OBJECTID|DescriptionOfMapUnits_ID|Category|Type|Symbol|Label|MapUnit|Name|FullName|Age|AgeType|AgeOldest|AgeYoungest|Description|HierarchyKey|ParagraphStyle|AreaFillRGB|AreaFillPatternDescription|GeoMaterialDictID|GeoMaterial|GeoMaterialConfidence|Notes|DataSourceMethod|DescriptionSourceID|created_user|created_date|last_edited_user|last_edited_date|GlobalID
|1|{D31EA4F8-D6A7-47F5-8715-1E96A7F1AE08}|map unit|map unit, generic|0000|md|md|mining dumps|mining dumps|Quaternary: Holocene|unprovided|Holocene|Holocene|Artificial fill composed of excavated, transported, processed, and emplaced rock and gravel. Consists mainly of dredged placer workings and dumps from lode mines.|01-01|dmu, map unit|255,255,255|217-K|{5B6BE598-6C3E-40CD-9082-7EF21AD7BF1D}|"Made" or human-engineered land|high||997|DAS01|||||{D31EA4F8-D6A7-47F5-8715-1E96A7F1AE08}
2|{BD677AD3-51FB-42AE-8B04-C22EA2D4965B}|map unit|map unit, generic|0010|Qal|Qal|alluvium|alluvium|Quaternary: Holocene|unprovided|Holocene|Holocene|Poorly sorted gravel, sand, silt, and clay along streams and their tributaries. Clasts are generally cobble size and smaller, and are subrounded to rounded. Thickness generally less than 6 m (20 ft).|02-01|dmu, map unit|255,255,222||{EFF14953-918D-4560-87E8-CB91351003C9}|Alluvial sediment, mostly coarse-grained|high||997|DAS01|||||{BD677AD3-51FB-42AE-8B04-C22EA2D4965B}
3|{0C77F988-E1C1-4939-9BF7-E7379C9A4408}|map unit|map unit, generic|AA50|Qac|Qac|alluvium and colluvium|alluvium and colluvium|Quaternary: Holocene|unprovided|Holocene|Holocene|Gravel, sand, and silt deposited by sheetwash alluvium and incorporated with locally derived colluvium. Commonly deposited in ephemeral stream drainages. Thickness generally less than 6 m (20 ft).|02-02|dmu, map unit|235,235,128||{EFF14953-918D-4560-87E8-CB91351003C9}|Alluvial sediment, mostly coarse-grained|medium||997|DAS01|||||{0C77F988-E1C1-4939-9BF7-E7379C9A4408}
4|{CAD0789D-31F5-4722-8A5A-04FE28B8D99A}|map unit|map unit, generic|0060|Qta|Qta|talus|talus|Holocene and Pleistocene|unprovided|Holocene|Pleistocen|Unconsolidated, locally derived, apron-like deposits with angular clasts on and below steep slopes. Includes some rock-slide deposits. Variable thickness, generally less than 10 m (33 ft).|02-03|dmu, map unit|255,255,102||{743EA93E-C344-4316-A975-A09F39CC0243}|Debris flows, landslides, and other localized mass-movement sediment|high||997|DAS01|||||{CAD0789D-31F5-4722-8A5A-04FE28B8D99A}
5|{3F7A37E4-A9FD-4950-965C-8A7D49296487}|map unit|map unit, generic|AA70|Qls|Qls|landslide deposit|landslide deposit|Quaternary: Holocene|unprovided|Holocene|Holocene|Unstratified, poorly sorted rock fragments deposited by slumps, slides, and debris flows. Typically characterized by hummocky topography and subdued landslide scarps. Most common in Cretaceous volcanic and Tertiary sedimentary deposits. Variable thickness, generally less than 30 m (100 ft).|03-01|dmu, map unit|235,235,077||{743EA93E-C344-4316-A975-A09F39CC0243}|Debris flows, landslides, and other localized mass-movement sediment|high||997|DAS01|||||{3F7A37E4-A9FD-4950-965C-8A7D49296487}
