Another thing that you need to contend with now in Colorado is where the Forest Service and County government are closing off roads to ATV's unless they are registered for the highway. The kicker here is that there is no way to register a ATV for the highway here in Colorado.
I had a friend that brought his Side by Side over last year to hunt with. He was stopped by a Forest Service Enforcement officer and was about to get a ticket when he told the officer that the vehicle was registered for the highway which can be done in Utah. He also had a Colorado ATV sticker on the machine so he was covered. They let him go on his merry way.