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
South Wall of the Caldera, from Eagle Cove to Kerr Notch
On the great face of the Eagle Crags, not a single layer of till can be found interbedded with the lavas, the only moraines being those between the highest flows and the overlying, youngest pumice deposits of Mount Mazama. Glaciated pavements close to Dyar Rock, at an elevation of more than 7800 feet, suggest that when these moraines were laid down the entire ridge separating Sun from Munson Valley, and perhaps even the tops of Garfield and Applegate peaks, were buried under a continuous sheet of ice. The Sun Valley glacier was then continuous over most if not all of Dutton Ridge, and united in a single gigantic field of ice with the Kerr Valley glacier. This must have been the time of maximum glaciation. It was then that the great U-shaped Sun and Kerr valleys were chiefly cut. Long afterward, when the glaciers had not only disappeared from the tops of Vidae and Dutton ridges, but retreated up Sun and Kerr valleys above the present rim of the caldera, dacite pumice explosions laid down between m and 50 feet of ejecta in the bottoms of Sun and Kerr notches. The ice then readvanced and buried the pumice with moraines. Except near the margins, these final moraines either are entirely bare or are covered only by the merest sprinkle of pumice. It therefore seems likely that when the last pumice eruptions took place glaciers still occupied the bottoms of Sun and Kerr notches. Such pumice as does occur on the surface of the last moraines may represent vestiges of thick piles that fell onto the ice, or ejecta washed into place at some later date.
The oldest record of glaciation in this section of the caldera wall appears between half and two-thirds of the way down the face of Dutton Cliff, immediately above the top of the Phantom cone (page 30 and plate 6).