Descripción: The main geomorphological features of a sector of Sierras Australes (Buenos Aires province) are described. Fluvial processes (mainly formation of alluvial fans), mass wasting (creep and debrisflows) and wind action (deflation and acumulation) are responsible for the configuration of the landscape of the region. At least three alluvial acumulation events and equal number of loess deposition were recognized for the late Cenozoic times. The development of a planation surface of pre-Cenozoic age, and developed in Palaeozoic rocks, is postulated. This surface and the piedmont acumulations were affected by erosional events related to tectonic, climatic and eustatic events (Andean Orogeny and glaciations). Six major geomorphological units are recognized. Today the pedogenetic processes predominate whereas morphodynamic ones are low.

Descripción: Although the depositational environment assigned by Darwin to the large erratic blocks and gravels in the Río Santa Cruz valley has been reinterpreted, his geomorphological and stratigraphic observations are still in force. The large erratic blocks he described as crowning the Condor Cliff terrace and spread at the bottom of the valley just east of this locality (Sites 2 and 3), are now interpreted as indicators of the maximum glacial expansion in Patagonia. Similar blocks, though of a different lithology, accumulated over a lower terrace located up-valley (Site 4), are now linked to moraines and glacifluvial terraces of the Penultimate Glaciation. Finally, in addition to the erratic block discovered by Darwin in the lower Río Santa Cruz valley (Site 1), there are others - recently discovered - which probably account for a catastrophic event ascribed to a big glacier-lake outburst during the last interglacial.