GEOLEX

Summary of Citation: Flathead

Publication:
Peale, A.C., 1893, The Paleozoic section in the vicinity of
   Three Forks, Montana, with petrographic notes by G.P. Merrill:
   U.S. Geological Survey Bulletin, 110, 56 p.

Usage in Publication:
Flathead formation*

Modifications:	Geologic Province:	Dominant Lithology:
First used	Montana folded belt province	Quartzite Shale Limestone

Summary:
First published use as a formation that rests on the Belt formation (new) and underlies the Gallatin formation (new) in Three Forks area, MT in Montana folded belt province. Mapped north of East Gallatin River and east of Missouri River in Gallatin Co, and west of Missouri River in Broadwater Co. Neither source of geographic name nor type locality stated. Consists of a persistent basal quartzite or sandstone 125 ft thick, and an upper shale 200 ft thick. These are called Flathead quartzite and Flathead shales, respectively, or Flathead formation collectively. Quartzite has uniform siliceous grains and is cemented by silica. Forms conspicuous outcrops. Is unfossiliferous. Shale is brown and green at base, and green and purple and interbedded with thin bands of sandstone and glauconitic limestone at top. Is considered Lower Cambrian on basis of correlation with Prospect Mountain quartzite of NV and with Potsdam sandstone of NY. Shales are fossiliferous (Lingulella, Hyolithes, Ptychoparia).

Summary of Citation: Flathead

Publication:
Weed, W.H., 1899, Description of the Fort Benton quadrangle
   [Montana]: U.S. Geological Survey Geologic Atlas of the United
   States, Fort Benton folio, no. 55, 7 p.

Usage in Publication:
Flathead sandstone*

Modifications:	Geologic Province:	Dominant Lithology:
Areal limits Revised	Sweetgrass arch

Summary:
Mapped (geologic map) in southwest part of quad in Little Belt Mountains, Cascade Co, MT, Sweetgrass arch, as one of seven units of Barker formation (first used). [Use of Barker was a mapping convenience as constituent units were not mappable at scale used; Barker probably not intended to be of group rank]. Consists of coarse sandstone grading into dense, hard quartzite. Is oldest Cambrian unit; rests on Archean gneiss; underlies Wolsey shale (first used) of Barker. Barker contains middle Cambrian fossils.

Summary of Citation: Flathead

Publication:
Weed, W.H., 1900, Geology of the Little Belt Mountains, Montana:
   U.S. Geological Survey Annual Report, 20, pt. 3, p. 257-462

Usage in Publication:
Flathead sandstone*

Modifications:	Geologic Province:	Dominant Lithology:
Revised Overview	Sweetgrass arch

Summary:
Removed from Barker formation and raised to formation rank (though mapped as one of seven units of Barker). Measured section in bluff of Belt Creek 8 mi south of Monarch, Cascade Co, MT, Sweetgrass arch. At measured section unit consists of 113.5-138.5 ft of quartzite and sandstone; in lower part is a 70-ft thick augite-syenite sheet. Also exposed along Sawmill Creek and over O'Brien Park. Flathead is basal Cambrian unit; underlies Wolsey shale (revised). Correlation of measured sections. Middle Cambrian Trilobite DICELLOMUS NANUS identified by Walcott.

Summary of Citation: Flathead

Publication:
Emmons, W.H. and Calkins, F.C., 1913, Geology and ore deposits
   of the Philipsburg quadrangle, Montana: U.S. Geological Survey
   Professional Paper, 78, 271 p., Also, U.S. Geological Survey
   Bulletin 1237.

Usage in Publication:
Flathead quartzite*

Modifications:	Geologic Province:	Dominant Lithology:
Revised Areal limits	Montana folded belt province

Summary:
Mapped in Philipsburg area which includes portions of Granite, Powell, and Deer Lodge Cos, MT in Montana folded belt province. Unconformably overlies Algonkian Spokane formation. Conformably underlies Cambrian Silver Hill formation (new). Outcrops in various localities in quadrangle including Anaconda Range, Lost Creek drainage basin, southern part of Flint Creek Range, between Philipsburg and Granite at Franklin Hill, and on Maywood Ridge. Thickness is variable, ranging up to about 200 feet. Geologic map. Measured section. Stratigraphic column. Cambrian age based on stratigraphic position.

