Ecoregions of Montana Second Edition

Total Page:16

File Type:pdf, Size:1020Kb

Ecoregions of Montana Second Edition DRAFT 2 Ecoregions of Montana Second Edition 116° 115° 114° 113° 112° 111° 110° 109° 108° 107° 106° 105° 104° 49° 49° BRITISH COLUMBIA 42d 42k ALBERTA CANADA SASKATCHEWAN 15d 41b 42q 42n 15h a s 17r NITED STATES u F 41a 42l U n l Plentywood a a 42n 42r 42m c t Scobey o h 42r e o a 42r K d R e i 42r 17r k v a 41c e r Fresno 15h L 42i 42b 42d K Reservoir o o Cut Bank N t e O n 41b 41b a S R i Rive a T r g Medicine 15t e Lake H Libby Shelby C Chinook D re Milk R 15q Havre ive A 42q ek r 42i Ma K r O 15l ias k R e i T ve e r A Lake r Malta 41a C Elwell y 15c d 15h n a 42j Kalispell S 42r g Glasgow i i uri R ver B o Conrad Wolf Point iss 43c 17r M ° 48° 15h 48 41d 43n e k 42r r 42r a 15l ive 43n L R 15o ri d 41b 42o ou 43c a ss e Teton River i 42r h 41e M t e 17r k a a l L Sidney F k Choteau ec 15k 15e 41b P 41c rt Fort Benton F o 15h Clar Polson 15o Thompson k F Mi or 43l ssour Falls k 15c 41d i River 42q r 43c e 15b iv R e 43l n Great Falls 42r to 17r s 15e i River w ur lo Fla o l thead Rive 41b s e r 41b is Jordan 43a Y 41b M M Superior 42q 43o 43n u s 15a s 15p e l 15a s 43n Glendive I h D 15c e A 43s l 15h l ° H R 47° 47 O i 43c 17r v 17r e 17x r 17p Lewistown Missoula 17aj 43s 43n 43a 43u 17t 43u 17al 17q 17q 16b 17x 17h 17w 43c 17al Helena White 17ak C Sulphur la 43e 43b rk 17v r Springs 43m e 17s 17x F v o i r Canyon Miles 43c R k t 17aj Ferry City 16e o 17q Harlowton Baker o 17h r Lake 43p r Roundup e t t 17ak Deer i ne River B wsto Lodge Yello Townsend 43p Hamilton 17am Musselshell River Forsyth 43t 17f Anaconda Boulder 17y 43p 43p 17ai ° 46° 46 43p 16h 17h 17g 17h 43c Butte 43o 43d 17ag 43n 17h 43p r 17ag 17y e Big Colstrip v Ri 17y r Timber e 16a 16h 43s d 43d 17w 17l 43p ow 17y 17i Billings Hardin P 43d 17ah 43n 43p Livingston 43p Columbus 17ac 17ab Bozeman 43p 17ab 17g 17h 17g 17i 43v Broadus 17ag 17ab 17z SOUTH DAK 17y 17g 43s 43e 17h 17z 43n S er 17l almon Riv 17u 17l 17aa 17e OTA 17ae 17h 43v 43k 17aa 43p Dillon 17h Salmon Red 43g 17ad 17m 45° 45° 17e 17ab Lodge 17m 43q 43g 17g 17i 17aa 18b 17ab 17e 17h 17h 17k WYOMING 17j 17e 17ab 17d Hebgen Sheridan 17e 17e Lake 17e 17l 17j 17af 17ab 17e 17h Yellowstone Cody Lake WYOMING IDAHO 115° 114° 113° 112° 111° 110° 109° 108° 107° 106° 105° Second Edition, 2002 15 Northern Rockies 17 Middle Rockies 17z Tobacco Root Mountains 42 Northwestern Glaciated Plains 43p Pine Scoria Hills 15a Grave Creek Range-Nine Mile Divide 17d Eastern Gravelly Mountains 17aa Dry Intermontane Sagebrush Valleys 42b Collapsed Glacial Outwash 43q Mesic Dissected Plains 15b Camas Valley 17e Barren Mountains 17ab