Crystal Springs Reservoir consists of a pair of artifical lakes
in a rift valley over the San Andreas Fault. The upper (southern)
reservoir was created with an earthen dam of Laguna Creek
in 1877 and the lower (northern) reservoir was created
with a concrete Crystal Springs Dam of San Mateo Creek in 1888. The reservoir
is fed by local rainfall and water piped from the Hetch Hetchy
Reservoir in Yosimite National Park.