A geomorphic history based on topographic evidence

The North Fork-South Fork Moreau River drainage divide area discussed here is located in northwest South Dakota, USA. Although detailed topographic maps of the North Fork-South Fork Moreau River 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 North Fork-South Fork Moreau River 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 ended when headward erosion of the north and northeast-oriented Little Missouri River valley captured all southeast-oriented flood flow.

Preface:

The following interpretation of detailed topographic map evidence is provided as evidence in the Missouri River drainage basin landform origins research project, which is compiling similar evidence for all major drainage divides contained within the Missouri River drainage basin and for all major drainage divides with and within certain adjacent drainage basins. The research project is interpreting evidence in the context of a previously unexplored geomorphology paradigm, which is briefly described in the introduction below. Project essays are listed on the sidebar category list under their appropriate Missouri River tributary drainage basin, Missouri River segment drainage basin (by state), and/or state in which the Missouri River drainage basin is located.

Introduction:

• The purpose of this essay is to use topographic map interpretation methods to explore South Dakota North Fork-South Fork Moreau River drainage divide area landform origins. 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 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 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 similar essays is a thick North American ice sheet, comparable in thickness to the present day Antarctic ice sheet, occupied approximately the North American region usually recognized to have been glaciated and through its weight and erosive actions created a “deep” North American “hole”, 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 North Fork-South Fork Moreau River drainage divide area landform evidence will be regarded as evidence supporting the “thick ice sheet that melted fast” paradigm.

North Fork-South Fork Moreau River general location map

Figure 1: North Fork-South Fork Moreau River general 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 North Fork Moreau River-South Fork Moreau River drainage divide general location map. The North and South Forks of the Moreau River begin in northwest South Dakota just east of the Montana border and both flow southeast before the South Fork turns northeast to join the North Fork and the Moreau River then flows east-northeast to join the south-oriented Missouri River east of the figure 1 map area. West of the North Fork and South Fork Moreau River source areas is the northeast-oriented Little Missouri River. North of the North Fork Moreau River drainage basin is the east-oriented South Fork Grand River drainage basin. South of the South Fork Moreau River drainage basin are headwaters of southeast oriented tributaries to the southeast and east-oriented Belle Fourche River and to the northeast-oriented Cheyenne River. The Little Missouri River-Moreau River drainage divide area essay, South Fork Grand River-Moreau River drainage divide area essay, and Moreau River-Cherry Creek (and Sulphur Creek) drainage divide area essay address nearby drainage divide areas and can be found under appropriate river names on the sidebar category list. Evidence presented here is interpreted in the context of an immense southeast-oriented flood that flowed over the entire figure 1 map area. Headward erosion of major east-oriented trunk stream valleys systematically captured the southeast-oriented flood waters and diverted the flood flow northeast and east. First the northeast-oriented Cheyenne River valley captured the southeast-oriented flood waters. Moreau River valley headward erosion shortly thereafter captured the southeast-oriented flood waters, which was probably closely followed by headward erosion of the Grand River valley and its capture of the southeast-oriented flood waters. At the same time as Moreau River and South Fork Grand River valley headward erosion reached their present day source areas headward erosion of the northeast-oriented Little Missouri River valley captured the southeast-oriented flood water and diverted the flood flow even further to the north and east. Essays published on this website for eastern and central Montana can be used to follow flood waters west and northwest toward the flood source in southern Alberta, although evidence presented here inadequate to determine the flood water source The southern Alberta flood source suggests flood waters were derived from a rapidly melting North American ice sheet and melt water from a rapidly melting thick North American ice sheet would be a logical flood source. Essays used in tracing flood waters headward include the Boxelder Creek-Little Missouri River drainage divide, Powder River-Boxelder Creek drainage divide, Mizpah Creek-Powder River drainage divide, and Pumpkin Creek-Mizpah Creek (Powder River tributaries) essays and can be found under appropriate river names on the sidebar category list.

North Fork-South Fork Moreau River detailed location map

Figure 2: North Fork-South Fork Moreau River detailed location map. United States Geological Survey map digitally presented using National Geographic Society TOPO software. 

