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 Union Peak Glaciers
The sides of the Union Peak volcano have suffered much more from glacial erosion than those of the younger Mount Mazama. Probably the volcano was already extinct before the onset of the main glaciation, and when the ice was at its greatest extent, the entire cone was covered. The direction of ice flow is shown on the map, figure 23. On the north and east sides, the glaciers fed the Castle and Annie Creek glaciers respectively; those on the south emptied into the great U-shaped canyon of Red Blanket Creek.
Since the col just south of Castle Point is covered with drift, the glaciers on the northwest side of the volcano were thereabouts 650 feet thick. Erratics from the summit tuff cone were carried down to Pumice Flat by the same glaciers that left the moraines bordering Pole Bridge Creek, near the Klamath Falls highway. A mile or so south of this locality, where the ice left Pumice Flat to join the Annie Creek glacier, a fine curved moraine is still preserved. Another and much larger arcuate moraine occupies the depression followed by the old road which leaves the Medford highway just west of Annie Spring, though this seems to have been built by the joint action of ice from the Union Peak volcano and Mount Mazama.
The highest moraines on Union Peak, in the cirque heads at the base of the summit pinnacle, are covered with a light sprinkle of pumice. Therefore, when the catastrophic destruction of Mount Mazama took place the glaciers of Union Peak either had disappeared altogether or were reduced to tongues measuring at most a few hundred yards in length.