Abstract:

This essay uses topographic map evidence to interpret Little Sioux River-Boyer River drainage divide area landform origins. The Little Sioux and Boyer Rivers are located in western Iowa and are southwest and south-southwest oriented Missouri River tributaries. Between the Little Sioux River and Boyer River are the south and southwest oriented Maple River and several tributaries and also the southwest-oriented Soldier River and several tributaries, which means the Little Sioux River-Boyer River drainage divide area actually consists of drainage divides between several south, southwest, and south-southwest oriented valleys. All south, south-southwest, and southwest oriented Missouri River tributaries in the drainage divide area eroded headward in sequence, with the Boyer River valley eroding headward first and the Little Sioux River valley eroding headward last. Headward erosion of the Boyer River valley captured southeast-oriented flood flow which had been moving to actively eroding southeast-oriented North Raccoon River tributary valleys, with the North Raccoon River draining to what was then the newly eroded southeast-oriented Des Moines River valley, which had eroded headward from the Mississippi River valley. Soldier River valley headward erosion beheaded southeast-oriented flood flow to the newly eroded Boyer River valley and Maple River valley headward erosion beheaded flood flow to the newly eroded Soldier River and Boyer River valleys. Finally Little Sioux River valley headward erosion beheaded flood flow to the newly eroded Maple River valley and also to the North Raccoon River valley (further to the north). Evidence supporting this flood origin interpretation includes valley orientations, barbed tributaries, and multiple through valleys eroded across 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-Boyer River drainage divide area landform origins in western 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-Boyer River drainage divide area landform evidence in western 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.

Little Sioux River-Boyer River drainage divide area location map

Figure 1: Little Sioux River-Boyer 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 map of western Iowa and a small region in eastern Nebraska (west of the south-southeast oriented Missouri River and illustrates the Little Sioux River-Boyer River drainage divide area this essay discusses. The Little Sioux River flows from Cherokee, Iowa (near figure 1 north edge , west of center) in a south-southwest direction to join the Missouri River near Little Sioux, Iowa (north of Omaha, Nebraska). The Boyer River originates south of Storm Lake, Iowa (located east and slightly south of Cherokee) and flows in a south and south-southwest direction to join the Missouri River near Missouri Valley (located between Little Sioux and Omaha). East of the Boyer River headwaters is the south- and southeast-oriented North Raccoon River, which flows to the southeast-oriented Des Moines River, which south and east of the figure 1 map area flows directly to the Mississippi River. The Boyer River-North Raccoon River drainage divide is the divide between the Mississippi River drainage basin to the east and the Missouri River drainage basin to the west. The Mississippi River drainage basin area on figure 1 is characterized by southeast and south-southeast oriented streams while the Missouri River drainage basin in western Iowa is characterized by southwest and south-southwest oriented streams. The western Iowa Missouri River drainage basin is much narrower than the Missouri River drainage basin to the west of the south-southeast oriented Missouri River and is also much narrower than the Mississippi River drainage basin in central and eastern Iowa.

• This essay focuses on the region between the Little Sioux River and the Boyer River, essays  describing drainage divides to the north include the Little Sioux River-North Raccoon River drainage divide in Cherokee, Buena Vista, and Sac Counties, Iowa; the Floyd River-Little Sioux River northern drainage divide area, Iowa; and the Floyd River-Little Sioux River drainage divide area in Woodbury and Monona Counties, Iowa essays and are listed under Iowa on the sidebar category list. The Missouri River-Mississippi River drainage divide seen in figure 1 was created during immense south-oriented floods, which flowed across the entire figure 1 map area. Flood waters were derived from a rapidly melting North American ice sheet and at the time the figure 1 Missouri River-Mississippi River drainage divide was created the ice sheet’s southern margin was probably located a short distance north of the figure 1 map area. Initially none of the figure 1 drainage routes existed and flood waters probably flowed in a south direction across the entire figure 1 map area. Flood water erosion probably significantly lowered regional elevations throughout the figure 1 map area, although because evidence for the removed bedrock materials no longer exists it is difficult if not impossible to determine how much earlier erosion occurred.

