Abstract:

This essay uses topographic map evidence to interpret landform origins in the Missouri River-Tarkio River drainage divide area located in Fremont and Page Counties, Iowa and Atchison County, Missouri. The Missouri River flows in a south-southeast direction along the Fremont and Atchison County western borders. The Tarkio River and its major tributaries flow in a south-southwest and south direction through Page and Atchison Counties to join the Missouri River. Between the Missouri River and Tarkio River is the south-oriented Nishnabotna River and its multiple south and south-southwest oriented tributaries. Major streams in the Fremont, Page, and Atchison County area are oriented in a south direction, flow roughly parallel to each other, and are closely spaced, suggesting the valleys originated as channels in what was once a south-oriented anastomosing channel complex. Shorter northwest oriented barbed tributaries flowing to the major south-oriented Missouri River tributaries are common and are linked by shallow through valleys with short southeast-oriented tributaries to the major south-oriented Missouri River tributary immediately to the east. These northwest and southeast-oriented tributaries suggest headward erosion of the deep south-oriented valleys beheaded and reversed multiple southeast-oriented flood flow channels such as might be found in a southeast-oriented anastomosing channel complex. Topographic map evidence illustrated and described in this essay suggests the entire region was eroded by an immense southeast-oriented flood, which was subsequently captured by headward erosion of a south-oriented anastomosing channel complex formed as the deep south-southeast oriented Missouri River valley eroded headward along the region’s southern and western boundary. The present day drainage system evolved as deep south-oriented tributary valleys eroded headward from what was then the actively eroding deep Missouri River valley. The deep south-oriented tributary valleys eroded headward in sequence from east to west to capture the southeast-oriented flood flow.

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 Missouri River-Tarkio River drainage divide area landform origins in Fremont and Page Counties, Iowa and Atchison County, Missouri, 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 Missouri River-Tarkio River drainage divide area landform evidence in Fremont and Page Counties, Iowa and Atchison County, Missouri 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.

Missouri River-Tarkio River drainage divide area location map

Figure 1: Missouri River-Tarkio River drainage divide area location map (select and click on maps to enlarge. National Geographic Society map digitally presented using National Geographic Society TOPO software.

Figure 1 provides a location map for the Missouri River-Tarkio River drainage divide area in Fremont and Page Counties, Iowa and Atchison County, Missouri. The Missouri River is the south-southeast oriented river flowing from the figure 1 north edge (west half) to the figure 1 south center edge. Nebraska is the state west of the Missouri River and Omaha and Lincoln are large Nebraska cities. Iowa is the state east of Omaha and Council Bluffs is located on the Iowa side of the Missouri River. Missouri is the state south of Iowa and Maryville is located in Missouri. The Tarkio River flows in a south-southwest direction near Stanton, Iowa to join the Missouri River near Craig, Missouri (near south center edge). West of the Tarkio River is an unlabeled south-oriented river with several south and south-southwest-oriented tributaries which joins the Missouri River in the Missouri northwest corner just south of Hamburg, Iowa. This unlabeled river is the Nishnabotna River and its easternmost major tributary is the East Nishnabotna River and its westernmost major tributary is the West Nishnabotna River. East of the Tarkio River is the Nodaway River which flows through Burlington Junction and Skidmore, Missouri before joining the Missouri River just south of the figure 1 south center edge area. Note how Missouri River tributaries and their tributaries in the southwest Iowa and northwest Missouri corners are oriented in south and south-southwest directions. In the figure 1 northeast corner southeast and east oriented Des Moines River tributaries are present, with the Des Moines River being a southeast oriented Mississippi River tributary, which is not included in the Missouri River drainage basin. The south-southeast oriented Thompson River eventually reaches the Missouri River south and east of the figure 1 map area. Other essays describe western Iowa drainage divide areas north of the Fremont and Page County Iowa area and include the Mosquito Creek-East Nishnabotna River drainage divide area in Pottawattamie, Cass, Mills and Montgomery Counties, Iowa essay, the Boyer River-Mosquito Creek drainage divide area in Pottawattamie, Harrison, Shelby, and Crawford Counties, Iowa essay, and the Boyer River-Nishnabotna River drainage divide area in Crawford, Carroll, Shelby, and Audubon Counties, Iowa essays. These and other regional drainage divide area essays can be found under Iowa on the sidebar category list.

