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<br />. <br /> <br />OC1012 <br /> <br />. <br /> <br />e <br /> <br />". <br /> <br />river is a rolling plains area. The elevation at Hoehne, located in the <br /> <br /> <br />plains section" is 5,742 feet. From the high plateaus and mesas on the <br /> <br /> <br />southern divide, the basin slopes steeply to the river. <br /> <br /> <br />16. From the confluence of North and Middle Forks, the Purgatoire <br /> <br /> <br />River flows through a valley in a narrow mountainous section to Trinidad, <br /> <br /> <br />river miles 186 to 157. This valley varies in width from a few hundred <br /> <br /> <br />feet to about one-fourth mile. Between Trinidad and the mouth of San <br /> <br /> <br />Francisco Creek, river nules 157 to 122, the valley reaches a maximum <br /> <br /> <br />width of about three-fourths mile. Topographic details of the Purga- <br /> <br /> <br />toire River valley from river mile 163 to river mile 122 are shown on <br /> <br /> <br />plates 2 to 7, appendix C. <br />17. Geology, - The principal rocks of the upper Purgatoire River <br />basin range in geologic age from pre-Cambrian through Tertiary with <br />minor amounts of Quaterna~ gravels and alluvium. Except for the small <br />representation of pre-Cambrian plutonics and metamorphics in the extreme <br /> <br /> <br />headwaters of the basin, the only igneous or metamorphic material present <br /> <br /> <br />occurs as dikes and flows of Tertiary age. Upstream from Sopris, Colo- <br /> <br /> <br />rado, due to an uplift of dlder rocks in the headwater reaches, the <br /> <br /> <br />streams flow over successively younger strata which dip steeply to the <br /> <br /> <br />east and Crop out in nOrth-south ridges. Downstream from Sopris, Colo~ <br /> <br /> <br />rado, the strata dip west, and exposures become successively older. In <br />