I haven’t done the full length of one but I’ve gone pretty far down one before
Basically you just need to figure out who owns the land and depending on that would depend on if you can legally or not
When I did it though I didn’t check first because I was basically banking on the fact it was near a national forest so if someone stopped me I’d claim (accurately) that I didn’t know it wasn’t a part of the national forest. Of course I’m not sure if it is a part of it or not, but if I did get stopped at least I’d know for sure. I didn’t get stopped but I did have a nice day out there.