IDAHO GEOLOGICAL SURVEY TECHNICAL REPORT 14-2 MOSCOW-BOISE-POCATELLO IDAHOGEOLOGY.ORG STEWART AND OTHERS TKi REGIONAL SETTING CORRELATION OF MAP UNITS 114° 113.5° Qa HOLOCENE TKi GEOLOGIC MAP OF THE GIBBONSVILLE , SHEWAG LAKE , AND ALLAN MOUNTAIN QUADRANGLES , AND PARTS 40’ 5061 38 Ydc e Qg g PLEISTOCENE CENOZOIC n x a e l R p Ydc e t fault OF THE OST RAIL ASS AND IG OLE ASS UADRANGLES , EMHI OUNTY , DAHO , AND AVALLI AND r L T P B H P Q L C I R i UNCONFORMITY m n h o p C p e e Ts ? Tfb 5060 a r g 40 S o n C a TKi 48 45 60 t EAVERHEAD OUNTIES , ONTANA R Tcv Tcr B C M 70 45 A’ o 50 t tains EOCENE 25 o o 65 r r o r oun Tcd oot detachme e r r 45 Ydc 55 54 40 t r t reek fault e t i t 45 e ? Lick C t Td B 50 t Eric D. Stewart, Travis D. Steel, David E. Stewart, and Paul K. Link 40 i tler M 5059 65 37 B in 40 60 Bit 46° UNCONFORMITY 2014 35 60 Ydc CRETACEOUS Yg onda-P onda detachmefault n TKi 40 Yg MESOZOIC 64 nac nac 40 A A Lick C 630 000 FEET Qa reek fault (MT) 58 Yg 5058 60 32 45 UNCONFORMITY MAP LOCATION AND SCALE Yg 75 Ys 60 LEMHI SUB-BASIN BELT BASIN? MESOPROTEROZOIC This Technical Report is independent mapping by Eric D. Stewart, Travis 40 alls D. Steel, David E. Stewart, and Paul K. Link. Its content and format may Map area ass Yg Yqjl eek 45 r not conform to IGS standards. 5057 a rail P which F T lk C n E a Lick Ck. fault er MN tains ost t Ylc v L O 114°07’30’’ 5’ 2’30’’ 113°52’30’’ GN 530 000 FEET (ID) n oun MONTANA 820 000 FEET (MT) 726000mE 727 728 729 730 490 000 FEET (ID) 732 733 45°37’30’’ 45°37’30’’ o 36 5056 Ysu Idaho 48 M ass 15.5° 40 67 Ys tain 5056000mN 26 ? 2°06’ 276 MILS 37ES08 Qa Ys ioneer M oun 37 65 P Ysl onsville 37 MILS 65 IDAHO 50 Big Hole Valley ibb ig Hole P 49 llan M G B Ys 58 A Qg 13 Yg 58 Yg 1 440 000 FEET 38 ? QUADRANGLE 20 (IDAHO) 45.5° 71 45 e UTM GRID AND 2001 MAGNETIC NORTH 45 LOCATION tain k 61 48 Ydc or DECLINATION AT CENTER OF SHEET Yg oun ag Lak 46 47 63 5055 th F 5055 Ys 40 45 40 sses M Nor hew S 50 Uly 69 45 54 Qa 70 Ys S DESCRIPTION OF MAP UNITS 45 detachmealmonn Basin 620 000 23 Ydc 86 FEET (MT) 65 Iron Lake fault Td 5054 ALLUVIAL DEPOSITS SCALE 1:40,000 5054 77 Ylc Ylc 56 59 51 Ys 40 1 0.5 0 1 Yg 35 t fault 41 30 55 MILE ? Qa Alluvium (Quaternary) - Stream deposits of locally derived mud, sand, and gravel. FEET 45 1000 0 1000 2000 3000 4000 5000 6000 7000 Along Ditch and Hughes Creek, reworked boulders (Tfb) are also common. 78 40 Salmon River Mountains KILOMETER 66 Qg 55 1 0.5 0 1 58 Ys 40 75 65 35 Contour interval 40 feet Qa 70 GLACIAL DEPOSITS 58 63 62 45 75 30 5053 36 miles 5053 78 55 Qg 50 40 eek fault Qg Glacial Till (Quaternary) - Surficial deposits consisting of locally derived angular Qg 67 26 51 72 35 Iron Lake fault 80 gravels to boulders. Very poorly sorted. 67 39 35 75 Yqjl 40 35 65 nderson Cr 55 53 40 A Compiled from Lewis unpublished mapping, Lewis (1998), Ruppel Yqjl 53 35 TERTIARY IGNEOUS AND SEDIMENTARY ROCKS 56 et al. (1993), Lonn and Berg (1996), Berg and Lonn (1996), Evans and Qg 40 53 Ydc Green (2003), Foster et al. (2010). 50 50 5052 MAP SYMBOLS 5052 47 B Qa 65 Tfb Outwash Flood Boulders (Tertiary) - Flood deposits. Boulders up to 70 centimeters 58 58 50 in diameter mixed with cobbles, gravels, and sand. Exposed only along a small section 50 50 34 45 67 35’ of Ditch Creek, though much of the Quaternary alluvium along lower Ditch Creek and Strike and dip of bedding 35’ 40 38 30 Yqjl 22 Hughes Creek are reworked flood boulders. 50 40 57 Strike and dip of bedding Ys 70 35 Ylc 55 40 24 right-side-up 65 30 Ta Alluvium (Tertiary) - Unconsolidated rounded cobbles of dominantly Challis 58 38 5051 50 5051 Ys 70 44 Volcanics and Proterozoic quartzites. Forms flat surfaces and is easily eroded. 65 Strike and dip of overturned 53 66 42 22 bedding, inferred 35 Tcr Challis Volcanics, Rhyolite (Tertiary) - Biotite-quartz-rhyolite porphyry. Rounded, 72 58 40 Td 50 55 50 millimeter long phenocrysts of quartz are common, as are pumice clasts (Lopez, 74 35 40 Ys 60 65 Strike and dip of overturned 60 37 1982a). The rhyolite is poorly to moderately welded, and has either a glassy or Qg 3554 bedding 74 Ylc 55 devitrified matrix (Lopez, 1982a). 