O’Shaughnessy Dam was built for the City and County of San Francisco from 1915 to 1922 under Mayor James Rolph Jr., with M.M. O’Shaughnessy as engineer and Utah Construction Co. as contractor. Its original work included a foundation elevation of 3388, bottom valves at elevation 3508, an initial crest elevation of 3726, a crest length of 600, storage capacity of 66,000,000,000 gallons, drainage area of 294,000 acres, reservoir area of 1590 acres, and concrete volume of 390,000 cubic yards. The structure was completed in 1938 with its height increased 68 feet through Federal Emergency Administration of Public Works Project No. 1429 during the mayoralty of Angelo J. Rossi, under the Public Utilities Commission and with M.M. O’Shaughnessy credited for design, L.T. McAfee for construction engineering, and Transbay Construction Co. as contractor. After that work, the dam stood 312 feet above the stream bed and 426 feet above the foundation, with a crest elevation of 3,812 feet, crest length of 900 feet, storage capacity of 117,300,000,000 gallons, watershed area of 459 square miles, reservoir area of 1,972 acres, and concrete volume of 675,000 cubic yards. From 1962 to 1964, the Canyon Power Tunnel connected O’Shaughnessy Dam to the early intake over a length of 10.1 miles; it measured 14'-0" by 14'-6" in horseshoe dimensions and had a capacity of 850 cubic feet per second. On July 11, 1998, the 75th anniversary of the completion of O’Shaughnessy Dam was recognized along with the contributions of Hetch Hetchy Water and Power personnel by Tuolumne County, the U.S. Forest Service, the National Park Service, and the City and County of San Francisco.