UNITED STATES D~RTMENT OF THE INTEJUOR 

I • 

Ray Lymtl{n Wilbur, Secretary 

GEOLOGICAL SURVEY 

W. C. Mendenhall. Director 

Professional Paper 17 4 

PHYSIOGRAPHY AND G.LACIAL GEOLOGY OF EASTERN 

MONTA.NA AND ADJACENT AREAS 

BY 

WILLIAM C. ALDEN 

UNITED STATES 

GOVERNMENT PRINTING OFFICE 

WASHINGTON : 1932 

For aale by the Superintendent of Documents. Washington, D. C. - - - - - - - - - - - - - Price fl.OO (Paper) 

CONTENTS 

Paae 

Summary ____________________________________________________________________________________ ----·- __ . ___ ----_ VII 

Introduction ____ --------·-- __________________________________________________________ ------ ______ --------_____ 1 

Fieldstudies--------------------------------------------------------------------------------------------- 1 

General characteristics of the northern Great Plains _______________________ ----------------------------------- 3 

~ountainoutliers---------------------------------------------------------------------------------------- 3 Rocks of the plains ___ ---- ______________________________________________________________________ .::_ ___ ------ 3 

Benchesandterraces-------------------------------------------------------------------------------------- 3 

()ligoceneepoch--------------------------------------------------------------~-----------------------~------- 4 

The Cypress Plain and underlying rocks------------------------------------------------------------------·-- 4 

Character of high-level gravel and relations to the Yellowstone terraces ____________________ ..;____________________ 10 

Gravel oil Tatman ~ountain, Wyo-.--------~----------------------------------------------------------- 10 

High gravel near the Yellowstone _______________________ · _______________________________ ----------------- 11 

~ioceneandPlioceneepochs---------------------------------------------------------------------------------- 12 

Flaxville Plain or ~o. 1 bench------------------------------------------------------------------------------ 12 

Age and correlation of the Flaxville terraces or No. 1 benches-------------------------------------------------- 13 

Flaxville Plain (No. 1 bench) bordering Rocky ~ounta4l front _______________________________ _:_________________ 14 

Flaxville Plain in Blaine County _______ ------------------ __________________________ ----- ________ --... -------- 18 

Bearpaw ~ountains and ~o. 1 bench--------------------------------------------------~-------------------- 18 

Little Rocky Mountains and ~o. 1 bench------------------------------------------------------------------- 19 

Flaxville Plain in Valley; Daniels, and Roosevelt Counties----------------------------------------------------~ 20 

Terraces of Judith River Basin ____________ ------ ____________________________________ :. ________ -------------_ 21 

Terraces of ~usselshell Valley _______ --------- ___________________________________________________ ... --------- 23 

~o. 1 bench in Yellowstone Valley----------------- __ ------------ __ ------------ ____ ---------------------.---- 25 BenchesaboveCuster _____________________________________________________ ..; _________ :._______________ 25 

Benches in the Crow Indian Reservation __ -------------------------------------------------~-..;.-------- 27 

~o. 1 or Flaxville terrace on the lower Yellowstone---------------------------------------------------.. - 29 

Pliocene and early Pleistocene epochs _____ --------- ___ ------- ______________ ------ ______ ----- _____ --------------_ 31 

Generalrelations----------------------------------------------------------------------------------------- 31 

Quaternaryperiod-------------------------~-----------------------------------------r-------------------- 32 Pleistocene epoch ______________________________________________ .- ____________ .. _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 32 . 

Early Pleistocene mountain glaciation on ~o. 1 and ~o. 2 benches ____ .:.-----------------------::----·----- 32 Glacial drift on ~akowan Butte, Alberta __________________________________ :._____________________ 32 

Drift on Kennedy Ridge _________ -------------------------------------------------------------· 33 Drift on Swiftcurrent Ridge ____ .;. _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 34 

Drift on Boulder Ridge _______________ :.. ________________________________________ --:..- __ --------- 34 

Drift on ridge west of Lower St. Mary Lake------------~------------------------.:.--------------- 35 

Drift on St. Mary Ridge __ ----------------------- __ -----'------ _______________________ .:._________ 35 

Drift on ~ilk River Ridge ____________________________ ---------------------------------------'-- 37 

Drifton Cutbank Ridge ___ ::---------------------------------------------------------:..---------- 38 

Drift on Two ~edicine Ridge _________________ ------------------------------------------------- 38 

Possible pre-Wisconsin glacial deposits ________ ------ ____________________ ----- __ --------------------_ 40 

Castle and Beartooth Mountains, ~ont·-------------------------------------------------------- 40 

Bouldery mesas bordering the Big Horn ~ountains, Wyo ________________________________ .:._________ 41 

Early and middle Pleistocene terraces __________________________________ ~ __________________ -- _ _ _ _ _ _ _ _ 44 

~o. 2 bench in ~ilk-~issouri Valley------- ______________ ::-- ______________ ----- _______ ----------- 44 

~o. 2 bench at the Little Rocky and Bearpaw Mountains----------------------------------------- 45 ~ o. 2 bench in Ponders., Teton, Lewis and Clark, and Cascade Counties ___ .,. _______ :.. ____________ ~___ 46 

Carlow Flat, Glacier County ____________________________________________________________ ~---·--- 47 

~o. 2 bench in the Judith River Basin ______________ :_ _________________________________ ..;_________ 50 

Gradients on branches of the upper ~issouri River ____ -------- _____________ .,.--------------------- 50 

~o. 2 bench in ~usselshell Valley_------ __ ----------------------------------------------------- M 

No.2 bench on the Yellowstone River and its tributaries.----------------------------------------- 51 

Terraces east of the Big Horn ~ountains-------------------------------------------------------- 55 

~o. 2 terrace on the lower Yellowstone------------------------------------------------..,--------- 56 

Diversion of the ~issouri and Yellowstone Rivers in ~orth Dakota________________________________ 58 

Lake basins ____________________________________ · __________________________________________ ---- 5i 

No.3 bench------------------------------------------------------------------------------------- .59 

Relations to glacial.drift ____________________________________________________ - _- ---------.------. 69. 

No.3 bench in ~orth Dakota _____________________________________ ..; _____________ ..;______________ 61 

~o. 3 bench in Judith Basin and Musselshell Valley ____________________________________ ..,;_________ 62 

~o. 3 bench in the Yellowstone Basin ______________________ ------------------------------------- 62 

m 
IV CONTENTS 

Pliocene and early Pleistocene epochs-Continued. 

Quaternary period-Continued. 

Pleistocene epoch-Continued. Missouri Valley filling in North Dakota _________________________________________ . ______________ ~ ____ _ 

Gravel underlying older Keewatin till __________________ .,.- __________________________ ---------- __ -----

Pre-Iowan·or pre-Illinoian(?) gravel in southern Alberta-----------------------------------------·-

Pre-Iowan or pre-Illinoian (?) gravel in Montana-------------------------------------------------

Gravel underlying Iowan or Illinoian(?) till of mountain glaciers ___________________________________ .. __ _ 

Erosion and refilling in Milk-Missouri Valley-------- ________________________________ -'---------------_ 

Illinoian or Iowan (?) stage of glaciation __ ~ ________________ ----- _________ ----- ___ --- _____ -------------------~---

Pre-Wisconsin drift of the mountain glaciers at low levels------------------------------------------------------

Pre-Wisconsin drift of the Keewatin glacier underlying later drift-----------------------------------------------

Pre-Wisconsin (Illinoian or Iowan?) drift bordering the Missouri River in North Dakota_ :.... _______________________ _ 

Pre-Wisconsin (Illinoian or Iowan?) drift north of the Missouri River---------------------------------------.,.--- Williams County, N. Dak __________________________________________________________ ---- ___ ----- __ -----

Thickness of the ice sheet in North Dakota--------------------------------------------------------------

Pre-Wisconsin (IllinQian or Iowan?) drift bordering the Missouri River in Montana __ - ___________________________ _ Drift near and east of Great Falls _____________________________________________________________________ _ 

Drift east of the Musselshell River _______________________________________________________ . _____________ _ 

Drift on the lower Y e11owstone __________________________________________________________________ .. _____ _ 

Pre-Wisconsin (Illinoian or Iowan?) drift in Valley and Roose:v~lt Counties, Mont_-_- ____________________ ~ __ - ___ _ Age of the drift bordering the Missouri River _______________________________________________________________ _ 

Stream diversion at the Illinoian or Iowan(?) stage of glaciation _______________________________ .:_ ______________ _ 

Upper ~i~ouri River---------------------------------------------------------------------------------

Pleistocene valley of Missouri and Yellowstone Rivers ________________________ - _________ -----_---.------- __ _ 

Stream changes near Great Falls __ -··-- ____________ -------- ________________ -_------ __ ---------------- __ _ 

Peorian (?) stage of deglaciation _________________________________________ ------------------_.:.-------------------

Wisconsin stage of glaciation ____________________________________________ -_------------------------------------- Age of the drift __________________________________________________________________________________________ · 

Early Wisconsin glaciation ______________________________ ------.---_------ ______ --------.: _______ ---------- __ _ General relations __ . __________________________________________________________________________________ _ 

Early Wisconsin terminal moraine (?) in North Dakota ____________________________ --------- ______ ----- __ _ 

Terminal moraine (?) in Roosevelt and Valley Counties, Mont----------------------------------.,-----------

Terminal moraine in Phillips and Blaine Counties, Mont--------------------------------------------------... 

Terminal moraine in Hill and Chouteau Counties, MonL-----------:---------------------------------------

Relations of the Great Falls lobe __ ·---- ________ -~ ______________ - __ - __ ----------------------------------_ 

Terminal moraine in Teton and Pondera Counties, Mont--------------------------------------------------

Terminal moraine in Glacier and Toole Counties, Mont., and in southern Alberta, Canada-----~--------------­

Relations of Two Medicine Glacier and the Keewatin ice sheet---------------------------------------------

Lacustrine deposits and boulder transportation ___________ ------------------------------------------------

Nunataks and slope of the top of the ice---~--------------------------------------------------------.:.---· Glacial Lake Cut Bank _____ · ____ ------- __________________ · ______ ------------- ____ ------------------ __ ---

Recessional moraines and drainage outlets ____________________ ----- __ -------------------------------- ___ .. 

Recessional moraines in Hill, Blaine, and Phillips Counties, Mont------------------------------------------

3tream diversion near Lake Bowdoin ____ ---------- __ -------------------------------------------.:. ______ _ 

Rece~ional moraines in the northeastern counti~s of Montana __ ------------------------------------------- Rocky Mountain glaciers of Wisconsin stage _________________________ --- __ --- __ ---_--_-----------------------

Generalrelations--~------------------------------------------------------------------------------~---

Belly River Glacier ________ --- _______________ -- __ -_---------------------------------------------------

Kennedy Creek Glacier-------------------------------------------------------------------------------

St. Mary Glacier----------------------------------------~--------------------------~---------~-------

Cut ·Bank Glacier _____ --·- _________________________ ---_-----------------------------------------------

Lake Creek Glacier __ ---- _____________________ :.. __________ ---------_---------------------------·--------

Two Medicine Glacier------ __________________________ ---------------_---------------------------------

Terrninalrnoraine------~-------------------------------------------------------------------------

An interlobate (?) moraine _______________ · _______ ---------------_--------------------------·---------

Recessional moraine ______________ . _____________________ - __ ----------------------------------------

Birch Creek Glacier----------------------------~------------------------------------------------------

Glaciers on Dupuyer and Muddy Creeks_~ _________ -------- __ -----------------------·--------------------

Teton River Glacier----------~----------------------------------------------------------------------­

])eep Creek glaciers----------------------------------------------------------------------------------

Sun River Glacier------------------------------------------------------------------------------------

Outerrnoraine---------------------------~------------------------------------------------------­

Innerrnoraines-------------------------~--------------------------------------------------------- Smith Creek Glacier _________________________ .- _______________ ------------~------------------------.----

])earqorn Glacier-------------------------------------------------------------------------------------

Castle Mountain glaciers ______________________________ .. ______ ------- __ ------ __ --------- ___ ------------

Crazy Mountain glaciers------------------------------------------------------------------------------

Yellowstone Glacier---_----- __________________________ - ____ --------.-----------------------------------

Pace 

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ILLUSTRATIONS 

Wisconsin stage of glaciation-Continued. 

Rocky Mountain glaciers of Wisconsin stage-Continued. Boulder River glaciers _______________________________________________________________________________ _ 

Stillwater Glacier ____________ · _____________________________________________________________ ~_~·-- ______ _ 

"' West Rosebud Glacier _______________________ _ ..: _____________________________ .:. ________________________ _ 

~:~ ~~::~u~a~~~~e~::::~=:=====================================~==================================== Clark Fork glaciers, Wyoming ____ - ________________________________________ ---- ___________ ~----- __ ----_ 

Big Horn Mountain glaciers, Wyoming ___________ ------ ________ -----------------------------------·--.. ----

Later Wisconsin stage of Keewatin ice sheet_--------------- _______ -------------------_-------- __ ------------

Altamont moraine in North Dakota __________ --------- _______________ -------------------~--~-----------

Altamont moraine in Montana and Saskatchewan ______________ ------------- ______ ------- ______ ---------- Late Pleistocene or Recent uplift _____________________________________________________________ . ___________ ,..- ____ _ 

Index_·-----------------------------------------------------------~--------------------------------------~--

ILLUSTRATIONS 

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Pap 

PLATE 1. Map showing physiography and glacial geology of eastern Montana and parts of adjacent States_ _ _ _ _ _ _ _ _ In pocket 

2. A, East Flattop Mountain, Glacier National Park, Mont.; B, Big Horn Mountains, Wyo____________________ 8 

3. A, Oligocene (?) conglomerate capping Cypress Hills: Alberta; B, Waterworn quartzite pebbles in Oligocene(?) 

gravel on Cypress Hills, Alberta; C, Eastern edge of Beartooth Plateau~ Wyo., near Clark Fork of the 

Yellowstone River-------------------------------------------------------------------------------- 8 

4. Big Sheep Mountain northwest of Terry, Mont.: A, Gravel-covered top and badlands; B, Lower gravelly bench 

being trenched by Recent drainage; C, ·Last stages of breaking down of a high-level plain__________________ 8 

5. Views illustrating destruction of high gravel-covered terraces and benches and development of lower plains and 

gravelly benches by erosion: A, Gravel-capped s(tndstone bluff south of Myers, Mont.; B, Pebbles and boulders 

on slope below a gravel~capped terrace· northeast of Clark, Wyo---------------------------------------- 9 

6. Little Rocky Mountains, Mont.: A, North front, showing great wall of upturned Paleozoic limestone; B, View 

along the top of the limestone wall600 to 700feet above the plains----------------,-------------·-------- 24 

7. A, Sun River, Mont., at mouth of canyon; B, Worn top of the Little Rocky Mountains, Mont.; C, View southeast of Zortman, Mont _________________________________________________________________ ._-~--_______ 24 

8. Little Rocky Mountains, Mont.: A, Near St. Paul's Mission; B, Flaxville Plain, or No., 1 bench, west of St. 

Paul's Mission _________________________________________________________ --------- ___ ------------___ 24 

9. Little Rocky Mountains, Mont.: A, Mission Gorge, south of St. Paul's; B, Natural bridge in Mission Gorge ____ · 24 

10. A, Flaxville Plateau west of Scobey, Mont.; B, Outcrop of Flaxville gravel6 miles northwest of Opheim, Mont.·; 

C, Cross-bedding of Flaxville gravell8 miles southwest of Scobey, Mont________________________________ ·24 

11. South Moccasin Mountains, Mont.: A, Remnant of highest No.1 gravel-capped bench on the west flank; B, View 

across the gravelly No.2 bench southwest of Lewistown---------------------------------------,------- 24 

12. A, Smoothly worn top and east front of Judith Mountains, Mont., and mouth of Maiden Canyon; B, View east 

of Roscoe, Mont.; C, Dissected No.2 bench south of Roscoe------------------------------------------- 24 

13. A, Highest (No. 1) bench and middle (No.2) bench east of Rock Creek, near Red Lodge, Mont.; B, No.2 bench · 

heading in mouth of Rock Creek Canyon; C, View in Shoshone National Forest, Wyo., looking across the upper 

valley of Clark Fork of the Yellowstone River ____ -------- ______ ------------ __ -----------------·------ 24 

14. Pre-Wisconsin drift of Rocky Mountain glaciers, Glacier National Park, M6nt., on remnants of the Flaxville 

Plain: A, Flat top of Swiftcurrent Ridge; B, Kennedy Ridge___________________________________________ 40 

15. Glaciated pebbles from pre-Wisconsin drift of Rocky Mountain glaciers in southwestern Alberta and Blackfeet 

Indian Reservation, Mont.: A, On remnants of the highest (No.1) bench (Flaxville Plain) and lower (No.2) 

bench; B, On remnants of the highest (No. 1) bench--------------------------,------------------------ 40 

16. Pre-Wisconsin drift of Rocky Mountain glaciers: A, Tillite on No. 1 bench north of Two Medicine Lake, Glacier 

National Park, Mont.; B, Bouldery deposit on No. 1 bench east of Roscoe, Mont------------~---------·- 40 

17. Stillwater Canyon, Beartooth Mountains, Mont.: A, Hanging valley of Woodbine Creek and high-level glacial 

ti11; B, Near view of part of same till exposure------------------------------------------------------- 40 

18. Big Horn Mountains, Wyo.: A, North Ridge, a boulder-capped mesa west of Buffalo; B, Ancient high-level Pli~ 

cene or Pleistocene valley, in the bottom of which is. cut Clear Creek Canyon ___ ~________________________ 40 

19. Big Horn Mountains, Wyo.: A, Bouldery crest of Moncrief Ridge, south of Sheridan; B, Boulder deposit on Moncrief Ridge _______________ ------ ______________ --------~------- ______________________ ------___ . 40 

20. Big Horn Mountains, Wyo.: A, Granite boulder on top of B~ld Ridge, west of Buffalo; B; Boulder deposit 

capping Bald Ridge ________________ ----- ________ -.- _________ ------------ __________________ --------- 40 

21. Topographic map of a part of the Big Horn Mountains west of Buffalo _________ ;.__________________________ 40 

22. A, No. 2 bench northeast of Malta, Mont., capped with nonglacial quartzite gravel and glacial drift; B, Pleistocene conglomerate on No.2 bench on Clark Fork of the Yellowstone River____________________________ 40 

23. Little Rocky Mountains, Mont.: A, No. 2 bench heading at a notch in the limestone wall; B, Beaver Creek Canyon as seen from No. 2 bench _____ ·----------------------------------------------------------------:-- 41 

24. Yellowstone River above Livingston, Mont.: A, View up Big Creek; B, View southeast to Emigrant Peak______ 66 

25. A, Inner box canyon of Clark Fork of the Yellowstone River, Wyo.; B, Laminatea clays of glaci.aJ.·Lake Cut Bank, 

Mont-----------~-----------------------------------------------------------------~--------~---· 56 

26. Yellowstone River, Mont.: A, Pompeys Pillar, 30 miles northeast of Billings; B, Bluff ~f Lance sandst.oDe east 
VI ILLUSTRATIONS 

27. Yellowstone, River, Mont.: A, Bluff south of Forsyth; B, Smooth, flat surface of the gravelly No.2 bench east of 

Forsyth----------------------------------------------------------------------------------------·-

28. Map of the Glendive quadrangle, Mont., showing the relations of the Keewatin ice sheet of the Iowan or 

Illinoian stage(?) of glaciation to the Yellowstone Valley and the remnants or the gravelly benches or terr&Cef\-

29. Map of region of Great Falls, Mont., showing plains and adjacent mountains during the Pleistocene or glacial 

epoch-------------------------~-----------------------------------------------------------------

30. Missouri River, Mont.: A, Shonkin Sag, a channel north of the Highwood Mountains; B, Missouri River issuing 

from the Belt Mountains above Cascade _____ - ____ -- __ --------------------------,..--------------------

31. Missouri River, Mont.: A, The river meandering on the plain below Cascade; B, Postglacial (or post..Iowan 

or post-Illinoian) gorge below Big Falls ______ -------------------------------------------------~----

32. Missouri River) Mont.: A, Rainbow Falls and dam of Montana Power Co. below Great Falls; B, Rainbow Falls 

prior to the construction of the dam ____________ - ___ - _--- _--------------------------------

33. Missouri River, Mont.: A, Big Falls and power house and dam of Montana Power Co.; B, Big Falls prior to 

the construction of the dam _________________ -------------------------------------------------------

34. Topographic map of portions of Hill and Blaine Counties, Mont---------------------.,--------------------

35. Map of Little Rocky Mountains, Mont., and their environs----------------------------------------------

36. A, Twin Buttes, Fort Belknap Indian Reservation, Mont.; B, Eagle Butte, Bearpaw Mountains, Mont ______ _ 

37. Map of eastern portion of Glacier National Park and its environs at the Wisconsin stage of glaciation ________ _ 

38. Moraines of the Keewatin ice sheet, early Wisconsin stage: A, Terminal moraine 25 mile8 north ofDut Bank, 

Mont.; B, Recessional moraine near Martin Lake, 25 mile8 north of Malta, Mont------------------------

39. A, Perched boulder on Snake Butte, 12 miles south of Harlem, Mont.; B, Glacial striae on sandstone on Signal 

Butte, 30 miles north of Havre, Mont ________ ---- _______ -------------------~------------------------

40. Views on Peoples Creek, Fort Belknap Indian Reservation, Mont.: A,· Glaciolacustrine deposits overlying 

glacial till; B, Till of Keewatin ice sheet overlying Judith River formation-------------------------------

41. Glacial boulders: A, Boulder of red granite 20 miles north of Malta, Mont.; B, Transported blocks of Paleozoic 

limestone 18 miles northeast of Malta, Mont-----------------'------------~---------------------------

42. Moraines of Two Medicine Glacier, Blackfeet Indian Reservation, Mont.: A, View southwest of Browning; B, 

View near Park to Park Highway; C, View northeast of Browning--------------------------------------

43. Sun River Canyon, Mont.: A, Mouth of the canyon from the east; B, View northeast to the mouth of the canyon 

and over the lower limestone wall from the west---------------------------·---------------------------

44. A, Terminal moraine of Sun River Glacier, 4 miles north of Gilman, Mont.; B, C, Blocks of Paleozoic limestone transported by Sun River Glacier _____ --------- __ ---------------------------------------------

45. Crazy Mountains, Mont.: A, Glaciated canyon of Big Timber Creek; B, Bouldery terminal moraine of 

Big Timber Glacier of Wisconsin stage __________ ----------------------------------------------------

46. Views near Crazy Mountains, Mont.: A, Morainal dam blocking vaUey of North Fork of Swamp Creek; B, Top 

of the moraine_-----------·------------------------------------------------------------...;----------

47. Moraines of East Rosebud Glacier south of Roscoe, Mont.: A, East Rosebud Canyon, Be.,.rtooth Mountains, 

and lateral moraine on No.2 bench; B, Older lateral moraine (Illinoian or Iowan?) on No.'2 bencband younger 

lateral moraine (Wisconsin) descending to valley bottom------------.::---------...,-------------~----------

48. East Rosebud Canyon, Beartooth· Mountains, Mont.: A, East Rosebud L&4.e and mountains; B, Alluvial fan 

that forms the dam at the foot of East Rosebud Lake------------------------------------------------

49. Views on Clark Fork of the Yellowstone River: A, Bouldery gravel on No. 2 bench northeast of Clark, 

Wyo.; B, Terminal moraine of Clark Fork Glacier as seen from above------------------------------,----

50. Views on Clark Fork of the Yellowstone River: A, Front of the terminal moraine of Clark Fork Glaclet"; B, 

Bouldery top of the moraine and mouth of Clark Fork Canyon _____________________________ : __________ _ 

51. Terminal moraine of the Keewatin ice sheet, later Wisconsin stage: A, Coteau du Missouri, Burke County, 

N.Dak.; B, View 20 miles north of Whitetail, Mont., west of Big Muddy Lake, Saskatchewan ___________ _ 

FIGURE 1. View north of Duck Lake, Mont_ __ ---------------------------------- _____ --------------------------

2. Section on St. Mary River south of Kimball, Alberta---------------------------------------------------

3. Section on St. Mary River north of Sloan's ranch, Mont-----------------------------,...------------------

4. Map of portions of southern Alberta and northern Montana--------------------------------------------

5. Section on Belly River near Lethbridge, Alberta-------------------------------------------------------

6. Map showing topographic features and drift boundaries in North Dakota------~----------------------·---

7. Sections showing the preglacial valley of the Missouri_~--- _______ --------------------·--------------~---

8. Cross sectio:r;t showing the drift in the valley through which Highwood Creek now flows ______ - ____________ _ 

9. Map showing the preglacial course of the Missouri River between Sand Coulee and th~ mouth of Highwood 

Creek------------------------------------------------------------------------------------------

10. Map of the vi~inity of Great Falls, Mont., showing location of the partly buried preglacial channel of the Missouri River-------------------------------------------------------------------------------------

11. Map showing the preglacial valley between the Missouri and Milk Riv~rs _______________________ , _______ _ 

12. Map showing preglacial river system of northern Montana _____________ .;. _______________________________ _ 

13. Map showing drainage of part of northern Montana when the Illinoian or Iowan (?).ice had maximum extent, 

and also preglacial river system _______________________ -- _____ -----------------------------:-------~ 

14. Map showing drainage of part of northern Montana ai early Wisconsin stage ____________________________ _ 

15. Map showing postglacial drainage system of part of northern ~ontana, with a part of the preglacial system __ 

16. Geologic section on Two Medicine Creek, 12 miles southwest of Cut Bank, Mont------------------.--------

17. Geologic section in the Fort· Belknap Indian Reservation, on Lodgepole Creek 6 miles below Lodgepole, Mont __ , 

18. Stream diversions east of Malta, Mont ______ ------------------------ ________ ---- ____ -----------------

19. Depths of water in St. Mary Lake, Glacier National Park----------------------------------------------:-. 

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,· 

SUMMARY 

Introd.uction.-The northern Great Plains rise gradually 

westward from about 2,000 feet above sea level on the Coteau 

du Missouri in North Dakota to 5,000 or 6,()()() feet at the Rocky 

Mountain front. Though largely smooth, the plains· are considerably dissected, having a relief of 500 to 1,500 feet. There 

are also several outlying mountain groups whose crests range 

in altitude from 6,800 to . 9,000 feet. The Crazy Mountains 

attain 11,000 feet and the Big Horn Mountains, in northern 

Wyoming, 13,000 feet. The plains rocks range in age from 

early cretaceous through Eocene, with a few remnants of 

Oligocene. 

Cypress Plain.-The Cypress Hills of southern Alberta and 

Saskatchewan are capped with coarse Oligocene river gravel 

ancl fossiliferous sands, now 2,000 feet above the South S.askatchewan River. These deposits and similar high-level gravelcapped erosion remnants tentatively correlated with them indicate that by Oligocene time the Rocky Mountains of Montana 

and Wyoming and the northern Great Plains were sufficiently 

high to aJford strong stream gradients for hundreds of miles 

to the east and northeast. These :flat-topped remnants represent the Cypress Plain, which headed at levels now high on . 

the Rocky Mountains. They appear to correspond with such 

old erosion surfaces as the subsummit peneplain on the Beartooth and Big Horn Mountains, which is probably not younger 

than Miocene. 

The development of the Cypress Plain was followed by differential uplift and dissection to depths ranging from 700 to 

l ,500 feet on the plains and possibly 2,000 to 8,000 feet in . the 

mountains. 

FZafiJ1J'II1le Plai.fl, or No. 1 bench.-There are throughout the 

region remnants of ·a series of well-marked gravel-covered 

alluvial terraces and benches which may be grouped into three 

sets, successively lower and younger than the Cypress Plain. 

These were originally miles in width, smooth, and :flat, and 

they bevel the upturned edges of·Umestones, shales, and sandstones, ranging in age from Mississippian to Eocene, showing 

that they are the product of stream erosion and deposition 

during successive long periods of freedom from uplift or deformation .. They are separated by vertical intervals ranging 

from 100 to 600 or 800 feet, so distributed in general as to 

indicate that the periods of planation alternated with ~riods 

of regional differential uplift which rejuvenated all the streams 

and caused them to cut to successively lower levels. 

The first set below the Cypress Plain is correlated with and 

includes the Flaxville Plain of northeastern Montana, described by ColHer and Thom. With the Flaxville are correlated the remnants of the highest of the alluvial gravel fans 

and terraces now preserved near the mountains. These originally coalesced in a very extensive piedmont terrace, 1,000 

to 1,500 feet below the position of the Cypress Plain at the 

mountain fronts. The presence of Pliocene fossils with those 

of Miocene age in sandy parts of the Flaxville gravel indicates 

that streams were :flowing on the Flaxville Plain late in Tertiary time. · · 

P'leistocene epoch . .......Onto the Piedmont part of the Flaxville 

Plain the first known Rocky Mountain gla~iers of ·this region 

extended before the plain was greatly dissected. The till on 

the high bench remnants at the east side of Glacier National 

Park has been considerably modified by w~tbering and is iD 

part cemented to a hard tillite. , Possible remnants of this 

early Pleistocene till farther south are also ~ weathered. 

It is not certain that the ·Keewatin ice sheet crossed the 

Coteau dn Missouri and invaded Montana as early as the Kansan stage of glaciation. 

l!JOtrl1f and middle Pleistocene terraces.-The second set of 

terraces comprises surfaces at two levels, which can not everywhere be differentiated. The lower of these is generally the 

most extensively preserved of all the terraces of this region. 

This appears to be the correlative of the Circle terrace of the 

Wind River Basin in Wyoming. The upper Missouri and Yellowstone Rivers probably :flowed to Hudson Bay until the 

formation of the second set of terraces. Their combined waters 

·were probably finally diverted southward through the Dakotas 

by the Kansan advance of the Keewa.tin lee sheet. 

The presence of a third set of terraces indicates another stage 

of do:wncutting by the streams, followed by lateral planation 

and deposition of river gravel. Away from the mountains the 

third terrace is. generally 100 to 200 feet or more below the 

lower second terrace and is confined between the. main lines of 

bluffs bordering the inner valleys, which are from ·1 mile to 

several miles wide. 

Before the invasion of Montana by the Keewatin ice sheet 

at the Illinoian or the Iowan stage of glaciation the Missouri 

River, which was then flowing in the valley now occupied by 

the Milk River east of Havre, had cut down well below the 

level of the present bottom of that valley. This cutting may 

perhaps have been due to rapid deepenh1g of the Missouri 

gorge through the Dakotas after the final diversion of the 

river southeastward. The refilling resulted fi.om subsequent 

obstruction of the drainage by advance of the Keewatin ice 

sheet at the Illinoian or the Iowan stage. 

Interglacial stream gravel found in places underlying WJ.s.. 

consin and pre-Wisconsin (Illinoian or Iowan) drift, both 

south and north of the international boundary, includes some, 

at least, of what Dawson and McConnell designated "Saskatchewan gravel." 

Illinoian or IO'Watn (f) ~ttage of gkwiation.-A.fter the erosion 

of the Missouri gorge in North Dakota the Keewatin ice sheet 

advanced to and across this gorge, and in Montana it diverted 

the Missouri River from the north side to the south side of 

the Bearpaw and Little Rocky Mountains. It extended nearly 

to the site of Great Falls and diverted the Missouri J:ljver, 

also in that vicinity. It seems probable that this incursion of 

the Keewatin glacier was as late as either the Illinoian or the 

Iowan stage of glaciation, to judge from the very large amount 

of erosion that had occurred previously during . Pleistocene 

time and from the relatively small amount of erosion and 

modification of the pre-Wisconsin Keewatin drift since . its 

deposition. There is evidence of a pre-WiscOnsin advance of 

the Rocky Mountain glaciers down to low levels, but the 

evidence noted in this part of Montana is not so conelllSive as 

at some other places. 

W i8oon-8'in stage of gZactation..-At the early or middle Wisconsin stage of glaciation the Keewatin ice sheet covered most 

of the area north of the present channel of the Missouri River 

and extended southwestward nearly to Great Falls, Mont. It 

VII 
VIII SUMM.A.RY 

reached some points that are now 3,500 to 4,450 feet above 

sea level. East of the Little Rocky Mountains the limit of 

the Keewatin drift is not very well marked. At a later Wisconsin advance the Keewatin glacier extended but 10 to 40 

miles into the northeastern townships of Montana. 

Topographic relations show that after the deposition of the 

high-level pre-Wisconsin drift of the Rocky Mountain glaciers 

on the piedmont portion of the Flaxville Plain, in early Pleistocene time, and before these glaciers readvanced at the 

Wisconsin stage, canyon cutting to depths of 1;000 feet or 

more occurred, and valleys were eroded across the plains to 

depths ranging from 1,000 fee~ near the mountains to 500 

feet or more in eastern Montana., 

The relations of the low-level moraines of tbe mountain 

glaciers to the adjacent moraine of the Keewa~ lee s~t 

are such that there is no doubt as to their approximate contemporaneity in Wisconsin time. The moraines of the ,mountain glaciers are mapped and desert~, but they have' not 

been clearly dtiTerentlated as of early, .middle. and late 

Wisconsin age. 

Recent.-Certain phenomena suggest that the regional uplifts continued through Pleistocene into Recent. time. 'The 

depths of Recent stream erosion range from 50 to 200 · feet, 

and m general the streams appear to be still actively ~tting 

downward. The glaciers now existing in the mountains are 

not described in this paper. 
PHYSIOGRAPHY AND GLACIAL GEOLOGY OF EASTERN MONTANA AND 

ADJACENT AREAS 

By WILLIAM c. AwEN 

. INTRODUCTION 

FIELD STUDIES 

In , the summers of 1911 and 1913 the writer was 

engaged in the study of the gl~cial ·phenomena of 

Glacier National Park in connection with a geologic 

survey being made by a party under the direction of 

M. R. Campbell. A part of the summer of 1912 was 

also spent in adjacent parts of the Blackfeet Indian 

Reservation, Mont., and in southern Alberta in.a reconnaissance on the plains adjacent to the east front 

of the mountains, in compap.y with Eugene Stebinger. 

In the course of these studies it was found that some 

of the high mesas and benches near the mountain 

front, the gravel caps of which had been regarded as 

. preglacial alluvial fans, also carried very old glacial 

till. The topographic relations of these till remnants, 

taken in connection with their partial cementation to 

hard tillite and their modification by leaching and 

weathering, seemed to indicate that the till was the 

product of early Pleistocene mountain glaciation, 

which occurred long before the extension of the mountain glaciers of the Wisconsin stage down the valleys 

that now !ntervene between the several high mesas or 

benches capped with the ancient till. The relations 

seemed to indicate that the mountain gorges and their 

valley extensions on the adjacent plains had been 

deepened 1,000 feet or more between the earlier and ' 

the later mountain glaciations. 

In 1915 Stebinger, with the assistance of E. S. Corbett, who had been the writer's assistant in Glacier 

National Park in 1913, and others, continued the 

geologic mapping of the park. In 1911 and later seasons Stebinger carried on studies of the relations of 

the glacial deposits and the high-level bench gravel in 

connection with areal mapping of the older ro<;ks on 

the part of the plains adjacent to the mountains. between the international boundary on the north and the 

vicinity of the Sun River on the south. These studies 

tended to corroborate the inferences drawn in 1911 

C9ncerning the relations of the high-level and the lowlevel drift of the mountain glaciers, although no highlevel glacial deposits were the;n identified near the 

mountain front south of Marias River, where the high 

benches have mostly been cut away. 

87949-32--.2 

Study of the drift of the Keewatin ice· sheet on the 

plains east of the mountains showed that F. H. H. Calhoun was probably right in concluding that the uppermost continental drift is of Wisconsin age. It was 

evident that its deposition took place .long after that 

of the high-level bench gravel, for thicknesses of hundreds of feet of shale and sandstone were removed 

from the plains of northeastern Montana, leaving only 

dissevered remnants of these high gravel-covered ter-

. races and benches before the Keewatin glacier of. the 

Wisconsin stage inva4ed Montana. A somewhat older 

sheet .of Keewatin drift extends outside the limit of the 

·Wisconsin glaciation to and across the Missouri River 

in Montana and northwestern North Dakota, and study 

shows that it also was deposited subsequent to the cutting down of the plains and even after the Missouri 

River had completed the deepening of its preglacial 

. valley in Montana and had been diverted to its present 

course and eroded its gorge in North Dakota_and after 

the Yellowstone Valley had reached its present depth. 

Si udies which gave the writer a wi.der personal 

acquaintance with the several drili sheets were car.;. 

ried on in the summers of.1914 and 1915, when he 

collaborated with M. M. Leighton, of the Iowa Geological Survey, in a 'britical field study of the Iow.an 

drift and associated deposits of ~astern Iowa, with 

examination of the older drifts at numerous plll.ces in 

Illinois Iowa and Nebraska. for comparison. Some 

:further' studi:s of the Kansan and Nebraskan drifts 

were also made in western Iowa and eastern Nebraska 

in 1919. All these studies might, in a sense, be regarded as preparatory to the regional study of which 

the present paper treats. 

Reports of the men engaged in geologic mapping 

on the plains of Montana and Wyoming showed that 

there are numerous remnants of -gravelpcapped terraces and high-level benches widely· scattered in ~e 

upper Missouri 1 and Yell~wstone drainage basins, but ' 

1 The . term " upper · Missouri River " as used, for convenience, .in 

this paper refers in the main to some, if not all, of that part of the 

river between Yankton, S. Dak., and the point where. the strea.m 

leaves the mountains, about 40 miles above Great Falls, Mont. It 

does not include the part of the river above the mountain front, 

which is, ·perhaps, more properly the real upper Missouri or should~ 

at least, be included under that term. In a few places, as is evident, 

the term as. used in this paper excludes the part of ~he cotil'Se below 

Williston, N. Dak. 

1 
2 PHYSIOGRAPHY AND GLACIAL GEOLOGY OF EASTERN MONTANA 

no one was making or had made any serious attempt 

at regional study, correlation, and interpretation of 

those features and of their relations to the glacial deposits. It therefore appeared· important to make a 

critical study of the character and age of the several 

drift sheets and of their relations to these several sets 

of gravel-covered terraces and benches, and a plan 

was made accordingly. 

The plan was to make a rapid and widely extended 

regional reconnaissance with the view of supplementing and correlating the results of the earlier studies 

of the drift by Calhoun and the more or less incidental observations of the· many other geologists 

above noted. In the summer of 1916 work was begun 

at the great Altamont moraine of the Wisconsin drift 

sheet, on the Coteau du Missouri, in the northwestern 

counties of North Dakota, and it proceeded westward 

with traverses by automo~ile crisscrossing the country north of the Missouri River at intervals of about 

8 or 10 miles and including a belt 10 to 50 miles wide 

north of the in~ernational boundary. It was thought 

that the Altamont moraine might be found to swing 

westward about the Wood Mountain upland in southern Saskatchewan, then to reenter Montana and extend southwestward to the Little Rocky_ Mountains, to 

connect with the line traced by Calhoun as the outer 

limit of the Wisconsin drift. As noted below (p.129), 

however, the moraine was not found to have such 

a trend. Apparently it continues northward and· 

northwestward in Saskatchewan beyond the region 

traversed. 

A. J. Collier and W. T. Thorn, jr., following C. E. 

Bauer, in 1915 had studied the Flaxville gravel of 

northeastern Montana, ~nd the fossils collected by 

them gave some basis of approximate age determination for one of the main sets of\erraces and benches. 

From this determination, taken in connection with the 

results of the earlier studies of the fossiliferous gravel 

on the Cypress Hills of southern Saskatchewan by 

McConnell, Cope, Weston, and Lambe, it appeared 

that there might be in this region data for working 

out the physiographic history of the northern Great 

Plains. From these beginnings it was hoped to proceed continuously, but not until 1920 was there opportunity to go ahead with the study. In the summer 

of that year and in 1921 to 1924 the study was ex~ 

tended until it covered the larger part of the plains 

of Montana, parts of northwestern North Dakota, the 

Big Horn Basin, Wyo., and the environs of the Big 

Horn and Wind River Mountains, and subsequently 

it was extended much farther· south. Except the 

studies in the mountains of Glacier National Park and 

a few trips in and near Yellowstone National Park 

and in the Big Horn Mountains, the investigations 

here described have been confined almost wholly to 

the plains. In most . places, the field examinations 

were extended up to the mountain fronts or up the valleys to the moraines of the mountain glaciers of the 

last great ice extension at the Wisconsin stage. In 

1921 and 1923 a preliminary attempt was made·. to 

· check .. across to the intramontane valleys in the region 

o:f Bozeman, Townsend, and Helena, Mont., and to 

correlate the writer's results with those of similar 

studies being initiated l?Y J. T. Pardee on the upper 

Missouri and on tributaries of Clark Fork of the 

Columbia River. Pardee's studies, and also those of 

the present writer, were subsequently extended westward into northern Idaho and eastern Washington. 

When it is realized that the vast area in which the 

writer's traverses were made east of the Rooky'Mountain front, including the Big Horn Basin, is eqmil in 

size to the whole of New York, Pennsylvania, New 

Jersey, Delaware, a.nd Maryland-nearly 112,000 

square miles--the necessarily general nature of the 

reconnaissance and more or less tentative character 

of the correlations and interpretations will be evident. 

During much of this time, however, detailed areal 

mapping was being done by others, principally by men 

engaged in mapping the coal, oil, and gas lands of 

Montana and Wyoming, and many of these men 

actively cooperated with the writer by locating and 

examining terrace gr·avel and glacial deposits. wherever they were found and by noting their absence 

from other parts of the region. The names of the 

following may be noted in this connection, and citations· of their publications and of many others will 

be found in the text: C. Max Bauer, A. L. Beekly, 

C. F. Bowen, W. R. Calvert, S. H. Cathcart, A. J. 

Collier, C. E. Dobbin, C. A. Fisher, M. l. Goldman, 

E. T. Hancock, C. J. Hares, F. A. Herald, D. F. 

Hewett, C. T. Lupton; L. J. Pepperberg, Frank 

Reeves, R. W. Richards, G. S. Rogers, Cad D. Smith, 

Eugene Stebinger, R. W. Stone, W. T. Thom,.jr., and 

L. H. Woolsey. 

The writer is under obligation to all the men cited 

above. Others have examined preliminary statements 

or outlines and have given suggestions. Among these 

may be gratefully noted T. C. Chamb~rJ41, Frank 

Leverett, M. R. Campbell, Eugene Stebinger, A. G. 

Leonard, H. E. Simpson, and N. M. Fenneman. An 

excellent paper by Calhoun 2 has been very useful, 

and considerable excerpts from it have been incorporated in the present paper. · 

A preliminary presentation of the results of. this 

study constituted the address of the writer as retiring 

president of the Geological Society of Washington, 

'December 13, 1922. A second presentation was made to 

the Geological Society of Alnerica at the Washington 

a Calhoun, F. H. H., The Monta,na lobe of the .Keewatin ice sheet: 

U. S. Geo1. Survey Prof. Paper 50, 1906. 
GENERAL CliARA.CTERISTICS OF THE NORTHERN GREAT PLAINS 3 

meeting December 27, 1923, and the first publication of 

these summaries was in the Bulletin of the Geological 

Society of America, volume 35, pages 385--424, 1924. 

GENE:Q,AL CHARACTERISTICS OP THE NORTHERN GREAT 

PLAINS 

The northern Great Plains rise graduaily westward 

from altitudes between 1,800 and 2,400 ·feet above sea 

level on the Coteau du Missouri east of the Missouri 

River, in North Dakota, to 5,000 or ·6,000 feet at the 

foot of the Rocky Mountains. The Rocky Mountain 

front in general ·rises abruptly from the prairies, and 

a short distance back from the front are peaks rising 

to altitudes of 9,000 to 10,000 feet fu Glacier National 

Park and 11,000 to 13,000 feet and more in the Big 

Horn Mountains and the rugged region north and east 

of Yellowstone National Fark. In this connection_ attention may be ealled to the fact, which is prob~bly 

already familiar to many, that the country east of the 

mountains, though known · as· the northern Great 

Plains, is far from being a smooth, ffat surface. It is 

true that there are some flat tracts and large gently 

rolling areas and that to an observer on a high point 

in the mountains the whole vast plain looks as flat as a 

floor in contrast with the boldness of the mountain 

ridges. This impression is, however, due to the fact 

that the features are much smaller and lower than the 

mountains and that the details are lost in. the hazy distances. Particularly outside the drift-coverd part of 

the plains-that is, in most of the plains region south 

. and west of the ]~issouri River-there are large areas 

of very rough country. Typical badlands occur in the 

breaks along the Missouri and Y ~llowstone Rivers, 

where there is deep and thorough dissection, and in 

the larger interst:ream tracts ridges rise in places 500 to 

1,500 f~et above the valley bottoms, with many bold 

cliffs and picture:sque towers and pinnacles, especially 

where the eminences are capped with sandstone. 

The Missouri and Yellowstone Rivers flow for the 

inost part in rather. narrow young valleys bordered 

by 'lines of abrupt bluffs 100 to several hundred feet 

in height. In 1nany places on t~e Missouri River 

below Great Falls, Marias River, the Teton, the lower 

Musselshell, and the Little Missouri the inner valleys 

are narrow gorges approached with difficulty except 

on the main graded roads. 

MOUNTAIN OUTLIERS 

The:r:e. are sev£~ral small outlying mountain groups 

which rise above the plains. With these may be 

grouped the Sweetgrass Hills, three igneous laccolithic buttes of early Tertiary age near the Canadian 

line, about 6,300 feet above sea level. The mountains 

c.omprise the Bearpaw Mountains, made up of postEocene volcanic rocks ( 6,000 to 7,000 feet above sea 

level) ; the Little Rocky Mountains ( 6,000 to 6,500 

feet) , laccoliths of early Tertiary age; the Highwood 

Mountains, volcanic rocks of Tertiary age (7 ,240 

feet) ; the North Moccasin, South ··Moccasin, and 

Judith Mountains, early Tertiary lacooliths (6,000, to 

8,600 feet) ; the Big Belt, Little Belt; and Big Snowy 

Mountains, early Tertiary anticlinal uplifts and 

faulted laccoliths (7,000 to 9,000 feet); and the Castle 

and Crazy Momitains, faulted laccoliths and intrusive 

rocks of Eocene age ( 8,000 to 11,000 feet). To the 

south are the Pryor Mountains (nearly 8~800 :feet) 

and the Big Horn Mountains (over 13,000 feet), separated by the lower Big Horn Canyon; both early Tertiary anticlines or uplifts. Farther east are the Black 

Hills. 

B.OCXS 0:1' THE PLAINS 

The rocks of the plains in Montana and Wyoming 

are mostly shale and sandstone ranging in age from 

early Cretaceous through· Eocene. The particular deposits described in this paper are mostly no;nglacial 

river gravel, ranging in age from Oligocene through 

Pleistocene, and glacial drift. 

In western North Dakota: there are several isolated 

buttes capped with deposits of supposed Oligocene 

age. One of these, 'Sentinel Butte, about 10 miles east 

of the Montana line, rises 3,430 feet. above sea level 

and is the second highest point in North Dakota. It 

is not certainly known that any Oligocene formations 

remain on the plains of Montana other than some 

remnants in the southeast cor·ner which are shown on 

geologic maps as of White River age. The possibility 

that there may be other small· remnants of Oligocene . 

or Miocene deposits is discussed below. Not since the 

deposition of the Cannonball marine member of the 

Lance formation, near the end of Cretaceous or the 

beginning of Tertiary time, has this region stood so 

low that marine waters invaded western North Dakota 

or Montana. 

BENCHES AND TERRACES · 

The term " bench " is generally used in this region 

but perhaps more loosely than in this paper. · The 

writer is applying it only to those nearly flat features which are clearly remnants of ancient river 

plains and which are not due simply to the stripping 

of softer .shale from harder flat-lying sandstone. 

Most of these benches bevel indiscriminately the upturned edges of shale and sandstone, and most of 

them .are thickly covered with coarse gravel below 

thin loamy soils. The name " bench " is here applied 

more or less indiscriminately to the tops of gravelcapped plateaus or mesas which, like the Cypress 

Hills, stand well above their imme~ate-surroundings, 

and also, in places, to typical terraces,. which are 

bordered on the one hand by lower lands and on the 

other by slopes rising to higher lands. These features 
4 PHYSIOGRAPHY AND G:LACIAL GEOLOGY OF EASTERN MONTANA 

·merge into one another. The plateaus and mesas are 

in many places, especially near the mountains, 

erosional remnants of- great alluvial fans. Some of 

these may have extended far out over the northern 

Great Plains and may have coalesced into continuous 

smooth, flat tracts of vast ·extent, such as are pre~ 

served· in the High Plains farther south. Others 

narrowed between somewhat higher lands on each 

side and extended down the valleys as broad, smooth, 

gravelly bottoms. These are now deeply diss~cted 

terraces. 

OLIGOCENE EPOCH 

THE CYPRESS PLAIN AND UNDERLYING ROCKS 

'With the end of Fort Union time in northern Montana and the adjacent parts of southern Alberta and 

Saskatchewan the great fresh-water lakes and marshes 

in which extensive deposits of sand, clay, and lignite 

had been accumulating appear to have been drained 

or desiccated to a large extent. This was probably 

an accompaniment, if not a direct result, of the elevation of the Rocky Mountains and bordering plains. 

Near the mountains in southern Alberta and northern 

Montana as far south as the Sun River west of Great 

Falls the latest of the plains rocks, which were involved in the folding and crumpling resulting from 

the orogenic movement, are beds of the Willow Creek 

(Paskapoo and Edmonton of McConnell) 'and St. 

Mary River formations. 

Fronting the Bridger Range the beds of the Livingston formation, partly Eocene and partly Upper 

Cretaceous, are upturned. In the region south of the 

Yellowstone River, including the Clark Fork andBig 

Horn Basins in Wyoming, the beds of the Wasatch 

formation and of the Linley conglomerate north of 

Red Lodge (which may' also be of Wasatch age) are 

upturned near the, mountain front, though unconformable on Fort Union beds. So also the Kingsbury conglomerate member of the Wasatch formation bordering the east front of the Big Horn Mountains was 

involved in the mountain uplift and is tilted. 

There is little evidence in hand to show the progress 

of. this uplift during Eocene time. Undoubtedly 

streams had been flowing eastward from the rising 

land areas into the contracting bodies of fresh water 

on the plains ever since. the last marine waters had 

disappeared. These streams swung to and fro across 

the plains and, cutting away the tops of the rising 

folds and faulted blocks in the disturbed belt bordering the mountains, beveled the edges of the early 

Tertiary and Cretaceous rock formations and may 

have maintained a fairly uniform surface. 

The altitude of the land at the beginning of the 

epoch of folding and faulting is not known, but apparently by Oligocene time it stoQd sufficiently high 

to induce vigorous stream flow for a long distance 

eastward, as shown by the character of the materials 

then laid down. Moreover, it also appears that by 

Oligocene time erosion of the folded and faulted rocks 

of the front range of the Rocky Mountil.ins in the 

Glacier National Park region had progr~ed far . 

enough to remove much of whatever mantle of. Cretaceous and ·early Tertiary sediments there was on 

the uplifted mass and to , uncover the limestone, 

quartzite, and argillite of the pre-Cambrian formations brought up in the Lewis overthrust fault. This 

conclusion appears to be justified by the discovery of 

Oligocene fossils in the stream deposits that cap the 

Cypress Hills Plateau in southern Saskatchewan. 

The lithologic composition of the conglomerates of the 

Big Horn Basin suggests that a good deal of erosion 

of the mountain belts had already occurred in Fort· 

Union and Wasatch time. 

The Cypress Hills Plateau (pl. 1) lieS mostly in 

southwestern Saskatchewan, in the districts of Maple 

Creek and Cypress, whence it extends westward about 

20 miles into the district of Medicine Hat, southeastern 

Alberta. It is a high tract nearly 80 miles in length 

from east to west and tapering westward, with some-

. what irregular outline, from a maximum width of 

about 20 miles in the eastern part· to a point, the 

Head of the Mountain, at the west. It is really a 

plateau, as its top is smooth where not dissected by 

coulees, and it slopes gra·dually eastward from an altitude of about 4,850 feet at the west end to 3,700 feet 

or less in the eastern part. The top is partly grazing 

l'and but largely under cultivation. The marginal 

slopes are generally steep, locally abrupt, and in places 

precipitous. The north slope, in the western part at 

least, is embraced ·in the Dominion Forest Reserve and 

is covered with beautiful spruce and pine trees which 

present a pleasing contrast to the vast expanse . of 

treeless plains below. It is the highest land in this 

part of the Great Plains and a prominent topographic 

· feature. 

The margins and top are somewhat dissected by 

coulees, and one "sag," the "Gap," about 6 miles in 

width, cuts entirely through~ severing . the western 

third from the brohder part of the plateau tQ the east. 

This western part was examined briefly by the writer 

in August, 1920; for additional information on this 

and the other parts he is indebted to the work of previous writers, Dawson, McConnell, and Lambe. 

The Cypress Hills Plateau forms part of the Continental Divide, and from its north slope the drainage 

goes principally to the South· Saskatchewan River and 

partly to some of the small and more or less saline 

lakes that dot the plains. Most of the plateau drains 

· southward and several of t:P.e streams are tributary 

to the. Milk River. One of these, the Frenchman 

River, flows close to the south margin of the eastern 

part of the plateau in a gorge several hundred feet 
OLIGOCENE EPOCH 5 

deep walled by precipitous cliffs of shale and sandstone. This gorge is now tra ver8ed by a branch of 

the Canadian Pacific Railway for about 15 miles west 

of the vicinity o:f the village of East. End. East End 

Coulee, through which the railway runs northeastward 

across the divide, separates the Cypress Hills Plateau 

from a somewhat lower tract to the east known as the 

Mud River Plat-eau, from which a high belt extends 

more or less continuously eastward through the district of N otukeu to the Wood Mountain upland, in 

the Willow Bunch district. 

The plateau is an erosion remnant in which the 

Cretaceous shale is. over lain by shale and sandstone 

of the Lance and Fort Union formations, which have 

boon entirely removed from the area·· to the north and 

south as far as the Missouri River and to the west for 

a distance of 100 miles. The western segment of the 

Cypress Hills Plateau is capped with a thick bed of 

coarse waterwor:n gravel, evidently a stream deposit. 

On the top of the ridge the gravel is fairly well covered by a thin ]loamy clay soil and is not generally 

reached by the plow. At the crests .of slopes and 

wherever this soil cover is washed away, however, 

smoothly rounded cobblestones strew the surface, and 

in places where seepage of water occurs there have 

been landslides on the slippery underlying clay. In 

some places the scarps develQped in this manner expose the gravel in section. One of the best of these 

exposures seen by the writer is at the north edge of 

the ·plateau about a mile from the west end. This 

scarp is a cliff about 30 feet high above a talus of 

loose pebbles and large blocks of conglomerate. (See 

pl. 3 .A.) The material exposed is gravel composed 

of smoothly rounded pebbles and cobbles of quartzite 

and fine-grained siliceous argillite, with some. chert 

and vein quartz, ranging in size from a fraction of an 

inch to 8 by 10 by 12 inches. A large percentage of 

the pebbles are over 6 inches in diameter. The interstices between the cobbles are filled with small pebbles and some sand, and the whole is cemented by 

calcium carbonate to a conglomerate. 

McConnell 8 states that 

west of the " Gap " this formation consists of a uniform sheet 

of hard conglomernte about 50 feet thick, which is well exposed in many plac,es in the valleys of Battle Creek, Fourmile 

Coulee, and along the edges of the plateau. In the eastern 

part of the hills the conglomerate is usually associated with 

beds of sandstone, sands, clays, and marls, and the thickness 

of the whole deposU increases to ·about 500 feet. 

The conglomerate~ which forms such a marked feature of the 

Miocene [Oligocene~] deposits of. the Cypress Hills is usually 

composed of quartzite- pebbles cemented together by carbonate 

of lime but also appears under a number of other forms. In 

some pl8.1Ces the pebbles lie loosely in a matrix of coarse yellowish sand, and in others they are consolidated by a ferruginous 

• • McConnell, R. G., Report on the Cypress Hills, Wood Mountain, 

and adjacent country : Canada Geol. Survey Ann. Rept., vol. 1, pp. 

30c-31c, 188ft 

cement. Beds several feet thick also occasionally occur which 

contain nothing but loose pebbles. The conglomerate sometimes contains interstratified beds of c9arse sandsJ into. which 

the pebbles seem to grade, and also beds o;f white or creamcolored clays and sands, which occasionally hold calcareous 

nodules, some of which when broken across were found to be 

spotted by small black concretionary grains of oxide of manganese. The pebbles of the conglomerate are nearly always composed of hard quartzite and vary· in size frOIJ1 coarse sand to 

8 and 9 inches in diameter, though the usual size is from 2 to 4 

inches. They are usually white on a fresh fracture, but gray 

and flesh-colored tints· are· also common. · They are sometimes 

found forming the lower . surface of hard sandstone beds or 

scattered more or less sparingly through them. Beds of pebble 

conglomerate, though more frequent and larger near the base 

of the Miocene [Oligocene], are found at irregular intervals an 

through it and are of all thicknesses, from a single layer of 

pebbles up to beds fully 50 feet thick. In many ·cases the for· 

mation consists of a single thick bed of this rock. B~ides the 

pebble conglomerate, beds composed of angular pieces of clays . 

inclosed in a matrix of hard sandstone and forming a species 

of breccia are occasionally found. 

The sands of the Miocene [Oligocene] sometimes form 

bard beds, from 1 to 2 feet thick, but are usually only slightly 

indurated and are nearly always a:tfected by false bedding. 

In one place, near the eastern escarpment, a bed was observed which consists of hard, clean, angular siliceous grains, 

ne-arly all of uniform size and apparently quite loose and 

unstratified. This bed contained a· few pebbles and roiled 

fragments of fossilized wood and bones. 

Small beds of impure carbonate of lime, or marl; are also 

occasionally found amongst the deposits of this . fQrmation. 

The best exposures in the eastern part of the plateau 

are north of the village of East End, iJI Bone Coulee, 

in which head the ·North Fork of Swift Current 

Creek and Farewell [lfrenchman] Creek. McConnell 4 states : 

The rocks exhibited in these sections consist of pebble and 

clay conglomerates, with occasional beds of loose. P,ebblea, 

hard and soft sandstones, the latter usually very coarse 

grained and fl,:ffected with false bedding, clays of various 

colors but usually dark gray, ·and small beds of impure lim&-

stones and whitish marls. The total thickness of the whole 

deposit at this place is about 500 feet, but going west it thins 

out rapidly, and in a few miles everything but the pebble 

conglomerate disappears. 

McConnell in 1883, T. C. Weston in 1884, 1888, and 

1889, and L. M. Lambe in 1904 collected vertebrate 

and a few invertebrate fossils, mostly from Bone 

Coulee, and the study of these resulted in the conclasion that the deposits capping the Cypress Hills are 

of Oligocene age. · Lambe 5 states: 

Cope, in his memoir of 1891, ·qualifies . McConnell's assignment of the uppermost beds of the Cypress IDlls to the Miocene 

by describing them as of Oligocene or lower Miocene age. 

Matthew would accord them a more de:O.nite horizon at the 

bottom of the Oligocene and has expressed the opinion that 

they are probably of approximately the same age as the 

Titanotherium beds at Pipestone Springs, Montana •. Thi$ opln-: 

' Idem, p. 82c. 5 Lambe, L. M., The Vertebrata of the Oligocene of the Cypress 

Hills, Saskatchewan: Canada Geol. Survey Contr. Paleontoloo, vol. 3, 

pt. 4. p. 7, 1908. 
6 PHYSIOGRAPHY AND GLACIAL GEOLOGY OF EASTERN :MONTANA 

ion appears to be borne out to some extent by the list of 

species from Pipestone Springs, published by Dr. Matthew in 

1003, aild the collections from the Cypress Hills, supplemented 

by the material secured in 1904. 

The 'vertebrate fossils are remains of 50 species of 

fishes, reptiles, and mammals, among which are lizards, 

snakes, crocodiles, marsupials, rodents, members of 

the cat and dog families, horses, hyracodonts, rhinoceroses, and titanotheres. Lambe says: 

Some of the groups have since become extinct; others have 

undergone great changes and are with difficulty recognized in 

their descendants of the present day ; whilst a few are represented by existing species that show but slight difference in 

form and structure. 

It seems ~o the present writer beyond question that 

the materials capping the Cypress Hills are principally, at least, alluvial deposits formed by a vigorous 

stream heading in the Rocky Mountains. This is well 

stated by Lambe as follows: 

That the Cypress Hills Oligocene deposits were the result 

of rapidly :flowing water from the west is evident. The thick 

basal beds of rounded pebbles represent the work· of a strong 

transporting force, such as would be supplied by a turbulent 

stream of considerable size carrying eastward material from 

the Rocky Mountains. The sands show false bedding as a 

result of varying currents. With the accumulation of material eastward, .and a consequent reduction of the transporting 

force, beds of finer material were depo.sited at a higher level 

and probably on extensive areas of over:flow. 

The pebbles examined by the present writer are 

mostly well rounded and have r~markably smooth and 

evenly polished surfaces, many of which are covered 

with percussion marks such as are produced by stones 

striking sharply against one another in a strong current. The source of the material is clearly the Rocky 

Mountains, 150 to 200 iniles west of the head of the 

plateau. In view of this distance, the size of the larger 

stones is remarkable. Of those shown in Plate 3 B 

the largest have dimensions of 8 by 10 by 12 inches. 

None of the stones examined show any evidence of 

transportation by glacier ice. 

McConnell 6 has pointed out that 

The area now covered by the Cypress Hills has been changed 

from a depression in Miocene [Oligocene] times into the highest 

plateau on the plains, which is its present position, entirely 

by the arrest of denudation over its surface by the hard conglomerate beds which cover it, whilst the surrounding country, 

destitute 9f such protection, has been gradually lowered and 

so affords an index of the amount of material removed from 

the neighboring plains in the age intervening between the deposition of the Miocene [Oligocene] and the glacial period. The 

conglomerate capping now overlooks, from a height of fully 

2,000 feet, the lowest part of the plains stretching from the 

western base of the plateau to the mountains. 

The bed of the ancient river must have risen rapidly 

upstream in order, as McConnell states, "to induce a 

current powerful enough to urge forward such ime McConnell, R. G., op. cit., pp. 69c, 70c; 

mense quantities of pebbles and boulders. 200 miles 

from their nearest source. For this. work an easterly 

slope of at least 15 feet per mile would be required." 

This is about the present gradient of the ·base of .the 

alluvial deposit that caps the plateau. The ~lope of 

the remarkably flat surface of the deposit on the western segment of the plateau is now about 12 or 13 feet 

to the mile. 

For convenience of reference the plain now · repre· 

sented by the top of the Cypress Hills Plateau is here 

designated the Cypress Plain. This name may be 

taken to include all other remnants of similar valley 

plains, alluvial fans, terraces, and benches within the 

basins of the Big Horn, the Yellowstone, the upper 

Missouri east of- the mountains, and_ .the South Saskatchewan and their tributaries that can be identified 

as representing approximately the same stage of 

physiographic development.6a 

In order to get some conception of the probable 

relations of the plains and mountains in Oligocene 

to Miocene time, a gradient similar to that found ·on 

existing remnants of the next lower terraces of the 

region may be projected from the head of the Cypress 

Hills to the mountains of the Glacier National Park.7 

The distance from Chief Mountain to the Cypress 

Hills is about 155 miles. The slope away from the 

mountain may be postulated as 5 miles at 100 feet 

to the mile 10 miles at 75 feet, 20 ·miles at 40 feet, 

and 100 miies at 10 feet-a total fall of 3,450 feet in 

155 miles-andit may have been even steeper. Such 

a gradient rising in a westerly direction from the 

head of the Cypress Hills at about 4,850 feet above 

sea level would reach the mountains at about 8,300 

feet--that is, about 750 feet below the crest o:f Chief 

Mountain-and, if continued westward at 100 feet ~o 

the mile, would overtop all but the highest peaks east 

of and along the Continental Divide in Glacier N ationa! Park. Mount Cleveland and Mount Siyeh 

would rise about 1,000 feet above it. It would be 

nearly 3,000 feet higher than the St. Mary River 

(which is 4,200 feet above sea level at the international boundary) and about 2,000 feet higher than the 

gravel-capped ridges bordering the mountain front as 

far south as Two Medicine Lake. Study of the later 

terraces described elsewhere in this paper leads to the 

oa M. Y. Williams (The physiography of the southwestern plains 

of Canada: Royal Soc. Canada Trans., vol. 23,, sec. 1:, p. 65, 1929) 

thinks it probable that the Cypress Plain on top of the Oligocene 

deposits "is early Miocene in age rather than 'Oligocene-Miocene.''·' 

'l In the projection of stream gradients and the attempted correlations on the basis of stream gradients, relative height above the 

present streams, and other physiographic relations in this study, 

there is no pretense of accuracy of detail ; approximation iff the best 

that can be hoped for, and there is necessarily considerab~ room for 

differences of opinion ·as to some conclusions. Barometric readings 

have generally been taken where. published data on altitudes were not 

available, and projected gradients have been assumed corresponding 

with those which are now found on . ~nches and . terraces ~ simlla.c. 

situations in this region, with some allowance for local modifying 

factors. 
OLIGOCENE EPOCH 7 

conclusion that the projected gradient is not too steep, 

especially if the E~ffect of subsequent eastward tilting 

of the plains is included. At a gradient not quite so 

steep the slope would coincide with the smoothly worn 

tops of some of the mountains, such as Flattop Mountain, north of St. Mary Lake. (See pl. 2 A.) So far 

as known to the writer, there is no evidence that the 

mountains have risen less than the bordering plains 

since Oligocene time. Probably they have risen more 

than the plains. 

The genetic relations of such a gravel-covered erosional surface to the development of the Lewis overthrust fault are not considered in this paper. It-may 

be noted in passing, however, that the lithologic composition of the Oligocene gravel on the Cypress Hills 

suggests that the Lewis overthrust faulting and the 

associated foldin~~ occurred long enough before the 

end of the Oligocene epoch for the pre-Cambrian rocks 

to be denuded of their covering of Mesozoic 

and Paleozoic rocks and so exposed as to yield the 

quartzite gravel. It thus appears that the Lewis overthrust is much older than Willis's "Blackfoot pene~ 

plain," 8 if by that is meant the plain of the highest 

benches now preserved near the mountains. As s~own 

below, the latter plain is probably the correlative of 

Collier's "Flaxville Plain." Because of these facts 

the name " Blackfoot peneplain " is not used in this 

' paper. 

It is notable that now.here back in the mountains of 

the Glacier National Park region are there, so far as 

known, any land forms of Oligocene time now preserved, unless thE~Y are the peaks of the mountains 

themselves, and even these have probably been greatly 

modified by erosion in subsequent ages. 

McConnell evidently regarded the Oligocene fluviatile deposits on the Cypress Hills as originally distributed along a valley bordered by higher land. This 

may really have been the case, inasmuch as remnants 

of deposits of similar age, character, and topographic 

position are not now found for long distances either 

to the north or to the south. 

Darton describE~ similar deposits of Oligocene and 

MioC?ene age that underlie a gently sloping, nearly flat 

plain which was originally continuous eastward from 

the front range o:E the Rocky Mountains south of the 

Wyoming-Montana line and which still extends over 

a large part of southeastern Wyoming, southwestern 

South Dakota, northeastern Colorado, and the western half of N ebrnska. Concerning the conditions of 

deposition, Darton 9 writes as follows : 

Later in Tertiary time, after the outlines of the great mountain ranges to the north and west had been carved, there was 

s Willis, Bailey, Stratigraphy and structure of the Lewis and Livingston Ranges, Mont. : Oeol. Soc. America Bull, vol. 13, pp. 310, 

836-343, 1902. 

•Darton, N. H., Prell.minary report on the geology and underground 

water resources of the central Great Plains: U. S. Geol. Survey 

Prof. Paper 32, pp. lSfi-186, 1905. 

a long period in which streams of moderate declivity flowed· 

across the central Great Plains region. These, with frequently 

varying channels and extensive local lakes. due to damming 

and the sluggish flow of the waters, laid dQwn the widespread 

mantle of the Oligocene or White River deposits. These began 

with the sands of the Chadron formation, which show clearly 

the course of old currents by channels filled with coarse sandstone and areas of slack water and overflow in which fuller's 

earth and other clays were laid down. The area of deposition 

of this series extended across east Colorado and Wyoming and 

west Nebraska and South Dakota and· probably also farther 

north, . for the deposits have b~en found in west Canada. 

Doubtless the original extent was much wider than tlle area 

in which we now find the formation, for much has been removed by erosion. The White River epoch was continued by 

the deposition of the Brule· clay under conditions in which 

the currents were less strong and local lakes and slack-water 

overflows were more extensive. The Brule clay has abOut the 

same area. as the Chadron and originally was much more 

extensive than it is at present. 

At the beginning of Miocene time the general conditions 

had not changed materially, but doubtless for a while an 

extensive land surface existed in the central Great ' Plains 

area. In the stream channels extending across this surface 

the Gering formation was laid down, one channel extending 

across west Nebraska for some miles just south of North 

Platte River. Next came the deposition of a widespread 

sheet of sand derived from the mountains to the west, probably spread over the entire central Great Plains region by 

streams, aided to a minor extent by winds. The streams of 

this time shifted their courses across the plains, spreading . 

the debris from the mountains in a sheet which in some part$ 

of the area attained a thickness of 1,000 feet-a :flat ~!uvial 

fan of wonderful extent. This is the Arikaree formation, 

which buried some of the lower ranges of the upliftS; as shown 

by the high altitudes to which it extends on the slopes of 

Rawhide Butte and along the front of the Laramie ·Range. 

It has been so widely eroded since its dei;>osition that we do 

not know its original extent, but doubtless it covered most of 

the central Great Plains far to the east. 

The character and topographic relations of th~ remnants of Oligocene deposits described above, ·the 

analogous relations of the Oligocene (White River 

format!on) in South Dakota, southeastern Wyoming, 

northeastern Colorado, and Nebraska, and the conditions which developed later and which are described 

on pages 12-13 appear to afford justification for drawing a picture of northern Montana and the adjacent 

parts of Canada in Oligocene time as follow_s: 

At the west the Rocky Mountains in Montana had 

by Oligocene or Miocene time risen to considerable 

height. The altitude above sea level is not known, but 

it seems probable that the crest of the range in the 

Glacier National Park region may have been within 

3,000 feet of the present height, possibly 6,000 to 7,000 

feet above the sea. Farther south the mountains may 

have been higher. Vigorous erosion in Glacier National Park had stripped off whatever covering oi 

Mesozoic and Paleozoic rocks overlay the Algonkian 

limestone, quartzite, and argillite, and much erosion 

had been accomplished farther south concordantly . 

with the rise of the mountains. The Great Plains had 

risen so.mewhat at the east and more at the west, so 
8 PHYSIOGRAPHY AND GLACIAL GEOLOGY OF EASTERN MONTANA 

that such fresh-water lakes as there were in Eocene I 

time were probably drained; the gradients of streams 

were increased, and vast quantities of coarse gravel and 

cobblestones and some clay and sand derived largely 

from the Algonkian rocks were swept. eastward across . 

the plains. 

Algonkian rock into the soft Cretaceous shale below 

the plane of the Lewis overthrust-a condition developed subsequently which resulted in ~uch slumping \ 

and consequent bold scarps. Neither had the streamcut valleys then had their side and head slopes over· 

steepened by the plucking and scouring action of 

glacial ice. Some of the writer's conclusions have: 

been discussed with reference to isostasy by ·Lawson.11 

There is no evidence of an Oligocene or· Miocene 

peneplain in the 1nountains of the Glacier National· 

Park. South of Marias Pass the mountains are less 

The eastern part of the Cypress Hills Plateau remnant of this ancient gravelly plain is about 850 miles 

from the nearest point of marine waters in Hudson 

Bay. If it is supposed that the altitude of the Cypress 

Hills has increased 2,000 feet since Oligocene time, the 

altitude of the head of the plateau at that time mus~ 

have been about 2,800 feet and that of the east end 

1,700 feet. This would mean an a.verage gradient in 

this distance of about 2 feet to the mile, or about the 

same gradient as that of the present South Saskatchewan River, for that stream in the part of its course 

riorth of the Cypress Hills descends from an altitude· 

· well known to the writer, but topographic maps give 

little indication of a peneplain; 

·of 2,142 feet at Medicine Hat to about 1,758 feet north 

of the east end of the Cypress Hills, and its waters 

reach sea level, by way of Lake Winnipeg and the Nelson River, at York Factory, the nearest point on Hudson Bay. This gradient is much lower than that postulated for the Oligocene stream from a point near the 

mountains eastward to and along the tract now representing the top of the Cypress Hills Plateau, and there 

is some doubt whether a stream flowing on such a 

gradient could have transported the coarse gravel now 

found scattered on lower areas far to the east. The 

presence of postglacial marine clay in the lower parts 

of the valleys tributary to the west coast of Hudson · 

Bay up to altitudes of 500 to 600 feet may indicate that 

the average gradient on the lower South Saskatchewan 

and Nelson Rivers has been reduced about 1 foot per 

mile since Pleistocene time. 

Dawson 10 in his journey westward on the Fortynfnth Parallel Su~ey found the first undoubted specimens of what he called." quartzite drift "-that is, 

quartzite pebbles from the Rocky Mountains like those 

of the Cypress Hills-about 145 miles east of the 

northeast corner of Montana. 

At the stream gradient assumed. west of the top of 

the Cypress Hills (p. 6), the streams would be issuing from the mountains of the Glacier National Park 

onto the plains on a surface somewhat above that now 

· represented by th~ top of Flattop Mountain-that is, 

at an altitude now about 8,300 feet, then perhaps 

5,300 feet, or not greatly different from that of the 

present streams at the mountain front. The mountains probably had. a worn-down aspect by the end of 

Miocene time, but some peaks probably still rose 

2,000 ·or· 3,000 feet above the bordering plain. The 

valleys had not then been cut through the hard 

1o :Pawson, G. M., Report on the geology • • • of the 49th 

parallel, p. 2.25, 1875. 

Some of the smooth parks on the Little Belt a;nd 

Big Snowy Mountains. suggest the presence of a peneplain, but they may be due, in part at least, to the 

nearly flat-lying positions of underlying rocks. In 

many places the condition was doubtless much the 

same as shown in·Plate 2 B, a view taken on the summit of the southern part of the Big Horn Mountains 

8,000 to 9,000 feet above sea level. Here the summit 

plain is underlain by gravel of supposed Oligocene or 

Miocene age, and in the background are mountain 

peaks rising 3,000 to 4,000 feet higher. 

Weed 12 states that at the end of the Eocene epoch 

[including what is now termed Oligocene time] the 

entire Little. Belt Mountains quadrangle was reduced 

to a gently hilly country bordered by a broad level · 

plain. In a paper on the glaciation of the Crazy 

Mountains Mansfield 18 writes: 

Reference has been made to the gentle outlines of the upper 

topography of the northern section of the mountains. Loco 

Mountain, the main massif of that region, has a nearly :tlat top 

3 or 4 miles long and 1 or 2 miles wide at an altitude of 9,000 

feet. A small knoll rising 200 feet above the general l~vel 

forms Loco Peak, the highest summit. The gentle outlines here 

mentioned have been produced upon bOth sedimentary and 

igneous rocks, regardless of structure, and represent an ancient 

surface of erosion. 

In the southern section the altitudes are greater and the 

general topography more rugged, but many of the ridges rise 

to fairly accordant levels, and here and there small remnants 

of a :tlat surface occur at an altitude of about 10,000 feet. 

Mansfield apparently connects this summit er~sion 

with the development of the surrounding high terraces 

(described on p. 25), of which remnants still persist. 

To the present writer, however, these terraces appear 

to be of later origin, and it seems possible that the 

smoothing of the top around Loco Peak· may da.te 

back to the time of the Cypress Plain (Oligocene or 

Miocene). 

u Lawson, A. C., The Cypress Plain : California Unlv .. Dept. Geol. 

Sci. Bull., vol. 15, pp. 153-158, 1925. 

u Weed, W. H., U. S. Geol. Survey Geol. Atlas, Little Belt Mountains folio (No. 7), 1899. 

13 Mansfield, G. R., Glaciation in the Crazy Mountains of Mootana. : 

Geol. Soc. America Bull., vol. 19, p. ~64, 1907. · 
U. S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 174 PLATE 2 

A. EAST FLATTOP MOUNTAIN, GLACIER NATIONAL PARK, MONT. 

View south ucross Swift Current. Valley. Sl. Mary Ridge, capped with pre-Wisconsin glacial drift, at the left.. Photograph by Bailey Willis. 

B. BIG HORN MOUNTAINS, WYO. 

Iligh plain of supposed Tertiary deposits, a part of the subsummit plateau. Near Canyon Creek, 10 miles west of Hnzleton. Altitude 9,000 feet. Peaks of the. central crest iu background, 11,000 to 13,165 feet. Photograph by N. H . Darton. 
U. S. GEOLOGICAL SURVEY 

A . OLIGOCENE (?) CONGLOMERATE CAPPING CYPRESS HILLS, ALBERTA 

Smooth waterworn pebbles, mostly quartzite. 

PROFESSIONAL PAPER 174 PLATE 3 

B. WATERWORN QUARTZITE PEBBLES IN OLIGOCENE m GRAVEL CAPPING CYPRESS 

HILLS, ALRF:RTA 

C. EASTERN EDGE OF BEARTOOTH PLATEAU, WYO., BETWEEN MONTANA-WYOMING LINE AND CLARK FORK OF THE YELLOWSTONE RIVER 
tr. S. GEOLOGICAL SURVEY PROPESSlONAL PAPER 174 PLATE 4 

B 

c 

BIG SHEEP MOUNTAIN NORTHWEST OF TERRY, MONT. 

Illustrating destruction of high gravel-covered benches and development of lower benches Ly erosion. A. Gravel-covered top of Big Sheep Mountain, at right; badlands on shale at left and below. B. Younger and lower gravelly bench being trenched by recent drainage. C. Last stages of breaking down of a high-level plain by broadening of a lower plain and dissection of t he di vide, Cedar Creek Valley northwest of Terry, Mont. 
U. S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 174 PLA'l'E 

A 

B 

VIEWS ILLUSTRATING DESTRUCTION OF HIGH GRAVEL-COVERED TERRACES AND BENCHES 

AND DEVELOPMENT OF LOWER PLAINS AND GRAVELLY RENCIH•:S BY EROSION 

A. Gravel-capped Lance sandstone at right; bad lands on dissected sandstone and shale at left. South of Myers. Mont., on th~ Yellowstone Hivcr. B. Pebbles and boulders moving down eroded shale slope from remnant of a gravelcapperl terrace (No. 2 bench) at top of a hill northeast of Clark, Wyo. 
OLIGOCENE EPOOH 9 

The structure of the Absaroka Range, south of Livingston, as described by Weed, u is that of a broad 

anticlinal fold accompanied by niinor crumples and 

modified more or less by profound -faulting. The uplifted axis of this anticline is exposed in the high 

plateaus and mountains of Archean gneiss and crystalline schist. The edges of the Paleozpic strata are 

beveled off on each flank at or below the edge of the 

summit plateau, parts ,of which are designawd East 

Boulder, West Boulder, and Lake Plateaus. This summit, though profoundly dissected by the branches of 

Boulder and other canyons, presents the appearance of 

~ fairly uniform erosional plain as seen in a crosscountry view from a high point. (See map of Livingston quadrangle.) The folded and faulted beds on the 

flanks include Cretaceous strata and that part of the 

overlying Livingston formation which is of Eocene 

age. From this it is evident that the summit plain is 

not older than Eocene, and it may be as much younger 

as Oligocene or Miocene. It is stated in the Livingston 

folio that 

The surface of the plateau of gneiss which is drained by the 

Boulder River and its tributaries appeare to have been plan~d 

to the level of an ancient sea. The streams then fiowing could 

cut no lower than their mouths, but the plateau has since been 

elevated with reference to the sea and is being carved by 

modern streams. 

It should be remembered, however, that the shore of 

that sea was probably as far distant then as now. 

The present rugged aspect of the topography on 

the east side of the Yellowstone Valley from Livingston south to Emigrant station, Mill Creek, and 

Mount Oowen is due largely to the spurs and reentrants of the dissected edge of this summit (or subsummit) plain as seen :from below. That part north 

of Mill Creek . culminating in Mount Cowen is in 

reality not higher than the broader plateau crests and 

peaks to the east. 

A rugged strip between Stillwater and West Rosebud Canyons in the Beartooth National Forest north 

of Cooke, Mont., is known as the Granite Range. 

Some of the peaks, such as Mount Hague ( 11,200 :feet) 

and Mount Wood (12,480 feet), rise above the broader 

parts of the crest, which is in reality one of the interstream segments of the· great granite plateau. Another of the higher and smoother crests in southwestern Carbon County, shown on some maps as the Beartooth Plateau, stands 12,000 feet or more above sea 

level. From these high crests the observer may··overlook a broad subsummit plateau, which constitutes 

u Iddings, J. P., and Weed, W. H., U. S. Geol. Survey GeoL Atlas, 

Livingston folio (No. 1), 1894. On the geologic maps in the Livingston folio this range is labeled "Snowy Range," but the name 

" Absaroka Range " was adopted by the United States Geographic 

Board. Geologists who studied the Livingston and adjacent quadrangles (Hague, Weed, Iddings, and others) appear not to have 

applied the na:me "Absaroka " to the mountains north of the Montana 

State line in their descriptions. 

the eastern peripheral part of the worn-off top. of the 

range and to which the name Beartooth Plateau 

is here applied. ' (See pl. 3 0.) . 

The highest known remnants of the gravel-covered 

terraces along the Yellowstone River are those described on page 28 as truncating the crests of the 

ridges east o:f Billings (east and west of Pryor Creek}, 

about 4,000 :feet above sea level. The more westerly 

one is about 65 miles northeast of the edge of the 

I~eartooth Plateau and about 1,000_feet above the Yellowstone River. To connect the plateau surface with 

this terrace remnant would require a steep stream 

gradient. It would extend the marginal slope of the 

plateau, which is fairly steep near the edge, outward 

some distance over the plains, and the gradient would 

decrease at a rate something like the following: 

Feet 

5 miles, at 400 feet to the mile _________ _:_____________ 2, 000 

5 miles, at 200 f~t to the mile------------------------ 1, 000 

10 miles, at 100 feet to the mi:e _______________________ 1, 000 

20 miles, at 50 feet to the mile------------------------ 1, 000 

25 miles, at 25 feet to the mile------------------------ 625 

Total descent (9,625 to 4,000 feet)-----.---------- 5, 625 

This gradient is high compared with that observed 

on the lower terraces of the same region, yet only 

that of the first few miles seems at all excessive. Perhaps so steep a gradient near the mountain front 

might be accounted for as the result of subsequent 

differential movement on the Beartooth fault in addition to general easterly tilting. Between 10 and 15 

miles from the edge of the plateau, however, this 

gradient would have declined 'to 100 feet to the mile, 

and the plateau surface would have been only about 

1,200 or 1,300 feet above the highest of the gravelcapped terraces no; preserved in the region of Red 

Lodge. . · 

The :facts stated above, taken in connection with the 

other phenomena of the regiQn described below, ~eems 

to the writer to make it unlikely that the Beartooth 

subsummit plateau is younger than Miocene, even if 

it is not so old as Oligocene. It resulted from, longcontinued erosion foll9wing the Heart Mountain over-: 

thrust, but whether or not the development of this 

plateau occurred prior or subsequent to the extrusion 

of the volcanic breccias of the Absaroka Range in late 

Miocene time, or whether or not the volcanic rocks 

extended northeastward over this plateau, is not 

known. If the volcanic rocks did so extend, the northeastward-flowing streams that now deeply dissect the 

plateau may haveoriginated on the slopes of the old 

volcano, the remnant of the filling of whose. throat 

constitutes the Crandall stock, a part of Hurricane 

Mesa 15 · south of Clark Fork. There is considerable 

11 Iddings, J. P., and others, Geology of Yellowstone National Park: 

U. S. Geol. Survey Mon. 32, pt .. 2, pp. 215--268, 1899. See also Hague, 

Arnold, U. s. Geol. Survey Geol. Atlas, Absaroka folio (No. 52), 1899. 
10 PHYSIOGRAPHY AND GLACIAL GEOLOGY OF EASTERN MONTANA ' 

volcanic material in the gravel capping the high 

ridges east of Billings, together with granite, purplish-red and yellow quartzites, quartz, agate, opal, 

chalcedony, and silicified wood. Some of this rna- . 

terial, however, probably came down the Yellowstone 

from points farther west. 

It is possible that some of the high-level gravel may 

have been deposited by Clark Fork when it was flowing in a more easterly course than now and.traversing 

the gap at the west end of the Pryor Mountains, formerly followed by the Chicago, Burlington & Quincy 

Railroad which is about 5,260 feet above sea level. ' . This gap is about 45 miles northeast of that part of 

the edge of the plateau near the Clark Fork Canyon. 

In this distance, a stream on a gradient similar to that 

postulated above would be flowing at about the level 

of this pass, and streams west of the Pryor Mountains would be at levels higher than the tops of any 

of, the ridges that now border the v·alley of Clark 

Fqrk on the east. 

CHARACTER OF HIGH-LEVEL GRAVEL AND RELATIONS TO 

TI:JE YELLOWSTONE TERRACES 

GRAVEL ON TATMAN MOUNTAIN, WYOMING 

A stream deposit farther south in the Big Horn 

Basin which is probably of either Oligocene or Mio- ' . cene age, is the cap of gravel on Tatman Mountain, 

25 to 30 miles west of Basin, Wyo. This so-called 

mountain is an erosional remnant, or butte, composed 

of nearly flat-lying Tertiary shale and sandstone, 

which rises 1,200 to 1,300 feet above the Greybull 

River· on the north. It was described by Fisher, and 

the fossil-bearing beds have been studied by Loomis, 

Sinclair, Granger, and others. The following statements are quoted from Sinclair and Granger.: 16 

That the Tertiary infilling of the Big Horn Basin has been 

subjected to enormous erosion is at once apparent to an observer standing on the flat-topped summit of Tatman Mountain 

and looking off over the great depression of Buffalo Basin to 

the south or the valley of the Greybull to the north. Tatman 

Mountain, in reality only a residual butte spared by erosion, 

is capped by stream-worn andesitic ·gravels which may be of 

Oligocene age, as will be suggested later. The gravel sheet 

is underlain by about 600 feet of sandstone and lignitk shales 

in which no fossils have yet been found except leaf impressions, fresh-water mollusks, and Entomostraca. These rest 

conformably on the Wind River (Lambdotherium zone), and 

this, in turn, is in direct stratigraphic continuity with the 

Wasatch. As shown by remanie gravels at lower levels, derived from the deposit on Tatman Mountain, erosion has 

spared but a small part of this once extensive formation. As 

no fossils have yet been found in the gravels, their age is 

uncertain, but on the strength of certain lithologic similarities to be referred to later, they may be regarded as Oligocene, 

1a Sinclair, w. J., and Granger, Walter, Eocene and Oligocene of the 

Wind River and Big Horn· Basins : Am. Mus. Nat. Hist. Bull., vol. 30, 

pp. 87-88, 111, 1911. See also Sinclair, W. J., and Granger, Walter, 

Notes on the Tertiary deposits of the Big Horn Basin : Idem, vol. 31, 

pp. 57-67, 1912. 

and the dissection of the Tertiary deposits of the Big Horn 

Basin fixed as later Oligocene and post-Oligocene. * * * 

Tatman Mountain is· capped by about 30 feet of stream gravels resting unconformably. ( ?) on the lignitic shales below. 

While the majority of the pebbles are of volcanic rocks, no 

particularly careful search is necessary to demonstrate -the 

presence of vein quartz and quartzite. As no fossils have yet 

been found in the Tatman Mountain gravels· and nothing in 

the shales below but traces of plants and a few invertebrates, 

their age can not l;>e fixed, and the questionable assumption 

that they are Oligocene is based en1iirely on their stratigraphic 

position above beds which may correspond to the so-called 

Bridger and perhaps also the known Uinta of the Wagonbed 

Spring section in the ·wind River Basin. The exposures on 

Tatmari Mountain are but fragments of a formation at one 

time more extensive but now almost entirely destroyed by 

erosion. 

The gravel cap on Tatman Mountain is 5,800 to .5,850 

feet above sea level ; 30 to 36 miles to the. west the 

worn-off tops of the Carter Mountains, spurs of the 

.Absaroka Range, rise from the head of Meeteetse Rim 

to altitudes of 10,000 to 12,000 feet or nwre. These 

mountains are composed of volcanic breccias and one 

or more basalt flows. If they are the same as those in 

the continuation of the same ridge inunediately to the 

west in the southeastern part of the Ishawooa quadrang. ie 17 they are of Miocene age. If the andesitic ' . gravel capping Tatman Mountain came from this 

ridge it was probably deposited not earlier than Miocene time. The included quartzite pebbles may have 

been derived secondarily from Wasatch conglomerate, 

which crops out between Tatman Mountain and the 

mountains to the west. Where examined by the writer 

at the top of the bluff east of Meeteetse, the pebbles 

in this conglomerate consist almost wholly of ~oothly 

waterworn quartzite, together with a small percentage 

of porphyry, limestone, quartz, and decomposing granite. No andesite or other volcanic rocks were found, 

though such rocks are abundantly represented in the 

later Tertiary and Pleistocene gravel of the Big Horn 

Basin. Apparently the andesitic pebbles in the grayel 

on Tatman Mountain could not have been derived from 

Wasatch conglomerate, but must have come from the 

Miocene volcanic rocks. · 

The Owl Creek Mountains, farther south, formerly 

called the Shoshone Mountains, which are at the headwaters of the ·wood River, are said by Darton 18 to 

consist largely of agglomerate and lava flows, in~erbedded with sandstone and shale. In these mountams, 

near the head· of the Middle Fork of Owl Creek, a 

large number of fossil leaves w~ich were cons~dered 

of Fort Union age were discovered in a shale In the 

interbedded mass. If this age determination is correct some of the volcanic rocks here, as farther northwest in the Absaroka Range, are of early Tertiary age · 

and possibly might have yielded andesite to the gravel 
OLIGOCENE EPOCH 11 

of Tatman Mountain in Oligocene time, if high enough 

in the mountain range. · 

A stream gradient projected eastward 30 to 35 miles 

from the edge of the smoothly worn top of the Carter 

Mountains, 10,000 feet above sea level, would coincide 

with the gravel cap of Tatman Mountain, if an initial 

slope of 250 feet to the mile is assumed to decrease 

gradually to a fall of about 40 feet to the mile. To 

judge from the grades of the lower terraces yet preserved in this basin, this would not have been an abnormally high gradient, inasmuch as it would have included the effects of post-Miocene differential elevation. Swinging toward the north as it. joined the Big 

Horn River, the stream that deposited this gravel on 

Tatman Mountain would have had to cross the Sheep 

Mountain and Little Sheep Mountain anticlines and 

the great Pryor-Big Horn Mountain uplift. The relatively resistant limestone and sandstone in these mountains undoubtedly would have retarded erosion, and 

as a consequence a stream with a gradient of but 10 feet 

to the mile projected northward for the next 80 miles 

from the gravel on top of Tatman Mountain would 

have issued at 5,000 feet above sea level from the sag 

in whose ·bottom is cut the lower canyon of the Bi~ 

Horn River. This is not far from the altitude of the 

Pryor Mountain gap (5,260 feet), to the west, and of 

the highest of the gravel remnants which Thorn 19 

found near the north flank of the Pryor Mountains 

and the northern part of the northeast flank of the 

Big Horn Mountains in Montana. (See p. 28.) A 

grade of 30 feet to the mile for the succeeding 35 miles 

would connect with the gravel-capped top of Pine 

Ridge between the converging Big Horn and Yell owstone Valleys. 

HIGH GRAVEL NEAR THE YELLOWSTONE 

· The occurrence of gravel on Pine Ridge is described 

by Rogers 20 as follows : 

Yellowstone and Big Horn Rivers meet at a rather acute 

angle, and Pine Ridge constitutes the high divide between them, 

the present shape and position. of the ridge being controlled 

partly by the geology. The top of the ridge is remarkably 

level and rises only slightly to the south, maintaining an average height of about 1,100 feet above the rivers. Because of 

the leve1 character of its crest and its thick covering of gravel 

it is believed to represent an old river terrace. In other words, 

at some time in the past the liver beds must have been about 

1,100 feet higher than at present, and the rivers, in meandering, deposited the gravel which now covers Pine Ridge. The 

ridge itself rises about 400 feet above the immediately surrounding country, and its level crest is in this district commonly less than 200 feet wide. Its slopes are everywhere steep 

and are broken into characteristic rounded hills. * "' *· 

[The gravel] is made up for the most part of pebbles from 

half an ·inch to 3 inches in diameter, although pebbles 6 qr 8 

1ll ThoDi, W. T., jr., personal communicattbn. 

. • Rogers, G. S., Geology and coal resources of the area southwest 

of Custer, Yellowstone and Big Horn Counties, Mont.: U. S. GeoL 

~urvey Bull. 541, p. 317, 1914. 

iiicbes in diameter are not rare. . There is also an interstitial 

filling ·of fine gravel and sand. The thickness of the gravel is 

difficult to estimate, owing to the fact that it constantly slumps 

down, never forming cut banks. The thi~ess of 40 feet given , 

in the columnar section probably represents a maximum, and 

the average thickness is probably less than· 30 'feet. As men~ 

tloned above, the gravel has exercised a distinct influence on 

the topography and drainage and is constantly being carried 

down and reworked by' the streams which have their sources 

in Pine Ridge. Probably more than half of the gravel is composed of quartzite, chert, and other slliceous rocks, but a very 

wide range of igneous rockS also enters into lts composition, 

and all the main t:vpes, from rhyolite to pyroxZnite, have been 

observed by the writer. 

At the time the above description was written but 

little was known concerning the relations of the terrace gravels of Montana and Wyoming, and Rogers's 

suggestion that this gravel is "either early Quaternary 

or possibly late Tertiary " was probably, in part at 

least, based on conference with the present writer~ 

From consideration of the factors discussed in the 

present paper it now seems more probable that the 

·gravel on Pine Ridge, as on the highest tops east and 

west of Pryor Creek, is to be correlated with the gravel 

on the Cypress Hills and Tatman Mountain as either 

Oligocene or Miocene. 

The change in the projected gradient· of this· Oligocene or Miocene stage of the Big Horn River from 10 

feet to the mile for the 80 miles between Tatman Mountain and the mouth of the lower canyon in· Montana 

to an average of 30 feet for the 35 miles between the 

Canyon and Pine Ridge might possibly be ~ccounted 

for as the result of a moderate uplift of the Pryor-Big 

Horn anticline, the effect of which would be t9 lessen 

the gradient of the Big Horn River in and above its 

lower canyon and to increase the gradient between the 

canyon and the Yellowstone River. · · . 

In a report on the Tullock· Cree~ co~l field, east of 

the Big Horn River, Rogers and Lee 21 describe gra'Vel 

deposits, the highest and oldest of which are the 

equivalent of those on Pine Ridge. In this connec;... 

tion the present writer is cited by Rogers and Lee as 

if concurring in the suggestion that the highest of 

the gravel deposits in the Tullock Creek field may be 

Pleistocene. Though that citation might have ·been 

permissible at the time the Tullock Creek report was 

written, 'in 1913-14, it does not now agree with the 

writer's opinion, which is that the highest of these 

gravels, like those on Pine Ridge, may be as old as . 

Miocene or Oligocene and may be equivalent to the 

gravel on the Cypress Hills. It is not clear from the 

descriptions given by Rogers and Lee whether or not 

remnants of the highest flat terraces are preserved on 

the divide between Tullock and Sarpy Creeks~ Evi~ 

dently most of the gravel has been let down from the 

:u Rogers, G. S., and Lee, Wallace, Geology of the Tullock Creek coal 

field, Rosebud and Big Horn Counties, Mont.: U. S. Geol. Survey Bull. 

749, pp. 44-:-47, 1928. 
12 PHYSIOGRAPHY AND GLACIAL GEOLOGY OF EASTERN MONTANA 

older and higher terraces by . erosion. Apparently 

these deposits are remnants of the Flaxville and lower 

terraces. (See pp. 27-29.) The gravel is said not to 

extend more than 23 miles south of the Yellowstone 

River except on the western edge of the coal field, 

where it is found also in a zone extending about 10 

miles back from the Big Horn River.· The general 

altitude of the highest gravel is 3,700 to 3,800 feet 

above sea level, or 1,100 feet above the rivers. No 

fossils indica:tive of. the age of the deposit were found. 

The graver of the Tullock Creek field is composed 

of pebbles r~presenting a wide range of rock types. 

Quartzite is one of the most abundant-a fact which 

is no doubt due more to its greater hardness than to 

its preponderance in the original series of rocks from 

which the gravel was derived. Jasper and quartz are 

common, and chalcedony is also found. Pebbles of 

very dense fossiliferous limestone are present, and 

crinoid stems were noted in one pebble. Of igneous 

rocks a fairly complete series is present, the types 

ranging in composition from basalt to granite and in 

texture from porphyritic to granitic. Sandstone of 

the type common in the Cretaceous and Tertiary rocks 

of the region was rarely found. The pebbles are for 

the most part smoothly rounded and are ovoid to flattish in shape. They are fairly well sorted locally, the 

average diameter being 2 to 3 inches. Pebbles 6 inches 

in diameter are common, however, and a few boulders 

10 to 14 inches in diameter were found. The interstitial material is chiefly quartz, generally in angular 

grains; very little clay is associated with the gravel. 

Dobbin 22 describes high-level gravel south and east 

of Forsyth as follows: 

OLIGOCENE OR MIOCENE (?) GRAVEL 

The oldest ·gravel deposit in the field caps a plateau on the 

divide between Arnells and Sarpy Creeks in the northwest 

corner of T. 3 N;, and the southwest corner of T. 4 N., R. 

39 E. Gravel occurs at the same level on the tops of the 

highest hills and ridges in the northern part of T. 4 N., R. 

41 E. These gravel deposits are but small remnants of a 

much larger river terrace and stand 1,050 to 1,100 feet above 

Yellowstone River. The gravel, which is 60 feet thick, is 

thoroughly cemented at the base into a conglomerate. The 

deposit contains boulders a foot or more in thickness and 

consists of igneous rocks ranging in composition from granite 

to basalt, particularly andesitic porphyries. Agate, silicified 

wood, and fragments of coal clinker occur in it, indicating 

. that at least some of the coal had been burned along its outcrop before the gravel was deposited. 

From the distribution of these highest terrace remnants it appears that the main stream of Oligocene 

or Miocene time may have flowed in a gravel-floored 

valley, 10 to 20 miles or more in width, south of the 

line of the present Yellowstone Valley between 

Billings and Miles City. 

112 Dobbin, C. E., The Forsyth coal field, Rosebud, Treasure, and Big 

Horn Counties, Mont.: U. S. Geol. Survey, Bnll. 812, pp. 20-21, 1929. 

