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 open to locatable mineral entry, open to mineral leasing (with moderate constraints), and open to mineral materials disposal. Mineral development is one of the threats to the area and allowing this type of development, with minimal restrictions, would result in surface disturbance that would cause adverse impacts to the values of concern. The 1,238 acres of high-potential for bentonite would be the most likely location of minerals development, because the development potential for oil and gas is very low and the potential for gypsum and sand and gravel is low. The very low potential for most minerals may minimize the potential for adverse impacts to the values of concern.
The Rainbow Canyon area is primarily open to ROW authorizations (1,222 acres), with the remainder managed as an ROW avoidance/mitigation area (221 acres). Managing most of this area as open to ROW authorizations would result in adverse impacts to the values of concern by increasing the potential for surface disturbance and ROW development.
Motorized vehicle use is limited to designated roads and trails, which may result in fewer roads available to motorized travel in the area, compared to areas limited to existing roads and trails.
The Rainbow Canyon area is open to livestock grazing under Alternative A. Livestock trampling and wallowing in areas of concentrated livestock use can damage exposed paleontological resources. While, in most instances, concentrated livestock use would result in adverse impacts to paleontological values, proper management of livestock grazing can mitigate these impacts by improving livestock distribution.
Applicable laws and regulations and management described in Section 4.5.2 Paleontological Resources control the collection of fossils under Alternative A. These decisions include protective management, such as surveying and monitoring surface-disturbing activities for PFYC 5 and, on a case-by-case basis, PFYC 4 formations that may protect paleontological values of concern.
Management for the Rainbow Canyon ACEC under Alternative B reduces adverse impacts to the paleontological and geological values of concern from surface disturbance and development. Management under this alternative requires avoiding or prohibiting surface-disturbing activities in the Rainbow Canyon ACEC, and prohibiting the use, occupation, construction, or maintenance of facilities in the Rainbow Canyon ACEC that are inconsistent with the management direction and objectives for the area. Allowing minor surface-disturbing activities in the Rainbow Canyon ACEC if they are preceded by a paleontological sensitivity survey and, if necessary, monitored during construction, would help protect paleontological resources. Restricting surface-disturbing activities could increase project costs and timeframes, but would continue to allow some activities while also protecting the integrity of fossil-bearing material in the area.
Withdrawing the Rainbow Canyon ACEC from appropriation under the mining laws, managing the area as administratively unavailable to mineral leasing, and closing the area to mineral materials disposal and geophysical exploration would result in greater adverse impacts to mineral development than Alternative A. Restricting mineral development would result in greater beneficial impacts to the paleontological and geologic values in the area than Alternative A. As noted for Alternative A, impacts from the withdrawal would be greatest on the 1,238 acres of high-potential for gypsum; the low potential for other mineral resources in the area may minimize impacts from other types of mineral exploration and development.
Management under Alternative B is more restrictive than under Alternative A for ROWs and livestock grazing. Therefore, adverse impacts to these resource uses would be greater than under Alternative A. Alternative B manages the Rainbow Canyon ACEC as a renewable energy and ROW avoidance/mitigation area and allows livestock grazing under existing regulations, provided it does not disturb the natural, educational, and scientific research values of the Rainbow Canyon ACEC. This management would reduce the potential for surface disturbance and would provide increased flexibility to further restrict activities (such as livestock grazing) determined to be adverse to the values of concern. Any restrictions on grazing could reduce the currently available 23 AUMs in the area and adversely impact livestock grazing.
Management of and impacts associated with motorized vehicle use under Alternative B are the same as under Alternative A.
Alternative B allows fossil collection, excavation, or removal in the Rainbow Canyon ACEC only under a permit issued by the Wyoming BLM State Director and only by institutions and individuals engaged in BLM-approved research, museum, or educational projects that provide for detailed recordation, reporting, care of specimens, and availability of specimens to other scientists and museums. Such requirements would, however, result in beneficial impacts by protecting the integrity of the resources and enable the advancement of scientific knowledge.
Alternative C does not designate the area as an ACEC; the BLM would manage the area in accordance with multiple use principles consistent with other resource objectives.
Management of and impacts associated with locatable and salable mineral development under Alternative C would be similar to those under Alternative A. However, the management of leasable minerals would be the least restrictive of any alternative because the area is managed as open to mineral leasing with primarily standard constraints (1,177 acres).
ROW management in the Rainbow Canyon area under Alternative C is less restrictive than alternatives A and B. The Rainbow Canyon area is managed as open to ROW authorizations (1,443 acres). Fewer restrictions on ROWs would result in more adverse impacts to the values of concern compared to the other alternatives.
Management of and impacts associated with motorized vehicle use under Alternative C would be the same as under Alternative A.
Applicable laws and regulations and management described in Section 4.5.2 Paleontological Resources control the collection of fossils under Alternative C. This management would be less restrictive to surface disturbance than under Alternative A, because it does not require on‐the‐ground surveys for PFYC 4 formations on a case‐by‐case basis.
Alternative D does not designate the area as an ACEC; the BLM would manage the area in accordance with multiple use principles consistent with other resource objectives.
Management of and impacts associated with mineral development under Alternative D would be the same as under Alternative A.
Under Alternative D, the Rainbow Canyon area is managed as an ROW avoidance/mitigation area and impacts would be the same as those under Alternative B.
Management of and impacts associated with motorized vehicle use under Alternative D would be the same as under Alternative A.
Applicable laws and regulations and management described in Section 4.5.2 Paleontological Resources control the collection of fossils under Alternative D. This management may be less restrictive of surface disturbance than under the other alternatives, because it does not require on‐the‐ground surveys for any PFYC class, although surveys and monitoring can be implemented on a case‐by‐case basis for PFYC 3-5 formations.
Alternative D would designate the PETM, in the Clarks Fork Basin/Polecat Bench, Foster Gulch, and McCullough Peaks South areas, as an ACEC (14,906 acres); alternatives A and C would not. Under Alternative B, the area of the PETM ACEC is entirely within the proposed Clarks Fork Basin/Polecat Bench West Paleontological Area, Foster Gulch, and McCullough Peaks South ACECs (58,189 acres total). The values of concern in the PETM ACEC are the same as those in the Clarks Fork Basin/Polecat Bench, Foster Gulch, and McCullough Peaks South ACECs (i.e., fossil resources and geochemical data from an ancient period of global warming). The PETM ACEC would manage a portion of the deposits of these resources protected under the Alternative B ACECs (referred to here as the greater-PETM area). Threats to the area of the PETM ACEC include surface disturbance from mineral (oil and gas, mineral materials, and possible locatable mineral mining), water withdrawals and irrigation outflow, timber extraction, recreational and OHV use, invasive and nonnative species infestations, and ROW development.
Management of and impacts from ACECs in the greater-PETM area under Alternative B, and management in this area without ACEC designations under alternatives A and C, are addressed in the Clarks Fork Basin/Polecat Bench West Paleontological Area, Foster Gulch, and McCullough Peaks South ACEC sections.