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 Rogue River Glacier
All the glaciers on the northwest, west, and southwest slopes of Mount Mazama ultimately united in a single glacier that flowed down the valley of the Rogue. From its source down to the confluence with Union Creek, tributary valleys entering from the east fed the main glacier with ice. Whether or not the Rogue River glacier was also fed from the west is uncertain, but it seems probable that such glaciers as existed among the ridges of the Western Cascades were confined to the summit regions and never extended as far down as the principal valleys.
It would be interesting to know just how far down the valley of the Rogue the ice extended, but the evidence has been removed by erosion or is buried by pumice. Perhaps the snout of the glacier never extended farther down than Union Creek Ranger Station, that is, below 3400 feet.
In the Cascade Range farther north, as Thayer has shown,4 the Pleistocene glaciers were much more extensive. Indeed, the earliest glaciers descended the North Santiam River valley to an elevation of approximately 700 feet, traversing two-thirds of the width of the Western Cascades, and even the late Wisconsin ice reached as low as 2000 feet.