A geomorphic history based on topographic map evidence

The Missouri Coteau-James River drainage divide area discussed here is located in Dickey County, North Dakota and McPherson and Brown Counties, South Dakota, USA. The Missouri Coteau is a region of small interior drainage basins and is underlain by thick glacial debris interpreted to have been deposited as the detached southwest margin of a thick North American ice sheet slowly melted. East of the Missouri Coteau is the well-drained east-facing Missouri Escarpment slope and a lowland drained by the south-oriented James River and various south-oriented James River tributaries. The Missouri Escarpment is interpreted to have originated as the west wall of a large south-oriented ice-walled and bedrock-floored valley sliced by an immense southeast and south-oriented melt water river into a rapidly melting thick North American ice sheet. The James River and tributary valleys were probably eroded into the floor of this ice-walled and bedrock-floored valley late during the ice sheet’s melt down history.

• The purpose of this essay is to use topographic map interpretation methods to explore landform origins between the Missouri Coteau and the James River in Dickey County, North Dakota and McPherson and Brown 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 landform evidence between the Missouri Coteau and the James River in Dickey County, North Dakota and McPherson and Brown 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 Coteau-James River drainage divide area location map

Figure 1: Missouri Coteau-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 Missouri Coteau-James River drainage divide area location map. The state of Minnesota is located east of the green boundary line along the figure 1 east edge area. West of the Minnesota the northern half of figure 1 is the state of North Dakota and the southern half is the state of South Dakota. The Missouri River is the major river flowing south from the figure 1 northwest corner area to Bismarck, North Dakota and then into Lake Oahe. Lake Oahe is a large reservoir flooding the Missouri River valley. The dam responsible for Lake Oahe is located south of the figure 1 map area. The James River flows south from the figure 1 north center edge to Jamestown, North Dakota and then turns to flow southeast to Oakes, North Dakota. At Oakes the James River turns to flow south-southwest into South Dakota and eventually to the figure 1 south center edge. Note the presence of an area lacking drainage routes located between the  west-oriented Missouri River tributaries and the east and southeast-oriented James River tributaries. That region lacking drainage routes is the Missouri Coteau, which is a region with many small interior drainage basins. The Missouri Coteau eastern boundary is the well-drained east-facing Missouri Escarpment slope, where many of the east-oriented James River tributaries begin. East of the Missouri Escarpment elevations are generally 100-200 meters lower than Missouri Coteau elevations. These major landforms are interpreted in this essay to have evolved late during the rapid melt down of a thick North American ice sheet, which was located in a deep “hole.” The south-oriented James River drainage basin is largely located where an immense south-oriented supra glacial melt water river, named here the Midcontinent River, sliced a giant south-oriented ice-walled and bedrock-floored valley, named here the Midcontinent Trench, into the rapidly melting thick ice sheet surface. The Missouri Escarpment is what remains of the Midcontinent Trench’s west wall. Headward erosion of the Midcontinent Trench valley detached the ice sheet’s west and southwest margin, named here the Southwest Ice Sheet, which at that time was located in the region between the Missouri Escarpment and the present day Missouri River valley. Because the thick ice sheet was located in a deep “hole”, melt water floods tended to move along the ice sheet margin until they could reach a south-oriented valley leading to the Gulf of Mexico. The Missouri River valley was eroded headward by these ice-marginal melt water floods. The Missouri Coteau represents the area where the Southwest Ice Sheet melted and deposited whatever debris it contained.

