A geomorphic history based on topographic map evidence

This essay is an overview of information contained in more detailed essays describing topographic map evidence found along drainage divides between South Dakota Missouri River tributaries. The detailed essays can be found under SD Missouri River on this website’s sidebar category list. Overview essays and related detailed essays for major South Dakota tributaries can be under names of those tributaries on the sidebar category list. The Missouri River flows in a south direction from the North Dakota border into South Dakota and in central South Dakota the Missouri River turns to flow in a southeast direction to the South Dakota-Nebraska border and then flows along that border to the southeast tip of South Dakota. With the exception of a very small area in northeast South Dakota the entire state of South Dakota is drained by the Missouri River or one of the Missouri River tributaries. The Little Missouri River in northwest South Dakota flows in a north direction into North Dakota before joining the Missouri River. All other South Dakota Missouri River tributaries join the Missouri River in South Dakota and include the Grand River, Moreau River, Cheyenne River, Bad River, White River, James River, and Big Sioux River and their tributaries. Detailed essays interpret South Dakota landform origins in the context of immense southeast and south-oriented floods associated with the rapid melt of a thick North American ice sheet. Areas in South Dakota west of the present day Missouri River valley, including Black Hills upland areas, were deeply eroded by immense southeast-oriented ice-marginal floods while the decaying ice sheet roots were located in South Dakota areas east and north of the Missouri River. The present day James River flows south in a broad lowland, which originated as an immense south-oriented ice-walled and bedrock-floored canyon sliced into the decaying ice sheet’s surface. Today the lowland is bounded on the east by the west-facing Prairie Coteau Escarpment and on the west by the east-facing Missouri Escarpment. Between the Missouri Escarpment and the Missouri River valley is the Missouri Coteau, which is where the ice sheet’s detached southwest margin slowly melted. East of the west-facing Prairie Coteau escarpment is the Prairie Coteau upland surface, which is where a detached Prairie Coteau ice sheet remnant slowly melted. The Big Sioux River valley originated as a much smaller and shallower (than the James River lowland) ice-walled and bedrock-floored canyon sliced into the detached Prairie Coteau ice sheet remnant surface. Detailed essays related to this overview essay and to South Dakota Missouri River tributaries (addressed by separate overview essays) illustrate and describe evidence from several hundred topographic maps from which this Missouri River drainage basin flood origin interpretation has been developed.

Figure 1: South Dakota Missouri River drainage basin location map (select and click on map to enlarge). National Geographic Society map digitally presented using National Geographic Society TOPO software.

South Dakota Missouri River drainage basin drainage history

This essay provides an overview of information contained in detailed essays using topographic map evidence to illustrate and interpret South Dakota Missouri River drainage basin landform origins. The detailed essays can be found under SD Missouri River on this website’s sidebar category list (or under the names of major South Dakota Missouri River tributaries). With the exception of a very small region in its northeast corner the state South Dakota is located entirely in the Missouri River drainage basin. The Missouri River, which originates in northern Wyoming and southwest Montana, flows across Montana and then into and across North Dakota before flowing in a south direction into north central South Dakota. Once in South Dakota the Missouri River continues to flow in a generally south direction to central South Dakota and then turns to flow in a southeast direction to form the border between southeast South Dakota and northeast Nebraska before flowing in a south-southeast direction along the Nebraska-Iowa border (see figure 1). Major South Dakota Missouri River tributaries from the west (from north to south) include the Grand River, Moreau River, Cheyenne River, and White River. The Cheyenne River and its tributary Belle Fourche River originate in northeast Wyoming and flow around the Black Hills as they enter South Dakota. The White River originates in the Nebraska northwest corner as a southeast-oriented stream before turning to flow in a northeast direction to enter South Dakota. Major South Dakota Missouri River tributaries from the north (or to the east) are the south-oriented James River and Big Sioux River. The James River originates in central North Dakota and flows for its entire length in a southeast and south direction on the floor of what is today a broad escarpment bounded lowland, which is also drained in North Dakota by the Sheyenne River, which after paralleling the James River route for a considerable distance makes a U-turn to flow to the north-oriented Red River and Hudson Bay. The Big Sioux River originates on the Prairie Coteau upland surface in northeast South Dakota and drains the Prairie Coteau upland surface in eastern South Dakota, southwest Minnesota, and northeast Iowa.

