IDAHO GEOLOGICAL SURVEY DIGITAL WEB MAP 54 MOSCOW-BOISE-POCATELLO BRECKENRIDGE AND OTHBERG Disclaimer: This Digital Web Map is an informal report and may be revised and formally published at a later time. Its SURFICIAL GEOLOGIC MAP OF THE WOOD RIVER VALLEY AREA, content and format may not conform to agency standards. BLAINE COUNTY, IDAHO CORRELATION OF MAP UNITS Artificial Mass Movements Deposits Alluvial Deposits Glacial Deposits Colluvial Deposits Deposits Outwash Till m Roy M. Breckenridge and Kurt L. Othberg Qta Qt Qad Qdf Qaf Qac Qas Qam HOLOCENE Qagsu Qags Qag Qgt QUATERNARY 2006 Qls 11 1 Qcv Qcvb Qcw Qcm Qcg Qcd Qagsu2 Qags2 Qag2 Qgt2 Qags Qgt Qagsu Qags Qag Qgt 33 3 ? PLEISTOCENE 114 15' ? ? ? 114 26'15'' 22'30'' R 17 E R 18 E ? Qag4 Qagc ? ?? ??? 48'45'' 43 48'45'' 43 Qags Qad Qcm k ? PLIOCENE TERTIARY North Qcw Qcm ? Qas ree C Qac Qt 2800 Qls Qags 36 31 36 Qcw Qgt SAWTOOTH k Qcw Qcm 1 Qgt1 2 T 6 N 0 urdoc T 6 N 0 M 2200 Qcw 0 3 Qt Qcw 2600 0 2 0 INTRODUCTION 4 0 Qcm T 5 N 0 Qad T 5 N NATIONAL 0 Qad Qac Qgt 2800 Fork The surficial geologic map of the Wood River Valley provides basic Qcm Qag2 R k Qcw o data on the geologic materials found at the surface and shallow e ck Qcw 2200 e Qag2 r 1 Qad Alluvial-fan and debris-flow deposits (Holocene)—Crudely bedded, C 1 6 2 Qgt subsurface, and is essential for planning. The information is directed at RECREATION Qad 600 Qt 1 Roll Qam 2400 a broad range of specialists concerned with land development and its poorly sorted gravel. Gravel is composed of subangular and angular Big Qcm Qac pebbles, cobbles, and boulders in a matrix of granules, sand, silt, and Canyon consequences as population growth andland-use changes place greater Qags Qag Creek 2200 Qac clay. Thickness varies, but typically ranges from 6-50 feet. Fans 3 Qad Qcw demands on the region's natural resources. Details from the map assist, AREA 2000 Qcw Qag2 Qac 2 for example, in assessing slope stability, foundation design, sewage composed of alluvium and debris flows occur in canyon bottoms Qag Qcw 8 1 Qad 0 Leroux 0 Qt 2000 below steep avalanche tracks and debris chutes (see Symbols). Qcm Qad drainage, solid waste sites, and the factors affecting recharge of the 2000 Qag2 Qad 2200 potable ground-water supply. The information depicted at this scale Includes variable amounts of trees and stumps mixed with rock and Qad Qcm Qcw Qas Qcv 0 soil emplaced by avalanches. Soil series include the Drage. 40 2400 furnishes a useful overview of the area's geology but is not a substitute Qcm 2 2 2000 2 Qt O 0 reg 0 0 Qt for site-specific geotechnical evaluations. All soil-series names are on 260 k 2600 Debris-flow deposits (Holocene)—Unsorted gravels, silts, and sands Qas Qad Qcm taken from Johnson (1991). Qdf Gulch Wood Qcw primarily deposited by debris flows and snow avalanches. Includes e Qags Cree Qad gl Qt The Wood River Valley of central Idaho is surrounded by the Boulder, variable amounts of trees and stumps mixed with rock and soil. Mainly Qcw Qcv Ea Qad Qcw restricted to valley side-slopes and debris chutes. Qcv Neal Qcm Qt Pioneer, and Smoky mountains. Geologists have focused much 0 Qas 0 attention to the stratigraphy and structure of the bedrock units in the Qls 8 2 Landslide deposits (Holocene and Pleistocene)—Poorly sorted and poorly Qag2 Qcm 2600 Qt Qcm area as summarized by Worl and Johnson, 1995. The bedrock geology Qac 0 stratified angular cobbles and boulders mixed with silts and clays. Qas 0 Qgt Qad 4 2 of this area is complex and comprised of several fault plates of Qcvb 2 Qt Qags Mainly translational earth flows. Slump blocks primarily composed of Qcw Creek Paleozoic marine rocks (see cross section below) (Batchelder and Hall, Qac C Qags anyon volcaniclastic sediments from the Eocene Challis Volcanics. In 0 on 1978, Hall and Batchelder, 1979, Hall and others, 1978, Lewis and 0 ils 2000 Qad W addition to the landslide deposit, the unit includes the landslide scarp 20 2200 others, 1988, Link and Rodgers, 1995, and Ratchford, 1994). Bounding 2 Qgt2 2 Qags2 and the headwall (steep area adjacent to and below the landslide 0 Qad 0 Creek structures originally interpreted as low-angle thrusts are now known to Qag 2000 scarp) from which material broke away (see Symbols). 