Valley. The ledgy white layer that caps the ridge is calcrete-cemented alluvial fan with loess beds. The calcrete-bearing unit lies in angular relationship with the underlying Elephant Mountain Basalt and grow to >25m thick in a synclinal trough (one of several secondary structures along the hinge of the larger fold). The calcretes didn't form on top of the ridge. They formed in a low-elevation, low-relief alluvial plain (alluvial parent materials) or on genntle slopes (fan-loess complexes) prior to ridge uplift. Tectonism brought them here - at least some of them. Beneath the fan-loess unit is a a dark red, heavily-cicada burrowed sandy silt unit that thickens locally to more than 5m. In places it is punctuated by pods of coarse fan gravels. Two thin alluvial units directly overlie the Elephant Mountain basalt, a.) an orange-white striped unit with a strong horizontal fabric and b.) a non-descript brown bed of unstratified alluvium (basaltic sandstone) containing locally-derived basalt clasts, some weathered. In places, it contains cicada burrows to 1-3cm in diameter. Beneath the Elephant Mountain basalt is a crossbedded tan sandstone baked red by the heat. At its base is the Cougar Point Tuff (11.8 Ma), a bright white airfall ash reworked and locally thickened.

Steep north face. Sediments between basalt flows are alluvial deposits - the stuff of valley bottoms, flowing streams and, to a lesser extent, wind (i.e., proximal sandy loess). Interbeds are sometimes just baked soils a meter or so thick. Were baked soils in the Columbia River Basalt province formed on high, rocky ridge crests (colluvium, regolith, dust, minimal transport), bare basalt surfaces (deeply weathered regolith), alluvial fans (repetitive gravel lenses, dusty swales), steep colluvial mountain slopes (angular clasts, unsorted seds, talus), or mucky bottomland (gleyed, clay-rich, vegetation-insect-rodent trace fossils)? The hike from Crab Creek up the north flank of Saddle Mountains only gains about 500m, but its a stiff go. Luckily, the view from the valley floor isn't too shabby. Calcrete-bearing strata at Saddle Mountains post-dates the 10.5 Ma Elephant Mountain flow (Tem). The reconnaissance geologist Israel C. Russell visited Crab Creek in 1892 and saw the 11.8 Ma Cougar Point Tuff ('Tel' in photo), a "white horizontal line just below the crest...preserved by the sheet of basalt above it" (Russell 1893 - USGS Bulletin 108).

Elevated calcretes. Most of the locations where I've described calcrete follow the regional topographic profile (thin gray line). But sometimes they don't. For example, point #590 atop Saddle Mountains. Same calcrete and similar parent materials as found in adjacent valleys, but its 500m higher due to offset by young faults. Topographic profile drawn between the Waterville Plateau and White Bluffs.

A previous study on calcrete in Pasco Basin-Palouse region. Relatively few studies have been published on calcrete-capped "ancient" flood deposits in Eastern Washington. I've redrawn and clarified the key figure from Bjornstad et al. (2001), who sampled cemented, pre-late Wisconsin flood and flood-related deposits at locations identified by Baker et al. (1991). At all sites, calcrete (yellow) predates the Missoula floods and is developed in loess (light gray) or flood gravel (dot pattern = low-relief, undulating terrain or coulee bottoms). Black is Miocene sediments. East is at left. Horizontal datum is the Bruhnes-Matuyama magnetic reversal at 780,000 year ago.

Another Pasco Basin study. Slate (1996, 2000) used borehole logs to identify pedogenic and groundwater-influenced morphologies (green) in calcretes (yellow) beneath the Hanford Site's 200 Area. 'Groundwater' or 'phreatic' calcretes are described by others (Malde 1955, Birkeland 1999, Budd et al. 2002, Moore 2003, Alonso-Zarza and Tanner 2006, Wright 2007). Flood gravels (large dot stipple), slackwater rhythmites (dashed), alluvial fan gravel-loess complex (small dot stipple), and Ringold Fm (orange). Light gray bars to the right of columns represents unit resistance. Packer and Johnston (1979) sampled DH-6 and DH-11 for paleomag. I've redrawn, correlated, and reinterpreted the strat columns in Slate's dissertation.

