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<br />deviations are not as great in'magnitude as the mbvement incurred
<br />by prolonged seasonal temperature differences. In none of the sta-
<br />tions are the daily deviations greater than a few thousandths of an
<br />inch, and in none of the stations are the overall' seasonal movements
<br />greater than a few hundredths of an inch. This m~tion is cyclical,
<br />with no cumulative deviation observed since the start of the monitoring
<br />program.
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<br />4.
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<br />Photogeology
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<br />On January 26, 1978, a series of 27 photographs were taken of Rainbow
<br />Bridge and the surrounding Bridge Creek Canyon area,. These photographs,
<br />with the lake elevation at 3625.61 feet, were compared with earlier sets
<br />of photographs taken from the 'same photopoints.
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<br />Results of the comparison show that no changes
<br />structure or foundation of Rainbow Bridge.
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<br />Slight displacements to a few loose cobbles and boulders have occurred
<br />along the sides of Bridge Creek Canyon. Wind, rain, gravity, and move-
<br />ment by tourists are the major contributors to this slow overall process
<br />of erosion and displacement.
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<br />With the elev&tion of the reservoir being low during January, changes
<br />in the stream channel itself were observed when compared to previous
<br />sets of photo~,', Sands and gravels have been rearranged in the channel
<br />due to flash floods and a slight contribution from reservoir action.
<br />This is also part of the process of erosion and is to be expected.
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<br />Thus far, the photogeology program is revealing minor displacements
<br />of some loose material due to erosion and tourists, and also reveals
<br />that no significant changes have occurred to Rainbow Bridge or the
<br />surrounding foundation.
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<br />Included in this report are four photographs which are examples of
<br />those used in the photogeology study. Two photographs were taken
<br />from nearly the same spot a small distance downstream from the bridge;
<br />one, P557-427-647NA, was taken in March 1974, and the other, P557-
<br />427-l8l8NA, in January 1978. The remaining two photographs, both
<br />taken from the same spot, show a closer, more detailed view of the
<br />right leg of the bridge. The first, P557-427-6l6NA, was taken in
<br />February 1974, and the more recent one, P557-427-l796NA, was taken
<br />in January 1978.
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<br />5.
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<br />Moisture Rock Samples
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<br />No additional data.
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