The northeastern flank of the Cordillera Real is known as the Yungas, from the Aymara word meaning "warm valleys." The steep, almost inaccessible slopes and peaks of this mainly semitropical valley area northeast of La Paz offer some of the most spectacular scenery in Bolivia. Rainfall is heavy, and lush vegetation clings to the sides of narrow river valleys. The land is among the most fertile in Bolivia, but poor transportation has hindered its agricultural development. The government attempted to build a railroad through the Yungas in 1917 to connect La Paz with the eastern lowlands. The railroad was abandoned, however, after completion of only 150 kilometers.

The eastern slopes of the Cordillera Central descend gradually in a series of complex north-south ranges and hills. Rivers, draining to the east, have cut long narrow valleys; these valleys and the basins between the ranges are favorable areas for crops and settlement. Rich alluvial soils fill the low areas, but erosion has followed the removal of vegetation in some places. The valley floors range from 2,000 to 3,000 meters above sea level, and this lower elevation means milder temperatures than those of the Altiplano. Two of Bolivia's most important cities, Sucre and Cochabamba, are located in basins in this vast region.

The eastern lowlands include all of Bolivia north and east of the Andes. Although comprising over two-thirds of the national territory, the region is sparsely populated and, until recently, has played a minor role in the economy.

Differences in topography and climate separate the lowlands into three areas. The flat northern area, made up of Beni and Pando departments and the northern part of Cochabamba Department, consists of tropical rainforest. Because much of the topsoil is underlain by clay hardpan, drainage is poor, and heavy rainfall periodically converts vast parts of the region to swamp. The central area, comprising the northern half of Santa Cruz Department, has gently rolling hills and a drier climate than the north. Forests alternate with savanna, and much of the land has been cleared for cultivation. Santa Cruz, the largest city in the lowlands, is located here, as are most of Bolivia's petroleum and natural gas reserves. The southeastern part of the lowlands is a continuation of the Chaco of Paraguay. Virtually rainless for nine months of the year, this area becomes a swamp for the three months of heavy rains. The extreme variation in rainfall supports only thorny scrub vegetation and cattle grazing, although recent discoveries of natural gas and petroleum near the foothills of the Andes have attracted some settlers to the region.

Most of Bolivia's important rivers are found in the water-rich northern parts of the lowlands, particularly in the Alto Beni (Upper Beni), where the land is suitable for crops such as coffee and cacao. The northern lowlands are drained by wide, slow-moving rivers, the three largest of which--the Mamoré, Beni, and Madre de Dios—all flow northward into the Madeira River in Brazil and eventually into the Amazon. Riverboats along the Beni and the Mamoré carry both passenger and freight traffic; rapids on the Madeira prevent river traffic farther into Brazil. Near the Paraguayan border, shallow sandy streams carry the seasonal runoff into the Pilcomayo or Paraguay rivers.