Geologically Colombia is formed by two great territorial zones, one submerged in the Pacific Ocean and the Caribbean sea covering a total area of 828,660 km² and the second is the emerged land which is formed by the Andes mountain range and the Llanos plains that are shared with Venezuela and cover an area of some 1'143,748 km². Colombian surface features form complicated land patterns. The western third of the country is the most complex, starting at the shore of the Pacific Ocean in the west and moving eastward at a latitude of 5 degrees north, a diverse sequence of features is encountered; In the extreme west are the very narrow and discontinuous Pacific coastal lowlands, which are backed by the Serranía de Baudó, one of the lowest and narrowest of Colombia's mountain ranges. Next is the broad region of the Río Atrato/Río San Juan lowland.
The western mountain range, the Cordillera Occidental, is a moderately high range with peaks reaching up to about 13,000 ft (4,000 m). The Cauca River Valley, an important agricultural region with several large cities on its borders, separates the Cordillera Occidental from the massive Cordillera Central. Several snow-clad volcanoes in the Cordillera Central have summits that rise above 18,000 ft (5,500 m). The valley of the Magdalena River, a major transportation artery, separates the Cordillera Central from the main eastern range, the Cordillera Oriental. The peaks of the Cordillera Oriental are moderately high. This range differs from Colombia's other mountain ranges in that it contains several large basins. To the east of the country, the sparsely populated, flat to gently rolling eastern lowlands called Llanos orientales part of the Orinoco river basin and the jungle covered Amazon region part of the Amazon river basin (both basins called eastern plains) cover almost 60 percent of the country's total land area. The northern plains are mostly part of the Caribbean natural region which includes the Sierra Nevada de Santa Marta mountain range, the highest coastal mountain in the world, and the Guajira Peninsula which is mostly arid with another separate formation from the Andes mountain range, the Serranía de Macuira to form the Guajira-Barranquilla xeric scrub.