Geologic Information: The Cottonwood Canyons and many of their tributaries and high-elevation basins were filled with hundreds of feet of glacial ice between 30,000 and 10,000 years ago.
The Little Cottonwood Canyon glacier reached beyond the mouth of the canyon and extended into Lake Bonneville, calving ice bergs into the Ice Age lake. The Big Cottonwood Canyon glacier, however, advanced only about 5 miles down its canyon. Presumably this was due to less snow accumulation in Big Cottonwood’s catchment area.
Valley (alpine) glaciers originate at the head of valleys in high mountain ranges and then flow down preexisting stream valleys. They erode and transport considerable amounts of rock debris, enabling them to significantly modify the landscape. Many distinctive erosional and depositional landforms result; however, this article addresses only the more prominent local features. Beautiful granitic rock that has been sculpted by glacial ice in both canyons enhances the spectacular rugged, mountainous scenery.
Erosional Landforms and Features: Glaciers pluck and abrade a staggering amount of rock from the canyon walls and floors, which is then carried along with the moving ice. Thus, the hefty mass of rock material and ice perform some serious erosion. The valley bottom and walls are scoured vigorously, creating a deeper and much wider U-shaped canyon—one of the most distinctive valley glacial features.