A geomorphic history based on topographic map evidence

The Missouri River-Apple Creek-Pipestem Creek drainage divide area is located in Burleigh, Kidder, and Stutstman Counties, North Dakota and is bounded on the west by the south-southeast oriented Missouri River valley and on the east by the south-southest oriented Pipestem Creek valley. Apple Creek is a southeast and southwest-oriented Missouri River tributary and Pipestem Creek is a south-southeast oriented James River tributary. Between the Apple Creek and Pipestem Creek drainage basins is the Missouri Coteau, which lacks an integrated drainage network. The Missouri Coteau northeastern boundary is the northeast-facing Missouri Escarpment. The lowland containing the James River-Pipestem Creek valleys is interpreted to have eroded north as an ice-walled and bedrock-floored valley sliced its way headward into a rapidly melting thick ice sheet. This ice-walled and bedrock-floored valley detached the thick ice sheet’s southwest margin. The Missouri River and Apple Creek valleys were eroded headward along the western margin of the detached ice sheet’s southwest margin. The Missouri Coteau represents the area where the thick ice sheet’s detached southwest margin slowly melted.

• The purpose of this essay is to use topographic map interpretation methods to explore Missouri River-Apple Creek-Pipestem Creek drainage divide area landform origins in Burleigh, Kidder, and Stutsman Counties, North 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-Apple Creek-Pipestem Creek (and James River) drainage divide area landform evidence in Burleigh, Kidder, and Stutsman Counties, North 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-Apple Creek-Pipestem Creek drainage divide area location map

Figure 1 provides a Missouri River-Apple Creek-Pipestem Creek drainage divide area location map and illustrates a large area in south central and southeast North Dakota. The north-oriented Red River is located near the figure 1 east edge and the state of Minnesota is located east of the Red River. The North Dakota-South Dakota state line is located along the figure 1 south edge. The Missouri River flows south-southeast from Lake Sakakawea (located in the figure 1 west edge area) to Bismarck and then to the figure 1 south edge. Lake Sakakawea is a large reservoir impounded behind Garrison Dam. Lake Oahe has flooded the Missouri River valley south of Bismarck and is another large reservoir. Apple Creek is the unnamed southeast and southwest-oriented tributary joining the Missouri River near Bismarck. The James River originates south of Harvey (northeast of the “D” in DAKOTA) and flows north, east, southeast and south to Jamestown and then flows southeast to the figure 1 south edge. South of figure 1 the James River flows south through South Dakota and joins the Missouri River in southeast South Dakota. Pipestem Creek is a southeast oriented James River tributary, which joins the James River at Jamestown. The Sheyenne River originates southwest of Harvey and flows northeast and east before turning to flow south to Valley City and Ft Ransom. At Ft Ransom the Sheyenne River begins to turn and eventually flows northeast to join the north-oriented Red River just north of Fargo. Water in the Sheyenne River eventually flows to Hudson Bay. Water in the James River (and Pipestem Creek) eventually reaches the Missouri River and Missouri River water eventually reaches the Gulf of Mexico. The north-south continental divide is located between the James and Sheyenne Rivers. The Missouri River-Apple Creek-Pipestem Creek drainage divide area discussed here is located south of highway 200 and north of Interstate highway 94 and is east of the Missouri River and west of Pipestem Creek. Note, the large region between southeast and southwest-oriented Apple Creek and Pipestem Creek where no drainage routes are shown. This region lacks an integrated drainage pattern and is referred to as the Missouri Coteau. The Missouri Coteau is bounded on the east and northeast by an east and northeast-facing escarpment known as the Missouri Escarpment. Pipestem Creek flows along the Missouri Escarpment base. The Missouri Coteau (or Prairie Coteau in Canada) is a region covered with glacial moraines typical of those left by a stagnant ice sheet and extends in a northwest-southeast direction from east central Alberta to southern South Dakota. For that entire distance the northeast and east boundary is the Missouri Escarpment and in North and South Dakota the western boundary is the Missouri River valley.

