This database present polygons (lines separating map units) for geoologic maps for all 44 of Idaho's counties. The database is derived from a new State Geologic Map of Idaho. The maps are presented on basemaps showing shaded relief, major lakes and streams, major highways, and major populated areas. Users can customize the presentation of the maps with the GIS data included in the database.
County geologic maps of Idaho for use in county hazard reports
Geology compiled from more than 85 sources. Basement geology in central and north Idaho, compiled on Lambert conformal conic 1:500,000 base from 1976. Surficial geology for the entire state and bedrock and basement geology south of the Snake River and in southeast Idaho, compiled on shaded relief base derived from 10 m NED data. NAIP (2006) images and Google Earth application was also used to help with surficial geology including relatively recent fault traces in the southeast and south areas of the state.
These data should not be used at scales larger than 1:500,000. For example, data should not be scaled up to 1:250,000 or 1:24,000 for printing or GIS analysis work. The maps are useful for general screening for hazards and for use in plans and other reports, but more detailed investigations are required to fully evaluate individual sites.
These data (polygons) are highly simplified and generalize for the purposes of generating a published map at a scale of 1:750,000. This is NOT a geologic data set but rather data resulting from a process of compiling a map for publication at a small scale. Positional accuracy is hard to determine for these data. Error in positional location of geologic boundaries cannot be quantitatively determined. Rather, numerous factors need to be taken into account to judge the accuracy and reliability of these data. The geology is highly simplified . Second, the original compilation base (Lambert conformal conic, 1:500.000) is not suited for regional compilation due to flaws in the topography and planimetrics (roads, boundary, streams, etc.), i.e., things don't fit well when compared to the real world. Efforts were made by the authors to resolve some of these issues and improve the over all quality and accuracy of the map data. One way to determine the best possible accuracy is to convert the linewidth of a polygon boundary (geologic contact) to real units. For example a .25 mm (about .25 points) line at 1:500,000 converts to about 410 feet (125 m). This represents the best possible accuracy. If the arguments above are added the positional accuracy must fall some where between 410-1000 feet 125-305 m). Obviously, these data should not be used for analysis purposes.
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Geologic map of Idaho: [Geol_Unit] (polygons). Geology compiled from more than 85 sources. Basement geology in central and north Idaho, compiled on Lambert conformal conic 1:500,000 base from 1976. Surficial geology for the entire state and bedrock and basement geology south of the Snake River and in southeast Idaho, compiled on shaded relief base derived from 10 m NED data.
A complete listing of geologic map units: DESCRIPTION OF MAP UNITS (3/25/2011) Ages listed below and in the correlation of map units conform to the 2010 U.S. Geological Survey Geologic Time Scale (U.S.G.S. Fact Sheet 2010-3059). Abbreviations are Ma (mega-annum, million years before present) and ka (kilo-annum, thousand years before present). The term "calibrated ka" refers to radiocarbon ages that have been corrected so that they correspond to calendar years. References for the age information provided below are listed in the booklet that accompanies this map. QUATERNARY SEDIMENTS Qa Alluvial deposits (Quaternary)-Gravel, sand, silt, and clay. Deposits in drainages consisting of gravel, sand, and silt. Includes younger terrace deposits. May contain some glacial deposits and colluvium in uplands. Qaf Alluvial