Joshua Tree National Park has shut down access to two mining sites following reports of theft.
The thefts have gradually been happening over the past several months at Carey's Castle and El Sid Mine.
El Sid Mine operated off and on beginning in the 1880s, and Carey's Castle is an old prospector's cabin fashioned from a Native American shelter in boulders, according to the Associated Press.
Superintendent David Smith has ordered inventories at the sites, along with increased patrols and surveillance, AP reports.
This isn't the first time the park's had to deal with problems affecting the aesthetics of the park. Last year, a French street artist tagged a rock and posted it online, sparking social media outrage. In 2013, somebody left graffiti on a granite boulder at Rattlesnake Canyon.
Joshua Tree spokesman George Land encouraged visitors to speak up when they see these kind of things happening.
"These parks belong to the citizens of this country. They're paid for by the taxes every year by you and me and everyone else that lives here. And it's a personal investment that everyone has," Land said.
Land would not offer details on exactly what was stolen from the mines.
The two sites are closed until further notice, but the park itself remains open.
No leads yet on any suspects.