This photo was originally posted correctly as Erigeron speciosus, but was recently moved, erroneously, to Erigeron grandiflorus.
I've just asked that it be moved back.
Here are some of the differences between these species: E. speciosus has a much different habit, branching rather than tufted. Also E. grandiflorus is much taller and has multiple flower heads, while E. grandiflorus has single flowers.