This study of mammals of the Bull Run Planning Unit has a dual character. First, mammals of special scientific or natural history interest such as threatened or endangered species were sought. This was in conjunction with a Mt. Hood Bull Run Planning Unit. Second, a zoogeographical study of mammals of the Bull Run was performed. Abundance and distributional data was recorded for each species observed. This data was related to availability to moisture as indicated by plant associations trapped. Difference in habitat utilization along a moisture gradient was investigated as a possible coexistence mechanism for sympatric small mammals in the Bull Run Planning Unit.