A geomorphic history based on topographic map evidence

The Poplar River-Big Muddy Creek drainage divide area discussed here is located in northeast Montana, USA. Although detailed topographic maps of the Poplar River-Big Muddy Creek drainage divide area have been available for more than fifty years detailed map evidence has not previously been used to interpret the region’s geomorphic history. The interpretation provided here is based entirely on topographic map evidence. The Poplar River-Big Muddy Creek drainage divide area is interpreted to have been eroded during immense southeast-oriented flood events, the first of which flowed on a topographic surface at least as high as the highest points in the present-day drainage divide area. Flood erosion in the drainage divide area ended when headward erosion of the present day Missouri River valley drained all remaining southeast-oriented flood flow.

Introduction

• The purpose of this essay is to use topographic map interpretation methods to explore Poplar River-Big Muddy Creek drainage divide area landform origins in northeast Montana, USA. Map interpretation methods can be used to unravel many geomorphic events leading up to formation of present-day drainage routes and development of other landform features. While each detailed topographic map feature provides detailed evidence to be explained, the solution must be consistent with explanations for adjacent area map evidence as well as solutions to big picture map evidence puzzles. I invite readers to improve upon my solutions and/or to propose alternate solutions that better explain evidence and are also consistent with adjacent map area and big picture evidence. Readers may do so either by making comments here or by writing and publishing their own essays and then by leaving a link to those essays in a comment here.

• This essay is also exploring a new geomorphology paradigm in which erosional landforms are interpreted as evidence left by immense glacial melt water floods. Implied in that interpretation is the immense floods were derived from a thick North American ice sheet that created a deep “hole” in the North American continent and also melted fast. The previously unexplored paradigm being tested in this and other 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 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 Poplar River-Big Muddy Creek drainage divide area landform evidence 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.

Poplar River-Big Muddy Creek drainage divide area location map

Figure 1: Poplar River-Big Muddy Creek 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 Poplar River-Big Muddy Creek drainage divide area location map. The Canada-United States border is shown. Saskatchewan is the Canadian Province north of the international boundary. Montana is the state in the western two-thirds of figure 1 and North Dakota is located in the eastern third of the United States area. The northeast oriented South Saskatchewan River is located north of the figure 1 map area. This essay will only address evidence in the United States and other essays address Canadian evidence (found under Saskatchewan on sidebar category list). The Missouri River flows east from Fort Peck Lake across northeast Montana to North Dakota. The northeast oriented Yellowstone River joins the Missouri River near the Montana-North Dakota border. West of the northeast oriented Yellowstone River is the northeast- and north-oriented Redwater River, which joins the east-oriented Missouri River near Poplar, Montana. Big Muddy Creek originates in Canada in the Big Muddy Lake area and flows northwest before turning southeast to flow through Big Beaver to the United States. From the border Big Muddy Creek flows southeast to Redstone, Plentywood, and Antelope, Montana and then turns to flow south-southwest to Reserve, Medicine Lake, and Homestead, and finally to the east-oriented Missouri River (near Culbertson, Montana). The Poplar River is located west of Big Muddy Creek and also begins in Canada. The East Fork Poplar River flows southeast to Scobey, Montana and the turns to flow southwest shortly before joining the east-oriented Missouri River at Poplar, Montana. This essay addresses evidence in the region located between the East Fork Poplar River-Poplar River and Big Muddy Creek located south of the Canadian border and north of the Missouri River. Evidence presented in other essays (for example see northeast end Redwater River-Yellowstone River drainage divide area essay, the Prairie Elk Creek-Redwater River drainage divide area essay and Missouri River-Yellowstone River drainage divide area essay-found under MT Missouri River on sidebar category list) provide evidence present day valleys were eroded headward in sequence to capture an immense southeast-oriented flood. [Other essays can be located under appropriate river names on the sidebar category list.] The Poplar River-Big Muddy Creek is interpreted in a similar manner.

