IDAHO GEOLOGICAL SURVEY TECHNICAL REPORT 08-1 MOSCOW-BOISE-POCATELLO WWW.IDAHOGEOLOGY.ORG ABPLANALP, PINK, POPE, AND WATKINSON

Geologic Map of the Southern Beaverhead Range (Parts of Copper Mountain, Shamrock Gulch, Scott This Technical Report is a reproduction of independent mapping by Butte, and Snaky Canyon Quadrangles), Clark, Jefferson, and Lemhi Counties, East-Central Idaho J.M. Abplanalp, C. Pink, M.C. Pope, and J.A. Watkinson of the University of Idaho and Washington State University. Its content and format may Abplanalp, J.M., Pink, C., Pope, M.C., and Watkinson, J.A. not conform to agency standards. 2008

112O51'13'' 112O41'40'' 44O15'00'' 44O15'00'' 23 27 Correlation of Map Units 80 Qal 20 IPMbm 47 Msp IPscb Unconsolidated Units Volcanic Units Sedimentary Units Msp Mbs

15 IPMbm Qal Quaternary Mm Msuc 11 Qal C 11 Cenozoic Tve Tertiary 70 64 IPscg 42 7 IPscj Tve Trd Triassic Mesozoic 20 26 66 75 78 26 IPMbm Mbs 68 IPscj Pp Permian 32 25 Msuc 20 38 75 Msp Tve 8 IPscg IPsc Pennsylvanian 41 43 27 30 Mbs C’ IPscb PMbm

63 68 IPMbm Mbs 28 33 Msuc Msuc 31 Mississippian Mm Paleozoic 26 Msc

36 Qal Msp 51 19 Mm IPMbm Tve 59 70 17 31 Devonian 38 37 Dj 12 72 22 19 72 54 IPscb 16 IPscb MD 55 Mbs 28 PZ-pC 40

Mbs 31 10 pCy Proterozoic Msp 23 30 11

18 58 77 18 21 26 IPMbm 31 4 23 Msc 63 25 58

5 IPMbm Tve 30 IPscb IPMbm 64 66 33 60 67 IPMbm Mbs INTRODUCTION 32 IPscb

21 17 The geologic map of parts of the Copper Mountain, Scott Butte, Msp Scott Peak Formation (Mid- to Upper Mississippian)—Light to medium bluish 61 70 48 Shamrock Gulch, and Snaky Canyon quadrangles indentifies the surficial gray limestone subdivided into three members. The upper member is a Mbs 15 59 bedrock and shallow subsurface bedrock within the Beaverhead Range of medium to thick bedded, cyclic, dark gray crystalline limestone. This east-central Idaho. The 50 square mile map area includes the northwest member may be bioclastic and also contains thin bedded intervals of fine 9 portion of the Snaky Canyon, the western side of the Shamrock Gulch, and grained, chert bearing limestone. The middle member is characterized by 36 the eastern sides of the Copper Mountain and Scott Butte 7.5 minute very thick, massive beds of dark, fossiliferous limestone. This member 61 Tve 35 27 20 quadrangles in Clark, Jefferson, and Lemhi counties of east-central Idaho. contains very little chert and often outcrops as distinct, massive gray cliffs. Mbs 15 36 11 The southernmost part of the map area, where Skipp et al. (1979) mapped is The cyclic lower member is composed of alternating thin beds of coarse IPscb 30 55 included in the 1:100,000 scale Geologic Map of the Idaho National bioclastic limestone and dark, fine-grained chert bearing limestone. This 15 61 Engineering Laboratory and Adjoining Area (Kuntz et al., 1994). The entire member may also contain thin intervals of sandy and silty, yellowish 46 Mbs map area is covered in the Dubois 30 x 60 minute sheet (Rember and carbonate. The formation outcrops along the entire western ½ of the study Msp 19 50 9 area. Outcrop patterns widely vary and range from covered slopes and talus 8 Bennett, 1979). This compilation map indicates the Scholten and Ramspott 52 (1968) geologic map terminates to the north at the Clark County-Lemhi to massive, sharp cliffs that dominate the western range. The contact with 44 19 Msc 25 61 36 39 IPscb 6 County boundary and that there were no previously detailed published the underlying Middle Canyon Formation is gradational. The total thickness

