A geomorphic history based on topographic map evidence

The White Earth River-Little Knife River drainage divide area discussed here is located in northwest North Dakota, USA. Although detailed topographic maps of the White Earth River-Little Knife 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 White Earth River-Little Knife River drainage divide area is interpreted to have been eroded during final stages of immense melt water flood events as ice-marginal floods deeply eroded a rapidly melting thick ice sheet’s southwest margin. Flood erosion in the drainage divide area ended when headward erosion of the present day Missouri River valley drained all remaining flood flow from the drainage divide area.

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

• This essay is also exploring a new geomorphology paradigm in which erosional landforms are interpreted as evidence left by immense glacial melt water floods. Implied in that interpretation is the immense floods were derived from a thick North American ice sheet that created a deep “hole” in the North American continent and also melted fast. The previously unexplored paradigm being tested in this and other Missouri River drainage basin landform origins research project essay is a thick North American ice sheet, comparable in thickness to the Antarctic ice sheet, occupied the North American region usually recognized to have been glaciated, and through its weight and erosive actions created a deep North American “hole”. The southwestern rim of that deep “hole” is today preserved in the high Rocky Mountains. The ice sheet through its weight and deep erosion (and perhaps deposition along major south-oriented melt water flow routes) caused significant crustal warping and tectonic change, through its action of melting fast produced immense floods that flowed across the continent, and through its action of melting fast systematically opened up space in the ice sheet created “hole” so headward erosion of newly developed north-oriented drainage systems captured immense south-oriented melt water floods and diverted immense melt water floods north into space the ice sheet had once occupied.

• If this previously unexplored paradigm is correct the geographic region explored by this essay should contain evidence of immense floods that were captured by headward erosion of new valley systems so as to cause the floods to flow in a different direction. Ability of this previously unexplored paradigm to explain White Earth River-Little Knife River 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.

White Earth River-Little Knife River drainage divide area location map

Figure 1: White Earth River-Little Knife River drainage divide area location map (select and click on maps to enlarge). National Geographic Society map digitally presented using National Geographic Society TOPO software.

Figure 1 provides a White Earth River-Little Knife River drainage divide area location map. The Canada-United States border is shown. Saskatchewan is the western Canadian province and Manitoba is the Canadian province in the figure 1 northeast corner. Montana is the state along the figure 1 west edge and North Dakota is located east of Montana. The northeast-oriented South Saskatchewan River is located north of the figure 1 map area. The Missouri River flows east from Culbertson, Montana into North Dakota and to Lake Sakakawea, which is a large reservoir flooding the Missouri River valley upstream from Garrison Dam. The northeast-oriented Yellowstone River joins the Missouri River near the Montana-North Dakota border. Southeast of the Yellowstone River is the unnamed (in figure 1) Little Missouri River, which flows north to the Theodore Roosevelt National Park (North Unit) area and then flows east to the Missouri River. The Souris River originates in Canada and flows southeast to Estevan, Saskatchewan and then flows east, with a northeast jog to Oxbow, Saskatchewan before turning to flow southeast to Minot and Velva, North Dakota. At Velva the Souris River turns to flow northeast and then northwest to the Canadian border. The Des Lacs River is located immediately west of the southeast-oriented Souris River in North Dakota and from near Portal, North Dakota to Kenmare and to join the Souris River near Burlington, North Dakota. The White Earth River is a south-oriented Missouri River tributary located southwest of the Des Lacs River and as shown in figure 1 flows south from near Powers Lake through the town of White Earth to the Missouri River. The Little Knife River on figure 1 is the unnamed southwest-oriented Missouri River tributary located between the White Earth River and southwest-oriented Shell Creek. The Little Knife River on figure 1 flows southwest from Stanley, North Dakota to join the Missouri River near New Town, North Dakota.