Dry Gneissic-Schistose-Volcanic Hills 42d Northern Missouri Coteau 43s Non-calcareous Foothill Grassland 15c Flathead Valley 17f Crazy Mountains 17ac Big Hole 42i Glaciated Dark Brown Prairie 43t Shield-Smith Valleys 15d Tobacco Plains 17g Mid-Elevation Sedimentary Mountains 17ad Western Beaverhead Mountains 42j Glaciated Northern Grasslands 43u Limy Foothill Grassland 15e Flathead Hills and Mountains 17h Alpine Zone 17ae Forested Beaverhead Mountains 42k Coteau Lakes Upland 43v Pryor-Big Horn Foothills 15h High Northern Rockies 17i Absaroka-Gallatin Volcanic Mountains 17af Centennial Basin 42l Sweetgrass Uplands 15i Clearwater Mountains and Breaks 17j Yellowstone Plateau 17ag Pioneer-Anaconda Ranges 42m Cherry Patch Moraines 15k Clark Fork Valley and Mountains 17k Granitic Subalpine Zone 17ah Eastern Pioneer Sedimentary Mountains 42n Milk River Pothole Upland 15l Salish Mountains 17l Gneissic-Schistose Forested Mountains 17ai Elkhorn Mountains-Boulder Batholith 42o North Central Brown Glaciated Plains 17aj Eastern Divide Mountains 15o Coeur d' Alene Metasedimentary Zone 17m Dry Mid-Elevation Sedimentary Mountains 42q Rocky Mountain Front Foothill Potholes Level III ecoregion 15p St. Joe Schist-Gneiss Zone 17p Foothill Potholes 17ak Deer Lodge-Philipsburg-Avon Grassy 42r Foothill Grassland Level IV ecoregion 15q Purcell-Cabinet-North Bitterroot Mountains 17q Big Snowy-Little Belt Carbonate Mountains Intermontane Hills and Valleys 43 Northwestern Great Plains County boundary 15t Stillwater-Swan Wooded Valley 17r Scattered Eastern Igneous-Core Mountains 17al Southern Garnet Sedimentary-Volcanic Mountains 43a Missouri Plateau State boundary 17s Bitterroot-Frenchtown Valley 17am Flint Creek-Anaconda Mountains 43b Little Missouri Badlands International boundary 17t Limy Foothill Savanna 18 Wyoming Basin 43c River Breaks 17u Paradise Valley 18b Bighorn Basin 43d Forested Buttes 16 Idaho Batholith 17v Big Belt Forested Highlands 16a Eastern Batholith 41 Canadian Rockies 43e Sagebrush Steppe 17w Townsend Basin 43g Semiarid Pierre Shale Plains 16b Lochsa Uplands 41a Northern Front 15 10 5 0 30 60 mi 17x Rattlesnake-Blackfoot-South Swan-Northern 43k Dense Clay Prairie 16e Glaciated Bitterroot Mountains and Canyons Garnet-Sapphire Mountains 41b Crestal Alpine-Subalpine Zone 43l Missouri Breaks Woodland-Scrubland 30 20 100 60 120 km 16h High Idaho Batholith 17y Townsend-Horseshoe-London Sedimentary 41c Western Canadian Rockies 43m Judith Basin Grassland Albers equal area projection Hills 41d Southern Carbonate Front Standard parallels 46° N and 48° N 41e Flathead Thrust Faulted Carbonate-Rich 43n Montana Central Grasslands Mountains 43o Unglaciated Montana High Plains.
