Abstract:

The Little Sioux River-North Raccoon River drainage divide area in Cherokee, Buena Vista, and Sac Counties, Iowa was eroded during immense south oriented floods from a rapidly melting North American ice sheet. Initially the melt water floods flowed across Cherokee, Buena Vista, and Sac Counties in a southeast direction toward what was then an actively eroding North Raccoon River valley, which was eroding headward from what were then newly eroded Raccoon and Des Moines River valleys. The Des Moines River valley had eroded headward from the south oriented Mississippi River valley. Headward erosion of the south- and southwest-oriented Maple River valley from what was then an actively eroding Missouri River valley beheaded and reversed southeast-oriented flood flow to North Raccoon River tributaries and shortly thereafter headward erosion of the south-southwest, west, and southwest oriented Little Sioux River valley (also from the actively eroding Missouri River valley) beheaded and reversed all southeast-oriented flood flow to what had been actively eroding Maple River, North Raccoon River, and tributary valleys. This essay illustrates and discusses topographic map evidence supporting this flood origin interpretation, which includes barbed tributaries, elbows of capture, valley orientations, and through valleys crossing drainage divides.

Preface:

The following interpretation of detailed topographic map evidence is one of a series of essays describing similar evidence for all major drainage divides contained within the Missouri River drainage basin and for all major drainage divides with adjacent drainage basins. The research project is interpreting evidence in the context of a previously unexplored deep glacial erosion paradigm, which is fundamentally different from most commonly accepted North American glacial history interpretations. Project essays available at this site may be found by selecting desired Missouri River tributaries and/or states from this essay’s sidebar category list.

Introduction:

• The purpose of this essay is to use topographic map interpretation methods to explore the Little Sioux River-North Raccoon River drainage divide area landform origins in Cherokee, Buena Vista, and Sac Counties Iowa, 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 essays in the Missouri River drainage basin landform origins research project 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 Little Sioux River-North Raccoon River drainage divide area landform evidence in Cherokee, Buena Vista, and Sac Counties, Iowa will be regarded as evidence supporting the “thick ice sheet that melted fast” paradigm (see menu at top of page for paradigm related essay). This essay is included in the Missouri River drainage basin landform origins research project essay collection.

Location map for Little Sioux River-North Raccoon River drainage divide area

Figure 1: Location map for Little Sioux River-North Raccoon River drainage divide area (select and click on maps to enlarge). National Geographic Society map digitally presented using National Geographic Society TOPO software. 

Figure 1 illustrates a region in northwest Iowa and provides a location map for the Little Sioux River-North Raccoon River drainage divide area. The Big Sioux River flows in a south direction from the figure 1 north edge (near northwest corner) to join the southeast and south-southeast oriented Missouri River at Sioux City, Iowa (in the figure 1 west center area). West of the Big Sioux River is the state of South Dakota and south and west of the Missouri River is the state of Nebraska. The Little Sioux River flows in a south direction from the figure 1 north center edge to Spencer and Sioux Rapids. At Sioux Rapids the Little Sioux River turns to flow in a west and west-northwest direction before turning again to flow in a south-southwest direction to join the Missouri River at Little Sioux, Iowa (near figure 1 south edge). The North Raccoon River begins a short distance east of Sioux Rapids and flows in a southwest direction until it is south of Sioux Rapids (where the Little Sioux River turns from flowing in a south direction to flowing in a west direction). Once south of Sioux Rapids the North Raccoon River turns to flow in a south-southeast and southeast direction to flow to the figure 1 south edge (near the figure 1 southeast corner). South of the figure 1 map area the North Raccoon River joins other streams to form the east-oriented Raccoon River, which joins the southeast-oriented Des Moines River at Des Moines, Iowa (south and east of figure 1). The Des Moines River flows from the figure 1 north edge (slightly east of center) in a south-southeast direction to the figure 1 southeast corner area. From Des Moines the Des Moines River flows in a southeast direction to join the Mississippi River. The Little Sioux River-North Raccoon River drainage divide is then also the Missouri River-Mississippi River drainage divide. The Little Sioux River-North Raccoon River drainage divide area discussed in this essay is located south and east of the Little Sioux River segment extending from Sioux Rapids to Cherokee and west of the North Raccoon River from its headwaters to near Newell. The Floyd River-Little Sioux River northern drainage divide area and also the Floyd River-Little Sioux River drainage divide area in Woodbury and Monona Counties, Iowa are located north, west, and southwest of the region discussed here and essays related to those drainage divide areas can be found under Iowa on the sidebar category list.

