Mountain Ash: Leaves have 7 to 15 leaflets. Leaves are alternate on stem. Fruit are clusters of purple to orange berries (pomes). Wild plants tend to be found from 2000 to 7000 feet in elevation. Domestic varieties are found in yards both west and east of the Cascades.
2B. 
Smooth Sumac: Leaves 8" to 14 " long. Leaves have 9 to 21 leaflets. Leaves are alternate on stem. Fruit are bright red in big clusters. Wild plant in the Columbia River Gorge, and east of the Cascade Mts.. Domestic varieties are found in yards both west and east of the Cascades.