By Dan Whitcomb, Reuters

Four ancient petroglyphs that were stolen from a historic site in Northern California last year have been recovered, but no suspects have been identified in the brazen theft, federal authorities said on Thursday.

The petroglyphs, which were carved into volcanic rock more than 3,500 years ago, were discovered missing in October from the site in the Volcanic Tablelands, east of Yosemite, near California’s border with Nevada.

They are said to represent a pristine example of Great Basin rock art that portrayed the daily hunter-gatherer activities that took place in the area at the time.

“Recovery of the petroglyphs was a priority from day one. I am pleased that they were returned,” Bernadette Lovato, manager for the bureau’s field office in Bishop, said in a statement.

“Now we need the public’s help to identify the vandals responsible for damaging the site,” Lovato said.

A Bureau of Land Management spokesman declined to release further details about the recovery of the petroglyphs, citing an ongoing investigation. The bureau said the suspects may have experience with masonry cutting and access to such tools.

The Volcanic Tablelands are described by the Bureau of Land Management as a vast volcanic landscape formed more than 700,000 years ago by materials spewing from the Long Valley caldera.

The high-desert site and its volcanic rock outcroppings are listed in the National Register of Historic Places, protected under the Archaeological Resources Protection Act and used by local Paiute Indians for ceremonies.

The Bureau of Land Management has offered a reward for information leading to the arrest and conviction of the people responsible for the theft. First-time violators of the Archaeological Resources Protection Act can be imprisoned up to one year and fined $20,000, according to the bureau.