The Hetch Hetchy Railroad (HHRR) was a 68-mile (109 km) standard gauge Class III railroad constructed by the City of San Francisco to support the construction and expansion of the O'Shaughnessy Dam across Hetch Hetchy Valley. Based in Groveland, the HHRR operated from 1917 to 1949. It primarily carried construction crews and materials, but also took excursion passengers, freight, and mail. The line extended from its western terminus at Hetch Hetchy Junction (a junction with the Sierra Railroad at Sierra milepost 26, 1,000 feet (300 m) elevation at 37°48′07″N 120°29′17″W / 37.802°N 120.488°W), topping out at Poopenaut Pass at 5,064 feet (1,544 m) elevation (37°54′04″N 119°50′17″W / 37.9012°N 119.8381°W), to its eastern terminus at about 3,800 feet (1,200 m) elevation on the rim of the Hetch Hetchy Valley (est. 37°56′49″N 119°46′59″W / 37.947°N 119.783°W) above the construction site. The mountainous terrain resulted in steep grades (over 4%) and extremely sharp curves (30 degrees, a 190-foot (58 m) radius), requiring trains to move slowly, at speeds of less than 8 miles per hour (13 km/h).
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