2018-01-03_PERMIT FILE - C1981010 (5)

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Between 9500 and 5500 BC*, a long drought occurs (interrupted once around 7000 BC*, coincident with Pryor Stemmed occupations). Aeolian sand seas form in Colorado, Wyoming and Nebraska, and drainages throughout the mountain west are choked with sediment and become braided; these are Kaycee equivalent deposits. Dunes form in places in western Colorado and are later preserved as clay dune cores, but Kaycee equivalent deposits varying from a few to several meters in thickness are ubiquitous in the LSFO area. The Pleistocene extinctions were completed early in this interval and Paleoindian big game hunters were subsequently replaced by Archaic hunter -gatherers. While extinction of most of the Pleistocene megafauna took place in Clovis times, mammoth (e.g., Agenbroad 1978), camel and horse persisted in some areas to around 9000 BC* (e.g., Miller and James 1986). Cooling temperatures between 5500 and about 3100 BC* sustained the middle Holocene incision. Capacity and competence increased, but not to the levels achieved during the Late Glacial. As a consequence, when incision exposed Late Glacial gravel, stream power was insufficient to erode the gravel and most drainages initiated a cycle of channel widening. Away from drainages, the middle Holocene loess accumulated. Pithouses were in wide use in the Rocky Mountains, Wyoming Basin, and Colorado Plateau in the interval, suggesting more sedentary populations; Yarmony Site in Eagle County and site 5ME16789 near Battlement Mesa are local examples. McKean Complex is well represented in western Colorado during the latter part of the interval and the period of transition to warmer climates that followed. After about 3100 BC*, warming temperatures led to erosion of the loess by 2500 to 1850 BC* and the deposition of the middle Holocene alluvium. Droughts in the late Holocene are best dated by periods of erosion, i.e., lacunas, identified by unconformities in loess deposits. Erosion in loess took place between 1850 and 950 BC*, 275 BC* and 165 AD*, and 1050 and 1350 AD*, and again in the last 150 years or so. The first interval coincides with the Middle to Late Archaic transition and the third interval coincides with the Medieval Warming Period in Europe. In the alluvial system, deposition of the middle alluvium ended after the first and interval, by 650 BC*. The first of Lightning equivalent alluvium is deposited during the second and interval, at some time after 650 BC*. As the suggested dates imply, the two deposits are nearly continuous and appear this way in sediment choked drainages, but on other ephemeral and small perennial streams, the deposits are more easily separated. 5.0 LITERATURE OVERVIEW North America's first human explorers arrived near the close of the Pleistocene as early as 18,000 years ago traveling by passage along Beringia the continental land bridge between what is now Siberia and Alaska. Local and regional archaeological studies indicate nearly continuous human occupation of Northwest Colorado for the past 12,000 years. The prehistory of the region is outlined in the Colorado Council of Professional Archaeologists' Colorado Prehistory: A Context for the Northern Colorado River Basin (Reed and Metcalf 1999), Synthesis of Archaeological Data Compiled for the Piceance Basin Expansion, Rockies 5