Project Fieldwork and Analysis: April 29 - August 22, 2011. University of California
Hopland Research and Extension Center (HREC), Hopland, CA
Bryan Gordon, Canadian Museum of Civilization
Theory behind our petroglyph dating
We look for chipped rock art and hammerstone chips that fell to the artist’s feet when the art was made. These chips differ from soil and weathered rock art particles by their larger size and their sharp edges that resulted from hammering. Hammerstone chips are fewer, harder, more resilient and have a different color than rock art chips. To isolate hammerstone chips we first remove disturbed soil under the art, often down to 10 cm, then scrape the soil contents of each successive ¼ inch (6 mm) level over a 8x12 inch (20x30 mm) area into a dustpan. After transferring the contents of each level to nested sieves and shaking them, the few large hammerstone chips and any rootlets are removed from the topmost or ¼ inch (6 mm) mesh sieve. This is done with tweezers to avoid contaminating datable cultural or natural material.