A geomorphic history based on topographic map evidence

The Little Missouri-Moreau River drainage divide area is located in northwest South Dakota, USA. Although detailed topographic maps of the Little Missouri-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. Based on the topographic map evidence the Little Missouri-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-oriented Little Missouri River valley captured the 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 Little Missouri River-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 Little Missouri River-Moreau River drainage divide area landform evidence will be regarded as evidence supporting the “thick ice sheet that melted fast” paradigm.

Little Missouri River-Moreau River drainage divide area location map

Figure 1: Little Missouri River-Moreau 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.

The North and South Forks of the Moreau River begins in northwest South Dakota and flow southeast before joining to become the east and northeast-oriented Moreau River, which flows to the south-oriented Missouri River. West of the Moreau River headwaters is the north-oriented Little Missouri River drainage basin. North of the Moreau River drainage basin is the east-oriented Grand River drainage basin and south of the Moreau River drainage basin is Belle Fourche-Cheyenne River drainage basin. The Little Missouri River-Moreau River drainage divide is an asymmetric drainage divide suggesting the north-oriented Little Missouri River valley was eroded headward to capture southeast-oriented flood flow moving into what is today the Moreau River drainage basin. Topographic map evidence presented in this essay suggests Little Missouri River valley headward erosion beheaded and captured southeast-oriented flood flow that had been eroding large headcuts northwest toward what is today the Little Missouri River-Moreau River drainage divide.

Little Missouri River-Moreau River drainage divide location map

Figure 2: Little Missouri River-Moreau River drainage divide location map. United States Geological Survey map digitally presented using National Geographic Society TOPO software. 

Figure 2 provides a more detailed view of the Little Missouri River-Moreau drainage divide area in southeast Harding County, South Dakota. The North Fork Moreau River begins at the Little Missouri River-Moreau River drainage divide just north of the East Short Pine Hills (unnamed in figure 2, but shown as the green Custer National Forest area immediately south of Lone Mtn). North of the North Fork Moreau River headwaters are northeast-oriented tributaries to the east and northeast-oriented South Fork Grand River. Headwaters of southeast-oriented South Fork Moreau tributaries begin at the Little Missouri River-Moreau River drainage divide in West Short Pine Hills area (another green Custer National Forest area, which is labeled West Short Pine Hills in figure 2). Continuing south along the Little Missouri River-Moreau River drainage divide are the southeast-oriented South Fork Moreau River headwaters and headwaters of southeast-oriented Alkali Creek, Fourmile Mile Creek, and Battle Creek, all of which flow to the east and northeast-oriented South Fork Moreau River. In other words, the southeast-oriented North Fork Moreau River and the major southeast-oriented South Fork Moreau River tributaries begin in the same general region of southwest Harding County along the present-day Little Missouri River-Moreau River drainage divide and then, after flowing along separate and diverging routes, converge where the North Fork and South Fork Moreau River join to become the east and northeast-oriented Moreau River. This evidence strongly suggests the North Fork Moreau River and the major South Fork Moreau River tributaries originated as headward erosion of deep headcuts along channels in what must have been a large anastomosing channel complex. Anastomosing channels complexes develop when floodwaters during immense flood events spill out of whatever preexisting channels were present. As flood erosion progresses the pattern of channels in an anastomosing channel complex can constantly change as headward erosion of headcuts on one channel capture flood flow moving on another channel. When flood flow ceases the anastomosing channel complex is preserved as it existed at that time. The interpretation presented here is the North Fork and the major South Fork Moreau River tributary valleys developed as channels in such an anastomosing channel complex and are preserved the way they existed when headward erosion of the north-oriented Little Missouri River valley beheaded and captured southeast-oriented flood flow that was developing the North and South Fork Moreau River anastomosing channel complex.

Little Missouri River-Grand River-Moreau River drainage divide at East Short Pine Hills

Figure 3: Little Missouri River-Grand River-Moreau River drainage divide at East Short Pine Hills. United States Geological Survey map digitally presented using National Geographic Society TOPO software. 

