Woody Island Coulee-Milk River drainage divide area landform origins, northwest Phillips and northeast Blaine Counties, Montana, USA

· Milk River, Montana
Authors

Abstract:

Topographic map interpretation methods are used to determine landform origins in the Woody Island Coulee-Milk River drainage divide area in northwest Phillips and northeast Blaine Counties, Montana. Woody Island Coulee is an east and south-oriented tributary which drains a large upland erosion surface near the Canadian border to southeast oriented Cottonwood Creek, which flows to a north-northeast oriented Milk River valley segment. Upstream from the north-northeast Milk River valley segment the Milk River flows on the floor of a large southeast and east oriented valley at elevations more than 200 meters lower than elevations of the upland erosion surface to the north. Woody Island Coulee headwaters are located in what is interpreted to be an east and/or northeast oriented abandoned headcut standing above the surrounding high level erosion surface to the east and the deep southeast-oriented Battle Creek valley to the west and southwest. Milk River tributaries between Battle Creek and Cottonwood Creek are generally oriented in southeast directions and are linked by through valleys to northeast-oriented Cottonwood Creek tributary valleys. This evidence suggests the southeast-oriented Milk River tributary valleys were eroded headward across northeast-oriented flood flow as the 200 meter plus deep Milk River valley eroded headward across the region. Flood waters were derived from a rapidly melting North American ice sheet and were generally flowing in southeast directions along the ice sheet’s southwest margin. The northeast-oriented flood flow was channeled between what were then the emerging Bears Paw Mountains and Little Rocky Mountains as melt water moved toward the melting ice sheet’s southwest margin. An internally consistent pattern of deep valley erosion can be constructed for the region.

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 Woody Island Coulee-Milk River drainage divide area landform origins in northwest Phillips and northeast Blaine Counties, Montana, 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 Woody Island Coulee-Milk River drainage divide area landform evidence in northwest Phillips and northeast Blaine 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.