Missouri River-Apple Creek-Pipestem Creek drainage divide area detailed location map

Figure 2: Missouri River-Apple Creek-Pipestem Creek 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 map of the Missouri River-Apple Creek-Pipestem Creek drainage divide area. Burleigh, Kidder, and Stutsman Counties are located in North Dakota. The south-southeast oriented Missouri River is located along the figure 2 west edge (southern two-thirds). Southeast-oriented Pipestem Creek is located in the figure 2 northeast quadrant and flows to the figure 2 east center edge. Apple Creek drains a large area in Burleigh County north of the Interstate highway (and parallel railroad track). Apple Creek headwaters are southeast-oriented and then turn to flow in a southwest direction to join the Missouri River south of Bismarck. Between the Apple Creek drainage basin and the Pipestem Creek drainage basin is a large area marked by numerous small lakes and no integrated drainage pattern. This region is the Missouri Coteau, which is a glacial moraine area. Pipestem Creek flows along the eastern and northeastern Missouri Coteau boundary and marks the Missouri Escarpment base location (see figure 10 below). The Missouri Escarpment is a rise of approximately 100 meters from a lowland region into which the Pipestem Creek valley has been eroded to the Missouri Coteau. The Missouri Coteau western boundary is where the well-defined drainage routes to the Missouri River become evident. Generally areas with integrated drainage patterns lack the thick glacial moraine characteristics found further to east, suggesting glacial moraine materials were eroded as integrated drainage basins evolved. This landscape pattern can be explained in the context of a rapidly melting thick ice sheet. The lowland east and northeast of the east and northeast-facing Missouri Escarpment is the floor of what was a large south-oriented ice-walled and bedrock-floored canyon sliced into a rapidly melting thick North American ice sheet by an immense south-oriented melt water river. The Missouri Escarpment is what remains of that ice-walled and bedrock-floored valley’s southwest wall. The ice-walled and bedrock-floored canyon detached the ice sheet’s southwest margin, which is named here as the Southwest Ice Sheet. Immense ice-marginal floods also flowed in a southeast direction along the Southwest Ice Sheet’s southwest margin. These floods deeply eroded the Southwest Ice sheet southwest margin and late during the thick ice sheet rapid melt down the southeast-oriented Missouri River valley eroded headward along the Southwest Ice Sheet southwest margin to capture the southeast-oriented ice marginal flood waters. The Apple Creek drainage basin was developed when headward erosion of the Missouri River valley reached the Bismarck area, but had not yet progressed further north. The southwest-oriented Apple Creek valley segment eroded to the northeast to capture southeast-oriented flood water. Headward erosion of the deep Missouri River then beheaded flood flow routes to the Apple Creek drainage basin. The Missouri Coteau represents the area where Southwest Ice Sheet remnants gradually melted and deposited whatever debris the ice contained.

Yanktonai Creek-Burnt Creek drainage divide area

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

Figure 3 illustrates the Yanktonai Creek-Burnt Creek drainage divide near Wilton, North Dakota. The south-oriented Missouri River valley is located along the figure 3 west edge. Yanktonai Creek is the north-northwest oriented stream beginning just west of Wilton and flowing to the figure 3 north edge. North of figure 3 Yanktonai Creek joins west-oriented Painted Woods Creek, which flows to the south-oriented Missouri River. A west-oriented Painted Woods Creek tributary is seen in the figure 3 northeast quadrant and north central areas (near the figure 3 north edge). Burnt Creek originates immediately south of Wilton and flows south to the figure 3 south center edge. Note how the Yantonai Creek-Burnt Creek drainage divide extends northeast and east from the west-oriented slope leading into the Missouri River valley (west of Wilton). Also note several shallow through valleys linking the north-northwest oriented Yanktonai Creek drainage basin with the south-oriented Burnt Creek drainage basin. The shallow through valleys provide evidence of multiple flood flow channels across the present day drainage divide, which suggests the presence of a south-oriented flood formed anastomosing channel complex. Such a channel complex would have been formed prior to headward erosion of the deep south-southeast oriented Missouri River valley, which captured the south-oriented flood flow as it eroded north-northwest across the region. The Painted Woods Creek valley eroded east from the newly eroded Missouri River valley to capture south-southeast-oriented flood flow that had not yet been captured by Missouri River valley headward erosion. At the same time headward erosion of the Painted Woods Creek valley beheaded south-southeast oriented flood flow channels moving water south-southeast (and parallel to the newly eroded Missouri River valley). Flood waters on the north-northwest ends of those beheaded flood flow channels reversed flow direction to flow north-northwest to the newly eroded and deeper Painted Woods Creek valley. The Yanktonai Creek valley was eroded by such a flood flow reversal. Probably the reversed flood flow captured yet to be beheaded (by Painted Woods Creek headward erosion) flood flow from further to the east and the capture of this flood flow helped erode the Yanktonai Creek valley. The north-northwest oriented Yanktonai Creek valley (adjacent to the south-southeast oriented Missouri River valley) and several shallow through valleys across the present day Yanktonai Creek-Burnt Creek drainage divide, in addition to the south-southeast oriented Missouri River valley, provide evidence of large ice-marginal south-southeast floods along the Southwest Ice Sheet southwest margin and that eroded the Southwest Ice Sheet southwest margin.

