Cloud Peak Glacier is a high-elevation glacier in the Cloud Peak Wilderness of Bighorn National Forest in north-central Wyoming, lying in a deep cirque northeast of Cloud Peak at about 11,800 feet. It is the only active glacier in the Bighorn Mountains and a significant feature of the Cloud Peak high country. Over the past century, it has shrunk rapidly in both area and thickness. Comparisons from 1905 to 2005 estimate its volume declined from about 506,000,000 cubic feet to 78,000,000 cubic feet. Its retreat has made it one of the clearest signs of long-term glacier loss in this part of the Rocky Mountains, and it was expected to disappear between 2020 and 2034.