A geomorphic history based on topographic map evidence

The James River-Wild Rice River drainage divide area investigated here is located in southeast North Dakota and northeast South Dakota and is the north-south continental divide. Water in the Wild Rice River eventually reaches Hudson Bay. Water in the James River eventually reaches the Gulf of Mexico. The James River-Wild Rice River drainage divide developed when immense south-oriented melt water floods sliced two giant intersecting ice-walled and bedrock-floored canyons headward into a rapidly melting thick ice sheet. Flood waters in the eastern canyon were beheaded and reversed to flow north when that eastern canyon intersected with east and later north-oriented ice-walled and bedrock-floored canyons.

• The purpose of this essay is to use topographic map interpretation methods to explore James River-Wild Rice River drainage divide area landform origins in southeast North Dakota and northeast 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 James River-Wild Rice River drainage divide area landform evidence in southeast North Dakota and northeast 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.

James River-Wild Rice River drainage divide area location map

Figure 1: James River-Wild Rice 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 James River-Wild Rice River drainage divide area location map. The state of Minnesota is located east of the north-south green boundary line. West of Minnesota are North and South Dakota, with North Dakota being located north of the purple boundary line and South Dakota located south of the red boundary line. The south-oriented Missouri River is located along the figure 1 west edge area. Lake Oahe is a large reservoir flooding the Missouri River valley. Missouri River water flows to the Mississippi River and then to the Gulf of Mexico. The north-oriented Red River forms the North Dakota-Minnesota border north of Wahpeton (south of Wahpeton the north-oriented Bois de Sioux River is the boundary). Red River water eventually reaches Hudson Bay in northern Canada. The James River flows southeast from the figure 1 north center edge to Jamestown and Oakes, North Dakota. At Oakes the James River turns to flow south and south-southwest into South Dakota and to the figure 1 south center edge. James River water eventually reaches the Missouri River in southeast South Dakota and then ultimately reaches the Gulf of Mexico. The Wild Rice River is not labeled on figure 1, but is the stream in the southeast corner of North Dakota flowing through Cayuga and Mantador and then flowing north parallel to Red River, before joining the Red River just south of Fargo, North Dakota. Wild Rice River water eventually reaches Hudson Bay. The James River-Wild Rice River drainage divide area considered here is located along the North Dakota-South Dakota border. Another river of importance in this discussion is the Minnesota River, which originates at Big Stone Lake (located in figure 1 southeast quadrant on the South Dakota-Minnesota border) and which flows southeast into Minnesota. Minnesota River water eventually reaches the Mississippi River, which flows to the Gulf of Mexico. The Little Minnesota River originates near Claire City, South Dakota (located in South Dakota northeast corner) and flows southeast to Browns Valley and Big Stone Lake. In other words, the James River-Wild Rice River drainage divide area investigated in this essay is the north-south continental divide, with water in the James River flowing south to the Gulf of Mexico and water in the Wild Rice River flowing north to Hudson Bay. The question this essay will attempt to answer is how did this north-south continental divide originate? Also of interest in this essay is the question, how did the James River-Minnesota River drainage divide develop?

