During the last Ice Age, a lobe of ice at least a half-mile high blocked the Clark Fork River in Idaho and created Glacial Lake Missoula. The ice dam failed over and over, sending billions of tons of water across the land. The torrent of water, icebergs, and mud raced at speeds up to 60 mph, stripping away tons of soil and rock as it crossed eastern Washington, passed through the Columbia River Gorge, and continued to the ocean. These immense floods carved steep-walled canyons, sculpted immense waterfalls, and left behind landscapes found nowhere else on earth. Geologists found evidence that Glacial Lake Missoula and other glacial lakes filled and emptied many times during the last Ice Age.