• Detailed maps illustrated below provide evidence of a large northeast-oriented through valley extending from the present day Missouri River valley near Poplar, Montana through the Medicine Lake area. Big Muddy Creek flows across that large northeast-oriented through valley and then flows to the much narrower east-oriented Missouri River valley near Culbertson, Montana. The northeast-oriented through valley extends into the North Dakota northwest corner, where on topographic maps the through valley appears to be blocked by glacial moraines. Without that blockage the through valley leads to a lower elevation region at the base of the northwest-southeast oriented Missouri Escarpment. That lower elevation in North Dakota essays (published on this website) is referred to as the Midcontinent Trench and the Missouri Escarpment will be referred to as the Midcontinent Trench southwest wall. What is important to this essay is the northeast-oriented through valley leads to a much larger southeast-oriented lowland located in northwest North Dakota. Also of importance is the through valley in northwest North Dakota appears to have been blocked by glacial moraines, although the “glaciation” responsible for the blockage does not appear to have significantly eroded or otherwise altered the regional landscape.

Poplar River-Big Muddy Creek drainage divide area detailed location map

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

Figure 2 provides a more detailed map of the Poplar River-Big Muddy Creek drainage divide area. Daniels, Sheridan, and Roosevelt Counties are located in Montana. The north-south Montana-North Dakota state line is located near the figure 2 east edge. The Fort Peck Indian Reservation land area is identified by the red shading. The west to east oriented Canada-United States boundary follows the figure 2 north edge. The Missouri River is located along the figure 2 south edge and serves as the Fort Peck Indian Reservation southern border. Big Muddy Creek flows southeast from the northeast corner of Sheridan County to Redstone and Plentywood and then turns to flow south-southwest and southeast along the Fort Peck Indian Reservation eastern boundary. The East Fork Poplar River flows south from the Canadian border to Scobey and into the Fort Peck Indian Reservation before turning southeast and finally turning to flow south-southwest to join the east-oriented Missouri River at Poplar, Montana. Figure 2 does not show topography, but if it did there would be a large northeast-oriented through valley extending from the Missouri River valley near Poplar through the Medicine Lake area in southern Sheridan County. Evidence of that through valley is illustrated in topographic maps shown in figures 7, 8, 9, and 10 below. The through valley extends into northwest North Dakota as described in the figure 1 discussion. The through valley is much larger than the present day Missouri River valley located east of Poplar (and illustrated in a topographic map in figure 10 below). West of Poplar the present day Missouri River valley is much larger than it is east of Poplar, suggesting the northeast-oriented through valley and the Missouri River valley west of Poplar were originally formed as one valley, with the Missouri River valley east of Poplar being formed by a somewhat different mechanism. The Missouri River-Yellowstone River drainage divide area essay illustrates the Missouri River valley east and southeast of Poplar and discusses its origin. This essay attempts to explain the origin of the northeast-oriented through valley along with the origin of the Poplar River valley, Big Muddy Creek valley, and their tributary valleys. Detailed maps below begin near the Canadian border and proceed south looking first at evidence north of the large abandoned northeast-oriented through valley. Next the detailed maps illustrate the northeast-oriented through valley and the essay concludes with a brief look at the present-day Missouri River valley.

Whitetail Creek-Big Muddy Creek drainage divide area

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

Figure 3 illustrates the Whitetail Creek-Big Muddy Creek drainage divide area located just south of the United State-Canada border. Big Muddy Creek flows south-southeast near the figure 3 east edge. Whitetail Creek flows east and east-southeast through Whitetail before turning northeast and finally southeast to join Big Muddy Creek. Note the multiple southeast-oriented Whitetail Creek tributaries from the north. South of Whitetail is the northeast-oriented South Fork of Whitetail Creek. Northeast-oriented Eagle Creek joins southeast-oriented Big Muddy Creek at Redstone in the figure 3 southeast corner, along with several east- and southeast-oriented Eagle Creek and Big Muddy Creek tributaries. The Big Muddy Creek valley appears to have been eroded by large volumes of water from north of the figure 3 map area (meaning Canada), although the Eagle Creek valley appears to have eroded southwest from the Big Muddy Creek valley to capture multiple southeast-oriented flood flow routes, such as might be found in a southeast-oriented anastomosing channel complex. After headward erosion of the Eagle Creek valley the Whitetail Creek valley appears to have eroded northwest along a southeast-oriented flood flow route and then to have eroded southwest and west to capture southeast-oriented flood flow routes moving flood waters to what was then the newly eroded northeast-oriented Eagle Creek valley. Southeast-oriented Whitetail Creek tributary valleys were eroded headward into the newly eroded Whitetail Creek valley wall along the captured southeast-oriented flood flow channels. A northwest-oriented Whitetail Creek tributary valley (located midway between Whitetail and Daleview) was eroded headward by reversed flood flow when headward erosion of the northeast-oriented Whitetail Creek valley beheaded a southeast-oriented flood flow channel. Flood waters on the northwest end of the beheaded flood flow channel reversed flow direction to flow northwest to the newly eroded Whitetail Creek valley.

