Moses Coulee the southern portion of the plateau. These streams had combined into a canyon that drained to the Columbia near the current mouth of Moses Coulee. These side drainages are still visible today along the coulee walls as truncated streambeds, interspersed with gable-like highlands. The Okanogan lobe of the Cordilleran Glacier moved down the Okanogan River valley, covering 500 mi² of the Waterville Plateau and blocked the ancient route of the Columbia River, backing up water to create Glacial Lake Columbia and Lake Spokane. Initially water discharged from Lake Columbia by running up through the head of Grand Coulee and down
Grand Coulee pumped from the Grand Coulee Dam, into Banks Lake to act as an Equalizing Reservoir and irrigation water source. Evidence of the waterfalls includes a plunge basin where the falls began, immediately south of Coulee City. It contains at least of gravel lower than the open flooring of the land. The river above the falls was shallow and much wider than the gorge. Thus, it wrapped around the lip of the main falls creating lateral falls. These flowed until the recession of the main falls denied them water. Northrup Canyon in Steamboat Rock State Park, contains a dry cataract as