Geochemical and Soil Micromorphological Properties of Archaeological Deposits in Coastal Southern California.

Geoarchaeological and soil studies were conducted in Los Angeles as part of the Playa Vista Archaeological and Historical Project prior to development of property formerly owned by Howard Hughes. Field investigations at CA-LAN-62 and other ancient settlements near the Ballona Lagoon and surrounding wetlands were completed to aid in interpreting the formation, preservation, and alteration of cultural deposits on alluvial fans along the base of the Ballona Escarpment. These settlements span the last 6,000+ years, with sites represented by Mission Period through Millingstone Period occupations. A variety of soil analyses were completed (e.g., pH, organic matter, nitrogen, calcium carbonate, electrical conductivity, particle-size, and bulk density analyses), but phosphorus analysis proved especially useful. Phosphorus concentrations were used to identify buried occupation surfaces that were not always visible macroscopically in the surficial and buried soils. Phosphorus analysis was also used to discern ancient activity areas in relation to cultural features represented by food processing, cooking, refuse disposal, and other activities. Micromorphological analysis of fire hearths revealed use of peat that may have served as fuel, lagoonal clay for hearth construction on sandy subtrates, and coprolites from large scavenging animals, as well as the identification of egg shells and other materials not documented by other archaeological recover methods. Soil micromorphology was used to identify alterations of cultural deposits, such as those caused by groundwater fluctuations marked by calcitic hypocoatings and redoximorphic features, burial by fan/alluvial deposits, and reworking of deposits by bioturbation.