New analysis from the University of Colorado Boulder reveals that the oldest known North American petroglyphs date between 10,500 and 14,800 years ago.
The petroglyphs, located at Winnemucca Lake in Nevada, consist of deeply carved dots and grooves, which form a complex design on several large limestone boulders. CU-Boulder researcher Larry Benson led the new effort to date the petroglyphs. The study was published this month in the Journal of Archaeological Science.
Benson and colleagues determined when the water level at the Winnemucca Lake sub-basin reached an elevation of 3,960 feet, which was marked the maximum height the ancient lake system would have reached before spilling excess water over Emerson Pass to the north. At this height, the petroglyph boulders were submerged, and therefore inaccessible for carving.
A white limestone layer had precipitated from the overflowing lake and coated some of the petroglyph carvings near the base of the boulders. Previous work by Benson indicated that, at that elevation elsewhere in the basin, the carbonate coating dated back some 11,000 years.
The team sampled the limestone boulder where the petroglyphs were carved, and the carbonate layer from the base of the boulder. Radiocarbon dates indicated that the carbonate layer underlying the petroglyphs dated to roughly 14,800 ago. Additional data from a sediment core from an adjacent lake sub-basin revealed the limestone boulders 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 the study, archaeologists believed the petroglyphs were extremely old. But whether they turn out to be 14,800 years or 10,500 years, they are still the oldest petroglyphs dated in North America.
Native American artifacts found in the surrounding basin have been dated to the time period of 11,300 to 10,500 years ago. But this does not rule out the possibility that the petroglyphs were carved 14,800 years ago.
The oldest dates calculated for the Winnemucca petroglyphs correspond with the time frame linked to fossilized human excrement found in a cave in Oregon. The excrement dates back to roughly 14,400 years ago, and was found alongside bones of horses and camels that went extinct in North America more than 13,000 years ago.
Petroglyphs found in central Oregon, previously thought to be the oldest examples in North America, share similar features with some of the rock art at the Winnemucca site. At least one of the petroglyph panels in Oregon was buried by ash by an erupting Mount Mazama roughly 6,700 years ago, proving that it was carved sometime before the eruption.
“We have no idea what they mean,” Benson said referring to the Winnemucca petroglyphs. “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.”