New Absolute Chronological Constraints to La Playa (Sonoran Desert) Archaeology between the American Southwest and Mesoamerica—From Long Period Human Resilience to Apparent Abandonment

Sonoran Desert archaeological settlement is one of the most representative sites in Northwestern Mexico/Southwestern United States of the Early Agriculture period because of various cultural processes involved, such as the introduction of the first cultigens and the construction of Pit Houses. These early desert village settlements used geomorphological features of the local landscape to facilitate their sophisticated form of agriculture. Most of the features and artifacts at the site are associated with the Early Agricultural period of 3150-1900 cal B.P., while most occupation dates are in the Cienega phase (2800-1900 cal B.P.). Later stages are poorly documented because of the apparent reduction in population, less marked archaeological features, and extreme erosion processes. Systematic archaeological excavation revealed evidence of completely burned Pit Houses. We analyzed 56 samples belonging to four Pit Houses and one different combustion feature (Kiln or Horno, as they are locally known) in different areas of the settlement. The experimental procedure included continuous susceptibility vs. temperature measurements and step-wise alternating field demagnetizations. Only 36 samples yielded technically acceptable determinations that allowed the determination of archaeomagnetic directions. Statistically indistinguishable results were obtained from all five studied features. This finding reinforces archaeological evidence of ritual-related paraphernalia and/or apparent abandonment or, at least, migration.