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-24- <br />mountainous western half of Colorado but is evidently extremely rare if <br />• present at all in the vicinity of the study area. I mention it here because <br />pictographs recorded at a rockshelter in Milk Creek Canyon (SMF435) depict <br />mounted hunters attacking an animal which is tentatively identified as a <br />bear. <br />Smaller mammals such as'marmots, ground squirrels, rabbits, etc. also <br />exist in the study area and would have been a potential food source at times <br />when other larger animals were unavailable. Armstrong (1972:85-91) includes <br />northwestern Colorado in the distribution of the White-tailed Jackrabbit <br />(Le us townsendii) and the Desert Cottontail (Sylvilagus audobonii) but no <br />jackrabbits and only a few cottontails were observed during our survey. <br />They were reported to be abundant only a few years earlier and it is likely <br />that our survey occurred during one of the periodic epidemics that occur <br />among rabbit populations. <br />With respect to other animal species, waterfowl, sage grouse, and doves <br />can be included as potential food sources. Sage grouse were encountered in <br />relatively high numbers on the Colowyo Mine site and on the first terrace <br />of the Yampa River near Round Bottom. <br />• As is true of the flora, the distribution of fauna in the study area <br />has been disturbed by recent human occupation. These disturbances have al- <br />ready been described in the discussion of the faunal resources. Climatic <br />changes, however, have also produced significant changes in the types and <br />frequencies of fauna in the area. Armstrong (1972:377-381) identifies four <br />"accessional modes" representing different patterns of mammalian distribution <br />within Colorado that reflect varying ecological conditions. His basal <br />accessional mode reflects a climate colder and wetter than present that is <br />more or less coterminus with the Pinedale Glaciation. This mode is charac- <br />terized by coniferous forest and a Cordilleran and Boreo-cordilleran mam- <br />malian element and was most of the Yampa Basin. The larger species of <br />this mammalian element include bighorn sheep, bison, wolverine, and Canadian <br />lynx. If present in sufficient numbers, bighorn sheep and bison would have <br />provided early hunters with an adequate subsistence base. There is no evi- <br />dence as yet for the presence of mammoth: in no_tliwestern Colorado during <br />Pinedale, the closest occurrence being the Union Pacific Mammoth Kill site <br />in south-central Wyoming (Irwin, et.al. 1962). The Union Pacific mammoth <br />. has been radiocarbon dated at 11,300 B.P., which places it at about the <br />