Sage Creek-O’Brien Coulee drainage divide area landform origins, Hill and Liberty Counties, Montana, USA

· Milk River, Montana, Sweet Grass Hills
Authors

Abstract:

Topographic map interpretation methods are used to determine landform origins in the Sage Creek-O’Brien Coulee drainage divide area located in Hill and Liberty Counties, Montana. Sage Creek originates in the high East Butte area of the Sweet Grass Hills and flows in a northeast direction to reach the surrounding plains before turning to flow in a southeast direction to join northeast-oriented Big Sandy Creek, which flows to the Milk River. O’Brien Coulee is an east-oriented Sage Creek tributary originating on the plains south of the East Butte high area. The Sage Creek-O’Brien Coulee drainage divide area is interpreted to have been eroded during immense south and southeast-oriented melt water floods, which deeply eroded the region surrounding East Butte. The ice sheet had been located in a deep “hole” and as the ice sheet melted gigantic melt water floods deeply eroded the deep “hole’s” southwest wall, which is today the upper Missouri River drainage basin. East Butte stands more than 1000 meters above the surrounding plains and is drained to the east by Sage Creek and Sage Creek tributaries, to the west and northwest by north and northwest oriented tributaries to the east-oriented Milk River in southern Alberta, and to the south by south-oriented tributaries to the Marias River. High level through valleys between some of the highest East Butte peaks link these diverging drainage routes and provide evidence of melt water flood flow routes and provide markers documenting the depth of melt water flood erosion, although it is possible delayed crustal warping caused by the ice sheet’s great weight uplifted the East Butte erosion resistant rock masses as flood waters were flowing across the region. Headward erosion of the deep east-oriented Milk River valley across southern Alberta (to the north) beheaded the south-oriented flood flow and flood waters on north ends of beheaded flood flow routes reversed flow direction to erode north and northwest-oriented Milk River tributary valleys.

Preface:

The following interpretation of detailed topographic map evidence is one of a series of essays describing similar evidence for all major drainage divides contained within the Missouri River drainage basin and for all major drainage divides with adjacent drainage basins. The research project is interpreting evidence in the context of a previously unexplored deep glacial erosion paradigm, which is fundamentally different from most commonly accepted North American glacial history interpretations. Project essays available at this site may be found by selecting desired Missouri River tributaries and/or states from this essay’s sidebar category list.

Introduction:

  • The purpose of this essay is to use topographic map interpretation methods to explore the Sage Creek-O’Brien Coulee drainage divide area landform origins in Hill and Liberty Counties, USA. Map interpretation methods can be used to unravel many geomorphic events leading up to formation of present-day drainage routes and development of other landform features. While each detailed topographic map feature provides detailed evidence to be explained, the solution must be consistent with explanations for adjacent area map evidence as well as solutions to big picture map evidence puzzles. I invite readers to improve upon my solutions and/or to propose alternate solutions that better explain evidence and are also consistent with adjacent map area and big picture evidence. Readers may do so either by making comments here or by writing and publishing their own essays and then by leaving a link to those essays in a comment here.
  • This essay is also exploring a new geomorphology paradigm in which erosional landforms are interpreted as evidence left by immense glacial melt water floods. Implied in that interpretation is the immense floods were derived from a thick North American ice sheet that created a deep “hole” in the North American continent and also melted fast. The previously unexplored paradigm being tested in this and other essays in the Missouri River drainage basin landform origins research project is a thick North American ice sheet, comparable in thickness to the Antarctic ice sheet, occupied the North American region usually recognized to have been glaciated, and through its weight and erosive actions created a deep North American “hole”. The southwestern rim of that deep “hole” is today preserved in the high Rocky Mountains. The ice sheet through its weight and deep erosion (and perhaps deposition along major south-oriented melt water flow routes) caused significant crustal warping and tectonic change, through its action of melting fast produced immense floods that flowed across the continent, and through its action of melting fast systematically opened up space in the ice sheet created “hole” so headward erosion of newly developed north-oriented drainage systems captured immense south-oriented melt water floods and diverted immense melt water floods north into space the ice sheet had once occupied.
  • If this previously unexplored paradigm is correct the geographic region explored by this essay should contain evidence of immense floods that were captured by headward erosion of new valley systems so as to cause the floods to flow in a different direction. Ability of this previously unexplored paradigm to explain Sage Creek-O’Brien Coulee drainage divide area landform evidence in Hill and Liberty Counties, Montana will be regarded as evidence supporting the “thick ice sheet that melted fast” paradigm (see paradigm related essay in menu at top of page). This essay is included in the Missouri River drainage basin landform origins research project essay collection.

