A sag pond is a body of
water, which forms as water collects in the lowest parts of the depression that forms between two strands of an active
strike-slip fault . The relative motion of the two fault strands results in a stretching of the land between them, causing the land between them to sink.
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(1) A small body of water occupying an enclosed depression or sag formed where active or recent fault movement has impounded drainage. (2) (California) One of many ponds and small lakes along the San Andreas Fault.