The three ranges of the Colombian Andes have distinct geologic characteristics. The Central Cordillera is an uplifted zone of crystalline rocks, mostly pre-Mesozoic in age. The Western and Eastern Cordilleras are composed, respectively, of eugeosynclinal and miogeosynclinal rocks, deposited during the Mesozoic, and deformed in Late Cretaceous and Tertiary time. Although the Andes as a topographic feature end at 8° N. lat, pre-Tertiary rocks are found to the northeast in the Santa Marta-Perijá region and the Guajira Peninsula. Recent work has shown that a three-fold structure, similar to that of the Andes, characterizes these regions as well, suggesting that the Andean mobile belt was more extensive than the present day topographic Andes.