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-16- <br />pottery vessels (Turner Gray Ware) and pottery figurines, and a distinctive <br />• rock art style (both petroglyphs and pictographs). Their absence in the study <br />area may be due to a number of factors. Although agriculture is obviously <br />practiced in the study area today, climate and soil types in the area may have <br />been unsuited to the kinds of crops (particularly Mexican Dent Corn) and <br />horticultural pa~ctices used by the Fremont. While the origins of the Fremont <br />Culture and its affiliations with adjacent agricultural groups is a matter <br />of considerable interest and speculation, an extended discussion of the prob- <br />lem is not appropriate here (cf. Aikens 1966, Ambler 1966, Breternitz 1970: <br />163-164, Sharrock 1966, and Sdormington 1955 for specific discussions of the <br />problem). <br />4.2 RELEVANT ENVIRONMENTAL FACTORS <br />4.2.1 Physical Geography <br />The subject area lies within the Wyoming Basin Province, which is one <br />of the nine generally recognized physiographic regions of Colorado. Charac- <br />terized by large areas or basins of relatively little relief separated from <br />• each other by eroded scarps .and cuestas, that part of the Province that lies <br />within Colorado is drained by the Yampa River and its tributaries. The study <br />area itself includes a section of the Yampa and several miles of one of its <br />major tributaries, the Williams Fork. The flood plains of the two rivers <br />within the study area are relatively narrow with the exception of two ex- <br />tensive bottomland areas along the Yampa - Big Bottom and Round Bottom (cf. <br />Figure 2). Of the two bottomland areas, Big Bottom is the larger with an area <br />of approximately 2'~ square miles while Round Bottom has an area of about 1 <br />square mile. Geographic relief along the rivers elsewhere tends to be high <br />with narrow terraces along most of their lengths and no terraces in some <br />areas. The Yampa is bordered on the south in the study area by Iles Mountain <br />and Duffy Mountain, both of which terminate in steep escarpments on their <br />south sides (cf. Figure 3). The escarpments descend sharply to the floor of <br />the Axial Basin, which varies from one to four miles in width in the study <br />area (cf. Figure 4). The Duffy and Iles Mountains are essentially the same <br />physiographic unit but are now divided by a steep-walled canyon cut by Milk <br />Creek, one of the minor tributaries of the Yampa. The Axial Basin is bordered <br />• on the south by a small plateau on which is located the proposed Colowyo Mine <br />site. The plateau surface within the mine site area slopes gradually down from <br />