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maximum of 100 frost -free days in a year. Annual precipitation is about 18 to 20 inches <br />(USDA SCS 1976). <br />Prehistoric land use was primarily hunting and gathering, which had little or no adverse <br />affect on the local environment. Present day land use includes cattle grazing, hunting, and coal <br />mining development. <br />4.0 PALEOCLIMATE <br />Paleoenvironmental data for the area is scant, but it is agreed that gross climatic <br />conditions have remained fairly constant over the last 12,000 years. However, changes in <br />effective moisture and cooling/warming trends undoubtedly affected the prehistoric occupation <br />of the area. Based on an analysis of the area's late Quaternary stratigraphy, the geologic history <br />of the last 18,000 calendar years in the region follows something like the following scenario <br />(Miller 2010: Chapter 2; Conner et al. 2011:2.35-2.36). [Dates (*) are calibrated.] <br />Late Pleistocene dissection scoured channels during the Late Glacial and deposited <br />thick sequences of large, e.g., boulder -sized, gravel in most drainages. About 13,400 BC* the <br />glaciers are retreating and capacity and competence decrease; the time between then and about <br />11,000 BC* is identified by Haynes (1991) as the Clovis drought. In areas dominated by <br />aeolian processes, deflation occurs. The Younger Dryas, from around 10,600 to 9000 BC*, the <br />last gasp of the glacial period, took place around Folsom times. During the period, drainages <br />are rejuvenated, surfaces stabilize, soil formation accelerates, and the late Pleistocene -early <br />Holocene loess is slowly accumulated. <br />Between 9500 and 5500 BC*, a long drought occurs (interrupted once around 7000 <br />BC*, coincident with Pryor Stemmed occupations). Aeolian sand seas form in Colorado, <br />Wyoming and Nebraska, and drainages throughout the mountain west are choked with <br />sediment and become braided; these are Kaycee equivalent deposits. Dunes form in places in <br />western Colorado and are later preserved as clay dune cores, but Kaycee equivalent deposits <br />varying from a few to several meters in thickness are ubiquitous in the LSFO area. The <br />Pleistocene extinctions were completed early in this interval and Paleoindian big game hunters <br />were subsequently replaced by Archaic hunter -gatherers. While extinction of most of the <br />Pleistocene megafauna took place in Clovis times, mammoth (e.g., Agenbroad 1978), camel <br />and horse persisted in some areas to around 9000 BC* (e.g., Miller and James 1986). <br />Cooling temperatures between 5500 and about 3100 BC* sustained the middle <br />Holocene incision. Capacity and competence increased, but not to the levels achieved during <br />