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The Physiographic History of Western Montana and Northwestern Idaho

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The Physiographic History of Western Montana and Northwestern Idaho Montana Tech Library Digital Commons @ Montana Tech Bachelors Theses and Reports, 1928 - 1970 Student Scholarship 5-1948 The hP ysiographic History of Western Montana and Northwestern Idaho John R. Kavanagh Follow this and additional works at: http://digitalcommons.mtech.edu/bach_theses Part of the Ceramic Materials Commons, Environmental Engineering Commons, Geology Commons, Geophysics and Seismology Commons, Metallurgy Commons, Other Engineering Commons, and the Other Materials Science and Engineering Commons Recommended Citation Kavanagh, John R., "The hP ysiographic History of Western Montana and Northwestern Idaho" (1948). Bachelors Theses and Reports, 1928 - 1970. Paper 251. This Bachelors Thesis is brought to you for free and open access by the Student Scholarship at Digital Commons @ Montana Tech. It has been accepted for inclusion in Bachelors Theses and Reports, 1928 - 1970 by an authorized administrator of Digital Commons @ Montana Tech. For more information, please contact [email protected]. THE PHYSIOGRAPHIO HISTORY OF WESTERN MONTANA AND NORTHERN IDAHO by JOHN R. KAVANAGli A.Thesis Submitted to the Departm It of Qeology in partial fulfill t of the Requirements for the degree of Baohelor of Soience in Geologioel Engineering MONTANA SCHOOL OF MINES BUTTE, MONTANA. Kay, 1948 THE PHYSIOGR~IC HISTORY OF WESTERN MONTANA AND NORTHERN IDAHO 1'Y JOHN R. KAVANAGH .a Theds SUbmitted to the Department of Geology in partial fUlf.illment of the Requir~mcnt3 fo~ tho degree of Baoheler of Scienoe in GeolQgiNLl Engineering 19753 MONTANA SCHOOL OF MINES , BUTTE. MONTANA ~ay, 1948 CONTENTS .Page Introduotion •••••••••••••••••••••••••••••••••••••••••••••••••• 1 General statement ••••••••••••••••••••••••••••••••••••••••• 1 SWmnary ot proposed drainage moditication ••••••••••••••••• 2 Aoknowledgmenta •••••••••••••••••••••••••••••••••••••••••••••••• 2 Present Land for.ms••••••••••••••••••••••••••••••••••••••••••••• 3 General statement ••••••••••••••••••••••••••••••••• ~••••••• 3 The Rocky Mountain trench ••••••••••••••••••••••••••••••••• 3 The Purcell trench •••••••••••••••••••••••••••••••••••••••• 4 The mountain systems •••••••••••••••••••••••••••••••••••••• 6 ROCky Mountain system (Daly) •.••••••.;••••••••••••••••• b Mountains between the two trenches ••••••••••••••••••• 6 The Selkirk system •••••••••••••••••••••••••••••••.••• 7 Summary ot the historical geology (Northern Rocky Mountains) ••• 8 Genera! statement ••••••••••••••••••••••••••••••••••••••••• 8 Mountains or Idaho •••••••••••••••••••••••••••••••••••••••• 9 Rocks ••••••••••••••••••••••••••••••••••••••••••• '••••• 9 Order of events •••••••••••••••••••••••••••••••••••••• 10 Mountains of the anadian Border •••••••••••••••••••••••••• 11 fhe Tertiary peneplain ••••••••••••••••••••••••••••••• 11 Alpine glaciation •••••••••••••••••••••••••••••••••••• 12 Rocks and structure •••••••••••••••••••••••••••••••••• 12 Mountains of southern Montana ••••••••••••••••••••••••••••• 12 Tertiary Basins ••••••••••••••• ·•.•••••..•••••••..•••••.•••• 12 Previous work regarding drainage modification •••••••••••••••••• 13 The controversy of the Salmon River area •••••••••••••••••• 13 Southwestern Montana •••••••••••••••••••••••••••••••••..•••• 15 Northern Idaho •••••••••••••••••••••••••••••••••••••••••••• 16 Glaciation ......................................•••••••••••. ~•.••. 16 General statement ••••••••••••••••••••••••••••••••••••••••• 16 Northern Idaho •••••••••••••••••••••••••••••••••••••••••••• 18 The Rocky Mountain trench ••••••••••••••••••• '••••••• ~ •••••• 19 The Clark Fork valley ••••••••••••••••••••••••••••••••••••• 20 Glaoial Lake Miss9ula ••••••••••••••••••••••••••••••••••••• 21 The major valleys ot northwestern Montana and northern Idaho ••• 22 Flathead valley . 22 Jooko River Talley •••••••••••••••••••••••••••••••••••••••• 23 Clark Fork valley ••••••••••••••••••••••••••••••••••••••••• 23 Kootenai-Pend Oreille depression •••••••••••••••••••••••••• 23 Kootenai River valley ••••••••••••••••••••••••••••••••••••• 24 The reoonstructed drainage pattern ••••••••••••••••••••••••••••• 25 General sta.tement •••••••••.••••••••••••••••••••••••.••••••.• 25 Proposed modifications •••••••••••••••••••••••••••••••••••• 27 Kootenai River •••••••••••.••••••••.•• ·.••••••••.•••.