This is the first of a series of bulletins issued monthly during the season to give information on subjects of interest concerning the natural history of Crater Lake. It is supplemental to the lectures and field trips conducted by the Park naturalist. Publications using extracts kindly credit the bulletin and author. For copies, which are free, address the Superintendent or Ranger-naturalist. The reader is advised to consult more recent literature to obtain a current understanding of the topic.
Crater Lake lies in the caldera of a once mighty mountain.
Mazama is the name given to the mountain that once stood here. Evidence that a peak did rise a full ten thousand feet above the lake bottom, or a full seven thousand above the Rim, is derived from four sources. First, glacial evidence is clear, and the source of the glaciers have been higher than the present rim, since there are no cirques, the cut edges of moraines show at the rim, and the valleys are broad and U-shaped at the very top. Second, dikes stand out boldly on the inside of the walls, indicating an angle toward an original peak. Fully ten of these can be counted.