Missouri River-James River drainage divide landform origins in Walworth, Edmunds, Potter, and Faulk Counties, South Dakota, USA

Authors

A geomorphic history based on topographic map evidence

Abstract:

The Missouri River-James River drainage divide area in Walworth, Edmunds, Potter, and Faulk Counties, South Dakota is located in north central South Dakota. Between the south-oriented Missouri River to the west and the south-oriented James River to the east in the drainage divide area is the Missouri Coteau and the east-facing Missouri Escarpment. The Missouri Escarpment is interpreted to be what remains of the west wall of an immense south-oriented James River lowland ice-walled and bedrock-floored valley, which had been sliced into the surface of a rapidly melting thick ice sheet. The Missouri Coteau is where the ice wall once stood, and the ice wall is interpreted to have been the ice sheet’s detached southwest margin. The Missouri River valley is interpreted to have eroded north and northwest along the ice sheet’s southwest margin. An indentation in the Missouri Escarpment is interpreted as being where ice marginal melt water floods breached the ice wall and flowed east to the lower elevation James River lowland valley floor.

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 are listed on the sidebar category list under their appropriate Missouri River tributary drainage basin, Missouri River segment drainage basin (by state), and/or state in which the Missouri River drainage basin is located.     

Introduction:

  • The purpose of this essay is to use topographic map interpretation methods to explore Missouri River-James River drainage divide area landform origins in Walworth, Edmunds, Potter, and Faulk Counties, South Dakota, 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 Missouri River drainage basin landform origins research project essays 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 Missouri River-James River drainage divide area landform evidence in Walworth, Edmunds, Potter, and Faulk Counties, South Dakota will be regarded as evidence supporting the “thick ice sheet that melted fast” paradigm. This essay is included in the Missouri River drainage basin landform origins research project essay collection.

Missouri River-James River drainage divide area location map

Figure 1: Missouri River-James 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 provides a location map for the Missouri River-James River drainage divide area in Walworth, Edmunds, Potter, and Faulk Counties, South Dakota. Figure 1 illustrates an area in north central South Dakota, with a strip of North Dakota near the figure 1 north edge. The Missouri River is the large river flowing south and southeast from Fort Yates, North Dakota to Mobridge, Pierre, and Chamberlain, South Dakota. Much of the figure 1 Missouri River valley is flooded by Lake Oahe, which is impounded behind Oahe Dam, and by Lake Sharpe, which is impounded behind Big Bend Dam. The south oriented James River is located in the figure 1 east half and flows from Oakes, North Dakota (figure 1 northeast corner area) to Columbia, Ashton, Frankfort, Huron, and Forestburg, South Dakota. Figure 1 does not show county names or boundaries, but the Walworth, Edmunds, Potter and Faulk County area is bounded on the west by the Missouri River and includes the region between west to east highways number 12 and 212. The Walworth, Edmunds, Potter, and Faulk County area does not extend east to the south-oriented James River valley, but does extend east to the south and southeast oriented James River tributaries located west of north-south highway number 281 and east of north-south highway number 45. Note on figure 1 how there is a large region without mapped drainage routes between west and southwest oriented Missouri River tributaries and southeast and south oriented James River tributaries. That region without any indicated drainage routes is the Missouri Coteau, which on detailed topographic maps is shown to contain many small closed or interior drainage basins, and is characterized by landscape features suggesting a stagnant ice sheet melted and deposited whatever debris it contained. James River tributaries in the indicated study region east of the Missouri Coteau area begin as east and southeast oriented streams along the crest of the east-facing Missouri Escarpment and generally turn to flow south at the Missouri Escarpment base before eventually flowing to the James River. The broad James River lowland is located at the Missouri Escarpment base and the present day James River valley has been eroded into the lowland’s floor and is located approximately in the lowland center. Near the figure 1 east edge is the west-facing Prairie Coteau escarpment, which marks the James River lowland east boundary.

Missouri River-James River drainage divide area detailed location map

Figure 2: Missouri River-James River drainage divide area detailed location map. United States Geological Survey map digitally presented using National Geographic Society TOPO software.

