Abstract:

This essay uses topographic map evidence to interpret landform origins in the Boyer River-Mosquito Creek drainage divide area located in Pottawatamie, Harrison, Shelby, and Crawford Counties, Iowa. The Boyer River and Mosquito Creek are south-southwest oriented Missouri River tributaries located in western Iowa with the Boyer River located north and west of Mosquito Creek and also having a longer route. Between the Boyer River and Mosquito Creek is south-southwest oriented Pigeon Creek. The Boyer River-Mosquito Creek drainage divide area was eroded by immense south- and southeast-oriented floods, with flood waters derived from a rapidly melting North American ice sheet located north of the study area. The Mosquito Creek, Pigeon Creek, and Boyer River valleys in that order eroded headward from what was then an actively eroding Missouri River valley head across an immense south-southeast or southeast oriented anastomosing channel complex. Headward erosion of the Mosquito Creek valley first captured the flood flow and Pigeon Creek Valley headward erosion next beheaded flood flow routes to the newly eroded Mosquito Creek valley. Next Boyer River valley headward erosion beheaded flood flow routes to the newly eroded Pigeon Creek valley and also to the longer and newly formed Mosquito Creek drainage basin. Missouri River valley and tributary valley headward erosion subsequently beheaded all flood flow routes to the newly eroded Boyer River valley. Topographic map evidence supporting this flood origin interpretation includes present day valley orientations, including secondary and tertiary tributary valley orientations, and numerous shallow 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 Boyer River-Mosquito Creek drainage divide area landform origins in Pottawattamie, Harrison, Shelby, and Crawford 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 providing 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 Boyer River-Mosquito Creek drainage divide area landform evidence in Pottawattamie, Harrison, Shelby, and Crawford 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.

Boyer River-Mosquito Creek drainage divide area location map

Figure 1; Boyer River-Mosquito Creek 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 for the Boyer River-Mosquito Creek drainage divide area in Pottawattamie, Harrison, Shelby, and Crawford Counties, Iowa. The Missouri River flows in a south-southeast direction from the figure 1 northwest corner to the figure 1 south edge. Iowa is the state east of the Missouri River and Nebraska is the state west of the Missouri River. The Boyer River flows in a south and south-southwest direction from the figure 1 north center edge (between Odebolt and Lake View) to Dennison, Woodbine, Logan, and Missouri Valley before joining the Missouri River. South and east of Boyer River in figure 1 are several unnamed south-southwest oriented Missouri River tributaries. The first unnamed south-southwest oriented Missouri River tributary shown is Pigeon Creek and the second south-southwest oriented Missouri River tributary shown is Mosquito Creek (Persia and Neola are towns located on Mosquito Creek). The Boyer River-Mosquito Creek drainage divide area illustrated and described in this essay is located between the Boyer River (downstream from Dow City) and Mosquito Creek, which originates south and east of Dow City. Note on figure 1 how Missouri River tributaries from the east are almost all oriented in south and south-southwest directions. Also note in the figure 1 east half how drainage routes have a distinctively different southeast and south-southeast orientation. The Des Moines River flows in a south-southeast direction from the figure 1 north edge (east half) to Des Moines and then turns to flow in a southeast direction to the figure 1 east center edge. East of the figure 1 map area the Des Moines River flows in a southeast direction to the south-oriented Mississippi River. Note how in the figure 1 northeast quadrant Des Moines River tributaries are oriented in southeast directions and in the figure 1 southeast quadrant the Des Moines River tributaries are oriented in southeast and northeast directions. The drainage divide between the Missouri River drainage basin and the Mississippi River drainage basin is easily identified by this rather obvious stream orientation difference.

• The difference in stream orientations between the Missouri River drainage basin and the Mississippi River drainage basin developed as deep valleys eroded headward into the figure 1 map area during immense south and southeast oriented floods. The floods were derived from a rapidly melting North American ice sheet, the southern margin of which at that time was located north of the figure 1 map area. Initially none of the present day figure 1 river valleys existed and flood waters could flow freely across the figure 1 map area. The ice sheet had been thick and had been located in a deep “hole”. The deep “hole” had been created by deep glacial erosion and also by crustal warping caused by the ice sheet’s great weight. Immense south-oriented melt water floods removed the deep “hole’s” south rim and today it is probably impossible to determine how much material was stripped from the region south of the ice sheet before present day valleys began to erode headward into the region. The first valley to erode headward into the region was the Mississippi River valley (located east of the figure 1 map area). When the Mississippi River valley was initially eroded is beyond the scope of this essay and other essays being written for the Missouri River drainage basin landform origins research project essay series, although it is possible the entire Mississippi River valley (from the Gulf of Mexico headward into Minnesota) was eroded by giant south-oriented melt water floods. In any case, south-oriented melt water floods moving the across the figure 1 map area were captured by the actively eroding Mississippi River valley and were diverted to flow in southeast directions. Just prior to Missouri River valley headward erosion into the figure 1 map area melt water flood flow across much of the region was in a southeast direction.

