A geomorphic history based on topographic map evidence

The Missouri River-James River drainage divide area in Charles Mix, Douglas, Hutchinson, Bon Homme, and Yankton Counties, South Dakota is located at the south end of the Missouri River-James River drainage divide area. Landforms are interpreted to have formed during immense floods when the margin of a rapidly melting thick North American ice sheet was located just north of the study region. The south-oriented James River lowland was eroded by immense south-oriented floods, which sliced a large south-oriented ice-walled and bedrock-floored valley into the decaying ice sheet surface. When headward erosion of the deep Missouri River valley first captured south-oriented James River lowland melt water floods, ice marginal flood waters flowed around the south end of the valley’s west ice wall to enter the south-oriented James River lowland and then flow south to the newly eroded Missouri River valley. Headward erosion of the deep Missouri River valley subsequently beheaded the northeast and east oriented flood flow route to the Jame River lowland, although south-oriented flood flow from further north continued to lower the James River lowland floor.

• The purpose of this essay is to use topographic map interpretation methods to explore Missouri River-James River drainage divide area landform origins in Charles Mix, Douglas, Hutchinson, Bon Homme and Yankton Counties, South 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 essays 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 Missouri River-James River drainage divide area landform evidence in Charles Mix, Douglas, Hutchinson, Bon Homme, and Yankton Counties, South Dakota 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.

Missouri River-James River drainage divide area location map

Figure 1: Missouri River-James 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 location map the Missouri River-James River drainage divide area discussed in the essay. South Dakota is the state occupying most of the figure 1 map area, Nebraska is the state south of South Dakota. Minnesota is the state seen along the northern third of the figure 1 east edge area and Iowa is the state south of Nebraska. The Missouri River flows southeast from the figure 1 northwest corner to the South Dakota-Nebraska state line and then serves as the South Dakota-Nebraska border all the way to the figure 1 southeast corner. The James River flows in a south-southeast and southeast direction from the figure 1 north center edge to Mitchell and then to join the Missouri River near Yankton in the figure 1 southeast quadrant. This essay addresses the southernmost Missouri River-James River drainage divide area located south of west to east oriented Interstate highway 90. More specifically the northernmost towns in the area illustrated and discussed here are from west to east are Bijou Hills, Corsica, and Dimock. The Missouri River forms the western and southern boundary and the James River represents the eastern boundary. Unnamed (on figure 1) southwest and south oriented Missouri River tributaries illustrated and discussed here include south and southwest oriented Platte Creek (flowing from White Lake to near Platte and to the Missouri River), Andes Creek (flowing from near Corisca to Lake Andes and the Missouri River), Choteau Creek (flowing from just east of Corisca to Wagner and the Missouri River), and Emmanuel Creek (flowing from near Tripp to the Missouri River near Springfield). Major landforms illustrated and discussed are the Missouri River valley and drainage divides between the various south- and southwest-oriented Missouri River tributaries. Evidence is interpreted in the context of an immense southeast-oriented flood. Based on evidence from hundreds of Missouri River drainage basin landform origins research project essay published on this website flood waters responsible for headward erosion of the Missouri River valley are interpreted to have been ice marginal melt water floods flowing along what was then the southern margin of a rapidly melting thick North American ice sheet, while flood waters responsible for erosion of the James River lowland came south in a large ice-walled and bedrock-floored valley, which had been sliced into the surface of a rapidly melting ice sheet located just north of the study area (see essays under James River on sidebar category list for example). The Missouri River valley and its various tributary valleys are interpreted to have eroded headward across the region to capture southeast-oriented ice marginal flood flow. Prior to headward erosion of the Missouri River flood waters were moving on a topographic surface at least as high as the highest figure 1 elevations today and were probably moving south into what is now Nebraska.

