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This photograph, taken in the early 1900s before the O'Shaughnessy Dam was constructed, shows the Hetch Hetchy Valley and the Tuolumne River, looking east. Wapama Falls is on the left, Kolana Rock on the right.

A modern photo, taken from much the same vantage point, shows the submergence of the valley floor under the waters of the reservoir.

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. Upstream from the valley lies the Grand Canyon of the Tuolumne. The reservoir supplies the Hetch Hetchy Aqueduct.

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.

Captain Jim, a leader of the Yosemite-Mono Lake Paiutes. Capt. Jim and his family roamed the Upper Tuolumne River and Hetch Hetchy Valley before it was dammed up. His Paiute name was Na’a (Father).

The name "Hetch Hetchy" comes from a grass with edible seeds that grows in the valley, in the Native American Sierra 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^[1] 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 F. Hoffmann of the California Geological Survey conducted the first survey of the valley, in 1867 ^[2].

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 seven-year environmental struggle with the Sierra Club, led by the environmentalist John Muir. Muir observed:

Dam Hetch Hetchy! As well dam for water-tanks the people's cathedrals and churches, for no holier temple has ever been consecrated by the heart of man. ^[3]

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. Because the valley was within Yosemite National Park, 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. However, environmental groups (including the Sierra Club) now advocate removing the dam.

Construction of the dam was finished in 1923. 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.

For more information on the controversial history of the dam and reservoir, see the O'Shaughnessy Dam article.

Like Yosemite Valley, Hetch Hetchy was also sculpted by glaciers as recently as 10,000 years ago. The more recent glacier there was larger than the one in the paleo-Yosemite Valley. 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.

Tueeulala Falls on the north side of the valley.

• Tuolumne River
• Grand Canyon of the Tuolumne
• O'Shaughnessy Dam
• San Francisco Water Department
• Yosemite National Park
• Timeline of environmental events
• Hetch Hetchy Railroad

• Simpson, John W. (2005). Dam!: Water, Power, Politics, and Preservation in Hetch Hetchy and Yosemite National Park. ISBN 0-375-42231-5. 
• Righter, Robert W. (2005). The Battle over Hetch Hetchy: America's Most Controversial Dam and the Birth of Modern Environmentalism. ISBN 0-195-31309-7. 

• John Muir on Hetch Hetchy Dam
• Restore Hetch Hetchy web site
• Sierra Club on Hetch Hetchy
• Discover Hetch Hetchy - Environmental Defense
• San Francisco Public Utilities Commission, Department of Hetch Hetchy Water and Power
• U.S. Geological Survey Hetch Hetchy images - About 30 are available, from both before and after the construction of the dam.
• Hetch Hetchy Early Native American People's History
• California Resources Agency Hetch Hetchy Restoration Study

Coordinates: 37°56′51″N, 119°47′13″W