6|{3F4261FE-154D-45A6-838A-DE2A59CFCB46}|map unit|map unit, generic|04X0|Tsc|Tsc|Sixmile Creek Formation, undivided|Sixmile Creek Formation of Bozeman Group|late to middle Miocene|unprovided|middle Miocene|late Miocene|Thin, unconsolidated deposits of subrounded to rounded pebbles and cobbles. Clasts include quartzite derived from the Mesoproterozoic Belt Supergroup, Paleozoic limestone, Paleozoic quartzite, and volcanic and intrusive rock fragments. Clasts are likely recycled from the Beaverhead Group on the basis of rounding and clast composition. Poorly exposed with no discernable bedding or sedimentary structures. Thickness as much as 120 m (400 ft).|04-01|dmu, map unit|255,153,000||{EFF14953-918D-4560-87E8-CB91351003C9}|Alluvial sediment, mostly coarse-grained|medium||997|DAS01|||||{3F4261FE-154D-45A6-838A-DE2A59CFCB46}
7|{55C7C35A-EFB2-46B8-A2DB-DD5B50AE973A}|map unit|map unit, generic|0270|Tml|Tml|Medicine Lodge beds|Medicine Lodge beds|Eocene-Oligocene?|unprovided|Eocene|Oligocene|Poorly consolidated gravel deposits consisting of subangular, pebble to cobble clasts of Mississippian limestone and quartzite. Poorly sorted with no discernable sedimentary structures. Thickness unknown.|04-02|dmu, map unit|255,204,077||{B1E5F115-8FCA-4B05-A257-4AADCD7CCBCD}|Conglomerate|medium||997|DAS01|||||{55C7C35A-EFB2-46B8-A2DB-DD5B50AE973A}
8|{02D13948-DE2E-4BCD-83FF-FB359C2C370B}|map unit|map unit, generic|25A0|Tba|Tba|basalt lavas|basalt lavas|Tertiary: Eocene–Oligocene|unprovided|Eocene|Oligocene|Dark gray to black basaltic lava flows that are slightly porphyritic containing <10 percent phenocrysts of olivine, clino-, and orthopyroxene with occasional plagioclase. In thin section, the groundmass has a trachytic texture consisting of aligned microlites of plagioclase, with some olivine and pyroxene. Thickness less than 30 m (100 ft).|05-01|dmu, map unit|204,128,235||{0EB35B4C-25D4-4CC4-B3F4-84063C5D7F3B}|Mafic-composition lava flows|high||997|DAS01|||||{02D13948-DE2E-4BCD-83FF-FB359C2C370B}
9|{8584EF1F-0A2B-4010-8E3B-82D31563594C}|map unit|map unit, generic|0730|Kms|Kms|McDowell Springs granodiorite|McDowell Springs granodiorite|Late Cretaceous|unprovided|Late Cretaceous|Late Cretaceous|Gray green to brown weathering granodiorite porphyry (63.0–62.6 wt. percent SiO2) containing phenocrysts of plagioclase, pyroxene, biotite, hornblende, and rare quartz in a groundmass of plagioclase and altered mafic microlites with abundant magnetite. Exhibits flow banding and columnar jointing locally, and commonly forms sheet-like bodies up to 300 m thick (985 ft). Weathers to prominent buttes and hoodoos locally. Two samples collected in the adjacent Bannack 7.5' quadrangle yielded U-Pb zircon ages of 71.9 ± 0.7 and 71.8 ± 0.5 Ma (Mosolf, in prep).|06-01|dmu, map unit|255,077,179||{CF5DFA93-4BF2-4B8D-9C5F-FE5ADE0A11B0}|Coarse-grained, intermediate-composition intrusive igneous rock|high||997|DAS01|||||{8584EF1F-0A2B-4010-8E3B-82D31563594C}
10|{8409F747-5B9C-4E6F-A108-1CB87F3FDE44}|map unit|map unit, generic|4770|Kcv|Kcv|Cold Spring Creek volcanic group|Cold Spring Creek volcanic group|Late Cretaceous|unprovided|Late Cretaceous|Late Cretaceous|Complex, intertonguing sequence of porphyritic lava flows, volcanic breccia, and ash-flow tuff. Porphyritic lavas (68.1–61.7 wt. percent SiO2) are generally dark colored and contain crowded phenocrysts of plagioclase, orthopyroxene, clinopyroxene, hornblende, biotite, and quartz in a plagioclase-phyric groundmass with abundant Fe-Ti oxides. Intercalated volcanic breccias commonly occur as massive, greenish gray intervals 3–5 m thick (10–16 ft) composed of poorly sorted, subrounded to subangular clasts of andesite–dacite porphyry. Discontinuous tuff interbeds 2–10 m thick (6–33 ft) contain broken phenocrysts of plagioclase, hornblende, rare