Field survey for bent-flower milkvetch (Astragalus vexilliflexus var. vexilliflexus) in the Stibnite Gold Project area, Valley County, Idaho

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The Midas Gold Idaho, Inc. (Midas Gold) Stibnite Gold Project is located near Stibnite, a historic mining town located in the Salmon River Mountains approximately 16 km (10 mi) east of Yellow Pine in Valley County, Idaho. The proposed disturbance footprint associated with the Stibnite Gold Project overlaps the occurrence of bent-flower milkvetch (Astragalus vexilliflexus var. vexilliflexus), a plant species of conservation concern in Idaho. I agreed to conduct a field survey in 2016 for bent-flower milkvetch targeting areas not searched in the past, but known or suspected to support potential habitat for the species. The intent of the field survey was to try and find new occurrences of bent-flower milkvetch, and if found, to document their location, extent, habitat conditions, and other relevant conservation information. The objective for the survey and gathering this information was to provide land managers a more comprehensive understanding of the conservation status of bent-flower milkvetch in the general Stibnite area. Areas selected for survey included the vicinity of the historic Cinnabar mine site; Cinnabar Peak and its upper flanks; the upper Cinnabar Creek drainage, north of both Fern Mine and Monumental Summit; and Sugar Mountain. Survey areas included lands owned either by Midas Gold, the Oberbillig family trust (optioned by Midas Gold and collectively known as Cinnabar), or the Payette National Forest. During the survey we discovered two new bent-flower milkvetch subpopulations in the vicinity of Cinnabar Peak and an extension to a previously known subpopulation south of the old Cinnabar mine site. The largest subpopulation covered approximately 25 acres centered around Cinnabar Peak and contained an estimated 7000 - 10,000 bent-flower milkvetch plants. Another smaller subpopulation covering approximately 1.5 acres was found a short distance east of Cinnabar Peak and contained an estimated 500 bent-flower milkvetch plants. The third site was located approximately 0.4 mile south of the old Cinnabar mine along the upper 1.6 km (1 mi) section of the jeep road that leads down to the old mine. A minimum of 300 bent-flower milkvetch plants were found at this site before it became confluent with a previously known bent-flower milkvetch subpopulation. We also relocated and updated information for a previously documented bent-flower milkvetch occurrence north of Monumental Summit during the survey. Bent-flower milkvetch was not found in any of the other areas we searched. The discovery of new subpopulations in 2016 improves the conservation status of bent-flower milkvetch in Idaho. However, the long-term conservation outlook for the species, especially at the large Cinnabar Peak occurrence, will probably largely depend on what level of protection subpopulations receive during any proposed mining operations for the Stibnite Gold Project.

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Reference Code: U16MAN06IDUS <br>

Full Citation: Mancuso, Michael. 2016. Field survey for bent-flower milkvetch (Astragalus vexilliflexus var. vexilliflexus) in the Stibnite Gold Project area, Valley County, Idaho. Report prepared by Mancuso Botanical Services for Midas Gold Idaho, Inc., Boise, Idaho. 10 pp plus appendices <br>

Location: ELECTRONIC FILE - BOTANY: PLANT SPECIES: {Astragalus vexilliflexus var. vexilliflexus} <br>

Keywords: bent-flower milkvetch, Astragalus vexilliflexus var. vexilliflexus, Midas Gold Idaho, Midas Gold, Stibnite Gold Project, Valley County, Idaho <br>