Early Olmec obsidian trade and economic organization at San Lorenzo

The Olmec were the first complex society to develop in Mesoamerica between 1800 and 600 cal B.C. The earliest large Olmec center during this period was the archaeological site of San Lorenzo which emerged as Mesoamerica's first large ritual and political center between 1400 and 1000 cal B.C. San Lorenzo's growth as a prominent center included the development of long distance trade relationships with adjacent areas of Guatemala and highland Mexico. High precision chemical analysis of obsidian imported for use in the fabrication of cutting tools is used to reconstruct the growth, size and extent of San Lorenzo's interregional exchange networks with areas of Mexico and Guatemala where obsidian occurs as raw material. A total of 852 obsidian artifacts were analyzed to reconstruct changes in obsidian procurement between 1800 and 800 cal B.C. This represents one of the largest samples of sourced obsidian from a Mesoamerican site and it provides a comprehensive picture for the development of interregional trade networks for Mesoamerica's first large Olmec center.