In 1928, Noel Morss was shown “irrigation ditches” along Pleasant Creek on the Dixie National Forest near Capitol Reef National Park, Utah, by a local guide who contended they were ancient. We relocated the site and mapped the route of an unusual mountain irrigation canal. We conducted excavations and employed OSL and AMS 14C showing historic irrigation, and an earlier event between AD 1460 and 1636. Geomorphic evidence indicates that the canal existed prior to this time, but we cannot date its original construction. The canal is 7.2 km long, originating at 2,450 m asl and terminating at 2,170 m asl. Less than half of the system was hand constructed. We cannot ascribe the prehistoric use-event to an archaeological culture, language, or ethnic group, but the 100+ sites nearby are largely Fremont in cultural affiliation. We also report the results of experimental modeling of the capital and maintenance costs of the system, which holds implications for irrigation north of the Colorado River and farming during the Little Ice Age. The age of the prehistoric canal is consistent with a fragmentary abandonment of farming and continuity between ancient and modern tribes in Utah.

Fremont societies of the Uinta Basin incorporated domesticates into a foraging lifeway over a 1,000-year period from AD 300 to 1300. Fremont research provides a unique opportunity to critically examine the social and ecological processes behind the adoption and abandonment of domesticates by hunter-gatherers. We develop and integrate a 2,115-year precipitation reconstruction with a Bayesian chronological model for the growth of Fremont societies in the Cub Creek reach of Dinosaur National Monument. Comparison of the archaeological chronology with the precipitation record suggests that the florescence of Fremont societies was an adaptation to multidecadal precipitation variability with an approximately 30-plus-year periodicity over most, but not all, of the last 2,115 years. Fremont societies adopted domesticates to enhance their resilience to periodic droughts. We propose that reduced precipitation variability from AD 750 to AD 1050, superimposed over consistent mean precipitation availability, was the tipping point that increased maize production, initiated agricultural intensification, and resulted in increased population and development of pithouse communities. Our study develops a multidecadal/multigenerational model within which to evaluate the strategies underwriting the adoption of domesticates by foragers, the formation of Fremont communities, and the inherent vulnerabilities to resource intensification that implicate the eventual dissolution of those communities.

A series of farming experiments was conducted between 2013 and 2017 in Range Creek Canyon, Utah, to better understand the opportunities and constraints faced by prehistoric farmers in the Southwest. The experiments were designed to collect data on the optimal amount of supplemental water that should be applied to maize fields given the costs in labor and benefits in greater yield. We investigate expected variation in water management strategies using an optimal irrigation model (OIM). The model makes clear that the payoff for farming is best understood as a continuum of relative success and that irrigation is one activity (probably of many) that may improve farming efficiency as well as increase harvest yields. The optimal harvest will always be less than the maximum harvest when there are significant operating costs associated with irrigation. Estimating the costs and benefits of irrigation in a specific area allows for an assessment of whether irrigation is expected, and if so, how much effort should be devoted to water management. A local dendroclimatological study is used to provide the prehistoric context for the Fremont who occupied Range Creek Canyon, and irrigation is expected even in periods of greater precipitation.