The great 1906 San Francisco earthquake destroyed key portions of the City of San Francisco's water system. The three days of unquenchable fires that followed the quake claimed more than four square miles of land, thousands of buildings and an untold number of lives. The devastation spurred City leaders to pursue a more reliable source of water for the future.
After intense national debate about building a reservoir and dam in a national park, Congress passed the Raker Act in 1913, granting San Francisco the rights-of-way and the use of public lands to build the Hetch Hetchy Water and Power Project. John Muir, who wanted the valley to remain untouched for wilderness preservation, had led the opposition.
This complex system of tunnels, pipelines and facilities took 20 years to build and transports snowmelt 167 miles entirely by gravity, without the use of pumps. Today this water serves more than 2.4 million people in four counties in the San Francisco Bay Area, as well as the residents of Groveland.
(caption) Phase I of construction of O'Shaughnessy Dam was completed in 1923 and phase 2 ended in 1938 when the dam was raised another 85.5 feet to 312 feet in height. Present capacity for the reservoir is 117 billion gallons of water or the equivalent of 177,914 Olympic-slzed pools The dam crest is 910 feet long and 289 feet wide at the base.
(caption) Steel anchor bars were constructed between old and new concrete at O'Shaughnessy Dam when its height was raised in 1937.
(caption) After serving for twenty years as Chief Engineer,Michael Maurice O'Shaughnessy died just twelve days before the public dedication of the completion of the project at Pulgas Water Temple in 1934.