Geology of a Part of the Southern Margin of the Gallatin Valley Southwest Montana
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University of Montana ScholarWorks at University of Montana Graduate Student Theses, Dissertations, & Professional Papers Graduate School 1963 Geology of a part of the southern margin of the Gallatin Valley Southwest Montana Martin David Mifflin 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 Mifflin, Martin David, "Geology of a part of the southern margin of the Gallatin Valley Southwest Montana" (1963). Graduate Student Theses, Dissertations, & Professional Papers. 6114. https://scholarworks.umt.edu/etd/6114 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]. NOTICE: THIS MATERIAL MAY BE PROTECTED BY COPYRIGHT LAW 3^ A tm GEOLOGY OF A PART OF THE SOUTHERN MARGIN OF THE GALLATIN VALLEY, SOUTHWEST MONTANA by MARTIN D. MIFFLIN A thesis submitted to the Graduate Faculty in partial fulfillment of the requirements for the degree of MASTER OF SCIENCE IN APPLIED SCIENCE With a Major in Geology Approved : Head, Major Department Chairman, Examining Committee an, Graduate Division MONTANA STATE COLLEGE Bozeman, Montana June, 1963 UMI Number: EP36915 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. UMT UMI EP36915 Published by ProQuest LLC (2013). Copyright in the Dissertation held by the Author. Microform Edition © ProQuest LLC. All rights reserved. This work is protected against unauthorized copying under Title 17, United States Code ProOuesf ProQuest LLC. 789 East Eisenhower Parkway P.O. Box 1346 Ann Arbor, Ml 48106 -1346 ItEfiTRtCTCO SfALK N 3 ’S' „!( VITA Martin David Mifflin was born on March 29, 1937, in Olympia, Washington. His parents are John P. Mifflin (deceased) and Eva Louise Mifflin. Mr. Mifflin attended public primary schools in Portland, •Oregon; Olympia, Washington; and Silver Springs, Maryland. He graduated from West Valley High School in Millwood, Washington, in 1955. He then entered Washington State College and attended until early in 1957. The spring quarter of 1957 he attended Eastern Washington College of Educa tion at Cheney, Washington. The fall of 1957 he entered the University of Washington and graduated in the spring of 1960 with a B.S. in geology In the fall of 1960 he entered Montana State College, in pursuit of a master's degree in Applied Science with a major in Geology. Professional experience other than this study consists of six months as an apprentice geologist for Pan American Petroleum Corporation in western Alaska in 1959, and three months as a geologist for the U.S. Geological Survey in the Lemhi Range in Idaho, in 1962. TABLE OF CONTENTS INTRODUCTION ............................................ 1 Previous Investigations . 2 Acknowledgements. ....... « .......... 3 GEOGRAPHY................................................ 3 Location............ 3 Topography........................... 4 Climate............. ..... 4 Land Economics............................. 5 Vegetation.......................................... 5 STRATIGRAPHY............................................ 6 PreCambrian ...... 6 Paleozoic ................ 8 Middle Cambrian................ 8 Upper C a m b r i a n ........................... 10 Devonian ............ 11 Mlssissippian . ................. ...... 12 Tertiary.................... 12 Eocene............ 12 Late Miocene......................... 15 Intrusive Rocks .............. 24 Surficial Deposits and Related Features . , ........... 25 West Gallatin River Floodplain (Qal) ............... 27 Terrace No. 1 (Qtgi) .......................... 29 Terrace No, 2 (Qtg2) .............................. 30 Terrace No. 3 (Qtgg)............................... 32 Other River Terrace Remnants....................... 34 Analysis of Terrace Slopes ................... 36 Pediment Remnants (Qpg^) ................. 41 High Gravels (Qpg2) 47 Other Terraces......... 56 Alluvial Fans (Qfg)............................... 56 Mass Wasting Deposits (Qm).......................... 57 L o e s s ............................................ 58 PALEOTOPOGRAPHY.......................................... 60 Pre-late Miocene Paleotopography...................... 60 Pre-middle Eocene Paleotopography .................... 64 STRUCTURE................................................ 68 Regional Structural Setting .......................... 68 Faults............................................. 72 The Salesville Fault ............................... 73 Elk Creek Faults .............................. 