Metadata: Identification_Information: Citation: Citation_Information: Originator: Skipp, Betty Originator: Lageson, D.R. Originator: McMannis, W.J. Publication_Date: 1998 Title: Digital files to accompany I-2634, "Geologic map of the Sedan quadrangle, Gallatin and Park Counties, Montana" Geospatial_Data_Presentation_Form: Map Publication_Information: Publication_Place: Denver, CO Publisher: U.S. Geological Survey Online_Linkage: Larger_Work_Citation: Citation_Information: Originator: Skipp, Betty Originator: Lageson, D.R. Originator: McMannis, W.J. Publication_Date: In press Title: Geologic map of the Sedan quadrangle, Gallatin and Park Counties, Montana Geospatial_Data_Presentation_Form: Map Series_Information: Series_Name: U.S. Geological Survey Geologic Investigations Series Issue_Identification: I-2634 Publication_Information: Publication_Place: Denver, CO Publisher: U.S. Geological Survey Other_Citation_Details: The printed version of I-2634 is in press; it will include supplemental figures, three cross sections, and interpretive text. Description: Abstract: This quadrangle lies 6.4 km (4 mi) northeast of Bozeman, Mont., in southwestern Montana. Metamorphic, sedimentary, and volcanic rocks of Precambrian to Tertiary age are exposed in the Bridger Range and southwestern margin of the Crazy Mountains Basin in a crustal cross section and a structural triangle zone. Surface geology records Precambrian extension, Late Paleocene east-vergent contraction, including backthrusts, and Holocene basin-range extension. Purpose: The geology of the Sedan quadrangle was mapped as part of a regional study of the western Crazy Mountains Basin. It was digitized for ease of production of the printed version and for greater distribution for analytical use. Supplemental_Information: A preliminary map was published as a U.S. Geological Survey Open-File Report in 1971. The geologic data was interpreted 1965-93, the interpretation being informed by data from two wells in addition to the original field work. The printed version of I-2634 is in press; it will include supplemental figures, three cross sections, and interpretive text. Users should be aware that of the many faults mapped, the only active one is the range front fault on the west side of the Bridger Range. Time_Period_of_Content: Time_Period_Information: Range_of_Dates/Times: Beginning_Date: 1965 Ending_Date: 1971 Currentness_Reference: The geology of the quadrangle was mapped 1965- 71. Status: Progress: In work Maintenance_and_Update_Frequency: As needed Spatial_Domain: Bounding_Coordinates: West_Bounding_Coordinate: -111.0 East_Bounding_Coordinate: -110.75 North_Bounding_Coordinate: 46.0 South_Bounding_Coordinate: 45.75 Keywords: Theme: Theme_Keyword_Thesaurus: American Geological Institute Glossary of Geology Theme_Keyword: Geology Theme_Keyword: Structure Theme_Keyword: Geologic map Theme_Keyword: Bedrock Theme_Keyword: Surficial geology Theme_Keyword: Metamorphic rocks Theme_Keyword: Sedimentary rocks Theme_Keyword: Volcanic rocks Place: Place_Keyword_Thesaurus: U.S. Board on Geographic Names (BGN) Geographic Names Information System (GNIS) Place_Keyword: United States Place_Keyword: Montana Place_Keyword: Gallatin County, Montana Place_Keyword: Park County, Montana Place_Keyword: Bridger Range Place_Keyword: Crazy Mountains Basin Stratum: Stratum_Keyword_Thesaurus: North American Stratigraphic Code Stratum_Keyword: Fort Union Formation Stratum_Keyword: Livingston Group Stratum_Keyword: Hoppers Formation Stratum_Keyword: Billman Creek Formation Stratum_Keyword: Sedan Formation Stratum_Keyword: Eagle Sandstone Stratum_Keyword: Telegraph Creek Formation Stratum_Keyword: Cody Shale Stratum_Keyword: Frontier Formation Stratum_Keyword: Mowry Shale Stratum_Keyword: Thermopolis Shale Stratum_Keyword: Kootenai Formation Stratum_Keyword: Muddy Sandstone Stratum_Keyword: Skull Creek Shale Stratum_Keyword: Fall River Sandstone Stratum_Keyword: Morrison Formation Stratum_Keyword: Ellis Group Stratum_Keyword: Phosphoria Formation Stratum_Keyword: Quadrant Formation Stratum_Keyword: Amsden Group Stratum_Keyword: Snowcrest Range Group Stratum_Keyword: Madison Group Stratum_Keyword: Mission Canyon Limestone Stratum_Keyword: Lodgepole Limestone Stratum_Keyword: Three Forks Formation Stratum_Keyword: Jefferson Dolomite Stratum_Keyword: Maywood Formation Stratum_Keyword: Snowy Range Formation Stratum_Keyword: Pilgrim Limestone Stratum_Keyword: Park Shale Stratum_Keyword: Meagher Limestone Stratum_Keyword: Wolsey Shale Stratum_Keyword: Flathead Sandstone Stratum_Keyword: Belt Supergroup Stratum_Keyword: La Hood Formation Temporal: Temporal_Keyword_Thesaurus: North American Stratigraphic Code Temporal_Keyword: Pleistocene Temporal_Keyword: Quaternary Temporal_Keyword: Tertiary Temporal_Keyword: Cretaceous Temporal_Keyword: Jurassic Temporal_Keyword: Mesozoic Temporal_Keyword: Permian Temporal_Keyword: Pennsylvanian Temporal_Keyword: Mississippian Temporal_Keyword: Devonian Temporal_Keyword: Ordovician Temporal_Keyword: Cambrian Temporal_Keyword: Paleozoic Temporal_Keyword: Precambrian Temporal_Keyword: Proterozoic Temporal_Keyword: Archean Access_Constraints: None Use_Constraints: None Point_of_Contact: Contact_Information: Contact_Person_Primary: Contact_Person: Skipp, Betty Contact_Organization: U.S. Geological Survey Contact_Address: Address_Type: mailing address Address: U.S. Geological Survey, MS964, Box 25046, Denver Federal Center City: Lakewood State_or_Province: CO Postal_Code: 80225 Country: USA Contact_Voice_Telephone: (303) 236-1242 Contact_Electronic_Mail_Address: bskipp@usgs.gov Data_Set_Credit: The geology of the Sedan quadrangle was mapped by Betty Skipp, D.R. Lageson, and W.J. McMannis; the map was converted to digital form by Techni Graphic Systems, Inc., of Fort Collins, CO, under contract with the U.S. Geological Survey, and by Nancy Shock, U.S. Geological Survey. The map was edited and proofread by Diane E. Lane, U.S. Geological Survey. Native_Data_Set_Environment: ARC/INFO v. 7.2.1, Solaris 2.6. Data_Quality_Information: Attribute_Accuracy: Attribute_Accuracy_Report: Strike and dip of bedding surfaces, eutaxitic layering in ash-flow tuffs, and layering in metamorphic rocks was measured and recorded to the nearest degree in the Bridger Range and to the nearest 5 degrees elsewhere in the map area. Logical_Consistency_Report: The density of observations was lower in parts of the Fort Union Formation as evidenced by the density of attitude symbols on the map. Completeness_Report: data set is complete Positional_Accuracy: Horizontal_Positional_Accuracy: Horizontal_Positional_Accuracy_Report: The accuracy of location of polygons, lines, and points is consistent with the mapping scale of 1:48,000. Lineage: Source_Information: Source_Citation: Citation_Information: Originator: Skipp, Betty Originator: Lageson, D.R. Originator: McMannis, W.J. Publication_Date: 1998 Title: Draft compilation of geologic map of the Sedan quadrangle, Gallatin and Park Counties, Montana Geospatial_Data_Presentation_Form: Map Source_Scale_Denominator: 48000 Type_of_Source_Media: stable-base material Source_Time_Period_of_Content: