Eastern Heart River drainage basin landform origins, southwest North Dakota, USA

Authors

A geomorphic history based on topographic map evidence

Abstract:

The eastern Heart River drainage basin is located in south central North Dakota, USA. Although detailed topographic maps of the eastern Heart River basin have been available for more than fifty years detailed map evidence has not previously been used to interpret the eastern Heart River drainage basin geomorphic history. The interpretation provided here is based entirely on topographic map evidence. Based on the topographic map evidence the eastern Heart River drainage basin is interpreted to have been eroded during immense flood events, the first of which flowed on a topographic surface at least as high as the highest points in the present-day eastern Heart River drainage basin, and which stripped the eastern Heart River drainage basin bedrock layers as deep and broad headcuts, often several kilometers in width, eroded headward along routes of the present-day southeast-oriented eastern Heart River valley segments and various southeast-oriented tributaries. Flood erosion ended when headward erosion of the deep north and northeast-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 North Dakota eastern Heart River drainage basin 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 eastern North Dakota eastern Heart River drainage basin landform evidence will be regarded as evidence supporting the “thick ice sheet that melted fast” paradigm.


Eastern Heart River drainage basin location map

Figure 1: Heart River drainage basin location map (select and click in maps to enlarge). National Geographic Society map digitally presented using National Geographic Society TOPO software.

The eastern Heart River drainage basin is located in south central North Dakota and drains to the south-oriented Missouri River. To the north is the east oriented Knife River drainage basin (see Knife River drainage basin essay under North Dakota Missouri Slope on sidebar category list). To the south is the east oriented Cannonball River drainage basin (see Cannonball River drainage basin essay). To the west is the north-oriented Little Missouri River drainage basin. For much of its course the Heart River has a southeast orientation, although before joining the south-oriented Missouri River the Heart River makes an abrupt turn to the north-northeast. This remarkable elbow of capture is similar to elbows of capture found in the Knife River and Cannonball River drainage basins and suggests the southeast-oriented Heart River drainage basin upstream from the elbow of capture was captured by headward erosion of a deep northeast-oriented valley. An unnamed (in figure 1) southeast-oriented Heart River tributary joins the Heart River just upstream from the elbow of capture and is aligned with an unnamed northwest-oriented Knife River tributary. The northwest-southeast alignment of these two opposing tributaries suggests the northeast-oriented Knife River has captured western Knife River drainage basin flow that once moved to the Heart River valley. Evidence for that capture is explored in the following detailed topographic map discussions and also in discussions of evidence contained in the Knife River drainage basin essay. Location of the north-oriented Little Missouri River just west of the east and southeast-oriented Heart River headwaters suggests headward erosion of the north-oriented Little Missouri River valley captured flood waters moving to the east and southeast-oriented Heart River drainage basin. Evidence the Heart River drainage basin has been beheaded is discussed in the western Heart River drainage basin essay.  Evidence that flood waters came from west of the present day north-oriented deep Little Missouri River valley is provided in the Beaver Creek drainage basin and the Yellowstone River-Beaver Creek drainage divide essays (under Little Missouri River on sidebar category list).

Jimmy Creek-Plum Creek through valleys

Figure 2: Jimmy Creek-Plum Creek through valleys. United States Geological Survey map digitally presented using National Geographic Society TOPO software.

Throughout the Heart River drainage multiple through valleys link the various Heart River tributaries and also link Heart River tributaries with adjacent drainage basins. These through valleys are especially noticeable where northeast-oriented Heart River tributaries have eroded valleys south and west of the southeast-oriented Heart River. These northeast-oriented tributaries cross a southeast-northwest aligned drainage pattern and are fed predominantly by southeast-oriented and northwest-oriented tributaries. The aligned drainage pattern reflects the southeast-oriented flood routes the northeast-oriented valley eroded south and west to capture. Northwest-oriented tributaries formed by reversals of flood flow on the northwest ends of beheaded southeast-oriented flood flow routes. Figure 2 illustrates through valleys between northeast-oriented Jimmy Creek and northeast-oriented Plum Creek (just east of figure 2 map area).  Note northwest-oriented tributaries to Jimmy Creek. Drainage shown on the east half of figure 2 goes to Plum Creek and usually begins with a southeast orientation. While one major northwest to southeast oriented through valley is present there are many secondary through valleys as well. This evidence suggests a southeast-oriented anastomosing channel complex initially was carved across the region, with water being concentrated in deeper channels prior to systematic capture by headward erosion of the still deeper Heart River valley and tributary valleys.

