Salar de Atacama is part of a larger depression hosting other salt flats. This depression, called La gran fosa by Reinaldo Börgel is bounded by north-south structures. At present this larger depression conforms a subsiding sedimentary basin. Comparing with neighboring areas of the Andes the depression is a major topographical anomaly thought to be caused by a lithospheric block that due to its high density has remained at lower position than the rest of the Andes. The high density would derive from the times the Salar de Atacama depression was a westward rift arm of the Salta Rift Basin located further east in Argentine territory.