• The Missouri River, Nishnabotna River, and Tarkio River valleys and their tributary valleys seen in the figure 1 map area were eroded by immense south-oriented melt water floods. The flood waters were derived from a rapidly melting thick North American ice sheet and at the time the figure 1 map area valleys were eroded the ice sheet’s decaying south margin was located north of the figure 1 map area, probably in southeast South Dakota and adjacent southwest Minnesota. The deep south-southeast oriented Missouri River valley eroded headward along what was an unusually large south and south-southeast oriented melt water river which was emerging from the mouth of a giant ice-walled and bedrock-floored canyon carved into the decaying ice sheet’s surface. Today the east and northeast facing Missouri Escarpment is what remains of the ice-walled and bedrock-floored canyon’s west and southwest wall. The Missouri Escarpment can be traced north and northwest from southern South Dakota into North Dakota, Saskatchewan, and Alberta suggesting the river flowing on the ice-walled canyon’s floor was draining a significant region of the decaying ice sheet’s surface. Essays describing evidence for the ice-walled and bedrock-floored canyon’s southern end can be found under James River on the sidebar category list. The giant south-oriented melt water river emerging from the mouth of this giant canyon in southeast South Dakota initially flowed in a south and south-southeast direction across the figure 1 map area and was systematically captured by headward erosion of southeast and east oriented Mississippi River tributary valleys (staring in the south and proceeding to the north). Headward erosion of the deep east and southeast-oriented Missouri River valley across the state of Missouri (south of the figure 1 map area) followed headward erosion of the more southern Arkansas and White River valleys. The south-southeast oriented Missouri River valley seen in figure 1 was eroded headward along what became a major south-southeast oriented flood flow route to the actively eroding Missouri River valley head.

• Prior to headward erosion of the deep Missouri River valley into the figure 1 map area there was no regional drainage system capable of handling the melt water flood flow and flood waters initially flowed in a south direction across the entire figure 1 map area. However the deep southeast-oriented Des Moines River valley was eroding headward towards the figure 1 northeast corner area at about the same time the deep east and southeast oriented Missouri River valley was eroding headward across the state of Missouri (south of figure 1). These deep valleys began to capture flood flow from the figure 1 map area and divert the flood waters in a southeast direction. Then as the deep south-southeast oriented Missouri River valley eroded headward into the figure 1 map area it captured the southeast-oriented flood flow by eroding south and south-southwest oriented tributary valleys headward across the southeast-oriented flood flow routes. These south-oriented tributary valleys eroded headward in sequence with the south-oriented tributary valleys in the east eroding headward in advance of the south-oriented tributary valleys in the west, which eroded headward slightly in advance of Missouri River valley headward erosion. Headward erosion of each south-oriented Missouri River tributary valley (or tributary valley to a south-oriented Missouri River tributary valley) beheaded flood flow routes to what was then the newly eroded south-oriented valley to the east. Probably all of the valleys were being eroded headward at the same time so as to form a south-oriented anastomosing channel complex, which was capturing flood flow from what was probably a southeast-oriented anastomosing channel complex. In time with Missouri River valley headward erosion and headward erosion of deep south-southwest and southwest oriented Missouri River tributary valleys north of the figure 1 map area all south- and southeast-oriented flood flow to the newly formed Nishnabotna and Tarkio River drainage basins ended.