fan deposits (Quaternary)--Gravel-rich deposits at mouths of canyons; largest fans are in Basin and Range Province in east-central and southeastern Idaho. Qls Landslide deposits (Quaternary)--Unsorted gravels, sand, and clay of landslide origin; includes rotational and translational blocks and earth flows. Qw Windblown sand deposits (Quaternary)--Fine- and medium-grained sand dunes in southern Idaho; includes Bruneau and St. Anthony dune fields. Ql Loess deposits (Pleistocene)--Wind-deposited quartzose and calcareous silt in southeastern Idaho. Only shown where thick enough to mask older units; commonly 7-15 m (23-50 ft) thick. Qp Loess of the Palouse Formation (Pleistocene)--(stipple pattern only)-Wind-deposited silt and clayey silt of the Palouse hills near Moscow. Qm Missoula Flood deposits (Pleistocene)--Gravel, sand, and silt near Coeur d'Alene and Sandpoint that were carried by outburst floods from Glacial Lake Missoula (20-15 ka). Floods also flowed back up the Snake and Clearwater rivers to Kamiah. Missoula Flood slack-water deposits cover Lake Bonneville deposits in the Lewiston area. Qbs Lake Bonneville deposits (Pleistocene)--Silt, clay, sand, and gravel deposited in and at margins of former Lake Bonneville (33-11 calibrated ka) and sand and gravel deposited in giant flood bars by outburst floods from the lake (17.4 calibrated ka). The 1575-m (5170 ft) Lake Bonneville shoreline was used to determine the maximum extent of the lake deposits. Flood deposits follow Bonneville flood path from near Downey and the Portneuf River westward along the Snake River. They include sand and silt deposited in slack-water areas to 740 m (2430 ft) elevation in the Boise, Weiser, Payette, and Snake river drainages. Qg Glacial deposits (Pleistocene)--Till and outwash consisting of gravel, sand, silt, and clay. Formed by valley glaciers at higher elevations and by the Cordilleran ice sheet in northern Idaho. Includes deposits of several glacial episodes. Includes rock glacier deposits and some modern alluvium derived from reworked till and outwash. Qs Fluvial and lake sediment (Quaternary)--Largely fine-grained sediment, in part playa deposits of evaporative lakes; includes Snake River Group, and Bruneau Formation in central Snake River Plain and glacial lake deposits in Bonners Ferry area of northern Idaho. Also includes travertine and tufa northeast of Bancroft and Lake Thatcher sediments in the Gem Valley south of Grace. QUATERNARY TO EOCENE CONTINENTAL VOLCANIC AND INTRUSIVE ROCKS Qb Basalt (Quaternary)--Flows and cinder cones of olivine tholeiite basalt and minor latite and alkaline basalt less than 15 ka; includes Shoshone, Craters of the Moon, Wapi, Cerro Grande, and Hells Half Acre lava fields. Little or no loess cover. Qr Rhyolite (Pleistocene)--Rhyolite tuffs, flows, and domes; includes Yellowstone Group (2.0-0.6 Ma) and isolated domes on Snake River Plain and north of Soda Springs (less than 2.0 Ma). QTb Basalt (Pleistocene and Pliocene)--Flows and cinder cones of olivine tholeiite basalt in and near Snake River Plain. Largely Pleistocene (<2.6 Ma) but includes flows as old as 3 Ma. Covered with 1-3 m (3-10 ft) of loess. Tpmr Rhyolite (Pliocene and Miocene)--Rhyolite tuffs and flows of Heise volcanic field (6.6-4.5 Ma; includes Blacktail Creek, Walcott, Conant Creek, and Kilgore tuffs), and rhyolite domes and flows of Magic Reservoir area (6.6-3 Ma). Tpmb Basalt (Pliocene and Miocene)--Flows and cinder cones of olivine tholeiite basalt, and shallow basalt intrusives (~15-3 Ma); includes basalt in Owyhee County and southwest of Twin Falls, basalt of Weiser (basalt to andesite), basalt of Cuddy Mountain (alkali basalt and picro-basalt) north of Cambridge, basalt in Mount Bennett Hills north of Gooding, andesite at Square Mountain near Magic Reservoir, and Cub River diabase sill east of Preston. Includes gabbro at depth in cross section D-D?