25 U.S.C. § 180

Every person who makes a settlement on any lands belonging, secured, or granted by treaty with the United States to any Indian tribe, or surveys or attempts to survey such lands, or to designate any of the boundaries by marking trees, or otherwise, is liable to a penalty of $1,000. The President may, moreover, take such measures and employ such military force as he may judge necessary to remove any such person from the lands.