John Williamson, a pioneer of the 1960s sexual revolution as co-founder of Topanga Canyon's Sandstone Retreat, where nudity and free love once took place with abandon, has died at age 80.

Williamson died of cancer March 24 at a hospital in Reno, Nev., said his wife, Barbara Williamson. The pair had lived on a Northern Nevada ranch for the past 18 years, taking in abandoned lions, tigers, cougars and other big cats.

They were a young newlywed couple in 1968 when they bought a cluster of rundown buildings on 15 acres overlooking the Pacific Ocean and turned it into the Sandstone Foundation For Community Systems Research.

It offered seminars on human bonding, relationships and sexuality, but its Sandstone Retreat, where as many as 500 people would gather on weekends to frolic in the nude, swap spouses and engage in group sex, quickly made its existence in the bohemian canyon notorious.

"We actually had open sexuality and nudity, but it was optional. Everything was optional," Barbara Williamson told The Associated Press on Thursday. "We provided a wonderful, wonderful environment in a natural setting, and that natural setting just sort of gave people permission."

As the retreat's frontman, Williamson became known as the messiah of sex, a title his wife said he always carried proudly.

The couple, together 47 years, exchanged partners themselves and it never put a strain on their relationship, said Williamson, who is writing a memoir of those years. They believed that monogamy wasn't fulfilling people's sexual needs and, as a result, was preventing them from living life to its fullest.

Many celebrities were said to have paid quiet visits to Sandstone over the years, and Williamson joked Thursday that she likely "saw more naked Hollywood stars than any other woman."

Author Gay Talese has said he spent a substantial amount of time there, much of it naked, when he researched his 1981 book, "Thy Neighbor's Wife" on the sexual revolution. Sandstone was also the subject of a 1975 documentary.

It was reading Ayn Rand's book "Atlas Shrugged" that John Williamson said prompted him to quit a defense-industry job in electronics and move to California in the early 1960s. The book portrays a society in which people, fed up with government and industry controlling their lives, walk away from their jobs.

But Williamson continued to work in a mainstream job, running an electronics company, until he met his wife when she came by his office one day in 1966 to try to sell him insurance. A few weeks later they were married, and soon after they were planning Sandstone.

Although membership flourished, Barbara Williamson said, the retreat never took in enough money to pay the bills. They sold the property in 1972, and Sandstone closed a couple years later.

After an effort to build a tribal community in Montana foundered, the couple moved to the San Francisco Bay area, then to Nevada. There they began to take in big cats whose owners wanted to get rid of them.

At the time of his death, Williamson was attempting to turn their property into a wild animal sanctuary and educational center.

In addition to his wife, he is survived by a daughter, Sheila Ellington, and a granddaughter.