Time_Period_Information: Range_of_Dates/Times: Beginning_Date: 1965 Ending_Date: 1971 Source_Currentness_Reference: The geology of the quadrangle was mapped 1965-71. Process_Step: Process_Description: Digitizing contractor scanned source stable- base material, vectorized scan, attributed files from author drafting and annotations, and produced check plots and coverages. Process_Date:199807 Process_Step: Process_Description: First author and map editor proofread check plots, and digital map specialist reviewed digital files. Process_Date:199808 Process_Step: Process_Description: Digitizing contractor corrected attributing as needed and produced new check plots. Process_Date:199810 Process_Step: Process_Description: Digital map specialist and editor proofread new check plots and reviewed digital files, making final corrections as needed, prepared metadata, and placed digital files on USGS ftp server. Process_Date:199811 Spatial_Data_Organization_Information: Direct_Spatial_Reference_Method: Vector Spatial_Reference_Information: Horizontal_Coordinate_System_Definition: Planar: Grid_Coordinate_System: Grid_Coordinate_System_Name: Universal_Transverse_Mercator: UTM_Zone_Number: 12 Transverse_Mercator: Scale_Factor_at_Central_Meridian: 0.9996 Longitude_of_Central_Meridian: -111 Latitude_of_Projection_Origin: 40 False_Easting: 0 False_Northing: 0 Entity_and_Attribute_Information: Overview_Description: Entity_and_Attribute_Overview: The dataset for the Sedan quadrangle consists of 10 coverages. The three coverages pnt_graphic, stpnt_graphic, and dvalues are not 'true' ARC/INFO coverages. They are graphic representations of symbols used on the geologic map: pnt_sym = pnt_graphic, stru_pnt and geo_pnt = stpnt_graphic, and dvalues = annotation for stru_pnt and geo_pnt. geo_net geo_pnt stru_net stru_pnt data_net data_pnt pnt_sym pnt_graphic stpnt_graphic dvalues The dataset also includes two plot files called sedangeology.gra and sedangeology.ps. Entity_and_Attribute_Detail_Citation: The geo_net coverage includes polygons that are map units and arcs that are contacts, veins, and dikes. The coverage consists of the following items: GEOCODE NAM ACC Items in the geo_net coverage are defined as follows: GEOCODE refers to the type of geologic feature. The value for GEOCODE in the geo_net coverage is one of the following: "Map unit," "Calcite vein," and "Waulsortian bioherm." To interpret the map unit symbols, refer to the explanation of unit symbols as coded by NAM. NAM refers to the map unit name and associated symbol (e.g., Qal, Td, KJr) as used in the following explanation (NOTE: The codes and items in the other coverages are explained in the sections following the description of map units and references cited): SURFICIAL DEPOSITS Qal Alluvium (Holocene to Upper Pleistocene)--Upper part consists of silt, sand, clay, and minor angular to round gravel; locally humic, nonbedded to parallel bedded. Lower part consists of pebble and cobble gravel; parallel bedding and both large- and small-scale crossbedding. Maximum exposed thickness about 8 m Qf Alluvial-fan deposits (Holocene to Upper Pleistocene)--Fan-shaped deposits of silt, sand, clay, and angular to round gravel mapped near head of Ross Creek on western margin, and in School Gulch at southern margin of quadrangle Qld Lake deposits (Holocene to Upper Pleistocene)--Coarse-grained gravel on shore grading into clay and marl in center. Thickness 0.3-3 m Qrt Rock talus (Holocene to Upper Pleistocene)--Accumulations of locally derived boulder- to pebble-sized angular detritus at heads of drainages on both sides of crest of Bridger Range Qls Landslide deposits (Holocene to Middle Pleistocene)--Pebble to boulder gravel; commonly silty sand to silty clay matrix; also includes largely intact slide blocks of bedrock; nonsorted to poorly sorted; clasts chiefly angular to subangular; nonbedded to crudely bedded. Includes deposits of avalanches, slumps, earth flows, debris flows, and mudflows. Locally includes colluvium in the larger deposits of east flank of Bridger Range. Characterized by hummocky topography. Thickness 0 to about 10 m Qc Colluvium (Holocene and Pleistocene)--Coarse- to fine-grained deposits derived from nearby bedrock. Includes (1) poorly bedded, coarse, angular to subrounded, gravel-size clasts containing variable amounts of fine-grained matrix material composing alluvial fans and cones in rugged terrain; and (2) sand, silt, and minor fine gravel containing variable amounts of fine-grained matrix forming slope-wash deposits chiefly on volcanic rocks in gentle terrain. Thickness generally 1-3 m Qg Glacial deposits (Pleistocene)--Boulder to pebble gravel; extremely coarse, irregular blocks as much as 10 m in diameter; unsorted; contains variable amounts of silty sand matrix; combination of morainal, outwash, and avalanche debris. Thickness as much as 80 m Qoa Older Alluvium (Pleistocene)--Chiefly boulder to pebble gravel containing variable amounts of silty sand matrix; includes glacial outwash gravels along east flank of Bridger Range, the North Fork of Carrol Creek, and along Cache Creek, and pediment gravels on northwest flank of Battle Ridge; locally subdivided into three members along Bridger Creek as described below Qt3 Older alluvium--Terrace gravels along Bridger Creek less than 45 m above present stream levels Qt2 Older alluvium--Terrace gravels along Bridger Creek 45-60 m above present stream levels Qt1 Older alluvium--Terrace gravels along Bridger Creek 60-90 m above present stream levels IGNEOUS ROCKS Td Mafic dike (Eocene?)--A composite, mainly basic, dike injected along the plane of the Pass thrust fault and along a fault south of Pine Creek; principally porphyritic, panidiomorphic olivine-augite-biotite diorite containing small segregations of biotite-augite syenite; thickness generally less than 90 m, but as much as 150 m in places Ts Composite sill (Eocene? or Paleocene?)--Sill confined to Middle Cambrian strata north and south of Cross Range fault; in places consists of upper chilled layer of biotite-augite microdiorite 30-60 cm thick, middle thin layer of syenodiorite, and lower thick layer of biotite-augite diorite; entire sill is 24-60 m thick. Offset by minor thrust. May be as young as earliest Eocene (Harlan and others, 1988) SEDIMENTARY ROCKS Fort Union Formation (Paleocene and Upper Cretaceous) Tfnp Conglomerate lens at Nixon Peak (Paleocene)--Interbedded brown and olive-gray sandstone and conglomerate (25 percent or more). Sandstone is medium to coarse grained, epiclastic, slightly calcareous, thin to medium bedded, and crossbedded; weathers into conspicuous vertical columns on Nixon Peak. Conglomerate and conglomeratic sandstone are medium to thick bedded, as much as 3 m thick; clasts include subangular to subrounded cobbles and boulders as large as 30 cm in diameter of Middle Proterozoic Spokane Formation and Greyson Shale (Belt Supergroup), Paleozoic limestone and quartzite, Proterozoic gabbro and diabase, and Cretaceous granodiorite derived from Big Belt Mountains to the northwest, mixed with other volcanic, sedimentary, igneous, and rare metamorphic rock fragments. Contacts