The Guapore presents many difficulties to continuous navigation; the Baures and Itonama offer hundreds of miles of navigable waters through beautiful plains; the Mamore has been sounded by the writer in the driest month of the year for a distance of 500 m.
The first includes the Guapay or Rio Grande, Piray or Sara, Yapacani and Marac6, upper tributaries of the Mamore, and the San Miguel, Blanco, Baures and Paragua, tributaries of the Guapore - both draining the western and northern parts of the department.
Its Brazilian tributaries are comparatively unimportant, but from Bolivia it receives the Baures and the San Miguel, both rising in the Sierras de Chiquitos and flowing north-west across the llanos to the Guapore.
The waters find their way to the falls of the Madeira by many great rivers, the principal of which, if we enumerate them from east to west, are the Guapore or Itenez, the Baures and Blanco, the Itonama or San Miguel, the Mamore, Beni, and Mayutata or Madre de Dios, all of which are reinforced by numerous secondary but powerful affluents.
San Antonio is the first of a formidable series of cataracts and rapids, nineteen in number, which, for a river distance of 263 m., obstruct the upper course of the Madeira until the last rapid called Guajara Merim (or Small Pebble), is reached, a little below the union of the Guapore with the Mamore.
The Guapore, or Itenez, an affluent of the Mamore, is the third large river of this Bolivian drainage basin, but it rises in Brazil, on the south slopes of the Sierra dos Parecis, where it flows in a great bend to the south and then west of north to the Bolivian frontier in 14° S.
Along the Sierra Ricardo Franco to the headwaters of the Rio Verde, a tributary of the Guapore.
West of the Cordillera Oriental, where special conditions prevail, a great desert plateau stretches entirely across one corner of the republic. Apart from the Andean system there is a group of low, broken, gneiss ranges stretching along the east side of Bolivia among the upper affluents of the Mamore and Guapore, which appear to belong to the older Brazilian orographic system, from which they have been separated by the erosive action of water.
North of this elevation, which formed the southern shore of the ancient Mojos Lake, are the llanos of Guarayos and Mojos, occupying an extensive region traversed by the Guapore, San Miguel, Guapay, Mamore, Yacuma, Beni and Madre de Dios rivers and their numerous tributaries.