Revision History for USGS 
  Crustal Studies Technical Letter Number 23

  J.C. Roller, W.H. Jackson, D.H. Warren, and J.H. Healy

  A Preliminary Summary of a Seismic-Refraction Survey 
  in the Vicinity of the Tonto Forest Observatory, Arizona

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  Posted online at http://pubs.usgs.gov/misc/tl/0023/
  February 14, 2013

  Initial release in paper form
  September 20, 1964

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