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Coa(Mefbane Drainage Projcd - Panek 16-24 Wert E!k Mine • Page 3-2 Many of the areas identified and mapped as steep slope areas are exposed bedrock outcrop and cliffs that may have rockfall potential depending on bedrock integrity. Generalized identification and mapping of geologic hazards has been completed by the Colorado Geologic Survey. Site-specific mapping of both geologic hazards and steep slope areas has been completed by MCC and the USFS, as represented by Map 1, Project Area Activities With Surface Stipulations. Site-specific geologic hazard maps are in the USFS files in the Paonia Ranger District Office. Eight azeas of high geologic hazard have been mapped in the project azea. Six of these areas are located along or near the West Bench Road. These six areas are distributed along the flanks of the West Flatiron, with two azeas in each of the watersheds of Box Canyon, Sylvester Gulch, and Raven Gulch. The two remaining azeas are on the flanks of a steep ridgeline extending to the northeast from the West Flatiron. One area of high geologic hazard was mapped in the upper headwaters of Deep Creek, where there is abundant evidence of recent mass wasting, and landslide, avalanche, and rock fall activity. The headwaters area is outside of the project area, but high energy flows from summer rainstorms have cazried sand, silt, and small boulders from landslide areas downstream partially blocking FR 711 at Deep Creek, which may affect access to the Upper Deep Creek Road, FR 711.A3. USFS plans include repairs and upgrades to the FR 711 crossing in 2002. The West Flatiron Mesa formed where breaks in the more resistant overlying beds allowed erosion of the less resistant underlying materials, fomung aflat-topped mesa with relatively steep sideslopes. The steepest slopes and a majority of the mapped landslides in the project azea aze located on the upper slopes of the West Flatiron Mesa and adjacent ridgelines. Slopes greater than 60 percent occur along the upper flanks of the West Flatiron, with high concentrations of steep slopes in the Box Canyon and Raven Gulch watersheds, largely to the northeast of Deep Creek and east of Sylvester Gulch. The project area includes many areas with low to moderate geologic hazard potential that are not displayed on Map Ml, Project Area Activities With Surface Stipulations. These areas include canyon slopes, where shallow colluvial soils can form minor surface slumps, particularly when wetted. Soft alluvial soils exist in some canyon bottom areas. colluvial soils, resulting from bedrock weathering, accumulate on canyon side-slopes and at the toe of the slopes. Alluvial soils formed by deposition of sediments by azea streams aze found in the bottoms of tributary drainages and drainage canyons. Most soils in the project area aze colluvial soils, generally occurring sepazately from the alluvium except along the toe of slope where soil mixing has occurred. Landslides in the project azea aze typically in the colluvial soils on steep canyon side-slopes. Bedrock ground water dischazge promotes formation of colluvial soils, but may also form springs, seeps, and wetted azeas that reduce soil cohesion and can result in down-slope soil movement. When dry, colluvial soils aze typically cohesive and less susceptible to movement. Soil movement is more likely to occur on east-facing and north- facing slopes due to regional bedrock dip to the northeast and groundwater movement. West- and south-facing slopes aze less susceptible to soil movement. Stipulations in the existing federal coal leases prohibit surface occupancy (No Surface Occupancy or NSO lease stipulation) on azeas identified as either high geologic hazazd azeas or steep slopes of greater than 60 percent. High geologic hazazd areas include active mudflows, eazthflows, landslides, and areas prone to avalanche. NSO restrictions apply to slopes greater than 60 percent to prevent impacts to soil resources through erosion, mass failure, or loss of productivity. An exception(s) to the stipulations would be necessary for surface disturbance or use of these areas. Refer to Appendix A for actual lease stipulation language. The coal leases also include Controlled Surface Use stipulations (CSU) for areas of moderate geologic hazard and moderately steep slopes of 40 to 60 percent. Moderate geologic hazards would include stabilized eazthflows, mudflows, and landslides, and slopes adjacent to failed slopes or active mass- m!um/m....+. u/G/~/~~..y r/./o~r,~hr e/r/az s EnviroxmenfalArrerrmenf t LJ t~ J