Figure 2: Regional map showing major drainage routes in northwest South Dakota and southwest North Dakota. National Geographic Society map digitally presented using National Geographic Society TOPO software.

Figure 2 provides a regional map showing major drainage routes in northwest South Dakota and southwest North Dakota. The Missouri River is the large south-oriented river in the figure 2 east half. Lake Oahe is a large reservoir flooding the Missouri River valley. Major east-oriented tributaries include the Cheyenne River, Moreau River, and Grand River in South Dakota and the Cannonball River and Heart River in North Dakota. The north-northeast oriented Little Missouri River (located along the figure 2 west edge) turns to flow in an east direction north of the figure 2 map area and is also a Missouri River tributary. Note how east-oriented Missouri River tributaries in figure 2 have southeast-oriented tributaries and/or headwaters and usually turn to flow in a northeast direction to join the south-oriented Missouri River. Also note how west-oriented Missouri River tributaries are significantly shorter than east-oriented Missouri River tributaries. Detailed essays describing figure 2 South Dakota map area drainage basins can be found under Cheyenne River, Moreau River, and SD Grand River on the sidebar category list and detailed essays related to North Dakota Missouri River tributaries can be found under North Dakota Missouri Slope and Little Missouri River on the sidebar category list. When looked at collectively evidence from more than 500 topographic maps in these detailed essays strongly supports interpretations provided here.

• Drainage history resulting in figure 2 drainage routes began with rapid melt down of a thick North American ice sheet. The ice sheet was comparable in size if not larger than the present day Antarctic Ice Sheet and was located in a deep “hole” The deep “hole” had been created by a combination of deep glacial erosion and of crustal warping caused by ice sheet’s tremendous weight. Crustal down warping under the ice sheet probably also affected regions further to the south and west, such as contributing to uplift of the present day Black Hills, Rocky Mountains, and Colorado Plateau. When fully developed the thick North American ice sheet probably was several kilometers thick and stood two or more kilometers above the surrounding non glaciated surface and the ice sheet “roots” may have extended more than one kilometer below the surrounding non glaciated surface. The pre-glacial surface on which the ice sheet was formed was completely destroyed by deep glacial erosion in regions where the ice sheet once stood and was destroyed by deep flood water erosion in regions surrounding the location where the ice sheet once stood. In other words, all figure 2 drainage routes developed as the thick ice sheet melted. The ice sheet southwest margin in the figure 2 map area cannot be determined because melt water floods destroyed and/or significantly altered much of the ice margin evidence, however at the time figure 2 drainage routes began to form the decaying ice sheet southwest margin was located a short distance east of the Missouri River figure 2 location. At that time the ice sheet no longer stood high above the surrounding region. The ice sheet surface at that time, at least in the figure 2 map area, had been lowered so it was significantly lower in elevation than what had been the elevation of the adjacent non glaciated regions. However, immense southeast-oriented melt water floods flowing along the decaying ice sheet’s southwest margin had also lowered regions adjacent to the decaying ice sheet’s southwest margin so there was a gradual northeast and/or east-oriented slope leading to the decaying ice sheet’s southwest margin and in most locations the ice sheet’s southwest margin still stood higher than areas south and west of the decaying ice sheet location and the southeast-oriented floods were still being channeled along the ice sheet margin.

• Immense south-oriented melt water floods flowing across the decaying ice sheet surface at the time figure 2 drainage routes were initiated were carving immense south-oriented ice-walled and ice-floored (and later bedrock-floored) canyons into the ice sheet surface. One giant ice-walled canyon was located east of the figure 2 map area and the floor of that canyon was significantly lower in elevation than the ice sheet’s southwest margin and also lower in elevation than the surface south and west of the ice sheet margin where massive southeast-oriented ice-marginal melt water floods were flowing. As ice sheet melting progressed this huge south-oriented ice-walled canyon became a bedrock-floored canyon and detached the ice sheet’s south-west margin, which then became an ice barrier located between the deep ice-walled and bedrock-floored canyon and the higher elevation southeast-oriented melt water floods to the south and west. Further complicating the situation as the ice sheet decayed the deep ice-walled canyons being eroded into the ice sheet surface intersected with each other, which not only detached additional ice sheet remnants, but also opened up new melt water flow routes providing steeper gradients than the former south-oriented melt water flood flow routes. The immense melt water river flowing on the floor of the giant ice-walled and bedrock-floored canyon east of the figure 2 map area, which had been flowing south was captured in southeast North Dakota when a south-oriented melt water river flowing in a tributary ice-walled and bedrock-floored canyon (located on the present day north-oriented Red River Valley alignment) reversed flow direction to first flow to the Gulf of Saint Lawrence and later to the Hudson Bay region. In other words, what had been an immense south-oriented melt water river on the floor of the immense ice-walled and bedrock-floored canyon east of figure 2 reversed flow direction and became a northeast-oriented melt water river flowing between decaying ice sheet remnants.