Figure 2 provides a somewhat more detailed location map for the Missouri River-James River drainage divide area located in Walworth, Edmunds, Potter, and Faulk Counties, South Dakota. Campbell, McPherson, Walworth, Edmunds, Potter, and Faulk are South Dakota county names and the location of the Walworth, Edmunds, Potter, and Faulk County region is shown. The south-oriented Missouri River is located along the figure 2 west edge. The James River is located in the figure 2 northeast corner, where it flows south and southeast to the figure 2 east edge, and then is seen again along the figure 1 (south half) east edge where the James River flows in a south-southwest direction almost to Redfield (in the figure 2 southeast corner), before turning to flow southeast to the figure 2 southeast corner. Maps illustrated and discussed in this essay begin in the Missouri River valley near the Walworth County-Potter County boundary and are used to interpret evidence from Missouri River tributary valleys and associated landforms. The maps and discussions then progress eastward along the Walworth-Potter County boundary into Edmunds and Faulk Counties and also into the Missouri Coteau region, which on figure 2 is the region without drainage routes and with small lakes. Maps and discussions conclude with the east facing Missouri Escarpment and James River lowland area along the Edmunds-Faulk County boundary (and also in northern Edmunds County). The east facing Missouri Escarpment location can be identified on figure 2 by the heads of the east and southeast oriented James River tributaries in northern Faulk County, Edmunds County, and McPherson County. These tributaries typically originate along the escarpment crest and flow in an east or southeast direction down the escarpment slope before turning to flow south on the James River lowland floor, which is located at the base of the east-facing escarpment. The Missouri Escarpment is interpreted here as being what remains of an immense south-oriented ice-walled and bedrock-floored valley, which had been sliced into a decaying ice sheet surface. The Missouri Coteau, which is located between the Missouri Escarpment and the present day Missouri River valley, is interpreted here to be where the ice wall once stood and gradually melted (depositing whatever debris it contained as it melted). The Missouri River valley eroded headward along the ice sheet’s west margin to capture immense southeast-oriented ice marginal melt water floods.

Missouri River valley near Walworth-Potter County line

Figure 3: Missouri River valley near Walworth-Potter County line. United States Geological Survey map digitally presented using National Geographic Society TOPO software.

Figure 3 illustrates the Missouri River valley near the Walworth-Potter County line. The flooded Missouri River valley is located in the figure 3 west half. The Missouri River flows south from the figure 3 north edge to the figure 3 south edge and has been flooded by Lake Oahe, which is impounded behind Oahe Dam (see figure 1). The flooded southeast-oriented valley in the figure 3 northwest corner is the Moreau River valley, which west of the figure 3 map area is northeast-oriented and further west in South Dakota is southeast-oriented. West of the Missouri River is Dewey County and the west to east oriented Walworth-Potter County line is located in the figure 3 south half. Alaska, South Dakota is the small town located in the figure 3 northeast quadrant. Alaska is located in the west-oriented Swan Creek valley. Note the northwest-oriented Swan Creek tributaries and also the northwest-oriented Missouri River tributaries in the figure 3 south center area. These northwest-oriented or barbed tributaries are evidence of an immense southeast-oriented flood, which was captured by headward erosion of the Missouri River valley and its tributary Swan Creek valley (and southwest-oriented Swan Creek tributary valleys). The Missouri River valley eroded headward into the figure 3 map area to capture southeast-oriented flood flow from multiple southeast-oriented flood flow channels, such as might be found in a southeast-oriented anastomosing channel complex. Northwest-oriented tributary valleys were eroded by reversals of flood flow on the northwest ends of beheaded flood flow channels. Flood waters on the northwest ends of the beheaded flood flow channels reversed flow direction to flow northwest to the newly eroded and much deeper Missouri River valley (and Swan Creek valley). Because the Missouri River valley (and Swan Creek valley) eroded headward it beheaded one flood flow channel at a time. Also, because the channels were anastomosing (or interconnected), reversed flood flow in one channel often captured significant yet to be beheaded flood flow from adjacent channels. Capture of this yet to be beheaded flood flow provided the volumes of water needed to erode the large northwest-oriented tributary valleys seen today. Southwest-oriented Swan Creek tributary valleys, such as the Rieger Creek valley, seen in the figure 3 northeast corner area, eroded headward to capture the southeast-oriented flood flow. At the time flood waters flowed across the figure 3 map area the ice margin was located a short distance east of the figure 3 map area and it is probable flood waters were flowing adjacent to the ice sheet margin and that longer west-oriented Missouri River tributaries were eroding ice-walled valleys into the decaying ice sheet surface.

Missouri River valley in Potter County, South Dakota

Figure 4: Missouri River valley in Potter County, South Dakota. United States Geological Survey map digitally presented using National Geographic Society TOPO software.

