the far edge 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 great Ice Age lake, "Glacial Lake Missoula", a glacier dammed lake with water up to deep, in northwest Montana and in 1940 he reported his discovery that giant dunes high and feet apart had formed the lake bed. In the 1920s, J Harlen Bretz looked deeper into the landscape and put forth his theory of the dam breaches and massive glacial floods from Lake Missoula. Of the Channeled Scablands, Dry Falls, one of the largest waterfalls ever known, is an excellent example (south of Banks Lake). It is probable that humans were witnesses, and victims, of the immense power of the Ice Age Floods. Archeological records date human presence back to nearly the end of the Ice Age, but the raging torrents erased the land of clear evidence, leaving us to question who, if anyone, may have survived. With the end of the last glacial advance, the Columbia settled into its present course. The river bed is about below the Grand Coulee. Walls of the coulee reach in height. Upper Coulee Grand Coulee is the longest and deepest of eastern Washington canyons. Its unique characteristics include a lower floor at the head of the channel than at its outlet and the widest and highest dry falls cliff in the middle. It was created through the process of cataract recession, which included a cataract twice as high as its existing Dry Falls. Grand Coulee is two canyons, with an open basin in the middle. The Upper Coulee, filled by Banks Lake, is long with walls tall. It links to the Columbia River at Grand Coulee Dam and leads southward, through the surrounding highlands. The entry to the coulee is above the Columbia. It began as the course of a Glacial Columbia River. The Cordilleran ice sheet's Okanogan lobe