Dr. David Kimbrough and Dr. Pat Abbott’s new paper where the authors investigated the geological origins and sources of sandstone cobble grinding tools.  This paper is the first use of U–Pb geochronology and Hf isotope geochemistry to source stone tools. The results show that hunter-gatherers carried the cobbles at least 4–10 km and up to 80 km. U–Pb geochronology identifies sandstone sources more precisely than petrography alone.

Sourcing sandstone cobble grinding tools in southern California using petrography, U–Pb geochronology, and Hf isotope geochemistry

Margie M. Burtona, Adolfo A. Muniza, c, Patrick L. Abbottb, David L. Kimbroughb, Peter J. Haproffa, George E. Gehrelsd, Mark Pechad,

aSan Diego Archaeological Center, 16666 San Pasqual Valley Rd., Escondido, CA 92027-7001, USA
b Department of Geological Sciences, San Diego State University, 5500 Campanile Dr., San Diego, CA 92182-1020, USA
c Department of Anthropology, California State University San Marcos, 333 Twin Oaks Valley Rd., San Marcos, CA 92096-001, USA
d Department of Geosciences, University of Arizona, 1040 E. 4th Street, Tucson, AZ 85721, USA


Procurement strategies for grinding tool lithic material among mobile societies are thought to rely on opportunistic selection of resources locally available at habitation sites and along migratory routes. In San Diego County, California, non-local appearing quartzarenite cobble handstones were identified in the ground stone assemblages of some hunter-gatherer archaeological sites dating from ca. 7000 years ago. Due to the nature of the cobble material, both natural and cultural processes may have played a role in the spatial distribution of the artifacts recovered by archaeologists. In this study we employ three techniques to investigate the geological origins and source location(s) of the quartzarenite cobbles: thin section petrography, U–Pb geochronology, and Hf isotope geochemistry. Results confirm the Neoproterozoic-lower Paleozoic age of the cobbles, while metamorphism of southern California basement rocks of similar age indicates that the cobbles must have been transported into the area, probably during Eocene times. People collected the cobbles from source locations and carried them at least 4–10 km and possibly farther. We consider the diagnostic value of the three techniques for characterizing resource distributions of sedimentary cobble material and related procurement strategies, and more broadly, their global applicability for sourcing other archaeological materials made of sedimentary and metasedimentary rock.

The Galapagos: A Natural Laboratory for the Earth SciencesBurton, Margie M., et al. “Sourcing sandstone cobble grinding tools in southern California using petrography, U–Pb geochronology, and Hf isotope geochemistry, Journal of Archaeological Science Volume 50, October 2014, DOI: 10.1016/j.jas.2014.07.015