Every Super Bowl Sunday, thousands of gamblers head to the Grand Sierra Resort and Casino, the largest of its kind in northern Nevada, to bet on the big game and party with fellow football fans. High rollers dine on all-you-can-eat buffets and the champagne flows in V.I.P. rooms throughout the massive complex. Long lines snake out of the William Hill Sportsbook just off the casino floor.

But the action this year was supercharged because the Super Bowl included the San Francisco 49ers, and many of the team’s fans in California, where sports betting is still illegal, crossed the border into Nevada to lay down bets and celebrate with their brethren.