• Figure 1 drainage routes were established by headward erosion of deep valleys along and across immense south oriented melt water floods, which flowed across the entire figure 1 map area. Flood waters were derived from a rapidly melting North American ice sheet, which at the time the figure 1 drainage routes were established was located near or just north of the figure 1 north edge. Initially flood waters flowed in a southeast or south-southeast direction toward the south-oriented Mississippi River valley (located east of the figure 1 map area). Headward erosion of the deep south-southeast oriented Missouri River valley altered flood flow routes and deep south-southwest oriented tributary valleys eroded headward across the southeast and south-southeast oriented flood flow routes. Note in figure 1 how the Little Sioux River flows in a southeast direction near Spencer and then turns to flow in a south direction to reach Sioux Rapids. At Sioux Rapids the Little Sioux turns to flow in a west and west-northwest direction before joining an unnamed south-southeast oriented tributary and then flowing in a south-southwest direction to the Missouri River. What has happened is headward erosion of the south-southwest oriented Little Sioux River valley captured a south-southeast oriented flood flow route, which had been supplying flood water to what was then the actively eroding North Raccoon River valley. The west-northwest oriented valley was eroded by a reversal of flood flow and the west-oriented Little Sioux River valley segment eroded headward to capture another south- and southeast-oriented flood flow route, which also was supplying flood flow to the actively eroding North Raccoon River valley. These captures beheaded all flood flow routes to the actively eroding North Raccoon River valley and diverted the flood waters to the newly eroded Missouri River valley. Topographic maps better illustrate the flood capture evidence.

Detailed location map for Little Sioux River-North Raccoon River drainage divide area

Figure 2: Detailed location map for Little Sioux River-North Raccoon River drainage divide area. United States Geological Survey map digitally presented using National Geographic Society TOPO software.

Figure 2 provides a somewhat more detailed location map for the Little Sioux River-North Raccoon River drainage divide area. Iowa county names and boundaries are shown. The south-southeast oriented Missouri River crosses the figure 2 southwest corner. The Little Sioux River flows in a south-southwest direction from the figure 2 north edge to Sioux Rapids near the Buena Vista County north center border. From Sioux Rapids the Little Sioux River meanders in a west and west-northwest direction into the O’Brien County (north of the Cherokee County) southeast corner and then turns to flow in a south-southwest direction across Cherokee and Woodbury Counties to join the Missouri River south of the figure 2 south edge. In western Buena Vista County Brooke Creek is a north-northwest oriented Little Sioux River tributary and joins the Little Sioux River near where it turns to flow in a west-northwest direction. Note in the O’Brien County southeast corner (north of the Cherokee County northeast corner) how a south-southeast oriented tributary joins the Little Sioux River at the point where the Little Sioux River turns to flow in a south-southwest direction. What has happened in the O’Brien County southeast corner is headward erosion of the deep south-southwest oriented Little Sioux River valley captured a major south-southeast flood flow route and diverted the flood water in a south-southwest direction to the newly eroded Missouri River valley. Flood waters on the north-northwest end of the beheaded flood flow route reversed flow direction to erode the west-northwest oriented Little Sioux River valley segment and also the north-northwest oriented Brooke Creek valley. The Little Sioux River valley then eroded headward to capture more south and south-southeast oriented flood flow routes. East of the south-southwest oriented Little Sioux River in Cherokee County is the south-oriented Maple River, which flows into Ida County and then turns to flow in a southwest direction to enter the Missouri River valley (south of where the Little Sioux River enters the Missouri River valley). Headward erosion of the deep Little Sioux River valley beheaded all south and south-southeast oriented flood flow routes to what had been the actively eroding Maple River valley.

