The sedimentary record of Otokomi Lake, Glacier National Park, Montana, was studied to determine the age of an adjacent Crowfoot moraine. The presence of Mt. St. Helens Jy ash near the bottom of the longest percussion core limits drainage basin deglaciation to before 11 400 14C years before present (BP), although 14 100 BP is the estimated basal age of the core. Correlative shifts in loss on ignition, coarse (>1 mm) grain size, magnetic susceptibility, and X-ray gray-scale data at a depth of 185 cm are interpreted to be related to a sedimentary change in Otokomi Lake brought about by the deposition of the adjacent Crowfoot moraine. The estimated age of the moraine is 10 590 BP, which is within the Younger Dryas interval. This information supports the hypothesis that Crowfoot moraines represent a regional western North American response to Younger Dryas cooling.