Gem Glacier is a small hanging glacier in Montana’s Glacier National Park, high on a cliff above Grinnell Glacier on the east side of the Continental Divide along the Garden Wall. Covering about 5 acres, it is the park’s smallest glacier and far below the roughly 25-acre benchmark often used for an active glacier. Its importance lies chiefly in what its decline reveals: from 1966 to 2005, Gem Glacier lost 30 percent of its area, while Grinnell Glacier below lost 40 percent. Together they illustrate the retreat of ice in the park.