Alternatives A and C do not designate the area as an ACEC; the BLM manages the area in accordance with multiple use principles consistent with other resource objectives. The proposed PETM ACEC is entirely within the Clarks Fork Basin/Polecat Bench West Paleontological Area, Foster Gulch, and McCullough Peaks South ACECs proposed under Alternative B. See the Detailed Analysis of Alternatives discussions for those ACECs for management of and impacts to this area under alternatives A and C.
Alternative B does not designate a PETM ACEC, but does manage a larger area as the Clarks Fork Basin/ Polecat Bench West Paleontological Area, Foster Gulch, and McCullough Peaks South ACECs to protect the same values of concern. See the Detailed Analysis of Alternatives for the Clarks Fork Basin/Polecat Bench West Paleontological Area, Foster Gulch, and McCullough Peaks South ACECs for management of and impacts to this area under Alternative B.
Under Alternative D, the BLM designates a portion of the area managed as the Clarks Fork Basin/Polecat Bench West Paleontological Area, Foster Gulch, and McCullough Peaks South ACECs under Alternative B as the PETM ACEC to protect paleontological resources and geochemical data.
Allowing surface-disturbing activities and the use, occupation, construction, or maintenance of facilities that are consistent with the goals of the ACEC, would result in fewer adverse impacts, similar to those described for alternatives A and C in the Clarks Fork Basin/Polecat Bench West Paleontological Area, Foster Gulch, and McCullough Peaks South ACECs. In the greater-PETM area boundary proposed under Alternative B, impacts to paleontological resources would be the same as under alternatives A and C, because only standard restrictions on surface disturbance would apply. Alternative D restrictions throughout this area would be less effective for protecting paleontological resources than Alternative B, but also would cause fewer adverse impacts to project costs and timeframes associated with surface-disturbing activities, such as range improvements.
Under Alternative D, management of mineral development in the PETM ACEC and the greater-PETM area is less restrictive than under Alternative B and similar or slightly more restrictive than management under alternatives A and C. As with alternatives A and C, Alternative D manages most of the area as open for mineral leasing with moderate constraints; however, this alternative also applies a more restrictive NSO stipulation on the PETM ACEC itself and contains less area open with standard constraints on the greater-PETM area. Alternative D manages the PETM ACEC and the greater-PETM area as available for locatable mineral entry. However, unlike similar management under alternatives A and C, the area in the PETM ACEC would require a plan of operations for most locatable mineral exploration and development. The PETM ACEC is closed to mineral materials disposal, as is this area under Alternative B, and the greater-PETM area is managed as open to mineral materials disposal, similar to alternatives A and C. Although these restrictions would result in adverse impacts to mineral uses, these impacts may be minimized in the ACEC and the greater-PETM area because these areas consist of 29,736 acres of very low and 28,456 acres of low development potential for oil and gas, and low-potential for bentonite, gypsum, and sand and gravel across most of the area. Restricting mineral development would result in beneficial impacts to the values of concern for the ACEC by reducing the potential for destruction or degradation of paleontological values and the other adverse impacts often associated with surface disturbance (e.g., the potential spread of invasive species).
Similar to Alternative C, under Alternative D approximately half of the PETM ACEC and the greater-PETM area are open to ROW authorizations and half is managed as ROW avoidance/mitigation areas. This management is more restrictive than Alternative A, but less restrictive than Alternative B. Alternative D would implement more restrictions on motorized travel within the PETM ACEC and the greater-PETM area than Alternative A, but fewer restrictions than alternatives B and C. Management of ROWs and motorized vehicle use under Alternative D would reduce the potential for impacts to these activities compared to Alternative B, but also would result in increased surface disturbance and other adverse impacts to the values of concern compared to that alternative. However, allowing ROW authorizations in the PETM only where consistent with the protection of paleontological resources would reduce these adverse impacts by allowing the further restriction of these activities where they would not be compatible with protecting the paleontological values of concern.
Management of and impacts from the collection, excavation, or removal of fossils in the PETM ACEC would be similar to in the Clarks Fork Basin/Polecat Bench West Paleontological Area, Foster Gulch, and McCullough Peaks South ACECs. In the greater-PETM area, the applicable laws, regulations, and management described in Section 4.5.2 Paleontological Resources control the collection of fossils under Alternative D. These decisions include protective management, such as surveying and monitoring surface-disturbing activities (on a case‐by‐case basis) and attaching standard Paleontological Resources Protection Stipulations for PFYC 3-5 formations, that would provide some protection to the paleontological values, but less than under Alternative B.
Alternative B would designate the Rattlesnake Mountain area as an ACEC (19,119 acres); the other alternatives would not. The values of concern to be managed for in the proposed Rattlesnake Mountain ACEC are special status species wildlife, varied vegetation communities and sensitive plants, and wildlife winter and transition habitat. Threats to this proposed ACEC include surface disturbance from mineral (including gravel pits) and ROW development, renewable energy developments (wind energy), timber extraction, heavy recreational and OHV use, and invasive, nonnative species infestations. These activities threaten rare plants and habitat for special status species, and have the potential to create disturbances for wintering wildlife.