Grand Coulee Dam and completion. Creation of the reservoir forced the relocation of over 3,000 people, including Native Americans whose ancestral lands were partially flooded. While the dam does not contain fish passage, neither does the next downstream dam, Chief Joseph Dam. This means no salmon reach the Grand Coulee Dam. The second large dam downstream, Rocky Reach Dam, has an intricate system of fish ladders to accommodate yearly salmon spawning and migration. The Grand Coulee is an ancient river bed on the Columbia Plateau created during the Pliocene Epoch (Calabrian) by retreating glaciers and floods. Originally, geologists believed a glacier that diverted
Grand Coulee of Lower Grand Coulee. The Great Cataract forms the divide from the upper to lower coulees. The Lower Coulee tends along the monoclinal flexure to Soap Lake where the canyons end and the water flowed out into Quincy Basin. Quincy Basin is filled with the eroded gravels and silts from the Coulee. The Lower Coulee, also created its own path across the plains. Evidence of this is found in the tilted flows visible at Hogback islands in Lake Lenore and tilted flows along Washington 17 from Dry Falls to Park Lake. Numerous canyons acted as a distribution system for the