• This essay uses topographic maps to illustrate how the White Earth River and Little Knife River are related to the Missouri Coteau and Missouri Escarpment, which are two prominent landforms not identified in figure 1, but which are shown in detailed topographic maps below. The Missouri Coteau briefly is a region of hummocky topography located between the Missouri River and the southeast oriented Des Lacs and Souris Rivers. Missouri Coteau area drainage is often to local depressions or small lakes, although southwest areas of the Missouri Coteau region drain to the Missouri River. The Missouri Escarpment is a northeast-facing escarpment located immediately northeast of the Missouri Coteau and which drains to the Des Lacs and Souris Rivers. The essay describing the region west of the White Earth River-Little Knife River drainage basin area is the Little Muddy River-White Earth River drainage divide area essay and can be found under ND Missouri River on the sidebar category list. Detailed maps illustrated below begin with the Missouri Escarpment located at the northeast margin of the Missouri Coteau and proceed south to the Missouri River. The Missouri Coteau is interpreted here as being glacial deposits left by decaying remnants of what had been a rapidly melting thick North American ice sheet that had occupied a deep “hole”. The lowland at the Missouri Escarpment base in other essays referred to as the Midcontinent Trench, which was eroded by an immense southeast and south-oriented glacial melt water river. The immense river, which originated as a melt water flow route on the thick ice sheet surface, will be named the Midcontinent River. The Missouri Escarpment will be interpreted to have been formed as the Midcontinent Trench’s southwest wall or the southwest wall of what at one time was the Midcontinent River’s ice-walled and bedrock-floored valley.

White Earth River-Little Knife River drainage divide area detailed location map

Figure 2: White Earth River-Little Knife River 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 White Earth River-Little Knife River drainage divide area. Burke, Divide, Mountrail, Renville, Ward, and Williams Counties are located in North Dakota. The north-south Montana-North Dakota state line is located near the figure 2 west edge. The west to east oriented Canada-United States boundary is located just north of the figure 2 north edge. The flooded Missouri River valley is located in the figure 2 southwest quadrant. The Missouri River valley is today flooded by Lake Sakakawea, which is a large reservoir impounded behind Garrison Dam. The southwest oriented White Earth River headwaters join White Earth Creek near the point where the White Earth River turns to flow straight south. The Little Knife River originates near Stanley (in central Mountrail County) and flows southwest and south-southwest to join the southeast-oriented Missouri River near New Town (located on the figure 2 south center edge). The Des Lacs River flows south and southeast through the Des Lacs National Wildlife Refuge in northeast Burke County and then flows southeast to join the south-southeast oriented Souris River near the figure 2 east edge. Note numerous short northeast-oriented Des Lacs River tributaries. Those tributaries are draining the northeast-facing Missouri Escarpment slope. In Burke County there are similar north-northeast streams ending in a swamp and Beaver Lake. Those Burke County streams are draining the east-northeast facing Missouri Escarpment slope in that region. This essay attempts to explain the origin of White Earth River and Little Knife River valleys and their relationship to the present day Missouri River and Yellowstone River valleys as well as their relationship with the Missouri Coteau and Missouri Escarpment. Detailed maps below begin with a look at the Missouri Escarpment in Burke County and proceed south from the Missouri Coteau along the White Earth River-Little Knife River drainage divide to the Missouri River valley. The essay concludes with a detailed look at a valley complex just west of where the White Earth River joins the Missouri River.

Missouri Escarpment and Missouri Coteau south of Lignite, North Dakota

Figure 3: Missouri Escarpment and Missouri Coteau south of Lignite, North Dakota.United States Geological Survey map digitally presented using National Geographic Society TOPO software.

Figure 3 illustrates the Missouri Escarpment and Missouri Coteau south of Lignite, North Dakota. Hummocky topography along the figure 3 south edge (with numerous small lakes) is the northern edge of the Missouri Coteau, which is illustrated further in figures below. The Missouri Coteau appears to be a region covered by glacial moraines and is interpreted here to be deposits left by a thick ice sheet remnant that slowly melted. The east-northeast facing Missouri Escarpment is the slope extending to relatively flat lowland located in the figure 3 north half. Glacial moraines appear to be absent or thin on the Missouri Escarpment slope and in the lowland region to the north. When looking at relatively small regions such as the area in figure 3 this pattern does not appear to make much sense (e.g. the lowland at the Missouri Escarpment base is lower in elevation than area around the present day Missouri River valley located to the south of figure 3). Yet when viewed from a bigger picture perspective the figure 3 landscape is quite logical. Figure 3 is illustrating a region that was on the floor of a thick North American ice sheet, which was located in a deep “hole”. Most if not all evidence of the deep “hole” rim was removed by deep melt water flood erosion that produced the present day Missouri River drainage basin (probably the topographic surface upon which the thick ice sheet was formed is today represented by high Rocky Mountain erosion surfaces, if it has been preserved at all). When the ice sheet began to rapidly melt the melt water flowed off the ice sheet surface to ice sheet margin areas and then flowed southeast along the ice sheet southwest margin until it could find routes to flow south to the Gulf of Mexico. Melt water on the ice sheet surface formed immense rivers that flowed to ice sheet margin areas. One such river flowed southeast and south across North Dakota to the present day Missouri River valley in southeast South Dakota. That southeast and south-oriented river developed a large drainage basin on the ice sheet surface that included much of southern Saskatchewan and areas in east central Alberta as well as large areas in North Dakota and is named in the Missouri River drainage basin research project essay series as the Midcontinent River. As rapid ice sheet melting continued the Midcontinent River sliced a deep ice-walled and ice-floored valley into the ice sheet and in time that valley became an immense southeast and south-oriented ice-walled and bedrock-floored canyon, which detached the rapidly melting ice sheet’s southwest margin. The deep ice-walled and bedrock-floored canyon is named here as the Midcontinent Trench. The Missouri Escarpment in figure 3 is the Midcontinent Trench southwest wall. The Missouri Coteau represents an area where the detached ice sheet’s southwest margin (named here the Southwest Ice Sheet) slowly melted.

