Revision History for USGS 
  Crustal Studies Technical Letter Number 7

  John C. Roller and John H. Healy

  Seismic-Refraction Measurements of Crustal Structure 
  Between Santa Monica Bay and Lake Mead

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  Posted online at http://pubs.usgs.gov/misc/tl/0007/
  July 27, 2012

  Initial release in paper form
  January 25, 1963

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