Sage Creek-O’Brien Coulee drainage divide area location map

Figure 1: Sage Creek-O’Brien Coulee drainage divide area location map (select and click on maps to enlarge).National Geographic Society map digitally presented using National Geographic Society TOPO software.

 

  • Figure 1 provides a location map for the Sage Creek-O’Brien Coulee drainage divide in Hill and Liberty Counties, Montana and illustrates a region along the United States-Canada border in north central Montana with the Saskatchewan southwest corner and Alberta southeast corner to the north. The Missouri River flows in a northeast direction from the figure 1 south edge (just west of center) to Fort Benton and Loma before turning to flow in a southeast and south direction around the Bears Paw Mountains south margin and then to the figure 1 east edge (just north of figure 1 southeast corner). The Milk River flows in a northeast direction from the Glacier Park region (just south of international border along figure 1 west edge) into southern Alberta and then flows in an east direction before turning to flow in a southeast direction back into the United States and to Havre, Montana. From Havre the Milk River flows in an east direction to the figure 1 east edge and east of figure 1 the Milk River joins the Missouri River with water eventually reaching the Gulf of Mexico. Big Sandy Creek is a northeast-oriented Milk River tributary flowing along the Bears Paw Mountains western flank and joining the Milk River a short distance west of Havre. Sage Creek is a southeast-oriented Big Sandy Creek tributary flowing from the near the international border west of and roughly parallel to the southeast-oriented Milk River segment upstream from Havre. Little Sage Creek is an east-southeast oriented Sage Creek tributary located south of Sage Creek. Sage Creek and Little Sage Creek originate in the East Butte area just south of the international border and Laird Creek is the unnamed southeast-oriented Sage Creek tributary. East and West Buttes shown on figure 1 represent high points in the Sweet Grass Hills, which rise significantly above the surrounding plains. O’Brien Coulee is not shown on figure 1, but drains in an east direction to Sage Creek and is located midway between Little Sage Creek and the highway from Chester to Gildford. West of O’Brien Coulee and east of south-oriented Eagle Creek is south-oriented Cottonwood Creek (not shown in figure 1) which drains to the Marias River. The Sage Creek-O’Brien Coulee drainage divide area investigated in this essay is located west of Sage Creek, north of O’Brien Coulee, south of the international border, and east of East Butte and south-oriented Cottonwood Creek. The Sage Creek-Milk River drainage divide area landform origins essay describes the region immediately to the east. Essays describing Milk River drainage divide areas are listed under the sidebar Milk River category.
  • Before looking at the Sage Creek-O’Brien Coulee drainage divide area in detail a brief summary of the regional big picture as determined from hundreds of previously written Missouri River drainage basin landform origins research project essays is given here. The figure 1 map area at the time the Sage Creek-O’Brien Coulee drainage divide area was eroded was located near the southwest margin of a rapidly melting thick North American ice sheet. The ice sheet had been located in a deep “hole” and had “roots” which at one time extended significantly below the surface on which the ice sheet had originally formed. The surface on which the ice sheet formed is today preserved, if it is preserved at all, in the highest level Rocky Mountain erosion surfaces, although those high level Rocky Mountain erosion surfaces have probably been uplifted since ice sheet formation. The deep “hole” in which the thick ice sheet was located was formed by deep glacial erosion under the ice sheet itself and by crustal warping caused by the ice sheet’s great weight. Crustal warping continued throughout the ice sheet’s rapid melt down and uplifted what are today high Rocky Mountain ranges as immense south and southeast oriented melt water floods flowed across them. Early during the ice sheet’s melt down history the ice sheet stood high above the surrounding landscape and melt water floods flowed in south and southeast directions along the ice sheet margin in whatever directions the regional topography permitted. Evidence for those early melt water flood flow routes has been removed from the plains regions, although can still be found in high Rocky Mountain regions. As ice sheet melting continued there came a time when the ice sheet surface no longer stood high above the surrounding landscape. By that time an immense southeast and south-oriented supra-glacial melt water river had carved a deep ice-walled canyon into the ice sheet surface and the floor of that ice-walled canyon was significantly lower in elevation than the bedrock surface south and west of the ice sheet southwest margin. The massive southeast and south oriented ice-marginal melt water floods were then captured by headward erosion of deep northeast and east-oriented valleys from the deep ice-walled canyon. Eventually the giant ice-walled canyon also became a bedrock-floored canyon and detached the ice sheet’s southwest margin. The northeast and east-facing Missouri Escarpment in Saskatchewan, North Dakota, and South Dakota is what remains today of that giant ice-walled and bedrock-floored canyon’s southwest and west wall. The present day Missouri River valley and its tributary Milk River valley eroded headward from that ice-walled and bedrock-floored canyon in northwest North Dakota during final stages of the ice sheet’s rapid melt down. Erosion of the Sage Creek-O’Brien Coulee drainage divide area occurred during those final rapid melt down history erosion events, although prior to those final melt down erosion events the region was probably deeply eroded by repeated ice-marginal melt water flood erosion events. How much material was removed from the figure 1 map region is difficult if not impossible to determine, although the Sweet Grass Hills provide a marker which may provide some clues.