• Prior to eroding headward into the figure 1 map area the deep Missouri River valley eroded headward across the state of Missouri (located south of figure 1) from the Mississippi River valley where it was capturing south and southeast oriented flood flow and diverting flood waters in an east direction to the south-oriented Mississippi River valley. The deep south-southeast oriented Missouri River valley segment seen in figure 1 was eroded headward along what very late in the ice sheet melt down history was a giant south-southeast oriented melt water river. The giant melt water river emerged from the mouth of a huge ice-walled and bedrock-floored canyon which supra-glacial melt water flow had carved into the decaying ice sheet’s surface. A remnant of the southwest and west wall of that huge ice-walled canyon is today preserved in the form of the Missouri Escarpment, which can be traced in a southeast direction from Alberta across southwest Saskatchewan to central North Dakota and then in a south direction to southeastern South Dakota. The river flowing on the ice-walled canyon’s floor drained large areas of the decaying ice sheet’s surface. Prior to headward erosion of the deep Missouri River valley flood waters from this giant melt water river flowed not only in a south-southeast direction along the present day Missouri River alignment, but also spilled in southeast-oriented directions toward actively eroding southeast-oriented Des Moines River tributary valleys, which had eroded headward from what was the actively eroding Des Moines River valley.

• As the deep south-southeast oriented Missouri River valley eroded headward into the figure 1 map area deep south-southwest oriented tributary valleys eroded headward from the actively eroding Missouri River valley to capture the southeast-oriented flood waters and to divert the captured flood flow to the newly eroded Missouri River valley. This process of south-southwest oriented tributary valley headward erosion was repeated over and over again as the deep Missouri River valley head eroded headward across the figure 1 map area toward the mouth of the huge ice-walled canyon (located at the ice sheet’s southern margin). Each successive south-southwest oriented Missouri River tributary valley beheaded south- and southeast-oriented flood flow routes or channels to the previously eroded south-southwest oriented Missouri River tributary valley located directly to the south and east. Some of the south-southwest oriented Missouri tributary valleys were more successful than others and some of the most successful Missouri River tributary valleys also beheaded south- and southeast-oriented flood flow routes to the actively eroding Des Moines River tributary valleys (note Boyer River valley headward erosion in the figure 1 north center area would have beheaded southeast-oriented flood flow to southeast-oriented Des Moines River tributaries). In the case of the Boyer River-Mosquito Creek drainage divide area the Mosquito Creek valley eroded headward from the actively eroding Missouri River valley first. Next Pigeon Creek valley headward erosion beheaded southeast-oriented flood flow to the newly eroded Mosquito Creek valley. And finally Boyer River valley headward erosion beheaded southeast-oriented flood flow to the actively eroding Pigeon Creek valley, and because the Mosquito Creek valley was more successful than the Pigeon Creek valley, Boyer River valley headward erosion also beheaded flood flow to what was then the actively eroding Mosquito Creek headwaters area and then continued to behead southeast-oriented flood flow to actively eroding Des Moines River tributary valleys.

