The Sierra Madre crosses the southern part of the state parallel with the coast, separating the low, humid, forested districts on the frontier of Tabasco from the hot, drier, coastal plain on the Pacific. The mountain region includes a plateau of great fertility and temperate climate, which is one of the best parts of Mexico and contains the larger part of the population of the state.
Coffee-planting is a new industry on the Pacific slope of the Sierra Madre at elevations of 2000 to 4000 ft., and has met with considerable success.
The surface of the state is much broken by the Sierra Madre Occidental, which extends through it from north to south and covers its entire width with parallel ranges, enclosing fertile valleys.
The longest is the Yaqui, which has its source on the eastern side of the Sierra Tarahumare in Chihuahua and breaks through several ranges of the Sierra Madre before reaching the gulf near Guaymas.
The line adopted starts from Lake Suches, the source of a small river of that name flowing into the north of Lake Titicaca, crosses the Cordillera by the Palomani to the Tambopata river, follows that stream to the mouth of the Lanza, thence crosses to the source of the Heath river, which forms the dividing line down to its junction with the Madre de Dios, descends that river to the mouth of the Torosmonas, thence in a straight line north-westerly to the intersection of the Tahu.amanu river by the 69th meridian, and thence north on that meridian to the Brazilian frontier.