| Summary: | This contribution reports sedimentological and paleobiological evidences fromthe upper Cenozoic outcrops in the south of Alto Pencoso (Occidental Ranges). They belongto: the Norwest Beazley, Desaguadero’s river valley and Salina del Bebedero basins. LasMulitas Formation crops out in Beazley (fluvial, Pliocene) and is characterized by the fossilsremains of Notoungulata y Dasypodidae, and is covered by Toro Muerto (alluvial, middle Pleis-tocene), Alto Grande (fluvial, late Pleistocene) and Barranquita (eolian, late Pleistocene) forma-tions. The latter with paleontological records assigned to Glyptodontidae and Macraucheniidae.At the river-bed of Jarilla stream crops out the Arco del Desaguadero Formation (fluvial, latePleistocene), where Chara contraria, C. cf. papillosa and C. hornemannii girogonites were rec-ognized. Likewise, in the foreshore deposits from Salina del Bebedero (fluvio-lacustrine, latePleistocene) Chilina mendozana, Heleobia parchappii, Biomphalaria peregrina and Sphaeriidaeshells were identified. The cretacic sedimentary rocks from the Occidental ranges were themain sedimentary source area during the Neogene, filling the tectonic depressions, with allu-vial plains and fluvial systems deposits that characterize the Beazley’s basin. Finally, the globalclimatic conditions related to the Last Glaciation in Los Andes range are represented by thefluvial sandy deposits of the Desaguadero’s river basin, the foreshore gravel sandy and cal-careous deposits from the Bebedero lake and the eolian sand and silt deposits that partiallycovers the surrounding plain Se presentan evidencias sedimentológicas y paleobiológicas del Cenozoico superioraflorantes al sur del Alto Pencoso (Serranías Occidentales), correspondientes a las cuencas:noroeste de Beazley, valle del río Desaguadero y Salina del Bebedero. En Beazley aflora laFormación Las Mulitas (fluvial, Plioceno), caracterizada por los restos fósiles de Notoungulatay Dasypodidae y cubierta por las formaciones Toro Muerto (aluvial, Pleistoceno medio), ...
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