Figure 2 provides a more detailed North Fork Moreau-South Fork Moreau River location map. The southeast-oriented North Fork Moreau River begins north of the Custer National Forest area just south of Lone Mountain and is linked to northwest-oriented Valley Creek, which flows to the northeast-oriented Little Missouri River. . Northeast-oriented drainage north of the North Fork Moreau headwaters flows to the South Fork Grand River. Southeast-oriented headwaters of the South Fork Moreau River extend further west to the Gustave area (figure 2 west center) and are linked to northwest-oriented Little Missouri River tributaries. Southeast-oriented drainage in the figure 2 southwest corner and along the figure 2 south edge flows to the southeast-and east-oriented Belle Fourche River. Note how nearly all North Fork and South Fork tributaries are southeast-oriented except those from the south and while tributaries from the south they may be northeast-oriented and they often include northwest-oriented segments. The predominance of southeast-oriented tributaries and the northwest-oriented tributaries from the south are evidence that both the North Fork and the South Fork valleys eroded west and northwest to capture multiple southeast-oriented flood flow routes, such as might be found in a large southeast-oriented anastomosing channel complex. The northwest-oriented tributaries (or tributary valley segments) developed as reversals of flood flow on the northwest ends of beheaded southeast-oriented flood flow routes. Detailed maps below provide additional evidence supporting this interpretation. The detailed maps begin at the west end of the North Fork-South Fork Moreau drainage divide, where the drainage divide is truncated by the north-oriented Little Missouri River drainage basin just south and west of the North Fork Moreau River source area. Detailed maps then follow the North Fork-South Fork drainage divide to the southeast until reaching where the North and South Forks join to form the Moreau River.

North Fork-South Fork Moreau River drainage divide in East Short Pine Hills area

Figure 3: North Fork-South Fork Moreau River drainage divide in East Short Pine Hills area. United States Geological Survey map digitally presented using National Geographic Society TOPO software. 

Figure 3 illustrates the North Fork Moreau River-South Fork Moreau River drainage divide in the East Short Pine Hills area where the North Fork-South Fork drainage divide is truncated by the north-oriented Little Missouri River drainage basin. The North Fork Moreau River begins in the figure 3 north center just north of the East Short Pine Hills and flows southeast to the figure 3 east center edge. Southeast-oriented drainage throughout the figure 3 south half flows to the South Fork Moreau River. North-oriented drainage in the figure 3 northeast corner flows to South Fork Grand River. Northwest-oriented drainage in the figure 3 northwest corner flows to the northeast-oriented Little Missouri River. Events recorded by this figure 3 evidence begin with southeast-oriented flood flow moving across a topographic surface at least as high as the present day East Short Pine Hills top. Evidence supporting this interpretation includes the northwest-southeast oriented valley cut into the East Short Pine Hills top now draining to Sand Coulee and the Little Missouri River. A large and deep South Fork Moreau River valley then eroded headward or west and northwest into the region and encountered a resistant rock mass where the East Short Pine Hills are located. The deep and somewhat smaller North Fork Moreau River valley headcut eroded northwest shortly thereafter and captured southeast-oriented flood flow east of the East Short Pines Hills resistant rock mass that had been moving to the newly eroded South Fork Moreau River valley and in doing so created the North Fork-South Fork Moreau River drainage divide. About the same time a large and deeper South Fork Grand River valley headcut eroded west to the north of the East Short Pine Hills and captured most flood flow moving to the newly eroded North Fork Moreau River valley. As these events were occurring the northeast-oriented Little Missouri River valley eroded headward into the region and captured all southeast-oriented flood flow to the South Fork Grand River, North Fork Moreau River, and South Fork Moreau River in that order. Flood waters on the northwest ends of beheaded southeast-oriented flood flow routes reversed flow direction to flow northwest to the newly eroded northeast-oriented Little Missouri River valley. Northwest-oriented drainage routes in the figure 3 northwest corner were created by such drainage reversals as was the Little Missouri River-Moreau River drainage divide.

