Could be Rose of Sharon. (Althea)Try a Google search and see if thats it.
Pondy

I have never seen a rose of sharon flower in the Twin Cities. I would suggest some kind of hydrangea.

Did you get a good look at the flowers at all? What color were they? The nursery industry has begun to standardize so many shrubs, that it may be a shrub that has been grafted into a tree (don't really know how to say that right, but that is the gist). That would open up the possibilies some. I have had sand cherries rebloom after a late summer pruning, and the new growth on my 'Red Prince' is tosssing out blooms, although not in full force like spring.

Helen.