DATING NORTH AMERICA’S OLDEST PETROGLYPHS

On the western side of the Winnemucca Lake Basin stands a tufa mound that was deposited beneath the waters of Lake Lahontan. The mound composed of broken spheres of calcium carbonate is deeply carved with abstract petroglyphs. The outer layer of the incised carbonate spheres contains a branching form of tufa that was deposited on or before 14,800 yr BP. A thin crust of porous carbonate coats the base of the mound and petroglyphs up to an elevation of 1206 m. The carbonate was deposited when lake level was held at 1207 m by spill across the Emerson Pass at the northeast end of the Pyramid Lake Basin. The oldest calibrated radiocarbon date on the porous carbonate is 10,200 yr BP. Thus the petroglyphs were carved sometime between 14,800 and 10,200 yr BP.

The Winnemucca Lake Basin is connected to the Pyramid Lake Basin by a spillway that funnels water to Winnemucca Lake when Pyramid Lake exceeds 1177 m. Thus, the elevation of Winnemucca Lake is determined by the elevation of Pyramid Lake when it rises above 1177 m. During spill over Emerson Pass, very little calcium carbonate was deposited in the sediments of the coalesced lake system. Measurements of carbonate in a precisely dated deep-water core from the Pyramid Lake Basin indicate that lake level dropped below the 1207-m spill level between 14,800 and 13,200 and between 11,300, and 10,500 yr BP, exposing the base of the tufa mound to petroglyph carving. Archaic Native American artifacts found in the Lahontan Basin date to the younger time interval. In addition, the earliest Native Americans inhabited the northern Great Basin during the older time interval, and numerous petroglyphs in that region share a number of attributes with the Winnemucca Lake Basin petroglyphs. Both time intervals remain candidates for petroglyph carving.