Detailed location map for Sage Creek-O’Brien Coulee drainage divide area

Figure 2: Detailed location map for Sage Creek-O’Brien Coulee drainage divide area. United States Geological Survey map digitally presented using National Geographic Society TOPO software.

 

  • Figure 2 provides a detailed location map for the Sage Creek-O’Brien Coulee drainage divide area in Hill and Liberty Counties, Montana. The Canada-United States border is just north of the figure 2 north edge. County boundaries and names are shown. The Milk River flows in a southeast direction across the figure 2 northeast corner. Sage Creek originates on Mt. Brown (East Butte high point on figure 1) in northern Liberty County and flows in northeast direction before turning to flow in a southeast and south-southeast direction to the figure 2 east edge (south half). Laird Creek is the east-southeast oriented tributary flowing from near Ikes Butte (near figure 2 north edge) to join Sage Creek at the elbow of capture where Sage Creek turns from flowing in a northeast direction to flowing in a southeast direction. Little Sage Creek originates on the Mt. Brown east flank and flows in an east-southeast direction to join Sage Creek in Hill County. South of Little Sage Creek is east and east-southeast oriented O’Brien Coulee, which originates in eastern Liberty County and which joins Sage Creek north of Gildford in Hill County. Note how O’Brien Coulee has north-oriented headwaters in Liberty County and how just west of the north-northeast oriented O’Brien Coulee headwaters is a southwest and south-oriented Cottonwood Creek tributary, which flows roughly parallel to Cottonwood Creek before finally joining it. This situation developed as deep valleys eroded headward into the region. Headward erosion of the deep east-oriented O’Brien Coulee valley reached the east margin of what was at that time a major south-oriented flood flow channel moving flood waters probably to the actively eroding Marias River valley, but was unable to capture the south-oriented flood flow route on the Cottonwood Creek alignment. Flood waters along the eastern margin of the south-oriented flood flow channel reversed flow direction to erode the north-northeast oriented O’Brien Coulee headwaters valley while south-oriented flood flow further to the west continued to flow south and eroded the south-oriented Cottonwood Creek tributary valley. Note how Cottonwood Creek headwaters are located on the Mt. Brown south flank, just south of the northeast-oriented Sage Creek headwaters. While figure 2 does not show contour lines and Mt. Brown will be seen to stand high above the surrounding region and this relationship suggests headward erosion of the Sage Creek valley may beheaded south-oriented flood flow to the Cottonwood Creek valley. If so, topography at that time was very different from it is today. Unlikely as it may seen Mt. Brown may have been uplifted as flood waters flowed across the region. Also, as will be seen in the detailed topographic maps illustrated below, there is good evidence the south- and southeast-oriented flood flow deeply eroded the figure 2 map area.

Laird Creek-Sage Creek drainage divide area

Figure 3: Laird Creek-Sage Creek drainage divide area. United States Geological Survey map digitally presented using National Geographic Society TOPO software.

