How do you come up with the conclusion that he was in the area illegally? Just because he thought the guy was a cop? Just because he thought it might be a cop, doesn't mean he was in the wrong. I've been confronted by cops/rangers/sheriffs many times while off roading and as long as you have the right to be there and/or the right permits/tags, then they are more or less just doing their job and patroling the area looking for those causing problems. When you're fishing on the shore of a lake and you see a ranger or sheriff coming your way...do you get worried that you shouldn't be there? You may have every right to be there...but he's going to make damn sure you have the license that allows you to be fishing.
I don't know the laws in Texas or Colorado...but here in AZ "trails" are considered open unless noted or posted closed. Also, unless the land owner has fencing up or has posted signs that you are entering private property, a restricted area, or a permitted area, you'd be allowed in the area legally (as long as you've satisfied the restriction or permit). If a private property owner wants people to stay out of an area, they post a no trespassing sign....just as the govt does with trust land...as does the BLM.
As I see it/treat it, around here the sign is merely a formality and extra step measure for the owner. I'm not going to go up to a fenced area and just assume I'm allowed in if there's no sign (like an obvious yard with structures). Here in AZ, there is so much open land that just has a 3 wire fence around it's perimeter and you do need to know what type of land it is...which is why signs are posted. Private land owners use the same 3 wire fencing that the govt does, so decifering which is which can only be done with signage and/or knowledge. Trust and BLM land will be posted with signs...as will *most* private property so you know which boundry you've come across in the middle of nowhere.
Many times you can come across these 3 wire fences in the desert and you'll not see any signs of structures or worked land in any direction. Since you're out in the middle of nowhere and it may not be posted, that's when YOU have the responsibility to make an educated decision based on the surroundings and to know where you are and what land lies beyond. An example of this judgement is coming across a 3 wire fence that has one of the panels cut open with a track leading through it. It may not have been open...but it is now. Doesn't mean you now have the right to enter just because the jack*** before you thought he did.
I'm on your side on the subject of irresponsible wheelers...but there are plenty of irresponsible people that wheel on open unrestricted land. I've been to numerous BLM/land use meetings with discussions always ending up at the subject of the "bubbas" (the irresponsible people) and how to thwart their destructive activities while at the same time not have the responsible people lose privaleges.
Only advice I can give the OP is that ultimately it's your responsibility to know if you should be there...based foremost on your local laws, then by common sense.
