Salar de Uyuni (or Salar de Tunupa) is the world’s largest salt flat covering approximately 4000 square miles. It is located in the Potosí and Oruro departments in southwest Bolivia and was formed as several prehistoric lakes merged over time.
Covered by a few meters of salt crust, the Salar has an extraordinary flatness with the average altitude variations within one meter over the entire area. The crust serves as a source of salt and covers a pool of brine, which is exceptionally rich in lithium and contains 50 to 70% of the world’s lithium reserves. 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.
1. Reddit, After some rain
2. Wikipedia, Salar de Uyuni