Upper Fremont Glacier, Glacier in Fitzpatrick Wilderness, Shoshone National Forest, Wyoming, US.

Upper Fremont Glacier is an alpine glacier in the Fitzpatrick Wilderness of Shoshone National Forest, Wyoming, on the north slope of Fremont Peak, the third tallest mountain in Wyoming. It sits at an average altitude of 13,450 feet (4,100 m) in the Wind River Range, part of the largest grouping of glaciers in the U.S. Rocky Mountains.

Like many glacier masses in the Rocky Mountains, it has changed over centuries showing patterns of shrinkage and expansion. Ice cores extracted from it reveal important information about climate changes over the past several centuries in North America.

The glacier's ice cores are the first from a mid-latitude North American glacier used to measure mercury deposition. They show mercury rising sharply during the Industrial Revolution and falling again after the mid-1980s, a decline linked to the Clean Air Act. Cores also record a tritium and chlorine-36 spike around 1963, the peak of above-ground nuclear testing.

Visitors can reach the glacier through established hiking trails in Fitzpatrick Wilderness, but need mountaineering equipment and experience for safe exploration. The high elevation and rough terrain require good physical preparation and clothing adapted for rapidly changing weather conditions.

Ice cores contain records of mercury levels that document the effects of the Industrial Revolution and subsequent environmental protection rules. These chemical traces allow scientists to understand how human activity became stored in the atmosphere.