 

  • Figure 3 illustrates the Laird Creek-Sage Creek drainage divide area north and east of East Butte and south of the international border. The Canada-United States border is located near the figure 3 north edge. East Butte in the Sweet Grass Hills is located in the figure 3 southwest corner and as can be seen rises more than 1000 meters above the surrounding plains. Sage Creek originates just west of Mount Brown and flows in a north-northeast, east, southeast, northeast, and east direction to the figure 3 east center edge. Laird Creek flows in an east-southeast direction from just south of Bingham Lake (in figure 3 northwest quadrant) to join Sage Creek near the figure 3 east center edge. East-southeast oriented Laird Creek is joined by several north- and northeast-oriented tributaries from the south including Long Coulee, Lily Coulee, Stratton Creek, Deer Creek, Big Coulee, Mac Coulee, and Chicken Coulee, all of which originate on the north or northeast flank of the East Butte uplift area. The north and north-northeast oriented valley segments were probably eroded by reversals of flood flow on north ends of beheaded south-oriented flood flow routes, although today its is difficult to see where the south-oriented flood flow could have gone. Also east-southeast oriented Laird Creek (and Sage Creek further to the east) are joined by a series of southeast-oriented tributaries. It is much easier to see how these southeast-oriented tributary valleys could have been eroded by southeast-oriented flood flow routes captured by headward erosion of the deep Sage Creek-Laird Creek valley. West of Long Coulee is northwest-oriented Dohrs Creek and south of Dohrs Creek (originating on the Mt. Brown north side are headwaters of north-northwest oriented Bengor Creek and Bear Creek with Dohrs Creek and Bengor Creek being Bear Creek tributaries west of figure 3) and also west-oriented headwaters of north-northwest oriented Breed Creek (originating on Mt Brown west side in figure 3 southwest corner). West and north of the figure 3 map area Bear Creek and Breed Creek join the east-oriented Milk River in southern Alberta (see figure 1). The north-oriented Bear Creek and Breed Creek valleys were eroded by reversals of flood flow on south-oriented flood flow routes caused by headward erosion of the deep east-oriented Milk River valley. The challenge in interpreting the figure 3 landscape is to try to visualize the landscape as flood waters were deeply eroding the region (and possibly while the East Butte erosion resistant rock masses were being uplifted). Figures 4-7 will look at the East Butte region using different map scales and locations to try to illustrate what happened.

Detailed map of Deer Creek-Sage Creek drainage divide area

Figure 4: Detailed map of Deer Creek-Sage Creek drainage divide area. United States Geological Survey map digitally presented using National Geographic Society TOPO software.

 

  • Figure 4 provides a detailed topographic map of the Deer Creek-Sage Creek drainage divide area north and east of Mount Brown (which was seen in less detail in figure 3 above). Mount Brown is located near the figure 4 southwest corner. Sage Creek flows in a north-northeast direction from the figure 4 south edge (just east of Mount Brown) into section 8 (just south of Black Jack Butte) where it turns to flow in an east and southeast direction in the north half of section 15 (north of Mount Lebanon) and then turns to flow in a northeast and east direction to the figure 4 east center edge. Deer Creek originates in the northeast corner of section 18 (on Mount Brown north flank) and flows in a north-northeast direction into section 8 where it flows in a north-northwest and north direction around the Black Jack Butte west flank and then turns to flow in an east direction north of Black Jack Butte. North and east of figure 4 Deer Creek joins Laird Creek, which then joins Sage Creek (see figure 3). Also originating on the Mount Brown north flank (and in section 18) is north and north-northwest oriented Bengor Creek, which flows to the figure 4 northwest corner area and west and north of figure 4 joins Bear Creek, which then joins the Milk River in southern Alberta. Originating in section 7 (between Bengor Creek and Deer Creek) is north-oriented Dohrs Creek, which flows across section 6 to the figure 4 north edge and then north and west of figure 4 to also join Bear Creek. West-oriented Breed Creek can just barely be seen in the figure 4 southwest corner and west and north of figure 4 flows to the east-oriented Milk River in southern Alberta. Note how through valleys link various drainage basins. Perhaps the most obvious through valley links the Deer Creek and Sage Creek valleys in section 8 just south of Black Jack Butte, The map contour interval is 20 feet and the through valley floor elevation at it lowest point is between 4800 and 4820 feet, which is approximately 100 feet higher than floors of the adjacent Deer Creek and Sage Creek valleys. However the through valley is significantly lower than Black Jack Butte to the north (5201 feet) and Mount Brown to the south (6958 feet). Using the Black Jack Butte elevation the through valley has been eroded to a depth of approximately 300 feet. The through valley was eroded by east-oriented flood water moving to what was then the east-oriented Sage Creek valley. The east-oriented flood water was moving in a south-southeast direction along what is today the north-northwest oriented Deer Creek valley segment and probably was moving in a south direction on the Dohrs Creek alignment before flowing south on the Deer Creek alignment and then east to the east-oriented Sage Creek valley segment. Headward erosion of the deep east-oriented Deer Creek valley north of Black Jack Butte beheaded the south-oriented flood flow to the actively eroding Sage Creek valley and diverted the water to what was then the actively eroding Laird Creek valley. Large volumes of south-oriented flood water were still reaching the north-oriented Deer Creek valley south of the Deer Creek-Sage Creek through valley because the Deer Creek valley was eroded more than 100 feet deeper after flood flow ceased to move in the through valley. Headward erosion of the deep east-oriented Milk River valley north of the figure 4 map region beheaded the south-oriented flood flow on the Bear Creek-Dohrs Creek and Bear Creek-Bengor Creek alignment and soon thereafter on the Breed Creek alignment and flood waters on the north ends of the beheaded flood flow routes reversed flow direction to erode the north-oriented Dohrs Creek-Bear Creek, Bengor Creek-Bear Creek, and Breed Creek valleys.