Study from U.S. Southwest showing calcrete-alluvium association. Alluvial units, highlighted in yellow, are commonly cemented by calcrete (Stage III-VI) in the U.S. Southwest. This figure is from a classic study by Machette (1985). It reveals a key relationship: Calcrete is intrinsically related to the presence of a valley. All of the yellow-highlighted formations in the figure have an allvuial origin. For example, the Muddy Creek Fm is a well-studied Pliocene basin fill unit composed of clay, silt, conglomerate, sand representing a low-angle bajada and adjacent playa. The Ogallala Fm is a Miocene-Pliocene fluvial sand and gravel shed east off the Rocky Mts (fans spilling to a low-relief plain). The Gatuna Fm is a Pleistocene sandstone, conglomerate, siltstone, and limestone (braided streams, terraces, floodplains, playas). The other units and surfaces also have alluvial origins. A later version of Machette's figure was published by Birkeland et al. (1991, Fig. 4.6) who added age estimates and climate information.

Calcrete chronosequence on Boise River terraces. Othberg et al. (1997) investigated pedogenic calcretes developed in a flight of terraces in the Boise River Valley, ID. Ages of the seven alluvial surfaces increase with elevation and Carbonate Stage from ~15 ka for the lowest terrace (B = Boise terrace) to ~1.7 Ma for the highest (T = Tenmile terrace). Study suggests plugged CaCO3 horizons require a minimum of ~130,000 years to form in west-central Idaho, which during the Pleistocene experienced similar climatic conditions as the Columbia Basin of Washington. Approximate ages shown. The larger point is that calcrete is associated with river terraces and a valley setting. A key difference is the Othello-area calcretes are mostly buried (buried paleosols), therefor did not continue to age and develop as those near Boise that remained exposed atop abandoned alluvial terraces did.

Calcrete on Beaver River terraces. Machette (1985) investigated pedogenic calcretes developed in alluvial terraces in the Beaver River Valley, UT. Ages of the seven surfaces (former floodplains) increased with elevation and Carbonate Stage from ~13 ka for the lowest terrace (Qbv) to ~750 ka for the highest (TG = Table Grounds). Approximate ages shown. Again, calcrete occurs with alluvium in lowland settings and may remain exposed, increasing in age over time with continued river incision and abandonment of terrace surfaces. This situation differs in a fundamental way from Eastern Washington calcretes. In Washington, thick calcretes formed over long periods of time, then were buried. They did not continue to age atop exposed, abandoned terraces like in ID and NM-NV-CO-UT. Their ages were fixed at burial, bracked by what lies above and below.

Gravel over calcrete over alluvium. Coarse flood gravel truncates a thick, welded calcrete developed in overbank alluvium of the Ringold Fm (floodplain of ancestral Columbia River). The valley during the Pliocene became a flood coulee during the Pleistocene. The sediments exposed here are not tilted, though the site is located on the north flank of Saddle Mountains anticline near its frontal thrust. At the base of the exposure, a deformed zone (soft sed deformation) is sandwiched between flat-lying strata. Similarly deformed zones are found elsewhere in the region. Orchard Scarp Site, Taunton Bench, WA.

Dirt party at MarDon. Calcrete ledge 40-50cm thick overlies green-gray-brown alluvium, slightly deformed and with abundant soil features. Hwy 262 roadcut on north flank of Frenchman Hills west of MarDon Resort (New Orchard Site).

Liesle Road. Slackwater rhythmites (Touchet Beds) unconformably overlie a calcrete ledge. Displacive fabric seen in calcrete. Quality exposures of rhythmites are not common in the this part of the scablands (eastern Quincy Basin). Sand dunes and sheets tend to dominate here. Liesle Rd Site is located north of Warden, WA.

