I finally found the American Mountainash, Sorbus americanus, seeing it wild on Hawk Mountain just northwest of Reading, PA this late August 2015. A beautiful tree, though it grows smaller and more shrubby on the rocky look outs. The European Mountainash or Rowantree was grown a lot in the 1960's to the 1980' the Chicago area. It was discontinued because this genus gets stressed by hot summers and drought and only live about 15 to 20 years like the European White Birch, both killed by borers. Mountainash is in the Rose Family like Apples, Cherries, Plums, etc. not related to the real Ash trees, Fraxinus.
What gorgeous red berries!
We used to have a Mountain Ash growing in our front yard - I'm not sure which species; it was there when we bought our house - but it started dying from fire blight so I had it cut down. From what I just read, it wasn't very well-suited to our area either.
Yes, these trees don't work in Zone 7, gets too hot. They love 3 & 4 and can survive for 20 years or some more in 5 & 6 if sheltered from the mid-day sun and heat and have good moisture in the soil.