• Based on topographic map evidence we can determine deep valleys eroded headward into the figure 1 map area, with valleys first eroding headward from the south-oriented Mississippi River valley, which was capturing the south-oriented flood flow. The deep Missouri River valley eroded headward across the state of Missouri (south of the figure 1 map area) to capture the south-oriented flood flow and to divert the flood waters to the Mississippi River valley. As the Missouri River valley was eroding across Missouri the Des Moines River valley and other southeast-oriented Mississippi River tributary valleys and their tributary valleys were eroding headward into eastern and central Iowa. South-oriented flood flow was diverted in southeast directions towards these actively eroding Mississippi River tributary valleys. The south-southeast oriented Missouri River valley seen in figure 1 eroded headward in the region along major south and south-southeast oriented flood flow routes emerging from the mouths of giant ice-walled and bedrock-floored canyons carved into the decaying ice sheet’s surface. Huge melt water rivers flowing through these giant canyons drained significant areas of the decaying ice sheet surface. As the deep south-southeast oriented Missouri River valley eroded headward across the figure 1 map area deep south-southwest oriented tributary valleys eroded headward from the newly eroded Missouri River in sequence (from south to north) to capture the southeast-oriented flood flow moving to the actively eroding Mississippi River tributary valleys. Note in figure 1 how Boyer River valley headward erosion would not only have beheaded southeast-oriented flood flow to more southern south-southwest oriented Missouri River tributary valleys, but also to southeast-oriented Des Moines River tributary valleys. Also note how Little Sioux River valley headward erosion captured southeast-oriented flood flow moving to what was then the newly eroded Boyer River valley and also to southeast-oriented Des Moines River tributaries. These captures of southeast-oriented flood flow by headward erosion of the deep south-southwest oriented Missouri River tributary valleys were responsible for the creating the Missouri River-Mississippi River drainage divide.

Detailed location map for Little Sioux River-Boyer River drainage divide area

Figure 2: Detailed location map for Little Sioux River-Boyer 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-Boyer River drainage divide area. The Missouri River flows in a south-southeast direction from Sioux City, Iowa (located in figure 2 northwest corner) to the figure 2 south edge and serves as the Iowa-Nebraska border, with Nebraska west of the Missouri River. County names and boundaries are shown. The Little Sioux River flows in a south-southwest direction from the figure 2 north edge (just west of center) across eastern Woodbury County and central Monona County to join the Missouri River in northwest Harrison County. A major Little Sioux River tributary is the Maple River, which flows in a south direction from the figure 2 north center edge to Ida Grove in Ida County and then turns to flow in a southwest direction across the Woodbury County southeast corner and into Monona County where it joins the Little Sioux River. While not apparent on figure 2 the Maple River enters the large south-southeast oriented Missouri River valley independently from the Little Sioux River and the Little Sioux River flows in a south direction along the broad valley’s east wall while the Missouri River flows in a channel further to the west in the same large valley. South and east of the Maple River is the southwest-oriented Soldier River, which originates in southeast Ida County. The Soldier River flows across the Crawford County northwest corner and then the Monona County southeast quadrant before flowing to the Missouri River in northwest Harrison County (just south of where the Little Sioux River joins the Missouri River). The Boyer River originates in southern Sac County and flows in a southwest direction diagonally across Crawford County and Harrison County and joins the Missouri River south of the figure 2 map area. Note in figure 2 how all Missouri River tributaries in Iowa are oriented in southwest, south-southwest, or south directions and how further east near the figure 2 east edge the streams are predominantly oriented in a southeast or south-southeast direction. The more detailed figure 2 drainage routes show the same pattern along the Missouri River-Mississippi River drainage divide as seen in figure 1. In other words, the figure 2 map evidence also supports the conclusion that headward erosion of the southwest and south-southwest oriented Missouri River tributary valleys (in sequence from south to north) beheaded southeast-oriented flood flow moving to what were then actively eroding southeast and south-southeast oriented Mississippi River tributary valleys.

