The Gobi consists of the Gaxun, Junggar (Dzungarian), and Trans-Altai Gobi in the west, the Eastern, or Mongolian, Gobi in the centre and east, and the Alxa Plateau (Ala Shan Desert) in the south.

The Gaxun Gobi is bounded by the spurs of the Tien Shan to the west and the Bei Mountains to the south and rises to elevations as high as 5,000 feet (1,500 metres). It is gently corrugated, with a complex labyrinth of wide hollows separated by flat hills and rocky crests sometimes rising more than 300 feet (90 metres) above the plain. The desert is stony and nearly waterless, though salt marshes lie in the secluded depressions. The soil is grayish brown and contains gypsum and halite (rock salt). Vegetation is rare, though richer in the riverbeds, where there are individual shrubs of tamarisk, saxaulon and nitre bush (a saltwort), and annual halophytes (salt-tolerant plants).

The Trans-Altai Gobi is situated between the eastern spurs of the Mongolian Altai and Gobi Altai mountains to the north and east, respectively, and the Bei Mountains to the south. The plain is elevated, sharp, and rugged. Alongside the plains and the isolated group of low, rounded hills is a fairly extensive mountain area that extends more than six miles out into the plain. The mountains are barren and broken up by dry ravines. The western section of the Trans-Altai Gobi is basically a plain, too, but it is interspersed with small raised areas and furrowed by dry riverbeds and, again, with extensive salt marshes. In the central portion this fragmentation increases, and mesas (flat-topped, steep-sided hills) appear along with dry gullies ending in flat depressions, occupied by takyr (clayey tracts). The Trans-Altai Gobi is parched, with annual precipitation of less than 4 inches (100 mm), though there is always water underground. There are virtually no wells and springs, however, and vegetation is very sparse and almost useless for livestock.

The Junggar Gobi is north of the Gaxun Gobi, in the Junggar Basin between the eastern spurs of the Mongolian Altai and the eastern extremity of the Tien Shan. It resembles the Trans-Altai Gobi, and its edges are fractured by ravines, alternating with residual hills and low mountain ridges.

The Alxa Plateau is situated between the China-Mongolia border to the north, the Huang He and Helan Mountains to the east, the Qilian to the south, and the northern reaches of the Hei River to the west. It consists of a vast, nearly barren plain that rises in altitude from northwest to southeast. Large areas of the Alxa are sand-covered.

The Eastern Gobi is similar to the western regions, with elevations varying from 2,300 to 5,000 feet (700 to 1,500 metres), but it receives somewhat more precipitation—up to 8 inches (200 mm) per year—though it lacks significant rivers. The underground aquifers have relatively abundant quantities of water and are only partly mineralized. They are also near the surface, feeding small lakes and springs. The vegetation, however, is sparse, consisting mainly of herb wormwood in coarse, grayish brown soil. In the moister depressions there are the usual salt marshes and grassy swamps. In the northern and eastern outlying regions, where more precipitation occurs, the landscape of the desert gradually becomes less harsh, or sometimes even steppelike.

The Gobi’s plains consist of chalk and other sedimentary rocks that are chiefly Cenozoic in age (i.e., up to about 66 million years old), though some of the low, isolated hills are older. The terrain contains small masses of shifting sands. In the central Gobi the remains of dinosaurs from the Mesozoic Era (about 252 million to 66 million years ago) and fossils of Cenozoic mammals have been found. The desert also contains Paleolithic and Neolithic sites occupied by ancient peoples. Successful excavations undertaken during the 1990s at the Tsagaan Agui (White Cave) in southwest-central Mongolia have produced artifacts up to 35,000 years old.