114o12’30” 44o52’00” 114o48’30” 44o48’30” Custer County, er iv R n Tcv o Idaho Tgs m l Qa a Kgd Tgs S Tcv k Ys r Ys o Qa F Tgdd le The map on this page has been reduced by 40% from dd Ys Mi Tcv Ys the map on the big page. So it is not to 1:500,000 scale. The scale bar was reduced with it though and should be Tgs Tcv Tcv Tcv close to correct. Kgd Qa Os Qm Kgd Qa Salmon Qa Ds Kgdh R. Mtns. Kgd Kgd Tcv Qs OCZ P A Qm H Kgd Challis Tcv S Pzl Kgdh Kgd OCZ IM E Os Qa Qa Qs RO PPPs Tcv Tgdd Tcv Ds Qs I Kgdh Cs V Pzl Tgs A L Kgd Qm Tcv DSs L OCs DSs E OCs Y Cs Ss Qa Tcv Kgdh Ss Tcv Ds Ybe Kis Sunbeam OCs Tcv o Tgs Qa Cs 44 21’30” Kis Kgd OCs Ss Ds 115o17’30” Kgdh Kgd PPPs Kgd Qs Kis Ms OCs Os Ts Qm 21 Ybe OCs PPPs Os 75 Os PzZm Kgdh OCs Ds Qs Ybe Qa River Kgd OCs DSs Kis Kis on Ms OCs Tcv Qs m Os OCs Ss Ts Os Qs Qg al Qa Sawtooth Rge. S 25 DSOs Ms Ss Tgs OCs Ss Ms Tcv Qs Stanley o Qg Tcv Ds 44 14’00” Kgd Ps PPPs Os Kgdh Tcv Tcv 93 Ms Qs Tcv Ms Qm Ts PzZm Redfish SOs Borah PK. Tcv Kgd Lk. Qa (12,662 ft) Ds Ts DSOs Qs Qm Ds Qm Qm Qa SOs Leatherman Kgd Pk Tgs Chilly Lost River Rge. Tcv Qa Tcv Ds Zs Ds Stanley 113o25’00” Basin Qs Qs Big Lost Rv Valley Tcv Kgd Qm Ms PPPs Tcv PPPs Ds PPPs Ms 43o56’00” Ms PPPs Tcv Mackay Res. 114o49’00” PPPs Ms PPPs Tgs DSOs Mackay Qs DSOs Tes Tcv Ms Ms Tes Trail Creek Tgs Tgs Fault Pioneer Tcv Thrust Tgs White Qm Knob DSOs Ms Ms Qa Tgs Copper Mtns. Tgs Xm Pioneer Basin Thrust Tcv PPPs Hyndman Pk. Mtns. Ms PzYsq Tgs Tcv PPPs Wildhorse PPPs Detachment Ms Ms

