It is drained by the Doce, Mucury, Jequitinhonha and Pardo, which have their sources on the eastern slopes of the Espinhago and cut their way through the Aymores to the sea.
The largest and most productive field is that of Diamantina on the head-waters of the Jequitinhonha River, where diamonds were discovered about 1725, and where the celebrated "diamond reservation" - an oval-shaped territory 8 leagues wide by 16 leagues long (Mawe), with Tejuco, now Diamantina, very nearly in the centre - was established in 1730.
The more important of these rivers are the Itapicuru, Paraguassu, Contas or Jussiape, Pardo or Patype, and Jequitinhonha, of Bahia; the Mucury, and Doce, of Espirito Santo; and the Parahyba do Sul of the state of Rio de Janeiro.
Of the Bahia group, the Jequitinhonha, sometimes called the Belmonte on its lower course, is the longest and most important, rising near Serro in the state of Minas Geraes and flowing in a curving north-east direction for a distance of about 500 m., 84 of which are navigable inland from the sea.
Diamantina is built partly on a steep hillside overlooking a small tributary of the Rio Jequitinhonha (where diamond-washing was once carried on), and partly on the level plain above.