quartz, and accidental volcanic clasts in a eutaxitic groundmass of devitrified and flattened glass shards. Tuff intervals commonly contain varying amounts of pumice fragments and accidental clasts of porphyry lava. Four samples yielded U-Pb zircon ages spanning 72.6 ± 0.5 to 71.8 ± 0.6 Ma, and three samples collected in the adjacent Bannack 7.5' quadrangle yielded U-Pb ages ranging from 73.1 ± 0.8 to 71.7 ± 0.6 Ma (Mosolf, in prep). Ivy (1988) reported 40Ar/39Ar hornblende ages spanning ~80–76 Ma for this unit. Thickness as much as 490 m (1,600 ft).|06-02|dmu, map unit|153,077,077||{E3EE99C3-9B29-42B9-8B0D-BAA9F18F385C}|Extrusive igneous material|high||997|DAS01|||||{8409F747-5B9C-4E6F-A108-1CB87F3FDE44}
11|{B0EC3C98-8DAA-437D-BAA4-229118518854}|map unit|map unit, generic|5550|Kgt|Kgt|Grasshopper Creek tuff|Grasshopper Creek tuff|Late Cretaceous|unprovided|Late Cretaceous|Late Cretaceous|White, light gray, yellowish gray, and pale red deposits of thin-bedded, vitric tuff and massively bedded, crystal-lithic rhyolite tuff. Contains varying proportions of sanidine, quartz, and plagioclase crystals, and accidental fragments of volcanic and sedimentary rock in a matrix of glass shards that are mostly zeolitized and silicified. Commonly exhibits compaction foliation formed by the collapse of pumice fragments; strongly welded intervals occur locally. A sample collected in the Eli Spring 7.5' quadrangle yielded a U-Pb zircon age of 74.7 ± 1.2 Ma, and a sample collected in the adjacent Bannack quadrangle yielded a U-Pb age of 73.3 ± 0.6 Ma (Mosolf, in prep). Kalakay (2001) reported a SHRIMP U-Pb zircon age of 75.1 ± 1.1 Ma for this unit. Thickness as much as 300 m (1,000 ft).|06-03|dmu, map unit|128,128,128||{88101E09-382A-430B-A876-DB479FDBC22B}|Felsic-composition air-fall tephra|high||997|DAS01|||||{B0EC3C98-8DAA-437D-BAA4-229118518854}
12|{18CE2E0E-0B8A-424F-B83F-4F016B17B9C8}|map unit|map unit, generic|4150|Kbeu|Kbeu|Beaverhead Group, upper|Beaverhead Group|Late Cretaceous—Paleocene?|unprovided|Late Cretaceous|Paleocene?|Poorly lithified, clast-supported conglomerate beds composed of well-rounded and imbricated pebbles and cobbles. Approximately 50–80 percent of conglomerate clasts are red to maroon weathering quartzite derived from the Belt Supergroup and the remainder are Paleozoic limestone, quartzite, chert, and rare dacite–andesite clasts that are deeply weathered. Conglomerate beds are 10–100 cm thick and have tabular and lenticular geometries. Sample ES-14 yielded a broad distribution of detrital zircon ages with prominent peaks at ~360–600 Ma, ~900–2,100 Ma, and ~2,200–2,900 Ma (fig. 2B). While no Cretaceous ages were recovered from sample ES-14, detrital zircon max depositional ages of 65.9 ± 1.3 and 71.6 ± 3.4 Ma were reported for the upper Beaverhead Group in the adjacent Dalys and Bannack 7.5' quadrangles, respectively (Laskowski and others, 2013; Garber and others, 2020). Thickness as much as 400 m (1,300 ft).|07-01|dmu, map unit|153,222,128||{B1E5F115-8FCA-4B05-A257-4AADCD7CCBCD}|Conglomerate|high||997|DAS01|||||{18CE2E0E-0B8A-424F-B83F-4F016B17B9C8}
