Adams

The Crow Tribe (“Tribe”) enacted the Railroad and Utility Tax Code (“RUTC”), which assesses a 3% tax on the full fair market value of all “utility property” located on tribal or trust lands within the exterior boundaries of the Crow Reservation (“Reservation”). Big Horn Electric Cooperative (“Big Horn”) filed an action in federal district court against several tribal officials for injunctive and declaratory relief, contending that the Tribe exceeded its regulatory jurisdiction in placing an ad valorem tax on the value of Big Horn’s utility property. The tribal officials appeal the district court’s grant of summary judgment to Big Horn. They argue that the Tribe’s inherent sovereign authority justifies the imposition of the tax. We have jurisdiction under 28 U.S.C. § 1291 , and we affirm in part and reverse in part.

I.

The Reservation, located in Southern Montana, was established by the 1868 Treaty of Fort Laramie (“Treaty”) between the Tribe and the United States. See Second Treaty of Fort Laramie, May 7, 1868, 15 Stat. 649 (1868). Although the Treaty originally granted the Tribe 8 million acres of land, see id., several subse *948 quent Acts of Congress reduced the total area…