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<br />. <br /> <br />. <br /> <br />J1~~~s an area of lesser resistance which influences the point <br /> <br />at which the salt can start to rise and dome the formations above <br /> <br />it. As another part of the movement of the salt, the chemical <br /> <br />change from anhydrite to gypsum in the presence of water brings <br /> <br />about a 60% increase in volume which adds still another force of <br /> <br />movement. Despite the theoretical nature of the mechanics, it is <br /> <br />generally agreed by all concerned that the gypsum in the Ruedi <br /> <br />basin has been squeezed and expanded upward and has taken on the <br /> <br />characteristics of a "salt plug". <br /> <br />This upward movement of the evaporite has undoubtedly caused, <br /> <br />or accentuated, fracturing of brittle, hard, formations such as <br /> <br />are found in the Maroon formation which overlies it. <br /> <br />At Ruedi, one particular point of contention is the question <br /> <br />of whether the salt is still moving and if so, how rapidly is it <br /> <br />moving and what damage can such movement cause. <br /> <br />Some of those opposing the use of the site at Ruedi contend <br /> <br />that the movement is continuing, is rapid and will cause collapse <br /> <br />of the reservoir and damage to the dam. The Bureau of Reclamation <br /> <br />geologists generally concede the continuing movement of the gypsum <br /> <br />but contend that it moves in terms of geologic rather than his- <br /> <br />torical time and that this rate is so slow that it is essentially <br /> <br />unmeasurable within the expected lifetime of the project. <br /> <br />At present, no factual evidence has been presented to show <br /> <br />that measurable movement of the gypsum has occurred at or near <br /> <br />Ruedi within historical time. The writer followed the suggestion <br /> <br />- 6 - <br />