SAN FRANCISCO -- Rainbows and good cheer will be out in force in the United States as hundreds of thousands of people pack gay pride events from New York City to Seattle, San Francisco to Chicago to celebrate a Supreme Court ruling legalizing same-sex marriage.

Organizers of San Francisco's Lesbian, Gay, Bisexual and Transgender Pride Parade, just called "Pride," expect about 1 million revelers. It will have 240 groups marching in a parade Sunday and more than 30 floats, its largest in 45 years.

"I just think it's going to be magical this year," said Gary Virginia, board president of San Francisco Pride.

That's because the U.S. Supreme Court issued a long-awaited ruling Friday giving same-sex couples the right to marry in all 50 states. Virginia's comments were echoed by leaders of Pride celebrations in other cities.

"It's going to be an epic weekend," said David Studinski, march director for New York City Pride. "I actually just wrote on Twitter that this is the most historic Pride march since the first."

New York City expects 22,000 people marching in a 2-mile route and more than 2 million people to visit. The event is considered a march, Studinski said, because the movement still has much to accomplish.

Seattle expects to draw nearly 500,000 parade watchers, said Eric Bennett, president of Seattle Pride. Chicago, the Twin Cities, St. Petersburg and St. Louis are also having Pride events on Sunday.

"This is definitely going to be a momentous Pride weekend all over the country," said Bennett. "It's just going to raise the celebration level of everybody who supports marriage equality

Pride festivities started as a way to honour the 1969 Stonewall rebellion, when gay patrons stood up to a police raid at a bar in New York City. In San Francisco, marchers took to Polk Street in 1970 and in 1972, the event became a parade.

This year's parade in San Francisco, which has the theme "Equality Without Exception," offers a bit of everything for spectators, from social justice to professional basketball.

The parade's celebrity grand marshal is Rick Welts, president of NBA champions the Golden State Warriors. Speakers include Alicia Garza, co-founder of Black Lives Matter, and Jim Obergefell, the named plaintiff in the landmark same-sex marriage suit decided by the U.S. Supreme Court.