I couldn't find anything in Title 25 prohibiting non-Indians from taking firearms onto an Indian reservation. Furthermore, a landmark United States Supreme Court case Oliphant v. Suquamish Tribe, 435 U.S. 191, 212, 98 S.Ct. 1011, 1022-23, 55 L.Ed.2d 209 (1978) held that the Indian tribes had no criminal jurisdiction over non-Indians. This rule of law has been cited by many federal and state courts, some as recently at 2006. I have discussed this issue with the "Indian Law" guru at Utah's U.S. Attorney's office (unofficially) who indicated he knew of no prohibitions or prosecutions of non-Indians having firearms on tribal lands. Based upon these findings (or lack of findings), I can only conclude that if you are simply passing through Indian lands on public highways, if you otherwise comply with Utah and federal law pertaining to vehicle carry (as described in this chapter and chapters VII and VIII), you should not be harassed.