Sag pond

A sag pond is a body of fresh water[1] collected in the lowest parts of a depression formed between two sides of an active strike-slip, transtensional or normal fault zone.

[2][3] A sag pond is formed along a strike-slip fault, which may create a depression in the earth.

[4][5] When water enters the depression from rivers, streams, rainfall or snowfall, it fills the low-lying area, and a pond is the result.

[6] Sag pond formation is common in California,[7] and many of them can be found on the San Andreas Fault, which runs through the western part of the state.

[11] Larger sag ponds are converted into reservoirs for public water sources, such as San Andreas Lake[12] Sag ponds of various sizes can be found along the San Andreas Fault, most notably within the Carrizo Plain and Sierra Pelona Mountains.