North Fork-South Fork Moreau River drainage divide in Davis Buttes area

Figure 4: North Fork-South Fork Moreau River drainage divide in Davis Buttes area. United States Geological Survey map digitally presented using National Geographic Society TOPO software. 

Figure 4 illustrates the North Fork Moreau River-South Fork Moreau River drainage divide area southeast of the figure 3 map area and includes an overlap area. The southeast oriented North Fork Moreau River flows from the figure 4 northwest corner to the figure 4 east center. South-oriented drainage in the figure 4 southwest quadrant and along the figure 4 south edge further east flows to the South Fork Moreau River. Most North Fork Moreau tributaries from the north are southeast oriented with the exception of a tributary located in the figure 4 northeast corner. Reasons for that exception are discussed in the South Fork Grand River-Moreau River drainage divide essay. North Fork Moreau River tributaries from the south frequently are northeast-oriented although they also include southeast and/or northwest-oriented headwaters or tributaries. For example, Soft Water Draw in the figure 4 northwest quadrant flows southeast before turning northeast and northeast-oriented Cowboy Creek has both southeast-oriented and northwest-oriented tributaries. Events recorded by this figure 4 evidence begin with southeast-oriented flood water flowing across the entire figure 4 map area on a topographic surface at least as high as the highest figure 4 elevations today. Headward erosion of the large and deep South Fork Moreau River valley headcut next captured the southeast-oriented flood water and diverted the flood flow east to the newly eroded east-northeast-oriented Moreau River valley. Southeast-oriented flood flow then began to erode southeast-oriented valleys headward into the newly eroded and large east-oriented South Fork Moreau River valley wall. Headward erosion of the North Fork Moreau River valley headcut then beheaded the southeast-oriented flood flow routes and diverted the flood water more directly to the newly eroded Moreau River valley and in doing so caused flood flow reversals on the northwest ends of the beheaded southeast-oriented flood flow routes. Those flow reversals were responsible for creating the north and northwest-oriented North Fork Moreau River tributary valleys. Northeast-oriented North Fork Moreau River tributaries probably eroded southwest to capture yet to be beheaded (by headward erosion of the North Fork Moreau River valley) southeast-oriented flood flow routes further to the southwest (e.g. Cowboy Creek).

North Fork-South Fork Moreau River drainage divide in South Cottonwood Creek area

Figure 5: North Fork-South Fork Moreau River drainage divide in South Cottonwood Creek area. United States Geological Survey map digitally presented using National Geographic Society TOPO software. 

Figure 5 illustrates the North Fork Moreau River-South Fork Moreau River drainage divide area southeast of the figure 4 map area and includes overlap areas. The North Fork Moreau River flows from the figure 5 north center to the figure 5 west center. The previously discussed Cowboy Creek drainage basin is located in the figure 5 north center. In the figure 5 center are the southeast-and northeast-oriented Cottonwood Creek and South Cottonwood Creek drainage basins. Cottonwood Creek and South Cottonwood Creek eroded southwest from what was then the actively eroding southeast-oriented North Fork Moreau River valley to capture yet to be beheaded (by North Fork Moreau River valley headward erosion) southeast-oriented flood flow routes. Northwest-oriented Cottonwood and South Cottonwood Creek tributary valleys, such as the northwest oriented Porter Creek valley were eroded by flood waters on northwest ends of beheaded southeast-oriented flood flow routes. South and southeast-oriented drainage in the figure 5 southwest corner and along the figure 5 south edge further to the east flows to the South Fork Moreau River. Events recorded by this figure 5 evidence are similar to events recorded by the figure 3 and 4 evidence and the North Fork Moreau River-South Fork Moreau River drainage divide was created when headward erosion of what was then a deep southeast-oriented North Fork Moreau River valley and its tributary valleys beheaded and captured southeast-oriented flood flow routes to what was then the newly eroded South Fork Moreau River valley and flood waters on the northwest ends of beheaded flood flow routes reversed flow direction to create north and northwest-oriented North Fork Moreau tributaries and the North Fork-South Fork drainage divide.

North Fork-South Fork Moreau River drainage divide in Hay Creek area

Figure 6: North Fork-South Fork Moreau River drainage divide in Hay Creek area. United States Geological Survey map digitally presented using National Geographic Society TOPO software. 