Recommended publications
  • Alteration Petrology in the Potosi Mining District Tobacco Root Mountains Montana
    University of Montana ScholarWorks at University of Montana Graduate Student Theses, Dissertations, & Professional Papers Graduate School 1975 Alteration petrology in the Potosi Mining District Tobacco Root Mountains Montana Michael James Burnside The University of Montana Follow this and additional works at: https://scholarworks.umt.edu/etd Let us know how access to this document benefits ou.y Recommended Citation Burnside, Michael James, "Alteration petrology in the Potosi Mining District Tobacco Root Mountains Montana" (1975). Graduate Student Theses, Dissertations, & Professional Papers. 7724. https://scholarworks.umt.edu/etd/7724 This Thesis is brought to you for free and open access by the Graduate School at ScholarWorks at University of Montana. It has been accepted for inclusion in Graduate Student Theses, Dissertations, & Professional Papers by an authorized administrator of ScholarWorks at University of Montana. For more information, please contact [email protected]. ALTERATION PETROLOGY IN THE POTOSI MINING DISTRICT, TOBACCO ROOT MOUNTAINS, MONTANA by Michael Burnside B.A., University of Montana, 1970 Presented in partial fulfillm ent of the requirements for the degree of Master of Science UNIVERSITY OF MONTANA 1975 Approved by: Chairman, Board o£/Examiners DeapC^ Graduate-^^hool ' Date Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. UMI Number: EP38525 All rights reserved INFORMATION TO ALL USERS The quality of this reproduction is dependent upon the quality of the copy submitted. In the unlikely event that the author did not send a complete manuscript and there are missing pages, these will be noted. Also, if material had to be removed, a note will indicate the deletion.
    [Show full text]
  • Montana Forest Insect and Disease Conditions and Program Highlights
    R1-16-17 03/20/2016 Forest Service Northern Region Montata Department of Natural Resources and Conservation Forestry Division In accordance with Federal civil rights law and U.S. Department of Agriculture (USDA) civil rights regulations and policies, the USDA, its Agencies, offices, and employees, and institutions participating in or administering USDA programs are prohibited from discriminating based on race, color, national origin, religion, sex, gender identity (including gender expression), sexual orientation, disability, age, marital status, family/parental status, income derived from a public assistance program, political beliefs, or reprisal or retaliation for prior civil rights activity, in any program or activity conducted or funded by USDA (not all bases apply to all programs). Remedies and complaint filing deadlines vary by program or incident. Persons with disabilities who require alternative means of communication for program information (e.g., Braille, large print, audiotape, American Sign Language, etc.) should contact the responsible Agency or USDA’s TARGET Center at (202) 720-2600 (voice and TTY) or contact USDA through the Federal Relay Service at (800) 877-8339. Additionally, program information may be made available in languages other than English. To file a program discrimination complaint, complete the USDA Program Discrimination Complaint Form, AD-3027, found online at http://www.ascr.usda.gov/complaint_filing_cust.html and at any USDA office or write a letter addressed to USDA and provide in the letter all of the information requested in the form. To request a copy of the complaint form, call (866) 632-9992. Submit your completed form or letter to USDA by: (1) mail: U.S.
    [Show full text]
  • Characterization of Ecoregions of Idaho
    1 0 . C o l u m b i a P l a t e a u 1 3 . C e n t r a l B a s i n a n d R a n g e Ecoregion 10 is an arid grassland and sagebrush steppe that is surrounded by moister, predominantly forested, mountainous ecoregions. It is Ecoregion 13 is internally-drained and composed of north-trending, fault-block ranges and intervening, drier basins. It is vast and includes parts underlain by thick basalt. In the east, where precipitation is greater, deep loess soils have been extensively cultivated for wheat. of Nevada, Utah, California, and Idaho. In Idaho, sagebrush grassland, saltbush–greasewood, mountain brush, and woodland occur; forests are absent unlike in the cooler, wetter, more rugged Ecoregion 19. Grazing is widespread. Cropland is less common than in Ecoregions 12 and 80. Ecoregions of Idaho The unforested hills and plateaus of the Dissected Loess Uplands ecoregion are cut by the canyons of Ecoregion 10l and are disjunct. 10f Pure grasslands dominate lower elevations. Mountain brush grows on higher, moister sites. Grazing and farming have eliminated The arid Shadscale-Dominated Saline Basins ecoregion is nearly flat, internally-drained, and has light-colored alkaline soils that are Ecoregions denote areas of general similarity in ecosystems and in the type, quality, and America into 15 ecological regions. Level II divides the continent into 52 regions Literature Cited: much of the original plant cover. Nevertheless, Ecoregion 10f is not as suited to farming as Ecoregions 10h and 10j because it has thinner soils.
