USCGS Bm reads - P386 / 1936 - New BM (HT0497) is reset of this one, as barrier rail added decades after bridge built made it impossible to put a survey rod on BM.
This bridge is built atop the Crystal Springs Dam, which when completed in 1890 was (and still is!) the largest concrete-block dam in the world. Originally 120 ft high, in 1911, it was raised to 149 ft. The lake in front of you is but one in a string of four in the San Andreas Valley, containing a collective total of 29 billion gallons. The dam rode out the '06 quake, but if it ever failed, it would flood San Mateo from Coyote Point to Foster City.