Lime Hills region through valleys linking Plum Creek and Beaver Creek

Figure 3: Lime Hills region through valleys linking Plum Creek and Beaver Creek. United States Geological Survey map digitally presented using National Geographic Society TOPO software.

Continuing southeast from the figure 2 map area the drainage divide between the northeast-oriented Plum Creek valley (extreme west edge figure 3) and the northeast-oriented Beaver Creek valley (southeast corner of figure 3) is also crossed by multiple through valleys. These through valleys are cut between several buttes including White Butte (unnamed butte at south edge of figure 3) and the Lime Hills. The multiple southeast-oriented through valleys eroded across this southwest to northeast-oriented line of buttes is strong evidence an immense southeast-oriented flood flowing on a topographic surface at least as high as the present-day butte tops flowed across the region and carved a southeast-oriented anastomosing channel complex. The flood creating this southeast-oriented anastomosing channel complex was responsible for stripping the landscape surrounding the present-day buttes and was systematically dismembered by headward erosion of the deep Heart River valley and tributary valleys. Note the southeast-orientation exhibited by most Beaver Creek tributaries and the northwest-orientation exhibited by most Plum Creek tributaries. The northeast-oriented Beaver Creek valley captured the southeast-oriented flood water first and the northeast-oriented Plum Creek valley subsequently beheaded flood flow to Beaver Creek. Northwest-oriented Plum Creek tributaries were formed by flood flow reversals when headward erosion of the deep Plum Creek valley beheaded southeast-oriented flood flow routes to Beaver Creek.

Beaver Creek elbow of capture

Figure 4: Beaver Creek elbow of capture. United States Geological Survey map digitally presented using National Geographic Society TOPO software.

Figure 4 illustrates the area immediately south of the figure 3 and shows the elbow of capture where southeast-oriented Beaver Creek headwaters have been captured by the northeast-oriented Beaver Creek valley. Southeast-oriented Beaver Creek headwaters begin at White Butte indicating the southeast-oriented flood event responsible for shaping the Heart River drainage basin landscape first flowed across a topographic surface at least as high as the top of White Butte. Note the maze of valleys between the small hills that formed as part of an anastomosing channel complex. Figure 4 also illustrates northwest-oriented tributaries flowing to the northeast-oriented Beaver Creek. These barbed tributaries were formed by reversals of southeast-oriented flood flow when headward erosion of the Beaver Creek valley captured the southeast-oriented flood flow and reversed flow on the northwest ends of the beheaded flood flow routes. Many beheaded flood flow routes led to the Cannonball River drainage basin and as Heart River and tributary valley eroded headward, southeast-oriented flood flow to the Cannonball River drainage basin was systematically captured. Numerous through valleys link the Heart River and Cannonball River drainage basins and both drainage basins appear to have developed on the same general topographic surface (i.e. there is no easy to observe topographic feature separating the two drainage basins like the Russian Springs Escarpment that separates the Heart River and Knife River drainage basins). The creek cutting across the figure 4 southwest corner is Thirtymile Creek and is a Cannonball River tributary. Note how a south-oriented Thirtymile Creek tributary begins at White Butte.

Antelope Creek (east) elbow of capture

Figure 5: Antelope Creek (east) elbow of capture. United States Geological Survey map digitally presented using National Geographic Society TOPO software.