Missouri River-James River drainage divide area detailed location map

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

Figure 2 provides a somewhat more detailed location map for the Missouri River-James River drainage divide area illustrated and discussed here. Brule, Davison, Hanson, Charles Mix, Douglas, Hutchinson, Bon Homme, and Yankton are South Dakota county names and county boundaries are shown. Gregory and Boyd are Nebraska county names. The region immediately north of Charles Mix, Douglas, and Hutchinson Counties was described in the Missouri River-James River drainage divide area landform origins, Buffalo, Jerauld, Brule, and Aurora Counties essay (found under either James River or SD Missouri River on sidebar category list). The red shaded area in Charles Mix County is Yankton Indian Reservation land. Yankton is the city located on the Missouri River in Yankton County near the figure 2 southeast corner. The James River is located in the figure 2 east half and flows south-southeast in southwest Hanson County into Hutchinson County and then into Yankton County and finally joins the Missouri River near Yankton in the figure 2 southeast corner. The region immediately to the east was illustrated and described in the James River-Big Sioux River drainage divide area landform origins south of Mitchell and Sioux Falls essay (found under James River or Big Sioux River on sidebar category list). The Missouri River flows in a southeast direction from the figure 2 northwest quadrant and forms the Charles Mix County southwest boundary. The Niobrara River flows north to join the Missouri River at Niobrara, Nebraska, which is located where the Missouri River turns from flowing southeast to flowing east-northeast along the Bon Homme County southern border. The Niobrara River drainage basin is located south of the Missouri River in Nebraska and is described in essays under Niobrara River on the sidebar category list. This essay begins with figure 3 which shows the Bijou Hills area along the Brule County-Charles Mix County border in the figure 2 northwest quadrant. Figure 4 illustrates the Platte Creek-Pease Creek drainage divide area located in northwest Charles Mix County near the town of Geddes. Figure 5 depicts the Pease Creek-Andes Creek drainage divide area in the Lake Andes area. Figure 6 shows the region in southeast Charles Mix County where Choteau Creek (which flows south along the Charles Mix County-Bon Homme County border) joins the Missouri River. Figure 7 illustrates the Missouri River valley region just upstream from Yankton. Figure 8 is a big area map illustrating the Choteau Creek-Emmanuel Creek drainage divide area near Tripp located in southwest Hutchinson County. Figure 9 provides a detailed map of a through valley crossed by that Choteau Creek-Emmanuel Creek drainage divide. Figure 10 concludes with a map of the Choteau Creek headwaters area near Corsica in north central Douglas County.

Through valleys in Bijou Hills area

Figure 3: Through valleys in Bijou Hills area. United States Geological Survey map digitally presented using National Geographic Society TOPO software.

Figure 3 illustrates the Bijou Hills area and Missouri River valley along the Brule County-Charles Mix County border. The Missouri River is located in the figure 3 west edge area and is flooded by Lake Francis Case, which is a large reservoir impounded behind Fort Randall Dam (see figure 5). Normal reservoir pool elevation is 413 meters and elevations of the upland surface adjacent to the Missouri River valley are approximately 150 meters higher. The upland surface is an erosion surface eroded by immense southeast-oriented floods prior to headward erosion of the deep Missouri River valley. Note how the Bijou Hills area has one hilly area next to the Missouri River valley (where the word “Bijou” is) and another large hilly area further east (where the word “Hills” is located). Between the two Bijou Hills hilly areas is a through valley, the south end of which is today drained by southeast and south-southeast oriented Snake Creek, which flows to Academy Lake and the figure 3 south center edge (before flowing to the Missouri River south of the figure 3 map area). The through valley and Snake Creek valley are evidence that south-oriented water once flowed between the two hilly areas and eroded the region between the two Bijou Hills areas. The hill tops are approximately 75 meters higher than the through valley floor. At the time water first flowed on the route between the two hills the water was flowing on a topographic surface at least as high as the hill tops. Elevations east of the large Bijou Hills hilly area are even lower than the through valley floor and figure 3 map evidence suggests some water flowing around the east end of the eastern Bijou Hills upland flowed in a southeast direction to the Academy Lake area and then to Missouri River valley. Figure 3 evidence suggests an immense southeast-oriented flood moved across the entire map area on a topographic surface at least as high as the Bijou Hills highest elevations today and that flood waters lowered the surrounding region by at least 75-125 meters before headward erosion of the deep Missouri River valley beheaded the southeast-oriented flood flow further to the northwest (the Missouri River-James River drainage divide area Buffalo, Jerauld, Brule, and Aurora Counties essay illustrates and describes Missouri River valley regions northwest of this figure 3 map area).

Platte Creek-Pease Creek drainage divide area

Figure 4: Platte Creek-Pease Creek drainage divide area. United States Geological Survey map digitally presented using National Geographic Society TOPO software.

