Map showing ice cover in the Yellowstone region
Map showing ice cover in the Yellowstone region. Light shaded areas bounded by black and red lines indicate areas covered during the Pinedale (about 20,000-15,000 years ago) and Bull Lake (about 150,000 years ago) glaciations, respectively. Blue lines are contours in thousands of feet on the maximum reconstructed Pinedale glacier surface. The circled numbers schematically depict the southwest migration of the center of mass of the greater Yellowstone glacial system through time (in thousands of years).