The Andes—South America's great mountain chain—occupy most of western Colombia. They consist of three distinct ranges, called cordilleras. From west to east they are the Cordillera Occidental, Cordillera Central, and Cordillera Oriental. They begin in a mountainous knot near the Ecuadorian border and extend north- and north-eastwards as far as Venezuela. All three ranges attain elevations of more than 13,000 feet (3,960 m); the two easterly ranges reach heights exceeding 18,000 feet (5,490 m). The highest of Colombia's Andean peaks is snowcapped Nevado del Huila (18,865 feet [5,750 m]) in the central range. Here too are most of Colombia's volcanoes.
Lowlands occupy the area north of the Andes as far as the Caribbean Sea. In many places, especially along the major rivers, the land is often marshy. At the coast, near the Venezuelan border, stands the enormous mountain block known as Sierra Nevada de Santa Marta. It rises abruptly to an elevation of 18,947 feet (5,775 m) at Cristóbal Colón Peak, the loftiest in Colombia.
Along the Pacific coast are both lowlands and mountains. The lowlands—wide, marshy, and sparsely inhabited—occupy the southern half of the coast. The north is dominated by the Serranía de Baudó, a low but rugged mountain range with peaks of almost 6,000 feet (1,830 m).
The region east of the Andes accounts for some three-fifths of Colombia's total area but most of the region is undeveloped and sparsely settled. The northern part is spanned by grassy plains, called llanos. The southern portion is lowland covered primarily by dense rain forests of the Amazon basin.
The 1,000-mile (1,600-km)Magdalena and its largest tributary, the Cauca, are Colombia's chief rivers. Both begin in the Andes of southern Colombia and drain northward to the Caribbean. For centuries they provided the principal avenues into the mountainous interior. Virtually all the other rivers of the Andean and coastal regions are short and relatively unimportant. In the eastern region many large rivers flow eastward as part of either the Orinoco or the Amazon system. Among them are the Putumayo, Caquetá, Guaviare, and Meta rivers. There are no large lakes in Colombia. Small ones, however, dot the Caribbean lowlands, especially the areas along or near the rivers.
Colombia has an equatorial location, but its climate varies enormously, primarily because of differences in elevation and location. The coastal areas are hot, with temperatures ranging from 75° to 100° F. (24°-38° C.), while cooler temperatures are found at higher elevations. At any one location, however, there is little seasonal variation in temperature. The greatest change in temperature occurs from night to day. Some areas in the high mountains are permanently covered by snow.
Precipitation also varies greatly from place to place. Most of Colombia, including the Andean region, receives 40 to 80 inches (1,015 to 2,030 mm) a year. The region in the Amazon basin gets considerably more. As much as 400 inches (10,160 mm) a year falls in the Pacific coastal area, including the Atrato river valleys—one of the rainiest regions in the world. Parts of the Caribbean coast, particularly the Guajira Peninsula, are semiarid, with less than 25 inches (635 mm) annually. Some areas are rainy all year; others have either one or two distinct rainy seasons, followed by dry periods.
Because of the wide climatic range in Colombia, vegetation is extremely diverse. There are tropical rain forests and grassy savannas in the tropical lowlands, while mossy tundra vegetation is typical in the bleak, high mountains. At middle elevations in the Andes, where the climate is subtropical or temperate, there are woodlands, and forests resembling those in the United States. More than 7,000 species of plants are found in Colombia.
Wild animals still abound, especially in the sparsely populated parts of the country. Large mammals include jaguars, pumas, bears, and tapirs. There are also peccaries, deer, sloths, anteaters, opossums, monkeys, and many rodents. Reptiles, such as caimans, turtles, lizards, and snakes, are abundant in the lowland areas. Colombia's bird life is exceptionally rich.