Withrow Moraine and Jameson Lake Drumlin Field erosion resulting from the Missoula Floods, which laid bare many layers of the basalt flows on the edges of the plateau at Grand Coulee and Moses Coulee. Two million years ago the Pleistocene epoch began and Ice age glaciers invaded the area. They scoured the Columbia River Plateau, reaching as far south as the middle of the Waterville Plateau highlands above the Grand Coulee and south to the head of Moses Coulee. In some areas north of the Grand Coulee they were as much as 3 km (10000 feet) thick. Grooves in the exposed granite bedrock are still visible in
Coulee ridgetops transitioning into tallgrass prairie when not turned into pasture or used for row crops. Coulees provide shelter from wind and concentrated water supplies to plants which would otherwise struggle to survive in the xeric sagebrush steppe. Trees are often found in riparian habitats along streams in coulees and at the base of their walls. Coulee </div> Coulee, or coulée ( or ) is a term applied rather loosely to different landforms, all of which refer to a kind of valley or drainage zone. The word "coulee" comes from the Canadian French "coulée", from the French word "couler" meaning "to