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Geologic Map of the Goldstone Mountain Quadrangle, Lemhi

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Geologic Map of the Goldstone Mountain Quadrangle, Lemhi MONTANA BUREAU OF MINES AND GEOLOGY WWW.MBMG.MTECH.EDU MBMG OPEN FILE 604 IDAHO GEOLOGICAL SURVEY WWW.IDAHOGEOLOGY.ORG IGS DIGITAL WEB MAP 134 GEOLOGIC MAP OF THE GOLDSTONE MOUNTAIN QUADRANGLE, LEMHI COUNTY, CORRELATION OF MAP UNITS Glacial Deposits Mass Movement Alluvial Deposits IDAHO, AND BEAVERHEAD COUNTY, MONTANA Deposits Qgty Qmg Qas Holocene Qtg1 Qaf 1 1 1 1 2 1 Qgt Qms Qls Reed S. Lewis , Kurt L. Othberg , Loudon R. Stanford , Russell F. Burmester , Jeffrey D. Lonn , and Mark D. McFaddan Qgo Qafo QUATERNARY Pleistocene ANACONDA RANGEKnown Qgoo Qgto Belt Supergroup 2011 Qtg3 rocks ana Mont Qtgh Idaho AINS 46 AINS 40 40 Goldstone 20 44 Sedimentary Deposits Mountain Ysq 18 WESTMOUNT PIONEER 40 Qmg quadrangle 10 17 Qgt Type location, B 30 30 E 25 42 40 Oligocene Yellowjacket Fm. A 30 Salmon ? Ysq Ysq V 20 TkgTsc x E 55 10 late R Qmg 80 H 29 50 15 55 E 35 45 Volcanic Rocks Intrusive Rocks LEMHI RANGEA Ysq 78 SALMON RIVER MOUNT D 35 Qgty R 28 A 35 55 CENOZOIC N G 66 Qgty middle E 30 Reference MONTANA 65 Qgt Tqs2 sections, 11 Qmg 29 30 Lemhi Group Ttcr Qmg Qgty 35 Qgty 70 IDAHO 40 40 Tlm TERTIARY 32 Figure 1. Location of Goldstone Mountain 7.5' quadrangle with respect to 45 22 Eocene 20 Qgty 20 Tgt known Belt Supergroup rocks and the reference and type sections of the 15 Tr Tpd Tmd Tdi Lemhi Group and Yellowjacket Formation. Shaded areas represent 20 Tldac 30 Qgt Qgt Qgty 50 mountain ranges containing Mesoproterozoic sedimentary rocks. 40 Tmd Qgty Ysq Qgt 40 15 Tcg2 60 Ysq 12 27 20 12 Tmd 40 Tqs1 45 31 Qgty 23 Qgt Tqt 25 Ysq 60 40 30 60 25 8 Tcg 60 1 early Qmg 35 50 A’ 40 10 Qgty Metasedimentary Rocks 50 50 15 10 Ysq 15 25 MESOPROTEROZOIC 25 20 Qgo 20 Ysq 25 20 15 40 16 15 Qgto Till deposits older than the last glacial maximum (Pleistocene)—Poorly sorted Ysq Siltite, quartzite, and argillite (Mesoproterozoic)—Dominated by laminated REFERENCES Qafo 50 INTRODUCTION 15 bouldery till. Mostly subangular to subrounded clasts. Found only by Sandy siltite and argillite, the unit contains coarser and thicker intervals. Finer Anderson, A.L., 1957, Geology and mineral resources of the Baker quadrangle, Creek at mountain front. Early Pinedale Glaciation or older. Soils moder- grained intervals have graded couplets and couples of dark siltite and darker, 10 23 Lemhi County, Idaho: Idaho Bureau of Mines and Geology Pamphlet 112, 40 50 The Idaho Geological Survey (IGS) and the Montana Bureau of Mines and ately well developed. Thickness 15 m (50 ft). gray to green argillite. Up to about one third of these intervals is white Qgt 45 71 p. 40 15 Geology (MBMG) selected the Goldstone Mountain 7.5' quadrangle in the (weathering) very fine-grained feldspathic quartzite that gives the rock a 15 Qgo Blankenau, J.J., 1999, Cenozoic structural and stratigraphic evolution of the Qas 45 50 central Beaverhead Mountains along the Montana-Idaho border for a Outwash gravels of last local glacial maximum (Pleistocene)—Subrounded to candy striped appearance. These quartzite layers commonly are discontinu- 45 20 southeastern Salmon basin, east-central Idaho: Utah State University M.S. 25 30 1:24,000-scale collaborative mapping project as part of a larger project to rounded, well sorted sandy cobble to boulder gravel. Primarily Pinedale ous and preserve hummocky and ripple drift cross laminations, some of thesis, 143 p., 3 plates. 