EARLY AGRICULTURAL PERIOD FLOODPLAIN RECONSTRUCTION: SURVEY OF IRRIGATION CANALS AT THE LA PLAYA SITE, SONORA, MEXICO

La Playa (SON F:10:3), located in northern Sonora, Mexico, has the remains of an irrigation canal system which date to the Early Agricultural period (2200 B.C.-A.D. 50). This site is the largest identified Early Agricultural period community in Northwest Mexico/U.S Southwest. Although occupied throughout much of the Holocene, it was during the Early Agricultural period that people began to manipulate the landscape to create features such as canals and aquecias in order to irrigate fields. These agricultural features are visible at La Playa.

La Playa is located on the floodplain of the Boquillas river. During the early Holocene, the Boquillas river changed from a high energy, braided stream to a low energy stream with frequent fine grained overbank deposition. This low energy depositional environment may have been attractive to the earliest agriculturalists in the region. Additionally, the extensive canal system may have created a feedback system in which frequent site-wide deposition was encouraged, creating an anthropogenically constructed wetland environment.

This paper presents the results of the first systematic survey of the canal network at La Playa. Over one hundred canals were mapped amounting to at least 2 km of canals. Episodes of sedimentation and repair of segments of canal channels were visible during survey. Agricultural features such as grid patterns, possibly delineating garden plots, were also located. These features likely served as water and sediment control features on the Boquillas floodplain. Other water control features include fire cracked rock, which may have been used as riprap to slow erosion of the earthen irrigation system. Reconstruction of the canal system at this site is an exercise in distinguishing natural floodplain depositional process from large scale anthropogenic construction and determining how they articulate with each other over time.