Geology of the Pacific Northwest along their course. The larger cataract was that of the upper Grand Coulee, where the river roared over an waterfall. The eroding power of the water plucked pieces of basalt from the precipice, causing the falls to retreat and self-destruct by cutting through to the Columbia River valley near what is now the Grand Coulee Dam. The other major cataract is now known as Dry Falls. It started near Soap Lake in Washington State, where less resistant basalt layers gave way before the great erosive power of this tremendous torrent and waterfalls developed. As in the upper Grand Coulee, the
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