Coyote Creek at Moses Coulee. Calcrete overlies a basalt-cobble stream gravel along Coyote Creek, a west-draining tributary to Moses Coulee. The creek does not grade smoothly to the floor of Moses Coulee, but to a higher elevation; it appears to predate the incision of Moses Coulee. Gravel at the base of the section rests atop basalt bedrock and all indications it is the bedload of ancestral Coyote Creek (not stuff carried in from elsewhere). Non-basaltic clasts in the float along the dry bed of the channel derive from younger, overlying glacial deposits (till, subglacial debris flows, flood deposits) and have toppled in from the banks. The gravel of ancestral Coyote Creek contains no exotics. Abundant granitic clasts and some light green quartzite clasts occur in higher terraces above. The quartzite does not appear to be from the Belt Supergroup of western Montana. Belt rocks do not crop out to the north of the Waterville Plateau, so the Okanogan Lobe may not have carried them here. Not sure. Their provenance may be the Addy Quartzite or maybe a Paleozoic unit in the Okanogan Valley (Limebelt area near Omak?). Estimated age on the calcrete is >200,000 years, though considerable scatter in the data exists. It is unclear if the calcrete drapes across modern Moses Coulee or was removed when the coulee was cut. Guessing its the latter. The calcrete appears to represent a low terrace that formed along the margin of ancestral Coyote Creek, built as the channel migrated slightly away. SWC photo May 2022.

Herman Railcut. A flood-laid boulder gravel lies atop Ringold Fm and beneath two calcrete ledges calcrete with loess and silt-pebble diamict between. The calcretes (>Stage IV) took several hundred thousand years to form, which means the flood gravel is likely >500,000 years old. These same calcrete-arrmored surfaces are found throughout the Othello-Saddle Mountains-White Bluffs-Wahluke Slope-Royal Slope-Quincy Basin area (Pasco Basin). I discovered this exposure in 2018.

Fancher Bar at East Wenatchee. "Nice festoon-bedded flood gravel capped with multi-layered petrocalcic horizons, totaling at least 4m thick by more recent measurements nearby." Description and photos c.1991 courtesy of Jim O'Connor, USGS. This gravel pit, located along a bedrock-confined reach of the Columbia River, is now mostly gone.

Harder Road. Thick calcrete overprints a high-energy gravel and loess north of Benge, WA. Was the gravel deposited low or high in the landscape?

White Bluffs. A calcrete rip-up gravel with south-dipping foresets was deposited by an ancient overland flood during pre-Wisconsin time. It truncates top the Ringold Fm. A variety of non-basaltic (exotic) clasts are found in the gravel (granite, schist, quartzite, felsic volcanic, cemented loess, mudstone, etc.). The flood-laid unit is traceable north to the parking lot across the entire exposure along Old Ringold Rd. I discovered this site in 2018.

George Gravel Pit. Thick calcrete caps a >4 meter thick pre-Wisconsin flood gravel in western Quincy Basin. The wise call this site 'Burke'.

Marengo. A pre-Wisconsin boulder gravel at the base of the expsoure is overlain by silt diamict (same flood as gravel), loess, and a calcrete ledge. A second flood gravel from at least one late-Wisconsin Missoula flood lies at the top of the exposure.

Low-angle fan gravels. Calcrete-cemented fan gravels deposited during Ringold time interfinger with Ringold valley deposits (lake beds and associated loess). Gently-sloping alluvial fans graded from modest ridges (earlier version of Yakima Fold Belt ridges) to former valley floors of Wahluke Slope, Royal Slope, and Crab Creek valley. Younger megafloods swept some of them away, leaving steep valley-facing escarpments. Field geologists Grolier and Bingham (1978) had these concepts well in hand decades ago, "The rising anticlinal ridges bounding parts of the lake were eroding rapidly with the result that alluvial fans in places reached or were flooded by the lake waters. Thus, the fans built a piedmont slope of basaltic fanglomerate [with] tuffaceous sand and silt...". These sediments interfinger with the lacustrine material a long the slopes of the ridges. Photo: Gully #6 at Smyna Bench.

