another nice one in MT is the state school trust lands; motorized vehicles are prohibited UNLESS it is designated to be open; which is rare;
so, say your bopping down your favorite BLM two-track rd (all legal) and that two track goes through one state section, and it is not marked as being ok, then you are breaking the law.....found that one out the hard way.....you could have just driven through 30 BLM sections, legally, and there could be 30 BLM sections on the other side of the state school trust ground, but if your road goes through it, and it isn't marked as being open, you are breaking the law.
this in of itself, renders thousands of acres of public ground off limits; Very few BLM two track roads through school trust grounds have DNRC signs saying it is ok.