-D?. Tmr Rhyolite (Miocene)--Rhyolite tuffs and flows (14-8 Ma); includes Juniper Mountain volcanic center, tuff of Little Jacks Creek, Cougar Point Tuff, Fir Grove Tuff, and Arbon Valley Tuff Member of Starlight Formation.. Volcanic sources include Owyhee-Humboldt (13.8-12.0 Ma), Bruneau-Jarbidge (12.5-11.3 Ma), Twin Falls (10.0-8.6 Ma), and Picabo (10.2 Ma) volcanic centers. Tmfo Older rhyolite, latite, and andesite (Miocene)--Rhyolitic domes and tuffs, and subordinate latite flows (17-14 Ma); includes rhyolites of Silver City and tuff of Flint Creek in the Owyhee Mountains and rhyolite of Timber Butte northeast of Emmett. Tcr Columbia River Basalt Group (Miocene)--Large-volume lava flows of tholeiitic basalt, basaltic andesite, and subordinate andesite in western Idaho; consists of Imnaha Basalt (17.5-16.5 Ma), Grande Ronde Basalt (16.5-15.6 Ma), Wanapum Basalt (15.6-14.5 Ma), and Saddle Mountains Basalt (14.5-6 Ma). Includes porphyritic basalt and basaltic andesite in western Owyhee County. Tov Volcanic rocks (Oligocene)--Alkali olivine basalt and trachyte of the ~26 Ma Potlatch volcanics; basalt, andesite, and rhyolite of the ~32 Ma Kamiah volcanics; and olivine basalt and andesite of the 26-31 Ma Salmon Creek volcanics southwest of Nampa. Toi Granite (Oligocene)--Biotite, muscovite-biotite, and muscovite granite of the Almo pluton (29 Ma) at City of Rocks National Reserve and Castle Rocks State Park southeast of Oakley. QUATERNARY TO EOCENE CONTINENTAL SEDIMENTS AND SEDIMENTARY ROCKS QTs Sediments and sedimentary rocks (Pleistocene and Pliocene)-Older gravel, sand, and silt deposited in fans, streams, and lakes. Includes older terrace gravels and Tuana Gravel northwest of Twin Falls. QTpms Sedimentary rocks associated with Basin and Range extension (Quaternary, Pliocene, and Miocene)--Fluvial, fan, and lacustrine deposits and intercalated volcanic rocks of the Basin and Range Province (~16-2 Ma); consolidated to weakly consolidated sandstone, siltstone, arkose, conglomerate, mudstone, tuffaceous sediment, basalt, basaltic tephra, and rhyolite tuff. Includes deposits of Lake Idaho (Idaho Group) in western Snake River Plain and Salt Lake Formation deposited in Basin and Range Province of eastern Idaho. Tms Sedimentary rocks associated with flood basalts (Miocene)--Fluvial and lacustrine deposits associated with Columbia River Basalt Group and equivalent basalts (17-8 Ma); consolidated to weakly consolidated sandstone, siltstone, arkose, conglomerate, claystone, and tuffaceous sediment; subordinate intercalated basalt and rhyolitic tuff. Includes Payette and Sucker Creek formations in southwestern Idaho, sediments associated with basalt of Weiser in western Idaho, and Latah Formation in northern Idaho. Includes sediment of uncertain origin in extreme southwestern Idaho. Toes Sedimentary rocks and sediments (Oligocene and Eocene)--Fluvial and lacustrine deposits; includes conglomerate, sandstone, and shale near Salmon; Pass Creek Gravel, Wet Creek Gravel, and Donkey Fanglomerate north of Mackay; Medicine Lodge beds of southern Beaverhead Mountains; and isolated deposits in northern Idaho. EOCENE CHALLIS MAGMATIC COMPLEX AND RELATED SEDIMENTARY ROCKS Tes Sedimentary rocks (Eocene)--Fluvial, lacustrine, and air-fall deposits of conglomerate, volcanic sandstone, mudstone, and tuff near Challis, conglomerate north of Sandpoint, and conglomerate and sandstone of the Wasatch Formation in extreme southeastern Idaho. Tcv Challis Volcanic Group (Eocene)--Dacite, andesite, and rhyolite tuffs and flows; subordinate basalt and latite flows; covers large area in south-central Idaho. Includes Absaroka Volcanic Group near Henrys Lake and scattered volcanic rocks in eastern and northern Idaho. Tei Challis intrusive rocks (Eocene)--Shallow roots of Challis volcanic field. Older suite of granodiorite and quartz monzodiorite and subordinate diorite, granite, and subvolcanic dacite; includes Jackson Peak, Beaver