WINNEMUCCA LAKE, NEVADA—Archaeologists have discovered a series of abstract petroglyphs in western Nevada are at least 10,500 years old and could possibly date to 14,800 years ago, making them the oldest known petroglyphs in North America. The team, led by University of Colorado Museum of Natural History archaeologist Larry Benson, radiocarbon dated layers of carbonate underneath the petroglyphs, which ancient Native Americans incised into limestone boulders near the now-dry Winnemucca Lake. "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," says Benson. But knowing the approximate dates still doesn't give archaeologists insight into what the symbols represent. "We have no idea what they mean," says Benson.