The mountains of the Basin Range region, known in Texas as the Trans-Pecos Province, rise in Guadalupe Peak near the border of New Mexico, to nearly 9000 ft.
Half rises in a succession of scarps or steps to an elevation of 2500 ft., to the Great Plains region, which extends westward past the valley of the Pecos river.
Corner of the Trans-Pecos Province is a smaller plain known as the Stockton Plateau, but the remaining portion of this province is traversed from N.E.
The Rio Grande and its principal tributary, the Pecos, drain narrow basins in the S.W.; these two rivers and the Canadian river rise in the Rocky Mountains in Colorado and New Mexico, but all the other rivers by which the state is drained rise within its borders.
On the Llano Estacado there are both freshwater and salt lakes, and there are a few salt lakes in the Trans-Pecos Province and near the mouth of the Rio Grande on the Coastal Plain.