13|{0897857B-A6A7-4954-8810-0BBCF83EBDB3}|map unit|map unit, generic|51X0|Kbel|Kbel|Beaverhead Group, lower|Beaverhead Group|Late Cretaceous|unprovided|Late Cretaceous|Late Cretaceous|Reddish brown to gray weathering, clast-supported conglomerate consisting of 1–10 m thick (3–33 ft) beds of subangular to rounded pebbles and cobbles. Clasts are mostly derived from Mississippian limestone with some quartzite clasts (<10 percent). Minor interbeds of sandstone are composed primarily of carbonate-cemented, medium- to coarse-grained quartz and chert sand. Underlain by a discontinuous andesite tuff in the adjacent Bannack 7.5' quadrangle that yielded a U-Pb zircon age of 79.3 ± 1.3 Ma (Murphy, 2000; Kalakay, 2001). Laskowski and others (2013) reported a detrital zircon max depositional age of 77.9 ± 1.3 Ma for a sample collected in the Bannack quadrangle. Thickness as much as 900 m (2,950 ft).|07-02|dmu, map unit|128,222,000||{B1E5F115-8FCA-4B05-A257-4AADCD7CCBCD}|Conglomerate|high||997|DAS01|||||{0897857B-A6A7-4954-8810-0BBCF83EBDB3}
14|{8CA22AB0-52D0-4DAF-BC14-D6E2BFFEA885}|map unit|map unit, generic|72X0|Kk|Kk|Kootenai Formation, undivided|Kootenai Formation|Late Cretaceous|unprovided|Late Cretaceous|Late Cretaceous|Three informal members (lower, middle, and upper) of the Kootenai Formation have been previously described in the nearby Blacktail Mountains (Tysdal, 1988), but only the middle and lower members are exposed in the map. The middle member is 120 m (400 ft) thick and is composed of reddish orange to maroon mudstone, siltstone, and minor sandstone, all of which are poorly exposed and form red weathering slopes. The lower member is 30–60 m thick (100–200 ft) and consists of white, medium-bedded, poorly cemented quartz sandstone and pebble conglomerate containing white quartz and black chert clasts; these intervals commonly form resistant ridges. The Kootenai Formation is eroded or covered by Quaternary deposits locally; minimum thickness is estimated to be approximately 50m (165 ft) where overlain by Kbel, and 150 m (490 ft) in the Hans Peterson Flats in the southwestern corner of the map.|07-03|dmu, map unit|077,204,000||{E6582AD1-79FA-4488-A0F6-E9FB6EBA3291}|Mostly sandstone|medium||997|DAS01|||||{8CA22AB0-52D0-4DAF-BC14-D6E2BFFEA885}
15|{CA04C343-B348-4674-B5FD-792BB8965B05}|map unit|map unit, generic|5120|J^ed|JTRed|Swift and Dinwoody Formations, undivided|Swift Formation of Ellis Group and Dinwoody Formation|Jurassic–Triassic|unprovided|Jurassic|Triassic|Swift Formation (Jurassic)—Green gray to pale green interbeds of marl, conglomerate, and shale. Fine-grained, laminated marl beds are 2–20 cm thick (1–8 in) and contain glauconite and occasional chert fragments. Conglomerate intervals are composed of poorly sorted pebble-sized clasts of quartz, black chert, green shale, and fossiliferous limestone in a calcareous to argillaceous matrix. Planar interbeds of red brown, argillaceous shale are 2–5 cm thick (1–2 in). Thickness as much as 13 m (42 ft).   Dinwoody Formation (Triassic)—Interbedded shale, limestone, and calcareous sandstone characterized by platy, thinly laminated beds that weather a distinctive chocolate brown to light gray. The upper part of the formation is composed of interbedded shale and calcareous sandstone beds and massive, gray weathering carbonate intervals. The lower part of the formation consists mostly of olive fissile shale interbedded with dark brown, silty limestone beds. Thickness as much as 200 m (655 ft).|07-04|dmu, map unit|128,222,204||{33F67A5B-8B6D-493B-BD7F-A3241BF3BB13}|Sandstone and mudstone|medium||997|DAS01|||||{CA04C343-B348-4674-B5FD-792BB8965B05}
