The Site of Uci in the Yucatan Peninsula of Mexico is noted by a major 18-Km elevated causeway along with pyramids and household structures.  Through geochemical analysis of stable C isotopes in the soil humin fraction, locations of ancient maize fields will be identified. The vegetative history of the soils will reveal where and how the ancient populations produced enough food to not only subsist, but create such elaborate infrastructure.   Results obtained through these studies will then be incorporated into a GIS model to predict the other areas most likely to reveal positive results for ancient maize agriculture.  Soil P and trace element analysis will be used to delineate household kitchen and workshop activity areas.