The scenic beauty of the Bighorn Mountains in Wyoming has long been a draw to outdoor enthusiasts. The stark contrast of rocky peaks jutting above a green forest is beautiful and awe inspiring. Snowfields blanket the high peaks most of the year, but at one time the ice and snow were more permanent. About 12,000 years ago, during the end of the Pleistocene epoch, also known as the last Ice Age, the Bighorn Mountain range, like most other mountain ranges in northern North America, was covered in thousands of feet of ice. The receding ice molded and formed the mountains into the appealing and dynamic landscape we see today.
In 1905, Nelson Horatio Darton, a geologist with the United States Geological Survey, explored the Bighorn Mountains and cataloged the few remaining glaciers. His 1906 USGS report, Geology of the Bighorn Mountains, noted three glaciers, one in upper Black Tooth Canyon, one in upper Penrose Canyon and one on the east side of Cloud Peak. Darton, a member of his party, photographed the largest glacier, Cloud Peak. In 2005, researches, Perry H. Rahn, Charles Michael Ray, and Michael W. Rahn, re-photographed Cloud Peak Glacier from a similar vantage point as Darton’s photograph. It had melted considerably in the 100 years that had passed. The researchers estimated it had gone from about 500 million cubic feet to about 80 million cubic feet in volume and they thought the Cloud Peak Glacier would be entirely gone by 2025.
According to Bonney and Bonney’s 1977 Guide to the Wyoming Mountains and Wilderness Areas, Darton estimated 14 glaciers once covered the Bighorn Mountains during the last Ice Age. Darton described seven glaciers on the east side of the divide of Tongue River, Dome Lake, Lighter, Kearny Lake, Meade Lake, North Clear Creek and South Clear Creek. On the west side of the divide he listed Willet, Shell Creek, Paintrock, Buckskin Ed, West Tensleep, and East Tensleep glaciers. Darton’s work estimated the thickest glacier, Paintrock, was roughly 1,500 feet thick. Willet Glacier was thought to be the smallest at about 500 feet thick.
If you are a keen observer you too can recognize the footprint left by these massive sheets of ice. Arêtes, u-shaped valleys and moraines are just a few of the interesting features left by glaciers that can be observed in the Bighorn Mountains.
Arêtes are ridges of rock left after two or more adjacent glaciers cut through a mountain.
U-shaped valleys or glacial troughs are what you would imagine, a valley with steep sides and a flat bottom. They are formed by the massive weight and movement of a glacier as it slowly slides along the landscape excavating large amounts of soil and rock. Moraines are the tumbled pile of rock and sediment left after a glacier recedes. Moraines are typically found along the edges or at the front end of the glacier.
An excellent place to see more subtle glacial evidence while hiking, biking or horseback riding is Tensleep Trail 156. This recently constructed non-motorized trail meanders along West Tensleep Creek taking visitors through moraine fields, ponds, meadows, and past views of wilderness peaks.
A loop can be made by combining Highline Trail 067 and East Tensleep Trail 068. High clearance and four-wheel drive vehicles can access East Tensleep Lake via Forest Road 430. Evidence of glaciation is abundant in this portion of the Bighorn National Forest.
Sara Evans Kirol is a public affairs officer for the Bighorn National Forest.