The Pilarcitos Creek watershed drains . The creek begins at on the south slope of Whiting Ridge east of the North Peak of
Montara Mountain, flows east-southeast, to
Pilarcitos Reservoir where it is joined by Spring Valley Creek. Pilarcitos Dam was built in 1864 and two miles downstream Stone Dam was built in 1871. Further downstream, Pilarcitos Creek is joined by Albert Gulch in Albert Canyon at
Highway 92. Albert Gulch is named for the ranch of the William C. Albrecht family, who lived here from the 1870s until 1954. Here Pilarcitos Creek turns to flow southwest for to the community of
Half Moon Bay. Along the way, it is joined on the right (heading downstream) by
Nuff Creek,
Corinda Los Trancos Creek, and
Apanolio Creek, then from the left by
Madonna Creek and
Arroyo León before heading and west-northwest for to enter Half Moon Bay and the Pacific Ocean at Elmar Beach. As early as 1860 a major diversion of Pilarcitos Creek was constructed to
supply water to the burgeoning population of
San Francisco. Two different tunnels carry water east from Pilarcitos Lake Reservoir and Stone Dam Reservoir, respectively. At the present time Pilarcitos Creek not only continues to supply water to
San Francisco and the Peninsula via the
Crystal Springs Reservoir, but it is also the principal source of
potable water for the city of
Half Moon Bay and coastside vicinity. Jurisdiction over land use decisions in the lower creek regions is under the city of Half Moon Bay. Land use decisions in the upper reaches are with the
San Mateo County. Both entities administer provisions of California's
Local Coastal Program. ==Watershed condition==