The regional geology of Colombia consists of a composite Palaeozoic to Cenozoic sedimentary basin overlying Precambrian shield rocks, which are exposed in the Eastern Cordillera, Magdalena Valley and at least part of the extensive Llanos Plains. A Palaeozoic metamorphic schist belt with abundant post-metamorphic igneous rocks comprises the Central Cordillera. A Mesozoic volcanic suite extends from the western flank of the Central Cordillera and accounts for the bulk of the Western Cordillera. A Cenozoic sedimentary sequence, probably overlying a Late Cretaceous oceanic crust and fore-arc complex, forms the Pacific Coastal Plain. The continental edge of central and southern Colombia is interpreted as a composite margin made up of successively-accreted oceanic island arc related sequences of Palaeozoic, Early Mesozoic and Late Cretaceous ages. The present-day cycle, which began in the Miocene, is not associated with island arc volcanism.