The oldest known petroglyphs on the west side of Nevada's dried-up Winnemucca Lake may be nearly 15,000 years old, according to a new analysis by researchers at the University of Colorado Boulder. The findings will be published in the December 2013 issue of the Journal of Archaeological Science.

These petroglyphs, otherwise known as rock engravings, resembled trees, leaves, ovals, diamonds in a chain, deeply carved large grooves and complex dot patterns.

Larry Benson, the research leader said that the petroglyph designs include a 'series of vertical, chain-like symbols and a number of smaller pits deeply incised with a type of hard rock scraper.' The researchers also noticed that the depictions of humans, animals or hand symbols were absent from the carvings.

"We have no idea what they mean," said Benson an adjunct curator of anthropology at the University Of Colorado Museum Of Natural History. "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."

Although the researchers were aware of the carvings for decades, the correct age of the carvings and the meanings of its art work has always been a mystery.

In order to determine the true age of the rock art, Benson and his colleagues had to find out when the ancient lake system reached its maximum height- 3,960 feet, because excess water would have started spilling out of the basin, which would have caused the boulders to submerge and therefore would have become inaccessible for carving.

The overflowing lake left telltale crusts of carbonate on these rocks.

"Benson sampled the carbonate into which the petroglyphs were incised and the carbonate that coated the petroglyphs at the base of the limestone boulder. The radiocarbon dates on the samples indicated the carbonate layer underlying the petroglyphs dated to roughly 14,800 ago. Those dates, as well as additional geochemical data on a sediment core from the adjacent Pyramid Lake subbasin, indicated the limestone boulders containing 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."

"Prior to our study, archaeologists had suggested these petroglyphs were extremely old. 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," Benson said.