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 West Slope of Mazama

The entire western rim of the caldera, with the exception of the summits of Hillman Peak and Llao Rock, shows the marks of passing ice. Moreover, glaciers continued to cross what is now the caldera rim until a very late stage, for most of the top of the Watchman lava flow, one of the youngest andesites of Mazama, is striated.

Except in the canyons of Copeland and Bybee creeks, the drift on the western slopes is covered only by a thin and patchy cover of pumice. Few well defined moraines occur on these slopes; instead, hummocky mounds of coarse drift rise from flats littered with gravelly and sandy outwash.

At the head of Copeland Creek, the river tumbles in a series of cascades, 125 feet high, over the end of a recessional moraine in which boulders up to 15 feet across may be found, and for a mile below, the pumice is considerably mixed with glacial debris. A similar recessional moraine is exposed beneath pumice on the tributary of Bybee Creek where it is cut by the meridian 122° 15′ west.

At the time of maximum glaciation, ice filled the canyons of both Copeland and Bybee creeks as far down as their confluence with the Rogue River.

 

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