When lighting conditions are right, dozens of shoreline traces may be seen along the mountains around Missoula, Montana. The traces mark the numerous different levels of one or more ice-dammed lakes, known as Lake Missoula, which occupied extensive areas of the Clark Fork River Basin between the Bitterroot Mountains and the Swan Range. The city of Missoula itself is built upon a lacustrine terrace of the same origin. Damming of the Clark Fork was effected by a lobe of Cordilleran ice which moved southward into the valley of the Clark Fork where the stream rounds the northern nose of the Bitterroot Mountains and begins to flow westward to join the Columbia River. The map below depicts the locations of Lake Missoula, the ice dams, and the Channeled Scablands section downstream which was scoured by more than one catastrophic floods from Lake Missoula.
Adapted from pp. 393-4 and page 455 in Thornbury, William D. 1965. Regional Geomorphology of the United States. New York: Wiley.