Essay On Yosemite

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The granite in the Sierra Nevada Range and the glacier-carved landscape of Yosemite National Park allows the geologic history of the area to be broken into two distinct parts. First, the deposition and deformation of metamorphic rocks and emplacement of granitic rocks during the Paleozoic and Mesozoic, and secondly, the uplift, erosion, and glaciation during the Cenozoic that produced the modern landscape (United States of America). Significant chapters in this geologic history include the assembly of California, the intrusion of the Sierra Nevada Batholith, building of the Sierra Nevada, and erosion by glaciers (United States of America). The glaciation has led to iconic landmarks that are known around the world, such as Yosemite Falls, Yosemite Valley, and Half Dome (United States).
It is well known that glaciation is the cause for how Yosemite looks today, but it is not as well known what happened before the relatively recent glaciation which happened about 15,000 years ago. The geologic history of Yosemite and the surrounding area starts 500 million years ago in the Paleozoic Era when the area was still under the waters of the Pacific Ocean (Beatty). This area had a passive fault, similar to the east coast of the United States today. The mud and silt from the ocean settled in the Yosemite area and eventually became shale, siltstone, and carbonate rocks (United States of America). By the end of the Ordovician Period, the fault changed from a passive to an active fault. The oceanic plate started to subduct under the continental crust and push the shale upward, forming the first mountains in the western United States. At first, these were volcanic islands off the coast. This formation is called the Shoo Fly Complex. T...

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...se two tectonic plates generated intense friction and pressure that generated enough heat to melt rocks. The descent of denser oceanic Farallon Plate into the asthenosphere produced magma that was made from basalt or andesite. Which is dark colored rocks with little silica. The buoyant magma pushed through the silica-rich continental crust, partially melting the crust that it moved though, and becoming more granitic in composition. About 100 million years ago, the granitic magma pooled at depths of only 2 to 5 miles beneath the surface (United States of America). The granitic terrain that makes up the Sierra, was once thought to have only local variations but was produced from one large mass of rock. It has been discovered however that hundreds of intrusions caused the variations in the granite that is displayed in Yosemite and in the Sierra Nevada range (Huber).

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