16|{1ABFFDA6-BB42-4A2C-AE9F-BFA89D6DAB20}|map unit|map unit, generic|6320|Pp|Pp|Phosphoria Formation|Phosphoria Formation|Late Permian|unprovided|Late Permian|Late Permian|From top to bottom, the formation includes interbedded yellowish brown, fine- to medium-grained glauconitic quartz sandstone; dark gray to black finely layered phosphatic mudstone; light gray dolomite that contains nodular chert and chert stringers; pale brown phosphatic mudstone; and pale brown, thin-bedded mudstone and interbedded sandstone. Bed thickness ranges from 10–35 cm (4–14 in) in dolomites, and 5–35 cm (2–14 in) in cherts and sandstones. Chert-rich intervals form resistant outcrops, otherwise recessive and poorly exposed. Thickness is approximately 100 m (350 ft).|08-01|dmu, map unit|102,179,204||{33F67A5B-8B6D-493B-BD7F-A3241BF3BB13}|Sandstone and mudstone|medium||997|DAS01|||||{1ABFFDA6-BB42-4A2C-AE9F-BFA89D6DAB20}
17|{D469FD1A-044B-4E25-8C7C-15AB1469CCD1}|map unit|map unit, generic|4A00|*q|IPq|Quadrant Formation|Quadrant Formation|Pennsylvanian|unprovided|Pennsylvanian|Pennsylvanian|Light gray to light yellowish brown, fine- to medium-grained, medium- to thick-bedded, vitreous, quartz sandstone. Trough crossbedding is common. Forms resistant ridges and cliffs that are typically covered with conifers. As thick as 300 m (985 ft).|08-02|dmu, map unit|153,235,255||{58AA9A01-133F-46B5-A023-A044212E1BD3}|Sandstone|high||997|DAS01|||||{D469FD1A-044B-4E25-8C7C-15AB1469CCD1}
18|{7C6F6D7F-D044-402D-98C7-16F2476CBA86}|map unit|map unit, generic|5330|*Msr|IPMsr|Snowcrest Range Group, undivided|Snowcrest Range Group|Late Mississippian to Pennsylvanian|unprovided|Late Mississippian|Pennsylvanian|Interbedded mudstone, siltstone, sandstone, and carbonate composing the Conover Ranch, Lombard, and Kibbey Formations; mapped as one unit. The thickness of individual formations was undetermined; total group thickness estimated to be 290–300 m (950–985 ft).|08-03|dmu, map unit|128,179,179||{33F67A5B-8B6D-493B-BD7F-A3241BF3BB13}|Sandstone and mudstone|medium||997|DAS01|||||{7C6F6D7F-D044-402D-98C7-16F2476CBA86}
19|{1EA2846D-4587-4944-970F-2CD4EFE45E62}|map unit|map unit, generic|6420|Mmc|Mmc|Mission Canyon Formation|Mission Canyon Formation of Madison Group|Mississippian|unprovided|Mississippian|Mississippian|Light gray, medium- to thick-bedded and locally massive limestone, oolitic limestone, and dolomitic limestone. Contains zones of evaporate-solution breccia and intervals of bioclastic debris consisting of crinoids, bryozoans, and brachiopods. Chert stringers are common and often coincide with bedding planes. Forms prominent outcrops and cliffs. Thickness estimated to be 400m (1,310 ft).|08-04|dmu, map unit|102,153,204||{17AAA689-8B7C-40D3-B384-264AAD16094A}|Limestone|high||997|DAS01|||||{1EA2846D-4587-4944-970F-2CD4EFE45E62}
20|{405CB184-6921-4731-A3EB-65CE9D2A1959}|map unit|map unit, generic|32A0|Ml|Ml|Lodgepole Formation|Lodgepole Formation of Madison Group|Mississippian|unprovided|Mississippian|Mississippian|Light to dark gray, thin- to medium-bedded limestone, mudstone, and red calcareous siltstone. Beds are planar to undulose and rhythmically bedded. The formation is abundantly fossiliferous, including bioclasts of crinoids, bryozoans, and brachiopods. Forms outcrops on steep slopes. Thickness estimated to be 370 m (1,210 ft).|08-05|dmu, map unit|179,204,235||{17AAA689-8B7C-40D3-B384-264AAD16094A}|Limestone|high||997|DAS01|||||{405CB184-6921-4731-A3EB-65CE9D2A1959}