Missouri Coteau-James River drainage divide area detailed location map

Figure 2: Missouri Coteau-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 Coteau-James River drainage divide area in Dickey County, North Dakota and McPherson and Brown Counties, South Dakota. In figure 2 McIntosh and Dickey Counties are located in North Dakota and McPherson, Brown, and Edmunds Counties are located in South Dakota. The James River flows southeast and south-southwest in eastern Dickey County and then south-southwest and south in Brown County. Some James River tributaries mentioned in this essay include the Maple River and Elm River in Dickey County and northern Brown County, southeast oriented Foot Creek in McPherson and Brown Counties (flowing through Aberdeen, South Dakota) and southeast and south-oriented Snake Creek in the northeast corner of Edmunds County. The Missouri Coteau is the region without an integrated drainage pattern and with numerous small lakes located in the western third of figure 2. The Missouri Escarpment is located just east of the Missouri Coteau and is where headwaters of the various east and southeast-oriented James River tributaries begin. The James River lowland extends east from the Missouri Escarpment to east of the figure 2 map area where the northwest and west-facing Prairie Coteau escarpment is located. At that escarpment crest is a region very similar to the Missouri Coteau region (see James River-Wild Rice River drainage divide area essay found under James River on sidebar category list). In other words the James River flows south in what is today a broad lowland bounded by erosional escarpments and poorly drained areas of thick glacial deposits. This evidence suggests the James River lowland originated as an ice-walled and bedrock-floored valley, which had been sliced by an immense south-oriented supra glacial melt water river into the surface of a rapidly melting thick ice sheet. The James River today empties into the Missouri River near the South Dakota southeast corner. The Missouri River valley downstream from the James River lowland south end is much wider than it is further upstream, suggesting large volumes of water from the James River lowland helped erode the larger downstream Missouri River valley. Present day drainage routes on the James River lowland floor probably reflect valley systems eroded late during the thick ice sheet melt down history.

Missouri Coteau-Maple River drainage divide area

Figure 3: Missouri Coteau-Maple River drainage divide area. United States Geological Survey map digitally presented using National Geographic Society TOPO software. 

Figure 3 illustrates the Missouri Coteau-Maple River drainage divide area in northern Dickey County. The Missouri Coteau is the poorly drained region with numerous small lakes located along the figure 3 west edge area. Immediately east of the Missouri Coteau is the east-facing Missouri Escarpment. Elevations at Merricourt are 125 meters lower than elevations in the nearby Missouri Coteau and elevations at Monango are 175 meters lower than typical Missouri Coteau elevations to the west. The Maple River flows south through the figure 2 northeast quadrant and turns to flow to the figure 3 east edge before reaching Monango (and then turns southeast east of figure 3). The south-oriented stream in Potsdam Township (figure 3 north center), which turns to flow east to the figure 3 southeast corner area is the South Fork Maple River, which joins the southeast-oriented Maple River east of figure 3. Note how many South Fork Maple River tributaries begin at the Missouri Escarpment crest and flow east down the escarpment slope. Note how those tributaries have not eroded valleys headward into the Missouri Coteau. This evidence suggests a different origin for the Missouri Coteau landscape than the origin for landscapes in the lowland east of the Missouri Escarpment. The Missouri Escarpment as already mentioned is here interpreted to have formed as part of the west wall of a large south-oriented ice-walled and bedrock-floored valley sliced into the surface of a rapidly melting thick North American ice sheet. Probably at the time the ice-walled and bedrock-floored valley was sliced into the thick ice sheet surface the ice sheet was hundreds of meters thick (if not more) in this figure 3 location. The south-oriented ice-walled and bedrock-floored valley was probably an immense south-oriented canyon that had been carved into the ice sheet surface. This south-oriented canyon (the Midcontinent Trench) was just one of several similar giant ice-walled and bedrock-floored canyons sliced into the rapidly melting thick ice sheet surface. These ice-walled and bedrock-floored canyons chopped the ice sheet up into a number of smaller ice sheets and in the process greatly hastened the ice sheet melting process. One of the smaller ice sheets was the Southwest Ice Sheet, where the Missouri Coteau now is located. Unlike in the James River lowland area, where melt water floods removed much of the ice transported debris, debris contained in and on top of the Southwest Ice Sheet simply settled and was deposited in place, or close to in place, as the ice sheet remnant melted.

Maple River-James River drainage divide area

Figure 4: Maple River-James River drainage divide area. United States Geological Survey map digitally presented using National Geographic Society TOPO software. 