Summary of Citation: Flathead

Publication:
Deiss, C.F., 1933, Paleozoic formations of northwestern Montana:
   Montana Bureau of Mines and Geology Memoir, no. 6, 51 p.

Usage in Publication:
Flathead quartzite

Modifications:	Geologic Province:	Dominant Lithology:
Overview Areal limits	Montana folded belt province

Summary:
Extends into area of Lewis and Clark, Flathead, and Swan Ranges in southeastern Flathead, northern Powell, and northwestern Lewis and Clark Cos, MT, in Montana folded belt province. Thickness averages 67 ft, ranging to as much as 118 ft in area of North Fork of Dearborn River. Unconformably overlies Missoula group (Algonkian); conformably underlies Wolsey shale. Seven measured sections. Correlation chart. Middle Cambrian age.

Summary of Citation: Flathead

Publication:
Deiss, C.F., 1935, Cambrian-Algonkian unconformity in western
   Montana: Geological Society of America Bulletin, v. 46, no.
   1, p. 95-124

Usage in Publication:
Flathead sandstone

Modifications:	Geologic Province:	Dominant Lithology:
Areal limits Overview	Montana folded belt province Sweetgrass arch Central Montana uplift

Summary:
Unit occurs throughout western MT as basal unit of Cambrian System. Study area includes Philipsburg quad, Helena area, Coopers Lake quad, Little Belt Mountains, and Big Snowy Mountains; within Montana folded belt province, Sweetgrass arch and Central Montana uplift. Thickness ranges from 300 ft in Helena mining region to 44 ft in Lewis and Clark Range at head of Moose Creek; average thickness is 108 ft over an area of more than 35,000 sq mi. (Thickness is 640 ft at Beaver Creek, 20 mi northeast of Helena, which is much greater than in any other area; this thickness not used in calculating average). Unconformably overlies Beltian rocks; conformably underlies Wolsey shale. Middle Cambrian age.

Summary of Citation: Flathead

Publication:
Deiss, C.F., 1936, Revision of type Cambrian formations and
   sections of Montana and Yellowstone National Park: Geological
   Society of America Bulletin, v. 47, no. 8, p. 1257-1342

Usage in Publication:
Flathead sandstone

Modifications:	Geologic Province:	Dominant Lithology:
Revised Overview	Montana folded belt province Sweetgrass arch Central Montana uplift Yellowstone province

Summary:
Type locality of Weed (1900) reexamined and section remeasured at Belt Creek, near Monarch, Cascade Co, MT and elsewhere in Little Belt Mountains, Sweetgrass arch. At emended type, sill is placed at top of Flathead rather than near bottom as described by Weed; revised thickness, not including sill is 243 ft; Weed measured 168 ft. Additional sections remeasured in central and southern MT within Montana folded belt province, Central Montana uplift and in Yellowstone National Park, Yellowstone province. Weed's definition of Flathead omits its most diagnostic characteristic which is presence of many small, water-worn, pure, glassy, quartz pebbles from Archean granites that were transported great distances. Only known fossils in Flathead are on Crowfoot Ridge, Gallatin Range, Yellowstone Park, where small brachiopods occur in association with hematite zone about 25 ft below top of unit. Thickness ranges from 276 ft in Beaver Creek area, Big Belt Mountains, to 93 ft on Crowfoot Ridge; thickness averages about 180 ft in study area; thins northwestward to an average of 90 ft in northwest MT. Flathead is better exposed, more complete and less metamorphosed on Crowfoot Ridge; Checkerboard Creek, Castle Mountains; and on Beaver Creek, northern part of Big Belt Mountains than at type. Plate 2 shows tentative correlation of revised Cambrian units at type sections. Middle Cambrian age.

