IDAHO GEOLOGICAL SURVEY DIGITAL WEB MAP 174 MOSCOW-BOISE-POCATELLO IDAHOGEOLOGY.ORG FEENEY AND OTHERS GEOLOGIC MAP OF THE HOG CREEK BUTTE QUADRANGLE, WASHINGTON AND CORRELATION OF MAP UNITS Artificial Alluvial Deposits Mass Wasting Deposits Deposits m ADAMS COUNTIES, IDAHO Qas Qaf Qlp Holocene Qls 0.01 ka QUATERNARY Dennis M. Feeney, Reed S. Lewis, William M. Phillips, Dean L. Garwood, and Skye W. Cooley Pleistocene 2016 2.6 Ma Pliocene Sedimentary Pyroclastic Volcanic Rocks BX6036 N Twp Deposits Rocks 14RL053 Rhyolite and Basaltic Basalt 14DF309 Tyob m andesite andesite 5.3 Ma Ts Ts? G007 Twp Weiser volcanics 14D 14RL051 ? Ts 5 12.5 Ma* Tyob 12.7 Ma* Twp Twb Twp? 14DG004 TERTIARY 2 Twp Qas Alluvium of side streams (Holocene)—Clayey sand, silt, and fragments of shale ences in composition may reflect separate flows. Interbeds of tuffaceous m 3 3 14RL054a Tyob in small channels draining landscapes underlain by Tertiary sedimentary material, breccia, or Ts are present locally between individual flows and 18 Tyob Tyob Twb Miocene deposits (Ts); includes broad unchanneled areas underlain by thin below or above units; no attempt was made to show the interbeds unless Ts? A’ Ts 2 14DG006 re-worked eolian sediments, and floodplain deposits of Crane Creek. Thick- mappable at 1:24,000 scale, as in the ashy tuffaceous bed present beneath Twb Twb nesses range from <1 to 2 m (<3 to 6.5 ft). Many tributary streams are Twb Crane Creek Reservoir (secs. 15 and 10, T. 12 N., R. 2 W.). 2 14RL055 1 2 432566 Ts ephemeral. Subject to seasonal flooding during spring snowmelt and 14.49 +/- 0.57 Ma* Weiser basalt 1 (Miocene)—Appears in cross section only. Projected from unit summer thunderstorms. Twb1 ª Ts m Twba mapped to the southwest on Nutmeg Flat quadrangle (Garwood and others, m Ts m 15.1 +/- 0.16 Ma* Qaf Alluvial fan deposits (Holocene)—Crudely bedded, poorly sorted, gray to 2014) and to the west on Midvale quadrangle (Feeney and Phillips, 2016). brown sand, silt, and clay derived from Tertiary sediments (Ts). Tyob Twp 415937 Twba Weiser basaltic andesite (Miocene)—Appears in cross section only. Projected Tmv Columbia River from unit mapped to the southwest on the Nutmeg Flat quadrangle m Twp ª Basalt Group ? (Garwood and others, 2014) and to the west on Midvale quadrangle Tyob MASS WASTING DEPOSITS Tgr1? (Feeney and Phillips, 2016). 5 BX6037 Qls Landslide deposits (Holocene and Pleistocene)—Rotational slumps of Tertiary N *Richard Gaschnig, personal comm., 2015. Qls m m Twp 14RL056 sediments (Ts) and basalt (Twb ); thickness estimated from topographic Other volcanic rocks 5 2 Ts profiles is about 43 to 37 m (140 to 120 ft); no recent failures observed on 14RL058 Tmv aerial images. Mixed volcanic rocks (Miocene)—Dark-gray and very fine-grained andesite and 14DG008 m rusty red to brown flow-banded rhyolite. Andesite is mostly aphyric with Tyob scarce phenocrysts of plagioclase < 2 mm long. The rhyolite has pheno- m Twb2 INTRODUCTION crysts of plagioclase as long as 3 mm in an extremely fine crystalline matrix. Tyob SEDIMENTARY DEPOSITS Most of the unit was mapped as Grande Ronde Basalt by Fitzgerald (1981 14DG005 Twp and 1982). It was later recognized as two rock types intimately associated as The geologic map of the Hog Creek Butte 7.5’ quadrangle depicts the rock Ts Tertiary sedimentary deposits (Pliocene and Miocene)—Primarily flat lying to Ts “mixed volcanics” by Idaho Geological Survey’s work in Indian Valley units exposed at the surface or underlying a thin cover of soil or colluvium; gently dipping fluvial arkosic sand with components of silty sand, to clayey (Garwood and Othberg, 2009, and Garwood and others, 2009a, 2009b). alluvial and man-made surficial deposits are also depicted where they form silt, tuffaceous material, and ash. Arkosic sand is medium to coarse grained, m Major and trace element chemical composition of both andesite and m significant mappable units. This map is a result of fieldwork conducted in subangular to subrounded grains of quartz, potassium feldspar, plagioclase rhyolite from this quadrangle (Table 1) are consistent with samples from Ts? the summer and autumn of 2014 by the authors. Previous work in the area feldspar, and in places trace amounts of biotite, muscovite and tuffaceous Indian Valley (Garwood and Othberg, 2009; and Garwood and others, Qas includes the surficial geology map of Othberg (1982), and geology of the material, volcanic ash, and quartzite cobbles and gravel. Present locally are Ts Twp thin (< 5 cm) laminar beds of clay, silt, and organic material, sets of climbing 2009a; 2009b). The vent is likely located to the east or southeast. Tyob Payette National Forest (Lund, 2004). The field maps, field notes, fluxgate N ripples and cross-cutting beds, and quartzite cobbles and gravels. Creates magnetometer data, XRF analytical chemistry, and posthumous Ph.D. by