Fundamental to understanding the late Cenozoic evolution of the central Andes is knowledge of the age that the Puna-Altiplano plateau became a unique tectonomorphic entity within the orogen. The two attributes that define the Puna-Altiplano are (1) its average elevation of ≥3 km and (2) regions of high elevation that correspond spatially to regions with internal drainage. The chronology of plateau uplift to elevations similar to modern ones is equivocal owing to an inability to define the absolute elevation of the plateau surface through time. However, because regions of the Puna-Altiplano have nonmarine evaporites nad because such evaporites must accumulate within regions of internal drainage, the chronology of these strata elucidates when the plateau became internally drained. We show that, for the southern Puna (between lat 24° and 26°S), internal drainage was established between 14.1 and 24.2 Ma, and probably by ∼15 Ma. These results corroborate and refine other workers' inferences that the Puna-Altiplano plateau became uplifted and paleogeographically isolated from the adjacent fore arc and foreland during middle to late Miocene time.