 The Manas river also serves as an international border dividing India and Bhutan.The bedrock of the savanna area in the north of the park is made up of limestone and sandstone, whereas the grasslands in the south of the park stand on deep deposits of fine alluvium.The combination of Sub-Himalayan Bhabar Terai formation along with the riverine succession continuing up to Sub-Himalayan mountain forest makes it one of the richest areas of biodiversity in the world.