James River-Wild Rice River drainage divide area detailed location map

Figure 2 provides a somewhat more detailed location map for the James River-Wild Rice River drainage divide area. Ransom, Sargent, and Richland are North Dakota counties. Marshall and Roberts are South Dakota Counties. Wilkin and Traverse are Minnesota counties. The red shaded area is the Sisseton-Wahpeton Indian Reservation. The James River flows southeast from the figure 2 northwest corner area to Oakes, North Dakota and then turns to flow south-southwest to the figure 2 southwest corner area. Bear Creek is a south-southwest oriented tributary, which joins the James River at Oakes, and which originates north of the figure 2 map area near the edge of the south-oriented Sheyenne River valley. Water in Bear Creek and in the James River flows to the Missouri River and eventually reaches the Gulf of Mexico. The Sheyenne River flows south before making a U-turn to flow north and northeast to the Red River (see James River-Sheyenne River drainage divide area essay found under James River on sidebar category list). The Sheyenne River U-turn can be seen in Ransom County where the Sheyenne River flows southeast to Lisbon and then turns to flow north to the figure 2 north edge. Water in the Sheyenne River eventually reaches Hudson Bay. The Wild Rice River originates in southwest Sargent County, east of the James River near the North Dakota-South Dakota boundary, and flows generally east to the northwest corner of the Sisseton-Wahpeton Indian Reservation where it turns to flow north, southeast, and then north (just west of Wahpeton, North Dakota) and parallel to the north-northwest oriented Red River. Water in the Wild Rice River eventually reaches Hudson Bay. A significant Wild Rice River tributary is Wild Rice Creek, which originates in northeast Marshall County and which flows northwest and north to join the Wild Rice River in southern Sargent County. The area with many small lakes in southeast Marshall County and southern Roberts County is the Prairie Coteau, which stands higher than areas to the east and west. The southeast-oriented Little Minnesota River flows along the Prairie Coteau northeast flank in Roberts County. Water in the Little Minnesota River flows to the Mississippi River and eventually reaches the Gulf of Mexico. The north-south continental divide is located between south-oriented Bear Creek and the Sheyenne River and between the south-oriented James River and the Wild Rice River. The Missouri River-Mississippi River drainage divide is located along the Prairie Coteau, which separates the James River drainage basin from the Minnesota River drainage basin. The north-south continental divide is also located at Browns Valley (southwest Traverse County, Minnesota) with Lake Traverse normally draining north to the north-oriented Bois de Souix and Red Rivers and the Little Minnesota River draining in a southeast direction to the Minnesota River.

Sheyenne River elbow of capture

Figure 3: Sheyenne River elbow of capture.United States Geological Survey map digitally presented using National Geographic Society TOPO software. 

Figure 3 uses reduced size maps to illustrate the Sheyenne River elbow of capture located north of the James River-Wild Rice River drainage divide area. The Sheyenne River flows in a meandering valley from the figure 3 north edge in a southeast direction to Lisbon, North Dakota and then south before turning to flow north and northeast to the figure 3 northeast corner. Along the west edge of figure 3 is south-oriented Bear reek, which flows to the south-oriented James River. Note how in the figure 3 northwest corner the Bear Creek valley is linked to the south-oriented Sheyenne River valley. Additional, but more subtle, north-south through valleys link the Sheyenne River valley with drainage routes further to the south. As previously mentioned water in the Sheyenne River eventually reaches Hudson Bay and water in Bear Creek eventually reaches the Gulf of Mexico. The through valleys (such as the through valley linking Bear Creek headwaters with the Sheyenne River valley) provide evidence water once flowed freely across what is now the north-south continental divide. How then did the north-south continental divide originate? To answer that question imagine a rapidly melting thick ice sheet located in northern Iowa, Minnesota, North Dakota, and South Dakota (at least east and north of the present day Missouri River, but perhaps further west and south). Also image two immense south-oriented melt water rivers flowing off that ice sheet surface. One the of immense melt water rivers (which probably is really a complex of anastomosing river channels) is located in the region north and west of figure 3 where the present day south-oriented James River and Sheyenne River valleys are located and continues south across South Dakota to the present day southeast-oriented Missouri River. The other immense south-oriented melt water river is located where the present day Red River valley is and continues from the southeast corner of North Dakota in a southeast direction across Minnesota and Iowa to the Mississippi River. Also image these two immense south-oriented melt water rivers have sliced deep ice-walled and ice-floored valleys into the thick ice sheet surface. Also imagine these two immense rivers are really anastomosing complexes of rivers and intersect with each other in southeast North Dakota. Then imagine similar melt water rivers flowing off the thick ice sheet surface in other directions, some flowing east through what is today the Great Lakes region and even some flowing north to what is today Hudson Bay. As the thick ice sheet melts and these immense melt water rivers slice their valleys headward into the thick ice sheet, sooner or later the east-oriented valleys will intersect with the south-oriented valleys and probably some time later the north-oriented valleys will intersect with the south-oriented valleys. When those intersections take place the immense melt water rivers will be diverted to flow through the valley with the shortest route to sea level (which probably is much lower than it is today). That is precisely what happened in the Red River valley. An immense south-oriented melt water river was reversed so as to flow north. And, because the eastern melt water river intersected with the western melt water river in southeast North Dakota, the reversal of flow in the Red River valley captured the eastern half of the western melt water river (the Sheyenne River loop is evidence of that capture). The western melt water river west half was not captured and continued to flow south (along the present day James River valley alignment).

