Some of the largest floods ever known swept through this pathway during the last Ice Age, carving steep-walled canyons, sculpting immense waterfalls, and leaving landscapes found nowhere else on earth. A lobe of ice at least a half-mile high blocked the Clark Fork River in Idaho and created Glacial Lake Missoula, and when this massive ice dam failed over and over, it sent billions of tons of water rampaging across the land. The torrent of water, icebergs, and mud raced as fast as 60 mph, stripping away tons of soil and rock as floodwaters surged across eastern Washington, through the Columbia River Gorge, and to the ocean. Geologists found evidence that Lake Missoula and other glacial lakes filled and emptied many times during the last Ice Age, though the exact number of floods remains unknown.