Moses Coulee Coulee, a National Natural Landmark, one of the largest examples of bars created by the Channeled Scablands outburst floods. Moses Coulee cuts into the Waterville Plateau, which lies in the northwest corner of the Columbia River Plateau. The plateau is part of the Columbia River Basalt Group, a large igneous province that lies across parts of the states of Washington, Oregon, and Idaho in the United States of America. During late Miocene and early Pliocene times, one of the largest flood basalts ever to appear on the earth's surface engulfed about 163,700 km² (63,000 mile²) of the Pacific Northwest, forming
Grand Coulee Dam residents were relocated. The Anti-Speculation Act was passed in 1937, limiting the amount of land farmers could own to prevent inflated prices. The government appraised the land and offered to purchase it from the affected residents. Many refused to accept the offers, and Reclamation filed condemnation suits. Members of the Colville Confederated and Spokane tribes who had settlements within the reservoir zone were also resettled. The Acquisition of Indian Lands for Grand Coulee Dam Act of , 1940, allowed the Secretary of the Interior to acquire land on the Colville and Spokane Reservations, eventually accounting for . By 1942, all