An 1891 geologic map of California depicting a large area of auriferous or gold bearing slate (dark blue) #geology #thestoryofslate http://pic.twitter.com/He2QGZRMrN
— John Van Hoesen (@Taconic_Musings) December 26, 2016
via Twitter https://twitter.com/Taconic_Musings
December 26, 2016 at 07:31PM
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