North America’s oldest known rock carvings have been confirmed in northern Nevada.

Several boulders were found in the dry Winnemucca Lake with petroglyphs that are at least 10,500 to 14,800 years old, according a new analysis by the University of Colorado at Boulder. Located 35 miles northeast of Reno, the limestone rocks have carved out grooves and dots that form complex designs.

"We have no idea what they mean," CU-Boulder researcher Larry Benson said in a statement. "But I think they are absolutely beautiful symbols. Some look like multiple connected sets of diamonds, and some look like trees, or veins in a leaf. There are few petroglyphs in the American Southwest that are as deeply carved as these, and few that have the same sense of size."

The rock formations have been known for decades, but it was only with recent analysis that included finding the water level of the dried-up lake and carbon dating that it could be determined when the carvings were made.

"Prior to our study, archaeologists had suggested these petroglyphs were extremely old," Benson said in a statement. "Whether they turn out to be as old as 14,800 years ago or as recent as 10,500 years ago, they are still the oldest petroglyphs that have been dated in North America."

In ancient times Winnemucca Lake was filled with water that would have submerged the petroglyphs. Researchers decided to find out when the boulders were above the water line, which would allow ancient people to draw carvings on them. Benson sampled a white layer of carbonate that coated the base of the boulders. Radiocarbon dating and geochemical data show the petroglyphs were exposed to air between 14,800 and 13,200 years ago and again between about 11,300 and 10,500 years ago.

The younger dates the scientists calculated with the boulders are aligned with the Spirit Man Cave, a cave 60 miles east of Reno that had the mummified remains of a man along with a fur robe, a woven marsh plant shroud and moccasins.

Until this discovery, to be published in the Journal of Archaeological Science, researchers held that the oldest rock carvings in North America could be found at Long Lake, Ore. The 6,700-year-old carvings were covered by ash after the Mount Mazama volcano erupted.