The Geology of Crater Lake National Park, Oregon With a reconnaissance of the Cascade Range southward to Mount Shasta by Howell Williams
The Parasitic Scoria Cones of Mount Mazama
The Younger Cones
Except for the cone of Wizard Island, there is none in the park that surpasses in symmetry the one which rises from Grayback Ridge near its southern end. It is referred to here as Diller Cone, in honor of Diller’s masterly pioneer work in this region. It stands more than 600 feet high on a floor of drift-covered dacite. The northern slope is blanketed with pumice, but near the top and on the eastern side there are plentiful exposures of red scoria and agglutinate accompanied by a little scoriaceous lava. Apparently the last weak explosions served to fill the crater, leaving the summit almost flat. Close to the east base there are isolated outcrops of vesicular olivine basalt, but there is no means of telling whether this lava issued from fissures at the foot of the cone or belongs to the much older, Pliocene plateau basalt series which underlies Mount Mazama.