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-25- <br />middle of the Pinedale Glaciation in Richmond's chronology. <br />According to Armstrong (1972:378) the end of the Pinedale Glaciation • <br />produced drastic changes in the ecology of northwestern Colorado. These <br />changes created an environment that was characterized by mammalian elements <br />of the xeric (drier) and thermal (warmer) accessional modes, an environment <br />that is similar to that existing in the area today. <br />4.2.5 Environmental Summary <br />Taken together, the environmental information presented in this section <br />indicates that the study area can be broken down into several resource zones. <br />The Colowyo Mine site has an abundance of plant foods of specific types <br />and a high concentration of mule deer and sage grouse. The lack of water <br />over most of the mine site, however, is a potential problem and would be <br />a greater problem if even slightly drier conditions prevailed. It is assumed <br />that water was a critical resource there, judging from the site pattern as <br />will be seen in a later section. <br />Although hard data is lacking, I would suggest that the Axial Basin <br />was an important area for the hunting of large game animals, principally <br />bison and probably the pronghorn antelope, during prehistoric times. The <br />several streams draining the area would have been a ready source of water. • <br />Iles and Duffy Mountains offered the plant resources of the pinyon pine - <br />juniper community and a moderate deer population. Availability of water on <br />Iles Mountain would be something of a problem, although at least two springs <br />are indicated on the USGS quad maps of the area. <br />A fourth resource zone consists of the bottomlands of the Yampa, Williams <br />Fork, and possibly hfilk Creek Canyon. This zone offers the presence of <br />waterfowl and the as yet undetermined riparian vegetational resources of the <br />more extensive bottomlands such as Big Bottom and Round Bottom. <br />Prehistoric sites, particularly hunting and gathering sites, are often <br />found at the boundaries between two resource zones. This pattern occurs <br />in the study area in several places and will be discussed in greater detail <br />in a later section. <br />4.3 PREVIOUS ARCHEOLOGICAL INVESTIGATIONS IN THE STUDY AREA <br />This section will be short since few archeological investigations have <br />been conducted in the study area. The nearest extensive investigation is <br />• <br />