Boyer River headwaters area

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

Figure 3 illustrates a reduced size topographic map of the Boyer River headwaters area south of Storm Lake. Cherokee, Iowa is the larger town located in the figure 3 northwest corner and the Little Sioux River flows in a south-southwest direction next to Cherokee. Storm Lake is the larger community located on the Storm Lake north shore. The Storm Lake outlet drains to the south oriented river near the figure 3 east edge, which is the North Raccoon River and which south and east of the figure 3 map area eventually reaches the southeast oriented Des Moines River. Note how North Raccoon River tributaries from the west tend to be oriented in a southeast direction. The Boyer River originates slightly south and west of Storm Lake and flows in a southeast and south-southeast direction to reach the figure 3 south edge. Powell Creek is the southeast oriented stream flowing to Storm Lake. North of Powell Creek in the figure 3 north center area are headwaters of north-oriented Brooke Creek, which flows in a north direction to join the Little Sioux River north of the figure 3 map area. The southeast- and southwest-oriented Boyer River tributary located south of Storm Lake is Boyer Creek. West of the Boyer River headwaters is south- and southwest-oriented Little Maple River, which flows to the south-oriented Maple River. The north-oriented stream in the figure 3 southwest quadrant (adjacent to the highway) is Silver Creek and joins the south-southwest oriented Little Sioux River as a barbed tributary near the figure 3 west center edge. What has happened in the figure 3 map area is headward erosion of the south-oriented North Raccoon River valley (from what was then the newly eroded Des Moines River valley) first captured southeast-oriented flood flow moving across the entire figure 3 map area. Next headward erosion of the Boyer River valley (from what was then the actively eroding Missouri River valley) beheaded and captured southeast-oriented flood flow in the area south and southwest of present day Storm Lake. Headward erosion of the Maple River-Little Maple River valley beheaded flood flow routes to the newly formed Boyer River valley complex while Maple River and tributary headward erosion beheaded and reversed flood flow to the actively eroding Powell Creek valley. South and southeast oriented flood flow apparently deposited debris in the valley east of Storm Lake forming what is now the Storm Lake depression. Headward erosion of the south-southwest oriented Little Sioux River valley next beheaded flood flow routes to the newly eroded Maple River valley, including a south-oriented flood flow route on the present day Silver Creek alignment. Flood waters on the north end of the beheaded south-oriented flood flow route reversed flow direction to erode the north-oriented Solver Creek valley. Continued headward erosion of the Little Sioux River valley (north of the figure 3 map area) beheaded and reversed south-oriented flood flow on the Brooke Creek alignment and eventually beheaded all south- and southeast-oriented flood flow to the what had been actively eroding North Raccoon River and tributary valleys.

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

Figure 4: Detailed map of Little Maple River-Boyer River drainage divide area. United States Geological Survey map digitally presented using National Geographic Society TOPO software.

