If you've never been to Colorado I suggest adding it to your Bucket List. It is a beautiful state especially when you get away from the tourist areas. Not that the Rocky Mountain National Park is not worth seeing, but be prepared for tons of fellow sightseers and photographers.
I've been a couple of times now and I would say the fall is the most crowded because that's when the elk come down from their high mountaintop homes to dwell among the residents near Estes Park.
It's quite a site when traffic in Estes Park is at a standstill because a herd of elk is in the crosswalk. Leading the herd is is the ever watchful bull who will not hesitate to defend his harem.
Who would dare walk up to a 700 pound bull during mating season just to get a photo? Well, it happens. We saw one photographer leave in an ambulance. I guess tourist think since they are in a 'park' the wildlife won't hurt them, or perhaps they are willing to take the risk to get that one perfect photo. I know I've put myself in harm's way a time or two, but I won't lie, I'm scared of the bulls!