Woody Island Coulee-Milk River drainage divide area location map

Figure 1: Woody Island Coulee-Milk River 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 is a location map for the Woody Coulee-Milk River drainage divide area in northwest Phillips and northeast Blaine Counties, Montana and illustrates a region of north central Montana with southwest Saskatchewan and southeast Alberta north of the international border. The Missouri River flows in a generally east direction from the figure 1 west edge (near the figure 1 southern margin) to Fort Peck Lake and then to the figure 1 east edge. The Milk River flows in a southeast direction from the figure 1 west edge (near international border) to Havre, Montana and then to Malta, Montana. At Malta the Milk River makes a pronounced north-northeast jog and then flows in a southeast direction to join the Missouri River downstream from Fort Peck Dam. Woody Island Coulee is located just south of the international border and is an east-northeast, east-southeast, and south-oriented tributary to southeast-oriented Cottonwood Creek, which joins the Milk River downstream from Malta. East of the Woody Island Coulee-Cottonwood Creek area is southeast-oriented Whitewater Creek. Whitewater Creek originates in southern Saskatchewan and crosses the international border almost directly north of Malta and joins the Milk River near Nelson Reservoir. West of the Woody Island Coulee headwaters is south-southeast oriented Battle Creek, which originates in the Cypress Hills area of southwest Saskatchewan and which joins the Milk River near Chinook, Montana. An unnamed (in figure 1) southwest and southeast-oriented Milk River tributary is located between Battle Creek and the Cottonwood Creek headwaters and on more detailed maps is named Thirtymile Creek. The Woody Island Coulee-Milk River drainage divide area investigated in this essay is south of Woody Island Coulee, north of the Milk River, east of Thirtymile Creek, and west of a north-south line through Wagner, Montana (just west of Malta). The Whitewater Creek-Milk River drainage divide area landform origins north central Phillips County, Montana essay describes the region between Whitewater Creek and the Milk River immediately to the east. Note also Beaver Creek which originates in the Little Rocky Mountains (near figure 1 south center) and flows in a northeast, east-southeast, north, and southeast direction to join the Milk River between Saco and Hinsdale. The Milk River-Missouri River drainage divide area landform origins between Beaver and Larb Creeks, the Peoples Creek-Beaver Creek drainage divide area landform origins and other essays listed under the sidebar Milk River category describe and illustrate regions south of this essay’s study region.
  • The Woody Island Coulee-Milk River drainage divide area in northwest Phillips and northeast Blaine Counties, Montana had a complex erosion history, which to properly understand requires the rapid melting of a thick North American ice sheet, with the ice sheet being located in a deep “hole”. The ice sheet had formed on a topographic surface now preserved, if it is preserved at all, on the highest level Rocky Mountain erosion surfaces. Those high level Rocky Mountain erosion surfaces were probably uplifted by ice sheet caused crustal warping, but what is important is massive melt water floods flowed in southeast directions on those high level erosion surfaces along the ice sheet’s southwest margin and as the ice sheet melted were captured by deep east and northeast-oriented valleys which eroded headward from the deep “hole” where melting ice had been. East of Rocky Mountain outliers, such as the Little Rocky Mountains and Bears Paw Mountains seen in figure 1, the deep east and northeast-oriented valleys generally captured south, south-southeast, or southeast oriented melt water floods and diverted the flood waters onto the ice sheet surface or into deep ice-walled canyons eroded by supra glacial rivers into the decaying ice sheet’s surface. However, the presence of mountains consisting of more erosion resistant rocks created more complex flood flow patterns, which are encountered in the figure 1 region. The deep east-oriented Missouri River valley eroded headward from a deep ice-walled and bedrock-floored canyon, the southwest wall of which today is the northeast-facing Missouri Escarpment in northwest North Dakota, and the southeast-oriented Milk River valley and Whitewater Creek valley were eroded headward along and across massive south, south-southeast, and southeast oriented ice-marginal flood flow until reaching the Nelson Reservoir area slightly north and east of Malta.
  • In the region between Malta and Nelson Reservoir the actively eroding and north-northeast oriented Milk River valley eroded headward across what were several well-developed southeast-oriented flood flow channels moving flood water to a major south oriented flood flow channel located along the route of the present day north-oriented Beaver Creek segment seen in figure 1. A deep and well-defined through valley links the north-oriented Beaver Creek valley with the “V” in Fort Peck Lake (located near figure 1 south center edge) and the north-oriented Musselshell River, which joins the Missouri River at the south end of the “V” (not shown in figure 1). This south oriented flood flow channel had probably eroded headward from the deep Yellowstone River valley, which was eroding headward from the same ice-walled and bedrock-floored canyon slightly in advance of the deep Missouri River and Milk River valleys. Headward erosion of the deep Missouri River valley probably captured the south-oriented flood flow channel slightly in advance of the Milk River valley capture further to the north. Flood waters on the north end of the flood flow channel beheaded by deep Missouri River valley headward erosion reversed flow direction and the deep Musselshell River valley then eroded headward to capture southeast-oriented flood flow, which had been moving to the newly eroded Yellowstone River valley. Milk River valley headward erosion next captured the south- and southeast-oriented flood flow channels feeding this major south-oriented flood flow channel and flood waters on north end of the beheaded flood flow channel reversed flow direction to erode the north-oriented Beaver Creek valley segment.
  • Further complicating the situation was west of the actively Milk River and Missouri River valleys elevations were much higher than they are today and massive southeast-oriented ice-marginal melt water floods were flowing on those high level surfaces. As deep valleys eroded headward into the figure 1 region those higher elevation southeast-oriented flood waters were diverted to flow towards the actively eroding deep valley heads. These water movements generally lowered the regional landscape, however as already mentioned the Rocky Mountain outliers are composed of much more erosion resistant materials than the surrounding regions. The presence of these erosion resistant masses worked to create more complex water movements where flood waters would flow in a southeast direction on the west side of a mountain mass and then turn to flow in a northeast direction towards deep southeast-oriented valleys located north and east of the mountain mass. In this essay we see evidence for northeast-oriented flood flow, which probably moved between the Bears Paw Mountains and Little Rocky Mountains to an actively southeast oriented Cottonwood Creek valley. Headward erosion of the deep Missouri River valley soon ended this northeast oriented flood movement, although the northeast-oriented flood flow occurred as the Milk River valley and some of its southeast-oriented tributary valleys were being eroded headward in the Woody Island Coulee-Milk River drainage divide area. To fully understand these flood water movements it is necessary to view a much larger region than is being shown in this essay or any of the single essays in this series. My major goal in this essay is to convince you the Woody Island Coulee-Milk River drainage divide area was eroded by immense floods.

