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I I I I I I I I I I I I I I I I I I I by West Elk eoal Company, surficial deposits are approximately 20- to 30-ft thick in the project site vicinity. Sedimentary bedrock outcrops along hillslopes on either side of the Dry Fork of Minnesota ereek. The sedimentary rocks are of the Barren member of the Mesa Verde Formation (Kmv). The Barren member (Kmvb) consists of upper eretaceous, interbedded, light brown to gray, fine grained sandstones, mudstones, and shales with minor coal seams. The Mesa Verde Formation strikes approximately N 650 W, and approximately 30 to the southwest. The degree and extent of faulting within the project site is somewhat obscure. Definite geologic lineaments are visible on aerial photographs. These lineaments run along the axis of the Dry Fork of Minnesota Creek, as well as nearly perpendicular to the creek following unnamed gulches. The lineaments strike approximately N 500W and NlOo-300 E, respectively. These lineaments have been interpreted by some as fault traces. Faulting within the project region strikes NlOO-150E and NI50-500W. The age of faulting in the project region is believed to be primarily pre-Neogene, and likely Paleozoic in origin. None of the major tectonic faults within the region have experienced any recorded or observed Quaternary activity (Kirkman, 1981). 6.5 Seismicity The project site lies approximately in the transition zone separating the eolorado Plateau and Western Mountain seismotectonic provinces. The estimated magnitude of the maximum credible earthquake in these seismotectonic provinces is summarized in Table 6.6. Figure 6.5 shows the epicenter locations, number of seismic events, and Modified Mercalli intensity for seismic events in the vicinity of the project site. TABLE 6.6 MAXIMUM eREDmLE EARTHQUAKE MAGNITUDE Province Magnitude eolorado Plateau . 5.5 to 6.5 Western Mountain 6.0 to 6.5 Reference: (Kirkham, 1981) According to the seismic risk map of the United States developed for the Uniform Building Code, the project site lies within Seismic Risk Zone 1. Areas within Zone 1 have the potential for experiencing seismic events with Modified Merca1li (MM) intensities of between V and VI. 9