Grand Coulee of the continental shelf. The web-like formation can be seen from space. Mountains of gravel as tall as 40-story buildings were left behind; boulders the size of small houses and weighing many tons were strewn about the landscape. Grooves in the exposed granite bedrock are still visible in the area from the movement of glaciers, and numerous erratics are found in the elevated areas to the northwest of the coulee. Early theories suggested that glaciers diverted the Columbia River into what became the Grand Coulee and that normal flows caused the erosion observed. In 1910 Joseph T. Pardee described a
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