Sitka mountain ash is an attractive shrub or small tree with several stems from 2-5 meters high. Younger stems and winter buds are heavily haired and have reddish-purple bark. The older bark is grayish-red. The leaves are pinnately compound with 7-11 oval or oblong leaflets with the tips rounded or blunt. The thick leaflets have a dark green color above and are paler green beneath with rufous hairs along the midvein. The leaflets range from 2-5 cm long and are usually 1/3-2/5 as wide. The margins are coarsely serrate, usually near the tip, but occasionally 3/4 of the way to the base of the leaflet.
The inflorescence is a dense corymb of 15-80 flowers. Individual flowers have 5 white petals. The petals are rhombic to oval in shape and 4-5 mm long. The fruit are ellipsoid or subglobose in shape, red with a bluish cast, and up to 1 cm long.
Sitka mountain ash is found in subalpine and alpine habitats, either in open forests or open slopes, or in old burns or clear cuts.
Sitka mountain ash may be found from Alaska and the Yukon south through the Cascade and Olympic Mountains of Washington, and in the Cascades of Oregon to northern California. It is found eastward in the mountains to eastern British Columbia, northern Idaho, and northwestern Montana.
