The celebration will include a special performance by. Gila River Resorts & Casinos opens its new Santan Mountain Casino today with a two-day, grand-opening celebration (June 30 - July 1). Read more Santan Mountain Casino Opens Today! J. The BetMGM Sportsbook is a 7,000 square-foot betting lounge with a 130-foot LED screen. The largest casino sportsbook in Arizona is located inside the new Santan Mountain Casino. News Headlines Santan Mountain Casino Boasts Largest Sportsbook in AZ J.