The Cabazon Band of Mission Indians (Cabazon) (defendant) operated bingo, poker, and other casino card games on the reservation in California. Gaming was open to the public and was enjoyed primarily by non-Indians who visited the reservation to play. The State of California (plaintiff) and Riverside County, California, attempted to impose state regulations on the gaming operations conducted on the reservation. The Cabazon sued Riverside County in federal court, seeking declaratory and injunctive relief against imposition of the regulations. California intervened, arguing that under Public Law 280, 28 U.S.C. § 1360, Congress granted states the power to regulate gaming on the Indian reservation. The district court granted summary judgment to the Cabazon, holding that neither California nor Riverside County had authority to enforce gaming laws within the reservation. The United States Supreme Court granted certiorari.