CaCO3 beards. Cobbles in an alluvial fan deposit with very thick lower-half rinds of CaCO3. Location is the top of Saddle Mountains 1000' above modern Crab Creek. Some interpret lower-half coatings on clasts as a sign of early-stage calcrete development. These rinds are remarkably thick, suggesting that rule of thumb might not be valid in all cases. Considerable time and countless evaporative cycles are preserved in these beards. In Columbia Basin, loess (not weathered limestone bedrock) provides the calcium. Rainwater, root decay, and microbial activity around roots provides the C and the O. Together, they conspire to form CaCO3 in the shallow subsurface.

Carbonate frosting. Calcrete pompadour.

High sedimentation rate = thinner calcretes. Numerous thin loess beds alternate with (mostly) thin calcretes along the western margin of the Palouse Slope. The stratigraphy at this transitional location (Booker Rd east of Othello) is similar to that at Lind Rd (east of Connell) and Pacific St (Ritzville).

Booker Canal Site. Alternating loess and calcrete reveal competition between wind deposition and soil development. Dust comes in pulses. Soils form when they can.

Tubes and filaments. Silty-sandy beds between thick calcrete ledges or fan gravels typically contain abundant root casts and filaments consistent with dust accumulation and soil development in moist swales atop an alluvial fan. Cemented rhyzoliths like these and denser calcrete have been sampled for U-series for dating (Staisch et al. 2018). Saddle Mountains crest.

Cicada in modern and ancient landscapes. Do colonies of cicada populate residual soils on barren, rocky ridge crests or do they prefer moist, cumulic soils in vegetated, alluvial bottomlands? Ridges are typically degredational parts of the landscape - places actively being stripped of their soil cover. Valleys accumulate sediment and water - wet, verdant, fertile places. Cicada are like Hobbits. They prefer lowlands where thick soils sustain lush gardens. Cicada feed on the fine roots of plants, not on desiccated lichen mats, soil crusts, or marmot droppings (like Golem). In fact, cicada species in Eastern Washington show a strong affinity for specific plant communities, namely sagebrush. In their study of modern cicada populations in the Columbia Basin, O'Geen et al. (2002) examined cicada-burrowed soils under four plant communities (sagebrush steppe, bunchgrass steppe, meadow steppe with pine stands, coniferous forest). Only beneath sagebrush rooted in loess (Haploxeroll and Haplocambid soils) were significant populations of genus Okanagana found. Okanagana is the most common cicada found in Eastern Washington. Cicada prefer sagebrush and "soils of aggrading landscapes". Sandborn and Phillips (2013) confirm the preference for sagebrush steppe habitats in other Columbia Basin cicada species, including Okanagana occidentalis, canadensis, fratercula, luteobasalis, gibbera, napa, and utahensis. O. striatipes, vanduzeei, lurida, and yakimaensis are found in the Palouse Hills (undulating prairie). O. vanduzeei is common to both sagebrush steppe and the Palouse prairie. Photo: Fossil cicada feeding burrow in Pleistocene loess at Rulo, WA.

Crust on cracked bedrock. Carbonate-silica cement fills cracks in the top of the Elephant Mtn basalt flow. This crust occurs in the uppermost meter of the basalt bedrock and often forms the base of the Ringold Fm. The crust follows an erosional surface that cross cuts the Pomona flow farther east. Take home message: Not all white crusts in south-central Washington are made of the same stuff. Some formed from in soils at the surface, others by shallow groundwater at depth. This is the same crust that is turned near vertical farther east along the Saddle Mountains crest.

Formerly low, now elevated basalt surface. Along the Saddle Mountains crest east of Wahatis Peak calcrete-cemented alluvial fan-loess packages commonly lie directly atop 10.5 Ma Elephant Mountain Basalt. The Elephant Mountain is the youngest basalt flow in the range. Sometimes another unit is sandwiched between: an alluvial variant of the Ringold Fm(?). The uppermost part of the basalt has weathered to a fine grained, friable, orange and white striped unit. Above it lie brown beds containing a few angular, weathered basalt clasts (regolith, not-far-traveled, colluvial chunks fallen from the bank). The beds are burrowed by cicada. Bedding is flat-lying and parallels the underlying basalt surface, consistent with a low-energy floodplain developed atop a more or less flat basalt surface (overbank setting). The alluvium appears to represent a sluggish drainage reestablished after the Elephant Mountain basalt invaded and cooled. The brown beds exhibit no characteristics of steep colluvial mountain slopes (talus, sheet wash, dry ravel). Nor do they resemble energetic debris flows or suaqueous fans. Deposition predated uplift.

