Seal Rock (or ''Seal Rocks'') is a group of small

rock formation A rock formation is an isolated, scenic, or spectacular surface rock outcrop. Rock formations are usually the result of weathering and erosion sculpting the existing rock. The term ''rock formation'' can also refer to specific sediment ...

island An island (or isle) is an isolated piece of habitat that is surrounded by a dramatically different habitat, such as water. Very small islands such as emergent land features on atolls can be called islets, skerries, cays or keys. An island ...

s in the

Lands End Land's End ( kw, Penn an Wlas or ''Pedn an Wlas'') is a headland and tourist and holiday complex in western Cornwall, England, on the Penwith peninsula about west-south-west of Penzance at the western end of the A30 road. To the east of it is ...

area of the Outer Richmond District in western

San Francisco, California San Francisco (; Spanish for " Saint Francis"), officially the City and County of San Francisco, is the commercial, financial, and cultural center of Northern California. The city proper is the fourth most populous in California and 17th ...

. They are located just offshore in the

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

, 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 in western San Francisco, California. Built in 1894, the Sutro Baths was located north of Ocean Beach, ...

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 C ...

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 United ...

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 gree ...

, 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 harbor defense installation located in the southwestern corner of San Francisco. Formerly known as the Lake Merced Military Reservation, the fort is now a protected area within the Golden Gate National Recreation Are ...

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 Mountain View, south of Palo A ...

, come from the northern aspect of the

Santa Cruz Mountains The Santa Cruz Mountains, part of the Pacific Coast Ranges, are a mountain range in central and Northern California, United States. They form a ridge down the San Francisco Peninsula, south of San Francisco. They separate the Pacific Ocean from ...

. 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 Mystery fiction, mystery serial drama television series created by Mark Frost and David Lynch. It premiered on American Broadcasting Company, ABC on April 8, 1990, and originally ran for two seasons until its cance ...

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

U.S. Coast and Geodetic Survey The National Geodetic Survey (NGS) is a United States federal agency that defines and manages a national coordinate system, providing the foundation for transportation and communication; mapping and charting; and a large number of applications ...

and describes the coastline here 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, f ...

sands, estimated to be deep. *

Colma Formation Colma may refer to: Art, entertainment, and media *Colma (album), ''Colma'' (album), 1998, by guitarist Buckethead *''Colma: The Musical'' (2006), an American independent film Places

*Colma, California, a town **Colma (BART station) *Colma Cr ...

Merced Formation The Merced Formation is a geologic formation in California, and also in Oregon and Washington state. It is named for Lake Merced, a natural lake on the western San Francisco coastline. Geology California In the coastal San Francisco Bay Area of ...

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

. 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 Landforms of San Francisco 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