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I I I I I I I I I I I I I I I I I I I at McGraw Bottom (sec 29, T22S, R24E) , approximately 2.5 miles northwest of Dewey, Utah (Maps I). l'\"> N ~ o The watershed consists of three subwatersheds that merge to form Sagers Wash main channel in the lower area of the watershed. These three subwatersheds are Sagers Wash, Pinto Wash and Nash Wash. Sagers Wash rises (7680 feet elevation) from the Book Cliffs on the western side of the watershed and drains through a low sloping area known as Sagers Flat. Pinto Wash rises (6966 feet elevation) from the Book Cliffs in the central area of the watershed and merges with Sagers Wash in the lower portion of the watershed (sec 16, T22s, R24E). Nash Wash rises (8987 feet elevation) in the Roan Cliffs and merges with Sagers Wash in the lower portion of the watershed (sec 16, T22S, R24E) (Map I). The confluence of Sagers Wash watershed with the Colorado River is approximately 4000 feet in elevation. The drainage areas of the subwatersheds are as follows: Sagers Wash (at junction) 83.3 square miles or 53,290 acres Pinto Wash 53.7 square miles or 34,400 acres Nash Wash 76.0 square miles or 48,640 acres Lower Sagers Wash 29.3 square miles or 18,765 acres GEOLOGY: The watershed is primarily composed of gently dipping sedimentary rocks of the Mesozoic Era with some Tertiary rocks in the upper reaches and Quaternary deposits in the central area. The general structure of the area consists of north dipping structural benches that developed over the last 10 million years as the Colorado Plateau was uplifted and streams incised into the sedimentary bedrock. Erosion- resistant sandstones and siltstones form the cliffs and high ground areas while erosive marine shales form the badland at and near the base of the cliffs. Alluvial deposits of Quaternary age occur south of the cliffs and badlands. These younger sedimentary deposits act as active flood plain areas (Sagers Flat) or form remnant alluvial terraces within the wide valleys of the central watershed area. The rock units that underlie the watershed are listed in order of increasing age and in sequence from the upper to lower portions of the watershed (generalized from Hintze, 1975; Williams, 1964; and Cashion, 1973): Tertiary age --- Wasatch Formation Cretaceous age - Mesa Verde Group Mancos Shale Dakota Sandstone Burro Canyon Sandstone Jurassic age ----Morrison Formation Bluff Sandstone Summerville Sandstone 3