East Fork Poplar River-Whitetail Creek drainage divide area

Figure 4: East Fork Poplar River-Whitetail Creek drainage divide area. United States Geological Survey map digitally presented using National Geographic Society TOPO software.

Figure 4 illustrates the East Fork Poplar River-Whitetail Creek drainage divide area west of the figure 3 map area and includes overlap areas with figure 3. Whitetail Creek is located in the figure 4 northeast quadrant and flows east-southeast through Whitetail. Northeast-oriented South Fork Whitetail Creek is located between Whitetail and Flaxville in the figure 4 east center area. The south-southeast oriented stream originating immediately west of Flaxville (in the figure 4 southeast quadrant) is the headwaters of Eagle Creek, which is better illustrated in figure 5 below. Eagle Creek flows south, southeast, north, and northeast to join southeast-oriented Big Muddy Creek at Redstone (as seen in figure 3 above). The East Fork Poplar River flows southeast in the figure 4 northwest corner and then turns southwest to join the south-southwest oriented West Fork just west of the figure 4 map area. Note northwest-oriented East Fork Poplar River tributaries, such as northwest-oriented Shannon Coulee. North of Shannon Coulee an unnamed northwest-oriented tributary flows to an unnamed southwest-oriented East Poplar River tributary. Figure 4a below provides a detailed map of the area immediately north and northeast of the East Fork Poplar River elbow of capture (where the East Fork turns from southeast-oriented to southwest-oriented). In figure 4a note the multiple northeast-southwest oriented through valleys and how the present day northwest-oriented East Fork tributaries ignore those through valleys. The northeast-southwest oriented through valleys provide evidence of a south- and southwest-oriented anastomosing channel complex that probably was eroded as the south-oriented Poplar River valley was eroded north to capture south- and southeast-oriented flood flow. The northwest-oriented tributary valleys were eroded by reversals of flood flow on the northwest ends of beheaded southeast-oriented flood flow routes. Flood flow through the anastomosing valley complex ended when headward erosion of the East Fork Poplar River valley west and north of the figure 4 map area beheaded flood flow routes to the anastomosing channel complex. Flood waters on the northwest end of the beheaded flood flow routes reversed flow direction to flow northwest to the newly eroded East Fork Poplar River valley. The northwest-oriented East Fork Poplar River tributary valley seen in the figure 4a northeast quadrant and the figure 4 north center was eroded at that time.

Figure 4a: Anastomosing channel complex northeast of East Poplar River elbow of capture. United States Geological Survey map digitally presented using National Geographic Society TOPO software.

