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, at times more than two miles wide and 30 miles long, failed over and over as rising water caused it to leak and crack, and water pouring through fractures beneath the surface eroded the dam from below until it suddenly gave way. Billions of tons of water then raced across the land at speeds up to 60 mph with icebergs and mud, stripping away tons of soil and rock, carving steep-walled canyons, sculpting immense waterfalls, and leaving landscapes found nowhere else on earth. The floodwaters surged across eastern Washington, through the Columbia River Gorge, and to the Pacific Ocean, and geologists found evidence that Lake Missoula and other glacial lakes filled and emptied many times during the last Ice Age.