“It would actually take some climbing on cliffs to get to where these petroglyphs are,” he said.
Authorities believe the vandals visited the site at least twice between July and November.
The bureau is offering a $2,500 reward for information leading to the arrest and conviction of those responsible for the damage.
Archaeologists say that Archaic Period hunter-gatherers who once lived in the area left the rock art about 2,000 years ago. The area later was settled by people archaeologists call Perry Mesa Tradition, about whom very little is known. The monument has about 400 recorded archaeological sites.
“It’s very rare, and so it’s irreplaceable,” Hawes said. “So much of it hasn’t been studied yet.”
When sites are vandalized, the information they contain can be lost.
“It’s losing our history, essentially,” he said.