IDAHO GEOLOGICAL SURVEY TECHNICAL REPORT 12-4 MOSCOW-BOISE-POCATELLO IDAHOGEOLOGY.ORG DIEDESCH, RODGERS, AND LINK GEOLOGIC MAP OF PORTIONS OF THE PHI KAPPA MOUNTAIN, HYNDMAN PEAK, AND GRAYS PEAK QUADRANGLES, BLAINE AND CUSTER COUNTIES, IDAHO T.F. Diedesch1, D.W. Rodgers1, and P.K. Link1 2012 MAP SYMBOLS DESCRIPTION OF MAP UNITS Contact - dashed where approximate, dotted where concealed ALLUVIUM (HOLOCENE) – Crudely stratified silt, sand, and Qal WOOD RIVER FORMATION, EAGLE CREEK MEMBER ELLA MARBLE (ORDOVICIAN) – Buff-weathering calc-silicate gravel deposited by present streams as channel or flood-plain Oe (Descriptions from Mahoney et al., 1991) marble. Forms prominent dip slopes. Upper part contains light-gray ? ? Fault - dashed where approximate, queried where uncertain materials; locally includes alluvial fan deposits. Description from to buff, thin- to medium-bedded marble with variable amounts of Dover (1983). WOOD RIVER FORMATION, MEMBER 6 (PENNSYLVANIAN- calcite, quartz, and calc-silicate minerals; mineralogical variations High-angle normal fault - dashed where approximate; ball PIPw6 7 PERMIAN) – Interbedded gray, buff- to brown-weathering, thick- emphasized by differential weathering. Siliceous partings and 26 COLLUVIUM (HOLOCENE) – Locally derived, incoherent Ok and bar on hanging wall bedded, fine- to medium-grained calcareous sandstone, calcarenite, quartzite interbeds increase in thickness and abundance toward the Qc accumulations of angular and poorly sorted rock debris; occurs as Oe and olive-brown, thick beds of fine-grained quartzite with interbeds contact with the overlying Kinnikinic Quartzite. Lower part is buff, Tei thin veneer or in talus cones along hill and valley sides; locally Low-angle normal fault - dashed where approximate; of laminated dark-gray to black carbonaceous and calcareous massive, more uniform and more coarsely crystalline and character- includes landslide deposits. Description from Dover (1983). half-circles on hanging wall siltstone. Crops out as rubbly, highly-fractured ledges on hillslopes istically crumbles to sand. Basal contact sharp and relatively concor- Os 60 40 41 and peaks. Contains fusulinids. Thicknesses approximately 1,700 m. dant. Thickness approximately 200 m. Description from Dover Strike-slip fault - dashed where approximate, dotted where TERRACE GRAVEL (HOLOCENE AND PLEISTOCENE) – (1983). 4851 Qt 48 Crudely stratified and poorly sorted gravel, sand, and silt in terraces 725 Ok 51 concealed; arrows show relative motion WOOD RIVER FORMATION, MEMBER 5 (PENNSYLVANIAN) – 39 41 727 standing as much as 30 m above present stream level; well-rounded IPw5 CLAYTON MINE QUARTZITE (ORDOVICIAN) – White, 37 Brown or olive brown, thick-bedded to massive, fine-grained Thrust fault - dashed where approximate; teeth on hanging clasts have a range of compositions reflecting that of drainage Oc 114°12’30” quartzite and calcareous quartz sandstone. Forms shelves abd vitreous, poorly sorted, thick-bedded to massive, micaceous and 42 patterns. Description from Dover (1983). wall benches throughout mid-elevations. Thickness 150-200 m. feldspathic gneissose quartzite; typically splits into slabs along mica 32 39 partings containing as much as 50% biotite; characterized by 36 Oe Wildhorse detachment fault - dashed where approximate, GLACIAL DEPOSITS, UNDIVIDED (PLEISTOCENE) – Boulder- well-developed coarse tabular cross-bedding. Contains some 48 DSla Qg WOOD RIVER FORMATION, MEMBER 4 (PENNSYLVANIAN) – 45 16 19 dotted where concealed; hachures on hanging wall rich, poorly sorted deposits present in most glaciated valleys; occurs IPw4 discontinuous layers and lenses of granule and pebble conglomerate 29 54 Carbonaceous and calcareous banded siltstone arranged in fining 724 10 in arcuate hummocky ridges representing terminal and recessional 49 upward cyclcic packages of micritic sandstone and silty micrite; with pink- to purplish-gray quartz clasts. Base generally concordant, 41 moraines, in linear patches of lateral moraine perched on valley Asymmetric anticline - axial trace; beds are upright, shorter complete Bouma sequences with base cut out; abundant sedimentary but locally slightly discordant and marked by about 2 m of quartz- 48 Pw7 Ok walls, and in irregular patches on cirque floors. Description from 50 arrow on steeper limb structures like tabular cross-lamination, convolute laminations, pebble conglomerate. Thickness about 300-425 m. Description from 48 Dover (1983). Oc 50 soft-sediment deformation; beds are laterally continuous with Dover (1983). Qg Asymmetric syncline - axial trace; beds are upright, shorter relatively sharp contacts. Thickness 250-200 m. 46 arrow on steeper limb Tcu CHALLIS VOLCANIC GROUP, UNDIVIDED (EOCENE) UNNAMED BANDED CALC-SILICATE (NEOPROTEROZOIC- CZbc