Creek, Marsh Creek, and Summit Creek stocks (49-45 Ma). Younger suite of granite and minor syenite and subvolcanic rhyolite; includes Sawtooth, Casto, Bungalow, and Lolo Hot Springs plutons (47-43 Ma). CRETACEOUS IDAHO BATHOLITH AND OLDER JURASSIC AND CRETACEOUS INTRUSIVE ROCKS TKg Granodiorite and granite (Paleocene and Cretaceous)--Granodiorite and granite containing biotite and local muscovite (66-54 Ma); composes northern (Bitterroot) lobe of batholith and is ~20 Ma younger than southern (Atlanta) lobe. Kg Granodiorite and two-mica granite (Cretaceous)--Granodiorite and granite containing biotite, commonly with muscovite; includes bulk of Atlanta lobe (85-67 Ma) and isolated plutons in northern Idaho (107-67 Ma). Kog Tonalitic orthogneiss and foliated granodiorite (Cretaceous)--Orthogneiss (primarily tonalite) and foliated granodiorite (~90 to ~80 Ma). Includes early phases of the Idaho batholith, migmatite, intrusions along major structures, and plutonic rocks of uncertain age along the Salmon River northwest of Salmon. Ktg Tonalite, granodiorite, and quartz diorite (Cretaceous)--Tonalite, granodiorite, and quartz diorite, typically hornblende-bearing; includes the Payette River tonalite (~90 Ma) along western border zone of the Atlanta lobe, and the ~99 Ma Croesus pyroxene-biotite quartz diorite south of Hailey. Also includes granodiorite with potassium feldspar megacrysts that is typically hornblende-bearing and foliated (~90 Ma in central Idaho and ~100 Ma in northernmost Idaho) and early mafic phases of the Bitterroot lobe (~70 Ma). KJmp Mylonitic plutonic rocks along the Salmon River suture (Cretaceous and Jurassic)--Granodiorite, tonalite, and quartz diorite; includes Little Goose Creek complex northwest of McCall dominated by porphyritic granodiorite (~105 Ma) and subordinate 87-160 Ma tonalite and quartz diorite. Kis Syenite and related rocks (Cretaceous)--Syenite, monzonite, quartz monzonite, and subordinate pyroxenite (115-110 Ma); includes Gem stocks north of Wallace, Gold Hill stock northeast of Potlatch, Benning Mountain stock along the Montana-Idaho border east of Sandpoint, syenite of Wall Mountain north of Bonners Ferry, and monzonite of Long Canyon (uncertain age) northwest of Bonners Ferry. Ji Tonalite, hornblendite, and gabbro (Jurassic)--Tonalite in upper part of House Mountain metamorphic complex southeast of Boise (~157 Ma), hornblendite and gabbro at South Mountain southwest of Boise (~160 Ma), and tonalite of Continental Mountain at the Canadian border (~168 Ma). MESOZOIC-PALEOZOIC ROCKS OF THE BLUE MOUNTAINS ISLAND ARC COMPLEX Ktt Tonalite and trondhjemite (Cretaceous)--Biotite- and hornblende-biotite tonalite and biotite-muscovite trondhjemite (120-110 Ma); rocks contain conspicuous magmatic epidote in plutons along eastern edge of arc complex. Includes tonalitic part of Hazard Creek complex northwest of McCall, Blacktail pluton southeast of Grangeville, and Sixmile Creek pluton southeast of Orofino. KJqd Quartz diorite (Cretaceous and Jurassic)--Primarily quartz diorite, with subordinate diorite, gabbro, granite, and amphibolite; largely undeformed except near eastern part of Blue Mountains island arc complex; wide age range (160-90 Ma). KPro Riggins Group, Orofino series, and related rocks (Cretaceous to Permian)--Metasedimentary and metavolcanic schist, gneiss, amphibolite, and marble, all of uncertain age, along eastern margin of island arc complex; typically hornblende-rich. Includes Pollock Mountain amphibolite southeast of Riggins, and gneiss of Swiftwater Creek near Lowell. KJcw Coon Hollow and Weatherby formations (Cretaceous and Jurassic)--Marine mudstone and subordinate conglomerate and sandstone of the Coon Hollow Formation south of Lewiston and turbiditic sandstone, mudstone, volcanic conglomerate, and andesite and rhyolite tuff of the Weatherby Formation north of Weiser. JT_sv Sedimentary and volcanic rocks (Jurassic and