We explored topographic patterns in forest composition and diversity on unlogged slopes along ≈3 km of Zoar Valley Canyon, a 150-m deep east—west gorge in western New York. We catalogued all trees along 3 north- and 3 south-facing 20-m wide vertical belt transects on slopes of up to 50°. North-facing exposures were the more mesic, and were dominated by Acer saccharum (Sugar Maple) on the lower slopes and by Tsuga canadensis (Eastern Hemlock) on the upper slopes. South-facing slopes were more xeric and displayed distinct upper- and lower-slope species assemblages. Lower slope-forest composition was generally similar to that across the canyon, but upper slopes and ridges supported sparse and stunted Quercus prinus (Chestnut Oak), Quercus rubra (Northern Red Oak), Pinus resinosa (Red Pine), and Pinus strobus (Eastern White Pine). Canopy trees on upper slopes were typically shorter (<6 m vs. 30 m) and had smaller diameter at breast height (40 cm vs. 80 cm) than those on lower slopes. However, some upper-slope trees exceeded 165 years of age. Results of non-metric multidimensional scaling ordination distinguished between north- and south-facing upper slopes, and showed a broad similarity among forests on lower slopes of both aspects and fluvial terraces at slope bases. The elevationally diverse southfacing slopes contributed more to site-wide (i.e., slopes and terraces) species richness (34) and gamma diversity (Shannon H' = 2.462), than did north-facing slopes.