Ice Age Floods National Geologic Trail
Ice Age Floods National Geologic Trail
June 18 (Alone) Wholly an imaginary thing. I traversed all roads to see remnants of the high distal part and the "conspicuous channels" around and across it. I did some footwork in inter-road tracks. Conspicuous, nonsense. Channels? No. Not even a trace of river gravel or sand...
June 18 (Alone) Wholly an imaginary thing. I traversed all roads to see remnants of the high distal part and the "conspicuous channels" around and across it. I did some footwork in inter-road tracks. Conspicuous, nonsense. Channels? No. Not even a trace of river gravel or sand on the thinly loess-covered basalt of the uplands where the delta toe remnants and bypass channel should be. I found three erratic pebbles in draw down in the basalt, below 1300. Bretz Field Notes— Bretz 1952
This is one of more than 1,800 field sites cataloged in the early scabland surveys — the bedrock of the Ice Age Floods scientific record. The Bretz-era researchers walked the ground first; modern cosmogenic dating, LiDAR, and remote sensing have since extended and refined what they mapped.
The Cheney–Palouse tract is the easternmost of the three major scabland belts that cross the Columbia Plateau, extending roughly 110 miles south-southwest from the Spokane area (Cheney, Marshall, Hangman/Latah Creek, the lower Spokane River) past Sprague, Ritzville, and Washtucna to the Snake River at Palouse Falls. The Davenport and Telford uplands sit to the west of the tract; the loess-mantled Palouse Hills define its eastern margin.
The Cheney–Palouse tract records the most intensely scoured ground in eastern Washington. Floodwater from glacial Lake Missoula entered the Columbia Plateau via the Rathdrum Prairie–Spokane Valley corridor, fanned out where the basalt plateau drops below the prairie surface, and then split into multiple flow paths controlled by the position of the Cordilleran ice sheet, the level of glacial Lake Columbia, and the underlying basalt structure. The Cheney–Palouse tract carried the southern lobe of that flow south-southwest across roughly 1,500 square miles of Columbia River Basalt Group bedrock, stripping the loess cover, plucking columnar basalt, scouring rock basins, cutting anastomosing channels, and depositing the longitudinal gravel bars and pendant bars that define the modern landscape.
Three of the tract's signature features make the routing legible. First, the divide crossings: floods repeatedly overtopped pre-flood drainage divides rather than following them. At the southern end of the tract the floods overtopped the south wall of the ancestral Palouse River valley, abandoned the river's older route through Washtucna Coulee, and cut a new canyon directly to the Snake River — the cataract retreat now hanging at Palouse Falls. Devils Canyon, Esquatzel Coulee, and the Othello channels are additional divide crossings carved by the same overtopping mechanism. Second, the scoured rock basins around Sprague, Cheney, and the Turnbull NWR area: thousands of small lake basins and bedrock potholes mark places where flow plucked basalt joints rather than carrying loose sediment along. Third, the bar fields: long flood bars on the lee side of basalt buttes, slackwater rhythmites in the Cheney sub-basin, and the giant gravel bars of the Cheney area record the deceleration zones at the downstream end of constrictions.
The routing of water through this tract evolved with the ice sheet. Early in the flood sequence, the Okanogan lobe of the Cordilleran ice sheet had not yet closed off the upper Columbia River valley west of Spokane. The largest floods, dated by Balbas and others (2017) using cosmogenic 10Be to 18.2 ± 1.5 ka, ran down the northwestern Columbia River valley as well as splaying south across the Cheney–Palouse and Telford–Crab Creek tracts. As the Okanogan lobe advanced, it dammed the Columbia and impounded glacial Lake Columbia behind it; later Missoula floods could no longer take the direct Columbia route and were forced south through the scabland tracts. Spillover from glacial Lake Columbia drained first through Foster Coulee, then Moses Coulee, and finally through upper Grand Coulee, whose headward cataract retreat eventually breached north into the Columbia valley. Once upper Grand Coulee opened (around 15.6 ka in the working chronology), it acted as a relief valve — it kept Lake Columbia low and routed the bulk of subsequent flood volume through the Quincy Basin and the central scablands rather than the Cheney–Palouse. Glacial isostatic adjustment compounded the effect: Hpken and colleagues (2022) showed that crustal rebound progressively raised the divide separating the Spokane Valley from the Cheney–Palouse entrance, further limiting flow into the eastern tract after about 15.5 ka.
