Moses Coulee

During late Miocene and early Pliocene times, one of the larger flood basalts ever to appear on the earth's surface engulfed about 163,700 km2 (63,000 mile2) of the Pacific Northwest, forming a large igneous province with an estimated volume of 174,300 km3.

[5][6][7][8][9] Pleistocene glaciers advanced onto the Waterville Plateau, with the Okanogan Lobe of the Cordilleran Ice Sheet reaching as far south as the town of Withrow.

[5][6][10][11] A precursor to glacial-flood-cut Moses Coulee existed prior to the glacial floods as a drainage basin with a number of side streams, draining the southern portion of the plateau.

Flowing across the current Grand Coulee and Dry Falls regions, the ice age Columbia then entered the Quincy Basin and joined Crab Creek, following Crab Creek’s course southward past the Frenchman Hills and turning west to run along the north face of the Saddle Mountains and rejoin the previous and modern course of the Columbia River just above the main water gap in the Saddle Mountains, Sentinel Gap.

[11] As the Okanogan lobe melted, the upper portions of Moses Coulee were littered with clear evidence of its passing in the Withrow Moraine.

This glacial till, made up of clay, silt, sand, gravel, cobblestones, and erratic boulders, covers most of the upper coulee.

Vegetation includes sagebrush, rabbitbrush, greasewood, hopsage, bitterbrush, bunchgrass, buckwheat and other vegetation once common to most of the Columbia Plateau,[12] however it is vulnerable to the same forces that are destroying shrub-steppe and big sagebrush throughout the western US such as development, wildfires, invasion by non-native annual species, and overgrazing.

It provide habitat for a rich variety of birds (lazuli bunting, common goldeneye, sage thrasher, sage sparrow, poorwill, mountain bluebird, loggerhead shrike, canyon wren, white-throated swift, golden eagle), plants (sagebrush buttercup, shooting star, sulphur lupine, serviceberry, mock orange, slender cryptantha, Tiehm's rush, big sagebrush, bluebunch wheatgrass and sego lily) and animals (mule deer, least chipmunk, bats, and marmot).