NEPA--Environmental Assessment

Silverton Grazing Risk Assessment
Minnie Gulch Allotment (BLM, vacant allotment):
Under current management, there is about 2,536 acres of overlap in the allotment with
mapped summer range for the S33 Pole Mountain/Upper Lake Fork bighorn sheep herd.
Within this area, only about 319 acres (13%) is suitable domestic sheep grazing range.
Under Alternative 3, the preferred alternative, the entire allotment would be closed to
grazing. The Minnie Gulch Allotment has been vacant since 1983.
Surveys conducted in the allotment by BLM staff over the past 4 summer seasons have
failed to detect bighorn sheep, but CDOW continues to receive regular reports of sheep in
the gulch during summer. It is thought likely that bighorn sheep reported in the gulch
may be coming from nearby Crown Mountain or the Pole Creek Mountain subpopulation
on the Rio Grande National Forest.
Much of this allotment is open alpine terrain providing a good mix of bighorn forage areas
and escape cover. It also provides areas of domestic sheep grazing opportunities. Bighorn
are known to use the adjacent Cottonwood Allotment (Gunnison NF) and the habitats in
Minnie Gulch Allotment provide a natural extension for bighorn sheep using the
headwaters of Cuba Gulch. Given the close proximity of Minnie Gulch to areas known to
be regularly used by bighorn sheep, the topography of the allotment that acts as a natural
extension for bighorns using the headwaters of Cuba Gulch, and regular reports of
bighorn sheep in Minnie Gulch, there appears to be a high risk for contact between
domestic and bighorn sheep in this allotment.
Summary of Risk Rating for Minnie Gulch Allotment:
Risk Rating: Alternative 2 – High
Alternative 3 – Low - Closed
Under Alternative 2, if the Minnie Gulch Allotment were to be restocked, the substantial
area of overlap between suitable domestic sheep grazing areas and mapped bighorn
summer range, the close proximity of the allotment to known bighorn use areas, the
potential expansion of the S33 bighorn herd, and the regularity of reports of bighorn in
the allotment, these factors in combination result in a rating of “High Risk” for contact. If
however, the allotment were to remain vacant under Alternative 2, the rating would be
“Low Risk” because domestic sheep would not be permitted in the allotment and there
would be a low risk for contact. However, because the allotment could be restocked
administratively at any time, the overall rating of this allotment under Alternative 2 would
be “High Risk”.
Under Alternative 3, the Minnie Gulch Allotment would be closed to domestic sheep
grazing. The rating would be “Low Risk” because domestic sheep would not be permitted
in the allotment and there would be a low risk for contact.
Gladstone Allotment (BLM, active allotment):
In the active BLM Gladstone Allotment there is a small area in the southern end of the
allotment that overlaps with mapped summer range for the S71 West Needles bighorn
sheep herd. Under current management, there is about 320 acres of overlap, with only
about 11 acres (3%) being suitable domestic sheep grazing range.
Surveys conducted in the allotment by BLM staff in summer 2008 failed to detect bighorn
sheep. The area of mapped overlap is immediately adjacent to the town of Silverton, on
the north side of town. Bighorns would have to pass through town or around town
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