James River-Bear Creek confluence north of Oakes

Figure 4: James River-Bear Creek confluence north of Oakes. United States Geological Survey map digitally presented using National Geographic Society TOPO software. 

Figure 4 illustrates the James River-Bear Creek confluence area near Oakes, North Dakota and south of the figure 3 map area (the northeast corner of figure 4 overlaps with the southwest corner of figure 3). The James River flows southeast from the figure 4 northwest corner to Oakes and then flows south to the figure 4 south edge. Bear Creek flows south from the figure 4 north center edge to join the James River near Oakes. Bear Creek as illustrated in figure 3 originates near the Sheyenne River valley and the Bear Creek valley is linked by through valleys with the south-oriented Sheyenne River valley. The Bear Creek valley provides evidence water once flowed from the present day Sheyenne River drainage basin (north of figure 3) to the present day James River valley (south of Oakes). To understand why the Sheyenne River no longer flows south again imagine the two immense and interconnected south-oriented anastomosing complexes of ice walled and ice and bedrock-floored valleys being sliced into the rapidly melting thick ice sheet. One complex is centered on the present day Red River valley-Minnesota River valley alignment and the other is centered on the present day James River and south-oriented Sheyenne River valley alignments. When a similar east-oriented complex sliced its way westward from the Great Lakes area and intersected with the south-oriented Red River valley complex (somewhere in northwest Minnesota or southern Manitoba), it captured south-oriented flood flow moving in the Red River valley-Minnesota River valley complex and diverted that flood water east. At the same flood waters on the north end of that beheaded flood flow route reversed flow direction to move toward the new and somewhat steeper gradient east-oriented flood flow route. That reversal in flood flow movement reached as far south as the present Bois de Souix River. Because the Red River valley-Minnesota River valley complex was interconnected with the James River-Sheyenne River valley south-oriented complex the flood flow reversal also enabled the present day northeast-oriented Sheyenne River valley (northeast of figure 3) to erode headward to capture south-oriented flood flow in the eastern half of the James River-Sheyenne River valley complex. The slightly steeper gradient Sheyenne River valley was then able to erode northwest and north along what had been south-oriented melt water flood flow routes. The Bear Creek valley provides evidence of those former south-oriented melt water flood flow routes.

James River-Wild Rice River southeast of Oakes

Figure 5: James River-Wild Rice River southeast of Oakes. United States Geological Survey map digitally presented using National Geographic Society TOPO software. 

Figure 5 illustrates the James River-Wild Rice River drainage divide southeast of Oakes, North Dakota and includes overlap areas with figure 4. The North Dakota-South Dakota border is located just south of the figure 5 south edge. The south-oriented James River is located along the west edge in the figure 5 northwest quadrant. Wild Rice River headwaters are located in Brampton Township in the figure 5 southeast quadrant. The James River-Wild Rice River drainage divide (or north-south continental divide) in this region is a low north-south oriented ridge, which varies considerably in elevation from location to location. The ridge may be the result of glacial deposition and “valleys” across it may not be water eroded channels, although north and south of figure 5 water eroded channels cross the north-south continental divide. The Wild Rice River as seen in figure 2 flows northeast, east, and northeast to join the north-oriented Red River. Also as seen in figure 3 north of the Wild Rice River headwaters is the Sheyenne River loop, where the Sheyenne River turns from flowing south to flowing north. This evidence suggests the Wild River Rice valley eroded southwest and west to capture south-oriented melt water floods prior to headward erosion of the Sheyenne River valley to the north. East of figure 5 the Wild Rice River headwaters flow in an easterly direction just north of the Prairie Coteau north end (see figure 6 below). At least some segments of the Wild Rice River valley may have eroded west to capture south-oriented flood flow on the Sheyenne River valley alignment prior to reversal of flood flow in the south-oriented Red River-Minnesota River valley melt water flood flow complex. When flood flow in the Red River-Minnesota River valley flood flow complex was reversed those preexisting valleys may have enabled the Wild Rice River valley to erode west and southwest faster than the Sheyenne River valley was able to erode southwest and west. However, headward erosion of the Sheyenne River valley to the north quickly beheaded south-oriented flood flow to what was then the newly eroded Wild Rice River valley. Probably the Wild Rice River valley was eroded into an ice-covered region and was an ice-walled valley which may have had an ice floor until shortly before the deeper Sheyenne River valley beheaded the south-oriented flood flow.

