I don't know your access to cell phones or reporting them but I would have mentioned it the next time you came into contact with a ranger or by cell if possible. When on vacation especially I don't drop what I'm doing to report something like that but I do like to make it known to the authorities when I can.

You made an effort to talk with the violators and that's good. Since they ignored you there is little else you should do (in my opinion).

jed