21|{F2D6701D-BD34-4656-8C62-C4BA7E60DFB9}|map unit|map unit, generic|5640|MDtj|MDtj|Three Forks and Jefferson Formations, undivided|Three Forks Formation and Jefferson Formation|Mississippian and Devonian|unprovided|Mississippian|Devonian|Interbedded shale, sandstone, limestone, and dolomite. Mapped as a single unit. Total thickness estimated to be 170 m (560 ft).|08-06|dmu, map unit|128,102,153||{33F67A5B-8B6D-493B-BD7F-A3241BF3BB13}|Sandstone and mudstone|medium||997|DAS01|||||{F2D6701D-BD34-4656-8C62-C4BA7E60DFB9}
22|{0F77EBDD-8FFA-4FCF-B936-432DDAD053B6}|map unit|map unit, generic|A330|_h|CBh|Hasmark Formation|Hasmark Formation|Late Cambrian|unprovided|Late Cambrian|Late Cambrian|Light gray to white, thin- to thick-bedded, crystalline dolomite with minor shale and limestone intervals. Weathers to a conspicuous light gray to pale brown color with a gritty, laminated surface. Forms ridges and cliffs. Thickness is approximately 70–80 m (230–260 ft).|08-07|dmu, map unit|235,179,179||{65F1F2FF-CA4E-498D-87C2-F198FC15ED62}|Dolomite|high||997|DAS01|||||{0F77EBDD-8FFA-4FCF-B936-432DDAD053B6}
23|{BA8C7C31-8BD7-42CF-9099-E9D6887D16D5}|map unit|map unit, generic|0430|_sh|CBsh|Silver Hill Formation|Silver Hill Formation|Late Cambrian|unprovided|Late Cambrian|Late Cambrian|Brown, dark red, and olive green interbeds of micaceous clay shale and thick layers of brown glauconitic quartzose siltstone. Poorly exposed, commonly forming a saddle between the Hasmark and Flathead Formations. Thickness estimated to be 70 m (225 ft).|08-08|dmu, map unit|255,153,179||{BA4AC2E3-4497-4C92-B603-75B4A05BC069}|Mostly mudstone|high||997|DAS01|||||{BA8C7C31-8BD7-42CF-9099-E9D6887D16D5}
24|{F92E4AB9-4DFA-4460-8C30-39CBA328B484}|map unit|map unit, generic|0530|_f|CBf|Flathead Formation|Flathead Formation|Middle Cambrian|unprovided|Middle Cambrian|Middle Cambrian|Light gray, tan, and maroon, mediumto coarse-grained, medium-bedded quartz sandstone. Commonly crossbedded with glauconite and quartz pebbles near the base of the unit. The contact with the underlying crystalline basement rocks is sharp and nonconformable. Thickness estimated to be 60 m (200 ft).|08-09|dmu, map unit|255,128,179||{58AA9A01-133F-46B5-A023-A044212E1BD3}|Sandstone|high||997|DAS01|||||{F92E4AB9-4DFA-4460-8C30-39CBA328B484}
25|{6802F181-433C-4EAC-B28E-6DCDCB0B4B6F}|map unit|map unit, generic|7760|Aag|Aag|Armstead Gneiss|Armstead Gneiss|Archean|unprovided|Archean|Archean|Heterogeneous assemblage of quartzofeldspathic gneiss and high-grade metasedimentary rocks. Quartzofeldspathic gneiss occurs as uniform intervals that weather to sparsely vegetated hills covered by rocky, pinkish orange soil containing abundant feldspar chips. Gneissic varieties include quartz–feldspar gneiss, quartz–feldspar–garnet gneiss, quartz–plagioclase–garnet gneiss, and quartz–orthoclase–hornblende gneiss. Thin, conformable lenses of amphibolite gneiss are commonly intercalated with the quartzofeldspathic gneiss units. Metasedimentary intervals include thinly interlayered intervals of metapelite, amphibolite, quartzofeldspathic gneiss, quartzite, and calc-silicate marble. The metasedimentary intervals are poorly exposed, commonly forming brown soil underlying low, flat, sage-covered areas. A planar mineral foliation generally parallels compositional layering, and centimeter-scale isoclinal folds are common. See Young (1982) for detailed petrographic descriptions of the Armstead Gneiss.|09-01|dmu, map unit|077,077,102||{0FC49D48-E133-40CE-B7A8-98ABA456D05A}|Schist and gneiss, of sedimentary-rock origin|medium||997|DAS01|||||{6802F181-433C-4EAC-B28E-6DCDCB0B4B6F}