Figure 4 illustrates the Missouri River valley in Potter County located south of the figure 3 map area and includes overlap areas with figure 3. The flooded south-oriented Missouri River valley is located along the figure 4 west edge. The south-southeast and southwest oriented Missouri River tributary in the figure 4 southwest quadrant is Little Cheyenne Creek (figure 6 below provides a detailed map of a Little Cheyenne Creek valley area). Note the numerous northwest-oriented or barbed Missouri River tributaries. As described in the figure 3 discussion these barbed tributaries provide evidence the Missouri River eroded headward and beheaded multiple southeast-oriented flood flow routes, such as might be found in a large-scale southeast-oriented anastomosing channel complex. Southeast-oriented flood water was coming from the region north and west of the present day Missouri River valley and was moving across the upland surface east of the present day Missouri River valley. In the figure 4 east half Green Lake and Flight Lake are located in what appears to be a northeast-oriented valley and some smaller lakes are located in what appear to be southeast-oriented valleys. These valleys provide evidence of some type of drainage route to the northeast, which maybe had eroded a valley headward from the northeast. If so, the valley was an ice-walled and bedrock-floored valley, because the ice sheet margin was located just east of the figure 3 and 4 map area. Figures 5 and 7 follow the northeast-oriented valley evidence into the Missouri Coteau region, where the decaying ice sheet margin was located. Figures 8 and 9 illustrate the Missouri Escarpment east of the Missouri Coteau and demonstrate how a northeast-oriented ice-walled and bedrock-floored valley could erode across the Missouri Coteau ice sheet wall. This northeast-oriented valley is roughly on the same alignment as the northeast-oriented Cheyenne River located south and west of the figure 4 map area (see figure 1). Prior to headward erosion of the Missouri River valley the northeast-oriented Cheyenne River valley was probably initiated by headward erosion of an east and northeast oriented ice-walled and bedrock-floored valley across the remnant Missouri Coteau ice sheet wall. The bedrock floor of that ice-walled and bedrock-floored valley initially was probably as high in elevation as the upland surface surrounding the present day Missouri River valley, if not higher. Southeast-oriented flood flow appears to have been captured by this northeast-oriented valley, which in turn was beheaded by headward erosion of the south-oriented Missouri River valley. Following headward erosion of the Missouri River valley the northeast-oriented valley was blocked in the Missouri Coteau area.

Walworth-Potter County line area south of Swan Creek

Figure 5: Walworth-Potter County line area south of Swan Creek. United States Geological Survey map digitally presented using National Geographic Society TOPO software.

Figure 5 illustrates landforms near the Walworth-Potter County line east of the figure 3 map area and north and east of the figure 4 map area and includes overlap areas with figures 3 and 4. Swan Creek flows southwest and west in the figure 5 northeast corner to Swan Lake and then west from Swan Lake in the figure 5 northwest quadrant. Flight Lake is located in the figure 5 south center area and the northeast-oriented valley seen in figure 4 extends northeast from Flight Lake to the area north of Hoven (in the figure 5 east center). Today a northwest-oriented Swan Lake tributary drains the valley floor to Swan Lake, which is drained to the west by the much narrower and deeper Swan Creek valley. This northeast-oriented Green Lake-Flight Lake valley appears on topographic maps to be oriented in a northeast direction and appears to have had some large southeast-oriented tributary valleys. However, today east of Hoven is the Missouri Coteau (see figure 7 below) and slightly higher elevation areas, which appear to be the result of glacial deposition. East of the Missouri Coteau is the east facing Missouri Escarpment and the lower elevation James River lowland. The interpretation provided here is the Green Lake-Flight Lake valley was eroded headward from a breach in the what was the detached southwest margin of a rapidly melting ice sheet. The ice sheet’s southwest margin was detached when the immense south-oriented James River lowland ice-walled and bedrock-floored valley was sliced headward into the decaying ice sheet’s surface. Prior to headward erosion of the Missouri River valley elevations west of the detached ice sheet margin were 100 or more meters higher than elevations on the floor of the south-oriented ice-walled and bedrock-floored James River lowland to the east. Ice marginal melt water floods breached the detached ice sheet margin at several points and east and northeast oriented valleys eroded headward from those breaches to capture the southeast-oriented ice marginal flood waters. The valley complex seen in figures 4 and 5 probably is related to one of those ice margin breaches and eroded headward from the breach to capture southeast-oriented ice marginal melt water floods. The present day northeast-oriented Cheyenne River valley west and south of the Missouri River valley and Moreau River valley west of Missouri River valley may have originally originated as a result of this breach (although at a much higher elevations than they are today). Headward erosion of the much deeper Missouri River valley beheaded the east-oriented flow routes moving to the breach in sequence from south to north, meaning northeast-oriented flood flow in the Cheyenne River was captured first. Southeast-oriented flood flow from the high elevation Moreau River valley continued to flow into the figure 5 map area and to the northeast-oriented Green Lake-Flight Lake valley. As the Missouri River valley eroded headward a reversal of flow in the Swan Creek valley resulted in headward erosion of the deeper and narrower west-oriented Swan Creek valley to capture yet to be beheaded flood flow from the high level Moreau River valley. Headward erosion of the Missouri River next captured that Moreau River valley water and enabled deeper erosion of that valley.

