Upper Fremont Glacier is in the Fitzpatrick Wilderness of Shoshone National Forest in the U.S. state of Wyoming.

[4] Ice cores from the glacier also showed increased levels of Tritium (3H) and chlorine-36 around the year 1963, which coincides with the peak period of above ground nuclear testing.

This is the first known instance in which ice cores have been used to determine mercury deposition from a mid-latitude glacier in North America, as all previous studies have been derived from other sources.

[5] The ice core samples from the Upper Fremont Glacier indicated that levels of mercury increased dramatically during the Industrial Revolution and have decreased significantly since the mid-1980s.

It is believed that the decrease in mercury deposition since the 1980s coincides with the passage of the Clean Air Act.