Ice age
During the last ice age glaciers shaped the landscape of the Columbia River Plateau. Ice blocked the Columbia River near the north end of Grand Coulee, creating glacial lakes Columbia and Spokane. Ice age glaciers also created Glacial Lake Missoula, in what is now Montana. Erosion allowed glacial Lake Columbia to begin to drain into what became Grand Coulee, which was fully created when glacial Lake Missoula along with glacial Lake Columbia catastrophically emptied. This flood event was one of several known as the Missoula Floods. Unique erosion features, called channeled scablands, are attributed to these amazing floods.