IDAHO GEOLOGICAL SURVEY TECHNICAL REPORT 14-2 MOSCOW-BOISE-POCATELLO IDAHOGEOLOGY.ORG STEWART AND OTHERS

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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

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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 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 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 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 Very poorly sorted. 67 39 35 75 Yqjl 40 35 65 nderson Cr 55 53 40 A Compiled from Lewis unpublished mapping, Lewis (1998), Ruppel Yqjl 53 35 TERTIARY IGNEOUS AND SEDIMENTARY ROCKS 56 et al.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. known, dashed where inferred, 17 Tcd dotted where covered. Arrows 27 40 25 25 29 35 46 Ysu Swauger Formation, upper (Mesoproterozoic) - Largely white to light pink, coarse to point in down-dip direction 53 35 35 Ysu 35 Qg 37 69 62 medium-grained, well sorted, potassium feldspar-rich subarkosic arenite (quartzite). The unit 34 Tcr 1 400 000 FEET 42 20 53 47 37 Yqjl A A’ Surface trace of cross-section (ID) Yqjl 29 41 is differentiated from the lower Swauger Formation in the Shewag Lake quadrangle by its 53 30 17 19 36 Tcd 30 22 from A to A’ 5043 53 16 26 lack of pebbles, but is otherwise the same. It contains upward fining cycles 75 cm to 1.5 m Qa 30 55 Yqjl thick. Fine-grained quartzite and siltite cap the upward fining cycles. The caps are generally 23 15 24 42 32 laminated and locally include small amounts of scapolite. In the sediment type 37ES08 Detrital zircon sample location 48 44 50 50 classification of Winston and Link (1993) this unit includes cross-bedded sand, 32 33 45°30’ 45°30’ flat-laminated sand, and even couple sediment types. 725 470 000 FEET (ID) 726 727 728 729 730 732 840 000 FEET (MT) 733000mE 266 267 268 269 270 271 274000mE 114°07’30’‘ 5’ 2’30’’ 114°00’ 57’30’’ 55’

5042000mN Ysl Swauger Formation, lower (Mesoproterozoic) - Largely white to light pink, coarse to medium-grained, well sorted, potassium feldspar-rich quartzite. Fining-upward Ysu cycles are common, grading from coarse- to medium-grained quartzite at the base to siltite and argillite caps at the top. Cycles average between 75 centimeters and 1.5 DETRITAL ZIRCON U-PB AGE SPECTRA 5041 meters. The base of cycles locally contain rip-up clasts, and usually show trough INTRODUCTION ANDERSON CREEK FAULT cross-bedding that is defined by hematite-rich heavy mineral laminations. Fine-grained quartzites and siltites above show ripples and climbing ripples; siltite to Gold mineralization along the Anderson Creek fault has been well known for more than a 5041 49ES08 - quartzite of Jahnke Lake (Yjl). 99 grains STRATIGRAPHY Geologic mapping took place during the summers of 2008 through 2013. Mapping was 10 argillite caps (~ 5-15 cm thick) are often laminated. Caps vary in color from dark green century (e.g. Bacorn, 1905; Lincoln, 1912; Livingston, 1919; Mayerle and Close, 1993). Tertiary? 38 20 20 undertaken as part of a larger regional effort led by the Idaho Geological Survey and Montana 25 to light purple. Small quartz arenite pebbles, likely formed as lag deposits, are common at diorite lies east of the main fault for much of its length, while Proterozoic quartzites lie to the 15 Bureau of Mines and Geology to understand the stratigraphy of the Lemhi sub-basin, and its 38 the base of the fining-upward cycles in the Shewag Lake quadrangle, but are not found to r 15 18 e west. A distributed zone of faulting extends to the east of the main strand. Mineralized veins, b 10 ? relation to the Belt Supergroup. The stratigraphy used here follows revisions to the Lemhi 18 5040 the northwest in the Allan Mountain quadrangle. These pebbles contain entirely Archean m generally striking NNW with a sub-vertical dip, are cut by later normal and reverse faulting u 9000 m quartzite of Jahnke Lake sub-basin stratigraphy proposed by Burmester et al. (2013). Qg 1 390 000 FEET detrital zircon ages (Steel and Link, 2013), and were likely sourced from the Craton