Eagle Creek-Wolf Creek drainage divide area

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

Figure 5 illustrates the Eagle Creek-Wolf Creek drainage divide area south of the figure 3 map area and southeast of the figure 4 map area and includes overlap areas with figure 4. Eagle Creek flows south in the figure 5 northwest corner and then turns southeast before turning to flow north through the figure 5 center area to join southeast-oriented Big Muddy Creek just north of the figure 5 map area. Redstone Creek flows north to join southeast-oriented Big Muddy Creek in the figure 5 northeast corner. Southeast-oriented Big Muddy Creek can be seen in the figure 5 northeast corner. Wolf Creek flows southeast from the Eagle Creek elbow of capture area (where Eagle Creek turns from flowing southeast to flowing north and northeast) to the figure 5 south edge. Note how Wolf Creek is linked to the southeast-oriented Eagle Creek headwaters valley. This linkage suggests headward erosion of the north-oriented Eagle Creek valley beheaded a southeast-oriented flood flow route on the southeast-oriented Eagle Creek-Wolf Creek valley alignment. Why was the north-oriented Eagle Creek valley eroding south when the figure 5 map area was being eroded by an immense southeast-oriented flood? Headward erosion of the deep Big Muddy Creek valley was capturing southeast-oriented flood flow from flood flow channels further to the south and southwest. These captures caused flood waters to move north to the newly eroded and deep Big Muddy Creek valley. The north-oriented Redstone Creek valley apparently eroded south first to capture southeast-oriented flood water and to divert the flood flow north into the newly eroded and deep Big Muddy Creek valley. Next the Eagle Creek valley eroded southwest and south to capture southeast-oriented flood flow routes and successfully beheaded the flood flow moving to the southeast-oriented Wolf Creek valley. Headward erosion of the Poplar River valley to the west then beheaded all southeast-oriented flood flow routes across the figure 5 map area.

Line Coulee-Smoke Creek drainage divide area

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

Figure 6 illustrates the Line Coulee-Smoke Creek drainage divide area southwest of the figure 6 map area and includes overlap areas with figure 5 (northwest corner of figure 6 overlaps with southwest corner of figure 6). South-southeast oriented Poplar River is located along the figure 6 west edge (south half). Line Coulee flows southwest to join the Poplar River near the figure 6 west center area. Smoke Creek originates in the figure 6 north center area and flows southeast to the figure 6 southeast corner. Headwaters of southeast-oriented Wolf Creek can just barely be seen in the figure 6 northeast corner. Note how a northwest-oriented Line Coulee tributary is linked by a through valley with a southeast-oriented lowland drained by an unnamed southeast-oriented stream in the figure 6 southeast quadrant. That unnamed stream flows to Smoke Creek southeast of the figure 6 map area. The through valley provides evidence that southeast-oriented flood flow once moved from the present day Line Coulee drainage basin to the present day Smoke Creek drainage basin. Headward erosion of the Poplar River valley and the southwest-oriented Line Coulee valley then beheaded the southeast-oriented flood flow route. Flood waters on the northwest end of the beheaded flood flow reversed flow direction to flow northwest to the newly eroded southwest-oriented Line Coulee valley. The reversed flow eroded the northwest-oriented Line Coulee valley and also created the Line Coulee-Smoke Creek drainage divide. The Poplar River valley is today approximately 120-140 meters lower than the upland surface on which the southeast-oriented flood flow moved. Flood waters crossed the figure 6 map area before the Poplar River valley was eroded. How much erosion was accomplished prior to Poplar River valley headward erosion cannot be determined from figure 6 map evidence. However, figure 6 map evidence demonstrates at least 120–140 meters of erosion in the Poplar River valley as headward erosion of that valley captured flood waters moving across the figure 6 map area and diverted the flood waters south to a large northeast-oriented valley.