Detailed location map for Boyer River-Mosquito Creek drainage divide area

Figure 2: Detailed location map for Boyer River-Mosquito Creek 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 Boyer River-Mosquito Creek drainage divide area in Harrison, Shelby, and Crawford Counties, Iowa. The Missouri River flows in a south-southeast direction from the figure 2 northwest corner to the figure 2 south edge. Nebraska is the state west of the Missouri River and Iowa is the state to the east of the Missouri River. Iowa county names and boundaries are shown. The Boyer River flows in a southwest and south-southwest direction from Denison in Crawford County to the Harrison County northeast corner and then across Harrison County to join the Missouri River in the Pottawattamie County northwest corner. Note the location of Picayune Creek and Mill Creek, which are Boyer River tributaries in northeast Harrison County and northwest Shelby County. Also note in northwest Pottawattamie County Honey Creek, which is a southwest-oriented Missouri River tributary located south and east of the Boyer River. Pigeon Creek originates west of Panama (located in Shelby County west center area) and flows in a south-southwest direction across southeast Harrison County and northwest Pottawattamie County to join the Missouri River. Note Potato Creek, which is a south-southwest oriented Pigeon Creek tributary originating in southeast Harrison County. Mosquito Creek originates in southern Crawford County (south of Buck Grove) and flows to Panama and Portsmouth in Shelby County, Persia and Yorkshire in southeast Harrison County, and Neola and Council Bluff in Pottawattamie County before joining the Missouri River. The Boyer River, Pigeon Creek, and Mosquito Creek drainage basins are remarkably narrow and relatively few tributaries are shown, most of which are also oriented in southwest and south-southwest directions. Southeast-oriented Des Moines River tributaries can be seen in the figure 2 northeast quadrant and also along the figure 2 southeast quadrant east edge and the drainage divide between the Missouri River drainage basin to the west and the Mississippi River drainage basin to the east can easily be identified.

Boyer River-Mosquito Creek drainage divide area near Missouri River valley

Figure 3: Boyer River-Mosquito Creek drainage divide area near Missouri River valley. United States Geological Survey map digitally presented using National Geographic Society TOPO software.

Figure 3 is a reduced size topographic map of the Boyer River-Mosquito Creek drainage divide area just east of the Missouri River valley. Missouri Valley is the name of the town located in the figure 3 northwest corner and the town is located where the southwest-oriented Boyer River valley enters the much larger south-southeast oriented Missouri River valley. Note northwest-oriented Euclid Creek and Timber Creek, which flow to the southwest-oriented Boyer River as barbed tributaries. Also note an unnamed northwest-oriented Missouri River tributary just south of where the Harrison-Pottawattamie County line crosses the Missouri River valley east edge. Neola is the town located in the figure 3 southeast corner and is located in the southwest-oriented Mosquito Creek valley. Pigeon Creek is the south-southwest oriented stream flowing from the figure 3 northeast corner region to the figure 3 south center area and then turning to flow in a west and southwest direction to the figure 3 south edge. Potato Creek is the south-southwest oriented tributary flowing from the figure 3 north edge (east half) and joining Pigeon Creek in the figure 3 south center area. Potato Creek also has south- and southeast-oriented tributaries from the west and northwest-oriented tributaries from the east. Onion Creek is the southwest and northwest oriented tributary joining Pigeon Creek in the figure 3 south center area. Note several shorter northwest-oriented Pigeon Creek tributaries. Honey Creek is the southwest and south-southwest oriented stream located between the Boyer River and Pigeon Creek and flows from the figure 3 north center region to the Missouri River valley at the figure 3 south edge. Note how Honey Creek has several south-southeast and south oriented tributaries from the north and a number of northwest-oriented tributaries from the south (the northwest-oriented tributaries are generally short in length).

• Study of the figure 3 map area also reveals shallow through valleys crossing all of the major drainage divides. The through valleys are best seen on more detailed topographic maps and figure 4 below provides a detailed topographic map of the Euclid Creek-Honey Creek drainage divide area to better illustrate through valleys there. The through valleys provide evidence of south and southeast oriented flood flow channels that existed prior to headward erosion of the deep valleys, including the Missouri River valley. The south and southeast oriented flood flow channels were components of an immense south and southeast oriented anastomosing channel complex. Deep valleys eroded headward into the figure 3 map area at approximately the same time, although headward erosion of the southwest-oriented Mosquito Creek valley captured the flood water first. Next headward erosion of the Pigeon Creek valley beheaded flood flow routes to the newly eroded Mosquito Creek valley. North and northwest oriented tributary valleys were eroded by reversals of flow on the beheaded flood flow routes. Potato Creek valley headward erosion from the newly eroded Pigeon Creek valley next captured the south and southeast oriented flood water. Honey Creek valley headward erosion from the actively eroding Missouri River valley head then captured flood flow and beheaded flood flow routes to the newly eroded Pigeon and Potato Creek valleys. Boyer River valley headward erosion from the actively eroding Missouri River valley head next beheaded and reversed all flood flow routes to the actively eroding Honey Creek valley. The northwest-oriented Euclid Creek and Timber Creek valleys were eroded by reversals of flood flow on beheaded flood flow routes. Reversed flood flow often captured yet to be beheaded flood flow from adjacent flood flow routes. Captures of yet to beheaded flood flow provided water volumes to erode the northwest-oriented valleys.