are gradational with unit Tfu. Thickness 0-914 m Tfu Upper conglomeratic and middle sandy members, undivided (Paleocene)-- Dusky-yellow-green and olive-gray sandstone, conglomerate, and minor siltstone and mudstone. Sandstone is slightly calcareous, fine grained to conglomeratic; composed of lithic volcanic, limestone, and quartzite grains. The thin- to medium-bedded (beds as much as 60 cm thick) sandstone is crossbedded and locally displays soft-sediment folds and slumps indicating western and northwestern sources; wood and leaf impressions are common; clay pebbles and limestone nodules are common in upper fine-grained sandstones that also contain rare freshwater gastropods and pelecypods. Conglomerate is composed of cobbles of subangular to subrounded multilithologic clasts of volcanic and igneous rocks, sandstone, chert, fetid limestone, and rare gneiss and schist in southeastward- thinning tongues (Piombino, 1979; Roberts, 1972; this paper); boulders as much as 60 cm in diameter are present in upper part. Siltstone is dusky yellow green and chiefly thin bedded; weathers to grayish yellow green. Mudstone is olive gray and chiefly massive; weathers light olive gray. Basal 60-90 m of unit may contain beds of latest Cretaceous age. Unit has gradational contacts with over and underlying units; thickness more than 2,130 m TKfc Basal conglomerate member (Paleocene? and Upper Cretaceous)-- Interbedded dusky-yellow-green and olive-gray sandstone, lenses of conglomerate, and minor siltstone and mudstone. Sandstone is medium grained to conglomeratic, calcareous, thin bedded and crossbedded; contains soft-sediment folds and slumps, and weathers dark yellowish brown. Conglomerate is gray and brown, medium bedded and crossbedded; clasts include pebbles, cobbles, and some boulders as much as 30 cm in diameter of intermediate volcanic rocks, basalt, chert, quartzite, limestone, minor coarse-grained intrusive rocks, and a few gneiss pebbles derived from Archean through Cretaceous terranes; no fragments of unequivocal Belt Supergroup origin were noted; western and northwestern sources are indicated by crossbedding. Siltstone is dusky yellow green and thin bedded; weathers grayish yellow green. Mudstone is olive gray and chiefly massive; weathers light olive gray. Unit forms ridge composed of Battle Ridge and Grassy Mountain and weathers to gravel-strewn slopes; contact with Hoppers Formation is abrupt and is placed at base of lowest cobble conglomerate; gradational upper contact with unit Tfu; unit thins to northeast; about 304 m thick in quadrangle; 228 m measured in sec. 35, T. 3 N., R. 8 E., 3.2 km east of quadrangle (Skipp and McGrew, 1972) Livingston Group (Upper Cretaceous) Kh Hoppers Formation--Light-greenish-gray, light-olive-gray, and minor gray and grayish-purple conglomerate, sandstone, siltstone, and mudstone. Unit chiefly is fine grained, volcaniclastic, and calcareous. Locally, coarse- grained and crossbedded sandstone and siltstone are exposed as thin friable beds that weather olive gray and yellowish brown and that contain imprints and carbonacous films of plants and woody material. Interlayered grayish-purple, green, and gray mudstone commonly is calcareous and locally bentonitic. Conglomerate is present as minor ridge-forming thin beds and lenses composed of granules and pebbles of mainly western-derived Paleozoic and Mesozoic sedimentary rocks and a few well-rounded gneiss pebbles as much as 20 cm in diameter (Skipp and McGrew, 1972). Formation contains limestone nodules throughout, though they are more common in lower part; rare ironstone nodules are found in upper part. Unit forms a steep slope below basal conglomerate member of Fort Union Formation (unit Tkfc). Contact with Billman Creek Formation (unit Kbc) is gradational and is placed at base of lowest thick (about 7.5 m) sandstone bed. Thickness ranges from 450 to 730 m; 730 m measured in secs. 26 and 35, T. 3 N., R. 8 E., 3.2 km east of Sedan quadrangle (Skipp and McGrew, 1972) Kbc Billman Creek Formation--Grayish-red, grayish-green and gray, volcaniclastic mudstone and siltstone interbedded with minor volcanic sandstone and conglomerate and vitric tuff. Unit is chiefly volcaniclastic mudstone and siltstone that are gray and green in lower 213 m and grayish red above; calcareous, containing common carbonaceous material and common yellowish-brown- weathering calcareous concretions; locally rich in magnetite and zeolites. Interlayered lenses of fine-grained to conglomeratic volcaniclastic sandstone are calcareous, containing 'cannonball' structures, are thin bedded to massive, and are locally crossbedded. Conglomerate lenses contain subangular to subrounded pebbles and cobbles of intermediate volcanic rocks and accessory Paleozoic limestone and quartzite. Conglomerate and sandstone lenses are common in upper beds in southern part of quadrangle and in lower beds in northern part. Freshwater mollusks and Hadrosaurian dinosaur bones are common in lower mudstone beds (Skipp and McGrew, 1972). Unit forms valleys. Contact with Lennep Sandstone Member of Sedan Formation (unit Ksle) is gradational and is placed at top of highest ridge-forming sandstone in that member. Estimated thickness 760- 914 m Ks Sedan Formation--Chiefly western-derived volcaniclastic sandstone and mudstone, and minor ash-flow tuffs; divided into the following five members; unit used only on cross sections Ksle Lennep Sandstone Member--Ridge-forming , olive-gray, greenish-gray, and light-gray, volcaniclastic sandstone, conglomerate, and minor mudstone and devitrified vitric tuff. Fine-grained to conglomeratic sandstone is calcareous, is poorly bedded to crossbedded, has local magnetite concentrations along bedding planes, contains reddish-brown-weathering "cannonball" concretions and abundant carbonaceous material, and weathers yellowish brown. Iron staining and zeolitic alteration locally are common. Lenses of volcaniclastic pebble and cobble conglomerate contain cobbles as much as 15 cm in diameter of intermediate volcanic rocks and a few pebbles of Paleozoic quartzite and limestone. Minor siliceous mudstone is brown and massive. Thin beds of light-green and light- gray, zeolitized (laumontite) vitric tuff are present in lower part of member. Unit contains rare dinosaur bone fragments, freshwater and brackish-water mollusks, and, in northern part of quadrangle, Ophiomorpha, a marine crustacean. Gradational lower contact of unit is placed at base of lowest prominent sandstone ledge. Thickness is about 106-152 m (Skipp and McGrew, 1977) Ksm Mudstone member--Greenish-gray and brownish-gray, volcaniclastic mudstone, siltstone, sandstone, and minor interbedded conglomerate and altered vitric tuff. Siliceous mudstone is sandy, silty, locally bentonitic, massive, and veined with calcite; contains abundant orange zeolite (clinoptilolite); mudstone may be chiefly altered vitric lithic tuff. Fine-grained to conglomeratic, volcaniclastic sandstone and siltstone are locally calcareous and zeolitic, crossbedded, and graded. Yellowish-gray bentonite and light-gray- weathering, altered vitric tuff are common in upper beds. Rare lenses