Two Antelope Creeks begin as southeast-oriented streams and then turn northeast to flow to the southeast-oriented Heart River. The western Antelope Creek is in Stark County and is discussed in the western Heart River drainage basin essay. Figure 5 illustrates the eastern Antelope Creek elbow of capture. Also visible in figure 5 are northwest-oriented tributaries to the northeast-oriented Antelope Creek segment. These northwest-oriented Antelope Creek tributaries are aligned with southeast-oriented Cannonball River tributaries. The northeast-oriented Antelope Creek headcut eroded south and southwest to capture southeast-oriented flood waters moving to the Cannonball River drainage basin. Flood flow reversed on the northwest ends of the beheaded southeast-oriented flood flow routes to create the present-day northwest-oriented Antelope Creek tributaries. Lowlands separating the isolated hills and uplands are remnants of a shallow anastomosing channel complex etched into the regional landscape. Note how the present-day Heart River drainage basin-Cannonball River drainage divide is hardly noticeable, indicating both drainage basins were formed by the same southeast-oriented flood events. The Antelope Creek (east) capture occurred before the Beaver Creek capture (figure 4). The Beaver Creek capture occurred before the Plum Creek capture (figure 3). The Plum Creek capture occurred before the Jimmy Creek capture (figure 2). The Jimmy Creek capture occurred before the Antelope Creek (west) capture (see western Heart River drainage basin essay). The Antelope Creek (west) capture occurred before the South Branch Heart River capture. All of these capture events diverted southeast-oriented floodwaters that had been moving into the southeast-oriented Cannonball River drainage basin to flow to the adjacent and parallel, but more northerly southeast-oriented Heart River drainage basin.

How the deep Knife River drainage basin captured Heart River drainage

Figure 6: How the deep Knife River drainage basin captured Heart River drainage. United States Geological Survey map digitally presented using National Geographic Society TOPO software.

Just east of Richardton is a Russian Springs Escarpment indentation eroded by headward erosion of a deep north-oriented abandoned headcut. Development of that deep north-oriented headcut beheaded and captured southeast-oriented flood flow moving toward the east oriented Branch Knife River located in the southeast corner of figure 6. Note how the Branch Knife River turns northwest (the figure 7 discussion below will further comment on this Branch Knife River abrupt direction change). North of figure 6 the Branch Knife River turns north and flows to the east and northeast-oriented Knife River. Beheading of the east oriented Branch Knife River drainage basin by headward erosion of a deep north-oriented Knife River tributary headcut illustrates how the Knife River and tributary headcuts systematically eroded into the Heart River drainage basin surface to capture east and southeast-oriented flood water. Once captured the east and southeast-oriented flood water flowed on the Knife River drainage basin floor as is evident by the anastomosing channel complex found at the Russian Springs Escarpment base (see figure 7 and related discussion for evidence those east and southeast-oriented floods went to the Heart River drainage basin and perhaps across the present-day Heart River drainage basin). The anastomosing channel complex shape and orientation suggests channels were carved by a large east or southeast-oriented flood, however the present-day drainage network indicates headward erosion of the deep northeast-oriented Knife River valley captured those east or southeast-oriented floods and diverted floodwaters to the northeast.

Knife River-Heart River drainage divide near Hebron

Figure 7: Knife River-Heart River drainage divide near Hebron. United States Geological Survey map digitally presented using National Geographic Society TOPO software.

