Near the end of the last ice age, a lobe of the Cordilleran ice sheet dammed the Clark Fork River and created Glacial Lake Missoula across western Montana. At its largest, it was the biggest known ice-dammed lake, filling multiple mountain basins and leaving visible strandlines near Missoula. Its significance lies in the repeated collapse of its immense ice dam, which unleashed the Missoula Floods about 40 times over roughly 2,000 years. Those catastrophic floods swept across parts of the inland Northwest, helped carve the Channeled Scablands and other major landforms, and left features such as giant current ripples and layered sediments that became key evidence for catastrophic flood geology.