Isan covers 160,000 km2 (62,000 sq mi) making it about half the size of Germany, and just under twice the size of the US state of Maine. It is roughly coterminous with the Khorat Plateau, which tilts from the Phetchabun mountain range in the west of the region (the location of several national parks) down toward the Mekong River. The plateau consists of two plains: the southern Khorat plain is drained by theMun and Chi rivers, while the northern Sakon Nakhon plain is drained by the Loei and Songkhram rivers. The two plains are separated by the Phu Phan mountains. The soil is mostly sandy, with substantial salt deposits.