DESCRIPTION OF MAP UNITS SEDIMENTARY AND VOLCANIC ROCKS .129 Qs Surficial deposits (Quaternary)--Alluvium in stream channel, flood plain, and terrace deposits; talus, colluvium, landslide deposits, rock glaciers, and glacial deposits (till, outwash, and glacial lake deposits) .131 Qt Travertine (Quaternary) .102 Qy Lava Creek Tuff of Yellowstone Group (Pleistocene)--Rhyolitic ash-flow tuff in Gardiner Area .56 Qb Basalt (Pleistocene)--Basalt flows in Gardiner area .98 Tv Absaroka Volcanic Supergroup (Eocene)--Volcanic and volcaniclastic rocks including basaltic, andesitic, and dacitic flows and flow breccias, rhyolitic ash-flow tuff and vitrophyre, tuff breccias, lahars, agglomerates, agglutinates, conglomerate, and minor andesitic and dacitic intrusive bodies .79 Tf Fort Union Formation (Paleocene and Late Cretaceous)--Conglomerate, sandstone and shale .381 Kal Andesite (Late Cretaceous)--Lava flows in Sliderock Mountain area .376 Kll Lahars of Livingston Group (Late Cretaceous)--Lahar deposits; mostly clast-supported; minor intercalated ash-flow tuff, lava flows, and flow breccias and epiclastic conglomerate, sand- stone, siltstone, and mudstone .164 Klc Sedimentary rocks of Livingston Group (Late Cretaceous)--Epiclastic conglomerate, sandstone, siltstone, and mudstone .28 Kad Andesite (Late Cretaceous)--Lava flows and flow breccias; at or near base of Livingston Group .166 Kus Sedimentary rocks (Late Cretaceous)--Includes Eagle Sandstone, Telegraph Creek Formation, Cody Shale, Frontier Formation, and Montana Formation; sandstone and shale .174 Kls Sedimentary rocks (Early Cretaceous)--Includes Mowry Shale, Thermopolis Shale, Kootenai Formation, and Cloverly Formation; sandstone, shale, limestone, and conglomerate .170 Ku Sedimentary rocks (Early and Late Cretaceous)--Sandstone, shale, limestone, and conglomerate .227 JTRs Sedimentary rocks (Jurassic and Triassic)--Includes Morrison Formation, Ellis Group, and Chugwater Formation; sandstone, shale, and limestone .309 PMs Sedimentary rocks (Permian, Pennsylvanian, and Mississippian)--Includes Phosphoria, Quadrant, and Amsden Formations and Madison Group; limestone, shale, sandstone, and dolomite .232 DOs Sedimentary rocks (Devonian and Odovician)--Includes Three Forks Shale, Jefferson Formation, and Bighorn Dolomite; shale, limestone, and dolomite .101 OCs Sedimentary rocks (Ordovician and Cambrian)--Includes Bighorn Dolomite, Grove Creek Formation, Snowy Range Formation, Pilgrim Limestone, Park Shale, Meagher Limestone, Wolsey Shale, and Flathead Sandstone; dolomite, limestone, sandstone, siltstone, and shale .40 Cs Sedimentary rocks (Cambrian)--Includes Grove Creek Formation, Snowy Range Formation, Pilgrim Limestone, Park Shale, Meagher Limestone, Wolsey Shale, and Flathead Sandstone; limestone, sandstone, siltstone and shale .308 Pz Undifferentiated sedimentary rocks (Paleozoic) INTRUSIVE ROCKS AND BRECCIA PIPES (TERTIARY AND CRETACEOUS) .374 Ti Intermediate and felsic rocks (Eocene)--Dikes, sills, and irregular- shaped bodies; andesite, quartz latite, dacite, and rhyolite; commonly porphyritic .34 Tlp Rhyolite porphyry of Lulu Pass (Eocene)--Laccolith and dikes .31 Tbh Breccia of Homestake mine area (Eocene)--Explosion-collapse breccia pipe composed of blocks of Cambrian sedimentary rocks, porphyritic intrusive rocks, volcanic rocks, and Precambrian gneissic rocks in chloritic matrix; altered and mineralized; intruded by later dikes of rhyolite and quartz latite porphyry .61 Tba Breccia of Alice E mine area (Eocene)--Collapse(?) breccia composed of blocks of Cambrian sedimentary rocks in a pulverized rock- flour matrix; locally altered and mineralized; intruded by later dikes of quartz latite porphyry .30 Thm Rhyolite porphyry of Henderson Mountain (Eocene)--Stock and dike .81 Th Rhyolite porphyry of Homestake mine area (Eocene)--Stock, sills, dikes, and irregular bodies; contains abundant rounded, commonly embayed, quartz phenocrysts; commonly altered and locally mineralized .33 Tfm Complex of Fisher Mountain area (Eocene)--Stock(?) composed of felsite, felsite breccia, and rhyolite porphyry; intruded by rhyolite porphyry and aphanitic dikes; strongly feldspathized, silicified, sericitized and (or) argillitized, and pyritized .32 Tsb Diorite of Scotch Bonnet Mountain (Eocene)--Stock and irregular-shaped intrusive bodies .7 Ta Andesite and trachyandesite porphyry (Eocene)--Sills in Cooke City area .373 Tgr Granodiorite porphyry of Emigrant area (Eocene)--Stock near head of Emigrant Creek .375 Tdp Dacite porphyry (Eocene)--Stock, laccoliths, sills, dikes, plugs and irregular-shaped