Detailed map of Little Cheyenne Creek valley area

Figure 6: Detailed map of Little Cheyenne Creek valley area. United States Geological Survey map digitally presented using National Geographic Society TOPO software.

Figure 6 provides a somewhat more detailed topographic map of the Little Cheyenne Creek valley area seen in less detail in figure 4 above. Lake Hurley is located in the figure 6 southwest corner. Little Cheyenne Creek flows in a south-southeast direction in the figure 6 northeast corner area and then turns west, south-southwest, and southwest to flow to Lake Hurley. From Lake Hurley Little Cheyenne Creek flows southwest and south-southeast to the figure 6 south edge and then turns west and southwest again to eventually reach the Missouri River (see figure 4). Note in figure 4 how the southwest-oriented Little Cheyenne Creek valley is roughly on the same alignment as the northeast-oriented Green Lake-Flight Lake valley. Probably the southwest-oriented Little Cheyenne Creek valley segments were initiated by reversals of northeast-oriented flood flow moving to the northeast-oriented Green Lake-Flight Lake valley and the previously described breach in the detached ice sheet southwest margin. Northeast-oriented flood flow to the ice sheet margin breach was beheaded and reversed by headward erosion of the much deeper south-oriented Missouri River valley. At that time southeast oriented flood flow was still moving into the figure 6 map area (i.e. the Missouri River valley had not yet eroded further north to capture the southeast oriented flood flow). In figure 4 the Little Cheyenne Creek valley downstream from Lake Hurley is much deeper than the valley upstream, which is the valley segment seen in figure 6. The deeper valley was eroded by southeast oriented flood water captured by southwest-oriented flow in the figure 6 map area and moving to the newly eroded and deeper Missouri River valley. Note how the figure 6 map area includes streamlined erosional residuals and how the Little Cheyenne Creek valley has multiple southeast- and northwest-oriented tributary valleys. Further note the south-southeast oriented Little Cheyenne Creek headwaters area. Also, note there is no through valley linking the deep southwest-oriented Little Cheyenne Creek valley with the deep northeast-oriented Green Lake-Flight Lake valley. Lack of a deep northeast oriented through valley (there is a shallow northeast-oriented through valley) provides evidence northeast oriented flood flow to the Green Lake-Flight Lake valley was moving on a topographic surface as high as the present day figure 6 elevations if not higher. Headward erosion of the much deeper Missouri River valley captured the northeast-oriented flood flow and reversed flow on the southwest end of the beheaded northeast oriented flow route. Yet to be beheaded southeast-oriented flood water was then captured by headward erosion of the reversed Little Cheyenne Creek valley, to create the figure 6 landscape seen today.

Walworth, Potter, Edmunds, and Faulk County boundary area in Missouri Coteau

Figure 7: Walworth, Potter, Edmunds, and Faulk County boundary area in Missouri Coteau. United States Geological Survey map digitally presented using National Geographic Society TOPO software.