50 30 30 5050 41 35 67 60 78 Strike and dip of foliation 46 35 20 40 Tcd Challis Volcanics, Dacite (Tertiary) - Vitreous biotite-hornblende-dacite porphyry. Yqjl Ys 38 30 45 eek fault 50 45 5 Flow banding is common. Phenocrysts are up to several millimeters long. In places 45 35 60 20 er Cr 35 33 likely deposited as an ash flow tuff, elsewhere as a hypabyssal intrusive. Strike and dip of volcanic 25 30 35 85 37 33 alz 25 50 S 73 50 25 25 54 32 70 20 15 45 86 35 10 75 20 72 65 Qa 10 Tcv Challis Volcanics and Tertiary Sediments, undivided (Tertiary) - Hypabyssal tuff, 75 Ylc Yqjl 15 Contact, solid where 5049 70 Ys 60 lava and dikes of quartz, potassium feldspar, hornblende dacite porphyry and quartz 44 44 15 65 57 82 known, dashed where Yqjl 45 30 rhyolite tuff. Phenocrysts are up to several millimeters long. Unconsolidated fluvial inferred, dotted where 55 49 43 46ES08 Yqjl sands and cobbles are interbedded within the volcanics. covered 30 39 40 30 40 31 32 15 Yqjl 80 Td Diorite (Tertiary?) - Greenish-black, medium grained diorite, containing plagioclase, 55 47 14 Ylc Normal fault, solid where 10 40 35 50 64 Ydc hornblende, pyroxene, biotite and magnetite (Lopez, 1982a, Lopez et al., 2004). Age 40 45 63 30 known, dashed where 50 Ylc 48 48 35 uncertain. inferred, dotted where 40 ? 61 75 37 55 32 28 covered Tcr 15 48 75 Yqjl 65 Qa 15 28 60 TERTIARY-CRETACEOUS INTRUSIVE ROCKS 69 Qa 45 30 58 47 80 75 64 50 Thrust fault, solid where 62 55 46 79 86 57 62 65 25 Qg 45 Intrusives (Tertiary-Cretaceous) - Undivided unit containing Tertiary and Cretaceous known, dashed where inferred, 32 47 40 45 55 TKi 57 70 25 37 46 12 biotite granodiorite and Tertiary biotite-muscovite granite (Desmarais, 1983; Lopez et dotted where covered Yqjl 31 13 15 32’30’’ 80 Tcd 30 al., 2004). 80 65 Tfb 25 67 81 32 65 85 48 45 Qa Fault (cross-section only), 20 Qg 22 30 Qa 8 where the circle surrounding 65 53 57 24 12 Ydc MESOPROTEROZOIC STRATA 28 a cross indicates movement 50 32 82 50 69 40 Yqjl 23 47 40 Ydc ? 53 10 13 57 56 48 16 ? Yqjl Quartzite of Jahnke Lake (Mesoproterozoic) - Generally pale grey to green, fine- to inner circle indicates 32 29 Lick Creek fault 25 70 20 57 85 very fine-grained plagioclase-rich quartzite. Interbedded siltite and argillite is movement out of the page 45 38 44 21 63 50 25 40 44 common. The quartzite is laminated to thinly bedded, and commonly shows ripples, 73 35 Ysu 56 Tcr 20 55 climbing ripples, load casts, and trough and planar cross-bedding. Fluid escape 52 20 Trend and plunge of fold hinge 74 Ydc 25 20 25 77 18 structures, convolute bedding, and hummocky cross-bedding are rare. In the 26 11 28 Ydc 63 sediment type classification of Winston and Link (1993) the most common sediment Yqjl 45 Tcd 20 25 20 B’ Plunging anticline, solid where 34 Tcd Ta 25 55 35 types are cross-bedded sand, flat-laminated sand, and even couples. It is slightly finer 36 Yqjl 60 Lick C 36 20 13 r known, dashed where inferred, 70 eek fault 5045 45 32 Lick Creek fault grained than the Swauger Formation, and is equivalent to quartzite type II of Berg 33 65 48 32 43 30 dotted where covered 57 Qa 35 50 22 20 30 (1977). 23 Qa 20 20 A 49ES0883 13 54 35 43 60 32 40 64 52 41 25 22 31 Plunging syncline, solid where 30 40 36 25 Ylc Lawson Creek Formation (Mesoproterozoic) - Varying from grey, fine-grained known, dashed where inferred, Qg 50 Tcr Ysu 50 Qa Ysu feldspathic quartzite to dark grey to black siltite and argillite. Fine-grained quartzite fines dotted where covered 74 18 Tcr 19 40 34 upward on the decimeter scale into siltite/argillite. Heavy mineral laminations, ripple 63 40 Tcv cross-beds, and climbing ripples are common. This unit contains significantly more siltite and Overturned syncline, solid where 5044 32 10 30 Qa Yqjl argillite than the Gunsight Formation and the Quartzite of Jahnke Lake.