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<br />. 0848 <br /> <br />. <br /> <br />. <br /> <br />. <br /> <br />Benton group (Carlil$ shaie, Greenhorn liiliestona and Grah~f6~ stiile), <br />Niobrara group (apish~pa shal~ and Tffupaslimetii6#e'; Pietr~ sh~te, <br />Trinidad sandston~ and tile Vermej 0 fqrmation (coa.i~ bea'i-1rig sandstones, <br /> <br />" '-:' <br />and shales). The Pierre shale exposed in and around Trinidad, Colorado, <br /> <br />is a dark gray to green clay shale and siindy shale j The formation is <br /> <br />essentially flat-lying and is generally eroded to form gentle slopes due <br />to the lack of resistant beds. Its tnidkness in this area is probably <br />several hundred feet. Tert:1ary.sedimentary rocks occupy the greater part <br /> <br />of the watershed. 'fhe formations exposed are; ascenc!ingi Raton formation <br /> <br /> <br />(coal, sandy shale, sandstone, and conglomerate), Poison Canyon formation <br /> <br /> <br />(sandstone, conglomerate, and clay or marl), and Cuchara formation <br /> <br /> <br />(sandstone). Tertiary and Cretaceous beds are intruded by many Tertiary <br /> <br /> <br />igneous intrusives and, in places capped by igheous flOWSI Quaternary, <br /> <br />or Recent, age is represented by Terrace deposits and alluvium in and <br /> <br />along the streams and rivers. The general areal distribution of the prin- <br /> <br />cipal geological formations in the Trinidad area is shown on plate 1. <br /> <br />3. Location and description of the site. - The Trinidad dam and <br /> <br />reservoir site is on the flll'ga,toire River about .four miles upstream from <br /> <br />the ci'tyof:!l'i:>..:i.hidad, Coloraao, in- se,c.6-,.;1'3J3; R04'\'T, UhI'. lJ. T~ city <br />or .Tr.lniaaCl" :Colorado is lo.aated aloljg the Purgatoire River \'ih.ere.ilt <br /> <br />emerges into a valley through the plains area. The Trinidad dam site <br /> <br />is about four miles above Trinidad at the downstream end of a canyon <br /> <br />through the frontal range. In the reservoir area, bluffs rise over 200 <br />, <br /> <br />feet above the stream bed in a series of promontories between canyons <br /> <br />entering from the sides. at the lower end of the reservoir, there is <br /> <br />a bench on the right bank occupied by the village of Sopris, Colorado. <br /> <br />At the dam site, the bottom width of the canyon is about 800 feet and <br /> <br />there is a promontary on the left bank about 200 feet above the canyon <br /> <br />floor which offers a good site for a spillway. <br /> <br />2 <br /> <br />!\rrENDIX F <br /> <br />