19 20 maps within this map area. of the Scott Peak Formation is 450 to 610 meters in this area (Skipp, 1984; 62 IPMbm Garmezy, 1981; Stamm, 1981). 27 8 19 10 The rocks in the Beaverhead Range are oldest in the west and become IPMbm Tve progressively younger to the east. The oldest rocks in the Beaverhead Range 20 Mm Middle Canyon and McGowan Creek formations (undivided) (Lower 18 25 are Precambrian metasedimentary strata that are unconformably overlain by Mississippian)—Dark gray to light gray and yellow to brown fine-grained 21 4 carbonate dominated Paleozoic-Mesozoic sedimentary rocks. The limestone and fine-grained sandstone to siltstone. Upper (Middle Canyon) 42 62 25 Precambrian-Mesozoic rocks were later deformed during the late Mesozoic- 37 40 marked by thin to medium bedded limestone and interbedded calcareous 16 10 42 10 21 early Cenozoic "thin skinned" Sevier Orogeny. The Precambrian to Mesozoic siltstone and very fine grained quartz sandstone without chert. Uppermost 22 22 47 55 sedimentary rocks were tilted and partitioned during Cenozoic extension to beds may be marked by coarsely fossiliferous, medium bedded and dark 81 61 19 12 68 produce predominantly eastward dipping successions below the Tertiary 21 Msp 31 limestones. Lower (McGowan Creek) unit is a gray to grayish black 23 42 and Quaternary sediments. On both sides of this range are valleys containing 25 22 Msp 39 51 48 33 17 crystalline limestone. The unit may contain dark chert interbeds and thin IPMbm thick successions of Tertiary and Quaternary sediments. To the south of the Mm 31 IPscb beds of siliceous mudstone or siltstone with minor plant debris. Both units 14 field area, the Snake River Plain is a flat-lying successions of basalt flows at are poorly exposed and may form rubbly, steep slopes. These units outcrop 61 the southern end of the uplifted ranges that formed by the eastward along the western flanks of the range. The lower McGowan Creek weathers 50 IPMbm 25 migration of the Yellowstone hotspot. to a light to dark brown soil and is most notably exposed as a rock outcrop in 56 81 For the completion of this geologic map, earlier geologic maps from the 22 mine cuts. The underlying contact with the Devonian Jefferson Formation is 40 59 IPscb surrounding areas by Scholten and Ramspott (1968), Rember and Bennett unconformable. The combined thickness is around 450 meters (Skipp, 1984; 25 Mbs (1979), Skipp et al. (1979), Kuntz et al. (1994), Janecke et al. (2001), and Evans Msuc 20 Garmezy, 1981). B 60 IPMbm and Green (2003) were reviewed and field checked. Field investigations of 24 8 surficial and bedrock geology were undertaken during the summer of 2006 Dj Jefferson Formation (Upper Devonian)—Yellowish tan to dark grayish brown 40 36 and results were reviewed again during the fall of 2006. During fieldwork, carbonate and fine grained sandstone to siltstone interbeds at base. May be 48 21 20 19 aerial photographs were utilized to aid in the identification of rock unit 43 44 36 locally dolomitic and conglomeratic with solution cavities. Unit is exposed in 36 boundaries and locations. Many of the rock units were sampled and 25 19 Mbs IPscb mining or road cuts in Long Canyon