Extra crusty. White carbonate-silica crust atop 12 Ma Pomona basalt. A crust of identical character and position occurs atop the 10.5 Ma Elephant Mountain basalt 27 km to the west, beneath tens of meters of overlying Pliocene and Pleistocene sediments remain, preserved in structural lows.The crust thickens downhilll somewhat and thins to nothing at the ridgeline. It appears to be the base of the Ringold - the local base to sediments in Ringold-position anyway. This is the same crust tilted to near vertical shown in photos later in this article. The crust did not form high on an airy ridge crest, but in fractures exploited by shallow groundwater. It formed prior to uplift. The crusted surface trncates both Pomona basalt (here) and Saddle Mts basalt (farther west). Uplift and beveling can be no older than latest Miocene; I suspect the erosional surface may be slightly older than 5 Ma, but the crust is younger. Uplift of Saddle Mountains seems to have occurred in two stages: A prolonged period of gentle warping and modest topographic rise (minimal topographic relief) and a later, more rapid uplift (signifcant topographic relief). Corfu Landslide Overlook, Saddle Mountains.

Muddy alluvium way up here? Weathered, fine grained, brownish-red-black sediments mapped as Ringold are preserved along the ridge crest of the Saddle Mountains 1000' above Crab Creek. The brown beds overlie the youngest basalt flows and contain abundant fossil cicada burrows. They appear to be former overbank and wetland muck. Cicada moved in after things dried out (an uplift signal?). Lobes of basaltic alluvial fan gravel invade some of the beds - gravelly channel fills sourced from the ridge above. That ridge and that gravel source no longer exists; this outcrop lies just a few meters down from the modern ridge crest. Valley alluvium like this received fan and debris flows from above, but was not itself transported downslope or mass wasted (e.g., no evidence of a steep slope during deposition). The brown beds when deposited were in a receiving position. The beds thin and thicken with the folds in the bedrock. Maughan Ranch, Saddle Mountains.

Faulted north flank of Saddle Mountains. The conspicuous red-tan-white 11.8 Ma Cougar Point Tuff draws your eye. The white ash grades upward into a tan crossbedded fluvial sandstone with ancestral Columbia River affinity, the top of which is baked red by the Elephant Mountain basalt. Both the clean white ash and the tan tuffaceous sandstone are very lightweight. Everything we see today at the crest of the Saddle Mountains ridge - CRBG lava flows, Miocene interbeds, Ringold Fm, and the capping fan-loess-calcrete unit - was originally deposited low in a structural trough or in the floodplain of a large river (Camp 1981, Tolan et al. 1984). Tectonic uplift along the Saddle Mountains Fault post-dates all of it except for Holocene loess, dune sand, and cow pies. There was no significant ridge here as late as 2 million years ago. Less than 1000m uplift in 2 m.y. is actually quite a modest uplift rate. If the faulted calcretes are 500 ka or younger, then things get a little spicier. I'm guessing the thick ledges like those at Offramp and Herman Railcut are about 800 - 1500 ka. Photo: Maughan Ranch.

