There are four extant recognized subspecies of caribou in North America, of which woodland caribou (Rangifer tarandus caribou) is the southernmost, having historically ranged throughout most of southern Canada and portions of the United States. Currently, southern mountain caribou are the only population with the potential to occur in the contiguous United States (recently occupied habitat in northeastern Washington and northern Idaho; ephemeral use by transient individuals in northwestern Montana).

Southern mountain caribou are located in steep, mountainous terrain west of the continental divide in the inland temperate rainforest ecosystem, which extends from east-central British Columbia to the inland northwestern United States and is characterized by the presence of arboreal lichens and deep winter snowpack. One feature that makes southern mountain caribou distinct is their dependence on arboreal (tree) lichens in the mid-canopy of forest habitats during the winter, while all other caribou populations depend on terrestrial lichens that grow in large mats on the ground. The U.S. Fish and Wildlife Service (Service) published a final rule in October 2019 designating the southern mountain caribou distinct population segment (DPS) of woodland caribou as endangered under the Endangered Species Act (ESA). This action amended the previously listed entity by defining the DPS, which includes the U.S.-Canada transboundary South Selkirk subpopulation (originally listed in 1983) and 16 additional subpopulations of caribou in Canada (some of which are extirpated).

The Service is working to recover the southern mountain caribou DPS population and recognizes the importance of bi-national and cross-sovereign collaboration with Canada on the potential development and implementation of a recovery plan. Southern mountain caribou are a medium-sized member of the deer family that have large hooves, broad muzzles, and distinct antlers that both sexes develop annually. The average lifespan for caribou is eight to ten years. Female caribou do not breed until they are 2.5 years old and produce only one calf per year. Only about three out of ten calves typically survive to adulthood. Individual caribou can display tremendous variability in appearance and body form even within the same population. Woodland caribou are generally described as dark brown with a white mane and some white on their sides and have a noticeable band of white hairs (called socks) along the upper edge of each hoof. They are larger and darker than both the Peary caribou (Rangifer tarandus pearyi) and the barren-ground caribou (Rangifer tarandus groenlandicus). Adult males of woodland caribou are described as having a mane of longer hairs along the bottom of the neck to the chest. During rut, the light color of the neck and mane contrasts with the darker colored body. In addition, their ears are short, broad, and not pointed. Height of the woodland caribou at the shoulder is a little over 3 to 4 feet (ft) (1.0 to 1.2 meters (m)). Females weigh about 240 to 330 pounds (lbs) (110 to 150 kilograms (kg)) and males about 350 to 460 lbs (160 to 210 kg). Both male and female caribou grow antlers, although up to half of females may lack antlers or have one antler. The antlers of woodland caribou may be denser and flatter than those of barren-ground caribou.

All caribou can withstand severe cold because their thick winter coat contains semi-hollow hair with strong insulative properties. However, woodland caribou are susceptible to overheating in summer months as their dark coat absorbs sunlight. One of the most distinctive characteristics of all subspecies of caribou is their large, rounded hooves. Their hooves reduce sinking into snow and wetlands and allow them to walk or stand on hard snowpack to reach tree lichens, and they can use their hooves as paddles while swimming. All caribou have prominent dew claws just above the hoof.