The Challis volcanic field is the largest of several Eocene volcanic fields in
the Pacific Northwest of the United States and Canada. In the Little
Wood River area of Idaho, rock types in the Eocene Challis Volcanic Group
include andesite lava flows and tuff breccia, dacite lava flows and flow
breccia, volcaniclastic sedimentary rocks, lithic tuff, nonvolcanic conglomerate,
and rhyolite dikes.
|Posted May 2005
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