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The Geology of Mount Rainier National Park



In discussing the physiographic features of the Park, a division should be made between the cone of Mount Rainier and the upland surface of the Cascades upon which it rests. Structurally, the higher Cascades in the vicinity of the mountain are a series of flows having either a horizontal attitude or thrown into gentle, undulating folds; while Rainier is composed of pyroclastics and flows all dipping away from a central vent. Both in time and in structure the rocks of the Cascades are separated from those of Rainier by a marked unconformity. Even topographically, the huge mass of the cone stands out in bold relief; towering 10,000 feet above the range beneath. So it is readily seen that this separation is necessary.

It is to be expected that the attention of the Park visitors should be attracted to the majestic summit and the spectacular glacial system of the mountain, while all else receives minor consideration. The glaciers, occupying one-tenth the area of the Park, are the only features which have received ample mention in the literature. Two excellent and detailed reports, as well as several smaller papers, have been published describing the glaciers. The remainder of the volcano, or another one-tenth of the Park, has a geologic literature (petrographic) totalling approximately 12 pages. No papers have been published dealing directly with the geology of the other eight-tenths of the Park.

Omitting for the time being all reference to the volcano, an attempt will be made to review, briefly, the literature on the Cascades.

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Last Updated: 28-Mar-2006