Summary of Citation: Flathead

Publication:
Deiss, C.F., 1938, Cambrian formations and sections in part of
   Cordilleran Trough: Geological Society of America Bulletin,
   v. 49, no. 7, p. 1067-1168

Usage in Publication:
Flathead sandstone, sandstone member

Modifications:	Geologic Province:	Dominant Lithology:
Redescribed Revised Overview	Montana folded belt province Bighorn basin Wind River basin	Sandstone Quartzite

Summary:
Redescribed from Flathead quartzite to Flathead sandstone in Lewis and Clark Range area in Flathead, Powell, and Lewis and Clark Cos, MT, in Montana folded belt province. Unit consists of sandstone and quartzite. Overlies Beltian rocks. Underlies Gordon shale (replaces Wolsey shale). Tentatively correlates with Flathead member of Depass formation in Wind River Canyon area, WY; in part with Brigham quartzite in Blacksmith Fork area, UT; with lower part of Howell limestone in House Range, UT; and with lower part of Comet shale in Highland Range, NV. In Wind River Canyon area in eastern part of Owl Creek Range, WY, Bighorn and Wind River basins, Depass formation divided into two members, Flathead sandstone member (rank reduced) in lower part and Gros Ventre member (rank reduced) in upper part. Here, member unconformably overlies pre-Beltian rocks. Measured sections. Correlation chart. Cross section. Columnar section. Middle Cambrian (Albertan) age.

Summary of Citation: Flathead

Publication:
Knechtel, M.M., Brockunier, S.R. and Hobbs, S.W., 1944, Plains
   adjacent to the Little Rocky Mountains, Montana: U.S. Geological
   Survey Oil and Gas Investigations Map, OM-4, 1 sheet, scale
   1:48,000

Usage in Publication:
Flathead sandstone*

Modifications:	Geologic Province:	Dominant Lithology:
Areal limits	Williston basin

Summary:
Extends name to Little Rocky Mountain region, Blaine and Phillips Cos, MT, Williston basin, for light-gray and light-tan sandstone and fine-grained conglomerate, in places altered to quartzite. Thickness 50 ft. Underlain unconformably by pre-Cambrian schist and gneiss; overlain by unnamed Cambrian rocks. Formerly included in Deadwood formation (Collier, Cathcart, 1922). Cambrian in age.

Summary of Citation: Flathead

Publication:
Sloss, L.L. and Moritz, C.A., 1951, Paleozoic stratigraphy of
   southwestern Montana: American Association of Petroleum
   Geologists Bulletin, v. 35, no. 10, p. 2135-2169

Usage in Publication:
Flathead sandstone

Modifications:	Geologic Province:	Dominant Lithology:
Areal limits Overview	Montana folded belt province

Summary:
Extends into extreme southwest MT south of Boulder batholith and west of Yellowstone National Park within parts of Beaverhead, Madison and Gallatin Cos, MT, Montana folded belt province. Over most of area unit unconformably overlies rocks correlated with early? pre-Cambrian Cherry Creek succession. Along western and northwestern margins of area, Flathead disconformably overlies Beltian series. Conformably and transitionally underlies Wolsey shale. Thickness ranges from 75-125 ft. Correlates with Brigham quartzite in southeast ID and with lower part of Garden Creek phyllite in central ID. Isopach map of Cambrian. Correlation chart. Cross section. Middle Cambrian age.

Summary of Citation: Flathead

Publication:
Hanson, A.M., 1952, Cambrian stratigraphy in southwestern Montana:
   Montana Bureau of Mines and Geology Memoir, no. 33, 46 p.

Usage in Publication:
Flathead sandstone

Modifications:	Geologic Province:	Dominant Lithology:
Overview Areal limits	Bighorn basin Central Montana uplift Sweetgrass arch Montana folded belt province

Summary:
Extends throughout southwest MT from Fergus and Carbon Cos on east to Mineral and Beaverhead Cos on west, which includes Bighorn basin, Central Montana uplift, Sweetgrass arch, and Montana folded belt province. Thickness ranges from 0 to nearly 300 ft and may exceed 500 ft west of Argenta, Beaverhead Co. Unconformably overlies pre-Cambrian rocks including Belt, Cherry Creek, or Pony series. Underlies Wolsey shale with gradational contact. Correlates with upper part of Langston formation in northeast UT. Many measured sections. Cross section, correlation chart, isopach map. Middle Cambrian age.