Figure 4 provides a detailed map of the Little Maple River-Boyer River drainage divide area seen in less detail in figure 3. The Little Maple River flows in a southwest direction across the figure 4 northwest quadrant. West and south of the figure 4 map area the Little Maple River flows to the south-oriented Maple River. Note the northwest and west-northwest oriented Little Maple River tributaries, especially in sections 22 and 23. The tributary valleys were eroded by reversals of flood flow on northwest ends of southeast-oriented flood flow routes beheaded by Little Maple River valley headward erosion. The Boyer River flows from section 24 in a southeast direction to the figure 4 south edge (near the southeast corner). South of the figure 4 map area the Boyer River flows in a south-southeast direction before turning to flow in a southwest direction to join the Missouri River. Note how the Boyer River headwaters valley is linked by a large west-northwest to southeast oriented through valley with Little Maple River tributary valleys. The through valley floor at its deepest point is between 1420 and 1430 feet in elevation (the map contour interval is ten feet). The hill to north rises to an elevation of 1477 feet and hills to the south rise to at least 1480 feet. The valley is at least 50 feet deep and is approximately two miles across (the sections are one mile square). The through valley is a water eroded feature and was eroded by southeast-oriented flood flow moving to what was at that time the actively eroding Boyer River valley. At that time deep valleys to the northwest did not exist, which meant the Little Maple River valley had not yet beheaded the southeast-oriented flood flow nor had the Maple River valley, Little Sioux River valley, or Missouri River valley eroded far enough north to capture the southeast-oriented flood flow. Headward erosion of the southeast-oriented Little Maple River valley captured the southeast-oriented flood flow to the actively eroding Boyer River valley. Flood waters on the northwest and west end of the beheaded flood flow route reversed flow direction to erode the west-northwest oriented Little Maple River tributary valley. Subsequently Maple River valley headward erosion beheaded flood flow to the actively eroding Little Maple River valley, and Little Sioux River valley headward erosion beheaded flood flow to the actively eroding Maple River valley. Finally Missouri River valley headward erosion captured all southeast-oriented flood flow.

Little Sioux River-Silver Creek-Maple River drainage divide area

Figure 5: Little Sioux River-Silver Creek-Maple River drainage divide area. United States Geological Survey map digitally presented using National Geographic Society TOPO software.

Figure 5 provides a reduced size topographic map of the Little Sioux River-Silver Creek-Maple River drainage divide area and includes significant overlap areas with figure 3. The Little Sioux River flows in a southwest and south-southwest direction from the figure 5 north center to the figure 5 southwest corner. Note how west oriented Little Sioux River tributaries have northwest oriented headwaters. Silver Creek is the north oriented tributary flowing from the town of Holstein (located near figure 5 south edge slightly east of center) to join the southwest oriented Little Sioux River as a barbed tributary near the figure 5 north center edge. Note how Silver Creek tributaries from the west are usually oriented in a southeast direction or have southeast oriented segments or tributaries. Also note how some Silver Creek tributaries from the east are oriented in northwest directions or have northwest oriented segments. The Maple River flows in a south direction near the figure 5 east edge and flows from the figure 5 north edge to the south edge. The figure 5 drainage network is intriguing because Silver Creek flows in a north direction while on either side it is bounded by south-oriented drainage basins. Study of the figure 5 map area reveals numerous shallow through valleys linking northwest and west oriented Little Sioux River tributary valleys with southeast and east oriented Silver Creek tributary valleys and west- and northwest-oriented Silver Creek tributary valleys with southeast and east oriented Maple River tributary valleys. Figure 6 below provides a detailed map of the through valley linking Fourmile Creek (which flows to the Little Sioux River) with a southeast oriented Silver Creek tributary valley (the figure 6 map location is in the figure 5 north center area). In the figure 5 northeast quadrant, just east of Silver Creek, is an unnamed southwest and west-oriented Silver Creek tributary, which has a west-oriented tributary. South of the west-oriented tributary is a north and east-oriented Maple River tributary, which has northwest-oriented headwaters and also a northwest-oriented tributary. Note how the west-oriented Silver Creek tributary is linked by a large northwest-southeast oriented through valley with the east-oriented Maple River tributary. The map contour interval is ten meters and the through valley is defined by two contour lines on either side. Numerous similar through valleys can be seen throughout the figure 5 map area. Again what has happened is headward erosion of the deep Maple River valley first captured southeast- and south-oriented flood flow in the figure 5 map area. East-oriented Maple River tributary valleys then beheaded and reversed some south-oriented flood flow routes. Headward erosion of the deep Little Sioux River valley next captured the south- and southeast-oriented flood flow and beheaded and reversed flood flow on a major south-oriented flood flow route. Reversal of flood flow on that major south-oriented flood flow route eroded the north-oriented Silver Creek valley.

