Chemical analysis of obsidian (volcanic glass) artifacts from many Mexican archaeological sites indicates that much of the raw material derives from the Zinapecuaro area in Central Mexico. In preliminary reconnaissances Dr. Dan Healan has located several specific sources, as well as cultural remains associated with the mining and working of this material. Through examination of surface scatters, he has also discovered several habitation sites. With NSF support, Dr. Healan will conduct a six month field season followed by a year of analysis. He and his colleagues will continue and expand the intensive surface survey. Exploratory excavation will then be conducted at selected quarry and related sites. A second series of excavations will then be undertaken at habitation sites. Materials recovered will be analyzed to shed light on the obsidian production system and to provide a detailed history of settlement and exploitation of the region. Obsidian hydration analysis will provide a chronological framework. Finally, data from the Zinapecuaro region will be synthesized with information from other areas in Mexico to show how economic and political relationships changed over time. Because obsidian is relatively easy to work and holds an extremely sharp edge, (and given the lack of metal implements before the arrival of the Spaniards) it was the preferred material for stone tool manufacture in Mexico. Given its volcanic origin, obsidian is found in only a limited number of areas and in prehistory was traded over large areas. Different sources are chemically distinct and, thus, it is possible to match implement with geographical point of origin. Archaeologists have come to realize that trade and control over scarce resources played a major role in the rise of Mexican civilization and believe that obsidian was perhaps the most important commodity involved. Thus, through study of production at a source area, it will be possible to understand more about how this trade originated, developed, and was maintained. This research is important because it will fill in a crucial blank in the archaeological map of Mexico. What happened in the Zinapecuaro region had a major effect in the development of complex societies elsewhere. The work will increase our understanding of how complex societies develop.