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, located along the West Coast of the United States, Pacific Coast. With nearly 39.2million residents across a total area of approximately , it is the List of states and territori ...

, and many of them can be found on the

San Andreas Fault The San Andreas Fault is a continental transform fault that extends roughly through California. It forms the tectonics, tectonic boundary between the Pacific Plate and the North American Plate, and its motion is Fault (geology)#Strike-slip fau ...

, 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 airborne platforms. When taking motion pictures, it is also known as aerial videography. Platforms for aerial photography include fixed-wing aircra ...

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 land forms 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 San Andreas Lake is a reservoir adjacent to the San Francisco Peninsula cities of Millbrae and San Bruno in San Mateo County, California. It is situated directly on the San Andreas Fault, which is named after the valley it is in. History Afte ...

Examples

Sag ponds of various sizes can be found along the

, most notably within the Carrizo Plain and

Sierra Pelona Mountains The Sierra Pelona, also known as the Sierra Pelona Ridge or the Sierra Pelona Mountains, is a mountain ridge in the Transverse Ranges in Southern California. Located in northwest Los Angeles County, the ridge is bordered on the north by the San An ...

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

San Bruno, California San Bruno (Spanish for " St. 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 and Millbrae, adjacent to S ...

. Various lagoons on the

plateau In geology and physical geography, a plateau (; ; ), 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. Often one or more sides ha ...

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

in the

Azores ) , motto =( en, "Rather die free than subjected in peace") , anthem= ( en, "Anthem of the Azores") , image_map=Locator_map_of_Azores_in_EU.svg , map_alt=Location of the Azores within the European Union , map_caption=Location of the Azores wi ...

are the result of a

graben In geology, a graben () is a depressed block of the crust of a planet or moon, bordered by parallel normal faults. Etymology ''Graben'' is a loan word from German, meaning 'ditch' or 'trench'. The word was first used in the geologic contex ...

Sources

{{pond Depressions (geology) Ponds Geology terminology