Shepard Glacier, a glacier remnant in Montana’s Glacier National Park just southeast of Cathedral Peak, has become a striking example of the park’s widespread ice loss. Once larger, it diminished sharply over the twentieth and early twenty-first centuries. From 1966 to 2005, it lost 56 percent of its surface area, and by 2009 it had shrunk to less than 25 acres, the minimum size regarded for an active glacier. Comparisons of photographs from 1913 and 2005 reveal the scale of that change. Its importance now lies chiefly in what it shows about rapid glacial retreat in the park, as tracked by the U.S. Geological Survey.