Salar de Uyuni is the world's largest salt flat, or playa, at over 10,000 square kilometres in area. It is in the Daniel Campos Province in Potosí in southwest Bolivia, near the crest of the Andes at an elevation of 3,656 m above sea level. The Salar was formed as a result of transformations between several prehistoric lakes that existed around forty thousand years ago but had all evaporated over time.