CHACO CANYON’S ANOMALOUS GEOMORPHIC AND CULTURAL HISTORIES—POSSIBLE CONNECTIONS

Chaco Canyon, in the San Juan Basin of NW New Mexico, was the center of a uniquely complex and influential Anasazi culture from about AD 800 to 1150. Its evolution overlapped development and filling of an arroyo system in time (i.e. the "post-Bonito channel" of Kirk Bryan is considerably older than he thought). Stages in the development of the culture can be tied to stages of fluvial evolution (Force and others, 2002). Construction of Pueblo del Arroyo, the southeast corner of Pueblo Bonito, and many other features had to await various stages of filling of the arroyo system (AD 1025-1090). Probably, accommodation to a filling arroyo led to Chaco Canyon’s complex water-control systems.

Chaco Canyon’s geomorphic development is anomalous in its region, and was governed by base levels at the junction of Chaco and Escavada Washes, apparently by a transitory eolian (+masonry?) dam. So how were Chaco’s unique culture and anomalous geomorphology related? The relation precedes the Bonito channel, for the Chacoan culture was already unique by the mid-AD 800’s, when multi-story greathouses first appeared. The Chaco unit of Hall, now thought to represent about AD 1-920?, and into which the Bonito channel is cut, has the answers.

The Chaco unit forms much of the valley floor, which is perched above Escavada Wash behind the eolian dune at the junction. Floodplain deposits predominate except at the downvalley end, where a delta grew over playa-lake deposits. Multiple thick (but poor) soils are present on the unit. Thus the pioneers’ choice of Chaco Canyon was a choice of some combination of an aggrading system that permitted ak chin farming at all side-tributary junctions, the main-valley part of the system where floodplain farming could be conducted in large areas, and/or something useful about the playa-lake itself.

Force, E. R., Vivian, R. G., Windes, T.C., and Dean, J. S., 2002, Relation of "Bonito" paleochannels and base-level variations to Anasazi occupation, Chaco Canyon, New Mexico: Arizona State Museum Arch. Series 194, 49 p.