    [Show full text]
  • MBMG 505-Jefferson-V2.FH10
    GEOLOGIC MAP OF THE CENOZOIC DEPOSITS OF THE UPPER JEFFERSON VALLEY MBMG Open File Report 505 2004 Compiled and mapped by Susan M. Vuke, Walter W. Coppinger, and Bruce E. Cox This report has been reviewed for conformity with Montana Bureau of Mines and Geology’s technical and editorial standards. Partial support has been provided by the STATEMAP component of the National Cooperative Geology Mapping Program of the U.S. Geological Survey under contract Number 03HQAG0090. CENOZOIC DEPOSITS OF THE UPPER JEFFERSON VALLEY Cenozoic deposits are the focus of the Geologic Map of the upper Jefferson Valley. The map is largely a compilation of previous mapping with additional interpretations based on aerial photos and limited additional field work. Older rocks are included to show their relations to the Cenozoic deposits, but they are generalized on the map. Lithologic descriptions of the Cenozoic deposits are given in the map explanation (p. 17). References used for the map compilation are shown on p. 15. The northern and southern parts of the map are discussed separately. NORTHERN PART OF MAP AREA Quaternary deposits A variety of Quaternary deposits blanket much of the slope area of the Whitetail and Pipestone Creek valleys between the flanks of the Highland Mountains and Bull Mountain (Fig. 1). East and southeast of these Quaternary slope deposits are more isolated areas of partly cemented Pleistocene gravels on pediments. One of these gravel deposits near Red Hill (Fig. 1) yielded a late Pleistocene vertebrate assemblage including cheetah, horse, camel, and large mountain sheep. Radiocarbon dates from the lowest part of the sequence range between 10,000 and 9,000 14C yr.
    [Show full text]
  • 6800-Year Vegetation and Fire History in the Bitterroot Mountain Range Montana
    University of Montana ScholarWorks at University of Montana Graduate Student Theses, Dissertations, & Professional Papers Graduate School 1995 6800-year vegetation and fire history in the Bitterroot Mountain Range Montana Anne Elizabeth Karsian The University of Montana Follow this and additional works at: https://scholarworks.umt.edu/etd Let us know how access to this document benefits ou.y Recommended Citation Karsian, Anne Elizabeth, "6800-year vegetation and fire history in the Bitterroot Mountain Range Montana" (1995). Graduate Student Theses, Dissertations, & Professional Papers. 6683. https://scholarworks.umt.edu/etd/6683 This Thesis is brought to you for free and open access by the Graduate School at ScholarWorks at University of Montana. It has been accepted for inclusion in Graduate Student Theses, Dissertations, & Professional Papers by an authorized administrator of ScholarWorks at University of Montana. For more information, please contact [email protected]. Anne- K a r s j a n i Maureen and Mike MANSFIELD LIBRARY TheM University ontana of Permission is granted by tlie author to reproduce this material in its entirety, provided that tliis material is used for scholarly purposes and is properly cited in published works and repoits. * * Please check "Yes'' or “No “ and provide signature Yes, I grant permission ..\1 No, I do not grant permission ----- Author’s Signature Date; ' n 1 Any copying for commercial purposes or financial gain may be undertaken only with ^he author’s explicit consent. ■ Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. A 6800-YEAR VEGETATION AND FIRE HISTORY IN THE BITTERROOT MOUNTAIN RANGE, MONTANA By ANNE ELIZABETH KARSIAN Presented in partial fulfillment of the requirements for the degree of MASTER OF SCIENCE UNIVERSHY OF MONTANA Department of Forestry 1995 Approved by: t' z o Chairperson 7 ^ ^ ^ /.
