Alternative A does not designate the area as an ACEC; the BLM manages the area in accordance with multiple use principles consistent with other resource objectives.
The area would be mostly open for locatable mineral entry with a withdrawal on 1,714 acres, open to mineral leasing (with primarily major constraints on 10,968 acres), and primarily open to mineral materials disposal (8,948 acres). Allowing mineral development would result in surface disturbance that would degrade wildlife and special status species habitat and may damage the glacial features and recreational setting values of the area.
The Clarks Fork Canyon area is managed as open to ROW authorizations on 5,399 acres and as an ROW avoidance/mitigation area on 5,740 acres. Managing a portion of the area as open to ROW authorizations would result in adverse impacts to the values of concern, including degradation of wildlife and special status species habitat and damage to glacial features and the recreational setting.
Alternative A limits motorized vehicle use to existing roads and trails (11,759 acres), and manages a small area with seasonal restrictions (500 acres).
Prohibiting surface-disturbing activities in the Clarks Fork Canyon ACEC would restrict and have an adverse impact on such activities as geophysical exploration and road construction. Restrictions on surface disturbance would benefit special status species plants and wildlife in the area by limiting the potential for disruptions, habitat fragmentation, or invasive species infestations that would degrade their habitat.
Restrictions on mineral development under Alternative B would result in greater adverse impacts to the use of these resources compared to the other alternatives. The ACEC is withdrawn from appropriation under the mining laws and administratively unavailable for mineral leasing. Adverse impacts from mineral withdrawal generally would be greatest in the approximately 596 acres with gypsum potential and 1,025 acres with bentonite potential, but because of the lack of commercial-grade resources, impacts to mineral development would be minimal. Adverse impacts to mineral materials disposal would be greatest on 4,293 acres with higher potential for sand and gravel. The very low development potential for oil and gas would minimize the potential for adverse impacts to leasable minerals development as a result of managing the area as administratively unavailable to leasing.
Alternative B manages the Clarks Fork Canyon ACEC as an ROW avoidance/mitigation area, a renewable energy exclusion area, and closed to motorized and mechanized vehicle use or limited to designated roads and trails. Adverse impacts to these resource uses would be greater under Alternative B than Alternative A because there would be more restrictions on use. More restrictive ROW management would reduce or mitigate surface disturbance and would result in greater protection for values of concern than under Alternative A. In addition, more restrictive motorized travel management would reduce disturbance to wildlife compared to Alternative A.
Allowing and seasonally stipulating vegetative treatments, invasive/nonnative pest species control, fuels management, and maintenance of existing facilities would protect wildlife and special status species during sensitive periods, while still allowing maintenance and treatments to occur.
Alternative C does not designate the Clarks Fork Canyon area as an ACEC; the BLM would manage the area in accordance with multiple use principles consistent with other resource objectives.
Management of locatable minerals would be similar to Alternative A (withdrawn on 1,766 acres), and the area would be open to mineral leasing (with moderate constraints on 8,654 acres and major constraints on the 3,585 acres) and primarily open to mineral materials disposal (9,097 acres). Alternative C would be less restrictive to mineral development than Alternative A, and adverse impacts to the values of concern in the area may be greater under Alternative C.
Alternative C manages the Clarks Fork Canyon area as primarily open to ROW authorizations (10,890 acres), manages a smaller area for ROW avoidance/mitigation (1,369 acres), and applies standard guidelines related to surface-disturbing activities. Alternative C manages motorized vehicle use as limited to designated roads and trails on 4,889 acres and under seasonal restrictions in the remaining 7,370 acres in the area. Alternative C is more restrictive to ROW and motorized travel management than Alternative A, but less restrictive than Alternative B. Under Alternative C, there would be more benefits to the values of concern than under Alternative A, but less than under Alternative B.
Allowing surface-disturbing activities in the Clarks Fork Canyon ACEC consistent with the goals of the ACEC would eliminate many of the beneficial impacts to special status species plants and wildlife, and the adverse impacts to surface-disturbing activities, predicted to result from the surface disturbance prohibition under Alternative B. However, because surface-disturbing activities would need to be consistent with the goals of the ACEC, this alternative may increase adverse impacts to resource uses and beneficial impacts to the values of concern compared to alternatives A and C, under which there would be standard restrictions on surface disturbance.
Under Alternative D, restrictions on mineral development would result in greater adverse impacts to the use of these resources than under alternatives A or C, but less than under Alternative B. Management of and impacts from the management of locatable minerals would be the same as under alternatives A and C. As with Alternative B, the ACEC is administratively unavailable for mineral leasing and closed to mineral materials disposal; however, similar to Alternative C, under Alternative D the additional area proposed under Alternative B is primarily managed as open to mineral leasing with moderate constraints (9,094 acres) and is open to mineral materials disposal. The very low development potential for oil and gas and low-potential for sand and gravel would minimize the potential for adverse impacts to mineral development in the administratively unavailable and closed portions of the Clarks Fork Canyon area.
Adverse impacts to renewable energy and ROWs and beneficial impacts to the values of concern would be similar to those under Alternative B across the Clarks Fork Canyon area.
Under Alternative D, management of and impacts from motorized travel in the area designated as an ACEC and the larger area proposed under Alternative B would be the same as under Alternative C.
Alternative D allows and seasonally stipulates vegetative treatments, invasive, nonnative pest species control, fuels management, and maintenance of existing facilities, resulting in the same impacts as Alternative B. However, these beneficial impacts would occur over a smaller area because these activities would be governed by other resource considerations in the additional area proposed under Alternative B.
Alternative B would designate the Foster Gulch Paleontological Area as an ACEC (27,302 acres); the other alternatives would not. The values of concern in the proposed Foster Gulch Paleontological Area ACEC are paleontological resources in the form of mammalian and paleobotanical fossils and geochemical data used in the study of a major Carbon Isotope Excursion recorded during an ancient period of global warming known as the PETM. Scenic and geologic features also are valuable in this ACEC. Threats to this proposed ACEC include surface disturbance from mineral (primarily oil and gas) and ROW development.