Detailed map of Euclid Creek-Honey Creek drainage divide area

Figure 4: Detailed map of Euclid Creek-Honey Creek drainage divide area. United States Geological Survey map digitally presented using National Geographic Society TOPO software.

Figure 4 provides a detailed topographic map of the Euclid Creek-Honey Creek drainage divide area seen in less detail in figure 3 above. The map contour interval is 20 feet. Euclid Creek flows in a northwest direction from section 29 to the figure 4 northwest corner and then to the southwest-oriented Boyer River (north and west of figure 4). Note other unnamed north and north-northwest oriented Euclid Creek tributaries and west and northwest oriented tributaries to a southwest-oriented Euclid Creek tributary. Honey Creek flows in a south-southwest direction from the figure 4 northeast corner to section 33 and then in a southwest direction to the figure 4 south center edge. Note northwest and north-northwest oriented Honey Creek tributaries from the south and south and south-southeast oriented tributaries from the north. Also note shallow through valleys linking the south-oriented Honey Creek tributary valleys with the north-oriented Euclid Creek tributary and headwaters valleys. For example in the section 32 northwest quadrant a through valley links a north-northwest oriented Euclid Creek tributary valley with a south-oriented Honey Creek tributary valley. The through valley is defined by two 20-foot contour lines on each side. Another through valley can be found in the section 31 east center area and links a north-northwest oriented Euclid Creek tributary valley with a south-southeast oriented Honey Creek tributary valley and is again defined by two contour lines on each side. Two additional through valleys are located in the section 31 southwest quadrant and also link northwest-oriented valleys with south-southeast oriented Honey Creek tributary valleys. Following the Euclid Creek-Honey Creek drainage divide in either direction reveals still more similar through valleys. The through valleys provide evidence of multiple south-southeast and south oriented flood flow channels that crossed the figure 4 map area prior to headward erosion of the deep Boyer River valley (north of the figure 4 map area). At that time the actively eroding Missouri River valley head was probably located west of the figure 4 map area and the deep Honey Creek valley was actively eroding headward across the figure 4 map area to capture south-southeast oriented flood flow. South and south-southeast oriented Honey Creek tributary valleys then eroded headward along the captured south-southeast oriented flood flow channels. Next headward erosion of the deep Boyer River valley from the actively eroding Missouri River valley head beheaded and reversed the south-southeast flood flow to erode the northwest and north-northwest oriented Euclid Creek and tributary valleys.

Boyer River-Mosquito Creek drainage divide area near Logan and Portsmouth, Iowa

Figure 5: Boyer River-Mosquito Creek drainage divide area near Logan and Portsmouth, Iowa. United States Geological Survey map digitally presented using National Geographic Society TOPO software.

Figure 5 provides a topographic map of the Boyer River-Mosquito Creek drainage divide area in the region between Logan and Portsmouth, Iowa and is located north and east of the figure 3 map area. Logan is the town located near the figure 5 west center edge and is in the south-southwest oriented Boyer River valley. Portsmouth is adjacent to the figure 5 east edge (north half) and is located in the south-southwest oriented Mosquito Creek valley. Persia is the small town located downstream in the Mosquito Creek valley. Pigeon Creek is the south-southwest stream flowing from the figure 5 north edge (east half) to the figure 5 south edge (just east of center). Sixmile Creek is the southwest and northwest oriented tributary flowing from the figure 5 north center area to join the Boyer River upstream from Logan. Richardson Creek is the southwest and northwest oriented tributary to the northwest-oriented Sixmile Creek segment. The stream originating south of the Richardson Creek elbow of capture (where Richardson Creek turns from flowing in southwest direction to a northwest direction) is Potato Creek. South of the figure 5 map area Potato Creek joins Pigeon Creek. Note the through valley linking the Richardson Creek elbow of capture with the Potato Creek headwaters. Figure 6 below provides a detailed topographic map of that through valley region. Note how many Boyer River tributaries from the southeast are oriented in a northwest direction. Harris Creek in the figure 5 southwest quadrant is a southwest and northwest oriented Boyer River tributary. For example, note how northwest-oriented Boyer River tributaries north and west of the southwest-oriented Harris Grove Creek segment are linked by shallow through valleys with the southwest-oriented Harris Grove Creek valley. The northwest-oriented tributary orientations and the shallow through valleys provide evidence of multiple southeast-oriented flood flow channels which once crossed the figure 5 map area. The through valleys are remnants of what was once an immense southeast-oriented anastomosing channel complex. Headward erosion of the Mosquito Creek valley first captured the southeast-oriented flood flow and diverted the flood waters in a south-southwest direction to the newly eroded Missouri River valley. Next Pigeon Creek valley headward erosion captured the flood flow and beheaded flood flow channels to the newly eroded Mosquito Creek valley. Headward erosion of the Potato Creek valley proceeded next and captured what became a major southeast-oriented flood flow route on the present day northwest-oriented Richardson-Sixmile Creek alignment. Boyer River valley headward erosion next beheaded and reversed flood flow routes to the newly eroded Potato Creek valley and in the process reversed flood flow on the northwest-oriented Richardson-Sixmile Creek alignment. The flood flow reversal (with the aid of yet to be beheaded flood flow captured from channels north of the actively eroding Boyer River valley) eroded the present day northwest-oriented Richardson-Sixmile Creek valley.