High-level gravel on the top of Big Sheep Mountain, at the h~d of C~dar Creek, in T. 15 N., R. 47 E., 

in the northwestern part of Prairie County, was examined by the writer in 1922. This mountain is. crossed 

by the Crowley road 25 or 30 miles northwest of Terry. 

The top, which is flat, constitutes the divide and the 

highest land in sight and is capped with 20 to 30 ·feet 

of coarse, well-rounded gravel with some included 

sand. (See pl. 4 .A.) In places this gravel is cemented 

by calcium carbonate to a conglomerate. The largest 

stones noted were 6 by 10 inches in diameter. In lithologic character the pebbles are much the same as those 

on the lower benches, comprising several varieties of 

porphyry and other crystalline rocks, a few· granites, 

numerous pink and reddish quartzites, vein quartz, 

chert, and silicified wood. No other fossils and no 

limestones were found. The notable thing about this 

deposit is its position and relatively high altitude: 

it is about 1,400 feet above the Yellowstone at Terry 

and 3,600 feet (baromet:dc) above sea level. This altitude, if even approximately correct, is about 400 feet 

higher than that of the highest gravel found by Rogers on Little Sheep Mountain, a few miles to the south. 

The deposit is so much higher ( 600 to 800 feet) than 

the remnants of the Flaxville Plain in the Glendive 

quadrangle that it quite possibly belongs to an earlier 

stage. It may be of Miocene or Oligocene age. The 

nearest remnant of deposits which have been referred 

to the White. River Oligocene caps Sentinel Butte, 

N.Dak. This point, which is a few miles south of the 

village of Sentinel Butte, on the Northern Pacific 

Railway and 10 miles east of the Montana-North Dakota State line, is about 90 miles from Big Sheep 

Mountain in a direction a little south of east. The 

top of Sentinel Butte is 3,430 feet above sea level, so 

that a grade of less than 2 feet to the mile would connect the two deposits. 

No features of the plains of . Montana or northern 

Wyoming rise above the projection of this supposed 

Oligocene or Miocene Cypress Plain, except the Sweet 

Grass Hills and outlying mountain groups and possibly the Bull Mountains, between the Yellowstone and 

Musselshell Rivers and' the Wolf and Rosebud Mountains and similar ridges oi" Eocene rocks east of the 

Little Horn River. 

MIOCENE AND PLIOCENE EPOCHS 

FLAXVILLE PLAIN OR NO. 1 BENCH 

The development of the Cypress Plain was followed 

by ~ regional uplift so that streams which had been 

shifting to and :fro on this plain now cut deep valleys. 

As the land ceased to rise, or perhaps during intervals 

of cessation which alternated with periods of renewed 

uplift, the work of planation was begun and carried 

on. The amount of the uplift is indicated by the verti""' 

cal distance between the Cypress Plain and the next 
MIOCENE AND PLIOCENE EPOCHS. 13 

lower plain (Flaxville Plain, or No. 1 bench 28 ). This 

a~ounts to about 700 to 1,000 feet east of meridian 

109° W. and 1,000 to 1,500 feet weRt of this meridian, 

possibly 2,000 feet in the Rocky Mountains of the 

Glacier National Park, and 3,000 feet or more northeast of the Yellowstone National Park. 

The process of planation was not simply the development and extension of flood plains along the main 

streams and their tributaries. Every ravine contributed to the result. The region under description is 

mostly underlain by soft indurated clayey shales ·with 

interbedded friable sandstones. These porous sandstones, as also the Oligocene gravel, absorbed rain 

water and transmitted it, and where there edges 

cropped out in eroded slopes springs and seeps ~sued 

and moistened underlying Tertiary or Cretaceous 

clays. In such places landslides frequently occurred, 

the fine mud was readily carried away in suspension, 

and friable sandstone blocir; slid down and crumbled 

to sand, which was later washed or blown away, and 

coarse gravel rolled and slid from the higher level 

onto the newly developed plain. By this process the 

. steep marginal slopes below the gravel-capped interstream remnants of the Cypress Plain gradually · re-

- ceded, narrowing the divides and developing a new 

and lower set of valley plains that sloped gently to 

the main streams. (See pls. 4 and 5.) To the accumulation of s~condary gravel let down from the Cypress 

Plain streams heading in the mountains made new contributions of similar gravel and sand brought directly 

· from the mountains, and in these deposits accumulating on the land, along stream channels and flood plai~ 

and in ponds on the newly made plain, were entombed 

remains of animals that have been identified as " not 

older than Miocene or younger than lower Pliocene.'' 

By the end of Miocene time or early in· Pliocene 

time the proeess of peneplanation had proceeded so far 

and divides had been so .much worn away that the 

whole of the northern Great Plains north of the Black 

Hills, the Big Horn. Mountains, and the Belt Mountains presented the aspect of a peneplain with but 

few eminences rising above it. East of the front 

range of the Rocky Mountains the most prominent 

of these remnants were the -Sweet Grass Hills ,and 

the Bearpaw, Little Rocky, Highwood, Moccasin, 

Judith, Big Snowy, and Crazy Mountains. The 

gravel cap of the Cypress Hills may have stood 1,000 

Jl3 Obviously there are so]Jle ·objections to applying serial numbers 

to the several sets of remnants of these dissected ancient plains, 

benches, and terraces ; on the other hand, there are equally strong 

tbougb somewhat different ·objections to applying names instead of 

numbers to these features, many of which already carry local names. 

After careful consideration of the various objections and advantages, 

the writer has adopted the plan of using the names " Cypress Plain " 

(Oligocene or Miocene) and "Flaxville Plain" (Miocene or Pliocene) 

and of numbering the FlaXville and the ·set of probable correlated 

remnants as No. 1 and the lower and younger sets of remnants, in 

order downward, as No. 2 and No. 3. It is hoped that these designations will be fairly clear to the reader without more detailed statements. 

feet or more above the surrounding plain, and off to 

the southeast in the Dakotas were the Killdeer Mountains, Sentinel Butte, and a few other like remnants 

of the Oligocene plain, with some in southeastern 

Montana. Cherrypatch Ridge, north of Harlem~ in 

Blaine County, Mont., is one of the minor remnants 

from which most of the older gravel has been removed. 

It is not certain that the top of this ridge is as high 

as the Cypress Plain. Close to the mountain fronts 

great alluvial fans may have coalesced in one continuous flat, but farther out this split up into broad valley, 

plains bordering the main streams and separated by 

low, worn-down divides-for example, the Bull 

Mountains. 

The altitude of this plain in eastern Montana was 

perhaps about 2,000 to 2,500 feet, where now it is about 

2,500 to 3,000 feet. The uplift was differential, increasing toward . the west, so that at the mountain 

front in and south of the Blackfeet Indian Reservation the altitude ·was probably about 4,500 feet .where 

now it is about 6,000 feet. 

The most extensive remnants of the Miocene or 

Pliocene plain and the gravel and sand thereon are 

north of Missouri River, in the .northeastern parts. of 

Blaine and Valley Counties and what are now Daniels 

and Roosevelt Counti~, Mont. They comprise a. 

total area of about 1,800 square miles and have been 

studied by Collier and Thom,24 who described them 

as Flaxville gravel. It was here that evidence of the 

age of this plain was found. From 'the Flaxville 

gravel Collier and Thorn collected fossils which were 

identified by Gidley as . remains of several forms of 

the ihree-toed horse, horned gopher, rabbit, rhinoceros, 

oreodont, camel, saber-tooth tiger, a doglike animal, 

and fish. Concerning these fossils Gidley made the 

following statement : 

None of the material is sufficiently good or complete to make 

positive specific determinations, and it is therefore of no value 

as .indicating ho'rizon, except in a broad way. With the exception of the specimen reported as Pleistocene, all the mate-

. rial appears to belong to the upper Miocene.· It ca.ti be stated 

positively, I think, that with the. exception noted the beds 

from which these fragments were ·collected can not be older 

than Miocene or younger than lower Pliocene. 

Further details concerning the fossils are given in 

Collier.and Thorn's paper. 

AGE AND CORRELATION OF THE FLAXVILLE TERRACES 

OR NO. 1. BENCHES 

The fossils as identified· by Gidley seem to afford 

ground for concluding, at least tentatively, that fluvial 

deposition continued on the Flaxville Plain into Plio24. Collier, A. J., and Thoro, W. T., jr., The Flaxville gravel and its 

relation to other terrace gravels of the northern Great Plains : U. S. 

Geol. Survey Prof. Paper 108, pp. 179-184, 1918. Collier, A .• J., 

Geology of northeastern Montana: U. S. Geol. Survey Prof. Paper 120, 

pp. 17-39, 1918. 
14 PHYSIOGRAPHY AND GLACIAL GEOLOGY OF EASTERN MONTANA 

cene and possibly even into early Pleistocene tiine, as 

remains of a Pleistocene camel were found. 25 Unfortunately, with one exception, no fossils have been 

found on any other remnants of this or the lower and 

younger sets of benches. The correlations presented 

in this paper are based almost wholly on physiographic 

relations and the relations of this surface to the glacial 

drift. As shown on the map, the benches surrounding 

the Bearpaw and Little Rocky Mountains lie midway 

between the remnant of the Flaxville Plain nort.h of 

.Harlem and remnants of similar benches comprising 

three sets in the Judith River Basin and about the 

flanks of the surrounding mountains. Correlation 

may also be made from the Missouri Valley in Sheridan and Roosevelt Counties across to three similar 

sets of benches or terraces on the lower Yellowstone 

in the Glendive quadrangle. As shown on the map 

and as described below, very meager and widely scattered remnants of No. i bench have been found along 

this· valley, but the next younger and lower bench,. or 

the second set of remnants of terraces, can be traced 

almost all the way up the Yellowstone to the mountains, though with numerous but shorter intervals 

where it has been cut away. The second set of remnants (No.2 bench) can also be correlated fairly well 

northward along the mountain fronts and across the 

upper Musselshell Valley to the Judith Basin and 

thence westward past Great Falls, up the ·sun River, 

and northward along the mountain front to the region 

of Glacier National Park. At intervals throughout 

this great extent of hundreds of miles isolated remnants of a higher set of gravel-capped benches are 

found, and these are consequently regarded as corl'elatives of the Flaxville Plain and are grouped together 

as No. 1 bench. These relations should be borne in 

mind in reading the following description of the 

Flaxville terraces. 

FLAXVILLE PLAIN (NO. 1 BENCH) BORDERING ROCKY 

MOUNTAIN FRONT 

For 175 miles west from Cherrypatch Ridge~ in R. 

21 E., Blaine County, to R. 8 W., in the Blackfeet 

Indian Reservation, Glacier County, degradation has 

destroyed the smooth gravelly Miocene or Pliocene 

plain and developed a lower and more uneven plain. 

In R. 8 W. are two small gravel-capped remnants, 

Landslide Butte and Horsethief Ridge, at 4,650 feet 

above sea level, and 10 to 15 miles further west and 

northwest larger remnants are found in the form of 

high gravel-capped benches or plateaus whose nearly 

flat surfaces rise gradually toward· the mountain front 

JG Hay, 0. P., The Pleistocene of the middle region of North 

America and its vertebrated animals: Carnegie Inst. Washington Pub. 

822A, p. 169, 1924. Dr. Hay states, concerning this supposed Pleistocene camel : " The geologists at present regard the formation as being 

of late Miocene or early Pliocene. There may, therefore, be some 

error about the specimen of OameZopB.'' 

in Glacier National Park. The deposits on these 

high benches have been studied'.and described by the 

writer and Stebinger. 26 The significance of. certain 

very old deposits of drift 'of the mountain glaciers 

found on these benches near the mountain front is discussed in a subsequent connection (p. 31). ':fhe presence of this drift and the absence of fossils render 

the correlation of these high bench remnants with the 

Flaxvill~ Plain of northeastern Montana somewhat 

uncertain. 

It is possible that the top of Milk River Ridge 

( 4,100-4,300 feet above sea ·level ( W)) in the Warner 

and Cardston districts, southern Alberta, in T. 3 N ., 

Rs. 17-21 W., is to be correlated with the highest 

benches south of . the international boundary in the 

Blackfeet Indian Reservation, though it appears to 

have been cut down to a somewhat lower level, and 

inquiries and a partial examination of the east end of 

• the plateau by the writer in 1920 seem to indicate that 

no Miocene or Pliocene gravel occurs in place on this 

upland beneath the glacial drift. 

The most easterly large remnant of a high gravelcapped bench, other than Landslide Butte and Horsethief Ridge, is between the North and South Forks of 

the Milk River in T. 11 N., Rs. 21 and 22 W., in the 

Cardston district, southern Alberta, whence· it extendsacross the international boundary into the Blackfeet 

Indian Reservation, Mont., in the northeastern part of 

the Blackfoot quadrangle, T. 37 N., R. 9 W. This is 

just outside the limit of continental glaciation, as the 

northeastern glacial drift at this place does not extend 

south of the North Fork Valley. At the international 

boundary this bench is 4,360 feet above sea level-that 

is, more than 300 feet above the branches of the Milk 

River to the north and south. Thence southwest and 

west to the mountain front there are many well-preserved flat-topped, gravel-capped remnants of former 

high-level plains, covering .a total area of about 100 

square miles. These mesas, which now stand hundreds 

of feet above the present streams, are all that remain 

of vast, remarkably smooth, gently sloping coalescent 

alluv~al fans, which in a former age bordered the whole 

eastern front of the Rocky Mountains far to the south, 

extending from the international boundary and probably also some distance to the north. On the interpretation of the relations of these benches or plateaus depen.ds much of our knowledge of the Cenozoic hist.ory 

of this whole region, both of the mountai:r;tS and of the 

Great Plains. Study of relative altitudes of the several high-lev~l tracts shows that they comprise two 

sets, a higher and a lower, separated by a vertical dis20 Alden, W. C., Pre-Wisconsin glacial drift in the .region of Glacier 

National Park, Mont. : Geol. Soc. America Bull., vol. 23, pp. 687-708, 

1912. Alden, W. C., and Stebtnger, Eugene,1dem, vol. 24, pp. 529-572, 

1918. Alden, W. C., Early Pleistocene glaciation in the Rocky Mountains of Glacier National Park, Mont.:. Internat. GeoL Cong., 12th 

sess., Canada, 1913, Compt. rend., pp. 479-484, 1914. 
MIOCENE AND PLIOCENE 'EPOO 15 

tance ranging from 100 to several hundred feet-that 

is, they comprise remnants of a higher or older and a 

lower or younger gently sloping alluvial plain. The 

vertical interval by which they are separated is due to 

erosion. For convenjence, as indicated, these may be 

designated respectively No. 1 bench (the higher) and 

No. 2 bench. A still lower bench (No. 3) is described 

below (p. 59). 

If there are bordering the mountain front any representatives of the Flaxville Plain .(Miocene or Plio-

-cene) to be correlated with those in northeastern Montana, they are these remnants of No. 1 bench. No 

fossils have been found in the .gravel on this bench, 

and there are undoubted evidences of the extension_ of 

. very old glaciers from the mountains out onto the 

bench, so that, as de$cribed below (p. 32), it is possible that the streams were still flowing on No. 1 bench 

in early Pleistocene time. It may be stated, however, 

in advance of further discussion of the subject, that it 

is the writer's opinion, after such field· studies as he 

has made in . the valleys of the upper Missouri and 

the Yellowstone and their tributaries in Montana and 

Wyoming, that the highest benches now preserved 

near the mountain fronts in the region under consideration are correlatives of the Flaxville Plain. 

In several places in the Blackfeet Indian Reservation, in Glacier County, remnants of both No. 1 and 

No. 2 benches are preser·ved on the top of a single 

interstream ridge. Bench No. 1 rises toward the 

mountain front from an altitude of about 4,700 feet 

in T. 37 N., R. 10 W., at an average rate of 100 feet 

to the mile (increasing in places from about 40 feet at 

the. east to 200 feet at the west), and reaches 5,950 

feet above sea level on Kennedy Ridge, east of Chief 

Mountain; 6,200 feet on Swiftcurrent Ridge, on the 

north side of Swiftcurrent Valley; 6,400 feet on Boulder Ridge, on the south side of that valley; 6,100 feet 

on St. Mary Ridge, east of Lower St. Mary Lake; 

and 6,200 feet on Two Medicine Ridge, north of Lower 

Two Medicine Lake.. No. 1 bench is also probably 

represented by the top of Makowan Butte (Lee 

Ridge), at 5,800 to 6,000 feet, northwest of Chief 

Mountain in W aterton Lakes Park, Alberta, on the 

east side of the Belly Riv~r. On most· of the ridges 

near the mountain front the upper 100 to 250 feet of 

the height is due to a thick deposit of glacial drift. 

Each of these remriants is capped with a deposit of 

coarse gravel, predominantly quartzite and argillite. 

The stones are partly subangular and partly smoothly 

rounded. The larger stones are 10 to 12 inches in 

maximum diameter, as far east as Landslide Butte. 

The maximum size increases westward from this locality to points where telations are complicated by the 

deposits of old glacial drift, with its content of smal1 

and large faceted and striated boulders. 

There are o remnants of No. 1 and No. 2 benches 

between the reat j Northern Railway and the south 

side of the T o Medicine River Basin. About 25 miles 

southeast of rowrHng the "Y. G. B. line" or Park 

to Park High ay, traverses a notch in the crest of the 

high flat-topp d 'gravel-capped- divide between Badger 

and Birch Cr eks. 27 

As would b expected from the fact· that the Paleozoic limeston form so large a part of the more. easterly mountai ridges south of Theodore Roosevelt 

Pass 28 (Mari s Pass), the pebbles on this and all the 

similar grav 1-capped ridges .to the south are pre- . 

dominantly o limestone. _ From this ridge southward 

to the Sun iver Basin and thence eaStward to the 

region of Gre t Falls there are numerous remna,nts of 

No. 1 and No 2 benches. 29 The grade of No. 1 bench 

as preserved n the divide between Badger and Birch 

Creek rises s uthwestward 300 feet in 7 miles, from · 

4,200 to 4,500 feet above sea level (more. than 40 feet 

to the mile), . and reaches 5,200 feet on a small crest 

2 miles north ast of Heart Butte, a further rise of 700 

feet in 12 m les (nearly 60 feet to· the mile). The 

ridge south f Dupuyer Creek rises southwestward 

from 4,500 to 5,200 feet above sea ·level, or 700 feet in 

8 miles, and eaches the mountain front at 5,900 feet 

abov.e sea lev I east of Dupuyer Mountain, a ·further 

rise of 700 fe t in 4 miles. 

Pendroy, t e terminus in 1920 of a branch of the 

Great N orthe Rail way, stands on one of the larger 

remnants of o. 1 bench. The flat surface of this. 

gravel-covere bench rises westward from an altitude 

of 4,000 feet (barometric) near the east end to 4,300 

feet at Pendr y and nearly to 4,600 feet at the Park 

to Park High ay near the· west end, a rise of 600 feet 

in 14 miles (n arly 43 feet to the mile). If this·grad~­

ent is projec ed westward 14 miles to the mountain 

front, withou increase, it rises to 5,200 ·feet above S0a 

level. Undo btedly, however, the grade was considerably steepe toward the mountain front, and the 

bench may h ve reached an altitude of 6,000 feet. 

Some road c ts on this bench near Pendroy expose 

5 feet or mor gravel below the thin loamy soil. The 

pebbles range in length from a fraction of an inch to 

8 or 10 inche and are fairly well rounded. Most of 

their surfaces are either coated with calcium carbonate 

or have been tched by solution. The pebbles consist 

m Most of the data concerning the bench gravel between Badger 

Creek on the nort and the Sun River on the south, both in . and east 

of the Heart But e and Saypo quadrangles, are taken from the :field 

maps and notes f Eugene Stebinger and M. I. Goldman. (See also 

U. s. Geol. Surv y Bull. 691, pl. 24, 1919.) Only a small part ·Of 

these deposits ha been examined closely by the writer. 

211 The name " T eodore Roosevelt Pass " was adopted June 2, 1920, 

by the United S tes Geographic Board for the pass tn the Rocky 

Mountains traver ed by the Great Northern Railway between Glacier 

Park Station and Belton, Mont. The . name Marias Pass is applied 

only to the pass t Summit Station on the Continental Divide. 

• Fisller, C. A. Geology and water resources of the Great Falls 

region, Mont. : U. S. · Geol. Survey Water-Supply Paper 221, pp. 24-25, 

pl. 1, 1909. 
16 PHYSIOGRAPHY AND GLACIAL GEOLOGY OF EASTERN MONTANA 

principally of gray limestone with a ~mall perc~ntage 

of dense green argillite and sandstone. 

About 20 to 25 miles southeast of Pendroy, in T. 

24 N., Rs. 2 and 3 W., is a narrow isolated remnant of 

No. 1 bench rising about 800 feet above the Teton · 

River on the north. This is known as Teton Ridge, or 

T. L. Ridge. The western part of its gravel top is 

4,340 feet above sea level.80 The margin of the continental glacial drift lies along the north slope of the 

ridge up to about 3,900 feet (barometric), and above 

this is the narrow, flat gravel cap. A large part of the 

pebbles here consist of limestone with etched surfaces, 

and a large part of reddish or greenish sandstone and 

argillite~ 

That No. 1 bench on Teton Ridge originally extended much farther east appears probable from the 

fact that similar gravel was found capping one of the 

higher hills on the divide at a paint 15 miles north of 

Great Falls at an altitude of about 3,900 feet (baro-· 

metric), near but above the limit of the glacial drift. 

Other parts of this divide were not examined. 

Certain buttelike remnants of higher levels on the 

divide between the Teton and Marias Rivers, 25 to 45 

miles east of Brady, ·rise to about 3,500 or 3,600 feet 

(barometric). The tops examined by the writer in 

1921 and by Collier in 1923 are thinly covered with 

continental glacial drift, but no bench gravel was seen. 

They are protected by caps of flat-lying sandstone 

overlying the shale and may have no definite relation 

. to the plane of No. 1 bench. · 

About 30 miles west of Teton Ridge, in the Saypo 

quadrangle, T. 23 N., R. 8 W., is Long Ridge, a_ re~­

nant of No. 1 bench 3 miles from the mountain front, 

which reaches 5,500 feet above sea level and stands 

500 feet above No. 2 bench and 800 feet above Deep 

Creek, 1 mile to the south. The grade from the top 

of Teton Ridge to the top of Long Ridge is about 37 

feet to the mile. This bench probably reached the 

mountain front at the bottom of the broad sag cut ~n 

the limestone wall, which was later trenched by the 

sharp, narrow gorge of the South Fork of Deep Creek. 

On the divide between Deep Creek and the Sun 

River in T. 22 N., R. 6 W., between 5 and 25 miles 

southwest of Choteau, are remnants of No. 1 and 

No.2 benches. In sec. 3, T. 22 N., R. 7 W., the west 

end of the bol<il plateau rises to 4,800 · feet above sea 

level, or over 800 feet above the Sun River. The 

terminal moraine of the Sun River Glacier of the 

Wisconsin stage skirts the marginal slope up to 4,600 

feet above sea level and in this moraine is cut the 

Sun River Slope Canal of the irrigation project. The 

divide is capped with coarse gravel and its flat top 

is thinly cov~red with loamy soil. 

00 Fisher, C. A., Geology and water resources of the Great Falls 

region, Mont. : U. S. Geol. Survey Water-Supply Paper 221, pl. 1, 

1909. 

The pebbles, which range in size from a fraction of 

an inch to 1% feet, consist of gray to brown limestone 

and red to brown quartzite and argillite, with perhaps 

some crystalline rocks. A sight taken westward along 

the smooth, gently sloping. top of this ridge from a 

point 8 miles east of the west end of the bench showed 

that the gradient of the top projected to the mountain 

front across the interval of 13 miles, where the bench 

has been cut away by erosion, would reach the mountains at the bottom of the sag 4 miles wide in the 

limestone wall, in which is cut the sharp inner 1,000-

foot gorge from which the Sun River issues. (See 

pl. 7 A.) This relation. is of importance as one indication of the horizon ( 5,300-5,500 feet) at which Sun 

River was issuing from the mountains when No. 1 

bench was formed. That horizon is about 1,200 feet 

above the present bed of the stream below the dam. 

The northeast end of No. l bench, which has been 

truncated by erosion, is near Priest Buttes, south of 

Choteau. Bordering the highest part of the crest 

on the south and east are several steplike drops, and 

the main one of these lower levels is probably the 

No.2 bench. 

A remnant of No. 1 bench, at an altitude of 3,900 

to 4;000 feet (barometric), is· the narrow gravel· 

capped flat top of the ridge north of the Sun River 

between 20 and 30 miles west of Great ·Falls. . This 

is crossed by the Custer Battlefield Highway north of 

Ashuelot, which stands on No. 2 .bench at 3,700 to 

3,800 feet (barometric). The broad plain known as . 

Greenfields Bench, between this ridge and Teton 

Ridge, to the north, is an undulating surface perhaps 

due to erosion of No. 1 bench but is not itself a definite 

bench of the gravel-covered type under description. 

The same is true of its eastward continuation, east of 

Gordon and Power, on which is the Benton Lake 

R.eservoir, north of Great Falls. The remnant of a 

high bench at 4,600 to 4,700 feet; 5 to 7 miles west 

of Augusta, is probably part of No. 2 bench. Though 

this was high enough to stop the advance of the Sun 

River and Smith Creek glaciers in late Pleistocene 

time, it is probable that No. 1 bench before . being 

removed by erosion was relatively still higher. 

About 12 miles south of .Augusta, in T. 18 N., R. 6 

W., there is a small remnant of what appears to be 

No. 1 bench. This bench, which is a few miles north· 

east of Bean Lake, on the south side of the upper 

Flat Creek Valley, at 4,740 feet above sealevel (barometric), is capped with a bed of coarse gravel, in 

which the pebbles consist of limestone, ·quartzite, and 

igneous rock~ derived from the mountains to the w_est 

on the Dearborn River. The tops of the ridges to the 

north rise but little if at all above the plane of this 

No. 1 bench, but those along Bird tail Divide, to the . 

east, rise much higher. The lower bench crossed by 
I 

MIOOENE AND PLIOOENE EPOOHS 17 

the moraines of the Dearborn River glacier is probably No. 2. At the time No. 1 bench was being formed 

· the Dearborn River was probably flowing on the bottom of the broad sag at the mountain front, now represented by the bench or shoulder above the inner 

gorge. There are remnants of benches on the Middle 

and South Forks of the Dearborn River just east of 

the mountain front, but it is not known that any of 

these are as high as No. 1 bench. Possibly No. 1 

bench is represented by the top of the caps of igneous 

rock on Fort Shaw, Crown, and Square Buttes at 

4~500 feet above sea level, or 1,000 feet above the Sun 

River. 

In this connection mention may be made of a highlevel gravel deposit farther up the Missouri drainage 

basin in the angle between Canyon and Little Prickly 

Pear Creeks, about 25 miles northwest of Helena. 

This gravel deposit, which is, perhaps, to be correlated 

with No. 1 bench, was described some years ago by 

Barrell.81 It caps a ridge a little more than 4 miles · 

long, known as the Gravel Range, whose crest slopes 

somewhat north of east from an altitude of about 5,650 

feet to about 4,700 feet at the top of the bluff, at whose 

pase the automobile road runs up Canyon Creek. The 

bouldery gravel is reported by Barrell to be 500 feet 

thick on the western part of the ridge. On climbing 

the head or west end of the ridge, which rises about 

~,000 feet above Little Prickly Pear Creek on the 

south, the present ,writer, in 1923, found the steep 

npper slopes and top covered with gravel and boulders, 

many of them 3 to 6 feet in nmximum diameter, mostly 

of red and pink quartzite, with .some purple, greenish, 

and yellow, together with irregular masses of andesitic 

_lava. Although the stones are fairly well rounded and 

no glacial striae were seen, the abundance of large 

boulders suggests the possibility tha.t an early Pleistocene glacier may have assisted in the transportation 

from ithe parent ledges. The material may, however, 

be a torrential stream deposit formed when the valley 

bot~m was higher than the tops of the present shaly 

hills between this locality and the head of the basin 

to the southwest. Farther east the stones are not so 

large and the deposit is seen to overlie shale and 

andesitic lava, though large masses of the rock project 

above the gravel. Barrell describes residual masses of 

conglomerate composed of this gravel, cemented with 

silica~ as capping smaller hills and lying on slopes to 

the south. Those on the slopes doubtless slid down 

fromhigher levels as the underlying shale slumped or 

was washed away. From the relations of similar highlevel deposits described in this paper it may be inferred that this bouldery gravel represents stream 

deposition at the mountain fronts near the end of 

Tertiary time or the beginning of Pleistocene time. 

81 Barrell, Joseph, Geology of the Marysville mining district, Mont. : 

U. S. Geol. Survey Prof. Paper 57, pp. 10-11, 34-38, 1907. 

~t is not kno~n whether or n.ot Little Prickly _Pear 

Creek was the~ tributary to the Missouri River. Reasoning from tij.e relations of fossiliferous Tertiary beds 

in the Missou~i River and Smith River: Valleys to the 

east, Barrell cbncluded that" these ancient .gravels are 

certainly Tertiary, and probably not far from-the end 

of the Miocen~." To the present writer it seems more 

probable that iif this bouldery gravel is not wholly· or 

in part the pr~duct of an early Pleistocene glacier, it is 

not older tha~ Pliocene, and, that its deposition was 

later than thb faulting, tilting, and erosion of the 

Bozeman bed~. This. relation can not, however, be 

demonstrated iat this place. 

Apparently/No. 1 bench, if it ever bordered the Belt 

Mountains so-qth of Great Falls, as it probably did, has 

been entirely 1 eroded, at least no bench gravel was 

found on top <j>f the f~othills, which were examined up 

to 5,000 feet .a~ove sea level. 

The top of iBelt Butte ( 4,700 feet), 20 miles ·southeast of Great :Falls, must be as high as the level of No. 

1 bench, but ~here is no gravel upon it. Eight miles 

northeast of :f3elt Butte is a small mesa at 4,100 feet 

(barometric) lriear the Upper Highwood Road. This 

is capped wi~h a deposit of p~bbles and boulders as 

much as 2 fee* in length. These stones are totally differ~nt f:r:om tJ;wse on the high benches described above 

and consist of igneous rocks derived from the Highwood Mount~ins, to the east. The stones are partly 

subangular· · a:p.d partly well rounded, and appear to 

represent a ~orrential fan deposited by Highwood 

Creek when i~ flowed at a level 400 or 500 feet above its 

present channel. ·Possibly this deposit belongs to No. 

2 bench, rath~r than No. 1. Examination of the top 

of Shepard ~utte, which rises to 3,850 feet above sea 

level 2 miles ~orthwest of Waltham, revealed no bench 

gravel but only thin glacial drift on the shale and 

sandstone. ! 

To one wh~ has examined the•remarkably well-preserved alluvi~l benches of the Judith River Basin, 

which head ~n the -foothills of the Moccasin, Big 

Snowy, Littll' Belt, and Highwood Mountains, there 

seems little oubt that the high gravel benches described abov~ are remnants of vast ancient alluvial 

fans, which ~ear the mountains probably coalesced in 

one nearly cpntinuous alluvial plain of remarkable 

smoothness. I The several components of this • plain 

headed at th~ mouths of the mountain gorges, at an 

altitude now ~anging from about 5,500 to 6,000 feet or 

more above sea level, and the resulting plain sloped 

~astward an4 northeastward along lin~ conv?rgin~ 

In a general jway to the bend of the ancient MISsoun 

River chanri~l (now Milk River Valley) north of the 

Bearpaw· Mo~tains, in the region of Havre. There 

was an initi~l slope near the mountains of 100 to 

200 feet or mpre to the mile, which gradually flattened 

to less than 10 feet in the first 12 to 15 miles. Some 
18 PHYSIOGRAPHY AND GLACIAL GEOLOGY OF EASTERN MONTANA 

small remnants are preserved as much as 35 or 40 

miles from the mountain front. Beyond this all traces 

have been cut away by erosion as far east as Harlem. 

If this plain was developed contemporaneously with 

the Flaxville Plain farther east, it sloped to a level 

which is now about 3,000 feet above. the sea in the 

region of Harlem-that is, to an altitude corresponding to the Twete Plain, north of Harlem, about 650 

feet above the level of the Milk River. This would 

he an average slope ranging from 7.4 to 9 feet to the 

mile across an area 160 to 180 miles wide, where no 

remnants of No. 1 bench are preserved. Most of this 

lower eroded area is now covered by glacial drift, so 

that it is not evident just how far the alluvial gravel 

extended. 

From 7 to 9 feet to the mile is a gradient for 

streams flowing in narrow valleys or canyons, and 

such streams readily transport coarse material. These 

streams, however, were not flowing in canyons beyond 

the mountain fronts hut were doubtless subdivided 

into numerous distributaries, which constantly shifted 

their courses from side to side on the . great alluvial 

fans as the channels became blocked by debris. 

FLAXVILLE PLAIN IN BLAINE COUNTY 

No remnant of the- Flaxville Plain closely borders 

the Milk River or the Missouri River east of Havre. 

South of Harlem, in and adjacent to the. Fort Belknap Indian Reservation, are notable remnants of 

gravel-capped benches about the flanks of the Little 

R.ocky Mountains, which are similar to those in th~ 

Blackfeet Indian Reservation, above described. 

North of Harlem, in the northeastern part of Blaine 

County and the northwestern part of Phillips County, 

is an extensive, nearly flat plain underlain by 40 to 70 

feet or more of gravel, in which were found some of 

the Miocene o~ Plio~ne fossils described by Collier 

and Thom.82 This plain, as mapped in the northeastern part of the Cherry Ridge quadrangle, has a 

general altitude of 3,000 to 3,200 feet. Northeast of 

Woody Island Coulee it is buried beneath a great 

deposit of morainal glacial drift. The plain is bordered on the west by Cherrypatch Ridge, whose dis~ 

sected slopes rise to a crest 3,300 to 3,500 feet above 

sea level. This ridge, which separates the gravel 

plain from the Milk River Valley, curves southeastward, and in Ts .. 34 and 35 N., Rs. 22-25 E., is repla~ed by or buried beneath a broad belt of knobby 

terminal moraine. This is all a part of what McConnell 88 designated the Boundary Plateau. 

811 Collier, A. J., and ·Thom, w. T., jr., The Flaxville gravel and its 

relation to other terrace gravels of the northern Great Plains: U. S. 

Geol. Survey Prof. Paper 108, pp. 180-181, 1918. 811 McConnell, R. G., On the Cypress Hills, Wood Mountain, and 

adjacent country : Canada Geol. Survey. Ann. Rept., new ser., vol. 1, 

p. 44, 1886. 

The position and trend of Cherrypatch Ridge su.g ... 

gest that it is a worn-down· spur of the Cypress Hills 

Plateau. It is capped with coarse gravel and con~ 

glomerate, whose pebbles are mostly less than 3 inches 

in diameter but with many 6 to 12 in.ches. The materials are mostly reddish, brownish, and greenish argillite and quartzite, with some diorite and amygdaloidal 

lava similar to the rocks of Glacier National Park. 

The presence of Cherrypatch Ridge, separating the 

Flaxville gravel on the northeast from the Milk River 

Va,lley, shows that this gravel could not have been 

washed· out directly from the mountains 200 miles or 

more to the west. Apparently it must have been let 

down from higher levels by erosion, in the process of 

pen~planation described above (p. 13) or have been 

washed southeastward along a broad basin from the 

Cypress Hills Plateau, 50 to 75 miles to the north and 

northwest. 

BEARPAW MOUNTAINS AND NO. 1 BENCB: 

The highest peaks of the Bearpaw Mountains, 25 

miles south of Havre, reach altitudes of about 7,000 

feet-that is, 3,000 to 4,000 feet above the immediately 

surrounding plain. The Missouri River in later Ter· 

tiary time is believed to have flowed northeastward 

on the west side of the Bearpaw Mountains to the 

vicinity of Havre, along the course now followed by 

Sandy Creek, and thence to have flowed eastward 

along the course of the present .Milk River.84 The 

Bearpaw Mountains were therefore subject to rapid 

and prolonged erosion by numerous streams rushing 

down to the Missouri. ·The mountain mass and the 

bordering foothills were; in consequence, deeply dissected and much worn down. The tops of only a few . 

of the foothills have been examined by the writer. 

The Bearpaw Mountains and most of the area between these mountains, the Little Rocky Mountains, 

and the Missouri River were mapped by Reeves 8

15 in 

1922 and 1923, and to him the present writer is in· 

debted for the location, extent, and differentiation of 

remnants of benches shown on Plate 1. Reeves also 

completed the mapping of some of those traversed by 

the writer east of Cow Creek, which head in the Little 

Rocky Mountains. In the area west of Cow Creek he 

found remnants (some of them extensive) of three sets 

of benches, which headed in the Bearpaw Mountains 

and which are probably to he correlated with· the 

three sets heading in the Little Rocky Mountains, 

to the east. These benches were all developed and 

probably all dissected before the invasion of the 

ice, which shifted the Missouri River from the north 

M Calhoun, F. H. H., The Montana lobe of the Keewatin ice sheet: 

U. S. Geol. Survey Prof. Paper 50, pp. 3445, 1906. 

a11 Reeves, Frank, Geology and possible oil and gas resources of the 

faulted area south of the Bearpaw Mountains, Montana : U. S. GeoL 

Survey Bull. 751, pp. 76-77, pl. 13, 1924. 
I 

:P.n0CENE AND PLIOCENE EPOC~ · lf 

to the' south side of the Bearpaw and Little Rocky seems fairly !rtain. The thin soil on· these beaehts 

Mountains. The largest remnant of No. 1 bench (Lone is underlain y. coarse gravel composed entirely of 

Tree Bench) is between Black Coulee and Bullwhacker rock from th local mountain mass, except in those 

Creek. It is about 15 square miles in extent and covers . places where ~he benches were overridden by the con• 

adjacent ·parts of Ts. 24 and 25 N., Rs. 18 and 19 E. tinental ice s~eet, in which pebbles &n.d boulders -o:f. 

It slopes gently southward from an altitude of 3,588 granite and 9ther rocks from Canada. ooour on ~he . 

feet at'. the north to an abrupt dissected margin nearly surface. N o~viden. ce of local. gla~iation o. f the moun1,000 feet above the level at which the Missouri River tains has bee found. 

now. flows in a narrow gorge 3 miles farther south. The grade f the highest bench (No. 1) in the vicinAnoth~r small remnant of No. 1 bench, about 12 miles ity of Lodge ole, if projected to the mountain slope 

farther northeast and nearer the mountains, has anal- across an int rval where the bench has been eroded, 

titude of 3,876 feet. Three small remnants of a high leads to the g'neral level of the top of the great lime .. 

gravel bench found by Reeves at the north front of the stone wall, a~d north and west of St .. Paul's Mission 

mountains west of Lloyd and one at the west side .of are remnants [which yet retain their connection with 

the mountains northwest of Centennial Mountain, at the top of thi$ wall. (See pis. 7 Band 8.) The rela.-

·about 3,600 feet above sea level, may also correspond tion of No.1 ~ench to the truncated edges of the limeto the· Flaxville Plain. · stone formatipns and to the general profile of the 

Bowen 86 mapped the boundary of the areas "cov- smoothly woJ.in slopes and crests of the mountains 

ered by drift or bench gravel" east of the Bearpaw above sho~what the great alluvial fans, of which 

Mountains, but did not differentiate the several these benches · re remnants, were the product of a long 

benches. period of deg adation. 

tiTTLE BOCXY KOUBTAIB'S AND NO. l BENCH Large re ·. ants of this bench, one of them 7 miles 

in length, lie ~ast and north of the village of LodgeAs stated above, there are no remnants of the Flax- pole on both s~des of a valley 300 feet deep, which waS. 

ville Plain closely borde~ing the Milk River Valley perhaps that qf Lodgepole Creek before it was blocked 

east of Havre, but 35 to 40 miles south of Harlem, in by glacial drift. The thin soil on this bench is underthe Fort Belknap Indian Reservation, notable rem- l~in by coarsf' gravel, and the smooth, flat top rises 

nants : of gravel-capped benches encircle the Little toward the m untains with a grade increasing from 50 

Rocky Mountains. A downward slope of about 10 to 100 feet to he mile. These grades if projected, with 

feet to the mile would connect the highest of those normal steepe ing, across intervals 2 to 3¥2 miles wide, 

bordering the north slope with the supposed level of where the be!fh has been eroded, would reach the top 

the former Flaxville Plain where now is the Milk of the limes ne wall. Below are remnants of a secRiver Valley near Harlem. ond bench 1 feet above the valley flat. There are 

Though deeply dissected, the Little' Rocky Moun- other small r mnants of No.1 and No.2 benches near 

tains appear much less worn down than their neigh- the north an northwest faces of the mountain wall 

bors, .the Bearpaw Mountains. The higher peaks, between Lod epole and St. Paul's Mission south of 

carved from the central mass of crystalline rock, rise Hays. Lo pole Creek and its tributaries now issue 

to altitudes of 6,000 feet or more-that is, 2,500 to from piotures~ue box canyons cute in the limestone wall • 

. 3,000 feet above the adjacent plain. Surrounding the About half ~ mile south of the mission the south 

crystalline core are the upturned edges of Paleozoic branch ?f ~e9ples Creek .issues onto a broad valley flat 

limestone and Mesozoic sandstone and shal-e. Wear- from MissiOn 1 Gorge, a picturesque box canyon cut 100 

ing away of the shale leaves the edges of the sand- to 300 feet d4ep through the great wall of limestone. 

stone projecting in places as hogback ridges or foot- (See pl. 9.) I Through this gorge runs the mountain 

hills, whereas the massive limestone forms a great road from H~ys'to Landusky. About 150 feet above 

encircling mountain wall hundreds ·of feet in height. the west side +f the flat, on the south branch of Peoples 

'(See pl. 6.) This wall is breached at intervals by Creek, is a re~ant of No.2 bench, and abou. t 400 feet 

picturesque gorges cut by outflowing streams. Bev-. higher is No.)1 bench. (See pl. 8 A.) As shown in 

eled across the edges of the upturned shale and sand- Plate 8 B, t ·is bench is unbroken to the top of the 

stone are remnants of smooth, gently sloping benches. limestone wa I, and its initial slope is practically a. 

(See pl. 35.) Tliese comprise three distinct sets so continuation of the general profile of the smoothly 

similar in their character and topographic relations worn tops o the mountains to the southeast. The 

to those described above as bordering the Rocky Moun- smooth and at but palmately dissected surface of . 

tain front and also to those farther east on the Mis- this bench ex ends far out to the north and northwest 

souri River that ~heir contemporaneity of formation until it is fi$lly lo. st in a maz-e of sharp branching 

ae Bowen, c. F., The Cleveland coal field, Blaine County, Mont.: coulees. Ab t much of the periphery of the mounu. s. Geoi. survey Bun. 541, pl. 20, 1914. tains, especi ly on the south and east sides, No. 1 ! 
20 PHYSIOGRAPHY AND GLACIAL GEOLOGY OF EASTERN MONTANA 

bench is mostly destroyed. One remnant at 3,750 to 

3,950 feet above sea level, on the west side of Bear 

Creek Gulch, stands 450 feet above the creek, and the 

road from Zortman to Malta crosses No. 2 bench several hundred feet lower on the west and traverses a 

gap due to erosion at .the north .end of No. 1 bench. 

(Se'e pl. 7 0.) 

Remnants of No. 1 bench. several miles southwest 

of the Little Rocky Mountains are the Joslyn. Bench, 

at 3,672 to 3,750 feet (barometric), west of Sipary 

Ann Butte, in sees. 3, 4, and 5-, T. 24 N., R. 23 E., and 

a smaller remnant about a mile farther north. Beneath the thin loamy soil on the Joslyn Bench is 

coarse angular to little worn gravel from the mountains. Some of the stones are 1 foot in length. A 

landslide near the west end of the steep north slope 

below the bench exposes, beneath the gravel, 10 to 15 

feet of buff clay with some gravel intermixed. No 

trace of fossils was seen on this or any other benches 

around the Little Rocky Mountains. This is about 21 

miles directly east of the extensive remnant of No. 1 

bench mapped by Reeves south of the Bearpaw Mountains. 

·North of the Joslyn Bench are very extensive tracts 

of No. 2 bench, which slope sharply from the mountain 

wall. 

FLAXVILLE PLAIN IN VALLEY, DANIELS, AND ROOSEVELT 

COUNTIES 

For nearly 80 miles east of the Fort Belknap Indian Reservation no traces of the No. 1 set of benches 

remain north of the Missouri River. The previous 

bowing up of the Cretaceous and the Tertiary formations in the Bowdoin dome 37 so facilitated late Tertiary and early Pleistocene erosion that the land surface has been cut well below the level of the Flaxville 

Plain (No. 1 bench) to the west and east. Even the 

tops of the Larb Hills, southwest of Glasgow, in 

southeastern Phillips County and southwestern Valley County, which rise to a maximum altitude of 

3,100 feet, or 800 to 900 feet above the level of the Milk 

and Missouri Rivers to the north and south, respectively, probably do not rise much above what was the 

level of this valley plain on the west and north~ 

East of Porcupine Creek the present surface of the 

land rises higher, and in the eastern half of Valley 

County and in Daniels and Roosevelt Counties, an 

area which is about 60 miles wide from east to west 

and · largely underlain by the sandstone and shale 

of the Lance and Fort ·union formations, there are 

large interstream tracts of nearly flat upland, representing the Flaxville Plain. (See pl. 1.0 A.) Over an 

area of nearly 1,800 square miles the loamy so.il and 

87 Collier, A. J., The Bowdoin dome, Mont., a possible reservoir of 

oil or gas: U. S. Geol. Survey Bull. 661, pp. 205-207, 1918 ; Geology 

of northeastern Montana: U. S. Geol. Survey Prof. Paper 120, pp. 

37-39,. 1919. 

thin glacial drift on this plain are underlain ·by deposits similar to those on the Cypress Hills, consistillg of coarse gravel, sand, marly clay, and P1 a few 

places about 15 feet of volcanic ash. The most con .. 

spicuous material is the gravel, which is in many 

places cemented by calcium carbonate to conglomerate, so that ledges project from eroded slopes. The 

pebbles, which are exposed in every gully and erosion 

slope, range from a fraction of an inch to 10 inches 

in longest diameter. They consist principally of 

brownish, reddish, and greenish quartzite and argil,. 

lite, evidently derived originally from the Rocky 

}fountains, over 300 miles to the west. The pebbles 

have smoothly rounded or even polished surfaces, and 

many of tp.em show percussion marks. There is also 

cross· bedded sand cemented to hard sandstone. (See 

pl. 10 B and 0.) The Flaxville gravel ranges from 

a few feet to 100 feet in thickness ·and rests on the 

eroded surfaces of the Bearpaw, Lance, and Fort 

Union formations. The following· details are given 

by Collier and Thorn: 88 

In the railway cuts west of Flaxville, where the best collection of fossils was made, about half the material exposed is 

gravel and the remainder clay and sand; about 1 foot of marl 

or concretionary calcite is also present. T:Pe bedding is very 

irregular, as might be expected of deposits on the :flood plain 

of a river. North of Flaxville the road to Whitetail crosses 

a considerable thickness · of gravel. Ten miles southeast of 

Flaxv11le, in the escarpment at the edge of a plateau, the formation consists of about 35 feet of cemented sand and gravel 

overlain by uncemented sand. Northeast of Scobey about· 55 

feet of more or less cemented sand and gravel is overlain by 

25 feet of uncemented gravel and soil. • • • The following 

section of a well southwest of Scobey was given by Martin 

Presnell, the owne~: 

Section of a well som]L.west.,.. of Scobey, Mont., in aec. $3, 

T. 35 N., R. 47 lil. 

Ft. in. 

Gravel------~--------------------------------------- 6 

CITaY---------------------------~--------------------- 52 

Lignite slack ---------------:-------------------------- 6 

ClaY---------------------------------------~-------- 2 

Lignite slack-----------------~----------------------- 1 

Gravel and bones; water. 

61 6 

In a well 2 miles southwest of the Presnell well 28 feet of 

coarse gravel, carrying bones, was found. About 20 miles west 

of Scobey. there are several good exposures of the lower 20 feet 

of the formation, together with the underlying Fort Union.' 

The gravel is uncemented and interstratlfied with cemented 

sand, and the surface is strewn with loose gravel containing 

bone fragments. A very striking exposure of the formation 

occurs 5 miles west of West Fork post office, south of Hell 

Coulee, in sec. 80, T. 84 N., R. 44 E.,. where about 80 feet of 

hard sandstone showing very marked cross-bedding caps the 

edge of the plateau. • * • The sandstone probably· rests 

on gravel, for an exposure of uncemented gravel was found 

near the bottom of the coulee. In sees. 19, 20, and 29,. T. 85 N., 

R. 43 E., 8 miles northeast of Avondale, south of Dawson 

1111 CoUier, A. J., and Thom, W. T., jr., op. cit., pp. 181-182·. 
I. 

MIOCENE AND PLIOCENE EPOCBiS 21 

Coulee, a slightly ditferent phase is presented, as Shown by 

the follpwing generalized section : 

Generalized sectum of Flaa;ville gravd in seos. 19, 20, (JI1I.(J; ie9, 

T. 35 N., R. 43 B. . 

[Thicknesses approximate] 

Feet 

Marl, containing a few scattered quartzite pebbles________ 15 

Sandstone cemented with calcite________________________ 30 

Volcanic ash, white to yellow, very pure but mixed with the 

underlying gravel at the base _________________ ..;_______ 15 

Gra-yel, more or less cemented-------------------------- 20 

Fort Union formation. 

80 

The marl (an impure soft white limestone) was either deposited by water flowing over the surface into a shallow pond 

or gathered from the underlying beds and brought to its present 

position by percolating waters. Similar occurrences are indicated by fragments Df marl in the soil of the townships to the 

west and north. This is the only locality where pure volcanic 

ash has been recognized, though similar material mixed with 

sand has been noted about 12 miles to the northeast. The 

gravel is very coarse, and well-rounded pebbles at least a foot 

in dlameter, which must have been derived from it, were noted 

on the surface a short distance away in Dawson Coulee. 

The Flaxville Plain, of which these dissevered upland tracts are parts, declines gradually southeastward 

from an altitude of 3,250 feet west of Opheim to 

2,780 feet near Flaxville and 2,620 feet in the northeastern part ofT. 31 N., R. 51 E., about 30 miles north 

of Poplar. This is the most southeasterly point on 

which the Flaxville gravel is preserved in place north 

of the Missouri River. 

Corresponding with the Miocene or Pliocene plain 

north of Harlem, in northeastern Blaine County, the 

several tracts comprising the Flaxville Plain in Valley, Daniels, and Roosevelt Counties are. not perfectly 

flat but are traversed by low, broad ridges trending 

northwest like worn-down remnants of spurs of a· 

main divide along the Cypress Hills and Wood Mountain upland. They form the present secondary. divides, as well as those of Miocene or Pliocene time. 

In places the retreating front of the last continental 

ice sheet appears later to have lain along these low 

ridges and to have left thereon some terminal-moraine 

deposits. The ridges are probably not wholly morainal, however. Such a ridge extends southeastward 

past Avondale from a point a few miles south of 

Opheim. • Another is on the upland 10 to 12 miles 

southwest of Scobey. One tract of high-level gravel 

southeast of Wood Mountain post office, in T. 3 N., 

R. 3 ·W ., in southern Saskatchewan, 25 to 30 miles 

north of Opheim, stands about 3,400 feet above the sea. 

Over much of the Flaxville Plain gladal drift is very 

thin on the gravel. In many places scarcely any erratic granite pebbles or boulders are seen. In other 

places, especially in tracts cut below the original level 

of the Flaxville Plain, boulders are plentiful and 

there is 30 to 40 feet of -glacial till. 

I 

There are $ remnants oi the Flaxville Plain n.orth 

of the Misso~ri River, either-close to or east of the 

Big Muddy Valley. It is possible that the highest 

parts of the Qoteau du Missouri innorthwestern Williams County J N. Dak., rise nearly to this· horizon. 

There is g*ound for the belief that· the Missouri 

River of Miocene or Pliocene time flowed northeastward across i Roosevelt County and southeastern 

Sheridan Coulnty and that· this was the beginning of 

the abandoned valley (deepened 1ater) which extends 

northeastward from a point 5 miles east of Poplar, 

as shown on I the Poplar, Brockton, and Homestead 

topographic aps. The stream at this stage probably flowed i a channel that would now be about 

2,500 or 2,60 feet above sea level in the vicinity of 

Poplar, had i not long since been lowered-that is, 

it was at ale el 500 or 600 feet higher than the present stream. he gradient of the present valley bottom from H rlem (altitude 2,350 feet) to Poplar 

(1,950 feet) i 400 feet· in about 180 miles, or about 

2.2 feet to the mile. The suppoSed altitude of the late 

Tertiary vall y bottom at 'Harlem was about 3,000 

feet, and a g ade equal to that of the present valley 

bottom woul reach 2,600 feet near Poplar, making 

no allowance for any subsequent differential uplift . 

increasing to he west. Approximately the same altitude is found by projecting the gradient of the Flaxville Plain so theastward to the high gravel benches 

bordering th Yellowstone River in the Glendive 

quadrangle. s indicated below (p. 30), these bench 

remnants are orrelated with the Flaxville Plain. 

TER ACES OF 1UDITll RIVER BASIN 

The Judith River Basin, which drains northward to 

th~ Missouri iver, is inclosed by several more or less 

isolated grou s · of mountains-the North and South 

Moccasin Mo ntains and Judith Mountains on the east, 

the Big Snow Mo~tains on the southeast, the Little 

Belt Mountai son the southwest, and the Highwood 

Mountains on the west. 

The floor o the basin rises from a general altitude 

of about 3,00 feet, on the brink of the Missouri River 

gorge, to 4,50 to 5,000 feet at the foot of the neighbor..-

ing abrupt m untain slopes. This floor consists in general, in the i terstream areas, of extensive tracts of 

smooth, nearl flat, gently sloping benches, on which 

the loamy soi is underlain by coarse alluvial gravel. 

The Judith iver and its tributaries have cut deeply 

into the smoo . bottom of the basin, so that the benches 

are dissevere by branching canyon and steep-sided 

coulees 100 to 600 feet or more in dep h. 

These bene es comprise remnants of two or three 

distinct sets f great coalescing allu ial fans, similar 

to those bord irig the front range of he Rocky Mountains in and orth of the Sun Rive Basin. The inference that he several sets of ben es in these twr1 
22 PHYSIOGRAPHY AND GLAOIAL GEOLOGY OF EASTERN MONT AN A 

regions were formed contemporaneously seems justified 

from a study of their topographic and physiographic 

relations. In the Judith River Basin what appear to 

be the No. 2 benches are the best preserved. Of the 

No.1 bench only small remnants have survived subsequent erosion. Planation at the third level ·had developed valley bottoms 1 mile to several miles in width, 

when it was interrupted by the canyon-cutting cycle 

that is still in progress. Contour maps by Calvert 89 

and Fisher 40 show the benclies in the upper {southern) 

half of the Judith River Basin but do not differentiate 

the several sets. Representatives of No. 1 bench are 

the flat tops of the Stanford Buttes at 4,600 feet, 3 

miles west of the village of Stanford. These tops are 

100 to 200 feet above No. 2 bench on the west and 300 

feet above No. 3 bench, on which stands the village to 

the east. The buttes are capped with 25 to 30 feet of 

conglomerate composed mostly of pebbles of limestone 

· and volcanic rocks, with some quartzite and sandstone, 

ranging from a fraction of an inch to 1 foot or more in 

length (mostly 2 to 6 inches) and cemented together 

by calcium carbonate. This is the Stanford conglomerate of Weed. 41 The pebbles are subangular to fairly 

well rounded and appear to be stream-transported material from the Little Belt Mountains, 5 or 6 miles to 

the south. 

The highest of the bench remnants east of Stanford 

appear to belong to the No. 1 bench which headed in 

the Little Belt Mountains. One tract 5 to 6 miles 

north of Windham is . at about 4,500 feet above sea 

level. The village of Benchland ( 4,324 feet) stands on 

No. 2 bench below a bluff that rises to the eroded 

south end of a table-land. Large blocks of conglomerate near the Great Northern Railway have slid down 

from the cap of No. 1 bench a.bove the bluff. What 

appears to be the same bench was crossed by the writer 

southeast of Denton, near Hoosac Tunnel on the Chicago, Milwaukee, St. Paul & Pacific Railway. At this 

place the gravel top is 3,800 to 3,900 feet above sea 

level. 

This bench is here 300 to 400 . feet above a lower 

(No.2) bench into which the Judith River has cut a 

gorge 150 feet deep. East of the river are benches 

heading in the Moccasin Mountains. One of these 

sloping benches high up on the west flank of the South 

Moccasin Mountains, which was examined by the 

writer, rises· nearly 250 feet in less than a mile and 

joins the mounta!n slope at a notch cut in the beveled 

edges of the upturned Jurassic formations (pl. 11 A), 

at about 4,700 feet above sea level, or about 1,100 feet 

above Warm Spring Creek, 2 miles north and 1,100 

811 Calvert, W. R., Geology of the Lewistown coal :field, Mont.: U. S. 

Geol. Survey BuU. 89Q, pp. 41-48, pl. 1, 1909. 40 Fisher, C. A., Geology of the Great Falls coal field, Mont.: U. S. 

Geol. Survey Bull. 356, pl. 1,' 1909. 

4.1 Weed, W. H., U. S. Geol. Survey Geol. Atlas, Fort Benton folio 

(No. 55), p. 2, 1899. 

feet below the crest of the mountains. It is really a 

torrential fan composed( of angular · to subanghla.r 

fragments, largely of limestone and porphyry, .~anging in size from those measuring only a fraction· of ~ul inch to blocks 4 feet long. · 

The travertine deposit forming The Park, a large 

bench mapped by Calvert 42 on the south slope of the 

North Moccasin Mountains, appears to have been 

formed on an erosion slope at about the same geologic 

horizon ( 4,000 to 4,600 feet above sea level) and perhaps at the same time as the No. 1 gravel bench. 

With these are probably to be correlated a similat' 

travertine deposit which Calvert found capping Flat 

Mountain, at the south end of the Judith Mountains, 

!.) miles east of Lewistown, and perhaps also the .highest of the gravel benches east of the Judith Mountains. 

The connection of the latter gravel.benches with the 

mountain slope . has been destroyed by erosion. A. 

high gravel bench at the south end of the McDonald 

Creek divide, where it lies on the flank of the 'Little 

Snowy Mountains, is 5,100 to 5,200 feet above Sea level. 

A long, narrow remnant qf No. 1 bench on. the. west 

side of Cottonwood Creek, west of Lewistown, rises 

south ward to 4,600 feet some distance from the slope of 

the Big Snowy Mountains, where it is cut away. 

Remnants near Judith Gap rise to 5,000 feet at· ·the· 

west end of the Big Snowy Mountains, and to the 

same level in places bordering the Little Belt Mountains. One of these, south of Utica, is 600 feet above 

the Judith River. 

There are finely developed benches about the west, 

north, and east margins of the North Moccasin Mountains and all around the Judith Mountains. Northeast of Deerfield, which is on No. 3 bench at an altitude of 3,600 · feet, and above a bluff of Eagle sandstone, is an extensive remnant of No. 1 bench which 

rises eastward from about 4,100 feet (barometric) to 

a higher level on the flank of the · North Moccas~ 

Mountains. This is probably 700 to 1,000 feet above 

the Judith River a few miles to the west. 

West of Armells the graded road traverses No. 1 

bench for several miles between Armells and Deer 

Creek. This bench heads in the reentrant north of 

Judith Peak at about 4,600 feet above sea level. In 

August, 1921, a cut on the newly graded road at the 

west margin of this bench, about. 2 miles from the· 

mountain slope, exposed 15 feet of very coarse, angular, little-worn alluvial material derived from the 

mountains to the south. Most of the stones were less 

than 6 inches long, but many were 1 foot or more and 

some 3 to 4 feet.· The slope of the flat surface of the 

bench is about. 100 feet to the mile at this place .. 

What appears to be another remnant of No. l bench 

extends from the vicinity of Roy southwest toward 

c Calvert, W. R., Geology of the Lewistown coal field, Mont.: U. S_ 

Geol. Survey Bull. 390, pp. 35-40, .1909. 
I 

MIOimNE AND PLIOOENE EPOCH~ 23 

Cone Butte. North o:f the Roy branch of the Chicago, The presen~ writer does not think-it probable that 

Milwaukee, St. Paul & Pacific. Railway most of the any of these g~' a vel deposits are as old as Oligocene. 

benches have been cut away by erosion of streams In 1911 Q lvert studied the geology of the Big 

draining to the Missouri and Musselshell Rivers. Snowy Moun ins, and in an unpublished manuscript 

Extensive tracts of flat bench land east of the Judith he describes t a-terrace gravel bordering these mounMountains in T. 16 N., R. 21 E., rise to about 4,500 tains on the squth as follows: 

feet above sea level within 2 to 3 miles of the moun- In the area so~th of the Big Snowy Mountains terrace gravel 

tain front. An eastward slope of less than 30 feet covers . much of 1 the interstream divides, .extending in places 

to the mile would connect these tracts with the terrace high up on the ~ountain flanks and effectu~ly concealing the 

on t_ he Musselshell River west of Mosby. They may underlying ro~ .. The gravel is composed almost entirely of 

. ' ce~nented limest~ne pebbles derived from the Madison, though however' represent No. 2 bench. As at the Little occasio~al fra~ents of strata higher ·in the section are presRocky Mountains, so here, the highest of these benches ent. They are 1 believed to have been formed as coalesci'tig 

was probably graded to the smoothly worn upper alluvial fans at I a time when the general stream levels were 

slope of the mountains above the abrupt marginal wall much higher thab at present and when precipitation was much 

of upturned limestone. · Subsequent erosion cut the ·~eater than no{v. No evidences. of ice action were observ~ . 

h l

"k M "d C S in the Big Sno~ Mountains, so that the gravel is· not consids arp, narrow gor.ges I e ai en anyon. ( ee pl. ered to be of gl cial origin, but the formatio.n of the gravel 

12 A.) terraces was pr ably attendant upon some one or more of the 

glacial epochs. 1 · TERRACES OF MUSSELSHELL VALLEY 

In the Musselshell Valley west of Roundup there are 

remarkably preserved benches, evidently the dissevered 

remnants of vast coalescent alluvial gravel fans, heading at the slopes of the adjacent mountains. On the 

southwest are the Crazy Mountains, on the west the 

Castle Mountains, on the northwest the Little Belt 

Mountains, and on the north the Big Snowy Mountains. Much of the basin has been mapped by Bowen, 

Woolsey, and Stone, and th~ gravel benches are shown 

on a structure map by Bowen 48 and are described as 

follows:. 

Terrace gravels, consisting chiefly of waterworn pebbles of 

limestone, chert, sandslone, and igneous rock of several types, 

in places well consolidated by calcareous cements into a true 

conglomerate, are widespread in this area. The gravel occurs 

at two ,or more levels, but the most prominent deposits are at 

the top of the highest buttes and ridges. These detached areas 

rise to about the same elevation, so that if the surface represented· by them were restored it would form a. plain rising 

gradualily toward the mountains. The thickness of the gravel 

ranges from a few feet far out on the plain to at least 80 feet 

nearer the mountains, where wells have penetrated it to that 

depth. Below these highest terraces there is at least. one other 

level at which the gravel occurs. No especial study was made 

of the relation of these two terrace levels, so that it is not 

known whether those at the lower level represent a reworking 

and red,istribution of those at the higher level or whether they 

are simply residual products that; have ~tied to their present 

position during the process of erosion. The age of the gravels 

has not ~en determined. Those at the higher level truncate all 

formations from the Fort Union- (exposed in adjoining areas) 

to the Kootenai. They are therefore younger than the Fort 

Union and are probably to be correlated with the Flaxville 

gravel of Miocene or early Pliocene age, north of Missouri 

River, described by Collier and Thom. It is possible, however, 

that they correspond to the Oligricene gravels of White River 

age occurring in the Cypress Hills of Canada, described by 

McConnell and Cope. 

48 Bowen, C. F., Anticlines in a part of the Musselshell Valley, 

Musselshell, Meagher, and Sweet Grass Counties, Mont.: U. S. Geol. 

Survey Bull. 691, pl. 25, p. 190, 1918. See also U. S. Geol. Survey 

Geol. Atlas, . Little Belt Mountains folio (No. 56), 1899. 

I 

No attempt w*s made in the field to outline the areas occupied by terrace -~ravel, though a large portion of the district 

immediately sojth of the Big Snowies is covered by . this 

material. , 

In 1921 the 1 present writer made a hasty reconnaissance of these1 gravel benches in an attempt to correlate the differ~nt sets with those of the Missouri an(J. 

Yellowstone 'ivers and their tributaries. In 1920 

Frank· Reeve~ mapped the gravel benches north of 

Roundup in~- 9, 10, and 11 N., Rs. 24 and 25 E., and 

to· him the wtiter is indebted for unpublished data. 

These have nqt been mapped quite up to the east end 

of the Big Snpwy Mountain uplift, where they head, 

but a few milfs out they reach altitudes of 4,050 feet 

or more. F.r. m these heights part of the benches 

decline eastw d 400 feet in 10 miles, or 40 feet to the 

mile, and oth rs slope southeastward about 400 feet 

in 16 miles, o 25 feet to the mile. It is thought that 

these remnant mapped by Reeves probably belong to 

the No. 2 ben h, as do also the most of the more extensive tracts *apped by Bowen we~tward to the. Little 

Belt, Castle, apd Crazy Mountains about the head of 

the Musselshe~l Valley .. There are, however, scattered 

throughout th~ basin west of Roundup numerous dis-

. severed and isplated higher remnants proba.bly repre-

~enting No. 1lbench. These generally stand 100 feet 

· or-more abov~the adjacent tracts of No.2 bench and 

clearly repres nt an earlier stage of mountain denudation and of lluvial erosion and deposition on the 

plains. The I fact that all benches bevel smoothly 

across edges o~ the Mesozoic and Tertiary shales and 

sandstones, ~herever they· are upturned, indicates 

that they repr~sent two long-continued stages of baseleveling on t~e plains separated by an interval of 

general dow~cutting by the streams induced by 

increased graqients. 

Seve.ral re~nants of N ?· 1 bench were crossed by 

the writer on ~ road running westward from the east 

end of the B~g Snowy Mountains past· Bercail post ! 

I 
24 PHYSIOGRAPHY AND GLACIAL GEOLOGY OF EASTERN MONTANA 

office, in T. 10 N., and thence to Judith Gap. From 

altitudes of 4,800 to 5,000 feet near the mountain front 

these smooth flat benches slope rapidly southeastward 

toward the Musselshell River. The remnants of No. 

1 bench mostly extend but a few miles before they 

give place to the more extensive No. 2 benches. The 

occurrence of remnants of the higher bench far to 

the south, however, indicates that No. 1 bench was 

probably continuous over the whole area north of 

the river before the lower benches were developed. 

One of these remnants is traversed by the main graded 

road between Hedgesville and Harlowton. This is 

400 to 450 feet above the Musselshell River, 3 to 4 

miles to the south. The higher remnants near the 

mountains are separated by strips of the second set · 

of terraces ·bordering the streams, and/ these in turn 

are trenched by rather broad flat-bottomed inner valleys. Most of the. re~nnants of No. 1 bench range from 

a few rods to a mile or two in width, though some 

are several miles wide; and they stand 50 to 150 feet 

or more above the remnants of No. 2 bench. The 200-

foot contour interval used on the Big Snowy Mountain and Little Belt Mountains topographic maps is 

too large and the horizontal seale too small to differentiate clearly the sets of bench remnants from each 

other and from intervening, gently undulating areas 

where the flat, graveJ:-capped tops have been worn 

away by erosion. 

The thin pebbly soil, which is cultivated on all these 

benches, is underlain by coarse waterworn gravel. 

The gravel ranges in size generally from fine pebbles 

to 8-inch cobblestones, but some stones are about a 

foot in longest diameter .. South of the Big Snowy 

Mountains and of the eastern part of the Little Belt 

Mountains the pebbles are mostly of limestone. West 

of R. 13 E. purplish and red quartzites are more 

noticeably intermingled. 

It is possible that the original connection of the 

highest benches with the mountain slope may have 

been at a position now as high as 6,000 feet above sea 

level. This was certainly the case west of Judith 

Gap, where No.1 bench formerly overtopped the foothill strike ridges of upturned Quadrant and Ellis 

formations at the southeast front of the Little Belt . 

Mountains. Considerable tracts of smooth, flat No. 1 

bench land under cultivation are traversed by roads 

north and northwest of Harlowton and east of Haymakers Creek at altitudes ranging from 4,500 feet near 

Harlowton to more than 5,500 feet a few miles from 

the mountains. The truncated heads of these benches 

stand to the south of and high above the road that 

leads west from Judith .Gap to the forest ranger 

station on Hopleys Hole Creek. 

No remnants of No. 1 bench were noted about the 

flank;s of the Castle Mountains between the Musselshell 

River and its South Fork, though, as stated below 

(p. 40}, there is a possibility that the high bench between . Alabaugh and . Warm Spring Creek;s 5 miles 

west of Lennep, which is covered with drift of a mountain glacier, may represent No.1. This.bench is 5,800_ 

to 6,000 feet above sea level, or at about the same altitude as the slopes north and south of the pa.ss at 

Loweth station. Alabaugh Creek has cut its narrow 

valley 300 to 400 ·feet below the top of this bench. 

The relations of most of the bench or terrace renlnants south of the Musselshell River hi southern 

Wheatland County and southeastern Meagher County 

have not been studied by the writer. South of Harlowton the road to Melville crosses broad tracts . of 

No. 2 bench bordering Lebo Creek and American Fork 

and at 13 to 14 miles runs through a notch in a narrow 

remnant of No. 1 bench at 5,000 feet above sea level. 

This bench, which is in northern Sweet Grass County, 

appears to be continuous southwestward. to a point 

north of the west side of Porcupine Butte, beyond 

which it is cut away. At this place the bench is 400 

feet or more above the streams on the north and 

south. It originally headed at the east base of the 

Crazy Mountains, at an altitude of probably more 

than 6,000 feet. 

The question arises at this point, Did No. 1 bench 

overtop the divide and extend southward without a 

break to the Yellowstone Basin, or was there even at 

this early stage a dividing ridge between the two basin~ 

higher than No. 1 bench and extending eastward from 

Porcupine Butte and the Cayuse Hills t<.> and beyond 

the Bull Mountains, southeast of Roundup~ As bearing on this question the following relations may be 

cited: 

To the south of the divide the nearest remnant .of 

No. 1 bench examined by the writer about 8 miles 

south of Porcupine Butte, is at about the same altitude 

as the one north of the divide ( 5,800+ feet). It thus 

appears that this level is sufficiently high to have been 

~ontinuous across the divide near 'the east base of 

Porcupine Butte. The strip of country to the easf is 

much dissected, and, so far as known to the writer, 

there are no remnants of the high benches in this area. 

The sandstone on the crest, 7 to 10 miles north of the 

village of Rapelje, is 4,600 to 4,800 feet above sea level, 

and 20 miles or nfore west of the Bull Mountains the 

. divide is mostly above 4,000 feet. Eldridge ~esa, in 

the Bull Mountains, stands at about 4,700 feet. The 

writer found no bench gravel ori the nearly flat top of 

this mesa in sees. 27· and 28, T. 6 N., R. 27 E. Due 

south of the Bull Mountains the flat-topp·eg. crest of 

the divide between the Yellowstone River and Pryor 

Creek, 7 to 8 miles east of Billings, is capped with 

bench gravel at 4,000 feet, or 900 to 1,000 feet above the 

river a few miles away. 'rhis may, however, be older 

than the No. 1 benches. Comparison of these altitudes 

with those of the other high remnants of benches sout~ 
U. S. GEOLOGICAL SURVEY PHOPESSIONAL PAPER 174 PLATE 6 

A 

B 

LITTLE ROCKY MOUNTAINS, MONT. 

A. North front of mountaius east of Hays 1-lost office, showing grea t. wall of upturnerl Valcm~o c limestone. The horizon of top of wa ll is correlative with Flaxville Plain (No. l bench). RemnanL of No. 2 bench at left .. B. View looking we::;L along the no lched Lop of the great north wall of limestone, 600 to 700 feet abov e the plains ut right. 
U. S. GEOLOGICAL SURVEY 

A. SUN RIVER, MONT., AT MOUTH OF CANYON 

Showing cross proiHe of ancient Pliocene or P leistocene high-level valley 't miles wide above the top of the 1,000-

foot lower wall of limestone. 

PROFESSIOXAL PAPER 174 PLATE 7 

B. WORN TOP OF THE LITTLE ROCKY MOUNTAINS, MONT. 

Looking east across the hevcled LO p of the limestone w~~l from n remnant of the Flaxville Plain, or No. l bench, north of St. P aul's Mission. 

C. VIEW SOUTHEAST OF ZORTMAN, MO!\T. 

Showing remnants of the Flaxville Plain, or No. l bench (upper), and No. 2 bench (middle). South wall of mountains at left. 
U. S. GEOLOGICAl, SURVEY PROFESSIONAL PAPER 174 PLATE 8 

A. NEAH ST. PAUL'S MISSION 

View across Peoples Creek (altitude 3,550 to 3,650 feet), showing No. l bench (3,950 to 1,300 feet) and No.2 bench (3,700 to 3,fi00 feet) , sloping norLhward from the mountnins at the left.. 

B. FLAXVILLE PLAIN, OH No. l flENCH, WEST OF ST. PAUL'S MISSION 

Graded to the top of the lim~stone wall and the general profile of the mountains at the left. 

LITTLE ROCKY MOUNTAINS, MONT. 
U. S. GEOLOGICAL SURVEY 

A. MISSION GORGE, SOUTH OF ST. PAUL'S 

Cut through the great limestone wall by Peoples Creek. 

PROFESSIONAL PAPER 174 PLATE 9 

B. NATURAL BRIDGE, WEST SI DE OF MISSION GORGE 

LITTLE HOCKY MOUNTAINS, MONT. 
U. S. GEOLOGICAL SURVEY PROFESSIONAL PAPER li4 PLATE 10 

B. OUTCROP OF CEMENTED FLAXVILLE GRAVEL IN ESCARPMENT OF PLATEAU, 6 MILES NORTHWEST 

OF OP HEIM , MONT. 

C. CROSS-BEDDING OF FLAXVILLE GRAVEL 18 MILES SOUTHWEST OF SCOBEY, 

MONT. 

All photographs by A. J. Collier. 
U. S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 174 PLA'l'E ll 

A. REMNANT OF HIGHEST (No. l) GRAVEL-CAPPED BENCH (IN FOREGROUND) ON WEST FLANK OF 

MOUNTAINS 

B. VIEW NORTH ACROSS THE GRAVELLY No. 2 BENCH SOUTHWEST OF LEWISTOWN 

SOUTH MOCCASIN MOUNTAINS, MONT. 
U. S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 174 PLATE 12 

A. SMOOTHLY WORN TOP AND EAST FRONT OF JUDITH MOU TAlNS, MONT. 

Mouth of Maiden Canyon in middle ground. 

B. VIEW EAST OF ROSCOE, MONT. 

Showing smooth fl at top of the highest (Flaxville or No.1) gravelly bench. Beartooth Mountains in background. 

C. DISSECTED No. 2 BENCH SOUTH OF ROSCOE, MONT. 

Heading at Beartooth Mountains, in background. 
U. S. GEOLOGICAL SURVEY 

A. HIGHEST (No.1) BENCH AND MIDDLE (No. 2) BENCH EAST OF ROCK CREEK, NEAR RED LODGE, 

MONT. 

Two irrigation ditches run northward (to left) along the steep slope above the bottol" of the valley. 

PROFESSIONAL PAPER 174 PLATE 13 

B. No. 2 BENCH (IN FOREGROUND AND MIDDLE G ROUND) HEADING IN MOUTH OF ROCK CREEK 

CANYON (AT RIGHT) 

Beartooth ~ountains in background. 

C. VIEW IN SHOSHONE NATIONAL FOREST, WYO., 12 TO 15 MILES SOUTHWEST OF CLARK POST OFFICE 

Looking southward across valley of upper Clark Fork of the Yellowstone River into basins of Sunlight and Dead Indian Creeks. Volcanic peaks of Absaroka lVIountai ns in background. Shows broad P liocene or l)leistoccnc valley eroded in Paleozoic rocks and, sharply cut into the bottom of this valley, the narrow branching box canyons of a la ter (Pleistocene?) cycle of erosion, more than 1,000 feet deep in Archean granite and gneiss. The broad bench , or bottom of the anciBnL valley, is probably to be correla ted with the highest (No. l) bench on t he p lains to the east. 
MIOCENE AND PLIOCENE EPOCHS 25 

of the Yellowstone River seems to' indicate that the 

Yalleys of ·the Yellowstone and Musselshell at the . . ' time of the formation of No. 1 bench, were broad 

sha,llow basins distinctly separated by a worn-dow~ divide whose crest was not more than 700 or 800 feet 

above either of the streams. There are no data in hand 

· showing that the slopes of this broad divide were ever 

covered with bench gravel east of the vicinity of Melville. Even if in Oligocene time the great reentrant 

encircled by the mountains from the Big Snowy 

Mountains on the north around the west end to the 

Pryor and Big Horn Mountains on the south constituted a single drainage basin, it is probable that by 

early Pliocene time it was definitely divided. 

NO. 1 BENCH IN YELLOWSTONE VALLEY 

BENCHES ABOVE CUSTER 

In the Yellowstone Valley No. 1 bench is well represented, though the location of the remnants and 

their height above the adjacent streams indicate a 

very large amount of erosion since the streams were 

spreading gravel on this ancient plain. A reconnaissance study of these benches was made by the writer 

in 1921 and 1922, but not all were mapped in detail. 

Here as elsewhere such detailed mapping as has been 

done is very largely the work of other geologists. 

There are a few remnants of No. 1 bench in the 

northeastern part of the Livingston quadrangle heading at the southeastern ba.Se of the Crazy Mountains. 

One of these on the north side of Swamp Creek at an 

altitude of 6,100 to 6,500 feet (barometric) stands 200 . 

feet or more above the extensive No. 2 bench. The 

grade of the upper bench projected to the mountain 

slope, across an interval of a mile or so where it has 

been cut away, overtops the summit levels of most if 

not all the adjacent foothills. This bench appears 

originally to have headed in the gulch south of Crazy 

Peak. The pebbles, mostly of igneous rock, range in 

size from a fraction of an inch to 3 feet. As far as 

noted none of them show evidence of glacial action. 

In the Shields River Basin there are several remnants of No.1 bench head_ing near the southwest, west, 

and northwest flanks of the Crazy Mountains. Some 

of these were examined by the writer in 1922. The 

Sheep Cliffs and some other hills, which are capped 

with igneous rock south and west of the mountains 

rise above No. 1 bench. At all other places the old 

surface has been cut away, leaving the present su1·face 

at lower levels. The most extensive remnant of No. 1 

bench heads at the south foot of the mountains, near 

the Absaroka National Forest boundary, on the east 

side of Rock Creek, 7,000 feet or more above sea level. 

According to the topographic map, it slopes thence 

southwestward toward Chadbourn, about 1,200 feet 

in 5 miles, or at a rate of about 240 feet to the mile. 

These remnants stand hundreds of feet above the beds 

87949-32-3 

of the present streams where they emerge from the 

mountain gorges. If there were benches on the w~st 

side of the· Shields River with similar grades and altitudes, they would almost, if not quite, oveittop the 

range of hills extending north . of Bozeman Pass and 

re~ch the . Bridger Range near the top. By early 

Phocene time, when the No. 1 benches were being 

formed, the Yellowstone River had probably notched 

the top of the wall of upturned .limestone south of 

Livingston down to 5,500 feet above sea level where 

now it flows at about 4,550 feet in the lower canyon,_ 

and farther east the stream may have be(m. flowing at 

a level about 1,000 feet below that of the top of the 

Sheep Cliffs-that is, at about 5,200 feet. 

Extensive remnants of gravel-capped benches are 

preserved on either side of the lower few miles of the 

· Boulder River south of Big Timber. (See Big Timber topographic map.) This stream is one of the 

principal tributaries of the Yellowstone River. Heading i:g. the Absaroka Range on the high plateau, north 

of Yellowstone National Park, the main stream. and 

the West Boulder traverse profound canyons. After 

being joined by the East and West Boulder the stream 

continues northward in a beautiful valley cut 300 feet; 

below the bordering No.2 terrace and 550 to 600 feet 

below the one remnant of No. l bench, which is on 

the east sicie of the stream 6 to 8 miles south of the 

village of Big Timber, at 4,750 to 4,900 feet above !Sea 

level. Farther south this bench appears to have been 

entirely cut away. It is probable that the surfaoe of · 

this bench projected southward with a normal increase in gradient would overtop all _the foothills and 

reach the mountain front 7,000 feet or more above sea 

level at the beveled top of the great wall of upturned 

limestone where the narrow V-shaped gateways of 

the canyons are 1,000 feet -or more in depth. The top 

of the limestone· wall is 2,000 feet or more below the 

East Boulder Plateau, to the south. 

From the Boulder River southeast to the Stillwater 

River no remnants of No. 1 bench are known to be 

preserved. The benchlike surfaces. shown on the 

sout~eastern part of the Big Timber topographic map 

are, In part at least, erosional,. corresponding· closely 

to dip slopes on the Lance sand~ones. · Some of the 

surfaces are, however, near what must have been the 

position of No.1 bench, especially south of Reed Point, 

where the upland is "800 feet or more above the river. 

As indicated above, it is unlikely that the ridges north 

of the Yellowstone and east of Sweetgrass Creek ever 

were truncated by No. 1 bench. . 

Most of the gravel-covered bench remnants above 

the bluffs of the inner valley of the Yellowstone, as· 

far downstream as Columbus, appear to correspond to 

the second set of terraces. At the mouth of the. Stillwater River these remnants are 400 feet above· the 

Yellowstone River. 
26 PHYSIOGRAPHY AND GLACIAL GEOLOGY OF EASTERN MONTANA 

In southwestern Stillwater County and in Carbon 

County the bold northeastern front of the Beartooth 

Mountains is bordered by a zone in which are numerous remnants of No. 2 bench and a few of No. 1. 

These were mapped by Calvert,44 and their altitudes 

were shown by contours. Some of these were examined by the present writer in an effort to discriminate the different sets and correlate them with the 

benches described SJ,bove. One of the best-preserved 

remnants of No. 1 bench heads about 3 miles east of 

Roscoe and extends thence northeastward more than 

5 miles to ap.d beyond the limit of the area mapped 

by Calvert. The smooth, flat top, which is 400 to 500 

feet higher than Butcher Creek, has an altitude of 

5,400 feet at the head, or truncated southeast end,. and 

slopes thence northeastward about 50 feet to the :rpile. 

(See pl. 12 B and 0.) At the head of the bench, and 

rising above its flat surface, is a small, smooth, grassy 

ridge whose composition, owing to lack of exposures, 

·was not ascertained. ·It is probably composed of 

wind-blown material lodged in the lee pf the crest 

of the steep eroded margin of the bench. The material underlying the thin top soil of the bench is exposed about the edges of the upland and in the sides 

of some coulees cut in the flat plain. It is coarse, 

unsorted g,:-avelly and bouldery granitic material, 

with no limestone. The stones are part;ly rounded 

but largely subangular and mostly range in size from 

a fraction of an inch to 1 foot. There are many 2 to . 

3 feet long, some as much as 4 feet, and one boulder 

3 by 4 by 6 feet was measured. The lack of sorting 

and stratificatio;n and the large size of many of the 

boulders, taken in connection with the fact that the 

her1d of the bench is about 7 miles from the mountain 

front, strongly suggest that the material is glacial 

dtift. No striated stones were found, however. The 

st~rfaces of most of the stones are etched, and many 

r f the pebbles and boulders are disintegrating ·as the 

result of long exposure to weathering. There are few 

hills in the region as high at that distance from the 

mountain front. If the sloping surface were proj~cted southwestward to the mountains, with a normal 

increase in gradient, it would probably overtop all 

the. foothills and rea~h the mountain front at a height 

which is now 6,500 to 7,000 feet above sea level. 

The gradient of these benches,. of course, decreased 

markedly downstream, but, even allowing for this, 

it seems improbable that No. 1 bench east of Roscoe 

would have overtopped all the divide between the 

Stillwater River and Clark Fork, inasmuch as the 

crest of the ridge, 9 miles southeast of Columbus, 

rises to 4,955 feet in the southeastern part of the Stillwater quadrangle. It seems more probable that a.fter 

"Calvert, W. R., Geology of the Upper Stillwater Basin, Stillwater 

and ·Carbon Counties, Mont. : U. S. Geol. Survey Bull. 641, pl. 20, 

1917. . 

shifting to and fro and beveling the rocks of the 

plains and spreading thereon their great · fans . of · 

gravel, with heads at the mouths of the moimtain 

canyons, the distributary channels gathered into less 

broad though still rather wide valleys tributary to 

the Yellowstone bottom lands of this early stage and 

left some of the interstream areas standing higher as· 

ridges. 

·East of Rock Creek there are high benches bordering the valley which were not mapped by Calvert. 

The most extensive appears to be No. 2 bench, and 

·above this abrupt erosion slopes rise to a narrow remnant of No. 1 bench. East of Red Lodge No. 2 bench 

is cut away, and the steep side of the valley rises about 

500 feet to the higher bench. About a mile south of the 

town No. 1 has an altitude of 6,150 feet (barometric). 

In the next mile it is cut away, and No.2 bench, which 

is 200 feet lower, extends to the mountain front. (See 

pl. 13 .A. and B.) Coarse gravel and boulders as much 

as 2 feet in diameter are exposed in a pit near the head 

of the upper bench, but nothing was noted suggesting 

that glacier ice had extended out of the mouth of the 

canyon onto this high plain. There are remnants of 

this plain for about 15 miles northeast of Red Lodge 

on the divide west of Clark Fork of the Yellowstone. 

One of these examined by the writer south of . the 

Roberts-Bridger road, in sec. 9, T. 6 S., R. 22 E., is 

4,850 feet above sea level (barometric )-that is, about . 

1,200 feet abov.e Clark F~rk at Bridger, to the east. 

This,. like the high bench near Red Lodge, is capped 

with coarse gravel and boulders. Some of the stones 

are 1 foQt in diameter ; most are less than 4 inches. 

They consist principally of gray and pink granite, porphyry, and other dense dark and greenish igneous 

rocks. The gravel is considerably weathered and in 

places is cemented by calcium carbonate to conglomerate. About the edges of the flat top the surface is 

a cobblestone pavement, and the exposed surfaces of 

the stones are wind-polished and oxidized to a brownish color. No quartzite pebbles similar to those along 

the Yellowstone farther northwest which were probably derived from the Belt rocks, were found either -

here or on the high bench near Roscoe. 

No ridges appear to rise above the level of this 

high bench for a long distance to the south nor to the 

east as far as the Pryor Mountains. There may be 

some lower remnants of this bench a 'few miles farther 

north, between Clark Fork and Elbow Creek west of 

Fromberg. 

· Numerous remnants of No. 2 bench were found by 

the writer farther south up Clark Fork, but none of 

No.1 bench, though there may be such remnants closer 

to the mountain front. If the same altitude and gradient are postulated for No. 1 bench on Clark Fork as· 

those of Polecat Bench, the divide to the southeast, it 

would stand about 5,000 feet above sea level at the 
MIOCENE AND PLIOCENE EPOOBS 27 

State line-that is, 1,QOO feet above the present stream. 

From this point an average gradient of but 50· feet to 

the mile for 20 to 25 miles southwestward would extend the bench into the _Clark Fork Canyon and connect with the bottom of the broad upper valley at 6,000 

to about 6,250. feet. Into the bottom. of this ancient 

valley the inner box canyon has since been cut to a 

depth of 1,200 feet or more, mostly in granite and 

gneiss. (See pl. 13 0.) This projected No. 1 bench 

would overtop all the hogbacks of the foothills near 

and north of Clark Fork, beveling the edges of the 

upturned Cretaceous and Tertiary formations. 

· It seems to the writer that this inferred projection 

is fairly safe, and on that basis the correlation may be 

extended on up Clark Fork. to the pass near Cooke, 

Mont., near the northeast corner of Yellowstone N a~ 

tiona! Park. It may be concluded, the:refore, that near 

. the end of the Tertiary period and perhaps at the beginning of Pleistocene time Clark Fork was flowing 

southeastward from the vicinity of Cooke in the broad 

valley whose bottom forms the bench above the inner 

·canyon walls_ and was i~uing at the mountain front 

onto a broad gravel plain which extended far to the 

north and which was continuous eastward across the 

present divide (Polecat Bench) into the Big Horn 

Basin northeast of Heart Mountain. 

tended to hold the streams· at rela.tiveiY high levelsthe relatively short distance of the main stream from 

the Big Horn and Pryor Mountain f1onts on the south, 

· and the fact that the edges of the sandstones, those of 

the Eagle, Judith River, and Lance. formations, are 

crossed by the Yellowstone River between Billings 

and ·the Big Horn River on the eastern ·limb of the 

Pryor Mountain anticline. None of these sandstones 

are very hard, yet they are cliff-making rocks as distinguished from the intervening shales, and they 

tended to retard the deepening of the valley and the 

widening of its bottom. This effect is well illustrated 

by present conditions near Billings. · The valley for 

several miles west of Billings is-broad, having a maximum width of 7 to 8 miles. In this part the stream 

ha,s cut through the Eagle sandst()ne on the top of the 

anticline and into the underlying Colorado shale. 

This has facilitated the widening of the valley and 

caused the recession of the sandstone cliff, which is 

350 feet in height on the north. Just east of Billings 

the sandstone lowers and the ledge swings aocross to 

the southeast side. Here the valley is constricted to 

less than 1 mile in breadth. 

There is difficulty in correlating the highest of the 

high bench remnants east of Billings and north of. 

the Big Horn Mountains with No.1 bench (Flaxville 

Plain) nearer the Rocky Mountains and in the Bi~ 

Horn Basin. · In fact, the highest benches are ·so high 

a,s to suggest that they may. really have been formed 

at an earlier stage and may be of Miocene or Oligoc~ne 

age, as indicated on Plate 1. · Either they are earlier 

or local deformation prior to the development of the 

second set of terraces raised these benches to disproportionately high altitudes. 

BENCHES IN THE CROW INDIAN RESERVATION 

In connection with his studies in 1921 Thorn 

mapped the benches in the Crow Indian Reservation, 

as shown on Plate 1, and he describes thein as 

follows: 45 

A grade of about 10 feet to the mile eastward along 

the Yellowstone from No. 1 bench near Big Timber 

and a grade of about 50 feet to the mile northeastward 

along the tributary valley from No. 1 bench east of 

Roscoe would cause the two to meet at about 4;200 feet 

above sea level at the mouth of the Stillwater River 

near Columbus-that is, No. 1 bench would be at a 

l~vel 650 feet above the river and 250 feet above the 

bench on top of the bluff south of Columbus Bridge, 

which is probably No. 2 bench. If the same grade, 

10 feet to the mile, were continued eastward along the 

Yellowstone 27 miles below Columbus, No. 1 bench 

near· the mouth of Clark Fork would be about 3,900 

feet above sea level, or about 600 feet above the river, 

and here it would be joined by No. 1 bench on Clark 

F k "f h h d d bo Large areas within the Crow Reservation are covered by 

or I t e latter a a gra e of a ut 30 feet to the deposits of sand, gravel, and boulders which are remnants of 

mile northward from the high bench west of Bridger. flood plains aggraded by streams issuing from the mountains. 

Not far from a corresponding altitude (3,900 feet, These flood-plain remnants now appear as terraced surfaces 

barometric) are remnants of a ben.ch observed a few which descend In steplike fashion to the present alluvial valmiles west of Silesia. A grade not steeper than 10 ley bottoms of · the Big Horn and Yellowstone Rivers. As 

f h ·1 d f L 1 1 h y l might be expected, the remnants representing the several 

eet to t e mi e eastwar rom aure a ong t e e - terrace levels are of unequal areal extent. but seem to indilowstone River would conn~ct at 3,600 feet with the cate a fairly uniform downcutting of l.lK) to. 200 feet between 

lower one of the high benches described below (p. 29) the periods of aggradation. No fossils have been collected 

crossed east of Billings by the Custer Battlefield from the deposits of terrace gravel in the reservation, and 

Highway. • their ages are therefore not definitely known. 

In the absence of immediate economic interest in the gravel Decision as to .what are probably remnants of No. 1 . deposits of the reservation the terraces received ·only inciden .. 

bench along the lower courses of the Stillwater River, tal study in the course of local stratigraphic or structUral 

Rock Creek, and Clark Fork depends somewhat on work. Therefore, although the conclusions here set forth are 

interpretations in the region north of the Pryor and believed to be essentially correct,· they probably could be made 

Big Hom Mountains. Here two factors may have 4lS Thom, w. T., jr., unpublished manuscript. 
28 PHYSIOGRAPHY AND GLACIAL GEOLOGY OF EASTERN MONTANA. 

\ 

much more complete and significant after more detailed field 

work. . 

There is in general a very close. parallelism of gradient between the present streams of the reservation and the older 

stream-laid terraces, indicating· that the periodic downcutting 

which has taken place has been induced by regional upwarp 

and not by differential elevation of the mountains with reference to the adjacent plains. As might be expected, the terraces 

locally blend together, particularly · toward the heads of 

streams where down cutting has been retarded by· resistant 

strata, but in the main the several surfaces are quite distinct 

and are represented by erosion planes truncating resistant 

beds as well as by aggraded surfaces. 

Following the present writer's suggestion,. Thom 

tentatively correlates the highest bench remnants with 

the Cypress Hills Oligocene: 

The terrace surface tentatively correlated with the Oligo-

~ene of the Cypress Hills on the basis of its altitude is well 

preserved on Pine Ridge, northwest of Hardin, on the plateau 

west of Fly Creek, and on the ridge between Pryor Creek and 

the Yellowstone, and a small remnant of it is preserved on the 

northwest side of the Shively Hill Dome. The reconstructed 

gradient .of this surface accords well with the altitude of the 

present divide in Pryor Gap (5,260 feet). 

These facts and relations of the remnants of benches 

observed by the present writer in the valley of Clark 

Fork and in the northern part of the Big Horn Basin, 

Wyo., lead to the suggestion that the highest benches 

ill the Crow Reservation may have been formed by 

Clark Fork or an earlier stream heading on the Beartooth Plateau and flowing through the Pryor Gap to 

join the Yellowstone in Oligocene or Miocene time. 

Subsequent uplift and accelerated erosion on the shale 

may have resulted in diversion of this stream westward 

to the present course of Clark Fork. To quote further 

irom Thorn, 

This Oligocene ( ? ) terrace i~ not known to be preserved 

south of the· Big Horn, but its approximate position is apparently indicated by an erosion plane truncating the beds on the 

higher slopes of the east flank of the Big Horn Mountains and 

by the eastward-sloping plateau surface of the Wolf and Rosebud Mountains. The tops of the Mowry ridges east and west 

-of Pryor Creek, in the western part of the reservation, also 

apparently present surviving remnants of this erosional sur-

:face. 

A second [or intermediate] terrace stage about 200 feet below 

the OligoCene ( ?) seems to be fairly well developed in the 

northwestern part of the reservation along the ridges east of 

Pryor Creek, and to a lesser extent on the Pryor Creek-Yellowstone divide. This terrace is strikingly developed between the 

Little Horn and Lodgegrass Creek, and minor remnants of it 

survive upon the higher buttes along the Rottengrass-Little 

Horn and Soap Grass-Rotteilgrass divides and are present at 

a number of places in the southern part of the reservation. 

Apparently it was at this stage that the Black Gulch Dome 

was truncated and that the Mowry and Cloverly ridges on the 

divides between Soap Creek and the Wyoming line were planed 

off at their present level. 

This intermediate terrace is grouped with No. 1 

bench on Plate 1. As indicated by relations, if the 

highest bench (No. 1) northeast of Cody in the Big 

Horn Basin were projected down the river it woul(} 

emerge irom the gorge at the northeast flank of the 

Big Horn Mountains,· at an altitude of about. 4,000 

feet. Thom found large remnants of a gravel-covered 

bench which stand 400 to 500 feet above what appears. 

to be No.2 bench along the west side of the Big Horn 

River from a point :near and south of the Chicago, 

Burlington & Quincy Railroad west of Hardin to the 

mountains. (See St. Xavier and Fort Custer topographic maps.) The gradient on these remnants increases southward from about 12% feet to the mile at 

the north to 1PO feet to the mile near the flank Qf the 

mountains, 25; miles distant, or at an average rate of 

15 feet to the mile. Five miles northwest of the mouth 

of the lower Big· Horn Canyon the bench is, about 700 

feet above the; river and 3,900 feet above sea. level. 

As shown on Plate 1, this terrace is regarded ~ the 

correlative of the Flaxville Plain. Thorn states that it 

is the one most • extensively d'eveloped within the reservation. 

Large gravel-covered uplands belonging to this surface form 

tl\e even tops of the higher hllls west of the Big Horn and 

south of Williams Coulee, and the same terrace ·level is well 

marked both by gravel beds and . by erosion surfaces in the 

valley of East Fork and elsewhere near the site of the. former 

station of Coburn. The Mowry ridge· between Woody Creek 

and the Big Horn River was truncated at this plane, .as were 

the Mowry ridges surrounding the Soap Creek Dome and the 

Cloverly ridge east of Limekiln Creek. Remnants of the Flaxville (?) are present upon the north end of the Big HornLittle Horn divide and cover considerable areas on the low 

part of the Litt~e Horn-Toniue River divide just southwest of 

Parkman, Wyo. 

.Thom found another set· of terrace remnants about 

200 feet below the Flaxville Plain. These perhaps 

represent the upper level of the No. 2 benches, · as 

grquped by the present writer, west of Clark Fork and 

along the Yellowstone (p. 53), and they are grouped 

with No. 2 b~nch on Plate 1. Thom states that this 

set 

is well developed west of Pryor Creek ·and to a lesser degree 

southwest of Hardin. This surface 1s also well developed in 

the Beauvais Creek Valley within the Mowry rim, which 

curves around the north end of the Big Horn Mountains, and 

within the Mowry hogbacks surrounding the Soap Creek dome. 

A set of terraces, which the present writer regards 

as the correlative of the main or lower level of the 

second set of terraces on the Yellowstone River 

(p. 56), is also described by Thom as about 150 feet 

below his fou!rth terrace and about the same distance 

above the pr~sent stream grade. . 

This terrace :(eatures the west banks of the Big Horn River 

• and of Pryor ¢reek and covers a considerable area at the 

north end of the Big Horn-Little Horn divide. Remnants of 

it are also present a short distance above stream grade in the 

Beauvais Creek· Valley within the Mowry shale escarpment 

and within the ·valleys of most of the other streams of this 

reservation. Since the development of this terrace the Big 

Horn has apparently been slowly reducing its area by lateral 

migration and cjlowncutting, and as a result the river is bor-
: -.--• 'KIQCEli'E AND PLIOCENE EPOCHS , 

dered on one side by a sloping plain descending from· the fifth 

terrace level down to the present alluvial bottom lands, in 

which the river is slightly intrenched. Hardin is built on this 

eroded or aggraded surface, which lies principally on the west 

side of the Big Horn below the Two Legging Bridge and on 

the east. side between the bridge and the mouth of Big Horn 

Canyon. 