of volcanic pebble and cobble conglomerate containing a few boulders as much as 0.9 m in diameter of coarsely porphyritic augite andesite that resemble Member H of Maudlow Formation are present in middle beds in northern part of quadrangle (Skipp and McGrew, 1977). Unit contains freshwater mollusks, wood, and dinosaur bones, including one femur identified as Gorgosaurus sp. (Nicholas Hotton III, written commun., 1971). Member forms valleys and low barren hills, and has a gradational contact with Middle sandstone member (unit Ksms) below. Thickness ranges from 274 to 304 m Ksms Middle sandstone member--Olive-green, olive-gray, and dark-greenish- gray, volcaniclastic sandstone, conglomerate, mudflow conglomerate, and minor siltstone and mudstone. Fine-grained to conglomeratic, but mainly medium- to coarse-grained sandstone is calcareous, locally mottled, and crossbedded; weathers brown; contains carbonaceous material and zeolites. Lenses of volcanic conglomerate and mudflow conglomerate in upper part contain fragments of intermediate volcanic rocks as much as 30 cm in diameter that resemble lava flows of Member F of Maudlow Formation of Livingston Group in Maudlow Basin, 12 km to the northwest (Skipp and McGrew, 1972; 1977); a K-Ar radiometric age on hornblende from Member F of Maudlow Formation is 76.6±1 Ma (Marvin and others, 1989). A light-gray, calcareous, biotitic quartzose sandstone present at base of unit in northern part of area is correlated with upper part of Parkman Sandstone Member in northern parts of western Crazy Mountains Basin (Skipp and McGrew, 1977). Unit forms series of ridges and disconformably overlies Ash- flow tuff member (unit Ksa); contact is placed at top of highest ash-flow tuff or ash-flow tuff conglomerate. Thickness is about 304-436 m Ksa Ash-flow tuff member--Pale-yellowish-green, light-greenish-gray, grayish-red, and pale-yellowish- brown, welded to nonwelded tuff and ash-flow tuff conglomerate, interbedded with volcaniclastic conglomerate, sandstone, mudstone, and porcelanite. Tuff is dacitic and fine grained, containing locally abundant phenocrysts of golden-weathering biotite and minor andesine, augite, hypersthene, and altered cognate inclusions; glass is mostly devitrified, but thin (90- to 150-cm-thick) zones of perlitic glass are present in northwestern part of quadrangle. Conglomerate composed of ash-flow tuff pebbles marks base and top of unit in some places. Welded tuff is composed of a maximum of three composite cooling units, each 0-91 m thick, separated by intervals of greenish- gray to light-gray, volcaniclastic sedimentary rocks including greenish-gray, olive-green, and brown porcelanite. Wood is present in volcaniclastic beds. Unit forms resistant knobs and ridges and disconformably overlies lower sandstone member (unit Ksl). Thickness about 60-152 m. Tuffs thicken to northwest ( Skipp and Peterson, 1965; Skipp and Hepp, 1968). Unit equivalent to Welded tuff member of Skipp and McGrew (1977) Ksl Lower sandstone member--Dark-olive-gray, greenish-gray, and yellowish- gray, volcaniclastic sandstone, siltstone, mudstone, altered crystal lithic tuff, minor volcaniclastic granule and pebble conglomerate, minor grayish-red- purple hornblende dacite, and minor lignitic coal. Volcaniclastic sedimentary rocks, chiefly sandstone, are fine grained to conglomeratic and calcareous, containing common calcareous concretions and carbonacous plant material, including leaf, needle, twig, and cone imprints; medium bedded and locally crossbedded. Magnetite-rich zones in the sandstone beds and ironstone nodules are common in lower part, and, locally, dark-brown lignitic coal is found at the base. A lens of dacite in upper part of member that was identified about 1 km southwest of northwest corner of quadrangle is correlated with Member B of Maudlow Formation of Livingston Group about 12 km to the northwest (Skipp and McGrew, 1977); a K-Ar age on hornblende from dacite of Member B is 80.8±1 Ma (Marvin and others, 1989). Unit forms a low ridge and has an abrupt contact with underlying Eagle Sandstone (unit Ket) throughout most of area, but units are gradational just south of quadrangle (Roberts, 1963, 1964a,b, 1972). Thickness is 152-304 m KJr Eagle Sandstone, Telegraph Creek Formation, Cody Shale, Frontier Formation, Mowry Shale, Thermopolis Shale, Kootenai Formation, Morrison Formation, and Ellis Group, undivided (Cretaceous and Jurassic)--Mudstone, sandstone, minor limestone, conglomerate, and porcelanite; includes Cross Range fault zone rubble comprising Morrison Formation, Ellis Group, and Kootenai Formation about 1.5 km east of Fairy Lake. Shown undivided primarily on cross sections Ket Eagle Sandstone and Upper Part of Telegraph Creek Formation, undivided (Upper Cretaceous)--Eagle Sandstone in upper part is light-olive-gray, yellowish-gray and medium-gray sandstone, minor gray shale, and thin black coal seams. Very fine grained to medium-grained sandstone is quartzose, feldspathic, biotitic, and chiefly calcareous, containing brown-weathering 'cannonball' concretions; crossbedded and weathers yellowish gray. Basal Virgelle Sandstone Member consists of dark-greenish-gray and greenish-gray, volcaniclastic sandstone that is magnetite-rich and forms a ledge. Upper part of Telegraph Creek Formation is medium-gray and light-olive-gray sandstone, siltstone, and minor mudstone. Fine-grained sandstone is quartzose, micaceous, biotitic, and calcareous, containing large 'cannonball' concretions; thin-bedded; contains fossils--mollusks, rare ammonites, and wood impressions; forms slopes and has a gradational lower contact. Thickness of map unit is 61-152 m ; thicker in southern part of quadrangle Ktc Lower part of Telegraph Creek Formation (Upper Cretaceous)--Medium-dark- to dark-gray mudstone and light-gray sandstone, siltstone, and minor bentonite. Silty and sandy mudstone and very fine grained sandstone are biotitic, micaceous, calcareous, containing limestone nodules, and carbonacous; thin bedded and fossiliferous, containing mollusks and ammonites. Unit forms valleys or gentle slopes and is poorly exposed throughout area. Formation has gradational basal contact with Cody Formation (unit Kc). Thickness about 61-122 m Kc Cody Shale (Upper Cretaceous)--Gray shale and mudstone interbedded with grayish-green and olive-gray sandstone and siltstone and minor brown-weathering nodular limestone and yellowish-gray bentonite. Mudstone and shale are both calcareous and noncalcareous, locally biotitic, silty and sandy; contain limestone nodules, ironstone nodules, and cone-in-cone structures. Fine-grained sandstone is quartzose but contains abundant detrital rock fragments, is calcareous, argillaceous, and thin bedded. Mudstone and shale form slopes in lower and upper parts of interval. Eldridge Creek Sandstone Member near center of interval consists of ridge-forming sandstone that is greenish gray and olive gray, fine grained, thin bedded, crossbedded, and ripple marked; locally contains abundant glauconite. Member is about 30 m thick. Entire formation is locally fossiliferous and contains fish scales, starfish, mollusks, and ammonites. Unit