El Capitan, Half Dome and Yosemite Velley

El Capitan, on the left, is composed almost entirely of El Capitan Granite, a pale, coarse-grained granite emplaced approximately 100 mya (million years ago). In addition to El Capitan, this granite forms most of the rock features of the western portions of Yosemite Valley. A separate intrusion of igneous rock, the Taft Granite, forms the uppermost portions of the cliff face. A third igneous rock, diorite, is present as dark-veined intrusions through both kinds of granite.

Along with most of the other rock formations of Yosemite Valley, El Capitan was carved by glacial action. Several periods of glaciation have occurred in the Sierra Nevada, but the Sherwin Glaciation, which lasted from approximately 1.3mya to 1mya, is considered to be responsible for the majority of the sculpting. The El Capitan Granite is relatively free of joints, and as a result the glacial ice did not erode the rock face as much as other, more jointed, rocks nearby.

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