Geology and Stratigraphy of the Challis Volcanic Groups and Related Rocks, Little Wood River Area, South-Central, Idaho

摘要

The southwestern part of the Challis volcanic field occupies the valley of the Little Wood River and its tributaries in the Hailey and Idaho Falls quadrangles of south-central Idaho. The Little Wood River area is a structurally controlled topographic basin that is partly filled by Eocene Challis Volcanic Group and younger rocks. Rock types in the Challis Volcanic Group of the Little Wood River area include, in order of decreasing abundance, andesite lava flows and tuff breccia, dacite lava flows and flow breccia, volcaniclastic sedimentary rocks, lithic tuff, nonvolcanic conglomerate, and rhyolite dikes. A basal nonvolcanic conglomerate, that locally rests on upper Paleozoic sedimentary rocks at a regional unconformity, was deposited prior to eruption of volcanic rocks.