Figure 4 illustrates the Maple River-James River drainage divide area east of the figure 3 map area and includes overlap areas with figure 3. The south and east oriented river in the figure 4 northeast quadrant is the James River, which generally is flowing southeast. The Maple River flows south from the figure 4 northwest corner and is joined by the east and northeast-oriented South Fork Maple River (east of Manango) in the figure 4 southwest quadrant. After being joined by the South Fork the Maple River flows southeast to the Fullerton area and turns to flow south to the figure 4 south center edge. The figure 4 landscape is typical of James River lowland landscapes in this region. Other than the river valleys the surface is relatively flat (at least compared with the Missouri Escarpment to the west and the Missouri Coteau region west of the Escarpment). This figure 4 map area is located on what would have been the floor of the ice-walled and bedrock-floored Midcontinent Trench. The Midcontinent Trench as previously described was sliced into the thick ice sheet surface by an immense south-oriented supra glacial melt water river. The James River valley and the Maple River valley were probably eroded during the final south-oriented melt water flood event to move across the lowland surface. The immense south-oriented melt water floods were captured further north and northwest in the Midcontinent Trench and diverted to flow north. These captures occurred as headward erosion of south-oriented ice-walled and bedrock-floored valleys into the thick ice sheet surface intersected with east oriented ice-walled and bedrock-floored valleys (leading to the present day Great Lakes and Saint Lawrence River drainage routes) and with north-oriented ice-walled and bedrock-floored valleys (leading to Hudson Bay). The east and north oriented ice-walled and bedrock-floored valleys offered shorted routes with steeper gradients to sea level (which probably was significantly lower than today) and flood waters were diverted to those steeper gradient and shorter routes. The first capture to behead south-oriented flood flow in the Midcontinent Trench occurred when a reversal of flood flow direction in the present day Red River valley captured the east half of south-oriented flood flow in the Midcontinent Trench and enabled the deep Sheyenne River valley to erode headward so as to behead all southeast and south-oriented Midcontinent River flow (see James River-Wild Rice River drainage divide, James River-Sheyenne River drainage divide, and Sheyenne River-James River drainage divide area essays found under James River on sidebar category list). However, at the same time as the Sheyenne River valley headward erosion was capturing the Midcontinent River, the Midcontinent River was also being captured further to the northwest (see Missouri River-Souris River drainage divide area essay found under ND Missouri River on sidebar category list).

Missouri Coteau-Elm River drainage divide area

Figure 5: Missouri Coteau-Elm River drainage divide area. United States Geological Survey map digitally presented using National Geographic Society TOPO software. 

Figure 5 illustrates the Missouri Coteau-Elm River drainage divide along the North Dakota-South Dakota state line and is located south of the figure 3 map area. Ellendale, North Dakota is the town located in the figure 5 east center edge area. The Missouri Coteau is located along the figure 5 west edge and the east-facing Missouri Escarpment marks the Missouri Coteau eastern boundary. Elevations on the Missouri Coteau in this figure 5 map area are approximately 200 meters higher than the elevation at Ellendale. The Elm River is the south-oriented river located between the Missouri Escarpment and Ellendale and is flowing to the figure 5 south center edge. The Missouri Escarpment in this figure 5 map area is about as high and as steep as the Escarpment gets in this Missouri Coteau-James River drainage divide area. North and south of this figure 5 location the Escarpment is less steep and less high. The sharp edge of the Missouri Coteau at the Missouri Escarpment crest supports the interpretation that the Missouri Escarpment is a remnant of the west wall of a large water eroded ice-walled and bedrock-floored valley. South-oriented melt water floods removed most ice contained debris as the immense south-oriented Midcontinent Trench was sliced into the thick ice sheet. Debris was probably removed from the Midcontinent Trench area by one of several means. Probably the melt water floods transported blocks of debris containing ice and these ice blocks were transported far south of the thick ice sheet margin (at least at the margin location at the time the Midcontinent Trench was formed). Late during the Midcontinent Trench history blocks of ice containing debris were probably stranded on the Midcontinent Trench floor as the final south-oriented floods waned. Melt water floods also probably picked up and transported finer grained debris and moved that material south, perhaps as far as the Mississippi River delta and the Gulf of Mexico. Larger debris probably was not moved as far, although flood water volumes were probably great enough to transport coarse-grained material. Flood transport of these ice-transported materials beyond the ice sheet margin may make it difficult to identify the thick ice sheet margin location by simply looking for the southern margin of glacially transported material.

Elm River-Maple River drainage divide area

Figure 6: Elm River-Maple River drainage divide area. United States Geological Survey map digitally presented using National Geographic Society TOPO software. 

