Читать книгу 50 Best Short Hikes: Yosemite National Park and Vicinity онлайн

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The complex landscape of peaks, meadows, lakes, streams, and cliffs is the backdrop, the milieu that allows Yosemite’s great biological diversity to exist. The geography owes its existence to the many different geologic processes that occurred over the last 100 million years. Here I introduce just three landmark geologic events and intertwined processes. The first is the creation of a vast block of granite, termed the Sierra Nevada batholith, between 105 and 85 million years ago. It formed deep underground as the Pacific and North American tectonic plates collided, forcing the west-lying Pacific Plate deep into the earth. The plate melted, and some of the resultant magma erupted to form massive volcanoes, while the rest solidified underground to form the Sierra Nevada batholith. Today the volcanic rock has eroded and disappeared, while the granite is at the surface. The batholith is composed of many different variants of granite, each comprising its own distinctive combination of minerals and termed a pluton. Extensive planes of weakness exist within the rock, dating from its formation, and once the rock emerges on the Earth’s surface, these weaknesses reveal themselves in several ways. First is exfoliation, whereby curved slabs of rock detach from the surface like the layers of an onion. Sentinel Dome and roadcuts along Tioga Road between Yosemite Creek and May Lake are excellent places to see this. Second are vast fractures that extend across the landscape, likely responsible for the general orientation of Yosemite Valley and many of its vertical walls, including the face of Half Dome.