GEOARCHAEOLOGICAL INVESTIGATION OF THE EARLY AGRICULTURAL PERIOD IRRIGATION CANALS AND STRATIGRAPHY AT THE LA PLAYA SITE IN SONORA, MEXICO

La Playa (SON F:10:3) is an Early Agricultural period (2100 B.C. – 50 A.D.) archaeological site in Sonora, Mexico. It is one of the largest identified Early Agricultural period sites in northern Mexico and has evidence of a canal system spanning over 3 km². The site has been severely eroded due to historic gullying and sheet wash erosion. Intact portions of the canal system were located using magnetic gradiometry survey and trenches were excavated to examine canal sections. This poster synthesizes results from the stratigraphic analysis of the canal system.

Canal profiles were measured and stratigraphic profiles were drawn. Sediment texture, color, and soil development were characterized. Additionally, multi-spectral photography assisted in the field identification of canal stratigraphy. Monochromatic silty soils at La Playa make canals difficult to distinguish in the field and in photographs. A digital camera was modified for full spectrum photography and used to document subtle stratigraphic changes which could not be recorded using visible light digital photography. A combination of visible spectrum and multi-spectral photography were used to document the canal cross sections and stratigraphy. This included full spectrum photography (approximately 300-1000 nm) and photography using an ultraviolet filter (300-400 nm) and infrared filters (720-1000 nm, 760-1000 nm, and 850-1000 nm).

These field observations were compared to previous stratigraphic investigations at La Playa to obtain relative age estimates of canal sections and characterize the degree of sheet wash erosion affecting canals in various portions of the site.