• As already stated, immense southeast-oriented melt water floods were flowing on the higher level surface south and west of the detached ice sheet southwest margin, which formed an ice barrier between those immense floods and the lower elevation floor of the giant ice-walled and bedrock-floored canyon to the east. As the detached ice sheet southwest margin melted flood waters began to breach the ice barrier and to erode deep east and northeast-oriented ice-walled and bedrock-floored valleys across the detached ice sheet southwest margin and then headward across the southeast-oriented ice marginal melt water floods. Headward erosion of these deep east and northeast-oriented valleys began in the south and progressed in sequence to the north. The northeast-oriented Cheyenne River valley was the first such major valley eroded in figure 2 with the Moreau River, Grand River, Cannonball River, Heart River, and Little Missouri River valleys following sequence. At the same time as these east and northeast-oriented valleys were being eroded headward many segments of the south-oriented Missouri River valley were also being eroded headward along the decaying  ice sheet margin, initially as tributary valleys to the east and northeast-oriented valley being eroded immediately to the south. Probably all of these figure 2 valleys were being eroded at approximately the same time, with the southern valleys being eroded headward slightly in advance of the valleys further to the north.

Figure 3: Regional map showing major drainage routes in southwest South Dakota and adjacent northeast Wyoming and northwest Nebraska. National Geographic Society map digitally presented using National Geographic Society TOPO software.

Figure 3 shows a regional map of drainage routes in southwest South Dakota and adjacent northeast Wyoming and northwest Nebraska. The south and southeast-oriented Missouri River can be seen in the figure 3 northeast corner area. Lake Oahe is a large reservoir formed behind Oahe Dam and floods the Missouri River valley. Major east-oriented Missouri River tributaries seen in figure 3 from south to north are the Niobrara River (in northern Nebraska), the White River, the Bad River, and the Cheyenne River. Note how the Cheyenne River drainage basin and its tributary Belle Fourche River drainage basin completely surround and includes the Black Hills upland region in western South Dakota and adjacent northeast Wyoming. The Cheyenne River originates west of the Black Hills in Wyoming and after reaching the Black Hills southwest margin flows in a southeast direction to the Black Hills south end and then turns to flow in a northeast direction to eventually join the south-oriented Missouri River. Note how many Cheyenne River tributaries both west and east of the Black Hills (and including those from the Black Hills) are oriented in a southeast direction. The Belle Fourche River also begins west of the Black Hills and flows in a northeast direction along the Black Hills northwest flank to the Black Hills north end and then turns to flow in southeast and east direction to join the northeast-oriented Cheyenne River. Note how the Belle Fourche River also has southeast-oriented tributaries. Detailed essays found under Cheyenne River and Belle Fourche River on the sidebar category list provide topographic map evidence suggesting the immense southeast-oriented ice-marginal melt water floods at one time flowed across what is now the Black Hills upland surface. The evidence suggests the Black Hills emerged as flood waters eroded the region. Emergence of what is today the 1000-meter plus high Black Hills upland region probably was caused by a combination of deep flood water erosion of the surrounding regions and of crust warping, perhaps related to the nearby thick ice sheet (and was perhaps delayed uplift related to the ice sheet weight) and/or perhaps due to the deep flood water of significant overlying bedrock.

