Читать книгу Hike the Parks Sequoia-Kings Canyon National Parks - Scott Turner - Страница 13

Around one hundred to two hundred million years ago, the Pacific Plate began to slide underneath the North American Plate in a process known as subduction. As the subducted Pacific Plate sank and melted into the earth’s mantle, a large pool of magma rose toward the surface and formed a large granitic mass, known as a batholith, about 10 miles (16.2 km) below the surface. Millions of years later, tectonic forces lifted the batholith toward the earth’s surface. As the batholith rose, overlying metamorphic rock composed of ancient ocean sediments eroded. New watercourses carried the overlying rock westward, filling the Central Valley and exposing the underlying granite.

Within the last three million years, the Sierra Nevada batholith began to tilt, with the western edge of the range sinking and the eastern side of the range rising. The disproportionate tilt in the Sierra Nevada is evident when one views the range from both the Central Valley and the Owens Valley. From the Central Valley, one observes gently swelling foothills that rise to the conifer belt before culminating at the Great Western Divide. From the Owens Valley, one observes a severe, precipitous wall of granite known as an escarpment that steeply descends more than 8000 feet (2450 m) from the Sierra Crest down to the Owens Valley floor.