With National Science Foundation support, Dr. James Neely and collaborators will reconstruct the prehistoric canal system located in the Tehuacan Valley, central Mexico. Archaeologists who wish to understand the processes which led to complex societies have focused on water management systems because of the significant role they played. In many regions of the world where early civilizations emerged, rainfall was not sufficient to permit large scale dependable agriculture and to meet subsistence needs extensive canal systems were constructed. Such large, labor intensive projects, require many people to work together in a coordinated fashion. Major systems require extensive planning, and decisions about allocation of land and water necessitate some form of central control. Therefore archaeologists believe that in many places canal irrigation is closely linked to the development of large scale societies and centralized systems of government and economics. A series of early states and empires, including the Aztec, developed in central highland Mexico and archaeologists have known for decades that canal systems were present. However canals are extremely difficult to date and therefore it is hard to correlate changes in irrigation and social development.
Dr. Neely and his colleagues have identified an extraordinary system of "fossilized" canals with the potential to obviate this difficulty. They have been incredibly well preserved due to the deposition of minerals (travertines comprised primarily of calcium carbonate) that were contained in the waters that passed through their channels. Thus the canal systems are preserved in stone that is in some places over 2.0 meters thick. These systems, constructed over an estimated 2700 year period were apparently renovated and extended through time. The travertine preserves a record of its construction sequence and provides a sensitive measure of the demand for agricultural production of the people who made and used them. Dr. Neely and colleagues will map the canals and selectively extract samples of travertine present as stratified layers in the canal cross-sections. Uranium-series dating and stable isotope analyses will be conducted and organics removed for radiocarbon dating. Associated pollen, phytoliths and diatoms will be recovered for paleoenvironmental reconstruction. Related archival studies will search out documents pertaining to late Prehispanic and early Colonial land and water use and tenure. On this basis it will be possible to construct a chronology of canal construction, subsequent expansions and improvements and the eventual demise of the systems. Vegetational ecology and insights into the cultivated and non-cultivated plants from fields adjacent to the canals will also be obtained.
