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-21- <br />area and is characterized by low to heavy growths of sagebrush (Artemesia <br />tridentata) with clumps of short grasses interspersed between individual <br />plants and understories of herbal plants. In the Axial Basin and on the <br />higher river terraces, the sagebrush reaches a height of one to three feet <br />and the plants are relatively dispersed. On low river terraces, sagebrush <br />is particularly heavy and some plants in Milk Creek Canyon reach heights of <br />12 feet. In a few places, particularly at the head of Milk Creek Canyon, <br />small patches of greasewood communities, dominated by Sarcobatus vermiculatus, <br />occur. <br />The sagebrush community also covers much of the Colowyo Mine site but <br />is interspersed with large stands of mixed shrub community, dominated in <br />varying proportions by Gambel's Oak (Quercus gambelii), Serviceberry <br />(Amelanchier alnifolia)and Chokecherry (Prunus virginiana). A grove of <br />aspen also occurs in an arroyo which feeds into Streeter Canyon. <br />A third significant plant community existing in the study area consists <br />of deciduous trees, such as cottonwood and poplars, which occur in varying <br />densities along the river flood plains. A cottonwood stand in Milk Creek <br />Canyon is currently being decimated at a rapid rate by beavers. <br />• <br />A fourth plant community of potential significance to prehistoric in- <br />habitants once existed in what must have been a marshy, poorly drained soil <br />environment in Big Bottom and Round Bottom. These areas, however, have been <br />under cultivation for at least the past 70 years and no remnants of the <br />original plant community remain. <br />The pinyon pine -juniper community, dominated by Pinus edulis and <br />Juniperus scopulorum, occurs in the area on the upper reaches of Iles and <br />Duffy Mountains. Within the surveyed area proper, juniper only occurred on <br />the upper parts of the colluvial ridges at the base of Iles Mountain escarp- <br />ment. No pinyon pine was observed but it presumably occurs at higher el- <br />evations in association with juniper. <br />The floral communities and their distribution described above do not <br />accurately reflect the vegetation as it must have existed in aboriginal <br />times. Agricultural modifications of the bottomlands have already been <br />mentioned. Also, a long history of livestock grazing has undoubtedly mod- <br />ified the vegetative pattern in other areas. Several authorities have sug- <br />gested that overgrazing has produced sagebrush communities in what was once <br />grassland. This would be particularly true of the Axial Basin. Chaining • <br />