How Was Yosemite Valley Formed?


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Patricia Devereux Profile
More than 200 million years ago, the area of what is now the Sierra Nevada mountain range of California lay under a shallow arm of the Pacific Ocean.
Sediments from neighbouring land masses accumulated to thousands of feet deep on the ocean floor, and about 400 million years ago, these layers were uplifted and folded into mountain ranges of slate, shale and sandstone.
About 130 million years ago, new strata were folded, crumpled, then invaded by molten granite welling up from below. A secondary range was formed in eastern California.
After many more million years, the granite ridges dominated the landscape, and the range shifted so that its eastern margin was at its present highest point of 14,500 feet Mount Whitney's summit). The Owens-Mono valleys to the east of what
is now Yosemite Valley downfaulted, and one of the world's most outstanding examples of a block fault emerged.
About 1-2 million years ago, the Sierra region turned wintry, with its higher regions blanketed with snow and ice. This became compacted into slowly moving glaciers. An 1,000-foot-deep glacier began to descend the canyon of the Merced River, grinding down the granite to the valley's current level of 4,000 feet.
The valley's profile changed from a broad, you-shaped river course to the deep, V-shaped valley with sheer walls and vertical waterfalls that so enthrals tourists today.

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