Hetch Hetchy is a valley that lies in the northwestern part of Yosemite National Park and is drained by the Tuolumne River . Starting in about 1901 , San Francisco started looking for a new supply of municipal water . Following the disastrous 1906 San Francisco earthquake and fire , this search intensified , and they finally chose the Tuolumne River as the " best " available water resource . The City and County of San Francisco bought most of the water rights to the Tuolumne River watershed in 1910 . The Hetch Hetchy project centered on damming the main Tuolumne River as it meandered through Hetch Hetchy 's wide glacial-cut valley . The river , with its source in a perpetual glacier on Mount Lyell , drains of watershed of the rugged granite mountains sloping west from the Sierra Nevada crest . The Hetch Hetchy water system 's goal was providing up to of water per day to San Francisco and the growing Bay Region and tap the hydroelectric power that would be generated by a dam and power stations . After a vigorous debate , the United States Congress passed the Raker Act in 1913 which authorized the building of dam ( s ) , hydroelectricity plant and municipal water supply system inside part of Yosemite National Park . The act was signed by President Woodrow Wilson in February 1916
1906 San Francisco earthquake
1906 San Francisco earthquake
History of California 1900–present