Rajasthan lies in the desert area to the west of the Aravali hills. This region has very low rainfall. The groundwater in this region is impregnated with salt, therefore various saline lakes are found. Out of these, there are two well-known saline lakes on the eastern edge of the Thar Desert. They are known as Sambhar end the Didwana. Both of these are the sources of common salts. The Sambhar is an example of a boson. Bolson is an extensive flat depression surrounded by hills in which the drainage is centripetal. The smaller lakes with flat floors are undrained basins in which water collects after rains and evaporates quickly are called Playas. The Didwana lake is a playa.