26|{D752691B-824C-4656-899F-7AAC1DA46F8F}|header|header, generic||||ANTHROPOGENIC DEPOSITS|ANTHROPOGENIC DEPOSITS|Quaternary|unprovided|Quaternary|Quaternary||01|dmu, header|||||||997|DAS01|||||{D752691B-824C-4656-899F-7AAC1DA46F8F}
27|{F4AC5D67-DC8D-4F46-BC8F-15395A9CC9CE}|header|header, generic||||ALLUVIAL AND COLLUVIAL DEPOSITS|ALLUVIAL AND COLLUVIAL DEPOSITS|Quaternary|unprovided|Quaternary|Quaternary|Grasshopper Creek, in northeastern corner of the quadrangle, is the only perennial stream in the map area and flows eastward towards its confluence with the Beaverhead River. Alluvial deposits along Grasshopper Creek have been extensively mined for placer gold in the Armstead Hills region. Widespread colluvium and talus piles cover the bedrock geology locally.|02|dmu, header|||||||997|DAS01|||||{F4AC5D67-DC8D-4F46-BC8F-15395A9CC9CE}
28|{9C2B7CAB-9226-4A75-A1C1-20670329F13D}|header|header, generic||||TERTIARY SEDIMENTARY DEPOSITS|TERTIARY SEDIMENTARY DEPOSITS|Tertiary|unprovided|Tertiary|Tertiary|The oldest Tertiary sedimentary deposits (Tml) occur in the southwestern part of the map and are equivalent to the Eocene–Oligocene Medicine Lodge beds in the adjacent Salmon 30' x 60' quadrangle based on extent and lithological similarities (Lonn and others, 2019). These sedimentary accumulations are composed of poorly consolidated gravels interpreted to be proximal fluvial and debris flow deposits formed in alluvial fans. The Medicine Lodge beds likely accumulated in an extensional half-graben (proto-Medicine Lodge basin) that was structurally controlled by the Muddy–Grasshopper Fault (VanDenburg and others, 1998). Relatively thin and seemingly younger intervals of unconsolidated gravel (Tsc) rest on an unconformity truncating the Cretaceous and older map units in the central part of the quadrangle; these deposits are tentatively correlated to the Sixmile Creek Formation (Sears, 2007).|04|dmu, header|||||||997|DAS01|||||{9C2B7CAB-9226-4A75-A1C1-20670329F13D}
29|{AF8DC674-640D-4414-82BC-86780B3B14CD}|header|header, generic||||EOCENE VOLCANIC ROCKS|EOCENE VOLCANIC ROCKS|Eocene|unprovided|Eocene|Eocene|A small outcrop of basalt unconformably resting on the northeastern limb of the Armstead Anticline was the only Tertiary volcanic unit identified in the map. Correlative Eocene–Oligocene basalt flows (Dillon Volcanic Group) in the adjacent Dalys 7.5' quadrangle exhibit high-K calc-alkaline signatures and are enriched in trace elements indicative of an active plate margin modified by subduction processes (Mosolf, 2016).|05|dmu, header|||||||997|DAS01|||||{AF8DC674-640D-4414-82BC-86780B3B14CD}
30|{9FA7BCB2-7C58-4854-83F6-565B2BD5F871}|header|header, generic||||LATE CRETACEOUS IGNEOUS ROCKS|LATE CRETACEOUS IGNEOUS ROCKS|Late Cretaceous|unprovided|Late Cretaceous|Late Cretaceous|The oldest igneous rocks in the map are Late Cretaceous lavas, volcanic breccias, tuff deposits, and subvolcanic intrusions, all of which have intermediate to evolved compositions (fig. 4; table 1). These units generally exhibit high-K, calc-alkaline compositions and are enriched in incompatible elements indicative of subduction zone magmatism. The assimilation of country rock by parental melts is supported by significant zircon inheritance (fig. 2A), as well as the entrainment of mid- to lower-crustal xenoliths in hypabyssal intrusions and lava flows (e.g., Mosolf, in prepb). The extrusive volcanic units are intercalated with sedimentary strata of the Beaverhead Group and together are deformed by contractional structures.|06|dmu, header|||||||997|DAS01|||||{9FA7BCB2-7C58-4854-83F6-565B2BD5F871}
