Grand Coulee in eastern Washington is an ancient river bed and one of the Columbia Plateau’s most dramatic erosional features. Formed atop far older granite and basalt, it was carved during the Ice Age when glaciers blocked the Columbia River and catastrophic outbursts from Glacial Lake Missoula swept across the region about 18,000 years ago. Those floods cut the largest canyon in the Channeled Scablands, including Dry Falls and the upper and lower coulees. In the 20th century, work by Joseph T. Pardee and J Harlen Bretz helped establish this geologic explanation. Since 1952, Banks Lake and irrigation works have reshaped the upper coulee for farming, recreation, and wildlife, while also displacing Native Americans.