Missouri Escarpment and Missouri Coteau southwest of Coteau, North Dakota

Figure 4: Missouri Escarpment and Missouri Coteau southwest of Coteau, North Dakota.United States Geological Survey map digitally presented using National Geographic Society TOPO software.

Figure 4 illustrates the Missouri Escarpment and Missouri Coteau southwest of Coteau, North Dakota and includes overlap areas with figure 3. The Missouri Coteau is located in southwest half of the figure 4 map area. The Missouri Escarpment rises gradually from the northwest-oriented railroad in the figure 4 northeast quadrant to  near the Missouri Coteau and then rises sharply to the Missouri Coteau edge. Note how the Missouri Escarpment slope is well-drained by numerous small northeast-oriented streams. Also note how the Missouri Coteau lacks external drainage and is composed of hummocky topography typical of glacial moraine areas. Just northwest of where the red highway crosses the Missouri Coteau edge there is a small indentation in the Missouri Coteau edge that suggests something different happened there. Thompson Lake and other lakes along the highway to the south of that indentation are at the north end of a chain of lakes (seen in figure 5 below) located in the Lostwood Wildlife National Wildlife Refuge. That chain of lakes appears to be related to the small indentation in the Missouri Coteau edge and suggests an interpretation that may explain more of the thick ice sheet’s history. As described in the figure 3 discussion the thick ice sheet was located in a deep “hole” (the hole had been created by deep glacial erosion and also by crustal warping caused by the ice sheet weight). While near the ice sheet southwest margin, landscape in this figure 4 map area was probably located at an elevation well below the topographic surface upon which the thick ice sheet originally formed. When rapid melting began the ice sheet stood significantly above the surrounding landscape and melt water flowed in immense rivers along the ice sheet margins and then flowed south to the Gulf of Mexico. However, as ice sheet melting progressed, the ice sheet gradually became lower than the surrounding landscape and melt water floods could move northeast onto the ice sheet surface. At the same time large supra-glacial melt water rivers, such as the Midcontinent River were carving deep valleys into the ice sheet surface. These deep valleys in time became deeper than the ice margin areas and were able to capture the ice marginal melt water floods. The Big Muddy Creek-Little Muddy River drainage divide area essay and the Little Muddy River-White Earth River drainage divide area essay illustrate and describe what were two large ice-walled and bedrock-floored that eroded headward from the deep southeast and south-oriented Midcontinent Trench (and are found under ND Missouri River on the sidebar category list). As ice sheet melting accelerated ice marginal melt water flood water probably broke through the detached Southwest Ice Sheet in many other locations, some of which did not develop into large ice-walled and bedrock-floored valleys, but instead may have been narrow ice-walled and ice-floored north and northeast-oriented valleys. The chain of lakes and the Missouri Coteau edge indentation may be evidence of such a narrow ice-walled and ice-floored north and northeast-oriented valley carved into the detached and decaying Southwest Ice Sheet ice wall.

Smishek Lake and Lostwood Lakes area on Missouri Coteau

Figure 5: Smishek Lake and Lostwood Lakes area on Missouri Coteau.United States Geological Survey map digitally presented using National Geographic Society TOPO software.

