Title18 USC Section 1151 defines Indian land as reservations, dependent Indian communities, and all land allotments (trust land) including rights-of-way.
Here is part of a three day course in a few paragraphs:
The Indian Country Crimes Act, The Assimilative Crimes Act, and the Major Crimes Act are the major laws governing federal jurisdiction in Indian Country.
Under the Assimilative Crimes Act, any crime that is not covered under federal law borrows the state law and prosecutes in federal court. If a non-Indian commits a crime against a non-Indian the state courts have jurisdiction. If a non-Indian commits a crime against an Indian, federal court has jurisdiction.
The tribes are serious about their no gun laws and violators can expect to face federal prosecution using state laws. It would be messy and difficult to defend.
Yeah, that is what I was thinking of. I should have clarified and stated governed by state law.