Figure 4 illustrates the Platte Creek-Pease Creek drainage divide area and is located southeast of the figure 3 map area (there is a gap between figures 3 and 4). The southeast-oriented Missouri River is located in the figure 4 southwest quadrant. Platte Creek is a southwest-oriented Missouri River tributary and can be seen in the figure 4 northwest corner. Note other southwest-oriented Missouri River tributaries including Cedar Creek, which flows to the Missouri River as a barbed tributary. Took Tay Hill near the Cedar Creek headwaters is approximately 175 meters higher than the Lake Francis Case normal pool elevation. Pease Creek is the south-southeast and south-southwest oriented Missouri River tributary located immediately east of the town of Geddes in the figure 4 east half. Note how Platte Creek has several northwest-oriented tributaries, including Edgerton Creek. Also note how northwest-oriented Edgerton Creek is linked by a broad shallow through valley with a southeast-oriented Pease Creek tributary (an abandoned railroad line is located in that valley and will be a reference line in figures 5, 6, and 7 below). Between the northwest-southeast oriented through valley and the present day Missouri River are higher elevation areas including Took Tay Hill. How did the northwest-southeast oriented through valley form and also why does Edgerton Creek flow in a northwest direction when the adjacent and much deeper Missouri River is flowing in a southeast direction? Prior to headward erosion of the deep Missouri River valley an immense southeast-oriented flood moved across the figure 4 map area on a topographic surface at least as high as the top of Took Tay Hill (if not higher). Flood waters were flowing in a large-scale southeast-oriented anastomosing channel complex with the northwest-southeast oriented Edgerton Creek-Pease Creek through valley being located on the alignment of one of those channels. The deep Missouri River valley then eroded northwest into the figure 4 map region and southwest-oriented tributary valleys eroded headward (in a northeast direction) to capture flood flow from adjacent channels. Headward erosion of the Pease Creek valley occurred first and captured flood flow from Edgerton Creek-Pease Creek through valley channel. Then as the Missouri River valley eroded further the Cedar Creek valley eroded  headward to capture southeast-oriented flood flow, but headward erosion of the Missouri River valley and its tributary Platte Creek valley soon beheaded flow to Cedar Creek and on the Edgerton Creek-Pease Creek through valley channel. Flood waters on the northwest end of the beheaded Edgerton Creek-Pease Creek through valley reversed flow direction to create the present day northwest-oriented Edgerton Creek valley.

• The southwest-oriented Missouri River tributaries may also be reflecting reversals of flood flow on northeast oriented flood flow routes beheaded by headward erosion of the deep Missouri River valley. Flood waters in this region had been flowing around the south end of the west wall of an immense south oriented ice-walled and bedrock-floored valley sliced into the surface of a rapidly melting North American ice sheet. The present day James River flows south on the floor of the former ice-walled and bedrock-floored valley, which drained to the southeast oriented Missouri River valley downstream from the Yankton, South Dakota area (the Missouri River valley downstream from Yankton is much than it is upstream). The floor of the ice-walled and bedrock-floored valley was significantly lower in elevation than ice marginal areas to the west and massive ice-marginal melt water floods flowed around the south end of the western ice wall into the much deeper south and southeast oriented James River lowland valley. Some of those flood waters were flowing northeast and east in the figures 3, 4, and 5 map areas. Headward erosion of the deep Missouri River valley beheaded the northeast and east oriented flood flow routes. Flood waters on the southwest ends of those beheaded flood flow routes reversed flow direction to create present day southwest-oriented Missouri River tributaries (such as Platte Creek). Further east the flow reversals became more south oriented as seen in figures below.

Through valleys in Lake Andes area

Figure 5: Through valleys in Lake Andes area. United States Geological Survey map digitally presented using National Geographic Society TOPO software.