N 5 10 throughout the distributed zone (Bacorn, 1905). The age of mineralization is unknown. 570 000 FEET 20 (ID) (MT) to the east. The loss of pebbles to the west indicates facies changes are present at the scale of 0 20 1200 1400 1600 1800 2000 2200 2400 2600 2800 3000 The Allan Mountain quadrangle was mapped by EDS, PKL and DES, the Shewag Lake quad- 10 this map. In the sediment type classification of Winston and Link (1993) this unit Underground workings on the main fault near the village of Gibbonsville suggest the Ander- U-Pb age (Ma) 8000 m rangle was mapped by TDS, PKL, and EDS, and the Gibbonsville, and parts of the Lost Trail Pass, includes cross-bedded sand, flat-laminated sand, and even couple sediment types. Lawson Creek Formation Schematic Stratigraphic Section son Creek fault is orientated N20E/70SE (Livingston, 1919). However, it is likely the fault merges of the Swauger Formation and Big Hole Pass quadrangles were mapped by EDS and DES. The geology and stratigraphy Cross-sections indicate the thickness of the lower Swauger is approximately 3000 to the south with a steeply west-dipping normal fault mapped in the North Fork 7.5’ quad- 15 20 46ES08 - upper Swauger Formation (Ys), 97grains. of the Allan Mountain quadrangle has been revised from the Stewart et al. (2010) map. 5039 meters. 2 m rangle (Lonn et al., 2013). Near the northern edge of the map area, our mapping along the 25 Ysu 7000 m Continental Divide also indicates the fault dips steeply west. Thus the fault may not have a 20 5039 Ys Swauger Formation, undivided (Mesoproterozoic) - White, light grey, or light pink r e 15 STRUCTURE consistent dip direction along its length. fine to coarse-grained feldspathic quartzite. Though quartzite grain sizes range from b 10 15 m 10 fine to coarse, most beds are medium grained. The unit is well sorted, and though it is u 6000 m Swauger Formation N 5 CLEAVAGE The fault kinematics also remain enigmatic. Lincoln (1912) and Lopez (1982) suggest west-side stratigraphically equivalent to both the lower and upper Swauger Formation, it

0 c up motion along the fault, while Mayerle and Close (1993) suggest east-side up motion. Based i 10 Qg 5038 contains no pebbles in its lower portion. Quartzite beds generally fine upward within

o 1200 1400 1600 1800 2000 2200 2400 2600 2800 3000 z on the revised stratigraphy of Burmester et al. (2013), our mapping favors the Mayerle and laterally continuous beds between 75 and 150 cm thick. Thin, laminated siltite and

o Mineral cleavages are common in the Proterozoic quartzites, often occurring sub-parallel to U-Pb age (Ma) 5000 m r 1 m Close (1993) interpretation, and is consistent with mapping to the south by Lonn et al. (2013). e 15

t bedding. The quartzite of Jahnke Lake from the southeastern corner of the Allan Mountain 5038 argillite caps are present on the tops of many cycles. Approximately 3400 meters thick

o We believe the units on the west, correlated to the Gunsight Formation, Swauger Formation, 09-TS-09 - lower Swauger Formation (Ys), 93 grains. r quadrangle also contains zones of strong NNE-striking, ESE-dipping cleavage. Some zones are 10 in the Allan Mountain quadrangle. The Swauger Formation is equivalent to quartzite p 27’30’’ o and quartzite of Jahnke Lake, are stratigraphically higher than the calc-silicate, quartzite and 27’30’’ 15

30 s mylonitic. These fabrics are the continuation of a series of N- to NNE-striking shear zones type I of Berg (1977). 4000 m e siltite of Dahlonega Creek (tentatively correlated to the Yellow Lake unit of the Lemhi Group) 15

r 25 mapped to the south in the Ulysses Mountain quadrangle (Lopez, 1982b). However, many of

M e 20 to the east, favoring down-to-the-west motion. 30 b the strong fabrics do not produce noticeable offset of the stratigraphic units in the Allan 5037 Yg Gunsight Formation (Mesoproterozoic) - Grey to grey-green to tan, fine-grained 15 m 5

u 10 Mountain quadrangle, suggesting that fabric strength does not necessarily correlate to strain. feldspar-rich quartzite with abundant heavy mineral laminations and common

