Seal Rocks is a group of small

rock formation A rock formation is an isolated, scenic, or spectacular surface rock (geology), rock outcrop. Rock formations are usually the result of weathering and erosion sculpting the existing rock. The term ''rock Geological formation, formation ...

islands in the Lands End area of the Outer Richmond District on the West Side of

San Francisco San Francisco, officially the City and County of San Francisco, is a commercial, Financial District, San Francisco, financial, and Culture of San Francisco, cultural center of Northern California. With a population of 827,526 residents as of ...

California California () is a U.S. state, state in the Western United States that lies on the West Coast of the United States, Pacific Coast. It borders Oregon to the north, Nevada and Arizona to the east, and shares Mexico–United States border, an ...

, United States. They are located just offshore in the

Pacific Ocean The Pacific Ocean is the largest and deepest of Earth's five Borders of the oceans, oceanic divisions. It extends from the Arctic Ocean in the north to the Southern Ocean, or, depending on the definition, to Antarctica in the south, and is ...

, at the north end of the Ocean Beach, near the Cliff House and

Sutro Baths The Sutro Baths was a large, privately owned public saltwater swimming pool complex in the Lands End area of the Outer Richmond District on the West Side of San Francisco, California. Built in 1894, the Sutro Baths was located north of ...

ruins. The name is derived from the population of Steller's sea lions (''Eumetopias jubatus'') and

California sea lion The California sea lion (''Zalophus californianus'') is a coastal eared seal native to western North America. It is one of six species of sea lions. Its natural habitat ranges from southeast Alaska to central Mexico, including the Gulf of Califo ...

s (''Zalophus californianus''), who haul out on the rock. Both species are often colloquially called "seals". The formations and wildlife are protected within the

Golden Gate National Recreation Area The Golden Gate National Recreation Area (GGNRA) is a U.S. National Recreation Area protecting of ecologically and historically significant landscapes surrounding the San Francisco Bay Area. Much of the park is land formerly used by the Unite ...

Geology

Near the end of the last

ice age An ice age is a long period of reduction in the temperature of Earth's surface and atmosphere, resulting in the presence or expansion of continental and polar ice sheets and alpine glaciers. Earth's climate alternates between ice ages, and g ...

, this part of the coastline was thought to be between eight and twenty five miles westward of its current position - around five thousand years ago, with the melting of the ice, the sea level rose to its current level. The coastal features found here today were formed by the actions of waves, wind, and the movement of sand. The geology of this part of the coastline of San Francisco consists of steep rocky cliffs which are punctuated by narrow sandy pocket beaches found at the north end of the city and long sandy stretches at Ocean Beach and

Fort Funston Fort Funston is a former Seacoast defense in the United States, harbor defense installation located on the West Side (San Francisco), West Side of San Francisco in the southwestern part of the city. Formerly known as the Lake Merced Milita ...

to the south. The local features, and indeed the entire

San Francisco Peninsula 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 Los Altos and Mountain View, ...

, come from the northern aspect of the

Santa Cruz Mountains The Santa Cruz Mountains ( Mutsun Ohlone: Mak-sah-re-jah, "Sharp Ridged Mountain of the Eagle" or "People of the Eagle Mountain") are a mountain range in central and Northern California, United States, constituting a part of the Pacific Coast R ...

. Before the urban development seen today, the area landward of Ocean Beach consisted of barren sand fields inland to

Twin Peaks ''Twin Peaks'' is an American Surrealist cinema, surrealist Mystery film, mystery-Horror film, horror Drama (film and television), drama television series created by Mark Frost and David Lynch. It Pilot (Twin Peaks), premiered on American Broad ...

. The first known map of the area, dating from 1852, was made by the

United States Coast Survey United may refer to: Places * United, Pennsylvania, an unincorporated community * United, West Virginia, an unincorporated community Arts and entertainment Films * ''United'' (2003 film), a Norwegian film * ''United'' (2011 film), a BBC Two f ...

and describes the coastline as being entirely unaltered by humans. The geologic layers beneath Ocean Beach, starting from the top (i.e. the youngest), are: *Placed fill, from various construction activities over the last 100 years or so. The depth of this placed fill varies, but in 1985 it was then estimated to be between deep. *

Dune A dune is a landform composed of wind- or water-driven sand. It typically takes the form of a mound, ridge, or hill. An area with dunes is called a dune system or a dune complex. A large dune complex is called a dune field, while broad, flat ...

sands, estimated to be deep. * Colma Formation * Merced Formation *

Bedrock In geology, bedrock is solid rock that lies under loose material ( regolith) within the crust of Earth or another terrestrial planet. Definition Bedrock is the solid rock that underlies looser surface material. An exposed portion of bed ...

. The depth to bedrock is estimated to be between . The Colma and Merced Formations consist generally of poorly-sorted sandy deposits, probably deposited during some earlier period of greater sea levels. The Colma Formation is found under the dune sands and also extends inland.

References

External links

NPS−Golden Gate National Recreation Area: Seal Rocks, vestiges of Lands End

— ''digital guidebook''. {{authority control Islands of San Francisco Islands of the San Francisco Bay Area Islands of Northern California Geology of San Francisco Golden Gate National Recreation Area Landmarks in San Francisco Richmond District, San Francisco Rock formations of California Uninhabited islands of California Pacific islands of California

Geology

See also

References

External links