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
Evidences of Early Glaciation on the Caldera Walls
Few parts of the caldera wall are more difficult of access than the cliffs overlooking Steel Bay, and much hazardous climbing will be required before the details of this section are determined. Enough is known, however, to say that in addition to the till which occurs almost everywhere just beneath the products of Mazama’s last explosions, there are at least two other glacial horizons. Their approximate positions are illustrated in the panoramic sketch, plate 28. The lower layer rests on the hummocky tops of the lavas whose dike feeders are exposed near the base of the caldera walls. It is not a continuous band, but a series of lenses composed partly of till and partly of well stratified fluvioglacial sands, from which water seeps at many places. Higher up the walls are thin flows of andesite, patches of pink pumice, and blocky explosion debris, associated with much morainic material. At one locality my assistant, Roy Turner, found a well striated pavement; at another we found a small cave at the base of a lava flow, and on the cave floor several glacial boulders. Many erratics also occur in the talus hereabouts.