Three German tourists are personae non gratae in Joshua Tree National Park after they were caught red-handed (or in this case, yellow-handed) following an act of paintball vandalism, according to the National Park Service. Citing a press release, KTLA reports that a ranger making his rounds in the Southern California park on August 4 spotted “fresh yellow paintball splatters” on various signs, dumpsters, restrooms and other buildings in the park, and that when other rangers were called to help, they spotted a slingshot “in plain sight in a vehicle.”

When confronted, the vehicle’s occupants admitted to “firing paintballs and slingshots the night before using a compressed paintball gun, known as a paintball marker,” the release said. Rangers say they found more slingshots and other paintball paraphernalia in the vehicle. “Defacement or alteration of the NPS landscape, no matter how small, is against the law,” Jeff Filosa, the park’s deputy chief ranger, said in a statement. “It harms the natural environment that millions of people around the world come to enjoy.” Filosa added that the time and energy spent cleaning up the tourist mess could be “better spent on other priorities.”

The NPS points out that graffiti like this in its parks is expensive and “extremely difficult” to remove, according to the BBC. New York Times reports that Joshua Tree has faced its own challenges in recent years: In addition to the 2020 wildfires that burned more than 1 million of the park’s signature yuccas, vandals wreaked havoc in 2019 during a partial government shutdown. The park service said the alleged vandals in this latest case received a federal misdemeanor notice for “vandalism, damaging or destroying property,” which carries a possible six-month jail sentence and a fine of up to $5,000. (More stories on Joshua Tree.)