Figure 6 illustrates the North Fork Moreau River-South Fork Moreau River drainage divide area southeast of the figure 5 map area and includes overlap areas. The North Fork Moreau River flows across the figure 6 northeast corner. The South Fork Moreau River flows across the figure 6 southwest corner to the figure 6 south center. The previously discussed South Cottonwood Creek drainage basin is located in the figure 6 northwest corner. Southeast-oriented Hay Creek flows to the figure 6 southeast corner and then to the South Fork Moreau River. Southwest of Hay Creek are southeast oriented House Creek and Flat Creek also flowing to the South Fork Moreau River. Spring Creek along the figure 6 west edge is not southeast oriented, but appears to have eroded north to capture southeast oriented flood water moving to the southeast-oriented Flat Creek valley. The previously discussed northeast-oriented Cottonwood Creek and South Cottonwood Creek valleys eroded southwest to capture southeast-oriented flood flow routes moving flood water to what were then the actively eroding southeast-oriented Hay Creek and House Creek valleys. Note how northeast-oriented Sweetwater Draw eroded southwest to capture one or more southeast-oriented flood flow routes and subsequently as the North Fork Moreau River valley eroded headward Fish Draw eroded southwest to capture the same  southeast-oriented flood flow routes and then eroded west-northwest along one of those flood routes, while North Fork Draw eroded west and southwest to capture southeast-oriented flood flow to what was then the newly eroded Fish Draw valley. Events recorded by the figure 6 evidence are similar to the previous figure events. The large South Fork Moreau River valley eroded west into a high level topographic surface that has now been almost completely removed and captured multiple southeast-oriented flood flow routes. The southeast-oriented flood flow routes then eroded southeast- and south-oriented valleys into the newly eroded South Fork Moreau River valley wall. Southeast-oriented flood flow routes were then captured by headward erosion of the North Fork Moreau River valley and its tributary valleys. Floodwaters on the northwest ends of beheaded southeast-oriented flood flow routes reversed flow direction to create northwest-oriented tributaries and to also create the North Fork-South Fork Moreau River valley.

East end of the North Fork-South Fork Moreau River drainage divide

Figure 7: East end of the North Fork-South Fork Moreau River drainage divide. United States Geological Survey map digitally presented using National Geographic Society TOPO software. 

Figure 7 illustrates the North Fork Moreau River-South Fork Moreau River drainage divide east end where the North Fork and South Fork meet to form the east-northeast-oriented Moreau River (figure 7 is located southeast of the figure 6 map area and includes significant overlap areas). The North Fork Moreau River flows southeast from the figure 7 northwest corner to the east-northeast-oriented Moreau River while the South Fork Moreau River flows northeast from the figure 7 southwest quadrant to the Moreau River. Note how tributaries to the east-northeast-oriented Moreau River are southeast-oriented from north and northwest-oriented from the south. This tributary arrangement is evidence the Moreau River was eroding headward (west) across multiple southeast-oriented flood flow routes such as might be found in a large southeast-oriented anastomosing channel complex. The southeast-oriented North Fork Moreau River valley eroded northwest along one of the captured southeast-oriented flood flow routes while the northeast-oriented South Fork Moreau River valley eroded southwest to capture additional southeast-oriented flood flow routes. Headward erosion of both the North Fork and the South Fork valleys proceeded simultaneously because flood flow routes to the actively eroding South Fork Moreau River valley head had not yet been beheaded by headward erosion of the North Fork Moreau River valley. For example, the South Fork valley captured southeast-oriented flood flow on the Hay Creek alignment before headward erosion of the North Fork valley and its tributary Cottonwood Creek-South Cottonwood Creek valley beheaded that flood flow route. By the time southeast-oriented flood flow on the Hay Creek alignment was beheaded the South Fork valley head had eroded further southwest and west and was being actively eroded by southeast-oriented flood flow routes further to the west. Headward erosion of the North Fork and South Fork valleys would have continued further west had headward erosion of the north-oriented Little Missouri River not captured all of the southeast-oriented flood flow.

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.