Summary of Citation: Flathead

Publication:
McMannis, W.J., 1955, Geology of the Bridger Range, Montana:
   Geological Society of America Bulletin, v. 66, no. 11, p.
   1385-1430

Usage in Publication:
Flathead formation

Modifications:	Geologic Province:	Dominant Lithology:
Areal limits	Montana folded belt province

Summary:
Extended to Bridger Range, Gallatin Co, MT, Montana folded belt province. Thickness ranges from 119 ft west of Bridger Peak, in southern part of range, to 142 ft on west side of Sacajawea Peak. Disconformably overlies Beltian arkoses; conformably underlies Wolsey formation with sharp contact. Mapped undivided with Wolsey, Meagher and Park formations. Cross sections. Stratigraphic chart. Middle Cambrian age.

Summary of Citation: Flathead

Publication:
Knechtel, M.M., 1956, Emerson formation of Cambrian and probably
   Early Ordovician age in Little Rocky Mountains, Montana:
   American Association of Petroleum Geologists Bulletin, v.
   40, no. 8, p. 1994-1995

Usage in Publication:
Flathead sandstone*

Modifications:	Geologic Province:	Dominant Lithology:
Revised	Williston basin

Summary:
Revised in that Flathead sandstone is overlain by Emerson formation (new) in the Little Rocky Mountains, Blaine and Phillips Cos, MT in Williston basin. Middle Cambrian in age.

Summary of Citation: Flathead

Publication:
Lochman-Balk, Christina, 1956, The Cambrian of the Rocky Mountains
   and southwest deserts of the United States and adjoining
   Sonora province, Mexico, IN Rodgers, John, ed., El Sistema
   Cambrico, su paleogeografia y el problema de su base; Symposium;
   Parte II, Australia, America: International Geological
   Congress, 20th, Report, Mexico City, 1956, p. 529-661

Usage in Publication:
Flathead sandstone

Modifications:	Geologic Province:	Dominant Lithology:
Areal limits	Wind River basin

Summary:
Extended into type locality of Depass formation, Wind River Canyon, east end of Owl Creek Range, WY, Wind River basin, where Flathead is used for lower 92-100 ft of what had been part of Depass formation (revised). Lower sandstone unit up to base of lowest, conspicuously glauconitic, SCOLITHUS-bored sands is lithic equivalent of Flathead.

Summary of Citation: Flathead

Publication:
Klepper, M.R., Weeks, R.A. and Ruppel, E.T., 1957, Geology of
   the southern Elkhorn Mountains, Jefferson and Broadwater
   Counties, Montana: U.S. Geological Survey Professional Paper,
   292, 82 p.

Usage in Publication:
Flathead quartzite*

Modifications:	Geologic Province:	Dominant Lithology:
Overview	Montana folded belt province

Summary:
Outcrops along flanks of anticline in Devils Fence quad, Jefferson and Broadwater Cos, MT, Montana folded belt province; also outcrops west of Elkhorn, Jefferson Co. Unconformably overlies Empire shale of Belt series with minor angular discordance; contact with Belt rocks located within a few feet though surface of contact was not observed. Conformably underlies Wolsey shale though contact not observed. Thickness ranges from 100-119 ft. Geologic maps; measured sections; generalized stratigraphic section. Middle Cambrian age.

Summary of Citation: Flathead

Publication:
Shaw, A.B., 1957, Cambrian of the southwestern Wind River basin,
   Wyoming: Wyoming Geological Association Field Conference
   Guidebook, no. 12, p. 8-16

Usage in Publication:
Flathead sandstone

Modifications:	Geologic Province:	Dominant Lithology:
Overview	Wind River basin

Summary:
Is the basal Cambrian unit in report area. Identified on subsurface cross sections in Fremont and Natrona Cos, WY in the Wind River basin. Consists of coarse-grained, brown sandstone, and minor amounts of arkose and shale. Ranges between 50 and 75 ft thick. Thickens to east and south. Top of formation has a resistant, ledge-forming quartzite on outcrop. In subsurface sections, top of formation shows an increase in spontaneous potential. Origin of this thin quartzite is unsolved. Is early and middle Middle Cambrian age. Considered to be a transgressive coarse clastic deposit; the lower part is probably non-marine but most of the formation is probably a littoral deposit.

