 The old earthen dam became a causeway between Upper and Lower Crystal Springs Reservoirs when the latter was formed by Herman Schussler's concrete Crystal Springs Dam, which dammed up San Mateo Creek in 1888 to form the lower reservoir.The causeway is now crossed by Highway 92.In addition to San Mateo Creek and its San Andreas Creek and Laguna Creek tributaries, the waters of Crystal Springs Reservoir consist of runoff from the eastern slopes of the Montara block of the Santa Cruz Mountains and imported Hetch Hetchy Aqueduct water deriving from the Sierra Nevada.