The Geology of Crater Lake National Park, Oregon With a reconnaissance of the Cascade Range southward to Mount Shasta by Howell Williams
The Glaciation of Mount Mazama
Evidence of Glaciation Outside the Caldera
The Bear Creek Glacier
A powerful glacier formerly poured northeastward across the caldera rim near Cloudcap, entered the valley of Bear Creek, and flowed down it to the plateau beyond. As it retreated within the present boundaries of the park, it left behind two huge lateral moraines about a mile apart. Of these, the southern is the most imposing in the park. It rises 250 feet above the valley floor, and is heavily charged with boulders, some of them 10 feet across.
Up to Cascade Spring, the source of Bear Creek, the floor of the valley is blanketed with lump pumice. The spring itself issues from the base of a bouldery moraine resting on lava. Still higher up the valley, the hummocky drift is only lightly covered with fine granular pumice.