Detailed location map for Woody Island Coulee-Milk River drainage divide area

Figure 2: Detailed location map for Woody Island Coulee-Milk River 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 Woody Island Coulee-Milk River drainage divide area located in northwest Phillips and northeast Blaine Counties, Montana. The north-south oriented county line is shown with Phillips County to the east and Blaine County to the west. The west-east oriented international border is located just north of the figure 2 map area. The Milk River flows from Fort Belknap along the figure 2 west edge in an east-southeast direction to Malta near the south edge of the figure 2 southeast quadrant and then turns to flow in a north-northeast direction before turning to flow in southeast direction to the figure 2 east edge (south half). Major Milk River tributaries from the north (from east to west) include south-southeast oriented Whitewater Creek, southeast-oriented Little Cottonwood Creek, southeast-oriented Cottonwood Creek, southeast-oriented Assiniboine Creek, south-southeast oriented Dodson Creek, south-southeast oriented Savoy Creek, south-southeast oriented Wayne Creek, and southwest and southeast oriented Thirtymile Creek (joining the Milk River near Harlem). Woody Island Coulee drains in roughly an east direction from the figure 2 northwest corner to near Chapman (south of figure 2 north center edge) and then turns to drain in a south direction to southeast-oriented Cottonwood Creek. Murray Coulee is a named east-southeast and north-northeast oriented Woody Island Coulee tributary. Note also northeast and southwest-oriented Cottonwood Creek tributaries including northeast oriented Black Coulee. The prevailing direction of Milk River tributaries from the north in the figure 2 map area is to the southeast, which suggests headward erosion of the deep Milk River valley captured multiple southeast oriented flood flow channels. However, the northeast and southwest oriented Cottonwood Creek tributaries (and southwest-oriented Savoy Creek tributaries and Thirtymile Creek headwaters) suggest the situation was somewhat more complicated.
  • To understand this complication first note north-northeast oriented Beaver Creek in the figure 2 southeast corner. Beaver Creek drains the north end of what is today a large north-south oriented through valley linking the Milk River valley with the Missouri River valley at the point where the north-oriented Musselshell River joins the Missouri River. Prior to headward erosion of the deep Missouri River valley and subsequent headward erosion of the deep Milk River valley this north-south oriented through valley was initiated (at a much higher elevation than it is today) as a south-oriented flood flow channel to the actively eroding Yellowstone River valley. Headward erosion of the deep Missouri River then captured the south-oriented flood flow channel and flood waters on the north end of the beheaded flood flow channel reversed flow direction to erode the north-oriented Musselshell River valley. Next headward erosion of the deep Milk River valley captured the south-oriented flood flow channel and its southeast-oriented tributary flood flow channels (including those on the present day Whitewater Creek, Little Cottonwood Creek, Cottonwood Creek, and Assiniboine Creek alignments). At this time the deep Milk River valley had not eroded headward west of the Malta, Montana region and flood waters were still flowing on a high level topographic surface where the Milk River valley is today. Flood flow moving around the south end of what was then an emerging Bears Paw Mountain area moved in a northeast direction to what was then the actively eroding and deep southeast-oriented Cottonwood Creek valley and other deep southeast-oriented Milk River tributary valleys (which had been initiated as tributary flood flow routes to the south-oriented through valley). Headward erosion of the deep east-southeast oriented Milk River valley and deep southeast-oriented Milk River tributary valleys soon captured this northeast-oriented flood flow, with northeast-oriented flood flow routes being reversed to erode southwest-oriented tributary valleys. At the same time headward erosion of the deep Missouri River valley south of the Bears Paw Mountains ended all northeast-oriented flood flow to the figure 2 map area.