Summary of Citation: Flathead

Publication:
Robinson, G.D. and Barnett, H.F., 1963, Geology of the Three
   Forks quadrangle, Montana, with sections on petrography of
   igneous rocks by H.F. Barnett: U.S. Geological Survey
   Professional Paper, 370, 143 p.

Usage in Publication:
Flathead sandstone*

Modifications:	Geologic Province:	Dominant Lithology:
Overview	Montana folded belt province

Summary:
Exposed only in Milligan Creek area, Gallatin Co, MT, Montana folded belt province, where it overlies North Boulder formation and in Willow Creek area where it overlies Precambrian crystalline rocks. Is 30-50 ft thick. Consists of thick beds of medium- to coarse-grained, subround sandstone cemented by quartz and tinted pinkish or brownish by iron oxide. Locally, has lentils of pebble conglomerate. Overlain conformably by Wolsey shale. Is a marine unit of first cycle sediments derived from Precambrian gneiss or schist. Sections measured in sec 10, T1N, R1W (35 ft thick) and in sec 8, T1S, R1W (50 ft thick). Geologic map.

Summary of Citation: Flathead

Publication:
Schmidt, R.G., 1963, Geology and ore deposits of the Cuyuna
   North Range, Minnesota: U.S. Geological Survey Professional
   Paper, 407, 96 p.

Usage in Publication:
Flathead Quartzite*

Modifications:	Geologic Province:	Dominant Lithology:
Overview	Montana folded belt province

Summary:
Mapped in southwesternmost part of quad, Lewis and Clark Co, MT, Montana folded belt province. Unconformably overlies Spokane? Shale of Belt Series; conformably underlies Wolsey Shale. About 200 ft thick. Middle Cambrian age.

Summary of Citation: Flathead

Publication:
Knopf, Adolph, 1963, Geology of the northern part of the Boulder
   batholith and adjacent area, Montana: U.S. Geological Survey
   Miscellaneous Investigations Series Map, I-381, 1 sheet,
   scale 1:48,000

Usage in Publication:
Flathead Quartzite*

Modifications:	Geologic Province:	Dominant Lithology:
Areal limits	Montana folded belt province

Summary:
Maps unit in northern Boulder batholith area in Lewis and Clark and Jefferson Cos, MT in Montana folded belt province. Outcrop trends northwest-southeast from northwestern to central part of mapped area, then trends easterly to southwestern edge of map. Thickness ranges from 86 ft at Helena to 170 ft southeast of Lenox, a suburb of Helena. Rests with angular unconformity on various formations of Precambrian Belt Series. For example, at Greenhorn Mountain, Flathead rests on Greenhorn Mountain Quartzite; at Helena, unit rests on Marsh Formation or Helena Dolomite; and further east in Belt Mountains, it rests on Helena Dolomite. Conformably underlies Middle Cambrian Wolsey Formation. Is Middle Cambrian in age. Geologic map.

Summary of Citation: Flathead

Publication:
Kauffman, M.E. and Earll, F.N., 1963, Geology of the Garnet-Bearmouth
   area, western Montana: Montana Bureau of Mines and Geology
   Memoir, no. 39, 40 p.

Usage in Publication:
Flathead Formation

Modifications:	Geologic Province:	Dominant Lithology:
Areal limits	Montana folded belt province

Summary:
Extends unit into northwest part of Garnet Range in west-central MT, Montana folded belt province. (Author also refers to unit as Flathead Quartzite). Exposed along Deep Creek Anticline at Deep Creek and Rattler Gulch where thickness is 100-150 ft. Unconformably overlies Pilcher Formation of Missoula Group of Belt Series; contact with Garnet Range Formation of Missoula is very slight angular discordance. Conformably underlies Silver Hill Formation with gradational contact. Geologic map. Cross section. Stratigraphic chart. Middle Cambrian (Albertan) age.

