Revision History for USGS 
  Crustal Studies Technical Letter Number 21

  Ronald Willden

  Seismic-Refraction Measurements of Crustal Structure 
  Between American Falls Reservoir, Idaho, and Flaming 
  Gorge Reservoir, Utah

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  Posted online at http://pubs.usgs.gov/misc/tl/0021/
  February 13, 2013

  Initial release in paper form
  July 15, 1964

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