A new high-tech analysis led by a University of Colorado, Boulder, scientist used several methods to date the stone carvings, including determining when ancient water levels reached the 3,960-foot elevation of the petroglyphs at the Winnemucca Lake site 35 miles northeast of Reno.
When the lake level was at this height, the petroglyph boulders were submerged and therefore not accessible for carving, researchers said.
A white layer of carbonate made of limestone precipitated from the ancient overflowing Winnemucca Lake 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, they said.
"Prior to our study, archaeologists had suggested these petroglyphs were extremely old," researcher Larry Benson said.
"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."
"We have no idea what they mean," Benson said of the Winnemucca Lake petroglyphs, which contain no people, animals or handprint symbols.
"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."