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The San Francisco Peninsula is a peninsula in the San Francisco Bay Area that separates San Francisco Bay from the Pacific Ocean. On its northern tip is the City and County of San Francisco. Its southern base is in northern Santa Clara County, including the cities of Palo Alto, Mountain View and Los Altos. Most of the Peninsula is occupied by San Mateo County, between San Francisco and Santa Clara counties, and including the cities and towns of Atherton, Belmont, Brisbane, Burlingame, Colma, Daly City, East Palo Alto, El Granada, Foster City, Hillsborough, Half Moon Bay, La Honda, Los Altos, Menlo Park, Millbrae, Mountain View, Pacifica, Palo Alto, Portola Valley, Redwood City, San Bruno, San Carlos, San Mateo, South San Francisco, and Woodside.
In 1795, Governor Diego de Borica gave José Darío Argüello a Spanish land grant known as Rancho de las Pulgas. This rancho was the largest grant on the peninsula consisting of 35,260 acres (142.7 km2).
As a local geographic term, the area referred to as "The Peninsula" is distinct from that denoted by "The City", and refers to the portion south of San Francisco. The appellation may date to the period, prior to 1856, when the City of San Francisco and the County of San Francisco were separate entities, the latter then coextensive with contemporary San Mateo County and San Francisco City-County. The City-County owns several disjunct properties along the whole of the Peninsula (mostly water pumping stations connected to the Hetch Hetchy Valley on which San Francisco has a permanent leasehold); thus, most of the larger communities in San Mateo County are de facto suburbs of San Francisco, with the neighboring communities of Pacifica, Daly City, Broadmoor, Colma, South San Francisco, Half Moon Bay, San Bruno, and Brisbane being immediate suburbs. The remaining suburban area of the Peninsula is on the east side of the Santa Cruz Mountains, along San Francisco Bay; the west and south-central portions of the Peninsula are mostly rural, unincorporated and unorganised areas.
A substantial portion of Silicon Valley is located on the peninsula. In Silicon Valley are the headquarters of some of the largest tech companies in the world, such as Google, Yahoo, Facebook and Apple. Over the last decade or so there has been an influx of immigration into the Bay Area from places like India and China to work in the technology industry. There are well over 6,600 tech startups in the Valley and new ones are created every day.
The east side of the peninsula is a densely populated and largely urban and suburban area that includes portions of Silicon Valley. It forms a commuter area between San Francisco to the north and San Jose to the south. A number of major thoroughfares run north-south: El Camino Real (SR 82) and US 101 on the east side along the bay, Interstate 280 down the center, Skyline Boulevard (SR 35) along the crest of the Santa Cruz Mountains, and Highway 1 on the west along the Pacific. The Caltrain commuter rail line runs roughly parallel to the El Camino Real (State Route 82) and Highway 101 corridors.
Along the center line of the Peninsula is the northern half of the Santa Cruz Mountains, formed by the action of plate tectonics along the San Andreas Fault. In the middle of the Peninsula along the fault is the Crystal Springs Reservoir. Just north of the Crystal Springs reservoir is San Andreas Lake, after which the geologic fault was originally named.
The San Francisco Peninsula contains a variety of habitats including estuarine, marine, oak woodland, redwood forest, coastal scrub and oak savanna. There are numerous species of wildlife present, especially along the San Francisco Bay estuarine shoreline, San Bruno Mountain, Fitzgerald Marine Reserve and the forests on the Montara Mountain block.
The county is home to several endangered species including the San Francisco garter snake, the Mission blue butterfly and the San Bruno elfin butterfly, all of which are endemic to San Mateo County. The endangered California clapper rail is also found on the shores of San Francisco Bay, in the cities of Belmont and San Mateo.
A number of noteworthy parks and nature preserves are found on the San Francisco Peninsula, including:
- Edgewood Park, San Mateo County
- Golden Gate National Recreation Area - several units are located on the Peninsula
- Midpeninsula Regional Open Space District - several preserves
- Sanborn Park, Santa Clara County
There are a number of well-known structures and complexes on the San Francisco Peninsula:
- Bay Meadows Racecourse, San Mateo (demolished in 2008)
- Carolands Mansion, Hillsborough
- Cow Palace, Daly City
- Crocker Mansion, Hillsborough
- Crystal Springs Reservoir, west of Interstate 280
- CuriOdyssey museum, San Mateo
- Dakin Building, Brisbane
- Facebook Inc., world headquarters, Menlo Park
- Filoli mansion and gardens, Woodside
- Frenchman's Tower, Palo Alto
- Google Inc., World Headquarters, Mountain View
- "The Flintstone House", east side of Interstate 280
- Notre Dame de Namur University, Belmont, with Ralston Hall
- Oracle World Headquarters, Redwood Shores (aka the "Emerald City")
- Pulgas Water Temple, Woodside
- San Francisco International Airport
- Sanchez Adobe Park, Pacifica
- Stanford University campus, Palo Alto
|Wikivoyage has a travel guide for Peninsula (Bay Area).|
- "Early days in Menlo Park". ci.menlo-park.ca.us. 2002. Retrieved 2010-05-04.
- Price, Robert. "History." Roadmap To Silicon Valley. Roadmaptosiliconvalley.org. Web. 21 May 2014.
- Carol S. Prentice, "Andrew Cowper Lawson", in Classic Cordilleran Concepts: A View from California, Special paper 338, Boulder, Colorado: Geological Society of America, 1999, ISBN 9780813723389, p. 70.
-  Archived November 15, 2011, at the Wayback Machine.