Original: 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.
Simplified: 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.