The Mahanadi Basin, which is also called Chhattisgarh Plain (19° 45′- 23° 15′ N and 80° 25′- 84° 20’E) occupies an area of about 72,940 sq. km in the districts of Raipur, Bilaspur, Durg, Raigarh (Chhattisgarh). The region is largely dominated by the Cuddapah sedimentaries resting unconformably over the Archaean granites and gneisses. It has two major landform types, i.e. the gently sloping Chhattisgarh Plain and the undulating Rimland.
The former is delimited by 300 m contour and is characterised by level surface surrounded on all sides by ancient crystalline rocks forming hills and plateaus. The Mahanadi with its tributaries like Seonath, Hasdo, Mand etc drain this area and form the radial pattern.
The area is characterised by red and yellow soils which are suitable for rice cultivation. The Raipur- Durg Plain forms the south-western, the Bilaspur Plain the north-western, and the Raigarh Plain the eastern sections of the basin floor.
The Chhattisgarh Plain is bordered by a series of hills and plateaus. The northern boundary is formed by the Lormi plateau, Pendraplateau, Chhuri hills and Raigarh hills. This area is largely formed by ancient granites and gneisses with their characteristic rounded rolling topography.
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The soils are of red and dark brown colour. The Korba coal deposits of the Gondwana rocks supply coal to Bhilai steel plant. The western rimland includes the Maikal range with crest-line of 700-900 m. The Durg Uplands are rounded and rolling granitic and gneissic areas.
The southern rimland includes the Rajhara Hills in southern Durg district and the Raipur Uplands in south-eastern Raipur district (300-500 m). The Rajhara Hills contain Dharwarian rocks in which iron ore is mined for Bhilai steel plant. In the extreme south-east stands the escarpment of the Bastar-Orissa Plateau which rises to a height of 800-900 m in the source region of Malianadi.