Teotihuacan Valley, Mexico, Postclassic chronology: Hydration analysis of obsidian from Cihuatecpan, an Aztec-period village

The Postclassic period in central Mexico was characterized by enormous population growth and expansion of settlement, but the timing of the onset of these processes has been poorly understood. Obsidian tools from residential contexts at the Late Postclassic village of Cihuatecpan in the Teotihuacan Valley have been analyzed to determine the extent of hydration, and thus the amount of time elapsed since the tools were manufactured. Estimated dates of manufacture range between A.D. 1221 and 1568, consistent with ethnohistoric accounts of the timing of establishment of Cihuatecpan and other rural villages, and their abandonment in the Early Colonial period. Ceramics found in the same contexts as the obsidian tools include Black-on-orange types, such as III, which may have come into use in the thirteenth century. This experiment in relative and absolute dating accords with other current research, indicating a needed revision of traditional chronologies toward an earlier onset of major processes.