Salt Flat Uyuni is the world's largest salt flat at 10,582 square kilometers (4,086 sq mi). It is located in the Potosí and Oruro departments in southwest Bolivia and is at an elevation of 3,656 masl (11,995 ft)
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.
Salt Flat Uyuni is part of the Altiplano of Bolivia in South America. The Altiplano is a high plateau, which was formed during uplift of the Andes mountains. The plateau includes fresh and saltwater lakes as well as salt flats and is surrounded by mountains with no drainage outlets.
The geological history of the Salar is associated with a sequential transformation between several vast lakes. Some 30,000 to 42,000 years ago.
The area has a relatively stable average temperature with a peak at 21 °C (70 °F) in November to January and a low of 13 °C (55 °F) in June. The nights are cold all through the year, with temperatures between −9 and 5 °C (16 and 41 °F). The relative humidity is rather low and constant throughout the year at 30 to 45%. The rainfall is also low at 1 to 3 millimeters (0.039 to 0.118 in) per month between April and November, but it may increase up to 70 millimeters (2.8 in) in January. However, except for January, even in the rainy season the number of rainy days is fewer than 5 per month.