Half Dome and Yosemite

Yosemite National Park reaches across the western slopes of the Sierra Nevada mountain chain and is internationally recognized for its spectacular granite cliffs, waterfalls, clear streams, Giant Sequoia groves, and biological diversity. The geology of the Yosemite area is characterized by granitic rocks and remnants of older rock. About 10 million years ago, the Sierra Nevada was uplifted and then tilted to form its relatively gentle western slopes and the more dramatic eastern slopes. The uplift increased the steepness of stream and river beds, resulting in formation of deep, narrow canyons. About 1 million years ago, snow and ice accumulated, forming glaciers at the higher alpine meadows that moved down the river valleys. Ice thickness in Yosemite Valley may have reached 4,000 feet (1,200 m) during the early glacial episode. The downslope movement of the ice masses cut and sculpted the U-shaped valley that attracts so many visitors to its scenic vistas today.


As late as the 1870s, Half Dome was declared "perfectly inaccessible". The summit was finally conquered by George Anderson in October, 1875, via a route constructed by drilling and placing iron eyebolts into the smooth granite. Today, Half Dome may now be ascended in several different ways. A rigorous 2 mi approach including several hundred feet of granite stairs, the final pitch up the peak's steep but somewhat rounded east face is ascended with the aid of a pair of post-mounted braided steel cables originally constructed close to the Anderson route in 1919.



El Capitan 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. El Capitan 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.