50 understand the structural and stratigraphic relationships between two equivalent; traceable to terminal moraine deposits of Qgt. Forms outwash which are distorted in loads, and rarely have lag bases that have more and 25 60 18 20 Evans, K.V., and G.N. Green, 2003, Geologic map of the Salmon National 35 Ysq 45 20 25 different Mesoproterozoic sedimentary rock packages. To the east and terrace 12 m (40 ft) above Sandy Creek. Soils weakly developed. Thickness coarser quartz. Thick siltite beds have more diffuse multi-mm to cm lamina- 30 3-9 m (10-30 ft). Probably overlies stream-cut surface on bedrock. Forest and vicinity, east-central Idaho: U.S. Geological Survey Geologic 20 northeast, in the West Pioneer and Pintler Mountains (Figure 1), are tions that are planar, gently undulating (hummocky), disturbed by soft 45 25 Ysq 55 30 Investigations Series Map I-2765, 19 p., scale 1:100,000. 5 exposures of known Belt Supergroup rocks (Ruppel and others, 1993; sediment deformation, or deformed into similar folds where cleavage devel- 15 Qgoo Harrison, S.L., 1985, Sedimentology of Tertiary sedimentary rocks near Salmon, 22 Outwash gravels older than last local glacial maximum (Pleistocene)— opment is extreme. Intervals contain sets of several to tens of dm to m thick 45 Qgto Lonn and McDonald, 2004a, 2004b), whereas to the southwest, in the Qafo 20 Subrounded to rounded, well-sorted sandy cobble to boulder gravel. Forms Idaho: University of Montana Ph.D. dissertation, 175 p. 10 white very fine- to fine-grained feldspathic quartzite beds with bases loaded 30 35 20 Lemhi Range and Salmon River Mountains, are the reference sections of 35 outwash terrace 18-24 m (60-80 ft) above Sandy Creek. Traceable to old Hipple, Karl, Karen Langersmith, Rulon Winward, Dal Ames, and Bradley 40 the Lemhi Group, Swauger Formation, and Yellowjacket Formation (Ross, into dark argillite tops of underlying beds. Thick beds typically have bedding moraine deposits (Qgto). Early Pinedale or older. Shows evidence of relict Duncan, 2006, Soil survey of Custer-Lemhi area, Idaho, parts of Blaine, Ysq 1934; Ruppel, 1975). In the intervening Beaverhead Mountains, both the defined by dark mm-scale laminations. Most laminations are planar, but Qafo 35 35 meltwater channels. Soils moderately well developed. Thickness 3-12 m Custer, and Lemhi counties: United States Department of Agriculture, stratigraphic and structural interpretations have been controversial among load and convolute lamination and dm thick stacks of cm-scale ripple cross (10-40 ft). Probably overlies stream-cut surface on bedrock. Probably Natural Resources Conservation Service, 1270 pages, soil maps at Tkg? previous workers (MacKenzie, 1949; Tucker, 1975; Ruppel and others, lamination are common. Attempts to map coarse intervals across the terrane 15 age-equivalent to gravel of third terrace (Qtg ). http://websoilsurvey.nrcs.usda.gov/app/. Qgoo 30 1993; Winston and others, 1999; Evans and