Lind Coulee East Fault at O'Sullivan Reservoir (lower Lind Coulee). Rubbly Roza basalt is shoved over calcrete-cemented loess. A white gouge zone highlights the fault. A sliver of brown mudstone comes and goes with the gouge. Footwall loess is steeply dipping to overturned. West and Shaffer (1988, p. 80) trenched this site and noted what is still mostly visible today in outcrop. Hanging wall Roza is brecciated near the fault and takes on a greenish-yellow hue typical of shattered, weathered basalt. Competent basalt eventually returns a few meters above. Grolier and Bingham (1971, 1978 Figs. 14, 23) first mapped the area, identified the fault as an eastern extension of the Frenchman Hills Fault, and loosely described the local stratigraphy. They did not, however, clearly delineate Pliocene Ringold-affinity sediments from Pleistocene alluvium of ancestral Crab Creek or from Palouse loess. Unit descriptions in the older literature is generally vague with respect to non-flood, non-loess sediments of this age. Packages of alluvium-loess-paleosols exposed in shoreline bluffs of lower Lind Coulee may be the "basal part of the Palouse loess" of Bryan (1927), the "red sandstone and terra cotta silt" of Calkins (1905), or the "alluvium" of Culver (1937). West and Shaffer (1988) punt, calling it "a poorly understood sequence of Pleistocene paleosols and loessial sediments". Grolier and Bingham also lacked confidence, "In this report, where the field identification of rocks was based solely on megascopic characteristics, a layer-by-layer correlation of the brown tuffaceous sand underlying the uplands with the sand intercalated in the buff laminated clay at or near the White Bluffs was not possible". I suspect some of the alluvial-paleosols in lower Lind Coulee correlate with paleosol intervals in the upper Ringold at White Bluffs Overlook, Watt Lane, and elsewhere in Pasco Basin. They represent shallow water and upland sediments deposited along the margin of Pliocene Lake Ringold.

Vertical crust. Steeply-tilted and faulted crust atop Elephant Mountain flow at Saddle Mountains crest. This unit has been mistaken (and sampled for dating) for pedogenic calcrete. It is, however, a groundwater crust that can be found at numerous location along the ridge, often lying flat. Sampling of calcrete has in the past been somewhat haphazard. The calcrete-bearing interval, of which this unit is a part, is here cut by the Saddle Mountains Fault and by the Frenchman Hills Fault in lower Lind Coulee. Same stuff.

Crust variant. Same platy groundwater crust on Elephant Mountain basalt is only gently tilted here. Not a great unit to sample for U/Th.

Weathered basalt up high. Ever notice that some basalt flows are deeply weathered, while the adjacent flow above or below is not? What controls the distribution of deeply weathered zones in individual CRBG flows? The spheroidally weathered Priest Rapids flow in the photo is located high on the Saddle Mountains ridge. It crumbles away in your hands. When did the deep weathering occur? Before uplift or after? Was it when the basalt was flat-lying, buried, and below the water table (low in the landscape) or after it was elevated and exposed to the elements (high in the landscape)? Is groundwater to blame or freeze-thaw action? If the former, then weathering profiles in individual Columbia River Basalt flows might indicate residence time in the subsurface (valley syncline position, saturated), thus weathering might help us say something about the timing of uplift. If the latter, then climate - acting primarily through rainfall (chemical) and freeze-thaw action (physical) - was incredibly efficient at chemically degrading basalt flows exposed on ridges. The YFB ridges are quite young. Flows above and below the Priest Rapids do not show the same weathering charcteristics, but here the depth of weathering is >4m with little vertical zoning. It seems likely groundwater with its capacity to degrade mafic rocks quickly was involved. I suspect deep weathering in most CRB flows mostly occured prior to uplift, when saturated and in valley positions (Miocene-Pliocene). I don't believe deep weathering occurred after uplift atop high, dry ridges (Pliocene-present). Soil profiles on ridges are not thick (i.e., uplift shuts off deep wetting and deep weathering). Could not a single flow be traced across several YFB ridges and its weathering characteristics mapped using some simple classification system (weathered, fresh, mixed)? Well logs might help fill in the blanks. Do deeply-weathered portions of flows correlate to old synclines? Could the timing and configuration of the paleo-landscape be reconstructed through weathering profiles in Columbia Basin's basalt province? A great Master's project.