Figure 6 illustrated how Branch Knife River headwaters begin at the Russian Springs Escarpment crest and flow east in a progressively deepening valley to reach a large northwest to southeast-oriented valley just east of the Hebron. The large valley is known as the Curlew Valley and southeast of Hebron is drained by southeast-oriented Big Muddy Creek, which flows to the southeast-oriented Heart River and northwest of Hebron is drained by the northwest-oriented Branch Knife River, which flows to the northeast-oriented Knife River. Figure 7 illustrates the Branch Knife River and Big Muddy Creek drainage divide area just east of Hebron, North Dakota. Downstream from the Big Muddy confluence the Heart River makes an abrupt turn to the north-northeast and a through valley continues to the southeast, suggesting a deep north-northeast valley captured southeast-oriented flood flow. The Branch Knife River makes an abrupt turn to drain the northwest end of the northwest-southeast oriented valley and then turns north to join the Knife River. This evidence suggests the Curlew Valley was eroded headward by floodwaters going southeast across the Heart River drainage basin. Headward erosion of the northeast-oriented Knife River headcut then captured the flood waters and reversed flow on the northwest end of the beheaded flood flow route to create the north-oriented Branch Knife River valley segment. This evidence suggests conditions were such that deep northeast-oriented valley eroded headward into the region to capture the immense southeast-oriented floods. The source of the flood waters cannot be determined from evidence presented here, nor can the reason why deep northeast-oriented valleys eroded southwest into the region be determined. However, rapid melting of a thick North American ice sheet, which through its weight and erosive actions created a “hole” in the North American continent and caused significant crustal warping elsewhere, would be a logical flood water source and ice sheet melting that permitted meltwater floods to flow northeast into the deep “hole” that had previously been filled by ice would be a logical reason why deep northeast-oriented valleys might erode headward into the region.

Heart River elbow of capture

Figure 8: Heart River elbow of capture. United States Geological Survey map digitally presented using National Geographic Society TOPO software.

The Heart River flows generally in an east and southeast-oriented direction to join the southeast-oriented Big Muddy Creek or Curlew Valley (northwest corner of figure 8). Approximately eight kilometers southeast of the Big Muddy Creek confluence the Heart River makes an abrupt turn to the north. A large through valley continues southeast from this elbow of capture suggesting the Heart River once flowed southeast to the Cannonball River and perhaps beyond. The Heart River elbow of capture was formed when a deep north-northeast oriented valley eroded southwest and south to capture southeast-oriented Heart River flood flow. A deep north-northeast oriented valley could not have eroded headward unless flood waters were spilling out of the Heart River and flowing north and northeast to some lower elevation. Today the Missouri River flows south and a southeast-oriented channel should have the advantage of going to lower elevations. However, still lower elevations are found north and east of the Missouri Escarpment, which means the deep north-northeast oriented valley must have eroded south and southwest from east and/or northeast of the Missouri Escarpment at a time when the Missouri River valley did not exist. Erosion of such a deep north-northeast oriented headcut can be explained if the immense southeast-oriented flood waters responsible for Heart River drainage basin erosion spilled over a detached stagnant ice mass occupying the Missouri Coteau area and sliced one or more deep ice-walled and bedrock-floored valleys headward in a southwest direction to capture southeast-oriented Heart River drainage basin flood waters.

Heart River-Cannonball River drainage divide near Flasher

Figure 9: Heart River-Cannonball River drainage divide near Flasher. United States Geological Survey map digitally presented using National Geographic Society TOPO software.

Figure 9 illustrates the through valley extending in a southeast direction from the Heart River elbow of capture to the Cannonball River drainage basin. Southeast-oriented Chanta Peta Creek flows to the Cannonball River. The southeast-oriented through valley is of sufficient size and depth that it must have been eroded by a large amount of southeast-oriented water and is another segment of the same southeast-oriented through valley seen in figures 7. Today the Knife River-Heart River drainage divide (figure 7) and the Heart River-Cannonball River drainage divide (figure 9) cross the through valley. Other researchers have argued the through valley extends further northwest and southeast and once served as an ice marginal diversion trench. Supporting this interpretation is evidence abundant glacial erratics, but no fine-grained glacial drift, can be found north and east of the northwest to southeast oriented through valley and south and west of the through valley glacial erratics are rare. While an ice sheet margin may have been present and may have played a role in locating the through valley position, landscapes between the through valley and the present-day Missouri River valley are flood eroded landscapes. Further, if the through valley served as an ice marginal diversion channel as previous workers have claimed, there is no reason why the present-day Missouri River valley should have formed. The through valley must be explained in the context of a flood-eroded landscape.

Heart River-Missouri River confluence region

Figure 10: Heart River-Missouri River confluence region. United States Geological Survey map digitally presented using National Geographic Society TOPO software.

