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State Reg. in mesa tops and benches, and recent alluvial sand and gravels restricted to stream flood plains (Williams, 1964). Thicknesses of these deposits are highly Variable owing to the nature of deposition. The maximum known thickness of alluvial sands near the mine is 18 feet on the south side of Tuttle Draw. Gravel deposits of unknown thickness are found along the San Miguel River at Naturita, Colorado. Mancos Shale (late Cretaceous). The youngest formation found in the Nucla Syncline, with the exception of Quaternary deposits, is the Mancos Shale. It is a drab dark gray, hrnxx3eneous, soft, fissle, marine shale which attains a maxirmsn thickness of ap- proximately 4,000 feet where fully present. Most of the Mancos has been removed by erosion in the Nucla Syncline except for the basal portion which forms a few isolated hills south of Nucla. Dakota (Naturita) Sandstone (Late Cretaceous). The contact be- tween the Marcos Shale and the underlying Dakota Sandstone is conformable, and in some cases, gradational (Lohman, 1965). Basically, the Dakota consists of resistant yellowish to gray, fissile sandstone aril conglareratic sandstones interbedded with dark gray carbonaceous shales, impure coal, and a basal con- glomPSate (see stratigraphic column, Figure 6-2 in Site Specific Geology Section). Total maximmm thickness for the Dakota in the area is estimated to be approximately 200 feet (Williams, 1964). Well exposed sections are found in Coal Canyon to the northwest of the mine site and along the rim of the San Miguel River Valley to the southwest. It outcrops extensively along the axis of the Nucla Syncline. With the underlying Burro Canyon Formation, it forms resistant mesa tops aryl sharp canyon walls. Burro Canyon (Cedar Mountain) Formation (Early Cretaceous). An erosional uniformity of regional extent marked by the basal con- 6-7