TIMING OF BASIN-PLATEAU SETTLEMENT DISRUPTIONS SUPPORTS CONTINENT-WIDE EFFECTS OF LATE HOLOCENE MEGADROUGHT ~2000 CAL BP: IMPLICATIONS FOR PREDICTING ARIDITY TRENDS UNDER FUTURE CLIMATE CHANGE

Archaeological and paleoenvironmental proxy records from the Plateau and Great Basin provide evidence for geographically extensive Late Holocene megadrought conditions correlating with settlement disruptions ~2000 cal BP. The nature and extent of these events have implications for predicting local- to continental-scale aridity trends under future climate change. At peak aridity Late Holocene megadrought signatures are generally synchronous from southern Nevada and eastern California north to Washington and southern British Columbia, with potentially much broader distribution, implying teleconnections in the Cordilleran climate. In the Great Basin, widespread settlement disruption correlates with a three-phase prolonged dry period between ~3100 and 1800 cal BP. The most extreme drought phase, ~2000-1800 cal BP, corresponds to what appears to be the most arid portion of the Late Holocene on the Plateau. An overall decline in human activities at this time has long been recognized by Plateau archaeologists, interpreted as a hiatus or transitional period between different settlement strategies. Radiocarbon data compiled as part of a recent cultural resources management project in the Pend Oreille River Valley on the northeastern Washington/Idaho border, provide additional evidence for widespread regional settlement disruption during the Late Holocene megadrought. Analysis of 273 radiocarbon dates from 40 archaeological sites reveals a complete gap in the archaeological record ~2100 to 1800 cal BP, reflecting a period of disruption in an otherwise continuous record of Indigenous land use from 3700 cal BP to today. As a full sequence of Holocene-age landforms is represented in the valley, geomorphic bias can be ruled out as a factor in the apparent settlement hiatus. We present this case study alongside other relevant Plateau and Great Basin records.