Detailed location map for Missouri River-Tarkio River drainage divide area

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

Figure 2 provides a more detailed location map for the Missouri River-Tarkio River drainage divide area in Fremont and Page Counties, Iowa and in Atchison County, Missouri. County names and boundaries are shown. The Missouri River is located along the western boundaries of Mills, Fremont, and Atchison Counties. Cass, Otoe, and Nemaha Counties are located in Nebraska. Mills, Montgomery, Adams, Fremont, Page, and Taylor Counties are located in Iowa and Atchison and Nodaway Counties are located in Missouri. The east-oriented river in the figure 2 northwest corner is the Platte River, which is a major Missouri River tributary. Note how the Missouri River flows in a south and south-southeast direction to the figure 2 south center edge and how Missouri River tributaries from the east are almost all oriented in south and/or south-southwest directions. The major south-oriented Missouri River tributaries in Fremont County is the south-oriented Nishnabotna River, which is formed at the confluence of the south-oriented West Nishnabotna River and the south-southwest oriented East Nishnabotna River. Note how south-southwest and southwest oriented Walnut Creek parallels the East Nishnabotna River before turning to flow in a southwest and west direction to join the south-oriented West Nishnabotna River. In western Page County the Tarkio River and its tributary West Tarkio Creek flow in a south-southwest direction into Atchison County where they join before flowing in a south direction to join the Missouri River just south of Atchison County. The west Nodaway River is the major south-oriented stream in eastern Page County and western Nodaway County. Note how with very exceptions almost all Nishnabotna River, Tarkio River, and Nodaway River tributaries are oriented in south and south-southwest directions. One significant exception is Mill Creek in southeast Fremont County which flows in a southwest, northwest, and west direction to join the south-oriented Nishnabotna River. As already mentioned these multiple converging south-oriented Missouri River tributary valleys were probably eroded headward along what were originally channels in a large south-oriented anastomosing channel complex. Also as mentioned previously this south-oriented anastomosing channel complex probably captured flood flow what was a previous southeast or south-southeast oriented anastomosing channel complex. Evidence supporting this flood origin interpretation is best seen on topographic maps, a few samples of which are shown below.

Rock Creek-Cow Branch drainage divide area

Figure 3: Rock Creek-Cow Branch drainage divide area. United States Geological Survey map digitally presented using National Geographic Society TOPO software. 

Figure 3 provides a reduced size topographic map of the Missouri River-Tarkio River drainage divide area in Atchison County, Missouri. Tarkio, Missouri is the town located near the figure 3 east edge and is located on the west bank of the south-oriented Tarkio River. Cow Branch is the south-southeast and southeast oriented tributary originating west of Tarkio and entering the Tarkio River valley south of Tarkio. The Missouri River flows in a south-southeast direction along the figure 3 west edge and is located near the west edge of the large south-southeast oriented Missouri River valley. The indefinite boundary located east of the Missouri River in the Missouri River valley represents the former Nishnabotna River channel, which once paralleled the Missouri River channel as a separate channel for a significant distance before joining the Missouri River channel. Rock Port is the town located just south of the figure 3 center area and is located on the west bank of south-southwest oriented Rock Creek. Note how Rock Creek has several short southeast-oriented tributaries from the west and several northwest oriented tributaries from the east. These northwest and southeast-oriented tributaries provide evidence the Rock Creek valley eroded headward across southeast-oriented flood flow channels. Flood waters were moving to what was at that time the actively eroding Tarkio River valley, which was eroding headward slightly in advance of Rock Creek valley headward erosion, which was slightly in advance of Missouri River valley headward erosion. Close study of the figure 3 map area reveals additional evidence supporting this flood flow channel interpretation in the form of shallow through valleys crossing present day drainage divides. These shallow through valleys are best seen on more detailed topographic maps, but can also be noted on less detailed maps such as the figure 3 map. Figure 4 below provides a detailed topographic map of the Rock Creek-Cow Branch drainage divide area, but before going to that map look at the Rock Creek-Cow Branch drainage divide on figure 3. The figure 3 map contour interval is ten meters. Note how there are multiple shallow through valleys linking the south-southeast and southeast oriented Cow Branch valley with heads of short northwest-oriented Rock Creek tributary valleys. The northwest-oriented Rock Creek tributaries are barbed tributaries flowing in a north direction to join a south-oriented stream. The shallow through valleys are defined by only a single contour line on each side, but they exist and can be seen. Study of other figure 3 drainage divides reveals many other such through valleys.

