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1 1 1 1 1 1 1 and quarrying of Lyons Sandstone West of the site for building blocks. Existing and former gravel pits are present along St. Vrain Creek just south of Dowe Flats from Lyons to Longmont. Farther to the east are several oil fields that produce from sandstones and limestones at depth. Coal mining occurred in the early part of the century from the Laramie formation, but is presently inactive in the area. 9.1 Regional Geologic Structure The Dowe Flats area is in the Foothills Belt, a transition zone between the Front Range physiographic province to the West and the Denver Basin physiographic province to the east. The Front Range, which is the eastern most range of the Southern Rocky Mountains, begins on the northern side of the Arkansas River in southern Colorado and extends northward for approximately 185 miles to the Wyoming border. The range varies from 25 to 95 miles in width (Boos and Boos, 1957), and was formed by vertical uplift and subsequent erosion of the sedimentary strata to expose the Precambrian core. Remnants of the original sedimentary cover, now present as truncated sedimentary rocks along the uplift flank, are tilted by drag along the uplift boundaries. The more resistant tilted rocks, generally sandstones and some carbonates, form linear hogbacks that parallel the mountain front. The less resistant shales have been eroded away to form linear valleys between the hogbacks. This linear system of valleys and ridges is present along most of the eastern Front Range boundary. The Denver Basin is a major structural basin east of the Rocky Mountains beginning south of Pueblo, Colorado and extending northward to the vicinity of Torrington, Wyoming. It spans approximately 180 miles at its widest point just south of the Colorado-Wyoming border. The basin is highly asymmetric with an 99