East Fork Battle Creek-Woody Island Coulee drainage divide area

Figure 3: East Fork Battle Creek-Woody Island Coulee drainage divide area. United States Geological Survey map digitally presented using National Geographic Society TOPO software.

 

  • Figure 3 illustrates the East Fork Battle Creek-Woody Island Coulee drainage divide area in northern Blaine County, Montana. The East Fork Battle Creek originates north of Cherry Ridge in the figure 3 southwest quadrant and flows in a northwest direction to the figure 3 west center edge. West of the figure 3 map area the East Fork Battle Creek turns to flow in a southwest direction to join south-southeast oriented Battle Creek, which then flows to the Milk River. The northwest-oriented East Fork Battle Creek valley was eroded by a reversal of southeast oriented flood flow caused by headward erosion of the deep southwest-oriented East Fork Battle Creek valley segment. The southeast-oriented flood flow had been moving to what is today a northeast, southeast, and east oriented Woody Island Coulee tributary valley seen in the figure 3 south center region. Woody Island Coulee originates in the Cherry Ridge upland region and drains in an east, northeast, and east direction to the figure 3 east edge (south of center) and eventually to southeast-oriented Cottonwood Creek, which then flows to the Milk River. The map contour interval is 20 meters and Cherry Ridge is located along the north edge of an upland region which forms an asymmetric drainage divide between the deeper Battle Creek drainage basin to the west and the more gently sloping Woody Island Coulee (and Cottonwood Creek) drainage basin to the east. This evidence suggests a large and deep southeast-oriented melt water flood flow channel eroded headward west of the Cherry Ridge upland from the Milk River valley roughly along the present day Battle Creek alignment with southwest-oriented tributary valleys eroding headward along the large and deep southeast-oriented valley’s southwest-facing wall. Note Irvins Coulee which drains in a southwest direction to join northwest oriented East Fork Battle Creek near the figure 3 west center edge. Irvins Coulee has southeast-oriented tributaries from the northwest and northwest-oriented tributaries from the southeast and is also linked by a through valley to an east-oriented Woody Island Coulee tributary, which can be seen draining in an east direction near the figure 3 north edge. The Irvins Coulee valley probably originated as a northeast-oriented flood flow channel which eroded headward across southeast-oriented flood flow. The southeast-oriented tributary valleys were eroded by southeast-oriented flood flow channels captured by that northeast-oriented flood flow channel while the northwest-oriented tributary valleys were eroded by reversals of flood on northwest ends of beheaded southeast-oriented flood flow channels. The reversal of flood flow caused by headward erosion of the deep southwest-oriented East Fork Battle Creek valley, which caused the reversal of flood flow that eroded the northwest-oriented East Fork Battle Creek valley segment, also beheaded and reversed flood flow on the southwest end of the Irvins Coulee valley, which then eroded the southwest-oriented Irvins Coulee valley.

Woody Island Coulee-Thirtymile Creek drainage divide area

Figure 4: Woody Island Coulee-Thirtymile Creek drainage divide area. United States Geological Survey map digitally presented using National Geographic Society TOPO software.

 

