In the Warner Mountains of California, two sympatric species of chipmunk partition their habitat primarily through the mechanism of competitive exclusion by social dominance and aggressive interactions. Forests are optimal habitats for both Neotamias amoenus and N. minimus. In this study N. amoenus actively excludes N. minimus from the forest through successful aggressive interspecific interactions, leaving N. minimus to occupy primarily the arid sagebrush scrub. Neotamias amoenus was observed to be the more social species. Neotamias minimus appears to lack the level of social structure of N. amoenus and was not observed to win any aggressive encounters. Neotamias minimus avoids interaction with N. amoenus.