Figure 5 illustrates the Pease Creek-Garden Creek drainage divide near Lake Andes and located southeast of the figure 4 map area (and includes overlap areas with figure 4). The Missouri River is located in the figure 5 southwest quadrant and Fort Randall Dam is located in the figure 5 south center edge area. South and south-southwest oriented Pease Creek is located in the figure 5 northwest quadrant. Garden Creek flows northeast and then southeast in the region immediately west of the town of Lake Andes and then flows south in the large valley through valley linking Lake Andes with the Missouri River valley. Note the northwest-southeast oriented through valley located northwest of the town of Lake Andes (the abandoned railroad is located in the through valley). The through valley links the south and south-southwest oriented Pease Creek valley with the large south-oriented valley located south of the town of Lake Andes. The through valley is additional evidence a large southeast oriented flood moved across the region prior to deep Missouri River valley headward erosion. Again, to explain the figure 5 landscape features it is necessary to begin with flood waters moving across the entire figure 5 map area on a topographic surface at least as high as the highest figure 5 elevations today. Again, elevations of hill tops between the Pease Creek-Garden Creek through valley and the present day Missouri River valley are approximately 175 meters higher than the normal Lake Francis Case pool elevation. Flood waters lowered the surrounding figure 5 landscape from that initial high level topographic surface to the landscape surface seen today as the deep Missouri River valley was eroding headward into the figure 5 map region. The south-oriented valley at Lake Andes was eroded headward as one of two deep anastomosing channels that eroded headward when headward erosion of the Missouri River valley reached the present day Fort Randall Dam area. The other deep channel that eroded headward was of course the present day deep Missouri River valley. Headward erosion of the south-oriented valley at Lake Andes captured southeast oriented flood flow in the northwest-southeast oriented Pease Creek-Garden Creek through valley channel. Subsequently, headward erosion of the Missouri River valley-Pease Creek valley beheaded southeast oriented flood flow in the Pease Creek-Graden Creek through valley. At the same the southwest-oriented valley now partially filled with water to form Lake Andes eroded to the northeast to capture flood waters from southeast- and east-oriented flood flow routes further north. Headward erosion of this southwest-oriented Lake Andes valley beheaded flood flow that was moving southeast in PLAIN CENTER township, roughly along the route of the abandoned railroad line. Figure 6 below illustrates where that water had been going.

Missouri River and Choteau Creek valley area

Figure 6: Missouri River and Choteau Creek valley area. United States Geological Survey map digitally presented using National Geographic Society TOPO software.

Figure 6 illustrates where south oriented Choteau Creek enters the Missouri River and is located southeast of the figure 5 map area and there is no overlap with figure 5. The southeast oriented Missouri River is located in the figure 6 southwest quadrant. Choteau Creek is the southeast and south oriented  Missouri River tributary located in the figure 6 east half and joins the Missouri River just south of the figure 6 map area. Dry Choteau Creek is the south oriented Choteau Creek tributary which forms the Charles Mix-Bon Homme County border. Avon is the town located in the figure 6 northeast corner area and the abandoned railroad line seen in figure 5 is the abandoned railroad line in the figure 6 northeast quadrant (and passing through Avon). The abandoned railroad is located in the northwest-southeast oriented through valley seen in figure 5. Hills located between the northwest-southeast oriented through valley and the present day Missouri River valley are approximately 125 meters higher than the Missouri River valley floor and approximately 75 meters higher than the through valley floor. Figure 6 map area evidence, like evidence in previous figure map areas, can best be explained in the context of an immense southeast-oriented flood, which initially flowed on a topographic surface at least as high (if not higher) than the highest figure 6 elevations today. Flood waters were flowing in multiple southeast-oriented anastomosing channels as the deep Missouri River valley eroded headward into the figure 6 map region. Water still had to be crossing the ridge of hills between the northwest-southeast oriented through valley and the present day Missouri River valley location when headward erosion of the deep Missouri River valley entered the region and the south-oriented Choteau Creek valley eroded headward from the newly eroded Missouri River valley to capture southeast-oriented flood flow from north of the hilly ridge. As the Missouri River valley continued to erode in a northwest direction additional south- and southwest-oriented tributary valleys eroded headward to capture southeast-oriented flood flow north of the hilly ridge and creating the present day drainage pattern and landscape features.

Through valleys in Gavins Point Dam and Yankton area

Figure 7: Through valleys in Gavins Point Dam and Yankton area. United States Geological Survey map digitally presented using National Geographic Society TOPO software.