Figure 5 illustrates the Smishek Lake and Lostwood Lakes area on the Missouri Coteau and is located south and west of the figure 4 map area (and includes overlap areas with figure 4). Smishek Lake is the northeast-southwest oriented lake in the figure 5 west center edge area. White Earth River headwaters flow southeast into Smishek Lake and then flow south-southwest from Smishek Lake to the figure 5 west edge. The northeast-oriented valley in which Smishek Lake is located may also have originated as a narrow northeast-oriented breach in the detached and decaying Southwest Ice Sheet ice wall. The previously mentioned north-northeast oriented chain of lakes in the Lostwood National Wildlife Refuge is located in the figure 5 east half just west of the north-oriented red highway. As mentioned in the figure 3 discussion those lakes may also be evidence of a narrow north-northeast oriented breach in the Southwest Ice Sheet wall. Note also that the town of Powers Lake is located in a northwest-southeast oriented valley and east of Powers Lake there is a south-oriented valley. The figure 5 southwest quadrant, while lacking a well-defined integrated drainage pattern, does appear to have been eroded by running water (unlike the Missouri Coteau areas further to the north and northeast in figure 5). The Southwest Ice Sheet southwest margin was probably subjected during late stages of the thick ice sheet’s rapid melt down to intense ice marginal melt water flood erosion. For this reason the thick ice sheet’s southwest margin location may be very difficult to identify, if it can be identified at all. Late during the thick ice sheet rapid melt down as the immense southeast and south- oriented Midcontinent River was step by step dismembered with flood waters diverted to flow north to Hudson Bay (for evidence of one such capture see the Souris River loop in figure 1). The rapid shift of melt water flood flow, which had been moving to the Gulf of Mexico, into Hudson Bay probably significantly changed Atlantic Ocean currents, which probably triggered a rapid Northern Hemisphere cooling event. That cooling event caused north-oriented flood waters to freeze on the former ice sheet floor at the same times as immense northeast-oriented floods were moving onto the ice sheet’s former floor. Freezing of flood waters and the climate change resulted in blockages that prevented flood waters from moving northeast and instead flood waters were forced to flow southeast along the Southwest Ice Sheet’s southwest margin. Headward erosion of the deep Missouri River valley, which proceeded from the southeast to the northwest, captured these flood waters and reinstated the former southeast and south-oriented drainage to the Gulf of Mexico. However, because the climate had changed there was no more rapid ice sheet melting and once headward erosion of the present day Missouri River valley drained remaining flood waters there were no more immense melt water floods. The figure 5 southwest quadrant was probably eroded as headward erosion of the White Earth River valley drained final flood waters from the region.

Little Knife River valley near Stanley, North Dakota

Figure 6: Little Knife River valley near Stanley, North Dakota.United States Geological Survey map digitally presented using National Geographic Society TOPO software.

Figure 6 illustrates the Little Knife River valley near Stanley, North Dakota and is located south and east of figure 5. The Little Knife River originates east of Stanley as a northwest-oriented stream and then turns to become a southwest-oriented stream as it flows east and south of Stanley to the figure 6 south edge. The figure 6 map area is located in the Missouri Coteau area, although the Missouri Coteau in the figure 6 southwest quadrant is quite different in appearance than the Coteau in the north half of figure 5. The difference is probably related to the amount of melt water flood erosion the different Coteau regions received. The north half of figure 5 was probably an area where the decaying ice sheet remnants were not affected by melt water flood erosion (except perhaps by narrow northeast-oriented ice-walled valleys). The figure 6 map area is located closer to what was the ice sheet’s final southwest margin and probably was intensely affected by ice-marginal melt water flood erosion, especially during final flood stages when incoming northeast-oriented flood waters could no longer move northeast and were forced to flow southeast along the ice sheet margin. This final stage of the immense melt water floods ended as the deep southeast-oriented Missouri River valley eroded into the region south of the figure 6 map area to drain the final flood waters. Headward erosion of the south-oriented Little Knife River valley occurred at that time. The Little Knife River valley probably eroded headward into what was then still a decaying ice sheet mass to capture and drain flood waters moving southeast on the surface of that ice mass (because of blockages of northeast-oriented flood flow routes across the detached Southwest Ice Sheet ice wall to located to the northeast (such as were located in the figure 5 north half area). Topography in the figure 6 map area was affected by different processes as flood waters eroded the region and then as ice sheet remnants gradually melted. Flood water erosion cut valleys in the decaying ice sheet mass and removed (or at least moved) sediments that had accumulated on the ice sheet surface as the thick ice sheet had melted. Later, as ice sheet remnants slowly melted there was considerable inversion of topography, with areas of thickest ice sheet remnants becoming valleys and areas of thickest glacially (and flood water) deposited debris becoming hills. As a result the figure 6 evidence reflects multiple processes, although headward erosion of what probably was then an ice-walled and bedrock-floored Little Knife River valley captured flood waters blocked by an ice wall to the northeast and forced to flow east-southeast and southeast on the surface of decaying ice sheet margin remnants.

