Haystack Cave, Gunnison County, Colorado, has provided the first collection of vertebrate remains from the Pleistocene (Rancholabrean) of western Colorado. Two carbon 14 analyses of bone apatite have produced dates of 14,935 ± 610 and 12,154 ± 1,700 years B.P. for this assemblage. This fauna, in conjunction with pollen studies, indicates the Gunnison Basin was largely unforested grassland/sagebrush shrubland in the lower basin, with open coniferous forests extending to the edges of the basin, during the late Pleistocene. The fauna also extends the known Pleistocene range of Lagurus curtatus, Phenacomys intermedius, Spilogale putorius, and Acinonyx trumani.