The formation of a salt dry flat lake (Salar)

The movements of the crust have been raising the sector of the central Andes during the Tertiary and Quaternary period, up to the current height. At the same time several mountain ranges were formed with north-south orientation, among which were elongated depressions. The young mountain ranges began to behave like high barriers not allowing the clouds to pass, so the plants and protected areas began to receive less rain. 
Slowly, what once was a subtropical humid region, it became a red desert. Approximately 20-15 million years ago, the earth began to throw up lava and ash which after several eruptions they began to form large volcanic structures along the Chilean-Argentine current milestone and some internal parts of the Puna. This event defined the closure of these elongated depressions,being then fully surrounded with mountains and volcanoes.
Given the drought in that region, the water collected in the Andean depressions evaporated, leaving different types of salt (depending on the degree of solubility). The salt flats have different geological ages - from the Miocene to the Quaternary period. 

The salt flats and lagoons that we can visit nowadays are the product of enormous salt basins and aquifers formed millions of years ago. The salt flats are therefore the product of various factors: an arid climate, depressions obtained by mountains and volcanoes, intense volcanic and thermal activity. 

Besides the polygonal formations, other figures will be determined according to the wind, the amount of water that falls, and depending on the mineral composition of the same salt flats. The crust of the salt flat deposits can be considered alive or dead according to their regeneration every year, caused by rainfall during the summer period. 

Source: La Puna Argentina, Ricardo N. Alonso