Geological Survey Professional Paper 3 The Geology and Petrography of Crater Lake National Park

INTRODUCTION.

The geological record of this country from the earliest epochs to the present time is replete with volcanic phenomena. but the climax appears to have been reached in the earlier portion of the Neocene, when one of the largest known volcanic fields of the world was vigorously active in our Northwestern States. This area of volcanic activity stretches from the Rocky Mountains to the Pacific, embracing a large part of Wyoming, Montana, Idaho, Washington, Oregon, and California, and presenting a great variety of volcanic phenomena concerning which, notwithstanding a copious literature, there has been as yet but a small amount of detailed investigation.

The central feature in the geology of the Crater Lake National Park is the wreck of Mount Mazama. and in order to describe this more clearly, it is necessary to consider briefly the general relations of the Cascade Range.

Plate I.—MT. MAZAMA AND CRATER LAKE NATIONAL PARK, OREGON.
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