Sperry Glacier lies on the north slopes of Gunsight Mountain west of the Continental Divide in Glacier National Park, Montana. Unlike the park’s older glacial landscape, it formed during the Little Ice Age, from around the 13th century to the mid-19th century. Once among the park’s largest glaciers, it has retreated sharply, from an estimated 930 acres at the end of that period to about 216 acres in 2005, including nearly 35 percent loss between 1966 and 2005. Named for Oberlin College professor Lyman B. Sperry, it has left moraines and milky aqua waters from glacial flour and remains a demanding destination for experienced hikers.