Nevada pictographs now thought to be the oldest known in North America

Via the History Blog

Rock art carved on limestone boulders in Winnemucca Lake, a dried lake bed in northwest Nevada, is at least 10,500 years old and may be as much as 14,800 years old, a new analysis confirms. Even at the lower age range that makes these petroglyphs the oldest known in North America, and at the higher range it makes them contemporary with some of the first people to migrate to the continent from Asia.

Winnemucca Lake had some water in it as recently as the 1930s before construction projects drained the shallows for good, but at various times in the past it was so filled with water that the boulders on the western end of the lake were completely submerged for thousands of years. The carvings could only have been done when the rocks were above the water line. In order to determine when the petroglyphs were made, therefore, University of Colorado Boulder geochemist Larry Benson radiocarbon dated crusts of carbonate left on the boulders when they were under water. He found that a carbonate film underneath the rock art is around 14,800 years old while the carbonate crust on top of the art is around 11,000 years old. Additional information from rock and sediment core samples from adjacent Pyramid Lake narrowed down the range further, suggesting the boulders were above water in two phases: once between about 14,800 and 13,200 years ago, the second time between about 11,300 and 10,500 years ago.