Summary of Citation: Flathead

Publication:
Keim, J.W. and Rector, R.J., 1964, Paleozoic rocks in northwestern
   Montana; a newly recognized occurrence: Geological Society
   of America Bulletin, v. 75, no. 6, p. 575-578

Usage in Publication:
Flathead Quartzite

Modifications:	Geologic Province:	Dominant Lithology:
Areal limits	Montana folded belt province

Summary:
Extended to Fishtrap Creek drainage basin near Thompson Falls, Sanders Co, MT, Montana folded belt province. Paleozoic rocks, including Flathead, crop out in an area 1-3 mi wide by a minimum of 12 mi long. Consists of a 25-ft thick red and white sandstone. Conformably underlies Wolsey Shale; overlies Libby Formation with no apparent unconformity. Middle Cambrian age.

Summary of Citation: Flathead

Publication:
Reeves, C.C., Jr., 1964, New Cambrian, Ordovician, Devonian,
   and Mississippian measured sections, west flank Teton Mountains,
   Wyoming: The Mountain Geologist, v. 1, no. 4, p. 213-225

Usage in Publication:
Flathead Sandstone

Modifications:	Geologic Province:	Dominant Lithology:
Overview	Yellowstone province

Summary:
First section known to be measured on west side Teton Range, Teton Co, WY in the Yellowstone province. Is the basal Cambrian unit lying unconformably above the Precambrian and beneath the Gros Ventre Formation. Measured along north side of north fork of Teton Canyon about 6 mi N 75 deg W of Grand Teton. Is 182 ft thick in measured section. Composed of interbedded: 1) conglomerate of well-rounded to angular quartz fragments, brick-red to dark-maroon matrix of fine to coarse sand and hematite cement; 2) gray, buff, to green, arenaceous, thin-bedded shale; 3) brown, gray, purple, white to buff, very fine, fine-, medium- to coarse-grained, thin- to thick-bedded, friable, feldspathic and quartzitic quartzite; and 4) gray, pink, very fine to fine-grained, subround, friable, micaceous sandstone with some crossbeds. Basal unit is a conglomerate. No fossils found. Middle Cambrian age.

Summary of Citation: Flathead

Publication:
McMannis, W.J. and Chadwick, R.A., 1964, Geology of the Garnet
   Mountain quadrangle, Gallatin County, Montana: Montana Bureau
   of Mines and Geology Bulletin, no. 43, 47 p.

Usage in Publication:
Flathead Quartzite

Modifications:	Geologic Province:	Dominant Lithology:
Overview	Montana folded belt province

Summary:
Within mapped area, thickness ranges from 50 ft in east-central part to 125 ft in northern part. Quad is within Montana folded belt province. Unconformably overlies Precambrian metamorphic rocks; conformably underlies Wolsey Shale. Mapped undivided with other Middle Cambrian units including Wolsey, Meagher Limestone and Park Shale. In east-central part of map area, where unit is thinnest, is unusually nonresistant.

Summary of Citation: Flathead

Publication:
Lowell, W.R., 1965, Geologic map of the Bannack-Grayling area,
   Beaverhead County, Montana: U.S. Geological Survey Miscellaneous
   Investigations Series Map, I-433, 6 p., 1 sheet, scale

Usage in Publication:
Flathead Sandstone*

Modifications:	Geologic Province:	Dominant Lithology:
Areal limits Overview	Montana folded belt province

Summary:
Mapped in central Beaverhead Co, MT, Montana folded belt province. Outcrops along flanks of Armstead anticline in southwest part of map area. Consists of 100-300-ft thick hard, white and maroon, fine- to coarse-grained cross-bedded sandstone; much of lower half is conglomeratic. Overlies with angular unconformity Precambrian Belt Series; grades upward, by interbedding, into Wolsey Shale. Middle Cambrian age.

