hree processes besides the earlier-mentioned glaciation have contributed to the physical shaping of the valley: weathering, stream erosion, and mass wasting. The different types of rocks themselves have also played a key role in how the valley has been formed.
For example, because El Capitan is made up of unjointed granitic rock, it is highly resistant to weathering and erosion, as it has almost no joints or fractures that would present vulnerabilities. Nearby, however, "intricately jointed granitic rocks . . . form castle-like landforms of striking appearance," eaten away by the forces of weather and water. The Yosemite region developed as a result of geologic events that affected all the Sierra Nevada--and all of the Western United States region in general (1:309).
During the Paleozoic era, an early series of prolonged sedimentation was followed by deformation, metamorphism, and erosion. The Jurassic and Triassic periods, at the beginning of the Mesozoic, saw the formation in
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