Triassic)--Marine limestone and marble of the Martin Bridge Formation and calcareous mudstone and phyllite of the Hurwal Formation exposed west of Riggins and south of Lewiston; basaltic andesite, rhyolite tuff (~202 Ma), and conglomerate along Salmon River southwest of Grangeville; and rhyolite tuff at Pittsburg Landing (~198 Ma). JT_of Olds Ferry terrane (Jurassic and Triassic)--Basaltic to rhyolitic (largely intermediate) arc volcanic and volcaniclastic rocks of the Huntington Formation; includes minor chert and limestone. T_Pi Intrusive rocks (Triassic and Permian)--Diorite, tonalite, granodiorite, gabbro, norite, quartz diorite, and trondhjemite; basement of, and feeders to, volcanic rocks in Seven Devils Group (Wallowa terrane) and Olds Ferry terrane. T_Psd Seven Devils Group (Triassic and Permian)--Basaltic to rhyolitic (largely mafic) arc volcanic and volcaniclastic rocks of the Wallowa terrane; includes minor limestone. Composed of Windy Ridge, Hunsaker Creek, Wild Sheep Creek, and Doyle Creek formations. MzPzb Baker Terrane (Paleozoic and Mesozoic)--Massive and ribbon chert, phyllite, argillite, cherty limestone, and limestone deposited in relatively deep water (forearc basin?). PALEOCENE TO NEOPROTEROZOIC SEDIMENTARY AND IGNEOUS ROCKS OF THE CORDILLERAN SYSTEM TKs Sedimentary rocks (Paleocene and Cretaceous)--Fluvial conglomerate and sandstone of the Beaverhead Formation northwest of Dubois. Ks Sedimentary rocks (Cretaceous)--Marine and deltaic sandstone and shale of Cordilleran foreland basin (Gannett Group, Frontier, Mowry, Kootenay and Thermopolis formations) in eastern Idaho thrust belt. Js Sedimentary rocks (Jurassic)--Marginal marine and marine sandstone and limestone; includes Nugget, Twin Creek, Preuss, Morrison, and Stump formations in eastern Idaho thrust belt. T_s Sedimentary rocks (Triassic)--Red mudrock and fine-grained sandstone and marine limestone; includes Dinwoody, Woodside, Thaynes, and Ankareh formations in eastern Idaho thrust belt. PMs Sedimentary rocks (Permian to Mississippian)--Only shown in Henrys Lake area and in cross section. Consists of Ms and PlPs. PlP_s Sedimentary rocks (Permian and Pennsylvanian)--Marine phosphorite, shale, and chert of Phosphoria Formation, fine-grained sandstone and mudrock of Wells, Quadrant, Amsden, and Shedhorn formations, and fine-grained sandstone, carbonaceous mudstone, and limestone of the Snaky Canyon Formation and Sun Valley and Oquirrh groups. Located in south-central and eastern Idaho. Ms Sedimentary rocks (Mississippian)--Marine limestone of Mississippian carbonate banks and turbiditic sandstone, mudstone, and conglomerate of Antler flysch trough; includes Madison and Lodgepole formations and Chesterfield Range Group of southeastern Idaho, McGowan Creek Formation, White Knob Limestone, and overlying carbonate bank of Lost River Range, and Copper Basin Group of Pioneer Mountains. Includes poorly dated Salmon River assemblage east of Stanley, consisting of argillite, siltstone, calcareous sandstone, and limestone. DCs Sedimentary rocks (Devonian to Cambrian)--Only shown in Henrys Lake area and in cross section. Consists of OCs and DSOs. DSOs Sedimentary rocks (Devonian to Ordovician)--Marine dolostone and limestone and quartz arenite sandstone in east-central and southeastern Idaho (Summerhouse, Kinnikinic, and Swan Peak sandstones, Fish Haven, Laketown, Jefferson, Three Forks, and Darby formations) and deep-water carbonaceous mudrocks of Phi Kappa, Trail Creek, and Milligen formations east of Ketchum. OCi Syenitic intrusive rocks (Ordovician and Cambrian)--Syenite, quartz syenite, alkali-feldspar granite, and subordinate gabbro (500-485 Ma) including Beaverhead, Arnett Creek, Deep Creek, and Yellowjacket plutons southeast and west of Salmon. OCs Sedimentary rocks (Ordovician and Cambrian)--Marine limestone, dolomite, and subordinate shale and sandstone of Cambrian carbonate bank of southeast Idaho