Vandals have defaced the exterior and interior of a historic stone building that was constructed by the Civilian Conservation Corps in the 1930s.

Virtually the entire interior of the building, in Tucson Mountain Park west of the city, is covered with graffiti — including some vulgar words and depictions.

Parts of the exterior of the structure have been defaced with bright blue paint.

The building, less than a quarter-mile from a parking lot atop Gates Pass, is a popular destination for people interested in the work of the Civilian Conservation Corps, which provided jobs and performed valuable work on public lands during the Great Depression in the 1930s. CCC structures can be found in Saguaro National Park and other Tucson-area sites as well as in Tucson Mountain Park.

“We have no idea who might be responsible for the graffiti out there,” said Karen Simms, division manager for natural resources with Pima County Natural Resources, Parks and Recreation. “Such vandalism is hard to understand. What is the motivation behind it and why do some people feel compelled to engage in that activity?”

Simms said she has talked with the manager of Tucson Mountain Park, which is part of the county’s park system

“He said that it’s unfortunately becoming more and more common,” she said. “They are regularly getting graffiti at Gates Pass. They periodically go in and remove the graffiti. But it’s pretty expensive to do, and often in a few weeks it’s back again.”

Costs of removing the graffiti vary depending on the extent and the type of equipment needed for the work, Simms said.

She said officials are exploring possible ways of stopping or reducing the graffiti damage.

“But when you’re talking about vandalism, there’s nothing you could put out there short of having a person watching over it 24 hours a day,” Simms said. “And that’s not practical.”

She acknowledged that one way of preventing more graffiti inside the building would be to install doors on the building’s two entrances and lock them.

“But you hate to take away the experience of going inside the building,” which many people enjoy, she said. “And it’s often better for the buildings not to be boarded and locked up. That can cause people to wonder what might be hiding in there and to break in.”

She wasn’t certain whether the graffiti defacement had been reported to the Pima County Sheriff’s Department.

Department spokesman Deputy Ryan Inglett said the department has received reports of graffiti at the site in recent years, but that it was difficult to determine how recently the vandalism had occurred or who was responsible.

Simms said county officials will continue looking into ways of limiting graffiti defacement.

“For right now, we’re in the mode of being aware and then saying we have to go out there and clean it up again,” she said. “But then it’s back before too long.”

Contact reporter Doug Kreutz at dkreutz@tucson.com or at 573-4192. On Twitter: @DouglasKreutz