is poorly exposed in quadrangle; sandstone ledges of Eldridge Creek Sandstone Member crop out locally. Basal contact is conformable. Thickness is about 304 m Kf Frontier Formation (Upper Cretaceous)--Ledges of light- to medium-gray, olive-gray, and dark-greenish-gray sandstone separated by mudstone and siltstone intervals that contain minor chert-pebble conglomerate, bentonite, and siliceous limestone. Fine- to coarse-grained sandstone is quartzose, feldspathic, lithic, calcareous, argillaceous, thin to medium bedded, and locally crossbedded; contains heavy-mineral concentrations on bedding planes; sandstone weathers brown and olive gray and forms prominent ledges. Distinctive sandstone at top of unit is light gray to light olive gray, friable, calcareous, and crossbedded. East of Ross Peak sandstones contain calc-silicate minerals that give them a mottled appearance. Dark-gray and greenish-gray mudstone and siltstone intervals as much as 30 m thick are siliceous and thin bedded, containing a few friable, fine-grained, calcareous sandstone beds. Marker beds in the upper mudstone intervals include thin, black chert-pebble conglomerate composed of well-rounded pebbles less than 2.5 cm in diameter, grayish-green siliceous limestone lenses, and thin beds of bentonite and fossil oyster (mollusk) banks. Basal contact is conformable. Thickness is about 152 m Kmf Mowry Shale, Muddy Sandstone, Skull Creek Shale, and Fall River Sandstone, undivided (Lower Cretaceous)--Medium-dark-gray and greenish-gray mudstone, sandstone, porcelanite, and minor coal. Formations are described in descending order. Mowry Shale is medium-dark-gray and greenish-gray mudstone, sandstone, and porcelanite. Muddy Sandstone is light-olive-gray to greenish- gray sandstone that is fine grained to conglomeratic; contains much volcanic detritus; is chiefly noncalcareous, thin bedded, and crossbedded, containing a thin, small pebble conglomerate bed near base. Muddy Sandstone forms a ledge about 12 m thick. Skull Creek Shale is grayish-green interbedded mudstone, siltstone, and fine-grained sandstone that is rich in volcanic detritus; laminated to thin bedded, crossbedded, and locally calcareous; contains minor thin coal beds. Fall River Sandstone is ridge-forming sandstone that is greenish gray to grayish orange, medium grained, quartzose and quartzitic, crossbedded, laminated, and ripple-marked; weathers yellowish brown; ledge is about 11 m thick. Unit is poorly exposed in quadrangle and has a disconformable basal contact. Thickness is about 182 m Kk Kootenai Formation (Lower Cretaceous)--Red, gray, and purple mudstone, interbedded with yellowish-gray and grayish-purple sandstone and minor conglomerate and medium-light-gray freshwater nodular limestone. Medium- to coarse-grained sandstone in upper part is quartzose, impure, and commonly hematitic. Medium-light-gray limestone in nodular layers is common in upper beds about 30 m below the top and just above the basal sandstone and conglomerate; commonly contains freshwater gastropods. Basal ledge-forming, coarse-grained sandstone and conglomerate are slightly argillaceous and are composed of salt-and-pepper chert and quartz grains as large as pebble size. Basal ledge is about 20 m thick. Formation is poorly exposed except for fragments of the basal sandstone and conglomerate. Unit disconformably overlies Morrison Formation (unit Jm). Thickness ranges from 111 to 121 m Jme Morrison Formation and Ellis Group, undivided (Middle and Upper Jurassic)--Poorly exposed, varicolored mudstone containing minor sandstone and limestone; mapped only along gully northeast of Fairy Lake Jm Morrison Formation (Upper Jurassic)--Red, green, and purple mudstone and hackly shale intercalated with light-gray, yellowish-brown, and yellowish-orange siltstone and sandstone. Upper 15-23 m includes light- to dark-gray carbonaceous shale and mudstone; locally, lower part contains irregularly bedded impure limestone and limestone nodules. Formation is poorly exposed and has a conformable basal contact. Thickness is 91-133 m Je Ellis Group (Upper and Middle Jurassic)--Consists in descending order of Swift Sandstone, Rierdon Formation, and Sawtooth Formation. Swift Sandstone is yellowish brown to grayish brown, medium to coarse grained, quartzose, very calcareous, and glauconitic, containing scattered chert pebbles; is crossbedded and fossiliferous (mollusks). Rierdon Formation consists of an upper yellowish- gray calcareous shale and impure limestone and a lower gray-weathering, medium- to thick-bedded, ledge-forming oolitic limestone. Sawtooth Formation includes an upper red and yellow calcareous mudstone and shale, a middle gray-weathering, dense, platy limestone and interbedded calcareous shale, and a basal sandy to pebbly limestone or conglomeratic calcareous sandstone. Unit thins northward and unconformably overlies Phosphoria or Quadrant Formation (unit PMpa). Thickness varies from about 36 to 91 m PCr Phosphoria and Quadrant Formations; Amsden , Snowcrest Range and Madison Groups; and Three Forks Formation, Jefferson Dolomite, Maywood Formation, Snowy Range Formation, Pilgrim Limestone, Park Shale, Meagher Limestone, Wolsey Shale, and Flathead Sandstone, undivided (Permian, Pennsylvanian, Mississippian, Devonian, Ordovician, and Cambrian)--Limestone, dolostone, mudstone, and sandstone; shown undivided only on cross sections PMps Phosphoria and Quadrant Formations and Amsden and Snowcrest Range Groups, undivided (Permian, Pennsylvanian, and Mississippian)--Poorly exposed mudstone, locally stained red, containing fragments of sandstone, dolostone, and limestone. See units PMpa and Msr. Mapped on eastern flank of southern part of Bridger Range; interval about 50-130 m thick PMpa Phosphoria and Quadrant Formations and Amsden Group, undivided (Permian, Pennsylvanian, and Mississippian)--Yellow, greenish-yellow, pale-gray- brown sandstone, white to yellowish-brown dolostone and limestone, red to purple dolomitic mudstone and shale, and minor green, nodular chert beds. Formations are described in descending order. Phosphoria Formation (Permian) is yellow to greenish-yellow sandstone containing scattered chert nodules; nodular chert beds with interstitial sand; soft, green, noncalcareous, nonphosphatic shale; and chert breccia or conglomerate. Thickness is 0-12 m; formation is absent north of Fairy Lake. Quadrant Formation (Pennsylvanian) is pale-gray-brown to white, fine-grained to very fine grained, medium-bedded to massive, crossbedded quartzose sandstone that contains some white to pale-yellow-gray, dense granular dolostone beds intercalated in lower part. Thickness is about 15-43.5 m. Amsden Group (Pennsylvanian and Mississippian) includes an upper pale-yellow- brown to white, dense, medium-granular, medium-bedded dolostone, containing a few thin beds of pale-gray-brown, fine-grained quartzose sandstone (probably the Devil's Pocket Formation) that unconformably overlies a lower red to purple dolomitic mudstone and shale interbedded with impure silty or argillaceous dolostone and limestone (probably Tyler Formation). Thickness of Amsden Group about 32-103 