    [Show full text]
  • Birding in the Missoula and Bitterroot Valleys
    Birding in the Missoula and Bitterroot Valleys Five Valleys and Bitterroot Audubon Society Chapters are grassroots volunteer organizations of Montana Audubon and the National Audubon Society. We promote understanding, respect, and enjoyment of birds and the natural world through education, habitat protection, and environmental advocacy. Five Valleys Bitterroot Audubon Society Audubon Society P.O. Box 8425 P.O. Box 326 Missoula, MT 59807 Hamilton, MT 59840 www.fvaudubon.org/ www.bitterrootaudubonorg/ Montana Audubon P.O. Box 595 Helena, MT 59624 406-443-3949 www.mtaudubon.org Status W Sp Su F Bird Species of West-central Montana (most vagrants excluded) _ Harlequin Duck B r r r Relative abundance in suitable habitat by season are: _ Long-tailed Duck t r r c - common to abundant, usually found on every visit in _ Surf Scoter t r r r moderate to large numbers _ White-winged Scoter t r r r u - uncommon, usually present in low numbers but may be _ Common Goldeneye B c c c c _ missed Barrow’s Goldeneye B u c c c _ o - occasional, seen only a few times during the season, not Bufflehead B o c u c _ Hooded Merganser B o c c c present in all suitable habitat _ Common Merganser B c c c c r - rare, one to low numbers occur but not every year _ Red-breasted Merganser t o o _ Status: Ruddy Duck B c c c _ Osprey B c c c B - Direct evidence of breeding _ Bald Eagle B c c c c b - Indirect evidence of breeding _ Northern Harrier B u c c c t - No evidence of breeding _ Sharp-shinned Hawk B u u u u _ Cooper’s Hawk B u u u u Season of occurrence: _ Northern Goshawk B u u u u W - Winter, mid-November to mid-February _ Swainson’s Hawk B u u u Sp - Spring, mid-February to mid-May _ Red-tailed Hawk B c c c c Su - Summer, mid-May to mid-August _ Ferruginous Hawk t r r r F - Fall, mid-August to mid-November _ Rough-legged Hawk t c c c _ Golden Eagle B u u u u This list follows the seventh edition of the AOU check-list.
    [Show full text]
  • Level IV Ecoregions of Montana
    DRAFT 2 Ecoregions denote areas of general similarity in ecosystems and in the type, quality, and quantity of environmental resources; they are designed to serve as a spatial framework for the research, assessment, management, and monitoring of ecosystems and ecosystem components. By recognizing the spatial differences in the capacities and potentials of ecosystems, ecoregions stratify the environment by its Ecoregions of Montana probable response to disturbance (Bryce and others, 1999). These general purpose regions are critical for Second Edition structuring and implementing ecosystem management strategies across federal agencies, state agencies, and nongovernment organizations that are responsible for different types of resources within the same 116° 115° 114° 113° 112° 111° 110° 109° 108° 107° 106° 105° 104° geographical areas (Omernik and others, 2000). ° 49° The approach used to compile this map is based on the premise that ecological regions can be identified 49 BRITISH COLUMBIA 42d through the analysis of the spatial patterns and the composition of biotic and abiotic phenomena that affect ALBERTA SASKATCHEWAN 42k or reflect differences in ecosystem quality and integrity (Wiken, 1986; Omernik, 1987, 1995). These 15d CANADA 15h 41b 42q 42n sa 17r ATE S phenomena include geology, physiography, vegetation, climate, soils, land use, wildlife, and hydrology. u F 41a 42l UNITED ST n l Plentywood a a 42n 42r 42m Scobey c th 42r o e The relative importance of each characteristic varies from one ecological region to another regardless of o a 42r K d R e i 42r 17r the hierarchical level. A Roman numeral hierarchical scheme has been adopted for different levels of k v a 41c e r Fresno 15h L 42i 42b 42d ecological regions.
