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Betancourt et al.(1) recently challenged the prevailing view that the central Andes were a generally arid zone during the mid-Holocene (2–7). This debate has wide implications regarding monsoonal and westerly paleocirculation in this area. The archives used by Betancourt et al.(1) are organic and inorganic alluvial deposits that formed in steep valleys along the western slope of the Central Andes between 7 and 3 14C kiloyears before present (ky BP). Consensus exists about the chronology, the calm wetland depositional environment, and the existence of higher groundwater tables at the deposit locations during that time. Disagreement exists about the interpretation of the high water tables. Whereas Betancourt et al.(1) interpret the Tulán and Puripica profiles as a result of wetter conditions and high regional groundwater tables, our studies (2, 3) have concluded that generally drier conditions prevailed. We argue that wet conditions result in higher river discharge and erosion, whereas accumulation of fine materials in a steep valley requires overall decreased river flow and a lowenergy environment. With dry conditions, finegrained but permeable sediments that accumulate in the valley bottom may form local aquifers and raise the groundwater table, despite a larger cross section in the valley and reduced discharge overall. Modern analogs show that groundwater tables in such wetlands are often self-sustained, very local, and disconnected from their surroundings, and are thus difficult to interpret in terms of climate conditions. Today, the rivers in both the Tulán and Puripica valleys are erosive and have dissected the mid-Holocene sediments …