Last week, Alta Historical Society did a “Fireside Chat” discussing how Little Cottonwood Canyon was formed and how that makes Alta so special. We loved the talk so much, we wanted to share it with you. Click the link above to learn more about the Alta Historic Society.
Both Little and Big Cottonwood Canyons are shaped from glaciers over thousands of years ago. Valley glaciers are derived from the top of the valley’s and flow down streams. As these glaciers erode and deteriorate they modify rock and reshape the canyons. Glacial ice originates at the top of the canyon and creates an “ampepheuter-shaped basin,” called a cirque. This landform has high, steep walls surrounding it. As the glacier flows down canyon it forms steep ridgelines and U-shaped valleys. While the main glacier moves down canyon, smaller glaciers flow down separate valleys to feed into the main glacier ─ much like small streams serve as tributaries to a larger river. These smaller glaciers drop into the main glacier forming a Hanging Valley (a Ushaped valley that ends abruptly with a steep cliff or hill falling into the main valley). These hanging valleys and steep ridgelines are easily seen at both Snowbird and Alta. All of the features are what has made Little Cottonwood Canyon one of the greatest ski locations in the world.
Little Cottonwood Canyon:
Around 30,000 years ago, a 12 mile long glacier spread through Little Cottonwood Canyon, starting at Albion Basin going beyond the mouth of the canyon down to the shore of Lake Bonneville. This glacier was the longest glacier in the Wasatch Range with a depth ranging from 450 feet to 850 feet. Little Cottonwood Canyon is known for it’s U-shaped valley carved from rocks scraping through and being carried out. Over tens of thousands of years ago, large repeated earthquakes created the steep slopes at the mouth of the canyon. 10,000 to 30,000 years ago, glacial ice filled the canyon.
Big Cottonwood Canyon:
Big Cottonwood Canyon was shaped by a smaller glacier only 5 miles long. It had a depth of 500 feet to 800 feet. This glacier ended abruptly, leaving the bottom 9 miles of the canyon glacier free. These first 9 miles into the canyon are narrow and windy, because of stream erosion, then the canyon opens up a bit more. This is because of the glacier shape and size. As the glacier melted and broke apart, it created a stream flowing out of the canyon from where the glacier ended out of the mouth of the canyon.This smaller glacier is due to less snow accumulation in the canyon.
Glacial striations are when pieces of rock that get stuck to the bottom of glaciers and will carve parallel lines into the ground and other bedrock. These carvings show the direction in which the glaciers move in. Glacial striations are visible in both Big and Little Cottonwood Canyon: Lake Blanche (Big Cottonwood Canyon) and Cecret Lake in Albion Basin (Little Cottonwood Canyon.)
These monumental landforms (cirques, arêtes, horns, etc.) that were created by glaciers thousands of years ago can be seen particularly on the canyon’s south side, near Albion Basin, when you are riding up Collins lift or hanging out on Devil’s Apron. This steep terrain that makes Alta so special is directly attributable to the glaciers that flowed through Little Cottonwood 16,000 years ago.
*Information obtained from Utah Geological Survey*