How do salt flats like Salar de Uyuni form?

Salt flats develop in closed basins where water flows in but has no outlet to the sea. As lakes or shallow seas evaporate, dissolved minerals become concentrated and crystallize on the surface and in layers below. Bolivia’s Salar de Uyuni, the world’s largest salt flat, is the residue of prehistoric lakes that shrank during the late Quaternary period. Its surface can hold a shallow layer of water after rain, creating the famous mirror effect. Salt flats may also contain valuable deposits of lithium-rich brines underground.