stratigraphically up to St. Charles Formation and Ordovician Garden City Limestone. Includes Bayhorse succession (Cash Creek Quartzite, Garden Creek Phyllite, Bayhorse Dolomite, Ramshorn Slate, and Clayton Mine Quartzite) of Clayton area and Pioneer Mountains, quartzite of Kamiak Butte north of Moscow, and Cambrian Gold Creek quartzite, Rennie Shale, and Lakeview Limestone east of Bayview. CZs Windermere Supergroup (Neoproterozoic and Cambrian)-Upper part consists of shallow marine and fluvial quartzose sandstone, and minor siltite, shale, and limestone of the Brigham Group of southeast Idaho, Wilbert Formation of east-central Idaho, and quartzites of unknown affinity west of Borah Peak. More highly metamorphosed equivalents are quartzite, metaconglomerate, metasiltite, calc-silicate marble, and schist of Gospel Peaks successions C and D in central Idaho, clean quartzite, biotite schist, and minor calc-silicate rocks of Syringa metamorphic sequence east of Moscow, and schist and quartzite in the Albion Range (Elba Quartzite, schist of Upper Narrows, quartzite of Yost, schist of Stevens Spring, quartzite of Clarks Basin, schist of Mahogany Peaks, and Harrison Summit Quartzite). Lower part consists of diamictite, immature sandstone, and bimodal volcanic rocks related to continental rifting. Includes Pocatello Formation (700-665 Ma), formation of Leaton Gulch near Challis, Shedroof Conglomerate in extreme northwest Idaho, and metamorphic equivalents (schist, marble, calc-silicate rocks, metaconglomerate, and metavolcanic rocks) of Gospel Peaks successions A and B in central Idaho. Zi Intrusive rocks (Neoproterozoic)--Syenite and diorite of the Acorn Butte, Ramey Ridge, and Rush Creek stocks along Big Creek northeast of McCall (665-650 Ma), and ~726 Ma granitic gneiss in lower part of House Mountain metamorphic complex southeast of Boise. METASEDIMENTARY ROCKS OF UNCERTAIN AGE (NEOPROTEROZOIC TO PALEOPROTEROZOIC) PzYs Metasedimentary rocks (Paleozoic to Mesoproterozoic)--Quartzite, feldspathic quartzite, calc-silicate gneiss, biotite gneiss, schist, and amphibolite north and east of McCall and as pendants in the southern part of the Idaho batholith; schist, quartzite, and marble in southwestern Idaho; argillite, siltite, quartzite, carbonate-bearing quartzite, dolomite, phyllite, and conglomerate of the Deer Trail Group in northwest corner of state; and quartzite, Hayden Creek diamictite, and siltite and stratigraphically above the Swauger Formation south of Salmon. ZXs Metasedimentary rocks (Neoproterozoic to Paleoproterozoic)--Schist, gneiss, and subordinate quartzite along North Fork Clearwater River and in the Pioneer Mountains. Includes small exposures of 695 Ma orthogneiss in the Pioneer Mountains. MESOPROTEROZOIC INTRUSIVE ROCKS Yag Augen gneiss (Mesoproterozoic)--Biotite granite and granitic augen gneiss near Elk City and northwest of Salmon (~1380 Ma). Abundant alkali feldspar and high iron content indicate A-type granite composition. Yam Amphibolite (Mesoproterozoic)--Amphibolite formed from metamorphism of mafic sills; includes rocks northwest of Salmon (~1380 Ma) and east of Elk City. MESOPROTEROZOIC BELT SUPERGROUP AND RELATED METASEDIMENTARY ROCKS Ymiu Upper Missoula Group (Mesoproterozoic)--Feldspathic quartzite and subordinate siltite and argillite. Includes Mount Shields, Bonner, Striped Peak, and Libby formations in northern Idaho and possibly correlative quartzite north of Salmon and in the Meadow Creek metamorphic sequence east of Elk City. Ymil Lower Missoula Group (Mesoproterozoic)--Siltite, argillite, and dolomitic siltite in northern Idaho; includes Snowslip and Shepard formations, rocks previously mapped as upper member of Wallace Formation, and correlative garnet-grade phyllite and schist south of St. Joe River. Also includes schist, micaceous quartzite, and calc-silicate rocks in lower part of Meadow Creek metamorphic sequence east of Elk City and