How did the Qarhan Salt Marsh become a major rock salt deposit?

The Qarhan Salt Marsh, located in the center of the Qaidam Basin in Qinghai province, became a major rock salt deposit primarily due to the region's unique geography and arid climate.

The basin is an area of interior drainage where rivers discharge into salt lakes and saline swamps rather than flowing to the sea. In this environment, the climate is characterized by minimal annual precipitation—less than 4 inches (100 mm)—and high rates of evaporation. As water evaporates from these enclosed bodies, dissolved minerals are left behind, eventually crystallizing into massive salt beds.123

Over time, this process has resulted in the Qarhan Salt Marsh becoming China’s largest surface-level rock salt bed, covering approximately 620 square miles (1,600 square km) with solid salt deposits reaching up to 50 feet (15 meters) in thickness. While many global rock salt deposits originated from the evaporation of ancient seawater, the Qarhan deposits are a result of the concentration of minerals within this isolated, high-altitude interior basin.14