It was visited by scientists and celebrities, from Carl Sagan to Martin Sheen. It was the year-round home of less famous activists for decades. And it was nearly lost, until archaeologists helped document the unique history that it enshrined.

For more than 50 years, protesters occupied a makeshift campsite outside the gates of the former Nevada Test Site, now known as the Nevada National Security Site, to protest the U.S. government’s development and testing of nuclear weapons there.

Today, the Peace Camp, as it came to be known, is empty, but archaeologists recently surveyed the traces left by a half-century of civil disobedience, recording what experts say is the last remaining site of its kind.

“This archaeological research is unique, because the Peace Camp is the only known intact Cold War protest camp in the world,” said Dr. Colleen Beck, archaeologist with the Las Vegas-based Desert Research Institute.

“Without this study of the Peace Camp, the entire camp area would have been destroyed, and no one outside the protest participants would have ever known about the rich heritage they created there.”

Over twelve years, Beck and her colleagues combed the Peace Camp site, some 100 kilometers northwest of Las Vegas, documenting tent pads, hearths, ornamental rock formations, and hundreds of pieces of graffiti painted in drainage tunnels that run under the nearby highway.

“When we began the field research, based on a few walkovers, we expected to record about 50 features,” she said.

“So we were very surprised to find more than 700 features within the Peace Camp.

“The features are from daily camping activities, markers for paths and places, and rock patterns on the landscape in the shape of spirals, flowers, crosses, and peace signs, a rock garden in honor of a peace activist, and people’s initials.”

Protestors began showing up at the site as early as 1957, when the Atomic Energy Commission was conducting Operation Plumbbob, a series of 29 explosions that would comprise the largest — and, in time, the most controversial — nuclear weapons tests in U.S. history.

But the detonations that year — which included the first underground explosion, the exposure of troops to nuclear blasts, and radiation tests involving nearly 1,200 pigs — would be followed by hundreds more. [Read more about the archaeology of America’s nuclear legacy: “Radioactive Wreck of WWII Aircraft Carrier Discovered Near San Francisco Bay“]

It wasn’t until the fall of 1986, when San Diego activist Art Casey established the first permanent residence at the entrance of the facility, that the Peace Camp was founded.

As a contract archaeologist, Beck had done research on the grounds of the Nevada National Security Site in the early 1990s and saw that the protesters encamped there were making their mark, literally and figuratively.

“On occasion, I would see the protesters on the road near the entrance to the facility and could see them congregating at the camp,” she said.

“I saw their activities as the other side of the story of the nuclear testing era.”

In 2002, with the help of colleagues and a small amount of grant money, Beck undertook the first archaeological study of the Peace Camp.

Of all the artifacts and features left behind, Beck said, the graffiti was of particular interest, because it offered rare insights into the direct, personal expressions of the site’s inhabitants.

Her team sought to compare the statements that the protesters made among each other, spray-painted in the relative privacy of the highway culverts, with those they made to the broader public, particularly in the placards they carried at the gates.

Using historic photographs of the protests, the researchers identified a sort of core lexicon of anti-nuclear protests, including 16 symbols — such as the peace sign and pictures of the Earth — along with 64 slogans, like “No More Nukes” and “Food Not Bombs.”

After comparing these words and images with those found in the tunnels, the researchers found that the graffiti often reflected similar sentiments, but were decidedly more personal.

“We were most surprised by the art in the tunnels,” Beck said.

“The tunnel graffiti, of course, had peace symbols but had very few other symbols or slogans that were used on the placards.

“Instead, most of the art and writings in the tunnels are personal in nature or art especially created for this setting.”

Some graffiti panels featured quotes about peace and activism from the likes of Martin Luther King, Jr., and Margaret Mead.

Others delved more into the artist’s personal identity politics, featuring symbols of gender, sexual orientation, or ethnic identity. [See how beer cans may help identify and preserve a historic gay and lesbian site: “At 50, Ring-Tab Beer Cans Are Now Officially Historic Artifacts“]

“This was not a place to show the slogans or chants of the protesters as would be expected.” Beck said.

“It was a place for private — within the protest community — expressions regarding nuclear testing and peace.

“So the tunnel graffiti has nothing in common with people who tag an area, which is why we talk about it as an artistic legacy.”

Recognizing the unique historic value of the site, Beck’s team submitted its findings as part of a recommendation that the Peace Camp be eligible for listing on the National Register of Historic Places.

The Nevada State Historic Preservation Office, along with the U.S. Bureau of Land Management (BLM), which has jurisdiction over the land, agreed.

“This means that any activity proposed for the camp area will be reviewed by the BLM and the state to determine if it will affect the site,” Beck explained.

“This has resulted in a large power line not being built through this area but far to the south, and it has ended off-road motorcycle groups riding there.”

Ultimately, Beck said, her team’s research has helped preserve a segment of 20th century American life that has seldom found its way into the historical record.

“The Peace Camp is historically significant because it is a landscape that represents the anti-nuclear and peace movements — these have been marginalized world-wide political movements,” she said.

“Marginalized political movements, like minorities in a community, historically have received little attention in mainstream history, although this is changing quickly now.” [Read more about the archaeology of the counterculture: “Vinyl Records Excavated at Famous ’60s Commune Challenge ‘Hippie’ Stereotype, Study Says“]

“Most protests took place in urban environments with no evidence of these activities remaining at the locations. This camp in its rural setting is well preserved, and the features there are tangible evidence of the protesters’ activities.

“This is the place of their history.”