White Earth River-Little Knife River drainage area near Ross, North Dakota

Figure 7: White Earth River-Little Knife River drainage area near Ross, North Dakota.United States Geological Survey map digitally presented using National Geographic Society TOPO software.

Figure 7 illustrates the White Earth River-Little Knife River drainage divide area west of the figure 6 map area and includes overlap areas with figure 6. The White River Earth flows south in the figure 7 west edge area. The southwest-oriented Little Knife River is located east and southeast of the figure 7 map area as seen in figure 6 (and also in figure 8 below). Note the broad west to east oriented through valley in which Ross is located (both the highway and the railroad make use of the through valley). The through valley floor is today uneven with several small lakes present, suggesting it may have been formed at a time when ice was still present in the region. The through valley is interpreted here to have been formed by east and east-southeast oriented flood waters moving along the Southwest Ice Sheet ice wall. At that time this figure 7 map area was probably located along the Southwest Ice Sheet southwest margin and considerable decaying ice was still present. Also, at that time the south-oriented White Earth River valley did not exist. As the southeast-oriented Missouri River valley eroded headward into the region south of figure 7 (see figures 8 and 9 below) the Little Knife River valley eroded headward to capture some of the east and east-southeast oriented flood water and to divert that flood water to the newly eroded Missouri River valley. The deep southeast-oriented Missouri River valley continued to erode northwest into the region and the south-oriented White Earth River valley next eroded north to capture the east-southeast oriented flood water and to divert that flood water more directly to the newly eroded Missouri River valley. The incised meanders in the White Earth River valley may be evidence the White Earth River valley was eroded into a region still covered with decaying ice sheet remnants, over which the flood waters were moving. Melting of decaying ice sheet remnants probably was responsible for formation of the various small lake basins and other depressions seen in figure 7.

White Earth River-Little Knife River drainage divide area northeast of Missouri River

Figure 8: White Earth River-Little Knife River drainage divide area northeast of Missouri River.United States Geological Survey map digitally presented using National Geographic Society TOPO software.

Figure 8 illustrates the White Earth River-Little Knife River drainage divide area south of the figure 7 map area and includes overlap areas with figure 7. The south oriented White Earth River valley can be seen along the figure 8 west edge. The southeast-oriented Missouri River valley is located in the figure 8 southwest corner. The south and southeast-oriented Little Knife River valley is located in the figure 8 northeast corner. East of figure 8 the southeast-oriented Little Knife River turns to flow southwest and can be seen again as a southwest-oriented stream in the figure 8 southeast corner. As a southwest-oriented stream the Little Knife River might be considered a barbed tributary flowing to the southeast-oriented Missouri River. The southwest-oriented Little Knife River valley segments may have been initiated at a time when flood waters were moving northeast toward breaches in the Southwest Ice Sheet ice wall. Flood flow on those northeast-oriented flood flow routes would have been beheaded and reversed when headward erosion of the southeast-oriented Missouri River valley occurred. Probably the situation was somewhat more complex because southeast-oriented tributaries to the southwest-oriented Little Knife River valley suggest headward erosion of the Little Knife River valley did capture southeast-oriented flood flow. Also, figure 9 below shows the Little Knife River turns to flow south to the southeast-oriented Missouri River. Incised meanders in the White Earth River valley, the Little Knife River valley, and the largest of the southeast-oriented Little Knife River tributary valleys may provide evidence these valleys eroded headward into a region still covered with decaying ice sheet remnants. The presence of several small lakes and closed depressions further supports this interpretation. If so, the figure 8 valleys were eroded as ice-walled and bedrock-floored valleys into the roots of what had been a thick North American ice sheet located in the bottom of a deep “hole”. The Missouri River valley eroded headward along the southwest margin of what remained of that thick ice sheet when a rapid climatic change (probably caused by when north-oriented melt water flood flow routes rapidly captured the immense south-oriented melt water flood flow routes and diverted the immense melt water floods north to Hudson Bay). That rapid climatic change caused north-oriented flood waters to freeze on the former ice sheet floor and to create a thin wet-based ice sheet in which reinvigorated remnants of the thick ice sheet were embedded. The thin ice sheet and reinvigorated Southwest Ice Sheet blocked northward movement of melt water floods still moving south and west of the former ice sheet margin. Headward erosion of the southeast-oriented Missouri River valley captured and drained those remaining flood waters and no new immense melt water floods occurred.

