The Merced Formation is a

geologic formation A geological formation, or simply formation, is a body of rock having a consistent set of physical characteristics ( lithology) that distinguishes it from adjacent bodies of rock, and which occupies a particular position in the layers of rock exp ...

California California is a state in the Western United States, located along the Pacific Coast. With nearly 39.2million residents across a total area of approximately , it is the most populous U.S. state and the 3rd largest by area. It is also the ...

, and also in

Oregon Oregon () is a state in the Pacific Northwest region of the Western United States. The Columbia River delineates much of Oregon's northern boundary with Washington, while the Snake River delineates much of its eastern boundary with Idah ...

and

Washington state Washington (), officially the State of Washington, is a state in the Pacific Northwest region of the Western United States. Named for George Washington—the first U.S. president—the state was formed from the western part of the Washingto ...

. It is named for Lake Merced, a natural lake on the western San Francisco coastline.

Geology

California

In the coastal

San Francisco Bay Area The San Francisco Bay Area, often referred to as simply the Bay Area, is a populous region surrounding the San Francisco, San Pablo, and Suisun Bay estuaries in Northern California. The Bay Area is defined by the Association of Bay Area Gov ...

of California the Merced Formation was deposited in a small sedimentary basin that formed along the

San Andreas Fault The San Andreas Fault is a continental transform fault that extends roughly through California. It forms the tectonic boundary between the Pacific Plate and the North American Plate, and its motion is right-lateral strike-slip (horizontal) ...

during the last two million years during the Pliocene age of the Neogene period, in the

Cenozoic Era The Cenozoic ( ; ) is Earth's current geological era, representing the last 66million years of Earth's history. It is characterised by the dominance of mammals, birds and flowering plants, a cooling and drying climate, and the current configu ...

USGS.gov: "San Andreas Fault and Coastal Geology, from Half Moon Bay to Fort Funston: Crustal Motion, Climate Change, and Human Activity"
Geologic Trips.com: Merced Formation in San Francisco and the Bay Area
/ref> The fault cut the basin into two pieces and moved the pieces apart. It is found on the east side of the fault in western

San Francisco San Francisco (; Spanish language, Spanish for "Francis of Assisi, 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 List of Ca ...

and northern

San Mateo County San Mateo County ( ), officially the County of San Mateo, is a county located in the U.S. state of California. As of the 2020 census, the population was 764,442. Redwood City is the county seat, and the third most populated city following Dal ...

. On the west side of the fault it was carried north to the

Bolinas Bolinas is an unincorporated coastal community and census-designated place in Marin County, California, United States. As of the 2020 census it had a population of 1,483. It is located on the California coast, approximately (straight line dis ...

headlands of western

Marin County Marin County is a county located in the northwestern part of the San Francisco Bay Area of the U.S. state of California. As of the 2020 census, the population was 262,231. Its county seat and largest city is San Rafael. Marin County is a ...

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 ...

is on a bluff made up of exposed sedimentary rocks of the Merced Formation, in San Francisco within the NPS

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 ...

Fossils

It preserves

fossils A fossil (from Classical Latin , ) is any preserved remains, impression, or trace of any once-living thing from a past geological age. Examples include bones, shells, exoskeletons, stone imprints of animals or microbes, objects preserved ...

dating back to the

Neogene The Neogene ( ), informally Upper Tertiary or Late Tertiary, is a geologic period and system that spans 20.45 million years from the end of the Paleogene Period million years ago (Mya) to the beginning of the present Quaternary Period Mya. ...

period.

References

Pliocene California Neogene geology of Oregon Neogene geology of Washington (state) Pliocene United States Geology of Marin County, California Geology of San Francisco Geology of San Mateo County, California {{Washington-geologic-formation-stub

Geology

California

Fossils

See also

References