It is located in the Potosí and Oruro departments in southwest Bolivia, near the crest of the Andes, and is at an elevation of 3,656 meters (11,995 ft) above mean sea level.
The Salar was formed as a result of transformations between several prehistoric lakes. It is covered by a few meters of salt crust, which has an extraordinary flatness with the average altitude variations within one meter over the entire area of the Salar.
The crust serves as a source of salt and covers a pool of brine, which is exceptionally rich in lithium. It contains 50 to 70% of the world's lithium reserves, which is in the process of being extracted. The large area, clear skies and the exceptional flatness of the surface make the Salar an ideal object for calibrating the altimeters of Earth observation satellites.
The Salar serves as the major transport route across the Bolivian Altiplano and is a major breeding ground for several species of pink flamingos. Salar de Uyuni is also a climatological transitional zone, for towering tropical cumulus congestus and cumulus incus clouds that form in the eastern part of the massive salt flat during the summer, cannot permeate beyond the salt flat's considerably more arid western edges, near the Chilean border and the Atacama Desert.
The geological history of the Salar is associated with a sequential transformation between several vast lakes. Some 30,000–42,000 years ago, the area was part of a giant prehistoric lake, Lake Minchin. Its age was estimated from radiocarbon dating of shells from outcropping sediments and carbonate reefs and varies between reported studies.
Lake Minchin (named after the Juan B. Minchin of Oruro) later transformed into paleolake Tauca having a maximal depth of 140 meters (460 ft), and an estimated age of 13,000–18,000 or 14,900–26,100 years depending on the source.