White Earth River-Little Knife River drainage area at the Missouri River

Figure 9: White Earth River-Little Knife River drainage area at the Missouri River.United States Geological Survey map digitally presented using National Geographic Society TOPO software.

Figure 9 illustrates the White Earth River-Little Knife River drainage divide area at the Missouri River valley and includes overlap areas with figure 8. Lake Sakakawea is a large reservoir flooding the southeast-oriented Missouri River valley, which extends from the figure 9 northwest quadrant to the figure 9 southeast quadrant. Note how the Missouri River valley is a deep and narrow valley, suggesting it was eroded headward across a preexisting landscape. The White Earth River joins the Missouri River in the figure 9 northwest quadrant (see White Earth Bay). Note how the south end of the White Earth River valley is southeast-oriented providing evidence the deep White Earth River valley eroded headward from the southeast-oriented Missouri River valley, which suggests the entire figure 9 map area may have been eroded by southeast-oriented flood water. The southwest and south-oriented Little Knife River is located in the figure 9 east half and joins the Missouri River in the figure 9 southeast quadrant at Little Knife Bay. Note how the Little Knife River circles around a butte to enter Little Knife Bay even though a large through valley provides a more direct route. The butte is an erosional residual between what were two adjacent south-oriented flood flow channels eroded at the time the deep Missouri River valley eroded headward into the region (and the deep Little Knife River valley eroded north to capture southeast-oriented flood flow north and east of the deep Missouri River valley). Additional figure 9 evidence for southeast-oriented flood flow can be seen in the uplands on either side of the deep Missouri River valley. Southwest of the Missouri River valley Little Antelope Creek flows southeast on the upland adjacent to the Missouri River before turning northeast to flow to the Missouri River. Northeast of the Missouri River valley note how a southeast-oriented Little Knife River tributary is linked by a through valley to an unnamed northwest-oriented Missouri River tributary. That through valley is better illustrated in figure 10 below and the northwest-oriented Missouri River tributary illustrates how headward erosion of deep valleys during immense flood flow events can reverse flood flow on ends of beheaded flood flow channels.

Detailed map of Missouri River tributary valleys

Figure 10: Detailed map of Missouri River tributary valleys.United States Geological Survey map digitally presented using National Geographic Society TOPO software.

Figure 10 provides a detailed map of Missouri River tributaries seen in less detail in figure 9 above. The southeast oriented stream flowing to the figure 10 southeast corner is a tributary to the Little Knife River, which joins the Missouri River at Little Knife Bay (see figure 9). In the figure 10 northwest quadrant a south oriented Missouri River tributary has captured southeast, south, and northwest-oriented drainage. Of most interest to this discussion is the northwest-oriented valley, which is linked by a well-defined through valley with the southeast-oriented Little Knife River tributary valley. The northwest-southeast oriented through valley provides evidence of a parallel southeast-oriented flood flow channel adjacent to the Missouri River valley. In other words, prior to headward erosion of the deep Missouri River valley there were multiple shallower southeast-oriented flood flow channels moving flood water across the figure 10 map area. The deep Missouri River valley eroded headward along one of those flood flow channels and in doing so captured flood waters from adjacent flood flow channels. Headward erosion of the deep Missouri River valley progressed from the southeast to the northwest and the deep Little Knife River valley eroded north when the deep Missouri River valley reached the Little Knife bay area. Headward erosion of the Little Knife River valley captured southeast-oriented flood water in the northwest-southeast oriented through valley (which at that time was probably at a much higher elevation than it is now) and also from the higher level southeast-oriented valley in the figure 10 northeast quadrant. Flood waters then lowered the northwest-southeast through valley to its present day elevation during the time interval it took the Missouri River valley to erode headward from the Little Knife Bay area to the figure 10 west edge and the time interval it took for the south-oriented Missouri River tributary valley to erode headward so as to behead southeast-oriented flood flow in the northwest-southeast oriented through valley. Flood waters on the northwest end of the beheaded flood flow route reversed flow direction to erode the northwest-oriented Missouri River tributary valley segment and the figure 10 landscape 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.