THE PURRÓN DAM COMPLEX REVISITED: RESULTS OF A PILOT GEOARCHAEOLOGICAL INVESTIGATION AT A PREHISTORIC WATER MANAGEMENT SYSTEM IN THE TEHUACÁN VALLEY OF SOUTHERN MÉXICO

The Purrón Dam is widely known as the largest prehistoric water management feature in Mesoamerica. The dam reached a total size of 400 meters in length, 100 meters in width, and 20 meters in height, with construction commencing during the Formative Period (750 B.C.). The Purrón Dam Complex (PDC), which consists of the Purrón Dam, associated water management features and archaeological sites, was initially recorded in the 1960s by Woodbury and Neely as part of the Tehuacán Valley Archaeological and Botanical Survey. Until 2004 there had been no additional investigations into how the dam functioned as part of a water management system, or of its geomorphic setting. In 2004 a new canal system, additional archaeological sites, and an artificial terrace in association with the PDC were recorded by Neely and colleagues as part of a re-survey of the PDC. In order to better understand these findings a pilot geoarchaeological study was conducted in 2005. This investigation was the first effort to place the PDC into its geomorphic context since the initial survey in the mid-1960s. The 2005 investigation identified a new series of small dams upstream of Purrón Dam, confirmed the identification of canals and artificial terraces, identified a preserved deep sedimentation sequence behind the dam, found likely prehistoric agricultural surfaces, and reevaluated the sequence of construction. Optically stimulated luminescence (OSL) and radiocarbon dating of the deep sedimentation sequence, canal fill sediments, and an infilled sluice provide the first direct dates of these archaeological features, as well as chronological control of valley sedimentation rates. The new radiometric dates, geomorphic observations, and archaeological findings facilitate new interpretations on how the PDC functioned, the complex cultural manipulation of the natural setting, catchment hydrology during the Late Holocene, and prehistoric settlement patterns in the Tehuacán Valley.