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bands to continue migrating southward (Merrill et al. 2009). <br />The Early Archaic (5500-3750 BC) exhibits a good deal of cultural continuity with <br />the preceding period. Semi-sedentary hunting and gathering remained the most effective <br />adaptive strategy. Procurement efforts centered on a broad spectrum of biotic zones that <br />were exploited through a central-place foraging strategy. The intensification in procurement <br />efforts is manifested in the burgeoning visibility of processing features as well as pit <br />(pithouse) and basin (house-pit) structures. This period marks the first half of the Middle <br />Holocene and represents the harshest drought conditions experienced by the prehistoric <br />population. Again, much of the data derives from surface finds of projectile points which <br />cross-date from other regions to this period. Radiocarbon dates from this period from <br />multi-component sites tentatively argue in favor of subsistence and settlement strategies <br />logistically organized on ecological economic zones that radiated out from a household <br />residential base. Evidence of decreased mobility and longer-term, seasonal residency in the <br />form of pithouses has been found in the mountain areas, but subsistence data are sparse. <br />Evidence of occupation of northwest Colorado in the Middle Archaic Period, ca. <br />3750-1250 BC, from excavation data greatly expands in comparison to the previous periods. <br />This cool moist period in the second half of the Middle Holocene is evidenced by a wide <br />variety of projectile point styles covering large regions of the Intermountain West, with the <br />greatest influences coming from the Great Basin and the Wyoming Basin, with some minor <br />contacts from the Southwest. The number of radiocarbon dates increases dramatically over <br />previous periods. The occurrence at several sites of radiocarbon dates from this period on <br />multi-component sites suggests that subsistence and settlement strategies were indeed <br />logistically organized on ecological economic zones that radiated out from a household <br />residential base. In fact, this adaptation had become so well established that what may have <br />once been simple, highly ephemeral, household residential bases had now become true 'base <br />camps', which later metamorphosed into 'localities' that were repeatedly and systematically <br />re-occupied. <br />The Middle Archaic roughly corresponds with the Neoglacial period, which <br />exhibited an overall increase in effective moisture and cooler temperatures. On the <br />Colorado Plateau, these conditions were conducive to the expansion of the pinyon pine <br />forest northward from New Mexico into central Colorado and eastern Utah by around 2750 <br />BC (Berry and Berry, 1986). With the advent of these more favorable environmental <br />conditions, a shift by the aboriginal populations down to the middle and lower elevation <br />levels would have been comfortably feasible. As the radiocarbon data reveal, there is an <br />overall drop in the date frequencies for the Colorado mountains along with a corresponding <br />rise in the date frequencies of the northern Colorado Plateau. By about 1700 BC, the pinyon <br />forest again expands northward with pinyon and juniper trees present in the canyon bottoms <br />and washes. <br /> Climatic fluctuations occurred during this period and two distinct dry episodes are <br />recorded by Peterson (1981) for the La Plata Mountains and by Chen and Associates for the <br />Battlement Mesa area (Conner and Langdon 1987:3-17). Data supporting the first dry <br />21