• While not shown on the figure 3 map the north-facing Pine Ridge Escarpment is located near the South Dakota-Nebraska border and the White River-Niobrara River drainage divide is located approximately along the escarpment crest. The Pine Ridge Escarpment is approximately 300-meters high and separates the high plains to the south from the low plains to the north. West of the Pine Ridge Escarpment a similar north-facing Hat Creek Breaks Escarpment is the approximate location of the drainage divide between the Cheyenne River drainage basin to the north and Niobrara River drainage basin to the south. These north-facing escarpments are erosional landforms and their origin is explained in the detailed essays. Evidence presented in detailed essays found under Niobrara River and White River on the sidebar category list suggests the Pine Ridge Escarpment is the south wall of what was once a 300-meter deep White River valley which eroded headward from the previously mentioned large ice-walled and bedrock-floored canyon across the decaying ice sheet’s southwest margin to the Black Hills south end. Probably a major reason the deep White River valley was eroded along that alignment was the Black Hills were emerging as an upland region and southeast-oriented ice marginal flood waters were being channeled around the emerging upland north and south ends. The north wall of the 300-meter deep east-oriented White River valley was completely removed by southeast-oriented flood flow moving into the newly eroded White River valley. The low plains north of the Pine Ridge Escarpment and the Hat Creek Breaks Escarpment were eroded by the southeast-oriented ice-marginal flood flow moving to the newly eroded White River valley. The deep northeast-oriented Cheyenne River valley subsequently eroded headward across the southeast-oriented flood flow with the result that the Cheyenne River captured all southeast-oriented flood flow to the White River valley and now originates west of the Black Hills while the  White River headwaters in northwest Nebraska represent the final southeast-oriented flood flow route to the what had been the actively eroding White River valley.

Figure 4: Regional map showing major drainage routes in northeast South Dakota, southeast North Dakota, and western Minnesota. National Geographic Society map digitally presented using National Geographic Society TOPO software.

Figure 4 is a regional map of northeast South Dakota, southeast North Dakota, and a strip of western Minnesota. The south-oriented Missouri River is located near the figure 4 west edge. The south-oriented James River flows from Jamestown, North Dakota (near the figure 4 north center edge) to the figure 4 south center edge. Further east in the figure 4 southeast quadrant the Big Sioux River flows in a south direction through Watertown, South Dakota to the figure 4 south edge. Also in the figure 4 southeast quadrant the southeast-oriented Minnesota River flows from Big Stone Lake at Ortonville, South Dakota to the figure 4 east edge. In the figure 4 northeast quadrant the Red River is the north-oriented river flowing from Fargo to the figure 4 north edge and the Sheyenne River is the south-oriented river at Valley City, North Dakota (east of Jamestown) which makes a U-turn near Lisbon, North Dakota to flow in a northeast direction to join the north-oriented Red River near Fargo. The James River and Big Sioux River are Missouri River tributaries, the Minnesota River flows directly to the Mississippi River, and Red River water eventually reaches Hudson Bay. The north-south continental divide is located between the north-oriented Red River drainage basin and the south-oriented James River, Big Sioux River, and Minnesota River drainage basins. The Missouri River-Mississippi River drainage divide is located between the south-oriented Big Sioux River drainage basin and the southeast-oriented Minnesota River drainage basin. Through valleys shown in detailed essays found under James River and Big Sioux River on the sidebar category list provide evidence melt water floods once flowed across what are today major drainage divides.

• To understand the figure 4 drainage history first note the region between the Missouri River and the James River where no drainage routes are shown. That poorly drained region is known as the Missouri Coteau and appears on topographic maps to be an area covered by glacial moraine materials. There are many low hills and small lakes suggesting it might have been the location where a stagnant ice sheet containing significant quantities of debris slowly melted. The Missouri Coteau eastern margin is the east-facing 100-200 meter high Missouri Escarpment, which is located approximately where the southeast-oriented James River tributaries appear to begin. Second note the region between the south-oriented James River and the south-oriented Big Sioux River where no drainage routes are shown. That poorly drained region is the western half of the Prairie Coteau and also appears on topographic maps to be an area covered by glacial moraine materials. A similar region is found east of the Big Sioux River and south and west of the Minnesota River, and is the Prairie Coteau eastern half. The western Prairie Coteau boundary is the west-facing Prairie Coteau Escarpment and the northeastern Prairie Coteau boundary is the northeast-facing Prairie Coteau Escarpment. The Prairie Coteau area is an upland surface generally 100-200 meters higher than floors of the lowlands to the west and to the northeast. The James River today flows on the floor of the broad lowland located between the east-facing Missouri Escarpment and the west-facing Prairie Coteau Escarpment. The James River lowland on topographic maps does not appear to be covered by the same types of glacial moraine materials found on the Missouri Coteau and Prairie Coteau upland surfaces.

