The mountain pine beetle, Dendroctonus ponderosas Hopk., showed a significant advance northward from the 1970 infestation boundary, encompassing almost one-third of the total Park acreage. A fall survey conducted in the Park showed an average of 71.1 trees per acre with red or fading foliage from previous year's attacks and 35.8 actively infested trees per acre attacked in 1971. Stocking levels were reduced from 276.2 trees per acre to 169.2 trees per acre.