Detailed map of Richardson Creek-Potato Creek drainage divide area

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

Figure 6 provides a detailed topographic map of the Richardson Creek-Potato Creek drainage divide area seen in less detail in figure 5 above. Richardson Creek is the southwest and northwest-oriented stream located in section 30 in the figure 6 northwest quadrant. Potato Creek is the south oriented stream in the west half of section 31, which flows into the section 4 east half before reaching the figure 6 south edge. Note the well-defined through valley in section 30 linking a north oriented Richardson Creek tributary with headwaters of south oriented Potato Creek. The map contour interval is 20 feet and the through valley is defined by at least five contour lines on each side. The through valley provides evidence of a south-oriented flood flow route beheaded by headward erosion of the northwest-oriented Richardson Creek valley. As noted in the figure 5 discussion the northwest-oriented Richardson Creek valley was eroded by a reversal of southeast-oriented flood flow to the actively eroding Potato Creek valley when headward erosion of the Boyer River valley captured the flood flow. The southwest-oriented Richardson Creek valley segment seen in the figure 6 northeast quadrant was eroded by yet to be beheaded and reversed flood flow routes north of the actively eroding Boyer River valley head. Pigeon Creek is the south-southwest oriented stream flowing across the figure 6 southeast corner. Note how south-southeast oriented Pigeon Creek tributaries originating in sections 29 and 28 are linked by shallower through valleys with north and northwest-oriented tributaries to the southwest-oriented Richardson Creek valley. The southwest-oriented stream flowing to the figure 6 southwest corner is Harris Grove Creek. Northwest and west oriented streams flowing to the figure 6 west edge are Boyer River tributaries. Note headwaters of northwest-oriented Boyer River tributaries are linked by shallow through valleys with the southwest-oriented Harris Grove Creek valley. These through valleys are evident in sections 33 and 34 west of the town of Hard Scratch. Also note in sections 25 and 26 shallow through valleys linking Harris Grove Creek headwaters valleys with north-oriented Richardson Creek tributary valleys. Again the shallow through valleys provide evidence of multiple south- and southeast-oriented flood flow channels. Flood flow routes were constantly changing as deep valleys eroded headward into the region. However, it is possible to reconstruct flood flow routes if one remembers the flood flow channels were components of a much larger anastomosing channel complex and the channels were beheaded one channel at a time.

Boyer River-Mosquito Creek drainage divide area near Woodbine and Panama, Iowa

Figure 7: Boyer River-Mosquito Creek drainage divide area near Woodbine and Panama, Iowa. United States Geological Survey map digitally presented using National Geographic Society TOPO software.

