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STUDY AREA RESOURCES NATURAL..R-ESOURCES Geology The area evaluated is located within the eastern margins of the Colorado Plateau, a physiographic province of some 150,000 square miles that is generally typified by gently dipping sedimentary rocks, high relief produced by deeply incised drainages, elevations above 5,000 feet and a semi-arid climate. Because soils are thin and vegetation is sparse in this dry region, infrequent episodes of brief but intense rainfall yield often massive runoffs of surface water. These, in concert with the more insidious chemical and mechanical effects of migrating groundwater, have eroded the nearly horizontal rock units of alternating hardness exposed in the province to create its characteristic stair-step topography. Though the resulting erosional escarpments and benches are dominant landforms throughout the Colorado Plateau, other features often reflect the distinct influence of a local tectonic disturbance. Among these rather anomalous structures is the Uncompahgre Uplift, a long, linear bulge in the earth's crust upon which the study area is also situated. During Mesozoic times (about 180 million years ago), sediments were laid down on the flat, eroded surface of much older rocks. The sedimentary rocks underwent periodic erosion and then were covered by volcanic flows, which subsequently were eroded away. The Gunnison River established its course, cutting downward into the relatively soft sedimentary rocks. Approximately two million years ago, as the river cut downward, the land began to gradually rise. The river, established in its course, continued to cut downward into the hard and resilient Precambrian rock. Paleontology There is one known paleontological site within the study area which consists of fragments of a theropod posterior caudal vertebrae, a sauropod dinosaur rib, and numerous fragments of vertebrae and limb bones that are unidentifiable. The bone fragments occur in the Salt Wash Member of the Morrison Formation. The formation is a well-cemented sandstone, mudball and pebble conglomerate. The site was located in the early 50s by uranium exploration miners. BlM became aware of the site in 1984. This site has been classified by BlM as a Category II. Category II classifications are identified as geologic formations or parts of formations that have produced fossils of scientific value or known vertebrate localities elsewhere, thus indicating potential for the discovery of fossils of scientific value. Outcrops of the Morrison Formation and other geologic formations elsewhere may also be Category II areas. A letter from the Museum of Western Colorado dated March 19, 1986, states, ....due to 9