Figure 6 uses reduced size maps to illustrate the Elm River-Maple River drainage divide area and includes much of the figure 5 map area. The Missouri Coteau is located in the figure 6 northwest quadrant and the east-facing Missouri Escarpment is located immediately east of the Missouri Coteau. In this region the Missouri Escarpment has a south-southwest to north-northeast orientation as does the James River valley to the east of figure 6 (see figures 1 and 2). Ellendale is the town located along the figure 6 north edge (where the north-oriented highway reaches the north edge). The Maple River is located east of Ellendale and flows south-southwest from the figure 6 north edge to the figure 6 south center edge. The Elm River flows south and southeast from the figure 6 north center edge area to the figure 6 south center, where it turns to flow east (with a north-northeast jog) to the south-southwest Maple River. The south-southwest oriented stream joining the Elm River at the north-northeast jog is the Dry Branch of the Elm River. The south-southwest orientation of the drainage routes as well as of the Missouri Escarpment suggests the Midcontinent Trench in this region also had a south-southwest orientation. The drainage routes on the Midcontinent Trench floor probably reflect routes of final melt water floods that moved south in the giant ice-walled and bedrock floored valley. The Midcontinent Trench floor was eroded into the thick ice sheet floor, which was located on the southwest margin of the deep “hole” the thick ice sheet had occupied.

• The thick ice sheet is interpreted here to have formed on a topographic surface at least as high as the highest level Rocky Mountain erosion surfaces today, if not higher. That surface has probably been significantly warped since, with the ice sheet weight causing down warping under the ice sheet and perhaps causing up warping along some ice sheet margins and elsewhere in the continent. In addition the ice sheet itself deeply eroded the region on which it was located. However, like with the present day Antarctic Ice Sheet, a significant per cent of the thick North American ice sheet probably was located below the original ice sheet rim elevation, which means this figure 6 map area was located at an elevation well below the original ice sheet rim elevation. At the same time, before the ice sheet melt down began, the ice sheet also probably stood high above the original ice sheet rim elevation. When ice sheet melting began to exceed new ice formation rates the ice sheet elevation above the original elevation began to decrease. Melt water floods moving from the ice sheet surface to the ice sheet margin probably moved along the ice sheet margin until flood waters could find routes to move south to the Gulf of Mexico. The Missouri River drainage basin research project essay series is reconstructing some of those south-oriented flood flow routes. In time the ice sheet elevation fell below the elevation of the original ice sheet rim. At that time the ice-marginal melt water floods started to move onto the ice sheet surface and to move south in large southeast and south-oriented supra glacial rivers like the Midcontinent River. These rivers first carved deep ice-walled and ice-floored valleys into the thick ice sheet surface. Later these valleys became ice-walled and bedrock-floored valleys like the Midcontinent Trench.

Elm River-James River drainage divide area

Figure 7: Elm River-James River drainage divide area. United States Geological Survey map digitally presented using National Geographic Society TOPO software. 

Figure 7 uses reduced size maps to illustrate the Elm River-James River drainage divide area south and east of the figure 6 map area and includes overlap areas with figure 6. The Elm River flows southeast from the figure 7 northwest corner, makes its northeast jog and then flows east before turning to flow south-southwest and then southeast and south to the figure 7 south edge. South of the Elm River northeast jog is Willow Creek Lake. Note how Willow Creek flows east and southeast from the figure 7 west edge and then turns northeast before flowing in a more easterly direction to reach Willow Creek Lake and the Elm River valley. A south-southwest oriented through valley links the northeast-oriented Willow Creek valley segment with southeast oriented Foot Creek in the figure 7 southwest corner. The through valley is evidence of a south-southwest oriented flood flow route that was dismembered by headward erosion of deeper east and southeast oriented valleys. Those deeper valleys were probably eroding headward from what was then the deeper James River valley, which was eroding headward on the Midcontinent Trench floor. The James River is the south-southwest oriented river flowing into the large Mud Lake and Columbia Road Reservoirs located in the figure 7 east half. Near the figure 7 south edge the James River turns to flow southeast and south. Headward erosion of the present day James River valley and its various tributary valleys probably occurred during the final large-scale south-oriented flood events to move through the ice-walled and bedrock-floored Midcontinent Trench valley. The final flood event probably occurred as headward erosion of the Sheyenne River valley was beheading southeast- and south-oriented flood flow to what is now the James River drainage basin (see Sheyenne River-James River drainage divide area essay) in what is today central North Dakota and as the southeast-oriented Midcontinent River was being captured in north central North Dakota (see Souris River loop discussion in Missouri River-Souris River drainage divide area essay). Prior to those captures this figure 7 map area was located on what was a major south-oriented melt water flood flow route draining melt water from the heart of the rapidly melting thick North American ice sheet. The captures further north diverted the south-oriented flood water to the east (probably to the present day Great Lakes area) and subsequently to the north (to what is today the Hudson Bay region). Those diversions of the immense south-oriented Midcontinent River melt water floods from the Gulf of Mexico to the north were probably responsible for the climate change that ended the thick ice sheet rapid melt down (and which froze melt water floods on the ice sheet floor).