Columbia River Basalt Group BX6033* James Fitzgerald (1981, 1982, and 1984) were consulted and incorporated knolls 31 to 84 m (100 to 275 ft) high across the central and north-central Ts part of the map but as interbeds between flows may range from < 1 meter to BX6039 where appropriate. Tgr Grande Ronde Basalt R1 magnetostratigraphic unit (Miocene)—Appears in 61 meters (< 3 feet to 200 feet). Unconsolidated sediments generally do not 1 Twb2 cross-section only. Projected from unit mapped on the Indian Valley quad- N The basement rocks of the Hog Creek Butte 7.5’ quadrangle are Miocene crop out in quadrangle; exposures include road cuts and small slumps or rangle to the northeast (Garwood and others, 2009b). Twp? Twp compositionally diverse flows of the Weiser volcanics. The Weiser volca- the landslides near Crane Creek Reservoir. Includes gravel deposits resistant nics were likely erupted along north-northwest trending linear vents that to erosion on Hog Creek Butte in the N ½ sec. 26, T. 13 N., R. 2 W., butte m Tyob? 14DG003 followed regional structures to the south and west and flowed over older 3389T in the S ½ sec. 2, T. 13 N. R. 2 W., and butte 3412T in the N ½, NE Tyob? Columbia River Basalt Group volcanics. We use stratigraphy, whole-rock ¼ sec. 36, T. 13 N., R. 2 W. These are lag deposits < 3 m (10 ft) thick of REFERENCES well-rounded cobbles and pebbles composed of basalt, basaltic andesite, Twb2 XRF geochemistry, paleomagnetic data, and morphology to differentiate m volcanic units. In evaluating the whole-rock geochemistry we use the total andesite, granite, quartzite, and gneiss (shown as a pattern within Ts). Also alkalis versus silica chemical classification of volcanic rocks from the includes gravel with basaltic clasts on the slope above the North Crane Feeney, D.M., D.L. Garwood, and W.M. Phillips, 2014, Geologic map of the Ts International Union of Geological Sciences (LeBas and Streckeisen, 1991). Creek terrace in the S ½ sec. 36, T. 13 N., R. 2 W. that might represent a Mann Creek SE quadrangle, Washington County, Idaho: Idaho Geological Twb2 Survey Digital Web Map 169, scale 1:24,000. m Hog Creek Butte quadrangle shows the thinning of the Weiser volcanics to younger deposit. Ts consists of undifferentiated Idaho Group and Payette m the east. The “mixed volcanics” unit on the southeast quarter of the map Formation. The unconsolidated sediments of the Payette Formation and Feeney, D.M, and W.M. Phillips, 2016, Geologic map of the Midvale quad- Qlp may mark the eastern extent of Weiser volcanics. The distribution of Tertiary Idaho Group have been well described (Lindgren, 1898; Kirkham, 1931; rangle, Washington County, Idaho: Idaho Geological Survey Digital Web sedimentary deposits across the central, northern, and eastern part of the Shah, 1968; Malde and Powers, 1962; McIntryre, 1976b; Nakai, 1979; and Map 179, scale 1:24,000. m Fitzgerald, J.F., 1981, Geology and basalt stratigraphy of the Weiser embay- m quadrangle indicates the depositional environment was largely channel- Smiley and others, 1975). The most definitive paper is a literature review m ized by preexisting volcanics. and interpretation by Kirkham (1931). Kirkham describes the Payette Forma- ment, west-central Idaho: University of Idaho Ph.D. dissertation, 121 p. m Fitzgerald, J.F., 1982, Geology and basalt stratigraphy of the Weiser embay- Ts tion as Miocene sediments interbedded between Columbia River basalt Ts flows, and Idaho formation (later redefined as Idaho Group) as Pliocene, ment, west-central Idaho, in Bill Bonnichsen and R.M. Breckenridge, eds., Ts m nearly flat lying sediments on top of Columbia River basalts. However, due Cenozoic Geology of Idaho: Idaho Bureau of Mines and Geology Bulletin N SYMBOLS to the poor exposure of Ts and a dearth of fossils, constraining the age is 26, p. 103-128. Fitzgerald, J.F., 1984, Geology and basalt stratigraphy of the Weiser embay- Qlp difficult. Our work leads us to believe that some flat-lying sediments are ment, west-central Idaho: Rockwell International Corp., Richland, WA, Twb m m concurrent with the later phases of Weiser volcanics and are older than the 2 m Rockwell Hanford Operations, RHO-BW-SA-217P, 121 p. Ts Contact: dashed where approximately located. proposed Pliocene age. We have mapped Ts as undifferentiated until we can resolve a more definitive stratigraphic break. Garwood, D.L., and K.L. Othberg, 2009, Geologic map of the Tamarack quad- rangle, Adams County, Idaho: Idaho Geological Survey Digital Web Map Ts m m Normal fault: ball and bar on downthrown side; dashed where approximately 105, scale 1:24,000. m m located; dotted where concealed. PYROCLASTIC ROCKS Garwood, D.L., K.L. Othberg, and J.D. Kauffman, 2009a, Geologic map of the Qas Council quadrangle, Adams County, Idaho: Idaho Geological Survey Ts 3 Approximate strike and dip of volcanic flows.