Prehistoric Irrigation in Central Utah: Chronology, Agricultural Economics, and Implications

Abstract

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.