Foot Creek-James River drainage divide area

Figure 8: Foot Creek-James River drainage divide area. United States Geological Survey map digitally presented using National Geographic Society TOPO software. 

Figure 8 uses reduced size maps to illustrate the Foot Creek-James River drainage divide area south of the figure 7 map area and includes overlap areas with figure 7. Aberdeen, South Dakota is the city located in the figure 8 southwest quadrant. Groton, South Dakota is the largest town located in the southeast quadrant. Columbia, South Dakota is the town located in the figure 8 north center area. The James River flows south from the figure 8 north edge to Columbia and then flows east a short distance before turning south and south-southwest to flow to the figure 8 south center edge. The Elm River flows south-southeast from the figure 8 north edge (north of Aberdeen) and then makes a U-turn to flow to the James River at Columbia. Foot Creek flows east and south from the figure 8 west edge to enter Richmond Lake and then to flow southeast past the west edge of Aberdeen before turning to flow south to the figure 8 south edge. The long north-oriented arm of Richmond Lake is in an unnamed Foot Creek valley, which is linked by shallow through valleys with the northeast and east-oriented Elm River segment seen in figure 7. Another interesting figure 8 drainage route is south-oriented Moccasin Creek, which originates north of Aberdeen almost at the edge of the Elm River valley (where the Elm River begins to make its U-turn from flowing south-southeast to flowing northeast). Moccasin Creek flows southeast and then turns south-southwest to flow past the east edge of Aberdeen and to join Foot Creek just south of Aberdeen. The Moccasin Creek valley provides evidence water once flowed from the Elm River drainage basin (north of the Elm River U-turn) south to the Foot Creek valley, which eventually joins the south-oriented James River. Also, between Aberdeen and the James River valley is evidence of a south-oriented anastomosing channel complex, which provides evidence of a large south-oriented flood event (figure 9 below illustrates these anastomosing channels in more detail). Why did the Elm River, which once flowed south to the James River, make a U-turn and flow northeast to join the James River at Columbia. Probably the present day northeast-oriented Elm River valley segment originated as a southwest-oriented flood flow route moving water from the James River valley upstream from Columbia to the south-oriented Moccasin Creek and Foot Creek channels, which were some of the anastomosing channels leading to the south-oriented James River. As the deep James River valley eroded north it eroded west to behead the southwest-oriented flood flow channels leading to the Moccasin Creek-Foot Creek channel. Flood waters on the northeast end of the beheaded flood flow channels then reversed flow direction to flow northeast to the newly eroded and deeper James River valley. This reversal of flood flow captured the Elm River (creating the Elm River U-turn) and beheaded south-oriented Elm River flood flow to the south-oriented Moccasin Creek and Foot Creek channel.

Anastomosing channel complex east of Aberdeen, South Dakota

Figure 9: Anastomosing channel complex east of Aberdeen, South Dakota. United States Geological Survey map digitally presented using National Geographic Society TOPO software. 

