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<br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />'I <br />,I <br />II <br />,I <br />I <br />I <br />I <br />I <br />I <br />I <br /> <br />SECTION 5. GEOLOGY <br /> <br />5.1 Geomorphology <br /> <br />Generally speaking, the geomorphology of the Study Area is characterized <br />by north-south striking cuestas. These cuestas are simply asymetrica1 ridges <br />which have a steep slope on their westerly sides and a rather flat slope on <br />their easterly sides. The formation of the cuestas is related to the erosion- <br />resistant rocks which cap them and to the eastward tilt of the rock <br />formations. <br /> <br />It is customary for geomorphologists to classify stream valleys according <br />to their stages of topographic development. These classifications are called <br />youth, maturity, and old age. In this respect the valley of South St. Vrain <br />Creek in the Study Area may be called mature. That is, tributary gulches in <br />the Study Area have extended themselves so that there is a well developed <br />dr,endritic drainage pattern in the Coffintop basin. The gulches and streams <br />have adjusted themselves well to local geologic structure and are entrenched <br />on less erosion-resistant rock formations and fault zones. Stream divides are <br />sharp and ridge-like and there are a minimum of inter-stream, flat uplands. A <br />profile of equilibrium (rates of erosion and deposition are approximately <br />equal) has been more or less attained by South St. Vrain Creek, but many of <br />, <br />the tributary gulches are yet ungraded. There is a lack of waterfalls in <br />South St. Vrain Creek. Maximum possible relief exists. The topography <br />consists not so much of flat valley floor and level upland tracts as it does <br />of slopes and valley sides. <br /> <br />5.2 Soil and Rock Materials <br /> <br />5.2.1 General Statements <br /> <br />Soil and rock deposits in the Study Area range in age from Pre-Cambrian <br />to very Recent. For a detailed account of stratigraphic names, ages, <br />thicknesses, and mechanical-lithological descriptions, the reader is referred <br />to Plate g. It should be noted here that the thicknesses presented on Plate 9 <br />are only approximate; the thicknesses presented for the various members of the <br />Fountain Formation (Pfs, Cfr, and Cfc) are even greater approximations. It <br />appears that there is considerable lateral variation in the thicknesses of the <br />Fountain members. <br /> <br />UEBLACKER ASSOCIATES. INCo <br />