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Calaveras Reservoir in Spring

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Calaveras Reservoir is a lake located primarily in Santa Clara County, California with a small portion and its dam in Alameda County, California. The reservoir has a capacity of 100,000 acre·ft (120,000 dam³). In Spanish, Calaveras means "skull".


Calaveras Dam, which creates the reservoir, used to be the largest earth-fill dam in the world. It is 210 feet (64 m) and was completed in 1925. The city and county of San Francisco owns the dam and reservoir.


Poverty Ridge and Oak Ridge lie to the east of Calaveras Reservoir, Milpitas and Monument Peak lie to the west, Sunol lies to the far north, and Calaveras Creek and Los Buellis Hills lie to the south.


Calaveras Reservoir is fed mainly by Arroyo Hondo and Calaveras Creek. Lying in the Calaveras Valley, the region is a geologically active area with the Calaveras Fault parallel to, and to the west of, the Dam site. Roads adjacent to the reservoir include Calaveras Road and Marsh Road, the latter which gained significant public attention due to a murder which occurred there in the early 1980s.


The Calaveras Valley is rich and diverse in wildlife. Some of the most common animals include deer, coyotes, squirrels, turkey vultures, red-winged blackbirds, yellow-billed magpies, red-tailed hawks, brewer's blackbirds, purple martins, barn swallows, bullock's orioles, and warblers. These have recently been joined by a nesting pair of bald eagles.


In the 1800s, the Calaveras Valley which the reservoir now fills was primarily an agricultural region known for its production of hay, strawberries, and tomatoes. Because of San Francisco's increasing demand for drinking water at the turn of the 20th century, the farmers in the region were forced to sell their land to the Spring Valley Water Company, which in turn sold it to the San Francisco Water Company. Although the first dam that was constructed collapsed due to engineering flaws, another dam was soon built. The flooding of the Calaveras Valley rapidly changed its sensitive hydrology and natural environment.


Today, the San Francisco Public Utilities Commission owns 36,000 acres (150 km²) in the Alameda Creek Watershed. Some lands in the watershed are leased to livestock companies for cattle ranching to control vegetation and prevent fires. Most of the land is closed to the public because of concerns over drinking water safety and quality.


Because the dam is located near a seismically active fault zone and was determined to be seismically vulnerable, the California Department of Water Resources, Division of Safety of Dams (DSOD) has limited since 2001 the amount of water that can be stored in the reservoir to approximately 40 percent of its former full storage capacity (full storage capacity is 96,850 acre-feet (119,500,000 m³) of water) until the safety deficiencies are corrected.


For more information, see


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© All rights reserved. John Krzesinski, 2010.

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Taken on April 13, 2010