•• 28 Clark Fork River ••••••••••••••••••••••••••••••••••••• 28 Bitterroot River ••••••••••••••• ·•••••••••••••••••••••• 30 Flathead River ••••••••••••••••••••••••••••••••••••••• 31 Rivers east of the .lathead and Bitterroot rivers •••• ,31 ILLUSTRATIONS Page Plate I Map showing distribution of Tertiary and Quaternary sediments in western Montana and northern Idaho •••••••••••••••••• In pooket II Map showing proposed Eooene (1) drainage pattern for northwestern Montana •••••••••••• In pocket Figure 1. Physiographic provinoes between the 41th and 53rd parallels of latitude ••••••••• 4 20 Index map of,the northern Rocky Mountains ••• 5 3. Map showing relation of Big Hole River to anoient valleys. the trends of whioh are shown by shading •••••••••••••••••••••••••••• 15 4. Glaoial Lake Missoula hemmed in by a bar- rier of ioe to the north •••••••••••••••••••• 17 5. Diagram of Mission Range. Montana. looking east ••.•.•.....•••..••••..•••....•..•..•••.•• 20 -THE PHYSIOGRAPHIC HISTORY -~=~;;.;.OF WESTERN ...MONTANA--~ ~NORTHERN IDAHO by John R. Kavanagh INTRODUCTION General Statement Millions of years of physiographic changes have co:m.ditionedU8 to the fact that our present drainage is a temporary feature. Rivers once flow- ing opposite to their present direction i8 not an unusual condition for physiographers to suggest. It i8 less common that they propose the exis- tence of a former major drainage system trending across that of the pre- sent time. Both of these conditions are suggested by the writer as having been in exi8tence during early Tertiary time in northwestern Montana. The purposes of this thesis are two-fold. First, a review was made, and is here presented, ot the previous physiographic work. that has been done on an area including: (1) The region in Montana west ot Butte and west of ,the front ranges ot the Rocky Mountains in northern Montana, (2) Idaho, north of the Snake River. Secondly, some possible drainage modification8 in northwestern Montana, which have heretofore not been suggested, are pro- posed. Particular emphasi8 will be placed on the Clark Fork and Flathead valleys. It should be emphasized at the outset that the drainage modifications herein suggested are presented as an hypothesi8, and nothing more. No field work in regards to this problem has been done by the author., and of course it i8 realized that intensive tield work must be done in oertain areas in order to either prove or disprove the hypothesis. The problem is an exoeedingly complioated one. For one reason, very little work ot thi8 nature has been done in this area; tor another, evi- dence i8 obsoured by earth uplift, glaoial erosion and deposition, and dense vegetation. For example, when one would desire to recommend drainage modi- fication on the basis of a "barbed" drainage pattern, he must reckon with those streams whioh naturally follow fault lines. And these fault lines are in turn obscured by glacial till or by heavy vegetation, or more gen- erally by both. Summary of Proposed Drainage Modification It would be proper to submit at this time a summary of the drainage changes proposed. The relationships of the various streams to the overall modification pattern might be better kept in mind if this preliminary summary is given. Primarily on the basis of the idealized drainage pattern presented by the piecing together of the major wide valleys of the region, the following modifications are proposed, (Refer to Plate II) (1) In early Tertiary times the Upper Clark Fork flowed in opposite direction throughout most of its present valley, (2) The Kootenai River flowed southward into Clark Fork valley, (3) The Flathead River had its CGurse the same as at present as far south as the town of Dixon. From Dixon, where it joined the old Clark Fork valley, it traveled southward through the Jocko River valley to Missoula, and then continued southward through the Bitterroot valley. It should be emphasized again that these proposals are made without the aid of field work and are therefore subject to question. The crux of the drainage modifications here proposed hinges about the Clark Fork and Flathead rivers and their tributaries, and therefore parti- pular emphasis will be placed on the description and analysis of these rivers. First, a general picture of the physiographic history of the larger area and a resume of previous work will be given. ACKNOWLEDGMENTS The writer espeoially wishes to thank Dr. Eugene S. Perry for the assis- tanoe he has given throughout the preparation of this thesis. Many thanks -2-, are due also to Mr. Charles E. Erdmann of the United States Geological Survey for his assistance during early phases of preparation and orien- tation. PRESENT LAND FORMS General Statement The area described in this report is essentially characterized by high mountains of bold and rugged relief. The eastern mountain front rises sharply from the Great Plains, and the area is marked by a series of great ranges and trenohes, trending in a general northwest to southeast direction. Parallel ranges continue to near the oity of Spokane, Washington, which lies on the eastern border of the Columbia Plain. Th,e follo'~'lingdesoript- ions of the major mountain ranges and systems, and of the major valleys and trenohes, are largely taken from the works of Daly, Calkins,
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