m. Unit unconformably overlies Snowcrest Range Group and is mapped separately in northern part of Bridger Range. Thickness of entire interval is 47-158 m Msr Snowcrest Range Group (Upper Mississippian)--Gray and gray-brown limestone and dolostone; red, pink, and yellow-orange sandstone; red and pink siltstone; red to purple shale; and a red-stained breccia. Group is divisible into three formations, described in descending order: The Conover Ranch Formation consists of ledge-forming, medium-bedded, gray to gray-brown, chert- nodule-bearing limestone and dolostone. Lower contact is gradational with Lombard Limestone, which consists of dark-gray to purplish-gray and black, fossiliferous shale or shaly limestone. Thickness of combined Conover Ranch Formation and Lombard Limestone varies from zero to about 61 m. Lombard Limestone unconformably overlies Kibbey Formation, which consists of three parts: upper part is red, pink, and pale-yellow-orange, platy to massive sandstone, sandy siltstone, and sandy dolostone, containing intercalated red siltstone; middle part is red and pink, blocky-fracturing dolomitic siltstone, and red to purple, hackly shale containing some thin pale-gray or cream-colored, purple-mottled, fine-grained dolostone; lower part is cream- and lavender- mottled, irregularly bedded, fine-grained dolostone or a red-stained breccia of limestone and dolostone fragments (McMannis, 1955). Thickness of Kibbey Formation varies from 11 to 71 m. Thickness of group varies from 11 to 122 m MDmm Madison Group, Three Forks Formation, Jefferson Dolomite, and Maywood Formation, undivided (Mississippian and Devonian)--Fault zone breccia consisting of limestone and dolostone fragments derived from these formations in a structural horse just north of southern border of quadrangle, southwest of Baldy Mountain Madison Group (Upper and Lower Mississippian)--Limestone and dolostone divided into an upper thick-bedded formation, the Mission Canyon Limestone, and a lower thin-bedded formation, the Lodgepole Limestone Mmc Mission Canyon Limestone (Upper and Lower Mississippian)--Pale-yellow- brown, massive, poorly bedded limestone and dolostone that weather light gray and form cliffs and castellated ridges. Chert and limestone nodules are common in middle and upper beds. Several conspicuous solution-collapse breccias occupy persistent stratigraphic positions. Unit has a gradational lower contact with Lodgepole Limestone (unit Mlp) and ranges in thickness from about 220 to 290 m; it is thickest near Sacagawea Peak Mlp Lodgepole Limestone (Lower Mississippian)-- Gray and brown limestone and minor dark-brown to black silty shale. Formation is divisible into three members: Upper Woodhurst Limestone Member consists of pale-yellow-brown, orange-brown, gray-brown, red-stained, thin-bedded, and fine-grained limestone, and intercalated medium- to thick-bedded, lighter colored, massive, cliff- forming, crinoidal, very fossiliferous (corals, brachiopods) limestone. Woodhurst Limestone Member is 134-146 m thick. Middle Paine Shale Member includes dark-gray-brown, mainly thin-bedded and platy, fine-grained, brittle, sparsely fossiliferous limestone, intercalated with yellow-weathering shaly limestone, and local Waulsortian bioherms (Stone, 1972; Smith, 1982). 'W' indicates positions of Waulsortian bioherms on map. Member is 94-99 m thick. Basal Cottonwood Canyon Member is dark-brown to black silty shale and siltstone. Member is 0.6-0.9 m thick. Formation unconformably overlies Sappington Member of Three Forks Formation (unit Dtm) Total thickness is 228-246 m Dtm Three Forks Formation, Jefferson Dolomite, and Maywood Formation, undivided (Upper Devonian)--Light- and dark-brown dolostone; gray and gray- green, nodular limestone; yellowish-brown sandstone; pink and gray siltstone; black and green shale; and minor dolostone breccia. Unit comprises, in descending order, three formations and their members. The Three Forks Formation is divisible into three members: Sappington Member at top consists of yellowish-brown, very fine grained, calcareous sandstone that grades downward to gray and gray-green silty shale and silty to sandy, nodular, oncolith-bearing limestone and a thin basal conodont-bearing, black shale. Sappington Member disconformably overlies middle Trident Member, which consists of gray, nodular limestone in upper part and green shale intercalated with some dolomitic siltstone in main part. Underlying basal Logan Gulch Member includes an upper ledge-forming, brecciated limestone underlain by evaporite-solution breccia and red to orange, nodular, limonitic shale; conformable lower contact. Three Forks Formation is conformable above Jefferson Dolomite and is 61-70 m thick. Jefferson Dolomite consists of light- and dark-brown, mainly medium- to thick- bedded, fine- to medium-grained, saccharoidal dolostone; dolomitic limestone; and limestone having a few intercalated yellow and pale-pink dolomitic siltstone and green dolomitic shale beds and associated dolostone breccia lenses. Lower contact is gradational with Maywood Formation. Jefferson Dolomite is about 152- 188 m thick. Maywood Formation in southern outcrops consists mainly of alternating thin beds of yellow to gray siltstone, dolomitic siltstone, and dolostone totaling about 12 m in thickness; northern outcrops include about 27 m of mainly reddish-orange to pale-yellow-gray, thin-bedded, platy siltstone and mudstone, and, at the top, 1 m or so of gray-brown, platy, fine-grained limestone. Unit disconformably overlies Upper Cambrian beds. Entire interval is 225-286 m thick OCsp Snowy Range Formation and Pilgrim Limestone, undivided (Lower Ordovician and Upper Cambrian)--Dark- and light-gray mottled and grayish-brown limestone, limestone-pebble conglomerate, and grayish-green shale. Snowy Range Formation is divided into two parts: Upper part, the Sage Pebble Conglomerate Member, consists of gray-brown, fine-grained, thin-bedded limestone; limestone- pebble conglomerate; and interbedded green shale conformably underlain by a thin, columnar algal limestone. Upper part has a conformable contact with lower part. Lower part, the Dry Creek Shale Member, is mainly gray-green fissile shale that contains a few intercalated yellow, calcareous siltstone or very fine grained sandstone beds. Basal contact of formation is conformable. Snowy Range Formation is about 51-84 m thick. Upper part of Pilgrim Limestone consists of dark- and light-gray mottled, medium- to thick-bedded, partly dolomitized, medium-grained, oolitic, locally crossbedded limestone and a few intercalated beds of flat-pebble conglomerate. Uppermost 3-4.5 m is dense, mottled limestone similar to that of Meagher Limestone. Upper part is 70-74 m thick. Lower part consists mainly of gray and yellow-brown, thin- to medium-bedded, dense to bioclastic limestone, limestone-pebble conglomerate, and edgewise conglomerate; includes interbedded gray-green, fissile, calcareous shale, and a 2.4- to 3-m- thick, gray-brown, massive, oolitic, vaguely mottled limestone at base. Lower part is 39-57 m thick. At Bridger Peak, a massive, pale-greenish-brown, vaguely