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
Glaciers on the North Slope of Mazama
Prior to the eruption of the Roundtop and Palisade lavas, as we have seen, large glaciers occupied the northeast slope of Mount Mazama for a long time. Even after the eruption of these lavas, ice again covered what is now the northeast rim of the caldera. The extent of these older glaciers is a matter for conjecture, for the heavy deposits of pumice on this side of the volcano effectually hide all evidence.
By the time the dacites of Cleetwood Cove and Grouse Hill were extruded, the glaciers on the north slope of Mount Mazama had been reduced to thin tongues only a few miles long. The absence of drift on the lower slopes of Timber Crater shows that this basaltic cone was also built after the period of maximum glaciation.
At their greatest extent the glaciers on the north slope of Mount Mazama were confluent with those from Mounts Bailey and Thielsen. A great field of ice then existed about the headwaters of the Rogue River and in the basin south of Diamond Lake. On the northern slopes of those two volcanoes the glaciers descended to approximately 4000 feet, to Toolbox Meadows and the upper part of Mowich Park, where copious streams issue from the terminal moraines to feed the North Umpqua River. The Desert Ridge volcano was the source of smaller glaciers tributary to those from Mount Mazama. The whole northwest corner of the park, even the top of Crescent Ridge, was then under ice, all of which found its way into the Rogue River glacier, to be united with the glaciers that flowed down the western slopes of Mount Mazama.