The introduction to Chapter 4 identifies the assumptions used in this impact analysis. Assumptions related to other resources and resource uses discussed in this section apply to the analysis of ACECs and other Management Areas. There are no additional specific assumptions.
To allow for a consistent analysis, the ACEC boundaries designated under Alternative B are used as the area of analysis for all alternatives. Using Alternative B boundaries, the analysis compares the impacts of key management (e.g., mineral development, ROWs, and travel management) to resources and resource uses in these areas. When an alternative proposes an ACEC, the BLM based the determination of impacts to resources and resource uses on the management actions listed in Chapter 2. When an alternative does not propose an ACEC, the BLM based the determination of impacts to resources and resource uses on a GIS analysis of management for that area under that alternative. For example, the BLM would not manage the Big Cedar Ridge area as an ACEC under Alternative C. However, to ensure the analysis is comparable across alternatives, Alternative C describes management for minerals, ROWs, and travel for this same geographic area. The adverse and beneficial impacts of not designating this area as an ACEC under Alternative C are then compared to the adverse and beneficial impacts of managing this same area as an ACEC under alternatives A and B.
Similar to the comparison of management across alternatives described above, the BLM used the Alternative B boundaries to determine mineral potential for locatable minerals, leasable minerals, and mineral materials. Based on GIS data and information in the Solid Mineral Occurrence and Development Potential Report and Reasonable Foreseeable Development Potential Report for Oil and Gas, mineral potential was overlaid with the Alternative B area being analyzed. The BLM used the mineral potential and the specific management of minerals in the area as the basis of analysis when comparing impacts to mineral resources from management under the alternatives.
Table 4.18. Existing and Proposed ACECs and other Management Areas by Alternative
| Area | Alternative | |||
|---|---|---|---|---|
| A | B | C | D | |
| Existing ACECs (no expansion proposed) | ||||
| Big Cedar Ridge | X | X | X | |
| Red Gulch Dinosaur Tracksite | X | X | X | |
| Sheep Mountain Anticline | X | X | X | |
| Spanish Point Karst | X | X | X | X |
| Existing ACECs (and proposed expansion) | ||||
| Brown/Howe Dinosaur Area | X | X | X | X |
| Carter Mountain | X | X | X | |
| Five Springs Falls | X | X | X | |
| Little Mountain | X | X | X 1 | |
| Upper Owl Creek Area | X | X | X | |
| Proposed ACECs | ||||
| Chapman Bench | X | X 2 | ||
| Clarks Fork Basin/Polecat Bench West Paleontological Area | X | –3 | ||
| Clarks Fork Canyon | X | X | ||
| Foster Gulch Paleontological Area | X | –3 | ||
| McCullough Peaks South Paleontological Area | X | –3 | ||
| Rainbow Canyon | X | |||
| Rattlesnake Mountain | X | |||
| Sheep Mountain | X | X | ||
| Paleocene-Eocene Thermal Maximum (PETM) | –4 | X | ||
Source: BLM 2009a
1Although not proposed for expansion under Alternative D, the BLM manages a portion of the proposed expansion area as the Craig Thomas Little Mountain Special Management Area.
2Although not proposed as an ACEC under Alternative D, the BLM manages a portion of this area as the Chapman Bench Management Area.
3Although not proposed under Alternative D, a portion of this area falls within the proposed PETM ACEC.
4Although not proposed under Alternative B, the entire area of the PETM ACEC is within the Clarks Fork Basin/Polecat Bench West Paleontological Area, Foster Gulch Paleontological Area, and McCullough Peaks South Paleontological Area ACECs.
| ACEC | Area of Critical Environmental Concern |