Figure 3 illustrates the Little Missouri River-Grand River-Moreau River drainage divide at the East Short Pine Hills. The Jumpoff in figure 3 is a northeast-facing escarpment that was eroded by northeast-oriented South Fork Grand River tributary valley headcuts eroding southwest to capture southeast-oriented floodwaters moving to the developing North Fork Moreau River valley. In the figure 3 southeast corner the southeast-oriented North Fork Moreau River has eroded headward into the western topographic surface drained by northwest-oriented Valley Creek and its tributaries to the north-oriented Little Missouri River. Along the southern edge of the figure 3 southwest corner can be seen the headwaters of a south-oriented drainage system that flows to southeast-oriented South Fork Moreau River. The North (Sand) Creek valley and Waddell Gulch valleys  (south center) have eroded northwest along southeast-oriented flood flow routes from the South Fork Moreau River.  Headward erosion of the North Fork Moreau River valley and the South Fork Grand River flood eroded basin northeast of the Jumpoff ceased when the north-oriented Little Missouri River valley eroded headward to behead and capture the southeast-oriented flood water that had been flowing into the North Fork Moreau and South Fork Grand River valleys. Flood water already on the northwest ends of the beheaded flood flow routes reversed direction to flow northwest to the newly formed and somewhat deeper north-oriented Little Missouri River valley. For a short period of time after southeast-flood flow to the North Fork Moreau River was beheaded flood flow was able to continue to flow on the yet to be beheaded flood flow routes moving to the developing South Fork Moreau River tributary valleys. Reversal of flow west of the East Short Pine Hills may have captured some that yet to be beheaded southeast-oriented flood flow, although headward erosion of the Little Missouri River valley soon beheaded and captured that continuing southeast-oriented flow to the South Fork Moreau River tributaries and the regional landscape has changed little since.

Little Missouri River-Moreau River drainage divide between West and East Short Pine Hills

Figure 4: Little Missouri River-Moreau River drainage divide between West and East Short Pine Hills. United States Geological Survey map digitally presented using National Geographic Society TOPO software. 

Figure 4 illustrates the Little Missouri River-Moreau River drainage divide between the East Short Pine Hills and the West Short Pine Hills. The figure 4 extreme northeast corner drains to the South Fork Grand River. Immediately south of the Grand River-Moreau River drainage divide Chalk Butte Draw drains to the North Fork Moreau River. The topographic surface between the East and West Short Pine Hills and southwest of the West Short Pine Hills is drained by north and northwest-oriented streams to the north oriented Little Missouri River. The deeply eroded basin area south and southeast of that topographic surface is drained by southeast oriented South Fork Moreau River tributaries. Note how the deeper southeast oriented South Fork Moreau River headcut eroded headward into the topographic surface now drained by north and northwest-oriented Little Missouri tributaries. Floodwaters initially flowed on a topographic surface at least as high as the present day East and West Short Pine Hills highest elevations. Waddell Draw flows from a southeast oriented flood-eroded headcut eroded northwest into the East Short Pine Hills bedrock mass, which could only happen if floodwaters flowed over what is today the East Short Pine Hills top. Likewise, Adams Gulch flows from a southwest-oriented flood-eroded headcut that was also eroded into the East Short Pine Hills bedrock mass, and again this could only happen if floodwaters flowed on a topographic surface at least as high as the East Short Pine Hills top. Hells Canyon is a southeast oriented flood-eroded headcut carved into the West Short Pine Hills south end and can only be explained by having floodwaters flowing southeast on a topographic surface at least as high as the present-day West Short Pine Hills top. Other southwest-oriented and northeast-oriented headcuts eroded headward into the West Short Pine Hills bedrock mass and can be explained by flood flow capture events as floodwaters lowered the prevailing topographic surface from a level at least as high as the topographic surface defined by the East and West Short Pine Hills tops to the topographic surface we see today. This means the lowland between the East and West Short Pines was carved by southeast and south-oriented floodwaters moving to what is today the South Fork Moreau River drainage basin. Headward erosion of the north oriented Little Missouri River valley beheaded and captured those southeast and south-oriented floodwaters and caused a reversal of flow on the northwest ends of the flood flow routes to create the north and northwest-oriented drainage to the Little Missouri River that prevails on that lowland today.

Little Missouri River-Moreau River drainage divide west and south of West Short Pine Hills

Figure 5: Little Missouri River-Moreau River drainage divide west and south of West Short Pine Hills. United States Geological Survey map digitally presented using National Geographic Society TOPO software. 