Hancock 46 described the high-level deposits of 

gravel and conglomerate east of Billings a.nd north of 

the Crow Indian Reservation and suggested that they 

were laid down at about the same time as the Flaxville 

gravel of northeastern Montana. Some of the gravel 

was examined by the present writer in 1921. That 

north of the road about 10 miles east of Billings, at 

3,600 feet above sea level, may represent No. 1 bench. 

The narrow, flat gravel-capped top of the ridge south 

of the road rises southward from about· 3,850 to 4,000 

feet and may be older. The pebbles near the road, the 

larger ones of which are 6 or 8 inches in longest diameter, are mostly rounded and polished. They appear to have been derived largely from the mountains 

to the west, inasmuch as there are pebbles of volcanic 

rock with the granitic pebbles, and also a large percentage of purplish, red, and yellow quartzites similar 

to those in the bench gravel farther up the Yellowstone 

River. There are also many pieces of agate, opal ( ~), 

chalcedony, and silicified wood. No pebbles of these 

kinds, excepting the volcanic and granitic rocks, were 

noted on No. 1 bench east of Roscoe or south of 

Roberts. 

If the grade of the No.1 or Flaxville bench (Thorn's 

"third terrace" on the Big Horn River) decreased in 

the 35 miles downsa-eam from the vicinity of Hardin 

to an average of about 6 feet to the mile, the altitude in 

the Yellowstone Valley east of Custer would be about 

3,300 feet. 47 

This would connect with a grade reduced to 6 to 7 

feet to the mile on the Yellowstone east of Huntley, 

which is about the same as that of the present stream. 

(See Huntley topographic map.) 

NO. 1 OR FLAXVILLE TERRACE ON THE LOWER 

YELLOWSTONE 

The bluff south of Myers station, which is about 14 

miles below the mouth- of the Big Horn River, rises 

about 600 feet above the river, or to an altitude of 

3,300 feet. Here the top of the sandstone is capped 

with a thick bed of· gravel. This is probably a remnant of No. 1 bench. 

Rogers and Lee 48 describe deposits of coarse gravel 

~n the ridge between Tullock and Sarpy Creeks east 

"' Hancock, E. T., Geology and oil prospeets of the Huntley field, 

Mont.: U. S. Geol. Survey Bull. 711, pp. 128-129, 1919. 41' According to the Fort Custer and St. Xavier topographic maps, 

the present average grade of the Big Horn River for 52' miles below 

the mouth of the canyon is a little less than 10 feet to the mile, 

minor bends being negleeted. 

• Rogevs, G. S., and Lee, Wallace, Geology of the Tullock Creek coal 

field, Rosebud and Big Horn Counties, Mont.: U. S. Geol. Survey Bull. 

749, pp. 44-47, 1923. 

ef the mouth of the Big Horn Ri¥er. · On the north ends 

of the main divides there are said to :IJEr,several wen .. marked benches at lower altitudes, bUt -tb.e. highest :of 

the deposits, at 3,700 to 3,800 feet, or about 1,100 feet 

above the streams, appea:t' to form a mOBot~nwus, series 

of bare, rounded hills, due to erosion of bench gravel 

and the underlying soft Lebo· shale. Some of this 

gravel was examined by the -present writer and found 

to consist of pebbles of the same kinds of rock as occur 

on Pine Ridge and the other high benches east of 

Billings. Doubtless some of the gravel1s ·to be eor..: 

related with the Flaxville gravel of No. 1 bench. ' -

Dobbin 49 states that the northern edge of the Olig<Jcene or Miocene ( ~-) gravel deposits described on page 

12 is about 12 miles south of the terrace along the 

Yellowstone River near Forsyth and that the vertical 

interval between _ thein is 900 to 1,000 feet. The intervening area is covered with a mantle of gravel 

which is not arranged in any well-defined system of 

terraces and has been reworked so many times that its 

relations are obscure. A small remnant· of a terrace 

with. gravel locally cemented to _a conglomerate 10 

feet thick, in the central part of T. 5 N ., R. 41 E., 

stands 700 feet above the river. If the higher gravel 

corresponds to that on the Cypress Hills, this ·may 

correspond to the Flaxville gravel. Where the gravel 

overlies the Bearpaw shale it gives rise to round~d 

hills and a monotonous landscape. It makes promi-

·nent benches on the divides ·where it overlies rooks ·of 

the Lance formation arnd is usually covered wl.th a 

scanty growth of pine trees. 

With the exception of the examination of the gravel~ 

capped hills between Tullock and Sarpy Creeks south 

of Hysham, described above, no search of the al'ea 

south qf the Yellowstone River and east of the Big 

. Horn River for remnants of No. 1 bench ·has been 

made by the writer. Parts of the •area east of the 

Tongue River have been examined by Collier and 

Smith 50 Herald 51 Bowen 52 Bauer 53 Wegemann 64 

' ' ' ' ' and Rowe and Wilson, 54l but their reports do :not describe any gravel-capped benches whieh can properly 

be correlated with No. 1 bench as here described. 

Now here west of Miles City are any remnants of No. 

1 bench knoWR to occur on the north side of the Yellowstone River, except those near the Crazy Moun411 Dobbin, c. E., The Forsyth coal field, Mont.: U. S. Geol. Surver 

Bull. 812, p. 21, 1929. 110 Colller, A. J., and Smith, C. D., The Miles City coal·fleld, Mont.: 

U. S. Geol,.Survey Bull. 341, pp. 36-61, 1909. · 

n Herald, F. A., The Terry lignite field, Custer County, M:ont. : 

U. S. Geol. Survey Bull. 471, pp. 227-27-Q, 1912. 

11:~ Bowen, e. F., The Baker lignite field, Custer County, Mont.! 

Idem, pp. 202-226. 

113 Bauer, C. M., · The Ekalaka lignite field, southeastern :Montana:' 

U. S. Geol. SurveY. Bull. 751,. pp. 231-267, 1925. 

., Wegemann, C. H., Notes on the coals of the Custer National 

Forest, Mont. : U. s; Gool. Survey Bull. 381, pp~ · 10~114, 1910. • 

IIIIRowe, J. P., and Wilson, R. ·A., Geology and ·economic deposits 

of a portion of eastern Montgna : Montana 'Ontv. Studies, se:t\ 1, 

58 pp., 1916. 

) 
30 PHYSIOGRAPHY AND GLACIAL GEOLOGY OF EASTERN MONTANA 

tains, described above. Northeast of Miles City, how-: 

ever, it appears that the Yellowstone spread gravel 

very widely on No. 1 bench west and northwest of its 

present course. 

In 1911 Rogers studied the Little Sheep Mountain 

coal field north of Yellowstone River in what is now 

Prairie County. He describes the gravel-covered 

benches· as follows : 56 

The dissected remnant$ of at least three old river terraces 

may be recognized. The highest terrace lies on the southeast 

fiank of Little Sheep Mountain at an altitude of 3,200 feet, 

and there is another on the north divide of Cherry Creek at 

an altitude of about 2,800 feet [No. 2]. This high terrace is 

probably also represented in T. 10 N., R. 45 E., where a considerable area is covered by alluvium· at an altitude only 

slightly greater than either of those mentioned above. The 

third terrace is best preserved near the bank of Yellowstone 

River in T. 10 N., R. 49 E., where its altitude is 2,550 feet. 

In these places and in the others where the terraces may be 

recognized they are covered with a 20 or 25 foot layer of 

alluvial pebbles with an interstitial :tiliing of fine gravel, sand, 

and silt. • * • · The pebbles on these terraces are well waterworn and usually more or less flattened ; their greatest diameter is commonly as mueh as 6 inches. The interstitial sand is chiefly 

quartz, generally in angular grains. An examination of the 

pebbles covering an area of about a square yard resulted in 

the identification of the following: Quartzite, vefu quartz, 

jasper and chalcedony, sandstone, quartz conglomerate, granite, 

trachyte, and olivine basalt. 

In 1921 the present writer drove from Miles City 

north to Crow Rock post office and thence down· 

Cherry Creek Valley to Terry. On this trip no wellpreserved flat benches were observed, but gravel very 

· similar to that on the high benches farther west was 

found at several places up to the highest altitude 

reached, 3,100 to 3,200 feet (barometric). The pebbles 

are in the main smoothly rounded and have a maximum diameter of 10 inches, though mostly about 2 

inches or smaller. They consist generally of very resistant rocks, such as were noted by Rogers, with but 

few granitic rocks, sparse deeply etched fragments of 

Paleozoic limestone, and many pieces of silicified 

wood. One deposit at· an altitude of 2,875. feet is 

partly cemented to a hard conglomerate. This may be 

a remnant of No. 2 bench. 

In 1920 the writer made ·a brief reconnaissance 

of parts of the Glendive quadrangle and found 

several erosional remnants of a high gravel bench 

which is probably to be correlated with the Flaxville 

Plain as of Miocene or Pliocene age. Studies of 

1921 and 1922 tended to confirm the opinion that 

this is the same as No. 1 bench farther west. (See 

pis. 1 and 28.) As shown on the topographic map, 

these high benches occur in a belt between 6 and 20 

miles west of the Yellowstone River; where they 

118 Rogers, G.· S., The Little Sheep Mountain coal field, Dawson, 

Custer, and Rosebud Counties, Mont., U. S. Geol. Su·rvey Bull. 531, 

pp. 161-162, 165, 1913. 

form the flat tops of eight or nine ridges · intervening between parallel southeastward-tloWing·.···intE:rmittent streams. The ridges are sharply tnin.catc;,d 

at their southeast ends by steep slopes \\l'hich drop several hundred feet to remnants of lower benches. The 

smooth, flat tops of the ridges range in width from le&t 

than 1 mile to 6 miles and are sharply. delimited by 

the steep side slopes of the intervening valleys or 

coulees, some of which are 300 to 400 feet in depth. 

One of these valleys is traversed by the Richey branch 

of the Great Northern Railway. This road crosses the 

divide at Enid, at an altitude of 2,450 feet, through a 

broad, flat-bottomed pass 300 feet in depth. The southeast ends of these benches are about 2,700 to 2,800 feet 

above sea level, or 700 feet above the Yell~wstone 

River, and from this level they rise gradually to an 

altitude of 3,000 feet on the narrow-crested divide that 

separates tributaries of the Yellowstone from those of 

Redwater Creek, which joins the Missouri near Poplar. 

The tops of most of the ridges have,.however, been 

narrowed and lowered by erosion so as to leave gaps of 

several miles between the benches and the divide. 

The loamy soil on these high benches. is underlain by 

gravel, 5 to 15 feet of which is exposed at the tops of 

the marginal. slopes. The pebbles, which consist of 

various dense ignoous and volcanic rocks, quartz, 

quartzite, and a few pieces of chalcedonized wood, are 

mostly less than 3 inches in diameter and have 

smoothly rounded waterworn surfaces. There are also 

a few larger pebbles 5 or 6 inches in diameter~ ·. The 

gravel is not so coarse as that on the lowest terraces 

near the river. There are fewer •ebbles of quartzite 

and more of crystalline rocks than on the Flaxville 

Plain and the Cypress Hills, to the northwest. The 

crystalline rocks are not, however' granite, such as is 

seen in the glacial drift on the lower ben'Ches at and 

north of Intake (" Headworks" on Glendive topographic map). This is evidently stream gravel which 

came down the Y ell.owstone Valley from the mountains, over 300 miles to the west. Some of it, perhaps, 

came from the Big Horn Mountains of Wyoming. A 

few granite boulders were seen near the east end of the 

top of the high bench northwest of Intake, in· T. 19 N ., 

R. 56 E.· It is possible, however, that the ·ice of the 

glacial lobe which extended south, up the. valley to 

Intake, crowded up onto the edge of the high bench 

and left these boulders there. 

The most northerly remnant of No. 1 bench noted. in 

the Glendive quadrangle is about 12· miles west of 

Sidney and 3- to 5 miles east of Three Buttes, iD; T. 23 

N., R. 56 E. This stands at an altitude of 2,650 feet, 

about 700 feet above the Yellowstone River, and very 

little of tB.e crest of the old divide to the northwest 

rises above this level. The crest of the ridge at Sioux 

Pass is very close to this altitude, but no gravel was 

seen upon it. 
PLIOCENE AND EARLY· PLEISTOCENE EPOCHS 31 

Frmn these descriptions it appears that at the· time 

of the fortnation of the Flaxville Plain or No. 1 bench 

the Yellowstone and Missouri Rivers near their junction must have been flowing at a level wll.ich is now 

about 2,500 feet above the sea-that is, 600 feet above 

the present channels. In the 280 miles from the high 

bench at 3,600 feet east of Billings to this level of 

2,500 feet at the junction of the Missouri and Yellowstone the average grade or slope would be about 4 feet 

to the mile. This gradient is somewhat higher than. 

that of· the present stream, even if the numerous 

meanders are negl~cted. At present the average fall 

on the Yellowstone River in 280 miles below Huntley 

is about 3. 6 feet to the mile, disregarding bends. In 

tlie same distance along the old course of the Missouri 

River between Havre and the mouth of the Yellow-

. stone the fall would be about 3 feet to the mile if the 

bench near Harl~m was at 3,000 ·feet, as described 

above. 

Comparison shows that No.1 bench on the Yellowstone is sufficiently high to have extended northeastward from the site of the present mouth of the stream 

along the line of the Missouri Valley to Williston and 

thence up the course of Little Muddy Creek (reversed), 

and to have crossed the Coteau du Missouri in the 

region of Crosby, N. Dak. There is, therefore~ nothing 

in the relations of No. 1 bench so far as known, or in 

those of its correlative, the Flaxville Plain, antagonistic to the idea that in preglacial time the waters .of the 

Missouri and Yellowstone Rivers flowed northeastward to Hudson Bay or its marine predecessor. . . PLIOCENE AND EARLY PLEISTOCENE EPOCHS 

GENERAL RELATIONS 

In 1911 the writer described,58 before the Geological 

Society of America, the occurrence of very old glacial 

till capping the high benches in front of the mountains 

of Glacier National Park, and in 1912 Stebinger and 

the writer 119 presented a second paper on the same 

subject. This glacial till, some of which is cemented 

by calcium carbonate to a hard tillite, caps the highest 

(No. 1) bench, which is now regarded as the physiographic correlative of the Flaxville Plain of northeastern Montana. The geographic and physiographic 

relations of this ancient till and of striated pebbles 

scattered on No. 1 and No. 2 benches for 20 miles out 

from the mountain front are such as to indicate that 

the first of the mountain glaciers extended out onto the 

No. 1 bench before that surface had been greatly dissected. It has been suggested that the striated peb-· 

bles on No. 2 bench were deposited by a second and 

~Alden, W. C., Pre-Wisconsin glacial drift in the region of Glacier 

National Park, Mont.:· Geol. Soc. America Bull, vol. 23, pp. 687-708, 

1912. 

• Alden, W. C., and Stebinger, Eugene, Pre-Wisconsin glacial drift 

in the region of Glacier National Park, Mont. : Idem, vol. 24, pp. 

529-572, 1918. 

later advance of the mountain glaeiers, but this has 

not been demonstrated. That the high-level gla.cial 

till is 'Very old, probably as old as the Kansan or Nebraskan drift of Iowa and adjacent State~, is indicated by the fact that before the mountain glaciers 

advanced at the Wisconsin stage the mountain gorges 

and their valley continuations on the adjacent plain 

had been deepened 1,000 feet or more, largely by inter~· 

glacial stream erosion, so that the relief of the mesas 

capped with till and gravel controlled to a consider.;. 

able extent the later glacial flow. . 

Careful consideration of the relations of the terrace 

remnants along the upper Missouri and Yellowstone 

and their tributaries ·to the remnants of the high 

plains bordering the monntain fronts and to the ancient glacial till on the highest of these remnants in 

the Glacier National Park region seems to warrant 

certain tentative conclusions, which may be rsuinmarized as follows: 

1. The highest of the benches or terraces bordering 

the mountain fronts are correlatives of the Flaxville 

Plain of northeastern Montana. 

2. Such fossils as have been found in the Flaxyille 

gravel indicate that the development of the Flaxville 

Plain was not completed before Pliocene time. 

3. The presence of. the O(liJ'J'I;elops tooth, which was 

identified by Gidley as " apparently Pleistocene," suggests that the streams may not have finished deposition of the Flaxville gravel until early Pleistocene 

time. 

4. The relations of the oldest drift of the mountain 

glaciers on the supposed remnants of the Flaxville 

Plain close to the mountain front lead to the inference that the Flaxville Plain had not been greatly 

dissected when climatic conditions became such as 

to bring on extensive glaciation in the mountains. 

5. The first Cordilleran glaciation was probably 

contemporaneous with the advance of the Keewatin ice 

sheet of the Nebraskan stage and is regarded as marking the beginning of Pleistocene time. . 

6. Abqut this time the streams began cutting below 

the Flaxville Plain, and this, taken in connection with 

the beginning of Cordilleran glaciation, leads to the 

inference that Pleistocene time in this region was 

initiated by a ·second regional uplift. The amount 

and character of this uplift are described below. 

7. The writer knows of no observational evidence 

for regarding as Pleistocene any features in this· region that are older than the pre-Wisconsin glacial 

drift on the remnants of the Flaxville Plain in front 

of the mountains of Glacier National· :J;lark. 

In eastern Nebraska and western Iowa the relations 

of the early Pleistocene drift sheets to the·underlying 

eroded surface of the Cretaceous, Oligocene, and Miocene deposits, so far as known, are such as to indicate 

that a large amount of erosion had been accomplished 
32 PHYSIOGRAPHY AND GLACIAL GEOLOGY OF EASTERN MONTANA 

by the Missouri River in that part of its course south 

of South Dakota between Miocene and early Pleistocene time. 

The apparent conflict between the evidence from 

(1) the region bordering the Missouri River in eastern 

Nebraska and western Iowa, (2) the region of the 

Missouri River and the Flaxville Plain in eastern 

Montana, and (3) the relations of the high-level 

glacial drift on the No. 1 benches in the region of 

Glacier National Park has led the writer to the 

further tentative conclusions stated below: 

A certain amount of regional uplift probably took 

place in Pliocene time. The lower Missouri followed 

its present course south of southeastern South Dakota, 

but for some distance north of this latitude in South 

Dakota, perhaps as far as Mitchell (see Todd) 60 it 

was flowing in the preglacial valley of the James 

River east of the Coteau du Missouri, the present 

channel below Williston, N. Dak., past Bismarck, 

Pierre, and Yankton not having yet been adopted. 

The Yellowstone and the Upper Missouri were still 

flowing northeastward across the Coteau du Missouri 

toward Hudson Bay. As a consequence of the uplift 

these streams cut below the level of the Flaxville 

Plain and the No. 1 terrace on the Yellowstone and 

its tributaries and then began anew the process of 

planation at a lower level, thus developing the No. 2 

benches described below. In eastern Montana and 

in the adjacent part of Canada the dissection and 

planation may have proceeded to a considerable extent before it· was interrupted by the eady Pleistocene 

continental glaciation. In the Glacier National Park 

region and the mountains to the south the uplift may 

have been less than to the east, erosion had not proceeded so far, and No. 1 bench was cut to only a moderate depth (100 to 200 feet ? ) , though it may have 

been worn away in considerable areas by the process 

of lateral planation before this was interrupted by -the 

development of mountain glaciers and their extension 

onto the plain bordering the mountain front. Both 

the No. 1 and No. 2 benches carry old glacial drift 

near the mountain front .in the Blackfeet Indian 

Reservation. 

Certainly the mountain streams had not cut below 

the planated surface of the upper level of the second 

set of. terraces· before the mountain glaciers extended 

onto it and left the cap ·of drift, though it is possible 

that No. 1 bench had beeri somewhat eroded before 

any of the glaciers reached it. The drift on the two 

levels may belong to one and the same stage, or it may 

comprise deposits of two different stages, to be cor-

-related with the Nebraskan and Kansan stages of eastern Nebraska and Iowa. It seems probable that in 

eastern Montana erosion had cut below the Flaxville 

CIO Todd, J. E., The Pleistocene history of the Missouri River: 

Science, new ser., vol. 39, p. 268, 1914. 

Plain (Miocene or Pliocene) and below No. 1 bench. 

on the Yellowstone River and its tributaries and had 

developed or was developing the upper level of the 

second set q:f terraces before the first continental. ice. 

invaded North Dakota and interfered with the northeastwB.fd disch~rge of the rivers. 

ClUATERNARY PERIOD 

PLE~STOCENEEPOCH 

EARLY PLEISTOCENE XOlJlrlTAilf GLAOU.TION ON NO. 1 Al1'D 

lfO. I BEJfCDS 

It will scarcely be questioned that.the earliest known 

· glaciation of this region was of Pleistocene·age. This 

being the case,- it is the opinion of the write}.' thltt 

among the oldest .Pleistocene deposits in the region are 

the caps of glacial drift on the highest levels of the 

plains near the mountain front, No. 1 and No. 2 

benches, in the Glacier National Park region. (See 

pl. 1.) These deposits were described by the writer 

and Eugene Stebinger in the papers cited above. They 

include the "Kennedy gravels," described by Bailey 

Willis 61 from the field notes of George I. Finlay and 

doubtfully referred by him to 1the Pleistocene. They 

also include a part of the "quartzite gravels" described by Calhoun 62 and regarded by him as of preglacial age. 

The geologic importance of such high-level deposits 

of ear:ly Pleistocene glacial drift and the rarity of 

their preservation in the mountains of the West seems 

to warrant considerable detail of description. The 

character a:dd relations of these deposits are set forth 

below in the order of their occurrence from north to 

south. (See pis. 1 and 37.) 

GLACiAL DRIFT ON M~OWAN BUTTE, .ALBEB.TA 

In southern Alberta between the Belly River on 

the west and the head of Lee Creek on the east a high 

ridge, known as Makowan Butte,68 extends northward 

to a point 5 miles north of the international boundary. 

.At the abrupt north end this ridge stands about 1,300 

feet above the Belly River, or about 5,750 feet above 

sea level. It is capped with about 100 feet of glacial 

drift, which is exposed in several places in sea.rps left 

by landslides on the underlying Cretaceous or Tertiary clay and shale. The drift is composed of angular to subangular or well-rounded pebbles and boulders 

as much as 5 feet in length, representing the· several 

kinds of rock from the mountains, embedded in a 

61 Willis, Bailey, Stratigraphy and structure of the Lewis and· Livingston Ranges, Mont. : Geol. Soc. America Bull., vol. 18, pp. 828--'330~ 

H~ . 

62 Calhoun, F. H. H., The Montana lobe of the Keewatin ice sheet : 

U. S. Geol. Survey Prof. Paper 50, pp. 13, 49-52, 1906. 

es See map of Waterton Lakes Park, Alberta, Dept. Interior, Canada. 

This ridge was designated Belly River Ridge in the paper by Alden 

and Stebinger, in 1913. Its southward continuation in the United 

States is Lee Ridge. (See map of Glacier National Park: U. S. Geol~ 

Survey Bull. 600, pl. 18, 1914.) 
PLEISTOCENE EPOCH 

matrix of clay. Glacially scored stones are not abundant, but search r~ulted in finding numerous wellstriated pebbles of greenish argillite. In the upper 

part of the ridge there are almost no pieces of limestone, though these are plentiful lower down. Evidently the limestone pebbles have been removed from· 

the higher levels by solution, and ledges of tillite that 

crop out 10 to 15 feet below the top of the section sho_w 

the results of cementation by the calcium carbonate 

carried down by percolating waters. , 

Drift of the same character is found 8 to 10 miles 

farther south on this same ridge, west of Chief Mountain, at 6,000 to 6,300 feet above the sea. 

These deposits are well above the upper limit of. the 

Belly River Glacier of the Wisconsin stage, although, 

as determined by C. S. Corbett in 1914, a small tongue 

of that ice spilled over the sag in the crest of the · 

ridge at the international boundary and extended a 

few miles down the valley of Lee Creek on the east. 

In Corbett's field notes is the following description of 

the high-level drift on the ridge just north of Gable 

Mountain, at a point near the Belly River trail 4 miles 

west of Chief Mountain. 

At 6,520 feet (barometric), top of cut. 

Broad cut showing exposure of drift about . 200 feet high. 

About 25 feet below the top is an exposure of the subsurface 

material, which is tillite. The clayey matrix is so indurated 

·It rings when struck with the hammer. The ·boulders and 

pebbles are probably over 90 per cent of limestone, most of 

which show the characteristics of the Altyn formation. Some 

of these limestone pebbles retain glacial striae. They range 

in size up to 8 feet in diameter. A few red and green argillite 

pebbles were found.,no diorite or lava. Also no Colorado shale 

material noted·. 

Benches on the west side of the Belly River Valley 

·were examined in 1911 by J. Elmer Thomas and the 

present writer; they are described as follows : 

Between 5,750 and 5,950 feet above the sea, or be~ 

tween 1,000 and 1,200 feet above the valley bottom, is 

a bare scarp face, the marginal slope of a shoulder 

standing out on the slope. The material exposed in 

this scarp is glacial till. All the pre-<Jambrian formations are represented in the pebbles and boulders of 

this drift-limestone, red and white quartzite, diorite, 

and amygdaloidal trap. Many of the argillite pebbles 

are. well striated. Numerous blocks of tillite were observed, but no ledges were seen in place. Above the 

scarp the bench rises westward to the base of the cliff 

of pre-Cambrian rock, but with a slope much less 

steep than the general slope of the valley wall below. 

A similar bench, but somewhat less well marked, occurs to the north just across the ravine. No exposures 

were seen to show whether or not this bench is on a 

deposit of till. Seen from the east side of the bottom 

of the valley, the two appear to be parts of one bench, 

cut through by a broad sag, in the bottom of which is a · 

sharp V -shaped ravine that drains two glacial cirques 

87949-32---4 

in the mountain sl,ope above.·. This . relation, ta.ken 

together with the form of the bench and the character 

of the underlying deposit, suggests that the ~ift·coiP• 

posing the bench was deposited undet ·the same CQlldi~ 

tions as that capping the flat-topped ridges a.nd mesas -

at a pre-Wisconsin stageof glaciation;·tha.t during the 

later extension of the Belly River gl3cler a tributary 

ice stream, heading in the cirques above, cut throug~ 

the bench, forming the broad sag; and that, after the 

melting of this glacier and. that in the valley, postglacial drainage cut the sharp notch. . _ 

At a point about half a mile south of the intern"'-

tional boundary there is a similar bench ~mnan:t. at 

about the same altitude, with an exposure in the steep 

marginal slope, showing glacial till similar to that described above. The sides of the valley are heavily 

wooded and no detailed examination. of them was 

made, so that the upper limit of the last glaciation was 

not determined. It is doubtful if the i~ overlapped 

these high-level deposits. These benches stand like 

remnants of high-level terraces and appear to represent a former stage in the development of the va])ey. 

They probably belong to the second set. · 

In 1914 C. S. Corbett and Campbell_R. Williams <Jetermined that the Kennedy Creek Glacier at the Wisconsin stage spilled over the col, 300 feet deep, 2 or 3 · 

miles east of Chief Mountain arid extended a small 

lobe northward or· down the valley of the East For~ 

of Lee Creek to a point within a mile of 'the interna~ 

tional boundary, but the ice barely overtopped the 

south end of the high bench on the eS$1 side of the ,col 

at 5,900 feet above sea level. Corbett concluded that 

the 75 feet of till exposed at the south end is probably 

of Wisconsin age, as it is fresh looking and con~~ 

plenty of striated limestone pebbles. This till forms 

a sharp-crested little ridge about 50 feet lower than the 

point of the main flat top (at 5,950 feet), whieh slopes 

gently down northeastward as the remnant· of an· old 

high bench. On this bench only green argillite pebbles 

retain striae. ' . DRIFT ON XENNlliDY BJDGE 

North of the North Fork of Kennedy Creek, in the 

area east of Chief Mountain, is a. hilly tract underlain 

by Cretaceous sandstone. Rising above the general 

level of this tract, just north of Kennedy· g~~' is a 

small, abrupt, flat-topped mesa having ·an altitude ·of 

5:800 feet above sea level, or 900 feet above the stream 

on the south. (See pl. 14 B.) This was described 

· by Willis 64 as " the typical occurrenc_e of · the Ken* 

nedy gravels." The slopes of this mesa are abrupt 

scarps due to landslides, and in places tf?.ese ·scarp 

faces are bare of vegetation and give good exposures 

of the componen~ material, l?f> feet or more· in height. 

64. Willis, :9ailey., op. cit .• pp. 828-330. 
34 PHYSIOGRAPHY AND GLACIAL GEOLOGY OF EASTERN MONTANA 

This ntaterial is coarse cobblestone gravel and small 

boulders. A large part of. the stones are subangular 

and faeeted, and some of them are well rounded. No 

evidence of assortment or bedding was notd, and, to 

the writer, the aspect -was rather that of gravelly 

glacial drift than of stream gravel. ·Moreover, careful search yielded numerous pebbles carrying striaj;ions. (See pl. 15 .A.) The stones, which are wholly 

pre-Cambrian rock from the mounutains, consist principally of buff limestone and quartzitic material from 

the Altyn limestone, and with this is .a subordinate 

amount of red and green argillite. Striations were 

found only on pieces of the greenish dense quartzitic 

argillite. The surfaces of other pebbles had been sufficiently etched and roughened by weathering to remove striations if any were present. The ridge stands 

so high and is so narrow and so exposed on all sides 

that conditions particularly favor the surficial modification of the material by the agencies of weathering. 

Three small knobs about 3 miles farther north are 

capped with the Pre-Wisconsin drift at 5,300 to 5,500 

feet above sea level. 

DRIFT ON BWDM."CURBENT BlDGlil 

The ridge between the South Fork of Kennedy 

Creek and Swiftcurrent Creek, on the north side of 

the Sherburne Lakes Reservoir, is kno-*n as Swiftcurrent Ridge. A subordinate part of this ridge ex-

- tends northward at right angles to the main ridge 

i-rom the Swiftcurrent Valley and forms the divide 

· between the St. Mary River on the east and the South 

Fork of Kennedy Creek on the west. The subordinate ridge, which rises 650 to 850 feet above the bottom -of the valley on the east, appears to have been 

overtopped by the St. Mary Glacier of the Wisconsin 

stage, inasmuch as morainal material is found on its 

crest. The summit of the main ridge, which trends 

in a general east-west direction, appears not to have 

been overtopped by the later ice moving down the valleys of either Swiftcurrent Creek or the South Fork 

of Kennedy Creek. For 2¥2 miles the top of this 

ridge is nearly flat (pl. 14 .A)' and has a width of 

about 600 yards. It gradually increases in altitude 

from about 5,800 feet above sea level at the east to 

6,000 feet at the west, so tha.t it stands about 1,150 to 

1,250 feet above Swiftcurrent Creek on the south. 

From this top stee.p slopes decline on both sides. At 

the top of the south slope is an abrupt scarp due to 

landsliding. This has a height of 200 to 300 feet, and 

below is an uneven slope marked by swells and sags 

and numerous small lakelets. This slope resembles 

morainal topography but is probably due principally 

to slumping of the drift over t~e soft Cretaceous 

shale. At least 200 feet of glacial till is exposed in 

the clean scarp faces at' the top of •the slope. This 

drift is of the same composition and appearance as 

that on the ridge across· the valley to the south, except 

that here, in addition to the other ingredients, frag• 

ments of Siyeh limestone and amygdaloidal trap rock 

are found. The·trap rock is present in the mountains 

at the head of the Swiftcurrent Valley. Many of the 

pebbles and boulders are striated. Blocks of the 

tHlite were seen, but· no ledges clearly in place. Part · 

of the diorite boulders are considerably weathered so 

as to be exfoliating shells half an inch thick, and some 

of the limestone pebbles in the upper part of the drift 

are etched but not removed by solution. 

At the west end of the high tract just described 

the ridge narrows and the crest is broken by a sag 

about 1% miles in length. This part is crossed by 

the boundary between the Blackfeet Indian Reservation and Glacier National Park. Here the drift cap 

has been removed and in places the Cretaceous sha.le 

is exposed. Beyond this locality the crest again rises 

a.nd a narrow remn8.Ilt of the old drift remains. This 

part of the ridge was examined by J .. E. Thomas but 

not seen by the writer. Mr. Thomas reports a rwtched 

flat crest rising from 6,100 to 6,200 feet above the sea, 

and scarps giving good exposures of 200 feet of glacial 

drift like that forming the top of the· ridge farther 

east, with ledges · of tillite in place. On the surface 

boulder·s of diorite and amygdaloidal trap are conspicuous, some being 4 to 6 feet in length. The drift . 

was observed in place within a few hundred feet of 

the pre-Cambrian Altyn limestone in the east end of 

Appekunny Mountain. West ·of a.· notch there is an 

abrupt rise to a bench at 6,300 feet above the 8ea. 

This is cut in solid limestone and extends for a short 

distance about the north side of the point .of the 

mountain. On this bench no drift was found. The 

top of the· drift· stands nearly 1,500 feet above Swiftcurrent Creek on the south and 800 feet above the 

South Fork of Kennedy Creek on the north. 

DRIFT ON BOULDER BIDGE 

On the crest of the ridge of Cretaceous shale between Boulder and Swiftcurrent Creeks is glacial till 

which appears to b~ 200 feet or more in thickness. 

It is exposed in scarps due to slumping at two or three 

places at the tops of the north and south slopes. The 

pebbles and boulders in the reddish till are of limestone, red and green argillite, quartzite, and diorite 

and are well faceted and striated. Ledges of tillite 

due to cementation protrude from the drift slope, but 

there is ito other notable evidence of weathering, and 

limestone pebbles are present nearly· or quite to the 

top. The- top of this highest part of Boulder Ridge 

is notably flat and has a length of about 2 miles. In 

this length the a.ltitude increases southwestward toward the mountain from about 6,100 to 6,300 feet. It 

thus stands 600 to' 800 feet above Boulder Creek on 

the south and 1,400 to 1,600 feet above the Sher·burne 
• 

.PLEISTOCENE EPOCH 35 

Lakes Reservoir in the Swift~urrent Valley on the 

. north. At the southwest end of this flat top a short ·• 

sharp ridge ·rises to an altitude of 6,400 feet. · The 

rise does not continue to the front of Point Mountain, 

but after reaching this high altitude the crest drops 

abruptly to a notch ·200 feet or more in depth, beyond 

which it again rises to Point Mountain. This sharp, 

highest part of the crest of Boulder Ridge· consists of 

angular fragments of limestone, white quartzite, and 

red and green argillite, such as compose Point Mount~rial seen on the surfaces of the kno'bs is like that of 

the drift described above. M. R. Campbell reported 

that ·he found tillite on top of one of the hills. · It is 

. probable that this is a remnant of tM· pre-Wisconsin . · 

drift. The surface of the ridge surrounding the line. 

o:f hills is marked by low swells and sags, the result 

of later drift deposition or of landsliding or a com .. 

bination of qoth. 

DRIFT ON ST. MARY IUDGJI1 

tain. No fragments of diorite were noted. The rna- Em~rging from the mountains bet~een the bold sali· 

terial does not look like glacial drift but like· talus, . ents known as Divide Mountain and Singleshot Mounand its character and relations lead to the suggestion· . tain, the waters of the St. Mary River flow in a genthat here is the last remnant of a disintegrated salient eral direction nearly due north through the lower lake 

of Point Mountain, which at the time of the deposi- and beyond across the international boundary. Bortion of the high-level drift extended 1% miles farther dering the lower lake and the lower part of.the upper 

to the northeastward than it does at p:resent. The lake on the east is an undulating tract about a mile 

fragmental material came from the pre-Cambrian in width composed of small hills and ridges ~f shale 

formations, which in the nearest part of Point Moun- mantled with later glacial drift and standing 100 to 

tain lie more than 800 feet higher than this remnant~ 300 feet above the lake levels. From this a stoop slope, 

This relationship indicates either that the pre-Cam- most of which is heavily timbered, rises eastward to 

brian rock of this remnant was let down from il higher the crest of a broad ridge known as St.· Mary Ridge .. 

level by gradual slumping or washing awa:f of the The crest of this ridge declines gradually in altitude 

underlying Cretaceous shale, or that, owing to a slight from south to north. It is highest between 2 and 3 

anticlinal fold, it originally stood lower at. this point miles north of Divide Mountain, there standing about 

than it does in Point Mountain, 1% miles away, where 6100 feet above sea level. In the interval between this 

the rock is now inclined upward in the. direction of highest part and the mountain ~here is a broad sag in 

the remnant. Owing to similarity in component rna- the crest line where the top of the ridge is 300 feet 

terial of the older and younger drift and to the lower. Where highest the top of St. Mary · Ridge 

slumped and wooded condition of the slopes it is stands over 1,600 feet above the level of the upper lake. 

difficult to determine just how high on the flanks of From this highest part the northward· decline carrie.~ 

Boulder Ridge the ice of the Boulder Creek and the crest line down to a level which; east .of the foot of 

Swiftcurrent Glaciers extended at the Wisconsin the lower lake, between 9 and 10 miles to the north, is . 

stage of glaciation. It seems clear, however, that the about 1,100 feet above the water in this lake and 5,500 

later ice did not overtop the higher part of the ridge,. feet above sea level. Duck Lake lies in .a big sag in .the 

that is, No. 1 bench, .but that it did override No. upland, so that the crest of ·the ridge may be said to 

2 bench, 125 feet lower, which is developed on the curve eastward on the south side of this lake. The top 

eastern part of the crest. of St. Mary Ridge is broad and smooth, and from it 

It is of interest to note in this connection that in the plain slopes gradually eastward. Much of this 

1914 C. S. Corbett found glacial· striae on the crest of surface has been lowered by erosion by the headwaters 

Point Mountain above the west end of Boulder Ridge, of tributaries of the Milk River, but in the interstream 

at 8,300 feet above sea level, .trending N. 30° E. and areas the higher tracts comprise remnants of the No.1 

N. 60° E., which he regarded as the product of pre- and No.2 benches. 

Wisconsin glaciation. North of the broad sag in which lies Duck Lake the 

DRIFT ON BJ;DGE WEST OF L()WER ST. MARY LAKE 

On· the west side of Lower St. Mary Lake a ridge 

of Cretaceous shale and sandstone lies between the 

lake on the east and Flattop Mountain and the 

B9ulder Creek Valley on the west. The crest of the 

ridge is narrow and serrate, consisting of a row of 

sharp hills extending north a~d south on the line between sees. 16 and 17, T. 35 N., R. 14 W. These peaks 

stand 5,700 to 5,900 feet above sea level, 1,200 to ·1,400 

feet above the lake, and 500 to 700 feet above Boulder 

Creek. There is· no very good exposure, but the maHudson Bay divide continues as a broad high rid~ 

similar to and really a part of St. Mary Ridge.-

On the steep west slope of St. Mary Ridge there has 

been ·considerable landsliding on th1) shale, which · 

probably forms the bulk of the ridge. At a few place13 

near the top of the slope this slumping. has produced 

fresh scarps, giving excellent exposures of the mate· 

I'ial capping the ridge. Follo-yving the old trail so~th:.: 

eastward from· the foot of Upper St. Mary Lake for 

about 1% miles and then climbing the wooded slope, 

the writer reached one of these scarp8 between 1,100 

and 1,400 feet above the lake. The ex~e has a 
36 PHYSIOGRAPHY AND GLAOIAL GEOLOGY OF EASTERN MONTANA 

height of nearly .300 feet and a length of 500 feet or 

more. The upper 30 to 50 feet of the section is grayish glacial till, in which the pebbles and boulders 

consist of red and green argillite, quartzite, gray sili-. 

ceous limestone fr()m the Siyeh formation, diorite, and 

some buff limestone from the Altyn formation. It 

looks as if most of the Altyn limestone pebbles had 

been removed by solution, and fragments of the Siyeh 

limestone are deeply etched. Beneath this is a 10 to 

15 foot band in which the till is·oxidized to an orange 

or yellowish tint. In this is more of the yellow 

oxidized limestone, some of the fragments of ·which 

are thoroughly rotted. Underlying this zone and 

. forming the greater part of the section is reddish till 

cemented by calcium carbonate to a hard conglomerate 

which projects from the slope as ledges. Most of the 

pebbles and boulders in this conglomerate have fresh 

glaciated surfaces, but some of the diorites are disintegrating; many of the buff limestones are etched by 

solution, and some have been removed, leaving only 

a yellowish powder in the cavities. The reddish tint 

is due to the large amount of red argillite. ·The calcium carbonate cement was probably derived by percolating waters from the solution of limestone fragments in the upper part of the section. It is the 

projecting ledges of conglomerate which give to the 

deposit, as seen from the valley below, the appearance 

of stratification. Close examination reveals no assortment of the material.or bedding. No fragments of 

rock were noted other than such as are derived from 

the mountains. About 250 feet of drift was seen, but 

the base was not exposed. About half a mile farther 

south an exposure of similar . material was examined. 

Here the yellow band was not so noticeable, but other 

evidences of weathering and cementation are the same. 

Four miles north of this scarp a third exposure was 

examined by J. E. Thomas, who reports 250 feet of 

drift of much the same composition as noted above. 

No limestone was noted at the top, though blocks of 

Siyeh limestone were seen in the conglomerate, which 

extends within 5 or 10 feet of the grassed top. 

From the material exposed at these points it is apparent that the cap of St. Mary Ridge is old glacial 

drift. Owing to the thick woods and the large 

amount of landsliding on the southern half of the 

steep slope, the upper limit reached by the St. Mary 

Glacier of the Wisconsin stage could not be determined 

there. Farther north, about a mile south of the point 

where the ridge is crossed by the Babb-Browning 

road, a small but definite morainal ridge begins to be 

developed somewhat below the crest of the smoothly 

curved top of the big ridge. This small drift ridge, 

which is evidently the lateral moraine of the St. Mary 

Glacier, was traversed for about 3 miles and found to 

be increasing in size toward the north. South of Duck 

Lake this ridge curves eastward with the crest ot:the 

~big ridge. This moraine carries plentiful blocks, .of 

limestone, but on the smooth broad top t.o :the. east 

little else than quartzite pebbles was noted. As .determined from the sections described, these quar.tz• 

ite pebbles represent the insoluble weathered residual 

material at the top of the older drift. Taking everything into consideration, it is clear that the thick drift 

forming the cap of St. Mary Ridge can not be re· 

fe-rred to the last St. Mary Glacier, although that ice 

stream so far filled the valley as to overtop ,the high 

slope of the ridge east of the lower lake. 

In 1912 the writer found an excellent exposure of 

the drift on the east side of St. Mary Ridge. In the 

woods on the north slope of the valley of. one of the 

· branches of Livermore Creek which cuts the east slope 

of the big ~idge 6 miles due west of Horse Lake, in 

the SE. % sec. 6, T. 34 N., R. 13 W., between 5,700 and 

5,800 feet above the sea, was a clean scarp due to 

slumping on the underlying Cretaceous shale. The 

scarp was about 75 yards long and had a maximum 

height of about 25 feet. In the western lullf of the 

exposlilre the upper 10 to 12 feet consisted of sand and 

gravel interstratified with glacial till; below this was 

15 feet of coarse, bouldery till. (See pl. 15 B.) Some 

·of the striated boulders in this till were 5 to 6 feet in 

length. The. pebbles and boulders were derived exclusively from the mountain rocks, mostly quartzite and 

red and green argillite, with some of diorite and some 

from the Siyeh and Altyn limestones. Many of the 

limestone pebbles in the upper part of the section were 

rotted to a loose buff powder, .as the result of solution. 

In places streaks of stratified sand were cemented to 

hard sandstone, and below the upper· 5 feet the till was 

cemented to a hard tillite by the calcium carbonate 

redeposited by the downward-:-percolating 'faters. 

Examination showed also that the flat top on that 

part of the Hudson Bay divide between a point south 

of Spider Lake and the gap near Galbraith's. ranch, 

south of the United States customhouse, well above 

the marginal moraine of St. Mary Glacier, is capped 

in the western part by 15 to 25 feet or more of glacial 

till, and ·farther east by thin gravelly dxift containing 

striated pebbles of greenish argillite. (See ,pl.15 B.) 

The superficial deposits on that part east of the gap 

ne~r Galbraith's ranch were not carefully examined. 

The top of the ridge where capped with this drift 

declines eastward in 5 miles from 5,300 feet above sea 

level to 5,100 feet. The marginal moraine of the St. 

Mary Glacier, looping back to the northw~ on the 

north side of Goose Lake (pls. 1 and 37), crosses the 

highest part of the ridge at the west end, doubles 

sharply back to an east-northeasterly trend, and 

gradually descends the steep north slope of the ridge 

until it lies on the plain several hundred feet below 

• 
PLEISTOCENB EPOCH 

the drift on the top of the divide. (See ftg. 1.) It 

is thus clear that the drift on the divide is not ·referable to the Wisconsin stage of glaciation. The altitude of the top of the ridge shows that it is correlative 

with that part of St. Mary Ridge bet~een Duck Lake 

and Divide Mountain as a remnant of the highest 

p1ain. · · 

There is some indication that ice of the Wisconsin 

stage spilled over the sag now traversed by the automobile road between the higher part of St. Mary 

Ridge and Divide Mountain on the south, though it 

did not overtop the old drift to the north. 

DRIFT ON MILK RIVEil RIDGE 

On the no:rth side of the valley. of the North Fork 

of Cut Bank Creek is another great ridge· of Cretaceous shale and sandstone left from the erosion of the 

high-level plain. This is known as Milk River Ridge 

from the .fact that tributaries of the Milk River head 

on its north slope. Down the great trough between 

Cut Bank Creek and Milk River Ridge 

the Cut Bank Glacier extended at Wisis -another remnant of the old· high-16vel drift.. At the 

east .end of this mesa an abrupt slope droJ>S down about 

500 feet to a second sag in the crest·l*. ·m~. es in Wl.· d·l.t t~ .. This broad sag in the crest, which 1$.eroSSed by~ 

automobile road, .afforded another ·spillway for t~ 

last Cut Bank Glacier, and through. this a ~ongue otf 

ice extended northward a distance of S miles into the 

Milk River Basin, spreading out on the lower ground 

as a lobe over 2 miles in width. This small lobe iS 

designated the Milk River Glacier by Calh~un.65 

East of this second sag a climb of about 350 feet up 

a steep slope reaches the top of the main part of Milk 

River Ridge. From the high west end can be seen 1\n 

extensive and remarkably smooth plateau, sloping 

down toward the northeast. In the first 1% miles 

the surface declines 300 feet; beyond this there 'is a 

fairly uniform slope of nearly 80 feet to the mile for 

5~ miles, the fp,rthest distance to which · the traqt 

wa.S traversed by the writer. Farther east deepening 

ravines cut the plateau into digitate flat-topped ridges, 

consin stage of glaciation, attaining a 

length of i2 miles east of the mountain 

front. A climb of 1,600 feet from the 

valley bottom to the point where Milk 

River Ridge joins the mountain front 

shows that the deposits are much disturbed by landslides, but it looks as if 

the ice emerging from the mountain 

valley extended this high up on the 

slopes. Overtopping the western end of 

Milk River Ridge, the glacier appears to 

have spilled across the crest, extending 

a small lobe about 2 miles northeast-

. . ·. 

.ll'IGURE 1.-View looking eastward from a point about 4 miles north of Duck Lake, . 

Mont. Shows relations of the terminal moraine of the St. Hacy Gia~. ot· tht 

Wisconsin stage of glaciation, to. the north slope of the Hudson Bay divide. on wboe(t. 

top lies pre-Wisconsin glacial drift (in the background and to the right). .From a 

photograph · ' 

ward down the slope on the north. Perhaps this was 

assisted somewhat by ice descending from a big cirque 

in the east slope of the mountain. Two well-formed 

lateral moraines are seen curving northward through 

the east side of a sag in the crest of the ridge. Across 

this sag, on the high flat top, which here stands 6,100 

feet above the sea, it is evident that the last ice just 

overtopped the north slope at the west end of this part 

of the ridge and left there a small marginal ridge of 

drift. This may be traced eastward about three-quarters of a mile on the top of the ridge; it then drops to 

a lower level and lies along the slope 100 feet or so 

below the top. On the high flat part of the top of the 

eminence, beneath and beyond th~ little marginal ridge, 

is a deposit of coarse gravelly drift, yellowed with age, 

. in which no limestone was observed, although a massive bed of limestone is exposed in the mountain slope 

to the west, and derived fragrt:\ents are plentiful in the 

later drift. This deposit does, however, contain stri-· 

ated pebbles. Its character and relations show that it 

and these in turn give place to successively lower sepi. 

rated buttes. 

The drift of the Wisconsin stage extends nearly to 

the top of the head of the high-level plain, reaching 

an· altitude of 5,800 feet and piling up in sharp· knoll$ 

and ridges. This drift, however, overlaps little if .any 

of the upper plain. Eastward from this point t;hemargin of the later drift gradually descends the 

eroded south slope until in about 5 miles it lies .300 

feet or more below the upland at the point. where th~ 

marginal moraine of the valley glacier swings off tothe south across the valley. plain. 

Underlying this extensive high"lavel plainjs a yeLlowish to brownish oxidized gravelly deposit, ·consisting principally of quartzite with much gr~. and retil. 

argillite, diorite, and some limestone. The stones are 

subangular tO' rounded. Numerous boulders 1 to 1% 

feet in diameter are found .2 to a mil~ from the heacil 

611 Calhoun F. H. H., The Montana lobe of the Keewatin ice sheet :. 

U. S. Geol. Survey Prof. Paper GO, p. 20, 1906. · 
38 PHYSIOGRAPHY AND GLACIAL. GEOLOGY O:f EASTERN MONTANA 

of this plain and 8 to 10 miles from the mountains, 

the source of all the material. . That exposed in a 

ravine in the NE.% sec. 12, T. 33 N., R. 13 W., consisted of clay, pebbles, and boulders mixed as in 

glacial till. In the SE. % sec. 12, 100 feet of unassorted material was found, and in the NW. % sec. 6, 

T. 33 .N., R. 12 W., a thickness of 150 feet was observed. Here and elsewhere glaciated pebbles were 

found, though these are nowhere abundant and consist 

mostly of the green quartzitic argilli~. Striated erratics were found in the sides of the valley of Arnold 

Creek as far out on· this plain as the traverse was 

e.xtended. 

DRIFT ON CUT BANK RIDGJC 

Between the South and North Forks of Cut Bank 

Creek is a ridge of Cretaceous shale, whose crest 1 mile 

:from the mountain front is 6,300 feet above the sea. 

An observer standing on this crest looks down 1,000 

feet to the stream on the south and 1,200 feet. to the 

bottom of the valley on the north. Both slopes are 

steep, that on the north being particularly precipitous. 

Shale is exposed within 100 feet of the top near the 

west end of the highest part of the crest. Here there 

is an abrupt drop in the crest line, and from this point 

to the mountain the crest is narrow, lower, and composed of shale. The highest part of the. ridge is 

capped with till and gravelly drift, which is exposed 

at several points in fresh scarps due to landslides. The 

material has the same lithologic composition as that 

on ·Two Medicine Ridge, and many of the green argillite fragments show glacial striations. (See pl. 15 B.) 

This rock is very dense, fine grained, and so difficultly 

soluble as scarcely to be etched at all, even after very 

long exposure to the weather. Some of the limestone 

blocks art3 6 to 8 feet in .length. The top of this ridge 

is broad, smooth, and gently sloping. The north slope 

is heavily timbered, and there has been'much slumping 

of the drift on the underlying shale, so that the upper 

limit reached by the North Fork Glacier during the 

later extension of the ice has not been accurately deter-

. mined. The conditions on the opposite side of the 

valley indicate that the surface of the later ice was at 

. least 200 feet ilelow the top of this ridge. 

Between 4 and 5 miles east of the mountain the crest 

drops 300 or 400 feet to a sag. Th.rough this. sag, 

which is traversed by the automobile road, the ice of 

the North Fork Glacier of the Wisconsin stage appears 

to have extended nearly or quite to contact with that 

of the South Fork Gl~;tcier. Beyond the sag the crest 

rises again .200 to 300 feet, maintains its height for 

about a mile, and once more drops to a much lower 

level, over which the later ice spread morainal deposits. Two miles farther southeast the ridge, here 

consisting of sandstone, rises again above the later 

drift and extends thence eastward with even, flat top. 

for 2 miles, to the point where it is cut by the postglacial gorge of the South Fork of Cut Bank Greek.. 

East of this creek the ridge continues toward Brown .. ing but is still lower and was overridden by the 1~ . 

ice. Both the isolated mesalike parts of the ridge ·are 

capped with coarse gravel, largely quartzite, evidently 

to be correlated with the drift farther .west and on Two 

Medicine Ridge, although here no till and no striated · · 

pebbles were observed. 

DRIF!' ON TWO MJUDIOINm ~m 

Issuing from the mountains about 7 miles northwest 

of Glacier Park station, the Two Medicine River 

swings southeastward and traverses the plain in a 

sharply cut, trenchlike valley. The Lower Two Medicine Lake lies about 600 to · 800 feet below the level 

of the rolling drift.,covered plain on the east. The 

upland north of the railway a:r;td along· and eaSt of 

the automobile road has a well-marked though mildly 

developed sag and swell morainal topography and is 

set with numerous little ponds. This marks the. marginal moraine of the Two Medicine Glacier of the 

Wisconsin stage. (See pis. 1 and 37.) In that part 

where the old automobile road runs eastward for a 

mile or more, near .the margin of this morainal belt, 

in sec. 25, T. 32 N., R. 13 W., and sec. 30, T. 32 N., 

R. 12 W., before dropping down the slope to the north, 

the moraine extends near~y to the highest part of the 

upland, but farther east the margin of the moraine 

is a fairly definite line near the foot of the south slope 

of a long fiat-topped sandstone ridge, p~rt of Two 

Medicine Ridge. · To the east the 'later ice extended 

through the gap in the sandstone ridge which is trav .. 

ersed by the Great Northern Railway and spread 

over the lower land toward Browning. Through a 

length of 3% miles· north and west of the railway the 

ridge was not surmounted by the later ice sheet. 

Above the abrupt slope the top is flat ex~ept where it 

is cut by a ravine that partly divides the ridge. It 

rises gradually westward from 5,300 to 5,700 feet above 

the sea in the part traversed by the· old automobile 

road. This plateau surface, which is a remnant of No . 

1 bench, is beveled across the edges of the Cretaceous 

sandstone, which at one point noted has a dip of 42° 

SW. The only constituents of the later drift not 

found on this part of the higher ridge are limestone 

and a quartzite conglomerate containing pebbles of 

black chert, which occurs principally in the drift some-· 

what farther south and is from ledges exposed in 

Marias (or Roosevelt) Pass and provisionally referred 

by T. W. Stanton to the Lower Cretaceous (Kootenaii 

formation). Fragments of this conglomerate ':tnay not 

have been deposited on this upland tract, and the limestone if deposited may have been removed by solution. 

The material capping the ridge wliere the old automobile road starts down the north slope and also· in 

cuts in the upper part of the slope consists of coarse 
i 

PLEISTOCENE EPOCH 39 

gravel and boulders, with stones ranging in size from 

a fraction of an inch to 3 feet. The stones are mostly 

subangular, being notably less rounded than the 

waterworn gravel on the Cypress Hills and the Flaxville Plain or the high benches along the Yellowstone. 

The constituents are mostly red and green finegrained siliceous argilJite, some white to buff quartz-

. ite and some badly decayed diorite. No limestone 

was found. Search revealed that some of the argillite pebbles are glacially striated. All the· drift exposed her~ has been. considerably weathered. 

For a mile or more northwest of the junction of 

the old automobile road and the old wagon road, 

north of the bench mark 5,649, the moraine of the 

later drift overtops the ridge. Farther west the 

sandstone ridge rises above the later drift plain, increasing rapidly in height, until it stands as a flat~ 

topped mesa with an altitude of 6,200 feet, or nearly 

400 feet above the margin of the later drift and about 

1,350 feet above the lake. Here there is a deposit of 

the same material, and among the pebbles a few of 

limestone were noted. This high tract has a length of 

about half a mile. Beyond this there is a sharp drop 

in the crest of 100 feet or more, and west of the sag 

the crest rises again until the 6,200-foot level is attained. On this top were found coarse gravel and 

boulders of the same character as noted farther east. 

Many of ~he stones, however, are much larger, some 

boulders being 8 feet in length. The deposit seems 

to thicken toward the Two Medicine Valley, and at 

the southwest extremity of the half-mile mesa top a 

scarp, due to slumping of the underlying Cretaceous 

material, exposes 150 feet or more of typical glacial 

till near the new automobile road, which was completed in 1929. (See pl. 16 A.) A large part of the 

deposit is cemented by calcium carbonate to hard· 

tillite. 

road crosses the crest of the ridge. This lower part its . densely timbered and was not examined. From th:iji 

narrowed divide the valley between the high mesa and 

the much higher mountain slope deepens rapidly 

northward to 1~000 feet below the top· of the mesa. 

The composition of the deposits on the several ridges 

described above, their topographic situations relative 

to the mountains, to th~ present drainage lines, and 

to the deposits made by· the glaciers of the Wisconsin 

stage, the modification by weathering, and the cementa .. 

.tion to heavy beds of tillite all indicate that these 

glacial deposits are of early Pleistocene age. 

Two Medicine Ridge is the most southerly of the 

remnants of the high benches bordering the front 

range of the Rocky Mountains on which pre-Wisconsin 

glacial drift has been found. For 30 miles to the southeast no traces of the high benches are found. South 

of Badger Creek there are many remnants of No. 1 

and No.2 benches, as described on pages 15.;...16, but on 

none of these has any evidence· of glacial action been 

found outside of or above the limits of the drift of the 

later mountain glaciers. Either the pre-Wisconsin 

glaciers south of Marias Pass did not extend as far 

beyond the mountain front as the present high bench 

remnants, or the evidence of glaciation has been obliterated by subsequent weathering. The pebbles on these 

high benches consist principally of limestone, and their 

surfaces have been etched and roughened by solution 

and are in large part coated with calcium carbonate. 

The dense greenish and reddish siliceous argillite 

which is so plentiful in the Glacier National Park 

region and which is best adapted of all the rocks com-. 

posing the pebbles or boulders at or near the surface 

to retain glacial striation is relatively scarce on the 

high benches south of the Two Medicine River. The 

relative altitudes and the topographic relations of No. 

1 and No. 2 benches north and south of the Two MediThis stood with nearly vert~cal face and with towers cine River are the same, however, so that it would seem 

25 to 30 feet in height, practically unchanged in the that their. age -relations would also be similar. 

interval between the first examination in 1911 and a The question arises, Was there more than one stage 

reexamination in 1921. Some of the stones are well of mountain glaciation before No. 2 bench was deeply 

· rounded, but a large part of the pebbles and boulders dissected~ Unfortunately, the evidence in hand on 

are suba.ngular, faceted, and distinctly striated. T~e this point is not decisive. The most easterly points 

material is wholly derived from the mountains, being at which striated pebbles have been found in gravel 

ofthe same lithologic character as the gravel f<>und on remnants of No. 1 bench are (1) about 4 miles 

on the ridge farther east. Limestone is rare among east of Duck Lake, in sec. 20, T. 36 N., R. 12 W., from 

the stones scattered over the mesa top and also in the which a narrow strip of this bench persists for nearly 

upper 25 to 30 feet of the 200-foot section. Farther 15 miles farther to the northeast and at its end is 100 

down the slope, however, it becomes more plentiful to ~QO feet above the Milk River; (2) 6 to 7 miles 

and shows less effects of weathering. It is probable northeast of Horse Lake, in sec. 12, T. 35 N., R. 12,W.; 

that the calcareous cement of the tillite was derived and (3) . 8 miles east of Horse Lake, in sec. 33, T. 35 

from solution of the limestone material in the upper N., R. 11 W. These narrow remnants of No. 1 bench 

part of the deposit. This exposure faces the mountain ·are capped by gravel, composed mostly of quartzite 

slope · ~t a distance of over a mile. Between the two a.nd red and green siliceous argillite, with some 

the ridge has been lowered and narrowed by erosion 

1 

diorite, all from the mountains. The· tops and slopes 

and slumping. It is here that the new automobile of the ridges are grassed over, and it is only at in-

... 
40 PHYSIOGRAPHY AND GLACIAL GEOLOGY OF EASTERN MONTANA 

tervals aroul).d the lJlargins of the tops that as much 

as 1 to 3 feet of the gravel, which is probably thin, 

is exposed. The stones range from small pebbles to 

boulders llh feet in length and are partly subangular 

and partly well rounded. Those most commonly 

showing glacial striae are of the dense siliceous 

greenish argillite. (See pl. 15.) Some of those on 

No. 1 bench have been found 20 miles ·east of the 

mountain front. The gravel is not well exposed, and 

it was not determined whether or not there is glacial 

till this far out on No. 1 bench. If the material is 

glaciofluvial (outwash) gravel, the ice may not have 

extended this far east, but the gravel must have been 

deposited before erosion cut down from No. 1 to No. 

2 bench, for No. 1 is 100 feet or more above No. 2 

bench, and where the two are found on the same ridge 

they are generally separated by a short, steep slope. 

Some of the remnants are separated by intervals of 

8 to 12 miles from the tracts that carry the old highlevel glacial till with which they are to be correlated. 

If it is supposed that the first advance of the mountain glaciers did not occur until after erosion had low:.. 

ered the general surface of the plain to the second 

bench level, the only way the striated pebbles could 

reach the outlying remnants of No. 1 bench would 

be for the ice to ha.ve extended eastward onto these 

remnants-that is, 20 miles out from the mountain 

front. If the advance occurred before the dissection 

of No. 1 bench the striated pebbles may have been 

washed out by streams flowing from the melting ice. 

fronts. In that event it is possible that asecond advance of the ice occurred after the dissection of No. 1 

bench and after No. 2 bench had been developed by 

planation over q.reas many miles in extent. 

The best-preserved remnant of No. 2 bench is on 

Milk River Ridge north of Cut Bank Creek. A small 

remnant of No. 1 be~ch at more than 5,900 feet above 

sea level is preserve1 above the abrupt slope on the 

east side of the notc}i crossed by the automobile road. 

This is slightly above the upper limit of the later ice 

that spilled through ~he notch. Within a mile and a 

half the smooth top i of the ridge drops 300 feet and 

then flatte:p.s out as iN o. 2 bench, nearly 4 miles in 

maximum width, anj:l continues more than 12 miles 

to the. northeastwar4, though palmately dissected by 

several sharp. coulees. As shown on Plate 1, there are 

numerous remnants of No. 2 bench in the Blackfeet 

Indian Reservation (Browning and Blackfoot quad;. 

rangles). All of these are adjacent to the headwater 

branches of the Milk River. 

The relations indicate that it was probably not 

until after the melting of the early mountain· glaciers 

from the No. 2 plain that the waters· of upper St. 

Mary, Red Eagle, Boulder, and Kennedy Creek Valleys were diverted toward the north. Before this diversion most if not all of this drainage probably went 

eastward to the Milk River, and it was the work of 

planation along the several branches that cut away all 

but a few narrow interstream remnants of No. 1 bench 

and developed No. 2 bench. 

Glacially striated pebble~ have been found in the 

gravel on all those remnants of No.2 bench which have 

been examined north of the Two Medicine River and 

as far as 20 miles east of the mountain front. (See 

pl. 15 A.) Many of the stones are 10 to 12 inches long, 

and some 1 to 2 feet. No unsorted till was found on 

No. 2 bench. This bench is 200 to 300 feet above the 

headwater branches of the Milk River and 500 to 600 

feet above Greasewood and Cut Bank Creeks. Either 

there was an extension of the mquntain glaciers after 

No. 2 bench was developed or the 'striated pebbles have 

been let down onto it by erosion from No. 1 bench in. 

the process of dissection and planation. 

No. 2 bench is clearly of Pleistocene age, and it includes the remnants of the upper levels of the second 

set of benches farther south and east. So far as 

known, however, none of the gravel on these remnants 1 

south of the Two Medicine River includes glacially 

striated material. 

POSSIBLE PRE-WISCONSIN' GLACIAL DEPOSITS 

CASTLE AND BEARTOOTH MOUNTAINS, MONT. 

Although there are no positive evidences of early 

Pleistocene mountain glaciation south of the Two 

Medicine River known to the writer, there are in a 

f£>w places features which, though requiring further 

investigation,. suggest the extension of the mountain 

ice before the high benches were greatJy dissected. 

One of the most definite of these is near the head of 

the Musselshell River, at the south side of the Castle 

Mountains. Between the Chicago, Milwaukee, St. 

Paul & Pacific Railway west of Lennep and Alabaugh 

Creek on the north is a ridge nearly 6 miles long whose 

top is 200 to 400 feet above the creek. The west end 

of this ridge joins the foot of the mountains near 

Castle, about 6,200 feet above ·sea level. It appears to 

be a remnant of one of the highest benches, such as 

occur farther east in the Musselshell Valley. The top 

of the ridge, which was examined by the writer in 

1922 and 1923, is thickly strewri with a great number 

of glacial boulders, mostly porphyry, which range in 

size from a foot or less to 5 feet in diameter. Weed 66 

described this deposit as glacial drift. He -also described a newer terminal moraine a short distance 

above the town of Castle, which " closes in the upper 

66 Weed, W. H., Geology of the Castle Mountain mining district, · Mont. : U. S. Geol. Survey Bull. 139, pp. 144-145, 1896; U. S. Geol. 

Survey Geol. Atlas, Little Belt Mountains folio (No. 56), pp. 3, 7, 

1899. 
U. S. GEOLOGICAL SURVEY PHOFESSIONAL PAPER 174 PLATE 14 

A . FLAT TOP OF SWIFTCUlUl.ENT RIDGE 

Looking uurthwest. to Yellow Mountain; Chi ef Mo:..~ntah at the rigltl,. 

B. KENNEDY RIDGE, 5 MILES EAST OF CHIEF MOUNTAIN 

l'hot.ograph by Bailey Willis. 

PRE-WJSCONSI DRIFT 01~ ROCKY JVIOU TAIN GLACIERS, GLACIER ATIONAL PARK, MONT., ON REMNANTS 

OF THE FLAXVILLE PLAIN (HIGHEST OR No. 1 BENCH) 
U. S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 174 PLATE 15 

A . ON REMNANTS OF THE HIGHEST (No. 1) BENCH (FLAXVILLE PLAIN) AND LOWE ll (No. 2) BENCH 

1 to 5 from No. l bench ; 6 to 8 from No.2 bench. Locations: 1, Makowan Butte, 5 miles north of international boundary; 2, Kennedy Ridge; 3, ridge between Dry 

Fork and Livermore Creek, 5 miles southeast of Duck Lake; 4, Two Medicine Ridge north of the lower lake; 5, east slope of St. Mary Ridge at head of 

Livermore Creek; 6, ridge 3 miles southeast of Duck Lake; 7, ridge north of Petersen Coulee; 8, Milk River Ridge 1 mile south of Horse Lake. 

B. ON REMNANTS OF THE HIGHEST (No. 1) BENCH 

Locations: 1, Hudson Bay Divide, 3 to 4 miles north of Duck Lake ; 2, ridge 4 miles east of Duck Lake ; 3, ridge 9 miles southeast of Duck Lake; 4, ridge 8 miles east of Horse Lake; 5, Cutbank Ridge. 

GLACIATED PEBBLES FROM PRE-WISCONSIN DRIFT OF ROCKY MOUNTAIN GLACIERS IN SOUTHWESTERN 

ALBERTA AND BLACKFEET INDIA RESERVATION, MONT. 
U. S. GEOLOGICAL SURVEY PROFESSIONAL PAPER li4 PLATE 16 

A. PRE-WISCONSIN GLACIAL DRIFT, LARGELY CEMENTED TO TILLITE 

Exposed at west end of highest (No. l) hc nch , north of Lower Two Medicine Lake, Glacier National Park, Mont, 

B. BOULDERY DEPOSIT ON HIGHEST (No. l) BENCH EAST OF ROSCOE, MONT. 

PRE-WISCONSIN DRIFT OF ROCKY MOUNTAIN GLACIERS 
U. S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 174 PLATE 17 

A. HANGING VALLEY OF WOODBINE CREEK 

High-level glacial till (pre-Wisconsin) at left. (light-colored), 800 t.o 1,300 feet above the river. 

B. NEAR VIEW OF PART OF HIGH-LEVEL TILL SHOWN IN A 

Mountain top shrouded in mist 

STILLWATER CANYON, BEAnTOOTH MOlJNTAINS, MONT. 
U. S. UEOLOllJCAL SV HYEY PROFESSIONAL PAPER 174 PLATE 18 

A. NORTH RIDGE AT EAST FRONT OF MOUNTAINS WEST OF BUFFALO, WYO. 

Probably a remnant. of Lhe Flaxville Plain (No. l bench), capped wiLh a bouldcry deposit, probably pre-Wisconsin glacial drift. 

B. ANCIENT HIGH-LEVEL PLIOCENE OR PLEISTOCENE VALLEY 

View from t.op of North Ridge looking west. In Lhe bottom of the valley is cut Lhe gulch traversed by t he automobile road (in 

middle) and Clear Creek Canyon (aL left.). Subsummit plaLeau aL left and right; central granitic peaks in background. 

BIG HORN MOUNTAINS, WYO. 
U. S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 174 PLATE 19 

A. BOULDERY CREST OF MONCRIEF RIDGE, 13 MILES SOUTH OF SHERIDAN 

Near east front of mountains. Many of Lhe boulders are 5 Lo 15 feet in diameter. 

B. HIGH-LEVEL BOULDER DEPOSIT CAPPING MONCRIEF RIDGE 

Boulders mostly granite and deeply weathered. 

BIG HORN MOUNTAINS, WYO. 
U. S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 174 PLATE 20 

A. GRANITE BOULDER ON TOP OF BALD RIDGE, WEST OF BUFFALO 

Boulder is 20 feet long. 

B. HIGH-LEVEL BOULDER DEPOSIT CAPPING BALD RIDGE 

Near the east front of the mountains. 

BIG HORN MOUNTAINS, WYO. 
U. S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 174 PLATE 21 

I07bo' R. 84W. Pl. 83 W. 50' R. 82 w. 

i 

l5 L~"-\1\i!Wl lii: 

"' 

44'~ 1 o· L ~~~107'1o' t!~~R. as w. ~~~~~~~ ~~ ~~~~~ ~~ ~~~ ~~~~~~~~~~~ ~:c~~ ~~~~~~:;~~~~~~~ ~~~~~~~~~~~~~~~ Base from U.S. Geological Survey maps of 

Cloud Peak and Fort McKinney quadrangles. 

Surveyed in 1897- 1900 TOPOGRAPHIC MAP OF A PART OF THE BIG HORN MOUNTAINS 

WEST OF BUFFALO. WYOMING 

Con.t.ourint.erv81100£eet.. 

Green lines show limots of glaciers of the Wisconsin stage. 

After E. S. Bastin and El iot Blackwelder. 

Purple dashed lines show possible lim its of 

Clear Creek glacier at an early Pleistocene 

stage of glaciation. By Wm . C. Alden. 
U. S. G~ OLOGICAL SURVEY PROFESSIONAL PAPER 174 PLATE 22 

A . No. 2 BENCH 17 MILES NORTHEAST OF MALTA, MONT. 

View near Lovejoy road, on west side of Milk River Valley. Shows Judith River sandstone underlain by Claggett shale and overlain by 10 feet of nonglacial quartzite gravel of No. 2 bench (Pleistocene), 350 to 400 

feet above the river. Upon this gravel is 30 feet of till of the Keewatin ice sheet. 

B. PLEISTOCENE CONGLOMERATE ON CLARK FORK OF THE YELLOWSTONE RIVER 

Capping a remnant of No. 2 bench 200 feet above the river, near the J. F. Allen ranch, 2 miles north of the Montana-Wyoming State line. 
U. S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 174 PLATE 23 

A. No.2 BENCH HEADING AT A GREAT NOTCH IN THE WALL OF UPTURNED PALEOZOIC LIMESTONE 

View south of Beaver Creek. The highest (No. 1) bench, corresponding to the Flaxville Plain, before its destruction headed at the top of the limestone wall, about 300 feet higher than No. 2 bench. 

B. BEAVER CREEK CANYON AS SEEN FROM No. 2 BENCH, 350 TO 400 FEET ABOVE THE PRESENT 

STREAM 

LITTLE ROCI{Y MOUNTAINS, MONT. 
PLEISTOCENE EPOCH 41 

mountain valley," and states that the recent aspect 

of this moraine 

is in marked contrast to the appearance of the adjacent 

boulder moraines previously noted. It fills the drainage valley and marks the front of an area in which the glacial rock 

polishing and other evidences of glaciation are remarkably 

fresh and well preserved. Both the contrast in appearance 

and the relative position of this moraine, with the morainal 

remains· found on the adjacent slopes, show that they are of 

very different age. 

A:fter noting similar relations on Fourmile and Willow Creeks east of White Sulphur Springs, Weed 

states : " These facts clearly indicate two periods of 

glaciation, one of which is much older than the other, 

the later being of much less severity." 

Another deposit of glacial drift which attracted the 

attention of the present writer, because of its anomalous position, was seen in 1921 and again in 1924 near 

the old Wood ranch (or Beartooth ranch) in Stillwater Canyon, in T. 5 S., R. 15 E., 8 miles above the 

Nye Bridge. Just opposite the ranch there is a beautiful waterfall where Woodbine Creek plunges down 

1,000 feet or more in a series of cascades from the 

mouth of a hanging valley that notches the east wall 

of the canyon. (See pl. 17 .A.) Just north of the falls 

and 800 to 1,300 feet above the valley bottom a great 

mass of glacial till several hundred feet in height is 

banked below the lip of the hanging valley. The bare 

gray face of the till surrounded by woods is conspicuous as seen from below. (See pl. 17 B.) Its grayish 

matrix is thickly set with pebbles and boulders as 

much as 5 feet in length, some of them balanced on 

knife-edge ridges of the semi-indurated till. The 

stones are largely coarse-grained granite, mostly gray, 

some pink, together with other igneous rocks~ The 

top of the deposit is about 6,300 feet above sea level 

(barometric), which is not far from the level at which 

No. 1 bench probably reached the mountain front at 

the mouth of the canyon. This unusual occurrence of 

so great a mass of till on a canyon wall and so high 

above its bottom strongly suggests that it may be a 

remnant left by a pre-Wisconsin glacier which extended down the valley and possibly out onto No. 1 

or No. 2 terrace at the mountain front. 

There are some other indications of early glaciation 

faJ;ther southeast near the mountain front. The occur~ 

renee of coarse bouldery material resembling· glacial 

till on the highest bench 3 miles east of Roscoe, at an 

altitude of 5,400 feet, 400 to 500 feet above the adjacent 

creeks, is noted above (p. 26; see also pl. 16 B). 

This deposit is about 8 miles northeast of the mouth 

of the canyon of East Rosebud Creek. At several 

places beside the road between Luther and Red Lodge, 

2 to 4 miles from the mountain front, boulders of granite and limestone 3 to 5 feet long were seen in positions 

·to which they may have been let down by the erosion 

of a high bench on which they had been left by 

glaciers. 

For miles east of the terminal moraine near the 

mouth of Clark Ff)rk Canyon in northern Wyoming 

the broad, flat gravelly terrace north of the· river is 

strewn with granite boulders 1 to 8 feet or more in 

diameter. But for the boulders the gravelly terrace 

might be taken for an outwash plain. It is, however, 

very unusual, so far as the writer's experience goes, to 

find any such number of large boulders so far distant 

from a terminal moraine. That· these boulders may 

have been let down from a higher bench by erosion is 

suggested by the fact that instead of being confined to 

the flat they are also sprinkled over the slope~ of several small hills that rise above the surrounding plain, 

and also by the fact that boulders 5 feet in length. 

were seen on remnants of No. 2 bench 12 miles down 

the valley, at points about 8 miles east of the mountain 

front. These facts give rise to the suggestion that a 

pre-Wisconsin glacier may have occupied the broad 

upper valley of Clark Fork and may have extended 

out beyond the mountain front onto either No. 1 or 

No. 2 bench at a time before the inner box canyon 

described on page 27 was eroded. 

BOULDERY MESAS BORDERING THE BIG HORN MOUNTAINS, WYO. 

Certain high-le~el bouldery deposits bordering the 

east flank of the Big Horn Mountains (pls. 18 and 19) 

which have been described .by Darton were examip.ed 

in 1923 and 1924 by the present writer. Under the 

heading" Tertiary system" Darton 67 gives a deSCription of which the following is a part: 

Among the most conspicuous features on the east slope of 

the mountains are the two high boulder ridges at the mouth 

of Clear Creek Canyon, west of Buffalo, and the similar ridge 

6 miles south of Big Horn. The southern one of the pair 

west of Buffalo is known as Bald Ridge and the northern 

one as North Ridge. Their altitudes are 6,900 and 6,800 feet, 

respectively. The sumn:i1ts are nearly fiat and but slightly 

lower than the limestone front ridge, from which they are 

separated by shallow saddles. The materials of these two 

ridges are granite boulders packed thickly in arkose sand 

and gravel and showing no evidence of stratification. The 

larger ones vary in size from 2 to 6 feet in diameter, but some 

are even larger. Most of them are rounded, and . they have 

the appearance of being the d~lta deposit of a large stream. 

The majority of the rocks are deeply decomposed, and the 

boulders of medium and small size are completely rotted. Apparently there are no limestones or sandstones in the deposits, 

notwithstanding the proximity of ledges of these rocks to the 

west. The thickness was not ascertained satisfactorily, but 

it amounts to several hundred feet. * * * To the north 

small masses occur on many of the divides lying against or 

near the limestone front range, at altitudes of from 6,000 to 

6,500 feet: Two of them are north of French ·and Johnson 

Creeks and three are on divides between branches of Piney 

6'1 Darton, N. H., Geology of the Big Horn Mountains: U. s. Geol. · 

Survey Prof. Paper 51, pp. 68-70, 1906; U. S. · Geol. · Survey Geol~ 

Atlas, Cloud Peak-Fort McKiDnef follo (No. 142), p. '9, 1906. 
42 PHYSIOGRAPHY .AND GL.ACI.AL GEOLOGY OF EASTERN MONTANA 

Creek west of Kearney, being clearly remnants of a deposit 

which at one time extended all along the front range. 

Moncrief Ridge, south of Big Horn, is similar in character 

to Bald and North Ridges. It has an altitude of about 6,300 

feet and a flat top, separated from the adjoining limestone 

ridge by a saddle. It is a conspicuous feature in the view 

south from Sheridan as a high, glistening white terrace ex-

'tending out from. the mountain slope. The deposit consists 

of granite boulders, mostly rotted and mixed with arkose sand 

and pebbles. Some of the finer ·materials are in large lensshaped masses exhibiting cross-bedding. · There are fine exposures on the northwest end of the ridge, of which the 

principal features are shown in Plate 19 of the present paper. 

Many of the boulders are 4 feet in diameter, and some are 

larger. Granite and occasional masses of diabase and quartz 

appear to be the only materials. The thickness is at least 

800 feet, and it may be much more, bllt the contacts are 

covered by talus. * * * 

The age of the high-level boulder deposits is not ascertained. 

The deep decomposition of the boulders on .Bald and North 

Ridges and other outliers shows that the deposits are much 

older than any of the morainal materials of the glaciers, and 

this may indicate either earliest Quaternary or late Tertiary 

age. The boulders show no signs of glaciation, but, owing to 

the decay, striae probably would not be preserved. Evidently 

the deposit or1ginally extended over a wide area east of the 

mountains, as is shown by the widely scattered remnants, 

especially on Kingsbury Ridge, and since their deposition there 

has been extensive erosion to the present low level of the 

plains. Boulders of such large size as those in Bald Ridge 

and the other areas would have required streams of great 

power for their transportation, but it is possible that floe 

ice was a factor in their origin. 

North and Bald Ridges, west of Buffalo, are situated like two remnants of a bisected alluvial fan oppo .. 

site the mouth of a broad high-level valley and 16 to 20 

miles distant from the mountain crest at the head of 

the basin. From the crest of the central granite ridge, 

which ranges in altitude from 10,500 to 12,887 feet, the 

eastern face slopes down in 6 to 10 miles to about 8,000 

feet. Beyond this a rolling granite plateau extends 

eastward 6 or 7 miles to the rim formed by the wornoff edges of the upturned Paleozoic limestones at 7,000 

to 7,600 feet .. The ancient valley of Clear Creek cuts 

across this plateau with a depth of 500 or 600 feet and 

a maximum width of a mile or more. The bottom of 

this high-level valley is represented by the bouldery 

bench at an altitude of 6,800 to 7,000 feet, into which 

is cut the deep gulch now traversed by the BuffaloTensleep automobile road. (See pl. 18 B.) For 4 

miles east of Hunters ranger station Clear Creek follows the course of this ancient valley and has cut its 

new gorge to depths of 200 to 300 feet along the south 

side; then swinging southward it flows around a ridge 

of granite for about 2 miles in a narrow canyon 600 to 

800 feet in depth. Returning to the axial line of the 

old valley, it emerges from the mountains between 

North and Bald Ridges, which rise to heights of 1,000 

to 1,300 feet. The top of Bald Ridge is nearly as high 

as the beveled edges of the upturned Paleozoic rocks 

at the edge of the plateau, and as shown on Plate 21 

(see also topographic maps of Fort McKinney and 

Cloud Peak quadrangles), the tops of Bald and North 

Ridges are several hundred feet higher than the hang· 

ing bottom of the ancient Clear Creek Valley. Th~e 

is no great mountain wall rising ·abrupt and high 

above the tops of North and Bald Ridges. They 

border a worn-down mountain top, yet granitic boulders 5 to 20 feet in diameter characterize the material 

composing these ridges. (See pl. 20.) The coarseness 

of this material in such a position suggests that the 

ridges are composed of glacial drift. The degree of 

decomposition which the granitic material has undergone indicates that the deposit is as old as early 

Pleistocene, if not older. · 

Owing to the sliding and rolling of the material 

down the steep slopes, Darton was unable to determine the actual thickness of the bouldery deposit or 

the altitude of the base on which it lies.· It seems unlikely, however, that the rock on which its rests could 

have been cut down below the grade of the No. 1 

benches at so early a time as Pliocene. 

What appears to be a remnant of No. 1 bencli is the 

flat sloping gravel-covered top of the ridge southeast 

of the Cross H ranch, about 6 miles south of Buffalo. 

The grade of the top of this mesa, if projected northwestward 6 miles with a normal increase in slope to 

about 150 feet to the mile, would pass under Bald 

Ridge at about 6,000 feet above sea level, and a further 

projection at 200 feet to the mile would extend it just 

under the bouldery filling of the bottom of the ancient 

high-level valley of Clear Creek, which forms the 

bench south of the automobile road. If this projected 

gradient is anywhere riear correct, it appears that Bald 

and North Ridges consist of 700 or 800 feet of bouldery 

material piled on the upturned and truncated edges of 

the Triassic ( ~) , Jurassic, and Cretaceous sandstones 

and shales. There is a small remnant of similar 

bouldery material about 100 feet thick on the·crest. of 

Kingsbury Ridge, about 5 miles south of Clear Creek 

and 3 miles from the mountain front, at 6,000 to 6,100 

feet above sea level. No other remnants are preservoo 

so far from the mountain front, 'and thus there is · · 

nothing to show how extensive the thick bouldery deposit originally was. It may be that Bald and North 

Ridges are the dissevered limbs of a great lobate terminal moraine which flanked and encircled the end·of 

a vigorous glacier that early in Plei~ocene time thrust 

its snout from the ancient mountain valley of Clear 

Creek 2 to 3 miles out ·onto the No. 1 pench or piedmont terrace. In this way the material may have been 

piled hundreds of feet higher than the bottom of the 

valley without having any such peripheral extent a.s 

would characterize so thick an alluvial cone. The apex 

of a cone with slopes so ·high, as the crests of these 

ridges at points 2 miles from the mountain front 

would probably have been at least 500 or 600 feet 
PLEISTOCENE EPOCH 43 

higher, or nearly 7,500 feet above sea level. This 

altitude is -nearly as high as the tops of the ridges on 

both sides of the ancient valley, where these crests are 

2 miles apart and 1¥2 miles back from the mountain 

front. If all the factors are taken into consideration 

they do not appear to be favorable for the laying down 

of so thick a deposit of material so coarse by a stream 

on so low a base in front of so worn-down a mountain 

range at a time so recent as that of the completion of 

No. 1 terrace. · 

The writer, is inclined to think that the deposit is 

either much older than the other terraces .under consideration or else is, in part at least, an early Pleistocene glacial deposit. Pre-Wisconsin bouldery drift' 

was mapped by Blackwelder as extending 2 to 3 miles 

beyond the limits of the drift of the Wisconsin stage 

of glaciation on the ridges on both sides of the Middle and North Forks of ·clear Creek-that is, to positions within 6 miles of the points where Bald and 

North Ridges join the mountain front. Although 

. bouldery material was not found on the upper slopes 

and· crests farther east, a . deposit of decomposing 

bouldery material caps the bench that represents the 

bottom of the an(!ient high-level valley. This, like 

the deposit composing Bald and North Ridges, was 

.mapped by· Darton as Tertiary ( ~) , though he recognized the possibility of its being an early glacial de-

, posit. No characteristic glacial striae, polish, or 

facets have been found on the pebbles and boulders, 

but so deeply weathered are the stones that any surficial markings must long ago have disappeared. The 

granites are crumbling or spalling off, and in places 

large feldspar crystals project 1 or 2 inches from the 

matrix before themselves falling out. There is thus 

little chance of ·proving tha.t the deposit is of glacial 

origin.68 · 

Further, as to. the possibilities of Bald and North 

Ridges being early Pleistocene glacial moraines, it 

may be noted that if a glacier of the dimensions of 

that which occupied the North Fork Valley at the 

Wisconsin stage. were projected 10 miles farther east, 

it would almost exactly fit the capacity of the old 

high-level valley of Clear Creek, and Bald and North 

Ridges would flank the outer 2 to 3 miles which projected onto the piedmont terrace beyond the mountain 

front. That there was so long a glacier here in early 

Pleistocene time, when the altitude of the mountains 

was probably about 1,000 feet lower than now, seems 

not at all improbable, in view of the fact that at that 

time the Keewatin ice sheet covered the plains but 300 

miles to the east and extended 250 miles farther south 

88 In 1924 the writer observed on the north slope of Bald Ridge a 

little-weathered 5-foot boulder of fine-grained pink granite having a 

smooth ftat face, which showed crescentic markings resembling chatter 

marks. It is not certain, however, that these marks were really 

produced by glacial action. 

in the Missouri V. alley than it did at the Wisconsin 

stage of glaciation. 

Moncrief Ridge, which is about 18. miles north of 

Clear Creek, is similar in composition to Bald and 

North Ridges. It is also so similar in its topographic 

·relations to the mountain front, to the worn-off mountain top (pl. 18 B), and to the bouldery deposits 

mapped by Blackwelder and Bastin as early glacial 

drift that the same considerations and tentative conclusions apply to it. The ridge wa.s examined by the 

present writer in ·1923 and again in 1924, but the 

glacial deposits on North and South Piney Creeks 

were not visited. The bouldery deposit capping 

Moncrief Ridge appears to overlie the 'upturned and 

beveled strata of the Kingsbury conglomerate member of the Wasatch formation, but the contact is not 

well exposed. It is not improbable that the base of 

the ridge is the No. 1 terrace at 5,500 to 6,000 feet 

above sea ·level and that there is 500 feet or more of 

bouldery material overlying that base. (See pl. 19.) 

The axis of the ridge, which is about 3 miles long, 

projects obliquely from the adjacent mountain front, 

and its narrow crest at 6,400 to 6,500 feet is about 

300 feet below the upturned and worn-off edges of the . 

·Paleozoic limestones and about 300 feet below and 

2 to 3 miles distant from the nearest of the early 

glacial deposits. These deposits lie on a broad high 

bench between the canyons of North and South Piney 

Creeks. If the early Pleistocene glacier extended 9 

miles farther than that of the Wisconsin stage of 

glaciation, its terminus lay against the southwest 

flank of Mo:acrief Ridge. Evidently here also there 

is reasonable ground for regarding the ancient bouldery deposit forming the ridge as closely associated 

with, if not wholly due to, early Pleistocene glaciation, after the development of the No. 1 or .Flaxville 

terraces. The narrow bouldery crest as it now stands 

resembles a glacial moraine. (See pl. 19 .A.) Many 

of the granite boulders range from 5 to 15 feet in 

.diameter. This deposit, together with that of North 

and Bald Ridges, is therefore tentatively correlated 

with the early Pleistocene drift of the mountain 

glaciers on the high. benches in front of Glacier N ational Park. According to Blackwelder,69 "If the 

drift here referred to be all early glacial and not 

partly fluviatile and of uncertain age, South Piney 

Creek has cut its valley 400. to 600 feet in solid rock 

since the early glacial epoch." North Piney Creek, 

after issuing from its mountain gorge, flows eastward 

at the south side of Moncrief Ridge and 1,000 feet 

below the level of its crest. Piney and Clear Creeks 

are tributary to the Powder River. The bouldery deposits comprising Moncrief, Bald, and North Ridges, 

"Blackwelder, Eliot, Geology of the Big Horn Mountains : U. s. 

Geol. Survey Prof. Paper 51, p. 89, 1906. 
44 PHYSIOGRAPHY AND GLACIAL GEOLOGY OF EASTERN MONTANA 

and the ancient valleys opposite whose mouths they 

lie, appear to be distinctly younger than the development of the broad subsumm.it plateau which is overlooked by the high central peaks. 

EARLY AND MIDDLE PLEISTOCENE TERRACES 

NO. 2 BENCH IN MILK-MISSOUBI VALLFJY 

It appears that No. 1 bench in the Blackfeet Indian 

Reservation (Glacier National Park region) had not 

been very deeply dissected before the extension of the 

first of the mountain glaciers onto it. Farther east, 

however, the amount of erosion may have gradually 

increased, so that in the region east of Havre a wellmarked valley was being developed below the level 

of the Flaxville Plain. If the Flaxville Plain is not 

itself of Pleistocene age, it seems probable that Pleistocene time in this region began with the uplift which 

caused the streams to cut below the Flaxville Plainthat is, the Pleistocene began a long time prior to the 

completion of the second set of terraces or No. 2 bench 

by planation and spreading of ·the gravel thereon. 

From the evidence now in hand, it seems necessary to 

regard the second set of terraces as representing ihe 

first of the Pleistocene benches. 

No. 2 bench is represented north of Harlem in the 

Cherry Ridge quadrangle by a broad dissected terrace 

or bench, 10 to 12 miles in width. Before the erosion 

of the sharp branching ravines and coulees which now 

dissect this surface it was a smooth plain sloping 

gently toward the stream. At the moraine now lying 

along the edge of the higher plain in the part where 

Cherrypatch Ridge lowers and flattens out there is an 

altitude of about 3,000 to 3,200 feet. From this altitude the surface descends about 200 feet in the first 

mile and flattens thence southward to a slope of 400 

or 500 fe~t in the next 8 to 10 miles, reaching an altitude of 2,500 to 2,600 feet at the crest of the short, 

abrupt 200-foot slopes and bluffs that now form the 

sides of the inner valley of the Milk River. The 

stream flowing in the broad valley represented by this 

dissected bench must have been at a level now about 

2,500- feet above the sea in the region of Harlemthat is, about 600 feet below the Miocene or. Pliocene 

Flaxville Plain to the north. 

· West of the region of Harlem (west of longitude 

109°) a vast area has been eroded below the level 

of this plain. Only the higher parts, if any, of the 

area are high enough to reach the level of a plain 

projected from the No. 2 benches near the mountains to 

No.2 bench north of Harlem. The present slope along 

such a projected plain is about 10 feet to the mile. It 

may have been about 7 or 8 feet to the mile wh-en 

. graded. No.2 bench has suffered a good deal of modification, due to several stages of erosion, the last in 

Recent time, and to mantling by glacial drift. The 

long, smooth slope of the remnants of this early 

Pleistocene bench is, however, the principal feature·. 

Though· much dissected by erosion, it is fairly well 

defined on the north side of the Milk River Valley, 

where seen by the writer, eastward through PhillipS 

County. 

About 17 miles north-northeast of Malta the roadco Lovejoy climbs to an altitude of 2,570 feet (barometric)-that is, to No.2 bench 350 to 370 feet above 

the valley, bottom. Overlying the sandstone at the top 

of the bluff is 10 feet of stratified gravel, and ab.ove 

this is about 30 feet of glacial till. (See pl. 22.) There 

is in the drift and on its surface an abundance of 

pebbles and boulders of pre-Cambrian granite from 

Canada _and of limestone, but no granite was seen. in 

the gravel. The pebbles of the gravel are smoothly 

waterworn and consist principally of brownish quartzite and reddish and greenish siliceous argillite _like 

pebbles of the Flaxville gravel. The material ranges 

from sand to pebbles 6 inches in diameter, mostly less· 

than 2 inches. Similar gravel-capped remnants of No. 

2 bench are preserved above the north bluff of the Milk · 

River Valley in the area between Little Cottonwood 

and Martin Creeks, in T. 33 N., Rs. 30 and 31 E. 

Collier and Thorn 70 described deposits on one of these 

tracts as follows : 

The best exposures seen are in sec. 23, T. ·33 N., R. 30 E., 

north of Malta, a few miles from Milk River, where about 25 

feet of interstratifted gravel and yellowish silt. c~ps _the edge. 

of the bench at an .altitude of about 2,500 feet a ove the sea, 

or 300 feet above Milk River. The gravel is ce ented, presumably with calcite, forming a conglomerate th t crops out 

in ·the form of a small cliff. Fragments of bone and a single 

tooth were obtained. from the face of the cliff.! Dr. Gidleyidentified the tooth as that of a horse resemblinjg the living 

species and states that it can not be so old as tlhe Flaxville 

fauna. The formation here rests upon the J)ldith River 

formation, but about 5 mile. s east of this locality t't rests upon 

the Claggett shale and consists of about 25 feet f yellowish 

silt containing two beds of gravel, one at its base and another 

15 feet higher. The gravel is comparatively fine, the pebbles 

being less than an inch in diameter. 

The long slope of the early Pleistocene No. 2 bench 

is one of the notable features on most of the roads 

north of the river leading from the undulating higher 

areas down to the crest of the river blufts. It is only 

here and there that the gravel is exposed below the 

drift in the eroded edge of the bench. The bench has 

been so much dissected by southward-flowing ·streams 

that there are few roads traversing. it from east to 

west. From the longitude' of Glasgow eastward in 

Valley and Roosevelt Counties the. No.· 2 bench is well 

rrtarked between the crest of the river blutfs and the 

Flaxville upland plain as far east as Poplar, as 

clearly shown on the topographic maps of the Por-' 

cupine Valley, Cuskers, Hay Creek, Nashua, Frazer, 

10 Collier, A. J., and Thom, W. T., jr., The Flaxville gravel RDd its. 

relation to other terrace gravels of the northern Great Plains: U. s: 

Geol. Survey Prof. Paper 108, p. 182, 1918. _ 
/ 

PLEISTOCENE EPOCH 

Oswego, Wolf Point, Chelsea, and Poplar quad- · 

rangles. Here also it is much dissected by southwardflowing streams. Some of the valleys are 200 to 300 

feet in depth. This second set of terraces embraces 

about all the interstream upland tracts between Porcupine. and Big Muddy Creeks north of the Milk and 

Missouri Valleys and below the edge of the Flaxville 

Plain. The altitude of the Flaxville Plain is about 

2,850 feet on the .west side of Porcupine Creek and 

2,620 feet at its southeast end, in sees. 6 and 7, T. 31 

N., R. 52 E. The lower. edge of the gently sloping 

No.2 bench has an altitude of abont 2,250 feet near 

Nashua and about 2,200 feet near Poplar. 

Until the advance of the first continental ice sheet at 

the Nebraskan stage of glaciation the upper Missouri 

River probably continued flowing northeastward to 

Hudson Bay from the vicinity of Poplar along the 

oldabandoned valley described by Bauer,71 which is 

well shown on the Poplar, Brockton, and Homestead 

topographic maps. There is now a certain amount of 

glacial drift in the bottom and on the sides of this 

valley, but the broad sag nearly 10 miles in width is a 

notable feature as seen from an adjacent ridge. Where 

it is cut across by the present inner valley of the Missouri River the old valley floor "hangs" nearly· 250 

feet above the present flood plain of the river, or about 

2,200 feet above sea level. 

While this valley was being eroded the Poplar 

River, Smoke Creek, Wolf Creek, and Big. Muddy 

Creek and their 'tributaries were busily engaged in dissecting the Flaxville Plain to the north. The Poplar 

River joined the Missouri River at a point about 11 

miles northeast of the village of Poplar, where the 

crest of the ridge east of the present lower course of 

the stream is cut through by a gap about 100 feet in 

depth. A broad winding channel, not now occupied 

by a stream, opens eastward to the old valley flat in 

T. 29 N., R. 52 E. This channel is shown on the 

Poplar top·ograph1c map. Smoke Creek joined the 

main valley about 13 miles farther northeast, in sec. 1, 

T. 30 N., R. 53 E., and Wolf ·creek and Big Muddy 

Creek came in near the site of Homestead. In the 

broad flat east of the latter place is now Medicine Lake 

(about 1,945 feet above sea level) and a broad belt of 

sand dunes. South of the old valley is the upland 

north of Culbertson and Mondak. Quartzite cobblestones are everywhere present on No. 2 bench, mixed 

with glacial drift, but few exposures of undisturbed 

gravel have been noted below the drift. Bauer reports 

the occurrence of 10 feet of quartzite gravel below 42 

feet of glacial till at one point in this old valley near 

Smoke Creek, in T. 30 N., R. 53 E. 

The .bench east of Havre appears to be an old erosion 

· surface rather than one on which there has been any 

n Bau~. C. M., A sketch of the late Tertiary history . of the 

upper Missouri River: Jour. Geology, vol. 23, pp. 52-58, 1915. 

notable deposition of gravel or sand as on the Flaxville Plain. East of the mouth of the Milk River., on 

the south side of the Missouri River, the, surface, is· 

generally much rougher, and No.2 bench is not known 

to be preserved. In many places, however, above the 

tnore recent slopes and bluffs, there are long, smooth 

slopes of the early Pleistocene·topography. 

While No. 2 bench was being developed the Musselshell River probably still flowed northward on .the west 

side of the Larb Hills in what is now the south-north 

middle course of Beaver Creek and joined the Missouri 

River near Bowdoin, in eastern Phillips County. The 

development of No.2 bench in the Musselshell Valley, 

as described below (p. 50), was thus in some measure 

controlled by the level of the stream on No. 2 bench 

east of Malta. 

