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| Moses Coulee | |
|---|---|
| Name | Moses Coulee |
| Photo caption | Aerial view of the coulee and basalt scablands |
| Location | Douglas County, Grant County, Washington, United States |
| Type | Coulee |
| Formed by | Ice Age floods and fluvial erosion |
Moses Coulee is a large, dry canyon in central Washington, notable for its deep basalt cliffs, braided terraces, and erosional landforms produced during the Pleistocene. The coulee lies within the Columbia Plateau and is a prominent example of scabland topography shaped by catastrophic flood events, glacial activity, and subsequent fluvial adjustments. Its cliffs, coulees, and benches are important for studies in paleohydrology, geomorphology, and Quaternary geology, and the area hosts a range of habitats supporting regional flora and fauna.
The coulee is situated in north-central Washington between the Grand Coulee and the Okanogan Highlands, crossing parts of Douglas County and Grant County. It opens to the east toward the Columbia River and is bounded by basalt flows of the Columbia River Basalt Group; nearby geographic features include Umatilla National Forest, the Waterville Plateau, and the Saddle Mountains. The landscape displays steep basalt cliffs, talus slopes, inner channels, and expansive benches that descend to a floor drained by ephemeral streams and springs connected to the Waterville Plateau scarp and local tributaries to the Columbia.
The coulee cuts through stacked flows of the Columbia River Basalt Group, deposited during the Miocene epoch, exposing columnar jointing and dike swarms associated with Grande Ronde Basalt and Saddle Mountains Basalt. Regional uplift related to the Cascade Range arc and tectonics of the North American Plate established gradients that guided later incision. During the Pleistocene, glaciation of the Cordilleran Ice Sheet and interactions with proglacial lakes produced high-energy discharge events; the coulee records mechanical and plucking erosion, pothole formation, and streamlined bedrock forms typical of catastrophic outburst flood erosion documented across the Channeled Scablands.
The coulee is widely interpreted as a product of multiple episodes of megaflooding associated with the Missoula Floods originating from the repeated failure of Glacial Lake Missoula ice dams in the Purcell Trench Lobe of the Cordilleran Ice Sheet. High-velocity floodwaters—recurring during the late Pleistocene Epoch—scoured the basalt to produce giant current ripples, plunge pools, and scabland features similar to those at Dry Falls and Wallula Gap. Erosional evidence indicates flood magnitudes rivaling flows documented at Bonneville Slide outbursts and contemporaneous events that shaped Palouse Falls and the Hanford Site scablands; stratigraphic sequences within terraces preserve slackwater deposits, tephra layers correlated with regional ash beds, and reworked glacial drift linked to ice-lobe interactions.
Vegetation on the benches and slopes includes shrub-steppe communities dominated by sagebrush species and bunchgrasses, with riparian corridors near springs and seeps supporting stands of willow and cottonwood. Faunal assemblages include small mammals such as pika-like rodents in rocky talus, raptors including golden eagle and peregrine falcon that nest on basalt cliffs, and populations of mule deer and pronghorn using coulee corridors. The coulee intersects migratory pathways for sage grouse and provides habitat heterogeneity important for endemic invertebrates and phytogeographic relics; plant communities reflect the rain shadow of the Cascade Range and biogeographic links to the Columbia Basin shrub-steppe ecoregion.
Indigenous peoples of the region, including groups associated with the Colville Confederated Tribes and the Confederated Tribes of the Umatilla Indian Reservation, utilized the coulee for seasonal resources, lithic procurement from basalt outcrops, and travel routes connecting riverine fishing sites on the Columbia River with interior hunting grounds. Euro-American exploration and settlement in the 19th century brought wagon roads, ranching, and shepherding tied to the expansion of Oregon Trail era routes and later railroad and highway corridors across the Columbia Plateau. During the 20th century, the area was surveyed for hydropower potential and impacted by land-use changes associated with agriculture and grazing on the Waterville Plateau and adjacent farmlands.
Today the coulee and surrounding scablands attract geologists, climbers, birdwatchers, hikers, and photographers drawn to features comparable to National Natural Landmark-quality exposures such as Dry Falls State Park and viewpoints along State Route 17. Conservation efforts involve federal and state agencies including the United States Fish and Wildlife Service and the Washington Department of Fish and Wildlife to protect shrub-steppe habitat, raptor nesting sites, and culturally significant archaeological locales; regional initiatives coordinate with the Bureau of Land Management to balance recreation, grazing allotments, and habitat restoration. Educational field trips from institutions such as Washington State University and Western Washington University frequently use the coulee as an outdoor classroom for studies in geomorphology, Quaternary science, and paleohydrology.
Category:Landforms of Washington (state) Category:Channeled Scablands