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<br />--,~ <br />","' <br /> <br />000355 <br /> <br />Vegetation resources within the project area are limited because of the nature of the rock canyon <br />walls, Chokecherry (Prunus virginiana), box-elder (Acer negundo), narrow-leaf cottonwood <br />(Populus angustifolia). and poison ivy (Rhus radicans) are common in the canyon along the river <br />banks (NPS 200l). The no action and proposed action are expected to have no effect on land use <br />or vegetation resources. <br /> <br />Geology and Landslides <br /> <br />The Gunnison River, cutting through Precambrian metamorphic and igneous rock created the <br />canyon. This resulted in steep sheer canyon walls. Upstream of Morrow Point Dam is a series <br />of major landslide areas. which area potential safety hazard (Figure 4), These Jandslidesare all <br />very old and existed many centuries prior to creation of the reservoir. The saturation of the toe <br />of these slides has. however. generated renewed movement in three areas, The landslide of <br />primary concern is the Area A. which is situated approximately 2.500 feet upstream of the dam <br />on the north side of the reservoir. <br /> <br />The slides have all involved bedrock material as well as overburden, The cause of the <br />movements is unknown but is suspected. at least in some instances. to be related to the weaker <br />mica schist rock and shattering of the rock by faulting (Barnes. 1973), <br /> <br />Landslide Area .-\ is outlined by a fresh crack almost entirely around the slide perimeter. <br />Vertical displacement across the crack varies from about 5 to 15 feet. Numerous cracks are also <br />found within the slide. mostly in the lower one-third near the toe, :Vlovement has reportedly been <br />observed in this area since the reservoir creation in 1968 but numerous "sags" and other features <br />demonstrate that the slide is very ancient. The present disturbed area has a width of about 1.250 <br />feet at the base and extends uphill to elevation 7.850 ft. From the top of the slide to the <br />shoreline. the average slope is about 40 percent. In 1973. surveyors established 1+ points in this <br />area to monitor movement (Barnes. 1973). <br /> <br />Landslide Area C is found 12.500 feet upstream from the dam on the north side of the reservoir. <br />The disturbed area is clearly marked by a continuous- crack around its border. ,Along its west <br />margin. the slide material has dropped IS to 20 feet away from a rock cliff. The outlining crack <br />is open as wide as 24 inches in several places. The top elevation of the slide is about 7.840 feet <br />and the average slope is 48 percent. At the shoreline. the slide width is about l.l 00 feet. The <br />rock involved seems to have been mica schist but some gneiss was also noted. The step-like <br />profile and numerous sags define the area as an ancient landslide. but the fresh cracks observed <br />1973 indicated recent movement. [n 1973. eleven survey points were established to monitor the <br />slide area. <br /> <br />II <br />