Ancient North Americans gouged elaborate rock art into a heap of big boulders northeast of Reno, Nev., more than 10,000 years ago and perhaps 15,000 years ago. That makes the carvings the oldest known petroglyphs on the continent, according to a paper published in the Journal of Archaeological Science.

Experts have known about these petroglyphs and believed they were old, but nobody knew just how old until paleoclimatologist Larry Benson used his expertise in the history of the climate of the West to date them.

“I think it’s really amazing that people that far back were creating such wonderful things,” Benson says.

The discovery is significant because the first people who lived on this continent are largely a mystery. They arrived more than 14,000 years ago, but archaeologists have found little to tell us about their culture — hardly any weavings, pottery or other handiwork.

“To get something this complex this early is very, very rare,” says Dennis Jenkins, an archaeologist at the University of Oregon’s Museum of Natural and Cultural History.

The new discovery shows that some of the earliest North Americans were surprisingly creative artists.

Benson has been interested in Native American artifacts since he was a boy hunting for arrowheads in farmers’ fields in Missouri. So he was thrilled when he got a chance to check out some rock art on the Pyramid Lake Indian Reservation about 10 years ago.

He recalls being entranced by how “incredibly beautiful” these petroglyphs are.