Bihar is mainly a vast stretch of very fertile flat land. It is drained by the Ganges River, including northern tributaries of other river. The Bihar plain is divided into two unequal halves by the river Ganges which flows through the middle from west to east. Other Ganges tributaries are the Son, Budhi Gandak, Chandan, Orhani and Phalgu. The Himalayas begin at foothills a short distance inside Nepal but influence Bihar's landforms, climate, hydrology and culture. Central parts of Bihar have some small hills, for example the Rajgir hills. The Himalayan Mountains are to the north of Bihar, in Nepal. To the south is the Chota Nagpur plateau, which was part of Bihar until 2000 but now is part of a separate state called Jharkhand.