FLOODPLAIN STABILITY CONTROLS THE GROWTH POTENTIAL AND RESILIENCE OF INDIGENOUS NORTHERN COLORADO PLATEAU AGRICULTURAL COMMUNITIES: A CASE STUDY FROM, DINOSAUR NATIONAL MONUMENT

Indigenous agriculturalists north of the Colorado River occupied the ecological margins of maize cultivation in western North America from 300-1300 CE. Fremont societies practiced diverse agricultural strategies designed to offset shortfalls in foraged foods caused by a dominant pattern of multidecadal precipitation variability. From this perspective, agriculture increased the robusticity of food sources leading to small but resilient local populations. Our previous work in northern Utah’s Uinta Basin demonstrates that in the absence of the dominant multidecadal precipitation variability regime between 750-1050 CE, agricultural conditions improved, and populations expanded to form villages along the floodplains of northern Colorado Plateau dryland alluvial systems thus creating the capitol necessary for incipient social complexity. But did the very same conditions (i.e., decreased precipitation variability) that allowed the growth of Fremont agricultural societies make them simultaneously vulnerable to arroyo formation, a key geomorphic risk to floodplain agriculturalists? In this study, we test the hypothesis that complex response in alluvial cycles limits the growth potential and resilience of dryland agricultural societies. We present preliminary results from Cub Creek in Dinosaur National Monument that shows rapid sedimentation punctuated by episodic arroyo formation characterized the last 2,000 years of the valley’s history. We present stratigraphic and chronological evidence of an arroyo-forming event between 900-1000 CE that corresponds with the final decades of the Cub Creek agricultural village. We conclude that arroyo formation combined with the return of the dominant multidecadal precipitation variability regime at 1050 CE was a key ecological constraint on the growth potential of local Fremont populations. These findings have potential implications for early Indigenous dryland agricultural systems throughout the interior of western North America.