 In 1903 , a dam in the northern portion of the park was proposed . Located in the Hetch Hetchy Valley , its purpose was to provide water and hydroelectric power to San Francisco . Muir and the Sierra Club opposed the project , while others , including Gifford Pinchot , supported it . In 1913 , the U.S. Congress authorized the O 'Shaughnessy Dam through passage of the Raker Act . 