Painted Woods Creek-West Branch Apple Creek drainage divide area

Figure 4: Painted Woods Creek-West Branch Apple Creek drainage divide area. United States Geological Survey map digitally presented using National Geographic Society TOPO software.

Figure 4 illustrates the Painted Woods Creek-West Branch Apple Creek drainage divide area east of Wilton and east of the figure 3 map area (and includes overlap areas with figure 3). North-oriented streams in the figure 4 north two-thirds flow to west-oriented Painted Woods Creek, which is located north of the figure 4 map area. The south-oriented Burnt Creek drainage basin is located in the figure 4 southwest corner area. Otherwise southeast-oriented drainage in the figure 4 south one-third flows to the southeast-oriented Apple Creek tributaries. The West Branch Apple Creek is located in the figure 4 south center area. The East Branch Apple Creek drains the figure 4 southeast corner area. Note the multiple through valleys linking the north-oriented Painted Woods Creek tributaries with headwaters of southeast-oriented West Branch Apple Creek and its tributaries. Those shallow through valleys provide additional evidence of multiple southeast-oriented flood flow channels moving a large southeast-oriented ice-marginal flood along the Southwest Ice Sheet southwest margin. Flood waters would have been “eating” into the Southwest Ice Sheet southwest margin, causing marginal ice to melt and also transporting away any finer grained debris contained within the Southwest ice sheet ice mass. Headward erosion of the deep Missouri River valley to the west of the figure 4 map then enabled the west-oriented Painted Woods Creek valley to erode east to capture the southeast and south-southeast oriented ice-marginal flood moving along the Southwest Ice Sheet southwest margin. North-oriented Painted Woods Creek tributary valleys were eroded by reversals of the flood flow along the north ends of beheaded southeast and south-southeast oriented flood flow routes. Again, reversed flow routes probably captured yet to be beheaded flood flow from flood flow routes further to the east. Such captures provided the water volumes required to erode the north-oriented valleys. The multiple through valleys and southeast-oriented West Apple Creek headwaters provide evidence of the southeast-oriented flood flow that moved across the figure 4 map area (and along the Southwest S southwest margin).

Painted Woods Creek-East Branch Apple Creek drainage divide area

Figure 5: Painted Woods Creek-East Branch Apple Creek drainage divide area. United States Geological Survey map digitally presented using National Geographic Society TOPO software.

