Granite, glaciers, and rockfall in Yosemite Valley, California
Roger L. Putnam, Greg M. Stock, Allen F. Glazner, John M. Bartley, Drew S. Coleman, 2013. "Granite, glaciers, and rockfall in Yosemite Valley, California", Geologic Excursions from Fresno, California, and the Central Valley, Keith Putirka
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Since the days of John Muir, the striking granitic topography of Yosemite Valley, California, has been understood to have been sculpted by glaciers and presently modified by rockfall. Glacial erosion has provided remarkably clean and extensive exposures of granitic rocks on the vertical walls that provide insights into intrusive relations and rockfall susceptibility. However, it is only with recent remote sensing methods that these exposures have been studied in detail. El Capitan presents an unparalleled exposure of the interior of a granitic plutonic system at the point of interaction between multiple intrusive suites and two sets of mafic dike swarms. The distribution and orientation of these units affected El Capitan's extensive rockfall history, including a huge postglacial rock avalanche at 3.6 ka. This two-day field trip will explore these ideas and apply them to some of the other classic cliffs of Yosemite Valley such as Glacier Point and Half Dome. We will present a new map of El Capitan and discuss the intrusive relationships exposed on the face while visiting several rockfall deposits and some of the classic vistas of Yosemite Valley, including El Capitan Meadow, Glacier Point, Taft Point, and Mirror Lake.
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In this volume we present seven field trip guides that span the breadth of the geology of central California. The trips are associated with the 2013 Cordilleran Section meeting of the Geological Society of America, convened in Fresno, California. These trips provide guides to some of the most remarkable of geologic localities, which are not only iconic, but form type examples of key geologic phenomena and include Yosemite National Park, the San Andreas fault, the Franciscan complex, and the Sierra Nevada Foothills near Fresno, California. The topics covered by these field trips include the nature of continental transform faults, the initiation of subduction, the origin of the Sierra Nevada batholith, the initiation of the Sierra Nevada arc, Pleistocene vertebrate fossils of the Central Valley, and debris flows triggered from burned watersheds.