The Chotanagpur Plateau (22°-25° 30’N and 83°47′-87° 50’E) covering an area of 87,239 sq. km includes Ranchi, Hazaribagh, Singhbhum, Dhanbad, Palamau, Santhal Parganas (Bihar) and Purulia districts (West Bengal). It is composed of Archaean granite and gneiss rocks with patches of Dharwar rocks (phyllite, mica-schists).
The Dalma range marks the belt of Archaean lava flows. The structural base of the region is provided by a series of batholithic intrusions of granite into Dharwar strata, which were intensely metamorphosed by orogenetic movements.
There is evidence of a peneplained ancient fold mountains across north Singhbhum; Jamshedpur lying on the central axis of this range. In the structural trough of the Damodar valley occur Gondwana rocks consisting of sandstones, some slates and clay.
The Pat land on the western margin is covered with Deccan Trap which is converted into laterite and bauxite due to weathering. Dunn (1944) has summarised the geological history of the region as follows : “A long period of erosion evening out the irregularities of gneissic and granitic pre-Cambrian land surface; an ice age in the Upper Carboniferous; major trough faulting in the Permian times that brought into being the Damodar valley when the Gondwana rocks were laid down in fresh water lakes; uplift in the hot desertic conditions of Triassic days when some five thousand feet (1520 m) of unprotected Gondwana sediments were stripped away and massive sandstones of Mahadeva series (Middle Gondwana) were formed; a volcanic outburst in the Jurassic; and minor faulting and tearing during Tertiary earth movements.”
Chotanagpur consists of a series of plateaus standing at different levels of elevation; the highest general elevation of about 1100 m in the mid-western portion known as the Pat lands. From here the land descends in all directions in a series of steps particularly towards the east until it merges gradually with the Lower Ganga Plain. The sharp break in slope are marked by steep scarps where the rivers like Barakar, Damodar, Subamarekha north and south Koels have carved out deep gorges and waterfalls. The most characteristic features of relief are revealed in the Hazaribag and Ranchi plateaus standing at same general elevation (600 m) but separated by the Damodar trough (Permo-Triassic trough fault).
The Baghmundi highland (600 m) is separa the Ranchi plateau by the Subarnarekha rivet- varying successive levels from Pat lands toC plain mark the successive uplifts of an old pe: during Tertiary era (Ram, 1968 andChatteijee,
Chotanagpuris drained in different dir by numerous rivers and streams of which the Dam Barakar, Subarnarekha, North Koel, South rivers have developed extensive drainage The northern fringe of the plateau is drain numerous small tributariesof the Punpun, thePh the Sakri and the Kiul rivers towards the South® Plain, while the Ajai, the Mor, the Brahmani, Gumani etc drain the Rajmahal highlands in par channels towards the Bengal Plain.
Chotanagpur region is broadly divided two physiographic regions: (1) Chotanagpur consisting of Palamau Uplands, Hazaribag Pla Damodar Valley, and Santhal Pargana Uplands; (2) Chotanagpur South comprising the Patland gion, the Ranchi Plateau and the Singhbhum regio The northern Chotanagpur, lying north of tiie Patland I is characterised by comparatively subdued rel« with isolated hills and rugged plateau fringes. T land descends in all directions from the cento position of Hazaribag Plateau. The southei Chotanagpur consists of three disctinct erosion su faces, i.e. the Patlands, the Ranchi Plateau, an Singhbhum region. Here the general slope lies fra west to east showing steps characterised by be scarps.