Figure 5 illustrates the Painted Woods Creek-East Branch Apple Creek drainage divide area east of the figure 4 map area and includes overlap areas with figure 4. Canfield Lake represents the easternmost point in the Painted Woods Creek valley system. Painted Woods Creek flows northwest from Canfield Lake and north of figure 5 turns west to flow to the Missouri River. North-oriented drainage in the figure 5 northwest quadrant flows to west-oriented Painted Woods Creek. Southeast-oriented West Branch Apple Creek drains the figure 5 southwest corner. The East Branch Apple Creek flows to the figure 5 southeast corner area. Note multiple shallow through valleys crossing the Painted Woods Creek-Apple Creek drainage divide. Those through valleys provide evidence of a southeast-oriented anastomosing channel complex moving large volumes of southeast-oriented flood water into what was at that time the developing Apple Creek drainage basin. The Apple Creek drainage basin was initiated when the southwest-oriented Apple Creek valley (see figures 1, 2, and 8) eroded headward to capture southeast-oriented flood waters moving along the Southwest Ice Sheet southwest margin. That southwest-oriented Apple Creek valley segment eroded headward from what was then the newly eroded south-southeast oriented Missouri River valley, which had yet to erode far enough north to behead the southeast-oriented flood flow moving across the figure 5 map area. When headward erosion of the deep south-southeast oriented Missouri River valley did erode north, the Painted Woods Creek began to erode headward or east to capture the southeast-oriented flood water and in the process beheaded southeast-oriented flood flow channels moving flood waters across the figure 5 map area. Flood waters on the northwest ends of the beheaded flood flow channels reversed flow direction to flow north to the newly eroded and deeper Painted Woods Creek valley. The Painted Woods Creek valley eroded headward from the west to the east, which meant flood waters continued to move southeast to the East Branch Apple Creek valley after flood flow to the West Branch Apple Creek valley had been beheaded, and this sequence continued up to the Southwest Ice Sheet southwest margin (where headward erosion of the Painted Woods Creek valley stopped). Also, headward erosion of the Missouri River valley and other tributaries further to the north subsequently beheaded the southeast-oriented flood flow routes to the Painted Woods Creek valley.

East Branch Apple Creek drainage basin-Missouri Coteau boundary

Figure 6: East Branch Apple Creek drainage basin-Missouri Coteau boundary. United States Geological Survey map digitally presented using National Geographic Society TOPO software.

Figure 6 illustrates the East Branch Apple Creek drainage basin-Missouri Coteau boundary and is located east of the figure 5 map area and includes overlap areas with figure 5. The southeast-oriented East Branch Apple Creek can be seen in the figure 6 southwest corner. Other areas of figure 6 have some well-defined valleys, although no integrated drainage pattern exists. Some of the valleys appear to have short streams in them, but the streams disappear, suggesting the water soaks into the underlying glacially deposited sediments. Drainage is to lakes or interior basins with no visible outlet. Probably much of this figure 6 map region was ice-covered by Southwest Ice Sheet remnants when flood waters were eroding the Painted Woods Creek-Apple Creek drainage divide just to the west. It is possible flood waters had eroded valleys into and even across the Southwest Ice Sheet to reach the large south-oriented ice-walled and bedrock-floored valley to the east (in which the present day south-oriented Pipestem Creek and James River valleys are located). The lowland in the figure 6 southeast quadrant may be evidence of such a valley, although based on topographic evidence alone I do not want to say for sure. If it is such a valley it probably was subsequently filled with flood deposited and/or ice deposited debris. Lakes probably originated as ice sheet remnants buried in flood and ice deposited debris and then gradually melted, leaving depressions where the buried ice masses had been. Some of the figure 6 valleys may have originated following the flood events responsible for headward erosion of the Missouri River valley and Apple Creek and Painted Woods Creek valleys. Evidence presented in other essays (e.g. Big Muddy Creek-Little Muddy River drainage divide area and Missouri River-Sheyenne River drainage divide area essays which can be found under ND Missouri River on the sidebar category list) suggests flood events responsible for headward erosion of the Missouri River valley occurred when a major climate change froze north-oriented flood waters on the floor of the mostly melted thick ice sheet and created a wet based thin ice sheet with remnants of the thick ice sheet embedded in it. There is no evidence melting of the thin ice sheet produced the immense floods the thick ice sheet melting had produced, although melt water from that subsequent thin ice sheet probably eroded some local valley segments.