    [Show full text]
  • Geologic Map of Ruby Dam Area Southwestern Montana
    Geologic Map of Ruby Dam Area Southwestern Montana Compiled and Mapped by Zachary C. St. Jean and Deirdre R. Teeter Montana Bureau of Mines and Geology Open File Report MBMG 488 2004 This report has had preliminary reviews for conformity with Montana Bureau of Mines and Geology’s technical editorial standards. Partial support has been provided by the EDMAP component of the National Cooperative Geological Mapping Program of the U.S. Geological Survey under Contract Number 01HQAG0157. Introduction This project was funded by the EDMAP program of the U. S. Geological Survey. Field studies, including geologic mapping and a gravity and magnetic survey, were conducted during the 2001 field season. These studies were undertaken to gain a better understanding of the geologic structure of the Ruby basin in the area of Ruby Dam in southwest Montana (Figures 1 and 2). Ruby Dam, which impounds Ruby Reservoir, lies within a seismically active region known as the Intermountain Seismic Belt. Delineation and detailed mapping of the Tertiary and Quaternary sediments has helped to understand better the occurrence of Quaternary faulting in the basin. No new faults of Quaternary age were recognized within the field area. However, a fault that offsets Quaternary deposits was newly mapped by the authors in a gravel pit two miles north of the north map boundary. This fault may change previously calculated ground acceleration values at the dam site, and may indicate a greater susceptibility of the dam to seismic activity than previously thought. The geologic map in this report combines previous work that focused on the bedrock of the area with new mapping of the Tertiary and Quaternary deposits by the present authors.
    [Show full text]
  • Geological Survey
    DEPARTMENT OF THE INTERIOR BULLETIN OF THE UNITED STATES GEOLOGICAL SURVEY No. 17O t, WASHINGTON GOVERNMENT PRINTING OFFICE 1900 UNITED STATES GEOLOGICAL SUKVEY CHARLES D. WALCOTT, DIRECTOR SURVEY OF THE BOUNDARY LINE BETWEEN IDAHO AND MONTANA FROM THE INTERNATIONAL BOUNDARY TO THE CREST OF THE BITTERROOT MOUNTAINS BY RICHARD TJRQUHART GOODE WASHINGTON GOVERNMENT PRINTING OFFICE 1900 CONTENTS. Page. Letter of transmittal - _. .... _..._......_....--..,.. ........... 9 Instructions ...............................1...^.......................... 11 Boundary lines.-. ....--..........---.-.--..-.-..-............-.-.-..---- 15 Account of operations ...........................-._._........... .--. 18 Latitude, longitude, base line, azimuth, and triangulation _...__.._.._..___ 21 Latitude _...-. .--.---.-... -.....-..-..........._................ 21 Longitude.........---.-..-..-..-.....-..--.. ............. ....-.-. 23 Spokane base line................J......................__._._.. 25 Azimuth .__.---.--.-.-.....___.. _..--...__.__.__.. ._._........--. 25 Triangulation ................... __........._.'......._._._.....-- 29 Transit and stadia work.................................................. 40 Monuments _. ..;......____.._._.,_._._._....__,, ._.....__. ..-..... 47 The international boundary west of the summit of the Eocky Mountains, and the Mooyie Trail monument..............................._..... 58 Financial statement ................... °........................_.i........ 63 Index ..............J.....................................................
    [Show full text]
  • MONTANA N7 4Qea
    E 12, p( /F- o77 (r 2) Sf(jji PGJ/F-077(82) National Uranium Resource Evaluation 6 BOZEMAN QUADRANGLE 41 MONTANA n7 4QeA/ University of Montana Missoula, Montana and Montana State University Bozeman, Montana E2T oFi Issue Date August 1982 SATESO9 PREPARED FOR THE U.S. DEPARTMENT OF ENERGY Assistant Secretary for Nuclear Energy Grand Junction Area Office, Colorado rmetadc957781 Neither the United States Government nor any agency thereof, nor any of their employees, makes any warranty, express or implied, or assumes any legal liability or responsibility for the accuracy, completeness, or usefulness of any information, apparatus, product, or process disclosed in this report, or represents that its use would not infringe privately owned rights. Reference therein to any specific commercial product, process, or service by trade name, trademark, manufacturer, or otherwise, does not necessarily constitute or imply its endorsement, recommendation, or favoring by the United States Government or any agency thereof. The views and opinions of authors expressed herein do not necessarily state or reflect those of the United States Government or any agency thereof. This report is a result of work performed by the University of Montana and Montana State University, through a Bendix Field Engineering Corporation subcontract, as part of the National Uranium Resource Evaluation. NURE was a program of the U.S. Department of Energy's Grand Junction, Colorado, Office to acquire and compile geologic and other information with which to assess the magnitude and distribution of uranium resources and to determine areas favorable for the occurrence of uranium in the United States. Available from: Technical Library Bendix Field Engineering Corporation P.O.