  • Figure 4 illustrates the Woody Island Coulee-Thirtymile Creek drainage divide area south of the figure 3 map area and includes overlap areas with figure 3. The Northwest Fork Thirtymile Creek flows in a southwest direction to the figure 4 southwest corner and then turns to flow in a southeast direction to join Thirtymile Creek. Thirtymile Creek begins as a west-oriented stream along the north side of the west end of Middle Butte (in figure 4 south center area) and then flows in a south-southwest direction to the figure 4 south edge (west half). South of figure 4 Thirtymile Creek flows in a south-southeast and southeast direction to join the Milk River (see figure 2). Other south-oriented streams flowing from the Middle Butte upland to the figure 4 south edge are Thirtymile Creek tributaries. Cherry Ridge is located in the figure 4 northwest quadrant. Choteau Coulee drains the west side of Cherry Ridge in a west and southwest direction to southeast-oriented Battle Creek. East-oriented Woody Island Coulee headwaters are located in the east and northeast-oriented basin located between Cherry Ridge and Middle Butte and then turn to flow in a northeast direction to the figure 4 northeast corner area. Note the southwest-facing wall of the large southeast-oriented Battle Creek valley located south and west of the Cherry Ridge-Middle Butte upland. Elevations on the upland exceed 1060 meters while elevations at the figure 4 southwest corner are approximately 860 meters and Battle Creek to the southwest is flowing at an elevation of approximately 760 meters. The elevation of the Woody Island Coulee floor near the figure 4 northwest corner is approximately 960 meters. The east and northeast-oriented basin drained by Woody Island Coulee is an abandoned headcut, which prior to headward erosion of the deep southeast-oriented Battle Creek-Milk River valley was eroded by east and/or northeast-oriented flood flow moving across the figure 4 map area. The flood flow was probably moving in a northeast direction around the what was then the emerging Bears Paw Mountains and was moving into the deep “hole” being created as the thick North American ice sheet melted. Most likely the water was moving to a breach through the decaying ice sheet’s decaying southwest margin to a large southeast-oriented ice-walled and ice-floored canyon, which had been carved by supra glacial melt water floods into the ice sheet’s surface (the northeast-facing Missouri Escarpment is what remains of that canyon’s southwest wall, although the Missouri Escarpment was not formed until the canyon became an ice-walled and bedrock-floored canyon). Headward erosion of the deep southeast-oriented Milk River-Battle Creek valleys captured the northeast-oriented flood flow (as did headward erosion of the deep Missouri River valley to the south) and the Cherry Ridge-Middle Butte upland basin was left as an abandoned headcut standing above the surrounding region.

Murray Coulee-Buckley Creek drainage divide area

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

 

  • Figure 5 illustrates the Murray Coulee-Buckley Creek drainage divide area located east of the figure 4 map area and includes a thin overlap area with figure 4. Hogeland is the town located in the figure 5 west center region and Turner is the town located just south of the figure 5 east center region. Woody Island Coulee meanders in an east-northeast and east-southeast direction near the figure 5 north edge. Murray Coulee drains in an east-southeast and north-northeast direction (south and east of Hogeland) from the figure 5 southwest quadrant before turning to drain in a north-northwest direction to join a southeast-oriented Woody Island Coulee valley segment. The north-northwest oriented Murray Coulee valley segment was eroded by a reversal of flood flow on the northwest end of a beheaded southeast-oriented flood flow route (which was beheaded by Woody Island Coulee valley headward erosion). Buckley Creek flows in an east direction to near Turner and then turns to flow in a north, north-northwest, and north direction to join a southeast-oriented Woody Island Coulee valley segment. Again the north and north-northwest oriented Buckley Creek valley segments were eroded by reversals of flood flow on north ends of beheaded south and/or south-southeast oriented flood flow routes. Note how with the exceptions of Woody Island Coulee, Murray Coulee, and Buckley Creek valleys the figure 5 map area shows very few topographic features and illustrates a gently sloping plain with elevations of approximately 980 meters in the west and of between 920 and 930 meters in the east. Compare this upland surface east of the Cherry Ridge-Middle Butte abandoned headcut with the steep southwest-facing Battle Creek valley wall seen in figure 4. Remember elevations in the Battle Creek valley to the west are today more than 200 meters lower than the elevation of this figure 5 gently sloping surface, which means the large Battle Creek valley did not exist at that time. Flood flow across this figure 5 upland surface either ended or was greatly reduced following headward erosion of the deep Battle Creek valley to the west. North of the figure 5 map area are east-oriented headwaters of the Frenchman River (or Frenchman Creek) as seen in figure 1. It is possible Frenchman River valley headward erosion in the north also played a role in eliminating south- and southeast-oriented flood flow across the figure 5 map area.

Buckley Creek-Black Coulee drainage divide area

Figure 6: Buckley Creek-Black Coulee drainage divide area. United States Geological Survey map digitally presented using National Geographic Society TOPO software.