The practical result is that the Cheney–Palouse landscape is dominated by the older, larger floods — the 18.2 ka anchor and the events immediately following — while the upper Grand Coulee–Quincy Basin–Drumheller corridor records the bulk of the post-15.6 ka discharge. The youngest dated floods (about 14.0–14.4 ka) came down the northwestern Columbia and likely represent drainage of residual glacial Lake Columbia after the Missoula floods had ceased. The last major flow to traverse the Rathdrum Prairie–Spokane Valley corridor reached its peak near 14.7 ka before the Okanogan ice dam thinned to failure.
J Harlen Bretz worked the Cheney–Palouse tract harder than any other piece of the scablands. He began field reconnaissance with University of Chicago students in the summer of 1922, returning every summer through the late 1920s. The tract's combination of clean exposures, accessible roads, and visually unambiguous features (divide crossings, cataracts, plucked basalt, hanging valleys) gave him the evidence base he needed to argue against the uniformitarian consensus of the day.
His 1923 paper, "The Channeled Scablands of the Columbia Plateau" (Journal of Geology 31: 617–649), coined the term Channeled Scablands and was built largely on field relationships he had documented from Cheney south to the Snake River. His 1925 follow-up, "The Spokane Flood Beyond the Channeled Scablands" (Journal of Geology 33), extended the argument and named the Spokane Flood as the agent. The two-part 1928–1929 paper "Valley Deposits Immediately East of the Channeled Scabland of Washington" (Journal of Geology 37: 393–427, 505–541) catalogued the slackwater, divide-crossing, and gravel-bar evidence along the eastern margin of the tract — Hangman Creek, the lower Spokane River, the Palouse drainage — and remains the densest single field record of the area. Richard Foster Flint's 1938 GSA Bulletin paper "Origin of the Cheney–Palouse scabland tract" attempted (unsuccessfully) to refute Bretz from this same ground. The 1969 Bretz, Smith, and Neff paper "The Channeled Scabland of Washington: New Data and Interpretations" closed the loop after a half-century of dispute. Many of the field localities Bretz logged in 1923–1929 — bar surfaces near Cheney, rock basins south of Sprague, the Palouse Falls cataract — are still the type localities cited in the modern literature.
LiDAR has rewritten the legibility of the tract over the past fifteen years. The Washington Geological Survey, the USGS, and the U.S. Fish and Wildlife Service have built bare-earth digital elevation models that strip away the loess and vegetation cover, exposing every flood channel, divide crossing, pendant bar, and giant current ripple. The USGS/FWS Turnbull NWR–Cheney scabland LiDAR (2013 and subsequent collects) revealed thousands of small flood-cut features that were invisible in the field. Recent DNR-published map posters of the Cheney–Palouse tract (2016 forward) are LiDAR-based interpretive maps.
The cosmogenic 10Be chronology of Balbas et al. (2017, Geology 45: 583–586) is the current age framework. Their direct dating of erosional and depositional surfaces gave the field an absolute anchor of 18.2 ± 1.5 ka for one of the largest flood events, plus a 14.0–14.4 ka cluster for the youngest floods down the Columbia valley. The implication for the Cheney–Palouse tract is that its largest features predate the opening of upper Grand Coulee; later, smaller floods were progressively diverted away from the eastern tracts.
