Rajmahal Hills named after the town of Rajmahal and situated at the head of the Ganges Delta near the border of Bihar and West Bengal of India in a north-south elongated narrow belt. They occupy the area between latitude 24°30' N and 25°15' N and roughly along the longitude 87°30' E. The average height of the range is about 1,000m. The volcanic activity during the Jurassic Period was confined to the area at the head of the Ganges delta in the Rajmahal Hills that forms the type area for the Rajmahal Group.

Rajmahal Basin Jurassic trap rocks interbedded with the beds of sedimentary rocks of the Rajmahal Hills area are known as the deposit of the Rajmahal Basin and the sequence mentioned as the Rajmahal Group (Series) from the hill ranges (24°30' N: 87°30' E) that takes it's name from the town of Rajmahal. The rocks of the Rajmahal Basin have been encountered in the foreland shelf of north-western Bangladesh and referred to as the Rajmahal Formation. [Mujibur Rahman Khan]