The salt flats are the result of a long paleoenvironmental evolution, starting with the formation of freshwater lakes during the Pleistocene, which became salinized early until their desiccation in the Holocene. The congenital development with volcanism led to a massive transfer of ions to the basins, the result of which is expressed in important volumes of diverse salts. With a predominance of chloride-sodium salts. The volumetric participation of salts in the total filling defines two major types of salt flats: crystalline and earthy. In general terms, the crystalline surfaces support a concentric facies zonation. Crystalline salt flats are impregnated with interstitial brine of diversified ionic content. Almost all of the brines are carriers of chemical elements of economic importance, especially boron and lithium.

The Pozuelos and Pastos Grandes salt flats share the same local stratigraphy. The basins are separated in the northeast of Pozuelos by the Pozuelo and Geste formations.

Quaternary rocks are observed in the form of evaporite accumulations that occupy the intermontane depression. The Pastos Grandes salt flats are the current expression of a larger sedimentary basin known as Sijes, developed since the Miocene. It is formed by sandstones, clays, tuffs, evaporites and travertines. Period. The lilac-white formation represents an ancient salar larger than the present one and is a potential aquifer that can store lithium-rich brine. The Pastos Grandes salar is filled with unconsolidated clastics (clays and silts), organic material and fine-grained sediments. Period. The age of these sediments is Quaternary and they are 30 m thick. The sediments contain lithium-rich brines, which has been demonstrated by exploration work.