Elberton, Georgia (CNN) -- In the beginning, there was the stone.

The blue-gray vein of granite that courses through northeastern Georgia spawned jobs in the quarries and finishing sheds of Elberton, where generations of stonecutters have turned slabs of rock the size of refrigerators into statues, tombstones and tile.

And one day, it brought a visitor who gifted the town with a landmark that leaves visitors scratching their heads decades later.

The nearly 20-foot high series of granite slabs known as the Georgia Guidestones are inscribed with a series of admonitions for a future "Age of Reason." Billed as "America's Stonehenge," it's an astronomically complex, 120-ton relic of Cold War fears, built to instruct survivors of an Armageddon that the mystery man feared was all too near.

The identity of the man who called himself "R.C. Christian" is a secret that Wyatt Martin, the banker who acted as his agent in Elberton, vows to take to his grave.

"He told me, 'If you were to tell who put the money up for this, it wouldn't be a mystery any more, and no one would come and read it.' That had to be part of the attraction, to get people to come and read his 10 rules that he came up with," Martin said.

People in Elberton, about 100 miles east of Atlanta, are proud of their eccentric landmark. But 30 years after its dedication, it has drawn the attention of a new generation of conspiracy theorists with very different fears.

"There are a lot of people who don't feel about it the same way we do," said Phyllis Brooks, president of the Elbert County Chamber of Commerce.

The four vertical slabs that dominate the Guidestones are inscribed back and front with Christian's 10 principles, each side in a different modern language. The capstone is inscribed in the alphabets of early human civilizations -- Egyptian hieroglyphics, Babylonian cuneiform, Sanskrit and classical Greek.

The center column has a slot through which the transit of the sun throughout the seasons can be observed, while a hole higher up focuses on Polaris, the north star. Another hole in the capstone focuses a beam of sunlight onto the central pillar at noon. Those features would allow the survivors of Christian's feared apocalypse to reproduce three of the basic tools of civilization: the calendar, clock and compass.

Loris Magnani, an astronomy professor at the University of Georgia, questions how useful the Guidestones would be to survivors of civilization-ending cataclysm. The devices incorporated into the stones are "relatively easy stuff" that most human societies have developed early in their histories, he said.

"Don't get me wrong. As a monument, it's fine. There's nothing wrong with doing that," Magnani told CNN. But he added, "Every decent civilization going back to a couple of millennia before Christ has figured this out. How to make gasoline? Now that would be useful."

But it's the written messages of the Guidestones that have drawn the most criticism.

Most are innocuous, calling on readers to rule their passions with "tempered reason," avoid "petty laws and useless officials" and "prize truth, beauty, love ... seeking harmony with the infinite." They end with the advice, "Be not a cancer on the Earth -- leave room for nature."

But the first two -- which call for limiting human population to half a billion, less than 10 percent of today's numbers, and guiding reproduction "wisely" -- have led some to call the Guidestones a call to genocide and the "Ten Commandments of the Antichrist."

In recent years, the monument has been hit by vandals who see in it the creed of a shadowy "New World Order" bent on subjugating humanity. It has been tagged at least three times since 2008, leaving scrawls of "God is stronger than the NWO," vague threats of destruction and various crudities across the granite.

"The worst was they put a two-part epoxy over two faces," said Mart Clamp, whose father helped carve the stones. "You just can't pressure-wash it off, you have to get in there with a hammer-type tool and beat it off."

Christian left behind a 1986 book, "Common Sense Renewed," that is still for sale at the Elberton Granite Museum. Many of the concerns he lists in it wouldn't be out of place at a modern Republican gathering: growing entitlement spending, stifling regulation, the breakdown of the traditional family.

But he also warned that the world's problems were symptoms of overpopulation, turning civilization as we knew into an "atomic tinderbox," and requiring some limited form of world government to save mankind from annihilation, he concluded.

It is that kind of talk that disturbs people like Van Smith, who has written extensively about the Guidestones on his Web site. Contacted at his home in Arkansas, said the future that Christian describes in his book "is totalitarian."

"It's Platonic in many ways, but it's extremely oppressive," Smith said.

And he says encoded within the dimensions of the stones is the height in feet of Dubai's Burj Khalifa, now the world's tallest building. To him, that suggests the builders knew of plans to build a new Tower of Babel, ushering in "the dawning of a new era in which man can become God."

"I'm not a conspiracy lunatic who spends all my time researching Freemasonry and things like that," said Smith, a computer industry analyst. But he told CNN, "This evidence is extremely real, and it's disturbing."

The locals don't buy it.

"I know the men who put this up, and they were all good men," said Clamp, who is working to clean up the stones ahead of their anniversary. "My father was one of those men. If this had been anything satanic or demonic, they never would have had anything to do with it."

Brooks said that most in Elberton view the stones as "a work of art" that draws tourists, and "we don't get wrapped up so much in what they say."

"But they do still have a draw to" -- she pauses -- "to a different sector of people."

And the chatter from that sector has made Elberton leery of celebrating their landmark's 30th birthday.

"With the damage that had been done to the Guidestones and a lot of things that were out there on YouTube, it was just decided that maybe we might wait for another year to do it," Brooks said.

The mystery man is dead now. Martin knows this because the man's son got in touch with him recently. Only two people in Elberton met him face-to-face -- Martin and Joe Fendley, the contractor who built the monument.

Fendley, who went on to become the town's mayor, is dead now, too. But Martin, now 79 and living a few towns down the road, said he remains bound by his pledge to keep the secret.

"That was a gentleman's agreement between us, and he lived with it and I've lived with it," he said. "When I'm dead and gone, nobody will ever know who put it there."

