“It was a woman's ass, that was the first thing you see, then a woman's tits, then a man's ass, then anything before a dick,” filmmaker John Waters says in an upcoming short documentary on the evolution of porn in America.

Smut Capital of America is a 15-minute short about San Francisco's role in breaking the hardcore porn barrier.

The documentary is directed by Michael Stabile, a veteran of the gay porn industry, who says he stumbled across the city's contributions to the industry while working on a feature length documentary about the life of Chuck Holmes, the founder of gay porn studio Falcon.

Porn before 1970, Stabile explains, was treated like narcotics: “You could go to jail if you were caught selling it or distributing it.”

The laws were also used to aggressively choke off discussions about being gay. Literature from early gay rights groups was considered obscene and subject to the same laws used to prosecute users of porn.

A landmark Supreme Court ruling, however, struck down such laws, and the porn industry evolved from pin up girls to hardcore sex almost overnight.

“It happened in 1969,” Jeffrey Escoffier, author of Bigger Than Life, says in the film. “And it happened in San Francisco.”

Waters rose to fame in the early 70s, producing cult films that straddled the line between porn and cinema.

“I think San Francisco when I came here was gayer than it is today,” the 64-year-old, openly gay filmmaker says. “South of Market there was a bar called The Hungry Hole, that was a glory hole that you put your ass though. That's fairly radical.”

Stabile has submitted the short for consideration in January's Sundance Film Festival in Utah.