When we had a fire in the hills, they discovered a house no one knew about. It was on Forest Service land and it had a piggybacked electrical off someone elses power. Guy claimed he "bought it" back in the 70's from some guy. He'd been there so long they actually let him have that.
I believe squatters rights in CO start at 15 years, but I'd have to go look it up. Might be 10.
Usually used for encroachment across property lines. Someone comes along 10-15 years after a neighbor built an improvement across a line and does a new survey and notices and then says it has to be ripped up... if the person who put it there can prove its been there longer than the statute, they get the property line moved.
Ironically, before the timeframe is up, or if the timeline can't be proven, and there's an over riding sub-division document -- you can't GIVE the property away. A friend tried to do that when he sold his house and found the neighbor had been over the line by a large margin on one end of the property for decades, but they couldn't PROVE when the fence and trees went up.
So the county wouldn't let them just sign away the 1/4 acre that was encroached claiming they'd need proof of how long it was all there so they could retroactively fix the property taxes back 20'years, and also that the subdivision bylaws wouldn't allow the "smaller" plot so there'd have to be a public meeting, and a variance issued, and yadda yadda yadda...
All both parties wanted to do was give the land to the neighbors and not worry about it. They're not the original neighbors, and nobody cares about the encroachment at all.
He ended up having to sell the place with warnings that the new owners were being encroached upon by the neighbors. The new owners didn't care, and as far as I know are also paying the property taxes for the 1/8 acre that was accidentally lopped off in the late 80s.
The only good part is the official clock is now ticking and someday someone will be able to file the squatters right paperwork to officially claim the land and then the county won't have any choice but to let state law override the subdivision filing, and start charging the taxes correctly.
I mention all that because I wonder if that's how the "found" house was allowed to stay. But I doubt the squatting laws apply to federal land.
Keeps a bunch of lawyers well fed, all of this, I'm sure. Ha.