Interandean Valles

Dry valleys in the central Andes of Peru, Bolivia, and Argentina, known as "valles", are marked by a rain shadow effect of the surrounding mountains, and thus rainfall is limited, and mostly falls in a brief rainy season. The interandean valles comprise most of the mid-elevation areas of the "sierra" of Peru, "los valles" of Bolivia and the "cuyo" region of Argentina

The rugged topography of the Central Andes creates the warm, dry valleys that typifies the valles. Generally lying between 1,200 and 3,500 meters above sea level (m.a.s.l.) or 4,000 - 13,000 feet above sea level. Much of the area features steep hillsides and deep canyons, including the world's deepest canyon, the Colca Canyon.

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 south and west, are the harsh, frigid deserts, salt flats and alpine grasslands of the altiplano. To the north and east are the lush, wet, dense cloud forests or "yungas" of the front-range, downslope, and foothills of the Andes. Higher ridges, peaks, and plateaus, dominated by high-elevation alpine puna grasslands, Polylepis woodlands, or snow-capped peaks separate the valles from both of these ecoregions.

The valles are marked by mild, wet summers, and cool dry winters. Timing of the seasons varies according to latitude. Generally, most rainfall occurs during summer ("el verano") from December through March. These rainy seasons can in fact be cool and damp for extended periods, though it can be quite warm during dry spells. Dry seasons are substantially colder; these dry winters ("el invierno") last from April through August. Any precipitation that does occur often falls as snow at higher elevations, though snow is extremely rare below 10,000 feet above sea level (3400m.a.s.l.). The warmest times of the year are the transitional months of Sep.-Nov.

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