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Sierra Nevada
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Geography
The Sierra Nevada stretches 400 miles (650km), from Fredonyer Pass in the North to Tehachapi Pass in the South. The Sierra are bounded on the West by California's Central Valley, and on the East by the Great Basin.
In East-West cross section, the Sierra is shaped like a non-equilateral triangle: the altitude gradually increases as you travel East, until you reach the crest, whereupon the altitude rapidly decreases. Thus, the Sierra crest runs along the eastern edge of the Sierra. Rivers flowing West from the Sierra crest drain into the Pacific Ocean, while rivers draining east flow into the Great Basin and do not reach any ocean.
There are several notable geographical features in the Sierra Nevada:
Lake Tahoe is a large, clear freshwater lake in the northern Sierra Nevada, with an elevation of 6225 feet (1,897m) and 191 square miles (489 sq km) of area. Lake Tahoe lies between the main Sierra and the Carson Range, a spur of the Sierra.
Hetch Hetchy Valley, Yosemite Valley, and Kings Canyon are beautiful, glacially-scoured canyons on the west side of the Sierra.
Yosemite National Park is filled with stunning granite features, such as domes.
Mount Whitney, at 14,505 feet (4,421m), is the highest point in the continental United States
Groves of Giant Sequoias occur along a narrow band of altitude on the western side of the Sierra Nevada. Giant Sequoia are the most massive trees in the world.
The height of the mountains in the Sierra Nevada gradually increases from North to South. Thus, the crest near Lake Tahoe is roughly 9000' (2,700m) high, the crest near Yosemite National Park is roughly 13000' (4,000m) high, and the entire range attains its peak at Mount Whitney. South of Mount Whitney, the range quickly dwindles.
Geology
The geological history of the Sierra Nevada begins in the Jurassic Era, approximately 150 million years ago. At that time, an island arc collided with the West coast of North America and raised a set of mountains, in an event called the Nevadan orogeny. This event produced metamorphic rock. At roughly the same time, a subduction zone started to form at the edge of the continent. This means that an oceanic plate started to dive beneath the North American plate. Magma from the melting oceanic plate rose and created plutons of solid granite, deep below the surface. These plutons formed at various times, from 115 million to 87 million years ago. By 65 million years ago, the proto-Sierra Nevada were worn down to a range of rolling low mountains, a few thousand feet high.
Starting about 25 million years ago, the Sierra Nevada started to rise and tilt to the West. Rivers started cutting deep canyons on both sides of the range. The Earth's climate cooled, and ice ages started about 2.5 million years ago. Glaciers carved out characteristic U-shaped canyons throughout the Sierra. The combination of river and glacier erosion exposed the granitic plutons previously buried, leaving only a remnant of metamorphic rock on top of some of the Sierra peaks.
Uplift of the Sierra continues today, especially along its eastern side. This uplift causes very large earthquakes, such as the Lone Pine earthquake of 1872
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