 

  • Figure 6 illustrates the Buckley Creek-Black Coulee drainage divide area east and slightly south of the figure 5 map area and includes overlap areas with figure 5. Turner is the town just north of the figure 6 west center. Turner Colony is located near the figure 6 southwest corner. Buckley Creek flows in an east, north, north-northwest, and north direction in the figure 6 northwest quadrant and joins Woody Island Coulee near the figure 6 north edge. Woody Island Coulee drains in an east direction near the figure 6 north edge and then turns to drain in a southeast, south, southwest, and southeast direction to the figure 6 south edge (east half). South and east of figure 6 Woody Island Coulee joins southeast-oriented Cottonwood Creek, which flows to the Milk River. Black Coulee is the northeast and east-southeast valley located near the figure 6 south center edge and which joins Woody Island Coulee at the elbow of capture where Woody Island Coulee turns from draining in a southwest direction to draining in a southeast direction. With the exception of the deep valleys (and a region in the figure 6 northeast quadrant) elevations in the figure 6 map area are greater than 900 meters and relief is very low. This high upland surface stands as much as 200 meters or higher than the floor of the Milk River valley to the south, the Whitewater Creek and Milk River valleys to the east, and is still significantly higher than the Battle Creek valley to the west and represents the topographic surface into which those deep valleys were eroded. It is probable the erosion surface was lowered significantly by deep melt water flood erosion prior to headward erosion of the present day deep valleys. Final drainage of flood water from the high level erosion surface was in an east and southeast direction. The railroad line in the figure 6 northeast quadrant uses an east and east-southeast oriented through valley linking the Woody Island Coulee valley with the south-southeast oriented Whitewater Creek valley (only the very west end of the through valley is seen in figure 6). As seen in figure 6 most flood water drained to the southeast-oriented Cottonwood Creek valley, which eroded headward from the north-northeast oriented Milk River valley segment. As previously mentioned north-oriented valleys were eroded by reversals of flood flow on north ends of beheaded south- and southeast-oriented flood flow channels. A good example of this is seen in the figure 6 northeast quadrant where Horseshoe Coulee drains in a south-southeast direction to south-oriented Woody Island Coulee and is linked by a through valley to an unnamed north-oriented Woody Island Coulee tributary valley.

Black Coulee-Assiniboine Creek drainage divide area

Figure 7: Black Coulee-Assiniboine Creek drainage divide area. United States Geological Survey map digitally presented using National Geographic Society TOPO software.

 

  • Figure 7 illustrates the Black Coulee-Assiniboine Creek drainage divide area located south of the figure 6 map area and includes overlap areas with figure 6. Cottonwood Creek is the southeast-oriented stream flowing in a deep valley from the figure 7 north center edge area to the figure 7 east edge (south half) and east and south of the figure 7 map area drains to the Milk River. Assininboine Creek is not shown in the figure 7 map area although the northwest-southeast oriented through valley in the figure 7 south center region is linked to the southeast-oriented Assiniboine Creek valley, which also drains to the Milk River. Black Coulee drains in a northeast and east-southeast direction from the figure 7 west edge (north of center) to the figure 7 north center edge where southwest-oriented Woody Island Coulee drains to southeast-oriented Cottonwood Creek. Note how Black Coulee is just one of many northeast oriented coulees draining to southeast-oriented Cottonwood Creek. Other named northeast oriented coulees include Reservoir Coulee, Coburg Coulee, Dry Coulee, Lemere Coulee, Joiner Coulee, and Wilson Coulee. Note how the Joiner Coulee valley and the Black Coulee valley are linked by through valleys with the northwest-southeast oriented through valley in the figure 7 south center edge area. Most of these northeast-oriented coulees are in well-defined northeast-oriented valleys, which were eroded by significant northeast-oriented flood flow. North and east of the southeast-oriented Cottonwood Creek valley are a number of somewhat less well-defined southwest-oriented valleys including the Alkali Coulee valley. Elevations of uplands on drainage divides between the northeast- and southwest-oriented Cottonwood Creek tributary valleys are generally greater than 900 meters except in the figure 7 southeast quadrant where elevations are slightly lower. Remember these elevations are approximately 200 meters higher than the Milk River valley floor to the south and east. The northeast-oriented flood flow responsible for eroding the large northeast-oriented coulee valleys (and which reversed when beheaded by headward erosion of the deep southeast-oriented Cottonwood Creek valley to erode the somewhat smaller southwest-oriented coulee valleys) preceded headward erosion of the deep Milk River valley south and southwest of the figure 7 map area. In other words, headward erosion of the southeast-oriented Cottonwood Creek valley captured the northeast-oriented flood flow first and subsequently headward erosion of the much deeper Milk River valley to the south and southwest of figure 7 captured the northeast-oriented flood flow and beheaded all northeast-oriented flood flow to the figure 7 map area.

