Gannett Glacier lies on the east and north slopes of Gannett Peak in Wyoming’s Wind River Range, within the Fitzpatrick Wilderness of Shoshone National Forest. The largest glacier in the Rocky Mountains within the United States, it is part of a cluster of glaciers and ice fields around the state’s highest mountain. Its meltwater feeds Dinwoody Creek and then the Wind River, connecting this alpine ice to downstream water supplies. Over the second half of the twentieth century, the glacier shrank in area and thinned substantially, reflecting warming and reduced moisture. Its retreat has reduced glacier contributions to streamflow, affecting mountain ecosystems and downstream agricultural and ranching uses.