NO.2 BENOH A.T THE LITTLJll ROOKY A.ND BEABPA.W MOUNTAINS 

There are notable gravel-covered remnants of No. 2 

bench about the Little Rocky Mountains in Blaine and 

Phillips Counties, and their relations are worthy of 

some further discussion. (See pl. 35.) Some of the 

best-p~eserved remnants are crossed by the Malta road 

southeast of Zortman. (See pl. 7 0.) They are several hundred feet lower than No. 1 bench, about whose 

eroded north end the road passes in descending to 

Bear Creek. There are other remnants of this bench 

near Coburn and Middle Buttes, south of Bear Creek, 

and also south of Beaver Creek, in sec. 6, T. 25 N., R. 

26 E. In 1 * miles the remnants south of Beaver Creek 

rise westward from 3,600 feet to· 3,950 feet above sea 

level, where· they head at great notches cut in the lime .. 

stone wall, whence the gravel-depositing streams of 

this stage issued onto No. 2 bench. (See pl. 23 . .A.) 

Several such notches " hang " at this altitude 350 to 

400 feet above the level at which Beaver Creek. now 

issues from its mountain gorge (pl. 23~B) and about 

300 feet below the beveled top of the wall where No. 1 

benchheaded. · 

No. 2 bench is nearly continuous, though dissected 

about the northeast flank of the mountains, from 

Beaver Creek. nearly around to Big Warm Springs. 

This bench also extends eastward in the southern part 

ofT. 26 N., R. 26 E., from sees. 32 to 36 and beyond 

nearly to the Malta road. In sec. 35 it is cut through 

by a broad sag, apparently an 0;utlet for glacial waters 

(p. 99) ; east of this sag it is partly covered by glacial 

drift. Like all the others about the Little Rocky 

Mountains, it is covered with coarse little-worn gravel 

derived from the local rocks; scattered on top of the , 

local gravel but not intermixed with it on this particular bench, and also on the benches near Coburn 

Butte, are foreign quartzite pebbles like tho~ of the 

Flaxville gravel north of Harlem arid also glacial 

boulders of granitic rocks from Canada. The sig-
46 PHYSIOGRAPHY AND GLACIAL GEOLDGY OF EASTERN MONTANA. 

nificance of the presence of these erratics is discussed 

below (p. 81). 

On the east side of Lodgepole Creek and 200 to 

250 feet above it is a narrow strip of No. 2 bench in 

the interval between the main. road about the eroded 

head of No. 1 bench and the great mountain wall of 

limestone on the south. West of. Lodgepole Creek 

there are several large notches in this wall, and in 

· their bottoms are box canyons from which the present 

streams issue. Like those near Beaver Creek and 

similar ones on all sides of the mountains, these 

notches appear to have been cut while No. 1 bench 

was being dissected and No. 2 bench was being 

formed. (See pl. 6 A.) There are two remnants of 

No. 2 bench south of the road from Lodgepole to 

Hays, in T. 26 N., R. 24 E. One of these remnants 

in sees. 1, 2, and 11 stands · 200 feet above the ·east 

bank of Jim Brown Creek. This is dissevered from 

the mountain wall. The other remnant southeast of 

Hays is cut by a notable rounded notch through which 

a road passes. This bench heads at a notch several 

hundred feet below the beveled top of the upturned 

limestone _where No. 1 bench formerly headed. No. 

2 bench is preserved a]ong the west side of the Peoples 

Creek Valley much ·of the distance between Hays and 

the gorge above St. Paul's Mission (pl. 8 A), where 

it is about 100 feet above the valley bottom and 300 

to 400 feet below No. 1 bench on the west. In and 

near the southwestern part of the Fort Bellmap Indian Reservation No. 2 bench spreads far out from 

the west flank of the mountains, and, where not dissected by branching coulees, the flat is almost as 

smooth as a city pavement. The grade decreases from 

200 feet to the mile near' the mountains to 25 feet or 

less to the mile in a distance of 7 or 8 miles. So great 

has been the erosion south of the mountains that there 

is little trace of No.2 bench between Sipary Ann and 

Saddle Buttes. (See pl. 35.) 

Though no fossils have been found in the bench 

gravel and though there is no drift left by mountain 

glaciers on any of these benches, nor indeed any evidence of local glaciation in the Little . Rocky Mountains, yet from the general relations near Glacier 

National Park and throughout the region, as described 

above, it appears that the grading of No. 2 bench may 

be regarded as having taken place in early Pleistocene 

time. With this is to be correlated a certain part of 

the dissection of the mountain mass due to deepening 

of the gorges; the formation of the box canyons came 

later. 

· .Apparently erosion has destroyed nearly or quite all 

remnants of No. 2 bench about the north and west 

flanks of the Bearpa w Mountains which the writer visited. In 1922, however, Reeves mapped several remnants of a second set of benches near the south and 

southeast flanks of these mountains in adjacent parts 

of Blaine and Chouteau Counties, and these may prob• 

ably be correlated with what is regarded as No. 2. 

bench about the Little Rocky Mountains. Those dissected by branches of Black Coulee and Birch Creek 

are much lower than. the nearest· remnants of No. 1 

bench and probably originally extended southward 

nearly to the line of the present Missouri River gorge 

at altitudes of about 3,000 feet, corresponding with 

No. 2 bench of the Judith ·River Basin. The Missouri 

River was at that time flowing northward past the 

west side of the Bearpaw Mountains, 1tnd the drainage 

of the southern &1.opes of these mountains and. of the 

Judith River Basin probably flowed. northwestward 

to the Missouri River in the sag between the smoothly 

sloping benches on the north and south. 

It is probable that most of the extensive high benchlands west and north of the North :Moccasin Mountains between Dog Creek and the Judith River may 

be correlated with No. 2 bench, as also may some of 

those west and north of the Judith Mountains. These 

have not been mapped in detail. On·~ of the benches 

crossed is 200 to 300 feet above Dog Creek and rises 

southward toward the North Moccasin Mountains 

from an altitude of about 3,800 feet (barometric) west ~&~k I 

NO. 2 Bl!lNOH IN PONDERA, Tll1l'ON, LEWIS .AND CLARK, .AND O.ASC.4DJC 

OOUNTIES 

Extensive remnants of a second set of benches were 

n1apped by Stebinger and Goldman between Birch 

Creek on the north and the Sun Riv•3r on the. south. 

One of these on the north side of Dut>uyer Creek is 

crossed by the Park to Park Highway. (See map of 

Heart Butte quadrangle.) This bench emerges from 

beneath the tenninal moraine of the Birch Creek 

Glacier (of the Wisconsin stage) 6 to 7 miles west of 

the village of Dupuyer and siopes th3nce down east-

. ward at a rate decreasing from about 50 f~t to the 

mile to a point about 4 miles southeast of·Valier, beyond .which it has been cut away. In the opposite 

direction, about 12 miles southwest of Dupuyer, the 

grade steepens to 100 feet to the mile and reaches the 

mountain front at a level about 400 feet above that 

at which Birch Creek issues from its mountain gorge 

7 miles to the northwest. The relations of the bench 

to the moraine west of Dupuyer show clearly that it is 

not a glacial outwash terrace but that it is much older 

and was dissected before the Birch Creek Glacier extended onto it (p. 119). . Remnants of this bench 

border Muddy Creek between 9 and 16 miles west 

of Bynum, and Still larger remnants border Willow 

and Deep Creeks between 6 and 25 miles above Choteau. .After running for 7 or 8 miles on the highest 

or No. 1 bench southwest of Choteau the Park to 

Park Highway drops down to two successively lower 

benches before reaching the lowest terrace on the 
PLEISTOCENE EPOCH 47 

Sun River. The Sun River irrigation canal· runs 

along the slope between these two. The lower one 

of the two, or perhaps both taken together, belong to 

the second set of benches. Each of them is about 120 

feet below the next higher one where the road crosses. 

The road cuts expose about 10 feet of coarse gravel, 

largely reddish quartzite, overlying the eroded surface 

of the shale. Numerous boulders 1 to 2 feet in 

· diameter were . seen on these benches; but none are 

clearly striated. Gravel of No. 2 bench caps the 

narrow ridge between the river and Gilman. 

A terrace remnant which bevels the upturned edge 

of the shale north of Gardner's ·ranch at 4,700 to 4,800 

feet above sea level on Elk Creek probably is a part 

of No. 2 bench, and there is also a remnant of what 

appears to be No. 2 bench about 100 feet lower than 

No. 1 bench on the south side of the Flat Creek Valley about 12 miles south of Gilman and 2 to 6 miles 

northeast of Bean Lake in T. 18 N ., R. 6 W. This 

may have been formed by the Dearborn River when 

it followed the course of Flat Creek, before the mountain glacier diverted it to its present channel. 

No. 2 bench is well preserved for part of the distance between Gilman and Great Falls on the north 

side of the Sun River. North of Gilman it is 200 to 

400 feet above the river. North of Fort Shaw it is 

about 200 feet above the river, or 3,700 to 3,800 feet 

above sea level, and several hundred feet below No. 

1 bench. Here it is crossed by the Chicago, Milwaukee, St. Paul & Pacific Railway, and on it is the 

village of Ashuelot. An extensive remnant of No. 

2 bench is 300 to 400 feet above the Sun River on the 

south side of the valley between Dry and Simms 

Creeks. At least the higher part of the "Sun River 

Bench " on the ·south side of the stream and east of 

Fort Shaw Butte appears to belong to this early 

Pleistocene stage. 

As in the vicinity of Glacier National Park, so 

throughout this region the relations of the . glacial 

moraines to the upper level of the second set of benches/ 

show clearly that the .latter were developed and in 

turn eroded b~fore the Wisconsin stage of glaciation. 

(See p. 118.) In most places the mountain glaciers of 

the Wisconsin stage were barely able to surniount the 

steep and high marginal slopes of outlying remnants 

of the upper No. 2 _bench and override their tops. 

This is particularly well shown west of Augusta, where 

the terminal moraine marking the southern limit of 

the Sun River Glacier loops back to the west several 

miles before it overtops the eroded west end of a high 

remnant of No. 2 bench at 4,700 feet above sea level, 

in sec. 17, T. 20 N., R. 7 W. (See pl. 1.) 

' OABLOW FLAT, GLACIER COUNTY 

It was quite inevitable that, as this study of the 

several cycles of erosion and· consequent terraces was 

extended farther and ·farther over-the plains, it would 

be necessary to make some changes in the grouping of " 

the dissevered remnants from those presented in· the 

preliminary paper.12 One of the most important is 

the interpretation to be placed on the terrace known 

as Carlow Flat, between Cut Bank and Browning, in 

the Blackfeet Indian Reservation, Glacier ·County. 

This was at first regarded as one of the typical remnants of a third set of benches. · 

Further studies, however, in the region farther 

south and especially about the Wind River Mountains, 

Wyo., make it fairly certain that it is with Carlow 

Flat that the terrace north o Dupuyer is to be ·correlated rather than with t e higher drift-covered 

benches of the Blackfeet Rese vation. (See pis. 1 and 

37.) Carlow Flat is now re rded by the writer as 

representing the completion o the main early Pleistocene stage of downcutting an planation and as a correlative of the lower level of t e second set of terraces 

on the Yellowstone (described below, pp. 53, 57) and 

of the Circle terrace· of the Wind River Basin in 

Wyoming. The relations of the terminal moraine of 

Two Medicine Glacier to Carlow Flat .seem clearly to 

support this belief and will therefore be presented 

somewhat in detail. Reference to page 119 shows 

how closely similar are the relations of the terminal 

moraines to Carlow Flat and to the second bench 

north ·of Dupuyer. 

For about 8 miles between Opal and Carlow, west 

of Cut Bank, Carlow Flat is traversed by the Great 

Northern Railway. From a dissected margin west 

of the gorge of Cut Bank Creek, at 3,840 to 3,880 feet 

above sea level, the smooth flat surface rises gradually 

in ~ west-soutl;twesterly direction to about 4,130 feet 

in 13 miles, an average of 22.3 feet to the mile .. At 

4,130 feet, in T. 33 N., R. 8 W., the flat is crossed by 

the terminal moraine of the Two Medicine Glacier. of 

the Wisconsin stage. The relations of the moraine to 

the gently sloping, gravel-covered plain in this place 

correspond to those of a m~raine bordered by an out.: 

wash plain. That Carlow Flat is not primarily due 

to outwash from the Two Medicine Glacier, however, 

i~ unmistakably shown by the relations at the north 

and south. Carlow· Flat is 3 to 5 miles in width from 

north to south and is cut off from other smaller remnants of the sam~ bench on the north and south by 

two broad channels more than a mile in width and 

100 feet or more in depth. The one on the north is 

traversed by the Great Northern Railway between 

Carlow and Bombay; the one on the south (known 

as Flat Coulee) is traversed by the Two Medicine 

Canal, and in part of its bottom Spring Creek has 

cut a channel. The significant fact· is that the terminal moraine of the Two. Medicine Glacier extends 

u Alden, W. C., Physiographic development of the northern Great 

Plains: Geol. Soc. America Bull., vot 35, pp. 414-415, 1924. 
-48 PHYSIOGRAPHY AND GLACIAL GEOLOGY OF EASTERN MONTANA 

westward down and along the eroded side of the 

coulee north of Carlow Flat, near Bombay, and on the 

south it extends down the north side of Flat Coulee, 

across its bottom for 1lh miles and up the 200-foot 

slope on the south. This shows clearly that not only 

did Carlow Flat exist before the Wisconsin stage. of 

glaciation but also that the two broad coulees had 

been cut into it to a depth of 100 or more feet before 

the Two Medicine Glacier formed its terminal 

moraine. 

Flat Coulee is a curious remnant of a former and 

higher channel of Two Medicine Creek. The drainage 

through it was probably changed several times. The 

highest floor of the coulee is cut off by the present 

valley between half a mile and 1lh miles east of the 

Park to Park Highway. It is, indeed, a beheaded 

hanging valley whose bottom is the broad sag about 

200 feet above Two Medicine Creek, or 4,180 feet above 

sea level, at the top of the cliff of Horsethief sandstone. 

The irrigation canal now runs along the base of this 

cliff and out onto a similar but narrower and lower 

floor of Flat Coulee at an altitude of 3,980 feet, 3 miles 

farther northeast. The canal extends thence northeastward through the moraine and along the lowering · 

side slope of the coulee until it reaches and crosses 

Carlow Flat. The high sag at the top of the sandstone 

cliff noted above evidently was the channel of the 

stream when Carlow Flat was formed. The main floor 

of Flat Coulee marks a l~ter stage when the stream 

had cut below the flat. At this later stage Cut Bank 

Creek was confluent with Two Medicine Creek at a 

point about 8 or 9 miles above their present junction. 

Still later, in interglacial time, Two Medicine Creek 

was diverted to approximately its present course along 

what before was the lower part of Badger Creek 

Valley. The bench known as Hagan Flat, north of the 

mouth of Badger Creek, probably represents an intermediate stage of down cutting ·by. Badger Creek. 

It appears, if the present correlation of Carlow 

Flat is accepted, that between the development of the 

higher drift-covered terraces near the mountains and 

that of this flat there occurred a cycle during which 

valleys were deepened 500 feet or more as the result 

of- a notable regional ;uplift that followed Pliocene 

tjme. 

It is probable that Greasewood Flat, the gently 

sloping gravel plain between Cut Bank and Grease~ 

wood Creeks, 4 to 6 miles north of Browning, in 

'I'. 33 N., R. 11 W., however, is either part of No. 3 

bench (p. 59) or an outwash plain of the Cut Bank 

Glacier. The terminal moraine of this glacier is 

traceable continuously in a broad sweeping curve 

across this flat for more than 4 miles in T. 33 N., 

R. 12 W., about 4 miles west of the Browning-Babb 

road. At the moraine border in the Cut Bank Valley this flat is 500 feet or more below the upper No. 2 

' Lench on Milk River Ridge, to the. north, and nea-r 

the Glacier National ~ark automobile road it must 

have been nearly as low as the present valley bottomthat is, 800 or 900 feet below No.1 bench, to the north, 

on which is the old glacial drift. 

Relations along the Milk River seem to indfc~te 

-that the lower level of the set of terraces that is now 

sharply trenched by the gorge of the North Fo~k to 

depths of 200 to 300 feet in the Blackfeet Indian 

Reservation headed in the broad sag in which Duck: 

Lake lies, at 5,011- feet above sea le-veL This sag is 

4 to 5 miles in width, and its botto-m is 300 feet or 

more below the top of the Hudson Bay divide, to the· 

north, on which is the old glacial drift on No. 1 bench. 

This sag is directly opposite the Swiftcurrent -and 

Boulder Creek Valleys, and. the probabilities are that 

before the St. Mary River headed south of the international boundary the waters from Swiftcurrent, 

Boulder, Red Eagle, and upper St. Mary Valleys, 

flowing at levels 500 feet or more above their present 

beds, joined and flowed eastward through the Duck 

Lake sag to the North Fork of the Milk River. At 

the same time Kennedy Creek probably flowed eastward through the Spider Lake gap, now traversed by 

the irrigation. canal. 

Where crossed by the writer in 1920 in southern 

Alberta, in T. 1 N., R. 22 W., what appears to be the 

low level of the second bench is represented by a wellntarked terrace about 4,100 feet above sea level, or 100 

feet above the North Fork of the Milk River. The 

terrace is capped with coarse cobblestone gravel, including many quartzite boulders 1 to 2 feet in diameter. In 132 miles of its course north of the international boundary (not including meanders) the present 

valley bottom has an average grade of about 11 feet 

to the mile, and the slope of what appears to be this 

lower branch is about 10 feet to the mile. In the 12 

miles between the point where the international boundary was crossed by the writer and the point upstream· 

where the North Fork crosses it the grade of the river 

is about 15.5 feet to the mile, and that of the terrace 

is about 17 feet to the mile. 

A chain of lakes north of Kremlin and _1 to 3 miles 

west of the Milk River probably marks the line_ of a 

preglacial channel of this stream when it cut below No. 

2 bench. 

It appears that while flowing on the upper level of 

the second set of terraces, the Missouri River cut a 

notch at the north end of the ·Belt- Mountains above 

Cascade and above the mouth of Little PriCkly Pear 

Creek. The stream is now flowing at a level300 to 400 

feet lower. The flat gravel-capped top of a small triangular butte between the mouth of Little Prickly 

Pear Creek and the village of Wolf Creek probably 

represents the second . set of benches. This is about 

3,900 feet (barometric) above sea level and is 400 feet 
PLEISTOCENE EPOCH 

or more above the Missouri River at the mouth of 

Little Prickly Pear Creek. It seems probable also that 

the broad gravelly plains constituting the higher parts 

of the floors of the adjacent intermontane basins 

northeast, north, and northwest of Helena at 4,000 to 

4,400 feet above sea level represent this same stage of 

terrace formation. The north end of this plain near 

Canyon Creek is 400 to 1,100 feet below the high 

bouldery bench (Gravel Range) in .the angle between 

Little Prickly Pear and Canyon Creeks, which is regarded ·as a remnant of No. 1 bench (p. 17). With No. 

2 bench also are probably to be correlated the higher 

of the gravelly benches that bevel the faulted and upturned Tertiary lake beds in the Missouri Valley 

below Toston.18 

So great has been the amount of erosion subsequent 

to the deposition of the gravel that there are few 

gravel-capped remnants of the second set of benches 

in the region of Great Falls between the Missouri 

River and the Little Belt and Highwood 1vlountains 

on the south and east. One tract that may represent this horizon is the gravel-covered flat on which 

stands the village of Wayne, in T. 19 N., R. 6 E. This 

flat is crossed by the Custer Battlefield Highway 15 

to 20 miles southeast of Great Falls. It·is 3,850 feet 

above sea level, or 300 to 380 feet (barometric) abovE. 

Belt Creek on the west. A pit near its western edge 

from which road gravel was taken in 1921 exposed 

. 8 feet of coarse gravel, partly cemented to conglomerate by calcium carbonate. Most of the pebbles are 

6 inches or less in diam.eter, bqt many are 1 foot or 

more. Glacial boulders of gran~te, brought here from 

Canada by the great ice sheet, are strewn on the surface, but no foreign material is intermingled with the 

gravel, which was deriv•~d by streams from the Little 

Belt Mountains, to the south . .!. narrow strip of this 

bench extends northward between Belt Creek and Red 

Coulee into sees. 2 and 11, T. 2~ N., R. 6 E., where it 

is crossed by the main :road fr<i>m Great Falls to the 

Highwood Mountains. Here there is 20 feet of coarse 

gravel which is about 400 feet ~hove Belt Creek and 

nearly that much lower than ~he remnant of No. ·1 

bench east of the valley. Thi~ No. 2 bench is probably, in part at le~st, the prodact of Belt Creek at a 

time before it had even cut its preglacial channel past 

Waltham (fig. 9) which is now followed by the Chicago, Milwaukee, St. Paul & facific Railway for a 

few miles northward. 

The altitude (3,800 feet) of o~e small gravel-capped 

butte shown on Fisher's map 14 on the south side of the 

Missouri River within the bend about 6 miles east of 

Ulm seems to indicate that it i$ a remnant of the old 

u Pardee, J. T., Geolojp' and ground-water resources of Townsend 

Valley, Mont.: U. S. Geol. Survey Water-Supply Paper 539, pp. 6-8, 

pl. 1, A, 1925. i 

'"Fisher, C. A., Geology of the Great :Falls coal field, Mont. : U. S. 

Geol. Survey BulL 356, pl. 1, 1909. 

valley bottom at th~s same stage. · It is now 400 feet 

above the river. There may also be some remnantS o:f, 

this terrace farther i south on both sides of the Smith 

River. None were :Q.oted, however, by the writer in the 

course of a trip acr~ss this area in 1922 .. 

In the region of Preat Falls the lower level of the 

second set of bencl¢s may be represented by the terrace north of the river, at 3,550 :feet above sea level, 

onto which formerly ran the old line of the Montana 

Central Railway. 1The plain that is now traversed 

for some distance ®rtheast of the Boston & Montana 

smelter by the road. to Fort Benton is eroded somewhat below the original flat top. , North of this bench 

is an irregular bluff of dark Colorado shale, which 

rises abruptly about 200 feet to a higher, gently undulating plain, the F\>rt Benton Bench.15 This higher 

bench, on which is the Benton Lake Reservoir, is either 

No. 2 bench or an :intermediate plain resulting from 

degradation of No~ 1 bench. 

East of Black Butte and the Great Northern Railway the terraces ~re obscured by erosion and by a 

mantle of glacial :drift. To the south and west a 

gravelly bench exttnds to the crest of the bluffs bordering the Sun Riter and Muddy Creek Valleys, except where it is dissected by sharp branching coulees~ 

In 1920 gravel, consisting principally of smoothly 

rounded quartz, qljlartzite, and argillite pebbles 2 to 

3 inches in diamete~, was being taken for road material 

for the Custer Battlefield Highway from excavations 

in the lower edge o:f this bench, at the top of the lower 

150 to 200 foot bluff on the north side of the Sun 

River Valley betw~en Great Falls and Manchester. 

This terrace is also represented by the " Ulm 

Bench" 76 or "Suh River Bench" 17 west of Great 

Falls, between the; converging valleys of the Missouri 

and Sun Rivers. The soil on this terrace is sandy, but 

gravel is exposed t~Jt some points along the road south~ 

west to Ulm. 'W~st of this is a broad sag beyond 

which the surface ~ises to the upper No.2 bench, northeast of Square Butfe. When flowing on- the lower level 

of the second ter:r~aces the Sun .and Missouri Rivers 

were probably shi,'fting to and fro on a broad plain 

extending eastward over the present site of the city of 

Great Falls and to the south and east. The Missouri 

River had not begun to cut the buried valley south 

and east of Great! Falls, much less its present gorge 

north of the city. : · 

Doubtless the ~econd set is represented ' in the 

benches about the llighwoo·d Mountains, but no careful 

examination of th!ese benches was made. One No. 2 

tract is probably the nearly flat, gently sloping area 

'115 Fisher, C. A., Geology and water resources of the Great Falls 

region, Mont. : U. S. $eol. Survey Water-Supply Paper 221, . pl. I~ 

1909. 

76 Fisher, C. A., Geoiogy and water resources of the Great Falls 

region, Mont.: U. S. $eol. Survey Water-SuppJ.y Paper 221, pl. 1, 

1909. 

'1'1' U. S. Bur. Recl~tion map of Sun River project, No. 16306.,. 

.. 
50. PHYSIOGRAPHY AND GLACIAL GEOLOGY OF EASTERN MONTANA 

southeast of the village of Highwood, between the 

cre8t of the south bluff of the Shonkin Sag and the 

mountains to the south. · · 

There are narrow remnants of two terraces in the 

valley of Highwood Creek down to a point a few miles 

above the Chicago, Milwaukee, St. Paul & Pacific Railway crossing. Below this point the gorge is narrow, 

and the relations are somewhat obscured by glacial 

drift. 

NO. 2 BENCH IN THE JUDITH BIVll1 BASIN 

In the Judith River Basin remna.nts of No.2 bench 

covering many square miles are pr~served. Two of 

the largest and least dissected of these areas lie on 

both sides of Cottonwood Creek between Lewistown 

and the Judith River. ·(See pl. 11 B.) So flat ·and 

smooth are the surfaces of these gr~at alluvial fans 

that one riding across them from nqrth to south, to-

. ward the Big Snowy Mountains, where they head, 

scarcely realizes that he is going uphill. As shown 

by Calvert's contour map,78 the grade increases gradually from 50 feet to the mile west o~ the South Moccasin Mountains to about 130 feet to the mile where 

the present streams emerge from the gorges cut in the 

upturned edges of the rock in the foothills bordering 

the mountain slope. At 6 or 7 miles southeast of 

Moore the bench reaches an altitude of 4,700 feet. 

The slope down to the north from. this altitude is 

1,000 feet in 19 miles. On these benches, which are 

mostly under cultivation, are scattered cobblestones 

and a few boulders, 1 to 3 feet in diameter, which 

have been gathered from the fields and laid along the 

fence lines. The thin loamy clay soil is everywhere 

underlain by a deposit of coarse gravel. This is not 

generally reached by plowing in the field but is exposed beneath the top soil in shallow road cuts and 

gullies, and in some places excavations show as much 

as 30 feet of the gravel. 

Calvert 79 describes this terrace gravel as follows: 

The materiai is gravel, sometimes rather loosely consolidated, with sand filling the interstitial spaces, but more often 

it is united :firmly by calcareous cement. The lithology of the 

pebbles indicates their source. in the western area they are 

composed almost entirely of limestones and occasionally quartzites, which have no doubt been derived from the Madison and 

underlying formations, for many of the calcareous pebbles 

contain Mississippian fossils. Near the Snowy Mountains the 

gravel is likewise composed chiefly of limestone pebbles, but 

sandstone pebbles are also present. Farther out on the plains 

the percentage of sandstone decreases, probably because it is 

less resistant than limestone. The size of the pebbles also 

var es inversely with the distance from their source .. Near 

the mountains many of the pebbles are of cobblestone dimensio s, but they gradually decrease in size as the distance from 

the mountains increases. The gravel adjacent to the Judith 

'11 alvert, w. R., Geology of the Lewistown coal field, Mont. : U. S. 

Geol Survey Bull. 390, pl. 1, 1909. 

711 dem, p. 41. 

and Moccasin Mountains is composed largely of ceystalllne 

pebbles which have been derived from the rock& compOS!Q.g 

the mountain groups. 

The altitude in sec. 1, T. 16 N., R. 16 E., in the 

northern part of the area mapped by Calvert, is 3,700: 

feet. An average slope of 17.5 feet to .the inile 

through the intervening 40 miles northward to the 

Missouri River would reach the upland along the 

gorge at 3,000 feet.. · 

GRADIENTS ON BRANCHES OF THE UPP'ii'IB MISSOUBI RIVER 

On the basis of the present altitudes, with no allowance for any subsequent differential movement, an 

average fall of about 12 feet to the mile on a projection 

of No. 2 bench for about 76 miles along the line of the 

preglacial course of the Judith River would join the 

Missouri River at 2,775 feet near the big bend east of 

Virgelle (pl. 1), and an average fall of 12lk feet to the 

mile along the Missouri River ·for 7 5 miles northeastward from No. 2 bench at about 3,700 feet, near Great 

Falls would connect with the Judith River at the same ' point. From this point an average fall of 5.5 feet to 

the mile for 34 miles f.!.long the present course of Sandy 

Creek would reach 2,590 feet south of Havre. Thence 

~astward 225 miles to the vicinity of Poplar the fall 

on No. 2 bench is about 1.75 feet. An average grade 

of about 14 feet to the mile from No. 2 bench west of 

Dupuyer, in sec. 1, T. 28 N., R. 8 W., projected to and 

along the course of Marias River to the sout~ward 

bend 24 miles southeast of Chester, at the east line of 

T. 29 N., R. 8 E., and thence somewhat north of east 

across the Lonesome and Boxelder quadrangles (between 2,800 and 3,000 feet above sea. level) would join 

the preglacial Missouri River in the Sandy Creek Valley near Boxelder at 2,650 feet. 

NO. 2 BENCH IN MUSSELSHELL V.ALLJDY 

Calvert 80 mapped extensive gravel-covered benches 

sloping eastward toward the lower Musselshell River 

from the east side of the Judith Mountains. 

In 1921 C. E. Dobbin 81 found a gravel terrace bordering the east side of the· Musselshell River ~elow 

Mecaha, in T. 19 N., R. 30 E., at · about. 2;400 feet 

above sea level. This is probably the same as the wellmarked terrace that borders the west side of this 

stream from Boxelder Creek northward for some distance to and beyond Mosby. Where examined by the 

present writer the surface of the latter bench is 

sprinkled with glacial boulders of red and gray 

granite. The surface at 2,800 to 2,900 feet above sea 

level or 300 to 400 feet above the river at Mosby, 

is u~derlain by 5 to 8 feet of gravel with 8ome sand, 

partly cemented to conglomerate. The smoothly 

so 1 dem. pl. 1. 

tl1 Personal communication. 
PLEISTOCENE EPOCH . 51 

rounded pebbles range in size from a fraction of an 

inch to 4 inches and consist mostly of gray limestone, 

red and yellow quartzite, porphyry, and fine-grained 

igneous rocks such as are found in the gravel on the 

benches west of Roundup, but with no intermingled 

granite pebbles like those in the glacial drift. 

The height of these terraces is such that if proje~ted 

northward to Bowdoin at a grade of 2% feet to the 

mile it would overtop whatever filling of glacial drift 

there is between the present mouth of the Musselshell 

River and Beaver Creek in southeastern Phillips 

County, and would connect with the supposed rem-

!lant of No. 2 bench north of the_ Larb Hills at about 

the same distance the present valley drops about 1,660 

feet, or nearly 12 feet to the mile. Fro,m the vicinity 

of the river west of R{)undup the grade of the bench 

increases northwestward from 30 to 100 feet or more 

to the mile toward the mountains. 

Extensive tracts of No. 2 bench occur south of the 

Musselshell. Those bordering Lebo Creek and American Fork were· crossed by the writer on the main 

road south from Harlowton to Melville~ The erosional surface beneath the gravel bevels ·the formations upturned in the Shawmut anticline. 

NO. 2 BENCH ON THE YELLOWSTONE. BIVEB AND ITS T.B.IBUTABIES 

2,250 feet above sea level. Mosby is about as far as Finely preserved remnants of No.2 bench are found 

Ha re from the supposed junction of the preglacial at the east front of the Crazy Mountains, some of 

Mu lshell and preglacial Missouri near Bowdoin- them cultivated and under irrigation. These border 

tha is, about 100 miles-and the bench ip. question has the middle courses of Otter, Big Timber, Swamp, ~nd. 

ab t the same altitude at these two places. There . Little Timber Creeks. These smooth, flat benches 

see s, therefore, nothing to conflict with the idea that slope southeastward with grades. of 100 to 200 feet to 

the Musselshell River continued flowing to the Mis- the mile, and their loamy soil is underlain by coarse 

sou i River, which was occupying its preglacial chan- gravel derived from the mountains. The streams. have 

nel in the Milk Riyer Valley, north of the Larb Hills, cut flat-bottomed ·valleys with steep bordering bluffs 

un il after No. 2 bench had been formed. If there is to depths of 200 to 300 feet below the smooth sloping 

no any considerable depth of glacial drift along this surfaces of the benches. 

co rse northward between the present mouth of the There are also numerous gravel-capped remnants 

M sselshell River and the Beaver Creek Valley, it of No.2 bench in the Shields River Valley which head 

wo ld seem that the river continued to follow this at the west and southwest flanks of the Crazy Mounco rse also while cutting below No.2 bench. tains. One of the most extensive of ~hese is north of 

ost of the smooth flat gravelly benches described Pine Creek and 200 to 500 feet or more .above that 

ab ve (p. 23) as mapped by Bowen and by Reeves stream. This heads at one side of the mouth of the 

in he Musselshell Basin north and west ·of Roundup canyon at an altitude of about 6,400 feet, slopes thence 

ap ar to belong to the second set. The distribution southwestward at a ·rate decreasing from about 200 

of relatively small remnants of No. 1 bench well out feet to 100 feet to the mile, and terminates at the top 

fr m the mountain fronts and in places nearly to the of the eroded bluff north of Clyde Park. North of 

bo ders of the inner valley of the Musselshell River Wilsall, the terminus of the railway branch in 1922, 

sh ws that No. 1 bench was developed over most, if there are remnants of No. 2 bench above the blufts 

no all, of that part of the basin west of Roundup. both east and west of the bottom lands bordering the 

B ween these higher remnants and bordering the river. Most of these bench lands are under cultivato s of the side slopes of the inner valleys are the · . tion, and some of them are irrigated, as are also the. 

N . 2 benches, in places several miles in width. They lower lands. 

be el the rocks at levels 100 to 200 feet or more lower Insufficient study of the Yellowstone Valley between 

th n No. 1 bench and are themselves covered with Livingston and Gardiner has yet been made to be 

co rse gravel beneath a thin loamy soil. The rela- certain concerning the development of terraces in this 

ti ns show clearly that the Musselshell River and part of the valley. A brief examination northwest 

ea h of its tributaries deepened its valley as the result of Daileys on Big Creek revealed a broa~ high-level 

of some definite change, such as a regional elevation bench or ancient valley bottom at about 6,300 feet 

or a lowering of the channel of its master stream, the above sea level, into which the stream has later cut its 

ssouri River1 and either contemporaneously or im- inner gorge to a deptp. of 400 feet or more. · (See pl. 

m diately thereafter . the process ·of planation devel- 24 A.) . It seems probable that there must have_ been 

o d smooth flat valley plains miles in width. No. 2 a definite terrace or bench in the Yellowstone Valley 

be ch near the Harlowton Cemetery has an altitude corresponding with so well-marked a feature on this 

of about 4,300 feet (barometric). . The grade from tributary, and that this represents the second stage, of 

t · s locality to the bench west of Mosby at 2,800 feet valley development and terrace formation. Although 

( arometric) is thus about 1,500 feet in 140 miles, or the granitic boulders 1 to 20 feet in d!ame~r which 

at an average rate of nearly 11 feet to the mile. In lie on the bench and on the slopes' for several hundred 
52 PHYSIOGRAPHY AND GLACIAL GEOLOGY OF EASTERN 'MONTANA 

feet above the bench were probably brought to their 

resting places from the other side of the Yellowstone 

Valley by ice of the Wisconsin glacial stage, yet it is 

possible, in view of the evidence found in the Glacier 

National Park region, that they were in reality transported by an earlier glacier before the streams had cut 

below No. 2 bench. In the lower course of Big Creek, 

however, some distance below the Gallatin National 

Forest boundary, a great mass of glacial drift extends 

down into the inner gorge like a later moraine, so that 

the road has to climb up over it. 

On the northeast side of the. valley opposite Gardiner is an extensive bench or terrace at 5,800 to· 6,000 

feet above sea level. This is about 600 feet above th£-

terrace on which the upper part of Gardiner is built 

and 700 or 800 feet above the river. It is capped with 

basalt overlying the· upturned and beveled edges of 

Paleozoic and Cretaceous formations. Overlying the 

basalt in part is a deposit of travertine. The surface 

of the bench near the road is hummocky like a moraine 

and is abundantly sprinkled with granitic boulders 1 

to 15 feet in diameter. To the north long, smooth, 

grassy slopes on the granitic rocks bordering Eagle 

Creek extend gradually down to this bench as to the 

bottom of an old valley. Bear Gulch deeply transects 

the bench. Ii is probable that the erosional surface 

beneath the basalt represents the bottom of the valley 

at the stage of No. 2 bench. On this valley bottom 

basalt was poured out in early Pleistocene time, and 

subsequently the valley was glaciated. The lower end 

of the third canyon of the Yellowstone is cut in granitic rock 800 feet or more deep below the upper end 

of this bench. 

South of Big Timber No. 2 bench is well marked 

along the Yellowstone and Boulder River Valleys. 

The smoothly sloping gravel-strewn bench is 250 to 

300 feet above the Boulder River and about the same 

distance below the highest bench to the ·south. With 

jt is probably to be correlated one of the sets of benches 

farther upstream above and below Livingston,82 as 

are also several tracts bordering Upper Deer and 

Lower Deer Creeks in Sweet Grass County southeast 

of Big. Timber. Farther east down the Yellowstone 

the inner valley narrows, and planation at this horizon 

is not so well marked on the sandstone and shale of 

the Fort Union formation; at least, no remnants of 

No.2 bench have yet been noted here. Between Merrill (Springtime post office) and the mouth of the 

Stillwater River near Columbus there is a well-marked 

dissected bench extending back a mile or more from 

the top of the steep 350 to 400 foot bluff of sandstone 

and shale of the Lance formation. This corresponds 

with the flat bench above the bluff at the south end 

112 Calvert, W. · R., The Livingston and Trail Creek coal fields, Park, 

Gallatin, and Sweet Grass Counties, Mont.: U. S. Geol. Survey Bull. 

471, pl. 29, 1912. ' 

of the bridge at Columbus, at an altitude of 3,950 to 

4,000 feet. (See Stillwater topographic map,· on _ 

which what is now Columbus is shown as "Stillwater.") From this· bench long smoothly rounded .... 

slopes rise to higher levels south of the river. These 

represent the worn-down mature topography of the 

upland that bordered the valley when the stream was 

flowing on No. 2 bench. These slopes -and ·th-e bench 

are now dissected by sharply· cut valleys of later stages 

of erosion. The bench south of the Columbus bridge 

is 350 to 400 feet above the river and is capped with 

smoothly rounded coarse gravel, with some cobblestones 1 foot in length. The material is partly red-. 

dish quartzite and largely granite, diorite, porphyry, 

and various other crystalline rocks; no limestone pebbles were seen. Apparently the gravel at this place 

came very largely from the Beartooth Mountains at 

the head of the Still water River ·and its tributaries, 

inasmuch as the constituent material is mostly different from that in the lower terrace on the north side of 

the Yellowstone west of Columbus. 

For 6 to 8 miles west of Absarokee on the south side 

of the Stillwater Valley there are remnants of No. 2 

bench. One of these is nearly 300 feet above the 

stream. It is covered with coarse waterworn gmvel 

ranging from fine material to stones 1 foot _in c:liameter and consisting mostly of granite and other crystalline rocks. 

No careful examination was made of the upland· 

near the Stillwater River farther east. Bordering the 

tributaries of the stream, however, from Absarokee 

southwestward to the Beartooth Mountains, is a very 

fine development of the second set of terraces. These 

tracts -comprise a large part of the "terrace gravel" 

are'}S mapped by Calvert.83 The flat, smooth, gently 

sloping surfaces extend for miles at . the top of the 

steep sides of the valleys, 200 to 400 feet above the 

present streams. The bench on the east side of East 

. Rosebud Creek, though very narrow in places, is con-

. tinuous for nearly 12 miles in Ts. 5 and 6 S., R. 18 E., 

and in this distance declines northward from an altitude of 6,100 feet near the mountains to 4,800 feet. 

From a slope of more than 200 feet to the mile near 

the mountain front the grade decreases in 12 miles to 

less than 100 feet to the mile. , (See pl. 47.) 

No. 2 bench is very well developed a1ong the east 

side of Rock Creek near and north of Red Lodge just 

outside the area mapped by Calvert. There are some 

small remnants in the lower part of the canyon, and 

at the canyon mouth No. 2 bench extends across the 

beveled edge of the upturned Paleozoic limestone 

(pl. 13 B), about 300 feet above the valley bottom. 

About a mile farther north a steep slope rises 250 feet 

liS Calvert, W. R., Geology of the Upper Stillwater Basin, Stillwater 

and Carbon Counties, Mont. : U. S. Geol. Survey Bull. 641, pl. 21, 

1917. 
PLEISTOCENE EPOOB 

from No. 2 bench at an altitude of 5,900 feet to No. 

l bench, which continues north past Red Lodge (el. 

13 A), where No.2 bench again.appears. In 14 miles 

it declines nearly 1,300 feet, from 5,900 to 4,660 feet 

(barometric) east of Robetts. This bench has a width 

of less than a mile, and east of it, where not cut by 

the sharp erosion of later stages, smoothly worn slopes 

rise to adjacent higher lands. Northeast of Roberts 

only small remnants of this bench are preserved at 

intervals. The main bench on the west side of Rock 

Creek has an initial height south of Red Lodge nearly 

the same as No.2 bench on the east side of the valley. 

It declines northward more rapidly, however, and at 

Roberts is 50 to 60 feet lower than No. 2 bench on the 

east side of the valley. This finely developed and 

irrigated bench, 1 to 2 miles in width, mapped by Calvert on the west side of Rock Creek ·Valley near and 

north of Red Lodge, thus appears to represent No. 2 

bench as finally left by the stream when it cut down to 

its present level. This relation has some significance 

when an attempt is made to correlate the benches along 

the Yellowstone below the mouth of Clark Fork. 

The higher of the small bench remnants on Rock 

Creek near Boyd and Joliet and the terrace about 100 

feet above the railroad at Silesia may represent the 

upper level of No. 2 bench. It should be noted that 

there are in many places certain intermediate benches, . 

-so that it is not everywhere clear just· which ones represent the main stages. · This is perhaps not a very 

serious. matter, however, if the fact of such interme-

(Jiate stages is clearly recognized. 

Remnants. of No. 2 bench were examined on both 

sides of the valley of Clark Fork of the Yellowstone 

.River north and east of Fromberg, where they are 

.about 200 feet above the bottom land. The coarse 

gravel here contains boulders 1 to 1% feet in diameter 

.and consists mostly of crystallin~ rock with a few or 

no limestone or quartzite pebbles. Near the cemetery 

.south of Belfry a remnant of the bench is about 3,850 

feet above 'sea level. Just east of the bridge at J .. F. 

..Ala en's ranch, which is 2 miles north of the Montanaw:yoming line;· a remnant is about 220 feet above the 

:st~eam, or 3,900 feet (barometric) above sea level-a 

ri$ of nearly 300 feet in about 30 miles upstream. At 

this place there are some stones 1 by 2 by 3 feet in 

.size. The pebbles are mostly 1 to 4 inches in diameter 

.and smoothly rounded; they are chiefly of crystalline 

rock, with little or no quartzite, agate, or silicified 

·wood. There are considerable amounts of limestone 

pebbles, and solution and redeposition of calcium carbonate from these has cemented the gravel to a con-

_glomerate, which projects as a ledge 20 :feet thick . 

. (See pl. 22 B.) Many of the crystalline pebbles are 

-di~integrating. There also appear to be other more 

-extensive remnants of this No. 2 bench between the 

-valley and the mountain. front 9 or 10 miles to the 

west. About 3·miles south of the Sta.te'line there are 

three small remnants at about 4,800 feet above sea 

level. At this place, which is 8 or 10 miles from the 

nearest point of the mountains to the west and 12 or 

13 miles downstream from the mouth· o-f the Cla.:rk 

Fork Canyon, most of the pebbles are 2 to 4 inches 

in diameter, but there are many boulders 1 to 2 feet 

in diameter and some 3 to 6 feet. (See pl. 5 B.) 

The average gradient as projected. from these 

gravel-capped buttes to a similar one at an altitude 

of about 4,950 feet (barometric) about 6 miles farther 

west is about 100 feet to the mile. The latter, a 

remnant of No. 2 bench, forms the :flat top of a mesa 

300 feet high, about 3 miles north of Clark post office, 

Wyo. A normal increase in gradient westward to 

200 feet to the mile across the intervening 5 miles 

would clear the tops of most, if not all, of the foothills and would extend this bench to the mountain 

front at about 6,000 feet. A continuation· of the grade 

of 100 feet to the mile along the river from the three 

remnants of No. 2 bench up the valley and into the 

canyon would extend this terrace to the lower part 

of the broad bench above the walls of the inner box 

canyon near the trail 6 miles above the canyon mouth 

(pis. 13 0 and 25 .A.),· at about 6,300 feet. It seems 

probable, therefore, that by the time No.2 bench was 

completed the cutting of the inner box· cany-on had 

not progressed to any great depth -nor more than 5 

miles up the canyon from the mountain front. 

The broad lower gravel terrace that spreads out 

in the angle between the converging Clark Fork .and 

the Yellowstone is below the upper level of No. 2 

set and corresponds with the 'lower terrace as developed on the west side of Rock Creek at and below Red 

Lodge. At first sight it may seem that this must be 

a distinctly later terrace, and, indeed, it may· be. As 

indicated below, however (p. 56), the~ are remnants 

of two rather closely associated terraces on the Y ellowstone east of Billings which are not readily differentiated as marking two distinct stages o:f regional 

uplift. There are also indications that for some distance east and west of Billings, where the Yellowstone· 

crosses the Pryor Mo1,1ntain anticline; the stream has 

not cut so far below No. 2 bench as farther east and 

west. With the lower terrace in the angle betweenClark Fork and Yellowstone_ River at 3,350 to 3,380 

feet (barometric) is correlated the broad gravel terrace north and east of Laurel. This is continuous 

northeastward down the north side of the valley 

nearly to Billings. 

Both levels of tlie. second set are crossed in numerous places belo\v Forsyth by the Yellowstone 

Trail. Possibly a fuinor ·uplift interrupted development or No. 2 bench, or it may be that this ·break 

marks the time when the Missouri River was diverted 

from Hudson Bay to the Mississippi Basin and began 
54 PHYSIOGRAPHY AND GLACIAL GEOLOGY OF EASTERN MONTANA 

the cutting of its new gorge through the Dakotas. In 

relocating across the dissected plain outside the border of the Keewatin ice sheet the stream would first 

cut through the crests of the divides and perhaps 

lower its bed rather rapidly. As the transected 

divides broadened at lower levels the rate of downcutting would become slower, and as the stream approached grade it would tend to broaden the valley 

bottom and develop a new flood plain. 

This part of the bench is irrigated and mostly 

under intensive cultivation. At Billings the terrace 

has been cut away. Passing the east end of the great 

sandstone bluff, the Yellowstone Trail runs up onto 

this bench north of the Fair Grounds at 3,200 feet 

(barometric) and continues thereon 100 feet or more 

above the river to the _bridge north of Huntley. The 

terrace extends north to Shepherd and thence northeastward 6 or 8 miles or more before it is cut away 

by the river's swinging to the north side of the valley. 

Much of this part of the terrace also is irrigated, and 

near Billings there are many truck farms upon it. 

Gravel, which underlies the loamy soil; is excavated 

in· several pits near the Fair Grounds and is exposed 

along the eroded margin and in the sides of coulees. 

· There are traces of this terrace along the south side of 

the valley from Huntley eastward.8 ' East of Ballantine the terrace broadens below the High Line Canal, 

from which it is irrigated, and for 3 or 4 miles it is 

traversed by the Chicago, Burlington & Quincy Railroad. From the foot of the bluff below this terrace 

the Jower irrigated valley flat slopes gently northward 

2 to 4 miles to the river. Pompeys Pillar (pl. 26 A) 

is a bit of the sandstone ledge underlying No. 2 bench 

which was left when the river cut down to its present 

bed. North of Anita station the terrace is nearly 2 

miles wide. Corresponding narrow benches border 

the Fly Creek Valley for several miles southward. 

This stream has cut 100 to 150 feet below the terrace. 

From the . village of Pompeys Pillar eastward to 

Custer No. 2 bench is narrow on the south side of the 

valley and much dissected by streams from the south. 

· It appears to be better preserved on the north side of 

the valley, but the writer has seen that part only from 

a distance. East of Custer the· Yellowstone Valley is 

abruptly constricted by a ledge of Lance sandstone, 

and upon this No. 2 bench extends nearly 2 ·miles 

northward directly across the valley to the river bank, 

at an· altitude of 2,850 feet (barometric), 150 feet or 

more above the water. This terrace was mapped by 

Rogers.811 The Yellowstone Trail crosses the river 

northeast of Custer and runs .eastward a short distance below the picturesque sandstone bluff shown in 

* Hancock, E. T., Geology and oil and gas prospects of the Huntley 

field, Mont.: U. S. Geol. Survey Bull. 711, pl. 14, 1920. 

• Rogers, G. S., Geology and coal resources of the area southwest 

of Custer, Yellowstone and Blg Horn Counties, Mont.: U. S. GeoL 

Surver Bull. 641, ·pl. 28, 1912. 

Plate 26 B, thence up onto No. 2 bench, 125 feet above 

t~ river. Here and also south of the stream above 

the railway tunnel there are two different levels to the 

bench. From 10 to 15 feet of coarse gravel is.exposed 

in cuts near the ·top of tlfe bluff. The pebbles are '---

smoothly waterworn and range from a fraction of an · 

inch to 8 inches in diameter. Besides plentiful red 

and yellow quartzite pebbles there is a great variety 

of granitic, porphyritic, and other crystalline rocks 

derived from the mountains to the south and west. 

Few, if any, pebbles of limestone are present. 

East of Custer the Yellowstone River is joined hy 

the Big Horn River, and at Hardin, about 30 miles 

to the south, the Big Horn is joined by the Little 

Horn, which heads in the Big Horn. Mountains near 

the Wyoming-Montana State line. The Big Horn 

River cuts through the. north end of the Big Horn 

Mountains in a deep, narrow canyon. It emerges 

from between the walls of upturned Pennsylvania 

limestone at the mountain front, about 85 miles southwest of Hardin, onto a broad alluvial flat which ranges 

from 2 to 4 miles in width and which is· mostly irrigated and under cultivation. Northward to a point 

about 7 miles above Hardin the river flows mostly at 

the west side of this flat at the foot of an abrupt line 

of bluffs, 100 feet or more in height. From the crest 

of these bluffs a broad flat terrace, No. 2 bench, extends westward to the eroded slopes of the bordering 

uplands. (See Thorn's description, pp. 27-28.) The 

main terrace is considerably eroded for about 6 miles 

below the canyon. Fro:rq this point, where it has an 

altitude of 8,250 feet, northward to Hardin, it is well 

preserved, except for transacting coulees. It is 500 feet 

or more below the remnants of No. 1 bench to the west. 

Gravel underlying the soil on No.2 bench was examined by the writer near the bridge and irrigation da-m 

·south of Two Leggip. Creek. The well-rounded pebbles are largely dense crystalline rocks, with some limestone, pink, yellow, and red quartzites, like those of 

the Belt series, and. yellow chert. There' is not the 

· great variety of porphyritic rocks such as are found 

in bench gravel along the Yellowstone. A lower 

gravel terrace (No.3) is present below the mouth of 

the canyon, ·and here there is an abundance of limestone pebbles and boulders. West of Hardin, No. 2 

bench where crossed by the Custer Battlefield Highway is more than 3 miles wide and carries fine farms. 

About 7 miles above Hardin the river swings across 

to the east side of the flat and leaves the broad lower 

plain on the west side of the river. In this part the 

surface drops 50 to 100 feet from No. 2 bench to the 

lower plain by an abrupt marginal slope. 

East of Hardin the site of old Fort Ouster is on a 

remnant of No. 2 bench which occupies the angle 

between the converging Big Horn and Little Horn 

Rivers. The bench here is 200feet above the level of 
PLE~STOOENE EPOCH 55 

their conflu~nce at the top of nearly vertic~! bluffs. . 

Southward from this locality to and beyond the vicinity of Custer Battlefield the Little Horn is bordered 

on the west by a narrow s~rip of the same terrace. 

Where examined by the writer the gravel on this terrace is mostly limestone, with fewer pebbles .of granite 

and porphyry than on the terrace along the Big Horn 

and so far as noted none of Belt ( ~) quartzite. 

Remnants of two levels of No. 2 bench, capped with 

limestone gravel, were noted nearly as far south. as 

Wyola, 250 to 450 feet above the stream. (See also 

pp. 27-28.) North of the yicinity of Hardin there 

appear to be remnants of No. 2 bench on both sides 

of the river, but these are narrow and much dissected. 

North of the sharp bend 16 miles below Hardin the 

road to Custer in places runs up onto No.2 bench, and 

east of this place the Big Horn terrace merges with 

that on the Yellowstone. In 56 miles below the canyon this No. 2 bench in the Big Horn Valley descends 

400 feet, from 3,250 to 2,850 feet above sea level, or at 

an average rate of about 7 feet to the mile. 

The quartzite pebbles and a large part, at least, of 

those of crystalline rocks were brought through the 

Big Horn Canyon at either this or an earlier stage 

from formations in or west of the Big Horn Basin and 

did not come from the Pryor or Big Horn Mountains. 

TERRACES EAST OF THE BIG HORN MOUNTAINS 

Darton and Fisher 86 mapped and described extensive gravel-covered terraces bordering the east side of 

the Big Horn Mountains, Wyo., and on a later map 

Ta:ff 81 showed these terraces as extending eastward to 

Goose and Little Goose Creeks riorth and south of 

Sheridan. Some of these were also examined in a 

brief reconnaissance by the present writer in ·1923. 

In character and topographic relations they are so 

similar to terraces of the Big Horn Basin and the 

Yellowstone and its tributaries in Montana th-at there 

can be no doubt that they have a corresponding history. The terraces west of Parkman are on tributaries of the Little Horn River. Those farther south 

in Sheridan County border the Tongue River and its 

tributaries. But little of the valley 9f the Tongue 

River in Montana has been examined by the writer. 

The best preserved of these terraces between the mountains and Sheridan comprise. extensive smooth, flat 

benches 50 to 100 feet above the rather broad, flat bot-

. tom lands along the several streams. These terraces 

appear to correspond· to the lower level of the second 

set of terraces of the region. On this set of terraces 

are Fort Mackenzie, the fair grounds west of Sheri-

• Darton, N. H., and Salisbury, R. D., U. S. Geol. Survey Geol. 

Atlas, Bald Mountatn-Dayton folio. (No. 141), 1906; Cloud PeakFort McKinney folio (No. 142), 1906. 

• Taff, J. A., The Sheridan coal field, Wyoming: U. S. Geol. Survey 

Bull. 341, pl. 8, 1909. 

dan, and the cemetery southwest of. Sheridan. From 

these localities the terrace is preserved almost continuously up the streams to the foot slopes of the 

mountains, 4,500 feet or more above sea level. Near 

the mountains th& terraces of this set rise· to or merge 

with. the head of a higher but less extensively preserved set of benches or mesas, which appear to rep-

.resent the upper level of the No. 2 terraces as elsewhere found. This relation is illustrated between 

Wolf and Goose· Creeks west of Beckton, where the 

narrow upper flat overlooks the more extensive lower 

one on the north from heights of 100'to several hundred feet. These benches appear to be remnants 

of what must originally have -been continuous or 

11early coalescent alluvial fans forming a smooth sloping piedmont plain. The remnants are now 400 to 500 

feet above the present streams and they appear to be 

preserved only within 4 or 5 miles of the mountain 

front. They truncate the upturned edges of the red 

beds and head at or near the foot of the great sloping 

limestone wall at altitudes ranging from 5,000 to 5,500 

feet. 

Taff's map does not show any remnants of these 

No.· 2 terraces east of Sheridan. From Moncrief 

Ridge northward, probably none of the drainage from 

the mountains at these stages went farther east than 

Prairiedog, McCormick, or Goose Creeks before being 

diverted to the TQngue River. A large part of the 

lower No. 2 benches, some of. the upper level, part of 

the gentler slopes below, and the bottom lands are 

under irrigation and carry fine farlns. 

None of the mountain glaciers approached within 5 . 

or 6 miles of the canyon mouths at the Wisconsin 

stage, so that the relation of the glacial waters to the 

lower of these terraces is not clearly indicated. It is 

probable, however, that the streams had already cut 

below the lower No. 2 terraces and were flowing on 

the bottom lands when the Wisconsin stage began. 

A few remnants such as the gravel-capped top of 

the Beaver Creek Hills, 7 or 8 miles southwest of 

Sheridan, and the narrow spur extending north from 

the foot of Moncrief Ridge may represent a still higher plain intermediate between the No. 2 set and the 

plain of the top of the latter ridge. 

From Piney Creek, near the Sheridan-Johnson 

County line, in T. 53 N., southward, the drainage from 

the mountains flows in a general northeasterly direction to the Powder River, and numerous remnants of 

the gravel-covered terraces and benches are preserved 

between them, as shown on Darton and Fisher's map 

of the Fort McKinney quadrangle. Most of these 

appear to belong to either the upper or the lower 

level· of the No. 2 set. Their character and relations 

are much the same as in the Sheridan and Dayton 

quadrangles to the north. 
56 PHYSIOGRAPHY AND GLACIAL GEOLOGY OF EASTERN MONTANA 

The following description is given by Gale and 

Wegemann: 88 

Skirting the foothills of the ;Big Horn Mountains and extending down the valleys of the principal streams that head 

within the mountains is a series of remarkably well-developed 

gravel-covered terraces. Some of them form broad alluvial 

· plains for a distance of 5 to 10 miles from the mountains, but 

beyond these plains they are con:fin~d to the larger stream 

valleys, which they follow for great distances. In some places 

four or five of these· gravel-covered terraces may be observed 

from one point, rising one above another. The slope of their 

surfaces away from the mountains is usually pronounced. The 

gravel cap is composed of rounded stream material which 

varies in size from small pebbles to fair-sized boulders and 

whose constituents represent most of the igneous and sedimentary rocks exposed in the mountains near by, from which 

they were probably derived. 

The mantle of sand and gravel on these surfaces is not 

heavy, a fair estimate being perhaps 5 to 10 feet on the stream 

terraces. Nearer the mountains the gravel is thicker, but probably its thickness does not exceed 40 or 50 feet in most places. 

On the surface the gravel has been concentrated by subaerial 

erosion into a layer 6 to 10 inches thick, forming a protecting 

cap to the terrace which tends to check its further degradation. This feature is well represented along Crazy Woman 

Creek near Trabing, where the gravel terraces form a line of. 

low hills along the stream valley, the country back of them, 

which is covered by a thinner mantle of gravel, having been 

reduced to a somewhat lower level. Unmistakable glacial 

polishing was observed on boulders included in som'e .of these 

deposits. One locality in which the glacial pebbles were found 

is on a broad terrace 1 mile north of Buffalo, in the SW. :!A, 

sec. 23, T. 51 N., R. 82 W. 

The higher gravel-capped mesas southeast of the 

Cross H ranch, which is 6 miles south. of Buffalo, 

appear to be remnants of a terrace higher than the 

upper No. 2 level. The terraces along the Powder 

River between those of the Fort McKinney quadrangle and the great terrace on the lower course of the 

stream south of Terry, Mont., have not yet been 

mapped. 

NO. 2 TERRACE ON· THE LOWER YELLOWSTON£ 

There is some uncertainty about the correlation of 

the remnants of No. 1 and No. 2 benches between the 

mouth of the Big Horn River and Miles City. The 

relatively low height of the representatives of No. 2 

bench above the Big Horn River and the Yellowstone 

west of Custer introduces some confusion, but they 

seem to have been-continuous with the prominent bench 

near the Powder River south of Terry, which, in turn, 

appears to be correlative with No.2 bench in the region 

of Glendive. Without attempting to clear up the matter finally with the data now in hand, the description 

may proceed with what seem to be remnants of two 

levels of the second set of terraces. 

Bench No. 2 appears to be nearly continuous east 

of. Custer at the top of the bluff north of the river 

1111 Gale, H. S., and Wegemann, C. H., The Buffalo coal field, Wyoming : U. S. Geol. Survey Bull. 381, p. 138, 19101 

most o£ the distance from the point where the Yellowstone Trail runs down off the bluff eastward to the 

Chicago, Milwa1;1kee, St. Paul & Pacific Railway· in 

Rosebud County, but it has been examined by the 

writer at only one or two places. South of the river 

it is represented in places by two distinct levels. Near 

Myers the bluff capped with Lance sandstone rises to 

a still higher bench (No. 1 ( ~) ) . About 6 miles west 

of Forsyth· the sandstone of the Lance formation 

comes down lower into the bluffs, and, owing to its 

somewhat more resistant character than that of the 

underlying shale,· the inner valley gradually narrows 

again to a width of about a mile at Forsyth. . 

From the mouth of the Big Horn River eastward 

for some distance the river has cut to increasingly 

greater -depths below No.2 bench. South of Forsyth 

the gravel caps the sandstone blu:ff at an altitude of 

2,775 feet (barometric), 250 feet above the Northern 

Pacific Railway (pl. 27 A) or nearly 300 feet abo~e 

the river, and on the north side of the.valley it occurs 

on two somewhat lower levels, 2,730 and 2,660 feet 

. (barometric) at the top of the bluff near the Chicago, 

Milwaukee, St. Paul & Pacific Railway station. Many 

of the pebbles here are 8 to 10 inches in maximum 

diameter and there are some stones 1 to 2 feet long. 

About 3 'miles east of Forsyth the Yellowstone Trail 

on the south side of the valley runs up the blu:ff to a, 

very extensive flat bench (pl. 27 B) on which are 

many farms. This is continuous eastward to Rosebud 

Creek at 2 600 to 2,700 feet above sea level, or 200 feet 

above the 'river. The Yellowstone Trail descends to 

cross Rosebud Creek but climbs again to the ·bench 

east of the village of Rosebud. All along here the 

two levels of No. 2 bench are well developed. From 

the bench east of Sweeney Creek the Yellowstone Trail 

runs down to the railway and follows this to Clermont 

siding. From this point eastward the road runs up 

onto and down off the bench repeatedly. Here and 

there are lower remnants, probably of No. 3 bench. 

The gravel is well exp<?sed in the Northern Pacific 

Railway gr·avel pit on ~his bench south of Hor~on, 

at 2,650 feet (barometric) above sea level. The Sides 

of the pit show at the top 1 to 3 feet_ of clay ~oil, 

dark above and whitish gray below, ow1ng to caliche 

concentration of calcium carbonate. Below the clay 

is about 30 feet of interbedded gravel and sand. The 

pebbles are smoothly rounded and· mostly less than 1 

inch in diameter, but a considerable percentage range 

from 1 to 3 inches, and some are 6 to 8 inches. They 

consist of vein quartz, brownish quartzite, reddish 

siliceous argillite (like the Belt rocks) , jasper, chalcedony, pink and gray granite, and. various porphyritic igneous rocks. Occasionally pebbles -of c~alced· 

onized wood are found, and one pebble contamed a 

silicified cup coral. The distribution of the Pleisto-
U. S . GEOLOGICAL SU Hv~ y l'HOFESSIQNA L l'Al'~H 174 PLATE 24 

A. VIEW UP BIG CREEK 8 MILES WEST OF EMIGRANT PEAK 

Showing the broad upper valley, probably equivalent to the No. 2 bench (early Pleistocene) , in the bottom of which is cut a gorge several hundred feet deep. 

B. VIEW SOUTHI•;AST ACROSS YELLOWSTONE VALLEY TO EMIGRANT PEAK 

Showing Lhe broad basalL-<.:apped bench. This is thinly covered with glacial d rifl, and below, al While Cliffs, is exposed 80 feel of gravel unconformably overlying tilted. aud eroded cream-colored Tertiary clay (Bozeman " lake heds ''). 

YELLOWSTONE RIVER ABOVE LIVINGSTON, MONT. 
U. S. GEOLOGICAL SURVEY 

A . INNEI\'•DOX .CANYON OF CLARK FORK OF THE YEL-

·;; LOWSTONE RIVER, WYO. 

Cut in Pleistocene lime about 1,300 feet into granite aod gneiss below the upper waJl of Paleozoic rocks. 

PROFESSIONAL PAPER 174 PLATE 25 

B. LAMINATED CLAYS OF GLACIAL LAKE CUT BANK, 

GLACIER COUNTY, MONT. 

Photograph by Eugene Stebinger. 
U. S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 174 PLATE 26 

A . POMPEYS PILLAR, 30 MILES NORTH(,;A.ST OF BILLI NGS 

An erosion remnant of Lance sandstone in the valley. On the opposite side toward the river, Capl. \Villinm Clark, of tho Lewis and Clark expedition, cut his name and the da te, July 25, 1806. 

B. BLUFF OF LANCE SANDSTONE EAST OF CUSTER 

Capped with quartzite stream gravel of the second terrace (No. 2 bench). The face of t he cliff shows the effects of differential weathering of the friahl e sandstone. 

YELLOWSTONE RIVER, MONT. 
U. S. GEQJ, QGICAL SURVE Y PROFESSIONAL PAPER 174 PLATE 27 

A. HLUFV SOUTH OF FORSYTH 

This bluff of Lauce sandstone and shale is cupped with quartzite river gravel of the second terrace (No. 2 bench), 250 to 300 feeL above Lhe river. 

B. SMOOTH, FLAT SURFACE OF THE GRAVELLY SECOND TEIU1ACE (No. 2 BENCH) 3 TO 10 MILES 

EAST Ol" FOHSYTH 

Traversed by the Yellowstone Tra il ; 200 fee t or more above the river. 

YE LLOWSTONE lUVER, MONT. 
PLBISTOOENE EPOOR 57 

cene terraces ~cross Rosebud County, as shown on 

Plate 1, is taken in part from Renick.89 

At Miles City the terrace on the northwest side of 

the river is about 250 feet ·above the stream, or 2,600 

feet (barometric) above sea level. The gravel here is 

. generally covered by clay soil so that it does not usually show in the plowed fields, but it is exposed at the 

top of the bluff near the bridge. Near and east of 

Miles City the Yellowstone Trail closely follows the 

Northern Pacific Railway on the valley bottom. East 

of Tusler it climbs 275 feet to a gravel bench at 2,620 

feet, which must belong to the second ~t, and then 

drops to a broad, somewhat lower terrace at 2,570 

feet. The road leaves this terrace near Shirley and 

continues thence northeastward beyond Blatchford on 

the broad valley flat. At 300 feet above this flat on 

the southeast is a broad gravel-covered bench (No.2), 

which extends northeastward nearly or quite to the 

Powder River. So far as could be seen from a distance there are no remnants of this bench on the 

opposite side of the valley between Sunday Creek near 

Miles City and Terry. 

The Powder River, which joins the Yellowstone 

from the south at a point 8 miles above Terry, is 

bordered by a finely preserved terrace several miles in 

width. The inner bluff ~f the Yellowstone Valley 

cuts directly across this terrace south of Terry. Taking the main road south from Terry, which is 2,264 

feet ·above sea level, the writer crossed the broad lower 

terrace on which the village stands and ascended the 

300-foot bluff. (See pl. 1.) From its crest the flat 

terrace or bench, several miles in width, rises gently 

southward between higher land on the east and west. 

At a distance of 15 miles south of Terry the barometer 

registered 2,600 feet. This flat is underlain by stratified sand and fine gravel, apparently not more than 

20 or 30 feet deep, overlying shale of the Fort Union 

formation. When the Powder River was flowing on 

this broad valley plain, which appears to correspond 

to the final stage of the second set of terraces, it evidently went directly north and joined the Yellowstone 

near or below Terry. It is now intrenched in a much 

narrower inner gorge cut nearly 300 feet along the 

west side of the older valley and joins the Yellowstone 

8 or 10 miles farther upstream than before. The 

pebbles on this No. 2 bench are mostly yellow chert, 

quartzite, agate, some few of granite, dense dark and 

greenish crystalline rocks, and some etched limestone 

and silicified wood. 

. Abo~t 4 miles east of Terry the bluff swings north 

nearly to the river, and above it is a remnant of No.2 

bench 3 miles in width and 2,590 feet (barometric) 

above sea level. There are some fine farms on this I 

w ~enick, B. C., Geology and ground-water resources of central 1 

and southern Rosebud County, Mont.: U. S. Geol. Survey WaterSupply Paper 600, ftg. 3, 1929. 

8794~2---G 

part of No.2 bench, whi~h is more than 350 feet above 

the river. The soil is· rather sandy·and· appears to be 

underlain by coarse gravel, as such gravel is exposed 

in road cuts at the margins. The Chicago, Milwaukee, 

St. Paul & Pacific Railway rims about the point of 

the bluff on the lower (No. 3) bench to enter the 

O'Fallon Creek Valley on the east. There is also a 

very broad gravelly bench at a corresponding level 

northeast of O'Fallon Creek. This bench extends 

northward to the top of the bluff on the southeast side 

of the Yellowstone to the vicinity of Marsh, and it is 

crossed by the Yellowstone- Trail on the route to 

Baker. Long, low slopes rise back of the terrace 

where they are not sharply dissected by more recent 

erosion. Evidently when the streams were on No. 2 

bench they were bordered in large part by smooth, 

rolling, little-dissected uplands of moderate slope. 

As nearly as can be det~rmined, the average grade of 

No. 2 bench between Billings and Terry is between 

3 and 4 feet to the mile. Crossing the Yellowstone 

near Fallon on the Red Trail to Glendive or traveli.ng 

_on the Northern Pacific Railway, . the observer may· 

see the abrupt slopes or bluffs below the flat . be,nches·, ·. 

off to the west. There are numerous dissevere(l ~em,· 

nants of No. 2 bench west, of ·Marsh, a:qd several· of . 

these in the Glendive quadrangle were traversed. by thee 

writer. 

The gray~l is similar to that on No. 1 bench, the 

pebbles being mostly roun~ed and polished and the 

larger ones 6 to 8 inches in diameter. The constituent. 

material is made up largely·of various.porphyries and 

other crystalline rocks, reddish and. yellow quartzites': ... 

like those of . the Belt. fonnation,., numerous; agates~.:· .. , 

pieces of silicified wood, and rarely fossiliferous frag..; · 

ments of Paleozoic limestone. The gravel is generally 

coarser than that south of Terry, though there is con-. 

siderable sand in places, as on Belle Prairie, east of 

the river below Glendive. As the limit of continental 

glaciation is · approached, boulders of granite and 

blocks of limestone are found scattered over the surface of the gravel and sand, but not intermingled with 

them. The most southerly glacial boulders were found 

on Belle Prairie between Cotton and Boxelder Creeks, 

about 7 miles northeast of Glendive, and about a mile 

north of Ousters Lookout, west of the river. As described below (p. 83) , these ~oulders were evidently 

dropped from icebergs floating on water ponded in the 

·valley· by the front of the great glacier as it ·lay in 

the valley north of Intake, long after the development 

of No. 2 terrace and after the river had cut more than 

300 feet below it. 

This bench is dissected and worn away to a much 

greater degree farther down the valley, and below 

Intake the relations have been somewhat obscured by 

the overriding glacier and by the deposits of drift 

which were left. The altitude of ~ o. 2 bench de-
58 PHYSIOGRAPHY AND GJ:,AOIAL ·GEOLOGY~ OP' EASTERN MONTANA 

clines from nearly 2,600 feet· near Terry to about 

2,200 feet west of Sidney-that is, 400 feet in 90 

miles, or nearly 4¥2 feet to the mile. When the Yellowstone was flowing at this altitude in early Pleistocene time it was probably still high enough to traverse 

the sag in the Coteau du Missouri south of Crosby, 

N. Dak., about 70 miles northeast of the present 

· mouth of the stream at Mondak, with a fall of nearly 

2~5 feet to the mile below Sidney. In other words, it 

· is probable that removal of the thick deposits of later 

glacial drift ~rom the Coteau du Missouri in northwestern· North Dakota would disclose, leading to the 

broad reentrant in the coteau south of Crosby, a broad 

sag corresponding in altitude to the grade of the 

second terrace as projected through the Glendive 

· quadrangle and thence somewhat east of north past 

Williston, N. Dak., and along the Little Muddy Val-· 

ley. The point of junction with the upper Missouri 

River at that time was probably somewhere near or 

north of the Canadian boundary. In this connection 

may be noted certain evidence of a valley buried beneath thick drift in the region of Crosby. In a letter to the writer June 26, 1923, Prof. Howard E. 

Simpson, .water geologist of the N orlh Dakota Geological Survey, states that the artesian well of Robert 

Brevis a few miles north of Crosby, in theSE.% sec. 

6,; T. 163 N., R. 97 W., was drilled 254 feet through 

glacial drift to co~rse drift gravel, wher~ a strong 

artesian flow was struck. The altitude of the curb 

was not stated, but to judge from the altitude along 

the Souris River about a mile farther llorth, as indicated on sheet 41 of the international-boundary map, 

the altitude is not far from 1,925 feet, and that of the 

gravel at the bottom of the well is about 1,670 ·feet. 

The altitude of the upper Missouri River on No. 2 

bench in the vicinity of Poplar . was about 2,200 feet, 

the same as that of the Yellowstone at Sidney, and the 

grade of the upper Missouri below Havre was about 

1.75 feet to the mile. 

DIVERSION OF THE MISSOURI AND YELLOWSTONE RIVERS IN NORTH 

DAKOTA 

Careful consideration of the relations of the phenomena discussed in this paper leads the writer to the 

opinion that the diversion of the upper Missouri from 

a. northeasterly course leading to Hudson Bay to a 

southeasterly course tlirough the Dakotas occurred 

while yet that stream and the Yellowstone were flowing 

on the No. 2 bench or second terrace, about 200 feet 

above their present levels. The upper Missouri, as 

relocated, cut across to the lower course of the Y allowstone between Mondak and Williston, and at the latter 

place the waters of the combined streams were deflected to the present co~rse o£. the Missouri in North· 

D~.tkota. The diver:sion was undoubtedly due to the 

advance of one of the early ice sheets from the. Hudson :. -- • ' _I ' ' • • ~ 

Bay region to the .Coteau du Missouri,00 at either the 

Nebraskan or the. Kansan stage of glaciation. 

When the ice sheet blocked the way to the HudsOn 

Bay region all the drainage of the r:egion ·north and· 

· we~t of the Dakotas was deflected southward and· 

forced to cut across cols between the tributaries of eastward-flowing streams. Until this cutting began to go 

· below the grade of No. 2 bench in Montana, the drainage was retarded and planation at this horizon continued. When the· cutting extended below the grade. 

the trenching of No. 2 bench began. Eviuently the 

Missouri was sufficiently intrenched along its new 

course in North and South Dakota by the end· of the 

Kansan stage of .glaciation to maintain that course , 

after the ice had melted away. 

LAD BASINS 

· No identifiable alluvial benches such as those described above are known to occur in the area. between 

the Yellt>wstone and Musselshell Rivers, except immediately adjacent to these main streams. There are, 

however, certain anomalous features which are perhaps to be correlated with the development of the second set of terraces. Such are Lake Basin, Hailstone 

Basin, and other similar features northwest of 

Billings. These are described by Hancock 91 as 

follows: 

The name of this field is very suggestive of its relation to 

the surrounding region. .Although the field is somewhat elevated above the valleys of ·Yellowstone and· Musselshell Riverst 

it is nevertheless in the nature of a basin. The Crazy Mountains on the west, the Big Snowy Mountains on the north, 

and the Bull Mountains and Pryor Range on the east and 

south present a striking contrast to the relatively low, ·undrained depression commonly known as Lake Basin. Intimately related to the basin itself are minor features whicb 

collectively are the topograp~ic _expression of the attitude of 

the different formations fDd the marked differences in the 

degree of resistance. they ~ave o:ffered. There are in this field 

great bodies. of shale whi~h alternate with beds of resistant· 

sandstone. Where the ov~lying sandstones have been eroded 

the shale is soon worn dbwn to a much lower level, and a 

basin or broad valley is ~ormed. Such a basin or valley ig 

almost invariably surrounjded by a bold escarpment formed 

by the. relatively resi.stan. tt

1 

sandstones~ In places streams cut 

back into th.e escarpment a d masses of sandstone are isolated~ 

which in the course of t e give rise to buttes out in the 

shale area. Battle Butte, lan~ark well known throughout 

this region, is an excellent example .. · · · 

Lake Basin is a broad d pression eroded out of the Bearpaw 

shale, and the Lennep s*dstone, which overlies the shale, 

forms, a rather pronounc~ esca:rJ>ment all along the west side 

of the basin. . ~ . . . Hailstone Basin is stru · turally a dome in whtch the Eagle 

sandstone and the over g .beds have been eroded, and the . . 

oo Todd, J. E.~ The Pleist cene · history of. the Missouri Riyer: 

Science, new ser~, vol. 89, pp 2Ga-;.274, 1914 ; Is the channel of the 

Missouri .River. tbr.nugh-N.ortb.l Dakota of. Tertiary origin? :. GeoL Soc. 

America Bull., vol. 34, pp •. 46~93, 1923. . . 

n Hancoc~, ~· T., , qeoi9gy ~nd oU ~'d . ga.tt. J,l~~.sJ,ieeta of the Lake 

Basin :field, ·Mont.: U. S. Geo~. Survey Bt1U·: 891. J,>~· 104-105, 19~9. 
PLEISTOCENI!) ~OCR 59 

present surface is well down into the underlying Colorado 

shale. The basin is limited on the north and east sides by 

the bold ·escarpment of Eatle sandstone,. and the sam~ condition exists along the sout margin of Big Coulee, along the 

stream leading down tow rd Painted Robe, and along the 

north edge of the Yellows one flats. The south rim of Hailstone Basin, on the contrary, is made up of a great series of 

fault blocks which erosion has carved into a long chain of low 

hills without any apparent topographic relationship. 

In the small uplift southwest of Broadview the. conditions 

are Yery different from those of Hailstone Basin. The Eagle 

sandstone has been removed only in part, and instead of a 

basin in. the underlying shale the sandstone forms the top of 

a roughly circular hill. This hia, together with the elevated 

area to the south,· separates Lake Basin proper from th~ broad, 

.depressed area around Comanche. 

The anomalous feature of these basins is that they 

are undrained-that is, their outlets are not deep 

enough to drain all of the nearly flat bottoms, so that 

they may formerly have been occupied by large lakes 

and if there were a greater rainfall they would now b~ flooded. There is some question as to the conditions 

under which the basins were developed and as to how 

the material was removed to make them basins. As 

stated by Hancock, the basins lie in belts of soft shale 

surrounded more or less completely by rims capped 

with sandstone. Undoubtedly during dry periods the 

wind has been a potent factor in removing dust from 

these tracts whenever the soil became bare and dusty. 

The action of the wind is, however, not so localized as 

these basins. It seems to the present writ-er that they 

may be the result of stream work at times when the 

Yellowstone River to the south was flowing on No. 1 

bench at 3,600 feet or more above the sea-that is, 1,000 

feet or more above its present channel west of Billings. 

Streams tributary to the Yellowstone from the north 

were not carrying coarse gravel like those from the 

south, and their lateral meanderings would tend to 

develop broad plains in the soft shale at altitudes corresponding to the valley plain along the mast-er stream. 

Once started, the surrounding abrupt inclosing es-

. carpments or rims would con'tinue to recede under the 

processes of planation described above (p. 13). With 

the downcutting of the Yellowstone to lower levels 

the outflowing drainage from these basins would tend 

to become shifted under the influence of sloping beds 

of alternating soft and harder strata. . It might thus 

result that as these streams cut down along newer 

courses the outflow from the basins might not be of 

sufficient volume to cut down an outlet through the 

rim to accordant depth, and continued removal of fine 

silts by the strong winds in dry seasons might lower 

much of the flat bottoms below the sill of the outlet 

and so result in an· undrained area. The flat bottom 

of one ·of these basins in western. Yellowstone County 

is traversed by the Great Northern Railway between 

Acton and Broadview. This plain' has an exte:p.t of 

more than 60.square miles. ·The village of Comanche, 

near its center, is 3,740 feet above sea level. This is 

not far from what was probably the original level of 

No. 1 bench· in! the region of Billings. Lake Basin 

(see Stillwater ~topographic map), in northern Still .. 

water County, ils traversed by a branch of the North .. 

ern Pacific Railrway. The terminus in 1921 was at the 

village of Rapelje, at about 4,100 feet above sea level 

'Vheat Basin is: north of Big Lake, and the village of 

Molt (formerly Stickley post office), about 5 miles 

east of the lake' at 3,950 feet (barometric) , is located 

at a sag which was probably the former outlet of the 

basin and throlljgh which the railway now runs. The 

sharp newer-cuu gorge of Canyon Creek passes within 

a mile of this outlet on its way down to the Y allowstone Valley. The altitude of the bottom of Lake Basin 

is about the same as that of No. 2 bench on the Yellowstone at Columbus, about 15 miles south. The rim on 

the southwest side of Lake Basin rises with steep marginal slope and' in places bluffs 800 to 1,000 feet or 

more above the nearly flat bottom of the basin. This 

ridge is the southeastward extension of the Cayuse 

Hills east of Melville. 

NO.3 BENCH 

RELATIONS TO GLACIAL DIUFr 

In many plac~s throughout the region here described 

there is.a well-~arked gravel-capped terrace or bench 

between the second set of terraces and the present 

valley bottoms. Thls may be designated No. 3 bench 

or terrace. The relations indicate that the completion 

of the second set of terraces was followed by a welldefined stage of downcutting of the streams· throughout the region, and this in turn was followed by lateral 

planation and deposition of river gravel on the broad 

valley bottoms t:hus developed. Away from the mountains this bench is generally 100 to 200 feet or more 

below the second benches and is confined between the 

main lines of bluffs bordering the inner valleys. The 

relations seem to indicate a period of regional uplift 

after the form~tion of the second benches, causing 

active downcutting by the streams as the result· of increased gradients, followed by a sufficiently long period 

of stillstand to permit lateral planation to broaden 

the valley bottoms· to widths ranging from 1 nrile to 

several miles. Oontemporaneously smaller tributaries 

actively dissected older benches and the bordering uplands. There is' conclusive evidence that No. 3 bench 

was completed as early as the oncoming of· the Wisconsin stage of glaciation. 

It now seems !Probable (see pp. 47--48) that 'Carlow 

Flat, between Cut Bank and Browning, in Glacier 

County, is som~what older than was formerly supposed and is not to be regarded as representative of 

the third set of terraces.92 It is now correlated with 

the broad bench north of Dupuyer and with the lower 

oa .Alden, W. C., P~ysiographic development of the northern Great 

Plains : Geol. Soc. A~erica Bull., vol. 35, pp. 385-424, 1924. 
60 PHYSIOGRAPHY AND GLACIAL GEOLOGY OF EASTERN MONTANA 

level of the second set of terraces throughout the 

region. The third set of terraces is probably more 

nearly represented by the broa.d bottom of Flat 

Coulee, the channel which the Two Medicine River cut 

100 to 200 feet through Carlow Flat terrace and which 

it later abandoned, when the Two Medicine Glacier 

extended out onto the plains. The terminal moraine 

of this glacier extends down the side slopes of Flat 

Coulee and across its broad bottom, showing clearly 

that the coulee, as well as Carlow Flat, is of preWisconsin age. Spring Creek has now cut a narrow 

gorge in the bottom of Flat Coulee. This bottom is 

about 200 feet above Cut Bank Creek, to the east, and 

the Two Medicine River, to the south. A similar 

broad-bottomed coulee was cut below Carlow Flat on 

the north. This is traversed for several miles by the 

Great Northern Railway and the Roosevelt Highway, 

between Bombay and Carlow sidings, where it lies 100 

feet or more below the top of the terrace and the crest 

of the moraine on the south. To the third set of 

terraces also belong Greasewood Flat, north of Browning, and the broad gravelly flat bordering Badger 

Creek where crossed by the Park to Park Highway at Piegan. The broad gravelly flat bordering 

Birch Creek is regarded by Eugene Stebinger as 

No. 3 bench, and he states in his notes that it might 

be mistaken for outwash of the Wisconsin .stage.98 

South of Birch Creek the moraine extends across No. 

3 bench and up the 200-foot slope to No.2 bench, about 

1 7 miles northwest of Dupuyer. No. 3 bench extends 

eastward, under the name Birch Creek Flats, to the 

west limit of the Keewa.tin glacial drift of Wisconsin 

age. It seems probable also that the great irrigated 

gravelly flat north of Choteau, on which stand the 

villages of Bynum, Agawam, and Farmington, in 

Teton County,94 is also to be correlated with No. 3 

bench. This flat is crossed by branches of the Great 

Northern and the Chicago, Milwaukee, St. Paul & 

Pacific Railways, and a few miles east of the latter 

the bench passes under the terminal moraine of the 

Keewatin drift. It is reported that a deep well drilled 

by the California Co. near Agawam, in the NE. 1,4 

sec. 25, T. 26 N., R. 5 W., passed through 40 feet of 

unconsolidated limestone gravel before entering the 

underlying shale. The altitudes at Farmington and 

Agawam are 3,889 and 3,800 feet, respectively, and at 

.Bynum 3,970 feet (Great Northern Railway). The 

altitude on No. 1 bench at Pendroy, 7 to 8 miles north 

<>f Bynum, is 4,264 feet (Great Northern Railway). 

The Teton River has cut its broad-bottomed valley in 

the vicinity of Choteau to a depth of 100 feet or more 

below this broad No. 3 bench. 

93 Calhoun, F. H. H., The Montana lobe of the Keewatin ice sheet: 

U. S. Geol. Survey Prof. Paper 50, p. 46, 1906.· 

H Fisher, C. A., Geology and water resources of the Great Falls 

region, Mont. : U. S. GeoL Survey Water-Supply Paper 221, pl. 1 

(shown as Burton Bench), 1909. 

In the vicinity of Gilman and Augusta the relations 

of the terminal moraines of the Sun River and Smith 

Creek· Glaciers are such as to show that the .second set 

of terraces is older than the drift deposited by the 

rrwuntain glaciers at their greatest extension,. which is 

referred to the Wisconsin stage of glaciation. It is 

not so clear, however, that the broad terrace bordering 

the outer moraine in the vicinity of Augusta and. 

Gilman is older than the moraine on the Sun River 

north of Gilman. The relations seem to indicate that 

the terrace is composed of outwash from the moraine. · 

It also seems probable that the Dearborn River ·was 

flowing eastward from the mouth of its canyon in 

the mountains to and down the broad valley of Flat 

Creek and not in its present narrow 300-foot gorge, 

1:3 miles south of Augusta, when No.3 bench was being 

formed. 

North of Gilman, in T. 21 N., R. 6 W., the inner 

valley of the Sun River is cut to a depth of about 100 

feet below No.3 bench, which is half a mile to a mile 

wide on each side above the gorge. The terminal 

moraine of the Sun River Glacier descends the eroded 

slope below No. 2 b~nch on both the north and the 

south and crosses the broad outer valley for nearly 

3 miles on No. 3 bench. The relations of the moraine 

to the second bench are clearly visible from the Park 

to Park Highway and the main road north of Gilman. 

·The Sun River terraces were not mapped in detail 

from Gilman eastward to Great Falls, but, as seen by 

the writer on two trips along the valley, it appears 

that No. 3 bench is well preserved on the north side 

of the river eastward nearly to Reibeling. There are 

also some narrow remnants on the south side, and the 

upper irrigation ditch west of Simms is on one . of 

them. No. 3 bench appears to have been developed 

about the north side of Floweree Butte along Big 

Coulee. Here there is 10 to 15 feet of stratified gravel 

overlying the shale beneath the bench. The Chicago, 

~filwaukee, St. Panl & Pacific R~ilway at and near 

Ashuelot station is on a higher Qr No. 2 bench,· described above (p. 47). Near and east of Great Falls. 

the relations of the third terrace are obscured by 

erosion, by the shifting of the course of the Missouri 

River, and by the deposition of the Keewatin glacial 

drift. 

It seems probable that some at least of the cut-off 

and abandoned parts of the inner valley of the old 

Missouri River are to be correlated with the development of No. 3 bench, and that as erosion proceeded 

Lelow this horizon local conditions resulted in the 

stream's diversion. One of these abandoned channels 

is traversed by the irrigation canals east of Malta and 

by the Great Nor.ihern Railway between Malta and 

Beaver Creek east of Lake Bowdoin. This old, partly 

drift-filled valley is 3 to 5 miles in width. The con-. 
PLEISTOCENE EPOCH 61 

ditions attending its abandonment are described below 

(p. 112). . 

The Great Northern Railway between the ·mouth of 

the Milk River and Wolf Point runs in places on 

remnants of a broad terrace extending 1 to 2 miles 

north of the · flood plain of the Missouri. (See 

Nashua, Frazer, Oswego, Chelsea, and Wolf Point 

topographic maps.) This terrace .rises gradually 

westward reaching about 2,140 feet above sea level, 

or 120 f:et above the river, west of Frazer. With 

this is probably to be correlated the abandoned former 

valley of Wolf Creek about 4 miles west of W o~f 

Point, in sees. 1, 12, and 13, T. 27 N ., R. 46 E. This 

is the continuation of No. 3 bench farther north along 

the west side of this creek and 60 to 80 feet above it. 

Another correlative is the abandoned valley 4 miles 

long which is cut through behind the ridge south of 

the river opposite Wolf Point 'and which leads from 

the Sand Creek Valley to the Fort Charles cut-off. 

A narrow terrace borders the foot of the bluff southeast of Wolf Point but it is mostly cut away between 

that place and Poplar. ·At Poplar the terrace appears 

to be represented by the ridge on which the village 

stands and this is the correlative of No. 3 bench farther n~rth along the Poplar River Valley. When thi8 

was being developed the Poplar River had abandoned 

and cut below its former outlet to the Tertiary Missouri River Valley in the northeastern part of the 

Poplar quadrangle. 

Between Brockton and Culbertson Big Muddy Creek 

joins the Missouri. This stream occupies part of a 

continuous broad, flat-bottomed valley which, as described below (p. 129), was, at one or more stages of 

glaciation, an outlet for water of the Saskatchewan 

River when ponded by the glacial margins. In this 

valley in southern Saskatchewan lie Big Muddy Lake 

and Willowbunch Lake, in the Bengough district, and 

Lake of the Rivers and probably other lakes farther 

northwest in Moose Jaw County. In Sheridan and 

Roosevelt Counties, Mont., this valley cuts directly 

across the broad Tertiary valley of the Missouri River. 

There are remnants of a well-marked gravel-covered 

cut terrace in several places along the Big Muddy 

Valley in Sheridan County, but the deposits have not 

been examined in sufficient detail to make sure whether 

or not the gravel is of nonglacial origin. It is suggested that this terrace may correspond to No. 3 bench 

on the Missouri and Yellowstone Rivers. Near Red-

.stone the terrace is 50 feet or more above the valley 

bottom. A similar broad terrace remnant was crossed 

about 5 miles southeast of Redstone and other remnants southeast of Plentywood, 2 miles south of Antelope, and also at Homestead. 

· From Culbertson to Lakeside the Great Northern 

Railway traverses an abandoned part of the Missouri 

River Valley.95 (See pl. 1.) This is also occupied in 

part by Little Muddy Creek and its tributaries. Alti· 

tudes along this channel, which is nearly 2 miles in 

width and may correspond with No. 3 bench,. ar~ at 

Culbertson 1 921 feet,· Lanark, 1,985 feet; BainVIlle, 

1,960 ' ' R '1 feet; Lakeside, 1,910 feet (Great Northern a1-

way). · 

NO. 3 BENCH IN NORTH DAKOTA 

Other similar terrace remnants and abandoned channels possibly to be correlate<} with No. 3 bench occur in 

North Dakota. These have been described by Wilder ,'6 

together with the possibilities of their irrigation. The 

Nesson-Hoffiund Flats are shown in part on the Ray 

topographic map. Here a flat 2 to. 3 miles in widt.h 

and 80 to 100 feet above the Missouri Valley bottom IS 

partly separated from the flood pl~in b~ one or ~wo low 

hills. Back of the bench is a curVIng line of dissected 

bluffs and steep slopes rising 200 to 300 feet to the 

smooth upland. A. J. Collier 97 states that lignite is .in 

place below the edge of the bench south of N esson 

post office. Shale and lignite are also exposed below 

the gravel covering a remnant of a similar terrace on 

the south side of the valley near the mouth of Tobacco 

Garden Creek. 

From these occurrences it would ~em that the valley 

here was not cut down to the present river level before 

this terrace was formed. Wilder 98 also refers to an 

abandoned channel of the Missouri between the 

mouths of Little Knife and Shell Creeks in the Fort 

Berthold Indian Reservation. The upper end of the 

valley is said to be about 140 feet above the river, and 

below is a terrace 80 feet above the stream. The old 

channel is separated from the present course of the 

river by a broad ridge 10 miles or so in length. This 

channel has also been described by Wood,99 Smith,1 

and~ Pishel. 2 

Terraces nearly opposite the mouth of t~e Little 

Missouri River and· farther east at the 9ld Indian 

agency in T. 147 N., R. 87 W., are 20 to 80 feet above 

the stream. The Fort Stevenson Flats are 30 to 70 

feet above the. river. (See Garrison topographic 

map.) 

It should be noted that not all the stream deposits 

in the abandoned channels or on the cut terraces cited 

above are known to be either pre-Iowan or not glacial 

9S Beekly, A. L., The Culbertson lignite field, Valley County, Mont.; 

U. S. Geol. Survey Bull. 471, pis. 26, 27, 1912. . 

96 Wilder, F. A., The lignite of North Dakota and its relation to irrigation: U. S. GeoL Survey Water-Supply Pape~ 117, pis. 2-4, 6, 8, 

1905. 

9'1' Personal communic'ation. • 

~ Idem, p. 35, pl. 6. 

oo Wood, L. H., North Dakota Geol. Survey Second Bienn. Rept., 

pp. 102-104, 1902. 

1 Smith, c. D., The Fort Berthold Indian Reservation lignite field; 

N. Dak. : U. S. Geol. Survey Bull. 381, p. 31, 1910. 

s Pishel, M. A., Lignite in the Fort Berthold Indian Reservation, 

N. Dak.: U. S. Geol. Survey Bull. 471, p. 171, 1912. 
62 PHYSIOGRAPHY AND G~CIAL GEOLOGY OF EASTERN MONTANA 

outwash. Further study. may show that at least some 

of them are not to be correlated with No. 3 bench. 

NO. 3 BENCH IN JUDITH RIVER BASIN AND MUSSELSHELL VALLEY 

Some tracts of No. 3 bench border streams in the 

Judith River Basin.8 The village of Stanford stands 

on one of these which border Wolf Creek. This is 

about 150 feet lower than No. 2 bench to the west . ' . . 

In T. 17 N., R. 16 E., the main road in the valley 

of Warm Spring Creek is on No. 2 bench westward 

nearly to Deerfield, at 3,700 feet above sea level. The 

road then runs down a short, abrupt 100-foot slope 

to No.3 bench, which extends far to the south and west 

to the Judith River gorge. Both of these benches 

are irrigated and produce fine crops of grain. It appea~s t~at l~teral planation was not nearly so extensive m this basin at the third stage as when No. 2 

bench was being formed. The Judith River and most 

of its tributaries, at least in their lower courses now 

flow in sharp, narrow gorges cut 100 to several' hundred feet below No. 3 bench. 

There are here and there some traces of a third 

' gravel terrace bordering the Musselshell River and 

its tributaries, but in most places seen the rather broad 

plains between No. 2 bench and the immediate flood 

plains are gently undulating erosional surfaces not 

co~ered with gravel. Harlowton is built partly on a 

th1rd terrace, and other remnants border the river 

farther west, as near Two Dot and Martinsdale. 

West of Groveland station there is 20 to 25 feet of 

coarse cob~lest?ne gravel exposed near the railwaY. in 

an excavatiOn In the edge of a terrace. This terrace 

extends so~thward up the Cottonwood Creek Valley 

and heads In the Crazy Mountains. 

NO. 3 BENCH IN THE YELLOWSTONE B.ASIN 

No. 3 bench appears to be better developed- or b~tter preserved ~long the Yellowstone River and its tributaries than on the Missouri River and its other tributaries. The relations to the glacial moraines above 

Livingston of what in reality may be the No. 3 stream 

terrace. are discussed on page 123. The automobile 

road from Livingston to Chico Springs on the east 

si~e of the valley, runs partly on and ~artly below 

tlus. broad gravel terrace. This is also traversed by 

the road. on th? west side of the valley part of the way 

below E1ghtmile Creek. Near this stream and Elbow 

Creek the terrace either merges with the outer moraine 

or emerges from. under it. Here the terrace is more 

than 100 feet above the river. Near Emi()'rant a ledO'e 

fb . b b 

o asalt proJects from the bluff below the terrace and 

above the roadway. Gravel is exposed below the level 

8 Fisher, C. A., Geology of the Great Falls coal field, Mont. : U. s. 

Geol. Survey Bull. 856, pl. 1, 1909. Calvert, W. R., Geology of the 

Lewistown ooal field, Mont. : U. S. Geol. Survey Bull. 890, pl. 1, i909. 

of the basalt but was not observed to extend under the 

lava. Southwest of the village the basalt caps a, ridge 

above the level of the terrace and 150 to 200 feet above 

the road, but no exposure of the underlying material 

was seen. A mile or more fa.rther southwest at the . ' railway spur where material has been excavated, a 

sheet of basalt 5 to 20 feet thick with some agglomerate 

at its base overlies sand and gravel. The smoothly 

rounded pebbles of the gravel range from less than 

1 inch. to 1 foot in diameter and consist of quartzite, 

granite, porphyry, and other igneous rocks. At 5 or 

6 miles above Emigrant upturned. and eroded creamcolored clay, of supposed Tertiary age, composes the 

conspicuous White Cliffs, rising above the east bank 

of the river. (See pl. 24 B.) This clay is unconformably overlain by 80 feet or more of very coarse, 

smoothly worn stream gravel. Above the gravel is a 

sheet of columnar basalt which caps the broad plateau 

or bench 250 feet or more above the river and which 

extends eastward a mile or more to the sag in which 

lies Duck Lake and southward about 5 miles opposite 

Point of Rocks. The relations, though some,what .obscured by erosion and by overlying glacial drift, 

strongly suggest that the broad gravel terrace farther 

down the valley, instead of being glacial outwash,. is 

older than the moraines of the Wisconsin stage and is 

the continuation of the thick deposit of stream gravel 

which underlies the basalt flow. These are tentatively 

correlated with the No. 3 set of terraces and benches. 

The basalt was probably originally continuous along 

the valley for at least 11 miles above Emigrant. It 

is not known that it ever extended farther up or down 

the val~ey. 

Two lower terraces, about 25 and 50 feet above 

the river, border the stream near Miner station and 

through much of the distance below Yankee Jim 

Canyon. 

No. 3 bench spreads out broadly on the east side 

of the river opposite Livingston. Here it consists of 

great coalescent alluvial :fans heading at the mouths 

of the gulches which dissect the mountain mass below 

Livingston Peak. A narrow strip of this terrace borders the hill north of the city, but Livingston itself 

stands on a lower terrace. 

