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 Kerr Valley Glacier
The lowest point on the rim of Crater Lake is at Kerr Notch, familiar to all visitors on account of its beautifully symmetrical U shape. At this point the caldera wall is only 550 feet high. Once, the notch was filled to the brim with a glacier that continued beyond for perhaps 8 miles, but when the last pumice eruptions took place the glacier had been reduced to a thickness of little more than 100 feet, and its snout lay only about a mile beyond the caldera rim.
The traces left by the Kerr Valley glacier at the time of its greatest extent are almost wholly concealed, but the presence of drift on the top of 6605 Hill, on the east side of Sand Creek, indicates that 3 miles beyond the caldera rim the ice was at least 600 feet thick. A mile to the northwest of this locality, on the south slope of Anderson Bluffs, an imposing lateral moraine is still preserved. At lower elevations, Sand and Wheeler creeks have yet to cut through the overburden of pumice to the drift below.