Most of the major cities and towns of the valles are found in broader, open valleys with expansive flat land created by ancient lakes or floodplains that is more amenable to agriculture than the highly erodible slopes.
To the north and east are the lush, wet, dense cloud forests or "yungas" of the front-range, downslope, and foothills of the Andes.
Most of the native vegetation has been replaced by agriculture or invasive exotics that are still widely used, such as Eucalyptus spp., Phragmites spp., Pinus radiata Notable endemic plants include Schinus molle and various cactus species, though some of those may be non-native as well.
A longer frost-free period, and a generally warmer climate makes the valles more amenable than the higher, colder altiplano for many crops.
Further, many valles feature broad plains created by river floodplains or ancient lake beds, that serve better than the steeper more formidable terrain of the yungas.