The Beni and its great affluent, the Madre de Dios, though of smaller volume and extent than the Mamore, are of much greater economic importance, owing to their navigability, the fertility of the region they drain, and the great forests along their banks.
They inhabit the western Sierra Madre region from Sinaloa southward to Chiapas, the higher plateau states, which region was the centre of their empire when Cortes conquered them, and parts of Vera Cruz, Tabasco, Oaxaca, Morelos, Aguascalientes and San Luis Potosi.
From the time it receives the Manu, the Madre de Dios carries its immense volume of waters 4 85 m.
Near the 10th parallel the great chain again divides, the eastern part crossing the southern end of the plateau, and the western, or Sierra Madre del Sur, following the shore line closely to Tehuantepec. The Sierra Madre Occidental has but few noteworthy elevations, its culminating points being the Nevado de Colima (14,363 ft.) and Volcan de Colima (12,750 ft.) in the state of Jalisco.
Long and has no ports or towns of importance, the slopes of the Sierra Madre del Pacifico being precipitous and heavily wooded and the coastbelt sandy, hot and malarial.
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.
The surface consists of a narrow coastal zone where tropical conditions prevail, a broad belt of mountainous country covered by the ranges of the Sierra Madre Occidental and their intervening valleys where oak and pine forests are to be found, and an intervening zone among the foothills of the Sierra Madre up to an elevation of 2000 ft., where the conditions are subtropical.
The most important are: Bezerros (17,484), Bom Jardim (40,160), Brejo da Madre de Deus (13,655), a town of the higher agreste region, Cabo (13,337), Caruaru (17,844), Escada (9331), Garanhuns (32,788, covering six towns and villages), Gloria de Goyta (24,554), Goyanna, Limoeiro (21,576), Olinda (8080), the old colonial capital and episcopal see, Rio Formosa (6080), Timbauba (9514) and Victoria (32,422).
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.
The mountain ranges which form part of the great Mexican Plateau consist of two marginal chains known as the Sierra Madre Occidental, on the west, the Sierra Madre Oriental, on the east, and a broken, weakly-defined chain of transverse ranges and ridges between the 18th and 10th parallels known as the Cordillera de Anahuac. All these chains are known locally under diverse names.