Detailed map of Fourmile Creek-Silver Creek drainage divide area

Figure 6: Detailed map of Fourmile Creek-Silver Creek drainage divide area. United States Geological Survey map digitally presented using National Geographic Society TOPO software.

Figure 6 provides a detailed map of the Fourmile Creek-Silver Creek drainage divide area seen in less detail in figure 5 above. The Little Sioux River flows in a southwest direction in the figure 6 northwest corner. Silver Creek flows in a north direction along the figure 6 east edge (in the southeast quadrant). Fourmile Creek is a northwest-oriented Little Sioux River tributary originating in the northwest corner of section 29 and joining the Little Sioux River near the figure 6 northwest corner. Note the unnamed southeast and east-northeast oriented Silver Creek tributary originating in the east half of section 29 and joining Silver Creek in section 27 and also note the well-defined northwest-southeast oriented through valley in section 29 linking the Silver Creek tributary valley with the northwest-oriented Fourmile Creek valley. The map contour interval is 10 feet and the through valley elevation is between 1360 and 1370 feet. Hills to the north of the through valley rise to elevations greater than 1420 feet and to the south of the through valley to more than 1450 feet. The through valley when eroded was at least 50 feet deep and probably deeper. The through valley was eroded by southeast-oriented flood flow moving to the Silver Creek valley, which was initiated as a south-oriented flood flow channel (although at a higher elevation than the Silver Creek valley elevation today). Headward erosion of deep Little Sioux River valley beheaded the southeast-oriented flood flow and flood waters on the northwest end of the beheaded flood flow route reversed flow direction to erode the northwest-oriented Fourmile Creek valley. Continued headward erosion of the Little Sioux River valley next beheaded the south-oriented flood flow route along the present day Silver Creek alignment. Flood waters on the north end of the beheaded flood flow route reversed flow direction and eroded the north-oriented Silver Creek valley. Actually the situation was more complicated as the unnamed Silver Creek tributary turns to flow in an east-northeast direction. This complication suggests enough flood water was still in the region as flood flow on the Silver Creek alignment was reversed to keep eroding valleys deeper. In other words, significant flood erosion was accomplished by reversed flow flood waters perhaps because flood waters were captured from yet to be beheaded flood flow routes.

Odebolt Creek-Boyer River drainage divide area

Figure 7: Odebolt Creek-Boyer 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 Odebolt Creek-Boyer River drainage divide area located south of the figure 3 map area. Ida Grove is the town located just south of the figure 7 west center edge area. The south and south-southwest oriented river flowing to Ida Grove is the Maple River and is joined at Ida Grove by the west-northwest and west oriented Odebolt Creek. Note how many Odebolt tributaries from the south are oriented in a northwest direction. The northwest oriented tributary valleys were eroded by reversals of flood flow on northwest ends of beheaded flood flow routes. Odebolt is the larger town located just east of the figure 7 south center area and Arthur is the smaller town located between Ida Grove and Odebolt. The south-oriented river located near the figure 7 east edge is the Boyer River. Note southeast-oriented Boyer River tributaries in the figure 7 southeast quadrant and southeast-oriented headwaters to northeast and east oriented Boyer River tributaries in the figure 7 northeast quadrant. These southeast-oriented Boyer tributaries or tributary valley segments provide evidence headward erosion of the deep south-oriented Boyer River valley captured multiple southeast-oriented flood flow channels such as might be found in a southeast-oriented anastomosing channel complex. Prior to Boyer River valley headward erosion flood waters were flowing to what were then actively eroding Des Moines River tributary valleys (located east of the figure 7 map area). Headward erosion of the south-oriented Maple River valley and its southwest-oriented tributary valleys next captured the southeast-oriented flood flow. Flood waters on northwest and west ends of beheaded flood flow channels reversed flow direction to erode the northwest and west oriented tributary valleys (and valley segments). Study of the figure 7 map area reveals shallow through valleys crossing drainage divides. The through valleys are best seen on more detailed topographic maps and figure 8 below provides a detailed map of the shallow through valley linking the west-oriented Odebolt Creek valley with a southeast-oriented Boyer River tributary valley (located at the town of Odebolt). Note how the southwest-oriented Odebolt Creek tributary located just east of Arthur has both northwest and southeast-oriented tributaries. Those tributaries provide evidence the southwest-oriented Odebolt Creek tributary valley captured southeast-oriented water flowing north of the actively eroding Maple River valley head and diverted the yet to be beheaded flood flow to the newly reversed Odebolt Creek alignment. Such captures of yet to beheaded flood flow provided water required to erode west, north, and northwest-oriented tributary valleys (such as the Odebolt Creek valley).

