The Andes form the world's longest exposed mountain range. They lie as a continuous chain of highland along the western coast of South America. The range is over 7,000 km (4,400 miles) long, 200-700 km (300 miles) wide (widest between 18° to 20°S latitude), and of an average height of about 4,000 m (13,000 ft).
The Andean range is composed principally of two great ranges, the Cordillera Oriental and the Cordillera Occidental, often separated by a deep intermediate depression, in which arise other chains of minor importance, the chief of which is Chile's Cordillera de la Costa. Other small chains arise on the sides of the great chains. The Cordillera de la Costa starts from the southern extremity of the continent and runs in a northerly direction, parallel with the coast, being broken up at its beginning into a number of islands and afterwards forming the western boundary of the great central valley of Chile. To the north this coastal chain continues in small ridges or isolated hills along the Pacific Ocean as far as Venezuela, always leaving the same valley more or less visible to the west of the Western Great Chain. The mountains extend over seven countries: Argentina, Bolivia, Chile, Colombia, Ecuador, Peru and Venezuela, some of which are known as Andean States.
The Andes mountain range is the highest mountain range outside Asia. The highest peak, Aconcagua, rises to 6,962 m (22,841 ft) above sea level. The summit of Mount Chimborazo in the Ecuadorean Andes is the point on the Earth's surface most distant from its center, because of the equatorial bulge.
There are many theories about the etymology of the name Andes. Some believe Andes derives from the Quechua word anti, which means "high crest". Some believe Andes derives from one of the four regions of the Inca empire, or Anti(s). Some believe Andes derives from the Spanish word andén which means terrace in reference to the cultivation terraces used by the Incas and other related peoples. Some believe Andes is Spanish shorthand for "Andenes" or "Andenerías".
The Andes fundamentally are the result of plate tectonics processes, caused by the subduction of the Nazca plate beneath the South American plate. The boundary between the two plates is marked by the Peru-Chile oceanic trench.
The formation of the Andes began in the Jurassic Period. It was during the Cretaceous Period that the Andes began to take their present form, by the uplifting, faulting and folding of sedimentary and metamorphic rocks of the ancient cratons to the east. Tectonic forces along the subduction zone along the entire west coast of South America where the Nazca Plate and a part of the Antarctic Plate are sliding beneath the South American Plate continue to produce an ongoing orogenic event resulting in minor to major earthquakes and volcanic eruptions to this day. In the extreme south a major transform fault separates Tierra del Fuego from the small Scotia Plate. Across the wide Drake Passage lie the mountains of the Antarctic Peninsula south of the Scotia Plate which appear to be a continuation of the Andes chain.
The Andes range has many active volcanoes, including Cotopaxi, one of the highest active volcanoes in the world.
The Andes is rich in fauna and flora. About 30,000 species of vascular plants live in the Andes with roughly half being endemic to the region, surpassing the diversity of any other hotspot. With almost 1000 species, of which roughly 2/3 are endemic to the region, the Andes is the most important region in the world for amphibians. For other major groups the numbers are equally impressive: Almost 600 species of mammals (13% endemic), more than 1,700 species of birds (c. 1/3 endemic), more than 600 species of reptiles (c. 45% endemic), and almost 400 species of fishes (c. 1/3 endemic).
Rainforests used to encircle much of the northern Andes but are now greatly diminished, especially in the Chocó and inter-Andean valleys of Colombia. The small tree Cinchona pubescens, a source of quinine which is used to treat malaria, is found widely in the Andes as far south as Bolivia. Other important crops that originated from the Andes are tobacco and potatoes. The high-altitude Polylepis forests and woodlands are found in the Andean areas of Colombia, Ecuador, Peru, Bolivia and Chile. These trees, by locals referred to as Queñua, Yagual and other names, can be found at altitudes of above sea level. It remains unclear if the patchy distribution of these forests and woodlands is natural, or the result of clearance which started during the Incan period. Regardless, in modern times the clearance has accelerated, and the trees are now considered to be highly endangered, with some believing that as little as 10% of the original woodland remains. A number of species such as the Royal Cinclodes and White-browed Tit-spinetail are associated with Polylepis, and consequently also threatened.
The Vicuña and Guanaco can be found living in the Altiplano, while the closely related domesticated Llama and Alpaca are widely kept by locals as pack animals and for their meat and wool. The nocturnal chinchillas, two threatened members of the rodent order, inhabits the Andes' alpine regions. The Andean Condor, the largest bird of its kind in the Western Hemisphere, occurs throughout a large part of the Andes, but generally in very low densities. Other animals found in the relatively open habitats of the high Andes include the huemul, cougar, foxes in the genus Pseudalopex, and, for birds, certain species of Tinamous (notably members of the genus Nothoprocta), Andean Goose, Giant Coot, flamingos (mainly associated with hypersaline lakes), Lesser Rhea, Andean Flicker, Diademed Sandpiper-Plover, miners, sierra-finches and Diuca-finches. The massive Lake Titicaca hosts several endemics, among them the highly endangered Titicaca Flightless Grebe and Titicaca Water Frog. A few species of hummingbirds, notably some hillstars, can be seen at altitudes above , but far higher diversities can be found at lower altitudes, especially in the humid Andean forests ("cloud forests") growing on slopes in Colombia, Ecuador, Peru, Bolivia and far north-western Argentina. These forest-types, which includes the Yungas and parts of the Chocó, are very rich in flora and fauna, although few large mammals exists, exceptions being the threatened Mountain Tapir, Spectacled Bear and Yellow-tailed Woolly Monkey. Birds of humid Andean forests include Mountain-Toucans, Quetzals and the Andean Cock-of-the-rock, while mixed species flocks dominated by tanagers and Furnariids commonly are seen - in contrast to several vocal, but typically cryptic, species of wrens, tapaculos and antpittas. As a direct opposite of the humid Andean slopes are the relatively dry Andean slopes in most of western Peru, Chile and Argentina. Along with several Interandean Valles, they are typically dominated by deciduous woodland, shrub and/or xeric vegetation, reaching the extreme in the slopes near the virtually lifeless Atacama Desert.
The Inca Empire developed in the northern Andes during the 1400s. The Incas formed this civilization through imperialistic militarism as well as careful and meticulous governmental management. The government sponsored the construction of aqueducts and roads, some of which, like those created by the Romans a thousand years before them, are still in existence today. The aqueducts turned the previously scattered Incan tribe into the agricultural and eventually militaristic masters of the region.
Devastated by deadly European diseases to which they had no immunity, and by a terrible civil war, in 1532 the Incas were defeated by an alliance composed by tens of thousands allies from nations they had subjugated (Huancas, Chachapoyas, Cañaris, etc) and a small army of 180 Spaniards led by Pizarro. One of the few Inca cities the Spanish never found in their conquest was Machu Picchu, which lay hidden on a peak on the edge of the Andes where they descend to the Amazon. The main surviving languages of the Andean peoples are those of the Quechua and Aymara language families.