argillite, siltite, phyllite, and calc-silicate rocks south of Lost Trail Pass. Ypi Piegan Group (Mesoproterozoic)--Calcareous and dolomitic siltite, quartzite, and subordinate argillite of the Helena and Wallace formations in northern Idaho; south of St. Joe River correlative rocks include garnet-grade feldspathic quartzite and calc-silicate gneiss. Yra Ravalli Group (Mesoproterozoic)--Feldspathic quartzite and subordinate siltite and argillite of the Burke, Revett, and St. Regis formations in northern Idaho; south of St. Joe River includes correlative garnet-grade quartzite and schist. Yp Prichard Formation (Mesoproterozoic)--Siltite, quartzite, and argillite in northern Idaho; deposited in deep water and contains voluminous ~1470 Ma mafic sills. Includes siltite, quartzite, fine-grained schist, and carbonate rocks structurally above anorthosite near Boehls Butte, northeast of Elk River. Ygs Gneiss, schist, and quartzite (Mesoproterozoic)--Kyanite and sillimanite gneiss, schist, quartzite, and amphibolite that is metamorphosed lower part of Prichard Formation (Hauser Lake Gneiss) and underlying quartzite of Gold Cup Mountain in the Priest River metamorphic complex. MESOPROTEROZOIC METASEDIMENTARY ROCKS OF LEMHI SUBBASIN OF BELT SUPERGROUP Yhs Swauger and Lawson Creek formations and Hoodoo Quartzite (Mesoproterozoic)--Quartzose medium- to coarse-grained quartzite of Swauger Formation and calcareous siltite and quartzite of overlying Lawson Creek Formation in east-central Idaho. Includes Hoodoo Quartzite west of Salmon whose stratigraphic relationship to the Swauger is uncertain. Yly Lemhi Group and Yellowjacket Formation (Mesoproterozoic)--Feldspathic fine-grained quartzite and siltite and subordinate argillite and carbonate-bearing rocks in east-central Idaho; includes West Fork, Inyo Creek, Big Creek, and Gunsight formations. Includes Yellowjacket Formation west of Salmon whose stratigraphic relationship to the Lemhi Group is uncertain, but which is stratigraphically below the Hoodoo Quartzite . Ym Gneissic and schistose metasedimentary rocks (Mesoproterozoic)--Biotite-rich paragneiss and schist, and subordinate feldspathic quartzite and calc-silicate rocks. Probably metamorphosed western facies of Lemhi subbasin. Characterized by igneous suite of Yam and Yag . Includes Elk City metamorphic sequence, and metamorphic rocks east of Moscow, along Salmon River northwest of Salmon, and in Pioneer Mountains. Yq Quartzitic metamorphic rocks (Mesoproterozoic)--Feldspathic quartzite and subordinate schist and calc-silicate rocks of central Idaho. Includes the Golden metamorphic sequence east of Grangeville that is probably metamorphosed western facies of Lemhi subbasin. MESOPROTEROZOIC TO ARCHEAN BASEMENT ROCKS Yagl Laclede augen gneiss (Mesoproterozoic)--Biotite granite augen gneiss southeast of Priest River (~1575 Ma). Unit is in structural contact with surrounding rocks. Abundant alkali feldspar and high iron content indicate A-type granite composition. Xan Anorthosite (Paleoproterozoic)--Metamorphosed anorthosite at Boehls Butte northeast of Elk River (~1787 Ma). Unit is in structural contact with overlying rocks of the Prichard Formation. Xog Orthogneiss (Paleoproterozoic)--Biotite tonalite gneiss and hornblende-biotite tonalite gneiss (~1870 Ma) north of North Fork of Clearwater River, and south of Coeur d'Alene. XAm Metamorphic rocks (Paleoproterozoic and Archean)--Pend Oreille granodiorite gneiss near Priest River (~2650 Ma); Kelly Creek granite gneiss northeast of Pierce (~2670 Ma); orthogneiss in Pioneer Mountains (~2600 Ma); granite gneiss, granite, schist, and amphibolite of Green Creek complex in Albion Mountains (~2600 Ma); granite gneiss in Beaverhead Mountains east of Leadore (~2450 Ma); and marble, quartzite, schist, and amphibolite of uncertain age near Henrys Lake.
Geologic map of Idaho, by Reed S. Lewis, Paul K. Link, Loudon R. Stanford, and Sean P. Long