How Yosemite Park Was Formed
A History of Controversy
Yosemite National Park is one of the most revered of the nation's national parks. Spanning 1,200 square miles, the park includes waterfalls, deep valleys, giant sequoia trees, spacious meadows, ancient rock formations, two rivers and expansive biological diversity. How Yosemite was formed is a subject of intense study and scientific dispute.
The earliest theory of how Yosemite came to be was postulated by Josiah Whitney, director of California's State Geological Survey in 1860. He believed a cataclysmic event cause the floor of the area to drop, forming the vast canyons, waterfalls and rock formations. John Muir, however, believed that Yosemite had been formed through the actions of glaciers. In fact, he had found remnants of a glacier and glacial action during his expeditions deep into the high Sierras. In geologist's Francois Matthes' book published in 1930, "Geologic History of the Yosemite Valley," Matthes confirmed Muir's theory but altered details. In 1989, Dr. King Huber of the U.S. Geologic Survey offered the definitive view of Yosemite's formation in his book, "The Geologic Story of Yosemite National Park."
How Yosemite Came To Be
Yosemite once laid beneath a shallow arm of the Pacific Ocean. Sediment began to form and continued until it piled up thousands of feet deep. About 400 million years ago, these layers of sediment were lifted and folded into layers of slate, shale and sandstone. New strata formed, but were invaded by molten rock from deep within the Earth. Soon, ridges of granite formed and shifted into various configurations. About 1 million to 2 million years ago, the Sierra region grew much colder, and snow and ice covered the higher elevations. These compacted into glaciers. According to the National Park Service's education website on Yosemite's ancient glaciers, these glacial sheets flowed; they ground through the granite down to its current 4,000-foot valley level, creating the sheer cliffs, the waterfalls and the deep valleys that make Yosemite famous. There are still glaciers within Yosemite, but they were never part of the great glaciers that created the formations and valleys of the early days of Yosemite. These smaller glaciers were formed by a more recent glacial event.
Yosemite Today
The Sierra Nevada range is characterized by its long, gentle western slope and a short, steep eastern slope. According to the National Park Service's site on Yosemite's geology, these are evidence of the powerful forces that pushed up and tilted the Earth's crust and of the forceful heat and intensity of the molten granite that created the rock formations we see today. The granite of Yosemite is composed of small pieces of many kinds of granite rock that were compressed into each other over 100 million years. This is why there are so many varieties of granite found in the park today.
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