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In an effort to address bison movement outside Yellowstone National Park (YNP) the Interagency Bison Management Program (IBMP) is addressing bison population size and its distribution. One of the alternatives is the creation of special management areas outside YNP where bison would be able to range freely across the landscape. The Gardiner Basin is a proposed management area. However, US Forest Service biologists are concerned about the impact bison may have on rangeland and watershed condition, especially if grazing becomes more common during summer months. We investigated which areas within the Gardiner Basin are most likely to be grazed by an expanding herd. Initial efforts to identify characteristics of bison summer habitat area based on information contained in the "Predicted Bison Habitat in Gardiner Basin Map" (PHGB), part of the IBMP plan, indicated potential errors in the estimation of the amount of available habitat, so we developed a similar GIS-based model to refine area estimates within both YNP and the Gardiner Basin. Our model added landform slope to the other habitat characteristics correlated to bison use of summer habitat within YNP. The outcome was revealing 98% of the summer habitat inside YNP area fall within the class of gently to moderately steep slopes (<35%), while the PHGB shows only 67.8% within the same class (<35%); 2) our model predicts only 7,950.4 acres what is much smaller than the 25,533 acres in the PHGB. Based on these outcomes it became clear that available bison habitat in the Gardiner Basin is not sufficient to sustain large herds for extended periods, therefore long term summer use by bison must be closely monitored to avoid overgrazing, changes to the grassland communities, loss of dominant grass species and corresponding declines in watershed condition.