You can go on at will but, and this is a big but. You have to be able to access it from a "Public" road. You cannot cross any private land to access the public. "Public roads" are defined basically as named roads be they county, forest service or blm, un named 2 tracks do not qualify if they cross private ground on the way to the public. Not all roads on public ground are public and usable, the ranchers are quick to get the oil and gas companies to label the 2 track roads to their well locations as private roads. This is a loophole that allows them to not allow access on roads that should be usable.
