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GEOLOGY o o .... CoO Strata exposed in the Sagers Wash area range from the Jurassic Entrada Sandstone to the Paleocene-Eocene Green River Fonnation. These fonnations are covered in places with minor Quaternary alluvial and colluvial deposits. However, the major part of the Sagers Wash drainage basin is made up of the Cretaceous Mancos Shale. The Mancos Shale appears to contain the largest concentrations of salt of any geologic unit in the drainage basin, and appears to be the largest contributor of salt to runoff in the drainage basin. Table 8.0 of this plan shows the Mancos containing 3.6% salt, and the Mesaverde containing 2.0% salt. However, detailed geochemical sampling specifically for salts in the unweathered fonnations which crop out in the Sagers Wash drainage basin has not been done. The saline marine depositional environment for these geologic units is the source of the salt which they contain. Therefore, some salt will be expected in runoff from the drainage basin during the natural course of erosion. Any activities that increase erosion can be expected to increase the salt content of the runoff. STRUCTIJRE The Sagers Wash drainage basin trends northwest-southeast, roughly parallel to both regional and local geologic structures, in the central part of the Colorado Plateau structural province, The drainage is located along the northeast edge of the Paradox Basin just off the edge of the Uncompahgre Uplift, Strata in Sagers Wash dip gently toward the axis of the Sagers Wash syncline which diagonals across the drainage basin from southeast to northwest with a slight northwest plunge. The steepest dips (about 20 degrees) are to the Northeast near the southwest edge of the drainage basin on the Dakota Sandstone and older beds, The topographic high in this area is referred to as the highlands, and is partly attributable to the erosional resistance of the Dakota Sandstone which fonned a dip slope off of the adjacent Yellowcat structural dome. Beds at the north end of Sagers Wash dip slightly to the North or are almost flat-lying. No significant faulting is reported to occur within the Sagers Wash drainage basin, although some small NW-SE trending nonnal faults are shown near the Sagers Wash synclinal axis in the center of the basin (Friedman and Simpson, 1980). STRATIGRAPHY The oldest stratigraphic unit in Sagers Wash, the Jurassic Entrada Sandstone, consists of 150 to 400 feet of orange, buff, and white, fme to medium-grained, massive and cross-bedded eolian sandstone, The Entrada is overlain by the terrestrial Summerville Fonnation which ranges in thickness from 60 to 150 feet. The Summerville is made up of red, gray, green, and brown 7