blackfoot-valley

centered and at its thickest west of Hudson Bay in northern Canada. At its maximum extent in Montana, the ice reached no more than 150 miles south of the present Canadian border in places. In our locale area, it mostly stopped short of the Blackfoot River. But some tongues of ice in the form of valley gla- ciers did periodically reach out somewhat farther south from the main ice sheet, and also independently from some highland areas well farther south. (A major example of the latter is the Yellowstone Park / Teton area, which during some periods supported what amounted to its own “mini” ice sheet roughly 150 miles long and 100 miles wide.) Tendrils of valley glaciers extended south of the Blackfoot and into the Nevada Creek Valley at various times, leaving their loads of transported material behind when they retreated. Glacial Lake Missoula and its Cataclysmic Floods Steeped in a most dramatic way in the geologic history of a huge region from the Ranch to the west all the way to the Pacific, is the story of Glacial Lake Missoula. This was Montana’s recurring “Great Lake” that formed and re- 18