along the western flanks of the range 37 63 examined for biostratigraphic correlation during the initial mapping. This 74 36 41 and often forms grassy, gentle slopes. The total thickness of the unit is 19 46 44 geologic map is intended to provide a detailed overview of the geology in 21 15 postulated to be between 15 and 60 meters (Garmezy, 1981; Skipp, 1984). Mm 29 Tve 18 29 the southern Beaverhead Range of east-central Idaho at scale. This map is 39 21 intended to be utilized as a reference tool and should not be used as a 52 35 MD Lower Mississippian and Upper Devonian—Undifferentiated Msc 46 substitute for site-specific investigations. 40 Lower Paleozoic—Undifferentiated 35 41 14 68 IPscb Pz-pC Msp 13 32 29 28 DESCRIPTION OF MAP UNITS 29 70 41 IPscg Proterozoic Meta-Sediments 19 36 Mbs 29 19 Autochthonous Cenozoic Rocks and Deposits pCq Belt Supergroup - Swauger Member (Mesoproterozoic)—Red and purplish to brownish red impure medium to coarse grained, thick bedded sandstone to 37 17 31 Tve 70 Qal Unconsolidated Sediments (Quaternary to Recent)—Very well to poorly 28 quartzite. May be locally conglomeratic and heavily crossbedded with large 62 13 82 sorted unconsolidated clays to gravels representing alluvium, landslide 46 18 foresets. Compositionally composed of around 70% quartz, 25% feldspar, 20 8 debris, talus, floodplain deposits, and fanglomerates. 28 27 29 27 and 5% opaques in thin laminations. Unit outcrops as small ledges and total 70 24 thickness is believed to be over 300 meters (Garmezy, 1981; Evans and Msp 78 76 20 56 Green, 2003). 36 6 21 Cenozoic Volcanic Rocks 41 44 50 45 58 IPMbm Tve Edie School Rhyolite (Eocene)(Challis Volcanic Group)—Gray to brownish 55 pink, glassy rhyolite volcanics and welded tuff volcaniclastics. Large pCq IPscb SYMBOLS 62 17 phenocrysts of biotite and hornblende and flattened pumic vessicles. Unit 18 17 outcrops as distinct ledges along the eastern margin of the map area and is 50 47 18 24 10 49 B’ Qal 11 meters in average thickness (Garmezy, 1981). 68 BEDDING SYMBOLS 11 73 49 15 46 strike and dip of bedding bedding overturned 42 26 46 66 34 Mesozoic Sedimentary Rocks 40 19 31 35 IPscb horizontal bedding vertical bedding 38 Trd Dinwoody Formation (Lower Triassic)—Tan, beige, to yellowish brown 52 18 calcareous and micaceous shale and siltsone with interbeds of brownish 27 35 gray limestone and very fine sandstone. Sharp contact with the underlying 67 Mm 57 15 IPscg Phosphoria Formation and upper contact unknown due to very poor, gentle slope exposure at southeast portion of map area only. Previous workers UNIT CONTACT SYMBOLS 18 68 87 have postulated a thickness of over 300 meters (Lucchitta, 1966; Evans and 30 9 31 79 Green, 2003). rock unit contact inferred rock unit contact 25 28 35 74 IPscb 6 32 67 46 Msp Paleozoic Sedimentary Rocks 31 37 IPMbm 29 Tve STRUCTURAL SYMBOLS 14 68 21 Pp Phosphoria Formation (Permian)—Interbedded gray to black carbonates and 39 19 10 79 8 7 blue siltstone with thick, massive black chert beds. Lower beds dominated normal fault (indicator on downthrown side; dashed where inferred) 12 60 26 21 45 61 by thick, lenticular to ropey chert while upper beds dominated by massive low-angle detachment normal fault (indicator on downthrown side; dashed 35 IPscb chert. Within the chert, lenses of black to purple phosphorite are present. 