A sag pond is a body of fresh water collected in the lowest parts of a depression formed between two sides of an active strike-slip, transtensional or normal fault zone.

Formation

A sag pond is formed along a strike-slip fault, which may create a depression in the earth. When water enters the depression from rivers, streams, rainfall or snowfall, it fills the low-lying area, and a pond is the result.

Scientific significance

Sag pond formation is common in

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 ...

, and many of them can be found on the

San Andreas Fault The San Andreas Fault is a continental Fault (geology)#Strike-slip faults, right-lateral strike-slip transform fault that extends roughly through the U.S. state of California. It forms part of the tectonics, tectonic boundary between the Paci ...

, which runs through the western part of the state.

Aerial photography Aerial photography (or airborne imagery) is the taking of photographs from an aircraft or other flight, airborne platforms. When taking motion pictures, it is also known as aerial videography. Platforms for aerial photography include fixed-wi ...

or high-resolution

topography Topography is the study of the forms and features of land surfaces. The topography of an area may refer to the landforms and features themselves, or a description or depiction in maps. Topography is a field of geoscience and planetary sci ...

can easily determine their locations.

Uses

Sag ponds have been converted into stock reservoirs. Larger sag ponds are converted into reservoirs for public water sources, such as San Andreas Lake

Examples

Sag ponds of various sizes can be found along the

, most notably within the

Carrizo Plain The Carrizo Plain ( Obispeño: ''tšɨłkukunɨtš'', "Place of the rabbits") is a large enclosed grassland plain, approximately long and up to across, in southeastern San Luis Obispo County, California, United States, about northwest of Lo ...

and

Sierra Pelona Mountains The Sierra Pelona, also known as the Sierra Pelona Ridge or the Sierra Pelona Mountains and originally known as the Liebre Mountains, is a mountain ridge in the Transverse Ranges in Southern California. Located in northwest Los Angeles County, t ...

. Some have been converted into reservoirs like the San Andreas Reservoir near

San Bruno, California San Bruno () is a city in San Mateo County, California, United States, incorporated in 1914. The population was 43,908 at the 2020 United States census. The city is between South San Francisco, California, South San Francisco and Millbrae, Cali ...

. Various lagoons on the

plateau In geology and physical geography, a plateau (; ; : plateaus or plateaux), also called a high plain or a tableland, is an area of a highland consisting of flat terrain that is raised sharply above the surrounding area on at least one side. ...

Pico Island Pico Island (''Ilha do Pico,'' ) is an island in the Central Group, Azores, Central Group of the Portugal, Portuguese Azores. The landscape features an eponymous volcano, Mount Pico, Ponta do Pico, which is the highest mountain in Portugal, the A ...

in the

Azores The Azores ( , , ; , ), officially the Autonomous Region of the Azores (), is one of the two autonomous regions of Portugal (along with Madeira). It is an archipelago composed of nine volcanic islands in the Macaronesia region of the North Atl ...

are the result of a

graben In geology, a graben () is a depression (geology), depressed block of the Crust (geology), crust of a planet or moon, bordered by parallel normal faults. Etymology ''Graben'' is a loan word from German language, German, meaning 'ditch' or 't ...

Sources

{{pond Depressions (geology) Ponds Geology terminology