Determining the Basaltic Source Rocks of Enigmatic Cogged Stones From Southern California

ABSTRACT Enigmatic cogged stones, found in southern California, are hand-sized Native American artifacts carved into the shape of a cogged wheel. They are found in 8,000–3,500-year-old sites, but their function is the subject of debate. Our goal is to determine the source of the basaltic rock used for cogged stones. Petrographic and geochemical analyses were performed on four cogged stone fragments and data were compared to basalt collected from outcrops across southern California. We found that basalt from El Modena and the Santa Rosa Plateau matches the material of two of the cogged stones. One sample from Catalina Island possibly matches a third. We conclude from our study that the likely source rock locations are near the locations where the cogged stones were found.