Figure 9 provides a somewhat more detailed map to illustrate the anastomosing channel complex between Aberdeen, South Dakota and the south-oriented James River. The east edge of Aberdeen is located along the figure 9 west center edge. South-oriented Moccasin Creek can be seen along the figure 9 west edge north of Aberdeen. The south-oriented James River is located along the figure 9 east edge (northeast and southeast corner areas). Between Moccasin Creek and the James River is a maze of mostly dry and intersecting channels. This anastomosing channel complex provides evidence of a large-scale flood event, which moved large volumes of water in a south-oriented direction across the entire figure 9 map area. This flood event was the final major flood event in the ice-walled and bedrock-floored Midcontinent Trench history and was the event responsible for beheading Moccasin Creek and for creating the Elm River U-turn described in the figure 8 discussion above. Probably the ice-walled and bedrock-floored Midcontinent Trench valley was carved by the erosive actions of similar anastomosing channel complexes from the time large volumes of melt water began to flow across the melting ice sheet surface. Initially these anastomosing channel complexes were carved into the ice sheet surface as complexes of ever-changing ice-walled and ice-floored valleys. These ever-changing supra glacial anastomosing channel complexes probably became concentrated along the Midcontinent Trench route and sliced that route deeper and deeper into the thick ice sheet surface. In time the Midcontinent Trench became an ice-walled and bedrock-floored valley and the anastomosing channel complexes were being eroded into the underlying bedrock surface, upon which the thick ice sheet had been resting. On a larger scale the Midcontinent Trench ice-walled and bedrock-floored valley was one of at least two immense south-oriented intersecting ice-walled and bedrock-floored valleys in southeast North Dakota, northeast South Dakota and western Minnesota. The other south-oriented ice-walled and bedrock-floored valley was located along the alignment of the present-day north-oriented Red River valley and the present day southeast-oriented Minnesota River valley. A flood flow reversal in that eastern ice-walled and bedrock-floored valley captured the east half of the Midcontinent River and diverted the flood water north (see James River-Sheyenne River drainage divide area and James River-Wild Rice River drainage divide area essays).

Missouri Coteau-Snake Creek drainage divide area

Figure 10: Missouri Coteau-Snake Creek drainage divide area. United States Geological Survey map digitally presented using National Geographic Society TOPO software. 

Figure 10 illustrates the Missouri Coteau-Snake Creek drainage divide area located west and slightly north of figure 8 (Aberdeen, South Dakota is located east of the figure 10 southeast corner). Lake Pamley in the figure 10 southeast corner area is located on Snake Creek, which flows south to eventually reach the south-oriented James River. The Missouri Coteau is located along the figure 10 west edge and the east facing Missouri Escarpment is located east of the Missouri Coteau. Note how the Missouri Escarpment is oriented in a south-southwest to north-northeast direction and is not as steep in figure 10 as it was further to the north. The Missouri Escarpment slope, unlike the Missouri Coteau at its crest, is well-drained by numerous east and southeast-oriented streams flowing to the lowland at its base. Water from these east and southeast-oriented streams collects in south-oriented Snake Creek tributaries along the Escarpment base and flows south to join Snake Creek. Note how the Missouri Coteau area shows evidence of thick glacial moraine deposits, evidence of the glacial moraines is largely absent from the Missouri Escarpment slope and from the lowland area to the east of the Escarpment. This pattern is consistent with the pattern seen further north and is consistent with the interpretation the Missouri Escarpment is what remains of the west wall of an immense south-oriented ice-walled and bedrock-floored valley that had been sliced into a rapidly melting thick ice sheet. The Missouri Coteau region is where the ice sheet’s detached western margin was located and melted, depositing whatever debris it contained pretty much in place. Immense melt water floods removed much of the ice sheet contained debris from the Midcontinent Trench floor and the Missouri Escarpment areas, although coarser grained glacially transported debris remained and also flood deposited debris is probably also present. The Missouri Escarpment segments seen in this essay do not show evidence of possible ice-walled and bedrock-floored valleys, which moved ice-marginal melt water floods from south and west of the ice sheet margin onto the ice sheet (and to the lower elevation Midcontinent Trench floor). Evidence for such valleys has been illustrated in the Big Muddy Creek-Little Muddy River drainage divide area, Little Muddy River-White Earth River drainage divide area, and Missouri River-Sheyenne River drainage divide area essays, among others, which can be found under ND Missouri River on sidebar category list). Additional east and northeast-oriented valleys crossing the Missouri Coteau area are located south of this figure 10 map area.

Additional information and sources of maps studied

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