San Bruno Mountain is a fault-block horst in northern San Mateo County, California; its northern slopes rise in San Francisco. It is surrounded by San Francisco Bay and the cities of Brisbane, Colma, Daly City, and South San Francisco.
Topped by a four mile long ridge, trails along the summit afford expansive views of the San Francisco Bay Area. Much of the mountain is in the San Bruno Mountain State Park or the adjoining State Ecological Reserve. Radio Peak (elevation ), the highest point, serves the hilly Bay Area with several radio/TV broadcast towers.
It is not a part of the nearby Santa Cruz Mountains, whose northern-most peak on Montara Mountain lifts only eight miles from Radio Peak. The Santa Cruz range is on the Pacific tectonic plate, while San Bruno Mountain is on the North American Plate.
Distinct geology and weather set San Bruno Mountain apart from other California coastal areas. The mountain soil provides habitat for rare and endangered plants (see below) and butterflies; the Callippe silverspot, Mission blue, and San Bruno elfin butterfly all inhabit mountain slopes. The mountain is also a cradle for economically-useful plants; the low-growing evergreem "San Bruno Mountain Manzanita" (Arctostaphylos uva-ursi) has become widely used in drought-resistant landscaping.
Location
The southern border of San Francisco runs along the base of the northern range; Daly City's initial "top-of-the-hill" community at the westernmost point of the mountain was founded on John Daly's dairy farm by SF residents fleeing the 1906 quake. The post-WW2 residential tracts of Southern Hills and Bayshore encircle the north side of the mountain - their construction inspired Malvina Reynolds song Little Boxes (a 1964 Billboard Hot 100 hit for singer Pete Seeger). The Bayshore neighborhood features the 1941 Cow Palace indoor arena, and faces a large bay-landfill.
Brisbane is on an eastern prominence, while the residential portion of the community of South San Francisco spills into the southeastern valleys. Almost two miles of the southern flank of the mountain abuts the large cemeteries of Colma, many developed after the City and County of San Francisco evicted all burial grounds from the county in 1912.
The 144-acre Guadalupe quarry on the south side of Guadalupe Canyon is presently owned and operated by American Rock and Asphalt, Inc., while the Crocker Industrial Park occupies much of the canyon floor. Radio towers occupy the highest (1,319 ft) peak, and may be accessed from the San Bruno County Park center, in the "saddle" between the north and south ridges.
A series of historic maps and photos of the area may be viewed at the website of the City of Brisbane.
Topography, Geology, Climate
San Bruno Mountain is a part of the Franciscan Formation; sedimentary rock laid down in the Mesozoic, then uplifted as fault-blocks starting in the Pleistocene; prior to the initial occurrence of the San Andreas transform-fault. The formation is centered on present-day San Francisco, composed of small ranges trending northwest-to-southeast from the peninsula up into Marin County.
The mountain pairs two parallel ranges separated by the Guadalupe Valley and Colma Canyon and united by a saddle. The lower north range (also called Crocker Hills) attains a peak of . The south range rises abruptly from Merced Valley at the south to the Radio Peak in a horizontal distance of only . Slightly to the east of the highest peak, south of the main range, a small block reaches in South San Francisco, called Sign Hill because of large concrete letters placed by the city of South San Francisco. Into the early 1900s, San Francisco Bay still lapped directly against the eastern flank of San Bruno Mountain; but today the entire bay shoreline is fill.
The region is drained by two streams: Guadalupe Valley Creek flows east between the two ranges to reach the Bay north of Brisbane - most of it now runs through underground culverts. Colma Creek rises from a source in San Bruno Mountain State and County Park, runs west into Colma Canyon, then turns southeast and runs south along the base of the mountain (fed by Twelve-Mile Creek along Westborough Boulevard, and at least eight other streams) until it reaches the San Francisco Bay north of San Francisco International Airport. Steelhead trout historically swam nearly to the headwaters of Colma Creek to spawn; boats carried supplies up to the Southern Pacific stop (now Molloy's Tavern on Old Mission Road in Colma). Seasonal creeks to drain runoff cut ravines in the south face; after a heavy rain a 12-foot waterfall regularly appears in Juncus ravine behind Hillside School, others may be found in Guadalupe canyon.