Smoke Creek-Wolf Creek drainage divide area

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

Figure 7 maps have been reduced to show a larger region and illustrate the Smoke Creek-Wolf Creek drainage divide area along the northwest wall of the large northeast-oriented through valley previously mentioned in the figures 1 and 2 discussions. Smoke Creek flows southeast from the figure 7 northwest corner to the figure 7 south edge and joins Big Muddy Creek south of the figure 7 map area. Big Muddy Creek flows south along the figure 7 east edge (south half) to the figure 7 southeast corner. Wolf Creek flows southeast through the figure 7 north center area to join Big Muddy Creek near the figure 7 east edge. Burshia Coulee flows southeast before entering a north and northeast-oriented through valley linking the southeast-oriented Smoke Creek valley with the southeast-oriented Wolf Creek valley. Upon entering the through valley Burshia Coulee today drains southwest and south to Smoke Creek, although the northeast end of the through valley drains northeast to Wolf Creek. Even by reducing the maps it is difficult to show the magnitude of the northeast-oriented through valley. Figures 8, 9, and 10 below further illustrate the large northeast-oriented through valley. The northwest wall represents a rise of approximately 200 meters from the Big Muddy Creek valley located in the figure 7 southeast corner to the upland surface in the figure 7 center region. This large northeast-oriented valley eroded southwest to capture multiple southeast-oriented flood flow routes such as might be found in a large southeast-oriented anastomosing channel complex. Immense volumes of flood water moved northeast in this valley. The Big Muddy Creek, Wolf Creek, Smoke Creek, and Poplar River valleys eroded north and northwest from this large northeast-oriented through valley along southeast-oriented flood flow routes and/or to capture southeast-oriented flood flow routes. Yet today the Big Muddy Creek flows across the large northeast-oriented through valley almost as though the northeast-oriented through valley did not exist. The much smaller Burshia Coulee through valley also provides evidence of reverse flow parallel to the much larger northeast-oriented through valley. Headward erosion of the Poplar River valley beheaded southeast-oriented flood flow to the southeast-oriented Smoke Creek valley before it beheaded southeast-oriented flood flow to the southeast-oriented Burshia Coulee and Wolf Creek valleys. Apparently southeast-oriented flood flow in the southeast-oriented Burshia Creek and Wolf Creek valleys was able to spill over drainage divides and flow southwest to the Smoke Creek valley before headward erosion of the Poplar River ended that flood flow.

Poplar River-Big Muddy Creek drainage divide area

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

Figure 8 better illustrates the large northeast-oriented through valley and is located south and west of figure 7. Figure 8 maps have also been reduced in size to show a larger region. The present day Missouri River can just barely be seen along the figure 8 south center edge. The Poplar River flows southeast in the figure 8 northwest quadrant (near the figure 8 west edge) and upon entering the large northeast-oriented through valley it turns to flow south-southwest along the through valley’s northwest wall. Big Muddy Creek flows south and southwest from the figure 8 northeast corner across the northeast-oriented through valley and then flows in a southeast-oriented valley cut into the upland region separating the northeast-oriented through valley from the present day Missouri River valley. Southeast-oriented Smoke Creek flows from the figure 8 north edge (just east of the center area) to join Big Muddy Creek in the figure 8 east center area. The drainage history recorded by this figure 8 evidence begins with southeast-oriented flood flow moving across the entire figure 8 map area on a topographic surface at least as high as the highest present day elevations in the Poplar River-Big Muddy Creek drainage divide area illustrated in this essay. The large northeast-oriented valley then eroded headward from the Missouri Escarpment in northwest North Dakota. While not illustrated in figure 8 the large northeast-oriented valley eroded headward across a region presently covered with glacial debris (the Missouri Coteau) into this northeast Montana region where topographic map evidence of glacial deposits is difficult to identify (if it is present at all). Southeast-oriented Wolf Creek, Smoke Creek, and Poplar River valleys eroded northwest from the large northeast-oriented valley along southeast-oriented flood flow routes. The present day southeast-oriented Big Muddy Creek valley between the northeast-oriented through valley and the present day Missouri River was eroded by reversed flow on a southeast-oriented flood flow channel beheaded by headward erosion of the northeast-oriented valley. In other words, that valley was initiated as a northwest-oriented valley. For reasons that may be apparent in figure 9 below the large northeast-oriented valley became blocked and flood waters spilled east and southeast from the northeast-oriented valley to what was then a newly eroded northeast-oriented Yellowstone River valley. The spillage eroded the present day Missouri River valley, which caused flood flow reversals that captured the Poplar River and Big Muddy Creek (and which also explains the reversed flow in the much smaller Burshia Coulee through valley seen in figure 7 above).

Medicine Lake area valleys

Figure 9: Medicine Lake area valleys. United States Geological Survey map digitally presented using National Geographic Society TOPO software.

