The O'Shaughnessy Dam is a concrete arch dam located in the Sierra Nevada mountains of California. It was completed in 1923 and is primarily used for water storage and hydroelectric power generation. The dam creates the Hetch Hetchy Reservoir, which supplies drinking water to the city of San Francisco and surrounding areas. The dam is named after Michael O'Shaughnessy, the chief engineer of the project. Standing at 430 feet tall, it plays a crucial role in managing water resources in the region. The surrounding area is also known for its scenic beauty, attracting visitors to Yosemite National Park.