• The North Raccoon River begins in the Buena Vista County northeast corner and flows in a southwest direction until it is south of Sioux Rapids, where it turns to flow in a south-southeast, south, and southeast direction to the figure 2 southeast corner area. Note the northwest-oriented Little Sioux River tributary in southeast Clay County (directly north of the Buena Vista County northeast corner). That northwest-oriented Little Sioux River tributary valley was eroded by a reversal of flood water on the northwest end of a flood flow route beheaded by Little Sioux River valley headward erosion. Prior to being captured the southeast-oriented flood flow had been moving to what was at that time the actively eroding North Raccoon River valley. Note also the southeast-oriented North Raccoon River tributary flowing through Storm Lake located in the Buena Vista County south center area and how Storm Lake is directly south of the north-northwest oriented Brooke Creek headwaters. Prior to being beheaded and reversed (by Little Sioux River valley headward erosion) south-southeast-oriented flood flow on the Brooke Creek alignment had been flowing to Storm Lake and then to the North Raccoon River. In Sac County (south of Buena Vista County) south and south-southwest oriented Boyer River headwaters are present. Prior to headward erosion of southeast-oriented North Raccoon River tributary valley through Storm Lake the south-southeast oriented flood flow had been moving into Sac County to the actively eroding Boyer River valley. Additional details will be visible and noted.

North Raccoon River headwaters area

Figure 3: North Raccoon River headwaters area. United States Geological Survey map digitally presented using National Geographic Society TOPO software.

Figure 3 provides a reduced size topographic map of the North Raccoon River headwaters area. The Little Sioux River flows in a southwest direction from the figure 3 north center edge area and joins east-southeast oriented Willow Creek (unnamed in figure 3). Downstream from the Willow Creek confluence the Little Sioux River makes a jog to the southeast before turning in a south-southwest direction to flow to Sioux Rapids. Upon reaching the Sioux Rapids area the Little Sioux River “meanders” in northwest and southwest directions as it flows to figure 3 west edge. Laurens is the town located near the figure 3 southeast corner. Between Laurens and Sioux Rapids is the smaller town of Marathon, which will be seen again in figure 4. Northwest of Laurens is Pickerel Lake, which is located next to the corner of Buena Vista, Clay, Palo Alto, and Pocahontas Counties. North of Pickerel Lake are headwaters of an east-oriented stream, which flows to Rush Lake and then eventually to the south-southeast and southeast oriented Des Moines River. Just west of Pickerel Lake in northeast Buena Vista County are headwaters of a south-southwest oriented stream. That stream is the North Raccoon River. The south-southeast oriented stream just north of Laurens is Cedar Creek, which south of the figure 3 map area flows to the North Raccoon River. Also note in Clay County, just north of the North Raccoon River headwaters north-northwest oriented Montgomery Creek, which flows to the Little Sioux River as a barbed tributary. Further note the presence of several other northwest-oriented Little Sioux River tributaries, which while shorter than Montgomery Creek are also barbed tributaries. These northwest-oriented tributaries are flowing in valleys eroded by reversals of multiple southeast-oriented flood flow channels which were beheaded by headward erosion of the deep Little Sioux River valley. Headward erosion of the deep Little Sioux River valley captured the southeast-oriented flood flow routes, which had been moving flood waters to actively eroding Des Moines River tributary valleys, and diverted the flood flow to newly eroded Missouri River valley.

Little Sioux River-North Raccoon River drainage divide area east of Sioux Rapids

Figure 4: Little Sioux River-North Raccoon River drainage divide area east of Sioux Rapids. United States Geological Survey map digitally presented using National Geographic Society TOPO software.

Figure 4 is a reduction of a more detailed topographic map of the Little Sioux River-North Raccoon River drainage divide area east of Sioux Rapids. Note in the northeast corner the Clay County-Buena Vista County boundary along the first section line south of the figure 4 north edge. The Little Sioux River is located in the deep valley seen in the figure 4 northwest quadrant and is flowing in a south and west direction to eventually reach the Missouri River. Marathon is the small town straddling the figure 4 east edge just north of the southeast corner. The North Raccoon River flows from the figure 4 east edge (near where the Clay -Buena Vista County line crosses the east edge) in a south-southwest and southwest direction to the figure 4 south edge. Near the south edge the North Raccoon River is remarkably straight suggesting the present day channel is not the original channel. However, the altered channel is located in the valley eroded by North Raccoon River valley headward erosion. Note the northwest-oriented Little Sioux River tributaries in sections 8, 9, and 10 east of Sioux Rapids. Those northwest-oriented tributaries are flowing in northwest-oriented valleys linked by through valleys with the southwest-oriented North Raccoon River valley, which south of the figure 4 map area turns to drain in a south and south-southeast direction. The map contour interval is ten feet and the through valleys are defined by at least 4 contour lines on each side (and more to the northeast). The through valleys provide evidence of southeast-oriented flood flow channels captured by Little Sioux River valley headward erosion. Prior to the capture the southeast-oriented flood flow was moving to what was then the actively eroding North Raccoon River valley. Headward erosion of the deep Little Sioux River valley beheaded and reversed the flood flow channels and the reversed flood waters eroded the northwest-oriented Little Sioux River tributary valleys. When viewing the figure 4 map remember the Little Sioux River-North Raccoon River drainage divide is the drainage divide between southwest-oriented streams flowing to the Missouri River and southeast-oriented streams flowing to the Mississippi River. Figure 4 evidence demonstrates Little Sioux River valley headward erosion captured southeast-oriented flood flow routes flowing to the Mississippi River valley.

