Most people were pleased in the summer of 1969 at how quickly the debris was cleared away following that summer’s Woodstock Music and Arts Festival in upstate New York. When half a million people descend on a single, 600-acre farm in the midst of a hot, rainy, muddy August, you can expect a mess. But the town and the concert promoters made quick work of all that, returning the farm to owner Max Yasgur in more or less the same state in which they’d found it. Half a century on, not everyone is happy about all the post-festival tidying.

“Unfortunately, they cleaned up pretty well,” says Maria O’Donovan, a project director with the Public Archaeology Facility at New York’s Binghamton University. “If you see the pictures, it’s amazing that they cleaned it up at all.”

The unfortunately, of course, is the archaeologist in O’Donovan talking. What starts off as trash can become priceless artifacts, and the more that’s left to be buried and preserved for decades or centuries or millennia, the more descendant generations can learn about the ones that came before. But that’s not to say the Woodstock site—which isn’t in Woodstock at all, but 46 miles away in Bethel—was left absolutely pristine. As part of a team developing a reconstructed trail network and art installation timed for the fiftieth anniversary of the concert, O’Donovan and her team, under the sponsorship of the Museum at Bethel Woods and the Bethel Woods Center for the Arts, have done impressive work learning what they can about the concert site from the little bit that’s left.

Easily, the most distinctive feature of the festival was the stage where The Who, Janis Joplin, Jimi Hendrix, Joan Baez, the Grateful Dead and 27 other acts performed. The stage was roughly 60 feet long by 45 feet deep, protected (imperfectly) by a huge canvas tarp overhead. Two speaker towers—one of them the height of a seven-story building—projected the music that made all the history. With no foundations dug to support all that infrastructure, however, only a whisper of it is left.

“The stage was a reasonably heavy piece of construction,” says O’Donovan. “But it was built mostly on the surface—more than you would have expected for a stage. The only other support was provided by cables overhead.”

That doesn’t mean there is nothing remaining at all. O’Donovan and her team located a post marker for a fence that surrounded the stage. Working from aerial photos and old concert maps, they were able to begin at that point and frame the area that held the stage. Their work was made especially challenging since, unlike the rest of the 600 acres, which have retained their original topography, the site of the stage has been altered. “There was another concert there since,” O’Donovan says, “and you can see the evidence of grading and filling.”

Much easier to study was an area on the festival site that was informally known as the Bindy Bazaar. Located away from the main stage area, the bazaar was set aside to provide space for pop-up booths, where concertgoers could sell—or, this being the counterculture, barter—crafts and clothes and other collectibles. The booths were exceedingly temporary—”ephemeral,” as O’Donovan lyrically describes them—but they left their mark, mostly in the form of rocks, stacked or lined to provide support or to mark a plot. Such lasting signs of human intervention that would be unlikely to form naturally are exactly the kinds of evidence archaeologists look for.

“I imagine we’d find more if we excavated,” O’Donovan says, “but our work is related to what our sponsor wishes to have done.” For the Bethel woods community, excavation clearly falls outside that scope. O’Donovan did find a few wires hanging from trees in the area that might have been used to support the booths.

The concert’s planners mapped spots within the bazaar area for about 25 booths, and that was more or less the number the archaeologists found. But in keeping with an event that was all about convention-breaking, the precise locations of the booths strayed from the blueprints. “The Woodstock experience was very, shall we say, informal,” says O’Donovan. “It was non-corporate. This wasn’t Pepsi. It was just people with things to barter or sell.”

It’s always possible that a more thorough scouring of Yasgur’s farm will yield other artifacts. The Binghamton archaeologists did find a scattering of aluminum pull tabs from beer or soda cans—the removable kind that caused additional litter before the industry switched to attached pop-up tabs. “You can actually date those, since there’s a chronological sequence to when they were discontinued,” says O’Donovan. If there were clothes left behind that escaped the initial cleanup, the cloth would have long since decomposed, but buttons or snaps or zippers might survive underground. Lost shoes would too, as would any evidence of the abundant pipes and other paraphernalia used for the abundant pot that also characterized the concert.

“Archaeologists study humans and try to interpret the past from material remains,” says O’Donovan. “Those remains are constantly being deposited.” Fifty years is a nano-second in the arc of history, and the four days of the Woodstock Music and Arts Festival were a tinier flicker still. But it was a flicker that helped define the nation at a turbulent moment, and its cultural marks—like its stacks of stones and abandoned pull tabs—remain.

Write to Jeffrey Kluger at jeffrey.kluger@time.com.