• The broad James River lowland is what remains of the gigantic ice-walled and bedrock-floored canyon carved by south-oriented melt water floods into the decaying ice sheet surface. The southeast-oriented lowland in which the Minnesota River is located was a southeast-oriented ice-walled and bedrock-floored canyon and the north-oriented lowland in the Red River flows was originated as an ice-walled and bedrock-floored tributary canyon to the southeast-oriented Minnesota River ice-walled and bedrock-floored canyon. The two ice-walled and bedrock-floored canyons intersected in southeast North Dakota and melt water floods were able to flow from one ice-walled and bedrock-floored canyon to the other. Late during the ice sheet melt down history flood waters in what was then the south-oriented Red River ice-walled and bedrock-floored canyon were beheaded and reversed when new outlets first to the Gulf of Saint Lawrence and later to Hudson Bay opened up. The melt water flood reversal in that Red River ice-walled and bedrock-floored canyon captured flood waters from the James River ice-walled and bedrock-floored canyon to the west. The Sheyenne River and Maple River U-turns located in southeast North Dakota provide evidence of the melt water flood flow capture and reversal (the Maple River is located directly north of the Sheyenne River and parallels the Sheyenne River route).  Probably for a time water also flowed in a north direction on the South Dakota figure 4 James River lowland floor to flow in a north direction in the Red River ice-walled and bedrock-floored canyon. Today the James River flows in south direction across the entire figure 4 map area so there must be an additional chapter, which is not given here.

• The final chapter in the figure 4 drainage history began as the south-oriented melt water floods were captured and diverted in a north direction in the large ice-walled and bedrock-floored canyon located where the Red River Valley is today. At that time deep east and northeast-oriented valleys were eroding headward across the detached ice sheet’s southwest margin and capturing massive southeast-oriented ice-marginal floods and diverting those ice-marginal floods into the deep ice-walled and bedrock-floored canyons which had chopped the decaying ice sheet up into a large number of detached ice sheet masses. The diversion of what had been massive south-oriented melt water floods from the Gulf of Mexico to the North Atlantic Ocean and Hudson Bay significantly altered Northern Hemisphere climates. When the melt water floods were flowing to the Gulf of Mexico flood waters displaced warm Gulf of Mexico waters which then moved north in the Atlantic Ocean to warm Northern Hemisphere climates. When the south-oriented melt water floods no longer displaced the warm Gulf of Mexico waters and instead displaced cold North Atlantic waters, the movement of cold water to the south cooled Northern Hemisphere climates. The resulting climate change stopped the ice sheet melting and caused north-oriented melt water floods to freeze on floors of the ice-walled and bedrock-floored canyons. What developed was for all practical purposes a thin ice sheet consisting of frozen melt water floods with rejuvenated thick ice sheet remnants embedded within them. The thin ice sheet did not deeply erode the underlying surface, although it did move some surface materials around. In time the thin ice sheet melted and while there were significant melt water floods, the thin ice sheet melt water floods were minor compared to melt water floods generated previously as the thick ice sheet rapidly melted. The present day James River route in figure 4 probably was established as the thin ice sheet melted.

Figure 5: Regional map showing major drainage routes in southeast South Dakota, southwest Minnesota, northwest Iowa, and northeast Nebraska. National Geographic Society map digitally presented using National Geographic Society TOPO software.

Figure 5 completes our tour of the South Dakota Missouri River drainage basin and is a regional map showing drainage routes in southeast South Dakota, southwest Minnesota, northwest Iowa, and a strip od northeast Nebraska. The Missouri River flows from Pierre, South Dakota (near the figure 5 west edge) in a generally southeast direction to Sioux City, Iowa (near the figure 5 south edge). The James River flows in a south direction from the figure 5 north center edge to Huron and Mitchell before joining the Missouri River near Yankton, South Dakota. Further east, near the South Dakota eastern border, the Big Sioux River flows in a south direction through Watertown, Brookings and Sioux Falls, South Dakota before joining the Missouri River near Sioux City, Iowa. South and west of the Missouri River is the east-oriented White River, which joins the southeast-oriented Missouri River south of Chamberlain, South Dakota. In northern Nebraska the Niobrara River makes an abrupt turn just south of Niobrara, Nebraska and flows in a north direction to join the Missouri River near the town of Niobrara. Note how the north-oriented Niobrara River segment is joined by a north-oriented Niobrara River tributary and is located south of south-oriented Missouri River tributaries and also south of the south-oriented James River route between Huron and Mitchell, South Dakota. Prior to headward erosion of the deep Missouri River valley south-oriented melt water floods emerging from the mouth of the giant James River ice-walled and bedrock-floored canyon flowed directly south across northeast Nebraska. The deep Missouri River valley eroded headward into the region and captured the south-oriented melt water floods. Headward erosion of the deep Missouri River valley beheaded the south-oriented flood flow across northeast Nebraska. Flood waters on north ends of the beheaded flood flow routes reversed flow direction to erode the north-oriented Niobrara River valley segment and the north-oriented Niobrara River tributary valley. Today the Missouri River valley size downstream from the Yankton, South Dakota area is much larger than it is further to the north and west. The reason for this valley size difference is the downstream valley was eroded in part by flood waters emerging from the gigantic James River ice-walled and bedrock-floored canyon.

