Calaveras Reservoir - Santa Clara & Alameda Counties, California

Jeff and I and our two chocolate Labradors, Summer and Skye camped at Coyote Lake in the hills east of Gilroy for the weekend.  While on our camping adventure we set out to several lakes and reservoirs over the weekend.  On Sunday morning we visited Calaveras Reservoir located in the hills 5 miles east of San Jose.  This 1,503 acre reservoir is located at an elevation of 781 feet above sea level.  Calaveras Reservoir is located primarily in Santa Clara County, California, with a small portion and its dam in Alameda County, California. In Spanish, Calaveras means "skulls".

The reservoir is fed mainly by Arroyo Hondo and Calaveras Creek. Lying in the Calaveras Valley, the region is geologically active with the Calaveras Fault parallel to and to the west of the dam site. The seismic hazard forced replacement of the original dam. The replacement dam began construction in 2011, with completion expected in 2019.

The Calaveras Valley has diverse wildlife including 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. Since at least 2008, a pair of bald eagles has nested regularly.

The dam site has an active earthquake fault nearby, and the original 1925 dam was seismically vulnerable.  If the dam had collapsed when full, it would have flooded part of Fremont, California with a wall of water 30 feet high.  Dam regulators for the state of California restricted the capacity of the original dam in 2001, to mitigate the seismic threat.  To restore lost capacity, the San Francisco Public Utilities Commission is constructing a replacement dam located 1,000 feet downstream from the original 1925 dam.

The design of the replacement dam allows for future capacity expansion, and the core is wider than needed initially.  The design allows the height to be raised by 150 feet, to quadruple the initial capacity of 100,000 acre feet of storage capacity.

In the 19th century, 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.

The first dam on the site, built in 1913 by the Spring Valley Water Company, rapidly changed the sensitive hydrology and natural environment of the Calaveras Valley. That dam suffered a collapse of the upstream slope in 1918 due to design and material flaws. Its replacement, the current Calaveras Dam, was the largest earth-fill dam in the world when it was completed in 1925. It is 245 feet high, with a length of 1200 feet at its crest. The city and county of San Francisco owns and operates the dam and reservoir for municipal water supply.

In the late 1980s and early 1990s, a drought affected California, and water levels in reservoirs throughout the state became extraordinarily low. By January 1991, the water at the reservoir was down 100 feet, and the aluminum body of an airplane became visible. Two skeletons were found at the site on January 5, 1991. Dental records and the plane's serial number were used to positively identify the remains as Clifford Gillman and his single-engine Ercoupe, along with Gillman's friend Robert Louviere. They had been missing since June 16, 1963. The wreck, minus the two men's remains, is still lying in the center of the reservoir.