Summary of Citation: Flathead

Publication:
Lochman-Balk, Christina and Wilson, J.E., 1967, Stratigraphy of
   Upper Cambrian-Lower Ordovician subsurface sequence in
   Williston basin: American Association of Petroleum Geologists
   Bulletin, v. 51, no. 6, p. 883-917

Usage in Publication:
Flathead Sandstone

Modifications:	Geologic Province:	Dominant Lithology:
Revised	Williston basin

Summary:
Revised in that Flathead Sandstone is overlain by Wolsey Member of Emerson Formation in the Little Rocky Mountains, Blaine and Phillips Cos, MT in the Williston basin. Middle Cambrian in age.

Summary of Citation: Flathead

Publication:
Chaudhuri, S. and Brookins, D.G., 1969, The isotopic age of the
   Flathead Sandstone (Middle Cambrian), Montana: Journal of
   Sedimentary Petrology, v. 39, no. 1, p. 364-368

Usage in Publication:
Flathead Sandstone

Modifications:	Geologic Province:	Dominant Lithology:
Isotopic dating	Montana folded belt province

Summary:
Seven whole-rock Rb-Sr analyses of relatively unmetamorphosed shales from upper part of unit indicate an apparent age of 555 +/-18 m.y. A single Rb-Sr age on glauconite in Flathead yields an age of 542 m.y. Both ages are in fair agreement with established Middle Cambrian age to which Flathead is assigned. Locations of samples not specified except that they are from southwest MT, Montana folded belt province.

Summary of Citation: Flathead

Publication:
Witkind, I.J., 1971, Geologic map of the Barker quadrangle,
   Judith Basin and Cascade Counties, Montana: U.S. Geological
   Survey Geologic Quadrangle Map, GQ-898, 1 sheet, scale
   1:62,500

Usage in Publication:
Flathead Sandstone*

Modifications:	Geologic Province:	Dominant Lithology:
Overview	Sweetgrass arch

Summary:
Outcrops in south half of quad, Judith Basin and Cascade Cos, MT, Sweetgrass arch. Thickness uncertain; in places at least 200 ft thick. Unconformably overlies undifferentiated pre-Belt rocks; conformably underlies Wolsey Shale. Middle Cambrian age.

Summary of Citation: Flathead

Publication:
Mudge, M.R., 1972, Pre-Quaternary rocks in the Sun River Canyon
   area, northwestern Montana, IN Geology of the Sun River
   Canyon, area, northwestern Montana: U.S. Geological Survey
   Professional Paper, 663-A, p. A1-A142, (incl. geologic map,
   scale 1:48,000)

Usage in Publication:
Flathead Sandstone*

Modifications:	Geologic Province:	Dominant Lithology:
Overview	Montana folded belt province

Summary:
Outcrops at Nineteen Mountain and near base of ridge extending from Prairie Reef north to Slategoat Mountain in western part of map area, Lewis and Clark Co, MT, Montana folded belt province. Thickness is 70-105 ft in Pretty Prairie and Glenn Creek quads (GQ-454, GQ-499, Mudge, 1966). Except at Slategoat Mountain, Flathead unconformably overlies Precambrian McNamara Formation of Missoula Group; conformably underlies Gordon Shale with gradational contact. At Slategoat Mountain, Flathead unconformably overlies lower part of Precambrian Bonner Quartzite of Missoula Group. Geologic map, stratigraphic chart, measured section. Middle Cambrian age.

Summary of Citation: Flathead

Publication:
Witkind, I.J., Hoskins, P.A., Lindsey, V.L. and Mitchell, E.L.,
   1972, Geologic map of the Henrys Lake quadrangle, Idaho and
   Montana: U.S. Geological Survey Miscellaneous Investigations
   Series Map, I-781-A, 1 sheet, scale 1:62,500

Usage in Publication:
Flathead Sandstone*

Modifications:	Geologic Province:	Dominant Lithology:
Areal limits	Montana folded belt province Snake River basin

Summary:
Occurs in Henrys Lake Mountains, Gallatin Co, MT, Montana folded belt province and Fremont Co, ID, Snake River basin. Thickness ranges from 20-200 ft. May locally include 5-10 ft of Wolsey? Shale equivalent at top. Unconformably overlies pre-Belt rocks; unconformably underlies Meagher Limestone. Middle Cambrian age.