76 Highline Canal Faults................. 79 iv Gallatin Range Front Fault.......................... 83 Brown Hollow Faults .............................. 88 Camp Creek Valley Fault........................... 91 Other F a u l t s ......................................' 95 Other structural Features.............. 96 Conclusions Regarding Structure........................ 97 GEOLOGIC HISTORY ........................................... 99 Precambrlan............................................. 99 Paleozoic to Early Late Cretaceous........................ 99 Late Cretaceous and Faleocene........................... 100 E o c e n e ................................................102 Ollgocene to late Miocene ............. ......... 103 Late Miocene to P l i o c e n e ............................... 105 Pliocene to early Pleistocene .......................... 105 Middle and late Pleistocene ........................... 107 Summary................ 107 LIST OF PLATES Plate I Geologic map of a part of the southern margin of the Gallatin Valley, Montana In Pocket Plate II Cross sections and profiles of the south margin of the Gallatin Valley, Montana After Page 36 Plate III Index map of fault relationships After Page 72 LIST OF FIGURES Figure 1 Southeast view of basic volcanic rock remnant .... 14 Figure 2 Ditch exposures of laté Miocene strata, and Qpg^ surface ................................. 15 Figure 3 Dipping late Miocene strata near Brown Hollow . 16 Figure 4 Late Miocene arkoslc conglomerate.............. 20 Figure 5 Tentative correlations of surficial features . 26 Figure 6 View of Qtgg, Qtgu, and Qpg^ surfaces................. 30 Figure 7 Gravels of Qpg^..................................... 33 Figure 8 Northerly view of High F l a t ......................... 43 Figure 9 Typical relationship of pediment gravels............... 44 V Figure 10 Gravels of Q p g g ........ 47 Figure 11 Southwesterly view of High Flat and Qpgg deposits . 49 Figure 12 Exposure of Qpgg deposits.......................... 50 Figure 13 Northerly view of Qpg, remnants and Qpg_ pediment h e a d ......... : ............... ^..............52 Figure 14 Loess deposits on Qpgg gravel....................... 58 Figure 15 View of partly exhumed Camp Creek paleotopographic valley ......................................... 61 Figure 16 View of the low relief developed on the bedrock of High Flat....................................... 64 Figure 17 Diagrams of two possible modes of development of the High Flat low relief surface.....................65 Figure 18 Gallatin Valley structure index map .............. 71 Figure 19 Diagram of the tilted fault block bedrock relation ships ................ 77 Figure 20 Middle Highline Canal Fault bedrock displacement. 81 Figure 21 Fault drag in late Miocene strata along Middle Highline Fault.................................. 82 Figure 22 View of the Gallatin Range Front Fault and W. Gallatin River canyon............................ 84 Figure 23 Late Miocene strata dipping 25° east................ 87 Figure 24 East Brown Hollow Fault scarp .................... 88 Figure 25 Two interpretations of the development of E. Brown Hollow Fault scarp.............. 90 Figure 26 Possible relationships on the SE portion of Camp Creek Fault..................................... 93 Figure 27 Relationships of Camp Creek fault post late Miocene movement ......................... • • . 94 Vi ABSTRACT A detailed study of an 88-square-inile area along the southern margin of the Gallatin Valley where late Miocene tuffaceous sediments rest with sinuous unconformable contact on Precambrian metamorphic rocks and Paleozoic strata indicates that structural features control the present configuration of the south margin of the valley. However, much of the evidence pertinent to the Cenozoic history of the area is either indirect or so sparse as to be only suggestive. The sinuous contact, which would suggest sediments partly filled the present valley rather than that structure controlled the valley margin, is the result of a partially exhumed pre-late Miocene paleotopography which displays 2,500 feet of relief and eastward paleodrainage subparallel to Laramide structural trends. Total exhumation of the pre-late Miocene paleo topography apparently would yield mountainous topography with 3,500 or more feet of relief. Some of the old topographic high areas have broad summits which may be remnants of a pre-middle Eocene subvolcanic erosion surface stripped of Early