The lower course of the Boulder River for several 

miles south of Big Timber is bordered on the east 

by a third gravel terrace. Its correlative in the Yellowstone Valley is traversed :for miles by the Yellowstone Trail. Th~s is above the railway on the south. 

side of the valley. Near Columbus the third terrace 

is well developed both north and south of the river. 

The gravel exposed west of Columbus near Bensons 

Bluff, though opposite the mouth of the Stillwater 

River, differs from the bench gravel along that stream 

and its tributaries in containing more quartzite and 
PLEISTOCENE EPOC:JR 63 

porphyry and less granitic rock. The terrace in this I 3 miles wide; the parts of which on, one or both sides 

vicinity is 50 to 100 feet above the river. It is well slope gently toward the crests .of the stream banks 

defined at Luther post office on Red Lodge Creek, in from what was probably the level of No. 3 terrace at 

T. 6 S., R. 19 E., also below Red Lodge ·on Rock the . outer margin.. On this valley :floor· are extensive 

Creek. It spreads out broadly between Joliet, on. irrigated tracts with finely impr2fed farms producing 

Rock Creek, and Edgar, on Clark Fork. alfalfa, small·grains, and sugarooets. This extends 

Farther south up Clark Fork traces of a No.3 bench for some distance east of Hysham on the south side 

were noted only here and here until the bridge near of the Northern Pacific Railway and of the valley. 

Allen's ranch, 2 miles north of the Wyoming-Montana At Sanders it is 30 to 40 feet above the railway, and 

line was reached. Extending thence southwestward its edge ·is followed by the irr:igati.on canal.. No. 2 · 

much if not all of the distance to the mountain front bench is 140 feet higher. No. 3 -bench is well marked 

is a terrace o'f bouldery gravel. Just north of Clark at the cemetery 1 mile east of Forsyth. Doubtless 

post office, Wyo., it is 4,309 feet above sea level, or 30 there are other remnants which C¥tn ·not be seen from 

feet above the broad :flat on which the buildings stand. the Y ellowston:e Trail. One of these is near Horton, 

The flat ri$eS westward to the glacial terminal moraine. about 100 .feet below No. 2 bench, OJl· which is the 

It may in-reality pass under the moraine and be rep- Northern Pacific Railway gravel pit.· From the Powresented by the terrace at the mouth of the Clark Fork der River down to the mouth of the ,Yellowstone there 

Canyon. The flat gravelly terrace in· front of the appears to be little chance of confusion of the second 

moraine appears not to be simply an outwash plain, and third terraces. Two beds of lignite are exposed in 

but the presence of the big boulders scattered upon it the bluff below the lower bench near the Chicago, Miland also on small hills, erosion remnants rising above waukee, St .. Paul & Pacific Railway Bridge west of 

it,. suggests that some at least of the pebbles and Terry. It is important to Iiote that here and at all 

boulders on the plain have been let down by erosion other places examined, both upstream and downfrom a higher terrace of which there are now but few stream, at least as_ far as Intake, the evidence -is conremnants in this vicinity. Near the bridge south of elusive that No. 3 bench, like the benches at higher 

Clark _post office the stream has cut 100 feet below levels, is a cut terrace merely veneered with gravel. 

No. 3 terrace. For miles southward from tlie stream At no place does it appear that the Yellowstone River 

the Cody road, or Black and White Trail, runs on ~ had previously cut dowtJ. to lower levels and then repart of this terrace, known as Chapman Bench, on the filled its valley to the height of No. 3 terrace. Fur7 · 

east side of Pat O'Hara Creek. ther consideration is given to this below (p. 64). The 

For some distance below the confluence of Clark town of Terry and both raiTways are on No.3 terrace, 

Fo;rk with the Yellowstone River No. 3 ·bench is not which is 50 feet or more above the river and nearly 

well developed or is npt much above the general flat 300 feet below No. 2 terrace. · 

along the river. It is through this same part that No. At 8 miles east of Terry the Yellowstone Trail runs 

2 bench is also relatively low (p. 53). The Northern up again to No. 3 bench. On· this the Chicago, MilPacific Railway runs mostly on the gently sloping flat waukee, St. Paul & Pacific Railway swings ··'to the 

just below the bluff that rises to No. 2 bench. There southeast and runs up the valley of O'Fallon ·Creek. 

is a low terrace near the village of Pompeys Pillar, 'Iihe village of Fallon is on the lower part. of this 

and as the valley deepens eastward below No. 2 bench~ sloping terrace at 2,231 feet above sea level. · East of 

No.3 bench becomes somewhat more· distinct. Fallon the Yellowstone Trail leaves the river and runs 

On the Big Horn.River below the lower canyon in eastward -up 240 to 250 feet onto No.2 bench .. The 

Montana the No.3 terrace, so far as seen, is not clearly Red Trail crosses the river below Fallon and runs 

distinct from the broad valley floor except tfor 5 or ·down the west side of the valley to Glendive, in places 

6 miles just below the mouth of the canyon. Here on No. 3 bench and in places on gently slop~ng_ surthere is a broad terrace of limestone gravel over shale · faces eroded to somewhat lower levels~ Near and 

75 to 100 feet above the river. "The irrigation canal below Glendive the Sidney· branch of the Northern 

is excavated along the eroded slope below the north Pacific Railwa,y is graded ·in many places along the 

margin of this terrace on which was the site of old foot or face. of the low bluff below the edge of No. 8 · 

·Fort C. F. Smith. (See topographic map of St. terrace. Wherever examined either shale or sandXavier quadrangle.) stone is in place beneath the bench gravel, s!towing 

. The Yellowstone River throughout its course is now that this is a cut terrace. The main road ·down th~ 

· deepening and broadening its flat below this No. 3 valley on the west side is .in, places .on this third·- ter~ 

terrace, so that most of the valley floor is not a flood race and in places on the valley bottom, 50 feet· or 

plain which is periodically submerged but a plain 1 to more below. · 
64 PHYSIOGRAPHY AND GLACIAL GEOLOGY OF EASTERN MONTANA 

Just west of Glendive the altitude near the edge o£ 

the terrace is 2,120 feet. Excavations at this place 

expose 10 feet of gray clay, overlying 10 feet of rusty 

stratified gravel containing streaks of sand. The pebbles are mostly 2 t~L-3 inches or less in diameter,· but 

some cobblestones 6•ro 10 inches long occur. Scratches 

seen on some of the stones resemble glacial striae, but 

possibly they were produced by river ice. North o£ 

.Burns there appear to be some intermediate bench 

levels between the main lower terrace. and No. 2 

bench, to the west. Near the south line of T. 21 N., 

southwest of Crane, the terrace passes below the grade 

of the diversion canal, and thence northward it is irrigated. Near Sidney the terrace is less well defined 

and the surface drops to t~e flat bordering the river 

by a series of low steps. 

The following description of that part of the terraced valley bottom in North Dakota is given by 

Wilder: 4 

Above the flood plain, which is covered with a dense growth 

of willows, is a wooded bench from 10 to 15 feet above high 

water, where large cottonwoods flourish. Its extent may 

equal 4,000 or 5,000 acres. Ten ~eet above this and 20 feet 

above the river at high water is the edge of a beautiful and 

extensive grassed terrace, which rises gradually for 2 miles 

to the foot of the bluffs and which has an area of about 15,000 

acres, below a contour line drawn 80 feet above the river. It 

is not cut up by ravines or gullies, and a trench can be carried 

along the SO-foot contour with but few flumes. With such an 

initial head, water can be taken to almost any point on the 

fiat. -

The present writer has ho data showing whether or 

not in the lower stretches the valley was formerly cut 

down to lower levels and subsequently refilled. It is 

probable, however, that there has been some refilling 

below Sidney cor·responding with the refilling that 

is known to have occurred along the Missouri River. 

The depth shown is, however, not very great. 

MISSOURI VALLEY FILLING IN' NORTH DAKOTA 

Herald 5 cites the following data bearing on the 

depth of erosion and refilling along the Missouri near 

and below the mouth of the Yellowstone River : 

Missouri River and Muddy Creek Valleys are filled with 

alluvium. The thickness of this filling is not well known, but 

a vertical exposure of the river bank near· Trenton shows 54 

feet of alluvium. It is probable that the maximum thickness 

in the field is but little greater. * * * 

That MissouTi River has not eroded far below its present 

channel is indicated by the following drill logs, which were furnished by the United States Reclamation Service. These borings were made in testing for a foundation for a pumping site 

· 4 Wilder, F. A., The lignite of North Dakota and its relation to 

irrigation: U. S. Geol. Survey Water-Supply Paper 117, p. 27, 1905. 

G Herald, F. A., The Williston lignite field, Williams County, N. Dak.: 

U. S. Geol. Survey Bull. 531, pp. 96, 156-157, 1913. 

(about a mile southwest of Buford, N. Dak~). The holes are 

all shallow and show very little lignite, but they are of v.rue 

in proving that Fort Union strata occur in place at shallow 

depths under the [north % of the] alluvium-covered valley 

[fiat]. 

List of United States Reolamat~ Ser'Vioe test bOf"ingB tor 

pumping-site foundJa.tion in 8608. 8, 16, and 17, T. 15! N., 

R. 104 W. 

No. of 

hole Location • Total Surface 

depth altitude 

(feet) (feet) 

--1·----------------------

1 500 feet north and 300 feet west of A.--------------------

2 450 feet west of A-----------------------------------~---

33 1, 902 

33 1,886 3 About 700 feet south and about 500 feet west of A ______ _ Z7 1,873 

4 About 000 feet south and about 1,200 feet west of A _____ _ 46 1,875 

5 77 1,908 550 feet west of A----------------------------------------

6 400 feet north and 30 feet west of A.--------------------- 76 1, 907 

7 700 51 1,886 feet west of A---------------------------------------

8 40 feet west of A----------------------------------------- 53 1,886 

9 Center of NW. W SE. ~sec. 16------------------------- 40 ----------

• Location of point A is center of south l!ne of SE. W sec. 8. 

Logs of UnitedJ States Reolamo,.tion Set"1Jioe test boriffl,gs for 

pumping-site fouAulation in seos. 8, 16, and 17, T. 152 N., 

R.104 W. 

Hole No. 1 Bole No. 6 

Ft. in. Ft. in. 

Gumbo_______________ 9 Gumbo. ______________ 19 

Sand and pebbles______ 4 GraveL _______________ 22 

Sand_________________ 5 2 Quicksand ____________ 16 

Sand, fine ____________ 15 3 Sandstone, soft _______ 10 

33 5 

.Hole No. 3 

Gumbo_______________ 9 Sand _________________ 23 

liand and pebbles ____ ..,. 1 

33 

Hole No. 3 

Gumbo, sandy_________ 1 

Gumbo_______________ 7 

Sand _________ - _ _ _ _ _ _ _ 10 

Quicksand __ -------___ 9 

27 

Hole No. 4 

Sand_________________ 5 

Gumbo _______________ 14 

Sand,fine _____________ 6 

67 

Hole No. '1 

Sand_________________ 1 7 

Gumbo_. ________ ._:_____ 7 5 

Gumbo and sand _____ 5 

Qmcksand_ ----------- 16 

SandL---------------- 4 Clay and sand _________ 15 

Lignite_______________ 11 

Sand, coarse___________ 1, 1 

51 

Hole No. 8 

Gumbo _________ .;.____ 9 

Sand, fine. ______ _, _____ 11 

QuicksandL----------- .7 7 

Sand, coarse__________ 2 5 

Lignite _______________ · 1 Clay_________________ 1 

Sand _________________ 20 7 Pebbles______________ 1 

Boulder--------------- 1 7 

46 7 

Hole No. 5 

Sand----------------- 4 Gumbo_______________ 8 Sand ___ !____________ 3 

Clay _______ ------- __ - 5 

GraveL _______ ----_-- 23 Clay _________________ 23 

Sandstone, soft.- __ - --- 11 

77 

Sand,eoarse __________ 11 

Quic~sand____________ 8 5 

53 

HoleN~ 9 

Sand ________________ 31 

Boulders_____________ 4 6 

Lignite:-·----·-------..: 1 

Sand----------------- 3 6 

40 

It is possible that the lignitic material in holes 7, S,. 

·and 9 is not in place but is washed over and redeposited material such as is occasionally found in· stream 

deposits. There is a distance of about a mile between 

the locations of these drill holes and the . side of the 

valley to the southwest, and the buried channel may be 

deeper in this interval. 
FLEISTOCENE EPOCH 65 

Herald 6 gives the following logs of United States 

ReClamation Service drill holes southeast of Williston, 

one in the northern part of the NW. :fU sec. 4, T.153 N., 

R. 100 W., and one in the western part of the SE.:JU 

sec. 4, both on the Missouri bottom land. 

Log of drill hole in NW. lA, sec. 4 

Feet 

ClaY--------------------------------------------------- 50 

Gravel and sand---------------------------------------- 4 

Clayandsand------------------------------------------ 6 

Gravel--------~---------------------------------------- 5 

ClaY--------------------------------------------------- 13 

Sandstone--~----------~-------------------------------- 7 

ClaY--------------------------------------------------- 5 Sandstone _______________________ ~...:_____________________ 10 

Log of drill hole in 8B. ~ Bee. 4 

Feet 

Gravel, sandy ------------,--------·------- 10 

Sand (trace of lignite>-------------·------- 16 

Sand -----------------------------·------- 12 

Sand, clay, ·and graveL~-----------·------- 3 

Clay, sandY-----------------------·------- 7 

48 

B 

The greater part of the material pene- A 

trated is regarded as alluvium. 

100 

In the- exposure -north of Lethbridge, described on 

page 73 (fig. 5), there is 10 to 15 feet of quartzite 

gravel about 100. feet above the stream, overlying the 

eroded surface of the Cretaceous shale and overlain by 

the lower glacial till (Iowan or lllinoian · ¥). This 

gravel may perhaps represent either the Sangamon or 

the Yarmouth stage of deglaciation as reeorded in . 

Illinois and in Iowa. In view of the relations of -thEl 

high-level and low-level deposits described above, it 

does not seem probable to the writer that the Belly 

River was flowing at so low a level in pre~Pleistoeene 

time. It is therefore inferred that this gravel has 

either been derived directly from the mountains, as 

the result of the deepening of the mountain gorges 

from the hori~on of No. 2 bench to that of No. 3 ·bench 

and lower levels, or that the gravel has been let down 

Borings made by the Great , Northern 

Railway in the channel of the Missouri 

River 3 miles west of Elbowoods and a 

few miles below the mouth of the Little 

FIGURlll 2.-Section on St. Mary River 1 mile south of Kimball, Alberta. A, Quartzite 

.gravel (" Saskatchewan "), interglacial ( ?) , 0 to 15 feet, overlying sandstQne ; B, 

glacial till of Keewatin glacier, 50 to 100 feet ; C, loesslike clay, 10 feet ; D, gravel 

overlain by a few feet of soil 

Missouri River, in T. 147 N., R. 101 W., northeastern 

Dunn County, formerly in the Fort Berthold Indian 

R~ervation, show the presence of quicksand and river 

mud to a depth of 60 feet. 

&lU.VEL UlfDEll.LYilf& OLD& XEEWATDJ TILL 

PRE-IOWAN OR PRE-ILLINOIAN ( ?) GRAVEL IN SOUTHlllBN ALBERTA 

·Probably few if any of the· streams of southern 

Alberta are flowing alorig exactly the same courses as 

they did prior to deposition of the glacial drift, but. 

there are places where the streams appear to cut across 

old filled channels. In some of these places deposits 

of the Wisconsin glaciers are underlain by till of an 

earlier stage of glaciation, and here and there this 

earlier till is in turn underlain by deposits of coarse 

quartzite stream gravel derived entirely from the 

mountains and showing no evidence of glaciation. 

Some of these deposits were described by Dawson and 

McConnell 7 under the name "Saskatchewan gravel." 

' Herald, F. A., The Williston lignite field, Williams County, N. 

Dak.: u. S. Geol. Survey Bull. 531, p. 137, 1913. 

' Dawson, G. M., and McConnell, R. G., Glacial deposits of southwestern Alberta in the vicinity of the Rocky Mountains : Geol. Soc. 

America Bull., vol. 7, pp. 35-66, 1895. 

87949-32--6 

by erosion from the former and older deposits on the 

higher levels of the plains and redeposited· by the 

streams. 

At the other places in southern Alberta where both 

Wisconsin and pre-Wisconsin tills of the Keewatin 

ice sheet have been observed in the same e~osure, 

either the streams have not cut deep enough • to uncover the base' of the lower till (see p. 66) or the lower 

till immediately over lies the eroded surface of the 

Tertiary or Cretaceous rocks, with no inteljvening 

gravel. The latter condition might occur at any place 

where the present stream was neither follo~g nor 

cutting across an old buried stream channel. A.t several places similar quartzite gravel was seen immediately overlying Cretaceous or Tertiary roqks and 

overlain by K. eewatin till, but ther. e. is ap~'. rently 

no way of determining whether the one till deposit 

exposed is of Wisconsin or pre-Wisconsin age Such 

a condition 'was noted 40 miles south o~ Lethbridge, in the St. Mary Valley, about 1 mil~ above 

Kimball (fig. 2) , where -0 · to. 15 feet of q¥artzite 

gravel is overlain by ·50 to 100 feet of till frjom the 

-Keewatin ice sheet, which apparently forms ~ single 

• 
66 PHYSIOGRAPHY AND GLACIAL GEOLOGY OF EASTERN MONTANA 

sheet of drift. As there is nothing here to show 

whether the till is the upper or the lower till, it is 

regarded as Wisconsin. The bed of gravel pinches 

out midway in the length of this exposure against the 

rising surface of the underlying· upturned and eroded 

sandstone, as if it had been deposited only in the 

bottom of a former channel. 

At the bend nearly ·opposite Sloan's ranch, a few 

miles farther south, 30 feet of coarse " quartzite 

gravel" lies on the eroded surface of the Cretaceous 

rocks and is overlain by 10 to 12 feet of till containing 

scattered pebbles of pre-Cambrian crystalline rocks 

and itself overlain by a 5-foot bed of gravel containing 

pebbles of pre-Cambrian rocks. The only evidence of 

mountain glaciation noted this· far north in this valley 

consisted of several 3-foot blocks of reddish argillite 

in a ~avine between the last two point$ mentioned. 

Farther southwest, upstream, another exposure 

shows 10 feet of quartzite gravel lying on the ·eroded 

surface of the Cretaceous sandstone and overlain by 

till containing pebbles of pre-Cambrian crystalline 

rocks and above this laminated sandy clay containing 

a few pebbles from the Rocky Mountains and pebbles 

of pre-Cambrian crystalline rocks from the northeast. 

At a point on the upper Belly River about 27 miles 

south of Macleod, in T. 5 N., R. 26 W., a fine exposure 

of the quartzite gravel was seen. 

DepoSits on Belly River 21 miles south of Macleod, Alberta 

Feet 

])ark soil--------------------------------------------

Laminated gray silt----------------------------------

Solid buff to gray clayey till of the Keewatin ice sheet ; 

pebbles mostly from the Rocky Mountains, but pebbles 

1-2 

8-10 

of pre-Cambrian crystalline rocks from the northeast 

scattered throughout-------------------------------- 10-12 

Stratified, waterworn gravel ("Saskatchewan," interglacial?) ; pebbles exclusively quartzite and other 

rocks from the Rocky Mountains, ranging from a fraction of an inch to 6 inches ln diameter. ·Partly cemented :fine material :fills· the interstices, and streaks 

of cross-bedded san.d occur in places. The upper 1 

foot of the gravel is oxidized to a dull orange tint, 

as if marking a zone of weathering. Bottom not 

exposed-------------------------------------------- 15 

At none of the sections· examined farther up this 

stream was the gravel exposed. In fact, although the 

stream has cut 60 to 75 feet in drift below the level 

of the plain, at several places examined within a few 

miles of Hillspring village, in T. 4 N., R. 27 W., it 

has not yet reached the bottom of the till of the Keewatin ice sheet except at one place, where it swings 

against the side slope of. the former valley. Farther 

up the valley, where the stream cuts through the .ter- · 

minal moraine of the Keewatin glacier and beyond 

this moraine, the stream at many places exposes the 

Cre~aceous sandstone an,d shale underlying the drift, 

but nowhere is quartzite gravel p:resent. Neither was 

the quartzite gravel found intercalated between the 

drift 1 and the Cretaceous rocks at the exposures examined on the Drywood Fork of the Waterton River. 

No sections were exammed on the W a.terton River 

except in the vicinity of its confluence with the Belly 

River. 

At most of the· exposures examined on the South 

Fork of the Oldman River. west of Pincher, in Ts. 

7 and 8 N., R. 30 W., till rests directly on the Tertiary / 

( ~) sandstone or shale with no intervening quartzite 

gravel. 

PRm-IOWAN OB PRJIHLLINOIAN ( ?) GRAVEL IN KON'.l'Al'f.A 

From the above descr~ptions it is clear that there is 

a deposit of stream gravel older than the lower till 

of the Keewatin ice sheet. The quartzite gravel underlying Keewatin till at the other places may be of 

the same age or later (pre-Wisconsin). · 

West of the point where the Chicago, Milwauke~, 

St. Paul & Pacific Railway crosses Highwood Creek 

near Highwood, Cascade County, Mont., eeveral cuts 

expose the following. section: · 

Section. on Chicago, MiZ1.{'atU7cee, St. Pinu c! Pg,cf,fl,o Ratilwav 

wed. of Hig1woooa 

Feet 

4. Dull pebbly clay, glacial tilL----------------------- 2()-4() 

8. Sand, about--------------------------------------- 5 

2. Sand and coarse graveL----------~--------...; _______ 10..-15 

1. Black shale. 

At one point the sand (No. 3) was replaced. by 2 

feet of laminated clay. It is probable that the gravel 

(No. 2) is a preglacial stream deposit derived from 

the Highwood Mountains, inasmuch as . no Belt ( ~). 

quartzite or granite pebbles were found in it by· the 

writer, although plenty of the former and a few of 

the latter were noted in the overlying glacial till. 

Railway cuts on the upper part of the blu:ff west 

of Fort Benton expo~ the following series of dePQsi.ts 

as noted by the writer in 1923 : 

· GlaoiaZ ana asBociated deposits west of Fort Bemon. 

Feet 

6. Recent: Dull gray, wind-blown ·silt which forms a 

small hiU rising above the upland, about--... ----.:.• 50 

5. Wisconsin stage: Glacial gravel composed principally 

of quartzite pebbles but with intermingled Fanitic 

pebbles from Canada, about _______________ ... ;.._____ 10 

4. Peorian ( ?) stage: Fine bu:II loesslike sandy clAy· 

with some small pebbles in the lower part, mostly 

finely laminated, and rippled .like . wind-blown 

silt _________________________ ,_ _____ . ____ . __ ). ______ ~ 

3. Iowan or Illinoian ( ?) stage: Unstrati:fied and semistratified buff sandy clay containing granitic and 

other pebbles from Canada. Probably glacial 

drift------------------------------~--------.--.:._- .10-12 

2. Nonglacial: Well-rounded stream gravel; pebbles 

mostly quartzite, none granitiC--------------~---:-- 8-10 

1. Cretaceous: Colorado shale comprising the lower 

two-thirds of the bluff along the river. 
PLEISTOOE:N E EPOCH 67 

Gravel similar to No. 2 is exposed beneath 40 to 

50 feet of glacial till near the tops of the bluffs both 

nortl~ and souch of Fort Benton. 

Bluffs along the lower few miles of the Teton River, 

. near its junction with the Missouri River, show in 

places a bed of gravel lying on the eroded surface of 

the shale and overlain by glacial till, which is as 

much as 100 feet thick. It seems probable.that much 

of the till in these bluffs is of pre-Wisconsin (Iowan 

or Illinoian~) age and that the gravel may be correlated with that cited above, though no intercalated 

soil or weathered zone separating an upper from a 

lower till has been found in these sections, either by 

Calhoun, Stebinger, or the present writer. 

G:a.AVEL UNDE:a.LYING IOWAN OR ILLINOIAN (t) TILL OF 

MOUNTAIN GLACIERS 

Other exposures than those described above have 

been observed where the quartzite gravel is overlain 

by drift of the mountain glaciers, and this in turn by 

drift of the Keewatin ice. The question o£ the age 

relations of the tills where this overlap occurs is discussed below (p. 105). 

Dawson 8 describes three sections where similar 

gravel underlies the mountain ti~l-one at a point on 

the North Fork of the Old Man River, 2 miles north 

of its junction with the Middle Fork; a second on the 

South Fork of this stream about 12· miles from the 

mountains ; and a third still nearer the mountains on 

Mill Creek. Concerning these he writes : 

The two last-mentioned localities are within the limit of the 

country characterized by moraines, evidently due to local 

glaciers from the Rocky Mountains,. and the indurated boulder 

clay of the Mill Creek section is . believed, like the moraines, 

to be a deposit of these _glaciers. The lower gravels in tbis 

case and in that of Pincher Creek are obviously due to preglacial streams flowing from the mountains, and, although the 

name Saskatchewan gravels may be applied to them, they here 

evidently antedate the eastern gravelly representative of the 

Rocky Mountains or earliest boulder clay. Farther to the east, 

where this boulder clay gradually passes into such gravels, 

there iS no means of distinguishing between wholly preglacial 

beds and those which may have been formed during the main 

period of the Rocky Mountain glaciers. Many expoeures of the 

Saskatchewan gravels may include both, and this without 

necessitating the supposition of any great chronologie break. 

At the international boundary the following section 

was observed by the present writer in 1912 and reexamined in 1920 : 

Gray clayey till of Keewatin ice .sheet; pebbles mostly 

from the Rocky Mountains, but with a small percentage of pebbles of pre-Cambrian crystalline rocks from 

Feet 

the northeast ·(~isconsin stage>-~~----~------------ 20 

Ill Dawson, G. M., and McConnell, R. G., Glacial deposits of south-

. western Alberta: Geol. Soc. America Bull., vol 7, p. 43, 1895. 

Gray till ; pebbles so far· as noted all from the Rocky reet 

Mountains (mountain drift)-----------------~----- 20 

Quartzite gravel (" Saskatchewan," interglacial?) ; 

pebbles exclusively from the Rocky Mountains, well 

rounded, ranging from less than an inch to 1 ¥.. feet 

in diameter-----------~---------------------------- 10-15 

Cretaceous rock. · 

This is the most southerly point at which the writer 

~bserved the quartz'ite graveltmderlying drift of the 

St. Mary Glacier that is in turn overlain·by drift of 

the Keewatin ice sheet. 

EROSION AND ltEFILLING Ilf XILX-XISSOlJlU VALLEY 

In this connection it is well to .• consider the depth 

and character of the filling in the old valley or the 

1\Hssouri River, now occupied by the Milk River below 

Havre and followed through most of its extent below 

the mouth of the Milk River in Montana by the. present Missouri River. 

Stebinger 9 quotes the log of a well drilled by the · ~ 

Quartermaster's Department, United States Army, at 

Fort .!ssinniboine, Mont~, between June, 1892, and November, 1893, which shows 65 feet of clay, gravel, and 

sand overlying. the Bearpaw shale. This is probably 

near the southeast side of the buried. valley. 

Calhoun 10 states that south of Havre there is a drift 

filling 140 feet thick in the old Missouri Valley. 

The west pumping station of the waterworks at 

Havre is in the mouth of a small coulee below the hospital, in the southwestern part of the ·town, in the 

SW. *sec. 8, T. 32 N., R. 16 E., at about 2,530 feet 

above sea level. In August, 1920, W. R. Crafts, in 

charge of the pumping stations, informed the writer 

that at this station there were 10 wells dug to an aver- · 

age depth of 110 feet in gravel, and at the east station 

at. Fifth Avenue and Third Street points had been 

driven to depths of 70 to 90 feet. The west station is 

SO to 100 feet lower than the upland to the southwest, 

which forms the bottom of a sag more than 2 miles in 

width beneath ·which lies buried the old Missouri 

River Valley. It is probable, therefore, that thereis 

at least 200 feet of filling in this old valley, whose bottom is less than 2,420 feet above sea level, or 50 to 75 

feet lower than the Milk River. 

In 1921 the writer made a hasty examination of an 

old gravel pit at a coulee cutting the south bluff of the-. 

Milk River Valley west of Toledo, in the NE. % sec. 5,. 

T. 32 N., R. 17 E. The sides of the pit were badly 

obscured and partly overgrown. There is here a thick 

bed of quartzite gravel in which no ·pebbles identifiable as glacial drift were found by the writer. At on& 

point overlying this stratified gravel was 5 to 10 f-eet 

of gravel which is clearly of glacial origin, inasmuch 

9 Stebinger, Eugene, Possibilities of oil and gas in north-central 

Montana: U. S .. Geol. Surve7 Bull. 641, p. 72, 1917. 

10 Calhoun,. F. H. H., The Montana lobe of the Keewatin ice sheet:. 

U. S. Geol. Survey Prof Paper 50, p. 38, i900 . 
68 PHYSIOGRAPHY AND GLACIAL GEOLOGY OF. EAS'.rERN MONTANA 

as it contains granitic pebbles such as occur in the 

glacial till. At another point the lower nonglacial 

gravel was overlain by a bed of dense gray jointed 

pebbly glacial till which was rusted along joint faces 

and presented the appearanqe· of having been disturbed by being overridden by a glacier. Overlying 

this was dull buff till of the Wisconsin drift sheet, 

and at another place the lower till was overlain by 20 

feet of glacial gravel. The exposure is poor, and the 

examination was too hasty to be conclusive. The conditions as seen suggest the presence of glacial gravel, 

of two deposits of glacial till, the older one possibly 

of Iowan or Illinoian age, and of an underlying bed 

of nonglacial gravel. This exposure is near the east 

side of the old buried valley · of the Missouri River 

where it is cut across by the present inner valley of the 

Milk River. The latter valley is less than half a mile 

in width in this vicinity, though about 8 miles farther 

eas~ it is nearly 3 miles wide. Other gravel pits near 

Chinook have not been examined. 

In 1890 a well was drilled at Chinook in an attempt 

to develop artesian flow. According to the log quoted 

by Stebinger ,u this well penetrated loam and sand 112 

~ feet and " stone. boulders " 12 feet over stiff clay 

(shale) and sandstone. It is not known that the 

" stone boulders " are glacial drift. 

The record of the deep well at Chinook; where 124 

feet of filling was penetrated, indicates that there is 

probably at least 125 feet of filling in the Milk River 

Valley at Harlem-that is, the bottom of the inner 

valley beneath this filling is about 400 feet lower than 

No. 2 bench north of Harlem, or 2,240 feet above sea 

level. 

In 1917 Collier examined excavations at Wolf 

Point where gravel was being dng from the bank 

no7th of the Great Northern Railway shops then being 

built. These were reexamined by the present writer 

in 1920, together with smaller pits near the cemetery 

northwest of the town. Wolf Point is about 25 feet 

above the Missouri River, and the bench in whose edge 

are the gravel pits is about 20 feet higher. Collier 12 

gives the following description of the deposits, which 

were better exposed in 1917 than in 1920: 

Section exposed in g·ravel pit at Wolf Point 

Feet 

Soil with a few scattered granite boulders on the surface__ 1 

Glacial till, containing granite cobbles__________________ 5 

Gravel, chiefly quartzite but containing fragments of sandstone, porphyry, and near the bottom shale____________ 13 

Shale, Bearpaw. 19 

The gravel is interstratified with lenses of sand, and the 

bedding planes are nearly horizontal. The gravel consists for 

n Stebinger, Eugene, op. cit., p. 81, quoted from Nettleton, E. s .. Final report on artesian and underflow investigation to the Secretary 

of Agriculture : 52d Cong., 1st sess., S. EX. Doc. 41, pt. 2 pp. 72-78 1~2 ' • 

u Collier, A. J., Geology" of northeastern Montana:. U. S. Geol. 

Survey Prof. Paper 120, p. 36, 1919. 

the most pal!t of well-rounded pebbles of quartzite, probably 

derived from the Flaxville gravel, but it contains some pebbles 

of porphyry and fragments of sandstone . and fossiliferous 

Bearpaw shale near the bottom. A thorough search failed to 

reveal any glacial material such as granite pebbles. ' 

There are some highly fossiliferous concretionary 

masses from the Cretaceous shale. Many pebbles and 

"boulders of limestone and granite were seen by the 

present writer in the till and also on the bottom of the 

excavations, but none were found in place in the undisturbed gravel. Apparently.the.granite and limestone 

pebbles came from the overlying. glacial till. It is 

probable, therefore, that the gravel was deposited in 

the valley before the advent of the glacier. The same 

relation was found in the pits near the cemetery and 

in those examined ·north of Malta (p. 44). 

Collier also writes : 13 

Another gravel pit 2 miles west of Brockton shows finely laminated sand. The bedding at the west end of the pit lies nearJ.r 

horizontal. whereas that at the east end dips east about 70°. 

The surface has been eroded irregularly an'd is covered with 

glacial till to a maximum depth of about 15 feet. The bottom 

of this· pit is about 40 feet above the present river level. 

The following log of the village well at Wolf Point 

shows the depth and character of the filling under the 

flat on which the village stands, at a point a short distance south of the railway, which is at the north side 

of the inner valley about 25 feet above the river. 

Lou. of well at Wolf Point, Mont.a 

Clay ___ ------- ______ --- __ ---- _______ --·------------------- ___ ---- Quicksand ___ -------------·--------------------------------------_ GraveL_------- ________________ ------------ __________ -----------_ Blue clay------- _________ ------ ____ ------------- _________________ _ Quicksand ___ ------------ ________________ ------ ___ --------- _____ _ 

Blue clay--------------------------------------------------------- Quicksand. __ ---------------------------------------------------- GraveL_---------------------------------------------------------

T::ak· Depth 

(feet) (feet) 

35 

6. 

15 

2 

17 

5 

11 

g 

35 

41 

56 

58 

76 

80 

91 

100 

• Record from Peter Lenz, superintendent of waterworks; well drilled in 1897. 

From these too meager observations it appears that 

before the invasion ·of Montana by the Keewatin ice 

sheet the Missouri River had cut down well below the 

present level of the Milk River at least as far west as 

Havre, and that after being cut the gorge was partly 

refilled with clay, sand, and gravel to a level above 

that of the present flood plain. Perhaps this cutting 

was due to rapid deepening of the Missouri gorge 

through the Dakotas after the Kansan stage of glaciation. It is not clear that it was due to regional uplift, 

inasmuch ltS there are no data in hand to show that 

deepening and refilling occurred more than a short 

distance up the Yellowstone Valley. 

During the advance of the Keewatin ice sheet at 

the Iowan or Illinoian ( ~) stage of glaciation an im13 Idem, p. 36. 
ILLINOIAN OR lOW AN ( ? ) STAGE OF GLACIATION 69 

mense amount of water must have been diverted southeastward from Canada into .the Missouri River. This 

would assist the cutting u,ntil the ice front reached 

and blocked the gorge in North Dakota and Montana. 

After that occurred the drainage was forced into temporary channels about the edge of the ice (p. 88) until 

the ice front again receded. 

ILLINOIAN OR IOWAN (?) STAGE OF GLACIATION 

Thete seems to be no clear evidence that the Keewatin ice sheet invaded Montana at either the N~­

braskan or the Kansan stage of glaciation. Neither 

is it certainly known that there was extensive development of the Keewatin glacier at the Illinoian stage, 

when the Labradorean tee sheet extended southwestward over most of Illinois and encroached on southeastern Iowa. After the Sangamon stage of deglaciation, however, there came on a new development and 

extension of the great Keewatin ice sheet centering 

in the Hudson Bay region. The ice spread southward across Minnesota into northern Iowa and left 

a deposit of drift of moder9:te thickness, which has 

been regarded as of pre-Wisconsin age but not so old 

as the Illinoian drift of the Labradorean ice sheet.14 

There are some good reasons, as it seems to the writer, 

for thinking that the drift found in the Dakotas and 

in Montana, outside what is regarded as the limit of 

the Wisconsin drift, is not older than the Iowan drift. 

It is possible, however, that it is really of Illinoian 

age. This may include the outer drift mapped by 

Calhoun along and south of the Missouri River, and, 

if so and if it is of Iowan age, it indicates that the 

Iowan ice sheet reached its maximum southwesterly 

extent in the region of Great Falls, Mont. 

There seems to be no reason for thinking that general altitudes above sea level in this region were very 

different, after the P.evelopment of the third set of 

terraces, from what they are now. The big uplift evidently had preceded. the formation of that bench or 

set of terraces. Perhaps an uplift amounting to a few 

hundred feet in the mountains accompanied the trenching ~f No. 3 bench near the mountains, and with this 

is perhaps to be correlated some of the filling of the 

inner valleys farther east, where the gradient was 

lower and there may perhaps have been some later 

uplift. This is discussed above (p. 104). If the advancing ice sheet first reached the Missouri River in 

the Dakotas, the waters in the valley above must have 

been ponded and forced to find a higher outlet somewhat farther west. This ponding of the waters would 

help to furnish the conditions required for deposition 

of the filling of clay, sand, and gravel described above. 

As the ice occupied the valley farther and farther west 

u Alden, W. C., and Leighton, M. M., The Iowan drift, a review of 

the evidences of the Iowan stages of glaciation: Iowa Ge<ll. Survey, 

- vol. 26, pp. 49-212, 1917. 

deposits of till and boulders were added to the filling, 

and in places, as at Wolf Point, Brockton, Malta, and 

Toledo (p. 67), glacial till overlies the nonglacial 

stream dep.osits. · 

PRE-WISCONSIN DRIFT OF THE XOUN'l'AIB' GLA.CIDS .A'l' 

LOW LEVELS -

It is of some importance to know whether there is 

any evidence of an advance of the mountain glaciers 

after the time of development of the lower level of the 

second set of terraces and yet prior to the well~marked 

extension of the Wisconsin stage-that is, of an exten· 

sion of the mountain glaciers ·at relatively low levels 

corresponding to the evidence that a pre-Wisconsin 

ice sheet invaded this region from the Hudson Bay 

region, after the plains had been degraded and the 

streams had cut down to or below their present levels. 

Good evidence· of such a glacial advance down onto 

the Circle terrace at the Bull Lake stage of glaciation· 

(of Blackwelder 15 ) is found ii;l the Wind River 

Mountains of Wyoming. There is some such evidence 

in the Glacier Park region, but it is very meager and 

is not regarded as conclusive. The evidence consists 

of the following section : 

Section of glacial ana interglacial aepolritB at GZaoier Park 

Btation 

Ft. in. 

Wisconsin glacial drift and outwash: Stratified gray 

gravelly drift, more clayey at top__________________ 15 

Interglacial deposits(?) : 

Sand and yellow laminated clay---------------- 5 

Black soil with rootlets------------------------ 5 Black sandy clay ___ .;___________________________ 3 

Iowan or Illinoian ( ?) glacial drift: Rusty pebbly 

drift, partly cemented to conglomerate ; stones becoming coarser downward to boulders 1 to 4 feet in 

diameter ; masses of black shale included__________ 15 

Cretaceous black shale; u:gper layers broken up and 

overthrust eastward in small folds as if. by ice 

push-------------------------------------~------ 5 

The exposure is in a rarine near the railway water 

tank. The deposits above the black shale suggest preWisconsin glacial drift overlain by an interglacial soil, 

and this in turn overlain by Wisconsin glacial drift 

or outwash. As this older drift is exposed at about 

4,750 feet above sea level, or about 1,300 feet lower 

than the base of the high-level pre-Wisconsin till un 

the ridge north of lower Two Medicine Lake, 7 miles 

northwest of Glacier Park station, and as it is composed entirely of fragments from the pre-Cambrian 

and from underlying Cretaceous rocks of the mountains to the west, it suggests a rather late stage Qf 

mountain glaciation. 

This section was in less satisfactory condition when 

reexamined in August, 1920, and July, 1921. There 

15 Blackwelder, Eliot, Post-Cretaceous history of the mountains of 

central western Wyoming: Jour. Ge<~logy, vol. 28, p. 310, 1916. 
70 PHYSIOGRAPHY AND GLACIAL GEOLOGY OF EASTERN MONTANA. 

was, however, a suggestion of two stages of glaciation, 

though all trace of buried soil had disappeared. At 

the bottom was exposed about 15 feet of rusty, very 

stony till overlain by 5 feet of gravel. Above this 

was about 4 feet of gray till, overlain in turn by 5 

. feet of gravel. 

About 1% miles farther down Midvale Creek, in 

sec. 29, T. 31 N., R. 12 W., the following section was 

seen in 1911 : 

Section of glacial and intergl.acial ( f) deposits southeast of 

Glacier Park statioo 

Feet 

Wisconsin glacial drift: Loamy E!Oil, gravel, and boulders----------------------------------------------- 5-10 

Interglacial ( ?) lake deposit: Fine laminated buff silt 

(loesslike)_~--------------------------------------- 15-25 

Iowan or Illinoian ( ?) glacial drift: Gravelly drift_ ___ , ( ?) 

Cretaceous deposits. 

About 25 miles farther east down the Two Medicine 

Valley, 3 miles east of Family, in sec. 31, T. 32 N., R. 

8 W., Stebinger observed the following section in 1912 

as shown b;y his field notes : 

Section of glacial antZ itnterglacial ( f) deposits on Two 

Med.icine Oreek in 1912 

Recent: Feet 

Gray sandy loam -------------------------------- 2 

Red soil with a few small pebbles________________ 1lh 

Wisconsin drift of Two Medicine Glacier : Clayey till 

containing striated pebbles of mountain rocks________ 10 

Interglacial deposits: "Old soil," a bluish-black clay___ 2 

Iowan·or Illinoian ( ?) drift of Two Medicine Glacier: 

Blue-gray pebbly clay and unassorted pebbles and 

boulders of mountain rocks, partly striated______ 2 

Yellow to buff pebbly clay and unassorted pebbles 

and boulders of mountain rocks, partly striated__ 3 

Cretaceous: Bearpaw shale, weathered at top __________ 100 

This section is at the apex o.f the sharp bend in the 

stream, so that there is active cutting and slumping, 

and the upper part of the section was almost inaccessible for close inspection in Sept-ember, 1920, when it 

was visited by the pr·esent writer. The section is 

about 1% miles south of the point where the irrigation 

-canal leaves the Two Medicine Valley and enters the 

lower of the two sags where Flat Coulee was beheaded, 

as described above. It is clear that all the drift exposed at this place was deposited after Two Medicine 

Creek had abandoned that coulee and had cut down 

within 100 feet of its present level. The following is 

the section as exposed in 1920 : 

.Se!Mm of glacial and interglacial deposits on Two M edioine 

Oreek in 1920 

Feet 

4. Recent: Gray loamy soiL------------------------- 1 

:S. Wisconsin drift of Two Medicine Glacier: 

Reddish-brown pebbly weathered zone___________ lh 

Clayey till, grayish, containing striated pebbles or 

mountain rocks onlY-------------------------- 5-10 

2. Interglacial ( ?) deposits: Dark rusty-gray clay, coa-- .Feet 

taining some decayed pebbles .. __________ .;._______ 2 

1. Iowan or Illinoian ( ? ) drift of Two Medicine 

Glacier: · 

Dull buff to gray till, containing pebbles of 

mountain rocks onlY-------------------~---- 5 

Cretaceous: Bearpaw shale, weathered brownish at 

tOP-------~------------------------------------ 100 

The section does not demonstrate pre-Wisoonsin glaciation at this place, though the oxidation of No. 2 

and the top of No. 1 and the presence of the decayed 

p~bbles seem to indicate an interval of exposure to 

weathering before the gray till (No.3) was deposited. 

In one place the clay (No. 2) appears to have been 

shoved up eastward and a thin ~tringer is drawn .out 

from this into the till above, as if due to drag of the 

later ice sheet as it advanced eastward down the valley. 

The weathered and eroded top • of the dark shale below the lower till is about 60 feet below the level of 

the canal in the sag to the north. 

The presence of hard cemented glacial gravel at 

several places on Badger and Little Badger Creeks 

also suggests pre-Wisconsin glaciation. . 

One section on the St. Mary River about 2 miles 

below the mouth of Kennedy Creek, in the SW.% sec. 

25, T. 37 N., R. 14 W., examined by the writer in 1911, 

and two sections close togethoc a n1ile or less below 

this point, about a mile above the Bureau of Reclamation camp at Fletcher, which were examined by 

Stebinger and the writer in 1912, suggest two extensions of the St. Mary Glacier after the valley had been 

cut nearly to its present depth. These sections are as 

follows: 

'sections of glacial and Zaoustrine deposits on St. Mary Rivey 

north of Babb · · 

No.1 

Feet 

Wisconsin drift of St. Mary Glacier: Glacial till con-

. taining mountain rocks and masses of clay from underlying beds-------------------------------------- 3-10 

Lacustrine deposits : Fine stratified saml and clay containing few or no pebbles except near the top, where 

small pebb~es of pre-Cambrian granite from Canada 

were found (probably berg-transported)------------- 35 

Iowan or Illinoian ( ?) glacial outwash: Gravel; pebbles 

of mountain rocks only, some striated______________ 3 

Cretaceous : Sandstone, partly disintegrated at top_____ 20 

Ne. 2 

Recent : Wind-blown sand---------------------------- 0-3 

Wisconsin drift of St. Mary Glacier: Glacial drift con· 

taining pebbles of mountain rocks------------------ 6-10 

Lacustrine deposits: Fine stratified sand____________ 4-S 

Iowan or Illinoian ( ?) drift of St. Mary Glacier : ' 

Sandy tiH containing striated pebbles of mountain rocks _____________________________________ .;.____ 3-12 

Interstrati:fied fine sand and silt laminated with 

some fine graveL------------------------------ 6 

Cretaceous : 

Fine rippled sand. or decomposed sandstone-------- 30 

Sandstone.,..------------------- ------------------- 80 

' 
ILLINOIAN OB IOWAN ( ? ) STAGE OF GLACIATION 71 

No.3 

.Recent:. Stratified clay and sand_-__________ ...;. ________ .,.._ 

cited above are regarded as suggestiv& of .what m~re 

F~~ detailed studies may reveal rather tha:a . .,.;very impor;. 

Wisconsin drift of St. Mary Glacier : Glacial till containing many pebbles of mountain rocks_____________ 6 

Lacustrine deposits: Stratified sand and clay__________ 20 

Iowan or Illinoian ( ?) drift of St. Mary Glacier: Glacial till containing many pebbles of mountain rocks__ 5 

.Cretaceous : Clay and sandstone---------------------- 30 

Although these three sections do not afford good 

dvidence of an intergla~ial stage, the presence of the 

lacustrine dep~sits between the two deposits of glacial 

drift shows at least ·a short interim between the advance~ of the St. Mary Glacier. The presence of the 

small pebbles of pre-Cambrian granite from Canada 

at the top of the lake beds at one place, on . the other 

hand, suggests that the ponding of water in the "valley 

was due to the Keewatin ice sheet. 

It is not yet certain that the relations of wind -blown 

deposits in the region of the mountain front . are particularly significant~ There are a few exposures where 

a deposit of loess occurs between the pre-Wisconsin 

and Wisconsin continental tills. If this loess corresponds in age to the main deposit of loess along ~he 

lower Missouri and Mississippi Rivers in Iowa, which 

overlaps Iowan till, it may be that the low-level mountain till which it overlies near the mountain front is 

also Iowan or older. 

In places where till or outw~sh gravel,of the mountain glaciers is overlapped by till o_f the continental ice 

sheet a deposit of loess and in some places a black 

soil intervenes. In these places it may be that the 

overlapped mounta~ till or outwash is either Iowa~ 

or Illinoian rather than Wisconsin, as Calhoun u 

supposed. It may also be that some, at least, of the 

lacustrine deposits in the sections cited by Calhoun 

are the results of ponding of the streams by the Iowan 

or Illinoian ice of the Keewatin glacier. If this 

is the case, the underlying mountain till and outwash 

gravel are probably also either Iowan or Illino~an. 

Calhoun 17 cites one section on the Belly Rivet at 

the terminal moraine of the Keewatin ice sheet, showing in order, beginning at the bottom : 

A, TUl formed by Belly River Glacier containing m~ny b::mlders, all of which are smoothed and striated to an unusual degree, 75 feet; B, soil, of which only a small exposure was aeen, 

which contained no fossils; C, till. forme4 by the Keewat~ ice 

sheet, 80 feet. 

He did not, however, regard the soil (B) as indicating any considerable lapse of time between the depo~ition of the mountain drift (A) and the overlying drift 

of the Keewatin ice sheet . (C). No such inter"9"ening 

bed as the soil (B) was observed by the present writer 

in any of the exposures where mountain drift was a;een 

overlain by drift from the E:eewatin ice. · The sections 

aocalboun, F. H. H., The Montana lobe of the Keewatin ice sheet: 

U. S. Geol. Survey Prof. Paper 50, pp. 46-49, 1906. 

1'l Idem, p. 49, fig. 31. 

tant or at all conclusive in themselveAJ. · 

PRE-WISCONSDI' DRIF.r OF THB XUWA~· euom 

UNDERLTiliG LATD DB.Ift . . . · . 

At several places west of the latitude of the Cyp~ 

Hills and Bearpaw Mountains exposures o:f pre-WlS0 

c 

B 

consin drift of the Keewatin ice 

sheet have been seen by StebiD;ger 

and the writer, and the fact that 

none of these are much more than 

100 feet above the present streams 

is regarded as evidence that the 

glacier making· the deposits did 

not invade -this· region until later 

than the time of development of 

the lower level of· the second set of 

terraces-that is, long after the 

time of deposition of the high-· 

level drift of the mountain glaciers found. on No. 1 bench and 

the upper No. 2 bench in tp.e · Glacier National Park region, and not 

very long before the Wisconsin 

stage of glaciation. On this basis 

it might. be inferred that the 'deposits are those of the Iowan stage 

of glaciation. The fact that it has 

not yet been demonstrated that 

there was at the Illinoian stage an 

ad vance of a glacier from the west 

side of Hudson Bay, corresponding to the Labradorean glacier of 

FIGURJJ 3.-Section on that. stage, 1ends weight to a tenta- st. Mary River north 

of Sloan's ranch, tive correlation of the deposits Mont. A, Shale; B. 

northeastern drift, 2 with the Iowan drift, as repre- feet, c o n t a 1 n 1 n g . 

sented in northeastern Iowa. ~ · ;:,:1:lra; d~C:Of~~ 

. Calhoun 18 illustrates a section · loess, 5 feet, con- taining concretions, observed by him. on the St. Mary hard shells aDd 

bones of small ani- River north of Sloan's ranch, a maliJ; D, ~DII, 10 

few miles nqrth of the interna- {':~ ;: , bla:n~!ti:r 

tional boundary, by a figure, re-. ~:pe~ h :a:~~he~i~ 

produced here as Figure 3. . :::.:~ A~et,bedJn~ 

The present writer examined at the top; F, norths eastern till, containnumerous exposures on the t. tng crystalline boul- . 

Mary River in 1912 and 1920, bOth ~~~~:.~om F. H. H. · 

above and below Sloan's ranch, but . " 

this section, if still preserved, is evidently one ·of 

those which were not examined. · This section is particularly interesting because, if the lowe~ bed of 

northeastern drift (B) is in reality um.nodified preWisconsin glacial till deposited by the Keewatin· ice 

sheet it means that the St. Mary Valley·had at the ' . - . .. - ... -. - .. - ·, 

lllldem, fig. 30. 
72 PHYSIOGRAPHY AND GLACIAL GEOLOGY OF 'EASTERN MONTANA 

time of t~at glacial extension been cut down approximately to its. present depth, more than 1,000 feet 

below the level of the pre-Wisconsin mountain drift 

on the Hudson Bay divide, 8 or 10 miles to the south 

and more than 1,600 feet lower than the drift capping 

Kennedy Ridge, a few miles farther southwest. 

In response to a letter of inquiry concerning this 

bed (B) of northwestern drift, Calhoun 19 wrote in_ 

part as follows : 

Along this river in the vicinity of Sloan's ranch there had 

been a great deal of slumping, and, with the time and help 

that I had at my command, I could not take the trouble to 

make any excavations. I was satisfied in my own mind that 

the lower bed (B) was really part of the older drift sheet, 

Scale o £ 2'4. 36 48M"lles 

decomposed igneous rocks occurred in considerable numb~. 

I am not sure whether the deposit was till or material let 

down by erosion. If it was till, it was very stony till. I· 

found no other deposit in the area which containro badly 

decomposed ign·eous rock of undoubtedly northeastern origin. 

It is not probable or, as it seems, possible, on accouni 

of the topographic relations, that the Keewatin ice 

was depositing the bed of drift (B) at so low a levelin the St. Mary Valley, in the vicinity of. Sloan's 

ranch, at approximately the same time that the mountain glaciers were depositing· the drift on the highlevel tracts. This is a reason for regarding thil preWisconsin drift in the valley as perhaps not older than 

Iowan. 

Farther north, on the Belly River near 

Lethbridge and on the Old Man River as 

far west as Brocket (fig. 4), there are considerable deposits of unmodified glacial 

till, a part of which evidently is and a part 

of which may be of .pre-Wisconsin age, 

exposed in the bluffs and unquestionably 

in place, not far above the present streams. 

FIGURE 4.-Map of portions of southern Alberta and northern Montana 

In the course of a reconnaissance trip in 

southern Alberta in 1912 the writer spent a 

day at Lethbridge and made an examination of the series of drift deposits described 

by Dawson. 20 In the time spent, however, 

there was opportunity for study of only a 

small part of the fine exposures in this vicinity. ·For some distance both north and 

south of the railway bridge at this place 

the drift deposits are. well exposed in the 

bluffs forming the sides of the valleys. 

The Belly River Valley is here about 300 

feet in depth, a steep-sided trench cut in 

the undulating plain. From the railway station down into the valley south 

of the railway bridge to the vicinity 

of the municipal coal mine, filter beds, 

and electric-power house, the following 

series of deposits was observed in the east 

bluff: 

but, although !looked for many days, I found nothing else in 

any other river valley to substantiate this. The age of the 

boulders in the two sheets, as shown by the amount of weathering to which they had been subjected, was very different, and if 

I remember rightly, as .far as I could make out from the badly 

weathered specimens, the rock material was also different. 

i: left the section very much pleased with what I thought was 

evidence that could not be disputed as to the existence of two 

different ice sheets from the northeast, but after many weeks 

of search··'l came to the conclusion that it would not do to claim 

the existence of another sheet upon the evidence of one section. 

The layer B was a layer of boulders-some of them igneous 

and every one badly decomposed. In this layer there was not 

one sound rock of igneous origin, although there were quartzite 

gravels in the formation which were not decomposed. These 

a Personal commubications, Nov. 25 and 80, 1912. 

Seotion at Plei8tocerne · de'Posits on Belly River at Lethbridge~ 

Alberta 

4. Wisconsin stage: ButT loose-textured to moderately 

compact clayey till of Keewatin ice sheet containing 

plentiful pebbleS! of pre-Cambrian rocks from the 

northeast and Paleozoic ( ? ) limestone pebbles, beFeet 

neath upper grassed slope ________________________ 15Qj: 

3. Interglacial : Fine gray compact cemented sand or silt 

with, in places, some intercalated thin layers ·of 

brown to black lignitic material ; locally contorted 

in part; clay-iron nodules in places at top of bare 

shoulders of the bluff ___ 7-------------~----~----- 10j: 

20 Dawson, G. M., and McConnell, R. G., Glacial deposits of southwestern Alberta in the vicinity of the RoeiQr Mountains: Geol. Soc. 

America Bull., vot. 7, pp. 89-41, 1895. 
. ~· 

lltLINOIAN OR lOW AN ( f) STAGE OF GLAOIATION 73 

Feet 

2. Iowan or Illinoian stage ( ?) : Dense, compact darkgray till of Keewatin ice sheet; pebbles mostly. 

from the Rocky Mountains; pebbles of pre-Cam-

- brian cry~talline rocks from the northeast plentiful 

but less abundant than in upper till ; forms bold 

salient of the bluff----------------------------- 40--50 

1. Interglacial: Stratified gravel ("Saskatchewan") 

composed mostly of 4 to 6 inch well-rounded pebbles 

of quartzite from the Rocky Mountains__________ 10-12 

Cretaceous shale and coal. 

The bluff on the opposite side ·of the river at the 

bend north of the wagon bridge expo8ed the following 

section. (See fig. 5.) ' 

Section of Pleistocene depo8it8 on BeUg River near Let11,lniil.ge, 

Alberta 

· 4. Wisconsin stage: Loose buff tlll of Keewatin ice sheet, 

with pebbles of pre-Cambrian crystalline rocks from 

Feet 

the northeast and pebbles from Rocky Mountains__ 3--13 

3. Interglacial : 

Laminated papery silL------------------------ 1-3 

Buff wind-bedded loess, alternating with beds of . 

fine stratified sand-------------------------- 0-50 

2. Iowan or Illinoian stage ( ?) :·Compact jointed till of 

Keewatin ice sheet, with pebbles of pre-Cambrian 

crystalline rocks from the northeast and pebbles 

from Rocky Mountains. Upper 15. feet oxidized 

buff in places, dark gray below------------------ 25-30 

1. Interglacial: Quartzite gravel (" Saskatchewan "), 

with .some interbedded sand--------------------- 10-15 

Cretaceous shale------------------------------------- 100 

The gravel (1) in the two sections, which represents 

the "Saskatchewan" gravel of Dawson and McConnell, is made up exclusively, where examined, of waterworn pebbles from formations exposed in the mountains 60 miles to the west and southwest, mostly of 

pink and white quartzite, with smaller percentages of 

maroon and greenish argillite, diorite, amygdaloidal 

trap rock, gray limestone, and conglomerate containing black chert pebbles. At one· point two or three 

fragments of granite were found among the loose 

pebbles in the excavation, but it was thought they 

might have rolled down from the drift higher in the 

slope, which was deposited by the Keewatin ice. No 

such fragments were found embedded in the stratified 

gravel. The top of the gravel is marked by a sharp 

horizontal line, and at only one point was there any 

evidence of disturbance of the bedding, such as might 

be expected to result from its being overridden by the 

continental ice sheet. Perhaps the gravel was cemented by ice to a solid mass when such overriding 

took place. 

By far the larger percentage of the ,pebbles in the 

dense, compact lower till (2) came from the Rocky 

Mountains, probably derived by the glacier from deposits of gravel in the valleys such as those composing 

the underlying bed. Intermingled with these are 

pebbles of granite and other crystalline rocks · from 

the pre-Cambrian formations west of ·;Hudson. BQ.y, 

showing that the till was deposited bY: ,;the Koow~ 

ice sheet. The surface of the lower. till is un~velJ, 

especially in the second exposure described, and·, the 

oxidation of the upper part of this till :is evidence of 

its exposure to weath~ring prior to the. deposition of 

the upper till. 

The stratified beds ( 3) indicate deposition during 

a stage of deglaCiation. At the exposure north of the 

bridge there is nearly 50 feet of interbedded fine sand 

and loesslike silt resembling an eolian deposit. Overlying this is 1 to 3 feet of fine laminated papery silt. 

The relations indicate that this deposition was followed by a period of erosion, for the. deposit thins 

abruptly toward the east side of the exposure until it 

pinches out entirely between the lower till (2) and the 

upper till ( 4). The 

upper till (4) man- 4~~~~"'­

tles the slope and extends thence up to 3 

··"··· \f::;~;.;::·~~G~:S:~zy~~~~ the upland as if it 

lay on the side of an 

interglacial valley. 2 

The extent of the interglacial deposit ( 3) 

northward down the 

valley was not determined. T h e r e 

seemed to be considerable . of the loesslike material on the 

east side north of the 

r a i 1 w a y bridge, 

where such material 

exposed in the sides 

of a ravine was being used in making 

brick. South of the 

railway bed 3 consists of partly ceFIGURE 5.-Section on Belly River near 

Lethbridge, Alberta. ·1, Quartzite gravel 

("Saskatchewan," interglacial), 10 to 

15 feet, overlying Cretaceous shale ; 2~ 

p~ Wisconsin till of Keewatin ice sheet 

(Iowan or Illinoian?), 25 by 30 feet ; s. 

loess and wind-blown san<J, 0. to 50 feet, 

overlain by. laminated silt, 1 to 8 feet 

(interglacial) ; 4, Wisconsin tUl -of 

Keewatin ice sheet, 3 to 13 feet 

mented, laminated grayish fine sand or silt. A· small 

opening in the grassy slope at. one point in the side of 

a ravine back of the power house exposed as part of 

these deposits the following beds : 

Partial section ot interglacial. be~ a,t Lethbridge, AlbertG 

Sand, top not exposed. Inches 

Soft, brownish vegetal materiaL ________ _:____________ -Q-% 

Sand---------------------------------·--------------- 4 

Brownish vegetal material in thin layers______________ 4 

Sand------------------------------------------------ ~ 

Black lignitic material, partly glistening coaL-------- lA-l 

Sand, bottom not exposed. 

The beds at this point were ·much contorted, ~ither 

as the result of slumping or possibly from having been 

overridden by the later ice sheet, so that it could not . 

be determined that the vegetal material had actually 

grown where deposited. ·At one point, however, fin& 
74 PHYSIOGRAPHY AND GLACIAL GEOLOGY OF . EASTERN :MONTANA 

rootlike fibers were noted extending downward from 

one of the vegetal layers into the sand below. The 

vegetal material probaoly corresponds to the peaty or 

Hgnitic material observed by Dawson 21 at this horizon 

several miles ·farther down the valiey and represents 

one of the several phases of interglacial deposition in 

this region. 

The upper till ( 4) is of looser texture, and .a higher 

percentage of the included pebbles are of pre-Cambrian crystalline rocks from the northeast than in the 

lower till ( 2), although even here a considerable proportion of them are from the mountains. 

About 200 yards below the confluence of Willow 

Creek and the Old Man River, a few miles northeast of 

Macleod, in T. 9 N., R. 25 W., the following section 

was observed: 

Secticm of Pleistocene depoaits on OZa MQ!n EWer near 

M{Wleoil, AJberta. 

Feet 

4. Gray sandy unstratified loam----------------------- 0-3 

3. Wisconsin stage : Buff to gray loose till containing 

pebbles from the Rocky Mountains and a good percentage of the pebbles from the pre-Cambrian crystalline rocks from the northeast------------------ 15-20 

2. Interglacial: Dark fine laminated silt, a few inches. 

1. Iowan or Illinoian stage ( ?) : Very dense, hard gray 

till containing pebbles from the Rocky Mountains 

and a somewhat smaller percentage of crystalline 

pebbles than in 3; overlies the ero(led surface of the 

Willow Creek fod:nation (Cretaceous or Tertiary) 

and fills two coulees eroded therein ________ :_ _____ -:-_ 20-,qO 

It is thought that deposits 1 and 2 in this section 

may correspond respectively to deposits 2 and 3 in 

the sections at Lethbridge. 

In none of the sections examined in this locality 

was the" Saskatchewan gravel" present, and in none 

other than those given above. was any evidence of more 

than one till observed. At some of the localities, however, the bottom of the drift filling the preglacial· 

·valley has not yet been reached by the stream. 

Farther west up the valley of the Old Man River 

a section was observed at the wagon bridge near 

Brocket, 16 miles southwest of Macleod, in the Piegan 

Indian Reservation, exposing the following beds: 

Section of Plei8tooone deposits near Brocket, AZber:a. 

4. Recent coarse gravel underlying a river terrace and 

lying on the eroded surface of the tilL____________ 15 

B. Wisconsin E!tage : Dense dark-gray till ; pebbles mostly 

from the Rocky Mountains, with a small percentage 

of pebbles of pre-Cambrian crystalline rocks from the 

northeast---------------------------------------- 0-20 

2. Interglacial : Dark laminated silt-------------------- 1-3 

1. Iowan or Illinoian stage ( ?) : Dense gray till, not very 

stony; pebbles mostly from Rocky Mountains, with 

a very small percentage of pebbles of pre-Cambrian 

crystalline rocks from the northeast_______________ 30 

m Dawson, G. M., Canada Geol. Survey Rept. Progress for 1882-1884, 

p. 144c, 188fi. 

Here again deposits 1 and 2 IJl&Y perhaps represent 

beds. 2 and 8, . respooti vely; in the Lethbridge exposure. 

This is the most west~rly point at which any evi .. 

' dence of more than one sheet. of till deposited by the · 

continental glacier was observed. At the ·nearest 

point the mountain _front ,is distant about 20 miles to 

the southwest. At the exposure near Brocket the river 

has not yet cut down to the bottoin of the drift filling 

in the preglacial valley. From thiS relation it appears 

that at least one of the main streams . ha.<l cut below 

its present level before the first invasion .of the region 

by the Keewatin ice sheet of which there is evidence.· 

In the vicinity of the confluence o-f the W aterton 

and Belly Rivers and southwestward to points wjthin 

a few miles of the village of Hill Spring, Alberta, in 

T. 4 N., R. 27 W., numerous places were observed 

where the bottom of the drift filling has not yet been 

reached by the streams. In these places, however, no 

conclusive evidence that the lowest till exposed is older 

than the Wisconsin stage was . noted. It can not be 

asserted, therefore, t at the valleys of these streams 

were deeper than no this far south at the time the 

lower drift was bei . g deposited in the vicinity of 

Lethbridge. The ge ' eral relations, however, suggest 

that there were pre- owan or pre-Illinoian channels 

about as deep as the resent ones, as indicat~d by the 

':Saskatchewan grav I" described a~ve. 

Evidence showing he presence of pre-Wisconsin till 

beneath the later d ift south of the international 

boundary is very me 1

ger. About 15 miles east of the 

Sweetgrass Hills, in small coulee tributary to Sage 

Creek from the nort in T. 36 N., R. 8 E., the following section was obs , ved in 1913 by Stebinger 22 in 

good exposures· exte ing several hundred .feet along 

the nearly vertical b nks of the c~ulee: 

I 

Section of Pleistocene posits near Sage Greek, f.'. 96 N., 

• 8 FJ., Mont. 

I Feet 

Wisconsin stage: Stony, ompact tlll of Keewatin ice sheet 

containing abundant bbles of pre-Cambrian crystalline 

rocks and Paleozoic ( ) limestone ·from the northeast. · 

This till is as fresh nd unweathered as that usually 

found in the drift of isconsln age-------------------- 5 

Iowan or Illinoian stag ( ?) : Stony, .compact, bUt much 

weathered till of Kee atln ice sheet, contai.ni.ntf many 

pre--Cambrian crystall e pebbles from the northeast but 

very few if any limes ne pebbles _________ .::._ _____ ..;.___ 6 

Cretaceous clay and san tone of Judith River formation. 

The recognition of two separate drift sheets in thi~ 

section rests entirely on the difference in amount of 

weathering, their genera~ composition and appearance 

being almost identical except· in this particular. In 

the older till the crystalline pebbles are so much deu Alden, W. C., and Stebinger, Eugene, Pre-Wisconsin .glacial drift 

in the region of Glacier National 'Park, · Mont. : Geol. Soe. America · 

Bull., vol. 24, pp. Ml--572, 1913. 
U,LLNOIAN OR lOW AN ( 1) STAGE OF GLAOIATION 75 

cayed and friable that they fall to pieces with a light 

blow from the hammer; in the upper till they are firm 

and fresh and practically unweathered. The limestone 

pebbles, which are fairly abundant in the upper till, 

are almost entirely leache4 out of the lower, which is . 

partly indurated in places and deeply iron-stained. 

The difference in the appearance of these two bands of 

till is so marked that they can easily be distinguished 

at a distance of a quarter to half a mile. From the . 

amoimt of weathering present it seems evident that the 

time interval between the lower and upper of these 

two tills is much greater than that between the upper 

(Wisconsin) till and the present. 

On the whole, it seems reasonable to infer that the 

lower till here found corresponds to the lower till 

foirnd on the Belly River at Lethbridge, Alberta, and 

also probably to the continental drift found south o:f 

the margin of the Wisconsin drift in Montana and 

western North Dakota. 

Evidence of pre-Wisconsin glaciation afforded 

by an old gravel pit on the south side of the Milk 

River west of Toledo, in the NE. %sec. 5, T. 32 N., 

R. · 17 E., is found in the section described above 

(p~ 67). At this place traces were seen in 1921 of a 

bed of dense gray jointed pebbly glacial till, which 

was rusted along the joint faces and presented the appearance of having been disturbed as by an overriding 

glacier. It is underlain by a bed of nonglacial gravel 

and overlain by glacial gravel and a later bed of glacial till. 

An exposure in a bluff on White Bear Creek in the. 

Fort Belknap Indian Reservation, southeast of Harlem, in T. 30 N., R. 24 E., examined in 1921 showed 

4 feet of gravel separating two beds of glacial till. 

~othing was noted, however, whl.ch indicated that the 

lower till 'Yas appreciably older than the upper one. 

PRE-WISCONSIN (ILLINOIAN OR IOWAN!) DRIFT BORDERING THE KISSOUB.I RIVER IN NOR~ DAXGTA 

That a pre-Wisconsin ice sheet extended some distance south and west across the present course of the 

Missouri River in North Dakota is shown by the presence there not only of scattered glacial pebbles and 

boulders but also by the existence of a considerable 

deposit of glacial till. Knowledge of the distribution 

of this glacial material is the result . of the work of 

numerous geologists-T. C. Chamberlin,23 R. D. Salisbury, A. G. Leonard, F. A. Wilder, J. E. Todd, C. M. 

Bauer, and F. A. Herald. The southwestern limit of 

=Chamberlin, T. C., Preliminary paper ·on the terminal moraine of 

the second glacial epoc:tt: U. S. Geol. Survey Third Ann. Rept., pis. 28, 

.35, 1883; The rock scorings of the great ice invasions: U. S .. Geol. 

Survey Seventh Ann. n.ept., pl. 8, pp. 155-156, isss. 

glacial material is shown in Figure 6 as drawn· by 

Leonard.24 

In the course of several traverses between the eastward trendhtg parts of the courses of the Missouri and 

Little Missouri Rivers in McKenzie County in .1916 

and 1921 the present writer· al'ro observed scattered_ 

boulders and numeroUs exposures of glacial till. ' One 

of these was on Charbonneau Creek s~mth of · Cartwright, where there is 10 _to 20 feet of dull brownishbuff pebbly clay till overlying stratified clay or shale. 

Shallow road cuts on the gently rolling and little dissected upland north of the creek show.the presence of a 

sheet of till. In this drift and on the surface are 

plentiful pebbles of red and yellow (Belt~) quartzite, agate, and chert, with pebbles and boulders of 

limestone and crystalline rocks (mostly granite) from 

Canada. Between Arnegard and Watford City a 

succession of cuts along the Great Northern Railway 

exposed thicknesses of 1 to 25 feet of glacial till overlying friable cross-bedded Fort Union · sandston~. 

\Vilder 25 reports 25 feet of glacial drift at Glass Bluff, 

4 miles southeast of Buford,. on the south side of the . 

Missouri River. 

Leonard 26 gives the following description of several 

excellent exposures of·drift in M~Kenzie County: 

Near the western boundary of Nor~h Dakota the pre-Wisconsin ice sheet reached 35 to . 40 miles south of the Missouri 

River and thus covered the greater part of M~Kenzie County, 

which lies between the Yellowstone, Missouri, and Little Missouri Rivers. The older drift left by this ice sheet is well 

shown ;,.n many places in this region, and the glacier also 

caused important drainage changes. The best exposures are 

found on Sand Creek, a short tributary of the Missouri· River 

several miles east of Tobacco Garden Creek, on Tobacco Garden Creek, and on Clear Creek, a tributary of the latter. 

Near the mouth of Tobacco Garden Creek appears 58 feet 

of till in a cut bank. It is yellowish gray or drab in color, 

contains many small boulders, anci rests on .Fort Union beds. 

Not far. from·here is seen 18 feet of bouldeJ: clay overlying 15 

feet of well-stratified sand and ·gravel. 

The valley of Clear Creek was partly filled with drift, and 

there are many goOd outcrops of boulder clay ln the freq{\ent 

cut banks along the s~eams, where from 80 to 40 .feet and over 

of tlll is exposed. The. greatest thickness found along thiS 

creek was in sec. 36, T. 152 N., R. 97 W., where in a high bluff 

100 feet of dark-gray till overlies 100 feet of soft Fort Union 

sandstone .. This outcrop lies within the morainic· area to be 

described later, which probably accounts ·for the exceptional 

thickness of the pre-Wisconsin drift at this point. 

Another excellent drift section ·occurs in this same morainic 

area 3 miles west and. one-half mile south of Charlson, or 5 

miles south of the Missouri River on a tributary of Sand 

21o Leonard, A. G., The surface features of North Dakota and their 

origin : North Dakota Univ. Quart. Jour., vol. 9, no. 8, map, 1919. 

:1111 Wilder, F. A., Lignite on the Missouri, Heart, and· Cannonball 

Rivers and its relation to irrigation : North Dakota Geol. Survey Third 

Bienn. Rept.1 pp. 19, 40, 1904. 26 Leonard, A. G., The .Pre-Wisconsin drlft of North Dakota: Jour . 

Geology, vol. 24, pp. 524-526, 1916. 

• 
104" 103" 102" 1()1" 100°. 99" 98"' 910 

--:-·----,;,.,;41. 

~ 

~ H 

z 

481 ~/~'? ~ / J! r / / / / / f / l)f / {?L~h o/ l):F:~~i~~~~~~--~~~''''"''"~%:\1 ~-'"•·•···•'A n.i ~;;:0 "' ·~5'~-.; 

10.3° 102° 98" 97' 

EXPLANATION 

~ ~ ~.-~,.· c==J j\--\ ,. ~ [ZZ] 

Altamont.(termina.l) Approximate limit. 

moraine of la..urWisconsin· ofearly Wisconsin ~la:cial drlf't. gls.c•al drift 

Approximate boundary Red River Valley Deltas of ~l~cial Missouri Plateau of pre-Wieconain(lowan Lake Aaas&i"i: la.s map- or lllinoi~n) gtacial pedbyWarren Upham) 

droft:. '2f> 0 50 

Drift plain 

Miles 

J'.IGP8E 6..-Hap sho-,vin.~ topograpJ;llc 1~~.tt~r~s ,~,tn~ .c;l.ritt bound~rl~s ~,J;l ;Npr:t.l;l. ;Q(l."'o:ta.. ~4tter ,4.. G,. J,.eQn.arcl, l.vith sllsh:t mpcll:flcations) 

......, 

~ 

~ 1<1 

[fJ. 

1-4 

0 

~ p:j 

1<1 

> 

~ 

1:::' 

~ 

~ a 

~ 
ILLINOIAN OR IOWAN (?>-STAGE OF GLACIATION 77 

Creek. Here the following section appears in the steep bluff 

which rises abruptly from creek level : 

Sandy clay and soiL. _______________________________ _ 

Sand and clay in altHrnating bands __________________ _ 

Gravel-------------·--------------------------------

Sand and clay in altE!rnating layers_"------------------

Gravel, coarse ------·--------------------------------

Sand-------------------~--------------------------­

Gravel---------------------------------------------

Till or boulder clay, dark gray in color, and containing large numbers of pebbles and boulders embedded 

in the tough, harcll clay. A large proportion of the 

boulders and pebbles are composed of compact limee;tone and the till contains considerable blue !Wale 

(Pierre?). Thickness of till exposed above the 

Ft. in. 

2 

8 

8 

3 

8 

2 4 

7 8 

ereek -------------------------------------------- 61 

85 4 

~L'he sand and gravel forming the stratified drift of the foregoing secfion are light yellow in color. The drift hills just 

ba<!k of the bluff rise 50 to 60 feet above the top of the section, 

so that the total th:ickness of the drift above creek level is 

from 140 to 150 feet. 

:East of Tobacco Garden Creek there is in places 

considerable drift. Leonard 27 has described a moraine 

which is traceablE~ in a southwesterly. direction from 

tho vicinity of the Missouri River bluffs near Davis 

Ferry, north of Charlson, in T. 153 N., R. 96 W., to a· 

point 8 or 9 miles northeast of Schafer, in sees. 14 and 

15, T. 151 N., R. 97 W. He states that it has a length 

of 16 miles, an av•erage width of 2 miles, and an area 

o£ about 30 square miles. This moraine was traversed 

by the present writer in 1916 through about two-thirds 

of its extent and was also seen in 1921. It consists . 

of an uneven ridge marked by sags and swells and 

carrying many crystalline boulders. East of Elidah 

its morainal chara.cter is very well marked. It is described by Leonard as follows: 

'l~is moraine shows well from Charlson, where its ridges 

ariel hills are seen rising from 100 to 150 feet above the fiat 

plain in the foreground. Within the morainic area the surface is rough and hilly and the ground is thickly strewn with 

boulders. The topo~~aphy is typically morainic, with numerous irregular hills and ridges, while scattered among the 

hills are great numbers of hollows or kettle holes, some contabling water and others dry. Many of the hills rise 50 to 

125 feet above the bottom of the kettle holes. 

"Where this moraine crosses the valley of Timber Prong 

Cre1ek it forms a dam, which holds back the waters of the 

upper valley and fonns a lake known locally as Dimick Lake. 

Thi,s moraine lake is very irregular in shape and has an area 

of between ·2 and 3 S(J[uare miles. 

.A.s will be noted from Figure 6, the approximate 

ma.rgin of the drift as mapped by Leonard loops about 

thE~ east and north sides of the Killdeer Mountains 

with a fairly sharp angle. This appears to mark the 

jui~ction of the Dakota and Montana lobes of the preW~onsin (Iowau or Illinoian~) ice sheet. In a 

traverse made by the writer in October, 1921, scattered 

:n Leonard, A. G., Th·e pre-Wisconsin drift of North Dakota: Jour. 

Geology, vol. 24, pp. 52~r-528, 1916. 

drift boulders were seen east of W at:ford City ·and 

north of Croff post office in Ts. 149-152 N., R: 96 W., 

but no glacial till was noted, although it is known to 

occur farther east between R. 96 W. and the northsouth channel of the Missouri Ril7er, in the Fort Berthold Indian Reservation (p. 77). It is possible, therefore, that the interlobate angle really headed· near or 

north of Blue Buttes. The southwestward trending 

moraine between Charlson and Watford City may thus 

be a terminal moraine on. the northwest side of this 

angle, and the scattered outlying bouldersJ may perhaps have been dropped from icebergs floating on 

ponded waters bordering the ~ fronts-. The writ.er 

offers this suggestion, but he has not himself made 

sufficiently detailed examination of the district to be 

sure that it is correct. Scattered boulders were also 

seen along the road south of W Oitford City to the gorge 

of ·the Little Missouri, but south of this none were 

noted on a traverse south past Grassy Butte post 

office, and east about the head of Charlie Bob Creek, 

in T. 145 N., Rs. 96-98 W., until a point was reached 

south of the Killdeer Mountains and within 5 or 6 

miles west of the village of Killdeer. East of this 

are scattered drift boulders. In a tramp of about :\ 

mile on the south end of the top of the Killdeer Mountains, no drift was seen, and no drift is reported as 

found anywhere on the top by ,Quirk~. 28 

A cut east of Dunn Center, <?n the Killdeer branch 

of the Northern Pacific Railway, examined by the 

writer in 1921, exposed 15 to 20 feet of very . stony 

clay till. There is much included limestone here, and 

one block. is 6 feet long. Among granitic boulders 

scattered on the surface, one 10 feet long was noted. 

Boulders were also seen scattered · over the surface 

southward nearly to and east of Dickinson., on the 

Heart River. 

In a report on the lignite i:r:t the western part of the 

Fort Berthold Indian Reser.vation Bauer and Herald 29 

give the following description of the glacial· deposits: 

Both stratified and unstratified d~ft * * * oover large 

portions of the field and were noted in many localities. In 

general, however, their thickness is· less than 5 feet, and in 

some places, particularly alon,g the larger streams, they are 

absent. On Little Missouri River the effects of glaciation 

can hardly be detected, except for the presence of scattered 

foreign boulders. In the NW. * sec. 27, T. 148 N~, R. 93 W., 

and in the NE. * sec. 23, T. 148 N., R. 92 W., there is some 

consolidated glacial drift, with a maximum thickness of 15 

feet, containing numerous concretions and boulders of shale 

and sandstone, with a few boulders of granite and limestone. 

The whole is cemented by gypsum and iron oxide. Along the 

creek in sec. 7, T. 152 N., R. 93 W., the drift is 37 feet thick 

but unconsolidated, and at several places in the township to 

the west· it was found to be as thick as 15 feet. 

I 

28 Quirke, T. T., The geology of th~ Killdeer Mountains, Nortb 

Dakota: Jour .. Geology, voL 26, pp. 260-!61, 1918. 29 Bauer, C. M., and Herald, F. A., Lignite in the west.ern. part of 

the Fort Berthold Indian Reservation, N. Dak., U. S. GOOI. Survey 

Bull. 726, p. 114, 1922. 
78 PHYSIOGRAPHY AND GLACIAL GEOLOGY OF EASTERN :MONTANA 

Leonard 30 gives the following description of a 

gravel deposit near Gladstone: 

That ·a lobe of the ice sheet crossed the Heart River at Gladstone is shown by the presence of thick deposits of drift gravP.ls on the upland 1 to 2 miles south of the Heart and at an elevation of between 100 and 200 feet above the river level. In 

places the gravel and sand have a thickness of at least 90 feet, 

and the deposit contains a number of good-sized granite boulders. A well-defined gravel ridge marks the edge of the drift 

for 3 or 4 miles in this area south of the Heart River at Gladstone. This ridge rises 30 to 40 feet above the surface on 

either side and falls away rather abruptly on the south, while 

on the north the slope is more gradual. 

In 1921, when the Gladstone deposit was visited by 

the present writer, sand and gravel were being takeP 

from a small pit near the top of the north slope. 

South of this is a larger excavation to which a spur 

track formerly led from the railway. These pits expose 10 to 30 feet of stratified cross-bedded sand and 

gravel, the pebbles in which more closely resemble the 

bench gravel along the Yellowstone River than the 

glacial drift. These pebbles range from less than an 

inch to 3 inches in diameter and consist principally of 

quartz, quartzite, and chert, with some agate and some 

dense dark and greenish crystalline rocks, diorite, and 

porphyry. None of the stratified material, so far as 

noted, is certainly glacial drift. There were about a 

dozen boulders of gray and pink granite gathered in a 

pile on the b9ttom- of the pit, and these are probably of 

glacial derivation, but they may have rolled down 

from the surface during excavation of sand and gravel. 

The deposit appears to cap the ridge for some distance 

to the south and east. It is possible that this is an 

erosional remnant of a late Tertiary or early Pleistocene gravel bench similar to the benches on the Yellowstone River. If the granite boulders were actually 

interbedded with the sand and gravel, however, as intimated by Leonard, it is probably a glacial deposit. 

No glacial drift was seen by the present writer on a 

traverse extending about 9 miles south of Gladstone 

and thence east and north to Richardton nor along the 

main road and railway between these two places.· 

Some of the glacial drift of the Bisniarck quad· 

rangle was examined in 1911 by the writer, in company with Dr. Leonard, who describes the drift west 

of the Missouri River as follows: 31 

The most interesting and notable occurrence of glacial till 

in Morton County is found in the basin of the Little Heart 

River, where the drift has been heaped up into morainic hills. 

During . the glacial period this basin was probably occupied by 

an ice Jobe of the continental glacier, and this lobe formed 

the belt. of morainic hills which nearly encircles the broad 

valley plain and deposited more or less drift in the preglaciaJ 

valleys of the Little Heart and its tributaries. As the ice 

melted, the waters 1lowing from it deposited much ·outwash 

silt in the form of valley trains sloping away .rom the mo80 Leonard, A. G., The pre-Wisconsin drift of North Dakota: Jour. 

Geology, vol. 24, p. 530, 1916. 81 Idem, p. 523. ~ee also U. S. Geol. Survey Geol: Atlas, Bismarck 

folio (No. 181), pp. 4-5, 1912. 

raines. A number of the morainic hllls have beeri partially 

buried by the outwash silt and rise like islandS from the level 

plain of the valley train. The morainic belt of boulder-covered 

hills and ridges is found near the base of the·lpes on either 

side of the two valleys tributary to that of th · Little H. eart 

River. Moraines cross the valley in three plac , and one belt 

Of ridges and hills COntiBUes unbroken along e south side 

of the valley of the South Branch' for a distan e of 12 miles. 

The cultivated fields extend up to the moraine nd end there, 

where the soil becomes too rocky and the sl pes too steep 

for cultivation. 

Wilder 3

·

2 makes the following statemen about drift 

west of the Altamont moraine: . · 

On the Cannonball River the extreme wester limit of the 

glacial drift seems to be about 10 miles west o the mouth of 

the Cedar River .. For many miles east of this oint the drift 

is represented only by boulders, which in places are quite 

abundant. * * *. The boulders here, as everywhere near the 

edge of the drift, lie directly on Laramie clays. Beyond the 

drift, in the southern part of the State, particularly in the 

Cannonball country, fragments of quartzite, which is regarded 

as residual, are very abundant, 9ften literally paving the 

hilltops. 

PRE-WISCONSIN (ILLINOIAN OR IOWAN!) DRIFT NORTH:, 

OF THE MISSOURI ltiVER 

. WILLIAMS COUNTY, NORTH DAKOTA 

On the upjand extending west and southwest of Ray 

to the Little Muddy Valley, till and boulders are generally present. The till is calcareous, and pebbles and 

boulders of limestone are included in it· up to the top, 

and limestones also lie on the surface. Other errs.tics 

. noted consist of granite, schist, and red quartzite. The 

slopes, except near the valleys, are genera.lly long and 

smooth. north of the dissected belt or" breaks" bordering the Missouri River. The valley of Little Muddy 

Creek is broad for 20 miles or more between· the Missouri River and the morainal deposits south of ~farmon. The region extending from the vicinity of this 

valley and latitude 103° W. westward to the Montana 

line has been examined and described by Herald.33 

At Williston well-stratified fine gravel is exposed in 

an excavation at the east end of Main Street both east 

and west of Little Muddy Creek. Gravel was also 

seen at a few places farther north. Grayish calcareous till containing good -sized granite boulders is exposed in an excavation west of the railway station, not 

far above the level of the Missouri River. 

The smoothly undulating plain of southwestern 

Williams County is· in general moderately eroded, and 

the main valleys, such as that of the Little Muddy, 

Cow, and Painted Woods Creeks,· are bordered by 

broad sloping benches like the bottom.s of. ·old valleys 

in which are sharper inner and young~r valleys. 

119 Wilder, F. A., Lignite on the Missouri, Heart, and Cannonball 

Rivers and its relation to irrigation : North Dakota Geol. Survey 

'l'hird Bienn. Rept., p. 40, 1904. 

118 Herald, F. A., -~he Williston lignite field, Williams County. N •. 

Dak.: U. S. Geol. Survey Bull. 531, pp. 9l-157, 1913. 
ILLINOIAN 0:& lOWAN <f) STAGllLOF GLAf:tATION <1tl 

The~ benches u.nd the upland slopes are rather P:a.E .. WIICO:Rillfi (ILUBOIA:I:.O:a XOWAlf1) DBIFT :ao.lpr.. 

sharply dissected by , V -shaped branching coulees at llfG TliB XISSO"'lU ~~B. m KO:RTA:RA 

the headwaters of the streams. Drift is generally DR:tFT NE1A.R ANI) EAST 'OF GREAT FALLS 

present in the form of a thin sheet of till, with scattered boulders o:f red and gray granite, schist, and 

buff limestone. It is not clearly apparent how much 

of the minor dissection has taken place since the drift 

was deposited. It is clear that the main valleys, such 

as that of Little JM:uddy Creek, are older. 

The amount of erosion appears to be about the 

same north of the outer disconnected line of morainal 

deposits, traced near Marmon, to the Altamont moraine, in which almost no erosion has been accomplished. :As stated by Herald, the lower courses of 

·the streams are in general marked by· sharply cut 

valleys ·of considerable depth, whereas their upper 

parts flow through very broad valleys which merge 

into long gentle slopes extending to the divides. At 

s~me places the bluffs along the streams are abrupt, 

but along the north side of the Missouri near and west 

of Williston they give place to a general slope from 

the upland. Glacial till is found on this. slope down 

to .the railroad at Williston. 

Although the main valleys undoubtedly have been 

glaciated, it seems probable that the minor sharp 

branching tributary ra-vines are postglacial. At 

least ·so far as seen they show little evidence of glacial 

modificati<?n. The narrow dissected belt bordering the 

MisisOJiri east of Williston is well shown in the southern part of the Ray topographic map~ There is here a 

maximum relief of about 500 feet. 

THICKNESS OF THE ICE SHEET IN NORTH DAKOTA 

Leonard 84 has made the following deduction concerning the thickness of the pre-Wisconsin ice sheet in 

western North Dakota : 

In the vicinity of Berg, in northeastern McKenzie Oounty, 

there are twelve or fifteen high buttes, .known as the Blue 

Buttes, which are irregularly distributed over an area of 15 or 

more square miles. Many glacial boulders occur on· top of 

these buttes at an elevation of over 2, 700 feet above sea level, 

or 1,000 feet above the Missouri River only 6 miles to the east. 

Since the buttes rise nearly 500 feet above the surrounding 

upland the ice sheet probably had at lt~ast this thickness in 

order to override tltlem and deposit bociders on their summits. 

Another explanation for the preSen.ce of the boulders on top of 

the high buttes is that the ice upon encountering these obstructions was buckled up as it passed over them. · But it seems 

more probable that the ice sheet which was able to push across 

the deep .valley of the Missouri River and advance 40 to 60 

miles beyond was thick enough to submerge the Blue Buttes 

and pass on over them. The terminus· of the continental gl~;t-

• cier was not far from 15 miles south of the Blue Buttes, since 

the ice advanced only as far as the Killdeer Mountains. 

Back about 15 miles from the edge the ice sheet therefore 

doubtless had a thickness over the upland ·plain of considerably over 500 feet. The ice which filled the Missouri River 

Valley must have had locally a thickness of 1,000 feet or over. 

... Leonard, A. G., J'our. Goology, vol. 24, ~p, 530-53,2, 1916. 

There· is ~me difficulty in: determining the -

southern limit of. the Wisconsin dri.ft on the plains·.of 

Montana. As far east as the -eastern. bounda.ey of 'the 

Fort Belknap Indian Reserv$tion the limit is fairly 

well defined and. is appro~mately as m.a.pped by 

Calhoun. 86 . Farther east there is no continuous well .. 

defined termin~l moraine, and the numerous reconn~ 

sance traverses made by the writer in 1916; 1920, and 

1921; together with such examinations as have been 

made by other geologists, h~ve not yielded d~nite 

results as to tM· location of this boundary. There is 

good reason for thinking that there was at least one 

incursion ·of tb.e Keewatin g~acier on the plains of 

Montana prior to the Wisconsin stage of glaciation, 

and to this earlier advance is probably to be r~erred 

the glacial drift south of the :.Missouri River in Mon-

. tana and North Dakota and also some of that north of 

the river. The location of the limit of the Wisconsin 

drift as show:n on Plate 1 is largely hypothetical. 

(See p. 96.) ,The drift south of this hypothetical 

boundary (see ' p. 69) is tentatively correlated . either 

with the Illin()ian drift or with the. Iowan drift of 

northeastern ~1wa. Although. th~s. correlation may ~e 

open to quest1~, the terms Illmman or Iowan ( 1) lee 

sheet and Illi ian 'or Iowan ( 1) drift are used here 

for convenienc of description. . 

The Missou i River had. reached its l.owest le. vel 

of erosion by the time the advancing Illinoian or 

Iowan ( ~) ice! front reached the old valley between 

Great Falls an. Havre and eastward along the course 

now followed y the Milk River below Havre. (See 

pis. 1, 29.) T ere had also been deposited in this,valley a certain ~ount of filling of nonglacial river 

gravel. (Seep. 68.) As the ice advanced it deposited 

. more or less .ti upon the gravel arid probably pressed 

forward again the north and west flanks of the Bearpaw Mountai ~as did the later ice of the Wisconsin 

stage. It. cro sed th~ preglacial valley of Marias 

River and t e Teton and Missouri Valleys and 

crowded· up o the benches· bordering the north base 

of the Highw od Mountains' to a level which is now 

about 3,600 fee above the sea. It overtopped Shepard 

Butte, west of Waltham, and on melting left boulders 

scattered on t e surface where now is the triangulation post of th Missouri River Comm~ssion, at an altitude of about ,800 feet (barometric). . This is about 

1,000 feet a ve the present level of the Missouri 

River at the outh of Belt Creek, 5 miles to the west. 

Passing this utte it advanqed up the old Mi$Souri 

River Valley o a. point abou~ a mile north of Ger~ 

II Calhoun, F. H. a:, The Montana lobe of the· Keewatln ice iheet : 

U. S. Geol. Survey rof. Pai)er 50, pl. ~. 1906. · 
80 PHYSIOGRAPHY AND GLACIAL GEOLOGY OF EASTERN MONTANA 

and left therein a great deposit of drift completely 

filling the valley. It crowded up on the edge of the 

upland to the east near the line of the Great Northern Railway to an altitude of 3,600 feet. (See fig. 10, 

p. 92.) Here the glacial boulders may be seen scattered ov.er the surface of the bench gravel. 

Northeast of Great Falls the Great Northern RaHway crosses the river above Rainbow Falls and climbs 

the slope to the upland on the north. In the cuts near 

the top of the slope, south of Goodale, the Cretaceous 

shale is overlain by about 30 feet of dull-grayish 

pebbly clay till. In the first cut south of the Big 

Falls road the till is overlain by 8 feet of dark to black 

laminated clay, somewhat distorted in places. This 

lacustrine clay is about 400 to 500 feet above the level 

of the river below Big Falls. The till extends down 

the slope to the rim of the gorge, about 180 feet above 

the river below the falls. (See pl. 31 B.) 

The dull-grayish till was also well exposed when 

seen in 1920, 1921, and 1922, in numerous . cuts 

along the line of the Chicago, Milwaukee, St. Paul & 

Pacific Railway between Great Falls and Highwood 

Creek. Some of these cuts are more than 100 feet 

deep and yet do not reach the base of the drift in the 

part where the railway crosses the buried valley of the 

Missouri River. Where the main road east from Great 

Falls to Highwood crosses Red Coulee, scarps due to 

slumping expose in places 50 feet or more of dull-g1·ay 

till over red to purplish Kootenai shale. In places 

chunks and stringers of the red shale have been dragged 

up into the till. One scarp south of the road exposed 

the following section : 

Section of drift in. Rea Ooulee ea8t ot Great FallB 

Feet 

3. Dull-gray pebbly clay tilL_________________________ 15 

2. Stratified dark clayt partlY like papery shale, partly 

pebblY------------------------------------------- 1-3 

1. Dull-gray pebbly clay till, with included masses of 

red shale--------------------------------~------- 5 

This exposure is near the southeastern limit of the 

glacial drift, and No. 3 may have been deposited when 

the ice readvanced, pushing forward over the silt 

(No. 2) deposited in the marginal glacial lake described on page 88. Nos. 1 and 3 are probably not of 

greatly different age. 

What may be a thin deposit of Illinoian or Iowan 

( ~) till is exposed in the bluff below the railway near 

the river bend west of Fort Benton. (See No. 3 of 

section on p. 66.) It overlies nonglacial stream gravel 

and is covered by wind-blown silt beneath the later 

drift. · 

About 100 feet of dull-gray clayey till, with few 

pebbles, is exposed in bluffs along the lower course of 

the Teton River. At the railway tunnel the narrow 

dividing ridge between the Teton and Missouri Rivers 

is nearly cut through. This ridge appears to be 

mostly drift filling the former course of the ·river, 

which had cut down nearly or quite to its present level. 

In places near Teton station there is a bed of gravel 

between the base of the till and the top of the under:. 

lying shale. 

Bowen 86 has mapped the boundary of the drift for 

about 25 miles along the west foot of the Bearpaw 

Mountains in the Big Sandy coal :field. He writes 

about the drift as follows : 87 

Over most of the district the drift consists of a heterogeneous mixture of sandt gravel, and boulderst vanable in size 

and in lithologic character. The most numerous and conspicuous erratics are granitest gne~sest and quartzites that 

obviously have been transported from distant regions, inasmuch as they are totally unlike any rocks occurring in· place 

in this part of Montana. Along Missouri River and its tributaries, however, the bluffs are capped by a deposit of lightyellow, partly consolidated loesslike sand and clay which· is 

in places apparently stratified and as a rule. contains a few 

small waterworn pebbl~. This deposit is doubtless due to 

some phase of glacial action .. 

Similar loamy clay was seen by the writer in 1920 

overlying the 10 feet of gravel which caps the bluff 

of sandstone and shale on the southeast side of the 

Arrow River opposite the mouth of. Steele Creek, at 

the east end of the Shonkin Sag. The loamy clay 

looks like wind-blown material, as it is heaped up in 

a small ridge along the crest of the bluff. Calhoun 88 

found the drift extending as far eastward· along the 

Missouri River as the mouth of the :Arrow nlver.' 

The east limit of the drift for about 20 miles north 

of the river is as mapped by Reeves.89 

The relations of the glacial front and the drift deposits to the Bearpaw Mountains were probably much 

the same at the Illinoian or Iowan ( ¥) stage as at the 

Wisconsin stage. (See pl. 29.) 

No evidence of pre-Wisconsin drift was noted by the 

writer about the north side of the Bearpaw Mountains 

nor in the area between the Bearpaw and Little Rocky 

Mountains. (See pl. 1.) . The same is true with regard 

to the north flank of the Little Rocky Mountains, at 

least as far east as the vicinity of LodgepQle Creek. 

The maximum height of land overridden by the marginal part of the Wisconsin ice sheet appears to be quite 

definitely shown by the liniit of the drift sheet on No. 1 

bench east and west of the road leading north from 

Lodgepole. In theN.% sec. 25, T. 7 N., R .. 23 E., the 

limit is 3,500 feet above sea level. It is about 3,550 

feet near the middle of the south line of sec. 19 and 

also in the NE. % NW. 1,4 sec. 28, T. 27 N., R. 25 E. 

Scattered drift pebbles and boulders ~ere noted • 

88 Bowen, C. F., The Big Sandy coal field, Chouteau C011nty, Mont. : 

U. S. Geol. Survey Bull. 541, pl. 21, 1914. 37 Idem, p. 365. 

as Calhoun, F. H. H., op. clt., p. 44. 38 Reeves, Frank, Geology and possible oil and gas resources of the 

faulted area south of the Bearpaw Mountains, Mont. : U. S. GeoJ. 

Survey Bull. 751, pl. 13, '1924. · ' 
U. S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 174 PLATE 28 

EXPLANATION 

Temporary outlet of M:tMOuri River and glacial II lake submersing lower slopes and lowest 

L__j f.:l].~~Y terra<eo (uMhaded) in Yellowstone 

~ 

~ 

Remnants of gnvelly terrace, of early Pleistoeeneage. 

~ Remnants of hif:h gravelly terrace of Miocene or Pliocene ( ) age, probable equivalent of Flaxvi11e gravel. 