Sage Creek-Little Sage Creek drainage divide area

Figure 5: Sage Creek-Little Sage Creek drainage divide area. United States Geological Survey map digitally presented using National Geographic Society TOPO software.

 

  • Figure 5 illustrates the Sage Creek-Little Sage Creek drainage divide area located south of the figure 3 map area and includes significant overlap areas with figure 3. Figure 5 better illustrates how East Butte stands more than 1000 meters above the surrounding plain. From topographic map evidence alone it is difficult to say exactly what East Butte is, although from the shape it appears to be some type of volcanic feature or igneous intrusion which has either been built above the surrounding plain or exposed by deep erosion of the surrounding region. It is also possible it was uplifted as deep erosion of the surrounding region was taking place. Bengor Creek flows in a north and north-northwest direction from the Mount Brown north flank to the figure 5 northwest corner. Breed Creek originates between Mount Brown and Mount Royal and flows in a northwest and west direction to the figure 5 west center edge. Dohrs Creek flows in north and north-northwest direction from the west side of Black Jack Butte to the figure 5 north edge (east of northwest corner). These streams all flow to the east-oriented Milk River in southern Alberta and flow in valleys eroded by reversals of south-oriented flood flow which occurred when headward erosion of the deep Milk River valley beheaded the south-oriented flood flow routes. Sage Creek originates on the east side of a through valley between Mount Brown and Mount Royal and flows in a north-northeast direction to the Black Jack Butte south flank and then turns to flow in an east direction, etc. as described in figure 3. Little Sage Creek originates west of Mount Lebanon and flows in an east and southeast direction south of Mount Lebanon and then in an east direction out onto the plains where it turns to flow in a southeast direction to flow to near the figure 5 southeast corner. Just south of the Little Sage Creek headwaters is southeast and south-oriented Tootsie Creek and west of Tootsie Creek is Government Creek, with Tootsie Creek joining Government Creek south of the figure 5 map area. South of the figure 5 map area Government Creek flows to south-oriented Cottonwood Creek, which flows to the Marias River. Note the through valley between Mount Brown and Mount Royal. On the through valley west side is Breed Creek, which today flows in a west and north-northwest direction to the Milk River in Alberta. On the through valley east side are headwaters of Sage Creek, which after flowing in a north direction for a short distance turns and flows in a southeast direction with water eventually reaching the Milk River in Montana. The map contour interval is 20 meters and the through valley floor elevation is between 1900 and 1920 meters. Mount Brown to the north reaches 2121 meters while Mount Royal to the south reaches 2107 meters, which means the through valley is approximately 200 meters deep. Something eroded that through valley, the floor of which today is almost 1000 meters higher than elevations in the figure 5 northeast corner. The through valley was eroded by south-oriented flood flow moving from the Breed Creek alignment to what was then the actively eroding Sage Creek valley. Note also how east of Mount Brown the Sage Creek valley is linked by another through valley with the south-oriented Tootsie Creek headwaters valley. Prior to headward erosion of north-northeast oriented Sage Creek valley southeast-oriented flood water flowed to what was then the actively eroding Government Creek-Tootsie Creek valley system and the Marias River valley.

Detailed map of Sage Creek-Little Sage Creek drainage divide area

Figure 6: Detailed map of Sage Creek-Little Sage Creek drainage divide area. United States Geological Survey map digitally presented using National Geographic Society TOPO software.