16 79 Mbs 51 8 15 23 IPscj This formation is poorly exposed along a gentle slope in the southeast where inferred) Msp 64 52 26 36 corner of the map area only. The thickness is estimated at 76 meters 21 42 31 thrust fault (teeth on upper plate; dashed where inferred) 41 40 (Garmezy, 1981). 81 38 11 19 7 32 30 29 IPsc Snaky Canyon Formation (Lower Pennsylvanian to Lower Permian) anticline (dashed where inferred axis) 18 56 22 21 syncline (dashed where inferred axis) 35 20 20 IPscj Juniper Gulch Member (Upper Pennsylvanian to Lower Permian)—Light 30 29 25 14 Mm IPscb gray to light brown, thin to thick bedded sandy limestone and dolomite. Dj 31 11 overturned anticline (dashed where inferred axis) 70 Weathers pinkish to olive gray. Fossiliferous and significant lensoidal to 32 15 18 IPMbm 19 37 nodular chert locally. Less fossiliferous than the lower Bloom Member and 80 26 61 overturned syncline (dashed where inferred axis) 74 30 20 67 bedding becomes increasingly thinner upsection. Forms small, linear ledges Msp 9 IPMbm 20 49 27 and cliffs along eastern ½ of map area. Thickness is approximately 600 42 IPMbm Qal 68 20 meters (Skipp et al., 1979; Garmezy, 1981). Mm 28 IPscj 22 Msp O IPscg Gallagher Peak Member (Mid- to Upper Pennsylvanian)—Tan to beige to 44O07'30'' 44 07'30'' IPMbm light brownish pink, thin bedded, fine grained calcareous quartz sandstone. Dj Mm 77 IPMbm Interbedded with minor, medium bedded sandy limestones. May be heavily REFERENCES Mm 26 18 35 18 IPscg crossbedded. Member outcrops throughout eastern ½ of the map area and 57 Msp Mbs 30 IPscb may form cliffs or ledges (as at Gallagher Peak), but commonly is signified by Beutner, E.C., 1968, Structure and Tectonics of the Southern Lemhi Range, IPscj Qal 38 IPscb IPMbm rubble covered slopes. The thickness of this member is 60 meters (Skipp, Idaho; PhD Dissertation, Pennsylvania State University, 128p. 16 46 25 1979; Skipp, 1984; Garmezy, 1981). Evans, K.V., and Green, G.N., 2003, Geologic map of the Salmon National 41 46 IPscb 43 52 28 Forest and vicinity, east-central Idaho; United States Geologic Survey, 38 54 14 IPscb Bloom Member (Lower to Upper Pennsylvanian)—Light gray to dark gray Map I-2675. 14 Mm Msp 54 Tve medium to coarse grained fossiliferous limestone and sandy to silty 59 61 Garmezy, L., 1981, Geology and Tectonic Evolution of the Southern 44 IPMbm limestone interbeds. Limestone contains heavy intervals of black, nodular Beaverhead Range, East-Central Idaho; Ms Thesis, Pennsylvania State 41 49 chert and is thin to medium bedded. Interbedded sandy limestones and University, 148p. 12 light brown, thinly bedded calcareous sandstones dominated by very fine to 43 IPscb 64 8 Janecke, S.U., Blankenau, J.J., Vandenburg, C.J., and Van Gosen, B.S., 2001, fine grained quartz and may be crossbedded. This member outcrops as Map of normal faults and extensional folds in the Tendoy Mountans 33 34 69 23 small, distinct ledges and intervening rubble slopes along the eastern ½ of and Beaverhead Range, southwest Montana and eastern Idaho; United