N 25 5 3000 m In addition, the Anderson Creek fault also contains a substantial right-lateral strike-slip Ysu Much of the strong NNE-striking cleavage also occurs in rocks that show evidence of at least 2 5037 soft-sediment deformation. The quartzite is well sorted, and is laminated to thinly 0 0 m component of motion. The Anderson Creek fault produced 11 kilometers of apparent right- fold events (Stewart et al., 2010). 17 bedded, commonly showing ripples, climbing ripples, load casts, and trough and 1200 1400 1600 1800 2000 2200 2400 2600 2800 3000 A Silt F C 25 rg ine oarse lateral offset of the two segments of the steeply south-dipping Lick Creek fault. This apparent U-Pb age (Ma) . planar cross-bedding. Sediment types (Winston and Link, 1993) in this unit include Gunsight F offset requires an unreasonably large amount of dip-slip motion on the Anderson Creek fault 17 2000 m ormation LICK CREEK FAULT 15 20 cross-bedded sand, flat-laminated sand, and even couples. It is slightly finer grained to be solely responsible for the apparent displacement. Right-lateral strike-slip movement was 15 03-TS-09 - Gunsight Formation (Yg), 99 grains. Key to Symbols 20 5036 than the Swauger Formation. In the western portion of the map area, the top of the also observed by late 19th century and early 20th century miners in the distributed zone of 20 30 Trough crossbeds Gunsight Formation contains approximately 400 meters of green to light grey, siltite Parts of the Lick Creek normal fault have been mapped by Lopez (1982a), Ruppel et al. (1993), 16 r 25 Parallel layers faulting east of the main fault. There they found mineralized veins were often offset by small 15 Ysl e 1000 m Evans and Green (2003), and in the far north by Desmarais (1983). Our mapping suggests the 5036 to fine-grained quartzite. The complete section is approximately 4500 m. thick.

b 20 Planar cross lamination faults containing right-lateral motion (Bacorn, 1905; Mayerle and Close, 1993). 15 m 15 Ripples Lick Creek normal fault strikes roughly east-west, and dips steeply to the south. It contains a u 15 N 10 Rip-up clasts northern and a southern segment offset by the Anderson Creek fault. Breccia occurs along the Ydc Calc-silicate, quartzite and siltite of Dahlonega Creek, (Mesoproterozoic) - 25 5 Convolute bedding 7 Fine-grained feldspathic quartzite and siltite, with common scapolite and calc-silicate 0 0 m Lick C length of the fault, but along the southern segment, near the Anderson Creek fault, the breccia ACKNOWLEDGEMENTS 3200 3400 3600 28 1200 1400 1600 1800 2000 2200 2400 2600 2800 3000 reek fault zone widens to more than two kilometers in width. Kinematic indicators were not observed 15 15 5035 bearing beds. Quartzite-rich and calc-silicate-rich intervals are interbedded with each U-Pb age (Ma) along the fault. We are particularly indebted to Reed Lewis and Jeff Lonn, who helped connect the local Ysl 15 other on the approximately 100 meter scale. Total thickness is difficult to estimate due geology of the Gibbonsville area to regional stratigraphy and regional structures. We also 5035 to intense folding, but is greater than 1 kilometer. May be correlative with the Yellow 37ES08 - Gunsight Formation (Yg), 97 grains Lake unit of the Lemhi Group (as redefined by Burmester et al., 2013). calc-silicates of We apply the revised stratigraphy of Burmester et al. (2013) to hanging wall and footwall rocks, thank Don Winston, Mark McFaddan, Russ Burmester, and Dave Rodgers for field help and 37 30 25 e te Silt ine and interpret the Lick Creek fault to be a major normal fault with significant stratigraphic suggestions throughout the mapping process. 25 illit F Dahlonega Ck. 17 r g oarse r C e 20 A -silica offset (>7000 meters). We tentatively suggest the Lick Creek fault merges with the Anaconda b alc 15 C 15 15 5034