CAMBRIAN) – Distinctively color-banded unit consisting of 7 WOOD RIVER FORMATION, MEMBER 3 (PENNSYLVANIAN) – 23 56 57 Qg RHYOLITE LAVA FLOWS – Discontinuous exposures of purple 40 Overturned syncline - axial trace, dotted where concealed; IPw3 Gray, typically pink- to purple-weathering, thin-bedded , platy alternating thin beds of various mineralogy. Relative proportions of 60 Tcr and lavender to yellow, flow-banded rhyolite. Crystals uncommon, arrows show dip direction of limbs limestone and shaly limestone. Locally, beds of interclastic limestone mineral constituents vary from band to band, and reflect primary but quartz and biotite are locally present. Maximum thickness 10 m. 71 at base of unit containing bioclastic grainstone, micrite, and chert- compositional layering in original sediment; rhythmically repeated 81 78 Granitic dike - Equivalent of Pioneer Intrusive suite granite pebble conglomerate of Hailey member. Contains fusulinids and sequences of compositional layers. Thickness of individual bands DACITE FLOWS – Gray to green-weathering, purple porphyritic 48 84 (Tei) 49 78 Tcd calcareous foraminifera. Thickness 75-200 m. ranges from a few millimeters to 15-20 cm; banding generally sharp Os dacite with abundant sanidine crystals. Upper part is finer-grained, and uniform and controls the characteristic splitting of the rock into Ok 4849 distinctly purple. Lower part is more coarsely crystalline and 722 Brecciated quartzite with sharp contact WOOD RIVER FORMATION, HAILEY MEMBER large slabs. Locally, soft sediment deformation disrupts composi- IPwh contains oxyhornblende in addition to sanidine. Weathers reddish- (Descriptions from Mahoney et al., 1991) tional layering. Basal contact sharp and generally concordant. 86 40 40 Strike and dip of inclined bedding - ball indicates top brown in places. Forms broad benches that define a flow foliation. Thickness about 100 m. Description from Dover (1983). New age 70 DSm 29 Thickness approximately 200 m. IPw5 85 26 direction known WOOD RIVER FORMATION, HAILEY MEMBER assignment from Link and Fanning (2009). IPw3/4 IPwh (PENNSYLVANIAN) – Contains Hall et al.’s (1974) Hailey 57 IPwh 37 PIPw6 71 Vertical bedding DACITE LAHAR – Gray to green-weathering with purple mottled- REFERENCES DSm 54 75 Tcl conglomerate and member 2. Lower cliff-forming unit of brecciated Oe porphyritic dacite clasts suspended in an ashy, greenish-gray matrix. Dover, J.H., 1983, Geologic map and sections of the central Pioneer Qg and sheared pebble conglomerate with subangular to rounded clasts 81 40 40 Clasts consist of fine-grained porphyritic dacite with abundant Mountains, Blaine and Custer Counties, Central Idaho: United States 60 Strike and dip of overturned bedding - ball indicates top 80 of quartzite, argillite, sandstone and chert; beds are tabular to lenticu- 48 47 Geological Survey Miscellaneous Investigations, Map I-1319, scale 48 ? direction known sanidine, plagioclase, and biotite crystals; enclaves within clasts are 82 lar and discontinuous, pinching out and possibly boudinaged along 72 common and consist of coarser-grained dacite fragments with 1:48,000. 61 40 major fault zones. Subordinate thin- to medium-bedded, fine- to 72 48 IPw3/4 ? 48 abundant sanidine crystals and less biotite than the fine-grained host. Durk, Kathleen, 2007, Geochronology of part of the Wildhorse Gneiss 722 Strike and dip of volcanic flow foliation coarse-grained sandstone. Upper member consists of blue-gray, 3171 I NW Tcu Os 3171 I NW Thickness approximately 125 m. Complex, Pioneer Moutains, Custer County, Idaho [Senior Thesis]: (PHI KAPPA MTN.) IPwh 79 (PHI KAPPA MTN.) 40 thin-bedded to massive, bioclastic grainstone and packstone, with ? Pocatello, Idaho State University, 38 p. 43°45’ 59 43°45’ Strike and dip of foliation 3171 II NW 40 3171 II NW micritic sandstone and siltstone; interfingers with chert-pebble (HYNDMAN PEAK) Qg 50 7 (HYNDMAN PEAK) DACITE PORPHRY – Blocky, reddish-brown-weathering silicified Hall, W.E., Batchelder, J.H., and Douglass, R.D., 1974, Stratigraphic 28 Tcp conglomerate. Bioclastic beds contain remnants of fusulinids, 39 porphyritic dacite with large, cm-scale grains of clay-altered section of the Wood River Formation, Blaine County, Idaho: U.S. 114°10’ Asymmetric minor fold hinge - bearing and plunge shown brachiopods, and calcareous foraminfera. Maximum thickness 150 m. 63 34 57 sanidine. Biotite crystals several millimeters to ~ 1 cm are rare, and Geological Survey Journal of Research, v. 6, n. 5, p. 579—592. commonly weathered to a copper-brown color. Forms at least two Link, P.K., and Fanning, C.M., 2009, Age and provenance of Precambrian 26 MILLIGEN FORMATION, UNDIVIDED (SILURIAN- Ok distinct subvertically foliated spires within the Challis Volcanic metamorphic rocks