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Hetch Hetchy Valley is a glacial valley in Yosemite National Park in California. It is currently completely flooded by O'Shaughnessy Dam, forming the Hetch Hetchy Reservoir. The Tuolumne River fills the reservoir.
The Hetch Hetchy Road drops into the valley at the O'Shaughnessy Dam, but all points east of there are roadless, and accessible only to hikers and equestrians.
The name 'Hetch Hetchy' is named for a grass with edible seeds that grows in the valley, in the Native American Central Miwok language [1]. It was first used in the English language by Joseph Screech, who in 1850 became the first European to enter the valley. Screech noted that Paiutes[2] had inhabited Hetch Hetchy and still gathered seeds, roots and acorns in and around it. Acorns are indeed available in the valley, but rare elsewhere in the high country.
Charles Hoffman of the California Geological Survey conducted the first survey of the valley, in 1867 [3].
In 1906, after a major earthquake, San Francisco applied to the United States Department of the Interior to gain water rights to Hetch Hetchy. This provoked a 7-year environmental struggle with the Sierra Club, led by the environmentalist John Muir. Muir observed:
Proponents of the dam replied that the valley would be even more beautiful with a lake. Muir predicted (correctly) that this lake would deposit an unsightly ring around its perimeter, which would be visible at low water. Since the valley belonged to the federal government, an act of Congress was needed to start the project. The federal government ended the dispute in 1913, with the passage of the Raker Act, which permitted flooding of the valley. It is said that the passage of the bill broke John Muir's heart: he died the following year. Construction of the dam was finished in 1923.
The city of San Francisco, in violation of the Congressional Act, sold the power to PG&E, which in turn sold it back to the general public at a profit. Harold L. Ickes of the Roosevelt Interior Department tried for many years to enforce the Raker Act, but he was unsuccessful. Control of Hetch-Hetchy-generated power remains in the hands of the PG&E corporation.
Water from the dam serves 2.4 million Californians in San Francisco, San Mateo, and Alameda Counties, as well as some communities in the San Joaquin Valley, and generates electricity for San Francisco. Some have advocated restoring the valley for the enjoyment of visitors to Yosemite National Park, where Hetch Hetchy is located. Others have opposed the plan because it would remove a storage place for Bay Area municipal water and a source of hydropower. In 2004, the State of California,through the Department of Water Resources, began examining alternatives to the O'Shaugnessy Dam. For more information on the history of the dam and reservoir, see the O'Shaughnessy Dam article.
Like Yosemite Valley, Hetch Hetchy was also sculpted by glaciers as recent as 10,000 years ago. The more recent glacier there was larger than the one in the paleo-Yosemite Valley. However, today the Hetch Hetchy area is drier.
On the upper portion of the valley beyond the reservoir there is evidence of relatively young lava flows. One recent flow formed the Little Devils Postpile which, as the name suggests, is a smaller version of the Devils Postpile near Mammoth Lakes to the southeast. Both formations are great examples of columnar basalt, a phenomenon that results from contraction of basaltic lava as it cools (forming hexagonal columns). Similar formations are found in the Giant's Causeway in Ireland, and the New Jersey Palisades in the United States, as well as other places throughout the world.