25 the map area. The lower contact with the Bluebird Mountain Formation is States Geological Survey, Map F-2362. 25 41 gradational. Total thickness is 647 meters (Skipp, 1979; Skipp, 1984; Mbs IPscb Kuntz, M.A., Skipp, B., Lanphere, M.A., Scott, W.B., Pierce, K.L., Dalrymple, G.B., Qal 39 Garmezy, 1981). Champion, D.E., Embree, G.F., Page, W.R., Morgan, L.A., Smith, R.B., 29 51 26 23 25 Mm 19 Hackett, W.R., and Rodges, D.W., 1994, Geological map of the INEL and 12 Bluebird Mountain Formation (Upper Mississippian to Lower Pennsylvanian)— 45 53 61 PMbm adjoining areas, eastern Idaho; United States Geological Survey, 20 53 71 Tan, gray, to light brownish pink fine to medium grained quartzose sandstone Miscellaneous Investigations Series Map I-2330. Mbs 44 20 and "orthoquartzite" interbedded with thinly bedded gray, fossiliferous Lucchitta, B.K., 1966, Structure of the Hawley Creek area, Idaho-Montana; 31 70 25 69 carbonates. Sandstones may be crossbedded and individual grains range PhD Dissertation, Pennsylvania State University, 235p. 24 Msp 30 from sub-rounded to sub-angular. Exposure is often signified by abrupt cliffs Rember, W.C., and Bennett, E.H., 1979, Geologic map of the Dubois 39 IPscb 30 67 IPscb Pp and ledges or by steep talus throughout a majority of the field area. Contacts Quadrangle; Idaho Department of Lands-Bureau of Mines and Geology, Mm 29 19 24 above and below are gradational and the total thickness of the unit is 107 Geologic Map Series (2° Quadrangle). 25 19 IPMbm meters (Skipp et al., 1979; Skipp; 1984; Garmezy, 1981). Scholten, R., and Ramspott, L.D., 1968, Tectonic mechanisms indicated by IPMbm structural framework of central Beaverhead Range, Idaho-Montana; IPscb TRd Mbs Big Snowy Formation (Upper Mississippian)—- Dark gray, blue, to black fissile Geological Society of America Special Paper 104, 71p. 35 15 Msp Msp 36 37 64 shale, phosphatic limestone, calcareous shale, and rare sandstone. Unit is 25 Skipp, B., 1984, Geologic map and cross sections of the Italian Peak middle 10 dominated by dark calcareous and noncalcareous shales, with limestone and Qal 44 49 60 roadless areas, Beaverhead County, Montana, and Clark and Lemhi 51 thin sandstones confined to middle of formation. Shale may be gypsiferous Counties, Idaho; United States Geological Survey, Miscellaneous Field Qal IPscb 46 10 Pp and fissile with calcareous concretions near base. Limestones may be 46 26 Tve Studies Map MF-1610B. 15 heavily fossiliferous and contain abundant dark fragments of phosphatic Skipp, B., and Haitt, M.H., Jr., 1977, Allochthons along the northwest margin Mm IPscg 40 brachiopods. This unit outcrops throughout the study area and is often of the Snake River Plain, Idaho; Wyoming Geologic Society Guidebook, 25 IPMbm 14 43 TRd 31 36 Mbs IPscj signified by poorly exposed gentle grassy slopes, landslides, and saddles. 29th Annual Field Conference, p. 499-515. 76 55 Qal A 24 The contact with the overlying Bluebird Mountain Formation is gradational Skipp, B., Hoggan, R.D., Schleicher, D.L., and Douglass, R.C., 1979, Upper 43 38 29 and the lower contact with the Surrett Canyon is sharp, yet conformable Mm 46 A’ Paleozoic carbonate bank in east-central Idaho-Snaky Canyon, Bluebird IPMbm 24 (Skipp, 1984; Garmezy, 1981). 70 Mountain, and Arco Hills Formations, and their paleotectonic 59 69 65 IPMbm 62 significance; United States Geological Survey Bulletin 1486, 78p. 28 43 44 57 Msuc Surrett Canyon Formation (Upper Mississippian)—Dark gray to dark blue Skipp. B., and Hall, W.E., 1980, Upper Paleozoic paleotectonics and 51 53 63 57 and black, fine to medium grained fossiliferous and medium to thick bedded Qal 34 39 30 paleogeography of Idaho, in Fouch, T.D., and Magathan, E.R., eds., 66 26 43 54 limestone. May weather to pale gray to pale yellowish gray and contain thin 49 41 Paleozoic paleogeography of the west-central United States; Society of 80 55 50 34 intervals of silty carbonate. This unit outcrops along the range crests of the Economic Paleontologists and Mineralogists, Rocky Mountain Section, 30 62 24 Copper Mountain quadrangle and often forms distinct ledges. This unit may 30 west-central United States. 31 15 43 12 pinch out laterally and total thickness is between 0 and 69 meters. The Stamm, R.G., 1985, Conodont biostratigraphy of the Scott Peak formation Mm 10 60 IPscg 52 IPscb contact with the underlying South Creek formation is gradational and (Upper Mississippian) of south-central Idaho; Ms Thesis, University of 34 30 Mbs IPMbm 44 conformable (Garmezy, 1981; Skipp, 1984). Idaho, 128p. 49 32 42 70 25 34 Msp Msc South Creek Formation (Upper Mississippian)—Dark gray to black, medium 30 53 28 70 to thin bedded unfossiliferous limestone. May contain significant 30 46 30 Tve interlayered chert and intervals of silty and fissile carbonate. The unit 31 51 IPscb 42 33 28 outcrops along the range crests of the Copper Mountain quadrangle and 20 forms rubbly talus slopes of blocky carbonates with thin, minor ledges. This 21 50 Mbs 34 32 53 IPscg 29 26 47 Tve unit may pinch out laterally and total thickness is between 0 and 122 meters. Qal The contact with the underlying Scott Peak Formation is gradational 56 31 IPMbm 34 27 10 19 Msp 20 31 (Garmezy, 1981; Skipp, 1984). 47 Msp 25 54 IPscj IPscb Mm 22 20 29 IPscb 23 34 46 70 47 61 Mbs IPMbm Qal 15 44O04'21'' 44O04'21'' 112O51'13'' 112O41'41''

