Bluebird aster.

" Bluebird" Aster laevis
Smooth aster

Along with chamisa, it's everywhere in the fall. Seems to like full sun. And butterflies appear around it in droves. Found in open, dry places
from Maine to Georgia, west to New Mexico...and British Columbia! Blooms September to October.

Photo above by Calvin J. Hamilton, taken at Petroglyph National Monument. Photos at left and below: as always, if uncredited, by moi.