Geology by Wm. C. Alaen 

MAP OF THE GLENDIVE QUADRANGLE, MONT., SHOWING THE RELATIONS OF THE 

KEEWATIN ICE SHEET OF THE IOWAN OR ILLINOIAN(?) STAGE OF GLACIATION TO THE YELLOWSTONE VALLEY AND THE REMNANTS 

OF THE GRAVELLY BENCHES OR TERRACES 
ILLINOIAN OR lOW AN < ! } STAGE OF GLACIATION 81 

somewhat farther south on the bench · east of the 

Lodgepole road and also up to the top of the 

Judith River sandstone ridge (altitude 3,650 feet) 

which extends southeastward from the gorge of 

Warm Springs Creek, in the SE. 1M sec. 1, T. 26 N., 

R. 25 E., into the SW.% sec. 27, T. 26 N., R. 26 E., 

though the Wisconsin terminal moraine appears to lie 

on the lower land to the northeast. Drift boulders of 

granite and quartzite pebbles are also sprinkled over 

the bottom of the valley southwest of the sandstone 

ridge and even on the gravelly top of No. 2 bench to 

the south and west nearly up to an ·altitude of 3,650 

feet near the base of the mountain wall. One of the 

granite boulders seen on this bench measured 3 by 4 

by 6 feet. Though it is possible that the foreign pebbles and boulders on the lower ground might have been 

dropped from icebergs floating on water ponded between the frop.t of the Wisconsin ice sheet and the 

mountain flank, it is not evident how those at the 

higher levels could have been so transported, because 

so far as known to the writer there is no ridge sufficiently high south of the Judith River sandstone ridge 

and east of the mountain wall, unless it be away off 

south of the Missouri River, to have ponded water in 

such a marginal glacial lake up to an altitude of 3,600 

feet or even 3,500 feet. Drift pebbles and boulders 

were found scattered on the lower slopes and benches 

surrounding the buttes in and near the southeastern 

part of the Fort Belknap Indian R~servation up to 

3,550 feet. No drift was found on the top of Middle 

Butte, which rises 600 to 700 feet above No. 2 bench, 

to 3,950 feet. On the top of East (Coburn) Butte, however, there were in July, 1921, scattered quartzite pebbles and one granite boulder measuring 2 by 3 feet. 

This was just south of the boundary post at 3,720 feet. 

· This boulder is 200 feet higher than the upper limit o:f 

the· Wisconsin drift on No. 1 bench north of Lodgepole, 15 miles farther northwest, so that there i~ little 

likelihood that it was placed here by the Wisconsin 

ice sheet, and much less that water was ponded· sufficiently high for it to have been dropped from floating 

ice. In September, 1916, the writer found a quartzite 

pebble on the top of West Butte, in sec. 31, T. 25 N., 

R. 26 E., but no drift was seen either on the sandstone 

ridge between West Butte and Bear Gulch Creek or on 

No. 1 bench or the lower areas near the south side of 

the mountains farther west. It seems probable that 

some at least of the foreign pebbles and boulders scattereq in the places noted were brought to their positions by an earlier and more extensive glacier. 

(See pl. 29.) 

Glacial pebbles and boulders were found sprinkled 

over the. surface of the shale along the road from sec. 

22, T. 24 N., R. 25 E., about 6 miles south of Zortman, 

to.the b:eaks north of the Missouri River near Wilder, 

but no glacial till was seen. Such pebbles and boulders are also scattered westward in Rs. 24 and 25. 

Calhoun's map 40 shows the. west -limit of this drift as 

near the mouth of Cow Creek, which is in sec. 8, T. 

23 N., R. 22 E., and crossing thence to ihe area south 

of Missouri River. In 1921 Frank Reeves mapped 

the approximate limit of this drift as shown in Plate 

1-that is, southward through Ts. 21 to 23 N., R. 21 E~, 

and eastward through T. 19 N., Rs. 23 to 29 E., and 

south through T. 18 N., R. 29 E. Reeves states 41 that 

the foreign pebbles and boulders were found scattered 

between this limit and the Missouri River but no glacial till was seen overlying the ·cretaceous shale and 

sandstone. Reeves also reports the presence of gravel 

on a ridge about 18 miles north of Roy, in T. 21 N., 

R. 22 E., but it was not determined whether this is 

glacial drift or a remnant of the bench gravel. The 

present writer found the outermost glacial pebbles and 

boulders 24 miles northeast of Winifred, in T. 23 N., 

R. 21 E., and about 11 miles northeast of Roy, in T. 

19 N., R. 23 E., but ·saw no till. 

C. F. Bowen informed the writer that in the course 

of a traverse of the country between the Judith and 

Musselshell Rivers in 1912, he saw an erratic granite 

boulder in T. 16 N., R. 28 E., about 15 miles:northeast 

of Winnett. 

DRIFT EAS.T OF THE MUSSELSHELL RIVER 

In August, 1921, the writer found boulders of red 

and gray granite scattered upon the bench west of the 

Musselshell River near Mosby and southward to the 

valley of Boxelder Creek. The granitic pebbles overlie the bench gravel, but none were seen intermingled 

with it. 

Glacial pebbles and boulders were seen by the writer 

in 1921 in Garfield County, within a few miles northeast of Mosby, on the east side of the Musselshell· 

River on the road to Sand Springs, and also on the 

South Fork of Lodgepole Creek below Tindall, in and 

below sec. 32, T. 18 N., B. 31 E. These consist principally of granite and other crystalline rocks, limestone, and quartzite. The region is very rough and 

much dissected. C. E. Dobbin 41 in 1921 found such 

erratics scattered from this locality northward to the 

Missouri River as mapped by Calhoun, but he did not 

·find any east of Devil Creek, in Ts. 21 and 22 N., as 

far east as Hell Creek, in R. 37 E., nor did . he ·find 

any glacial till south of the Missouri River. No erratics were seen by the writer on traverses between 

Jordan, Chalk Buttes, Hazny, and Edwards. 

W. T. Thorn, jr.,41 in 1921, found a 2 by 3 by 1 ¥.a 

foot granite _ boulder about 15 miles south of Sand 

Springs, in sec. 9, T. 13 N., R. 34 E. This gives rise 

to the suggestion that some, at least, of the scattered 

4» Calhoun, F. H. H., op. cit., pl .. 1. 

4-1 Personal communication. 
82 PHYSIOGRAPHY AND GLACIAL GEOLOGY OF EASTERN MONTANA 

glacial pebbles and boulders may have bee~ transported by ice floating on water ponded in front of 

the ice. sheet as it lay along or near the present course 

of the Missouri River and that there may have been an 

Qutlet for this lake southeastward from the Musselshell Valley to the Yellowstone near Forsyth. There 

must have been a great deal of water flowing eastward 

or southeastward somewhere through this region for 

a time, for all the drainage of that part of the upper 

Missouri Basin outside the margin of the ice sheet, 

together with water from the glacier itself, must have 

had an outlet to the Yellowstone. The absence of any 

kn~wn glacial till south of the Missouri River within 

this tract makes it somewhat questionable whether or 

not the ice lobe between the Little Rocky Mountains 

and the Larb Hills on the east extended southward 

beyond the present line of the Missouri. It may be . 

noted, however, that neither have lacustrine clays, such 

as are present in the region of Great Falls, been observed in the tract described above. There is no question that the ice between the Little Rocky Mountains 

and the Larb Hills advanced nearly if not quite to 

that part of the Missouri's present course here under 

discussion. 

Thicknesses of 15 to 50 feet of dull-buff to dark-

. gray pebbly clay till were observed either by A .. J. 

Collier or the writer all along Beaver Creek, in southern Phillips County, between the Fort Belknap Indian 

Reservation . and the confluence of Beaver and Flat 

Creeks, in T. 27 N., R. 32 E., and by the writer on 

Telegraph Creek about 10 miles north of the Missouri 

River, in the southeastern part ofT. 24 N., R. 31 E. 

In 1920 Collier observed glacial boulders on the highest part of the Larb Hills, about 3,100 feet above sea 

level. Boulders were also observed by the writer in 

1916 in the valley which transects the Larb Hills and 

·is continuous from the head of Larb Creek to Timber 

Creek, also along the road from Carpenter's ranch, ,in 

T. 23 N., R. 35 E., in southwestern Valley County, 

northeast to Glasgow, and boulders and some till were 

seen along the road from Glasgow south to Lismas 

Ferry .. Glacial boulders occur in northeastern Garfield 

County south of the Missouri River scattered along the 

valley of Dry Creek and over the upland to the west 

as far along the road from Haxby post office toward 

Jordan as the head of Flat Creek, in or near the southeastern part ofT. 22 N., R. 40 E. (Patterson's ranch). 

In 1919 and 1920 W. T. Thom, jr.,41 examined the 

northern part of what is now McCone County, south 

of the Missouri River and east of Dry Creek. C. E. 

Dobbin also examined part of McCone County in 1922. 

Thorn reports numerous exposures of glacial till, 20 to 

30 feet in thickness, over shale and sandstone, so that 

the ice unquestionably extended south of the Missouri 

gorge in this tract. ·A part of this area was traversed 

4.1 Personal communication. 

by the ~riter in 1916 and again in 1920. . Glacial 

pebbles and boulders of limestone, granite, and other 

crystalline rocks and. qaartzite are scattered over the 

whole area, at least as far south as T. 23 N. The till 

where. seen is dense calcareous gray clay, containing 

few pebbles and cobbles. In places, as south of the 

Wolf Point Ferry, nearly 50 per cent of the pebbles 

and boulders are of limestone. With these are quartz-

. ite, gray and red granite, diorite, diabase, and other 

crystalline rocks. One granite block· 8 to 10 feet long 

was noted. These erratics ··are sound and show little 

evidence of long .exposure to the weather. 

Glacial boulders were found scattered eastward in 

T. 24 N. to and across.the divide at the head of West 

Charley Creek, in R. 53 E. (See Glendive topographic map.) 

DRIFT ON THE LOWER YELLOWSTONE 

Boulders were not noted along the Richey branch of 

the Great Northern Railway through the pass 

between Lambert and Enid, nor for 8 or 9 miles north 

of Enid. The ice, however, evidently overtopped the 

hills and high benches as far south as the railway in 

Fox Creek Valley between Lambert and Gettysburg 

station, where there are boulders. (See pl. 28.) In 

1921 thin glacial till and boulders were observed by the 

writer between the Yellowstone and a line passing 

through Three Buttes, Lone Butte, and Sioux Pass. 

A low ridge at the north edge of the high No. 1 

bench south of Lambert and 450 feet above the village 

looks like a small morainal ridge and suggests that 

possibly the ice may, at its maximum, have filled )fox 

Creek Valley and banked against and barely overtopped the slope to the south. Where examined the 

ridge consists of buff clay inclosing peb~les as much 

as 6. inches in diameter. The fact that the pebbles are 

mostly quartzite and quartz and that none were foimd . 

of limestone or granite, such as are characteristic of. 

the glacial drift, however, makes it doubtful if the ice 

·really reached the edge of the high bench. It is clear, 

nevertheless, that the glacial. front extended around 

the east end of the high bench _and that a lobe of ice 

extended up the Yellowstone Valley for a distance of 

25 miles south of the Fox Creek Valley-that is, to the 

vicinity_ of the United States Bureau of Reclamation 

dam at Intake (shown on the topographic map as 

"·Head works "), about 18 miles below Glendive. 

Abundant glacial· boulders ·of. red, pink, and gray 

granite and limestone, 1 to 5 feet in length, are found 

scattered over the slopes .and middle benches (early 

Pleistocene) as high as 500 feet above the river, or 

about 2,450 feet above. sea level. 

The presence of a few small granite.-boulders on 

the end of the·high bench 10 miles·west of Burns, 800 

feet above the river, or 2,000 feet above sealevel, leads 

. to the suggestion that the ice may perhaps ·at first 
ILLINOIAN OR IOWAN ( ?) STAGE OF GLACIATION 83 

have crowd~d ·against t.he end s~o~~ of the ridge and · are largely unde~ cultivation. Rather generally, how-

<>vertopped It. There Is a possibility, however, that ever, in the area traversed south of the Missouri the 

these stones may h~ve been hauled up from the lower slopes of this older topography· bordering the· valleys 

bench to th~ east, as they were seen near other stones are sharply dissected by branching V -shaped coulees 

that. had ev1dentl:y been colle~te~ for the purpose of of a later cycle, which represent the topographic de-

~aking a foundatw~ for a ~u1lding. No other gran- velopment since the region was glaciated and give the 

Ites were seen on this bench In the course of a 10-mile "break" along the Missouri and in places badland 

traverse. . tracts. The later slopes are largely bare shale and 

Several sm.all granite boulders and a block of lime- sandstone, and the pebbles and boulders on them :ap.:. · 

sto~e measunng 3 by 3 by 6 feet were observed by the pear to have been let down by erosion of the upland 

wnter on No.2 .bench wes~ o.f the rive: _about 6 miles deposits. The drift in the larger valleys, however, 

north of Glendive, and srnular erratiCs were found appears to be as left by the ice-that is, deposited since 

scattered over the correlated bench east of the river the main drainage lines were eroded. 

known as Belle Prairie. These were probably dropped · . 

from icebergs floating on a lake held in the Yellow- PRE-WISCONSIN (ILLINOIAN OR IOWAN!) DRIPT IN 

stone Valley when the front of the glacier blocked VALLEY AND ROOSEVELT COUNTIES, liONT. 

the valley: at Intake. During· the exami!nation of 

the Sidney lignite field, in 1910, Stebinger 41 found 

11. large glacial boulder of crystalline rock on the upland between Smith and Dry Creeks, east of Burns 

in T. 19 N., R. 58 E., and in 1921 the writer found 

boulders scattered most of the way along the road 

<;ast and northeast from Intake to Skaar post office, 

near the State line on upper Smith Creek in south~ 

€astern McKenzie County, N.Dak. 

Brown 42 states that glacial dri~ is abundant between the Missouri and Yellowstone Rivers and on 

ridges near the Yellowstone is several feet thick, also 

that near the Missouri River the drift is more eroded · 

~nd only large boulders remain. · Apparently Brown 

Included some of the nonglacial gravel under the term 

" drift," or at any rate, the statement is ambiguous, 

as no southern limit is giv~n for the district described. 

With the exception of a boulder seen by W. T. Thorn, 

j r ., 15 miles south of Sand Springs and another seen 

by Thorn in the Redwater Valley near Circle and of 

what appeared to be glacial till observed by A. J. 

Collier in 1928 northeast of Circle, in sec. 14, T. 21 N., 

R. 49 E., no glacial drift has been reported to the 

writer as found south of the limit noted above and 

shown on the map. 

In McCone C~unty two well-marked cycles of topographic development are represanted, one a mature 

erosion topography with long slopes. In places, as 

southwest of Nickwall, in the southeastern part of 

the Chelsea quadrangle, this has been but little modi-

. fied, being represented by a broad abandoned valley 

with long side slopes. This valley extends north from 

Re~water Creek to the. Missouri. Its bottom, a poorly 

drained flat about 1 mile in width, lies about 2,015 to 

2,020 feet above the sea, or 40 to 50 feet above the 

Missouri River bottom land. Back from the valley the 

long smooth upland slopes are but little dissected and 

~ Personal communication. 

c Brown, Barnum, The Hell Creek beds of the Upper Cretaceous of 

Montana: Am. Mus. Nat. Hist. BulL, vol. 23, p. 824, 1907. 

South of the broad basin in which lies Medicine 

Lake, a smooth plain marking the position of Bauer's 

" Tertiary " valley (see p. 21), the surface rises gradually toward the south in the direction of the Missouri ... 

Valley. This belt-east of Big Muddy Valley is underlain by the shale, sandstone, and lign~te beds of the 

Fort Union formation, with red clinker formed by 

burning of the lignite. It is considerably dissected by 

short tributaries of .the Missouri. From the erest 

there is a slope to the top of· the steep, irregular bluif 

bordering the abandoned valley of the Missouri, whieh 

is traversed by the Great Northern Railway fron1 Culbertson east to Bainville and thence south to the present valley at Lakeside. Similar irregular bluffs, or iu 

places smoother steep slopes, bound the large islandlike upland, 250 to 350 feet high, which lies between 

the old valley and the present valley. Near the head 

of. Riprap Coulee, a few miles southeast of Lakeside, 

the highest hilltops are from 400 to 500 feet above 

river level. The topography of the belts bordering the 

Missouri on both the north and the south contrast 

strikingly with the broad. plain. and long, smooth 

slopes of the preglacial valley to the north, though 

the total maximum relief is not greatly different. 

Beekly 43 ~aps the Fort Union beds as generally 

concealed by glacial drift on the uplands. He states 

that the drift in this area ranges from a thin film to a 

deposit 25 feet thick where exposed in . sections on 

eroded slopes. Crystalline boulders are frequently 

seen but they are not abundant. Northeast of Bainville there seems to be considerable drift present, a.nd 

the lowland between the bluffs shows an undulating 

topography. Evidently the area was occupied by ice 

since the old valley traversed by the railway was 

excavated. 

Smith, who examined the old Fort Peck Indian 

Reservation, covering the area between the. Big Muddy 

4,3 Beekly, A. L., The Culbertson lignite field, Valley County, Mont.: 

U. S. Geol. Survey Bull. 471, p .. 321, 1912~ 
84 PHYSIOGRAPHY AND GLACIAL GEOLOGY OF EASTERN MONTANA 

Valley on the east and Porcupine Creek on the west, 

together with two tiers of townships south of the Missouri River and northward to the old reservation line 

in T. 33 N ., describes the topography as follows: 44 

North of the river for a distance of 15 to 20 miles the slopes 

are as a rule gentle and, with a few exceptions, the valleys are 

broad witb gently sloping sides. Farther north the relief becomes bolder and the large streams are in places bordered by 

abrupt escarpments and hills ranging in elevation from 200 to 

500 feet. The interstream areas are usually broad and flat. 

In the north-central part of the reservation, south of Poplar 

River and Cottonwood Creek, is a gravel-covered terrace 

about 300 feet above stream level, which slopee gently to the 

southeast. A remnant of a similar terrace appears in the highlands north of Cottonwood Creek [the Flaxville Plain, bench 

No.1]. 

South of Missouri River bluffs and hills rise abruptly from 

the edge of the flood plain to an elevation of several hundred 

feet. Near the river the topography is rougll. and in placee the 

country is dissected into badlands, but farther to the south the 

badlands blend with rolling prairies of low relief. 

The entire field considered here lies within the area once 

~ covered by the great continental ice sheet, whose effects on the 

topography are everywhere evident. Preglacial etreams have 

been caused to abandon their channels, which now appear 

either as broad depressions containing intermittent lakes or as 

broad valleys occupied by streams of insignificant size. The 

movement of the glacier over the region has no doubt had a 

tendency to smooth away preexisting- inequalities of the surface, and the retreating ice sheet has left a mantle of drift 

which has protected underlying formations from the erosion 

into badland forms common in regions not so protected. South 

of Missouri River evidences of glaciation are not so marked as 

they are north of the river. 

. The topography of most of this area is shown on the 

maps of the Porcupine Creek, Spring Creek, Todd 

Lakes, Tule Valley, Cuskers, Hay Creek, Smoke Creek, 

Homestead, Nashua, Frazer, Oswego, Wolf Point, 

Chelsea, Poplar, and, Brockton quadrangles. Concerning the glacial deposits in this area, Smith writes 45 : 

Overlying the greater part of the field is a mantle of glacial 

material of varying thickness, made up principally of igneous 

boulders and clay but containing some fossiliferous limestones. 

These boulders vary in size from mere pebhles to masses weighing probably 20 tons. It is probable that this drift formerly 

covered the entire region like a huge blanket, but stream action 

and weathering agencies subsequent to the retreat of the continental ice sheet have cut deep channels through the drift and 

into underlying formations. 

That part of the old Fort Peck Reservation lying 

in Roosevelt County south of the Cottonwood Creek 

Valley and. T. 32 N. and extending to the Missouri 

River shows little evidence of morainal deposit's that 

can be regarded as marking the southern limit of the 

Wisconsin drift. A lobe of the Wisconsin ice sheet 

may have occupied the Big Muddy Valley and the preglacial valley west of Manning Lake about as far 

south as that ·la:ke. The unpublished field notes of 

C. M. Bauer's party cite numerous exposures of gla-

"' Smith, C. D., The Fort Peck Indian Reservation lignite field, 

Montana : U. S. Geol. Survey Bull. 381, pp. 40-41, 1910. 

'" Idem, pp. 43-44. 

cial drift ranging in thickness from 1 foot to 42 feet. 

The thicker of these may belong with the,later deposits 

cited below. At one place west of Homestead, in T. 31 

N., R. 55 E., the partial consolidation of several feet 

of drift suggested pre-Wisconsin age. ·The relations 

of the drift to the topography show, however, that it 

was deposited after mature erosion of the Flaxville 

gravel plain (No.1) bench), which developed the long 

old valley slopes and No. 2 bench, and even after these 

had been dissected by the Missouri and its ma.in 

tributaries. 

Some of the slopes, such as that of the west side of 

the Poplar Valley, for example, have been considerably modified since the ice covered the region. Only 

scattered drift boulders, mostly of crystalline rock but 

some of limestone, appear on the grassed slopes, 

though these are well sprinkled with quartzite vehbles 

derived from the Flaxville gravel. Between the valleys and the sharply cut coulees the- upland slopes are 

smooth and very gently l,lndulating. 

Some scattered drift knolls occur 8 to 10 miles 

north of Chelsea, in the Boxelder Creek Valley in 

T. 29 N., R. 49 E. These lie on the :flat or lower part 

of the long slope which extends down to the sharp-cut 

inner valley. West of this occur the big boulders and 

morainal knolls described below. The. Todd Lakes, 

about 16 miles north of Oswego, lie in a small 

. transverse gorge due either to stream capture or to the 

discharge of glacial waters. The triangulation station 

north of this gorge,.in the NW. % sec. 26, T. 30 N., 

R. 44 E., is on a kamelike knoll of quartzite gravel. 

The intricate dissection of the slopes along part8 of 

the Wolf Creek Valley and the valleys farther west is 

probably due to the fact that the sandstone is higher 

in the slopes than farther east and has been cut a way 

from most of the area west of Little Porcupine Creelt 

in Valley County, so that the soft shale is more readily 

eroded. The Little Porcupine Creek Valley is cut to 

a depth of 300 feet below the Flaxville Plain (No. 1 

bench). This valley and the pass to the Cottonwood 

Creek Valley at its head probably constituted an outlet 

for much glacial water at one stage (possibly early 

Wisconsin)'. The steep irregular slopes of this valley 

in Ts. 30 and 31 N. are in striking contrast with the 

long smooth slopes of the glaciated upland. Crystalline boulders are sparsely scattered over the · nplancls 

west of Little Porcupine Creek, but there is little other 

evidence of glaciation. Quartzite pebbles derived 

from the Flaxville gravel are everywhere present. 

A rather striking combination of old and newer 

topography was seen near the heads of Bear and Lime 

Creeks, 18 to 25 miles north of Tampico. Here the 

uplands are marked by long smooth benches sloping 

southward. These are cut diagonally across at the 

west and northwest by an escarpment below which tO 

the west is a semibadland topography. The youthful 
ILLINOIAN OR IOWAN ( ? ) STAGE OF GLACIATION 85 

tributaries of Rock and Willow· Creeks ar~ here cutting headward into the side of an older drainage 

topography. 

Drift is generally present, though thin- and largely 

composed of local material. Even the steep Recent 

slopes of nearly bare shale and sandstone are sprinkled 

with pebbles of · quartzite and some of crystalline 

rocks but these were let down from the higher levels 

by erosion. ' Here and there limestone boulders also 

occur. 

West of Rock Creek the cQmbination of long old 

upland slopes ·cut by later eroded valleys continues. 

The quartzite pebbles abound everywhere, though no 

remnants of the Flaxville Plain (No. 1 bench) with 

the deposits in place are preserved. 

The writer observed till and boulders southwest of 

Glasgow, and Collier found glacial boulders even on 

the highest parts of the Larb Hills, 3,100 feet above 

sea level. 

AGE OF THE DRIFT BORDERING 'l'HE MISSOURI RIVER 

The character and relations of the glacial drift in 

northern McKenzie County, N.Dak., and in the Missou:ri River gorge have considerable significance in 

regard to the age of the pre-Wisconsin drift. Leonard 46 states : 

The topography of the older drift and the large amount 

of erosion it has suffered compared with the Wisconsin till 

have been mentioned on a previous page, where it was shown 

that in many places only the coarser materials of the driftthe pebbles and boulders-remain as evidence that the ice 

sheet once covered the region. But the color of the pre- • 

Wisconsin till is generally unlike that of the Wisconsin drift. 

The latter is commonly light yellow to light gray in color as 

exposed in railroad cuts or along stream valleys, but where 

the deeper till appears in fresh excavations it is seen to have 

the blue color of the unoxidized clay. The pre-Wisconsin till, 

on the other hand, where best exposed on Sand and Clear 

Creeks in northeastern McKenzie County, is dark gray in color 

throughout the. maximum observed thickness of over 100 

feet. 

Except in the morainic areas the thickness of the preWisconsin drift is not great. West of the Missouri River it 

is seldom as much as 8 or 10 feet, and genel'ally the thickness 

is not over 2 or 3 feet or less. The thinness of the older 

drift is dna partly to erosion, which has removed much of the 

glacial material and over a large part of the area left only 

boulders or a thin veneer of gravel, but partly, perhaps, also 

to the fact that the drift may never have been very thick in 

this region. 

Leonard has called attention to .the presence of 

glacial drift in the Missouri River gorge as evidence 

that this gorge is of preglacial age. He writes 47 : 

There is abundant evidence that the Missouri Valley below 

the mouth of Snake Creek is preglacial, and that the river was 

not forced .by the ice sheet to take its present southerly course 

"'Leonard, A. G., The pre-Wisconsin drift of North Dakota: Jour. 

Geology, vol. 24, p. 529, 1916. 

4!1 Leonard, A. G., Pleistocene drainage changes in western North 

Dakota: Geol. Soc. America Bull., vol. 27, pp. 296-299, 1916. 

through North Dakota. This evidence is ba~ on the IJresence of glacial boulders. on the valley bottom and at many . 

points on a terrace representing a former :tloo.d plain of' the 

Missouri. Boulders have been encountered in two wells in 

Bismarck at a depth of 125 feet below the surface, or 80 feet 

below river level. These wells are near the edge of the terrace bordering the Missouri Valley at Bismarck, and since 

the .boulders rest on the bedrock they indicate that the valley 

was excavated to this depth prior to the glacial period. In 

several borings made for the Northern Pacific Railroad previous to the building of its bridge across the river at BismaTck from 70 to 80 feet of slit and gravel were passed 

through before rea!ching the bedrock, and in· one boring a 

boulder was struck at a depth of about 50 feet below the 

river bed. 

On the west side of the Missouri Valley, between Mandan 

and the mouth of the Knife River,' there is a well-developed 

terrace which in places is a mile and more wide. This terrace 

has an elevation of 55 to 60 feet above the river, and the 

upper portion of it is in many places composed of g:acial 

gravel and good-sized boulders. A· railroad cut in this terrace a mile northeast of Mandan, near the cemetery, shows 

the following sectton : 

Ft. in. Soil ______________________________________________ 2-3 

Boulders and graveL __________________________ .:_ __ 5-9 

Sand, finely laminated, with several thin layers 

of gravel--------------------------------------- .2-5 

Boulders and pebbles______________________________ 6-12 

Lance beds, exposed above ·railroad track__________ 15 

In another cut less than one-quarter of a mile south a bed 

of boulders, many of them several feet in diameter, mixed ' 

with gravel and resting on the Lance beds, extends a dJ.s.. 

tance of at least 100 yards along the railroad. 

Several miles south of Price the upper part of the terrace 

is composed of boulders and coarse gravel, the deposit having 

a thickness of 5 to 6 feet. Between Sawyer and Price the 

terrace is finely developed and is covered in some places by a 

layer of gravel and boulders, in other places by unstratified 

glacial drift or boulder clay. In the vicinity of Hensler the 

Missouri Valley is several miles wide, and here, as well as 

in other places, numbers of low rounded drift hills, covered 

with numerous boulders, rest on the valley :tloor. Some of the 

railroad cuts show the boulder clay to be 30 to 40 feet thick. 

Before the time of the earlier ice fn-yasion, when the ice 

sheet advanced 40 to 59 miles beyond the Missouri River, that. 

stream must have :tlowed in its present broad, terraced valley, 

and on the :tloor of this valley the. glacier deposited the boulders, gravel, and till so well exposed at many points. These 

. deposits, shown in the railroad cuts of the terrace, lie about 

40 feet above the ordinary stage of the river and vary considerably in thickness. 

Additional evidence that the present valley is preglacial 

and that the trench of the river was excavated to its present 

depth at the time of the earlier ice invasion is shown by the 

boulder bed less than half a mile below the mouth of Tobacco 

Garden Creek. This bed of boulders, which lies just above 

river level, is at least 12 to 14 feet thick and extends along 

the water's edge for a distance of 100 yards, while scattered 

boulders and ferruginous gravel occur at intervals for another 

200 yards. Overlying the boulders are 15 feet of gravel. 

While some of the boulders of this deposit ~ay have been 

brought here by :tloating ice, it is probable that most of· the 

deposit was left here by the pre-Wisconsin ice sheet when it 

advanced south of the river. The :finer materials of the drift, 

if they were ever present, have been carried . away, leaving 

the gravel and bottklers. 
I 

86 PHYSIOGRAPHY AND GLACIAL GEOLOGY OF EASTERN MONTANA 

In 1916 the present writer examined the boulder 

·bed at the foot of the bluff east of Tobacco Garden 

Creek and also a ravine cut in unmodified glacial 

till to a depth of 20 feet below the flat bottom of the 

creek, in sec. 2, T. 53 N., R. 96 W. 

A. J. Collier 48 reports that in i917 he and Doctor 

Leonard found an exposure of 60 feet of dense pebbly 

clay ti.U overlying the sloping eroded surface of the 

Fort Union shale and sandstone in the lower bluff near 

Fortner's ranch, in sec. 34, T. 153 N., R.100 W., on the 

east side of the Missouri River about 10 miles below 

Williston, N .. Dak., and 3 miles east of Baker's Ferr,Y. 

So close was the lower part of the till to the water's 

edge that the face of th:e tHl had been gouged by floating river ice. .Collier also found 10 feet of till exposed 

at the water's edge on the west side of the river in sec. 

20, T. 153 N., R. 100 W:, about 1¥2 miles above Baker's 

Ferry. The till is overlain by 7 feet of cross-bedded 

sand and gravel, and this in turn by 10 feet of alluvium covering the terrace. 

From these occurrences and those cited above (p. 75) 

it appears unquestionable that the Missouri River had 

occupied its present course through North Dakota 

and had cut its gorge to at least the present depth, 

and probably to depths 100 feet or more below its 

present level, before the advance of the ice sheet which 

deposited the drift south and west of its channel. In 

this sense the gorge is preglacial. Whether or not it 

is of pre-Pleistocene age-that is, Tertiary-depends 

on whether or not the drift is correlated with the 

earliest stage of glaciation (Nebraskan) or with a 

much later one. Concerning the age of this drift, 

Leonard 49 wrote : 

That the drift west of the Missouri River is much older 

than the Wisconsin drift is evident from the great amount of 

erosion it has undergone. Over much of the region the finer 

materials. of ·the till have been swept away, leaving only 

boulders and gravel. The older drift also differs in color, being 

considerably darker than the Wisconsin. The pre-Wisconsin 

drift has been commonly regarded as Kansan, and there is 

perhaps more reason for referring it to the invasion of the 

Kansan ice sheet than any of the other early ice invasions. 

. In a later paper 50 Leonard describes this as "an 

older drift, which may ·be referred to provisionally 

as the Kansan, though it may prove to be younger." 

Wilder,51 who also was familiar with the several 

drift sheets in Iowa, wrote : 

About Coal Harbor, which is 80 miles north of Bismarck, 

there .are rather positive indications that an older Wisconsin 

drift occurs, which probably crosses the Missouri here and at 

points farther north. Unmodified and rather fresh drift is 

here found in the Missouri Valley only a few feet above 

present high water. The topography of the upland at Coal 

Harbor is not more mature than that of the Iowan drift. 

48 Personal communication. 411 Leonard, A. G., Jour. Geology, vol. 24, p. 532, 1916. 50 Leonard, A. G., The geology of North Dakota: Jour. Geology, vol. 

27, p. 22, 1919. 61 Wilder, F.· A.., North Dakota Geol. Survey Third Bienn. Rept., p. 4, 

1904. 

According to Leverett, 52 

In North Dakota the pre-Wisconsin drift in the vicinity 

of the Missouri River has well-preserved moraines, ·and the 

drift forms a veneer on rather steep slopes as well ·as on 

hilltops and valley bottoms. The preservation of these morainic features and of the deposits on the hillsides seems to 

indicate· an Illinoian or Iowan age rather than Kansan. 

The writer concurred with Leonard in 1911 in regard to the probable Kansan age of the drift west of 

the Missouri River, as described in the Bismarck folio, 

after examining the drift there in company with him. 

Subsequently, however, in 1914-15, a careful study of 

the Iowan drift in northeastern Iowa was made by 

the writer and M. M. Leighton,53 and at that time the 

Kansan and Nebraskan drifts were also studied in 

southern Iowa. Studies of these old drift deposits in 

1919 in western Iowa and eastern Nebraska have given 

the writer a still better personal acquaintal}ce with the 

indications of relative age of the several drift sheets. 

There are several considerations which lead to the 

suggestion that this drift west and south of the Missouri River is probably not as old as Kansan, and the 

examinations made in 1921 tend to support the opinion · 

that this drift is not older than the Illinoian or perhaps not older than the Iowan stage of glaciation. 

The occurrence of the till in the Missouri River gorge 

and in the bottom of the broad valley of Tobacco 

Garden Creek shows that the greater part of the dissection of the region below the general upland level 

occurred before this drift was deposited. Much, if not 

all, of this vaJley deepening clearly occurred subse-

"quent to the development of No. 2 bench along the old 

Missouri Valley and Yellowstone Valley in Montana, 

which is regarded by the writer as of early Pleistocene age. The amount of this erosion accomplished 

in North Dakota is, considering its location, commensurate with though not equal in depth to that which 

occurred in the Glacier Park region after the deposition of the oldest drift glaciers of the mountains on 

the high· benches bordering the mountain front 

(p. 31). -4\.fter the early mountain glaciation the 

valleys there appear to have been deepened 1,000 feet 

or more before the later glaciers extended from the 

gorges onto the· bordering plains. This amount of 

erosion certainly took considerable time in the Pleisto~ 

cene. When the plains bordering the Missouri were 

first glaciated, slopes' and uplands were mantled with 

drift, but the major valleys were probably only partly 

filled, and there has been no very great amount of 

erosion since. This is a reason for thinking that the 

drift on the plains is not very old. If the outer drift 

in North Dakota is not older than Iowan or Illinoian, 

12 Leverett, Frank, Glacial formations in the western United States 

(abstract) : Geol. Soc. America Bull., vol. 28, p. 144, 1917. 

I 

53 Alden, W. C., and Leighton, M. M., The Iowan drift, a review of 

the evidences of the Iowan stage of glaciation: Iowa Geol. Sul'Tey, 

VOL 26, pp. 49--212, 1917. . 
ILLINOIAN' OR IOWAN ( ?) STAGE OF GLACIATION 

there seems no reason for regarding the river 'gorge 

as pre: Pleistocene. · 

It has been shown by Leonard 54 that the Little Missouri River formerly flowed northward through the 

broad valley of Cherry Creek near· Watford City and· 

thence through a sag to and along the valley of Tobacco Garden Creek. The Little Missouri .was blocked 

by the advancing ice sheet and adopted the present 

eastward-trending course in McKenzie and Dunn 

Co~ties when the ice melted aw:ay. Along this course 

it has cut a narrow sinuous gorge in the soft shale and 

sandstone. Where crossed by -the writer south of W atford City the gorge is 500 feet deep. The bluffs are 

very abrupt and both they and the bordering upland 

are dissected by a multitude of short branching coulees 

with no approach to maturity. Owing to the preva-

'lence and softness of the shale and the proximity and 

depth of the Missouri River gorge, there has of course 

been considerable erosion since the deposition of the 

drift. Over most of the area the ·drift is thin, and in 

many places the steeper. slopes are bare or carry only 

scattered boulders. There are, however, smoothly rolling upland tracts which are no more dissected than the 

Iowan drift plain of northeastern Iowa. This is also 

true of tracts north of the Missouri River and of tracts 

west of the lower Yellowstone Valley. 

None of the drift of the Keewatin ice examined 

by the writer on the plains of North Dakota and 

Montana shows such evidences of long exposure to 

the weather as the Kansan and Nebraskan drifts of 

ea~tern Nebraska and southern and western Iowa.. In 

the latter region most of the soluble constituents, 8Uch 

as calcareous rock flour and pebbles and boulder3 of 

limestone, have been dissolved out to depths of several 

feet, in places as much as 10 or 15 feet from the surface. Mu6h of this material has been redeposited at 

lower levels as calcareous nodules and fillings of joint 

cracks. In plac~ even the crystalline pebbles and 

boulders that were included in the upper part of the 

till have been decomposed, leaving at the top of the 

till a dense sticky residual clay with sparse pebbles, 

the gumbo til of Kay. 55 Where this is developed the 

color of the weathered upper part of the drift, where 

seen by the writer in southern Iowa, is generally 

bleached to ash-gray. In eastern Nebraska it is in 

many places brick-red. Where· the gumbotil has; been 

removed by subsequent erosion in southern Iowa, or 

where deposition has not proceeded so far, the color 

.of the upper part of the drift is oxidized to rusty 

brown or brick-red, grading downward through brownish yellow. Oxidized bands 1 inch to several inches 

wide also border the sides of joint cracks, and in 

placeS_ where the clayey till is gypsiferous joint cracks . 

" Leonard, A. · G., Pleistocene drainage changes hi western North 

Dakota: Geol. Soc. America Bull., vol. 27, pp. 300-801, 1916. 115 Kay, G. F., and Pearce, J. N., The origin of gumbotll: Jour. 

Geology, VOL 28, pp. 8~125, 1920. 

are filled with plates of selenite crystals. These; ·fea-\ 

tures, together with the mature erosional topoiraPby 

d~veloped on the Kansan drift, are considered indica· 

tive of very long exposure of the Kansan·.-.nd Nebt._.. 

· kan drifts to atmospheric action prior to their being 

covered by later drift or by loess, which is regarded as 

of post-Iowan (largely Peorian) age. Whether or net 

Kay's interpretation .of the origin of the gumbotil· is 

accepted, there is abundant evidence of· the relatively 

great age of the Kansan drift. 

In the parts of North Dakota and Montana.· under 

description no such phenomena indicative of great age 

have been observed by the writer. The till here is not 

leached of its soluble constituents, and it is not highly 

colored as· the result of oxidation, being generally 

dark gray to nearly black, like the clay shales from 

which it is so largely derived. In places, especially 

where it is somewhat sandy, the upper part of the till 

has a dull buif tint. Pebbles and boulders of limestone 

are plentiful clear up to ·the top of the till and even 

scattered over its surface. Some of these pebbles 

within a few feet of too surface still retain their gla· 

cial polish- and striations. The upper faces ·of limestone pebbles and boulders lying on the surface of the 

drift are somewhat roughened and pitted by solution. 

Their under surfaces as well as those of the quartzite 

and granitic erratics are generally coated with white 

· calcareous caliche. 

Taken as a whole, the phenomena in this region 

3eem to the writer to indicate that this drift is not as 

old as either the Kansan or the Nebraskan drift of 

southern Iowa ·and eastern Nebraska, and that its . 

age is more nearly the same ·as ·that of the Iowan 

drift of northeastern· Iowa. Its deposition is therefore tentatively referred to either the Illinoian or th& 

Iowan stage of glaciation. It is recognized that some 

of the differences between the present condition of this 

drift and of the Kansan and Nebraskan drifts of the 

more southerly areas are undoubtedly due to differ-. 

ences in climatic conditions between the two regions 

and not wholly to difference in age. For example, 

the mean annua( rainfall, which ranges from 20 

inches or more in eastern Nebraska to, 30 inches or 

more in southeastern Iowa, declines from 20 inches or 

more in eastern North Dakota to 15 inch~ or less _in 

the western part of the State and in eastern Montana •. 

In this semiarid northern region there is now, at least, 

little downward leaching of soluble salts by percolating water. On the contrary, under the prevailing 

high rate of evaporation, such salts· as are moved are 

carried upward by capillary action instead of downward and tend to form caliche in the soil or subsoil, 

or even to coat with cal~che the surfaces of pebbles 

partly covered at thP. surface of the ground. 

Just what climfttic differences there were between 

the two regions in pre-Iowan and post-Kansan time 
U. S. GEOLOGICAL SURVEY 

10 E3:::::E~=c::=o:i::======':Eo==:===========23:0=====3::io Miles 

MAP OF REGION OF GREAT FALLS, MONT .. SHOWING PLAINS AND ADJACENT 

MOUNTAINS DURING THE PLEISTOCENE OR GLACIAL EPOCH 

PROFESSIONAL PAPER 174 PLATE 29 

Base 1:500,(X)() map of Montana, reduced. 

Shading by I. M. Pistorro, based on topographic 

and geologic maps. 

Unshaded areas are uQdulating plains cut in 

places by sharp gorges and gulches. 

EXPLANAIION 

Hocky 

~ Mountain piedmont glaciers and Keewatin ice 

sheet. (Restored ; extent 

of glaciers west of Rocky 

Mountain front not shown. 

Marginal glacial lakes and 

outlets (restored). 

Remnants 

~ 

~ of lower gravelly 

piedmont terraces of esrly Pleistocene age. 

Remnants of highest gravelly 

piedmont terraces, probably equivalent of Flaxville 

gravel, of Miocene or Plio- cene age. 
88 PHYSIOGRAPHY AND GLACIAL GEOLOGY OF EASTERN MONTANA 

is unknown~ The climatic factors can not be fully 

evaluated, and no full discussion of them is attempted 

here. 

.STREAM: DIVERSION AT THE ILLINOIAN OR IOWAN (t) 

STAGE OF GLACIATION 

UPPER MISSOURI RIVER 

Calhoun 56 discussed in considerable detail the 

drainage changes which resulted in the Missouri River 

abandoning its old valley above the mouth of the 

Milk River and taking its present course. He did not, 

however, specifically state whether this change oc-

.curred as the result of glaciation at the Wisconsin 

stage or at an earlier stage. The stream must have 

been shifted southward temporarily at the earlier 

(Illinoian or Iowan~) stage of glaciation through 

practically the whole extent of 700 miles between Sand 

Cou1ee, south of Great Falls, Mont., and the mouth of 

the Cannonball River in North Dakota. East of the 

· mouth of the Milk River, however, after the recession of the earlier ice front the stream finally re·· 

·turned to its earlier course, which was about the same 

as the present course, except for the cut-off chanJlel between Culbertson and Lakeside, Mont. Between the inouth of the Milk River and Virgelle, however, if the stream reverted to its previous course after 

the melting of the earlier glacier, it was again shifted 

south of the Bearpaw and Little Rocky Mountains 

.and the. Larb Hills by the Wisconsin ice sheet, and it 

had become so deeply intrenched along its present 

.channel by the time the early Wisconsin ice front retreated that it never regained its former course, which 

is now followed in the main by Sandy Creek and the 

Milk ):tiver. 

It is evident that the presence of such an ice sheet 

.extending southward across the Missouri River and 

damming the lower valley of the Yellowstone must 

have caused very notable changes in drainage. Not 

()nly was there much water escaping from the melting 

ice, but the run-off from all that part of Montana 

south of the glacial margin and east of the Continental 

_Divide and also the drainage of much of northern 

Wyoming was blocked and forced to find a temporary 

()Utlet eastward through the Glendive quadrangle. 

Calhoun 57 has shown how the waters ponded in_ the 

upper Missouri Valley submerged the whole region 

:about Great Falls beneath the waters ot a marginal 

· glacial.lake, which he named "Great Falls Lake." 

(See pl. 29.) This discharged eastward at first 

through the remarkable channel known as the Shonkin 

Sag (pl. 30 A), which cuts across the present drainage lines and the gently sloping plain just north of the 

14 Calhoun, F. H. H., op. cit., pp. 34-45. 117 Calhoun, F. H. H., op. cit., pp. 30-31, pl. 5. See also Weed, W. H., 

11. S. Geol. Survey Geol. Atlas, Fort Benton folio (No. 55), 1899 ; 

and Pirsson, L. V., Petrography and geology of the igneous rocks of 

the Highwood Mountains, Mont.: U. S. Geol. Survey Bull. 237, 1905. 

High wood Mountains. These waters, with those of 

-the Arrow and Judith Rivers and other streams, found 

their way eastward to the Musselshell by way of trib- · 

utary channels and across intervening cols along the 

present course of the Missouri River. -

There is a possibility that water ponded in the Musselshell Valley found an outlet for a time southeastward to the Yellowstone near Forsyth, but no abandoned channel has yet been located either there or 

leading directly eastward from the Musselshell. 

In 1922 Dobbin 18 found what appears to have been 

the temporary channel by which the waters of the 

upper ~issouri River escaped eastward to the Yellowstone Valley outside the margin of the Illinoian or 

Iowan ( ~) ice sheet. This channel trends eastward 

across northeastern Garfield County and McCone 

County, mostly through Ts. 21 and 22 N., as shown 

on Plate 1. 

The~glacial river entered the Glendive quadrangle 

near Monrock and crossed the divide through the notch 

400 feet deep at Enid, now traversed by the Richey 

branch of the Great Northern Railway, at about 2,450 

feet above sea level. The water at first evidently 

swung southwestward for about 6 miles from the 

vicinity of Fox Lake and, passing a second col at about 

2,450 feet above sea level, entered the Burns Creek 

Valley. As the gladal lobe prevented eastward flow 

along the present course of Dunlap Creek, it turned 

southward along the ice margin and opened the present anomalous course of Burns Creek to its junction 

with the South Fork. Thence it continued southward 

past the east end of the next high bench-topped ridge 

through a channel, now dry, at about 2,450 feet, to 

Thirteenmile Creek and the end of the ice lobe. Water 

must have ponded for about 90 miles in the Yellowstone Valley, nearly as far up as Miles City, for a time 

at least, for the lowest outlet near the drift limit appears. to have_ been in a general north~asterly direction 

from the end of the ice lobe at Intake through a series 

of notches in the divides between -Boxelder, Cottonwood, Dry, Smith, Shadwell,, and Benny Pierre Creeks, 

at 2,300 to 2,350 feet above sea level, as shown on the 

Glendive topographic map. Thence to and beyond the 

Little Missouri Valley the glacial river followed tern· 

porary channels. The presence of blocks of limestone 

and granite boulders on the edge of the bench north of 

Ousters Lookout ~nd on Belle Prairie, north of Glendive, is probably the result of transportation southward from the glacial front by icebergs floating on 

the lake held in the valley. Probably theJobe of ice 

was not competent to hold the vigorous glacial river 

to its outer channel very long, so that the stream SQon 

cut back the ice or cut a channel across it and. went 

directly easj;ward down the Fox Creek Valley and 

1111 Personal communication. 
U. S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 174 PLATE 30 

A. SHON KI N SAG NEAR HIGHWOOD 

A channel eroded hy the Missouri ·River about t he north busc of the Highwood M'ountains when temporarily diverted by 

the Keewatin ice sheet, now traversed by the Chicago, Milwaukee, St. Paul & Pacific Railway. This part is 200 to 300 feet deep. 

B . MISSOURl R IVER ISSUING FROM THE NORTH END OF THE BELT MOUNTAINS ABOUT 10 MILES 

ABOVE CASCADE 

MISSOURI RIVER, MONT. 
U. S. GEOLOGICAL SURVEY PROF'ESSIONAL PAPER 174 PLATE 31 

A. THE RIVER MEANDERING ON THE PLAIN A F I!:W MILES BELOW CASCADE 

There is probably considerable fi lling iu Lhe preglacial channel beneath the river bed. 

B. POSTGLACIAL (OR POST-IOWAN OR POST-ILLINOIAN) GORGE BELOW l:IIG FALLS, 10 MILES 

BELOW GHEAT FALLS 

Inner gorge about 200 feet deep cu t in Cretaceous shale aud sandstone below the bottom of a broader valley 

200 to 300 feet deep. 

MISSOURI Rl VER, MONT. 
U. S . GEOLOGICAL SURVEY PROFESSIONAL PAPER 174 PLA'l'E 32 

A. RAINBOW FALLS AND DAM OF MONTANA POWER CO., 4 MILES BELOW GREAT FALLS, IN 

SEPTEMBER, 1920 

B. RAINllOW FALLS PRIOR TO TilE CONSTR UCTION OF THE DAM 

Fall 37 feet. Photograph from C. A. Fisher. 

MISSOURI RIVER, MONT. 
U. S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 174 PLATE 33 

A. RIG FALLS, JO MILES BELOW GREAT FALLS, AND POWER HOUSE AND DAM OF MONTANA 

POWER CO. IN SEPTEMBER, 1920 

B. BIG FALLS PRIOR TO THE CONSTRUCTION OF THE DAM 

Fo.ll 75 feet. !'~olograph from C. A. J<'ishcr. 

MISSOURI RIVER, MONT. 
ILLINOIAN OR IOWAN (?)STAGE OF GLACIATION 

· across to and up the valley of Benny Pierre Creek to 

the gap in the divide noted below. 

PLEISTOCENE VALLEY OF THE MISSOURI AND 

YELLOWSTONE RIVERS 

The temporary channels of Missouri River in North· 

Dakota have been described, by Leonard 5 " as follows; 

But while the Missouri River probably occupied its present 

valley for a . considerable time prior to the glacial period 

[that is, prior to the glacial invasion which in the present 

paper is tentatively referred to the Illinoian or Iowan. stage] 

the ice sheet, when it invaded the region, blocked the valleys 

of both the Missouri and Yellowstone Rivers and also the 

preglacial valley of the Little Missouri, forcing these streams 

tQ seek new channels. Lakes were formed in the valleys of 

the Yellowstone and Little Missouri Rivers, the water rising 

until it overflowed the -divide between the latter and the 

Knife River south of the Killdeer Mountains. The combined 

waters of the three rivers flowed east across Dunn County 

and southeast across Morton to the mouth of the Cannonball 

River. The valley thus formed crosses the divide between 

the Knife and Heart Rivers and also that between the Heart 

and Cannonball. The length of this Pleistocene valley of the 

Yellowstone and Missouri Rivers from the head of the Knife 

to the mouth of the Cannonball is 155 miles. It is followed 

by the Northern Pacific Railroad for 30 miles between Almont 

and Hebron, this portion of the valley being to-day occupied by 

Curlew Creek. The Heart River follows the valley for 6 to 8 

miles below the mouth of Curlew Creek, and the broad depression continues its southeasterly course through the divide to 

the Cannonball, being followed for many miles by Louse 

Creek, a tributary of the Cannonball. 

Two broad valleys connect the Knife River Valley with that 

of Curlew Creek. One enters the latter valley between 3 and 

4 miles below Glen Ullin and is followed by the northward-

:flowing Elm Creek throughout a portion of its extent~ Between the latter and the tributary of Curlew Creek the valley 

bottom is occupied in part by a hay marsh. The other valley, 

which joins that of Curlew Greek just below Hebron, is known 

as Farmers Valley and extends to the head of Deep Creek, a 

tributary of Knife River. · 

It will be noted that the Knife, Heart, and Cannonball 

Rivers, together with several of their tributaries, n(lw occupy 

parts of this old Pleistocene valley of the Missouri and YelllJWstone Rivers. The valley is clearly much too large to have 

been formed by several of the streams which to-day flow 

through it, such as Curlew, Elm, or Louse Creeks, and some 

portions now have no streams. Throughout much of its course 

the old valley has a broad, :flat bottom one~half to one mile. 

and more wide, with gently sloping sides. 

Quirke 60 discusses the effect on the erosion of. the: 

Killdeer Mountains of the diversion of the Little Mis-; 

souri River t(\its present west-east course in McKenzie: 

and Dunn Counties. This course, which was assumed: 

as ·.the front of the Illinoian or Iowan ( ~) ice sheet: 

was melted back from the outermost limit, was much· 

nearer the north flank of the Killdeer Mountains than~ 

111 Leonard, A. G., Pleist~cene drainage changes in western North • 

Dakota: Geol Soc. America Bull., vol. 27, p. 299, 1916. 80 Quirke, T. T., The geology of the Killdeer Mountains, North, 

Dakota: Jour. Geology~ vol. 26, pp. 260-263, 1918. 

87949-32--7 

the former channel past Watford City to .and~ 

Tobacco Garden Creek, and as the gorge was rapidly 

deepened in the soft shale . and sandstone the gn.dients of· certain tributaries were ·greatly increased,· and 

in consequen~ these streams- gained ascendancy over 

those not so affected. 

STREAM CHANGES NEAR GREAT FALLS 

In the region of Great Falls the relations . of, the 

course the Missouri assumed after the ;meltmg of ·the 

Illinoian or Iowan ( 1) ice to the several temporary 

channels and to the earlier ones now buried in drift are 

of considerable interest. The present studies have 

added. but little to our knowledge of these relations. 

Inasmuch as there are but few copies of Calhoun's 

paper now available, it seems wise to reproduce some 

of the details which he worked out. The following description (pp. 89-93) is taken with slight modifications from that paper : -

61 

The Missouri River rises in the extreme southwestern portion of Montana and flows northeastward. For 

the first 300 miles it is confined by mountains, but 

after passing between tlie main ranges of the Rocky 

Mountains at the north end of the Belt Mountains it 

escapes to the plain. (See pl. 30 B.) From this place 

to Great Falls the -river meanders over a wide flood 

plain, flowing 75 miles with a fall of but 85 feet. 

(See pl. 31 .A.) At Great Falls an abrupt change in 

the cha.racter of the stream takes place. Leaving the 

plain, it flows through a canyon with high shale and 

sandstone walls and falls 612 feet in about 10 miles.62 

In this part of its course the river· runs in a gorge, 

·in which cataracts have developed (pis .. 31 B, 32, 33) 

because of the harder ferruginous layers found in the 

sandstone. The unequal rate at which the falls have 

retreated is due to the varying hardness of these 

layers. It is not known exactly at what point the falls 

originated, but it was doubtless where the superimposed Missouri found its way over the side of an old 

valley wall, either into its own pre-glacial channel or 

into that of one of its tributaries. This, so far as now 

known, may have happened at any one of a number 

of places. At a point near the mouth of Belt Creek 

the valley suddenly broadens and at the same ti.Die 

turns abruptly to the north. Here· the river flows 

through an old drift-filled pre-glacial valley. The 

post-Illinoian or post-Iowan river does not e-verywhere flow in the old channel but crosses it at. all 

61 Calhoun, F. H. H., op. cit. 1 pp. 34-43. 

o:a Calhoun gives the fall as 512 feet in 12 miles. C. A.. Fisher 

( G('ology and water resources of the Great ·Falls region, Mont. : u. s. 

Geol. Survey Water-Supply Paper 221, p. 76, 1909) gives the total fall 

as 612 feet in approximately 10 miles between the Great Northern 

Railway bridge at Great Falls and the mouth of Belt Creek. 

·~· 
90 PHYSIOGRAPHY AND. GLA.OlAL GEOLOGY OF EASTERN MONT AN A 

angles. This pnconformity of the old· channel to the 

·present one is shown in the sections forming .Figure 7. 

At the big bend of the Missouri, at the mouth of 

Little Sandy CJ"eek, there is another abrupt change in 

the character and direction of the valley. · The river, 

which has been flowing northeastward, turns abruptly 

to the southeast. The valley narrows and becomes 

more canyonlike, and the drift disappears. · The upland on both sides of the stream slopes to the north, 

but the river flows south. At the mouth of the Arrow 

River there is a sudden turn to the east, though the 

character of the valley does not change. The river 

continues to flow between high rock walls, with little 

bottom land, in a valley that narrows and widens 

without apparent cause. From the mouth of the 

(A} c 

.~t ~ 

d 

{B) 

A well on the Odell ranch, ·On the Mi$souri. south of· 

Great Falls, went through the following m~terial :· 

Record ot well on MiB80Uri Ri-ver south of 01-eat Fa:Us, Mont. . . 

Feet Feet 

Soil~-----------------~- ·20 Gravel-----------------~ 7 

Quicksand -------------- ~ 

ClaY----~--------------- 60 212 

These two . well sections show conclusively that the 

valley of the Missouri was formerly much deeper and 

that it has been filled with deposits. 

The reasons for thinking that Sand Coulee Creek 

now occupies the old channel of the Missouri ·are as 

follows: (1) The topographic relat~ons are such that a 

broad valley like that now occupied by Sand Coulee 

FIGURII 7 .-Sections showing the preglacial valley o t the Missouri. A, Old valley of the Missouri, 12 miles wide; a and a' represent the exposed sandstone bluffs of the preglacial valley; b is the drift filling. B, Section across the postglacial gorge (o), which is cut through 

Creek could not.have been formed 

by that stream or by any stream 

flowing westward; ( 2) the cross 

section of Sand Coulee Valley, 

though not quite a~ large as that 

of the Missouri, is of the same 

general shape; ( 3) Sand ·Coulee 

Valley contains great meanders, 

and if the Missouri could be 

turned into it the resemblance to 

the Missouri from Ulm · to the 

junction of Sand Coulee would be 

striking; (4) the tributary val 4 

leys which now join Sand Coulee 

Valley have their acute angles on 

the donwstream side and therefore appear to have been formed 

when the water in the valley 

flowed in the other direction; ( 5) 

at the lower end of Sand Coulee 

Valley there is a deposit o~ lacustrine clay' and at the upper end a 

deposit of boulder clay, which ap. 

pears to block the old channel at 

this point. 

· glacial drift (a) and through the sloping older gravelly bed of the river (b) and into sandstone. 0, Section exposed iiii side of the postglacial gorge above the present. stream bed 

(b a" c) showing the older valley (a a" a') filled with glacial drift.· (From F. H. H. Calhoun) 

Musselshell to that of the Milk River the valley is, 

narrow, with walls 600 to 1,000 feet high. 

It is evident that the river near Great Falls is not· 

·in its old valley. Between the 1neandering stream 

west of the town and the river in its great drift-filled 

valley east of the mouth of Highwood Creek extends· 

a canyonlike valley with a series of rapids and falls. 

·Well borings along the river southwest of the town· 

show that the stream is now flowing on a flood plain 

about 270 feet above the bottom of the preglacial 

valley. A well at Ulm, drilled by the Great Northern Railway Co. about 1888, went down sqme 270 

feet. through sand and clay into a gravel layer.68 . 

• This information was given by P. W. Bradford, of Great Falls. 

No record was kept of the depth and of the material by the railway 

company, but his figures agree essentially with those of Mr. Cha.ftie, a 

well digger of Gr~t Falls, who has sunk other wells in th~ vicinity. 

East of Gibson's ranch Sand Coulee runs ir1to a 

broad plain, the southern edge of which inarks the 

limit of the drift. Here the old valley has· been filled 

by a drift dam to such a height that the water ponded 

in front of the moraine found its outlet to the north 

·over Cretaceous sandstone. (See fig. 8.) The waters 

of the diverted stream entered the old talley near the 

mouth of Highwood Creek, and it was doubtless at 

this point that the falls originated. (See fig. 9.) Fig:.. 

ure 10 gives some idea of how the new channel cut 

across the meanders of the old. 

At the mouth of Little Sandy Creek, east of Virgalle, the abrupt turn.to the south, the narrow rockwalled valley, and the wide ·drift-filled valley stretching off northeastward to the Milk River all suggest 

that the river has again been diverted. Tl,le latter 
ILLINOIAN OR IOWAN ( ! ) STAGE OF GLACIATION 91 

valley is 35 miles long and is occupied by two streams 

7 Sandy Creek, flowing north into the Milk River, 

and Little Sandy Creek, flowing into the Missouri. 

(See fig. 11.) 

The thickness of the drift deposit in the Sandy 

Creek Valley north of the Missouri could not be determined. Little Sandy Creek has cut a 

channel 60 feet into the drift without 

reaching rock. From this point to Havre 

there is no cut of more than 20 feet. 

This valley joins that of the Milk River 

feature of its position is that it is superimposed. ,~n· 

the sloping upland bordering the northern foot of the 

Highwood Mountains. It would be impossible for a 

river in the normal course of development to erode 

such a channel. At the time of the maximum extent 

of the ice sheet Great Falls Lake drained eastward. 

east of Havre. South of Havre there is a FiouRE s.-cross section showing the drift in. the valley through which Highwood 

drift filling 140 feet thick. Plate 34 shows Creek now flows. Looking north, downstream. (From F. H. H. Calhoun) 

the relations of the present streams to the old valley. 

The valley of the Milk River above its junction 

with the preglacial valley of the Missouri ranges in 

width from a quarter to. half a mile, but below the 

junction it is 2 to 3 miles wide. Southward from the 

turn at the mouth of Little Sandy Creek the Missouri 

flows between h i g h rock 

walls. The bottoms are few 

and small and the current 

rapid. The Arrow, Judith, 

and Musselshell Rivers and 

Dog Creek are tributaries in 

this part of its course, and 

each one has· been affected by 

the change "in the direction of 

the trunk stream. 

In order to. illustrate the 

conditions under which these 

changes took place and the 

reason for each change Figures 12, 13, 14, and 15 have 

been prepared. Figure 12 

illustrates the preglacial 

drainage system, Figure 15 

the post-Illinoian or postIowan system, and Figures 

13 and 14 intermediate stages. 

Figure 12 is more or less 

ide a I, for, owing to the 

weath~ring of the soft sandstone, valley contours have 

been greatly modified by the 

drift, making difficult the 

work of restoring the minor 

5 0 

The west end of the Shonkin Sag must have been cov· 

ered by the ice edge, because the waters touched the 

3,900-foot contour level. At thi~ level a wide, shallow 

valley extends 200 or more feet above Belt and Highwood Creeks and runs at right angles to them. 

Though most plainly marked between these two 

drainage lines. · The m a 1

. 0 r changes in FIGURlll 9.-Map showing the preglacial course of the Missouri River between Sand Coulee and the· 

mouth of Htglawood Creek. (From F. H. H. Calhoun) 

drainage caused by the Illinoian or Iowan ( ¥) ice sheet appear to be closely connected with the history of the Shonkin Sag, a valley 

which runs from Highwood Creek to the Arrow River. 

(See pis. 29 and 30 ..4..) The sag is in places nearly 

a mile wide and over 500 feet deep. It is entirely 

independent of rock structure and runs across the present drainage lines at right angles. Another curious 

streams, the same valley is found at interv&ls along 

the south bank of the sag, in places with two banks,. 

in places with only one, the north wall having been. 

formed by the ice itself. 

The valley is such as would be formed by a great 

quantity of water flowing for a short time from a lake. 

After this valley had been cut and the floating ice hadi. 
92 PHYSIOGRAPHY AND GLACIAL GEOLOGY OF EASTERN MONT AN A 

Jl'IGURE 10.-Map of the vicinity of Great Falls, Mont., showing location of the partly buried preglacial channel of Missouri 

River. Contour interval 100 feet. (Modified from C. A. Fisher) 
PEORIAN ( t) STAGE OF DEGLAOIATION 93 

carried·· the boulders over the region covered by Great 

Falls Lake, the ice front was melted back to the north 

bank of the sag and allowed the waters to flow at a 

lower levet The method of formation of the sag 

seems to have boon as follows : The drainage of the 

lake was forced by the position -of the ice edge across 

the streams flowing from the Highwood Mountains. 

The waters took advantage of each col and tributary 

and swung in great meanders around the mountains. 

The sag appears to be the result of superimposing 

across the preglacial valleys ~ drainage system determined partly by topography and partly by the position of the ice edge. The manner in which this 

change was brought about is illustrated· in Plate 29. 

The sag continued to be the outlet for the waters of 

the lake until the ice front had retreated north of 

Fort Benton. 

It is not known whether or not the Missouri River 

returned to its former course west and north of the 

Bearpaw Mountains after the front of the Illinoian 

or Iowan ( ~) ice retreated. If it did it was again 

diverted south of the Bearpaw Mountains when the 

ice readvanced at the early Wisconsin stage. In 

North Dakota and eastern Montana, east of the present mouth of the Milk River, the Missouri River 

returned to its former course, and it has continued 

flowing there since. It is not known that the Keewatin ice obstructed the present course of the Missouri 

at the Wisconsin stage anywhere in this region. In 

its lower course the Little Missouri adopted the present eastward-trending channel and never returned to 

the Tobacco Garden Valley. 

PEORIAN (?) STAGE OF DEGLACIATION 

It is not certain that renewed uplift immediately 

preceded the invasion of the Wisconsi:q. glaciers. In 

the Mississippi Valley conditions favorable to dust 

storms seem to have prevailed for some time immediately after the n1elting of the Iowan ice sheet and to 

have resulted ·in the formation of a notable deposit of 

loess. Loess or loesslike material overlies the older 

Keewatin drift and underlies the Wisconsin till at · 

one of the exposures examined by Calhoun on the 

St. Mary River (fig. 3) and at one of the exposures 

seen by the writer near Lethbridge, Alberta. This 

may or may not be significant. In the section observed by Calhoun there· is 10 feet of black clayey loam 

in the midst of the loess, underlain by 5 feet of loess 

and overlain by 6 feet of loess, above which is Wisconsin till. Possibly this black loam represents the 

soil at the top of the Sangamon loess in Iowa and 

Illinois; 

The relations of certain wind-blown silts exposed 

in the railway cut west of Fort Benton are shown on 

page 66. Tpe sandy clay (No.4) of that section is, in 

places, crumpled into small folds. overturned toward 

the southeast as if pushed by an overriding glacier. 

(See pl. 1.) 

During the Peorian ( ~) interval a moderate amount 

of erosion of the I~linoian. or Iowan drift ( '} was 

probably accomplished, but the upper part of the drift 

was in this region modified very little as ·the result 

of leaching and oxidation. · The pre-Wisconsin till 

observed by Stebinger on Sage Creek (p. 74) is considerably weathered. There is only 6 feet of the till, 

and it contains very few limestone pebbles, most of 

them probably having been removed by solution, as 

such pebbles are fairly abundant in the overlying 

FIGURE 11.-Map showing the preglacial valley between the 

Missouri and Milk Rivers. (Redrawn from F. H. H. Calhoun. Space between heavy lines !!!bows width of the old 

valley) 

vVisconsin till. Included crystalline pebbles . from 

Canada are much decayed and friable.. The t~ll is 

partly indurated in places and deeply iron stained. 

In the exposures of the older Keewatin drift seen 

by the writer on the Belly and Old Man Rivers in 

Alberta less modification due to pre-Wisconsin weathering was observed 

WISCONSIN STAGE OF GLACIATION 

AGE OF THE DRIFT 

Considerable diversity of opinion concerning the age 

of the drift in Montana and western North Dukota. 

I 
\' 

94 PHYSIOGRAPHY AND GLACIAL GEOLOGY OF EASTERN MONTANA 

·has been expressed on maps in published papers. 

This apparently is due in part to indefiniteness of the 

evidence and in part to lack of adequate field observa10 

Missouri in northwestern North Dakota, so that its 

delineation on the maps has v;tried but little. It is 

shown by Chamberlin 64 as extending northwestward 

MTS 

betwleen theiMouse [Souris] 

and Missouri Rivers to the 

northwest corner of what 

· was then Dakota Territory. 

The age of the drift outside 

this moraine is not indicated, but its approximate 

limit as drawn is not 

greatly different from. that 

on Leonard's maps in 

North Dakota. Chamberlin's map covers but little 

of the area west · of the 

lower Yellowstone~ The 

map accompanying a later 

p a per by Chamberlin 611 

shows the same extent of 

later di.-ift and labels all the 

drift outside this limit on 

the plains of the Dakotas 

and Montana as "earlier 

drift." 

FIGURE 12.-Map showing preglacial river system of northern Montana. (After F. H. H. Calhoun) 

On Upham's map of the 

glaciated area of North 

America 06 the boundary 

of the.later drift (or" East 

Wisconsin s t a g e ") · was 

drawn westward through 

what was then southern 

Assiniboia (now Saskatch~ 

ewan) to the southeast corner of Alberta, and the 

drift along and south o~ 

the international boundary 

_was referred to the " early 

Kansan and east Iowan 

stages of glaciation," undifferentiated. 

llll~oian or 

~ Iowan(?} terminal 

moraine and contemporaneous dra,ina·ge 

tiia:o ::&e::soi::::=:::llliEi!i=---===:;30.' Miles 

In · ·1899 this supposed 

" older drift " in southern 

Assiniboia and · Montana 

. outside the limit .of what 

was then designated Wisconsin drift ·was shown by 

Leverett. 67 ~s Kansan. 

61 Chamberlin, T. C., Terminal 

FIGURE 13.-Map showing drainage of part of northern Montana when the Illinoian or Iowan ( ?) ice bad moraine of the second glacial epoch : 

maximum extent, and also preglacial river system. (After F. H. H. Calhoun) (J. S. Ge.ol. SurveJ Third Ann. Bept., 

tions, and it must be admitted that the present investigation has not done very much toward stabilizing 

these opinions. The outer great moraine of the later 

Wisconsin drift is fairly well defined on the Coteau du 

pl. 85, 1883 .. 

• Chamberlin,· T. C., ·Rock scorings of the great ice invasions: U. S. 

Geol. SUrvey Seventh Ann. Bept., pl. 8, U~88. 

oo Upham, Warren, The glacial Lake Agaasiz : U. 18. Geol. Survey 

Mon. 25, pl. 16, 1895. 

• Leverett, Frank, The Illinois glacial lobe : U. 8. Geol. Survey Mon. 

38, pl. 1, 1899. ' 
WISCONSIN STAGE OF GLArCIATION 

In 1906 was published Calhoun's paper 68 giving the drift i~ North Dakota is the so-call~ .Altamont rooreSults of several seasons' study of the drift of the raine, a. broad, strongly marked mor~inal belt which 

continental'ice sheets in Montana and of the Rocky extends northwestward along the Coteau du Missouri· 

Wisconsin 

~ terminal mora1ne 

and contemporaneous drainage 

to o 40 Miles ~~==~==~==~== 

Mountain glaciers. Calhoun concludedthat ID:Ost 

of· the drift north of the 

Missouri River in Montana was of Wisconsin 

age, and his map shows 

the extent of Wisconsin 

drift approximately the 

same as that on Plate 1 

of the present. paper as 

far east as the east sideo f the Little Rocky 

-Mountains. The drift 

south of this margin was 

shown as "older drift." 

He .states 69 : "The fact 

that .there is · such a 

border of drift without 

the terminal mora,ine 

suggests two different ice 

epochs,· but very little 

was found in the field to 

support this theory." 

His investigations did 

Figure 14.-Map showing draiuage of part of northern Montana at early W1aconstn stage. (After F. H~ H. 

· not extend as fa,r east aB 

North Dakota. EXPLANATION 

Postglacial 

lB~B Pre~lacial Moraine 

dratnage drainage 

Calhoun) 

JO 0 A 8 A 10 20 aoM11es·. 

i. 

As shown by Calhoun 70 and by Stebinger 

and the writer, 71 there 

can be little doubt that 

the drift of the Keewatin 

ice sheet in the Blackfeet 

Indian Reservation and 

thence south to t he 

moraine north of the 

Missouri River between 

Great Falls and the 

Bearpaw Mountains is of 

Wisconsin age. Calhoun 

traced the margin of this 

drift eastward along the 

north side of the Bearpaw 

and Little Rocky Mountains, but farther east no 

moraine was definitely 

mapped. What has been 

regarded as the outer 

moraine of the Wisconsin FIGUBII 15.-:Map showing postglaeial drainage system of part of northern Montana, with a part of the 

preglacial system. (After F. H. H. Calhoun) · 

81 Calh~, F. H. H., The Montana lobe of the Keewatin lee sheet : I 

U. S. Geol. Survey Prof. Paper 50, 1906. _ 

• I&!m, p, 55. · . 

,. Idem, pp. 52-54. 

n Alden, W. C., and Steblnger, Eugene, Pre-Wisconsin glacial drift 

in the region of Glacier National Pf.rk, Mont.: Geol Soc. America 

Bull., vol. 23, pp. 687-708, 1912; vol. 24, pp. 529-57~, 1913. 

into the northeast corner of Montana, in Sheridan 

County. In 1916 the writer ma,de a series of traverses 

from north to south across that part of Moi?-tana lying 

between the Missouri River and the· Canadian bOundary and northward 40 to 50 miles into southern Sas-
96 PHYSIOGRAPHY AND GLACIAL. GEOLOGY OF EAsTERN M:ONTAN A 

katchewan in the expectation that this moraine would 

be found extending around the higher part of the 

Wood Mountain upland and thence southward or 

southwestward again into Montana to the region of 

the Little Rocky and Bearpaw Mountains. Other 

trav~rses were made in 1920, but no evidence of such 

southwesterly trend of the Altamont moraine was 

found. The writer has therefore been forced to the 

conclusion that the limit of the later Wisconsin glaciation marked by the Altamont moraine as described 

below (pp. 126-129) probably continues northwestward 

from the northeast corner of Montana and that the 

Keewatin ice, which formed the moraines near the 

mountains, was that of an earlier Wisconsin substage. 

Careful study of the topographic relations of such 

morainal deposits indicates that the limit of the early 

Wisconsin drift is very indefinite but probablty lies 

along approximately the sinuous line traced on Plate 

1. The character and relations of these depOsits are 

described below. · 

EARLY WISCONSIN GLACIATION 

GENERAL RELATIONS 

The conditions outlined above seem to the writer to 

indicate that ear tier Wisconsin drift emerges from 

beneath the later Wisconsin in northwestern North 

Dakota and extends thence westward to the limits of 

the "later drift" north of the Missouri River in 

Montana, approximately as rna pped by Calhoun. 

This is in harmony with conditions in northeastern 

Minnesota, Wisconsin, and Illinois, where Leverett 72 

has mapped Wisconsin drift ~xtending in places far 

beyond the limits of later readvances of the Wisconsin 

ice sheet. 

Traces of a terminal moraine east of the Little 

Rocky Mountains are scant and discontinuous and so 

may be described somewhat in detail. Further field 

examinations are necessary before their correlation 

can be considered satisfactory. 

·EARLY WISCONSIN TERMINAL MORAINE (?) IN 

NORTH DAKOTA 

Willard and Erickson,73 on a map of a part of 

northwestern North Dakota, showed the deposits of 

the Altamont moraine extending southwestward along 

the divide between the valley of Shell Creek and that 

of the Little Knife River and also extending across 

the line of the Great Northern Railway in the area 

south of Ross and west of the Little Knife Valley. 

In the accompanying description 74 they state that 

n Leverett, Fran}(, The Illinois glacial lobe : U. S. Geol. Survey Mon. 

38, pl. 6, 1899 ; Moraines and shore lines of the Lake Superior region : 

U. S. Geol. Survey Prof. Paper 154, pl. 1, fig. 15, 1929 ; Quaternary 

geology of Minnesota and parts of adjacent States : U. S. Geol. Survey 

Prof. Paper 161, 1932. . 

'fa Willard, D. E., and Erickson, M. B., A survey of the coteaus of 

the Missouri : North Dakota Agr, Coli. Survey Second Bienn. Rept., 

pl. 3, 1904. . 

'74 Idem, p. 26. 

• " Long lubes pushed out from the front of the ice also, 

and thus the outer edge of the great deposit from ·the 

ice, which is known as the moraine, is very irregUlar 

and uneven." There is some rea$on for thinkiilg that 

these deposits, instead of representing lobes of the 

Altamont moraine, belong with· a. somewhat earlier 

moraine which is here emerging from beneath the late. 

Wisconsin deposits. 

Leonard 75 refers to the ·occurrence of. ·morainal deposits near the White Earth Valley, in western Moun~ 

trail County, and near Temple, in eastern Williams 

County. The deposits near Temple are contoured on 

the Ray topographic map. This belt was cl'OSSed in 

1916 by the writer in company with ·Dr. Leonard on. 

a trip from the Missouri River north to the ~reat 

Northern Railway at White Earth, and a well-:-marked 

moraine belt was traversed most of the way .. ea.stwa.rd 

to Stanley, on the south side of the railroad. 

Wood 76 states tha.t 

the lakes at the head of the Shell Creek a:re a part of t.be headwaters of the stream which have been obstructed, and cut 1 off 

from the valley by the accumulation of drift . The ~kes near 

the head of the Little Knife and White Earth Rivers probably 

have similar origin. The sloughs at the head of the White 

Earth are undoubtedly of glacial origin. . The abrtlpt termination of the Little Knife River Valley, just south ~f ;Stanley, 

may be related in some way to the formation of the sloughs 

and lakes lying to the north and east of that' place. . . 

To the present writer it seems probable that these 

sloughs and lakes are due to blocking of . valleys by 

pre-Altamont morainal drift such as may he seen 

along and south of the Great Northern Railway west · 

· of Stanley. Southwest of Stanley morainal deposits 

.occur between the Little Knife and White Earth Valleys. In T. 155 N., Rs. 9.2 ~nd 93 1V., and T. 154 N., 

R. 93 W., is a strongly marlted morainal ridge roughened with knolls and pitted with kettle holes, SOUle. of 

which contain ponds. It is possible that this to.pography continues north to the belt seen along th~ rail- · 

way, tho'!lgh such is not known to be the case. Cuts . 

in these deposits expose gray calcareous ·till, neither 

leached nor oxidized. Limestone pebbles are plenti-' 

ful up to and on the surface, though most of the, pebbles and boulders are of granite. This moraine extends westward to the White Earth Valley,. :lnd, erossing the valley in 1'. 155 N., it was found strongly developed on the upland to the west. It appears- to have 

a northwesterly trend and is perhaps to be correlated 

with the morainal tract surrounding Temple, but it 

was not traversed so as to be definitely mapped. This 

tract appears to end at the northwest between 4 a·1d 8 

miles north of Ray, in T. 157 N., R. 97. W. ·The 

50-foot contours of the Ray topographic map 8how no 

'l1i Leonard, A. G., The p·re-Wisconsin drift of Nt}rth :Oakota: Jour. 

Geology, vol. 24, pp. 528-532, 1916. 

'76 Wood, L. H., Preliminary report on Ward County and adjacent 

territory with special reference to the lignite: NO.rth Dakota Geol. 

Survey Second Bienn. Rept., p. 91, 1903. 
EARLY WISCONSIN GLAOU.TION 97 

continuation of this moraine to the west, though a few 

slight sags and swells were seen about 6 miles northwest of Ray and also southwest of Angie, in T. 158 N., 

R. 99 W; South of this the area is sharply dissected 

by the branches of the East Fork of Little 1\'Iuddy 

Creek. Near the west line ofT. 157 N., R. 99 W., a 

valley appears to be partly or wholly blocked by drift. 

Thence a belt of morainal knolls extends westwttrd in 

T. 157 N., R. 100 W., to the Little Muddy Valley. 

This valley .is broad and open above Marmon and also 

to the sou.th, but for a mile or two below Marmon 

there is a well-developed moraine on the bottom land 

west of the stream. 

The upland to the west has long smooth slopes, but 

its borders are sharply dissected. On this upland, 

where crossed from east to west and south to north, 

no trace of a moraiu.e was seen except a. few slight 

sags and swells on the divide between Sand and. Cow 

Creeks. Morainal knolls and sags are encountered 

·a.gain a few miles northwest of Bonetraill post office, 

in T. 157 N., R. 102 W., and these are thought to be 

continuous on the southwest with the broad morainal 

belt that extends to and across the State line near Bull 

Butte, in T. 156 N., R. 104 W. This butte is a conical 

hill rising above the adjacent drift knolls and capped 

with drift and fragments of red clinker. On the top 

is a Coast and Geodetic Survey triangulation station 

at 2,530 feet above sea level. The body of this hill 

may be composed of shale, but there are morainal 

knolls and sags not far to the northeast and north and 

extending thence ~ross the State line on to the lower 

ground to the northwest; masking the erosional 

topography. 

TERMINAL M .. RAINE (?') IN ROOSEVELT AND 

VALLEY COUNTIES, MONTANA 

The moraine plays out to the west and was not seen 

again in two traverses of the area between the Montana State line and the Big Muddy Valley. In its 

place throughout much o:f this area is a smooth littledissected plain sloping gently northwestward to the 

broad preglacial trough in which lies Medicine Lake. 

West of the Big Muddy Valley, in the old Fort 

Peck Indian Re~;ervation (now Roosevelt County), 

but little evidence of morainal deposits to be correlated with the morainal belt under discu~ion was seen, 

although the area was traversed from north to south 

over ten or twelve diff4~rent routes. C. M. Bauer, 

who studied the lignite deposits of the area, pointed 

out to the writer most of the occurrences here mentioned but stated that he failed to find any continuous 

moraine. C. D. Smith, who also studied part of this 

reservation, makes but very brief mention of the drift 

in his report. 77 Except on the steep eroded slopes, 

. Tr Smith, C. D., The Fort Peck Indian Reservation lignite field, 

Mont. : U. S. Geol. Survey Bull. 381, pp. 43-44, ·1910. · 

87949-82-8 

there is a thin sheet of glaei$.1 drift spread generally 

over the area. of the reservation, covering the Tertiary 

and Cretaceous formations. In several parts Bauer 

found thicknesses of 10 to .40. feet of drift exposed, 

and with his observations those of the writer agree. 

The drift consists generally of calcareous ~gray or little 

oxidized clay with plentiful crystalline and limestone 

pebbles and boulders. There is also generally a.large 

admixture of smoothly rounded and polished quartzite pebbles like those in the Flaxville gravel. 

On the upland west of Homest;ead, in see. 19, T. 31 

N., R. 55 E., and sec. 25, T. 31 N., R. 54 E., and also 

in sec. 5, T. 29 N., R. 53 E., are a few isolated knobs 

rising abruptly 30 to 40 feet above the surrounding 

broad smooth plain. that has been' described 78 as a 

drift-filled preglacial valley (p. 2l). So smooth is 

this plain that· the knolls are conspicuous features. 

Those exami.ned.by··thew.riteJr app.ear.J.o- be of glacial 

drift, although· only the surface .and· material brought 

up by rodents could be examined. The tops are thickly 

strewn with crystalline and limestone boulders, mostly 

the former. These few knolls are in two groups at 

about 2,100 feet above . sea level. and about 12 to 14 

miles apart. The groups seem to have no connection 

with each other or with definite morainal deposits. 

They may be merely isolated kames or may, perh~;a.ps, 

be correlative with the morainal belt. Northwest of 

the north group of knolls the surface rises gradually 

to 2,400 feet, and on this crest are slight sags and 

swells·. An ice lobe may have lain in the Big Muddy 

Valley · and the preglacial Missouri Valley without 

leaving more than these isolated knolls .. The margin 

may have swung thence northward along the rising 

slope to the high land bordering Smoke Creek on the 

southwest at 2,400 feet. 

In the northern part of .the. Hay Creek quadrangle 

and farther north, in the northern part of Ts. 31 and 

32 N., R. 5_1 E., and extending northwest into T. 33 N., 

Rs. 49 and 50 E., there is an extensive nearly flat upland (a remnant of the Flaxville gravel plain or 

No. 1 bench) between the valleys oii Smoke Creek and 

the Poplar River. On this there is a belt of morainal 

topography 12 to 15 miles long extending northwestward to the western edge of the upla~d near the north 

line of the old Fort Peck Indian Reservation. Slight 

sags appear in sec .. 1, T. 31 N., R. 51 E. ,These continue west to a mild morainal topography of drift 

knolls extending north-northwest from sec. 5. In 

places, as at· the triangulation stati~ml.2,753 feet above 

sealevel in the southwestern part ofT~ 33 N., R. 50 E., 

in southeastern Daniels County, there are strongly 

marked knobs and kettle holes. From this point the 

belt was traced west-northwestward to the edge of the 

upland overlooking the Poplar Valley. Some swells 

'18 Bauer, C. M.; A sketch of the late 'rertiary history of the upper 

Missouri River: Jour. Geology, .vol. 23, pp. 53--54, 19t5; 
98 PHYSIOGRAPHY AND GLACIAIJ GEOLOGY OF EASTERN MONTANA 

appear to continue down the long dissected slope. A cial water at certain :stages when outlet to the P plar 

line of scattered low knolls also extends southwest- Valley was blocked by .~ce, -as, for instance, when the. 

ward~ down the valley slope nearly to the Poplar ice front was at or near the line under discu,ssion. LitRiver, about 3 miles southeast of Cusker's ranch. . tle Porcupine Creek, to the south, traverses· a great 

Some of these knolls may consist of shale, but one trough cut in the shale to a depth of nearly 300 feet. 

examined near the road appears .t'o be drift. The· On the upland northwest of the pass· above mentioned, 

surfaces of the knolls on the upland show mostly in T. 33 N., R. 48 E., and adjacent tracts, is an area 

quartzite gravel, but pebbles of igneous crystalline characterized by knolls and ridges whose contours sug- · 

rocks and limestone are intermingled with . .the gest morainal .deposits, but here again there is a susquartzite. · picion that they may really .be erosion remnants of the 

On the lower land to the. north, in sec. 35, T .. 32 N., · higher part of the Flaxville gravel deposit. The only 

R. 50 E., there is a sinuous esker like ridge 10. to 30 , . materia! ~xposed on these so· far as seen is quartzite 

feet in height, with an uneven knobbed crest. A line gravel. A single granite boulder was noted in the 

of swells appears. to extend thence some distance: vicinity, though scattered boulders were seen farther 

southeastward; and .there .is some suggestion of con-: south. The belt extends northwestward toward Avon- · 

nection with the moraine to the west. A well drilled : dale .. 

on this lower land in sec. 18, T. 33 N., R. 50 E., is said· ; About 20 miles farther northwest on the upland 

to have penetrated 2-:\ feet of clay (drift), above gravel; south of ·Opheim a similar belt of morainelike knolls, 

and to have ended in gravel at a depth of 45 feet. A: possibly a continuation of that near Avondale, was 

well on the upland in or near the moraine is said to . crossed. Here again the knolls so far as examined 

have penetrated 40 feet of gravel below the drift clay.; appear to be composed entirely: of quartzite gravel, 

. An ice lobe may have .lain in the Poplar Valley "for though. scattered granite boulders occur both to the. 

a time, and the margin may have swung thence north- , north and south.. For a long distance westward from 

westward up onto and along the upland crest north- the line thus traced no suggestion of glacial moraines 

east . of Boxelder Creek, through ·adjacent parts of . was seen, though the q.rea was traversed by the writer 

Ts. 30 and 31 N., R. 49 E., and 'I\ 31 N., R. 48 E., · in general north-south directions at intervals of 6 to 15 

where there is a belt of knolls and slight marshy sags. miles. Neither do A. J. Collier and H. H. Bennett, 

These features, however, fade out after extending a. who have examined this area, report any· such occurfew. miles toward the northwest. Most of the rna- rences. 

terial is quartzite gravel, but igneous crystalline peb- The area west of Porcupine Creek comprises the 

hies and boulders ·are generally intermingled. . This i basins of Ro.ck and Frenchman Creeks, which are eut 

upland stands 500 feet or more above the bottom of principally in the soft shales of the Montana group. 

the Poplar Valley to the northeast, and the long valley · No remnants of uplands underlain by the Fort Union 

slopes are sharply dissected. beds and capped with the Flaxville gravel ·are pre-

~en the. ice front was in this position its margin, served soutA of the. Wood Mountain plateau of southif having a general northwesterly trend, would prob- ern Saskatchewan. The general ievel is lower, and it 

ably lie along the slope and crest south of Cottonwood . may be supposed that, if . the ice front lay along the 

Creek in T. 31 N., although no morainal features were uplands to the northeast as traced, a broad lobe would 

noted where it was crossed. For some miles south 1Jf have extended farther south in western Valley County. 

this crest hardly any . crystalli~e or limestone drift rhere ·are knolls in places below the western edge 

material is mingled with the quartzite pebbles. One of the upland in R. 37 and 38, but the belt is difficUlt 

interesting feature is a series of cols cutting through to traverse and has not been carefully examined. It 

the crest of the upland and leading to the heads of the is possible that the ice front extended on the low 

branches of Tule Valley and Wolf Creek. On~ of ground to .and across the line of the Milk River west 

these, traversed by. the road leading down the east of Hinsdale. Certain fea.tures shown on the Hinsdale 

valley of the East Fork of Wolf Creek, is 40 to 50 topographic map, 3 to 5 miles northeast of Hinsdale, 

feet deep. A person ascending the 300-foot dissected in sees. 21-23, T. 31 N., R. 36 E., suggest the blocking 

slope south of Cottonwood Creek is surprised at the of the Rock Creek Valley by morainal deposits. 

top to find himself in the head of a valley leading 

southward rather than on the broad smooth upland. 

A more notable pass is that between the heads of 

Cottonwood and Little Porcupine Creeks in sec. 34, 

T. 32 N., R. 44 E. Here the broad, nearly flat valley 

floors are continuous, and Little Porcupine Cre~k has 

evidently captured some of the headwaters of the other 

stream. This pass m~st have afforded. outlet for gla-

\ 

TERMINAL MORAINE IN PIULLIPS AND·. BLAINE 

COUNTmS, MONTANA. 

There are also drift knolls near the railway west of 

Hinsdale. A ridge in the Larb Creek Valley 2 miles 

south of Beaverton suggests that the ice front may 

have crowded into the mouth of this valley and forced 

the drainage to flow southward through the pass. in T. 
EARLY WISCONSIN GLACIATION 99 

26 N. leadingc. to Timber Creek. ·West· of this valley · 

there is also. a belt of low drift knolls between the 

Great Northern Railway and the foot of the bluff. 

Some low• swells south of Beaver Creek along the 

Roosevelt Highway and the Great Northern Railway, 

west of Saco, may be morainal. One of these in sec. 

32 (see Saco topographic map) appears to have been 

wholly removed for railway ballast. Similar kamelike knobs are to be seen near the foot of the west 

slope of the hills east of Beaver Creek and, as shown 

at the south margin of the Bowdoin quadrangle, in 

sees. 21, 22, 27, and 28, T.- 29 N., R. 32 E., about 10 

miles south of the railway, a group of morainelike 

knobs 20 to 60 feet in height obstruct the broad bottom of the valley. 

It is possible that some of the low drift ridges that 

lie across the old buried valley of the Missouri River 

south of Bowdoin village and Lake Bowdoin (see 

Bowdoin topographic map) are morainal, but there is 

no strongly marked morainal topography. At one 

place where the south canal cuts through a narrow 

place in the ridge, in sees. 11 and 12, T. 30 N.,. R. 31 E., 

5 to 10 feet of pebbly drift overlies what appears· to 

be fine wind-blown clayey sand. Such swells also 

occur n9rth and east of Lake Bowdoin {p. 112). The 

upland slopes to the south are considerably more dissected than those north of Lake Bowdoin. The possibility that the southern limit of the early Wisconsin· 

ice advance passed somewhere in this vicinity is also 

suggested by conditions found south of Malta and 

farther west. A rough, bouldery morainal deposit lies 

along the south slope of Malta above the south canal, 

and a gravel pit in this deposit exposes very stony, 

poorly sorted subangular crystalline pebbles and boulders. The unev~n topography continues for about 2 

miles south; beyond this the surface for a few miles 

is smoother. At 8 or 9 miles south of Malta, in T. 29 

N., R. 30 E., there is another belt of morainal hills. and 

marshy lake basins, which is crossed by the roads 

leading to Regina and to Flat Creek On one of the 

abrupt boulder-strewn hills is a United States Geological Survey triangulation station. Though these 

appear clearly to be marginal glacial moraines, their 

continuations either to the northeast or southwest are 

not· well marked. A faint morainal belt is traceable 

westward to the Fort Belknap Indian Reservation 

through T. 29 N., as noted below (p.111). Though no 

marginal moraine has yet been traced southwestward 

through the country northwest of Beaver Creek, yet 

the relations of the moraine near the Little Rocky 

Mountains seem to indicate that the limit bf the early 

Wisconsin ice advance·must extend through this area.· 

After passing Alkali Creek on the road southwest from 

Malta toward Zortman no signs of a mo~aine were 

seen until Little Warm Springs Creek was passed. 

In the southwestern part ofT. 26 N., R. 2'(' E., a low 

morainal ridge, well sprinkled with quartzite pebbles· 

and boulders, extends westward across the road· and 

breaks up into a pelt of knolls· which continue west-. 

ward across No. 2 benbh to the vicinity of -the gap · 

through which Little Warm Springs Creek crosses 

the ridge of Judith River: sandstone near the east 

line of the Fort Belknap Indian Reservation. -From: 

this locality a hilly belt strewn with abundant crystal .. 

line boulders extends northwestward through T. 26 N., 

R. 26 E., on the low ground bordering the northeast. 

side of the sandstone ridge. This appears to mark the 

limit of the early Wisconsin ice invasion. 

When the ice front stood in this position (pl. 35}. 

waters held between the glacier and the Little Rocky 

Mountains must have escaped southward through the 

sag which is now traversed by an irJjgation ditch and 

in which is the reservoir held by the dam at the Malta 

road, in sec. 11, T. 25 N., R. 26 E. Doubtless it was 

after a slight recesaion of the ice front~ if not at the 

earlier ice invasiQn, that Wa.nn Springs Creek cut 

through the sandstone ridge, making the narrow· gorge 

250 feet or more in depth in the SE. % sec. 1, T. 26 N., 

R. 25 E. The ridge in sec. 1 north of the gorge now 

separates this stream from what appears to have been 

its former· broad valley. 

From this valley westward the margin of the early 

Wisconsin drift was traced by the writer with some. 

care clear across the reservation (pl. 1) in 1921,. 

when A. J. Collier al}d S. H. Cathcart were making 

their detailed geological survey .

79 

In the NW.% sec. 34, T. 27 N., R. 25 E., are pillars 

of sandstone which appear not to have been overrid- · 

den by the early. Wisconsin ice, but about three..quar~ · 

ters of a mile north of these the moraine is found ly-i 

ing along the upper slope just beyond the edge of No. 

1 bench. The ice crowded southward on top of the 

bench to the knolls in the NE. 1A, NW. % sec. 28 up to 

3,500 feet above sea level. In the valley to the west a. ·, 

small lobe extended half to three-quarters of a mile 

farther south, and west of this the ice barely reached 

the top at the north end of No. 1 bench, in the N. % 

sec. 25, T. 27 ~., R. 24 E. The limit of the advance is 

marked by a marginal drift ridge above and a quarter 

to half a mile north of the crest of the sandstone blutf 

that borders the Lodgepole Creek· Valley. On the. 

lower ground to the west the ice extended 1 to 2 miles 

farther south, and the limit of drift runs first southwest, then west to Hays. There are boulders, till, and 

a few ponds in this part, but no well ... marked mor-aine.· 

West of Hays the drift limit is a sinuous line 

through the southern tier of sections of T. 27 N., 

R. 23 E. This lies north of the sag along which 

passes the irrigation ditch running to the reservoir 

2 miles west of Hays. Beyond the south dike of the 

'ill Collier, A. J., Geology of the Fort Belknap Indian . Reservation 

and Little Rocky Mountains, Mont. (in preparation). 

' 
100 PHYSIOGRAPHY AND GLACIAL GEOLOGY OF EASTERN MONTANA 

reservoir the sag is continuous to the west. Evidently 

it was by this sag that waters ponded by the glacier 

in the Peoples Creek Valley escaped. Apparently the 

ice was bordered by a westward-flowing stream and 

did not crowd up onto the dissected north end of the 

high bench. In ·R. 22 E., however, a lobe extended 

southward 2 to 3 miles on the lower land in the .former 

valley of Section Creek, and a mild moraine is traceable westward from the middle of the south line of 

sec.12 through sees. 11 and 10 to and across the re,:)ervation boundary. The present course of Section 

Creek is probably due to diversion westward by the 

ice front. 

At its most southerly point the moraine ha.s an altitude o~ about 3,000 feet. About 12 miles in a direction somewhat east of north from this point the higher 

of the Twin Buttes (pl. 36 A) rises to an altitude of 

3,850 :feet, or about 850 feet higher than the plain at 

its base and the moraine at its most southerly point. 

Inasmuch as drift pebbles were found on the top of 

t.his butte, it appears that the ice must have been at 

least 850 feet thick within 12 miles of its limit. This 

butte is about 7 miles farther north and 350 feet higher 

than the limit of the ice advance on the high benches 

north of Lodgepole. The tov of this butte is about 

1,500 feet higher than the flat along the Milk River 

20 to 95 miles to the north and northeast. ProbaLly 

there· was a considerable thickness of ice even on top 

of the Twin Buttes, but if it is supposed that the 

highest point was barely covered and if a southward 

slope of only 20 feet to the mile is assumed for the surface o:fthe glacier, there must have been about 1,000 

feet of ice on top of Snake Butte and at least 2,000 

feet of ice over the flats along the Milk River. 

It is probable that the Little Rocky and Bearpaw 

Mountains were heavily covered with snow during 

both the earlier and later si ages of glaciation, but 

neither Collier, Cathcart, nor Weed and Pirsson report evidence of local glaciation in the Little Rocky 

Mountains, nor did Weed report any in his descriptions of the Bearpaw Mountains.80 No suggestion of 

local glaciation was found by the pre~ent writer on 

the short traverses which he made in these mountains. 

At several points on the mountains scratches which 

closely resembled · glacial striae were noted on small 

exposed surfaces of limestone. Inasmuch as these 

were seen only in trails which had been used for 

dragging logs and in positions where no other phenomena indicated glaciation it was concluded that 

they were not glacial striae. 

West of the Fort Belknap Indian Reservation the 

limit of the drift runs somewhat west of north 20 to 

80 Weed, W. H., and Pirsson, L. V., The geology of the Little Rocky 

Mountains: Jour. Geology, vol. 4, pp. 401-402, 1896; The Bearpaw 

Mountains, Mont.: Am. Jour. Sci., 4th ser., vol. 1, pp. 283-301, 

851-362 ; vol. 2, pp. 136-148, 1~s-lP!) 1 1896. 

25 miles to the vicinity of Eagle Butte, in sec. 6,. T .. 

29 N., R. 21 E., the most northeasterly. outlier of· the 

Bearpaw Mountains. In this part the limit of the 

drift as shown on Plate 35 has not been traversed by 

the writer but is approximated from Bowen's map of 

the Cleveland coal field.81 On this map several lines 

are shown as marking " Boundary of areas covered by 

drift or bench gravel." It is assumed by the present 

writer that the most easterly of those southeast of 

Eagle Butte is probably at or near the limit of glacial 

drift. 

Eagle Butte was surrounded by the ice on the east, 

north, and west. For about a mile east of the butte 

the main road runs on: a gravel terrace bordering the 

south front of a well-marked boulder-strewn moraine 

50 to 60 feet high. (See pl. 36 B.)· , 

The altitude here is about 3,500 :feet (barometric). 

Scattered boulders were also found on the lower slopes 

of Eagle. Butte up to a few hundred feet above . the 

base. Southwest of this butte there are unglaciated 

curiously weathered ledges of sandstone not far south 

of the road to Cleveland. The actual limit of the drift 

across the foothills west of Eagle Butte was located by 

the 1vriter at only a few points; between these the limit 

as shown on the rna p is only approximate. 

