A long, glaciated valley extending from British Columbia this far into Idaho brought part of a continental ice sheet past here thousands of years ago. Rocks and boulders transported here by glacial ice backed up Lake Coeur d'Alene. Then a gradually warming climate let an outlet from Lake Pend d'Oreille discharge past here, sometimes with catastrophic results. As ice receded, Kootenai River also flowed past here before lower channels in British Columbia no longer were blocked by a glacial barrier. In those days, this was Columbia River's main channel.