Figure 7 illustrates through valleys in the Gavins Point Dam and Yankton area and is located east of the figure 6 map area and there is no overlap with previous figures. Lewis and Clark Lake is the reservoir impounded behind Gavins Point Dam on the east-oriented Missouri River located in the figure 7 south half. Yankton is the city located in the figure 7 southeast corner. The south-southeast oriented James River is located along the north half of the figure 7 east edge area. Beaver Creek is the James River tributary which begins in the figure 7 northwest quadrant and flows southeast, northeast, southeast, northeast, and southeast to join the James River in the figure 7 northeast quadrant. South of Beaver Creek, along the north margin of the hilly area in the figure 7 south center is northeast and southeast oriented Marne Creek, which flows to the Missouri River at Yankton. Tabor is the small town located in the figure 7 west center area and south of Tabor is southwest-oriented Charley Creek. Just a short southeast of Charley Creek is a parallel unnamed southwest-oriented stream, which flows along the hilly area northwest edge to also join the Missouri River as a barbed tributary. The abandoned railroad line seen in figures 5 and 6 is located between Tabor and Napa Junction northwest of Yankton and has been following the northwest-southeast oriented through valley located northeast (and east) of and parallel to the present day Missouri River valley. Again there is a high hilly area located between the east-oriented through valley and the east-oriented Missouri River valley. Figure 7 evidence strongly suggests that prior to headward erosion of the deep Missouri River valley across the hilly area in the figure 7 south center region large volumes of flood water flowed northeast into the Tabor area and then northeast, east, and southeast to the James River valley area (downstream from the Yankton area the Missouri River valley is much wider and larger than it is upstream-see James River-Big Sioux River drainage divide area south of Mitchell and Sioux Falls essay). Headward erosion of the deep Missouri River valley across the present day hilly area beheaded the northeast-oriented flood flow. Flood waters on the southwest ends of the beheaded flood flow route reversed flow direction to erode the present day southwest oriented Charley Creek and parallel unnamed stream valleys. Northeast-oriented Beaver Creek valley segments are probably northeast-oriented flood flow relics. Southeast-oriented Beaver Creek valley segments probably are relics of southeast-oriented flood flow that probably was coming south along the floor of what was an immense south-oriented James River lowland ice-walled and bedrock-floored valley to the north.

Choteau Creek-Emmanuel Creek headwaters through valley

Figure 8: Choteau Creek-Emmanuel Creek headwaters through valley. United States Geological Survey map digitally presented using National Geographic Society TOPO software.

Figure 8 illustrates the Choteau Creek-Emmanuel Creek drainage divide area near Tripp and is located north and slightly west of figure 7 and north and slightly east of figure 6. There is no overlap with either figure 6 or 7. The south-southeast oriented stream located south of Tripp is Emmanuel Creek, which flows to the Missouri River near Springfield (located between figures 6 and 7-see figures 1 and 1). The northwest-oriented stream adjacent to the old railroad grade in the figure 8 northwest quadrant is a tributary to south oriented Choteau Creek, which is located west of the figure 8 map area. Note how the Emmanuel Creek headwaters and Choteau Creek tributary headwaters flow in opposite directions in the same through valley. That through valley is seen in more detail in figure 9 below. East and southeast oriented streams in the figure 8 northeast quadrant and east center area are James River tributaries, which flow to the south and southeast oriented James River, which is located east of the figure 8 map area. The lowland on which those east and southeast oriented James River tributaries flow is the James River lowland. Note the northwest-southeast oriented slope or low escarpment, which marks the James River valley lowland west and southwest margin. Also note the northwest-facing escarpment in the figure 8 west center area. That northwest-facing escarpment is the southeast wall of a large east and northeast oriented through valley linking the present day southeast-oriented Missouri River valley with the south-southeast oriented James River valley. Today that through valley is drained by various south- and southwest-oriented Missouri River tributaries including Choteau Creek (seen in figure 6) and Platte Creek (seen in figure 4). Note how the floor of that east and northeast oriented through valley is higher in elevation than south-southeast oriented James River lowland floor. This evidence suggests large volumes of flood water moved northeast and east from the Platte Creek area to the James River valley area prior to headward erosion of the deep Missouri River valley into the figure 4 map area. Probably at that time the Missouri River valley head was still located in the Yankton area and it was receiving immense volumes of south-oriented flood flow from the south-oriented ice-walled and bedrock-floored James River lowland valley which had been sliced into the surface of a rapidly melting North American ice sheet just to the north. Southeast-oriented ice marginal floods moved northeast and east into the south end of that south-oriented James River lowland and then south to the actively eroding Missouri River valley. At the same time immense southeast-oriented floods were moving directly across the region south of figure 8 and in time eroded the Missouri River valley headward to behead the northeast and east oriented flood flow route into the figure 8 map area. Flood waters on the southwest of that beheaded flood flow eroded the southwest-oriented Platte Creek valley. Following beheading of the northeast and east oriented flood flow south-oriented flood flow continued to erode the James River lowland area, which accounts for the lower elevation of that region today.