Fox Run-North Raccoon River drainage divide area

Figure 5: Fox Run-North Raccoon River drainage divide area. United States Geological Survey map digitally presented using National Geographic Society TOPO software.

Figure 5 provides a topographic map of the Fox Run-North Raccoon River drainage divide area located south and west of the figure 3 map area and includes overlap areas with figure 3. The west-oriented Little Sioux River meanders across the figure 5 north edge. Sioux Rapids is the town straddling the north edge somewhat east of center. The north oriented Little Sioux River tributary in the figure 5 west half, flowing from the figure 5 south edge to join the Little Sioux River near the figure 5 northwest corner is Brooke Creek. The north and northwest-oriented Little Sioux River tributary located just east of Brooke Creek is Fox Run. The North Raccoon River flows in a southwest and south direction from the figure 5 east center edge area to the figure 5 south edge (east half). Note southeast-oriented North Raccoon River tributary valleys. Significant sections of the North Raccoon River and also of some tributaries appear to be flowing in human constructed channels, although the valleys were eroded prior to human intervention. Note how in the figure 5 center area a northwest-southeast oriented through valley links the Fox Run valley with the valley of a southeast-oriented North Raccoon River tributary. The map contour interval is ten meters and the through valley is defined by at least two contour lines on each side. Rembrandt is the small town located just east of the figure 5 center and north of Rembrandt another through valley links north-northwest oriented Soldier Creek with another southeast-oriented North Raccoon River tributary. These through valleys provide further evidence of multiple southeast-oriented flood flow channels which were captured by headward erosion of the deep Little Sioux River valley. Flood waters on the northwest ends of the beheaded flood flow routes reversed flow direction to erode the northwest-oriented Fox Run and Soldier Creek valleys. The north-oriented Brooke Creek and Fox Run valleys were also eroded by reversals of south-oriented flood flow routes to southeast-oriented North Raccoon River tributary valleys located south of the figure 5 map area and explains why in the figure 5 west half the streams flow in a north direction while in the east half the streams are flowing in a south direction.

Detailed map of Fox Run-North Raccoon River drainage divide area

Figure 6: Detailed map of Fox Run-North Raccoon River drainage divide area. United States Geological Survey map digitally presented using National Geographic Society TOPO software.

Figure 6 provides a reduction of a detailed topographic map of the Fox Run-North Raccoon River drainage divide area seen in less detail in figure 5 above. Rembrandt is the town located just east of the figure 6 north center edge area. Fox Run flows in a north direction near the figure 6 west edge. The North Raccoon River meanders in a south direction near the figure 6 east edge and for significant distances is flowing in human constructed channels. A southeast-oriented North Raccoon River tributary originates in the northeast corner of section 4 (west of Rembrandt) and after flowing in human constructed channels joins the North Raccoon River in section 17 (in figure 6 southeast quadrant). The southeast-oriented North Raccoon River tributary is linked by a northwest-southeast-oriented through valley in sections 32 and 33 with the north oriented Fox Run valley. The map contour interval is ten feet and the through valley floor elevation is between 1320 and 1330 feet. Hills on either side of the through valley rise to elevations greater than 1390 feet, although the 1390 plus elevations are separated by a distance of approximately four miles (sections shown in figure 6 are one mile square). The map evidence suggests not only is the through valley 70-80 feet deep, but it is several miles across. This through valley provides evidence of a major southeast-oriented flood flow route that at one time supplied flood water to the North Raccoon River valley. As already noted the North Raccoon River water eventually reaches the Des Moines River, which flows directly to the Mississippi River. Southeast-oriented flood flow in the through valley was beheaded and reversed by headward erosion of the deep Little Sioux River valley to create the north and northwest-oriented Fox Run valley. And as already noted the Little Sioux River drains to the Missouri River. In other words, Little Sioux River valley headward erosion from what was then the newly eroded Missouri River valley captured southeast-oriented flood water moving to the Mississippi River valley and in the process created what is today the Missouri River-Mississippi River drainage divide (in sections 32 and 33).