Wild Rice River at Prairie Coteau north end

Figure 6: Wild Rice River at Prairie Coteau north end. United States Geological Survey map digitally presented using National Geographic Society TOPO software. 

Figure 6 illustrates the Wild Rice River flowing east along the Prairies Coteau north end and is located south and east of figure 5 (figure 6 includes overlap areas with figure 5). Wild Rice River headwaters are located north of Brampton in the figure 6 northwest quadrant. Note how the Wild Rice River flows in an easterly direction across the top of the figure 6 map area. Also note northwest and north-oriented Wild Rice Creek flowing from the figure 6 south center area across the red north-south highway and then north to join the Wild Rice River northwest of Havanna, North Dakota. The east-west North Dakota-South Dakota border is located just south of Havanna. The V-shaped escarpment-surrounded upland in the figure 6 southeast quadrant is the Prairie Coteau. Remaining figures in this essay provide additional illustrations of the Prairie Coteau upland and its surrounding escarpments. The Prairie Coteau upland appears to be covered by glacial moraines (much more prominent than glacial moraines on the surrounding lowlands, suggesting moraines on the upland are much thicker or least have experienced significantly less erosion). West of the James River valley is another escarpment, the east-facing Missouri Escarpment, and west of the Missouri Escarpment is the Missouri Coteau. The Missouri Escarpment and Missouri Coteau are almost mirror images of the west-facing Prairie Coteau escarpment and the hummocky topography at the escarpment’s crest. The lowland region between the Missouri Coteau and the Prairie Coteau is today the south-oriented James River drainage basin in South Dakota. While covered with glacial moraines, the James River lowland region glacial moraines generally are thinner (or least more eroded) than glacial moraines on the surrounding Missouri Coteau and Prairie Coteau upland surfaces. The reason for this difference in glacial moraine cover and also for the escarpments is related to the locations of the south-oriented ice-walled and ice-floored (and bedrock-floored) valleys the immense south-oriented melt water floods sliced into the rapidly melting thick ice sheet surface. As previously noted there were two such south-oriented valleys in eastern North Dakota. The eastern valley roughly was located on the present day Red River-Minnesota River valley alignment. That eastern valley was located east of the Prairie Coteau and the northeast-facing escarpment in the figure 6 southeast quadrants is a remnant of that valley’s west or southwest wall. The western south-oriented valley was located along the alignment of the James River valley (and Sheyenne River-Bear Creek valley further north). The northwest-facing escarpment in the figure 6 southeast quadrant is a remnant of that valley’s east or northeast wall.

Wild Rice River drainage northeast of Prairie Coteau north end

Figure 7: Wild Rice River drainage northeast of Prairie Coteau north end. United States Geological Survey map digitally presented using National Geographic Society TOPO software. 

