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The Diamond Valley Lake local fauna from southwestern Riverside County, California is characterized by a classic suite of well-preserved late Pleistocene (Rancholabrean NALMA) vertebrates, including over 100,000 identifiable fossils representing more than 105 vertebrate, invertebrate and plant taxa from 2646 localities. The fauna is the largest open-environment, non-asphaltic late Pleistocene assemblage known from the American southwest. Located within the northern Peninsular Range physiographic province of southern California, the Diamond and Domenigoni Valleys contain bedded silts and clays intercalated with coarse-grained channel fill representing a braided stream environment. These fluvial sediments, yielding AMS dates from similar to 19 ka to similar to 13 ka, unconformably truncate older silts, clays and an organic black clay at depth. The clay is lacustrine in origin, with AMS dates from similar to 46 ka to similar to 41 ka. Numerous diagnostic vertebrate remains occur in both of these sediment packages. The Diamond Valley Lake local fauna constitutes a valuable source of new data on the relative density and diversity of late Pleistocene species from a geographic area where such data are largely absent. The assemblage differs dramatically in preservation and composition from other late Pleistocene coastal and desert localities in southern California. (C) 2009 Elsevier Ltd and INQUA. All rights reserved.