m detachment fault beneath the western Big Hole valley, indicating footwall rocks belong to the 17 u REFERENCES 10 15 Ysu N 5 Anaconda Core Complex and the normal fault was strongly oblique. The Anaconda detach- 15 0 ment fault was active during the Eocene and possibly into the early Oligocene (Foster et al., 5034 20 Bacorn, H.C., 1905, A Complicated Fault-System: The Engineering and Mining Journal, v. LXXIX, p. 324. 1200 1400 1600 1800 2000 2200 2400 2600 2800 3000 2010). If the Lick Creek fault is part of the Anaconda detachment fault, then it presumably has Berg, R.B., 1977, Reconnaissance geology of southernmost Ravalli County, Montana: Montana Bureau of Mines and 15 U-Pb age (Ma) a similar age. Geology, Memoir 44, scale 1:40,000, sheet, 39 p. text. Berg, R.B., and J.D. Lonn, 1996, The Preliminary Geologic Map of the Pass 30’ x 60’ Quadrangle: Montana Bureau of Mines and Geology Open-File Report 339, scale 1:100,000. 5033 Lemhi Subbasin of the Belt Supergroup: Northwest Geology, v. 42, p. 187-1-19. SOUTHWEST 25’ 28 25’ NORTHEAST 5033 15 Desmarais, N.R., 1983, Geology and geochronology of the Chief Joseph plutonic-metamorphic complex, Idaho-Montana A 33 [Ph. D. dissert.]. Seattle, University of Washington, 143 p. Evans, K.V., and G.N. Green, 2003, Geologic map of the Salmon National Forest and vicinity, east-: U.S. A’ 15 09-TS-09 9000 ft. 15 20 Geological Survey Geologic Investigations Series Map I-2765, 19 p., scale 1:100,000. Foster, D.A., W.C. Grice, and T.J. Kalakay, 2010, Extension of the Anaconda metamorphic core complex: 40Ar/39Ar 26 5032 8000 ft. 15 thermochronology and implications for Eocene tectonics of the northern and the Boulder batholith: Lithosphere, v. 2, p. 232-246. 25 24 25 20 Lewis, R.S., compiler, 1998, Geologic map of the Butte 1 x 2 degree quadrangle: Montana Bureau of Mines and Geology 7000 ft. 5032 35 33 Lick Creek fault 28 Open-File Report 363, scale 1:250,000. 37 25 6000 ft. Ys 40 Yqjl 40 Livingston, D.C., 1919, Tungsten, Cinnabar, Manganese, Molybdenum, and Tin in Idaho: University of Idaho 25 17 Yg 540 000 FEET School of Mines Bulletin 2, v. 14, 72 p. 5000 ft. 51 Ydc (MT) Lonn, J.D., and R.B. Berg, 1996, The Preliminary Geologic Map of the Hamilton 30’ x 60’ Quadrangle: Montana Bureau of Mines and Geology Open-File Report 340, scale 1:100,000. Lonn, J.D., Othberg, K.L., Lewis, R.S., Burmester, R.F., Stanford, L.R., Stewart, D.E., 2013, Geologic Map of the North Fork 1 360 000 FEET Ysl (ID) 25 Quadrangle, Lemhi County, Idaho: Idaho Geological Survey Digital Web Map DWM-160, scale 1:24,000. Lopez, D.A., 1982a, Reconnaissance Geologic Map of the Gibbonsville Quadrangle, Lemhi County, Idaho and Beaverhead WEST 25 County, Montana: Geological Survey Miscellaneous Field Studies Map M-1446, scale 1:24,000. EAST 28 18 Lopez, D.A., 1982b, Reconnaissance Geologic Map of the Ulysses Mountain Quadrangle, Lemhi County, B Idaho: United States Geological Survey Miscellaneous Field Studies Map MF-1445, scale 1:48,000. 27 30 25 15 5030 Lopez, D.A., J.M. O’Neill, E.T. Ruppel, 2004, Preliminary Geologic Map of the Big Hole Pass-Lost Trail Pass Area Southwest- Ysl 9000 ft. B’ ern Montana: Montana Bureau of Mines and Geology Open-File Report MBMG 522, scale 1:48,000. Yg 53 15 Mayerle, R.T., and T.J. Close, 1993, Mineral investigation of the Anderson Mountain study area, Lemhi County 5030 03-TS-09 8000 ft. 15 25 Idaho: U. S. Bureau of Mines, Mineral Land Assessment Open File Report 25-93, 36 p. Salzer Creek fault 30 25 Ruppel, E.T., J.M. O’Neill, and D.A. Lopez, 1993, Geologic map of the Dillion 1 degree x 2 degree quadrangle, Idaho and 37 Montana: U.S. Geological Survey Miscellaneous Investigations Series Map I-1803-H, scale 1:250,000. 7000 ft. 35 20 25 Steel, T.D., and Link., P.K., 2013, Mesoproterozoic strata in the Shewag Lake quadrangle, Idaho and Montana: Northwest Cool Gulch fault Ysu Ysl 15 Geology, v. 42, p. 57-70. Ys Anderson Creek fault Yg 5029000mN 6000 ft. 30 Stewart, E.D., P.K. Link, and D.W. Rodgers, 2010, Geologic Map of the Allan Mountain Quadrangle, Lemhi County, Idaho 25 25 Gibbonsville 20 40 and Ravalli County, Montana: Idaho Geological Survey Technical Report T-10-1, scale 1:24,000. Ydc 5000 ft. 5029 20 Winston, D., and P.K. Link, 1993, Middle Proterozoic rocks of Montana, Idaho, and Washington: The Belt Supergroup: in Ys Lick C Reed., J., P. Simms, R. Houston, D. Rankin, P. Link, R. Van Schmus, and P. Bickford, editors, Precambrian of the conterm- Ydc 15 4000 ft. Ydc reek fault Ysl inous United States: Boulder, Colorado, Geological Society of America, The Geology of North America, v. C-3, p. Yqjl 28 Yg 487-521. 45°22’30’’ 45°22’30’’ 276 277 540 000 FEET (ID) 279 280 900 000 FEET (MT) 283 284000mE 113°52’30’’ 50’ 47’30’’ 113°45’

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