Tcv Digital Atlas of Idaho, Nov. 2002 PPPs 0 5 10 miles Tcv http://imnh.isu.edu/digitalatlas Ms Compiled by Paul K. Link, 43o31’30” 113o38’00” Idaho State University, Geosciences Dept. 0 8 16 kilometers http://www.isu.edu/departments/geology/ Custer County Custer County lies in the heart of Idaho, and contains as diverse geology as many states and some countries. The county is mainly rugged mountains, with flat habitable terrane only in the Lost River, Pahsimeroi, and Sawtooth Valleys. The oldest rocks in the county are Paleoproterozoic gneiss in the core of the Pioneer Mountains core complex of the Pioneer Mountains above Copper Basin and Ketchum. Above this gneiss are Proterozoic and Paleozoic metasedimentary rocks, all intruded by an Eocene pluton. The core complex is uplifted on the Wildhorse detachment fault, which forms a domal pattern, and which moved from Eocene until Oligocene time. In the Pioneer and Boulder mountains north and south of the core complex is the thrust belt of Paleozoic rocks. Ordovician, Silurian and Devonian deep marine strata are found in the hanging wall of the Pioneer thrust fault, faulted below Pennsylvanian and Permian Sun Valley Group. East of the Pioneer thrust is the thick Mississippian Copper Basin Group, which contains the black conglomerates found in the Copper Basin and East Fork Lost River areas. The White Cloud Peaks, on strike to the northwest, contain similar strata to the Pioneers and Boulders. Here Cretaceous granodiorite, that underlies Castle Peak, highest in the White Clouds, intruded Devonian to Permian sedimentary rocks. Across the Salmon River at the Thompson Creek molybdenum mine, Cretaceous intrusions have produced mineralization still being mined in the 21st century. This entire area, plus the Smoky Mountains west of Ketchum contain dark-colored organic-rich sedimentary rocks of the central Idaho Black Shale Mineral Belt, Mineral exploration and production in these rocks controlled the early economic development of the area. The White Knob Mountains, west of Mackay, contain Mississippian limestone intruded by and Eocene granite. Extensive copper mineralization is found on the margins of the granite, and the Empire Mine and associated properties immediately west of Mackay are found in these rocks. East of the huge Lost River Valley and in the footwall of the west-dipping Lost River fault, are folded Paleozoic limestones and quartzites of the Lost River Range. Borah Peak, highest in Idaho looms above Chilly and the ISU Geoscience Lost River Field Station at its base along the Big Lost River. The northern half of the Lost River Range, north of Willow Creek Summit is the Pahsimeroi Mountains, which contain folded Mississippian strata on the south and unusual breccia at Grouse Peak on the north end immediately east of Challis. East of the Lost River Range, in the northeast corner of the county are Eocene and Oligocene conglomerate and tuff in the Donkey Hills and a western corner of the Lemhi Range underlain by Mesoproterozoic Belt Supergroup. The Pahsimeroi Valley extends north into the Salmon drainage, and lies on the hanging wall of the Lemhi fault. The northern third of the county, north of the Salmon River, is underlain mainly by Eocene volcanic rocks of the Challis Volcanic Group, cut by northeast-striking faults of the trans-Challis fault system, which controlled location of vents and hydrothermal systems that controlled mineralization, mainly of gold in the Yankee Fork area. On the western edge of the co0unty are the spectacular Sawtooth Mountains, looming west of Stanley Basin or Sawtooth Valley. These glaciated peaks are formed of both Cretaceous granodiorite of the Idaho batholith, and Eocene granite associated with the Challis Volcanic Group. See geology and regional discussions in Rocks, Rails and Trails, plus the Link and Janecke article in Guidebook to the Geology of Eastern Idaho P.K. Link, 10/02 Description of Units for Custer County, Idaho

Qa Quaternary alluvial deposits Qm Quaternary moraine (unsorted boulders, cobbles and sand) and glaciofluvial outwash (bedded stream deposits formed from streams draining active glacial ice). Qs Quaternary surficial cover, including colluvium, fluvial, alluvial fan, lake, and windblown deposits. Included fluveolian cover on Snake River Plain, (Snake River Group). Tcv Eocene Challis Volcanic Group, volcanics and volcaniclastics; Older andesitic lavas, intermediate age dacite lava and tuff and younger rhyolite flows and tuffs; 51 to 44 Ma. (Includes Potato Hill and Kamiah volcanics of northern Idaho). Tgs Eocene granite, pink granite, syenite, rhyolite dikes, and rhyolitic shallow intrusive; last phase of the Challis magmatic event (46 to 44 Ma). Forms craggy scenic mountain landscape in central and northern Idaho. Tgdd Eocene granodiorite and dacite porphyry intrusive, also includes diorite and, in northern Idaho, minor granitic rock; intermediate phase of Challis magmatic event (50 to 46 Ma). Summit Creek stock. Kgd Cretaceous granitic rocks of the 2 mica suite. Idaho batholith and related plutons; granite and granodiorite that contains both muscovite and biotite. Sodium (Na) rich. Intruded between 80 and 65 Ma. Kgdh Cretaceous granitic rocks of the hornblene-biotite suite; granite, granodiorite and megacrystic granodiorite. Potassium (K) rich. Age about 80 to 90 Ma. Kis Cretaceous syenitic rocks, northern Idaho; small stocks about 120 Ma. Pzl Lower Paleozoic sedimentary rocks (includes roof pendants near Stanley). PPPs Permian and Pennsylvanian sedimentary rocks. PPPMs Permian and Carboniferous sedimentary rocks (Snaky Canyon Formation). Ms Mississippian sedimentary rocks. Ss Silurian sedimentary rocks. Ds Devonian sedimentary rocks. DSs Devonian and Silurian sedimentary rocks. DSOs Devonian, Silurian, and Ordovician sedimentary rocks. SOs Silurian and Ordovician sedimentary rocks. Os Ordovician sedimentary rocks. OCs Ordovician and Cambrian sedimentary rocks. Zs Neoproterozoic sedimentary rocks undivided. Ybe Belt Supergroup undivided; contains siltite, argillite, sandstone (quartzite) and minor conglomerate in Lemhi Range and near Salmon; includes Meadow Creek metamorphic sequence east of Elk City in the Clearwater River drainage. PzYsq Paleozoic/Mesoproterozoic schist and quartzite; age uncertain. PzXm Paleozoic/Paleoproterozoic metasedimentary rocks (includes metamorphic rocks on Mt. Harrison in Albion Range). Xm Paleoproterozoic gneiss in the Centennial Mountains. Symbols