    [Show full text]
  • Stratigraphy and Structure of the Rock Creek Area, Beaverhead County, Montana by James Franklin Peters
    AN ABSTRACT OF THE THESIS OF JAMES FRANKLIN PETERS for the Master of Science (Name) (Degree) in Geology presented on (Major) (Date) Title: STRATIGRAPHY AND STRUCTURE OF THE ROCK CREEK AREA, BEAVERHEAD COUNTY, MONTANA Abstract approved:Redacted for Privacy Dr. David A. Bostwick The Rock Creek area consists of 53 square miles located in the eastern foothills of the Pioneer Mountains, Beaverhead County, Montana. Approximately 8, 500 feet of late Paleozoic and early Mesozoic contact-metamorphosed sedimentary rocks and late Meso- zoic sedimentary rocks are exposed in the area of study. Most of the late Paleozoic and Mesozoic rocks were deposited along the eastern edge of the Cordilleran miogeosyncline.The old- est exposed rocks in the map area belong to the Amsden Formation of Late Mississippian to Early Pennsylvanian age.Other late Paleo- zoic rock units include the Quadrant Formation of Pennsylvanian age and the Phosphoria Formation of Permian age.Mesozoic forma- tions include the Dinwoody Formation of Triassic age and the Kootenai Formation and Colorado Group of Cretaceous age. The Tertiary is represented bybasin depositsand basaltic andesite extrusives.Unconsolidated Quaternary glacialand fluvial deposits complete the stratigraphicsuccession. Granodiorite intrusive rocksoccupy the southwestern corner of the area mapped andcompose part of the eastern margin of the Mount Torrey Batholith, whichis probably genetically relatedto the Boulder Batholith.Along the margin of the intrusive,contact meta- morphism has destroyed the originalsedimentary characteristics of the late Paleozoic and earlyMesozoic Formations. During the Late Cretaceous Laramideorogeny the sedimentary rocks were tilted and faulted. Thestructures in the area are related to the main episode of Laramidedeformation, emplacement of the Mount Torrey Batholith, and laterphases of structural adjustment.
    [Show full text]
  • The Archean Geology of Montana
    THE ARCHEAN GEOLOGY OF MONTANA David W. Mogk,1 Paul A. Mueller,2 and Darrell J. Henry3 1Department of Earth Sciences, Montana State University, Bozeman, Montana 2Department of Geological Sciences, University of Florida, Gainesville, Florida 3Department of Geology and Geophysics, Louisiana State University, Baton Rouge, Louisiana ABSTRACT in a subduction tectonic setting. Jackson (2005) char- acterized cratons as areas of thick, stable continental The Archean rocks in the northern Wyoming crust that have experienced little deformation over Province of Montana provide fundamental evidence long (Ga) periods of time. In the Wyoming Province, related to the evolution of the early Earth. This exten- the process of cratonization included the establishment sive record provides insight into some of the major, of a thick tectosphere (subcontinental mantle litho- unanswered questions of Earth history and Earth-sys- sphere). The thick, stable crust–lithosphere system tem processes: Crustal genesis—when and how did permitted deposition of mature, passive-margin-type the continental crust separate from the mantle? Crustal sediments immediately prior to and during a period of evolution—to what extent are Earth materials cycled tectonic quiescence from 3.1 to 2.9 Ga. These compo- from mantle to crust and back again? Continental sitionally mature sediments, together with subordinate growth—how do continents grow, vertically through mafi c rocks that could have been basaltic fl ows, char- magmatic accretion of plutons and volcanic rocks, acterize this period. A second major magmatic event laterally through tectonic accretion of crustal blocks generated the Beartooth–Bighorn magmatic zone assembled at continental margins, or both? Structural at ~2.9–2.8 Ga.
    [Show full text]