Rusk Glacier lies on the eastern face of Mount Adams in Washington state, beginning below The Castle at more than 10,200 feet and descending eastward to about 7,500 feet, where it ends at a rock-covered moraine. Much of its surface is covered with rock debris, and near 9,200 feet a small ice-free rock island breaks the ice. The glacier was named for Claude Ewing Rusk, who made the first ascent of The Castle in 1921, with the name bestowed by Harry Fielding Reid. In modern times it has shrunk markedly, losing 23 percent of its surface area between 1904 and 2006.