Little Sioux River-Maple River drainage divide area

Figure 7: Little Sioux River-Maple River drainage divide area. United States Geological Survey map digitally presented using National Geographic Society TOPO software.

Figure 7 provides a reduced size topographic map of the Little Sioux River-Maple River drainage divide area and includes overlap areas with figures 3 and 5. Cherokee is the larger town located in the figure 7 southwest quadrant. Sioux Rapids is located in the northeast quadrant. The Little Sioux River flows in a south-southwest, west, west-northwest, and south-southwest direction from the figure 7 northeast corner region to the figure 7 southwest corner region. Note south- and southeast-oriented Little Sioux River tributaries in the figure 7 west edge area. Mill Creek is the larger southeast-oriented tributary joining the Little Sioux River at Cherokee and Gray Creek is the south-oriented tributary joining the Little Sioux River in the same region. Brooke Creek is the north-oriented tributary joining the Little Sioux River in the figure 7 north center area. South of the Brooke Creek headwaters note headwaters of southeast-oriented Powell Creek, which flows to the figure 7 south edge (Powell Creek will be seen again in figure 9 and is a North Raccoon River tributary). North and northwest oriented Fox Run can be seen just east of Brooke Creek. The southwest and south oriented North Raccoon River is located in the figure 7 east center and southeast quadrant areas. The south-southwest and south oriented stream directly east of the Little Sioux River in the Cherokee region is the Maple River. Alta is the town located near the figure 7 south center edge and Aurelia is the smaller town located midway between Alta and Cherokee. The south-southwest and west oriented Maple River tributary joining the Maple River near Aurelia is Maple Creek. Note how both the Maple River and Maple Creek originate and flow in the region between north-oriented Brooke Creek and the south-southwest oriented Little Sioux River. Note the northwest-oriented Maple Creek tributary flowing between Aurelia and Alta. As seen in figures 1 and 2 south of the figure 7 map area the Maple River flows in a south and southwest direction to join the Missouri River. Headward erosion of the Maple River valley from the newly eroded Missouri River valley occurred slightly in advance of Little Sioux River valley headward erosion. Maple River valley headward erosion captured the southeast-oriented flood flow first and beheaded and reversed flood flow routes to create northwest-oriented tributary valleys. Little Sioux River valley headward erosion soon thereafter beheaded all flood flow routes to the actively eroding Maple River valley and by doing so ended Maple River valley headward erosion (and Maple Creek headward erosion as well).

Detailed map of Little Sioux River-Maple River drainage divide area

Figure 8: Detailed map of Little Sioux River-Maple River drainage divide area. United States Geological Survey map digitally presented using National Geographic Society TOPO software.

Figure 8 provides a detailed topographic map of the Little Sioux River-Maple River drainage divide area seen in less detail in figure 7 above and is located north and east of Cherokee. The Little Sioux River flows in a south-southwest direction in the figure 8 northwest quadrant. Note the northwest-oriented Little Sioux River tributaries. The Maple River flows in a south direction near the figure 8 east edge and turns to flow in a south-southwest direction in the southeast quadrant. The unnamed south, southwest, and south oriented stream originating in section 26 and flowing to the figure 8 south center edge is a Maple River tributary. Note multiple shallow northwest-southeast oriented through valleys linking the northwest-oriented Little Sioux River tributary valleys with the unnamed Maple River tributary valley. These through valleys are generally defined by two or three 10-foot contour lines on each side. Also note the north-south oriented through valley in sections 2 and 3 linking the south, southwest, and south oriented Maple River tributary valley with the Maple River valley. This through valley appears to be almost 2 miles across and is defined by four 10-foot contour lines on each side (the sections are one mile square). These through valleys provide evidence of flood flow routes that existed prior to being captured by valley headward erosion. The Maple River valley eroded headward into the region first and captured the south- and southeast oriented flood flow. Next the south, southwest, and south oriented Maple River tributary valley eroded headward and beheaded the south- and southeast-oriented flood flow to the newly eroded Maple River valley. Subsequently the deep Little Sioux River valley eroded headward into the region and beheaded and reversed multiple southeast-oriented flood flow routes to the newly eroded Maple River tributary valley. Flood waters on northwest ends of newly beheaded flood flow routes reversed flow direction to erode the northwest-oriented Little Sioux River tributary valleys. Remember, the Little Sioux River and the Maple River, while both are Missouri River tributaries, flow along independent although roughly parallel south-southwest oriented routes to reach the south-southeast oriented Missouri River (see figures 1 and 2).