Figure 7 illustrates the Wild Rice River drainage route north of the Prairie Escarpment north end. Note how the Wild Rice River flows east in the figure 7 northwest quadrant to Lake Tewaukon and flows northwest to the figure 7 north edge. That northwest-oriented Wild Rice River valley segment developed as a reversal of flood flow on a southeast-oriented flood flow. Where was the southeast-oriented flood flow going? In the figure 7 southeast corner area are headwaters of the Little Minnesota River, which flows in a southeast direction along the base of the Prairie Coteau northeast-facing escarpment (see figure 8 below). Water in the Little Minnesota River eventually reaches the Mississippi River, which flows south to the Gulf of Mexico. Water in the Wild Rice River, as previously stated, flows north and eventually reaches Hudson Bay. Near the figure 7 south center edge note how Little Minnesota River headwaters flow northeast down the Prairie Coteau eastern escarpment and then turn to flow east. Also note just north of the Little Minnesota River headwaters are Shortfoot Creek  headwaters, which also flow in a northeast down the Prairie Coteau eastern escarpment, but then turn north to flow to the figure 7 north edge. North of figure 7 Shortfoot Creek turns to flow in a northwest direction to join the Wild Rice River. North America’s north-south continental divide is located between Shortfoot Creek and the Little Minnesota River headwaters on that northeast-facing escarpment slope. The continental divide as previously described was formed when an immense south-oriented melt water flood moving in a large ice-walled and bedrock-floored valley along the present day Red River-Minnesota River alignment was captured in northwest Minnesota or southern Manitoba and diverted east to the present day Great Lakes area. Flood waters on the north end of the beheaded flood flow route then reversed flow direction to flow north to the newly developed east-oriented flood flow route. That reversal of flood flow created the present day Red River drainage basin in eastern North Dakota and western Minnesota, which includes the Wild Rice River. The north-south continental divide represents the southern end of the region affected by that flood flow reversal. South of the continental divide flood waters continued on their south-oriented course. North of the continental divide flood waters reversed flow direction and flowed north. Valleys eroded into the escarpment face were probably eroded as a remnant thick ice sheet ice mass on top of the Prairie Coteau gradually melted.

Wild Rice River-Minnesota River drainage divide east of Prairie Coteau

Figure 8: Wild Rice River-Minnesota River drainage divide east of Prairie Coteau. United States Geological Survey map digitally presented using National Geographic Society TOPO software. 

Figure 8 better illustrates the Wild Rice River-Little Minnesota River drainage divide area and is located south and east of figure 7 (and includes overlap areas with figure 7). The west to east North Dakota-South Dakota state line is located near the figure 8 north edge. The Little Minnesota River headwaters flow northeast down the escarpment slope to the figure 8 center area and then after flowing east turn to flow southeast to the figure 8 southeast corner. Shortfoot Creek headwaters are located in the figure 8 west center area and flow northeast down the escarpment face and then turn north to flow to the figure 8 north edge. Note the multiple small lakes on the lowland northeast of the northeast-facing Prairie Coteau escarpment. The previously described capture and reversal of flood flow in the Red River-Minnesota River ice-walled and bedrock-floored valley was not instantaneous, but probably occurred in stages. As more and more water was diverted east, flood flow in the figure 8 map area diminished and the rate of flood movement also probably slowed. Those small lakes might be kettles, which originated when diminishing flood waters stranded blocks of ice on the floor of the ice-walled and bedrock-floored valley and then buried (or partially buried) those ice blocks with flood transported materials. The ice blocks then melted leaving depressions where they had been located. Lakes on top of the Prairie Coteau also probably represent locations of remnant ice masses that gradually melted, however those ice masses were remnants of the thick ice sheet mass that remained on the Prairie Coteau upland. The thick ice sheet in that location was not deeply eroded by melt water floods. By slicing ice-walled and bedrock-floored valleys headward into the rapidly melting thick ice sheet the immense melt water floods were effectively chopping the thick ice sheet up into a large number of smaller detached ice sheets. This process of chopping up the thick ice sheet accelerated the ice sheet’s melting rate. One of the detached ice masses was located on top of the Prairie Coteau. These detached ice masses eventually melted, although without the spectacular and immense melt floods melting of the thick ice sheet had produced.

Wild Rice River headwaters on Prairie Coteau upper surface

Figure 9: Wild Rice River headwaters on Prairie Coteau upper surface. United States Geological Survey map digitally presented using National Geographic Society TOPO software. 