Summary of Citation: Flathead

Publication:
Wells, J.D., 1974, Geologic map of the Alberton quadrangle,
   Missoula, Sanders, and Mineral Counties, Montana: U.S.
   Geological Survey Geologic Quadrangle Map, GQ-1157, 1 sheet,
   scale 1:62,500

Usage in Publication:
Flathead Quartzite*

Modifications:	Geologic Province:	Dominant Lithology:
Areal limits Overview	Montana folded belt province

Summary:
Outcrops in northern part of quad, with best exposures near head of Cromwell Creek and along Clark Fork in Mineral and Missoula Cos, MT in Montana folded belt province. Thickness is 40-100 ft. Rests with regional angular unconformity on Middle Proterozoic Pilcher Quartzite or Garnet Range Formation of Belt Supergroup, or diabase sills of Late Proterozoic age. Conformably underlies Middle Cambrian Silver Hill Formation. Middle Cambrian in age. Cross section. Geologic map.

Summary of Citation: Flathead

Publication:
GNU Staff, 1989, GNU Staff remark by T.W. Judkins.  Stratigraphic
   chart for Cambrian formations of western Montana (adapted
   from Tysdal, 1976, USGS Bull. 1405-I).: U.S. Geological
   Survey, unpublished geologic names committee note

Usage in Publication:
Flathead Sandstone

Modifications:	Geologic Province:	Dominant Lithology:
Figure	Montana folded belt province

Summary:
[We apologise. The figure for this synopsis is being reconstructed.]

Summary of Citation: Flathead

Publication:
GNU Staff, 1992, GNU Staff remark by T.W. Judkins.  Stratigraphic
   chart for Cambrian formations of Butte quadrangle, western
   Montana (modified from Wallace, 1987, USGS MF-1925).: U.S.
   Geological Survey, unpublished geologic names committee note

Usage in Publication:
Flathead Quartzite

Modifications:	Geologic Province:	Dominant Lithology:
Figure	Montana folded belt province

Summary:
Butte quadrangle, MT. (Compare with 1989 GNULEX Staff remark where Silver Hill Formation correlates with Flathead Sandstone and Wolsey Shale in sw MT and Bozeman, MT area.) [We apologise. The figure for this synopsis is being reconstructed.]

Summary of Citation: Flathead

Publication:
Macke, D.L., 1993, Cambrian through Mississippian rocks of the
   Powder River basin, Wyoming, Montana, and adjacent areas, IN
   Evolution of sedimentary basins; Powder River basin: U.S.
   Geological Survey Bulletin, 1917-M, p. M1-M174

Usage in Publication:
Flathead Sandstone*

Modifications:	Geologic Province:	Dominant Lithology:
Areal limits Overview	Greater Green River basin Wind River basin Powder River basin Williston basin Bighorn basin

Summary:
Assigned to lowermost part of author's stratigraphic sequence 1 (Middle Cambrian through Lower Ordovician). Stratigraphic sequences, which are bounded by major unconformities, emphasize relationships between sedimentation and tectonics. Replaces Fremont Canyon Sandstone (not used) at its type at Fremont Canyon, Natrona Co, WY, Wind River basin because sandstone called Fremont Canyon can be traced southwest to Rawlins Hills, Carbon Co, WY, Greater Green River basin, where this sandstone is Flathead. Flathead pinches out to east of Fremont Canyon in area of Alcova. Isopach map (fig. 13) shows thickness ranging from less than 20 ft in Powder River basin, thickening to greater than 200 ft along trend of Black Hills and Miles City arch in Williston basin, to greater than 240 ft in areas of Bighorn and Wind River basins. Regional stratigraphic evidence indicates unit has an early Middle Cambrian age in western WY and becomes younger to east. Upper part of Flathead near Rawlins, WY, correlates with middle or lower part of Park Shale of western WY and also, occurs within BOLASPIDELLA Zone of Lochman-Balk (1972). An isotopic age of about 550 m.y. on presumed authigenic glauconite in Flathead in MT was reported by Chaudhuri and Brookins (1969) suggesting Middle Cambrian age. Cross sections; correlation charts. Unconformably overlies Precambrian rocks; conformably underlies Gros Ventre and equivalent units within study area.