Figure 10 illustrates details of the Heart River-Missouri River confluence region. As previously noted at its elbow of capture the southeast-oriented Heart River makes an abrupt turn to flow almost straight north. Further downstream the Heart River takes on a northeast orientation and then about twelve kilometers before joining the Missouri River the Heart River turns to flow east-southeast. This last turn is puzzling because in many respects it can be viewed as a second elbow of capture where an east-southeast oriented valley has eroded headward to capture north and northeast-oriented flood flow. Does the map evidence support such an interpretation? Several lines of evidence support the hypothesis. First a southwest-oriented tributary joins the Heart River at the point where it turns from a northeast orientation to an east-southeast orientation. This barbed tributary and its valley suggest northeast-oriented flood flow was captured and that flow was reversed on the southwest end of the beheaded flood flow route. Second, a through valley continues north from the southwest-oriented tributary valley and is drained by north oriented Missouri River tributary (the tributary flows to east-oriented Otter Creek and then to the Missouri River). This north-oriented through valley is evidence a north-oriented flood flow route was captured. While not as prominent as the through valley extending southeast from the Heart River elbow of capture to Chanta Peta Creek and the Cannonball River the north-oriented flood flow hypothesis appears possible.

Overview of Heart River drainage basin evolution

  • The earliest Heart River drainage basin history event determinable from topographic map evidence was a topographic surface at least as high as the present-day Heart River drainage basin butte tops. Age of the resistant butte bedrock masses can be debated although there is general agreement the butte bedrock masses are composed of fluvial and/or lacustrine sediments. Presence of fluvial and/or lacustrine sediments indicates the butte areas were once streams and/or lakes and surrounding regions were higher in elevation. The fact fluvial and/or lacustrine sediments remain while surrounding material is gone implies the surrounding material was more easily eroded than the butte sediments. Yet existence of the butte bedrock masses indicates the regional erosional history began from a topographic surface at least as high as the butte tops. Also, the fact the regional aligned drainage pattern cuts across and through the butte regions suggests the same northwest to southeast oriented floods that produced the present-day Heart River drainage system also stripped surrounding rock layers to leave the buttes as modern-day monadnocks.
  • There is abundant evident topographic map evidence throughout the Heart River drainage basin to suggest immense southeast-oriented floods carved the regional landscape. Evidence, especially in the form of the Heart River elbow of capture and the north and east-oriented Little Missouri River valley, suggests the southeast-oriented flood water was captured and diverted to flow north and northeast. Small-scale anastomosing channel complexes can be observed at several locations and many of the larger valleys can be viewed in bigger perspective as being part of a large-scale anastomosing channel complex. A northwest to southeast oriented drainage alignment prevails across the region. Numerous elbows of capture provide evidence of a rapidly evolving drainage system characteristic of a large-scale flood event. Numerous through valleys link the Heart River drainage basin with adjacent drainage basins and also cross drainage divides between Heart River tributaries. Asymmetric drainage divides and erosion produced escarpments provide further evidence of massive flood caused erosion.
  • Stripping of regional rock layers to leave the buttes as isolated monadnocks probably was done when immense southeast-oriented floods eroded adjacent large and deep southeast-oriented headcuts in a northwest direction across the region. While much stripping probably occurred prior to erosion events for which there is good evidence, initial stripping was probably just an earlier stage in what were a progressive and continuing series of flood caused erosion events. Earlier flood erosion events probably were similar to the later flood caused erosion events for which there is good topographic map evidence, although most earlier flood erosion event evidence has been eroded away.