Green, 2003; O'Neill, 2005; 3 were unsuccessful. This possibly indicates that they are channels, not sheets, 15 Janecke, S.U., J.J. Blankenau, C.J. VanDenburg, and B.S. Van Gosen, 2001, Map Tysdal and others, 2005; and O’Neill and others, 2007). In 2008 the but structural dissection of the stratigraphy probably contributed to their 55 of normal faults and extensional folds in the Tendoy Mountains and Beaver- Qgo 40 MBMG and IGS mapped the Goldstone Pass quadrangle to the north discontinuity. Thickness uncertain because of deformation, but a minimum Qgto 55 TERTIARY SEDIMENTARY DEPOSITS OF head Range, southwest Montana and eastern Idaho: U.S. Geological Qas 40 (Lonn and others, 2009) and the Kitty Creek quadrangle to the east (Lewis of 2400 m (8000 ft) likely. Tentatively correlated with the type Inyo Creek 45 45 Survey Miscellaneous Field Studies Map MF-2362, scale 1:100,000. 40 and others, 2009a) and our collaborative team plans to continue THE SALMON BASIN Formation of the Lemhi Group (Ruppel, 1975) and rocks below the Inyo 65 55 Lane, E.W., 1947, Report of the subcommittee on sediment terminology: Trans- 40 25 22 1:24,000-scale mapping along the Beaverhead Range in an attempt to Creek that are not exposed in the Lemhi Range. Shown as Apple Creek 20 45 actions of the American Geophysical Union, v. 28, no. 6, p. 936-938. resolve some of the long-standing controversies. Tkg Kriley Gulch formation (Oligocene and Eocene)—Matrix- and clast-supported Formation on the Salmon National Forest map (Evans and Green, 2003). 45 45 Lewis, R.S., R.F. Burmester, L.R. Stanford, J.D. Lonn, M.D. McFaddan, and K.L. 30 30 pebble to boulder conglomerate interbedded with lithic sandstone and Qgoo 27 Tr 20 Othberg, 2009a, Geologic map of the Kitty Creek quadrangle, Lemhi Qtg1 Bedrock mapping in 2009 by Lewis, Burmester, Lonn, and McFaddan minor tuff. Forms steep slopes with coarse gravelly soils and resistant ridges 40 55 County, Idaho and Beaverhead County, Montana: Idaho Geological Survey Qafo 50 followed reconnaissance work by Lonn, Burmester, and Lewis in 2006- capped with common lag pebbles and cobbles, and infrequent lag boulders Qgo 30 30 25 2008. Mapping in 2009 and 2010 of Tertiary strata was by Lewis, Stanford, as long as to 3 m (10 ft). Outcrops of cemented beds are common lower in Digital Web Map 112 and Montana Bureau of Mines and Geology Open- 15 15 Othberg, and McFaddan, and of Quaternary deposits by Othberg and the section but rare higher in the section. Exposures along Kenney Creek File Report 582, scale 1:24,000. 15 Qas Ysq Stanford. Attitudes from previous mapping by Anderson (1957 and unpub- described by Tucker and Birdseye (1989) show primarily matrix-rich, Lewis, R.S., K.L. Othberg, R.F. Burmester, J.D. Lonn, L.R. Stanford, and M.D. poorly sorted conglomerate with highly angular clasts typical of proximal McFaddan, 2009b, Geologic map of the Bohannon Spring quadrangle, 60 lished mapping) and Tucker (1975) were used to supplement the structural 15 35 25 Lemhi County, Idaho and Beaverhead County, Montana: Idaho Geological 35 data collected by the authors. Mapping and unit descriptions by Blankenau facies in alluvial fans that are dominated by debris-flow deposition.
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