Figure 7 provides a topographic map of the Boyer River-Mosquito Creek drainage divide area between Woodbine and Panama, Iowa and is located north and east of the figure 5 map area. Woodbine is the town in the figure 7 southwest quadrant and is located in the south-southwest oriented Boyer River valley. The southwest, northwest, and southwest oriented stream flowing through the figure 7 center area and joining the Boyer River near Woodbine is Picayune Creek. North Picayine Creek is the west and southwest oriented Picayune Creek tributary originating in the figure 7 north center area. South Picayune Creek is the north and north-northwest oriented tributary joining Picayune Creek on the west edge of the Boyer River valley. Little Pigeon Creek is the south-southwest stream originating in the figure 7 south center area just south of the Picayune Creek elbow of capture (where southwest oriented Picayune Creek turns to flow in a northwest direction). Mosquito Creek is the southwest- and south-oriented stream located adjacent to the highway and railroad in the figure 7 southeast quadrant and adjacent to the figure 7 east edge. Panama is the small town located in the Mosquito Creek valley. The south-southwest oriented stream joining Mosquito Creek in the figure 7 east center edge area is Moser Creek (which will be seen again in figure 9). The south-southwest oriented stream between the south-southwest oriented Picayune Creek headwaters and Mosquito Creek is Pigeon Creek. Note how the Little Pigeon Creek headwaters valley and the Pigeon Creek valley are both linked by multiple through valleys with north- and northwest-oriented Picayune Creek tributary valleys. The map contour interval is ten meters and the through valleys are generally defined by one or two contour lines on each side. Through valleys are best seen on more detailed topographic maps and figure 8 below provides a detailed topographic map of the through valley linking the south-oriented Pigeon Creek and Little Pigeon Creek valleys with a north-northwest oriented Picayune Creek tributary valley. Again through valleys and orientations of tributary valleys to the southwest and south-southwest oriented trunk streams provide evidence the deep trunk stream valleys eroded headward across multiple south and south-southeast oriented flood flow channels.

Detailed map of Picayune Creek-Pigeon Creek drainage divide area

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

Figure 8 provides a detailed map of the Picayune Creek-Pigeon Creek drainage divide area seen in less detail in figure 7 above. The southern end of the Picayune Creek elbow of capture is located near the north edge in the figure 8 northwest quadrant. Note the north and north-northwest oriented Picayune Creek tributaries in sections 23, 24, 14, 13, 18, 7, and 8. Pigeon Creek flows from the figure 8 east edge (in section 16) in a southwest direction to the figure 8 south center edge. An unnamed Pigeon Creek tributary flows from the figure 8 north edge in section 8 through section 17 to join Pigeon Creek in section 20. Note the numerous short southeast-oriented tributary valleys to the unnamed Pigeon Creek tributary and the Pigeon Creek valley downstream from section 20. Those short southeast-oriented tributary valleys are linked by shallow through valleys with north- and northwest oriented Picayune Creek tributary valleys. The map contour interval is 20 feet and the through valleys are defined by up to four contour lines on each side. The through valleys provide evidence the southwest-oriented Pigeon Creek valley eroded headward across multiple south and southeast oriented flood flow channels such as might be found in large-scale south and/or southeast oriented anastomosing channel complex. Prior to headward erosion of the Pigeon Creek valley flood waters were flowing to what were then actively eroding southeast-oriented Mosquito Creek tributary valleys, which had eroded headward from what was then the newly eroded Mosquito Creek valley. Northwest-oriented Pigeon Creek tributary valleys (see figure 8 southeast quadrant) were eroded by reversals of flood flow on northwest and north ends of beheaded flood flow routes. Headward erosion of the Boyer River valley next beheaded and reversed flood flow channels in sequence from the south to the north so as to erode the northwest oriented Picayune Creek valley segment and the northwest and north oriented Picayune Creek tributary valleys. Flood flow channels shifted position and orientation as deep valleys eroded headward into the region, although the general pattern can be determined from the present day valley orientations (including orientations of what appear to be minor tributary valleys) and the through valley orientations.

Boyer River-West Fork Nishnabotna River drainage divide area

Figure 9: Boyer River-West Fork Nishnabotna River drainage divide area. United States Geological Survey map digitally presented using National Geographic Society TOPO software.

