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Hetch Hetchy Water and Power System

Hetch Hetchy 2005 - Photo courtesy of Thad Waterbury


John Muir referred to the Hetch Hetchy Valley when first seeing it in 1871 as “Tuolumne Yosemite,” a wonderful counterpart of Yosemite Valley, with its walls of gray granite rising above flowering meadows and graceful waterfalls.  The Hetch Hetchy project was a major contributor to the history of Tuolumne County affecting its natural environment and economic development.  The project construction spanned twenty-five years from 1913 to 1938.  The Hetch Hetchy project was created to find and deliver drinking water to San Francisco and the Bay Area.  In 1965, water was also provided to Tuolumne’s south county Groveland Community Services District via the Hetch Hetchy aqueduct. 

            Starting with the damming of the main Tuolumne River at 3,800 feet elevation, it created a reservoir in the Hetch Hetchy Valley to deliver water to the Bay Area using a unique gravity fed transmission system of complex tunnels above and through the ground and solid rock mountainsides in the Sierra Nevada.  The magnitude of the over one-hundred-million-dollar project brought money, jobs, and challenges to the Groveland area and to the Sierra Railway located in Jamestown.

  History and Background

            American Indians have lived in Hetch Hetchy Valley for more than 6,000 years, gathering seeds and plants, hunting and trading.  In the 1850s, the first Euro-Americans came in search of gold and a place to graze livestock.  The valley name probably derived from the Miwok (Me-Wuk) word hatchhatchie, which means “edible grasses.”  

            The Hetch Hetchy project had its beginning in early 1900s when the City and County of San Francisco gained generous rights to the Tuolumne River watershed in 1910.  The project centered on damming the main Tuolumne River as it meandered through Hetch Hetchy, a wide glacial-cut valley almost as grand as Yosemite.  The river, with its source in a perpetual glacier on 13,000-foot-high Mount Lyell, drains 650 square miles of watershed in rugged granite mountains sloping west from the Sierra Nevada crest.  The Hetch Hetchy water system design had an ultimate goal of providing 400 million gallons of water per day to San Francisco and the growing Bay Region. 

            The struggle over property rights, water rights, environmental and tourism issues, and the preservation of the beauty of the Hetch Hetchy Valley went on for twelve years.  John Muir fought for environmental protection and led the Sierra Club in a campaign to protect the Hetch Hetchy Valley, a part of Yosemite National Park, from being filled with a reservoir.  This battle was one of the first grassroots lobbying efforts, getting citizens to contact elected officials.  Despite opposition, the Raker Act of 1913 was passed by the U. S. Congress and signed by President Woodrow. 

            In February 1916, the Hetch Hetchy rail line began as a connection of the Sierra Railway at Hetch Hetchy Junction, fifteen miles west of Jamestown and extended another sixty-eight miles to the O’Shaughnessy Dam site for delivery of materials.  The Sierra Railway also delivered dry cement to the dam site for several years.  The project headquarters and the Hetch Hetchy rail line Maintenance Facility were located in Groveland from 1915-1925.

            The vast undertaking created miles of tunnels, peripheral dams and reservoirs, hydroelectric power houses, and a 150-mile aqueduct to deliver the water and electricity to the Bay Area.  Of the many dams, reservoirs, and power plants, three were in the high country of Tuolumne County.  The main and largest, O’Shaughnessy Dam (named after the Project Manager Michael O’Shaughnessy) and Hetch Hetchy Reservoir are located in the Hetch Hetchy Valley.

            The main dam was built in two phases, initially built to a height of 226 feet in 1923; later it was raised to 312 feet in 1938.  The later raising of the dam was supported by the Sierra Railroad under contract to refurbish track, operate and deliver materials on the original Hetch Hetchy rail line.   Later phases of the Hetch Hetchy system in the 1960s increased storage to serve expanded water supply and electric power requirements.  

            Large pipes called penstocks channeled water down the mountain to the main Moccasin Power Plant completed in 1925.  Completing the final leg into the Bay Area, the Hetch Hetchy Dumbarton Pipe Line Bridge was constructed solely to suspend the penstocks used to travel over the San Francisco Bay to the final water distribution system.  It was 1934, when the first Hetch Hetchy water was delivered to the Bay Area.

            A trade magazine praised the project as “one of the world’s most important engineering projects” at the time.  In addition to meeting its water delivery capacity goals, the Hetch Hetchy provides three hydroelectric power systems sending power via high voltage lines to Turlock and Modesto Irrigation Districts, Pacific Gas & Electric Company, and the City of San Francisco.  The Hetch Hetchy Power System produces two billion kilowatt hours of electricity a year.

  Current Features

            You can visit the town of Moccasin, which is a small “company town,” where the penstocks come down the mountain to the hydroelectric power plant.  There is also a fishery in the town.  Activities at or around the Hetch Hetchy Reservoir include fishing, back packing, hiking, camping, photography, and picnicking.  Trailheads start at the Hetch Hetchy Entrance Station and at the dam with roundtrip distances from three or up to thirteen and a half miles.  Facilities include a backpacker campground and vault toilets.  Pets are prohibited on all trails and on the dam.  Swimming and boating are prohibited on Hetch Hetchy Reservoir.

 How to Get There—GPS Coordinates: N37° 48.62' W120° 17.99'

            Take either Highway 49 or Highway 120 to Chinese Camp.  Continue past Don Pedro Reservoir to Moccasin just over nine miles from Chinese Camp.  To reach O’Shaughnessy Dam, continue on Highway 120 to one mile west of Yosemite’s Big Oak Flat entrance station, turn north on the Hetch Hetchy turnoff, which is Evergreen Road.  Evergreen Road becomes Hetch Hetchy Road after seven and one-half miles.  The Hetch Hetchy entrance station is about two miles beyond the junction of Evergreen and Hetch Hetchy Roads.  Drive another six and one-half miles beyond the entrance station on Hetch Hetchy Road to the parking lot above the dam.  The road is open until the first snow storm and reopens after the snowmelt.


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