Geranium cuneatum subsp. tridens is a compact, erect, many-branched shrub 3-10 dm tall. The stems and branches are reddish to black, covered with persistent stipules, and densely leafy only toward the apex. The leaves are alternate, oblong-cuneate (long and rounded-wedge shaped) at 1.5-5 cm long, 0.5-1.4 cm wide, usually 3-8-nerved, green, and glabrous to moderately strigose, occasionally more densely so in lines along veins, or densely silky strigose on both surfaces or only on the lower surface, margins entire, nearly always 3-toothed, apex truncate to sometimes rounded, petioles 0.3-2 cm long, stipules subulate, ca. 5-6 mm long, strigillose. There are 7-30 flowers in compound cymes, forming large corymbose inflorescences that project beyond the leaves with pedicels 0.5-2 cm long. The sepals are narrowly lanceolate (lance-shaped) at 5-9 mm long, densely silky strigose to sparsely villous or merely ciliate, apex mucronate. The petals are white or cream, sometimes with purple veins and sometimes purple at the base, narrowly obovate (egg-shaped narrow base) at 9-15 mm long. The staminal filaments are usually 9-12 mm long, glands pubescent. The styles are 5-6 mm long at anthesis, elongating to 15-28 mm long in fruit, essentially beakless, filiform, and reflexed branches. Carpel bodies are 2-4 mm long and sparsely to densely pubescent. The seeds are 1 per cell; dark reddish brown; oblong; ca. 1.9 – 2.6 mm long; the surface is reticulate.