Geologic unit contacts with unit Overturned anticline: trace of axial Yp designation. plane.

Normal fault: certain; dashed where Overturnedsyncline: trace of axial approximately located; dotted where plane. concealed. Location of ISU Rockwalk rock Thrust fault: certain; dashed where from each county. approximately located; dotted where concealed. Cities Detachment fault: certain; dashed Feature location where approximately located; dotted where concealed. Roads Anticline: trace of axial plane: large Interstate Route arrow indicates direction of plunge. 15 U.S. Route Syncline: trace of axial plane: large 95 arrow indicates direction of plunge. 1 State route 114o12’30” Custer County, 44o52’00” 114o48’30” Idaho 44o48’30”

er iv R n Tgs o Tcv m Tgs l Qa a Kgd Tcv Ys S Ys k r Qa o Tgdd F le Ys dd Mi Tcv Ys

Tgs Tcv Tcv Kgd Qa Os Qa Qm Qa Kgd Salmon Ds Kgdh R. Mtns. Kgd Kgd Tcv Tcv Qs OCZ P Qm A H Kgd Challis Tcv S Pzl Kgd OCZ IM Kgdh E Os Qa Qs RO Tgdd Qm PPPs Tcv I Tcv Cs Ds Qs Kgdh V Pzl Tgs A Qa L Kgd Tcv DSs L OCs DSs E Qm OCs Qs Y Qa Kgdh Kgdh Cs Ss Tcv Tcv Ss Ds Ybe Kis Sunbeam OCs Tcv 44o21’30” Tgs Qa Kis Kgd OCs Ss Ds 115o17’30” Kgdh PPPs Kgdh Kgd Ms OCs Qs Os Kgd Cs Qs Ybe Ts 21 PPPs 75 OCs PPPs Os OCs Ds DSs Os PzZm r Kgdh Qs Ybe Qa ive Kgd OCs Kis Kis R Ms OCs Tcv Qs on Os OCs Ss Ts Os Qs Qg lm Qa Sawtooth RangeQm a 25 S DSOs Ss Tgs OCs Ss Ms Tcv Qs Stanley Tcv Ms Ds 44o14’00” Kgd Qg Ps PPPs Os Kgdh Tcv Tcv 93 Ms Qs Tcv Ms Qm Qs Ts PzZm Redfish Qm SOs Lk. Borah PK. Tcv Kgd Qa (12,662 ft) Qm Ds Ts DSOs Qm Qs Ds Qm SOs Leatherman Kgd Qa Pk Tgs Tcv Chilly Lost River Rge. Qa Stanley Tcv Zs Ds Ms Ds o Basin Tcv Qs 113 25’00” Qs Big Lost Rv Valley Tcv Kgd Ms PPPs Tcv PPPs Ds Ms 43o56’00” PPPs Tcv PPPs Qm Mackay Res. 114o49’00” PPPs Ms PPPs Tgs DSOs Qs DSOs Tes Tcv Mackay Tes Trail Creek Ms Ms Tgs Fault Pioneer Tcv Tgs Thrust Tgs White Qm Knob Qa Qa DSOs Ms Ms Qa Tgs Mtns. Tgs Xm Copper Pioneer Basin Tcv PPPs Hyndman Pk. Mtns. Thrust Ms PzYsq Tgs PPPs Wildhorse Tcv PPPs Detachment Ms Ms 0 5 10 miles PPPs Ms Tcv 0 8 16 kilometers 1:500,000 Digital Atlas of Idaho, Nov. 2002 Tcv http://imnh.isu.edu/digitalatlas Compiled by Paul K. Link, Idaho State University, Geosciences Dept. o o 43 31’30” 113 38’00” http://www.isu.edu/departments/geology/