Black Coulee-Dodson Creek drainage divide area

Figure 8: Black Coulee-Dodson Creek drainage divide area. United States Geological Survey map digitally presented using National Geographic Society TOPO software.

 

  • Figure 8 illustrates the Black Coulee-Dodson Creek drainage divide area located south and west of the figure 7 map area and includes significant overlap areas with figure 7. Black Coulee drains in a northeast direction from the Black Coulee National Wildlife Refuge (in figure 8 north center area) to the figure 8 north edge (east of center) and north of the figure 8 map area turns to drain in an east-southeast direction to southeast-oriented Cottonwood Creek. Other closely spaced and roughly parallel northeast oriented Cottonwood Creek tributaries can be seen in the figure 8 northeast quadrant. South-southeast and south oriented Savoy Creek flows across the figure 8 southwest corner region and is west of Dodson Creek. Black Creek is a Savoy Creek tributary in the figure 8 southwest quadrant and is linked by through valleys with northeast oriented Cottonwood Creek tributary valleys. South of the figure 8 map area Savoy Creek flows to the Milk River. Note the northwest-southeast oriented through valley leading to the figure 8 southeast corner, which south and east of the southeast is linked to the southeast-oriented Assiniboine Creek valley, but which is drained to a west-southwest oriented Dodson Creek tributary valley. The southeast-oriented stream flowing to the figure 8 south center edge is Dodson Creek, which also flows to the Milk River. Note how the southeast-oriented Dodson Creek valley is linked by a through valley with the west-southwest oriented Black Creek tributary valley. Note how the Savoy Creek valley has been deeply eroded into the upland surface seen in the figure 8 northwest quadrant. The southwest-facing Savoy Creek valley wall can be seen in the figure 8 west center region with elevations to the north and east rising to more than 950 meters while Savoy Creek crosses the 800 meter contour line before flowing to the figure 8 south edge. This deep south-southeast oriented valley eroded headward from the actively eroding Milk River valley to the south and beheaded northeast- and east-oriented flood flow to the newly eroded southeast-oriented Cottonwood Creek valley and to the southeast-oriented Assiniboine Creek valley. Flood waters on west and southwest ends of beheaded flood flow routes reversed flow direction to erode west- and southwest-oriented Savoy Creek tributary valleys, such as the west-southwest oriented Black Creek headwaters valley. The southeast-oriented Dodson Creek valley was not eroded as deep as the Savoy Creek valley, and was beheaded by headward erosion of the west-southwest and southwest oriented Black Creek valley, which captured east- and southeast-oriented flood flow moving to the actively eroding Dodson Creek valley.

Dodson Creek-Assiniboine Creek drainage divide area

Figure 9: Dodson Creek-Assiniboine Creek drainage divide area. United States Geological Survey map digitally presented using National Geographic Society TOPO software.

 

