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<br />0977 <br /> <br />. <br /> <br />. <br /> <br />and underlain by the Belden formation, a firm, dark gray, inter- <br /> <br />bedded shale and sandstone complex with occasional thin layers of <br /> <br />limestone. <br /> <br />In the Ruedi area these formations have been arched into an <br /> <br />anticline which crosses the reservoir basin in a northwest-south- <br /> <br />west direction. Erosion of the crest of this anticline by the <br /> <br />Fryingpan River and its tributaries has exposed the gypsum in the <br /> <br />center of the reservoir basin and the Belden shale in the eastern <br /> <br />part of the reservoir and left a rim of Maroon formation on the <br /> <br />south, west and north sides of the basin. The damsite is located <br /> <br />in the canyon on the west side of the basin and on the westward <br /> <br />dipping flank of the anticline where the Fryingpan River has cut <br />a channel through the resistent Maroon formation. <br /> <br />Because the evaporite consists of gypsum, anhydrite and halite, <br /> <br />which are rocks proven to be subject to plastic flowage, they have <br /> <br />become intensely distorted and swollen by the various forces re- <br /> <br />lated to the formation and erosion of the anticline. These forces <br /> <br />have come from without and within the evaporite mass. Although <br /> <br />the exact nature of these forces and movements can only be recon- <br /> <br />structed theoretically, there are certain basis conditions which <br /> <br />we know must have occurred. l~e believe that the compressive forces <br /> <br />of anticlinal folding tended to put stresses on the salt mass <br /> <br />which caused it to flow plastically and to seek points of crustal <br /> <br />weakness where it could intrude. We know that removal of super- <br /> <br />incumbent load by erosion, from local areas above a salt mass <br /> <br />- 5 - <br />