LEWISTON, Idaho (AP) – Federal officials say they are sending a team of investigators to look into vandalism of some ancient tribal pictographs near Lewiston’s Hells Gate State Park.

“We view these violations as a serious matter and we intend to refer them to local law enforcement so they can determine who is responsible, and ultimately, bring these perpetrators to justice,” Joseph Saxon, a spokesman for the U.S. Army Corps, told the Lewiston Tribune. “In the meantime, we’ll need to determine how to undo the damage that was done.”

Some of the animal figures and geometric pictographs on a basalt wall were recently covered with spray-painted graffiti. Archaeologists believe the red pigment pictographs are at least 2,500 years old.

Damaging the pictographs violates the federal Archaeological Resources Protection Act of 1979.

The vandalism was discovered Wednesday at the Red Elk Shelter managed by the corps and likely occurred in the last two weeks. The spray-painted graffiti includes references to marijuana, with the words “Vote to Toke,” and a pot leaf with “Ganga” written below. There are also peace signs, the initials T.C., and the names Freddy B and “Kotton Mouth Kings,” a marijuana-themed rap band.

Carolynne Merrell, a Moscow-based consultant specializing in ancient rock art, said the damage at the site is extensive. The graffiti defaces the most prominent pictograph at the site, one depicting a red elk.

She said the shelter was used by the Nez Perce Tribe and could have been visited by other tribes from the Snake and Columbia river basins. Restoration of the images will be a challenge, she said.

“If we’re lucky, we can remove the spray paint. But it’s going to be costly,” said Merrell, who has done rock art recording work for the National Park Service and National Forest Service. “There are very few people qualified to do the restoration.”

The Nez Perce Tribe has not yet issued a statement on the damage.