  • Figure 9 illustrates the Dodson Creek-Assiniboine Creek drainage divide east and south of the figure 8 map area and includes overlap areas with figure 8. Cottonwood Creek flows in a southeast direction across the figure 9 northeast quadrant and northeast oriented Cottonwood Creek tributary valleys can be seen. Assiniboine Creek, which at long last is now visible, flows in a southeast direction to the figure 9 southeast corner and like Cottonwood Creek flows to the north-northeast oriented Milk River valley segment east and south of the figure 9 map area (see figure 2). Dodson Creek flows in a south-southeast and south direction across the figure 9 southwest corner region and flows to the east-oriented Milk River valley south of the figure 9 map area. Note how the south-southeast oriented Dodson Creek valley is linked by east-northeast oriented through valleys with the southeast-oriented Assiniboine Creek valley. Also note northeast and north-oriented through valley link the southeast-oriented Assiniboine Creek valley with the southeast oriented Cottonwood Creek valley. Headward erosion of the deep southeast-oriented Cottonwood Creek valley first captured northeast oriented flood water moving across the figure 9 map area. Next headward erosion of the southeast-oriented Assiniboine Creek valley captured the northeast-oriented flood flow. Remember the Assiniboine Creek valley eroded headward from a point on the Milk River valley upstream from where the Cottonwood Creek valley enters the Milk River valley. Headward erosion of the southeast-oriented Assiniboine Creek valley beheaded flood flow routes to the Cottonwood Creek valley and caused reversals of flood flow to erode south and southwest ends of through valleys linking the Cottonwood Creek and Assiniboine Creek valleys. Next headward erosion of the Dodson Creek valley (from the actively eroding Milk River valley at a point still further upstream on the present day Milk River route) captured the northeast- and east-oriented flood flow and beheaded flood flow routes to what was then the actively eroding Assiniboine Creek valley. Flood waters on west and southwest ends of beheaded flood flow routes reversed flow direction to erode the west ends of the west-southwest oriented through valleys linking the southeast-oriented Assiniboine Creek valley with the south-southeast oriented Dodson Creek valley and also captured the southeast-oriented headwaters of the newly eroded Assiniboine Creek valley (note southeast and west-southwest oriented Dodson Creek tributary just west of the figure 9 center region. This sequence of deep valley erosion is internally consistent with the concept that deep valleys (200 meters deep or more) were being eroded headward into an upland erosion surface equivalent in elevation or higher to the gently sloping upland surface seen in earlier figures.

Assiniboine Creek-Milk River drainage divide area

Figure 10: Assiniboine Creek-Milk River drainage divide area. United States Geological Survey map digitally presented using National Geographic Society TOPO software.

 

  • Figure 10 illustrates the Assiniboine Creek-Milk River drainage divide area south of the figure 9 map area and includes overlap areas with figure 9. The Milk River flows on the flow of its deep and broad east-southeast oriented valley in the figure 10 southwest corner and continues in an east direction south of the figure 10 southeast quadrant before turning to flow in a north-northeast direction downstream from Malta (see figures 1 and 2). Dodson Creek flows in a south-southeast direction from the figure 10 north edge (just east of northwest corner) to join the Milk River near Dodson (near figure 10 south edge). Note the west-southwest oriented Dodson Creek tributary flowing from the figure 10 north center edge. That tributary has southeast-oriented headwaters north of the figure 10 map area (see figure 9), which were captured from the east-southeast oriented Assiniboine Creek valley, which is located in the figure 10 northeast quadrant. East of the south-southeast oriented Dodson Creek valley is the south-southeast and south oriented Spring Coulee valley which drains to the Milk River near the figure 10 south center edge. Note how the south-southeast oriented Spring Coulee headwaters valley is linked by a through valley with a west-southwest oriented Dodson Creek tributary valley. Exeter Creek flows in a southeast direction to the figure 10 southeast corner. Note how elevations in the large Milk River valley are generally less than 700 meters, which is more than 200 meters lower than the 900 meter plus elevations seen on the upland erosion surface further to the north. Evidence for northeast-oriented flood flow seen on that high level erosion surface cannot be explained unless the deep Milk River valley did not exist at the time northeast-oriented flood waters flowed across the region. In other words the deep Milk River valley seen in figure 10 was eroded headward into a topographic surface at least 200 meters higher than the present day valley floor. As the Milk River valley eroded headward across the region southeast-oriented tributary valleys eroded headward from the newly eroded Milk River valley north wall in sequence from east to west. In terms of valleys seen in this essay headward erosion of the southeast-oriented Cottonwood Creek valley was first and was followed by headward erosion of the southeast oriented Assiniboine Creek valley. Exeter Creek valley, Spring Coulee valley, and Dodson Creek valley then followed in that sequence, with some valleys eroding much deeper and larger valleys than others.

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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