Mountain St. John's Wort - Hypericum graveolens - St. John's-wort family.
To make the most of limited time while hunting wildflowers, I'll often wait until I get home to consult the guide books for a proper identification. But relying on photos and memory alone has its drawbacks. One habit I need to adopt is to stop and smell the flowers while I have the opportunity. When I found the description of this plant in Wildflowers of the Smokies, I learned that these flowers "smell sweetly of butterscotch," and that graveolens means "heavy-scented" in Greek.