One Hundred Hikes in Yosemite

Evolution of the Yosemite Landscape

Padre Pedro Font, on the second Anza expedition, in April 1776, saw a distant range to the east, as other Spaniards had, but he was the first to give it a name: Sierra Nevada, or Snowy Range. John Muir would see the range almost a century later, in April 1868, but did not write about it until 1894, in his first book, The Mountains of California. In it he questioned the range's name, saying:

... after ten years spent in the heart of it, rejoicing and wondering, bathing in its glorious floods of light, seeing the sunbursts of morning among the icy peaks, the noonday radiance on the trees and rocks and snow, the flush of the alpenglow, and a thousand dashing waterfalls with their marvelous abundance of irised spray, it still seems to me above all others the Range of Light, the most divinely beautiful of all the mountain-chains I have ever seen.

Although he doesn't explicitly say so, Muir could have added that the pastel colors of the High Sierra's granitic bedrock-generally light gray but almost creamy in places-made it more luminous than the dark, volcanic Cascade Range, the variegated, geologically complex Rocky Mountains, or the metamorphic, heavily vegetated Appalachian Mountains. But the high country of Yosemite and the rest of the High Sierra would not be very luminous if the overlying rocks intruded by molten "granite" had not been removed, if the volcanic rocks that blanket the northern Sierra had buried the entire range, and if glaciers had not developed on numerous occasions to remove the soil and create vast tracts of barren lands. If its complex geologic history had taken a different course, the Sierra Nevada might not have gotten its three national parks-Yosemite, Sequoia, and Kings. All three were set aside because of their groves of giant sequoias and because of their glaciated high country. Additionally, Yosemite National Park was set aside because of its renowned Yosemite Valley, arguably the world's most spectacular, which owes its origin not to special geologic processes, but rather to a unique pattern of major, generally vertical fracture planes in its granitic rock.

Today's masterpiece was long in the making, created over a few hundred million years. How was it produced? The modern answer is very different from that which we geoscientists (geologists, geographers, etc.) believed as recently as the early 1990s. Before then, most of us thought that the range was first raised to great heights during the Nevadan orogeny, which presumably lasted from about 160 to 155 million years ago. After that a several-mile thickness of various rocks was eroded by streams and rivers over tens of millions of years to greatly reduce the height of the range and to expose the formerly subsurface granitic rock. Then in the last 500,000 to 50,000,000 years-for lack of definitive evidence, geoscientists could not decide-the range was raised again to great heights. Finally, in concert with this postulated uplift, rivers steepened their gradients and so were able to erode very effectively downward, creating deep canyons, which in turn were made considerably deeper, more broad-floored, and steeper-sided through massive erosion by ensuing glaciers. In Yosemite Valley, a large, deep lake presumably formed after the last glacier retreated.

Nothing in this account is true, as I document in my book, The Geomorphic Evolution of the Yosemite Valley and Sierra Nevada Landscapes: Solving the Riddles in the Rocks (see "Recommended Reading and Source Materials"). This "Riddles" presents the history of geological research in the range as well as presents evidence of uplift and glaciation. It does not address the range's complicated history before about 80 million years ago. That has been largely revealed by the work of other geoscientists in the 1980s and '90s, working not only in the Sierra Nevada, but also around the world, where analogs of the early Sierra Nevada have been found.

Some of the range's relevant uplift and glacial evidence lies in Yosemite National Park, and where each is encountered along some of the hiking routes in this guidebook, I identify and describe it. For example, like the postulated-but-imaginary trans-Sierran river canyon at Deadman Pass, a few miles southeast of the Park, there is another equally imaginary river canyon near Rancheria Mountain, and I discuss it in Hike 14.


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