31|{7F47F4FF-6FE7-4CDE-BE2D-1E71FCEEC5A3}|header|header, generic||||MESOZOIC SEDIMENTARY ROCKS|MESOZOIC SEDIMENTARY ROCKS|Mesozoic|unprovided|Mesozoic|Mesozoic|Triassic through Late Cretaceous sedimentary strata record sedimentation in shallow marine and marginal-marine environments (J^ed) followed by extensive continental sedimentation (Kk, Kbel, and Kbeu) linked to the growth and eastward propagation of the Cordilleran fold-thrust belt. Clast compositions and detrital zircon of the Beaverhead Group (Kbel and Kbeu) indicate these synorogenic deposits were derived from the erosion of Proterozoic–Paleozoic formations exhumed in the hinterland of the Cordilleran fold-thrust belt (fig. 2B) with max depositional ages spanning approximately 77.9–65.9 Ma (Laskowski and others, 2013; Garber and others, 2020). The stratigraphic subdivisions of the Beaverhead Group are inconsistent in the literature, due in part to the correlation of lithologically complex and laterally discontinuous units. Informal subdivisions used in this map follow the nomenclature defined by Lowell (1965) and Johnson (1986).|07|dmu, header|||||||997|DAS01|||||{7F47F4FF-6FE7-4CDE-BE2D-1E71FCEEC5A3}
32|{B7D5E687-328F-4207-87D2-50E5CC8055D8}|header|header, generic||||PALEOZOIC SEDIMENTARY ROCKS|PALEOZOIC SEDIMENTARY ROCKS|Paleozoic|unprovided|Paleozoic|Paleozoic|Mississippian through Permian strata exhibit marine and marginal-marine facies that record multiple marine incursions into southwest Montana. Previous work inconsistently refers to the Mississippian units as either the Snowcrest Range Group or the Amsden Formation and Big Snowy Group. The Snowcrest Range Group is adopted here (after Wardlaw and Pecora, 1985), which includes the Conover Ranch, Lombard, and Kibbey Formations.|08|dmu, header|||||||997|DAS01|||||{B7D5E687-328F-4207-87D2-50E5CC8055D8}
33|{00913A72-29A8-4C73-A76C-59D088E25975}|header|header, generic||||METAMORPHIC ROCKS|METAMORPHIC ROCKS|Archean|unprovided|Archean|Archean|Archean quartzofeldspathic gneiss and high-grade metasedimentary intervals consisting of metapelite, quartzite, and calc-silicate rocks were mapped as one unit (Armstead Gneiss; Aag). These units preserve a polyphase metamorphic history, with peak metamorphism reaching granulite facies conditions (Young, 1982). U-Pb zircon data (figs. 2C–E) suggest the Armstead Gneiss protolith formed by ~2.7 Ga or older, and was subsequently metamorphosed ca. ~2.4–2.5 Ga during the Tendoy orogeny (Jones, 2008; Cramer, 2015). While no Proterozoic ages were obtained in this study, Mueller and others (2012) reported U-Pb ages of ~1.8 Ga for the Armstead Gneiss that likely reflect a tectonothermal event termed the Big Sky Orogeny (e.g., Harms and others, 2004; Cramer, 2015). The protolith of the Armstead Gneiss has been previously interpreted to represent a volcanic complex formed above an ancient subduction zone (Young, 1982; Mueller and others, 2012).|09|dmu, header|||||||997|DAS01|||||{00913A72-29A8-4C73-A76C-59D088E25975}
34|{6821253F-5E04-4169-AB12-5D48F5282F7E}|header|header, generic||||MASS WASTING DEPOSITS|MASS WASTING DEPOSITS|Quaternary|unprovided|Quaternary|Quaternary||03|dmu, header|||||||997|DAS01|||||{6821253F-5E04-4169-AB12-5D48F5282F7E}