Figure 9 illustrates the Prairie Coteau north end and includes overlap areas with figures 6, 7, and 8. Note White Lake near the figure 9 west center edge. The northwest-oriented stream flowing down the Prairie Coteau northwest-facing escarpment to the White Lake north end is Wild Rice Creek. From White Lake Wild Rice Creek flows northwest and north to join the east-oriented Wild Rice River (see figure 6). Northwest-oriented drainage routes down the northwest-facing Prairie Coteau escarpment face to the south of White Lake eventually flow to the south-oriented James River. Just as the north-south continental divide is located between Shortfoot Creek and Little Minnesota River headwaters flowing down the Prairie Coteau northeast-facing escarpment face, the north-south continental divide is located between streams flowing down the Prairie Coteau northwest-facing escarpment face. The reversal of flood flow in the present-day Red River valley reached as far southeast as the north end of the northwest-facing Prairie Coteau escarpment face. Landscape features on the Prairie Coteau upper surface are similar to features found elsewhere on the Prairie Coteau upper surface and also on the Missouri Coteau surface on the James River lowland western side. These features are characterized by hummocky topography and numerous lakes and probably represent areas underlain by thick glacial moraines deposited by stagnant ice masses. As already described the Prairie Coteau is interpreted here to have been the location of an isolated thick ice sheet remnant after the southern margin of the rapidly melting ice sheet had been chopped up into a number of smaller detached ice sheets. This Prairie Coteau ice sheet mass will be here named the Prairie Coteau Ice Sheet. The Prairie Coteau Ice Sheet was originally an integral component of the thick ice sheet, which deeply eroded the underlying bedrock. This deep glacial erosion probably resulted in considerable debris being included in the ice mass. As the ice sheet melted debris accumulated on the ice sheet surface. Finer grained materials were removed by melt water, especially along major melt water flood flow routes. However, the Prairie Coteau Ice Sheet survived because it was not located along major melt water flood flow routes (at least near the end of the thick ice sheet melt down). Consequently much of debris contained within or accumulating on top of the Prairie Coteau Ice Sheet simply stayed in place. As the Prairie Coteau Ice Sheet gradually melted this debris probably slid into low spots exposing ice underneath it, but it was not moved far. The lakes probably represent where the final Prairie Coteau Ice Sheet remnants melted away, leaving depressions which are now filled with water.

James River-Wild Rice River drainage divide area west of Prairie Coteau

Figure 10: James River-Wild Rice River drainage divide area west of Prairie Coteau. United States Geological Survey map digitally presented using National Geographic Society TOPO software. 

Figure 10 illustrates the region west of the northwest facing Prairie Coteau escarpment and includes overlap areas with figure 9. The south-oriented James River is located along the figure 10 west edge and flows from the figure 10 northwest corner area to the figure 10 west center edge (and continues to flow south to the Missouri River). White Lake and northwest and north-oriented Wild Rice Creek are located in the figure 10 northeast quadrant (While Lake is located near the figure 10 east edge). The lowland between the west-facing Prairie Coteau escarpment and the James River continues east of the James River until the east facing Missouri Escarpment is reached. At the Missouri Escarpment crest is the Missouri Coteau. The James River lowland is interpreted here to have been formed as the floor of what was an immense south-oriented ice-walled and bedrock-floored valley sliced into the rapidly melting thick ice sheet. The east facing Missouri Escarpment and the west-facing Prairie Coteau escarpment are remnants of that immense valley’s walls. At one time the valley may have been an immense south-oriented canyon bounded on both sides by high ice walls, which may have been many hundreds of meters (or more) in height. Much of the valley’s east and northeast wall was removed by melt water flood erosion, but the Missouri Escarpment provides evidence of the valley’s extent to the north and northwest. The Missouri Escarpment can be traced north into central North Dakota and then northwest to northwest North Dakota and across southwest Saskatchewan into east central Alberta. Headward erosion of this immense southeast and south-oriented ice-walled and bedrock-floored valley into the thick ice sheet surface not only detached the Prairie Coteau ice sheet, but it also detached the thick ice sheet’s southwest margin. The thick ice sheet’s detached southwest margin is here named the Southwest Ice Sheet. The immense southeast and south-oriented ice-walled and bedrock-floored valley is here named the Midcontinent Trench and the immense melt water river that carved the Midcontinent Trench is here named the Midcontinent River. Because the thick ice sheet was located in a deep “hole”, created by crustal warping caused by ice sheet weight and also by deep glacial erosion, the Midcontinent Trench floor was lower in elevation than areas along the thick ice sheet southwest margin (wherever that southwest margin was located). Melt water floods moving along the thick ice sheet southwest margin broke through the Southwest Ice Sheet at various points and carved east and northeast oriented ice-walled and bedrock-floored valleys, which chopped up the Southwest Ice Sheet into a string of even smaller detached ice sheets.

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.