A rather extensive system of burrows from a few inches to a foot or two beneath the surface, and piles of freshly excavated earth are also evidence of the workings of this animal. The typical site chosen for development is ordinarily moist, probably not because the aplodontia is a lover of water, but because it is in such locations that suitable food plants abound. The burrows are constructed as exploratory routes in foraging, with what appears to be a main gallery intersected by a number of branches. These burrows emerge in thick cover or under logs, with the openings often connected by well-beaten runways where the overhanging plants and shrubs afford concealment. Such extensive workings were found along the Wonderland Trail in Stevens Canyon in 1947 and 1948. The first indication of the activity of mountain beavers was the undermined condition of the trail in several places, where burrows crossed under the path and caved beneath the feet. Upon investigation many freshly cut stems of bracken were discovered, and several piles of recently excavated earth, in some instances sufficient to fill a bushel basket. This site was typical: excellent cover; several small streams; and deep, very moist soil with few rocks and an abundance of food plants. Natural enemies of aplodontia undoubtedly include nearly all of the predatory animals, particularly the skunks and weasels, which can invade the dens without difficulty. YELLOW-HAIRED PORCUPINE _Erethizon dorsatum epixanthum_ Brandt The porcupine is a large, short-legged rodent (total length about 30 inches), clumsy and awkward appearing, slow-moving, bearing long, sharp quills or spines over most of the body and on the short, club-like tail. The pelage is composed of soft, brownish-black or black hair. Intermixed with the pelage, and extending beyond it are the quills and long, stiff, shiny, yellowish-tipped hairs, which give a yellow tinge to the underlying dark color. It is impossible to confuse this unique animal with any other found in the park. [Illustration: The almost impregnable armor of the porcupine is adequate protection against most predators.] _Specimens in park collection:_ RNP-42, RNP-47, and a mounted specimen, Longmire Museum, Park Headquarters. The several species of porcupine are widely distributed, ranging in the timbered regions of the northeastern states, the Rocky Mountains from near the Mexican boundary northward, and from northern California into Canada and Alaska. Formerly rare, the first actual record was of a single individual in Paradise Valley in 1933, porcupines are increasing throughout the forested areas of the park, although the animal is still considered uncommon.