Hetch Hetchy Valley/Definition

A glacial valley in Yosemite National Park in California flooded in the 1920s by O'Shaughnessy Dam on the Tuolumne River, forming the Hetch Hetchy Reservoir, part of the water supply for the city of San Francisco, California. Damming the Tuolumne and flooding the beautiful valley was a major environmental controversy at the time. Protest activities were spearheaded by John Muir and the Sierra Club.