 

  • Figure 6 provides a detailed topographic map of the Sage Creek-Little Sage Creek drainage divide area on the east side of the East Butte upland region. Mount Lebanon is the high point near the figure 6 center and reaches an elevation of 5807 feet. The high elevation near the east edge of section 30 (near figure 6 southwest corner) is 6566 feet. Deer Creek originates in section 18 and flows in north-northeast direction across the figure 6 northwest corner. Sage Creek originates near the figure 6 west center edge in section 19 and flows in a north-northeast direction to the figure 6 north edge and then turns to flow in an east and southeast direction into section 15 where it turns to flow in a northeast and east-northeast direction to the figure 6 north edge (east half). Little Sage Creek originates near the section 21 northwest corner and flows in a southeast, northeast and east direction around the Mount Lebanon south flank to the figure 6 east edge. East and south of figure 6 Little Sage Creek joins southeast-oriented Sage Creek, which flows to northeast-oriented Big Sandy Creek (see figure 1). Tootsie Creek originates in the northeast corner of section 30 (figure 6 southwest quadrant) and flows in a north-northeast direction to the section 20 north center before turning to flow in southeast and south direction to the figure 6 south edge (east half). Government Creek originates in the section 29 southeast corner and flows in a south-southeast direction to the figure 6 south edge (west half). South of figure 6 Tootsie Creek joins south-oriented Government Creek, which flows to the Cottonwood Creek. South-oriented Corral Creek can just barely be seen in the figure 6 southwest corner and is another south-oriented stream which joins Government Creek to form south-oriented Cottonwood Creek, which then flows to the Marias River. Note the through valley near the section 17 south center margin linking the north-northeast oriented Sage Creek valley with the Tootsie Creek elbow of capture (where north-northeast oriented Tootsie Creek turns to flow in a southeast direction). A spot elevation indicates the through valley floor elevation is 5455 feet. The hill immediately to the northeast is shown as having an elevation of 5885 feet and elevations to the southwest rise even higher. In other words the through valley is at least 430 feet deep and was eroded by southeast-oriented flood flow moving to what was at that time the actively eroding Tootsie Creek valley. Headward erosion of the deep north-northeast oriented Sage Creek valley beheaded the southeast-oriented flood flow. To the northwest in section 18 a somewhat shallower and higher level through valley links the Deer Creek headwaters valley with the Sage Creek valley and is a northwest extension of the southeast-oriented Tootsie Creek valley segment alignment. Careful study of the East Butte region reveals many other similar through valleys, which can be used to reconstruct flood flow routes as deep valleys eroded headward into the region. These through valleys and the drainage histories can be worked out if one is willing to assume massive quantities of flood water deeply eroded the region and perhaps simultaneous uplift of what are today the East Butte resistant rock masses.

Cottonwood Creek-O’Brien Coulee drainage divide area

Figure 7: Cottonwood Creek-O’Brien Coulee drainage divide area. United States Geological Survey map digitally presented using National Geographic Society TOPO software.

 

  • Figure 7 illustrates the Cottonwood Creek-O’Brien Coulee drainage divide area south and east of the East Butte upland area and includes overlap areas with figure 5. The southeast flank of the East Butte upland area can be seen in the figure 7 northwest quadrant. Government Creek is labeled and flows in a south direction from the figure 7 north edge (west half) to join Corral Creek in the figure 7 southwest quadrant. Corral Creek flows in a south and south-southeast direction from the figure 7 north edge (near northwest corner) to join Government Creek and to form south oriented Cottonwood Creek which flows to the figure 7 south edge (west half). Horse Creek is a south-southeast oriented stream flowing across the figure 7 southwest corner. South of the figure 7 map area Cottonwood Creek flows to the Marias River, which in turn flows to the Missouri River (see figure 1). Little Sage Creek flows in a southeast direction across the figure 7 northeast corner. O’Brien Coulee originates as a north-oriented drainage route in the figure 7 south center area and then quickly turns to drain in an east direction to the figure 7 east edge (south half). East of the figure 7 map area O’Brien Coulee drains to southeast-oriented Sage Creek, which flows to northeast-oriented Big Sandy Creek, which in turn flows to the Milk River. North of O’Brien Coulee is east-oriented Fourmile Coulee, which east of the figure 7 map area drains to O’Brien Coulee. Note how the east-oriented O’Brien Coulee valley is linked by a through valley to the valley of a southwest and south-oriented Cottonwood Creek tributary. The through valley floor elevation is between 1120 and 1040 meters (the map contour interval is 20 meters). Elevations along the figure 7 south center edge rise to at least 1100 meters and to the north rise even higher. The through valley is at least 60 meters deep and provides evidence of a major east-oriented flood flow channel, which once moved south- and southeast-oriented flood flow from what were then actively eroding Government Creek and Corral Creek valleys to the Sage Creek valley (probably at the same time that flood flow was also moving south on the Cottonwood Creek alignment). Headward erosion of the deeper Cottonwood Creek valley from what was then the actively eroding Marias River valley to the south  of figure 7 beheaded the east-oriented flood flow on the east-oriented O’Brien Coulee flood flow channel to the Sage Creek valley. Subsequently headward erosion of the deep Sage Creek valley and deep Sage Creek tributary valleys beheaded south and south-southeast oriented flood flow to the Government Creek valley while soon thereafter headward erosion of the deep east-oriented Milk River valley across southern Alberta (north of the figure 7 map area) beheaded and reversed the south- and south-southeast oriented flood flow routes to the Corral Creek valley. Since that time the East Butte region landscapes have not significantly changed.

