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Fossil packrat (Neotoma) middens provide an important source of paleoecologic data in the arid West. This study describes and tests a predictive GIS model that uses the weights-of-evidence method for determining areas with a high probability of containing fossil middens in central Nevada. Model variables included geology, elevation, and aspect. Geology was found to be the most important variable tested. We produced a map of 4 probability classes validated by field-checking 21 randomly selected 1-km(2) sites throughout the study area. Our high-probability category reduced the search area to only 3.5% of the total study area. Fossil middens were found on 8 of 21 sites (38%). Geologic types that contained middens were granite, limestone, and volcanic tuff. A 2nd run of the model with the new midden localities added to the training set helped narrow the total search area even further. This analysis demonstrates that the weights-of-evidence method provides an effective tool both for guiding research design and for helping locate midden sites within specific localities. With only a limited training dataset and a simple set of mapped criteria, a model can be constructed that is both predictive and testable. We intend to continue development of the model to improve our ability to predict the location of Pleistocene-age middens and to locate middens on low-probability sites. This method, designed for mineral exploration, has wide potential application within the natural sciences.