Bihar has three parts on the basis of physical and structural conditions: the Southern Plateau region, Bihar’s Gangetic Plain, and the Shivalik region. The southern region lies from the Kaimur district in the west to Banka in the east. It is made of hard rocks like gneiss, schist, and granite. The region also has many concail hills.
Bihar’s plain is located between the Southern plateau and northern mountains. It is bounded by a contour line of 150 m in the north and south. The vast fertile region of Bihar plain is divided by the Ganges river in two unequal parts North Bihar and south Bihar. Northern Bihar plain lies in East Champaran and west Champaran and plains of samastipur, Burhi Gandak, Bagmati, Kamla Balan, kosi, and Mahananda. Southern Bihar Plain is narrower than the northern Bihar plain and is triangular in shape as it has several hills in gaya, Rajgir Giriyak, Bihar Sharif, Sheikhupura, Jamalpur and Kharghar. The third Shivalik region is the sub-himalayan foothills of Shivalik ranges that shadows the northern parts of West Champaran. Here lies the deciduous forests.
Bihar has the lowest climate ranging from 0 to 10 degree Celsius in the winter months during December and January. In summer months it is hot and humid about 35 to 48 Celsius during April to mid June. The monsoon months are from mid June, July, August, and September that see good rainfall. October, November and then February, March usually have cool and pleasant weather.