  • Topographic map evidence indicates the present-day deep western Heart River drainage basin erosion began when the southeast-oriented Heart River valley and various tributary valleys eroded headward to capture southeast-oriented flood waters coming from west of the present-day north-oriented Little Missouri River valley. Northeast-oriented Heart River tributary valleys eroded to the southwest in sequence and probably rapidly to capture southeast-oriented flood waters moving to the Cannonball River valley. Beginning in the east the Antelope Creek (east) valley eroded southwest first. The Beaver Creek valley eroded southwest next. The Plum Creek valley next eroded southwest. Next the Jimmy Creek valley eroded southwest. The Antelope Creek (west) valley eroded southwest next. And finally the South Branch Heart River valley eroded southwest. All of these northeast-oriented Heart River tributary valley erosion events diverted southeast-oriented flood waters that had been moving into the southeast-oriented Cannonball River valley to flow to the adjacent southeast-oriented Heart River valley
  • There is considerable topographic map evidence along the Heart River-Cannonball River drainage divide suggesting headward erosion of the Heart River valley system beheaded and captured southeast-oriented flood waters moving to the Cannonball River drainage basin. There also is evidence southeast-oriented flood waters moving to southeast-oriented Heart River tributaries, such as Russian Springs Creek and Big Muddy Creek were captured and diverted to the Knife River drainage basin to the north. Flood waters from the northwest were captured by headward erosion of the north-oriented Little Missouri River valley and that event ended flood flow across the Heart River drainage basin.
  • A similar, but somewhat more complicated erosion sequence can be observed along the Knife River-Heart River drainage divide where the Knife River systematically captured southeast-oriented flood flow that had been moving to the Heart River. In other words, the Cannonball River, Heart River, and Knife River drainage basins developed in sequence with the southern drainage basin evolving first and the northern drainage basin forming last. At the same time flood waters responsible for creating the present-day drainage basin landforms came from west of the north oriented Little Missouri River valley and that north-oriented valley eroded south, meaning the north and east-oriented Little Missouri River valley formed last and captured flood waters that had been moving to the Knife, Heart, and Cannonball River drainage basins.
  • Today Cannonball, Heart, and Knife River drainage basins all empty to the south-oriented Missouri River. Headward erosion of the Missouri River valley and tributary valley during an immense southeast-oriented flood event does account for the sequence in which the three drainage basins were formed, however it does not account for a deeper Knife River drainage basin nor does it account for headward erosion of the deep north-oriented Little Missouri River valley and the capture of the southeast-oriented flood. Evidence to help solve this problem is found where the southeast-oriented Cannonball, Heart, and Knife Rivers each turns northeast to join the south-oriented Missouri River. While an immense southeast-oriented flood initiated the Cannonball, Heart, and Knife River drainage basins, the Cannonball, Heart, and Knife River elbows are evidence that immense flood was systematically captured by deep northeast-oriented valleys and diverted to flow to the northeast.
  • The deep northeast oriented Cannonball, Heart, and Knife River valleys that eroded southwest and another deep east-oriented valley that eroded west along what is today the east-oriented Missouri River valley upstream from Garrison Dam, systematically captured southeast-oriented flood waters moving in the evolving Cannonball, Heart, and Knife River drainage basins. These deep northeast and east-oriented valleys probably eroded headward from east of the Missouri Escarpment and sliced as deep narrow valleys through a detached northwest-southeast oriented glacial ice mass located where the present-day Missouri Coteau is located. This glacial ice mass, the Southwest Ice sheet, became detached when the south and southeast-oriented Midcontinent River sliced a broad ice-walled and bedrock-floored valley (the Midcontinent Trench) into a rapidly melting thick continental ice sheet. The northeast and east-oriented valleys formed in sequence with the southernmost and shallowest valley forming first and the northernmost and deepest valley forming last.
  • While much evidence for the deep northeast-oriented Cannonball, Heart, and Knife River valley and the south and southeast-oriented Missouri River valley today lies outside the present-day Cannonball, Heart, Knife, and even Missouri River drainage basins, those progressively deeper valleys explain why the Knife River drainage basin has been eroded deeper than the Heart River drainage basin and also why the deep Little Missouri River valley was able to capture all southeast-oriented flood waters flowing to the Cannonball, Heart, and Knife River drainage basins. The deep Little Missouri River valley development is discussed in separate essays found under Little Missouri River on the sidebar category list.

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.

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