Boston Glacier, in Washington’s North Cascades National Park, fills a broad cirque beneath several prominent peaks and is the park’s largest glacier, about one mile long and nearly three and a half miles wide. Curving north of Forbidden Peak, it lies between Boston Peak and Buckner Mountain below Ripsaw Ridge, while a nearby ridge separates it from the Quien Sabe and Forbidden Glaciers, contributing to this jagged, heavily glaciated alpine landscape. Since the Little Ice Age ended around 1850, the glacier has generally shrunk. After a moderate advance from 1950 to the mid-1970s, retreat resumed, and its terminus receded 1,470 feet between 1972 and 2006.