High Quality Content by WIKIPEDIA articles! The OShaughnessy Dam is a curved gravity dam on the Tuolumne River in the Hetch Hetchy Valley of Californias Sierra Nevada. The dam is located in Yosemite National Park, and creates the Hetch Hetchy Reservoir. It is named for former San Francisco chief engineer and the original chief engineer of the Hetch Hetchy Project Michael M. OShaughnessy.