bodies; includes some andesitic and rhyolitic rocks .371 Tdi Diorite porphyry and basaltic andesite (Eocene)--Small stock (or plug) at head of Mill Creek and plugs northwest of Cooke City .66 Tmz Monzodiorite of Independence area (Eocene)--Stock composed of multiple phases of andesitic intrusive breccia, monzodiorite, and quartz monzodiorite and quartz monzonite; cut by minor granite dikes .377 TKi Intermediate and felsic intrusive rocks (Tertiary or Late Cretaceous)-- Laccoliths, plugs, dikes, sills, and irregular-shaped bodies of fine-grained and porphyritic rhyolite, dacite, quartz latite, andesite, and diorite .390 Ka Andesite (Late Cretaceous)--Dikes in Sliderock Mountain area .328 Kd Diorite of Sliderock Mountain (Late Cretaceous)--Stock, variable grain size and textures may indicate multiple phases; locally altered .182 Ki Rhyolite and quartz latite porphyry (Late Cretaceous)--Sills, dikes, and irregular-shaped bodies in Goose Lake area .6 Kgl Syenite of Goose Lake (Late Cretaceous)--Stock composed of multiple phases of syenite and monzonite of variable grain sizes and textures; locally altered and mineralized .270 d Intermediate and mafic intrusive rocks (Eocene and Precambrian)--Dikes and sills of andesite and basalt INTRUSIVE ROCKS (PRECAMBRIAN) .305 mi Mafic intrusive rocks (Archean and Proterozoic)--Includes sills, dikes, stock, and irregular-shaped bodies of alkali olivine dolerite, metadolerite, metanorite, metagabbro, and quartz dolerite and dikes of uncertain or unknown affinities .359 Ahd Hornblende quartz diorite (Archean)--Small bodies associated with quartz monzonite of Stillwater area .147 Agr Granitic intrusive rocks (Archean)--Includes stocks and irregular-shaped bodies of fine-, medium-, and coarse-grained quartz monzonite and aplite of the Stillwater area and of granite in the Gardiner area Stillwater Igneous Complex (Archean)--Stratiform mafic to ultramafic rocks; divided into seven units as follows: .343 Asw7 Upper mixed, upper gabbro, and upper anorthosite zones .344 Asw6 Middle anorthosite zone .345 Asw5 Lower mixed, middle gabbro, and middle mixed zones .346 Asw4 Lower anorthosite zone .347 Asw3 Norite and lower gabbro zones .348 Asw2 Bronzitite zone .349 Asw1 Peridotite zone .355 An Metanorite and metagabbro (Archean)--Stock .11 Agn Granitic gneiss (Archean)--Predominantly granitic gneiss and migmatite; commonly consists of alternating bands of more felsic and more mafic gneiss; contains inclusions of metasedimentary and metaigneous rocks .360 Au Ultramafic rocks (Archean)--Irregular-shaped bodies and lenses of olivine-bearing rocks and serpentinite METASEDIMENTARY AND METAIGNEOUS ROCKS (PRECAMBRIAN) .83 As Biotite schist (Archean)--Includes minor quartzite, iron formation, and amphibolite .132 Aag Amphibolite and hornblende gneiss (Archean)--Mostly tabular and lensoid bodies enclosed in granitic gneiss and migmatite .156 Aga Amphibolite and gneiss (Archean)--Includes trondhjemitic gneiss- amphibolite, paragneiss, and heterogeneous gneiss sequences; trondhjemitic gneiss, tonalitic gneiss, amphibolite; minor schist, quartzite, and iron formation .144 Anc Nappe core complex (Archean)--Includes Barney Creek Amphibolite, George Lake Marble, and Jewel Quartzite; amphibolite, dolomitic marble and marble, and quartzite; minor schist and iron formation .146 Aqa Quartzite and amphibolite (Archean)--Interlayered quartzite and orthoamphibolite; minor schist .118 Ash Schist and hornfels (Archean)--Metasedimentary rocks consisting predominantly of schist and hornfels with minor quartzite, amphibolite, and iron formation; contact metamorphosed to hornblende-hornfels and pyroxene-hornfels facies at and near the base of the Stillwater Igneous Complex; host for Homestake-type gold deposits near Jardine .90 Am Undifferentiated metamorphic rocks (Archean)--Includes amphibolite, micaeous quartzite, and some gneiss. Also includes some small bodies of chromite-bearing serpentinite EXPLANATION OF MAP SYMBOLS CONTACT--Dashed where approximately located or inferred; dotted where concealed FAULT--Dashed where aproximately located or inferred; dotted where concealed. Bar and ball on downthrown side. U indicates upthrown side; D indicates downthrown side. MYLONITIC SHEAR ZONE TRACE OF SURFACE OF TECTONIC DENUDATION OF HEART MOUNTAIN DETACHMENT--Dashed where approximately located This surface occurs near Cooke City within the map area. THRUST FAULT--Dashed where approximately located or inferred; dotted where concealed. Sawteeth on upper plate TRACE OF AXIAL PLANE OF MAJOR ANTICLINE TRACE OF AXIAL PLANE OF MAJOR SYNCLINE