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| | Summary of Citation |
 | | In northwest part of quad, Potosi is a 1,200+ ft thick unit divisible into: 1) a basal gray, coarse-grained tuff and overlying flow breccia; 2) middle gray, banded, cliff-forming flows that are separated by thin tuffs; and 3) upper red to pink, slope-forming, thin flows and tuffs. |
 | | In southeast part of quad, it is composed of quartz latite and felsitic rhyolite. |
 | | Map unit described as light-gray to grayish-brown predominantly devitrified quartz latite welded ash-flow tuffs; moderately crystal rich with biotite, pyroxene, feldspar, and quartz most common in a eutaxitic and vitroclastic matrix; vertically columnar jointed; locally absent in map area owing in part to nondeposition and in part to erosion. |
| ngmdb.usgs.gov /Geolex/Refsmry/sumry_9892.html (942 words) |
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