A GIS model to predict the location of fossil packrat (Neotoma) middens incentral Nevada

Fossil packrat (Neotoma) middens provide an important source of paleoecolog ic data in the arid West. This study describes and tests a predictive GIS m odel that uses the weights-of-evidence method for determining areas with a high probability of containing fossil middens in central Nevada. Model vari ables 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 t he study area. Our high-probability category reduced the search area to onl y 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 v olcanic tuff. A 2nd run of the model with the new midden localities added t o the training set helped narrow the total search area even further. This a nalysis demonstrates that the weights-of-evidence method provides an effect ive tool both for guiding research design and for helping locate midden sit es within specific localities. With only a limited training dataset and a s imple set of mapped criteria, a model can be constructed that is both predi ctive and testable. We intend to continue development of the model to impro ve our ability to predict the location of Pleistocene-age middens and to lo cate middens on low-probability sites. This method, designed for mineral ex ploration, has wide potential application within the natural sciences.