About 2% ·miles north of Lloyd the road, after crossing the craggy ridge of igneous rock, runs north down 

to the margin of the drift at about 3,820 :feet (barometric) as noted by the present writer. About 5 miles 

northeast of this point glacjal pebbles and boulders, 

one measuring 2 by 3 by 4 feet, were found on top of 

Bean Butte, a mass of igneous rock that rises abruptly 

400 to 500 feet above the plain in sec. 5, T. 30 N., 

R. 19 E. It is possible that the highest erratics-those 

found by Reeves east and west of Beaver Creek in 

·T. 30 N.; Rs. 15 and 17 E., at 3,890 and 3,898 :feetwere deposite~ by the pre-Wisconsin ice sheet. 

In the course of his mapping about the north and 

west flanks of the Bearpaw Mountains in 1924, Reeves 

made some observations on the drift which have been 

communicated to the writer. The "southern limit of 

areas covered by glacial drift " shown by Reeves 82 is 

not the outer limit of the ice advance but the limit of 

areas where the bedrock is almost wholly concealed 

beneath drift. The ice advanced southward nearly 

across T. 30 N. and crowded against the craggy, broken 

north face -of the mountains. 

Owing to the relatively short distance from the 

Bearpaw Mountains to the Milk River and the consequent high gradient of the streams the tract between 

the mountains and the river has been considerably 

81 Bowen, C. F., The' Cleveland coal field,· Blaine County, Mont.: 

U. S. Geol. Survey Bull. 541, pl. 20, 1914. 

s2 Reeves, Frank, The structure of the Bearpaw M~ntalns, Mont. : 

Am. Jour. Sci., 5th ser., vol. 8, fig. 2, p. 299, 1924; Geology and oll 

and gas resources of the faulted area south of the Bearpaw 1\:lotmtains. 

Mont. : U. S. Geol. Survey Bull. 751, pl. 12, 19.24. 
EARLY WISCONSIN GLACIATION 

-dissected by sharp coulees 50 to 200 feet in depth, 

since the early Wisconsin ice disappeared. . In this 

area thicknesses· of 10 to 50 feet of glacial till are 

exposed at many places in the steep sides of the coulees 

,and. in stream banks, and in some of these places the 

full thickness of the drift is not uncovered. 

TERMINAL MORAINE IN HILL AND CHOUTEAU 

COUNTms, MONTANA. 

The Beaver Creek Valley, in the old Fort Assinniboine Military Reservation, has been filled with 

glacial drift southward to a point about 16 miles south 

of Havre in the southernpart ofT. 30 N., R. 16 E., 

and partly reexcavated. Thicknesses of 50 to 60 feet 

or more of buff pebbly clay till are exposed at many 

places along this valley. The ice appears to have 

crowded against the north slopes of the craggy peaks 

of igneous rock east and west of this valley but could 

not overtop them. Reeves found glacial boulders up 

to 3,898 feet above sea level between Little Boxelder 

and Beaver Creeks in sec. 6, T. 30 N., R. 17 E., and 

up to 3,890 feet west of Beaver Creek, in sec. 26, T. 

30 N., R.15 E. 

West of the Bearpaw Mountains the ice advanced 

much farther south along the old valley of the Missouri River and on the plain to the west. Two traverses into the foothills bordering the west side of the 

n10untains were made by 'the writer in 1920, but the 

Hmit of the drift was not mapped. Four miles east 

of Boxelder is Square Butte., a prominent landmark 

rising 900 to 1,000 feet above the nearly flat plain at 

its western base. It is capped with a sill of hard 

gray intrusive crystalline rock whose surface is nearly 

flat. This top, which is about 3,650 feet above sea 

l.evel, is sprinkled with glacial boulders of granite and 

limestone. In several places smooth bare surfaces of 

the rock retain the glacial polish and show glacial 

striae. Those near the south edge of the top. trend 

S. 8° E., and those a little farther east trendS. 4° W. 

The divergence is probably due to deflection of the 

basal ice by the. bold cliffs around the sides of the 

butte. Evidently the ice was thick enough to move 

readily across the top of the butte. Thus, it must 

have been more than 1,000 feet thick. The limit of 

the drift is about a mile east of Square Butte, as the 

hilltops beyond are very rough in that direction. 

lteeve~,83 in 192~, found drift to extend several miles 

farther east up the Boxelder Valley, and south of 

Duck Creek the drift limit lies across the remnant of 

a high gravelly bench. At a point about 10 miles 

northeast of. Sandy Creek, near Gorman Creek, a terminal moraine, marked by sharp bouldery knolls, sags, 

and ponds, was seen by the present writer. This appeared to extend northward up onto a remnant of a 

high bench west of Centennial Mountain. 

'!3 Personal communication. 

South of ·T. 29 N. the drift that extends eastward 

ta the limit mapped by Bowen and Reeves appears to 

represent a somewhat earlier stage of · glaciation 

(Iowan or Illinoian ( ~), pp. 79--80). It is qui.te possible that some of the highest erratics noted above were ' 

deposited by this earlier .and more extensive ice sheet. 

Tracing the moraine from west to east in southwest .. 

ern Chouteau County, Calhoun 84 wrote: 

The character of the moraine changes abruptly after it 

passes over Teton Ridge. There is no ·longer a well-defined 

ridgelike edge, but more often a low, broad rise, usually too 

slight to be noticeable. 

This moraine may be traced,· with few breaks, directly · 

across the country from Teton Ridge to the Bearpaws. It is 

better developed than the [outer] terminal moraine, which, 

while having the essent:al elements of the. kettle morabi~ 

often shows them in a feeble state of development. 'South of 

Tunis the moraine is between 3 and 4 miles wide and is 

covered with laJ,{es and lake basins, some of which extend 50 

feet below the general level. This moraine is again seent 

though not so clearly defined, along the north bank of the 

Missouri, near the mouth 'of the Teton. Between the head· 

waters of Big and Little Sandy Creeks there is another excellent example of morainic topography, continuing to the foot 

of the west slope of the Bearpaws. 

There are low morainal swells near the railway at 

and south of Verona station, also south of the automobile road that follows the old rai~way grade for some 

distance southwestward between Verona and Lorna. 

The ice front probably lay on the bench between the 

Teton and Missouri Rivers as far west as Tunis and 

Carter, and from the vicinity of Floweree a belt of low 

swells extends westward to the outer limit of the 

glacial drift, near the northeast corner of sec; 36, 

T. 23 N., R. 3 E. At this place, 15 miles north of 

Great Falls, the moraine front is fairly definite where 

the surface rises northward with low undulations 

sprinkled with granitic boulders. The relations of the 

deposits exposed in the railway cut west of Fort Benton are described on page 66. 

RELATIONS OF THE GREAT FALLS LOlJE 

Near the Teton River, 6 or 8 miles northeast of 

Choteau, Teton County, the margin of the· Keewatin 

drift curves and extends thence northward in a· sinuous course to the international boundary near the 

northeast corner of the Blackfeet Indian Reserva.:. 

tion, in Glacier County. This line, together with that 

described above, delimits the area of the most sout~­

westerly lobe of the great Keewatin ice sheet. ·(See 

pis. 1 and 29.) The breadth of this lobe, measured on 

a line drawn in a northwesterly dire.ction from the 

Bearpa w Mountains near Square Butte to tbe interIlational boundary at the point indicated; is approximately 125 miles, and the length of the lobe, measured 

in a south westerly direction from this line to the mo- ' . 

84. Calhoun, F. H. H., op. cit., p. 27 ; see also pl. 5. 
102 ;rHYSIOGRAPHY AN:O GLACIAL GEOLOGY OF EASTERN MONTANA 

raine on the Teton River east of Farmington, Teton 

.County, is about 66 miles. The lobe that extended 

southward to the location of the Great Northern Railway southeast of Gr.~at Falls at the Illinoian or 

Iowan ( W) stage of glaciation probably had about the 

same width but was about 1~ miles longer. The area 

of this great lobe at the Wisconsin stage was about 

5,600 square miles. This is between three and four 

times the area of the great Malaspina Glacier of 

Alaska,85 which covers about 1,500 square miles. This 

lobe in Montana was nearly as large as the combined 

area of Connecticut and Rhode Island. 

The data here given concerning the position and 

character of the marginal glacial deposits along the 

west side of this great lobate area from the Teton 

River northward to the Canadian boundary" are taken 

almost entirely from the field rna ps and notes of Eugene Stebinger, made in connection with detailed 

stratigraphic work in 1911 to 1916. The sinuosities 

of the glacial margin in Teton and Pondera Counties 

were due in large measure to the alternation of salients 

of the remnants of the high gravel-covered No. 1 and 

No. 2 benches, described above (p. 46), with broad 

valley plains and embayments where the surface of the 

land had been reduced to lower levels by pre-Wisconsin erosion. North of the Great Northern Railway 

and east of Cut Bank the rim of Virgelle sandstone 

rises to a height of 500 to 600 feet above the plain to 

the east. This bold eastward-facing escarpment and 

the high upland to the west controlled the deployment 

of the ice in adjacent parts of Toole and Glacier Counties. The height of these topographic features was 

sufficient .to stop the advance of the ice front through 

an extent of 75 IQ.iles from north to south. The significance of this topographic control of the ice movement 

warrants a somewhat· detailed presentation. 

TERMINAL MORAINE IN TETON AND PONDERA 

COUNTIES, MONTANA 

feet. Some of these may be berg-transported, as, according to Calhoun, this was about the upper limit of 

water ponded by the ice in the upper Teton Valley. 

In Pondera Basin, in Ts. 27 and 28 N ., Rs. 4 and 

5 W., a lobe of the ice e:x;tended on the low ground to. 

a point 12 miles. west of the railway near Cpnrad. 

On the gravel-capped ridge (No. 1 bench) to the 

south, however' the glacier was able to ~dvance only 

to a point 8 miles farther east (about 3,800 feet above 

sea level) , and here water ponded along the glacial 

margin cut a trench 60 to 80 feet deep through the 

crest of the ridge. As the ice front to the south receded this channel was extended southea.stward to 

Muddy Creek as Kropp's Coulee. A sharp reentrant 

in the glacial margin was also caused by the wedgelike ridge north of the Pondera Basin, which is capped 

with No. 1 gravel. The head of this reentrant w~s 

about 4 miles west of Conrad. Calhoun founcl in the 

Pondera Basin a "well-defined ·moraine of pronounced topography," with lakes as numerous as in 

the moraine near the international boundary. 

Calhoun 86 reasoned from the height of the ridges 

north and south of the Pondera Basin, which were 

not overridden, that the westward slope of the surface 

of the ice in the basin could not have been more than 

30 feet to the mile. 

South of Williams station another reentrant in the 

glacial margin was caused by the butte in sec. 32, T. 

29 N., R. 4 W., on which is the triangulation station 

at 4,165 feet above sea level. Drift pebbles a~ reported to have been found on the top of this butte. 

A channel formed by marginal drainage near by has 

an altitude of about 4,000 feet. North of this locality 

the drift margin swings 15 miles or more to the west, 

in the broad b.asin traversed by the lower courses of 

Birch Creek and Two Medicine Creek. (See pl. 1.) 

On the former stream the ice advanced westward onto· 

the b_road· gravel-covered Birch Creek flat (No. 3 

bench), which· is about 30 feet above the flood plain. 

An observer looking eastward from the flat plain Here there is not a well-defined terminal moraine. 

(No.3 bench~) on which stands the village of Farm- Water must have been ponded in all these valleys up 

ington can see the western edge of the drift sheet to the height of the lowest· available outlets, and in 

extending northward as a broad r~dge 100 feet or many places laminated lacustrine clay is exposed in 

more· in height at the east edge of the flat between the the creek banks overlying the mountain gravel west of 

Teton River and Muddy Creek, about 5 miles east of the glacial limit. Berg-transported boulders of granthe railway. For several miles along the road east to ite were noted by the writer along the Park to Park 

Collins the bouldery surface is marked by mild sags Highw~y between 3,900 and 4,000 feet above~ level 

and swells. Stebinger's notes record exposures of 50 . near Birch Creek, north of Dupuyer. 

to 200 feet of glacial till along the Teton River west Thus. far ~orth there is no contigui~y bet~een the 

of Collins and of 20 to 100 feet of till on Muddy Keewatin dnft and that of the mountam glaciers. In 

·creek. On the north slope of Teton Ridge, which I the Birch Cree~ ~alley, however, t.he. mount9:in ice 

is about 500 feet high ( 4,200 to 4,

300 feet above sea and the Keewat~n Ice approached Within 1~ miles of 

level) glaci~l boulders were ;noted. up to about 3,900 . eacht otfheVr, li~nd In 1T.t3h1 ~.d, R. 7bWt., 1\~ mmili~es no~dh. · wes o a er, on y · e r1 ge a ou 72 es WI e, 81 Russell, I. c., Malaspina Glacier: Jour. Geology, Vol: 1, p. 224, which is capped in part with No. l bench gravel, sep1893. The Malaspina glacier measures 20 to 25 miles from front to 

back and 70 miles from east to west along the coast. 88 Calhoun, F. H. H., op. cit., p. 25. 
lU.RL Y WISOONSIN GLAOIATION 108 

ti,rated the Keewatin ice from the Two Medicine 

Glacier~ 

TERMINAL MOBAINE IN GLA.C:IER. AN» TOOLE COUN· 

, TIES, MONTANA, AND SOU'THERN ALBERTA, CANADA. 

tent ponds. T. 36 N., R. 4 ~ W.1 includes some of- the . 

roughest parts -of the ·moraine belt. 

The outer front of": the moraine in this part: ia not 

a striking feature of the la.ndsc&pa as ·ieen in a genera~· 

view. It is clearly traceable, -however,, and in many 

N·orth of Two Medicine Creek the margin of the places appears as a distinct bouldery ridge- 5 to .. 50 feet 

Keewatin drift extends northeastward past the ponds in height running in a sinuous course up and down 

in sec. 21, T. 32 N., R. 6 W.; to the gorge of Cut Bank over the hills and -across the .hollows and,-showing .in 

'Creek (near SE. corner ''sec. 6, T. 32 N., R. 5 W.) detail the relations of theice margin to the preexistabout 7 miles south of Ctit Bank village. (See pl. 37.) iug erosional topography; No glacial .outwash gravel 

There is no definite terminal moraine between the · was noted at any point along. the. outer ·margi.J:l of. the 

two streams e~t of Cut Bank Creek. The ice was n10raine north of the railway .unles$ the fine--stratified 

stopped by hilJS. rising 4,000 to 4,100 feet above sea gravel exposed below the flat west of Hay Lake is of 

level, but it advanced on the lower ground to the that origin. The gravel-capped hill· crossed by; the 

northeast and southwest so· that a reentrant 4 miles margin of the drift in the SW. %, sec. 18, T. 36 N., R .. 

deep was f~rmed. The margin is marked by a· small· 5 W., appears to be a remnant of one of the high 

but definite sinuous ridge in most places on these hills. benches, as the gravel consists wholly of pePbles from 

Within a few miles this margin varies_ 400 feet in the Rocky Mountains. The inner margin of ·the moaltitude-that is, between 3,700 and 4,100 feet. (See raine is very indefinite, and the bounda.ry·1s drawn 

Cut Bank topographic map.) About 12 feet of till is . · more· or less arbitrarily to include the roughened moexposed in a Great Northern Railway cut weSt of rainal topography. The area. to the north is mostly 

Baltic, and greater thicknesses are seen in the sides of well covered with till. · 

coulees. North of the Great Northern Railway the About 25 miles north of Cut Bank and less than half 

Virgelle sandstone forms an irregularly dissected, east- -a mile south of the international boundary,.· in sec. 2, 

ward-facing escarpment, whi~h extends in a sinuous T. 37 N., R. 6 W., the outer margin of the drift.swmgs 

course northward nearly to the international bound- to the west again and climbs to the top of a gravelary. This reaches a maximum altitude of 4,300 feet capped ridge, a remnant of No. 1 bench. (See pl. 

about 20 miles northeast of Cut Bank, in sec. 5, T. 35 · 38 .A.) The crest of this ridge is one of -the highN., R. 3 W., and it varies in height from 600 to nearly est points covered by the ice west of the Adirondack 

1,000 feet above the low ground to the east that is trav- Mountains.- Here it took an altitude which is now 

ersed by the Sweet Grass branch of the Great North- about 4,400 feet to stop the advance of the ice. At the 

ern Railway. In this part rough, knolled, and pitted north flanks of the Bearpaw and Little Rocky MoQ.D.-

morainal topography is found throughout much of a tains the limit reached is about· ·3,500 feet. The ice 

belt ranging from 2 to 8 miles in width, lying partly in the valley of the South Fork· of the Milk River 

above and partly below the escarpment. · crowded against the north slope of the ridge and laid 

The distribution of the moraine shows that between its mor·aine along the narrow crest but did not cross 

the high point mentioned above and the main line of the divide. It advanced up the valley to, the ·sharp 

the Great Northern Railway the ice crowded westward bend 4 miles northeast of Landslide Butte. Here the 

1 to 4 miles on the upland above the crest of the es- · drift margin curves to the northwest again and in 

carpment. Ravines cutting the escarpment expose 20 7 miles more crosses the boundary line into Alberta at 

to 40 feet of till, and in places the former irregulari- the northeast corner of sec. 6, T. 37 N., R. 8 W. 

ties appear wholly "drowned" in drift. North of A small lake was held in the valley of the South 

the. highest point above noted the escarpment lowers Fork of the Milk River, and this discharged southeasttoward the Milk River, ·and the moraine turns sharply ward through Antelope Draw to glacial Lake Cut 

arnd extends in a broad curve, first westward in T. 36 Bank. The bottom of this outlet is now 4,000 . feet 

N., Rs. 3 to 5 W., then northward in Ts. 36 and 47 N., above sea-level, and many boulders of pre-Cambri~ 

Rs. 5 and 6 W., until the outer margin is less than half granite from Canada dropped from bergs floating on 

a mile south of the Canadian boundary. This shows this lfl.ke are found scattered on the slopes northeast;, 

that a minor lobe of the ice nearly 20 miles in width north, and northwest of. Landslide Butte. Most of 

advanced southward onto the upland in northwestern these are below the 4,000-foot level, but a fe'W, as on 

Toole County and northeastern Glacier County and Flag Butte, lie at 4,000 .to 4,200 feet. . Possibly the. outovertopped hills 4,100 to nearly 4,300 feet above sea let was at first 100 to 200 feet higher than now and was 

level. In this part the moraine ranges from 2 to 9 cut deeper by the outflow~ng water. Stebinger's notes 

miles in width and is marked by many knobs and hills , suggest the possibility that either the Wisconsin ice 

/ intt:rspe~d ~th numerous small lakes and inte~t- or an earlier she~t advanced a mile beyo11d the well .. 
R .l4- E . 

Base from U.S. Geological Survey maps of 

Thibedeau Lake and Zurich quadrangles 

Surveyed in 1902 and 1909 

PROFESSIONAL PAPER 174 PLATE 34 

R. l8 E . 20' R . l9 E. 109' 10' R.20 E. 

TOPOGRAPHIC MAP OF PARTS OF HILL AND BLAINE COUNTIES, MONT., SHOWINGLOCATION OF THE PREGLACIAL MISSOURI RIVER VALLEY 

Scale 1.2 s~oo 

Contour i·n.terval ZO teet . 

..I)a:t;u;rn_ is rn.e.an, sea, Uvd. 
104 PHYSIOGRAPHY AND GLACIAL GEOLOc;JY OF EASTERN MONTANA. 

marked outer limit of the moraine, for a sharp ddge 

in sec. 30, T. 37 N., R. 7 W., was found to be thickly 

covered with drift. From 50 to 60 feet of till is 

exposed where the river cuts through the moraine. 

In 1920 the writer crossed No. 2 bench south of the 

North Fork of Milk River and west of Shanks Lake 

in adjacent parts ofT. 1 N., Rs. 21 and 22 W., Alberta, 

and found no Keewatin drift on the bench gravel 

whose surface is about 4,300 to 4,350 feet above sea 

level near the international boundary. North of the 

river· the road to . Magrath runs for .several miles 

through a belt of sags and swells with numerous 

ponds. Evidently the terminal moraine passes westward through T. 2 N., R. 22 W. About 12 miles to 

the southwest it recrosses the boundary from sec. 6, 

T. 1 N., R. 23 W., Alberta, into sec. 5, T. 37 N., R. 11 

W., Montana, on the Hudson Bay divide northwest of 

the North Fork of the Milk River. (See international 

boundary map, sheet 21; also Browning topographic 

map.) At the head of Emigrant Gap Stebinger 

found " very heavy moraine " with " kamelike masses " 

80 to 100 feet high and rising to 4,500 feet or more. 

This gap and another to the east permitted How of 

the glacial waters to Milk River. For 4 miles southwest of Emigrant Gap the front of the Keewatin ice 

lay along the north slope of the ridge, and drift was 

found up to 4,685 feet.87 Calhoun describes that part 

of the moraine north of the international boundary as 

follows: 

Northeast of this point [Emigrant Gap] the ice reached the 

fiat top of Milk River Ridge and spread over it to the south, 

forming a wide moraine characterized · by lakes, undrained 

depressions, and hummocky topography of strong relief, the 

difference between the tops of the knolls and the ~ttom of the 

kettles in many cases being 120 feet. At the ,point where the 

moraine swings to the top of the ridge it has an altitude of 

about 4, 720 feet, and at a point 6 miles to the west, of about 

4,800 feet; this gives a slope of 70 feet per mile to the edge 

of the ice of the northeastern ice sheet. 

Although the ice reached the summit of Milk River Ridge, 

it did not move for any considerable distance across its 

plateaulike top. The ridge separated the ice into two parts, 

one lobe entering St. Mary Valley while the main sheet was 

forced farther east, cimslng a great reentrant to be formed. 

East of the road leading from th~ gap at Hall's 

ranch (now Galbraith's) north to the United States 

customhouse (formerly Galbraith's ranch) the ice 

front extended northwestward across the valley. The 

exact western limit of the Keewatin ice, however, is 

not very plainly marked, for here both the Keewatin 

ice sheet and the lobe of the St. Mary Glacier heading 

in the mountains to the west deposited morainal drift. 

Some of the boulders of pre-Cambrian granite from 

the northeast scattered over drift of the mountain ice 

may have been dropped from bergs floating in a lake 

held between the two glaciers after the mountain ice 

had begun to retreat. Such a lake would find an outlet 

87 Calhoun, F. H. H., op. cit., p. 24. 

to the Milk River first through the-gap at Galbraith~l!l 

ranch (formerly Hall's) a_nd later through Emigrant 

Gap, which is n_ow tra verseq by the St. Mary C11.nal. 

In 1914 Clifton S. Corbett, assisting Mr. S~binger, 

found crystalline boulders of Keewatin drift on a 

knob in or near the NW.% sec. 24;:T. 37 N.; R.l3 W., 

about 3 miles aouthwest of the United States custom·' 

house and 3 miles east of Spider Lake. 

About 3 miles northwest of the United States·customhouse the margin of the Keewatin drift curves 

about the nort~ end of the ridge about half a mile 

south of ·the boundary, at -4,600 feet above- sea level, 

and runs southwestward down the sl-ope to' the St. 

Mary River. In this valley the Keewatin ice extended 

1% miles south of the boundary to the middle of sec. 8, 

T. 37 N., R. 13 W. For about a mile on tl,.e east side 

of the river and for nearly 2· miles on the west side 

there are remnants of an outwash terrace sloping 

southward up the valley from the margin. ,This ter-

-race is capped with gravel containing pebbles of preCambrian granite from the northeast, and. in places 

the gravel overlies till deposited by the St. Mary Glacier and containing pebbles and boulders of mountain . 

rocks only. The relations seem to indicate that after 

the front of the St. Mary Glacier had . receded to 

an unknown distance gravel was washed from the ice 

dam formed by the front ·of the Keewatin ice sheet 

into a lake held in the valley. The outlet of the lake 

was eastward through the Spider Lake gap, now 

traversed by the irrigation canal. Similar relations 

are indicated by cut banks farther north whieh expose 

Keewatin till overlying till of the mountain ice. On~ 

of these, examined by the writer in 1912 and again in 

1920, showed the following section: · 

Section of drift on St. Mary River at international 1JoutuJ.arv 

Feet, 

Drift of Keewatin ice sheet: Buff pebbly clay. Most of the 

pebbles are quartzite and argillite from the Rocky Mountains; intermingled with these are many pebbles of pre· 

Cambrian crystalline rocks from the northeast_________ 00 

Drift of St. Mary Glacier: Very stony tUl containiJ:lg pebbles of mountain rocks only, including limestone and 

diorite, but no pebbles of pre-Cambrian crystalline rocks 

from the northeast----------------------------------- ~ 

Cretaceous shale, upturned and eroded. 

When examined in 1912 the sha~e was not exposed,. 

and the ·lower till was underlain by 12 tO. .lS feet of 

waterworn quartzite gravel from the .mo~tains. Noglacial striations were seen on any .of the stones ex~­

amined, some of which were as JiO.Uch as 1lh feet in 

diameter. Between 1912 and 1920 the gravel ·was 

w·ashed away and the shale was exposed. Neither in 

1912 nor in 1920 was any trace seen ofan-intercalated 

soil or weathered zone such as would indicate 'QXpOSUJ!e 

of the mountain drift for any considerable time before 

it was covered by the Keewatin· till. The possibility 
U. S. GEOLOGICAL SURVEY PROFESSIONAL P APER 174 PLATE 36 

\ 

\ \ 

EXPLANATION 

kTI 

~ 

Remnants of high gravelly piedmont terrace of Miocene or Pliocene age. Probably equivalent of Flaxville gravel. 

~ Remnants of lower gravelly piedmont terraces of early b&..:::::J Pleistocene age. 

~ 

~ 

Margin of Keewatin ice sheet and marginal glacial water of Wisconsin stage of glaciation. 

Shading by C. A. W eckerly, based on topographic map. 

' .. --..... _.-., .. 

1-~ 

I 

I 

I 

I 

I 

I 

I 

--;'-

I 

I 

.\ / -- 1 

' ' ., -+-

- ~-· \t ~-

\ ' - J' . ' I 

I ' I ' 

'J.. ' 

.....-

\ 

0 SMILES 

' ' ' 

' 

,/',\ 

' ' ' ' ' ' ' I 

I 

\ 

\ 

MAP OF LITTLE ROCKY MOUNTAINS, MONT., AND THEIR ENVIRONS SHOWING RELATIONS OF THE KEEWATIN 

ICE SHEET IN PLEISTOCENE TIME TO THE MOUNTAINS, TO THE REMNANTS OF THE HIGH 

GRAVELLY BENCHES AND TERRACES, AND TO THE STREAMS 

/ \ 

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I 

Geology by Wm. C. Alden 

• 
U. S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 174 PLATE 36 

A . TWIN BUTTES, FORT BELKNAP INDIAN RESI•:HVATION, MONT. , 9 MILES NORTH OF HAYS 

On the top, 850 feet above the pla in, are drift pebbles showing that the buttes were overridden by the glacier. 

B. EAGLE BUTTE, BEAHPA W MOUNTAINS, MONT. 

View looking west along lop of terminal moraine of the early \Visconsin stage of the Keewatin ice sheet. The icc front reached the foot of the north (right) slope of the butte. 
U. S. GEOLOGICAL SURVEY 

Shadmg by H. F. Clark, based on topographic maps. 

Dissected drdtless plains and lowest terraces 

unshaded. 

•r / 

5 

I I 

0 15 MILES 

PROFESSIONAL PAPER 174 PLATE 37 

· ................. . ... ....___ 

... -. -..... 

.. '\ I 

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,. ' 

. ~ :' 

\ . 

~0 

"'"" 

., .. ··L .. . ake 

;, 

\1 •\. 

EXPLANATION 

Areas in which glaciers exist at present. 

Rocky Mountain ~laciers and Keewatin ice sheet of the Wisconsi n stage of glaciatiOn (restored ). 

Mountain crests and rock surfaces probably nQt covered by the glaciers. 

Drift deposits of early Pleistocene mountain glaciers (probably of Nebraskan or Kansan stage) on remnants of highest gravelly piedmont terraces. 

Remnants of lower gravelly piedmont terrac e~ of early Pleistocene age. 

Remnants of highest gravelly piedmont terraces of Miocene or Pliocene age, probably equivalent of Flaxville gravel. 

I 

\ 

By Wm. C. Alden, Eugene Stebinger. and aSSIStants 

EASTERN PORTION OF GLACIER NATIONAL PARI{ AND ITS ENVIRONS 

AT THE " ' ISCONSIN STAGE OF GLACIATION 
U. S. GEOLOGICAL SURVEY PROFESSIONAL PAPER li4 PLATE 38 

A. TERMINAL MORAINE ABOUT 25 MILES NORTH OF CUT BANK, MONT., IN SEC. 11, T. 37 

R. 7 w. 

View looking east along t he crest of the mora ine where it lies on a gravell y bench 4,300 to 4,400 feet a hove sea level at the crest of the bluff south of the M ilk River. Photograph by Eugene Stehinger. 

B. RECESSIONAL MORAIN !,; N~;AR MARTIN LAKE, 25 MILES NOil.TH 0 1'' MALTA, MONT. 

View northwest along crest of moraine. The cabins are on Lhe vlain j usl south (oulsid e) of the moraine. 

MORAiNES OF THE KEEWATIN ICE SHEET, EARLY WISCONSIN STAGE 
U. S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 174 PLATE 39 

A. PERCHED BOULDER ON SNAKE BUTTE, 12 MILES SOUTH OF HARLEM, MONT. 

B. GLACIAL STRIAE ON LEDGE OF JUD ITH RIVER SANDSTONE ON SIGNAL BUTTE, ABOUT 30 MILES 

NORTH OF HAVRE, MONT. 

Photograph by Eugene Stebinger. 
U. S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 174 PLATE 40 

A. GLACIOLACUSTRINE DEPOSITS OVERLYING GLACIAL TILL 

Tov of Lill is at line of stones below t.he man's feet. Photograph by A. J. Collier. 

B. TILL OF KEEWATIN ICE SHEET OVERLYING JUDITH RIVER FORMATION 

VfEWS ON PEOPLES CREEK IN FORT BELKNAP INDIAN RESERVATION, SEC. 

20, T. 29 N., R. 25 E. , 15 MILES SOUTHWEST OF DODSON, MONT. 
U. S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 174 P LATE 41 

A . BOULDER OF RED GRAN ITE ON UPLAND 20 MILES NORTH OF MALTA, MONT. 

SPORTED BLOCKS OF PALEOZOIC LIMESTONE ON UPLAND NORTH 

NELSON RESE HVOIH, 18 MILES ORTHEAST OF MALTA, MONT. 

GLACIAL BOULDERS 
EARLY WISCONSIN GLACIATION 

that some o:f the lower till, that of the· mountain ice, 

is of pre-Wisconsin age is discussed above ( p. 69) . 

Cuts exposing till of the mountain glacier were observed as far down the valley as Sloan's ranch, about 

2 miles north of the international boundary, in sec. 9, 

T.l N., R. 25 W., Alberta. Some cuts expose only one 

of the tills, without the other, though .boulders of preCambrian gran!te from the northeast are generally 

sct:tttered over the adjacent land. 

Near Sloan's ranch the edge of an upturned bed of 

oyster shells in the . Horsethief sandstone showed glacial polish in 1912 and striations trending S. 30°-50° 

W., toward Chief Mountain. At another point above 

Kimball, where the St. Mary River cuts through the 

folded rocks, striae were observed trending S. 55 o -60° 

W. These are probably the product of the Keewatin· 

ice sheet ~oving southwestward and are the only glacial striae that have been observed on the plains of 

southern Alberta and Saskatchewan by the writer or, 

so far as known· to him, by anyone else. On Signal 

Butte, north of Havre, Mont., in sec. 28, T. 37 N., 

R. 15 W. (pl. 39 B), a striated ledge of sandstone was 

seen by Stebinger, but unfortunately this ledge had 

been tilted somewhat out of place, so that the exact 

origi.nal bearings of the southward-trending striae 

could not be determined. 

At the sharp bend in the St. Mary River just below 

the mouth of Boundary Creek, in the NW. % sec. 4, · 

· T. 37 N., R. 13 W., there was exposed in 1912 about 60 

feet of dull buff to gray till, containing a small percentage of pre~Cambrian crystalline pebbles from the 

northeast, overlying the eroded surface of friable gray 

sandstone. The presence of scattered granite boulders on the hills between the river and Pike Lake is 

probably due to berg transportation. The limit of the 

Keewatin drift west of the St. Mary River crosses 

the Canadian line in the vicinity of Boundary Creek 

alid extends thence northwestward to the Belly River 

Valley. It is probable that Boundary Creek owes the 

peculiar direction of its course in T. 1 N., R. 26 W., 

Alberta, and 1ts return southward across the boundary· 

to its junction with the St. Mary River to the position 

of the Keewatin ice front. The moraine was not 

mapped north of the boundary by the writer, though 

it was ·examined in 1912 where it is crossed by the 

Belly River, about 9 miles north of the line. 

There are on the Belly River deposits of till south 

of the terminal moraine, which include pebbles of 

pre-Cambrian crystalline· rock from the northeast and 

which suggest the. possible presence of pre-Wisconsin 

drift in the valley bottoms, as on the St. Mary River. 

At the terminal moraine, which is well marked by 

botildery knolls, sags, and ponds, the following·.~-

tion was exposed : . 

8eotian of drift on Belly .River 

Drift of Keewatin ice sheet: Loose dull-buff clayey tin 

containing, besides pebbles of mountain rocks, preCambrian crystalline pebbles from the northeast____ 20 

Drift of Belly River Glacier: Very stony till in wblch 

pebbles and boulders are wholly of mountain rocks __ 2Q-80 

Tertia:ry ( ?) gray sandstone------------------.-------- 80-60 

The face of the exposure was somewhat obscured, 

but nothing was seen which indicated long exposure 

of the mountain drift before it was covered by drift 

of the Keewatin ice. ss 

RELATIONS OF TWO MEDICINE GLACmR AND TBB 

KEEWATIN ICE SHEET 

The valleys of Two Medicine and· Cut Bank Creeks 

had been cut down 100 to 200 feet below the lower 

level of the second bench represented by Carlow Flat, 

before the Two Medicine Glacier, heading in the mountains, and the Keewatin ice sheet approached each 

other at the early Wisconsin stage of glaciation. 

Only the narrow inner gorges and tributary coulees 

have been cut since the disappearance of these glaciers~ 

Not until the line of the Great Northern Railway is 

reached southeast of Cut Bank by one going northwara is the Keewatin drift found to be bordered by a. 

well-marked terminal moraine. Stebinger has, however, traced the approximate limit of the Keewatin 

drift in a sinuous line over the hills and across the 

valleys with considerable care. (See pl. 1.) He 

found 15 to 70 feet. of Keewatin pebbly clay till overlying 5 to 10 feet of mountain stream gravel exposed 

above the Cretaceous rocks in the sides of the gorges 

on lower Birch Creek and Two Medicine Creek. 

Fr·om this section it appears that Two Medicine 

Creek had cut down its channel to ~ level less than 50 

feet above that of its present bed before the early Wisconsin stage of glaciation-that is, about 600 feet below 

the nearest remnants of the high No. 1 gravel bench. 

This channel was then floored with 15 feet of stream 

gravel. When the Keewatin ice blocked the valley 

and formed a lake, laminated silts were deposited 

therein, and as the ice continued its .advance it overrode the lacustrine beds for some distance and left 

thereon a deposit of glacial till containing mari.y 

pebbles and boulders of pre-Cambrian granite from 

the northeast. After the ice disappeared the stream 

cut down again about 100 feet. 

ss Observations by the writer and Eugene Steblnger in 1912 on the 

drift northward to the Old Man River are described in Geol. ·Soc. 

America Bull., vol. 24, pp. 545-566, 1913. 
106 PHYSIOGRAPHY AND GLACIAL GEOLOGY OF EASTERN' MONTANA 

Stebinger states in his notes of June 19, 1912, that 

the relations of the several .deposits exp9sed in the 

east bluff on Two Medicine Creek a~e very clear, as 

seen on looking east from the southwest corner of 

sec. 6, T. 31 N., R. 6 W. (See fig.16.) The section, 

which is about 1 mile long, is cut across a pre-Wisconsin channel of Two Medicine Creek by a bend in the 

present gorge of the stream. · 

·The thicknesses given in Figure 16 are from notes 

on part of ·this section or another near by which was 

observed ·a few days previously. The surface of the 

gravel (B) is said to be the same as that of the fourth 

(from the bottom) of a set of gravel terraces developed upstream from this locality within the area 

covered by the Two Medicine Glacier. This terrace 

had been formed and the stream was cutting down to 

the next terrace level when interrupted by the advance 

of the mountain ice. In the sections in this vicinity 

described by him, Calhoun 89 interpreted the _gravel 

(B) as outwash from the mountain glacier of the Wisconsin stage and, inasmuch as the gravel is overlapped 

by Keewatin drift, he concluded that the Keewatin ice 

th~ glacial lake clay overlying drift of the mountain 

ice in some sections and underlyipg drift of the Keewatin ice in others. Stebinger states in his notes of 

June 19,1912, that he 1ound ~n sec.l, T. 31 N., R. 7W., 

about a mile .west of the section described above and 

500 feet inside the outer edge of the terminal moraine 

of the Two Medicine Glacie:r, a small mound of .unmistakable continental drift and that " this must mark 

the west limit of advance of the Keewatin ice-that is, 

the ice sheets .actually overlapped e~h o~her's area." 

He finally concludes, however, that the drift of this 

mound mayhave been dropped from floating ice, like 

the boulders of pre-Canibtian .crystalline rocks found 

farther up the. valley. One of these boulders, 4 feet 

in diameter, he found about 2% miles northeast of 

.Piegan, in sec. 9, T. 31 N., R .. 8 W~, resting on the slope 

beside Badger Creek a.t 3,895 feet above sea . level. 

This place ie 11 miles up the valley, outside the limit 

of the Keewatin drift . and 10 miles inside the limit 

reached by the mountain ice. The outlet .of the lake 

was probably southward to the Birch Creek Valley 

close to the front of the Keewatin ice sheet .. 

Stebinger suggests t~at the Two Medicine 

drift was deposited first, although the time 

between the two· invasions may have been 

very short. The till of both the Keewatin 

and Two Medicine Glaciers, which is exposed in these sections, is regarded as representing the early Wisconsin stage. There 

seems to be no strong reason for thinking 

that either one is older than this. It is possible, however, that some of this drift was 

deposited by the Two Medicine Glacier at 

the Illinoian or Iowan ( ~) stage. Calhoun . 

Fioua:m 16.-Geologic section on Two Medicine Creek 12 miles southwest of Cut 

Bank, Mont. A. Cretaceous clay and sandstone of Two Medicine formation, 45 

feet thick; B, nonglacial stream gravel from Rocky Mountains, with its surface 

60 feet above the present stream, 15 feet thick; C, glaciolacustrine beds-laminated clay, 22 feet thick; D, dark pebbly clay till of Keewatin glacier, 50 feet 

thick ; E, preglacial stream channel 

found fine, loesslike, wind-blown material 

present in one section underlying the lacustrine clay 

where that is overlain by ;Keewatin till; . in another 

place an eolian deposit overJies lacustrine clay . with 

reached its maximum extent later than the mountain 

glaciers and after their fronts had been melted back 

somewhat. He states that a few of the pebbles in the 

gravel are striated but that most of them have been 

subjected to so much water action that all trace of 

glaciation has been removed. From the relation .of 

the mountain drift to the gravel terraces on Two 

Medicine Creek Stebinger concluded that this gravel 

(B) was older, and as he found no striated pebbles in 

it, he thought it nonglacial. Whether or not the 

gravel is outwash from the mountain ice of the early . 

Wisconsin stage, the same general conclusion as to 

the relations of the two ice sheets is supported by 

other observations of both men, for Calhoun 90 found 

• Calhoun, F. H. H., op. cit., pp. 46-48. 

• Calhoun used. the name " Blackfoot Glacier " for the ice which is 

designated in this paper "Two Medicine Glacier." The change of 

name was proposed by the writer in Geol. Soc. America Bull., vol. 23, 

p. 688, 1912, because of the fact that the largest of the ~xisting 

glaciers in Glacier National Park, but 10 miles from the head of Two 

Medicine Valley at the nearest point, bears the name "Blackfeet." 

The name " Two Medicine Glacier " seems to the writer better for the 

extinct glacier, which headed. principally in valleys tributary to the 

Two Medicine River. 

·no till above and with mountain gravel below; in .a 

third place an eolian deposit overlies lacustrine .clay 

that is underhtin by till of the Two Medicine Glacier. 

LACUSTRINE DEPOSITS AND BOULDER 

TRANSPORTATION 

Inasmuch as the drainage from the north side of the 

Little Rocky Mountains and from the Fort Belknap 

Indian Reservation goes mostly northeastward to the 

Milk River by way of Peoples Creek and its tributaries, there was much water ponded along the ice 

fronts in this area, both· during the stages of advance 

and during those of retreat and in connection with 

both the earlier and the later ice invasions. The 

lacustrine deposits observed here, however, appear to 

belong, at least mostly, to the early Wisconsin stage 

of glaciation. . 

When the ice front lay along the northeast flank of 

t.he Judith River sandstone ridge between Warm 
EARLY WISOONSIN GLACIATION 107 

:::3pring and Little Warm Spring Creeks, in T. 26 N., 

R. 26 E., these streams were blocked, and the ponded 

water escaped southward through the sag in which 

is the reservoir on the Malta road. (See pl. 35.) 

Ponded water in the Lodgepole Creek Valley probably 

escaped westward toward Hays and thence t~ Section 

Creek (p. 100). About a mile south of the point where 

the Harlem-Lodgepole road crosses Lodgepole Creek 

the writer observed, in 1921, an exposure of 15 feet of 

dull-gray glacial till overlying lacustrine clay (fig. 

17), the strata of which were disturbed and upturned 

as by the push of the glacier advancing from north 

to south over the bottom of the lake. Collier found 

similar relations in an exposure a few miles to the 

west on Jim Brown Creek. Numerous other exposures were ~n by Collier which showed stratified 

lacustrine clay overlying glacial · till. As the ice 

front melted back northward down the slope the 

marginal lakes: either enlarged or shifted down the 

slope in the valleys and on top of the till. At one of 

the exposures on Peoples Creek in the NE. % sec. 20, 

T. 29. N., R. 25 E., there is about 10 feet of stratified 

clay overlying the glacial till. In the lower part of 

the clay (near the feet of the man shown in pl. 40 A) 

were found shells identified by W. H.· Dall 91 as "a 

species of Lyrnnaea common to the northern portion 

of North America and named L. 'IJahli by March from 

Greenland specimens, but is common all over the 

northern regions from Alaska to the St. Lawrence 

drain~ge." In the upper part of this section (pl. 40 A., 

near the man's hand) were found fragments of a lower 

jaw with teeth and other bones, which were identified by C. W. Gilmore .as from a recent bison. From 

these fossils it would seem that when the lower part 

of the stratified clay was deposited snails had come 

into the basin of Peoples Creek and that by the time 

the upper part of the clay was being laid down ~isons 

were feeding along the streams. It is possible that 

the upper part of the clay ·here ·and in some of the 

other places is really alluvial rather than fluviatile, 

that the.lakes had been drained, and that the streams 

were silting up hollows but had not yet cut their 

present trenchlike valleys. 

Till overlying lacustrine or stream deposits was observed by V. H. Barnett on Snake Creek 9 to 10 miles 

west of the Fort Belknap Indian Agency, in the 

NW.% sec. 25, T. 32 N., R. 21 E. The following sec- . 

tion is taken from Barnett's riotes, July 20, 1908: 

Bec~ion of drift on OretlWeOU8 aandatcme, Snake Oreek, 'W68t ot 

Harlem 

Feet 

Glacial till ; hard yellowish boulder clay with some 

lenses of stratified sand and graveL_________________ 15 

Glacial tlll ; hard dark-colored boulder clay with many 

small pebbles and few large ones____________________ ? 

Stratified sand, clean, ftne, and dark-colored----------- . 5 

• Letter of Nov. 7. 1921. 

Feet Silt, stratified ___________________ .:._.;. ______________ ~_!.:. 2~ 

Gravel, clean; some pebbles 8 inches in diam~ter_______ · ·a ~taceous sandstone---------------~----~---~-------- 15 

Another feature referable to water ponded or flowing al~ng the ice front. is a line of great boulders. of 

rock such as forms the uppe,r cliffs and top of Snake 

Butte, which . extends southeastward from. that butte 

across T. 30 N., R. 23 E., into T. 29 N., R. 24 E. 

Inasmuch as no ledges of such roCk are known to 

occur anywhere northeast of Snake Butte, and as the 

general direction ·of glacial movement ·across the reservation appears to--have been southerly or south"+Yesterly, these boulders seemingly can not be referred to 

glacial transportation from Snake Butte. If; bowever, at one stage of recession of the glacial margin 

the ice front extended from northwest to southeast 

across the reservation along a line south of the Milk 

River, a large amount of water would probably be 

ponded or flowing southeastward. between the ice dam 

and the higher land to the south and escaping thence 

eastward to Alkali Creek or Warm Springs Creek 

and so across Phillips C9unty to the Missouri River. 

FIGURE 17.-Geologic section in the Fort Belknap Indian 

Reservation, on Lodgepole Creek 6 miles below Lodgepole, 

. Mont. A, Upturned laminated clay, glaciolacustrine; B, 

till of Keewatin ice sheet. Arrow indicates direction of 

. ice movement 

Great masses of ice, freezing about blocks fallen from 

the cliffs of Snake Butte and drifting thence southeastward with the water, might transport such big 

boulders and drop them at the places where they now 

lie. That the ice front actually did halt for a time in 

such a· position is suggested by mild morainal deposits 

observed at several points and described on page 110. 

In this connection may be noted the occurrence of 

many loose blocks of sho~nite- on top of Snake Butte. 

One of these, a boulder 15 feet long, is perch~ on a 

pedestal several feet high. (See pl. 39 A.) Though 

composed of the local rock it appears to have been carried or lifted by the moving glacier and there let down 

in a balanced position upon the pe4estal as . the· ice 

melted away. One side of another large block seen is 

planed and · coarsely striated by the glaeial action. 

The rock appears to disintegrate readily after long 

exposure to the weather, so that most of the surfaces 

are roughened by etching, and there is much. loose 

· granular material from crumbling of the rock, and 

more has doubtless been blown away. ·At the highest 

part of the butte the surface of the rock is curiously 
108 PHYSIOGRAPHY AND GLACIAL GEOLOGY OF EASTERN MONTANA 

etche~. by weathering, which has produced hollows 

from 1 to 10 feet across and from a few inches to 3 feet 

deep. Some are steplike, others like seats with rounded 

backs and sides but open toward the south. Apparently this weathering has mostly taken place since the 

disappearance of the ice. There are many small boulders of. pre-Cambrian granite from Canada and pebbles of quartzite scattered over the top of the butte. 

Great gaping cracks permit entrance of snow and water, and freezing tends to disrupt the rock and break 

great .masses off the face of the cliffs. · 

Other large boulders were brought into this region 

by the glacier from regions far to the northeast. Several large boulders of gray granite occur on Warm 

Spring Creek by the bridge ·near Brookside, in T. 27 

N., R. 27 E., one of them measuring 5 by 7 by. 15 feet. 

Others lie on the hills off to the east. Charles T. 

Redfield, surveyor, marked the location of a granite 

boulder on the plat ofT. 26 N., R. 27 E., near the 

north line of the NE.% NW. %, sec. 4. This boulder . ' which was not seen by the present writer, is stated as 

measuring 20 by 50 by 75 feet. If thi.s notation is 

correct, it is one of the largest known glacial boulders 

in the United States. A boulder of red granite measuring 7 by 8 by 8 feet was seen by the writer on the 

smooth upland north of Little Cottonwood Creek, 

about 20 miles north of Malta, in T. 33 N ., R 30 E. 

(See pl. 41 A.) 

Three large blocks of limestone were seen on the 

upland 6 or 8 miles northeast of Lake Bowdoin and 

north of Nelson Reservoir, in T. 32 N., R. 32 E. The 

largest (pl. 41 B) measured 3 by 12 by 22 feet. No 

fossils were seen here, but it is probabh:l that these 

are blocks of Devonian or Silurian liinestone derived 

from ledges somewhere in the vicinity of Lake Winnipeg, whence they were carried more than 400 miles 

southwestward by the ice and left in their present 

resting place. The exposed sides of the blocks do not 

show the effects of glacial abrasion, yet their uneven 

surfaces appear not to have been much roughened by 

weathering. The corners have been polished by the 

rubbing of countless buffaloes and range cattle. 

NUNATAKS .AND SLOPE OF. THE TOP OF THE ICE 

About 20 miles east of the sandstone escarpment in 

western Toole County is West Butte of the Sweetgrass 

Hills; about 10 miles southeast of this is Middle 

Butte; and about· 10 miles farther east, in northwestern Liberty County,. is East Butte. Qalhoun 92 gives 

the following data concerning these buttes : 

. Of these, West Butte is the highest, its summit being about 

6,800 feet (aneroid) above sea ievel. The East Butte is several 

hundred feet lower, while Middle Butte, the smallest 'of the 

three, is but 6,000 feet hi height. * * * 

A careful examination of these buttes showed conclusively 

that they were not covered by the ice sheet but that thev 

stood as great nunataks about 2,000 feet above its gener;l 

• Calhoun, F. H. H., op. cit., pp. 11, · 28. 

level. Not only were they not covered by the ice of the Keewatin ice .sheet, but there is no evidence that they were locallT 

glaciated. The ice from the northeast, when it reached them, 

was near the end of its ·long journey al was a depositin~ 

rather than an active b. ody. On the west, orth, and east sides 

of West Butte a well-defined terminal oraine is banked 

against the slope. On the south side therie is no such terminal moraine, and for some distance south the country is driftless. The ice, divided by the butte, did not come together till 

it reached a point about 2 miles south of its foot. The mo-

. ralnes left by these two ice edges as they circled the butte and 

pushed south over the plain are well defined. The moraine 

on the west slope of the butte is 1,200 feet above . the plain ; 

along Milk River on the north side it is 1,500 feet, and on the 

southeast side it is 1,300 feet. This, then, would· m~e the 

average thickness of the ice about 25 miles from its edge. In 

this distance the slope of the upper surface of the ice averaged 

about 50 feet per mile. On the southeast side of West Butte 

the slope of the ice, as determined. by the slope of the moraine, 

was 70 feet per mile. Thus it is seen that along the edge of 

the ice the slope was low, due in great measure to the level 

plain over which the ice traveled. 

W e&ther conditions were not favorable for accurate 

barometric readings when the present writer visited 

East and West Buttes in 1920. Such readings as were 

made, however, indicate that the moraine near the 

south west flank of West Butte is about 4 100 feet 

(barometric) above sea level. The height ot' the surface of the ice was thus not much different here ·from 

what it was at the, head of the reentrant in its outer 

margin on the sandstone escarpment ( 4,200 feet), in 

sec. 1, T. 35 N., R. 4 W., about 25 miles away in a 

direction somewhat south of west. The moraine on 

the eastern flank rises northward from 4,470 feet at 

a point east of the coal mine to 4,700 feet (barometric) . Some drift boulders were seen at · 4 800 feet 

(barometric), but the upper limit was not de~rmined. It seems probable that ice passing the east flank of 'Y e~t Butte moved southwestward to the limit of glaciation on or near Two Medicine Creek south· of Cut 

Bank, 55 miles from West Butte, where the altitude 

is about 3,600 feet. The average slope of the surface 

of the ice along this line must, therefore, have been 

about 22 feet to the mile. .At the north flank of East 

· Butte the moraine is developed near the county road 

on the bench below Black ·Butte at about 4 350 feet 

(barometric). No drift was seen on top ~f Black 

Butte ( 5,050 feet, barometric) or on its slope. ):f 

these barometric determinations are anywhere near 

correct, the ice did not crowd up on East Butte as 

high as on West Butte. Ice passing East Butte probably reached eastern Teton County,, 80 miles away, 

where the moraine front has an altitude of about 

~,700 feet. (See pl. 1.) It would seem, th~refore, that 

the slope of the surface of the ice along this line, which 

is near the axis of the lobe, could not have been more 

than 10 feet to the mile. 

GLACIAL LAKE CUT B.ANK 

The front of the Keewatin ice sheet, when standing 

in the position described ahove, completely blocked 
EARLY WISCONSIN GLACIATION 109 

the valley of Cut Bank Creek so that for 20 miles the 

ice dam was bordered by the water of an extensive 

Jake (pl. 37), which has been designated glacial Lake 

<JI;It Bank.93 

Granitic pebbles and boulders such as those found 

.by the writer on top of the hill southeast of Cut Bank 

.are present at several places in the basin farther north 

.and west at altitudes below 4,000 feet. These were 

dropped from icebergs floating on this lake. Lami-

:naied silt was also observed at several places by 

· Stebinger. (See pl. 25 B.) The silt apparently un-

<lerlies the flatter parts ·of the basin, as much as 30 

feet being exposed by some of the coulees. Stratifi~d 

::Sand and gravel are also seen in places. The actual 

-extent of the lacustrine deposits, however, has not been 

.determined. Now here have any definite shore lines 

been seen. The area mapped as covered. by the lake 

includes that lying below the 3,900-foot contour, together with some of the slopes·' between · 3-,900 and 

-4,000 feet. Carlow Flat was also probably submerged 

part of the time as far west as the canal south of 

.Seville. Pebbles of pre-Cambrian granite from Canada were observed on this flat about 4 miles west of 

.Cut Bank at 3,915 feet above sea level. About 8 miles 

southwest of Cut Bank granite pebbles were found at 

4,050 feet. This may mark the maximum and first 

level of the water. The outlet of the lake was southward along the ice front near this place. Later the 

water fell to 3,900 feet and flowed through the sag 

-occupied by the ponds in sec. 21, T. 32 N., R. 6 W. 

The present inner gorge of Cut Bank Creek was cut 

after this lake was drained. This lake not only reeeived the drainage from the adjacent land area but 

also from all the north front of the Two Medicine 

Glacier for a distance of 50 miles from the Squaw 

Buttes, southwest of Cut Bank, westward to the mountains, the drainage from the Cut Bank Glacier, and 

water from the South Fork of the Milk River. Water 

from the great St. Mary Glacier and from both the 

mountain glaciers and the Keewatin ice sheet for an 

unknown distance north of the international boundary 

was diverted to the South Fork of the Milk River and 

thence to glacial Lake Cut Bank by way of an abandoned channel in the southern part ofT. 37 N., R. 7 

W., which leads from the Milk River northeast of 

Landslide Butte to the head of Rocky Coulee. 

The lamination in such deposits as are shown in 

Plate 25 B is due to an alternation of very fine grained 

sediments with coarser-grained silt. It is believed 

that the coarser material is that which was washed 

into the lake during spring and summer storms and 

that the denser layers consist of the finest sediment 

which remained in suspension, to be precipitated only 

during the winter. when freezing so co" ered the lakes 

• 83Alden, W .C., Glaciers of Glacier National Park, pl. opp. p. 32, U. S. 

Dept. Interior, 1914. 

with ice that no more coarse material was washed in 

and the waters were not disturbed by waves oi· cur .. 

rents. 

If it were assumed that each layer of the laminated 

clay deposited in this lake is a varve. representing one 

season's deposition, careful study of the clay · might 

make it possible to compute a minimum number of 

years that the lake was held in by the dam of · glaeial 

ice, just as the age of a tree is determined by counting 

the number of annual rings of growth. 

RECESSIONAL MORAINES AND DRAINAGE OUTLETS 

Within (north of) the terminal moraine desm~ 

above (pp. 96-103) are certain morainal tracts or belts!, 

some of them well marked, others patchy and·· very 

poorly marked, which appear . to represent positions 

of halt (or read vance and halt) of the glacial margin 

during t~e_ ~ne:rial. progress. of final deglacia.tm:n:-~fff · 

the plains of Montana. These have been noted by 

the writer at various times in making crisscross traY,. 

erses of the area, and were they traced in detail they 

might be found :biore continuous than is now knowrl . 

Certain hypothetical lines of correlation might be 

drawn on the map to show successive probable posi!. 

tions of the retreating ice front. The general relations, together with the distribution of these faint 

morainal deposits and the shifting of drainage lines, 

indicate that deglaciation was accomplished by pro~ 

gressive melting back of the glacial front from southwest to northeast. As the ice front receded down the 

general slope south of the Milk River Valley draina~ . 

lines shifted, and in places great trenchlike abandoned 

watercourses mark temporary positions of the shifting 

streams. A remarkable series of such ancient w·atel'-

courses is found in Alberta and Saskatchewan, Can~ . 

ada. Many of these; called· coulees, are not now 

traversed _throughout their length even by intermittent streams. They cut across divides between the 

present drainage lines, and some are occupied in part 

by chains of elongated shallow lakes or marshes~ sa 

Similar features are found in Montana, but not all 

have been mapped. One such trench near the outer 

limit of the ice in Pondera and Teton Counties leads 

from the Pondera Basin, south west of Conrad, to 

~[uddy Creek, noritlwest of Collins. . 

A second such drainage course leads southward 

across the international boundary at Coutts, Alberta. 

This is followed by the Sweetgrass branch of the Gr-eat 

Northern Railway to Virden, Mont., by the main line 

to Shelby, and by ~he Great Falls branch from Shelby 

across the Marias-Teton divide between Conrad and 

Brady. By this course waters from far to the north 

reached the Teton and Missouri Rivers as soon as the 

Teton Valley was cleared qf ice. Near and south of 

eaa Williams, M. Y., The physiography of the southwestern plains of 

Canada : Royal Soc. Canada Trans., vol. 23. sec. 4, pp. 71-:-76, 1929. 
110 PHYSIOGRAPHY AND GLACIAL GEOLOGY OF EASTERN MONTANA 

Shelb~ the trench is a broad flat-bottomed valley with 

abrupt si~ slopes. Stebinger found two other trenches 

cut aeross the divide between Marias River and the 

Dry Fork, north of Conrad. The Wittley trench between Conrad and Brady is 100 to 125 feet deep. Another such outlet 100 to 150 feet deep crosses the divide 

between Pondera Creek and the Teton River about 20 

miles east of Brady, in T. 26 N., R. 2 E. This may be 

the correlative of a similar trench, Dead Indian Coulee, 

130 feet deep, which Stebinger noted as cut across the 

divide between Marias River and Pondera Creek in 

T. 29 N., R. 2 E. Yet another outlet was crossed east 

of Egly, in or near the southeastern part of T. 27 N., 

R. 6E. 

Some features suggestive of a recessional moraine 

are belts of low bouldery drift swells north of Shelby 

and east of the Sweetgrass branch of the Great Northern Railway, in Ts. 34-36 N., R. 2 W. Similar belts 

were also seen between Collins ~nd Brady and about 

15 miles east of Brady. A belt of gravel knolls was 

also observed by L. J. Pepper berg's party 94 north of 

Lonesome Lake Coulee, southwest of Boxelder. This 

belt extends northeastward to the flat ·between Sandy 

Creek and the Great Northern Railway and may be 

correlative with a similar belt crossed by the writer 

in 1921 south of Boxelder. This belt might perhaps 

be traced northeastward to the outer moraine east of 

Square Butte. 

The abrupt change in direction of' Marias River 

from an easterly course in southern Liberty and Hill 

Counties to a southerly course in Chouteau County 

suggests that the latter .course is the result of permanent diversion when the ice front had receded to a 

position somewhere to the northeast. The presente of 

a buried former channel of Marias River extending 

eastward from the vicinity of the sharp bend through 

T. 29 N., Rs. 9-13 E., toward the buried former valley 

of the Missouri River southwest of Boxelder has not 

been demonstrated, but the probability of its existence 

seems very strong. Northeast of the bend, near the 

middle ofT. 29 N., R. 9 E., Black Coulee is for some 

distance cut wholly in drift to depths of 30 to 80 feet. 

Farther south the coulee is cut into black shale. East 

of Black Coulee a broad nearly flat plain slopes eastward toward Boxelder between gW!tly sloping higher 

land on the north and south. (See Lonesome and 

Boxelder topographic maps.) 

Pepperberg's and Barnett's field maps (1908) show 

. no exposures of sandstone or shale beneath the glacial I' 

drift between Lonesome Lake Coulee on the south, in 

secs.19 and 20, T. 29 N., R. 13 E., and Barneys Coulee, 

5 miles farther north, in sec. 30, T. 30 N., R. 13 E.,'' 

and it seems probable that through this interval the 

ancient Marias joined the contemporary Missouri 

River. The present gorge of Marias River, for some 

N Field .maps, 1908. 

distance above and below the bend, was cut deep and 

narrow into the Colorado shale as the master stream, 

the Missouri River, reexcavated its gorge after the 

disappearance of the ice. Farther west up Marta:s 

River the valley is broader, and remnants of benches 

observed at certain points may represent the bottom of 

an older and shallower valley which drained eastward 

toward Boxelder. That the present southerly lower 

course of Marias River is due to glacial diversion is 

also indicated by the fact that sandstone-capped· buttes~ 

the so-called Goose Mountains, which are remnants of· 

a high old divide, are but a few miles west of this 

southward-trending gorge. The tops of these buttes 

are 500 or 600 feet higher than the broad plain.· east 

of the bend of Marias River. Stebinger recorded in 

his field notes having observed thicknesses of 50 to 175 

feet of gla<?ial till exposed in bluffs along Marias 

River in what is now southeastern Toole County. 

RECESSIONAL MORAINES IN HILL, BLAINE, AND 

. PHILLIPS COUNTIES, MONTANA 

The next line along which the retreating ice front 

halted appears to be ea~ of· Sage Creek and along o~ 

near the Milk River Valley, and to this may perhaps 

be due the parallelism of the two streams west of . 

Sandy Creek. Traces of morainal topography were 

noted by the writer north of Gildford, in T. 33 N., 

R. 11 E., and in 1915 W. P. Woodring 115 traced a welldefined morainal belt east of Sage Creek for 12 ·miles 

in a northwesterly direction in Ts. 35 and 36 N., 

R.10E. 

The glacial till east and west of the Milk River was 

found by Stebinger's party to range generally from a 

few feet to 150 feet in thickness, but in many places, 

especially near the international boundary, 100 to 150 

feet was seen. A gravelly drift ridge which may belong to the same morainal belt was noted by Barnett 

in 1908 about 6 miles northeast of Kremlin, and with 

this is perhaps to be associated a peculiar feature, 

Chain of Lakes Coulee, shown on the Kremlin topographic map. Examination of this map and that of 

the Assinniboine quadrangle, on the east, shows that 

the elongated depression in which lies the Chain of 

Lakes cuts across a detour made by the present course 

of the Milk River and is more nearly on a median line 

between the divides on each side than that part of the 

present stream to the east. The relations give rise to 

the suggestion that the Chain of Lakes lies in a partly 

filled pre-Wisconsin (or preglacial) valley of the Milk 

River. 

Farther south and east on the same general correlation line is the thick drift filling of the old Missouri 

Valley south and east of Havre. Data are given elsewhere (p. 67) indicating the depth of this drift 

GG Unpublished field maps and notes of Eugene Stebinger•s party, 

September, 1908. 
EARLY WISOONSIN GLACIATION -11:1 

filling. · Extending eastward from a point about·· 3 

miles east of Havre there is a tract covering m&:te than 

20 square miles on the north side of the river which is 

evidently a part of the same deposit. Pepperherg's 

and Barnett's field maps (1908) show extensive belts 

of "kames" and some gravelly ridges designated 

" eskers." • Some of these features ·seem likely to be 

recessional moraine deposits, but too few of them have 

been seen by the present writer to warrant more than · 

the suggestion. . Some of them may mark a slightly 

later stage in the glacial recession, when the glacial · 

front had been melted back north of the valley. Such 

are. a belt of gravel knolls and ridges extending westward on the south side of Coal Cou.lee for several miles , 

from a point about 6 miles north of Toledo; a belt of 

small hills noted in 1915 by J. D. Sears near Thibedeau Lake, together, perhaps, with nlllllerous ponds 

and other features to ·the . northwest and southeast; 

gravelly hills· 2 miles· north of Chinook; and a narrow morainelike ridge cut through by ·Deadhorse · 

Coulee about 7 or 8 miles farther north, in sees. 1 and ·: 

12, T. 34: N., R. 19 E. . . 

The uneven surface of the bench that borders the 

south side .of the Milk River Valley from a point 2 

miles west of Lohman (formerly Yantic) eastward to 

the Fort Belknap Indian Agency ·south of Harlem · 

(see Yantic, Chinook, and Harlem or Zurich and 

Cherry Ridge topographic maps) suggests morainal I 

deposits formed along the glacial front while the 

river channel was occupied by · ice. The peculiar 

coUrse followed by the Milk River near Chino~k, the 

course of Threemile Coulee, and. the presence of a sag 

leading from Sixmile Coulee 8 to 10 miles eastward 

to Snake Creek south of a low belt of hills all suggest 

the presence for a while along this belt of an ice dam 

that prevented the drainage from passing directly to 

the broad valley to. the north. A belt of small knolls 

and ridges in the ·midst of the broad valley flat . between Chinook and Harlem may represent a brief· 

stand of the ice front after the southern part of the 

flat was freed from ice and occupied by border drainage. The presence of an ice dam along such· a line 

would explain why the river cut th~ough the ridge 

southeast of Chinook instead of flowing directly eastward along the line followed by the Great Northern 

Railway. · 

East of the· Fort Belknap Indian Agency morainal 

deposits border the south side of the valley for several 

mileS. They are best defined where a gravelly knolled 

ridge forms the retaining barrier on the north side of 

the irrigation reservoir in T. 31 N., R. 24 E. A line 

of low swells rising above the flat to the east may represent the continuation of the morainal belt. A somewhat earlier and more southerly line was found extending eastward in T. 29 N., Phillips County, from 

the ·Vicinity of Peoples Creek to the Malta-Zortman 

road~ This is marked by gravelly knolls and numerous sags and pon~s. ·It probably joins the outer.lme 

of morainal deposits in· the hilly beltS south of Malta, 

described above . (p. 99). 

Two of the best-developed moraines of the Keewatin 

ice sheet in Montana are on the upland west of Whitewater Creek, ·in the northwestern part of Phillips· 

County and ·the· northeastern part of Blaine County. 

Parts of both of these moraines are· shown on the 

Cherry Ridge topographic map. On the plain.S to the 

south and west the advancing glaciers found little but 

fine material, mostly clay, from the-Cretaceous shales, 

with some sand from the niable- sandStones. -With 

this were mixed some pebbles and boulders from more 

distant sources. Moreover, at most places the iec;, 

front was bordered ei~her by ponded waters in which· 

only the finest silts could be spread out, o:r by great 

streams of diverted waters which swept away most of 

the fine material and rafted away many of the larger 

boulders on floating icebergs, leaving ·lit tie that could 

be piled up in the form of mt>rainal ridges and bmes.-

The stronger development of moraines on the uplan~ 

north of the Milk River, on·the contrary, may balfe 

been the result of two factors in contrast with those 

noted above~ (1) The glacier, in advancing , across 

the upland, found an abundance of coarse gravel (the" 

Flaxville gravel), which was carried forward an<l 

dumped with many crystalline boulders at the melting 

ice front, forming a wilderness of morainal knolls 

and ridges. (2) The ice front here was bordered 

neither by a glacial lake nor by a great river. The 

drainage, especially from the outermost of ·these-two 

n10raine8, flowea directly away from the ice front to 

the Milk River Valley in -the form· of numerous sma.ll 

streams. ·Doubtless some. of the fine material was 

swept away, but most of the coa.rse gravel and the 

boulders were left to forin the moraine. The topographic map shows some of the many branching cou· 

lees which head at the more southerly of the two 

moraines.· This moraine is best developed between 12 

and 18 miles north of Harlem, Savoy, Coburg, and 

Dodson. It extends in a northwesterly direction .as a 

belt about 4 miles wide, thickly set with bouldery knolls 

and ridges of gravelly drift interset with a multitude' 

of sags and elongated hollows, many of which contain 

ponds or marshes, except in the dry seasons.· North 

of Harlem and Savoy the moraine is la.id at 3,100 to 

3,300 feet above sea level along the southern border of · 

the upland plain described above (p. 18) as. underlain 

by Flaxville gravel. Atl2 miles north of·Hal"lem the 

remnant of an old gravel-capped divide begi.il.s to rise· 

'(on Judith River sandstone) above the plain to the 

northeast and e:Jtends thence with much , dissected 

western slope ancl crest in a northerly . direction as 

Cherrypatch Ridge to and across the international 

boundary in ~- 21 E. As this ridge· rises the moraine 
112 PHYSIOGRAPHY AND GLACIAL GEOLOGY OF EASTERN MONTANA 

curves northward and is not so well defined. One feature developed in connection with_ the formation of 

this moraine is about 8 miles west of Turner. From 

a low altitude south of Woody Island Coulee, in the 

northeastern part ofT. 36 N., R. 24 E., there extends 

in a southerly direction a line of small hills or ridges 

for a distance of 8 or 9 miles. This line curves gradually toward the southwest and passes east of Twete 

toward the moraine described above. The trend of 

this line of hills, as shown ori the Cherry Ridge topographic map, is nearly normal to the moraine, and this 

and its contours suggest that it is an esker. Where 

examined, however, it is seen to be a succession of 

knolls rather than a sinuous ridge. It resembles a 

moraine or a belt of kames rather than an esker. The 

crests of some of the knolls are covered with abundant 

crystalline boulders, mostly gray granite. The southeasterly extension of the moraine on the dissected upland north of Malta has not been mapped. It seenis· 

probable, however, that when this moraine was formed 

the Milk River Valley northeast of Malta was not yet 

cleared of ice~ Small, sharp, bouldery hills below the 

west bluff in the valley 12 miles northeast of Malta 

may perhaps be morainal, but on the other hand they 

may be shale hills sprinkled with boulders. They 

were not carefully examined. 

The second of the two well-marked moraines crosses 

the international boundary and enters northeastern 

Blaine County in T. 37 N., Rs. 23 and 24 E., as shown 

·on the Cherry Ridge topographic map. Where crossed 

by the writer in 1920 north of Turner, in T. 37 N., 

R. 22 E., the moraine is nearly 4 miles wide, very 

rough, and marked by bouldery hills and hollows. 

For a distance of nearly 30 miles in a southeasterly 

direction the moraine is bordered on the south by 

Woody Island Coulee. Where crossed north of Turner 

this valley is 100 feet deep and nearly a mile wide, 

cut in the flat grayel plain. Apparently the ice front 

here was bordered by good-sized streams, but the coarse 

n10:r:ainal material was not washed away. At 11 miles 

east of Turner, in the southeastern part of T. 36 N., 

R. 27 E., the valley bends sharply to the south and the 

drainage enters a· deep gorge leading first south and 

then southeast along Cotton wood Creek to the Milk 

River below Malta. The relations near and west of 

Horseshoe Lake suggest that the drainage was diverted 

as a result of the position and trend of the glacial margin and of the moraine. North of Horseshoe Lake and 

for some distance eastward the 111oraine is about 6 miles 

wide. Through most of its southeasterly course across 

T~ 35 N., Rs. 29 and 30 E., the south front of the 

moraine is particularly well defined, especially on the 

flat upland plain. (See pl. 38 B.) The basins of 

Horseshoe Lake and Martin Lake appear to be due to 

blocking of a former valley by the morainal deposit. 

Just at the eastern edge of the upland the sharp 

.fr-ontal ridge of the moraine swings abruptly s®thr 

ward and drops down the slope, and the moraine. l$ 

lost in the hilly eroded tract between Whitewater and 

Martin Creeks. The topographic relations and the 

presence. of patches of morainal ·knolls farther ;south 

indicate that the ice front at this stage extended in 

a southerly direction ~long the hilly belt west of 

Whitewater Creek to the morainal hills near the foot 

of Nelson Reservoir, in · T. 32 N ., R. 34 E. East of 

Nelson Reservoir, in sees. 19, 20, and 28, T. 32 

N., R. 33 E., the road passes along the. north side of 

a well-marked narrow moraine which. separates. the 

flat on the north from the flood plain of Beaver Cr~k 

on the south. The irrigation canal is excav•ted in the 

south slope of this ·moraine. 

STREAM DIVERSION NEAR LAKE BOWl)OIN 

In the relations of the ice front to the valle:ys at the · 

several' stages of reeesSion described above is probably 

to be found an explanation of the diversion of the 

· Milk River from . the old Missouri Valley east of 

Malta. The Missouri River is thought originally to 

have flowed eastward through the Lake Bowdoin sag 

and to have been joined by the Musselshell River 

fiowing from ·the south in the Beaver Creek Valley. 

(See fig. 18, A.) Just what was accomplished by the 

Illinoian or Iowan · ( ~) ice sheet in the way of stream 

diversion in this locality can not now be determined. 

Probably Cottonwood and Little Cottonwood Creeks 

originally flowed southeastward to the river by way 

of the sag in which is now Nelson Reservoir (the 

trough in which are shown Lone Tree Lake and Mud 

Lake on the Bowdoin topographic map), inasmuch as 

this sag heads westward at the east side of the Milk 

River Valley, where it is cut off and left hanging weU 

up in the slope. These creeks may have .been turned 

southward by the Illinoian or Iowan ( ~) ice to join the · 

river near Malta. · 

If the early Wisconsin ice sheet deployed to the limit 

described above (p. 99) , it pressed agai~t the north 

slope of· the Larb Hills and reversed the flow in the 

Beaver Creek Valley, sending the stream southward 

as the ice lay across the hills south of Malta (fig. 18, . 

B, .A'-.A-4). At this time also a stream. was probably 

flowing ·southward along the valley of Larb Creek, a 

remarkable valley cutting directly through the hills to 

the Timber Creek Valley, whi~h. dra.ilt~ southward to 

the Missouri River. (See Saco topographic map.) 

From the outer position (A' -A) the glacial front was 

melted back to positions A"~A"-.A ~d A"'-A"'-

A" -A as indicated by morainal deposits south and 

east of Malta. When the ice front receded to the moraine that is so well marked north of Harlem it probably also retreated to the upland north of Malta and to 

the belt of morainal knolls north and east of ·Lake 

Bowdoin- (fig. 12, B, B-B-B) while yet hold~ the 
EARLY WISOONSIN GLACIATION 

···-···~ 

Present streams 

A Preg,lacial streams 

LARS 

.s..r~?.iii=o?.:.a. B Probab~e successive positions of Wisconsin ice front 

(') 

~ \. 

\ \ 

~ey \ 

"\ 

·--~ ... 

... ~ ..... ?~!'... 0 

Probable pt~sition of Wisconsin ice front 

'-... ~ ... --··.,__,. ..... LARs· 

c 

\ ~. ~?' 

Fxouu 18.-Stream diversions east of Malta, Mont. A, Probable relation of preglacial streams (dashed) 

to the present stream valleys; B, probable relation of outlets of glacial waters from the front of the 

Keewatin ice sheet, Wisconsin stage of glaciation, at its mo~;t advanced position (A.'-A.-..4.) and at sue·\ 

cessive later positions (A."-A."-A-A, A.'"-A."'-A-A., and B-B-B-A.-A.); C, probable relation of outlets 

of glacial waters just preceding the opening of the present courses of the streams by further melting 

of the ice. (See text for additional· explanation) 

113-
114 PHYSIOGRAPHY AND GLAOIAL GEOLOGY OF EASTERN MONTANA 

position A-A. Water from the region west of Malta 

and from the ice front west of Saco would then continue flowing to and southward along the Beaver 

Creek Valley. If the ice front receded to the line 

0-0-B (fig. 18, C) while yet holding the position 

A-A-that is, pressed against the slopes of the up-

. lands on the south and east-the southwestward flow 

to Malta and thence east through the Lake Bowdoin 

sag to the Beaver Valley would be increased by waters 

from Woody Island Coulee, by way of Cottonwood 

. Creek Valley, and this would be joined through a col 

at D by glacial waters froiQ. the Martin Creek Valley 

and from the southeastward-trending part of the Milk 

River Valley (reversed) (fig. 18, C, E-E), which was 

probably the original valley of Martin Creek. · Whitewater Creek probably originally joined the Missouri 

River through the broad sag (Fig. 18, A) 7 miles 

northwest of Saco. When the ice finally left this sag 

it was blocked by a morainal :ridge. Whitewater 

Creek may also have been diverted westward around 

. by Malta when the ice front receded east of its southeastward-trending valley, and so also in turn may 

Stinking Water Creek when its valley was cleared. 

In this way the valley now followed by the Milk River 

below Malta may have been deepened down to the 

level of the low divide south of Lake Bowdoin by 

water flowing toward Malta. Frenchman Creek probably previously followed its present course to the main 

stream east of Saco. · When all these valleys were 

finally cleated of ice there was thus ready for the 

Milk River a valley along its present course northeast 

of Malta which was fully as deep as the sag south of 

Lake Bowdoin. As the ice front receded strong flows 

came from the north, first through the valley of 

Whitewater Creek and then by way of ·Frenchman 

Creek, and these reached the Missouri River below 

Nashua. As a consequence southward flow through 

the Beaver Valley ceased, and the Lake Bowdoin sag 

·was abandoned. 

There is a great morainal tract covering more than 

a township south of the international boundary between the east and north forks of Whitewater Creek. 

Collier 96 states that morainal features were observerl 

by his party farther south, on the east side of this 

creek. These may mark the next position of halt after 

the ice front receded from the moraine at Horseshoe 

Lake. The relations north of the boundary are not. 

definitely known, though the writer made north-south 

traverses on four routes south of the Cypress Hills. It 

is probable,,however, that by the time the Whitewater 

Creek Valley was cleared of ice the glacial margin had 

receded to the east end of the Cypress Hills Plateau 

and that glacial waters were flowing through the gap 

96 Personal communication. 

now traversed by the Canadian Pacific :&ail way northeast of East End village, thence westward up . the 

Frenchman Creek Valley and through the sag occupied by Cypress LaJte and Jt.Cross to the Battle Creek 

Valley, by which it would reach the Milk River a:t 

Chinook. 

RECESSIONAL MORAINES IN THE NORTHEASTERN 

COUNTIES OF MONTANA 

By the time the basins· of Frenchman Creek and 

Rock, Creek were wholly cleared of ice the glacial margin ·must have been receding northeastward .across the 

upland plains of northeastern Valley County and 

Daniels and· Roosevelt Counties to or beyond the Poplar.River Valley. On the upland east of the Poplar 

River there is a well-marked belt of terminal moraine which crosses the south line of Daniels County. 

Northwest of this, on the upland· between the main 

and west forks of the Poplar River, is a mild morainal 

belt with a northwesterly trend. It .is not well 

marked, however, elsewhere, though at severa1 places 

along this divide as far northwest as the highland 

south of Wood Mountain post office, in T. 4 N., R. 1 

W., Willow Bunch district, Saskatchewan, morainelike knolled tracts were observed by the writer in 

1916 and 1920. 

A bit of a moraine also borders a high gravel-covered upland 10 to 15 miles north of Scobey and ~xterids 

across the international boundary between the middle 

and east forks of the Poplar River. A well-marked 

morainal tract within a few miles of the international 

boundary northeast of Whitetail may ·perhaps be 

correlated with the later Wisconsin moraine east of 

the Big Muddy Valley. When the ice front stood 

here the drainage went westward from the head of the 

Beaver Creek Valley through a pass at the boundary 

nearly· 200 feet deep and thence to the Poplar River. 

It will be evident to the reader of the foregoing descriptions of morainal deposits that the correlations 

suggested from the data in hand and presented to 

show the successive stages of recession of the front 

of the melting early Wisconsin glacier can not be· 

regarded as established. The most that cari be hoped 

is to systematize such information as is available and 

present an outline to be filled in or revised from later 

observations. To the writer it seems fairly certain 

that the ice front receded from the plains of Montana. 

not directly northward across the whole area but from 

southwest to northeast toward a center of dispersion 

west of Hudson Bay. At the next stage of melting 

beyond those prese~ted above the ice front probably 

receded northeastward within the limits of the later 

Wisco~sin invasion. How far the iee was melted 
l:tOCKY MOUNTAIN- GLACIERS OF WISCONSIN STAGE 1J;5 

back before it readvanced to the great moraine on the 

Coteau du Missouri in North Dakota is unknown. 

ROCXY KOtrlfTAD' GLACIERS OF WISCONSIB STAGE 

GENERAL RELATIO:NS 

It is .not intended to present in this paper a ·fun 

discussion of the phenomena of the Pleistocene glaciers of the Rocky Mountains in ·Montana. A description of the deposits of the glaciers that extended 

out nearly to or beyond the eastern front of the mountains, beginning at the north with the Belly River 

Valley in southern Alberta, is given in order to show 

the conditions on the plains. Since the time the glacial deposits as far south as the Sun River were described by Calhoun,91 they have been mapped somewhat more in detail, partly by the writer but princ.i~ 

pally by Eugene Stebinger, to whose field maps and 

notes the writer is indebted. · 

The. continental ice sheet that formed the terminal 

moraine in southern Alberta and in Glacier, Toole, 

Pondera, and Teton Counties, Mont., is regarded as 

that of the early Wisconsin stage of glaciation. As 

was first shown by Calhoun, this Keewatin ice. reached 

its maximum extension in this part some time after 

the mountain glaciers began to melt back, and it laid 

drift of northeasterly derivation on' top of drift 

brought from the mountains. It appears, therefore, 

that the part of the mountain drift thus covered must 

be of either early Wisconsin or pre-Wisconsin age. 

The possibility of its belonging to the Illinoian or 

Iowan stage is discussed on pages 69-71. The relations 

of the glacial deposits on the plain below the W aterton 

Lakes have not been studied by the writer. 

BELLY RIVER GLACIER 

.In October, 1912, the writer, in .company with 

Eugene Stebinger, examined some of the glacial deposits in the Belly River Valley between 6 and 10 

miles north of the international boundary. (See pl. 

37.) It is clear from the exposures ~en that there 

is in this valley drift of the mountain glaciers overlain. by drift of the Keewatin ice sheet. Insufficient 

study was made, however, to determine clearly 

whether this buried mountain drift is of early Wisconsin age or older. About 6 or 7 miles north of the 

boundary and about 2 miles south of the moraine of 

the Keewatin ice, there is a sharp moraine formed by 

the monntain ice, and from this a· lateral moraine 

extends southward on the upland to the weSt. Under 

a. well-defined terrace that heads at the moraine in 

the valley the following section was seen : 

~~'~'Calhoun. F. H. H., op. cit .• pp. 14--22. 

SeotUm. of drift in ·.Be~zv .RWet- Valie1/, Albert•. 

; Nt: 

6. Coarse bouldery gravel. composed entirely of moutain. . , ; 

rocks --------------------------------------------~ ll 

5. Buff sandy silL------------------.,---------------.... - .10 

4. Grayish-but! glacial till in which a few granitic pebbles 

from the northeast were seen _____ :..----------"------ '8 

3. Coarse mountain graveL-----------.. -----.:..-_____ .,.... ... _ ... _ 8 

2. Interstratlfied fine gravel and sand from the mountaint ... , 6. 

1. Very stony mountain tilL _ _. __________________ .,. __ ...___ ·1.5 

Bluish shale (Cretaceous). 

It is possible, though not certain, that the moraine: 

noted marks the limit of either the early or the later 

Belly River Glacier of the Wisconsin· stage, that 

with this goes the upper till (4), and that the lower 

till ( 1) and buried mountain ·till farther down the 

valley are pre-Wisconsin. Another section a little Jar .. 

ther north showed 10 feet of stratified clay with fine 

pebbles, some of northeastern crystalline rocks, overlying about 50 ·feet of pinkish, very stony mountain 

till. . 

The northeastern crystalline pebbles in these two 

sections may have been dropped from ice floating on a 

lake held in front of the Keewatin ice. There are some 

indications that the Belly River Glacier was ne~rly 

1,000 feet thicl.r near the international boundary, as 

C. S. Corbett found evidence in 1914 that a lobe of the 

ice cros.sed the sag in the top of the ridge on the east tQ 

the head of Lee Creek, north of Chief Mountain. (See 

pls. 1 and 37.) This ice of the Wisco~ ·stage apparently did· not reach the higher part of Ma.kowan 

Butte, on which is the pre-Wisconsin drift north of 

the boundary, by a vertical distance of 400 or 500 

feet. 

About 4 miles north of the bOundary is another mo,.. 

raine constricting the valley. Farther south is a great 

alluvial fan heading at the mouth of the North Fork 

Valley, which has forcedlthe main stream over to the 

east side of the bottom land. This ·valley was evidently deepened 1,000 feet or more between the time 

of the deposition of the pre-Wisconsin drift on top of 

Makowan Butte and the time· of the advance of the 

glaeier of the early Wisconsin stage. The top of the 

butte is 1,300 feet above the Belly River. 

KENNEDY CREEK GLA.CIBR . 

One of the tributaries of the great St. Mary Glacier 

occupied the valley of Kennedy Creek just south 

of Chief Mountain. In 1914 C. S. Corbett and 

C. R. Williams, assisting Mr. Stebinger, found that 

the ice. ·had spilled over the sag eaSt of Chief Mountain 

and extended a lobe 3 or 4 miles down the valley of 

the East Fork of Lee Creek to a. point less than a 

mile south of the internat1onafboundary, where there 

is a low terminal moraine.· The ice in ~the Kennedy 
116 PHYSIOGRAPHY AND GLACIAL GEOLOGY OF EASTERN MONTANA 

Creek Valley was not, howeyer, thick enough to override the west end of the ridge 3 miles east 'of Chief 

Mountain, which is capped with pre-Wisconsin drift 

(p. 33), though it extended almost to the top of this 

ridge. East of this the ice entirely surrounded Kennedy Ridge (pl. 37), 'which stood as a nunatak. 

The small ridge 2 miles to the northeast, which is 

capped with older drift, was also a nunatak at this 

time, the St. Mary Glacier being on the south and east 

sides. Between this and Kennedy Ridge and east of 

the latter is a strongly marked moraine, probably 

interlobate. Evidently there was a continuous ice 

field east of Yell ow Mountain formed by the coalescence of the glaciers in the valleys of the North and 

South Forks of Kennedy Creek with that in the St. 

Mary Valley north of the east end of Swiftcurrent 

Ridge. 

ST. MARY GLACIER 

Conditions show that the St. Mary Valley was occupied at the Wisconsin stage by a great glacier 36 

1niles or more in length, which was joined by branch 

glaciers heading in the valleys of Swiftcurrent, 

Boulder, Red Eagle, and Divide Creeks. So thick was 

the ice in the main glacier that it crowded up onto the 

west slope of St~ Mary Ridge to a height of 1,200 feet 

above the level of Lower St. Mary Lake and formed 

there a small but well-defined lateral moraine. This 

moraine curves northeastward, forming a loop and 

showing that . the ice crowded through the broad sag 

in which lie Duck and Goose Lakes to the head 

branches of the North Fork of the Milk River. Duck 

Lake is 500 feet hig4er than Lower St. Mary Lake, 

and the glacial lobe thrust into this sag was about 6 

miles long and 6 miles wide where it left the main 

glacier. After recurving about the west end of the 

Hudson Bay divide, a mile north of Goose Lake, the 

moraine swings sharply to the east again and gradually descends the north slope of the divide, thus 

showing that ice from the St. Mary Glacier also 

crowded through the gap now traversed by the St. 

Mary Irrigation Canal and containing Spider Lake 

and extended at least 6 miles down the Willow Creek 

Valley. Extending thence northwestward to the St. 

1\{ary River is the moraine of the Keewatin ice sheet. 

In the St. Mary Valley north west of Goose Lake, 

above the United States Bureau of Reclamation 

bridge and siphon at Fletcher, the ice was fully 1,000 

feet thick. 

The relations of the drift of the St. Mary Glacier 

to that of the Keewatin ice sheet (seep. 104) seem to 

show that the front of the St. Mary Glacier was 

Inelted back somewhat before the Keewatin ice reached 

the limit of its advance, inasmuch as Keewatin drift 

overlaps drift of the mountain ice for about a mile 

south of the international boundary. The possibility 

of some of this low-level mountain drift being of preWisconsin age is discussed on page 69 .. A small lobe 

of the glacier may have extended eastward to the 

head of Fox Creek through the high-level sag north 

of Divide Mountain where now runs the automobile 

road. Several more or less .definite benches ~ark the 

slope below the highest lateral moraine east of Lower 

St. Mary Lake. These rise and converge southward 

and probably mark successive positions of the ice 

margin as the glacier was being reduced by melting. 

Between these and the lake is a belt of ground moraine 

about a mile in width, marked by marshes and ponds 

and by smoothly rounded elliptical swells and ridges 

somewhat resembling small drumlins. 

After the melting of the St. Mary Glacier great 

~ouldery fans were formed in the valley opposite the 

mouths of the valleys of Kennedy, Swiftcurrent, 

Wild, and Divide Creeks. The latter two form the 

dam at the north or lower end of St. Mary Lake, and 

that formed by Swiftcurrent Creek holds in Lower 

St. Mary Lake. ·Three soundings made in 1914 by 

Stebinger's party in the south half of the lower lake 

show depths of 50 to 70 feet of water. Three test borings made by the United States Bureau of Reclama~ 

tion in a line across the valley bottom, not far below . 

the lower end of the lake, penetrated to depths ·of 

105 to 188 feet in gravel, boulders, sand, and clay, 

without reaching bedrock. The lower lake, therefore; 

does not lie in a rock-rimmed basin, though the stream 

below the outlet is cutting in sandstone, having been 

crowded over by the alluvial fan onto the rock at the 

east side of the valley. 

It is probable also that there is no rock ledge at the 

foot of St. Mary Lake. It is not known, however, to 

what depths the alluvial gravel extends nor how much 

drift or other loose material may lie beneath it on top 

of the rock. 

Sixteen soundings made in 1914 by Stebinger's 

party on transverse lines in St. Mary Lake below The 

Narrows show depths of water ranging from 82 to 

230 feet.- The depths exceeding 200 feet were all 

found less than 3 miles below The Narrows. , (See 

fig. 19.) This part of the basin is excavated in Cretaceous sh8Je. In The Narrows depths of 71 to 145 

feet were found, and above The Narrows nine soundings showed depths ranging from 130. to 296 feet. 

The greater depths were found within a mile above 

The Narrows. These are due to glacial scour in the 

Appekunny argillite back of the massive upturned 

ledge of Altyn limestone,. To the resistant character 

of the limestone is due the constriction of the basin 

forming The Narrows. Before the ledge was notched 

there was probably a waterfall here similar to McDermott Falls, in the Swiftcprrent Valley. 
ROOKY MOUNTAIN GLACIERS OF WISCONSIN STAG¥ · :ll7 

CUT BANK GLA.CmR 

At the early Wisconsin stage a great glacier 20 miles 

long extended down the valley of the North Fork of 

Cut Bank Creek to a position 6 to 8 miles northwest 

of Browning, where a small but distinct moraine 

curves across that flat gravelly plain. This plain 

look~ like an outwash plain. The terminal moraine 

is double and · merges into lateral moraines on the 

north and south, showing the bulbous end of the glacier to have been nearly ·5 miles wide between the high 

benches (No.2), which are capped with the pre-WE;-

consin drift and gravel. 

About a mile inside the outer limit is a second concentric moraine, and 3 n1iles farther up the valley is a 

third. Each of these n1oraines merges with lateral deposits on the north and south sides. Where the automobile road crosses the valley the ice was 700 to 800 

feet thick at the maximum, so that it extended nearly 

to the tops of the high benches. At this stage it spilled 

a well-m~rked ridge about 1.00 feet high crosses the 

valley and merges with strong lateral .morain~s on the 

north and south. It is possible ~hat the loop thus 

formed marks the limits of a later Wisconsin advance 

of the glacier rather than being. simply . a recession.,! 

moraine. It is bordered on the east by a gravelly flJ!t 

like an outwash terrace. Two miles farther. w~t' an 

inner moraine loop is cut through· by Lake. Creek. 

Traced westward the south moraine extends up the 

slope onto a sandstone ridge rising 675 feet in 2 m!Ies. 

TWO MEDICINE GUCIER 

TERBXNAL MORADIE 

The largest of the piedmont glaciers oecupi~d the 

greater part of the Two Medicine Creek Basin. It 

had a maximum width of 27 _miles, extended nearly, 

40 miles east of the mountain front; ·and covered approximately 800 square miles on the plains. Contributing to it were glaciers heading in the great 

0 I 2MILE5 

Contour interval SOO f'l. 

Oatu:m, mean.- sea wv~ 

FIGURE 19.-Depths of water in St. Mary Lake, Glacier National Park, from soundings by Eugene Stebinger's party in 1914. Stippled 

areas, alluvial gravel fans 

through the notch in the crest of the north ridge, 500 

feet above the stream, where the road now crosses, and 

extended a small lobe 3 miles northeastward down the 

valley of the South Fork of the Milk River. The outline of this lobe is shown by a small encircling moraine. From 2 to 3. miles farther west a similar but 

smaller lobe spilled over a notch whose bottom. is 800 

feet above Cut Bank Creek. 

LAKE CREEK GLACmR 

.A small glacier about 10 miles long occupied the 

valley of Lake Creek, extending eastward beyond the 

present automobile road, to a point· within half a mile 

of the moraine of the Two Medicine Glacier. Northeast of the road the knolled and pitted morainal deposits merge with those of the south moraine of the 

Cut Bank Glacier. Where crossed by the road· the 

moraines are poorly marked, but a little farther west 

valley in which are the Two Medicine Lakes and 

heading in Theodore Roosevelt Pass ·and in all the 

valleys southward to Heart Butt&-a. mountain frontage of 26 miles. The north bonndary of the traet 

covered by this great glacial lobe is marked by 'a 

well-developed moraine ranging in width from a·quarter of a mile or less to 3 miles. (See Browning, Blackfoot, and Cut Bank topographic maps.) The southeastern limit of the drift is not generally marked :by 

a Inoraine, but it is clearly tracea.ble by the presence 

of either till or boulders derived from the mountains. 

B~sides the other mountain rqcks, one characteriStic 

constituent is conglomerate thickly set with blaek 

chert pebbles. These boulders :were derived from. 

ledges of Kootenai ( ~) ·conglomerate exposed at·.setcral places between Glacier Park ·station and Summit 

station. The presence of boulders of this conglomerate in the drift ·west, north, ·and east of Browning 
118 PHYSIOGRAPHY AND GLACIAL GEOLOGY OF EASTERN MONTANA 

shows that ice from Marias Pass followed approximately the course of the railroad and crowded about 

the east end of the high bench 6 n1iles northeast of 

Glacier Park station, entered the valley of the South 

Fork of Cut Bank Creek, and came almost into contact with the ends of the Cut Bank and Lake Creek 

Glaciers. The same conglomerate is found clear to 

the east limit and is particularly noticeable along the 

Park to Park Highway northwestward from the point 

where it crosses the ridge 6 miles north of Birch Creek 

to the moraine west of Browning. Drift deposited 

by this glacier is exposed in the cuts along the old 

automobile road from Two Medicine Creek north of 

Glacier Park station up the slope to the top of the big 

bench east of Lower Two Medicine Lake. On this 

bench is a typical morainal topography marked by 

bouldery knolls and ponds, showing that the Two 

Medicine ice crowded nearly across the top of the 

ridge at a level about 1,000 feet above the lake. This 

ice did not, however, overtop the higher part of the 

ridge north of the lake, where the pre-Wisconsin drift 

occurs, by several hundred feet. East of the old road 

the outer moraine is well developed between the railroad and the Park to Park Highway (pl. 42 .A), but 

not at the highway. The knolled and bouldery belt 

crossed at the jog about 4 miles west of Browning is 

an inner moraine. (See pl. 42 B.) From a point 

about a mile northeast of that where the Browning 

automobile road leaves the old St. Mary road the 

outer moraine extends northeastward along the south 

side of the Cut Bank Creek Valley. It is 2 miles 

wide where crossed by the main road north of Browning and nearly 3 miles wide north of Blackfoot. 

Stebinger observed the following section near the 

bridge north of Browning: 

Section of drift iin m.ora4ne north Uf Browning, Mont·. 

Feet 

Soil -----------------~--------------------------------- 1 

Gray loamy clay (wind-blown?)------------------------ 3 

Gray stony clay, till of Two Medicine Glacier___________ 5 

Nonglacial ( ?) graveL--------------------------------- 4 

Cretaceous sandstone. 

Parts of the moraine north of Blackfoot are very 

rough, in striking contrast with the smooth plain outside. (See pl. 42 0.) The railway and the Roosevelt 

Highway cross the moraine where Willow Creek 98 has 

cut a small postglacial gorge. Beyond this the railway runs eastward along the abandoned valley (Carlow Coulee) cut into Carlow Flat. East of Carlow 

station it runs up onto that flat, and thence east to the 

_gorge west of Cut Bank both the railway and the highway traverse this terrace. This flat bench rises westward· at the rate of 20 to 40 feet to the mile to the 

118 Tliere are numerous Willow Creeks in this region, and to avoid 

contusion in following the descriptions it is necessary to keep in mind 

which one ts meant. 

front of the moraine like an outwash plain. As shown 

above (pp. 47--48), however, this gravelly bench is older than the moraine and was considerably eroded before the T~o Medicine Glacier encroached upon it. 

About 3 miles southwest of Carlow the margin of the 

moraine lobes down into a coulee cut in the flat, and 4 

miles southeast of Carlow Stebinger found the moraine distinctly traceable down the 200-foot north side 

of Flat Coulee and thence more than a mile across the 

broad bottom and up onto the hills on .the south side. 

Clearly Flat Coulee, which is now traversed by the 

Two Medicine Canal, is of pre-Wisconsin age, hence 

Carlow Flat is not an outwash plain. In fact, at no 

place did Stebinger find clear evidence of · outwash 

deposits bordering the moraine of the Two Medicine 

Glacier. 

The presence of drift along Two Medicine Creek 

down to a level100 feet or less above the stream shows 

that the valley had been eroded nearly to its present 

depth before the Wisconsin stage of glaciation-that 

is, to levels 700 or 800 feet below the top of the gravelcapped remnants of No. 1 bench on the south. The 

eastern extremity of the lobe was in T. 31 N., R. 7 W. 

At its nearest poin~ in sec. 1 the ice front was less than 

a mile distant from the west limit of the Keewatin 

ice sheet. The relations of the two drift sheets are 

described on pages 105-106. Stebinger found that the 

ice was just thick enough on the south side to crowd 

onto the edge of the tops of the high bench remnants 

west and east of the Park to Park Highway an::lleave 

there a small but definite drift ridge, in places 30 to 

50 feet high, but the ice did not cross these tops. A 

small lobe crowded into the gap in sec. 36, T. 31 N., 

R. 7 W., but the ice did not reach the top of the, high 

bench remnant east of this sag. 

In the vicinity of Four Horns Lake a lobe 4 miles 

wide extended a few miles through a sag between high 

bench remnants and nearly to Blacktail Creek. Some 

features of the drift of this small lobe seemed to 

Stebinger distinctly older than the drift along a line 

directly southwest of Four Horns Lake. Four miles 

farther south west the ice coalesced with that of a 

glacier in the Birch Creek Valley. 

