New 10Be surface exposure ages from adjacent valleys in the upper Arkansas River basin, Colorado (United States), indicate that Pinedale maxima culminated asynchronously at 22.4 ± 1.4, 19.2 ± 0.2, 17.8 ± 0.6, and 15.8 ± 0.4 ka, but that deglaciation initiated synchronously between ca. 16 and 15 ka. These data are combined with published glacial chronologies across the western United States, and indicate that although the ages of Pinedale terminal moraines vary within individual ranges as well as regionally, most western United States glaciers remained near their Pinedale termini until ca. 16 ka, at which time widespread deglaciation commenced. We hypothesize that the near-synchronous demise of glaciers across the western U.S. between ca. 15 and ca. 13 ka was driven by the first major Northern Hemisphere warming following the Last Glacial Maximum, but that some differences in Pinedale culmination ages can be explained by nonclimatic factors intrinsic to individual valleys. These results suggest the need for caution in focusing exclusively on climate forcings to explain apparent asynchrony in Pinedale maxima.

You do not currently have access to this article.