Mich. Comp. Laws § 750.493

Sec. 493. Protection of exploration pits and holes—Any person who shall sink, dig or cause to be sunk or dug, any shaft, pit, hole or trench on any uninclosed or unoccupied land within this state to a depth of 4 feet or more, for the purpose of exploring for minerals or making other discoveries, and shall fail and neglect to fill the same or erect or cause to be erected and maintain or cause to be maintained around the same a good substantial fence or enclosure not less than 4 feet high, shall be guilty of a misdemeanor.