It is a deciduous shrub or small tree that most often grows to 1–8 m (3–26 ft), rarely to 10 m or 33 ft, in height. Its growth form spans from suckering and forming colonies to clumped.
The leaves are oval to nearly circular, 2–5 cm (3⁄4–2 in) long and 1–4.5 cm (1⁄2–1+3⁄4 in) broad, on a 0.5–2 cm (1⁄4–3⁄4 in) leaf stem, margins toothed mostly above the middle. The foliage is browsed by deer, elk, rabbits, and livestock.
As with all species in the genus Amelanchier, the flowers are white, with five quite separate petals. In A. alnifolia, they are about 2–3 cm (3⁄4–1+1⁄4 in) across, and appear on short racemes of three to 20 somewhat crowded together, in spring while the new leaves are still expanding.
The fruit is a small purple pome 5–15 mm (3⁄16–19⁄32 in) in diameter, ripening in early summer in the coastal areas and late summer further inland. They are eaten by wildlife including birds, squirrels and bears. It is also a larval host to the pale tiger swallowtail, two-tailed swallowtail, and the western tiger swallowtail.