Two more recent threads matter. First, the glacial isostatic adjustment argument (Lehnigk and others, 2022, PNAS): differential crustal rebound across the plateau means that the relative elevation of divides changed during the flood sequence, biasing later flow toward routes other than the Cheney–Palouse. Second, the tunnel-channel and subglacial flood literature (Waitt and others, on the Okanogan lobe and Moses Coulee, 2024) is rewriting how floods interacted with the ice margin itself. Waitt and Atwater's 2021 chapter "Upper Grand Coulee: New views of a channeled scabland megafloods enigma" reframes how the upper Grand Coulee cataract retreat partitioned the flood system. The Missoula and Bonneville floods review (Waitt and others, USGS, 2021) is the current synthesis.
Sun Lakes–Dry Falls State Park (north end of the system, just outside the Cheney–Palouse tract proper but the keystone of the regional flood story) contains the Dry Falls cataract — a 3.5-mile-wide, 400-foot-high horseshoe scarp recognized in 2023 by the International Union of Geological Sciences as one of the First 100 IUGS Geological Heritage Sites. The Dry Falls Visitor Center closes in April 2026 for a full renovation and is expected to reopen in winter 2026. Steamboat Rock State Park, 21 miles north on SR 155, preserves an 800-foot basalt butte carved free by flood scour in upper Grand Coulee.
Palouse Falls State Park is the signature destination at the southern end of the Cheney–Palouse tract: a 198-foot active waterfall plunging into a flood-carved canyon, marking the headward retreat point of the cataract that diverted the Palouse River from Washtucna Coulee to the Snake. The Columbia Plateau State Park Trail follows a rail grade through scabland country from Cheney south to near Pasco.
Within the city of Spokane, Riverside State Park (Bowl and Pitcher), Palisades Park, and the Spokane Falls in the city center are accessible flood features. The Turnbull National Wildlife Refuge south of Cheney protects a representative scabland pothole-lake landscape. The Ice Age Floods Institute's Cheney–Spokane Chapter and Palouse Falls Chapter both run public field trips, lectures, and bus tours annually; the Cheney–Spokane Chapter typically leads outings to Spokane Falls, Bowl and Pitcher, Palisades Park, Dishman Hills, the Hangman Creek–Spokane River confluence, and Spokane Valley overlooks.
Active: 1914-1979 (primary IAF fieldwork 1922-1932; Penrose Medal 1979) Affiliation: University of Chicago (Instructor 1914, Professor 1926, retired 1947, emeritus through 1979) Key paper: Bretz, J H. (1923). "The Channeled Scabland of the Columbia Plateau." Journal of Geology 31(8): 617-649.
Bretz spent seven summer field seasons beginning in 1922 walking the basalt coulees, dry cataracts, and giant gravel bars of eastern Washington and concluded that the landscape required a catastrophic flood at a scale no existing process could produce. He coined the term "Channeled Scabland" in his 1923 paper and over the next decade defended the hypothesis against a uniformitarian geology establishment that had no plausible source for the water and viewed catastrophism as scientifically illegitimate. Bretz refused to name a source until Pardee's 1942 paper supplied one: Glacial Lake Missoula. He continued publishing on the scablands as an emeritus professor through the 1950s and 1960s, including his synthesis "Washington's Channeled Scabland" (1959). The Geological Society of America awarded him the Penrose Medal in 1979 at age 96; he reportedly remarked to his son, "All my enemies are dead, so I have no one to gloat over."
Source: J Harlen Bretz - Wikipedia; HistoryLink.org; University of Chicago Magazine
Every site along the trail will receive the full Terrain360 capture treatment: ground-level 360° panoramas, drone aerial imagery, and photogrammetry-based 3D models that visitors can spin in their browser. This page reserves the slots; the imagery flows in as field capture completes.
Ground-level 360° panorama, every step along the feature, captured by Terrain360 field crews.
Drone flyovers reveal the geometry of catastrophe — ripple marks, gravel bars, and scour patterns invisible from the ground.
Photogrammetry and Gaussian-splat models let visitors rotate, measure, and inspect features in detail-page WebGL viewers.
Satellite imagery and LiDAR have revealed that these coulees are among the largest flood-carved features on Earth. Grand Coulee alone is 50 miles long, up to 6 miles wide, and 900 feet deep — carved by floodwaters traveling at highway speeds.