Field work conducted 2006. Base map from USGS Digital Raster Graphic files of the Copper Mountain, Scott Butte, MN MN h SCALE 1:24,000 c Shamrock Gulch, and Snaky Canyon quadrangles. All quadrangles published in 1969. n The authors would like to acknowledge the EDMAP program for 1 0.5 0 1 Ra ie For all quadrangles, topography by photogrammetric methods from aerial photographs d providing funding for this reseach. MILE E GN GN Scott Peak Copper Mnt. taken in 1967 and field checked in 1969. FEET Digital cartography by Theresa A. Taylor and Jane S. Freed at the Idaho Geological Survey’s Digital Mapping Lab. Po lyconic projection. 1927 North American Datum. o o o o 1000 0 1000 2000 3000 4000 5000 6000 7000 1 16 17.5 1 10 17.5 IDAHO h s Note on printing: The map is reproduced at a high resolution of 600 dots c g 1000-meter Universal Transverse Mercator grid ticks, zone 12, shown in blue. n KILOMETER ul ri 1 0.5 0 1 p per inch. The inks are resistant to run and fading but will deteriorate with ck G t S ro long-term exposure to light. m Ho Contour interval 40 feet Quadrangle Location Copper Mnt. a Sh Lidy Map version 9-11-2008. PDF (Acrobat Reader) map may be viewed online at UTM Grid and 1969 Magnetic North UTM Grid and 1969 Magnetic North www.idahogeology.org. Declination at Center of Map Declination at Center of Map SE n o [Copper Mountain and Scott Butte [Shamrock Gulch and Snaky Canyon ngs ri p quadrangles] quadrangles] Cany S y t k a Scott Butte Ho Sn y id L B Adjoining Quadrangles B’ 11,000 11,000

Msuc Msc IPscg 10,000 10,000

9,000 9,000 IPscb FEET FEET 8,000 Msp 8,000

IPMbm 7,000 IPscb 7,000 Mbs

6,000 6,000 Mm pC– q Mmg_Dt IPMbm

5,000 Msp 5,000 Mbs Tve Qal IPscb Pz_pC– IPscb 4,000 4,000

A A’ C C’ 9,000 9,000 11,000 11,000

8,000 8,000 10,000 Msuc 10,000

IPscb TRd Tve 7,000 IPscb Mbs 7,000 9,000 9,000 IPMbm IPscg Mbs IPMbm IPMbm Pp FEET FEET Qal FEET FEET IPscb 6,000 6,000 8,000 8,000 Mbs Msp IPMbm

Msp IPscj Msp Mbs IPscb IPscb 5,000 5,000 7,000 Mbs 7,000 Mm Mm IPscb Msp Msp Tve IPscg 4,000 IPscb 4,000 6,000 Mm 6,000 Mm Mbs Mm IPMbm

3,000 3,000 5,000 5,000 Pz-pC– Pz-pC– Pz_pC– Mbs Msp IPMbm Pz-pC– Msp Mm Msp Msp Mbs 2,000 2,000 4,000 4,000

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