Figure 7 illustrates the Walworth, Edmunds, Potter, and Faulk County boundary area east and slightly north of the figure 5 map area. Hoven, South Dakota is located in the figure 7 southwest corner. Swan Creek flows south-southeast and southwest in the figure 7 northwest quadrant. Other than Swan Creek the figure 7 map area does not show any drainage routes. Instead the region is covered with many small and intermediate size lakes, indicative of numerous small closed drainage basins. In addition there is evidence of low hills and hummocky topography typical of glaciated regions. The region along the figure 7 west edge between Hoven and Swan Creek is where the northeast-oriented Green Lake-Flight Lake valley seen in figures 4 and 5 above appears to end. Figure 7 evidence suggests the valley (if it extends further east or northeast) must be buried in glacial deposits. This figure 7 region is located on the Missouri Coteau, which is a glacial moraine region typical of regions of where a stagnant ice sheet has melted and deposited whatever debris it contained. Figures 8, 9, and 10 below illustrate evidence for the presence of a large and deep south-oriented ice-walled and bedrock-floored valley east of the figure 7 map area. Presence of that ice-walled and bedrock-floored valley suggests the Missouri Coteau area seen in figure was the detached west margin of what must have been a decaying ice sheet. This detached west ice sheet margin was oriented in a north-south direction and acted as an ice wall, preventing ice marginal melt water floods west of the ice wall from reaching the lower elevation south-oriented James River lowland ice-walled and bedrock-floored valley east of the ice wall. As previously described the Green Lake-Flight Lake valley (and the northeast-oriented Cheyenne River valley further to the southwest-see figure 1) suggests the presence of a major breach through the ice wall. Water flowing northeast (and/or southeast) to the ice wall breach must have passed through the ice wall somewhere in the figure 7 region. Following headward erosion of the Missouri River valley flow through the breach ended and the breach may have closed. Evidence provided by other essays (e.g. James River-Wild Rice River drainage divide area essay, James River-Sheyenne River drainage divide area essays, Sheyenne River-James River drainage divide area essay, and Missouri River-Souris River drainage divide area essay suggests ice sheet melting was halted and the ice sheet was rejuvenated when south-oriented melt water floods were captured and diverted north. If so, the ice sheet rejuvenation may have closed the ice wall breach. [Essays for the James River drainage basin can be found under James River on the sidebar category list. The Missouri River-Souris River essay can be found under ND Missouri River on the sidebar category list.]

Missouri Escarpment near Faulkton, South Dakota

Figure 8: Missouri Escarpment near Faulkton, South Dakota. United States Geological Survey map digitally presented using National Geographic Society TOPO software.

Figure 8 illustrates the Missouri Escarpment near Faulkton, South Dakota and is located in Faulk County east and south of the figure 7 map area. Faulkton is the town located in the figure 8 south center. The western fourth or more of the figure 8 map is the eastern edge of the Missouri Coteau region at the Missouri Escarpment crest. The eastern fourth of the figure 8 map area is the James River lowland floor at the Missouri Escarpment base. South-oriented drainage routes are James River tributaries. The east-facing slope between the Missouri Coteau region and the James River lowland floor is the Missouri Escarpment. Near the figure 8 south edge (south of Faulkton) the Missouri Escarpment is much steeper and higher than further north and there is evidence a large indentation has been eroded into the east-facing Missouri Escarpment slope. The Escarpment crest near the figure 8 south edge is almost 170 meters higher than the adjacent James River lowland floor elevation. Further north the elevation difference is significantly less (almost 100 meters less). This large indentation is perhaps some of the best topographic map evidence that a large east-oriented valley once crossed the Missouri Coteau region and carried water eastward from the region west of the Missouri Coteau into the lower elevation James River lowland area. Location of this valley in central Faulk County suggests water movement through the ice wall barrier was eastward not northeastward, even though the Green Lake-Flight Lake valley west of the Missouri Coteau suggested northeast-oriented flow. Also, the figure 8 valley does not appear to have been eroded into the Missouri Escarpment base, suggesting that south-oriented melt water floods (from north of the figure 8 map area) eroded and deepened the ice-walled and bedrock-floored James River lowland valley after Missouri River valley headward erosion beheaded east-oriented flood flow routes west of the ice wall barrier. If interpreted correctly this evidence suggests the Missouri River valley eroded headward at the same time the James River lowland ice-walled and bedrock-floored was being eroded by south-oriented melt water floods and before south-oriented melt water floods were captured and diverted north. Diversion of the immense south-oriented melt water floods north triggered a major climate change, which froze flood waters on the floors of the ice-walled and bedrock-floored valleys separating the thick ice sheet remnants. These frozen flood waters created a wet based thin ice sheet with thick ice sheet remnants embedded in it. This climate change and the subsequent thin ice sheet was responsible for rejuvenating the detached ice sheet west margin, which later melted and deposited debris in the former east-oriented valley.