2 Qcv Qas Qcm include normal (extensional) faults. These plates are intruded by the Qcm Qt Qcvb Qcv Qt Cretaceous Idaho batholith and Eocene dikes and stocks, and overlain Qags Qags Qas by sedimentary and volcanic rocks of the Eocene Challis Volcanic COLLUVIUM k Qcm 2 e e Qad Qac r Group (Challis Volcanics). Base- and precious-metal mineralization in Qdf C Qad River Qcv Colluvium from Eocene volcanic rocks (Holocene and Pleistocene)— Canyon the area is hosted by the Paleozoic sedimentary rocks and the Idaho Sawmil ulch Qad Trail Qls G Poorly sorted gravel comprised of angular and subangular volcanic l batholith. Although no historically active faults are known in the area, Qcw Qad pebbles, cobbles, and boulders in a matrix of silt and sand. Emplaced Qag1 Qcw Sun Valley is located in the center of the Idaho Seismic Belt and is ip Qad Qcm by gravity movements on steep-sided canyons. Includes outcrops of Qcvb Creek D Qcw among the most seismically active areas in Idaho (Sprenke and Qcw Qags2 45' 0 45' resistant andesite dacite, and rhyolite of the Eocene Challis Volcanics, 00 Breckenridge, 1992). Earthquakes in 1944, 1945, several in the 1960s, Qcm Qags Antelope 2 slopes of tuffs and pyroclastic deposits, and outcrops of Eocene dikes. Qad 2 1983, and 1984, resulted in intensity V to VI shaking and some Qad 2200 600 Qt r o l y a Fox T Qac Qas Qt building damage in Ketchum and in Hailey, the county seat. Mines in Distribution and thickness of colluvium dependent on slope aspect, Qls Qcv Qac Qas Qcw upper and lower slope position, and erodability of volcanic units. 2400 2 Qcm the Wood River Valley area date back to the 1860s and are partly 0 Qag2 0 Qcm C Includes landslides too small to map separately and unmapped areas 0 Qad Badger responsible for the establishment of the Idaho Territory. The mining Qls Qagreesk 2 Qac Qad Qcm Qcm of talus. Soil series include the Elkcreek, Elksel, Friedman, Gaib, 0 districts include the Mineral Hill, Bullion, Warm Springs, and Camas 220 Qcw Qt Qad Qcm Qad as well as the Hailey Gold Belt. These mines produced silver, gold, Smelter, Starhope, Winridge, Winridge, and Winu. Qad Qags Qt Qam Qcv Qt Qad 2 Qad lead, and zinc, some as recently as the 1960s. Although no longer Qcvb Colluvium from volcanic breccias, tuffs, sedimentary interbeds of the Qags 2400 C Qags2 Qas Creek Qls a Qt active, the effects of mining still play a major role as significant Qdf n Corral Eocene Challis Volcanics (Holocene and Pleistocene)—Poorly sorted e y 0 Qcvb k o 00 cultural and historical resources as well as posing some environmental n 2 0 Qls La Qad colluvium comprised of angular and subangular volcanic clasts in a 0 Griffin Qcv Qad concerns. Reclamation of the Triumph Mine was recently completed 4 Qad 2 Qad Qags matrix of clay, silt and sand, generally finer in texture than Qcv and Butte Qac SAWTOOTH by the state of Idaho and industry. The present valley is a topographic Qac Qags2 2200 more prone to slope movement. Contains altered volcanic tephra and 2564 Qags Qad reflection of the Wood River graben, which is filled by Cenozoic Qcm weathered sediments and clasts. Emplaced by gravity movements on Qad deposits. Quaternary geology of the area is a product of Pleistocene steep-sided canyons. Includes outcrops of resistant andesite dacite, Qad 0 glaciation in the upstream source areas, in the form of outwash Qas Qls 0 Qad Qac Creek 4 and rhyolite of the Eocene Challis volcanics, slopes of tuffs and Qls 2 240 Big Qad Qcw deposits and terraces developed in the Wood River Valley and 0 36 31 2 Qt pyroclastic deposits, and outcrops of Eocene dikes. Distribution and 20 tributary valleys. Snow and debris avalanches are common and Qcv 0 Morga n Ridge thickness of colluvium dependent on slope aspect, upper and lower Qad Boundary 36 dangerous on slopes at upper elevations and in narrow tributary Campground 24 Qt slope position, and erodability of volcanic units. Includes landslides 2200 0 valleys. Post-glacial surficial deposits are mainly the result of active Qcvb 0 Qags2 too small to map separately and unmapped areas of talus. Soil series T 5 N Qac Qcv T 5 N slope processes, including landslides, that tend to thicken the valley Wood Qad Qt include the Elksel, Friedman, and Winridge. NATIONAL 2 Qcm fill, and active river-channel processes that redistribute gravel and 0 0 Qdf T 4 N Qag 0 Qt sand. The Holocene drainage system has made little effect on the 2000 2 Qt Qas Qcm T 4 N Qcw Colluvium from sedimentary rocks of the Permian Wood River Formation Qad removal of the Pleistocene and post glacial deposits. Many smaller Qcv Qls Qac Qagc l (Holocene and Pleistocene)—Primarily poorly sorted gravel comprised A da Qag tributaries have intermittent surface streams that have not established of angular and subangular pebbles, cobbles, and boulders in a matrix 1 18 Qt m Qcv Trai graded profiles through valley side deposits.