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IRIS <br />MITIGATION AND DESIGN, INC. <br />SCHWARTZWALDER MINE PHASE 1 - UPSTREAM CUTOFF WALL AND LOW FLOW BYPASS <br />PIPELINE - BIOLOGICAL ASSESSMENT <br />10 feet wide and is bordered by a relatively narrow riparian corridor. As described below, the riparian <br />habitat surrounding the creek in the proposed work area ranges from disturbed to fairly pristine. <br />4.2.1 Upland Road Crossing <br />The upland road crossing refers to a previously disturbed upland habitat that extends for a width of <br />approximately 40 feet and is colonized by upland grasses and weedy species (see Figure 2 and <br />Appendix B). It is the location for construction of the cutoff wall described in Section 2. The cutoff wall <br />will measure approximately 1 '/2 feet thick, 30 feet deep and 125 feet long. <br />The upland road crossing was created by the placement of fill to provide an unpaved crossing of <br />Ralston Creek. As such, it is characterized by a gravel substrate to allow for vehicular use and a high <br />quantity of bare ground. Grasses and forbs found interspersed throughout the road crossing include: <br />crested wheatgrass, orchardgrass, smooth brome, aster (Aster spp.), field pennycress (Thlaspi <br />arvense), and pigweed (Amaranthus spp.). <br />The north side of the crossing has been subjected to fewer disturbances over time than other portions <br />of the crossing. Consequently, this area supports several native plant species. On June 16 and 21, <br />2011, the following native woody plants were documented on the north side of the upland road <br />crossing: 7 medium mountain mahogany shrubs, 4 medium ponderosa pine trees, 5 large currants <br />(Ribes spp.), and 1 western juniper (Juniperus occidentalis). Canada wildrye and needle and thread <br />grasses were also observed in the understory. <br />4.2.2 100 Feet Upstream from Road Crossing <br />Previously disturbed riparian habitat extends approximately 50 feet upstream from the road crossing <br />described above (see Figure 2 and Appendix B). This area was likely disturbed during the construction <br />of the road crossing and possibly during mine waste rock transport. This area has an abundance of <br />established willows with only four smaller riparian trees. Additional riparian shrubs such as snowberry <br />(Symphoricarpos occidentalis), and wood's rose (Rosa woodsii) are located on the east side of the <br />willow wetland. The area between 50 to 100 feet upstream of the road crossing is less disturbed <br />riparian habitat. This area is characterized by 44 larger riparian trees and a solid understory of willows. <br />The riparian area upstream of the road crossing is relatively high - quality habitat. The riparian area <br />located over 100 feet upstream of the road crossing is previously undisturbed riparian habitat. <br />Characterized by a dense cover of large native trees and understory shrubs, this riparian vegetation <br />community provides an array of functions such as shading for the creek, flood attenuation, cover and <br />Page 26 August 2011 <br />