Hetch Hetchy Railroad No. 6 was a standard-gauge three-truck Shay locomotive built in 1921 by Lima Locomotive Works for the City of San Francisco’s Hetch Hetchy Railroad, which supported construction of O'Shaughnessy Dam in Hetch Hetchy Valley as part of the city’s water-supply system. It was the largest of the railroad’s four Shay locomotives, the only three-truck Shay on the line, and more than twice as heavy as the others, fitting it for demanding mountain construction work. After the dam’s completion in 1923, it was sold to Pickering Lumber Corporation, served in logging until 1958, and is now preserved near El Portal.