mottled, fine-grained, reefoid, partly columnar (algal) limestone is between the upper and lower parts. Basal contact is gradational. Pilgrim Limestone is 110- 131 m thick. Entire interval is about 161-215 m thick Cpf Park Shale, Meagher Limestone, Wolsey Shale, and Flathead Sandstone, undivided (Middle Cambrian)--Green and maroon, micaceous shale; dark-gray and yellow mottled limestone; and red, pale-orange, and white sandstone. Unit comprises, in descending order, four formations. Park Shale includes green and maroon, very finely micaceous, fissile shale intercalated with thin-bedded limestone at top and local beds of arkosic limestone and arkose; is locally glauconitic in lower part. In northern Bridger Range, the lower 30 m consists of interbedded arkosic sandstone, siltstone, and shale (Fryxell and Smith, 1986). Formation has a conformable lower contact. Park Shale is about 66 m thick. Meagher Limestone consists of three parts: Upper part is thin-bedded, dark-gray, dense limestone and interbedded green shale. Main middle ledge- forming part is massive, dark-gray and yellow mottled, dense limestone. Lower part includes thin-bedded, dark-gray, dense limestone and interbedded green and yellow, silty shale. Lower contact is conformable. Meagher Limestone is about 112 m thick. Wolsey Shale consists of green and maroon, micaceous shale interbedded with micaceous sandstone and siltstone; in places it contains conglomeratic arkosic limestone and arkose. Lower contact is conformable. Wolsey Shale is about 45-65 m thick. Flathead Sandstone contains red, pale- orange, and white sandstone, locally quartzitic, and some glauconitic beds. Flathead locally contains feldspathic sandstone and arkose beds, conglomeratic in places. Sandstone is about 36-42 m thick. Unit unconformably overlies arkose of Belt Supergroup (unit Yl) in northern part of area and on Archean metamorphic rocks in southern part. Entire interval is 259-285 m thick Yl La Hood Formation of Belt Supergroup (Middle Proterozoic)--Dark-gray- green, reddish-weathering, coarse, massive, poorly bedded arkose and conglomeratic arkose. Formation contains very coarse gneiss boulder conglomerate in which boulders are as much as 2.4 m in diameter in southwestern exposures. Intercalated dark-gray argillite and siliceous limestone beds are common in upper part in northern exposures. Base is not exposed. Minimum thickness ranges from about 2,134 m to more than 3,048 m. Unit is in fault contact with Archean metamorphic rocks (McMannis, 1955, 1963) Wm Metamorphic rocks (Archean)--Intermediate to felsic gneiss, amphibolite, schist, metaquartzite, marble, and numerous small pegmatite dikes and veinlets (McMannis, 1955; Lageson, 1989). Thickness is unknown NOTE: The following explanation covers graphic representations of symbols used on the Sedan quadrangle map: Contact-Long dashed where approximately located; short dashed where gradational; dotted where concealed Fault-Dashed where approximately located; dotted where concealed; queried where doubtful Normal or oblique slip-Arrows indicate sense of relative movement; U, upthrown side; D, downthrown side Thrust-Sawteeth on upper plate; U, apparent upthrown side; D, apparent downthrown side; arrows on map indicate oblique slip and in cross sections they indicate relative movement Detachment-Filled half circles indicate upper deformed plate Anticline-Showing crestline and plunge of fold. Dashed where approximately located; dotted where concealed Overturned anticline-Showing crestline and direction of dip of limbs. Dashed where approximately located; dotted where concealed Syncline-Showing troughline and plunge of fold. Dashed where approximately located; dotted where concealed Overturned syncline-Showing troughline and direction of dip of limbs. Dashed where approximately located; dotted where concealed Strike and dip of beds in sedimentary rocks Horizontal Inclined Vertical Overturned Estimated Crumpled, vertical Eutaxitic layering in ash-flow tuffs Inclined Overturned Strike and dip of layering in metamorphic rocks Inclined Vertical Calcite vein Waulsortian bioherm Oil test showing lease name and operator's name Spring Gravel pit REFERENCES CITED IN THE DESCRIPTION OF MAP UNITS Aleinikoff, J. M., Evans, K.V., Fanning, C.M., Obradovich, J.D., Ruppel, E.T., Zieg, J.A., and Steinmetz, J.C., 1996, SHRIMP U-Pb ages of felsic igneous rocks, Belt Supergroup, western Montana: Geological Society of America Abstracts with Programs, 1996 Annual Meeting, p. A-376. 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Skipp, Betty, and Peterson, A.D., 1965, Geologic map of the Maudlow quadrangle, southwestern Montana: U.S. Geological Survey Miscellaneous Geologic Investigations Map I-452, scale 1:24,000. Smith, D.L., 1982, Waulsortian bioherms in the Paine Member of the Lodgepole Limestone (Kinderhookian) of Montana, U.S.A., in Bolton, Keith, Lane, H.R., and Lemone, D.V., eds., Symposium on the paleo-environmental setting and distribution of Waulsortian facies: El Paso, Texas, and Alamagordo, N. Mex., El Paso Geological Society and the University of Texas at El Paso, p. 51-64. Stone, R.A., 1972, Waulsortian type bioherms of Mississippian age, central Bridger Range, Montana: Montana Geological Society Guidebook, 21st Annual Field Conference, 1972, p. 36-55. Thompson, G.R., Fields, R.W., and Alt, David, 1982, Land-based evidence for Tertiary climatic variations-Northern Rockies: Geology, v. 10, p. 413-417. Tysdal, R.G., 1986, Thrust faults and back thrusts in Madison Range of southwestern Montana foreland: American Association of Petroleum Geologists Bulletin, v. 70, p. 360-376. Winston, Don, 1986a, Stratigraphic correlation and nomenclature of the Middle Proterozoic Belt Supergroup, Montana, Idaho and Washington, in Roberts, S.M., ed., Belt Supergroup-A guide to Proterozoic rocks of western Montana and adjacent areas: Montana Bureau of Mines and Geology Special Publication 94, p. 69-84. Winston, Don, 1986b, Middle Proterozoic tectonics of the Belt Basin, western Montana and northern Idaho, in Roberts, S.M., ed., Belt Supergroup-A guide to Proterozoic rocks of western Montana and adjacent areas: Montana Bureau of Mines and Geology Special Publication 94, p. 245-257. Wooden, J.L., Mogk, D.W., and Mueller, P.A., 1988, A review of the geochemistry and geochronology of the Archean rocks of the northern part of the Wyoming Province, in Ernst, W.G., ed., Metamorphism and crustal evolution of the Western United States [Rubey Volume VII]: Englewood Cliffs, N.J., Prentice Hall, Inc., p. 383-410. Woodward, L.A., 1982, Tectonic map of the fold and thrust belt and adjacent areas, west-central Montana: Montana Bureau of Mines and Geology Geologic Map 30, scale 1:250,000. ACC refers to accuracy of location of contacts. 