A new study reported in the Journal of Archaeological Science shows Winnemucca petroglyphs, the oldest known petroglyphs in North America, date to at least 10,500 years ago and perhaps even as far back as 14,800 years ago.

Study lead author Dr Larry Benson of the University of Colorado Boulder explained: “the petroglyphs located at the Winnemucca Lake petroglyph site 35 miles northeast of Reno consist of large, deeply carved grooves and dots forming complex designs on several large limestone boulders that have been known about for decades.”

Although there are no people, animals or handprint symbols depicted, 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.

Dr Benson with colleagues used several methods to date the petroglyphs, including determining when the water level the Winnemucca Lake subbasin – which back then was a single body of water connecting the now-dry Winnemucca Lake and the existing Pyramid Lake – reached the specific elevation of 3,960 feet.

“The elevation was key to the study because it marked the maximum height the ancient lake system could have reached before it began spilling excess water over Emerson Pass to the north. When the lake level was at this height, the petroglyph-peppered boulders were submerged and therefore not accessible for carving,” Dr Benson explained.

According to the team, a white layer of carbonate made of limestone precipitated from the ancient, overflowing Winnemucca Lake had coated some of the petroglyph carvings near the base of the boulders. Previous study showed the carbonate coating elsewhere in the basin at that elevation had a radiocarbon date of roughly 11,000 years ago.

The scientists 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,” Dr Benson concluded.

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Bibliographic information: Benson LV et al. 2013. Dating North America’s oldest petroglyphs, Winnemucca Lake subbasin, Nevada. Journal of Archaeological Science, vol. 40, no. 12, pp. 4466–4476; doi: 10.1016/j.jas.2013.06.022