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Dowe Flats Quarry Soils and Geology Report <br /> with the underlying Fort Hays limestone make up all the ore mined at Dowe Flats to produce <br /> cement. <br /> However, characterization of the Smoky Hill Member as shale on a regional scale does not <br /> account for several separate limestone beds present in the Dowe Flats vicinity. At Dowe Flats, <br /> limestones within the Smoky Hill Member have been described at an outcrop along the Little <br /> Thompson River (Quam 1932) and mapped in the Dowe Flats valley (Mallette 1962). An 1I- <br /> foot-thick limestone unit was mapped 100 feet above the base of the Smoky Hill Member by <br /> Mallette in Dowe Flats but was not described by Quam in the Little Thompson River outcrop. <br /> All the other materials in the bottom 200 feet of the Smoky Hill Member are dark gray to black, <br /> pyritiferous, calcareous, marine shales. A second 20-foot-thick limestone bed was mapped at <br /> Dowe Flats and measured in the Little Thompson outcrop at the interval from 200 to <br /> approximately 220 feet above the bottom of the Smoky Hill. A final limestone bed, with a base <br /> about 256 feet above the Smoky Hill Member, was also located in both field efforts; however, its <br /> thickness was measured as 12 feet by Mallette (1962) and 43 feet by Quam (1932). Based upon <br /> interpretation of geophysical logs from oil exploration wells drilled 10 to 15 miles south and east <br /> of the site (Lowman 1977), the 43-foot value appears to be more realistic. <br /> The fact that the limestones in the Smoky Hill Member are not discussed in regional geologic <br /> summary papers indicates that they are local in nature and probably disappear to the north and <br /> south. <br /> 3.2.1.4 Pierre Shale <br /> The lower Pierre Shale is the uppermost unit considered in this report. Only the lower 500 feet of <br /> the Pierre Shale are found in Dowe Flats; the remainder has been eroded away. The lower 2,500 <br /> feet of Pierre Shale are homogeneous dark brown to gray-black marine shale that weathers to a <br /> buff color. The basal portion of the Pierre Shale, immediately above the Niobrara Formation, is <br /> sandy, but the sand content decreases in the main portion of the shale. <br /> 3.2.2 Local Structure <br /> The area surrounding Dowe Flats is structurally complex with several types of structural features <br /> of differing scales overprinted upon each other. Despite detailed studies, interpretations, and <br /> reinterpretations, the origin and exact relationship between all the structural features remains <br /> unclear. <br /> The regional Dakota hogback that parallels the eastern side of the Front Range through central <br /> and northern Colorado forms the ridge that separates Dowe Flats from the town of Lyons. The <br /> hogback ridge is normally a monocline formed by the uplift of the Front Range, but in this area, <br /> it appears as the eastern limb of a doubly plunging anticline with an axis approximately located <br /> on the eastern edge of the Lyons town limits. <br /> On the northern side of Dowe Flats, in the vicinity of Dowe Pass, the regional hogback has been <br /> offset approximately 2 miles by a major northwest-trending high-angle fault with a trace along <br /> the Little Thompson River. This fault is one of the many large faults that have offset the <br /> hogback. The southwest side containing Dowe Flats is the downthrown block, with displacement <br /> estimated at 600 feet (Hunter 1947). <br /> Rabbit Mountain is a large, southward-plunging anticline that forms the ridge east of Dowe Flats. <br /> It has a steeply dipping eastern limb and a gently dipping western limb, a structural style <br /> 6 May 2, 2022 <br />