Detailed map of Cottonwood Creek-O’Brien Coulee drainage divide area

Figure 8: Detailed map of Cottonwood Creek-O’Brien Coulee drainage divide area. United States Geological Survey map digitally presented using National Geographic Society TOPO software.

 

  • Figure 8 provides a detailed topographic map of the Cottonwood Creek-O’Brien Coulee drainage divide area seen in less detail in figure 7 above. O’Brien Coulee originates south of section 22 in the figure 8 southeast quadrant and drains in a north and then east direction to the figure 8 east edge. Cottonwood Creek flows in a south direction along the figure 8 west edge (south half) to the figure 8 southwest corner. A Cottonwood Creek tributary flows in a south-southeast direction in section 10 (northeast quadrant) and in section 15 turns to flow in a west-southwest and southwest direction to join Cottonwood Creek south of the figure 8 southwest corner. Note how the Cottonwood Creek tributary and O’Brien Coulee almost intersect and are linked by a through valley even though they flow today to quite different river basins. The through valley floor elevation in the section 15 southeast quadrant and section 22 northeast quadrant is between 3350 and 3360 feet (the map contour interval is ten feet). Elevations in section 28 near the figure 8 south center edge rise to 3581 feet and a short distance south of the figure 8 map rise to more than 3600 feet. Elevations along the figure 8 north edge in section 7 (near northwest corner) rise to more than 3500 feet, although north of the figure 8 map area elevations rise to more than 3600 feet. The through valley is at least 240 feet deep and provides evidence of a major east-oriented flood flow channel. The north oriented O’Brien Coulee headwaters valley and the north- and northwest-oriented tributary valleys to the Cottonwood Creek tributary valley were eroded by reversals of flood waters on the north ends of beheaded south-oriented flood flow routes. The south-southeast oriented Cottonwood Creek tributary valley was eroded by south-oriented flood flow on that flood flow north of the O’Brien Coulee valley. Probably the south-oriented flood flow was first captured by headward erosion of the deep east-oriented O’Brien Coulee valley, which probably eroded headward into the region at approximately the same time as the deep south-oriented Cottonwood Creek valley eroded headward into the region. The two deep valleys competed with each other as they captured the massive south-oriented flood flow moving across the region and while flood waters were removing considerable thicknesses of what was probably easily eroded bedrock. In the end the Cottonwood Creek valley successfully captured the west end of the O’Brien Coulee valley including the south-southeast-oriented Cottonwood Creek tributary headwaters valley.

Little Sage Creek-O’Brien Coulee drainage divide area

Figure 9: Little Sage Creek-O’Brien Coulee drainage divide area. United States Geological Survey map digitally presented using National Geographic Society TOPO software.