Figure 5 illustrates the Little Missouri River-Moreau River drainage divide west and south of the West Short Pine Hills. The large southeast-oriented escarpment-surrounded basin is an abandoned headcut eroded by southeast-oriented floodwaters responsible for carving the South Fork Moreau River drainage basin. The size of this escarpment-surrounded basin or abandoned headcut provides a measure of the magnitude of southeast-oriented flood flow that moved across this region, just prior to capture by headward erosion of the north-oriented Little Missouri River valley. The Little Missouri River can be seen flowing north along the figure 5 west edge. Note the northwest-oriented tributaries to the north-oriented Little Missouri River. These northwest-oriented tributaries originated as reversals of flood flow on the northwest ends of southeast-oriented flood flow routes that were beheaded when the Little Missouri River valley eroded south. Northeast and north-oriented drainage routes east of the West Short Pine Hills flow to northwest-oriented Valley Creek and the north-oriented Little Missouri River. Southwest-oriented headcuts (Sheep Draw and Sawmill Gulch) carved into West Short Pine Hills bedrock mass probably were eroded as tributary headcuts to larger southeast-oriented headcuts that eroded northwest into the high level topographic surface (defined by the Short Pines Hills top) to create the topographic surface now drained by northwest-oriented Fortyeight Mile Creek. Note how Sawmill Gulch has a northwest-oriented tributary, suggesting headward erosion of the southwest-oriented Sawmill Gulch headcut beheaded and reversed flow on a high-level southeast-oriented flood flow route.

Little Missouri River-Moreau drainage divide in southwest Harding County

Figure 6: Little Missouri River-Moreau drainage divide in southwest Harding County. United States Geological Survey map digitally presented using National Geographic Society TOPO software. 

Figure 6 illustrates the Little Missouri River-Moreau River drainage south of the figure 5 map area (with a significant overlap area to better illustrate the southeast-oriented South Fork Moreau River escarpment-surrounded basin or abandoned headcut). South Fork Moreau River headwaters flow southeast from the escarpment-surrounded basin or abandoned headcut located north of Gustave Butte in the Harding County southwest corner. Southeast-oriented streams south of Gustave Butte are headwaters of southeast-oriented Fourmile Creek, which eventually flows to the South Fork Moreau River. The north-oriented Little Missouri River can be seen in the figure 6 northwest corner. Note the pronounced northwest-southeast oriented drainage alignment that prevails across the entire figure 6 map area. The southeast-oriented drainage routes are relics of the southeast-oriented flood flow routes that crossed the region just prior to capture of the southeast-oriented floodwaters by Little Missouri River valley headward erosion into the region. The northwest-oriented Little Missouri River tributaries are relics of those same southeast-oriented flood flow routes that were preserved by reversals on the northwest ends of the beheaded flood flow routes.

Little Missouri River-Moreau River-Belle Fourche River drainage divide

Figure 7 completes our journey south along the Little Missouri River-Moreau River drainage divide and overlaps significant areas of figure 6. Southeast-oriented Battle Creek in the figure 7 southeast corner and all southeast oriented streams north of Battle Creek flow to the South Fork Moreau River while southeast oriented Porcupine Creek and North Indian Creek (south center) and all southeast oriented streams southwest of North Indian Creek flow to the southeast- and northeast-oriented Belle Fourche River, which today joins the northeast-oriented Cheyenne River. In other words the Moreau River-Belle Fourche River drainage divide is located roughly along a southeast-northwest oriented line going through Battle Creek Butte and Flat Top (butte) and extending northwest to the Little Missouri River drainage basin. Headwaters of northwest-oriented Little Missouri River tributaries can be seen along the figure 7 west edge. Close study of figure 7 evidence shows several Belle Fourche River tributaries have been beheaded by headward erosion of other Belle Fourche River tributaries and likewise several Moreau River tributaries have been beheaded by headward erosion of other Moreau River tributaries. For example, in the Belle Fourche River drainage basin headward erosion of the Crooked Creek valley has beheaded southeast-oriented Porcupine Creek and diverted what used to be  Porcupine Creek headwaters flow to the North Indian Creek basin. A somewhat more subtle beheading can be observed in the Moreau River basin where the unnamed southeast-oriented stream located between Battle Creek and Fourmile Butte has been beheaded by headward erosion of deeper Moreau River tributary valleys both to the northeast and to the southwest. These stream captures suggest the ever-changing channel locations that occur in anastomosing channel complexes associated with large-scale floods. In this case we are seeing evidence of such an ever-changing anastomosing channel complex preserved as it existed at the time the north-oriented Little Missouri River valley eroded south and captured the southeast-oriented flood flow that had been flowing southeast across the figure 7 region.

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 the detailed 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 were created using National Geographic 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.