McCaslin Mountain is a four-mile long quartzite hill with a local relief of more 200 feet. The hill's shallow soils, numerous rock outcrops, and shaded quartzite cliffs are unusual in this region where most such features are buried under glacial till. Scattered within the hill complex are bedrock glades, balds, perched wetlands, and vernal ponds on the slopes and in the saddles between the rocky knolls. The site supports a high quality northern mesic forest of red oak with beech, sugar maple, basswood, aspen, and some white oak. Many of the largest canopy trees occur in ravines, on slopes, or on the saddles between the knolls of the ridge complex. Older stands of hardwoods located within the range of beech are scarce in Wisconsin. Southeast of the hill, the area is flatter but rocky with several intermittent streams and poorly drained soils that support stands of hemlock, yellow birch, black ash, and balsam fir. Composition of the groundlayer is varied and diverse. The shrub layer is dominated by beaked hazelnut and maple-leaved viburnum while Pennsylvania sedge, big-leaved aster, and wild sarsaparilla dominated the groundlayer. Other plants include meadow-rue, white baneberry, American starflower, rosy twisted-stalk, beech-drops, and several species of club-moss. McCaslin Mountain is important habitat for a rare bird that requires large stands of tall trees for nesting. Other breeding birds include wood thrush, yellow-billed cuckoo, great-crested flycatcher, least flycatcher, yellow-throated vireo, ovenbird, and hermit thrush. McCaslin Mountain is owned by the U.S. Forest Service and was designated a State Natural Area in 1996. This site is also recognized by the Forest Service as an established Research Natural Area.