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Prehistoric land use patterns that primarily involved hunting and gathering practices <br />had little or no adverse affect on the local environment. Prehistoric camps most likely <br />occurred on the south-facing benches above the river. The study area was not directly <br />affected by the advent of coal mining in the early 1900's, except for the establishment of the <br />existing road on the north side of the river. The narrow valley bottom was used for farming <br />and pasture. <br />Palcoclimatc. <br />Reconstruction of palcuenvironmental conditions is essential to the understanding of <br />population movement and cuhural change in prehistoric times (Cofer et al. 1979). Changing <br />environmental conditions altered the exploitative potential of an area and put stress upon <br />aboriginal cultures by requiring adjustments in their subsistence patterns. To interpret <br />whatever changes arc seen in the archaeological record, an account of fluctuations in past <br />climatic conditions must be available or inferences must be made from studies done in <br />surrounding areas. Generally, only gross climatic trends Itavc been established for western <br />North America prior to ?000 B.P. (Antevs 1955; Mehringer 1967; Madsen 1982; Wendlund <br />and Bryson 1974; Peterson 1931). Scientific data derived Gom investigations of prehistoric <br />cultures and geoclimatic and bioclintatic conditions on the southern Colorado Plateau over <br />the past two millennia leave aclticvcd a much greater degree of resolution (Dean et al. 1985). <br />• A study by Berry and Berry (1986:313-313) summarizes the gross climatic episodes <br />of the Colorado Plateau and Basin and Range provinces over the past 13,000 years, as <br />determined from radiocarbon-dated pollen samples. Between 11,000 and 3,000 B.C., <br />conditions shifted from glacial to non-glacial; i. e., there was an overall decrease in effective <br />moisture and an increase in temperature. The ensuing pre-Boreal/Boreal period (3000-6500 <br />B.C.) brouglu cooler, drier conditions to the region. The Atlantic period (6500-3100 B.C.) <br />was one of complexity. In large part, it corresponds to Antev's Altithermal, but evidences <br />two comparatively short phases (6500-5500 and 4750-3950 B.C.) of increased coolness. <br />Between 3100 and 300 B.C., the Sub-Boreal episode saw an increase in effective <br />moisture and, on the Plateau, a corresponding increase in pinyon pine forest. Steger (1981: <br />107-108) suggests pinyon pine disappeared I}om the Gumiison Basin during this time and <br />was replaced, in part, by ponderosa pine. <br />The Sub-Atlantic period (300 B.C -A D. 400) was mainly a time ofdrying and <br />warming and, on the Plateau, contraction of~tlte pinyon forest, although warm wet conditions <br />prevailed toward the end of this period. r\ brief, cool dry phase occurred early (A.D. 350- <br />450) in the Scandic/ Neo-Atlantic (A. D. 400-I 100), but the remainder of this episode is <br />characterized as warm and wet. r\ period of cool, dry conditions--tlte Pacific episode-- <br />followed and lasted approximately 600 years. <br />3 <br />