Historic Resource Study, Crater Lake National Park, Oregon, 1984
V. Geological and Biological Information on Crater Lake Area
E. Points of Geological Interest in Crater Lake National Park
1. Rim Slopes
Studying the scene from the Lodge on the rim where the automobile-stage has left you, the most vivid impressions of detail are those of the conformation of the inner rim, the cliffs which rise above it, and the small volcano which emerges from the blue waters of the lake.
The marvellous inner slope of the rim is not a continuous cliff, but a highly diversified succession of strata. Examination shows the layers of volcanic conglomerate and lava of which, like layers of brick and stone, the great structure was built. The downward dip of these strata away from the lake is everywhere discernible. . . 
The caldera rim at one point is so broken by crags and pinnacles among bristly trees that this spot is called Rugged Crest; its spires were formed by fracturing.