Human Response to Climate Change in the Bonneville Basin, Western North America: The Bonneville Estates Radiocarbon Chronology

Abstract:

We present a comprehensive and detailed radiocarbon chronology of Bonneville Estates Rockshelter, a prehistoric archaeological site located along the western margin of ancient Lake Bonneville in western Nevada. Bonneville Estates contains a well-stratified record of human occupation spanning from about 13,000 calendar years ago to just a few centuries ago, and its position today at the sagebrush-to-shadscale ecotone (~1585 m above sea level) of the mid-latitude Great Basin desert makes it uniquely suitable for interpreting the significance of local environmental and regional climate change on human technology, subsistence, and settlement organization. Here we present an assemblage of 168 radiocarbon age estimates obtained chiefly from fire-hearth features but also from perishable artifacts, coprolites, and other plant and animal remains. We report a calibration analysis, Bayesian modeling, and summed-probability analysis of these age estimates, and we interpret the results in the context of various proxy records of human behavior, paleoenvironment, and paleoclimate preserved in the rockshelter as well as across the Bonneville basin. Although in general the resulting radiocarbon chronology indicates repeated and frequent use of the rockshelter through the Holocene, in particular there are obvious episodes of intensive human use versus periods of little to no occupation. These patterns associate temporally with shifts between relatively cool, mesic and hot, arid conditions, respectively, some short-term (century-scale) and others long-term (millennial-scale). We conclude that human use of Bonneville Estates was very much influenced by local environmental conditions, which were in turn were driven by regional climate. However, the record from this single site should not be used to interpret regional demographic trends, and our documented correlation between human occupational intensity and environmental/climatic conditions should not be considered as evidence of 'environmental determinism' in this desert setting. Instead our results demonstrate the flexibility of Great Basin foragers, who successfully adapted to short-term and long-term climatic changes, a testament to their intimate knowledge of their natural and cultural circumstances.