JOSHUA TREE NATIONAL PARK (AP) — Acts of graffiti have become so pervasive at Joshua Tree National Park’s most popular hiking spots that officials have had to close them to the public, and they blame the big bump in vandalism on social media.

Rangers said they’ve found graffiti spray painted on 17 sites, including the famous rock formations and historic Native American sites, at the Southern California park’s Rattlesnake Canyon. They put historic Barker Dam off limits after vandals carved their names into the cement of the Old West landmark.

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National Parks officials said the graffiti started with just a few markings, but quickly spread. They blame vandals who posted pictures of their handiwork on social media sites such as Facebook, which enticed others to the same spot and leave their own illicit marks.

“I’ve worked at six national parks, and this is the most extensive I’ve seen in 20 years,” ranger Pat Pilcher told reporters this week during a tour of some of the damage.

For visitors who cherish the isolation of this harsh desert terrain about 140 miles east of downtown Los Angeles, the graffiti are an unwelcome reminder of urban blight.

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“You kind of feel like you’re alone. In ancient times. There’s nothing like this place,” Butch Wood, 51, a visitor from North Aurora, Ill. told the Los Angeles Times. “You don’t like to see the modern world intruding on history. It’s a shame.”

Pilcher said park service law enforcement officers are investigating the vandalism. If caught and convicted, vandals could face up to $5,000 in fines and six months in jail. He said the penalty could be stiffer for those convicted of defacing a historic Native American site.

Meanwhile, the San Bernardino County Sun reports officials are closing 308 acres of the canyon until April 30 while volunteers from the Urban School of San Francisco help scrub the graffiti off the giant granite boulders.

It wasn’t clear how the park service will repair the damage at Barker Dam.

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