Water-lain ash. Pure white volcanic ash at the base of the Cougar Point Tuff (formerly part of the 'Beverly Member', now mapped as Miocene Ellensburg undifferentiated) fell into a shallow, quiet body of water. The ash almost looks varved, but I suspect that's just bedding produced by a slow current rather than seasonal cycles. The ash eruption at 11.8 Ma blanketed the landscape, collected and thickened near the former Columbia River-Crab Creek confluence, temporarily choking the drainage. The deposit, thick in a pumicite mine abaove the Columbia near Mattawa (Carithers, 1946, p. 64-65; Mackin, 1961, p. 28-30), thins to the east (Smyrna Bench) and west (Kittitas Valley) of the river. Photo: Saddle Mountains, just below the ridge crest east of Sentinel Peak.

Cougar Point Tuff. The rhyolitic airfall tephra erupted from the Owyhee-Jarbidge volcanic center on the ID-NV border blanketed parts of central Washington. The slug of ash was dumped on the landscape and subsequently reworked by water. Here, the ash is several meters thick and overlain by a tan crossbedded sandstone and then the Elephant Mountain flow, which bakes the ashy sand red. The depositional setting was not a ridge crest, not a perched terrace, but the low-elevation floodplain of the ancestral Columbia River, what Mackin called the "Beverly-Selah alluvial plain" (Mackin 1961, p. 36) . The white lower portion is almost pure ash (glass shards) several meters thick. It contains laminae that resemble varves, but are not. Tan sediments above, a variant of the Ellensburg Fm, is a sandstone with crossbeds and other ripple forms, evidence of reworking by a channel of some size. The rather abrupt color change from white to tan to red is often conspicous, but is not seen everywhere. The white to tan transition may represent a lateral shift in the stream channel (fluvial sediments over pond sediments). Or perhaps it marks the point when the ash-choked channel, temporarily defeated, recovered and resumed its usual flow. Mackin (1961, p. 30) notes, "The very perfect sorting suggests that it was airborne, lamellar bedding, crossbedding, and ripple marks at different levels indicate that it probably was depositd in part in quiet water and in part on dry land." Carithers (1964, p. 65-68) suggests the pumicite at Mattawa is also found in the Selah Member at its type locality near Yakima. Modern correlations would seem to agree (i.e. Tolan et al., 2009, Fig. 13).

Nearly an interbed. I've become convinced that the Ringold and overlying calcrete-bearing unit (up to 25m thick), the so-called "Plio-Pleistocene unit", is very similar to Miocene sedimentary interbeds in the Columbia River Basalt Group; they are valley fills, packages of alluvial sediment deposited atop nearly flat basalt flows in the centuries following eruption and cooling. These valley bottom sediments represent the reestablishment of the drainage network and that of adjacent hillslope channel systems. The upper Ringold at Saddle Mountains is about the same thickness and of similar geographic extent as many of the named Miocene interbeds lower down in the CRBG. The northern Pasco Basin during the Miocene wanted to be a broad floodplain where large rivers of the region converged (a slowly subsiding basin), but business-as-usual fluvial activity kept getting interrupted by invading flood basalts. Eventually faults began warping the bedrock, further diverting streams around the noses of modestly rising ridges. The only reason we don't call the Ringold Fm an interbed today and group it with its bretheren is because basaltic volcanism shut off too early. That last flow never came to bury it. If volcanism would have shut off earlier, then Ringold sediments would sit directly on older sediments of the Ellensburg. Along the margins of certain basalt flows, Ringold does rest on Ellensburg, but current mapping does not clearly distinguish the contact. Photo: Saddle Mountains.

Acknowledgements

A big thank you to Eric Cheney for encouraging me to pursue this work. Sometimes meeting your heros works out. Others that have provided tremendous help include Jim, Michael, Kevin, Kathleen, Richard, Nick, Bruce, Lydia, Andrew, and Katie. The work continues.

Real geologists. Geology used to be blue collar work. For some of us, it still is. This photo shows a U.S. Geological Survey party led by Israel C. Russell working the moraines of the Malaspina Glacier, Yakutat District, Alaska. That part of Alaska remains today a vast, wild, and miserable wilderness. They had it rough, yet succeeded in their work in part due to Scandinavian blood, but mostly because they were tough buggers. Certainly tougher than me and you.

