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NEPA--Environmental Assessment

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of 1,272 acres of mineralized soil from grazing. The largest amount of mineralized still likely to be<br />

grazed are in Prospect Gulch, and the proposed action intends to limit the number of days sheep are<br />

allowed in Prospect Gulch. Compared to the mineral soil exposed to erosion from historic mining<br />

activities, any small increase due to sheep grazing is expected to be minimal. Gladstone Allotment<br />

was observed during rainstorms in 2008, and found that trailing and grazing from sheep that day and<br />

the previous day was producing no sediment-laden runoff, but water in roadside ditches below mine<br />

dumps was carrying significant sediment load.<br />

CUMULATIVE IMPACTS<br />

The largest impact to watersheds and water quality in this analysis area is past mining, milling and<br />

road building. This is described under the affected environment (above). Other activities that can<br />

negatively impact watersheds and water quality include: private land development (mining, summer<br />

homes, ski area, etc.), new road construction, road and trail use, road maintenance, and recreational<br />

pack stock use.<br />

Past and ongoing mine reclamation projects undertaken by members of the Animas River<br />

Stakeholders Group are a beneficial impact to water quality. The impact from domestic sheep<br />

grazing under Alternative 3 (adaptive management) is expected to be inconsequential in the context<br />

of cumulative effects.<br />

Vegetation & Soils________________________________<br />

AFFECTED ENVIRONMENT<br />

The Silverton project area occurs in a mountainous landscape dominated by alpine vegetation and<br />

spruce-fir forests. Mixed conifer forests, aspen forests, and mountain grasslands also occur to a<br />

limited extent, and riparian areas and wetlands are scattered throughout the area. Most of the project<br />

area is associated with volcanic deposits of volcaniclastic and near-source facies, volcanic deposits<br />

of the Henson and Burns geologic formation, and sedimentary deposits of the Cutler, Rico, Hermosa,<br />

and Molas geologic formations.<br />

This section focuses on the vegetation and soils of the alpine zone (the alpine major vegetation type)<br />

within the project area, since this is the area most affected by sheep grazing. Vegetation and soils of<br />

the other vegetation types of the project area display no effects or only minor adverse effects from<br />

sheep grazing.<br />

The alpine zone on San Juan Public Lands occurs at elevations above about 11,500 feet where the<br />

growing season is short, the winters are long, the winds are high, and the sun is intense. The alpine<br />

landscape was shaped by geologic events and glaciation, and is both steep and rugged, and gentle<br />

and smooth. Rock outcrop and talus slopes are common. Soils are shallow and rocky on steep slopes<br />

and exposed ridges, and deeper, less rocky, and more productive on other sites. There is tremendous<br />

diversity of species and vegetation types within the alpine zone and plant communities often change<br />

quickly and abruptly over short distances, due to small-scale topographic changes that exert a<br />

significant influence on snow and moisture conditions and the associated vegetation.<br />

Alpine rangelands have been used for sheep grazing since the mid 1800s. Prior to government<br />

control, sheep were herded in tightly grouped bands and usually bedded in the same location for<br />

several nights in a row, which resulted in large forage losses and in soil damage (Paulsen 1960).<br />

Some sites in the project area still display these historic effects (ID team observation 2008).<br />

Currently sheep (including the ones in the project area) are herded loosely but will aggregate in large<br />

groups when resting or drinking and then gradually split up into smaller groups as they graze away<br />

55

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