A Hike in Sunol Regional Wilderness: 22 November 2006

On the day before Thanksgiving, Gene and I cruised down to Sunol Regional Wilderness and did a little 4.3 mile hike on a small network of trails referred to as the "Little Yosemite" loop. Betsy, Gene's wife, the stalwart trooper that she is, stayed home to prepare and cook the bird. About 2 hours and 10 minutes on the trails, and about 1,031 feet of climbing.

Our hiking route was a mile or so north of the Calaveras Reservoir dam head.

In the 1870s, San Franciscans were questioning the adequacy of their water supply. Despite the increasing volumes of water being brought into the City by Spring Valley Water Company, there never was really enough, and memories were fresh of the numerous fires which had devastated the young City.

A special study committee recommended in 1875, that San Francisco buy a reservoir site, on a branch of Alameda Creek in Alameda and Santa Clara Counties, as the beginning of a future municipal water supply. The City was unable to act quickly and the Spring Valley Water Company effectively blocked this threat of competition by promptly purchasing the land and water rights for itself.

Construction of the earth-and rock-fill-type dam did not start for another 38 years, until 1913. A series of engineering errors culminated in a failure of the partially completed dam on March 24, 1918, when the upstream face of the dam sloughed off and the water gate tower collapsed. The engineering diagnosis was that the rock fill had been improperly compacted leaving voids in the bulk of the dam. San Francisco City Engineer Michael O’Shaughnessy, foreseeing Spring Valley’s acquisition by the City, turned his attention to the Calaveras construction. Unofficially, he kept “a watchful eye on this proposition so that the City will not inherit a `gold brick’ if it should take this property over.” As it turned out, Spring Valley Water Company heeded O’Shaughnessy’s advice. The Spring Valley Water Company was subsequently purchased by the City of San Francisco in 1930, and thus San Francisco acquired the Calaveras Reservoir.

The dam and reservoir provided a valuable addition to San Francisco’s water supply; it was completed in 1925. At 215 feet high, at that time it was the highest earth-fill dam in the world, with the capacity of impounding 31.56 billion gallons of water. The lower portion of the dam is built up by an hydraulic fill method, and the upper part was constructed with a rolled clay core supported on either side by loosely dumped material containing a large proportion of rock. In 1931, a tunnel was completed by the San Francisco Water Department from upper Alameda Creek to the Calaveras Reservoir, as planned by the Spring Valley Water Company. The upper Alameda tunnel increased available storage capacity in Calaveras Reservoir. The dam was strengthened by the San Francisco Water Department in 1975 to meet then current earthquake standards.

The dam is 1,200 feet long and 1,500 feet wide at the base. The outlet tunnel has two branches: one into the Hetch Hetchy Aqueduct through the Sunol Filtration Plant via the 44 inch Calaveras pipeline, and the other to an aerating basin with a capacity of 74 million gallons per day. Calaveras impounds water from a number of streams flowing down the gorges of the Coast Range in the general direction of Niles Canyon. Two of these streams, Smith and Isabel creeks, after circling Mount Hamilton, unite to form the Arroyo Hondo, which flows through Calaveras Valley. Calaveras has a watershed area of 101.28 square miles for Calaveras Creek and 38.2 square miles for Arroyo Hondo, or a total of 139.48 square miles. Mount Hamilton is the highest peak in the area, rising 4,448 feet above sea level.

Calaveras Reservoir's dam head can be seen in the center of the below photo

Scroll to see the complete panoramic photograph=============>

Canon SD-700is, 9 separate images stitched together

A topographic map with the route superimposed

Scroll to see a Google Earth satellite photo of the area with the route superimposed =============>

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