Vandals have damaged priceless petroglyphs - ancient rock carvings - at popular Picture Rocks northwest of Tucson.

The vandalism incidents, which occurred over the past three years, prompted owners of the site to post warning signs and call for vigilance by visitors.

"People have been seen vandalizing petroglyphs. There has been some damage - defacing of the rocks," said Peter Tran, assistant director of the Redemptorist Renewal Center, 7101 W. Picture Rocks Road.

The center owns the land where rock outcrops are covered with more than 100 petroglyphs dating from about A.D. 900 to 1350. The carvings, believed to be the work of ancient Indians known as the Hohokam, depict animals, human-like figures, solstice and equinox markers, spirals and other designs.

Archaeologist Allen Dart - executive director of the Old Pueblo Archaeology Center and a principal investigator for the EcoPlan Associates consulting firm - inspected the site this week for signs of vandalism.

It's not possible to determine how many vandalism incidents have occurred in recent years, but Tran and Dart noted at least two serious examples.

One, said Dart, was an image that apparently was partly pecked into the rock and partly formed using chalk.

"It looked kind of like an owl's face," he said.

Tran said a nun reported an incident last year in which she observed a woman and girl "vandalizing part of the petroglyph underneath the goat" - referring to a carving that resembles a bighorn sheep.

"The sister saw that a piece of rock was missing where they had been chipping at it," Tran said.

He said he has noted another defacement - the letters "MML" carved on a rock above the bighorn sheep figure.

Dart said even seemingly minor defacements bring lasting consequences.

"The recently added designs and graffiti can be seen from some distance away, which greatly detracts from the overall view and contextual integrity of the prehistoric rock symbols," he said. "Vandalism incidents at Picture Rocks and other petroglyph and pictograph sites also cause problems for native peoples, anthropologists and art historians who study rock art and its archaeological context."

Tran said the site, which is open to the public at no charge, now is posted with signs warning that thieves and vandals will be prosecuted. Center officials are keeping close watch over the area, and they ask that visitors check in at the center's office and report any incidents of vandalism.

"We need to sensitize people that this a treasure handed down to us from those people so long ago," Tran said.

Contact reporter Doug Kreutz at or at 573-4192.