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<br />activities occurred, the Dolores River: remained in its original channel, <br /> <br />across the anticline, and in combination with other erosional forces <br /> <br />removed the collapsing materials to form the valley. The sides of the <br /> <br />valley are now characterized by numerous faults, slides and collapsed <br /> <br />structures. <br /> <br />Investigations <br /> <br />The rlureau of Reclamation initiated feasibility investigations in 1971 <br /> <br />to study and formulate a plan to prevent the salt from entering the <br /> <br />river. Major investigations have included literature reviews, geologic <br /> <br />studies, resistivity surveys along the river, installation and operation <br /> <br />of an observation well network in the valley, drilling test wells, <br /> <br />conducting aquifer tests, and collection of meteorologic data. The <br /> <br />quality and quantity of surface waters entering and leaving the valley are <br /> <br />continously monitored as well as the quality of the ground water adjacent <br /> <br />to the river. Environmental, social, and economic data have also been <br /> <br />collected. <br /> <br />Geological investigations have shown that the Dolores River has <br /> <br />deposited from 60 to 130 feet of modern alluvium on top of the underlying <br /> <br />Paradox Member of the Hermosa Formation of Pennsylvanian Age. The <br /> <br />a~luvial material generally consists of silty sand near the surface, <br /> <br />coarse sand and fine gravel with numerOUti clay lenses of various <br /> <br />thicknesses beneath, and a coarse gravel-sand-clay-Silt mixture at the <br /> <br />bottom of tne alluvium. In the Paradox Hember underlying the alluvium, <br /> <br />the more soluble salts have been leached from the upper 650 to 1,000 feet <br /> <br />to form a residual cap, which is predominantly gypsum with large amounts <br /> <br />of crumbly, gypsiferous, and extensively brecciated carbonaceous shale. <br /> <br />Underlying the residual cap, a halite-rich core extends to a depth of <br /> <br />approximately 14,000 feet. <br /> <br />3 <br /> <br />''\",(,r. r. ,0 <br />\}TJ ~~\jd <br />