Field notes matter. Some of my field notes. If you watch Nick Zenter's YouTube video "Saddle Mountains with Skye Cooley", this is some of what you see me writing. Field notes are a combination of facts and measurements, thoughts and ideas, answers and questions. You often only get one chance to visit a place, so make it count by taking good notes. Notetaking is a bit of a dance. Your skills improve with practice. Record what the rocks are telling you, but listen to that quieter voice in your head, too. Get all those thoughts, those sketches, those questions down on paper before you leave the outcrop. The field is often ambiguous and physically uncomfortable, factors that at best distract, at worst keep many geologists indoors. You don't control the weather or the terrain. You'll always miss something. There's always more to see. Smarter people came before and will come after. People will discourage you from going. People will tell you are wrong. Get used to it. Resist. Go. The central goal of the Field Geologist is to efficiently characterize and document what matters, missing as little as possible in the process. Its a lot like work. Sketches are the center of my notetaking. Sketches help organize my thoughts and fill about half the pages of my notebooks. In short, the Field Geologist fills her notebooks and gains confidence, legitimacy page by page.

Extra: Old Channels in the Landscape

Entrenched meanders reveal old river channels. Ancient rivers left evidence of their passage in the form of sedimentary deposits and valley remnants. The first 3 images above show entrenched meanders of the modern Yakima, Touchet, and Snake Rivers. The 4th shows remnants of meanders in the Crab Creek Valley left by the ancestral Columbia River. The Columbia appears to have occupied Crab Creek's valley for a time, though details remain a bit fuzzy. Erosion of Grand Coulee and a portion of Drumheller Channels were in part eroded done by the Columbia. The Yakima River's meanders (1st image), now incised and captured between high bedrock walls, were originally established in alluvial sediments of a low-relief valley plain that existed prior to uplift of the Manastash and Umtanum ridges. Its plan form pattern is inherited, or antecedent. The Touchet and Snake Rivers (2nd, 3rd images) are also conspicuously meandered, their patterns also established earlier though their courses are similarly confined by bedrock. The Columbia meanders in Crab Creek (4th image), what's left of them anyway, were similarly established during the early-middle Pleistocene atop a Pliocene valley fill surface composed of Ringold Fm, some loess, and alluvial fan gravels. The fossil meanders now sit perched, abandoned above the valley floor. Its unclear how much valley fill the river had to contend with, but it was likely a significant amount. Early glacial outburst floods bypassed Crab Creek, roundedd the nose of Saddle Mountains, carved the Eagle Lake scabland, and exited via Ringold Coulee. A profile line drawn north to south from Royal Slope to Smyrna Bench shows the benches match up across the gap; the profile defines the Pliocene valley fill surface. Crab Creek today is deeply incised due to scour by Missoula flooding and a minor work done by the Holocene creek itself. Quite a history to Crab Creek: During the Miocene its valley was inundated by flood basalt. The post-CRB, pre-glacial valley was filled (aggraded) by sediment of an ancient floodplain and alluvial fans shed from rising folds. The ancestral Columbia occupied it for a time. Ice Age floods deepened its channel between benches of older sediment. Today, the humble, determined little creek has resumed its path to Beverly. Its still-fishable waters, depleted by irrigators, continue to flow between banks baked by the summer heat.

Ancestral Columbia River in Crab Creek. Remnant meanders look like they were created by a river, not the Missoula floods.

Pre-glacial channels? Thick calcretes originate in an older landscape that has since been dissected by Ice Age floods and incised by younger streams. However, remnants of the dendritic, pre-flood drainage network (pink lines) can still be seen in slightly-elevated, loess-covered hills of the Palouse Slope. The E-W trend of pre-glacial channels contrasts with the N-S and NE-SW trend of scabland tracts. Streams are truncated at scabland margins (black bars). Hasty interp by me using Illustrator and base layers from the National Map 3DEP Viewer.

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