Garhjat Hills, also called as Orissa Highlands, (17° 15′-22° 34’N and 82° 27′-86° 25’E) stretch NE-SW along the Utkal coast for about 382 km and occupy an area of about 76,800 sq. km. It is bordered by Chotanagpur in the north, Mahanadi Basin in the west, and Eastern Ghats in the south-west and Utkal Plains in the east. The region is mainly composed of Archaean crystalline rocks like granites, gneisses and magmatic rocks.
The Gond’ system consisting of shales, sandstones and occupies the faulted basins and troughs in Dhei and Sambalpur districts which is divided into bearing Talchir, Barakar and Kamathi series.
The region is an interesting complex of nuded hills, plateaus, sharp ridges and mature leys. The Mahanadi flowing from west to east vides it into two parts.
The northern part is extension of the Chotanagpur plateau and the so ern part of the Eastern Ghats. It has three distil physiographic units: (i) northern uplands, (ii) Malianadi valley, and (iii) south-western hilly religion.
The northern uplands are undulating, frequen intersected by hill ranges, with a general slope for, north to south (average elevation 900 m). Hi notable hill ranges include Malaygir (1169 nl Manakamacha (1099 m) and Meghasani (1157 m).
The Mahanadi basin is demarcated by 150 m contour and occupies parts Of Sambalpur, Bolangir and Dhenkanal districts. The south-western hilly regit (above 900 m) consists of wide-open plateaus fringi by hills with thick forests. Mahendragir (1490 m, Gajapati district) is the highest peak of these hills.