Paleogene clastic sedimentary rocks in the Puna plateau of northwestern Argentina contain valuable information about the timing and location of early mountain building in the central Andes. Because these rocks generally lack tuffaceous facies, only paleontological ages have been available. We present U-Pb ages from detrital zircons in the conglomeratic Eocene Geste Formation of the central Puna plateau. The zircon ages indicate that the Geste Formation was derived from nearby high-relief ranges composed of Ordovician metasedimentary rocks. A small population of ca. 37–35 Ma grains also confirms the late Eocene stratigraphic age of the Geste Formation, and suggests that U-Pb detrital zircon ages may provide a new tool for determining depositional ages and provenance of widespread Paleogene deposits in the central Andes.