San Fernando Valley is a sun-drenched, suburban enclave in southern California. You may know it by another name: Porn Valley.

(There's also "Silicone Valley" and "San Pornando Valley." Clever.)

Since the 1970s, the hills above Hollywood have played host to a booming pornography industry. A majority of American sex films are shot there in warehouses and private homes — helping the San Fernando Valley rake in $4 billion in annual sales in its '90s heyday.

How did an out-of-the-way desert suburb become the porn capital of the world? Location, location, location.

Porn star Ariana Marie has her makeup touched up on set of an adult shoot. Melia Robinson/Tech Insider

At its onset, the porn industry stretched across Los Angeles, San Francisco, and New York, where the entertainment industry concentrated. As Paul Fishbein, cofounder of AVN Media Network (porn's trade media organization) explained to the Associated Press in 2002, the business migrated to San Fernando Valley because of "low rents and access to the mainstream movie business."

San Fernando Valley is situated just 20 to 30 miles north of Los Angeles. Its proximity helped create a pipeline of talent from Hollywood, which included directors, crew, and actors when they needed a little side income.

The valley's dirty little secret offered particularly attractive job prospects in the '90s, as the mainstream television and film industry began to dry up. Studios were shipping mainstream productions abroad, where they cost less to shoot. Entertainment jobs in Los Angeles shorted, and thousands of employees marched Hollywood Boulevard in protest.

Legendary erotic photographer Holly Randall snaps an image during a shoot. Melia Robinson/Tech Insider

Meanwhile, the days of picking out porn in a curtained back-section of your local video rental store and paying for it started to disappear. The growing popularity of the internet made it easier than ever for people to access adult content. The industry exploded.

While feature film-making plummeted 13% in 1999, adult movie production rose 25%, the LA Times reports. And the funnel between Los Angeles and San Fernando Valley grew even larger.

But times are tough these days in Porn Valley. In 2012, Los Angeles County approved a ballot measure that requires adult actors to wear condoms on-camera — causing a mass exodus from San Fernando Valley. The number of adult video permits filed in the county sunk 90% that year, and many employees fled to Las Vegas, Nevada, where a restriction has yet to be passed.

Porn Valley may not be the porn capital for long.