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Core activity areas are the most important sites within an animal’s home range as they contain the greatest density of critical resources. Because these areas are small and intensively used, they can affect the total distances covered by animals searching for resources. Our objective was to document which habitat variables affect core area selection by female mule deer (Odocoileus hemionus) in an arid environment, and to learn which variables affect their displacement within these areas. Using radiotelemetry, from 2012 to 2014 we monitored seven female mule deer. We estimated their core areas, and with this information we identified and classified the location records as inside or outside of the core area. For each record, we also recorded variables related to time (month, time of day), environmental conditions (temperature, relative humidity), and habitat characteristics (plant association, distance to the nearest water body, slope), and used them to predict the presence of the deer in the core area using Classification and Regression Trees (CART). The same variables were analyzed using a GLM to determine which factors explain variations in displacement distance. The most important variable in core area selection was the distance to the nearest body of water (<933.71 m at the population level and <1375.11 m on average for individual deer), followed by two plant associations that included the dominant species Prosopis glandulosa, Pleuraphis mutica, Larrea tridentata, Opuntia rastrera and Fouquieria splendens in areas with a gentle slope or none. Displacement distances within the core area were shorter than those outside and were affected by time of day and month. Our results are the first to elucidate the use of the core area by female mule deer in the Chihuahuan Desert, and allow us to start understanding the connection between the habitat resources essential to the survival of these deer and their movement under desert conditions. (C) 2017 Deutsche Gesellschaft fur Saugetierkunde. Published by Elsevier GmbH. All rights reserved.