San Bernardino Ranch is a site in the southern San Bernardino Valley in the region of the San Bernardino National Wildlife Refuge in extreme southeast Cochise County, Arizona that is significant for its association with the beginning of cattle ranching in southern Arizona and northern Mexico. The ranchland and valley are part of the headwater region of the Yaqui River. In 1911, during the conflict known as the Border War, a United States Army camp was established at the ranch and was called Camp San Bernardino Ranch, or the Slaughter Ranch Outpost.