Figure 9 is a reduced size topographic map illustrating the Boyer River-West Fork Nishnabotna River drainage divide area north and east of the figure 7 map area. Arion is the small town located near the figure 9 north center edge and Dow City is the small town a short distance to the southwest. Arion and Dow City are located in the southwest and south-southwest oriented Boyer River valley. Dunlap is the town in the Boyer River valley further to the southwest and near the figure 9 west edge. Note how most Boyer River tributaries from the north and west are oriented in south and southeast directions and from the south and east are oriented in northwest directions. Exceptions to this rule are found in the figure 9 southwest quadrant where southwest and west oriented Mill Creek has northwest and southeast oriented tributaries. The southwest-oriented stream located south of Mill Creek and flowing to the figure 9 south edge (near the southeast corner) is North Picayune Creek. The northwest-oriented tributary joining the Boyer River near Arion is Buck Creek. Note how south-oriented Mill Creek tributary valleys are linked by shallow through valleys with northwest-oriented Boyer River tributary valleys. The through valleys provide evidence the Mill Creek valley eroded headward slightly in advance of Boyer River valley headward erosion. Boyer River valley headward erosion beheaded and reversed flood flow channels to the newly eroded Mill Creek valley. Earling is the town straddling the figure 9 south edge (just east of center) and is located on a southwest-oriented tributary to south-southeast and south-southwest oriented Moser Creek, which is located east and north of Earling. As seen in figure 7 Moser Creek is a Mosquito Creek tributary and the Moser Creek drainage basin is a northern extension of the Mosquito Creek drainage basin. Note how Moser Creek originates on what appears to be an upland remnant located between the south-southwest oriented Mill Creek headwaters valley and a north-oriented Buck Creek tributary valley. This Buck Creek-Moser Creek drainage divide area is shown in more detail in figure 10 below. The figure 9 evidence indicates Boyer River valley headward erosion beheaded and reversed southeast-oriented flood flow, some of which was flowing to what was then the actively eroding Moser Creek valley. However the northwest-oriented Buck Creek valley originates west of the Moser Creek headwaters area, suggesting the southeast-oriented flood flow was also going somewhere else (diverging and converging channels are common in anastomosing channel complexes). Note where the power line crosses Buck Creek. The southwest and south-southwest oriented stream just to the southeast of that point is Willow Creek and Willow Creek flows to the south-southeast oriented West Fork Nisnabotna River. Defiance is the town located in West Fork Nishnabotna River valley in the figure 9 southeast quadrant. Study of the Buck Creek-Willow Creek drainage divide area reveals northwest-southeast oriented through valleys (the railroad makes use of one such through valley).

Detailed map of Buck Creek-Moser Creek drainage divide area

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

Figure 10 provides a detailed map of the Buck Creek-Moser Creek drainage divide area seen in less detail in figure 9 above. Mill Creek is the south-southwest oriented stream in section 26 near the figure 10 west edge. The north-northeast and north oriented stream originating in section 24 and flowing through section 13 in the figure 10 northwest quadrant is an unnamed Boyer River tributary. Note how the north-oriented Boyer River tributary is linked by a north-south oriented through valley with the south-oriented Mill Creek valley. The map contour interval is 20 feet and the through valley is defined by three contour lines on each side. The through valley provides evidence of a south-oriented flood flow route to what was then the actively eroding Mill Creek valley. South-oriented flood flow was beheaded and reversed by headward erosion of the deep southwest-oriented Boyer River valley (north and west of the figure 10 map area). Other northwest-southeast oriented through valleys link northwest-oriented Boyer River tributary valleys with southeast-oriented Mill Creek tributary valleys and provide evidence of other flood flow channels. Buck Creek is the west-southwest and west-northwest oriented stream adjacent to the railroad line near the figure 10 north edge in the northeast quadrant. North-oriented streams in the northeast quadrant and north center area are Buck Creek tributaries. Moser Creek originates in section 30 and flows in a south-southeast direction to the figure 10 south center edge. A shallow through valley in the section 30 northeast quadrant links the Moser Creek headwaters with a north-oriented Buck Creek tributary valley. Other similar shallow through valleys can be found further downstream along the Moser Creek route, however deeper through valleys link the Buck Creek tributaries with a different south-oriented drainage route. Willow Creek is the south-southwest oriented stream in the southeast quadrant located near the figure 10 east edge. Note the south-southeast oriented Willow Creek tributary originating in section 28. Note in section 28 how the south-southeast oriented Willow Creek tributary is linked by through valleys with a north-northwest oriented Buck Creek tributary valley. The deepest through valley is defined by three contour lines on each side and has a floor approximately 40 feet lower than the through valley floor extending south to the Moser Creek headwaters. The figure 10 evidence suggests more water was flowing to the actively eroding Willow Creek valley than to the actively eroding Moser Creek valley. Such differences in flood flow to different anastomosing channels is common and probably flood waters were moving to both valleys at the time Boyer River valley headward erosion beheaded and reversed 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.