It was during the Cretaceous period that the Andes began to take their present form , by the uplifting , faulting and folding of sedimentary and metamorphic rock of the ancient cratons to the east . It was during the Cretaceous Period that the Andes began to take its present form , by the uplifting , faulting and folding of sedimentary and metamorphic rocks of the ancient cratons to the east .