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Yosemite National Park

Pywiack Dome, Mount Dana, and Tenaya Lake, as seen from near Olmstead Point

Yosemite National Park (pron. yo-sem-mi-tee) is a national park largely in Mariposa County, and Tuolumne County, California, United States. The park covers an area of approximately 3,079 square kilometers and stretches across the western slopes of the Sierra Nevada mountain range. Over 3 million people visit Yosemite each year. The park is about 3.5 hours driving east of San Francisco.

Landscape and Ecology

Notable park features include numerous waterfalls along the glacially formed Yosemite Valley of the Merced River and the majestic Half Dome and many steep cliffs for rock climbing. These cliffs are more than 3000 feet in height.

Most park visitors fail to realize the scale of the cliffs in Yosemite Valley because they just look like normal rocks from a distance. Many people would be awed by the sheer size of those rocks if they were able to spot some ant-like rock climbers hanging on the cliffs. Another way to get a sense of the scale of the cliffs was to look for full size trees on the top of the cliffs which appear like hairs on the rocks.

About 95% of the park is protected wilderness area, which was established in 1984 by an act of congress. However, the majority of tourists stay within or around the Yosemite Valley which is only a tiny fraction of the national park.

To the north of Yosemite Valley is Hetch Hetchy Valley, which was considered by many, including John Muir, to be nearly identical in beauty and significance to Yosemite Valley. The valley was flooded in 1923 by the O'Shaughnessy Dam blocking the Tuolumne River to form the Hetch Hetchy reservior. The dam supplies water and cash (from electricity sales) to the San Francisco area. Congress authorized the O'Shaughnessy Dam in 1913. Passage of the law is said to have led to John Muir's death (from despair).

The high country of Yosemite contains beautiful areas, such as Tuolumne Meadows, Dana Meadows, the Clark Range, the Cathedral Range, and the Kuna Crest. The Sierra crest runs through Yosemite, with peaks of red metamorphic rock, such as Mount Dana and Mount Gibbs, and granite peaks, such as Mount Conness.

It has groves of ancient sequoia trees and also hosts mule deer and black bearss. The black bears of Yosemite are famous for breaking into parked cars to steal food.

Yosemite is surrounded by wilderness areas: the Ansel Adams Wilderness to the southeast, the Hoover Wilderness to the northeast, and the Emigrant Wilderness to the north.


An Act of Congress signed by Abraham Lincoln in 1864 set aside Yosemite Valley and ceded control of it to the State of California. It became a national park on September 25 1890.

Wawona was an Indian encampment in what is now the south western part of the park before white settlement. Settler Galen Clark discovered the Mariposa Grove of giant sequoia in Wawona in 1856 and in 1864 he became the first guardian of the grove after it was set aside as a state preserve. In 1879 the Wawona Hotel was built there to serve tourists visiting the nearby Grove.

The original national park did not include Yosemite Valley or the Mariposa Grove of giant sequoias. In May, 1903, Theodore Roosevelt, who was then President of the United States, went camping with John Muir near Glacier Point. On that trip, Muir convinced Roosevelt to take control of the Valley and the Grove away from California and give it to the federal government. In 1906, Roosevelt signed a bill that did precisely that. In 1916, the United States Park Service was formed, and Yosemite was placed under the jurisdiction of that agency.

In the late 1990s, there was a high profile murder case in the park and some serious rock slides; one rockslide from the face beneath Glacier Point ended near the Happy Isles of the Merced River. It created a debris field at least the size of a football field. Tourism dropped a little after those scary incidents.

Photographer Ansel Adams was famous for his pictures of Yosemite.


Main article: Geology of the Yosemite area

Most of the current landform of Yosemite National Park is composed of granitic rock which was formed during the mid to late Cretaceous. This plutonic rock was emplaced as molten plutons about 6 miles under the surface at that time as a result of heat generated from subduction off the coast of North America (forming massive plutons that later solidified). Over time most of the overlying rock (made mostly of sedimentary and volcanic rock) was transported or eroded away from the area. This exposed the granitic rock to surface pressures and it responded by exfoliation (responsible for the rounded shape of the many domes in the park) and mass wasting following the numerous fracture joint planes (cracks; especially vertical ones) in the now solidified plutons.

During much of the early Cenozoic, warm wet climates caused a great deal of chemical weathering of the granite and other rocks in the area of the park. The water especially took advantage of the numerous joint planes so that relatively joint-free features, such as El Capitan and much of Half Dome changed little relative to more highly jointed features (which are now mostly gone).

Beginning about 30 million years ago a series of glaciations further modified the area which accelerated exfoliation and mass wasting through ice-wedging, glacial plucking, scouring/abrasion and the release of pressure after the retreat of each glaciation. Severe glaciations formed very large glaciers that tended to strip and transport top soil and talus piles far down glacial valleys while less severe glaciations deposited a great deal of glacial till further up in the valleys.

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