All the rock debris shown in the foreground of this photo constitutes ground moraine. The material was formerly beneath Grinnell Glacier. Debris in moraines ranges in size from fine silt, which we cannot see in this photo, to large boulders; thus, moraine deposits are unsorted. The rock debris eroded and eventually deposited by glaciers also tends to be angular. The sharp, angular edges of the rocks are evident in the photo. Ground moraine is exposed as glaciers retreat. Grinnell Glacier is located off the photo to the left. A large proglacial lake containing floating slabs of ice occupies the lower-middle portion of the photo.