The cool, wet climate of the Pleistocene produced a series of large lakes in the Great Basin of the American West. The last of these was Lake Bonneville, which developed 34,000 years ago and eventually spread across most of western Utah and parts of eastern Nevada and southern Idaho. At its peak, 15.5 thousand years ago, this Lake covered 20,000 square miles and had a depth of 1000 feet; its surface elevation was 5100 feet, recorded by the "Bonneville Shoreline," visible across the Great Basin ranges today.
About 14.5 thousand years ago, an alluvial dam along its northern rim (near Red Rock Pass in southern Idaho) broke down, triggering a year-long flood that lowered Lake Bonneville by 350 feet; the resulting "Provo Shoreline" is also evident across the regional mountains. This massive flood scoured the landscape of southern Idaho and greatly augmented flow through the Snake and Columbia Rivers; their impressive canyons are, in part, a product of this deluge. Near the end of the Pleistocene, a gradual warming and drying of the climate caused the smaller lake to receed and disperse into regional basins; today, the Great Salt Lake, Sevier Lake and Utah Lake are all remnants of Lake Bonneville.