• The White River valley probably eroded headward from the west wall of the south-oriented James River ice-walled and bedrock-floored canyon shortly after headward erosion of the deep Missouri River valley captured the immense south-oriented melt water river flowing on the canyon floor. At that time the entire region south and west of the detached ice sheet margin was at least as high the high plains located south of the north-facing Pine Ridge Escarpment, which extends into the figure 5 map area and which forms the approximate boundary between the White River drainage basin to the north and the Niobrara River drainage basin to the south. The lowering of base level caused by Missouri River valley headward erosion into the figure 5 map area enabled the 300-meter deep White River valley to erode headward across the southeast-oriented ice marginal floods (probably slightly behind the much shallower Niobrara River valley, which was also eroding headward to capture the same southeast-oriented ice-marginal floods). Headward erosion of the deep White River valley beheaded actively eroding southeast-oriented Niobrara River tributary valleys such as the Keya Paha River valley and the Ponca Creek valley (Ponca Creek is the unlabeled southeast-oriented Niobrara River tributary directly north of the Keya Paha River). Note how the Keya Paha River and Ponca Creek roughly parallel the southeast-oriented Missouri River route between the White River mouth and the Niobrara River mouth. That southeast-oriented Missouri River valley segment probably was initiated as a southeast-oriented tributary to south-oriented flood route across northeast Nebraska and was probably eroded headward at the same time the east-oriented White River valley eroded across the detached ice sheet southwest margin (just to the north). For a time flood waters probably flowed in both valleys with remnants of the detached ice sheet located between them. Detailed essays provide evidence of small detached ice sheet masses located between what were probably ice-walled and bedrock-floored canyons and deep ice-marginal valleys.

Introduction to Missouri River drainage basin research project essay series

• This Missouri River drainage basin in South Dakota landform origins overview essay and its related detailed essays is one of a series of overview essays and related detailed essays in the Missouri River drainage basin landform origins research project. The research project goal is to use topographic map evidence to describe the evolution of drainage divides separating each significant present day Missouri River tributary valley and also to describe the evolution of drainage divides separating the present day Missouri River drainage basin from adjacent drainage basins. Each overview essay and its related detailed essays pertains to a specific Missouri River tributary, tributary to a present day Missouri River tributary, or a present day Missouri River valley segment. Each detailed essay illustrates and discusses detailed topographic map evidence describing the evolution of a secondary drainage divide separating specified Missouri River tributary valleys.

• The Missouri River drainage basin research project introduces a new regional geomorphology paradigm. An essay titled “About the ‘thick ice sheet that melted fast’ geomorphology paradigm” provides a brief introduction to the new paradigm and how the new paradigm emerged. Detailed evidence illustrated and discussed in the Missouri River drainage basin research project builds a strong case for (1) deep glacial erosion of the North American continent by a thick North American ice sheet that created and occupied a deep “hole”, (2) rapid melting of that thick North American ice sheet, (3) immense floods of south-oriented melt water, (4) headward erosion of deep east, northeast and north-oriented valley systems to capture the south-oriented melt water floods and to divert the melt water further and further northeast into space the ice sheet had once occupied, (5) deep flood water erosion of the North American continent surface, and (6) crustal warping that resulted in uplift of mountain ranges as flood waters were deeply eroding what are now high mountain regions. This interpretation is fundamentally different from most previous interpretations. The Missouri River drainage basin in South Dakota landform origins evidence in this overview essay and its related detailed essays is presented for review and discussion by qualified research geomorphologists and geologists.

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.