Missouri Escarpment along Edmunds County-Faulk County line

Figure 9: Missouri Escarpment along Edmunds County-Faulk County line. United States Geological Survey map digitally presented using National Geographic Society TOPO software.

Figure 9 illustrates the Missouri Escarpment along the Edmunds County-Faulk County line and is north of the figure 8 map area and there is an overlap area with figure 8. The figure 9 east half illustrates the James River lowland floor. The North Fork Snake Creek is the south-oriented James River tributary located at the Missouri Escarpment base. Preachers Run is the south-oriented James River tributary located near the figure 9 east edge. Elevations on the James River lowland floor near the Missouri Escarpment base are 60-70 meters lower than elevations along the figure 9 west edge (compare this elevation difference with the difference near the figure 8 south edge). Further north the elevation difference increase again, suggesting the presence of a major east-oriented indentation in the Missouri Escarpment. Note the presence of lakes on the Missouri Escarpment slope. These lakes appear to be kettle lakes, suggesting they are filling depressions where ice masses were once buried in ice or melt water deposited debris. If so, these lakes may be evidence the Missouri Escarpment slope in this region is composed of ice and/or melt water deposited sediments. Figure 9a below shows the Missouri Escarpment further north in Edmunds County. Note in figure 9a that there are no lakes on the Missouri Escarpment slope and the Missouri Escarpment is steeper and higher than in figure 9, suggesting the Missouri Escarpment in figure 9a has been eroded into bedrock underlying the glacial and/or melt water deposits. Figure 8, 9, and 9a evidence suggests a major indentation is present in the Missouri Escarpment, meaning the Missouri Escarpment was formed prior to the east-oriented valley responsible for the indentation. Figure 8, 9, and 9a evidence further shows the east-oriented valley was subsequently filled with ice and/or melt water deposited sediments and that further erosion of the Missouri Escarpment slope occurred following deposition of those sediments. This evidence supports an interpretation that the Missouri River valley eroded headward along the ice sheet west margin at the same time melt water floods were still eroding the south-oriented ice-walled and bedrock-floored James River lowland valley. Climate change late during the ice sheet rapid melt down may have further contributed to the evidence seen today.

Figure 9a: Missouri Escarpment slope in northern Edmunds County (north of figure 9). United States Geological Survey map digitally presented using National Geographic Society TOPO software.

James River lowland east of the figure 9 map area

Figure 10: James River lowland east of the figure 9 map area. United States Geological Survey map digitally presented using National Geographic Society TOPO software.

Figure 10 illustrates the James River lowland floor east of the figure 9 map area and includes overlap areas with figure 9. Preachers Run is the south-oriented James River tributary meandering along the figure 10 west edge. The south-oriented James River is located just east of the figure 10 map area. As seen in figures 8 and 9 the James River lowland is bounded on the west by the east-facing Missouri Escarpment. East of the James River the James River lowland is bounded by the west-facing Prairie Coteau escarpment (see James River-Big Sioux River drainage divide area north of Redfield and Watertown, South Dakota essay). The west and east facing escarpments are what remain of the east and west walls of the immense south-oriented ice-walled and bedrock-floored James River lowland valley (referred to as the Midcontinent Trench in some essays). The Midcontinent Trench was an immense southeast and south oriented ice-walled and bedrock-floored valley sliced into the surface of a rapidly melting thick ice sheet. Much of the east wall evidence has been removed by subsequent melt water flood erosion, although the west and southwest wall evidence in the form of the Missouri Escarpment is still intact. The Missouri Escarpment can be traced north into central North Dakota and then northwest across North Dakota into Saskatchewan and eventually into east central Alberta. North and northwest of the James River headwaters in central North Dakota the Midcontinent Trench floor is drained today by several rivers, which flow in a southeast direction along the Midcontinent Trench floor and then turn to flow northeast and eventually to reach Hudson Bay. These elbows of capture provide evidence the immense southeast and south oriented melt water floods responsible for eroding the Midcontinent Trench ice-walled and bedrock floored valley were systematically captured and diverted to the north. The figure 10 map area contains evidence of the last large-scale south-oriented melt water flood to flow in the ice-walled and bedrock-floored valley. The figure 10 east half provides evidence of a large-scale south-oriented anastomosing channel complex, which was eroded by that flood. South-oriented channels in the figure 10 west half are probably related to that final flood event. Smaller lakes may be kettle lakes formed where flood waters deposited sediment around stranded ice masses, leaving depressions when the ice masses melted.

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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