Detailed map of Choteau Creek-Emmanuel Creek headwaters through valley

Figure 9: Detailed map of Choteau Creek-Emmanuel Creek headwaters through valley. United States Geological Survey map digitally presented using National Geographic Society TOPO software.

Figure 9 provides a detailed map of the Choteau Creek tributary-Emmanuel Creek headwaters area seen in less detail in figure 8 above. Note the old railroad grade extending in a southeast direction from the figure 9 northwest corner area to Tripp near the figure 9 east edge. That railroad grade is located in a northwest-southeast oriented through valley. The northwest end of that through valley is today drained by a northwest-oriented Choteau Creek tributary. West of the figure 9 map area the tributary eventually flows to south-oriented Choteau Creek, which flows to the Missouri River (see figure 6). The southeast end of the through valley is drained by headwaters of south-oriented Emmanuel Creek, which flows to the figure 9 southeast corner area. South of the figure 9 map area Emmanuel Creek flows south to join the Missouri River near Springfield, which is located between the figure 6 and figure 7 locations (see figures 1 and 2). The through valley is evidence large volumes of water once flowed in a southeast direction to the Emmanuel Creek valley. That southeast-oriented flood flow was then beheaded by headward erosion of the south-oriented Choteau Creek valley. Flood waters on the northwest end of the beheaded flood flow route then reversed flow direction to flow in a northwest direction to the newly eroded south-oriented Choteau Creek valley. This sequence of events is consistent with the sequence of events which would be expected if headward erosion of the Emmanuel Creek and Choteau Creek valleys was related to headward erosion of the Missouri River valley. The Emmanuel Creek valley should have eroded north first to capture northeast and east oriented flood flow to what was then the south-southeast oriented James River valley and to divert the flood water south to the newly eroded Missouri River valley. Next, as the Missouri River valley eroded headward it would have been possible for the Choteau Creek valley to erode north to capture the northeast and east oriented flood flow and to behead flood flow routes like this flood flow route to the Emmanuel Creek valley. This process was repeated multiple times as the Missouri River valley eroded northwest and north into South Dakota.

Choteau Creek-Twelvemile Creek drainage divide area

Figure 10: Choteau Creek-Twelvemile Creek drainage divide area. United States Geological Survey map digitally presented using National Geographic Society TOPO software.

Figure 10 illustrates the Choteau Creek-Twelvemile Creek drainage divide northeast of Corsica and northwest of the figure 8 map area (there is no overlap with previous figures). Corsica is the town in the figure 10 southwest corner. Choteau Creek originates in Aurora Township in the figure 10 northwest quadrant and flows south before turning to flow east to Garfield Township. In Garfield Township Choteau Creek turns to again flow south to the figure 10 south edge. The northwest-oriented Choteau Creek tributary observed in figures 8 and 9 joins Choteau Creek south of the figure 10 map area. Twelvemile Creek originates in Baker Township in the figure 10 center north area and flows southeast, northeast, southeast, and northeast to reach the figure 10 east edge. East of figure 10 Twelvemile Creek turns to flow southeast again and flows to the south-southeast oriented James River, which is located east of the figure 10 map area. The South Fork Twelvemile Creek is located south of Twelvemile Creek and flows southeast into Washington Township and then turns to flow northeast to the figure 10 east edge. The southeast and northeast oriented Twelvemile Creek valley segments in the figure 10 northeast quadrant are located on the James River lowland floor. The Choteau Creek headwaters area is located on the higher elevation northeast and east oriented broad through valley linking the present day Missouri River valley with the present day James River valley. As previously stated the northeast and east oriented through valley was probably used by ice marginal flood waters prior to headward erosion of the deep Missouri River valley (beyond the present day Yankton area). These flood waters were flowing around the south end of the west ice wall of the ice-walled and bedrock-floored James River lowland valley. Headward erosion of the deep Missouri River valley into and beyond the figure 3 and 4 map areas beheaded the northeast and east oriented flood flow routes to the figure 10 map area, however south-oriented flood waters continued to move south in the large James River lowland ice-walled and bedrock-floored valley to the north. That continued south-oriented flood flow was responsible for eroding the James River lowland valley floor lower than the northeast and east oriented flood flow route floor coming from the southwest.

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.