Andean natural region
The Andes mountains form the most populated region of Colombia and contain the majority of the country's urban centers. They were also the location of the most significant pre-Columbian indigenous settlements. Beyond the Colombian Massif in the south-western departments of Cauca and Nariño, the Colombian Andes divide into three branches known as "cordilleras" (from the Spanish for "mountain range"): the West Andes run adjacent to the Pacific coast and is home to the city of Cali. The Central Andes run up the center of the country between the Cauca and Magdalena river valleys (to the west and east respectively) and includes the cities of Medellín, Manizales and Pereira. The East Andes extend northeast towards the Guajira Peninsula, and includes the cities of Bogotá, Bucaramanga and Cúcuta.
Eastern Frontal Fault System
The long Afiladores Fault runs through a geographic area of the Andes where the Central and Eastern Ranges merge into a single range known as the "Cordillera Centro-Oriental de Colombia". The fault offsets Precambrian gneisses and schists, metamorphic Paleozoic rocks, Mesozoic granitic rocks, and Tertiary sedimentary deposits. The fault extends south into the Republic of Ecuador and probably connects with the Chingual Fault.