1=accurate 2=approximate 4=concealed 5=gradational The geo_pnt coverage includes points that are orientation of beds in sedimentary rocks and orientation of eutaxitic layering in ash-flow tuffs. The coverage consists of the following items: GEOCODE STK DIP POS ACC CON Items in the geo_pnt coverage are defined as follows: GEOCODE refers to the type of surface for which orientation is given. The value for GEOCODE in the geo_pnt coverage is one of the following: "BEDDING SURFACE" and "ASHFLOW SURFACE." STK for bedding surface refers to strike of beds in sedimentary rocks and for ashflow surface refers to strike of eutaxitic layering in ash-flow tuffs. DIP for bedding surface refers to dip value for beds in sedimentary rocks and for ashflow surface refers to dip value for eutaxitic layering in ash-flow tuffs. NOTE: The info files give the azimuth for strike and the value for dip; the direction of dip is not readily apparent from the info files. The user should refer to the plotted graphic to determine direction of dip. POS refers to position of the bedding in sedimentary rocks or to position of eutaxitic layering in ash-flow tuffs. 1=inclined 2=overturned 3=horizontal (bedding in sedimentary rocks only) 4=vertical (bedding in sedimentary rocks only) ACC refers to accuracy in terms of whether the orientation of beds or layering was measured or estimated. 1=measured 2=estimated (bedding in sedimentary rocks only) CON refers to whether the bedding surface in sedimentary rocks is crumpled. 1=other (i.e., other surfaces not designated as crumpled) 2=crumpled The stru_net coverage includes arcs that are faults and folds. The coverage consists of the following items: GEOCODE TYP ACC DIR POS Items in the stru_net coverage are defined as follows: GEOCODE refers to the type of geologic feature. The value for GEOCODE in the stru_net coverage is one of the following: "FAULT" and "FOLD." TYP refers to the type of fault or fold. 1=normal or oblique slip fault 2=thrust fault 5=detachment fault 6=queried (really an element of ACC but was included with GEOCODE; queries used on fault where fault doubtful) 7=anticline (shows crestline of fold) 8=syncline (shows troughline of fold) NOTE: The direction of the arcs is significant in that it determines on which side the sawteeth or half circles are placed on the thrust and detachment faults. The sawteeth or half circles are on the upper plate. If these coverages are cleaned the arcs can 'flip' and the sawteeth or half circles will end up on the incorrect side of the fault. Please refer to the graphic file for correct placement of sawteeth or half circles. ACC refers to accuracy of location of faults and folds. 1=accurate 2=approximate 4=concealed DIR refers to sense of relative movement on normal or oblique slip faults or to sense of oblique slip on thrust faults. 1=right lateral 2=left lateral POS refers to position of the axial surface of folds. 1=upright or inclined 2=overturned The stru_pnt coverage includes points that are orientation of layering in metamorphic rocks. The coverage consists of the following items: GEOCODE STK DIP POS ACC GEOCODE refers to the type of surface for which orientation is given. The only possible value for GEOCODE in the stru_pnt coverage is "FOLIATION" (i.e., layering in metamorphic rocks). STK refers to strike of layering in metamorphic rocks. DIP refers to dip value for layering in metamorphic rocks. NOTE: The info files give the azimuth for strike and the value for dip; the direction of dip is not readily apparent from the info files. The user should refer to the plotted graphic to determine direction of dip. POS refers to position of the layering in metamorphic rocks. 1=inclined 4=vertical ACC refers to accuracy in terms of whether the orientation of layering was measured or estimated. 1=measured 2=estimated (no instances mapped in the Sedan quadrangle) The data_net coverage includes lines that form the quadrangle boundary and lines of section (three cross sections are part of the printed version of this map, which is in press). The coverage consists of the following items: GEOCODE XTA GEOCODE refers to the type of line. The value for GEOCODE in the data_net coverage is one of the following: "BOUND" and "Xsection" XTA refers to the specific line of section: A-A', B-B', or C-C'. The data_pnt coverage includes points that are locations for gravel pits, test wells, and springs. The coverage consists of the following item: GEOCODE GEOCODE refers to the type of feature located. The value for the GEOCODE in the data_pnt coverage is one of the following: "GRAVEL PIT", "OIL TEST" (Robinson Ranch no. 1 Amoco prod. and Wilsall no. 1 Statescat drilling), and "SPRING." The pnt_sym coverage includes points that locate arrows for faults and folds and U and D symbols for faults. (NOTE: On this map the "U" indicates the APPARENT upthrown side of a thrust fault and "D" the APPARENT downthrown side. Please refer to the graphic file for correct placement of sawteeth that indicate the upper plate.) The coverage consists of the following item: TYP The value for TYP in the pnt_sym coverage is one of the following: "ANTICLINE," "ANTI_OVER," "LL/SLIP," "NORMAL/D," "NORMAL/U," "PLUNGE," "RL/SLIP," "SYNCLINE," "SYNC_OVER." (NOTE: NORMAL/D and NORMAL/U as used here also includes "U" and "D" on thrust faults.) Distribution_Information: Distributor: Contact_Information: Contact_Organization_Primary: Contact_Organization: U.S. Geological Survey, Geologic Division, Central Publications Group Contact_Person: Nancy Shock Contact_Position: Digital Map Specialist Contact_Address: Address_Type: mailing address Address: U.S. Geological Survey, MS902, Box 25046, Denver Federal Center City: Lakewood State_or_Province: CO Postal_Code: 80225 Country: USA Contact_Voice_Telephone: (303) 236-7684 Contact_Electronic_Mail_Address: nshock@usgs.gov Resource_Description: Geologic Investigations Series I-2634, Geologic map of the Sedan quadrangle, Gallatin and Park Counties, Montana Distribution_Liability: Any use of trade, product, or firm names is for descriptive purposes only and does not imply endorsement by the U.S. Government. Although this data set has been used by the U.S. Geological Survey, no warranty, expressed or implied, is made by the USGS as to the accuracy and functioning of the data set and related material nor shall the fact of distribution constitute any such warranty, and no responsibility is assumed by the USGS in connection therewith. Standard_Order_Process: Digital_Form: Digital_Transfer_Information: Format_Name: ARCE Format_Version_Number: 7.2.1 File_Decompression_Technique: gzipped tar file Digital_Transfer_Option: Online_Option: Computer_Contact_Information: Network_Address: Network_Resource_Name: Fees: No cost for the digital files. Technical_Prerequisites: ARC/INFO 7.2.1 Metadata_Reference_Information: Metadata_Date: 19981112 Metadata_Contact: Contact_Information: Contact_Person_Primary: Contact_Person: Nancy Shock Contact_Organization: U.S. Geological Survey, Geologic Division, Central Publications Group Contact_Position: Digital Map Specialist Contact_Address: Address_Type: mailing address Address: : U.S. Geological Survey, MS902, Box 25046, Denver Federal Center City: Lakewood State_or_Province: CO Postal_Code: 80225 Country: USA Contact_Voice_Telephone: (303) 236-7684 Contact_Electronic_Mail_Address: nshock@usgs.gov Metadata_Standard_Name: FGDC Content Standard for Digital Geospatial Metadata Metadata_Standard_Version: 199806 Metadata_Access_Constraints: None Metadata_Use_Constraints: None