The geological process that lead to the creation of the Andes began when the Andean Geosyncline (a large linear trough along the margin of a continent) extended along what is now the entire western and part of the northern coast of the continent. There are indications that movements of the earth's crust leading to the rise of the Andes were active during the early part of the Mesozaic era. It is assumed that the movements started even earlier; however, they ewre most forcefull during the Middle and Upper Tertiary periods, when the uplifted process of the Andes reached its peak, although it actually continued into the Pleitocene epoch. The sick sediments of the Andean Geosycline when uplifted by movements of the earth's crust were intensely folded and faulted, thus forming the ranges of the Andes.
This mountain-building process, accompanied by large introsions of igeneous rock and by much volcanic activity, formed some of the earth's thickest formations of volcanic materials (in Peru and Chile). The Andes asumed most of their present form toward the end of the Tertairy period, when they were already the continuous formidable wall along the entire western fringe of the continent.
One of the last major events affecting the continental surface was the extensive glaciation during the Pleistocene epoch, when glaciers covered much of the Andes from the extreme south to Ecuador