It appears to be Late Boneset (Eupatorium serotinum):
Late Boneset (Eupatorium serotinum)
The most reliable way to separate White Snakeroot from Late Boneset is that the involucral bracts of White Snakeroot are all about the same length, while the involucral bracts of Late Boneset are uneven in length and overlap each other (imbricate is the technical term). I'm pretty sure that you've captured some of the flower heads in the first picture clearly enough to say that the involucral bracts are imbricate.
