The National Institute for Occupational Safety and Health (NIOSH) received a request for a health hazard evaluation (HHE) at a base camp supporting the Siskiyou and Ukonom fires in the Klamath National Forest, California. Federal agency managers submitted the request due to concerns about carbon monoxide (CO) exposures of personnel working at base camps who support firefighters during wildland fire suppression activities. NIOSH findings and recommendations are detailed.