Brooke Creek-Storm Lake drainage divide area

Figure 9: Brooke Creek-Storm Lake drainage divide area. United States Geological Survey map digitally presented using National Geographic Society TOPO software.

Figure 9 provides a topographic map of the Brooke Creek-Storm Lake drainage divide area located south and east of the figure 7 map area and includes overlap areas with figure 7. Alta is the town located on the highway northwest of the town of Storm Lake. The northwest-oriented stream flowing from the Alta region to the figure 9 northwest corner is the unnamed Maple Creek tributary seen in figure 7. The south and southwest oriented stream originating near Alta and flowing to the figure 9 west edge (just north of southwest corner) is the Little Maple River and is a Maple River tributary. Powell Creek, which is located just east of Alta, flows in a southeast direction to Storm Lake and the Storm Lake Outlet Creek drains to the south-oriented North Raccoon River, which is located near the figure 9 east edge. The north-northwest oriented stream originating in WASHINGTON township (located north of Storm Lake) is Brooke Creek and is a Little Sioux River tributary. Poor Farm Creek is the northeast-oriented tributary flowing from just north of the town of Storm Lake to join the south-oriented North Raccoon River in the figure 9 northeast quadrant. South and southeast oriented streams flowing to the figure 9 south edge are Boyer River headwaters. As in previous maps many of the figure 9 drainage routes appear to have altered by human construction. Note how headward erosion of the Little Maple River valley in the figure 9 southwest quadrant beheaded southeast oriented flood flow to a southeast and south-oriented North Raccoon River tributary. Also note how reversal of flood flow in the figure 9 northwest quadrant (caused by Maple Creek valley headward erosion) also ended southeast oriented flood flow to Powell Creek and to the Little Maple River. Reversal of south-oriented flood flow on the Brooke Creek alignment occurred slightly later and was triggered by Little Sioux River valley headward erosion. The origin of Storm Lake is not totally clear from topographic map evidence. It is possible the lake basin was the location of an ice sheet remnant around which flood transported debris was deposited, although the lack of other lake basins nearby argues against the hypothesis. Another possibility is the basin was formed when south-oriented floods in the figure 9 east half blocked a southeast- or east-oriented valley, which had been eroded headward from the North Raccoon River valley before southeast-oriented floods were beheaded and reversed by Maple River and Little Sioux River valley headward erosion. Field evidence is needed to confirm the second hypothesis.

Detailed map of Maple Creek-Little Maple River through valley west of Alta

Figure 10: Detailed map of Maple Creek-Little Maple River through valley west of Alta. United States Geological Survey map digitally presented using National Geographic Society TOPO software.

Figure 10 provides a detailed topographic map of the Maple Creek-Little Maple River through valley west of Alta, which was seen in less detail in figure 9 above. The north oriented stream in sections 21 and 28 is the headwaters of the unnamed northwest-oriented Maple Creek tributary seen in figure 7. The south-oriented stream originating in the section 28 southeast corner and flowing through section 34 is the headwaters of the Little Maple River, which joins the Maple River south of the figure 7 map area. Note the through valley linking the north oriented Maple Creek tributary valley with the south-oriented Little Maple River headwaters valley. The through valley floor elevation is between 1430 and 1440 feet (the map contour interval is 10 feet). Elevations rise to more than 1510 feet in sections 22 and 27 (northeast of the through valley) and to more than 1490 feet in section 5 (south of section 32 and just south of the figure 10 map). The through valley is at least 50 feet deep and maybe was deeper when eroded and is at least two miles wide (between high points on either side). This through valley is a water eroded feature and was eroded by south-oriented flood water moving to what was then the actively eroding Little Maple River valley, which had eroded headward from what was then the actively eroding Maple River valley. Headward erosion of the Maple River-Maple Creek valley beheaded and reversed the south-oriented flood flow (see figure 7) to erode the unnamed north- and northwest-oriented Maple Creek tributary valley. Similar through valleys are found throughout the Little Sioux River-North Raccoon River drainage divide area. Many of the through valleys are shallower, but each through valley provides evidence of a previous flood flow channel, which flowed across the region prior to headward erosion of the deep southwest and south-southwest oriented valleys, which captured the flood flow.

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.