Detailed map of Odebolt Creek-Boyer River drainage divide area

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

Figure 8 provides a detailed map of the Odebolt Creek-Boyer River drainage divide area near Odebolt, Iowa. Odebolt Creek flows in a southwest and west-southwest direction from the figure 8 north center edge to the figure 8 west center edge. A west-northwest tributary flows along the Odebolt northern city limits. The west-northwest oriented Odebolt Creek tributary is linked by a shallow through valley in section 35 with an unnamed southeast-oriented Boyer River tributary, which flows to the figure 8 southeast corner. The map contour interval is 20 feet and the through valley floor elevation is between 1380 and 1400 feet. Hills on either side of the through valley rise to elevations greater than 1440 (north and south of the figure 8 map area). The distance between high points on either side of the through valley is at least four miles suggesting the through valley when eroded was a broad valley several miles across and perhaps only 40-60 feet deep. Erosion of such southeast-oriented channels was probably common as immense south-oriented melt water floods crossed the region. Erosion of such channels stripped and lowered the regional landscape perhaps many times before reaching the level seen today. There may be no way to determine how much bedrock material was removed prior to reaching the level of the surface seen today. The southeast oriented through valley seen today was most likely eroded by southeast-oriented flood water moving to what was then the actively eroding south-oriented Boyer River valley, which had captured the southeast-oriented flood flow route. Prior to capture by the Boyer River the southeast-oriented flood flow had been moving to what were then actively eroding southeast-oriented North Raccoon River tributary valleys, with the North Raccoon River draining to the newly eroded southeast-oriented Des Moines River valley. Headward erosion of the Boyer River valley beheaded flood flow to those North Raccoon River tributaries and in the process created the Missouri River-Mississippi River drainage divide (located east of the Boyer River). Headward erosion of the Maple River valley (west of the figure 8 map area) next beheaded and reversed the southeast-oriented flood flow. The southwest, west, and west-northwest oriented Odebolt Creek valley was eroded by the reversed flood flow. The reversed flood flow captured yet to be beheaded flood flow from southeast-oriented flood flow routes north of the actively eroding Maple River valley. The captured flood water provided the water volumes required to erode the Odebolt Creek valley.

East Soldier Creek-Boyer River drainage divide area

Figure 9: East Soldier Creek-Boyer River drainage divide area. United States Geological Survey map digitally presented using National Geographic Society TOPO software.