 

  • Figure 9 illustrates the Little Sage Creek-O’Brien Coulee drainage divide area east of the figure 7 map area and there is no overlap area between figure 7 and figure 9. Sage Creek is labeled and flows in a south-southeast direction from the figure 9 north edge (east half) to the figure 9 southeast corner. Little Sage Creek flows in an east-southeast and east direction from the figure 9 northwest corner to join Sage Creek in the figure 9 northeast quadrant. South of Little Sage Creek is east-southeast, northeast, and east-southeast oriented Big Coulee, which joins Sage Creek in the figure 9 east center region. South of Big Coulee is east and east-southeast oriented O’Brien Coulee, which drains from the figure 9 west edge to join Sage Creek just south of the figure 9 southeast corner. Fourmile Coulee joins O’Brien Coulee near the figure 9 west edge. The figure 9 map contour interval is 20 meters and the figure 9 map area appears to be a region of low relief. However a close look reveals a northwest-southeast oriented through valley linking the Big Coulee and O’Brien Coulee valleys. The through valley is best seen by observing the streamlined northwest-southeast oriented low hill in the figure 9 southeast quadrant defined by the 940 meter contour line and a 949 meter spot elevation. The low hill is an erosional remnant between the south-southeast oriented Sage Creek valley and the northwest to southeast oriented Big Coulee-O’Brien Coulee through valley and provides evidence of how southeast and south-southeast oriented flood waters deeply eroded the surrounding valleys. The streamlined hill is best seen on more detailed maps such as figure 10 below where it appears as a much more impressive landscape feature. While the low hill provides evidence of deep flood erosion in the figure 9 map area the evidence only documents erosion in the few tens of meters range and not in the thousand meter plus range suggested by high level through valleys in the East Butte region seen in figures 3-6. The question can validly be asked was more than one thousand meters of bedrock material was removed from the entire region surrounding East Butte (including the figure 9 map area) or was the East Butte resistant rock mass was being uplifted as flood waters flowed across the region? While the latter hypothesis may appear far-fetched delayed crustal warping related to the nearby thick ice sheet’s great weight could very well have been taking place at the same time as the thick ice sheet was melting and the East Butte uplift could very well have occurred as massive melt water floods flowed across the region. The alternate hypothesis requires removal of tremendous amounts of bedrock material, which then had to be deposited somewhere else.

Detailed map of Big Coulee-O’Brien Coulee drainage divide area

Figure 10: Detailed map of Big Coulee-O’Brien drainage divide area. United States Geological Survey map digitally presented using National Geographic Society TOPO software.

 

  • Figure 10 is a reduction of a detailed topographic map of the streamlined erosional remnant in the Big Coulee-O’Brien Coulee drainage divide area seen in less detail in figure 9 above. Sage Creek flows in a south-southeast direction from the figure 10 north edge (east half) to the figure 10 southeast corner. Big Coulee make a jog to the north in the figure 10 northwest corner and then turns to drain in an east-southeast direction to join Sage Creek in the figure 10 northeast quadrant. O’Brien Coulee drains in an east-southeast direction from the figure 10 west edge (south half) to the figure 10 south center edge and joins Sage Creek south and east of the figure 10 southeast corner. The northwest-southeast oriented streamlined erosional residual is located near the figure 10 center and has a spot elevation of 3129 feet at its highest point. Compare that elevation with the top of Mount Brown, which was 6958 feet. Elevations in the Sage Creek valley to the east are in the 2870 to 2880 foot range while the floor of the Big Coulee-O’Brien Coulee through valley to the west has an elevation of between 3030 and 3040 feet at its lowest point along the drainage divide. If the high point on the erosional remnant is used as a reference marker the large northwest-southeast oriented Big Coulee-O’Brien Coulee through valley west of the streamlined erosional residual has been lowered by approximately 100 feet and the Sage Creek valley has been lowered by almost 240 feet. The valleys on either side of the streamlined erosional remnant document significant melt water flood erosion of the regional bedrock surface without even looking at the East Butte region to the north. However, as seen in the earlier figures the East Butte region documents much deeper flood water erosion of the entire Sage Creek-O’Brien Coulee drainage divide area. Whether present day East Butte elevations can be used as reliable markers to determine the true depth of melt water flood erosion can be debated. However, there can be no question that melt water floods significantly lowered landscapes throughout the entire Sage Creek-O’Brioen Coulee drainage divide area.

Additional information and sources of maps studied

This essay has provided only a sample of the detailed topographic map evidence supporting the flood erosion interpretation. Many additional illustrations could be provided. Readers are encouraged to look at mosaics of detailed topographic maps to see the abundance of available data. Maps used in this study were created and published by the United States Geologic Survey and can be obtained directly from the United States Geological Survey and/or from dealers offering United States Geological Survey maps. Hard copy maps can also be observed at United States Geological Survey map depositories, which are located throughout the United States and elsewhere. Illustrations used here were created using National Geographic Society TOPO software and digital map data. TOPO software and map data can be obtained from the National Geographic Society and/or dealers offering National Geographic Society digital map data.

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