Detailed map of Rock Creek-Cow Branch drainage divide area

Figure 4: Detailed map of Rock Creek-Cow Branch 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 Rock Creek-Cow Branch drainage divide area seen in less detail in figure 3. Rock Creek flows in a south-southwest direction in the figure 4 northwest quadrant to the west edge (south half). Cow Branch is the south-southeast oriented stream flowing to the figure 4 south center edge. Note how in the section 1 southeast quadrant the south-southeast oriented Cow Branch valley is linked by shallow through valleys with northwest-oriented Rock Creek tributary valleys. An additional parallel through valley is located in the section 6 west half. Through valleys can further be seen in section 12. The map contour interval is ten feet and generally the through valleys are defined by two or three contour lines on each side. The multiple northwest-southeast oriented through valleys provide evidence of multiple southeast-oriented flood flow channels to what was once the actively eroding Cow Branch valley, which had eroded headward from what was then the newly eroded Tarkio River valley. At that time the deep Rock Creek valley did not exist nor did the deep Missouri River valley exist west of the figure 4 map area. Headward erosion of the deep Rock Creek valley beheaded the southeast-oriented flood flow channels in sequence from the south to the north. Flood waters on northwest ends of the beheaded flood flow channels reversed flow direction to erode northwest oriented Rock Creek tributary valleys. In addition to the through valleys linking the Cow Branch valley with the Rock Creek valley the figure 4 map area also shows through valleys linking southwest-oriented Cow Branch tributary valleys with northeast oriented tributary valleys to east-oriented West Tarkio Creek tributary valleys. One such through valley is located in section 5 and another in the section 9 northwest corner. Floors of the section 5 and 9 through valleys are slightly deeper than floors of through valleys crossing the Rock Creek-Cow Branch drainage divide. The section 5 and 9 through valleys were eroded by southwest-oriented flood flow channels flowing to what was then the actively eroding Cow Branch valley. At that time the deep West Tarkio Creek valley had not yet beheaded and reversed the southwest-oriented flood flow to erode the northeast and east-oriented West Tarkio Creek tributary valleys seen in the figure 4 northeast corner. Study of the figure 4 map area reveals many additional shallow through valleys suggesting an ever-changing flood flow channel pattern as deep valleys eroded headward into the region.

West Nishnabotna River-East Nishnabotna River drainage divide area

Figure 5: West Nishnabotna-East Nishnabotna 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 Walnut Creek-East Nishnabotna River drainage divide area west of Shenandoah, Iowa and is located north and west of the figure 3 map area. The West Nishnabotna River flows in a south direction in the figure 5 west half. Walnut Creek is the southwest and west oriented West Nishnabotna River tributary flowing from the figure 5 north edge (east half) to join the West Nishnabotna River in the figure 5 northwest quadrant. Shenandoah is the larger town located near the figure 5 east center edge and is located on the East Nishnabotna River southeast bank. The East Nishnabotna River flows in a southwest direction from the figure 5 east edge (north half between Shenandoah and northeast corner) to join the West Nishnabotna River just south of the figure 5 map area. Note how the East Nishnabotna River and Walnut Creek both have barbed tributaries flowing in north and northwest directions to join what are really south oriented drainage systems. These barbed tributaries provide evidence the deep East Nishnabotna River valley eroded headward across multiple southeast-oriented flood flow channels and captured the flood flow. Flood waters on northwest and north ends of beheaded flood flow channels reversed flow direction to erode the northwest and north oriented tributary valleys. At that time the deep West Nishnabotna River valley and its tributary Walnut Creek valley did not exist, although they eroded headward across the southeast-oriented flood flow shortly thereafter. West Nishnabotna River-Walnut Creek valley headward erosion captured the southeast-oriented flood flow next and beheaded flood flow routes to the newly eroded East Nishnabotna River valley. Soon thereafter headward erosion of the south-oriented West Nishnabotna River valley (north of the figure 5 map area) beheaded southeast-oriented flood flow to the newly eroded Walnut Creek valley. A close look at the Walnut Creek-East Nishnabotna River drainage divide reveals a number of shallow through valleys linking northwest and north oriented Walnut Creek tributary valleys with south- and southeast-oriented East Nishnabotna River tributary valleys. The map contour interval is 10 meters and on the figure 5 map the through valleys are defined by a single contour line on each side and are better seen on more detailed topographic maps. Figure 6 provides a more detailed topographic map of the Walnut Creek-East Nishnabotna River drainage divide area north and west of Shenandoah to better illustrate the through valleys.