Figure 9 uses a reduced size topographic map to illustrate the East Soldier Creek-Boyer River drainage divide area located south and slightly west of the figure 7 map area. Dennison, Iowa is the larger town located in the figure 9 east center area. The Boyer River flows in a south-southwest direction from the figure 9 northeast corner to Dennison and then in a southwest direction to the figure 9 south center edge. Charter Oak is the town located in the figure 9 northwest quadrant. The west-southwest oriented river at Charter Oak is the East Soldier River and is joined just west of the figure 9 map area by the southwest-oriented Middle Soldier River, which flows across the figure 9 northwest corner. Slightly further west the combined river joins the southwest-oriented Soldier River, which in this region flows between the south-southwest oriented Maple River and the Boyer River (see figures 1 and 2). The figure 9 map area is closer to the deep Missouri River valley than previous map areas and as a result the major southwest and south-southwest oriented Missouri River tributaries have eroded deeper valleys than were seen further upstream. Note how the Boyer River has several northwest-oriented tributaries in the figure 9 southeast quadrant and also how many Boyer River tributaries from the north are oriented in south and/or southeast directions. This evidence suggests the Boyer River valley eroded headward across multiple south- and southeast-oriented flood flow routes. Note also how in the Charter Oak area the East Soldier River has several northwest-oriented tributaries, with Emigrant Creek being the most significant. A railroad line is located in the Emigrant Creek valley and crosses the Emigrant Creek-Boyer River drainage divide in a through valley before traveling along the valley of an unnamed Paradise Creek tributary, which flows to south-oriented Paradise Creek, which is a Boyer River tributary. The map contour interval is ten meters and the through valley in which the railroad is located is defined by three contour lines on each side (figure 10 below provides a detailed map of the through valley region). The through valley provides evidence of a southeast-oriented flood flow route, which was beheaded and reversed by headward erosion of the deep East Soldier River valley. Close study of the figure 9 map area reveals many other through valleys eroded by south- and southeast-oriented flood waters which flowed across the region prior to being beheaded by headward erosion of deep Missouri River tributary valleys.

Detailed map of Emigrant Creek-Boyer River drainage divide area

Figure 10: Detailed map of Emigrant Creek-Boyer River drainage divide area. United States Geological Survey map digitally presented using National Geographic Society TOPO software.

Figure 10 provides a detailed topographic map of the Emigrant Creek-Boyer River through valley area seen in less detail in figure 9 above. The East Soldier River flows in a southwest direction across the figure 10 northwest corner and is located northwest of Charter Oak. Emigrant Creek is the northwest-oriented tributary joining the East Soldier River near Charter Oak. Paradise Creek flows in a southeast direction to the figure 10 east edge (south half) and then east and south of the figure 10 map area turns to flow in a south direction to join the southwest-oriented Boyer River. Note the through valley in section 32 (near figure 10 center) linking the northwest-oriented Emigrant Creek valley with the valley of an unnamed southeast and south-southeast oriented Paradise Creek tributary (the railroad line is located in the through valley). Note how south and west of the through valley in which the railroad line is located there is another northwest-southeast oriented through valley in the section 32 southwest corner. Follow the drainage divide further to the southwest to the section 6 northeast quadrant and note still another northwest-southeast oriented through valley. In the section 6 northwest quadrant there is still another through valley, although somewhat shallower. Go back to section 32 and follow the drainage divide to the northeast of the through valley with the railroad line. Note in the section 32 northeast quadrant two more through valleys and in the section 29 southeast quadrant still two more through valleys. Additional through valleys can be seen by following the drainage divide further in both directions. The railroad is located in what is probably the deepest of the through valleys, although some of the others are almost as deep. Some other through valleys are not as deep. The map contour interval is 20 feet and the through valley in which the railroad is located is defined by at least four contour lines on each side. All of the through valleys are water eroded features and were eroded as southeast-oriented flood flow channels moving flood waters to what were then actively eroding Boyer River tributary valleys, which were eroding headward from what was then the newly eroded Boyer River valley. The multiple southeast-oriented channels were probably components of a giant southeast-oriented anastomosing channel complex. At that time there were no deep East Soldier River, Middle Soldier River, Soldier River, Maple River, Little Sioux River, or Missouri River valleys to the northwest and flood waters were able to flow freely across the entire region. Headward erosion of the deep East Soldier River valley beheaded and reversed the southeast-oriented flood flow to the actively eroding Boyer River tributary valleys. The flood flow reversals (aided by capture of yet to be beheaded flood flow) eroded the north and northwest oriented East Soldier River tributary valleys.

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.