Burnt Creek-Hay Creek drainage divide area

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

Figure 7 illustrates the Burnt Creek-Hay Creek drainage divide area south of the figure 3 map area (there is no overlap with figure 3). The south-oriented Missouri River valley is located along the figure 7 west edge. Burnt Creek flows south and southwest from the figure 7 north center edge area to join the south-southeast oriented Missouri River in the figure 7 southwest quadrant. Hay Creek originates in the figure 7 center area (just west of the north-south red highway) and flows south to the figure 7 south center edge. A close look at figure 7 reveals a through valley north of Arnold linking the south-oriented Hay Creek headwaters with the south-oriented Burnt Creek valley to the north. A west and northwest-oriented Burnt Creek tributary is located at the north end of that through valley. That northwest-oriented tributary joins south-oriented Burnt Creek as a barbed tributary. Also, additional shallow through valleys link southeast and east-oriented Hay Creek tributaries with the southwest-oriented Burnt Creek valley west of Arnold. These through valleys provide evidence the Hay Creek, Burnt Creek, and Missouri River valleys originated as channels in an ever-changing south-southeast oriented anastomosing channel complex. At one time flood flow moved south simultaneously in interconnected channels along the present day Burnt Creek-Hay Creek alignment, the Missouri River valley alignment, and the Burnt Creek-Missouri River valley alignment. Flood flow also spilled southeast from the southwest Burnt Creek channel alignment into the south-oriented Hay Creek channel. Headward erosion of the deep Missouri River valley along the channel using that alignment then enabled the flood flow on the southwest-oriented Burnt Creek alignment to erode a deeper channel, beheading flood flow to the Hay Creek alignment. Flood waters on the north end of the beheaded flood flow channel reversed flow direction and eroded the northwest-oriented Burnt Creek tributary. Reversed flow probably captured yet to be beheaded (by headward erosion of the Burnt Creek and Burnt Creek tributary valleys) flood water moving further to the east and the west oriented headwaters of that northwest tributary probably provide evidence of that capture. The captured flood waters helped erode the west and northwest-oriented Burnt Creek tributary valley.

Apple Creek valley east of Bismarck

Figure 8: Apple Creek valley east of Bismarck. United States Geological Survey map digitally presented using National Geographic Society TOPO software.

Figure 8 illustrates the Apple Creek valley east of Bismarck and is located south and east of figure 7 (and includes overlap areas with figure 7). The West and East Branches of Apple Creek meet in the figure 8 northeast corner area and Apple Creek flows south-southwest, northwest, west, southwest into the figure 8 southwest quadrant. South-oriented Hay Creek flows along the figure 8 west edge in the figure 8 northwest quadrant and then turns southeast to join Apple Creek in the figure 8 southwest quadrant. Note how southwest-oriented Apple Creek has captured several southeast and south-oriented streams (including Hay Creek) and how these present day southeast-oriented tributaries flow to southwest-oriented Apple Creek as barbed tributaries. Also note the broad southeast-oriented valleys located south and east of the southwest-oriented Apple Creek valley. What has happened here is the southwest-oriented Apple Creek valley eroded headward from what was then the newly eroded Missouri River valley (located east and southeast of figure 8) to capture an anastomosing complex of southeast-oriented flood flow channels. The southeast-oriented flood flow channels had yet to be beheaded by headward erosion of the south-oriented Missouri River valley and the tributary Painted Woods Creek further to the north. Flood waters were moving southeast along the Southwest Ice Sheet southwest margin and were “eating” into that ice sheet margin by melting the ice and removing finer grained materials contained within the ice mass. Headward erosion of the southwest-oriented Apple Creek valley beheaded flood flow routes to the areas southeast of the Apple Creek valley. Subsequently, headward erosion of the deep Missouri River valley and its tributary Painted Woods Creek valley beheaded southeast-oriented flood flow to the newly developed Apple Creek drainage basin.

Missouri Coteau near Woodworth

Figure 9: Missouri Coteau near Woodworth. United States Geological Survey map digitally presented using National Geographic Society TOPO software.

