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U.S. Rock Art in the Twenty-first Century: Problems and Prospects

Microscopic thin section of the rock varnish that naturally coats rock surfaces in deserts, eventually covering the engraved portions of petroglyphs. The alternating layers are the result of major changes in prehistoric climate. The layering sequence for a given region is constant and can be calibrated using rock-varnish-coated geological surfaces of known age. Recent calibration for the last ten thousand years in California's Mojave Desert greatly enhances archaeologists' abilities to date petroglyphs using varnish microlamination dating. Photo: Courtesy of VML Dating Lab.