Glacial drift ,is spread all over the 800 square miles 

covered by the Two Medicine Glacier, but it is not 

known to be very thick anywhere. Rarely are thicknesses of more than 25 feet seen, and exposures of the 

underlying shale and sandstone are numerous. 

.AB INTERLOB.A.TB 0} KOBAIItE 

Branching at right angles from· the outer moraine 

just. east of Willow Creek, in sees. 22 and 23, T. 33 N., 

R. 9 W., a. strongly developed, very rough moraine, 

half a mile to a mile in width, extends southwestward 

in a broad curve to a point on top of the ridge about 

4: miles southeast of Blackfoot. station. Possibly this 
ROCKY MOUNTAIN .. GLA.OlERS OF WISCONSIN STAGE 119 

is really an interlobate moraine developed where the 

ice split over the divide between the valleys of Two 

· Medicine and Willow Creeks. This divide stands 700 

· feet higher than Two Medicine Creek and about 500 

. feet higher than Willow Creek. 

llEOESSIOJJAL KORADJE 

From 15 .to 18 miles west of the eastern limit of the 

Two Medicine glacial drift is an inner moraine marking a stage when the glacier was considerably sn1aller 

than its maximum. This moraine is crossed by the 

Park to Park Highway about 6 miles west of Browning. (See pl. 42 B.) From this place the moraine 

curves and extends eastward, just north of Browning. 

About a mile east of the village it curves again and 

extends southeastward across the Park to Park Highway and the railway and for several miles across the 

hills beyond. About 4 miles southwest of the highway· 

bridge a small but very· distinct moraine, probably 

. part of the same belt, runs up the south side of the 

valley and curves and extends southwestward 7 miles 

or more along the Badger Creek divide, as if marking 

the southeast side of the shrunken Two Medicine Glacier~ ·Branching from this a small moraine extends 

. southward, marking the end of a contemporaneous 

small lobe in the Badger Creek Valley. Here the 

drift is composed principally of limestone from the 

Paleozoic formations south of Marias Pass, but that 

of the Two Medicine Glacier is filled with reddish 

argillite from the mountains· of Glacier Park. Here 

again there is the possibility that these inner moraines may mark the limits of a later Wisconsin readvance of the ice. Morainal deposits in T. 29 N., 

R. 10 W., indicate that at this stage a small separate 

glacier occupied the upper valley of Blacktail Creek 

north of Heart Butte and extended about 4 miles 

onto the plain. 

BmCH CREEK GLACmR 

· T;he distribution of the deposits of the piedmont 

glaciers in Pondera and Teton Counties and the 

northern part of Lewis and Cla:rk County, as mapped 

by Stebinger and Goldman in 1914; is shown on their 

map of the Birch Creek-Sun River region,"9 but the 

phenomena are not described in Stebinger's paper. 

The deposits had been earlier studied and described, 

but not mapped in detail, by Calhoun.1 The deposits 

. north of the Sun River Valley have not been examined 

by the present writer. The descriptions given here 

are based principally on Stebinger's notes and maps. 

The distribution of glacial drift in the Birch Creek 

Valley shows that a glacier about 10 miles· wide ex88 Stebinger, lllugene,. Oil and gas geology of the Btreb Creek-Sun 

River area, northeastern Montana : U. S. Geol Survey Bull. 691, pl. 24 

1918. • 1 Calhoun, F. H. H., op. elt., pp. 14--22. 

tended down the valley about 12 miles from the mountain front to a position 6 miles west of the Park to 

Park Highway north of Dupuyer. 

As in Carlow Flat, west of· Cut Bank, so here an 

extensive gravel-covered bench (north of Dupuyer) 

slopes eastwar<1: from the moraine like an outwash terrace. (See pls. 1 and 29.) . The gravel ·on this flat, 

which is thought to be a remnant of No. 2 bench 

(p. 46), is clearly shown not to be glaeial outwash from the moraine by the fact that the ~mina.l 

moraine extends down the eroded marginal slopes into 

the valleys on both sides of the bench. Evidently the 

gra-vel-covered bench was eroded long before the last 

Birch Creek Glacier advanced on to it.· It appears 

from Stebinger's mapping that the Birch Creek Glacier was really distinct from the' great Two Medicine . 

Glacier and not tributary to it. At the maximum 

stage, however, the ice of the two glaciers appears 

to have coalesced for a _few miles east of Heart Butte. 

Beyond this they were separate. The outer morainal 

ridges are in places 30 to 50 feet high. Within the 

limits indicated there is a large amount of drift ~nd 

numerous hollows, many of them occupied by ponds. 

The morainal drift laps up around the flanks. of Scoffin Butte, a remnant of No. 1 bench 9 miles southwest 

of Dupuyer, in sec.,36, T. 28 N., R. 9 W., 300 feet 

above the creek on the north, but does not overtOp. t,he 

butte by more than 200 feet. In 7 miles the margin 

of the drift descends 700 feet from the upper linlit on 

Scoffin Butte northeastward to the point where it is . 

crossed by Birch Creek. Whether the ice entirely overwhelmed the great mountain wall on the west or 

whether it all issued from the canyon portals cut in the 

·wall has not yet been fully determined. 

Examination of the terraces on Birch Creek within 

the outer moraine led Stebinger to conclude that, of 

three levels, the highest and the second, 50 to 70 feet 

above the stream, were pre-Wisconsin; that the lowest 

probably was formed in connection with the Wisconsin 

glaciation; and that since the ice front retreated the 

stream has cut down 10 to 12 feet and developed a 

flood plain about 1,500 feet ·wide. 

GLACIERS ON DUPUYER A.Nl> MUDDY CREEKS 

The next piedmont glaciers to the south were small 

ones on the North and South Forks of Dupuyer Creek. 

These extended out across the foothills to points about 

4 miles beyond the outer mountain wall of limestone. 

As shown by the moraines, they converged to the low 

tract. between the gravel-capped mesas or bench rem-

. nants in T. 27 N., Rs. 8 and 9 W. Two smaller glaciers 

barely crossed the foot sl~pe to the great alluvial fan 

of Blackleaf and Muddy Creeks, in T. 26 N~ R. 8 W. 

These four glaciers headed but a few miles back of the- · 

front wall of the mountains. Calhoun described th~ 
120 PHYSIOGRAPHY AND GLACIAL GEOLOGY OF EASTERN MONTANA 

moraine on Blackleaf Creek as. a sharp ridge 200 feet 

in height. 

TETON RIVER GLACIER 

Two streams but half a mile apart issue from deep, 

narrow gaps in the mo~tains and, joining a mile or 

two below the mouth of the canyon, form the Teton 

River. The ice apparently entirely filled the north 

and south gorges cut through the Teton anticline 

(pl. 29), east of the mountain wall, being 700 to 800 

feet thick in the north gorge and about 600 feet thick 

in the south gorge, and it extended 4 miles farther east 

on the low flat plain. Of this glacier Calhoun 2 wrote : 

The glacier thus formed, though extending but a few miles 

east ot the mountains, gives evidence of having been very 

powerful and active. The terminal moraine on the north side 

of the river consists of a series of sharp ridges, which form a 

belt over a mile wide. They are so steep and are covered 

with so many limestone boulders that the moraine is difficult 

to cross on horseback. The terminal moraine is covered with 

a growth of stunted pine trees, which are found neither on 

the ground moraine nor on the plain to the east. The north 

and south edges of the ice formed two moraines which extend 

parallel to each other for a distance of 6 miles from the mouth 

of the canyon. They are about 3 miles apart and are well 

developed throughout their entire extent. This development 

of the moraines along the side of the glacier is in sharp contrast to that formed at the end of the ice. 

' A small glacier south of Ear Butte, at the head of 

the South Fork of Willow Creek, scarcely reached the 

plain. 

DEEP CREEK GLACIERS 

Stebinger found moraines extending about 2 miles. 

from the mountain front on both sides of the North 

·and South Forks of Deep Creek, in T. 23 N., R. 8 W., 

showing that two small glaciers reached the plain west 

. of Long Ridge, an outlying gravel-capped mesa (remnant of No. 1 bench), and 500 feet lower thl\njts top .. 

The mountain canyons on these streams are only about 

6 miles long. 

SUN RIVER GLACIER 

OUTER :MORAINE 

The piedmont glacier on the North Fork of the 

Sun River in Lewis and Clark and Teton Counties 

was exceeded in size only by the great Two Medicine 

Glacier. As shown by the moraines mapped by 

Stebinger, the ice filled the canyon "gateway" or 

"portal" {pl. 43) and overrode the top of the lower 

mountain wall (pl. 7 A) as a valley glacier 4 miles 

wide. Passing the foothills it deployed on the gently 

undulating plain until it reached a maximum width of 

about 15. miles, north to south, and a length of 18 

miles, measured southeastward to the point where the 

North Fork of the Sun River cuts through the termi-

~Calhoun, F. H. H., op. cit., p. 17. 

nal moraine ~orth of Gilman. It covered more than 

200 square miles on the plains. On. :the· north ijle ice 

reached the high bench on the ·south side of Deep 

Creek and extended down that valley to a point 14 

miles southwest of Choteau. At 12 miles ·a little 

north of east from the canyon· "portal" the ice encountered the JVedge-shaped west end of the gravelcapped mesa (No.1 bench) and crowded up the steep 

slope 400 feet above the plain to the west. It did not 

overtop the head of. the bench by 100 feet or more. 

From this point the terminal moraines gradually descend along the slope to the northeast and to the 

southeast. In the latter direction the moraine is 

traversed for several miles and finally overtopped. by 

the Sun River Slope Canal. In places,·as shown by 

the position of the moraine (pl. 44 A) the ice just 

overtopped No. 2 bench. · This may be seen north of 

the North Fork of the Sun River and also on the 

ridge between Gilman and the south side of the North 

Fork. The ice was therefore over 200 feet thick at 

these points on the margin. It was about 1,500 feet 

thick at the mouth of the canyon. For 5 or 6 miles 

northward from the vicinity of Augusta and Gilman 

the Park to Park Highway ru.p.s near or along the 

knolled and bouldery terminal moraine. 

In the Sun River Valley north of Gilman and ·in 

the vicinity of Gilman and Augusta a broad gravelly 

flat borders the front of the moraine like an outwash 

terrace. This extends down the valley to the east 

as the No. 3 terrace. No evidence was noted here 

that the gravelly flat is older than the moraine. The 

'stratified gravel beneath the terrace extends westward 

into or under the moraine. 

The outer moraine extends in a broad curve across 

the plain north of Augusta. At and west of the cemetery it lies on a low ridge, then passes about the east 

end of the high bench remnant and lies along its 

north slope. About 6 miles west of Augusta the moraine runs up on to the head of the No.2 bench remnant, crosses it, and recurves sharply eastward in sec. 

17, T. 20 N., R. 7 W.· Evidently for nearly 5 miles 

in the sag west of this high point the ice of the Sun 

River Glacier coalesced with that of the next ,glacier 

to the south. 

INNER :MORAINES 

Branching from the outer moraine on the slopes of 

the high benches north and south of the Sun· River 

are two well-marked and very bouldery inner moraines. These indicate one of two things-either that 

the ice continued tightly crowded against the slopes 

of the high mesas while its front in the valley between 

was melted back about 3 miles;. or that these inner moraines are the ·product of a later Wisconsin read vance 

of the ice against the high mesa slopes, but not so far 

down the valley. The Willow Creek Re~ervoir lies 
U. S. GEOLOGICAL SURVEY PROFESSIONAl, PAPER 174 PLATE 42 

A. VIEW 7 MILES SOUTHWEST OF BROWNING, SHOWING NUMEROUS SMALL LAKES 

B. VIEW 4. MILES WEST OF BROWNING, NEAR .PARK TO PAHK HIGHWAY 

C. VIEW fl MILES NORTHEAST OF BROWNING, ALONG THE CREST 

S howing the frorlt of the mora ine curving oft' to the left in the background . Photograph hy Eugene Stebinger. 

MORAINES OF TWO MEDICINE GLACIER, BLACKFEET INDIAN RESERVATION, 

MONT. 
U. S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 174 PLATE 43 

A. MOUTH OF THE CANYON FROM FOOTHILLS SEVERAL MILES EAST 

Showing the notch cut nearly 1,000 feet deep through the lower limestone wail, probably in interglacial time. 

B. VIEW NORTHEAST TO THE MOUTH OF THE CANYON AND OVER THE TOP OF THE LOWER WALL 

OF LIMESTONE FROM THE INSIDE 

At the \V isconsin stage of glaciation the icc fil led the big notch and overtopped the lime:slouc wall. The Bureau of Reclamation dam is in the gorge at the righL 

SUN RIVER CANYON, MONT. 
U. S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 174 PLA'.rE 44 

A. TERMINAL MORAINE OF SUN RIVER GLACIER 4 MILES NORTH OF GILMAN, MONT. 

View north from Park to Park Highway, showing the moraine extending from the Sun River Valley up onto No. 2 hench in Lhe background. The glacier lay aL the 'left (west). Photograph by Eugene Stebinger. 

B. BLOCKS OF PALEOZOIC LllVIESTONE TRANSPORTED BY SUN RIVER GLACIER, 

ON TilE PLAIN ll MILES EAST OF THE MOUTH OF THE SUN RIVER CANYON 

The blocks arc l 0 hy 13 by 30 feeL. 

C. BLOCKS OF PALEOZOIC LIMESTONE TRANSPORTED BY SUN RIVER GLACIER 

4 MILES NORTHWEST OF AUGUSTA, MONT. 

On moraine 15 miles southeast of the mouth of the Sun River Canyon. The blocks are 15 to 20 feet 

long, 
U. S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 174 PLA'l'}~ 45 

A. GLACIATED CANYON OF BIG TIMBER CREEK 

fl. BOULDERY TERMINAL MORAINI•: OF BIG TIMBER GLACIER, <W WISCONSIN STAGE 

lu foothills 2 miles east of Lhe mounla ius. 

CHAZY MOUNTAINS, MONT. 
U. S. GEOLOGICAL SURVEY PROFESSJONAL PAPER 174 PLATE 46 

A . VIEW LOOKING UP NORTH FORK OF SWAMP CREEK 

The moraine forms a dam 150 feet high completely blocking the valley in the middle background. 

B. TOP OF TilE MORAINE 

Swamp Creek Valley in middle grou nd at left; remnant of No. 1 bench in background. 

VIEWS NEAH. CRAZY MOUNTAINS, MONT. 

Showing terminal moraine of glacier that occupied the valley of South Fork of Dig Timber Creek. 
U. S. GEOLOGICAL SURVEY PROFESSION ~ PAPER li4 PLATE 47 

A. EAST ROSEBUD CANYON, BEARTOOTH MOUNTAINS 

Lateral moraine on edge of No. 2 bench in left foreground. 

B. OLDI>R LATERAL MORA ·~ (ILLINOIAN OR IOWAN~) ON No. 2 BE CII (AT RIGHT) AND 

YOUNGER LATERAL MORAINE (WISCONS IN) DESCENDING TO VALLEY BOTTOM (IN LlWT 

MIDDLE GROUND) 

MORAINES OF EAST ROSEBUD GLACIEH SOUTH OF ROSCOE, MONT. 
u. S . GEOLOGICAL SURVEY PROFESSIONAL PAPER 174 PLATE 48 

A. EAST ROSEBUD LAKE AND MOUNTAINS 

B. ALLUVIAL FAN THAT FOfiMS THE DAM AT TilE FOOT OF EAST HOSEBUD LAKE 

EAST ROSEBUD CANYON, BEARTOOTH MOUNTAINS, MONT. 
U. S. GEOLOGICAL SURVEY l'ROFESSIONAf, .I'AP]!]R 174 PLATE 49 

A . COARSE BOULDI<:RY GRAVEL (PLEISTOCENE) CAPPING A REMNANT OF No. 2 R~~NCH 

NORTHEAST 01' CLARK, WYO., 4 MILES SOUTH OF THE MONTANA-WYOMING STATE LINE 

Beartooth Plateau in background. 

B. TERMINAL MOHAINE OF CLARK FORK GLACIER, OF WISCONSIN STAG~: . AS SEEN FROM 

HIGH BUTTE ON THE NOHTH, 4 MILES WEST OF CLARK, WYO. 

The moraine is in the, right rn.iddlc grou;1d ; the bordering bouldery plain al the left and in the backgruuml. 

VIEWS ON CLARK FORK OF THE YELLOWSTONE RIVER 
U. S. GEOLOGICAL SURVEY PROFESSIONAT" PAPER 174 PLATE 50 

A . FRONT OF TERMINAL MORAINE OF CLARK FORK GLACIER, OF WISCONSIN STAGE, 4 MILES 

WEST OF CLARK, WYO. 

Showing granite boulders 5 to 15 feet in diameter. 

B. BOULDER¥ TOP OF TERMINAl" MORAI NE OF CLARK FORK GLACIER 

Mouth of Clark Fork Canyon in middle background, 2 miles distant; Bald Mountain at left. 

VIEWS ON CLARK FORK OF THE YELLOWSTONE RIVER 
, 

J 

U. S. GEOLOGICAL SURVEY PROFESSIONAL PAPER li4 PLATE 51 

A. COTEAU DU MISSOURI, BURKE COUNTY, N. DAK. 

B. VIEW 20 MILES NORTH OF WHITETAIL, MONT., WEST OF BIG MUDDY LAKE, WILLOWBUNCH 

DISTRICT, SASKATCHEWAN 

TERMINAL MORAINE OF KEEWATIN ICE SHEET, LATER WISCONSIN STAGE 
• 

. . 

ROCKY MOUNTAIN GLAOIEBS OF WISCONSIN STAGE· 121· 

within the inner of these two belts. Similarly- an 

inner moraine incloses the basin of the Pishkun Reservoir and extends thence west to the mountain front 

about 2 miles south of the outer north moraine. Co-

. ordinate with this is a moraine extending northwestward from Willow Creek on the east side of Barr 

, Creek, 1 to 2 miles inside the upper southwestern limit 

of the ice, which is traceable but not marked by a 

definite moraine. 

Inside ·these limits drift composed o:fl mo:unt~n 

rocks is generally present. There are many ponds 

when the season is not too dry. Some of the low 

ridges may be of shale rather than drift. Among the 

many. boulders are some very large ones. One of 

limestone (pl. 44 B) at the cross roads north of the 

North Fork of the Sun River in· sec. 17, T. 22 N., 

R. 7 W., about 7 miles east of the mountains, measures 

30 feet long and 13 feet high. It is split into two 

parts, each about 10 feet thick. Its weight is estimated as about 100 tons. · Two similar blocks 15 to 20 

feet long (pl. 44 0) lie on the slope above the road 3 

miles west of Augusta Cemetery. 

SMITH CREEK GLACIER 

Conditions on the plain west of Augusta and north 

of Haystack Butte show that ice on the headwater 

branches of Willow, Ford, and Smith Creeks combined in one glacier which extended about 10 miles 

out from the mountains. The outer moraine is con-· 

tinuous with that of the Sun :a,iver Glacier on the head 

of the gravel-capped ridge (No. 2 bench) 7 to 8 miles 

west of Augusta. Curving sharply to the east, it runs 

down the south slope of the ridge and extends 3 to 4 

miles down the valley. It crosses the plain in a broad 

curve and may be traced thence southwest along the 

slope north of Haystack Butte. Northeast of the latter butte the ice crowded into Swallow Canyon, and 

here there are several lakelets in basins in the drift. 

Northwest of this butte a great dam of drift blocks 

what appears to have been the preglacial valley o1 

Gap Creek when it was tributary to Smith Creek. 

DEARBORN GLACIER 

A piedmont glacier extended 6 miles or more northeast of the mouth of Dearborn Canyon down what 

appears ·to be the pre-Wisconsin valley of the river. 

This valley, northeast of Bean Lake, is now traversed 

by an irrigation ditch; and that part nef!.r the Park 

to Park Highway is drained by Flat Creek. Several 

moraines cross the valley within 4 or 5 miles northeast of Bean Lake. ·These were not mapped in detail. 

The ice extended nearly 2 miles north of Bean Lake, 

and on the southeast it extended to the ridge east of 

the Dearborn River bridge. Till with striated boulders was exposed in the road cut south of the river 

when seen by the writer in 1921. 

87949--32-9 

CASTLE MOUNTAIN GLACIERS 

For more than 50 miles southeastward from Dear• ., 

born Canyon on an air line to the Castle Mountains no 

glaciers are known to have extended from the mountain gorges out onto the plains, and no evidence ~f 

glaciation has been found in the outlying mountain 

groups. Weed found no evidence of glaciation in the 

Little Belt Mountains unless it be the presence of two 

cirquelike amphitheaters on the southeast side of Big 

Baldy Mountain, 8 miles east of Neihart, at 8,000 to 

9,000 feet above sea level. 

In the Castle Mountains (pl. 1), the highest point 

of which, Elk Peak, rises to 8,606 feet above sea level, 

in the southern half of Meagll:er County, there were 

glaciers at the Wisconsin stage of glaciation. The 

possibility that some of the bouldery drift on the 

ridges bordering Alabaugh Creek on the south side 

of the .mountains west of Lennep was deposited at ~, 

earlier stage of glaciation is discussed on page 40. 

A later terminal moraine described by Weed as 

blocking the valley north of Castle probably marks 

· the limit of the glacier at the Wisconsin stage. It has 

not been examined ·by the present writer. A brief 

examination of the Fourmile Creek Valley, on the 

north side. of the mountains, 8 miles east of White 

Sulphur Springs, was made in August, 1921, and 

bouldery morainal deposits were found at and above 

the ranger station, about 3 miles up the gorge from 

the main road. Weed describes a moraine farther· 

up the valley as belonging to the "retreating phase"· 

of the glacier. It is quite possible that some of the 

drift on the interstream ridges on the flanks of the 

mountains, like that on Alabaugh Creek, is really preWisconsin. · 

CRAZY MOUNTAIN GLACIERS 

Evidences of glaciation in the Crazy Mountains 

were described by W olff,3 by Iddings and Weed,' and 

later. by Mansfield. 5 The relations of the terminal moraines of several of the glaciers were examined by the 

present writer in the course of brief recoiUUtissanees 

about the margins of the mountains, in 1921 and 1922~''" 

These mountains are extremely rugged, with very 

steep slopes and numerous pyramidal peaks rising 

high above timber line and culminating in . Crazy 

Peak, 11,178 feet above se11 level. There is a whole 

row of glacial cirques high on the north slope of the 

north group of the mountains, but glaciers from these 

appear not to have reached low levels. Several of the 

other glaciers extended far enough out of the mountain 

gorges to show their · relations to remnants of the 

a WoUf. J. E., The geology of the Crazy Mountains, Mont.,: GeoL Soc. 

America Bull., vol. 3, p. 446, 1892. 

· 'Iddings, J. P., and Weed, W. H., U. S .. Geol. Survey Geol .. Atlas, 

Livingston folio (No. 1), pp. 1-2, 3, 1894. Weed, W. H., idem, Little 

Belt Mountains folio (No. 56), pp. 6, ·1, 1899. 11 Mansfield, G. R., Glaciation in the Crazy Mountains of Montana : 

Geol. Soc. America Bull., vol. 19, pp, 5ti8-56_7, 1907. 
• 

122 PHYSIOGRAPHY AND GLACIAL GEOLOGY OF EASTERN MONTANA 

benches described above (pp. 24, 51). Drift mapped 

by Weed on upper Bi~ Elk Creek, which was deposited by ice heading in the eastward-facing chambered 

a1nphitheater formed by the flanks of Cinnamon, Loco, 

and Lebo Peaks, was not examined by the writer. 

The Sweetgrass Canyon was occupied by a glacier 

which had a length of 16 to 18 miles. The thickness 

of this glacier was so great (700 to 1,000 feet) where 

it issued from the mountain gorge that it overtopped 

the high ridge on the east and laid a lateral moraine 

along its crest. A few miles farther north it entirely 

overrode the lower end of this ridge and spread eastward onto the plain below. Not far north of the pond 

on the rock ridge the main ridge of the moraine loops 

across a· ravine and ther'e is a smaller drift ridge outside; east of this there is no drift on the rock spur. 

To the north the ravine bifurcating the rock ridge becomes a U-shaped trough, down which the ice moved 

and from which it spread out to the east. The lateral 

moraine curves sharply to the east and extends down 

the bluff to the plain below. 

On this plain is a broad tract which is marked by 

bouldery knolls and basins extending eastward to the 

road' on the gravel terrace at about 5,600 feet above 

sea level. The main stream of ice extended down the 

valley, about the north end of the rock ridge, and also 

spread over the upland to the north. Weed's map 

shows drift extending northward to American Fork. 

Cuts for an irrigation ditch and for the road on the 

face of the south side of the gorge near the bridge expose 75 feet of coarse bouldery material. The upper 

10 feet, at least, of this is glacial till. The material 

below is more waterworn and contains less fine material but is not well bedded. To the north of Porcupine Butte can be seen the abrupt west end of a remnant of No. 1 bench. Similar high remnants are in 

view off to the south. Since the melting of the glacier 

Sweetgrass Creek has cut a gorge about 100 feet deep 

west of Porcupine Butte, but this depth of cutting 

does not extend far up the valley. Part of the valley 

bottom is flat and marshy. 

About 4 miles above the boundary of the Absaroka 

National Forest the wooded canyon is narrowed by 

projecting rock spurs, and the stream plunges over a 

great ledge of porphyry down into a small box canyon, forming a series of beJI.utiful cascades in a tortuous channel marked by great potholes. The rock 

ledges along the trail above the sides of the box 

canyon are smoothed, scratched, and grooved as the 

result of the glacial action. At one point the trail 

follows a large glacial groove for several yards. The 

box canyon is postglacial. Glacially scratched ledges 

were seen more than 1,000 feet above the forks of the 

creek on the north side of the canyon. The heads of 

the gorges are scalloped by many high-level cirques. 

The valley of Big Timber Cneek (pl. 45 A) is obstructed about 2 miles east of the national :forest 

boundary in the foothills by a great deposit of morainal drift, thickly strewn with large boulders (pl .. 

45 B), many ·of which are 10 or 15 feet in diameter. 

About a mile farther west similar blocks of porphyry 

15 to 30 feet long appear to have slid down from the 

hill at the north. About a mile inside the nationa,l 

forest boundary the ice completely filled the trough 

and laid its south lateral moraine on top of the narrow-crested ridge on th~ south. This crest rises west-

-ward to the flank of Crazy Peak. In the adjacent 

part of the gorge the ice was 700 to 1,000 feet or more· 

thick. All the foothills up to nearly 7,000 feet abov-e 

sea level were probably overtopped by No. 1 bench, S() 

that there was probably nearly 1,000 feet of valley 

deepening at the mountain front below No. 1 bench 

before the Wisconsin glaciers advanced. 

The valley of the middle fork of Big Timber Creek 

was not examined by the writer. The canyon of the ' 

south fork is anomalous, in that it appears to have· 

. been tributary to Swamp Creek prior to the Wisconsin 

stage of glaciation. The Swamp Creek Valley is 

bordered by finely preserved remnants of both No. 1 

and No. 2 benches. The north branch of the north 

fork of Swamp Creek is cut across the heads of thesebenches and 200 to 500 feet below their smooth tops 

and separates them from the foot slope of the· mountains. On going up this branch valley the writer 

found it completely blocked, just inside the national 

forest boundary, by a great morainal dam (pl. 46) 100 

feet in height. The relations show clearly that a 

glacier in the canyon of the south fork of Big Timber 

Creek crowded into this branch of the Swamp Creek 

V a,lley and deposited the morainal drift dam. Inasmuch as the valley of the south fork of Big Timber 

Creek was seen by the writer only from a distance, 

it can not be asserted positively that the canyon formerly drained to Swamp Creek, though this is 

suggested by what was seen of the relations, which 

are not accurately shown on the Livingston topographic map. The stream now flows eastward through 

a sharp postglacial cut 600 to 800 feet below the level 

of the top of No. 1 bench (Raspberry Butte). 

The canyon on the south fork of Swamp Creek was 

occupied by a glacier about 5 miles in length, which 

headed north of Fairview Peak and extended a short. 

distance beyond the national-forest boundary and 

made a moraine there. The ice was so thick that it 

overtopped the big ridge on the south and laid a. 

bouldery lateral moraine along its crest. 

A glacier heading in high-level cirques on the westerly flanks of Iddings Peak extended sou.thward and 

curved to the southwest in the trough between the high 

remnants of No.1 bench, ending near one of the south-
ROCKY MOUNTAIN GLACIERS QF WISCONSIN STAGE 

west corners of the national forest, about 6,000 ·feet 

above sea level. 

Mansfield refers to a glacier having occupied the 

Pine Creek Canyon, in the western part of the mountains. Apparently it did not extend far outside the 

national-forest boundary, as no moraine was seen by 

the present writer in a trip along the valley below 

the big bench (No.2) on the north. 

Glacial ice heading west of Sunlight Peak extended 

northward a few miles down tributaries of the Shields 

River. The Inost westerly part of this ice was so thick 

as to overtop the long ridge on the west and Ia y its 

bouldery lateral moraine along lhe crest of the ridge, 

but not to overflow to the west. This ridge is probably a remnant of No. 1 bench. 

It is clear that the outer moraines of all these glaciers in the Crazy Mountains were formed after the 

valleys had been cut nearly to their present depths, 

hundreds of feet below No. 1 and No. 2 benches. The 

third bench was not found developed in such places 

as to show clearly its relations to the glacial moraines. 

YELLOWSTONE GLA.CmR 

Evi,lences of glaciation in the Yellowstone Valley 

and in the Boulder River canyons north of the national park were described by Weed.6 Brief examinations were also made by the present writer in 1921, 

1922, and 1923. A great glacier heading in and adjacent to Yellowstone National Park extended down the 

river valley to the vicinity of Chicory station and the 

mouth of Mill Creek. The bouldery terminal moraine 

is crossed by the automobile road on the west side of 

the valley at a point about 18 miles from Livingston 

and 5,100 feet above sea level. The moraine is in distinct contrast with the smooth gravel plain in front, 

but it is not a high or bulky ridge. It appears to be 

laid down on a great alluvial gravel fan heading to 

the west on Eightmile Creek. This may be No. 3 

bench, and not an outwash terrace. The hummockv 

moraine is strewn with boulders as :thuch as 15 feet i~ 

diameter. After the recession of the ice front the 

creek cut back through the moraine northeast of Chicory station. The moraine can scarcely be seen from 

the railway, down in the inner valley which the river 

has cut about 20(;) feet deep through the moraine and 

underlying terrace. About a mile south of Chicory 

station an in.ner moraine appears to extend down over 

the eroded edge of the bench and to have originally 

extended across the bottom of the inner valley to and 

up the eroded edge. of the bench on the east side. 

The automobile road on the east side of the valley 

runs partly on and partly below No. 3 bench. About 

23 miles from Livingston on this side the terminal 

8 Weed, W. H., The glaciation of the Yellowstone Valley north of 

the park : U. S. Geol. Survey Bull. 104, 1893 ; U. S. Geol. Survey Geol. 

Atlas, Livingston folio (No. 1), 1894. 

moraine is found on No. 3 bench between Elbow,.._. 

:Mill Creeks. The boulder-strewn humps and hollo\vs 

extend in a belt half a mile wide southward from the 

eroded edge of the terrace to the foot of the mountain 

slope. Apparently a glacier heading in the Mill Creek 

Valley here joined the Yellowstone Glacier. From 2 

to 3 miles west of Mill Creek the very· bouldery inner 

terminal moraine . extends southward across the :flat 

terrace to the mountain front. Near the Hot Springs 

Hotel and the old village of Chico the road ~rts the 

east side of the moraine. Just west of Chico Emigrant Creek cuts through the big moraine. TMnce 

southwestward the moraine extends for seve:ral miles 

up the valley at the foot of the mountain slope to the 

vicinity of Duck Lake. Beyond this point it was· not 

examined by the writer. 

Glaciers extended down several of the gorges which 

cut the west flank of the Absaroka Range from Liv .. 

ingston Peak and Mount Delano to Mount Cowen, 

north of Mill Creek. Not all these gorges have been 

examined by the present writer. On the north fork 

of Deep Creek the terminal moraine is at 5,500 to 

5~'700 feet above sea level, at the head of a smooth 

bouldery terrace about a quarter of a mile below the 

national forest boundary. 

The relations of the several moraines and terraces 

require further study for their clear interpretation .. 

but, so far as seen, there seems to be evidence of two 

advances, either an earlier and a later phase of the 

Wisconsin glaciation, or the earlier one is of Iowan 

or Illinoian age and a correlative of Blackwelder'$ 

" Bull Lake stage " of glaciation in ·the Wind River 

Basin, Wyo. . 

Between Pool and Pine Creeks is a steep narrowcrested spur about '700 feet high extending out from 

the foot of the mountain. This appears to be a great 

lateral moraine, or else it is a ridge capped by boul• 

defy drift. The ridge lowers rapidly to the west 

and is separated from a similar ridge on the opposite 

(south) side by a narrow gorge cut 200 to 300 feet deep 

in gray bouldery till. Outside this and somewhat to 

the south an outer moraine extends nearly to the road,. 

and from this moraine a very bouldery ·dry channel 

extends to the river. 

The inner moraine of the Yello-wstone Glacier appears to extend down over the eroded edges of the big 

terrace and across the inner valley bottom· just· south 

of Chicory. Nothing was noted below the mouth of 

Mill Creek, near Pray station, however,· which could 

be regarded as indicating clearly that the outer mo ... 

raine is younger than the main big terrace. If it 

ever extended down into the inner valley it was later 

cut away in forming the lower terrace levels, so that 

no trace remains. The big terrace is, however, equally 

well developed and preserved inside both ·the outer 

and the inner moraines, giving rise to the suggestion 
124 PHYSIOGRAPHY AND GLAC~ GEOLOGY OF EASTERN MONTANA 

that it is older even than the outer moraine, just as 

Carlow Flat, in the Blackfeet Indian Reservation, is 

·older than the outer moraine of the Two Medicine 

Glacier, whose front it borders. The relation of the 

.gravel to the basalt farther up the valley is discussed 

on page 62. If the gravel of the terrace is really the 

·same as that overlain by the basalt at and above Emigrant, it is evident that the terrace is older than the 

outer moraine, which was laid down upon it, like the 

inner moraine. 

BOULDER RIVER GLACIERS 

The relations of morainal and other deposits on the 

bottums of the three branches of the Boulder River 

Valley show that these valleys and that of the trunk 

stream had about the same depths and other dimensions prior to the Wisconsin stage of glaciation as 

-now. No. 3 terrace is well preserved for 5 or 6 miles 

above the Big Timber bridge, and below the third terrace is a fourth 10 to 20 feet above the flood plain. It 

seems probable, though it was not certainly determined, that this fourth terrace was formed at the Wisconsin stage of glaciation. It is about 250 feet below 

the level of No. 2 bench and 500 to 600 feet below that 

of No. 1 bench. Farther up the valley the third and 

fourth terraces appear to merge; at least they have not 

been differentiated. This lower terrace and the bed of 

the stream are notably bouldery, there being many 

well-rounded boulders 1 to 3 feet in diameter near the 

Big Timber bridge, and about 12 miles up the valley, 

near the bridge below McLeod,7 3 to 4 foot boulders 

of a great variety of igneous rocks are numerous 

along the road. Just above the McLeod bridge a 

great bouldery moraine half to three•quarters of a 

mile wide lies in the mouth of. the West Boulder 

Valley. The road crosses this moraine at 4,800 to 

4,900 feet above· sea level to the less-filled valley above. 

This moraine marks the limit of the West Boulder 

Glacier. About 4 or 5 miles farther up the valley is 

another more extensive and very bouldery moraine on 

the broad valley bottom and extending west of the 

river for about 1% miles up into the recess in the slope 

that is traversed by the Livingston road. There are 

many big crystalline boulders here, some 20 to 30 feet 

in ~aximum diameter. For several miles south of the 

bridge the ice was so thick ( 500 to 600 feet) that it 

overtopped the bluffs and, on the east side, laid a great 

lateral moraine along a bench a mile in width which 

borders the higher driftless part of the ridge north of 

the Absaroka National Forest boundary. 

·The main Boulder Glacier appears to have not quite 

reached a junction with that on the West Boulder 

'l McLeod post office in 1921 was at the junction of the Boulder and 

West Boulder Rivers, not at . the poitit indicated on the Livingston 

topographic map. · 

River. The moraine, as seen from the road, is less 

than a mile above the confluence of the streams. It is 

. possible that at some stage the ice entirely overtopped 

the sag in the crest of the big ridge a few miles farther 

southwest. In this main valley there is an inner moraine just north of the belt of red shale near the national-forest boundary. ·The valleys of the -East 

Boulder River and Elk Creek combine into. a broad 

basin, in which there is an extensive deposit of glacial 

drift, 50 to 60 feet being exposed in the stream banks 

in places. This drift appears to have been deposited 

by a glacier heading in the East Boulder Canyon, 

though the canyon portal is narrow and rather sharply 

V -shaped where cut through the upturned Paleozoic 

limestone at the national-forest boundary~ 

The scenery at the portals of the Boulder Canyons 

is most impressive. Weed 8 gives the following description of the main canyon: 

The principal stream draining this alpine area is the 

Boulder River. Heading in the - many lakelets which He 

nestled in the mountain basins about Haystack . Peak, the 

stream :flows rapidly through a narrow gorge which it has 

cut through the granites in past glacial times to the point 

where its volume is augmented by a considerable stream 

called Bridge Creek. From here northward it :flows in a 

boulder-choked channel through the great canyon of the 

Boulder, whose glistening walls of polished gneiss rise 3,0oo 

· feet high on either side. For the last few miles of its course 

through this impressive gorge the str~am meanders .somewhat 

slowly through a network of channels bordered ·by dense 

growths of spruce and fir, with thickets of brushwood, 

then quietly glides through boggy meadows past the cottonwood-covered islands at the gate of the mountains. Immediately above the Natural Bridge the stream :flows in a lime-. 

stone bed, in which it soon cuts a rapidly deepening gorge as it 

:flows northward in a series of ·rapids and cascades to disappear in a snowy-white feathery fall of 25 feet into the 

tunnel of which the Natural Bridge forms the portal. Emerging a hundred yards to the north and 100 feet below, the 

stream falls into a tranquil pool at the head of a gorge that 

is a mile or so long and has limestone walls 100 feet high. 

The roof of the first short tunnel is a, dry river bed, the :floor 

of a gorge that is a cont!nuation of the picturesque cutting 

above the Natural Bridge. The numeri>US potholes and waterworn ledges show that the river must flow over this channel 

in time of :flood, to fall over a vertical wall into the pool 100 

feet below. The beautiful canyon cut in a low limestone anticlinal north of this is, however, immediately deserted by the 

river, which at once enters a tunnel in the western wall, only 

to emerge at the northern end of the canyon. That this gorge 

is occasionally occupied by the· river is attested by the driftwood and gravel in its bottom; but the great slopes of talus, 

where firs 60 feet high are growing, show that such occupancy 

is but temporary. 

The peaks about the head of ;Elk Creek, as seen· 

from a distance, do not appear to have supported 

glaciers. 

s Weed, W. H., The glaciation of the Yellowstone Valley north of 

the park : U. S. Geol. Survey Bull. 104, p. 35, 1893. · 
/ 

I 

. BOOKY KOUN'TAIN GLACIERS OF WISCONSIN' ft.AGB 

STILLW:ATBR GLACIER 

Calvert 9 mapped areas covered by glacial drift on 

the Stillwater River and southeastward along the 

border of the plains to the vicinity of Luther, Carbon County, but he gave no description of the relation of the deposits. Some of these were seen by the 

present writer in 1921, 1922, and 1924. 

A glacier more than 30 miles long occupied the 

Still~ater Canyon. It extended down the valley to 

a point near the coal mines about 2¥2 miles above Beehive, in T. 4 N., R. 16 E., at. 5,000 feet above sea level 

and occupied the basin inclosed by bluffs on the north 

and east. The moraine, which is marked by very 

bouldery ·knolls, extends nearly 3 miles up the Little 

Roc~ Creek,V alley, southeast of N ye. The bouldery 

m~raine also extends 1 to 2 miles west of the N ye 

bridge. Between 4 and 5 miles above this bridge a 

great ledge otf upturned gray limestone, plunging 

down to the west, extends two-thirds the distance 

across the canyon from the north side, constricting 

the floor, and about a mile farther upstream an enormous ledge of .igneous rock projects nearly across the 

canyon floor. These ledges may be remnants of an 

earlier stage of the canyon cutting, but they were 

P.robably entirely ·overridden by the Wisconsin glaCiers. A very stony terrace, with many 3 to 5 foot 

boulders, extends at least 15 miles down the steepwalled valley below Beehive. It is there about 300 

feet- lower than No. 2 bench at the top of the south 

bluff. It is not clear whether this is glacial outwash 

(a, valley train) or a remnant of No. 3 terrace. Apparently the valley was cut within 100 feet of its 

present depth before the Wisconsin glacier advanced. 

Moraines of glaciers that occupied gorges at the heads 

of Fishtail and Fiddler Creeks have not been examined by the writer. 

WEST ROSEBUD GLACIER 

· The great glacier that occupied the West Rosebud 

Canyon extended about 5 miles down the valley beyond the mountain front, to a point about 2 miles 

south of the main road. The ice overtopped the high 

gravelly No. 2 bench on the east and laid upon it a 

strongly marked lateral moraine. In the last mile the 

moraine descends the eroded edge of the bench to the 

valley bottom, about 250 feet below. Two distinct and 

parallel lateral moraines lie along the great ridge on 

the west side of the valley, the outer one 100 to ·150 

feet above the inner one. On these moraines, as high 

as 300 to 400 feet above the stream, are many granitic 

. boulders l to 15 feet in diameter. High in the west 

face of the ridge at the east side of the valley is a big 

scarp which, as seen from a distance with field glasses, 

apl?~ars to expose coarse stratified bouldery gravel 

9 Calvert, W. R., Geology of the Upper Stillwater Basin, Stillwater 

&lld Carbon Counties, Mont. : U. S. Geol. Survey Bull. 641, pl. 21, 1916. 

with an oxidized. brownish zone at the top, overltlia 

by the east lateral moraine. · · . ·, . ; 

EAST ROSEBUD GUCD!IB 

A similar glacier occupying the East ~bud Canyon extended northward 3¥2 miles . between the .high 

bench remnants beyond the .mountain front and laid a 

very bouldery terminal moraine across the vall,y 

bottom about 2 miles south of Roscoe and 5,400· feet 

above sea level. Late:ral moraines extend southwestward up the valley on both sides. That on the ~ast 

gradually climbs the slope, forming a spur between 

which and the main slope is a small coulee. In about 

a mile the moraine reaches the top of No. 2 bench, 

300 feet or more above the main valley bottom. 

ThenC6 southwestward to the mountain front it lies 

on the edge of the bench above the steep ·wooded 

slope 400 to 500 feet high. (See pl. 47 .A.) This moraine was evidently formed at the Wisconsin stage of 

glaciation.• Nearly parallel to this and separated :from 

it by the coulee noted above is an outer and older moraine (pl. 47 B) extending northeastward on top of 

No. 2 bench to and about a quarter of a mile beyond 

the road leading to Luther, where it ends on the 

smooth flat top of No. 2 bench about 250 feet above 

the creek. There is no indication, so far as noted, that 

this moraine ever extended down off the bench into the 

valley. This outer moraine carries many granitic 

boulders, some of them 10 to 20 :feet in length, but 

its surface has a more smoothed-down appearance . ' . ' being not nearly so rough and stony as that o:f the 

inner moraine. There is a similar outer lateral on 

the west side of the valley, but no terminal connects 

the eroded ends. These relations suggest, if they do 

not prove, that an earlier (pre-Wisconsin) glacier 

occupied the East Rosebud Canyon and extended out 

onto the No. 2 piedmont terrace before the valley 

was cut much if any below its original top. The 

relations of the outer moraine are similar to those of 

the moraines of Blackwelder's " Bull. Lake stage " of 

glaciation in the Wind River Basin, Wyo. : ·. 

Both East Rosebud and yv est Rosebud Canyo:ps are 

profound gorges 3,000 to· 4,000 feet or more in depth. 

In these are numerous beautiful lakes. East Rosebud 

Lake appears to be due to damming of the valley by a 

great alluvial fan formed, after the melting of the 

glacier, by wash from a gorge that breaches the east 

wall of the canyon. (See pl. 48.) High in the moun~ . 

tains at the head of the West Rosebud Canyon; north 

of Cooke, are Grasshopper Glacier and several Qther 

small existing glaciers . 

ROCK CREEK GLACIERS 

It is evident from the absence of a terminal moraine outside and from the presence of the ragged 

edge and pinnacle on the. upturned, rieady vertical 
~~.-~ .. ~. 

126 PHYSIOGRAPHY AND GLACIAL GEOLOGY OF ;EASTERN MONTANA 

ledge of liinestone known as Poin~ of Rocks, at the 

mouth of the Rock Creek Canyon, 3 miles above Red 

Lodge, that no glacier has extended through this portal since the dissection of No. 2·bench. This gravelly 

bench is beveled across the limestone ledge and extends 

through the portal at a height fully 300 feet above 

the valley bottom. Ther.e are many large boulders 

in the lower part of the West Fork Valley and also 

in the canyon of the main Rock Creek, where great 

boulder fans lie at the mouths of the gulches. The 

first suggestion of a terminal moraine was found 

2 or 3 miles above the canyon mouth, where there are 

Yery bouldery swells about 6,300 feet above sea level 

but no definite ridge. The profile of the gorge as seen 

looking upstream from a point near the ranger station 

certainly suggests modification by a glacier. In the 

angle between the main stream and Lake Fork above· 

Riebel Lodge and the State fish hatchery, about 13 

miles above Red Lodge, is a big bouldery moraine 150 

to 200 feet high, about 6,700 to 6,900 fee! above sea 

level. If not the outer moraine, this is an inner one 

iormed by the junction of two converging glaciers, 

12 to 15 miles long, in the branches of the canyon. 

CLARK FORK GLACIERS, WYOMING 

Dake 10 states that " the valleys of Line Creek and 

::Bennett Creek, Wyo., near where they emerge from 

their canyons in the granite onto the plains of the 

Big Horn River, are occupied by well-marked Inoraines." About a mile above A. A. Trumbull's ranch 

-on Little Rock Creek· is a morainal loop marking the 

limits of a glacier that extended a short distance outside the canyon mouth. Boulders are so plentiful on 

t.he foothills just north of this locality as to suggest 

the possibility of an older and higher level glaciation. 

A great glacier nearly 50 miles in length headed in 

the mountains north of Cooke, Mont., extended 

thence down the upper Clark Fork Valley (pl. 13 0) 

and the box canyon cut .in its bottom (pl. 25 .A) , and 

protruded 1 to 2 miles beyond the canyon mouth. 

About a mile directly east of the portal is a segment 

of a hogback ridge of upturned Wasatch conglomerate 

about 1,000 feet in height, one of several forming a 

north -south strike ridge bordering the mountain front. 

On emerging from its canyon Clark Fork swings to 

the -southeast and flows through a gap south of this 

hogback segment. ·A similar gap traversed by the 

road at the north end may have been occupied by the 

stream at an earlier stage. This gap is now blocked 

by a great bouldery moraine. Emerging frmn the canyon mouth the glacier advanced until it reached the 

foot of the hogback and squeezed into the gaps on the 

north and south. In front of the north-gap ~oraine 

10 Dake, C. L., Glacial features on the south side of Beartooth 

Plateau, Wyo. : Jour. Geology, vol. 27, p. 128, 1919. 

is a flat gravelly plain abundantly strewn with large 

granite boulders (pl. 49 B), the derivation oi which 

is . discussed on page 41. From this flat plain thefront of the remarkably fine moraine rises abruptly 

about 60 feet. The slopes and ·broad uneven top 

(:pl. 50) are strewn with granite boulders, many of 

them 5 to 15 feet in diameter. This morain~ is at 

least 1,000 feet below what was probably the grade of 

No. 1 bench, or Flaxville Plain, and at least 500 feet 

below the grade of No. 2 bench. The flat bouldery 

plain in front of the moraine is probably not' a glacial 

outwash terrace but No. 3 bench and somewhat older 

than the moraine. It is certain that the glacier of the 

Wisconsin stage did not advance and deposit this moraine until the box canyon had been cut 1,000 to 1,300 

feet into the granitic rocks that underlie the broad 

bottom of the upper valley. (See pp. 26-27.) 

Dake describes moraines on tributaries of upper 

Clark Fork 10 to 12 miles southwest of the canyon 

mouth, which seem to him to indicate that ice of the 

Clark Fork Glacier crossed the main canyon and .advanced southward and southwestward several miles up 

the tributaries Sunlight, Elk, and Dead Indian Creeks. 

The presence of granitic boulders on these moraines 

several miles south of the exposed pre-Cambrian crystalline rocks was regarded as evidence that the ice 

moved up rather than down the valleys in which they 

lie. The present writer has not seen these moraines; 

he has observed striations on the granite ledges nea-r 

and above the north brink of the box canyon at points 

nearly opposite the mouth of Sunlight Creek. These 

striae trend parallel to and not southward across the 

canyon of the main stream. 

BIG HORN MOUNTAIN GLACmBS, WYOMING 

In the Big Horn Mountains, Wyo., none of the glaciers of the Wisconsin stage, of which there were 17 

large ones heading in 70 different cirques on the high 

central peaks, extended as far as the canyon mouths or 

reached the plains. The deposits left by these glaciers 

are described by Salisbury and his assistants.11 

LATER WISCONSIN STAGE OF KEEWATIN' ICE SHEET . 

ALTAMONT MORAINE IN N~RTH DAKOTA 

The Altamont moraine of Chamberlin and Upham,12 

which has been regarded as the outermost of the moraines of the Wisconsin stage of the Keewatin ice 

sheet in the Dakotas, has been traced northward along 

n Darton, N. H., Geology of the Big Horn M<luntains : U. S. Geol. 

Survey Prof. Paper 51, pp. 71-91, 1906 (Quaternary system, by R. D. 

Salisbury and assistants). Darton, N. H., and Salisbury, R. D., U. S. 

Geol. Survey Geol. Atlas, Bald Mountain-Dayton folio (No. 141), pp. 

9-10, l906; Cloud Peak-Fort McKinney folio (No. 142), pp. 9-12, 

. 1906. 

u Chamberlin, T. C., Preliminary paper on the terminal moraine of 

the second glacial epoch :. U. S. Geol. Survey Third Ann. Rept., p. 388, 

1883. Upham, Warren, The glacial Lake .Agassis: U. S. Geol. Su"ey 

Mon. 25, p. 139, 1896. 

\' 

\ 
\ 

LATER WISCONSIN STAGE OF KEEWATIN ICE S:S:EET 

the Missouri Plateau by · Todd, Chamberlin, and 

others 13 to and across the international boundary near 

the northwest corner of North Dakota. In 1875 the 

drift deposits piled along the face and top of the 

.coteau· were examined by Da wson.14 Though recogllizing these deposits as composed of drift, Dawson 

did not regard them as forming a terminal moraine 

9f the continental glacier. 

·" Wood 15 gives some description of the drift deposits 

· in an area including what are now Burke, Mountrail, 

Ben ville, and Ward Counties and part of McLean 

County. The plain of the Souris River east of the 

.coteau in this area ranges in altitude from 1,540 to 

1.,958 feet. From this the surface rises gradually 

westward to about 2,250 feet. Wood states that a 

line drawn from Surrey, on the Great Northern Railway in the eastern part of Ward County, to the prairie 

level at Stanley, on the Coteau du Missouri, rises from 

1,635 to 2,225 feet, or 618 feet. West of Des Lacs 

there is a rise of 361 feet in 24 miles. The ascent to 

the hills is in general more abrupt both to the ~orth 

and to the south than along the Great Northern Railway. . The Altamont moraine, which lies along the 

eastern edge of the plateau in this area, is stated by 

Wood to range from 15 to 25 miles in width, between 

limits which have not been very sharply defined. He 

describes the topography as follows: 

No extended observations have ever been made, so far as 

can be learned, upon the moraine belt of the county. It is generally known as an exceedingly rough area, consisting of 

lmoblike hills interspersed with many sloughs and small lakes. 

The eastern boundary of the moraine is well marked, as it 

can be seen 15 miles away, appearing not unlike a great river 

blu:tr, except that its upper edge had a more serrate outline. 

The western limit is much more difiicult to assign, because it 

gradually shades o:ff into the plateau beyond it. Some of the 

hills are veneered buttes without doubt, but the majority of 

them, as appears from the railroad cuts, consist of till from 

bottom to top. The till is not unlike that of the g!round moraine, though the per cent of gravel and assorted material is 

greater in the hills. The varied topographic forms of the 

terminal moraine are due to deposition, only slightly modified by erosion. Postglacial erosion, mainly in the. coulees 

along the eastern slopes, has drained but few of the multitudes of sloughs. 

The roughness of the hills is almost equal to that of the 

badlands, but the nature of the relief is entirely difrerent. 

Badland topography is due to erosion ; this to deposition. 

The badlands are characterized by few undrained areas. In 

u Chamberlin, T. C., op. cit., p. 398. Willard, D. E., and Erickson, 

M. B., ·A survey of the coteaus of the Missouri : North Dakota Agr. 

Coli. Survey Second Bienn. Rept., pp. 17-27, pl. 3, 1904. Wilder, 

F. A., Lignite on the Missouri, Heart, and Cannonball Rivers and its 

relation to irrigation : North Dakota Geol. Survey Third Bienn. Rept., 

pp. 34-85, 1904. 

u Dawson, G. M., Report on the geology and resources of the region 

in the vicinity of the 49th parallel, 387 pp., Montre.al, British North 

American Boundary Commission, 1875 ; On the superficial geology of 

the central region of North America : Geol. Soc. London Quart. Jour., 

VOl. 31, p. 614, 1875. 

u Wood, L. H., Preliminaey report on Ward County and adjacent 

territory with special reference to the lignite : North Dakota Geol. 

Survey Second Bienn. Rept., p. 84, 1902. 

this belt the slope of one bill so blends with that of otbera 

about it that sloughs, potholes, and lakes are inevitable.- ;; J.s one traverses the area he may pass for miles th'rough a ~ 

tion where all the hills have about the same height, ~' 

and regularity of arrangement, and then comes suddenly uPon. a broad amphitheaterlike depression Slll"i"ounded by a wan Qf 

hills, from which there seems to be no exit to the area beyond. 

Sloughs 100 feet below the average level -are not uncommon, 

and small ones are so numerous that a dozen may be counted 

from a single hilltop in some parts of the belt. Many of the 

shallow sloughs are valuable grasslands, sought out by the 

ranchers, who come several miles to cut the rich marsh grass 

that grows along their margins. 1 

This morainal belt was crossed by the, present writer 

once in western Burke County, near the west limit of 

the area described by Wood, and in five different 

places in Divide County. On these traverses are 

based the limits shown on Plate 1. 

South of Larson, in _western Burke Cou:p.ty, there is 

a relief of nearly 400 feet (barometric) between the 

higher parts of the moraine and the nearly flat plain 

traversed by the Soo Lin~ ·and the Great Northern 

Railway at Larson. The north slope of the coteau, 

which here trends in a direction somewhat north of 

west, is considerably cut by ravines, and from its crest 

there is a very extensive view to the. north and east 

over the broad plain of the Souris River. The higher 

parts of the moraine in Ts. 160 and 161 N. are very 

rough. The abrupt oouldery knolls and numerous 

ponds and marshy depressions make crossing with an 

automobile difficult where there is not a well-graded 

road. (See pl. 51 .A.) The roughness of the moraine 

also decreases southward from its maximum to the sag 

traversed by the Grenora branch of ~he Great Northern Railway from McGregor westward. 

The coteau escarpment lowers somewhat toward the 

west, in R. 96 W., and gives place in R. 97 W. to a 

broad reentrant in which lies the smooth basin south 

of Crosby. The morainal features gradually decrease 

in roughness from the center of the moraine northward, passing into sl;ght sags and gentle undulations 

near the crest of the marginal slope of the coteau. A 

small marginal lobe occupied this basin, as the main 

moraine shifts southwestward from Upland Township (T. 161 N., R. 97 W.) to Frederick Township 

(T. 160 N., R. 98 W.). This basin may mark the 

location of the preglacial Yellowstone Valley (p. 58). 

West of the reentrant the moraine swings north on 

the higher ground. Where crossed by the writer, in B. 

99 W., southwest of Ambrose, there is a relief of a.bout 

400 feet, and then a breadth of about 25 miles southward to the Grenora branch of the Great N ortherh 

Railway near Cottonwood Lake. There is continuous 

and more or less strongly developed morainal topography near the southern border, in T. 159 N~ The 

surface is scored by eroded coulees, and the moraine 

may here be merging with the earlier belt south of the 

railway line. 

i I-
128 PHYSIOGRAPHY AND G~CIAL GEOLOGY OF EASTERN MONTANA 

In T. 159 N., R. 100 W., between Rudser and the old 

Vandalia post office, the headwater tributaries of Little 

Muddy Creek appear to have been blocked by morainal 

deposits inclosing some small lakes. They are surrounded by a strong knob and kettle topography. 

· Where crossed by the writer, in R. 101 ,V., the moraine mantles big ridges and intervening sags, prob- ~ 

ably of an old erosion topography. The appearance 

suggests that the coteau was cut by a preglacial valley 

and by tributaries discharging northeastward through 

the sag.or reentrant traversed by the Soo Line from· 

Alkabo to Colgan. This may be the position of the 

outlet of the late Tertiary Missouri Valley described 

by Bauer.16 

North: of the Soo Line the surface rises rapidly again 

with a relief of 300 or 400 feet above the plain to the 

east, reaching an altitude of 2,300 to 2,400 feet or 

more. Froin Fortuna., on the railway, the writer went 

northward diagonally up the long slope, which is 

much broken by knolls, swells, sags, and ponds of the 

morainal topography, to the international boundary a.t 

2,337 feet above sea level. From this point there is a 

very extensive view over the lower plain to the east and 

southeastward, across the broad reentrant traversed by 

the railway to the eastward-trending slope of the 

coteau on the north. Going east 2 miles along the 

international boundary and th-ence northward 2 miles 

into Canada, the writer turned westward and for 7 

miles traversed morainal topography, ranging from 

mild to strong in its development and continuing about 

2,300 feet above the sea. The same topography continues south, back into the United States, and west and 

southwest along the route traversed to the vicinity of 

Westby. From the highest parts in DeWitt Township 

(T. 163 N., R. 101 W.) the general altitude decreases 

westward to a broad sag along the Montana line. 

Measured northeastward from the vicinity of Westby 

in a direction at right angles to the general trend of 

the GOteau, the moraine belt has a width of about 25 

miles. Many ponds and marshy depressions are interspersed among the ridges, knobs, and low swells such 

as are characteristic .of the unmodified Wisconsin kettle moraine. Boulders are not particularly abundant. 

They are mostly of granite, but numerous blocks of 

limestone occur. With these a large percentage o£ 

smoothly rounded quartzite pebbles and cobbles are 

intermingled. These are the same in character as the 

pebbles of quartzite from the Rocky Mountains which 

make up the Flaxville gravel on the upland remnants 

of the Tertiary plains farther west in Montana. Such 

pebbles were noted by Dawson 17 in the drift along the 

18 Bauer, C. M., A sketch of the late Tertiary history of the upper 

Missouri River: Jour. Geology, vol. 23, pp. 52-58, 1915. 

l'f Dawson, G. M., lteport on the geology and resources of the region 

in the vicinity of the 49th parallel, pp. 228-229, Montreal, British 

North American Boundary Commission, 1875 ; On the superficial 

geology of the central region of North America : Geol. Soc. London 

Quart. Jour., vol. 31, p. 614, 1875. 

international boundary as far east as the first crossing 

of the Souris River. Some quartzite, possibly of the 

same derivation, was also noted by Dawson as much as 

10 miles east of Turtle Mountain.18 Dawson's description of the coteau and of the morainal deposits where 

crossed by the 49th parallel 19 ·seems to be the first if 

not the only published description of this part of this 

notable feature. Although he did not interpret tlte 

drift deposits here as the terminal moraine of a con"-.. 

tinental ice sheet, his description is good and may well\ .. 

be cited in this connection: # \ 

Where cut somewhat obliquely by this [49th] parallel, the 

coteau may be said to extend from the 290 to the 335 mile 

point, b. dlstance of 45 miles. At right angles to' its general 

course, however, its extr~me width at this point can not be 

more than about 30 miles. On approaching it from the east, 

on the trail from Wood End, which, as already stated, is 

somewhat more elevated than the prairie lying east of it, a 

gradual ascent is made, till the edge of the coteau is reached, 

amounting in a distance of 25 miles to about 150 feet. The 

country at the same time becomes more distinctly undulating-as on approaching Turtle Mountain from the east-till 

almost before one is aware of the change the road is winding 

among a confusion of abruptly rounded and tumultuous hills, 

whi~h consist entirely of drift material and in many cases 

seem to be formed almost altogether of boulders and gravel, 

the :finer matter having been to a great extent washed down 

into the hollows. Where it appears, however, it is not unlike 

that of the drift of the lower prairies, being yellowish and 

sandy. Among the hill are basinlike valleys, round or 

irregular in form and without outlet, which are sometimes 

dry but generally hold swamps or small lakes, which have 

frequently been :filled in with material washed from the hllls 

so as to beconie· flat-bottomed. The hills and valleys have·. 

in general no very determinate direction, but a slight tendency 

to arrangement in north and south lines was observable in 

some parts of this region. The hills culminate on the line 

abo'ut the 305-mile point, and westward from this place they 

are neither so steep nor so stony. The country gradually 

subsides from its rough and broken character to that of rather 

boldly undulating prairie, without, however, falling much in 

general elevation below the tops of the bolder hills farther 

east. We have, in fact, passed up over the margin of the 

third great prairie steppe. ' 

The whole of the coteau belt is characterized by the absence 

of drainage valleys, and in consequence its pools and lakes are 

very often charged with salts, of which those most abundantly 

represented are sodic and magnesic sulphates. The saline 

lakes very generally dry up completely toward the end of the 

summer and present wide expanses of white efflorescent crystals, which contrast in color. with the crimson SaiUoornea, 

with which they are often fringed. The crystalline crust 

generally rests on a thick stratum of soft black mud. 

The boulders and gravel of the coteau were here observed 

to be chie:O.y of Laurentian origin, with, however, a good deal 

of the usual white limestone and a slight admixture of quartzitic drift. On the western margin some rather large disused 

stream valleys were seen, holding chains of saline lakes ; but 

their relation to the drift materials of the coteau were not so 

clearly shown as in other localities farther north. 

In passing westward from the last exposures of the Tertiary rocks near Wood End to the localitY of their first appear18 Dawson, G. M., op. cit. (report on 49th parallel), p. 225. 

19 Idem, p. 222. 

''\ 

\ 

I 

\ 
LATER WISCONSIN STAGE OF KEEW A.TIN' 10» SUET 

ance within the coteau, a distance of about 70 miles, we rise 

.about 600 feet and attain ·an elevation of about 2,500 feet 

above the sea. The slope of the surface of the Lignite Ter-

. tlary, then, assuming it to be uniform, is a little less than 100 

feet per mile; and on and against this gently inclined plane 

the immense drift deposits of the coteau hills are piled. 

ALTAMONT MORAINE IN MONTANA. AND 

SA.SKA.TCBEW AN 

From the Montana-North Dakota State line south 

of Westby the south border of the morainal belt continues fairly well defined· westward. Beekly 20 • describes this belt as follows : 

The fiat centr~l part of the field gradually merges on the 

north and east into a region of more or less prominent hills 

and ridges separated by cuplike and troughlike depressions. 

Toward the north these hills and ridges are smaller and more 

clqsely huddled together and continue so beyond the nortb'ern 

limit of the field [the international boundary]. Practically 

all the forms characteristic of morainal topography are represented in the surface.of this area, which though comparatively 

rough contains few hills or ridges rising more than 200 to 

800 feet above the lowest depressions~ The entire surface is 

grass covered. Glacial boulders ranging in size from a few 

inches to several feet in diameter are more or less thickly 

scattered over the well-rounded tops of the hills and ridges. 

No precipitous bluffs or steep valley walls, affording exposures 

of the rocks underlying the glacial material, occur in this 

part of the field. * * * 

No opportunity is offered for measurement of the drift, but 

its geneni.l appearance and the topographic forms here present 

seem to indicate that the maximum thickness is between 100 

and 200 feet. The glacial material consists of silty boulder 

clay containing, in addition to sand and gravel, a great many 

angular fragments and boulders of limestone and various igne-

. ous rocks. The boulders, which are usually somewhat worn, 

. range in size from coarse pebbles to rocks weighing a ton or 

more. They are thickly scattered over a large part of the 

surface and were used as criteria for mapping the boundary 

of glacial material. 

Many exposures of the drift are now afforded by the 

cuts along the Soo Line in the vicinity of Raymond. 

The traverses made by the present writer in 1916 and 

1920 seem to indicate that the southwest border of the 

main belt passes northwestward across the boundary 

north of Comertown, in R. 56 E., but that two more 

or less well-defined branches lie farther west, one 

crossing the international boundary north of Raymond, in R. 54 E., and another reaching the valley of 

Big Muddy Creek just south of the boundary, in 

R. 52 E. Altitudes along the boundary range from 

2,200 feet .at and near the northeast corner of Montana to 2,385 feet about 10 miles farther west, toward 

Big Muddy Creek. 

The moraine· that runs northwestward from Dooley 

is strongly marked north of Raymond, in the northeastern part ofT. 37 N., R. 54 E. West of this locality 

is a smoother tract, and beyond is the outermost branch 

of the moraine, which is lost in the sharply dissected 

• Beekly, A. L., The Culbertson lignite field, Valley County, Mont. : 

U. S. Geol. Survey Bull. 4:71, pp. 323, 326, 1912. 

tract bordering the Big Muddy Valley. The OOJ\fll~ 

uration of this great moraine\ through a .belt 60: 'nutes· 

long and 2 mil~s wide bordering the intematicm:ll 

boundary is shown on sheets 38, 391 · a11d 40 of -topographic maps of the international. boundary,. 

Numerous reconnaissance trips were made north· 

ward near and west of the Big Muddy Valley aS far 

as the southern lines of the Canadian National Bailwa.ys and the Canadian Pacific Railway-that is, to 

Bengough, Viceroy, Vantage, and other· points far-. 

ther west in Saskatchewan, in an attempt to deter;. 

mine whether or not the great terminal moraine 'of 

the later Wisconsin ice sheet passed westward .around 

the Wood Mountain upland .. .As a result of these trips . 

it was concluded that what has been called the Altamont moraine in northwester_!l North Dakota, which 

there marks the limit of advance of the later Wisconsin ice sheet, probably continues northwestward in 

southern Saskatchewan, mostly on the east side of the 

great through valley, 100 to 300 feet deep, in which lie 

Lake of the Rivers, Willowbunch Lake, and Big 

Muddy Lake, al).d which is continuous southward as 

the Big Muddy Valley through Sheridan and RooseYelt Counties, Mont., to the Missouri River. Thio 

valley was evidently a very important outlet for · 

drainage while the ice front stood at the Altamont 

moraine. Not only did it carry drainage from the ic& 

front from regions far to the north, but all the water 

from the South Saskatchewan River and its tributaries 

west of the ice front, and possibly also from the 

North Saskatchewan River, was diverted through this 

valley to the Missouri River. Where it crosses the 

international boundary the Big Muddy Valley has a 

width of about a mile and a depth of about 300 feet. 

What may be a part of the Altamont moraine lies 

on both sides of the high divide between Big Muddy 

Lake and the heads of Beaver Creek, in Saskatchewan. Near the south line ofT. 3 N., R. 24 W., the 

south front of the moraine is very well defined, being 

1narked by a hummocky, boulder-strewn ridge (pl. 

51 B) which is in marked contrast with the smooth, 

gently sloping plain to the south. In 1916 a morAinal 

belt was seen by the writer between Bengough and 

Viceroy. This belt is .said to continue southeastward 

and may connect with either the main Altamont moraine or one of the branches seen near the international boundary east of the Big Muddy Valley .. It·is 

also well marked on the ridge north of Viceroy. On 

going west and north past the south end of. Lake. of . 

the Rivers, the writer encountered what may be tbe 

same moraine southeast of Vantage, in T. 10 N., R. 

1 W., near the Assiniboia branch of the Canadian 

Pacific Railway. It is probably croe¥3ed by, the 

Gravelbourg_ branch of the Canadian.Na.tional Railways near Ettington and. may extend thence northwestward, though it was not seen again by the writerr 
130 PHYSIOGRAPHY AND GLACIAL GEOLOGY OF EASTERN MONTANA 

With the recession of the ice front from the Altamont moraine· the glacial history of this part of the 

northern Great Plains ended, and conditions graded 

.into those of Recent time. 

LATE PLEISTOCENE OR RECENT UPLIFT 

There is no very definite evidence that uplift oc-

-curred in this region in connection with or since the 

Wisconsin stage of glaciation. Almost everywhere 

the streams appear to be actively cutting downward. 

"The depths of post-Wisconsin erosion range from 50 

feet or less to 100 feet or more on the plains, and some 

-of the mountain canyons, as on the Sun River, have 

narrow tortuous gorges cut to depths of 100 to 200 

feet in their bottoms. The Milk River is wandering 

about and tying itself in bowknots on a valley fill 

be.cause it can not cut down faster than the Missouri, 

to which it is tributary. The Missouri cut across cols 

west of the Milk River after its relocation that followed the pre-Wisconsin (Illinoian or Iowan~) stage 

-of glaciation, and it has cut a great trench in shale 

and sandstone 100 to 500 feet in depth, but how much 

·Of this has been cut in post-Wisconsin time is not evi-

.dent. Below the city of Great Falls the Missouri 

plunges over a series of cascades and rapids, descend-

. ing 612 feet in 12 miles of its new course. (See pl. 31 

B.) Above the city it is meandering on a valley fill. 

It is not certain just how much of this depth of ero-

.sion has occurred since the early Wisconsin glaciation, 

inasmuch as the ice sheet of that stage is not known 

to have crossed or diverted the river. Taken altogether, the streams certainly have not yet had time 

to reach the limit of downcutting and do any consider-

.able amount of lateral planation since the last regional 

.uplift. 

There are certain facts which are not clearly evalu-

.ated but which suggest that a differential regional uplift with easterly or northeasterly downward tilt has 

·occurred since the early Wisconsin ice invasion, if not 

.since that of later Wisconsin time. There is a gradual 

westerly increase in the present altitudes of points west 

-of Minnesota that were just high enough to stop the 

.advance of the Wisconsin- ice front. These facts are 

-cited below for consideration for what they are worth. 

.It is quite possible that there are in some places, if not 

in all, modifying factors that should be taken into con-

.sideration for their true interpretation. 

1. The altitude at the head of the Coteau des Prairies, the great wedge that separated the Des Moines 

lobe from the Dakota lobe of the Keewatin ice, is about 

:2,000 to 2,100 feet in northeastern South Dakota. 

2. A few miles north of the line between North 

Dakota and South Dakota, on the west side of the 

Dakota lobe, the ice front reached altitudes which are 

now 2,100 to 2,200 feet and then stopped on top of the 

Coteau du Missouri, forming a reentrant south of 

which on the lower ground it advanced 60 miles farther west . 

3. ~ear Stanley, where the margin of the early Wisconsin drift swings west on top of the coteau in northwestern North Dakota, the altitude is about 2,260 feet. 

Higher points on the coteau reached by the later Wisconsin ice stand at 2,300 to 2,400 feet or more, but tll.e 

ice did not extend much beyond them. .. . 

4. On the Flaxville Plain near Opheim, in north-\" 

eastern Montana, where there was probably the head '\. 

of a great reentrant in the early Wisconsin ice mar- \ 

gin, barometric readings indicate an altitude of 3,200 \ . \ 

to 3,300 feet. 

5. At the north side of the Little Rocky Mountains 

th~ limit of the early Wisconsin drift on high· remnants of the Flaxville Plain· near Lodgepole is 3,500 

feet. · 

6. Northeast of Choteau the west limit of the advance is about 3,800 feet. 

7. North of Cut Bank the points that caused reentrants 8 or 10 miles deep in the ice margin now stand 

4,200 to 4,400 feet above sea level. 

Were these several altitudes west of Minnesota those 

of the shore line of a great lake or sea they would certainly be regarded as indicating subsequent tilting of 

the land. Although such an explanation is not so 

strictly applicable to the edge of an ice sheet, the 

present westerly increase in these altitudes is worthy 

of consideration as suggesting, if not proving, th3t 

such tilting with uplift of the mountain belts has oc~ 

curred since early Wisconsin time. Any inferences 

regarding regional tilting that may be drawn from the 

above data must also be checked with the results of 

studies by Upham, Tyrrell, Dowling, Mclnness, and 

Johnston of the southward tilting of beaches of Lake 

Agassiz during and since the retreat !>f the fronts of 

the ice sheets of the Wisconsin stage. 

Postglacial marine deposits are reported as found 

at altitudes of 500 to 600 feet in the valleys draining 

to the south and west shores of Hudson Bay. In this 

connection it may be noted that any southerly tilt or 

reduction of northward slope of the. land between 

Hudson Bay and southeastern South Dakota subsequent to the southward diversion of the Missouri 

River through the Dakotas, especially if it occurred 

at about the same time as uplift of the plains and 

mountains of Montana and Wyoming, would tend to 

accelerate cutting along the Missouri and the Yellowstone and all their-tributaries. Uplift in the Hudson 

Bay region, however, must have tended to retar~ 

erosion on the Red, Nelson, and Saskatchewan Rivers. 

Whether or not there is evidence of any sueh retardation on those streams is not discussed in the present 

paper. 
/ 

r 

J 

/ 

INDEX 

A Page 

Absaroka Range, structure of---------------------------------· -------r------ 9 

/ Absarokee, Mont., remnants of No.2 bench, near---------------------------- 52 

- Acknowledgment.'!.-------------------------------------- ___ -----____________ 2 

Alberta, Canada, terminal moraine in __ -~--------------------------------- 103-105 

Altamont moraine, ~neral footures of, in Montana and Saskatchewan _____ 129-130 

general footures of, in North Dakota----------------------------------- 126-129 

Augusta, Mont., gravel-capped bench near---------------------------------- 16 

B 

:Bauer, C. M., and Herald, F. A., quoted·----------------------------------- 77 

Bearpaw Mountains, Mont., NV: 2 bench at--------------------------------- 45-46 relations of No. 1 bench to( _________ -_ ____________________________________ 18-19 

Beartooth Mountains, Mont., gravel-capped benches in ______________ ; ___ .___ i> 

possible pre-Wisconsin glacial deposits on-------------------------------- 40-41 

Beartooth Plateau, Wyo., eastern edge of·----------------------------------- pl. 3 

Belly River, Alberta, sections of Pleistocene deposits on------------- 66,72-73, 105 

Belly River Glacier, general features oL.~----------------------------------l· 115 

Belly River VaJley, section of drift in---------------------------------------- 115 

Benches, characteristics of ____ ----------------------------------------------- 3-4 

Bench No. 1. See Flaxville Plain. 

Bench No.3, relations of, to glacial drifL----------------------------------- 59-61 

Big Fa1ls, Mont., views of--------------------------------------------------- pl. 33 

Big Horn Mountains, Wyo., bouldery mesas bordering ______________________ 41-44 

glaciers of, general features oL------------------------------------------- 126 terraces east of _________________________________ -----------~---~---------- 55-56 

topographic map of part of, west of BufialO------------------------------ pl. 21 

. vifi!WS in----------------------------------------------------------- pis. 2,18-20 

Big Hi>rn River, No. 3 terrace on-------------------------------------------- 63 

Big S~eep Mounta~, high-level gravel on·---------------------------------- 12 

views of features on------------------------------------------------------ pl. 4 

Big Snowy Mountains, gravel-capped benches bordering _____________________ 23-24 

B~gs, Mont., gravel-capped terraces I!.ear --------------------------------- 53-54 

BitCh Creek Glacier, general footures of---------------------------------,·--- 119 

:Blackfeet Indian Reservation, gravel-capped benches in •. ------------------- 15 

/Blackfoot Glacier. See Two Medicine Glacier. 

, ' BlackleBf Creek Glacier, general features of-----------------------------:-- 119-120 

/ Blaine and Hill Counties, Mont., topographic map of portions of.. __________ pl. 34 

Blaine County, Mont., Flaxville Plain in.---------------------------------- 18 

recessional moraines in._---------------- ___ --------------------------- no-112 

terminal moraine in----------------------------- _______ -'---------------- 98-101 

Boulder Ridge, drift on------------------------------------------------------ 34-35 

Boulder River glaciers, general features of.__________________________________ 124 

Boulder Ri~r Valley No.2 bench in---------------------------------------- 52 

Boulder transportation in early Wisconsin time, occurrence of. ____________ 106-108 

Bowen, C. F., quoted------------+----------------------------------------- 23,80 

:Brocket, Alberta, section of Pleistocene deposits near-------------------·---- 74 

Browning, Mont., section of drift in moraine north of ____________________ ·--- 118 

Buffalo, Wyo., bouldery deposits near----------------------------~------·--- 42-43 

c 

Calhoun, F. H. H., quoted·--------------------------------- 71, 72,101, 104,108, 120 

Calvert, W. R., quoted------------------------------~----------------------- 23,50 

Canyon Creek, high-level gravel dei.'OSit on ridge n83r----------------------- 17 

Cardston district, Alberta, gravel-capped bench in___________________________ 14 

Carlow Flat, interpretation of----------------------------------------------- 47-50 

Cascade, Mont., Missouri River near---------------------------------------- pl. 31 

Cascade County, Mont., No.2 bench in------------------------------------- 46-47 

Castle Mountains, Mont., glaciers of, general features of_____________________ 121 

possible pre-Wisconsin glacial deposits On-----------·-------------------- 4o-41 

Chouteau County, Mont., terminal moraine in------------------------------ iOl 

Clark, Wyo., pebbles and boulders on slope northeast of _____________________ pl. 5 

Clark Fork, gravel-capped benches on--------------------------------- 26-27,53,63 

glaciers of, general features oL------------------------------------------- 126 

views on------------------------------------------------------- pis. 22, 26, 49,50 

Collier, A. J., and 'J'hom, W. T., j~ •• quoted------------------------------ 2o-21,44 

Columbus, Mont., gravel-capped bench near-------------------------------- 52 

CQrbett, C. B., quoted---·------------J·------------------------------------- 33 

Coteaudu Missouri, Burke County, N. Dak., terminal moraine in ...... 127, pl. 51 

Crazy Mountains, Mont., glaciers of, general feat~ of ___________________ 121-123 

gravel-capped remnants of No.2 bench in------------------------·------ 51 

surface of erosion in upper portions of-----------------------------·------ 8 

viewa in and near---------------------------------------------------- pis. 4.5, 46 

87949--32 

PC row Indian Reservation, benches in-----------------~---·-·····:··--t--·--·-r '2'f ... 3) 

Custer, Mont., benches above·-----------------------------~-------~-------: $-27 

bluff of Lance sandstone, east oL------~--------------·----------"·------ pl. 2IS 

gravel-capped terraces near .• ---------------------------------------~---- M 

Cut Bank, Mont., terminal moraine north of----------------------•--------;. pl. S3 

Cut Bank Glacier, general features of---------------------------·-·-·-------· 117 

Cut Bank Ridge, drift on--------------------------------------------------;.. 3S 

Cypress Hills, Alberta, Oligocene (?) materials on·-------------------------- pl. 3 

Cypress Hills Plateau, fossils oL-----------------------------------------·-· IHI 

general features of. ______ ------------------------------------------------ 4-6 

stream gradients in---~-~---------------------------------------------- &-1, S. 9 

Cypress Plain, development of------------------------------------------· vn, 4-10 

l~ 

Daniels County, Mont., Flaxville Plain in--------------------------\------- 20-21 

reces'iional moraine in ____________ -------------------------------------- 114-115 

Darton, N.H., quoted---------------------------------------------------- 7,41-42 

Dawson, G. M., quoted ••• -----------------------------------~--------- 67,128-129 

Dearborn Glacier, general features of •• -------------------------------------- 121 

Dearborn River, benches on------------------------------------------------- 1..,17 

Deep Creek glaciers, moraines of._.----------------------------------------- 120 

Dobbin, C. E., quoted·------------------------------------------------------ 12 

Drainage outlets, general features of.------------------------!------------- 109-110 

Dupuyer Creek, glaciers on forks o'-------------------------·--------------- 119 

E 

Eagle Butte, Bearpaw Mountains, Mont., view of--------------------------- pl.~ East Flattop Mountain, Glacier National Park, Mont., view of _____________ pl. 2 

East Rosebud Canyon, Beartooth Mountains, Mont., views in-------------· pl. 48 

East Rosebud Glacier, general features of--------------------~--------------- 12ti 

moraines of..~'----------~-----------------------------------------------· pl. f7 

Emigrant, Mont., bench No.3 near----------------------------------------- 62 

F 

Field studies. ______ -------------------------------.-------------------------- 1-3 

Flaxville gravel, sections oL------------------------------·------------------ 20,21 

views of. ________ -------------------------------------------------------· pl. 10 Flaxville Plain, character of, in region bordering Rocky Mountsin front _____ 14-18 

general features of---------------------------------------------------- VU.l2-13 

Flaxville terraces, age and correlation oL------------------------------------ 13-14 

Forsyth, Mont., high-level gravel near----·--·------------------------·------ 12 

views near--------------------------------------------------------------- pl. 27 

Fort Benton, Mont., section of glacial and associated deposits west oL------ 68 

Fort Berthold Indian Reservation, N.Dak., abandoned channel of Missouri 

River in-------------------------------·----·-----------------·-· 61 

G 

Gale, H. 8., and Wegemann, C. H., qU()ted _______________ ~----------------- 56 

Gidley, J. W., quoted.---------------------------·-------------------------- 13 

Glacial Lake Cut Bank, features oL-------------------------------------- JA&.l09 

laminated clays oL---------------------------·-----------·-------------· pl. 25 

Glacier County, Mont., terminal moraine in--------------------------~--- 103-106 

Glacier National Park, Mont., map of eastern portion of, at the Wisconsin 

stage of glaciation •••••••••••• ----------------------------------·- pl. 87 

pre-Wisconsin drift in.---------------------------------------------.. ---· pl. lit: 

Glacier Park station, sections of glacial and interglacial deposits at and Dear- 69, 70 

Glendive quadrangle, character of gravel deposits in.-------------~-----·--·· 67 

high gravel bench in.--------------------------------·--·------·---------- 81) 

map or, showing relations of Keewatin ice sheet in.-------------······--· pl. 28 

Granger, Walter, Sinclair, W. J., and quoted------------------------·------ 10 

Great Falls, Mont., map of region oL--------------··--------------~-------·· pl. 29 

pre-Wisconsin drift near and east oL--------------r--------------~------ 79-81 

record or wen on Missouri River south oL------------··-···--------·--- 90 

stream changes near-----------------------.-----------·------------·----- .,. 

Great Falls lobe of Keewatin ice sheet, relations of-------·---·------------- 101-102 

Great Plains, northern, general characteristics of •• :·--·----------·----------- 8 northern, mountain outliers hi. •• ________________________________________ 3 

rocks of-------------------------------------------------------------· 3 

Greenfields Bench, character of--------------------------------------------·- 16 

131 
132 INDEX 

H Page 

Hancock, E. T., quoted.---------------------------------------------------- 58-59 

Hardin,-Mont., remnants of No.2 bench near-----------------------~------- 54-55 

Herald, F. A., quoted·------------~----------------------------------------- 64 

Bauer, C. M., and, quoted-------------------------------.--------------- 77 

Highwood, Mont., section of gravel deposits on Chicago, Milwaukee, St. Paul 

& Pacific Railway west of-------------------------------------__ 66 , Hill and Blaine Counties, Mont., topographic map of portions of ____________ pl. 34 

Hill County, Mont., recessional moraines in------------------------------- 111}-112 

terminal moraine in_---------------------------- ______________ ---------- 101 

Horsethief Ridge, gravel-capped benches near __ ----------------------------- 14 

Horton, Mont., gravel pit on bench No.2 near------------------------------ 56-57 

I 

Iddings, I. P., and Weed, W. H., quoted.·---------------------------------- 9 

Illinoian or Iowan (?) drift, occurrence of, along Missouri River in Montana .• 79-85 

occurrence of, along Missouri River in North Dakota-------------------- 75-78 

in Valley and Roosevelt Counties, Mont_ ___________________________ 83-85 

north of Missouri River--------------------------------------------- 78-79 

Illinoian or Iowan (?) stage of glaciation, general features of. ________________ vn, 611 stream diversion at ______________________ ------------------ ______________ 88-93 

lllinoian or Iowan(?) till of mountain glaciers, gravel underlying____________ 67 

J 

1udfth Mountains, Mont., view of---~--:·----------------------------------- pl. 12 

1udith River Basin, No.2 bench in------------------------------------------ 50 

No.3 bench in----------------------------------------------------------- 62 terraces of ______ ---- _______ --- ___________ ------- _________________________ 21-23 

K 

Keewatin Glacier, pre-Wisconsin drift of, underlying later drift ______________ 71-75 

Keewatin ice sheet, later Wisconsin stage oL.----------------------------- 126-130 

moraines of _________ -------------------------------______________________ pl. 38 

terminal moraine of later Wisconsin stage o'----------------------------- pl. 51 

Keewatin till, gravel underlying older--------------------------------------- 65-67 

Kennedy Creek Glacier, general features of ________________________________ 115-116 

Kennedy Ridge, drift on_----------------------------------------------; ____ 33-34 view of. _______________________________________________________________ -- pl. 14 

L 

Lacustrine deposits of early Wisconsin age, occurrence.and character of. ___ 106-108 

Lake basins, features of------------------------------~----------------------- 58-59 

Lake Bowdotn, stream diversion near_------------------------------------ 112-114 

~ preek Glacier, general features oL------------------------------------ 117 

La lle, L. M., quoted·----------------------------------------------------- 5-6 

Landslide Butte, gravel-capped benches near________________________________ 14 

Leonard, A. G., quoted ••• ----------------------------------- 75-77,78,79,85, 86,89 

Lethbridge, Alberta, partial section of interglacial beds at..----------------- 73 

Leverett, Frank, quoted ____________ ------------------_______________________ 86 

Lewis and Clark County, Mont., No.2 bench in---------------------------- 46-47 

Long Ridge, gravel-capped bench on·--------------------------------------- 16 

Little Belt Mountains, Mont., erosion in·----------------------------------- 8 

Little Prickly Pear Creek, Mont., gravel-capped ridge on____________________ 17 

Little Rocky Mountains, Mont., map of._---------------------------------- pl. 35 

No.2 bench at----------------------------------------------------------- 45-46 

relations of No. 1 bench to----------------------------------------------- 19-20. 

views of------------------------------------------------------------ pis. 6-9,23 

Little Sheep Mountain coal field, gravel-covered benches in_________________ 30 

Livingston, Mont., No.3 bench near---------------------------------------- 62 

Lower Et. Mary Lake, drift on ridge west of---------------------------------- 35 

~ 

Makowan Butte, Alberta, glacial drift on------------------------------------ 32-33 

Malta, Mont., bench northeast of------------------------------------------- pl. 22 

glacial boulders near---------------------------------------------------- pl. 41 

Mansfield, G. R., quoted---------------------------------------------------- 8 

Map showing physiography and glacial geology of eastern Montana and parts 

ofadjacent States------------------------------------- pl. 1 (in pocket) 

Martin Lake, recessional moraine near-------------------------------------- pl. 38 

McConnell, R. G., quoted--------------------------------------------------- 5, 6 

Miles City, Mont., tenaces near--------------------------------------------- 57 

Milk-Missouri Valley, eroshn and refillin~ in-------------------------------- 67-69 

No.2 bench in----------------------------------------------------------- 44-45 Milk River Ridge, correlation of gravel deposits on. _________________________ · 14 

drift on _______________ ,_------------------ _________ -------- ______________ 37-38 

Miocene and Pliocene epochs, events of-------------------------------------- 12-31 

Missouri and Yellowstone Rivers, Pleistocene valley of______________________ 89 

Missouri River, diversion of, in North Dakota through advance of an early ice sheet ________________________________ ----·____________________ 58 

diversion of upper, at lllinoian or Iowan(?) stage of glaciation ___________ 88-89 

gradients on branches of upper_----------------------------------------- 50 

views on.------------- ___ ------.- ____ --------- _______ ------------ ____ pis. 31}-33 

Missouri Valley, ftlJing of, in North Dakota ___________ ---------------------- 64-65 

Pace 

Mocoosin Mountains, benches beading in------------------------------------ 22 

Moncrief Ridge, bouldery deposit OD---------------------------------·----·- 43-44 Muddy Creek Glacier, general features of ________ .:___________________________ 119 

Musselshell River, pre-Wisconsin drift east of. •• ---------------------------- 81--&! 

Musselshell Valley, No.2 bench in •• ---------------------------------------- 51H1 

No.3 bench in---------------------------------------------------------- 62 

terraceS of_-------------------------------------- _____ ------------ ______ 23-25 

Myers, Mont., gravel-capped sandstone bluti south oL---------------------- pl. IJ 

N 

Nesson-Hofilund Flats, N.Dak., correlation ot, with No.3 bench____________ 61 

0· 

Old Man River, section of Pleistocene deposits on.-------------------------- 74 

Oligocene epoch, events of-------------------------------------------------~ 4-12 

features of northern Montana and adjacent parts of Canada during______ 7-8 

Opheim, Mont., Flaxville gravel near----------------------------------- 21, pl. 10 

p 

Pendroy, Mont., gravel-covered bench at----------------------------·------- 1~16 

Peoples Creek, Fort Belknap Indian Reservation, Mont., views on _________ pl. 40 

Peorian (?) stage of deglaciation, events of----------------------------------- 03 

Phillips Co.unty, Mont., recessional motaines in--------------------------- 111}-112 

terminal· moraine in.--------- __ ---------------------------------------- 98-101 

Physiography and glacial geology of eastern Montana and parts of adJacent 

States, map showing_-------------------------------- pl. 1 (in pocket) 

Pine Ridge, high gravel on •• -------------------------·---------------------- 11 

Pleistocene epoch, deposits of---------------------------~------------_. _______ 32-09 

Pleistocene mountain glaciation, early, on benches No.1 and No.2----------- 32 

Pleistocene terraces, early and middle, occurrence of _____________________ Vn. 44-59 

Pliocene and early Pleistocene epochs, general relations of deposits of. _______ 31-32 

Pliocene and Miocene epochs, event.El of-------------------------------------- 12-31 

Pompeys Pillar, 30 miles northeast of Billings._------------------------- 54, pl. 26 

Ponders Co\).Dty, Mont., No.2 bench in-----------------------------------· 46-47 

terminal moraine in_------------------------------------------·------- 102-103 

Pre-Iowan or pre-illinoian (?)gravel, occurrence of, in Montana ______________ 66-67 

occurrence of, in southern Alberta·-------------------------------------- M-OO 

Pre-Wisconsin drift bordering Missouri River, age of. _____________________ £_ 85-BS 

Pre-Wisconsin drift of Rocky Mountain glaciers, materials of.. __________ ~· 14-16 occurrence of, at low levels ______________________________ :·--·----------~ 69-71· 

·Pre-Wisconsin ice sheet, thickness of, in North Dakota---------------------~., 79 

\; __ Q \ 

Quaternary period, deposits oL-------------------------------------------- 32-U~ 

R 

\,,, Rainbow Falls, Mont., views oL-------------------------------------~----- pl. 82 

Recent time, events Of-------------------·-------------------------------- VTII, lliO ··, . .,_ 

Recessional moraines of early Wisconsin age, general features of--~--------- 109-110 '\ Red Coulee, Mont., section of drift in ______________ ;.________________________ 80 

Red Lodge, Mont., remnants of No.2 bench near_------------------- 52-53, pl. 13 

Rock Creek Canyon, view of bench in--------------------------------------- pl. 13 

Rock Creek glaciers, general features of------------------------------------ 125-126 

Rogers, G. S., quoted.-------------------------------~---------------------- 11,30 

Roosevelt County, Mont, Flaxville Plain in ;.1------------------------------ 20-21 

pre-Wisconsin drift in_-------------------------- ___ -------------~------- 83-85 

recessional moraine in _______________ ---------------------------------- 114-115 

Wisconsin terminal moraine (?) in--------------------------------------- 97-98 

Roscoe, Mont., views near_--------------------------------------------- pis. 12, 16 

Sage Creek, Mont., section of Pleistocene deposits near---------------------- , 74 

St. Mary Glacier, general features of--------------------------·-------------- 116 

St. Mary Ridge, drift on •• -------------------------------------------------- 36-37 

St. Mary River, sections of deposits on, at international boundary ________ 67,104 

sections of glacial and lacustrine deposits on, north of Babb-------------- 71}-71 

St. Mary Valley, Alberta, pre-Iowan or pre-Illinoian(?) gravel in ____________ 6!HI6 

St. Paul's Mission, Mont., gravel-capped benches near-~-------------------- 19 

views near----------------------------------------.--------------------- pis. 6, 9 

Scobey, Mont., Flaxville gravel near __ --------------------------------------· pl. 10 

section of well southwest of---------------------------------------------- 20 

Sheridan, Wyo., gravel:-eovered terraces near-------------------------------- 55 

Shonkin Sag, view of-----------------------------·-------------------------- pl. 30 

Shoshone National Forest, Wyo., view in---~------------------------------- pl. 13 

Signal Butte, glacial striae on sandstone OIL------------~-------------------- pl. 39 

Sinclair, W. J., and Granger, Walter, quoted---~------.--------------------·-- 10 

Smith, c. D., quoted-------------:..------------.:.----------------------------- 84 

Smitb Creek Glacier, general features oL------------------------------------ 121 

Snake Butte, perched boulder on--------------~-------~·-------------------- pl. 39 

Snake Creek, Mont., ~tion of drift on----·-·--··-----------------------~--- 107 

South Moccasin Mountains, Mont., views oJbenches in-------------------·- pl. li 

Stillwater Canyon, views in---------------~------------·-------------------- pl. 17 
I 

INDEX 133 

Page 

Stillwater Glacier, general features oL-------------------------------------- 125 Summary of report ___ _-__________________________________________ ---------- vu-vm 

Bun River, Mont., gravel-capped benches near.···-------------------------- 16 

Bun River Canyon, Mont., views in---------------------------·--------- pis. 7, 43 

Sun River Glacier, blocks of limestone transported bY----------------------- pl. 44 

inner moraines o'---------------·-·-------- -~------------------------ •. 120-121 outer moraine of _______________ ------- ______ .------ ___ . _________________ • 1::0 

terminal moraine of.---------------------------------------------------· pl. 44 

Swiftcurrent Ridge, drift on ••• ·--------------------------------------------- 34 

view of .•• ·------------------------------------------------------------ __ pl. 14 

T 

.'Tatman Mountain, Wyo., high-level gravel on, character of. ________________ 10--11 

/Terraces, characteristics of.·------------------------------- ___ ---------______ 3-4 

/' Teny, Mont., gravel-capped benches near.__________________________________ 57 

/ Teton County, Mont., No.2 bench in--------------------------------------- 46-47 

J tenninal moraine in·--------------------------------------------------- 102-103 

'

/ Teton Ridge, gravel-capped bench on.·------------------------------------- 16 

Teton River Glacier, genefal features of..___________________________________ 1:i:O 

Tbom, W. T., jr., quoted·--------------------------------------------------- 27-29 

Collier, A. J., and, quoted-------------------------------------------- 20--21,44 

Toole County, Mont., terminal moraine in.------------------------------- 103-105 

Tullock Creek coal field, gravel deposits in.--------------------------------- 11-12 

Twin Buttes, Fort Belknap Indian Reservation, Mont., view oL ___________ pl. 36 

Two Medicine Creek, sections of glacial and interglacial deposits on_________ 70 

Two Medicine Glacier, Blackfeet Indian Reservation, Mont., moraines 

of.----------------------------------------------------- 117-119, pl. 42 

relations of, to the Keewatin ice sheet. ________________________________ 105-106 

Two Medicine Ridge, drift on.---------------------------------------------- 38-40 

u 

United States Reclamation Service, logs of test borings of, along Missouri 

River in North Dakota------------------------------------------ 64-60 

Uplift, late Pleistocene or Recent, indications oL·--------------------------- 130 

v 

Valley County, Mont., Flaxville Plain in ••••••••••••••••••••••••••••••••••• 20--21 

occurrence of pre-Wisconsin drift in ..••••••••.••••••••••••••••••••••••••• · 83-85 

0 

Page 

Valley County, Mont., recesSional moraines in--~----------·----------~--- 114-116 

tenninal moraine (?) in-----·------------------------···-----.-~---------- 9'1-98 

w 

w ~!:.J. ~~:d: ~;~t;d:::::::::::::::::::::::::::::::::::::::::::::. n, 1~ Wegemann, C. H., Gale, H. S., and, quoted------------------·---------•---· 56 

West Rosebud Glacier, general features oL---------------------------------- 126 

Whitetail, Mont., terminal moraine north Gf-------------------------------- pl. 61 

Wilder, F. A., quoted·-----------------------~------------·---·---··----- M, 78,86 

Williams County, N. Dak., Illinoian or Iowan (?) drift north of Missouri 

River in---------------------------------·----------.-•• -----····· 78-79 

Wisconsin stage of glaciS.tion, age of drift oL.----------·----~-----: •••••.••• 93-96 

deposits of 7 • ------------------------------------------·-------- vu-~, 96-115 

general relations of Rocky Mountain glaciers of-----------------------~-- lli 

Wisconsin terminal moraine(?), early, in North Dakota ••••••••••••••••••••• 9&--9'1 

Wolf Point, Mont., log of well at. .• ·------------------------------~--------- 68 

section exposed in gravel pit at.----------------------------------------- 68 

Wood, L. H., quoted ... -------------------------------------------~-------- D6, 127 

y 

Yellowstone and Missouri Rivers, Pleistocene valley of---------------------- 89 

Yellowstone Basin, No.3 bench in------------------------------------------ 62-64 

Yellowstone Glacier, general features of.----------------------------------- 123-124 

Yellowstone River, diversion of, in North Dakota through advance of an early 

· ice sheet--------------------------------------------------------- 58 Flaxville terrace on lower ________________________________________________ .2fHJ1 

gravel-covered terraces on •• --------------------------------------------- · 9 

high gravel deposits near.----------------------------------------------- 11-12 

No.2 bench on·-------------------------------------------------·-·----- 51-65 

No. 2 terrace on lower--------------------------~----·------------------- ~ . 

pre-WisConsin drift on lower •....••.•.••• -------------------------------- 82-83 

views on.---------------------------·--------------------------_:- pls. 24, 26, '1!'1 

Yellowstone Valley, No. 1 bench in-------------------------------------·--·- 25-31 

z 

Zortman, Mont., benches near--·-·-------------------------------------~- 20, pl. 7 

., . 

.! 

./ 
• 

~ .--- > 

-: .; 

, 

. \ 

: '