At first glance, there’s not all that much exciting about what has been called the “world’s biggest rock.” It’s as huge as its nickname suggests—a freestanding boulder about seven stories high and covering about 58,000 square feet in California’s Mojave Desert.

But visitors to the rock don’t typically go there for geology; they come, often, because of the rock's association with a race of space creatures with “good healthy tan[s]."

Giant Rock, as it is formally called, was once just one of many boulders scattered over an arid swath of unused government land. Native Americans may have viewed it as a spiritual site, but it wasn’t inhabited until the 1930s, when Frank Critzer arrived, as Sasha Archibald writes in Cabinet Magazine.

No one knows how he came upon the rock, and technically he was a squatter, but he sure did settle in. He dug out a cave under the boulder, built a runway for small private planes and carved out 33 miles of road leading to the nearest paved street. In 1942, during a visit by police, Critzer was killed when an old box of dynamite exploded.

With the first owner gone, Giant Rock only became weirder.

That same year, perhaps intrigued by Critzer’s exploits, George Van Tassel, a 32 year-old Ohio native and aviation tradesman, visited the site and decided to live there. He bought the land around Giant Rock from the Bureau of Land Management and, in 1947, moved himself, his wife, Eva and three daughters from Los Angeles to their new desert home.

As Archibald explains, most of what's known about Van Tassel is gleaned from his own writings and from his devotees—not exactly objective sources. By his death in 1978, he had become a kind of new-age philosopher, UFO “expert” and the leader of Ministry of Universal Wisdom, a religion he created. One thing is clear, though: Van Tassel believed he was in contact with aliens.

In his first book, I Rode a Flying Saucer, published in 1952, he describes meeting those tanned space creatures, who transmitted knowledge to him through telepathy. Van Tasssel claimed that Solganda, the aliens’ leader ultimately instructed him on how to build a time machine that would heal and strengthen humans—and so, about three miles south of Giant Rock, he built a two-story-high white dome, The Integratron. Though he worked on it for the rest of his life, it was never quite finished.

Van Tassel claimed at one time that the machine’s design came from a 17-page alien equation. The more likely inspiration was the research of a Russian scientist named George Lakhovsky, whose theories included the idea that human bodies were electrical conductors and that cancer could be cured by his Multiple Wave Oscillator. The Integratron time machine was a variation on these ideas. Archibald writes:

“Like an automatic car wash, the Integratron was an amalgam of architecture and machine. Its purpose was not to transport a fixed body to a different time, as time machines typically do, but to eliminate time’s effect on a body; the machine produced time, rather than suck it away.”

Beginning in the early 1950s, in order to raise money for himself and the development of the machine, Van Tassel held UFO conventions around Giant Rock. At the height of its popularity, the convention is thought to have attracted over a thousand attendees. Life even shot a series of photos documenting the participants in the “Flying Saucer Convention of 1957,” where believers shared alien experiences and theories on extraterrestrial life.

Today, the unfinished Integratron still stands out in the desert, cared for by the current owners, who put it to use as a site for “sound baths” which, according to their website, are “60-minute sonic healing sessions that consist of 25 minutes of crystal bowls played live.” And though Van Tassel's conventions ended in the 1970s, in 2006, devotees convened for convened for a day-long “Retro UFO Convention." The Independent reports:

Old-timers recalled the glory days of spotting mysterious lights in the desert sky. Present-day believers spoke enthusiastically about their own close encounters, everywhere from Arizona to New York City. Those blessed with actual contact with the aliens - known in the vernacular as "contactees" - were welcomed like prophets for the new millennium, complete with shiny silver hats and cloaks that looked eerily like cast-offs from the Star Trek wardrobe department.

Van Tassel would have felt right at home.