The photo above is from 1960 and is a north facing aerial view of Crystal Springs Reservoir. Crystal Springs Reservoir is a pair of artificial lakes located in the rift valley created by the San Andreas Fault to the west of the cities of San Mateo and Hillsborough. The lakes are part of the San Mateo Creek watershed.
The original name of the southern or Upper Crystal Springs Reservoir was Laguna Grande. The Portolà expedition of 1769 camped on November 5 at a ‘laguna grande’ which is covered by the Upper Crystal Springs Lake today. The Laguna Grande place name is also shown on the 1840s diseño del Rancho Cañada de Raymundo and on an 1856 plat of Rancho de las Pulgas. Lower Crystal Springs Reservoir now covers the town of Crystal Springs which grew up around a little resort town of the same name, located just northwest of the present dam. (The Crystal Springs Hotel was demolished on Feb. 6, 1875, and the area was depopulated. By 1887, the lower Crystal Springs dam was on the rise, and its namesake village vanished beneath the water forever.)
The two Crystal Springs lakes and San Andreas Lake used to be known as Spring Valley Lakes for the Spring Valley Water Company which owned them. The original spring for which Spring Valley Water Works (later named Spring Valley Water Company) was located between Mason and Taylor Streets, and Washington and Broadway Streets in San Francisco. When the company went south for more water, the Spring Valley name was carried south too.
The southern lake, Upper Crystal Springs Reservoir, was formed when a tributary, Laguna Creek (or Lake Creek), which joined Laguna Grande at the south end, was submerged by construction of an earthen dam (this was the first Crystal Springs Dam) in 1877. The old earthen dam became a causeway between Upper and Lower Crystal Springs Reservoirs when the latter was formed by Herman Schussler’s 150 foot tall concrete Crystal Springs Dam, which dammed up San Mateo Creek to form the lower (northern) reservoir in 1888. The causeway is now crossed by Highway 92.