Figure 9 illustrates the large northeast oriented through valley northeast of the figure 8 map area (the figure 9 southwest corner roughly corresponds with the figure 8 northeast corner). Southwest, southeast, south-southwest, and south oriented Big Muddy Creek is located near the figure 9 west edge. The large northeast oriented through valley extends in a northeast oriented direction across the figure 9 map area. Medicine Lake and many of the other lakes are located on the through valley floor. As previously mentioned this large northeast oriented valley eroded headward from the Missouri Escarpment in northwest North Dakota across the Missouri Coteau area. The Missouri Coteau is covered with thick glacial moraines, which suggests the large northeast oriented valley eroded headward across a stagnant ice sheet remnant. Essays for northwest North Dakota drainage divides (see Big Muddy Creek-Little Muddy River drainage divide and Little Muddy River-White Earth River drainage divide essays for example-under ND Missouri River on sidebar category list) describe how the Missouri Escarpment was eroded by an immense southeast-oriented river (which is named the Midcontinent River) moving across North Dakota and then south into South Dakota to the present day Missouri River valley in southeast South Dakota. This figure 9 northeast oriented valley was one of several northeast and east oriented valleys that eroded headward from the Midcontinent River across stagnant remnants of a decaying ice sheet to capture immense southeast-oriented floods moving along the ice sheet’s southwest margin. Many of these northeast- and east-oriented valleys are today blocked or partially blocked by glacial deposits, suggesting a minor glacial event reinvigorated stagnant ice sheet remnants and caused the Midcontinent River route to become covered with glacial ice. Getting back to evidence seen in figure 9 the numerous small lakes in the figure 9 northeast corner are located along the southwest margin of the blockage area. What is important in this essay is the valley was eroded across the Missouri Coteau area, which probably at that time was covered by a decaying ice sheet remnant. Flood waters moved from southwest of the decaying ice sheet margin onto the former ice sheet floor (in northwest North Dakota) and then flowed southeast and south to what was then the actively eroding Missouri River valley in southeast South Dakota. This flood movement ended when for some reason flood waters on the former ice sheet floor froze to create what might be called one or more thin ice sheets forcing flood waters still moving northeast to the ice sheet margin to spill east and southeast to create the present day Missouri River valley (between Poplar and the present day northeast-oriented Yellowstone River valley).

Lake Creek-Missouri River drainage divide area

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

Figure 10 illustrates the Lake Creek-Missouri River valley located south and east of the figure 8 map area and includes significant overlap areas with figure 8. The east-oriented Missouri River valley is located near the figure 10 south edge. The large northeast-oriented through valley is located in the figure 10 northwest section. Big Muddy Creek flows southeast in the figure 10 east half to join the east-oriented Missouri River. In the figure 10 southeast corner northwest-oriented Hardscrabble Creek can just barely be seen where it enters the Missouri River valley. The northwest-oriented Hardscrabble Creek valley and the southeast-oriented Big Muddy Creek valley have been eroded along the same northwest-southeast alignment. As previously mentioned headward erosion of a northwest-oriented valley occurred on this northwest-southeast alignment when headward erosion of the northeast-oriented valley beheaded a southeast-oriented flood flow channel. Flood waters on the northwest end of the beheaded flood flow channel reversed flow direction to flow northwest to the newly eroded and much deeper northeast-oriented valley (the east-oriented Missouri River valley did not exist at that time). The reversed flood flow eroded a northwest-oriented valley now used by northwest-oriented Hardscrabble Creek and by southeast-oriented Big Muddy Creek. The east-oriented Missouri River valley was eroded when flood waters moving northeast in the large northeast-oriented valley became blocked (perhaps by freezing of flood waters further to the north) and flood waters were forced to spill east and southeast to what was then the newly eroded Yellowstone River valley (see Missouri River-Yellowstone River and Redwater River-Yellowstone River drainage divide area essays for more details). Headward erosion of the present day Missouri River valley then caused a reversal of flood flow on the present day southeast-oriented Big Muddy Creek valley segment. The Lake Creek route was established by flood waters draining from the blocked northeast-oriented valley to the newly eroded Missouri River valley. Note how the present day Missouri River is much narrower than the northeast-oriented through valley. The present day Missouri River valley drained flood waters already southwest of the ice sheet, but once those flood waters were drained the immense southeast-oriented floods ceased and the Missouri River drainage basin has changed little since.

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.