.47 Tl Potassium-rich andesite, latite, and basalt lava .55 Tdm Tuff of Degan Mountain .48 Te Tuff of Ellis Creek .49 Tdf Dacitic and rhyodacitic lava .50 Tmz Intermediate lava and breccia of mixed zone .51 Tlt Lithic tuff of Corral Creek .52 Tfr Flow-laminated rhyolite or quartz latite lava Twin Peaks caldera and southern part of Van Horn Peak cauldron complex Intrusive rocks .56 Trf Rhyolite dikes, plugs, and flows .57 Tfd Felsic dike rocks .10 Tqp Quartz porphyry intrusions .58 Tpe Intrusive rocks of Pats Creek-Upper Eddy Creek .59 Tdc Diorite complex .15 Tgp Gray porphyry .60 Tii Intermediate dikes or flows .31 Tdi Dikes and plugs of intermediate composition .61 Tip Intermediate intrusive rocks of Spider Creek-Parker Creek .53 Tinm Intermediate and mafic intrustions Extrusive rocks Tuff of Challis Creek .62 Tsd Caldera-wall slump debris (megabreccia) .63 Tcru Tuff of Challis Creek, upper unit .64 Tcrm Tuff of Challis Creek, middle unit .65 Tcrl Tuff of Challis Creek, lower unit .54 Tcr Tuff of Challis Creek, outflow unit .37 Tqb Quartz-biotite tuff .40 Tc Tuff of Camas Creek-Black Mountain .66 Tmb Megabreccia of Ibex Creek .43 Tp Tuff of Pennal Gulch .44 Trb Rhyolite of Red Butte .46 Tem Tuff of Eightmile Creek .47 Tl Potassium-rich andesite, latite, and basalt lava .48 Te Tuff of Ellis Creek .67 Trm Rhyolite of Mill Creek Summit .68 Tsb Sedimentary breccia .49 Tdf Dacitic and rhyodacitic lava .69 Tvs Volcaniclastic and sedimentary rocks Custer graben area Intrusive rocks .31 Tdi Dikes and plugs of intermediate composition .9 Trd Rhyolite dikes .70 Td Dikes .11 Tr Rhyolite intrusions .71 Tgi Intrusive rocks east of Bonanza Extrusive and sedimentary rocks .72 Trl Rhyolite lava .73 Tpc Tuffs of Pennal Gulch and Camas Creek- Black Mountain, undivided .74 Tvc Volcaniclastic rocks .46 Tem Tuff of Eightmile Creek .67 Trm Rhyolite of Mill Creek Summit .49 Tdf Dacitic and rhyodacitic lava .69 Tvs Volcaniclastic and sedimentary rocks .75 Tar Arkosic sandstone and conglomerate Southeastern part of quadrangle Intrusive rocks Rhyodacite domes and plugs at Bradbury Flat .76 Tdbi Rhyodacite plugs .77 Tdb Rhyodacite domes .78 Tib Mafic intrusive rocks .79 Tdl Diabase and lamprophyre dikes .80 Til Potassium-rich andesite, latite, and basalt intrusions .81 Tsy Syenite intrusion .31 Tdi Dikes and plugs of intermediate composition Extrusive and sedimentary rocks .82 Tbau Mafic lava .83 Trr Tuff of Red Ridge .54 Tcr Tuff of Challis Creek, outflow unit .43 Tp Tuff of Pennal Gulch .74 Tvc Volcaniclastic rocks .84 Th Tuff of Herd Lake .47 Tl Potassium-rich andesite, latite, and basalt lava .67 Trm Rhyolite of Mill Creek Summit .81 Tbam Mafic lava .69 Tvs Volcaniclastic and sedimentary rocks .49 Tdf Dacitic and rhyodacitic lava .81 Tbal Mafic lava .85 Tgc Tuff of Germania Creek .86 Tbc Lava and ash-flow tuff of Burnt Creek .87 Tsc Tuff of Sage Creek .88 Tcg Conglomerate and fanglomerate