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Dowe Flats Quarry Soils and Geology Report <br /> opposite to the general trend of folding along the Front Range. In addition, several smaller faults <br /> and canoe folds overprinted on this anticline distort and disrupt the bedding to produce further <br /> structural complexity. <br /> Dowe Flats itself is underlain by a southward-plunging syncline. This syncline is nearly <br /> symmetrical with no significant folding and faulting at the south end of Dowe Flats. Its northern <br /> boundary is the extremely complex Dowe Pass area, an intensely folded area containing <br /> numerous anticlines and synclines along with some faulting. <br /> Two faults are shown within the eastern portion of Dowe Flats by Mallette (1962). One high- <br /> angle northeast-trending fault is in the northwestern quadrant of Section 15. The other fault is in <br /> the eastern half of Section 15 and trends northwest. Both faults are inferred and are shown with <br /> very small offsets. However, documentation of evidence for these faults is not provided by <br /> Mallette's report, and they were not mapped by the several other major investigators of the Dowe <br /> Flats area. In addition, examination of large-scale aerial photography in connection with this <br /> study did not reveal any evidence for the northeast-trending fault and only limited evidence for <br /> the northwest-trending fault. Therefore, the northeast-trending fault is not believed to be present, <br /> and the northwest-trending fault, if present, is only a localized small-scale feature. <br /> All these units are upper Cretaceous in age. The synclinal structure of the central Dowe Flats <br /> basin is such that the youngest (Pierre Shale) formation is exposed over much of the eastern <br /> portion of the valley bottom with the older strata forming concentric horseshoe-like rings as they <br /> outcrop around the valley perimeter on the east and west margins. <br /> Structurally, the region surrounding Dowe Flats is extremely complex with both intense and <br /> sometimes superimposed folding as well as post-Cretaceous faulting. In this context, the <br /> simplicity of the central interior portion of Dowe Flats is almost anomalous. Interpretation of <br /> available information does not indicate the presence of major faulting, shearing, or significant <br /> folding in the interior portion of Dowe Flats. <br /> 4 References <br /> Boos, M.C. and M.F. Boos. 1957. Tectonics of Eastern Flank Foothills of the Front Range, <br /> Colorado. American Association of Petroleum Geologists Bulletin, Vol. 41, Pages 2603- <br /> 2676. <br /> Fox Consultants, Inc. 1985. Report on Geotechnical Feasibility and Preliminary Embankment <br /> Design, Proposed Dowe Flats Dam and Reservoir near Lyons, Colorado. Report prepared <br /> for St. Vrain Mutual Reservoir and Water Company. 7348 Ute Highway, Longmont, <br /> Colorado 80501. <br /> Hunter, Z. 1947. Structural Geology of Boulder County. Ph.D. Dissertation, University of <br /> Colorado, Boulder. <br /> Lowman, B.M. 1977. Stratigraphy of the Upper Benton and lower Niobrara Formations (Upper <br /> Cretaceous) Boulder County, Colorado. Master's Thesis, Colorado School of Mines, <br /> Golden. <br /> Mallette, C.M. 1962. Raw Materials Investigation, Dowe Flats, Colorado. Unpublished report <br /> prepared for Ideal Basic Industries, 23 pp. <br /> 7 May 2, 2022 <br />