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
Coulee Dam, Washington Coulee Dam, Washington Coulee Dam is a town in Douglas, Grant, and Okanogan counties in the State of Washington. The Douglas County portion of Coulee Dam is part of the Wenatchee–East Wenatchee Metropolitan Statistical Area. The population was 1,098 as of the 2010 census. Coulee Dam was founded by the U.S. Bureau of Reclamation in 1933, to serve as headquarters for the construction of the Grand Coulee Dam. The Okanogan County portion was known as Mason City, location of the head contractor. The Portions in Douglas and Grant Counties was known as Engineers Town and was government owned. In 1942