A basin of ancient water
Salinas Grandes is a high-altitude desert basin sitting at 3,450 meters (11,319 feet) above sea level. This vast salt flat, covering approximately 212 square kilometers (82 square miles), is the remnant of an ancient lake. Millions of years ago, the uplift of the Andes mountains created this endorheic basin—a closed drainage system with no outlet to the sea. Over geologic time, water from rain and snowmelt flowed down from the surrounding volcanic terrain, filling the basin. The intense solar radiation and dry air at this altitude caused the water to evaporate, leaving behind concentrated layers of minerals.
This process continues today. During the rainy season (December to March), a shallow layer of water can cover the salt flat, creating a massive natural mirror. As the water evaporates during the dry season (April to November), new layers of salt crystallize on the surface. The salt crust has an average thickness of about 30 centimeters (12 inches), consisting mainly of halite (sodium chloride). Beneath the solid crust lies a mineral-rich brine that contains significant deposits of lithium, potassium, and boron. This has made the region a focal point for lithium exploration, a process that requires vast quantities of water and is a concern for the 33 local Indigenous Kolla and Atacama communities who rely on the basin's delicate water balance.