The general slope of the southern part is southward to the river Balsas, or Mescala, which forms its boundary-line with Guerrero.
The Lerma, on the northern frontier, and the Balsas on the southern, are the only rivers of importance of the state, their tributaries within its boundaries being small and swift-flowing.
Of Morelia in a fertile valley of the Rio de las Balsas basin.
The more important rivers of the first division, which are described in more detail under the titles of the Brazilian states through which they flow, are the following: the Gurupy, Tury-assu, Mearim, Itapicuru and Balsas, in the state of Maranhao; the Parnahyba and its tributaries in Piauhy; Jaguaribe in Ceara; and the Apody and Piranhas in Rio Grande do Norte.
It receives only one important tributary from Maranhao - the Rio das Balsas, 447 m.