Figure 9 illustrates the Missouri Coteau area near Woodworth, North Dakota. The Figure 9 map area is east of the figure 6 map area and there is a gap of approximately 40 kilometers between figures 6 and 9. The region between figures 6 and 9 is similar to what is illustrated in figure 9 and is a region of hummocky topography with numerous small lakes, suggesting it is a region where a stagnant ice sheet gradually melted. Figure 9 illustrates typical Missouri Coteau landscape and the evidence along the Missouri River-Apple Creek-Pipestem Creek drainage divide suggests the stagnant ice sheet was approximately 50 kilometers across in this region. As noted in earlier figures the western margin of this stagnant ice sheet was deeply eroded by southeast and south-southeast oriented floods prior to headward erosion of the south-southeast oriented Missouri River valley. Figure 10 below illustrates the Missouri Escarpment, which marks the eastern or northeast edge of the Missouri Coteau (or of where the stagnant ice sheet was located). As previously described this stagnant ice sheet is interpreted to have been the detached southwest margin of a rapidly melting thick ice sheet. The thick ice sheet’s southwest margin was detached when an immense southeast and south-oriented melt water river sliced a giant southeast and south-oriented ice-walled and bedrock-floored valley into the ice sheet surface. The immense melt river is named here the Midcontinent River and the giant southeast and south-oriented ice-walled and bedrock-floored valley is named here the Midcontinent Trench. The Missouri Escarpment is what remains of the Midcontinent Trench southwest and west wall. The detached ice sheet southwest margin is the Southwest Ice Sheet as discussed here. As already described the Southwest Ice Sheet southwest margin was deeply eroded by ice-marginal melt water floods, which makes it difficult if not impossible to determine where the original thick ice sheet southwest margin had been located. Also, the thick ice sheet was located in a deep “hole” that had been created by crustal warping (caused by the ice sheet weight) and by deep glacial erosion. Essays in this Missouri River drainage basin research project series are building a case the thick ice sheet originally formed on a topographic surface preserved today (if it is preserved at all) as high level Rocky Mountain erosion surfaces. If so, the elevation of this North Dakota region was significantly lower in elevation than the deep “hole” rim, which was deeply eroded by ice-marginal melt water floods, which first moved south and which were later captured by headward erosion of northeast-oriented valleys that diverted the melt water floods into the deep “hole” and into space the rapidly melting ice sheet had once occupied.

Missouri Coteau, Missouri Escarpment, and Pipestem Creek valley

Figure 10: Missouri Coteau, Missouri Escarpment, and Pipestem Creek valley. United States Geological Survey map digitally presented using National Geographic Society TOPO software.

Figure 10 illustrates the Missouri Coteau eastern boundary, which is the Missouri Escarpment. Pipestem Creek flows south-southeast along the Missouri Escarpment base. Figure 10 is located immediately east of figure 9 and includes overlap areas with figure 9. Note the abrupt change in topography at the Missouri Escarpment crest. The Missouri Escarpment in this figure 10 map area represents a rise of approximately 100 meters (or slightly more than 300 feet) above the lowland located east of the Pipestem Creek valley. The lowland east of the Pipestem Creek valley originated as the Midcontinent Trench bedrock floor and the Missouri Escarpment is a remnant of the Midcontinent Trench’s southwest wall. The Midcontinent Trench was an ice-walled and bedrock-floored valley and most of the southwest wall was ice, which has since melted. The Pipestem Creek valley and James River valley (located east of figure 10) are eroded into the Midcontinent Trench’s floor and were probably eroded headward late during the thick ice sheet’s rapid melt down. As previously mentioned headward erosion of the Midcontinent Trench ice-walled and bedrock-floored valley detached the rapidly melting thick ice sheet’s southwest margin (to create the Southwest Ice Sheet). Probably the depth of the Midcontinent Trench ice-walled and bedrock-floored valley at that time cannot be determined, although it is possible and in fact probable the Midcontinent Trench was a gigantic ice-walled and bedrock-floored canyon as deep and as wide as any of the world’s largest present day canyons. If so, the Southwest Ice Sheet when first detached was a very significant ice mass standing perhaps hundreds of meters high, if not higher. Also, as shown in earlier figures the Southwest Ice Sheet’s southwest margin was deeply eroded by melt water flood erosion. While today the Missouri Coteau ranges from 20-50 kilometers in width, it is possible and in fact probable that when first detached the Southwest Ice Sheet was much wider. Length wise the Southwest Ice Sheet extended from southern South Dakota north and northwest across North Dakota and southwest Saskatchewan and into east central Alberta, although it was detached as the southeast and south-oriented Midcontinent River sliced the ice-walled and bedrock-floored Midcontinent Trench canyon headward into the thick ice sheet. In other words, the southern end was detached first and the northwest end was detached last. The Missouri Coteau is where the final Southwest Ice Sheet remnants gradually melted and deposited whatever debris that had accumulated in or on what eventually became a stagnant and slowly melting ice mass.

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.