Hetch Hetchy Valley, in Yosemite National Park, central Calif., on the Tuolumne River. It once rivaled Yosemite Valley in beauty and grandeur. O'Shaughnessy Dam (completed 1923; enl. 1938) turned the valley into a lake c.9 mi (14 km) long, which is used for generating power and for supplying water to San Francisco by an aqueduct 156 mi (251 km) long.
The Columbia Electronic Encyclopedia, 6th ed. Copyright © 2012, Columbia University Press. All rights reserved.