Detailed map of Walnut Creek-East Nishnabotna River drainage divide area

Figure 6: Detailed map of Walnut Creek-East Nishnabotna River 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 Walnut Creek-East Nishnabotna River drainage divide area north and west of Shenandoah, which was seen in less detail in figure 5 above. Shenandoah is located in the figure 6 southeast corner. The East Nishnabotna River flows in a southwest direction across the figure 6 southeast quadrant. Walnut Creek flows in a southwest direction from the figure 6 north center edge and then turns to flow in a west-southwest direction to the figure 6 west edge. Note the northwest-oriented Walnut Creek tributaries and the south and southeast oriented East Nishnabotna River tributaries. The northwest-oriented Walnut Creek tributaries and southeast-oriented East Nishnabotna River tributaries are barbed tributaries in that they flow to streams flowing in the opposite direction. Follow the Walnut Creek-East Nishnabotna River drainage divide across the figure 6 map area and note the numerous shallow through valleys linking northwest-oriented Walnut Creek tributary valleys with south and southeast oriented East Nishnabotna River tributary valleys. The map contour interval is ten feet. The through valleys range in-depth from being defined by a single contour line on each side to being defined by four contour lines on each side (see east half of section 16). Through valleys defined by two or three contour lines on each side are common. These through valleys are water eroded features and were eroded as water eroded channels in a southeast-oriented anastomosing channel complex which crossed the figure 6 map area prior to headward erosion of the deep Walnut Creek valley. Headward erosion of the deep East Nishnabotna River valley captured the flood flow first and diverted the flood water in a southwest and south direction to the newly eroded Nishnabotna and Missouri River valley. At that time neither the West Nishnabotna River valley nor the Missouri River valley had eroded far enough north to capture the southeast-oriented flood flow moving across the figure 6 map area. Headward erosion of the deep Walnut Creek valley first beheaded and reversed the southeast oriented flood flow to erode the northwest-oriented Walnut Creek tributary valleys.

East Nishnabotna River-Tarkio River drainage divide area

Figure 7: East Nishnabotna River-Tarkio River drainage divide area. United States Geological Survey map digitally presented using National Geographic Society TOPO software. 

Figure 7 is a reduced size topographic map of the East Nishnabotna River-Tarkio River drainage divide area south and somewhat east of the figure 5 map area and includes overlap areas with figure 5. Note the west to east oriented Iowa-Missouri state line near the figure 7 south edge, which separates Atchison County, Missouri in the south from Fremont County, Iowa (west) and Page County, Iowa (east) to the north. Shenandoah, Iowa is located just north of the figure 7 north center edge and Farragut is the town located in the southwest oriented East Nishnabotna River valley located in the figure 7 northwest quadrant (Riverton is the town located where the East Nishnabotna River crosses the figure 7 west edge). The Tarkio River flows in a south direction near the figure 7 east edge and Coin, Iowa is the town adjacent to the Tarkio River near the figure 7 east center edge with Blanchard being the town in the figure 7 southeast corner. West Tarkio Creek is the south-southwest oriented stream flowing from the figure 7 north edge (east half) to the figure 7 south center edge. Rock Creek is the south-southwest oriented stream immediately to the west of West Tarkio Creek. West Tarkio Creek as seen in figure 3 joins the Tarkio River at Tarkio, Missouri, while Rock Creek flows on an independent route to the Missouri River valley (see figure 3). Other southwest oriented streams in the figure 7 southwest quadrant flowing to the south edge also flow directly to the Missouri River valley. Fisher Creek is the northwest oriented East Nishnabotna River tributary in the figure 7 north center area. Ledgewood Creek is the northwest oriented East Nishnabotna River tributary just east of Riverton and Mill Creek is the northwest, southwest, and northwest-oriented tributary joining the East Nishnabotna River just downstream from Riverton (and west of the figure 7 map area). Note how northwest-oriented Fisher Creek headwaters and tributary valleys are linked by numerous northwest-southeast oriented through valleys with southeast oriented West Tarkio Creek tributary valleys. Also note how the southwest-oriented Mill Creek valley segment is linked by numerous northwest-southeast oriented through valleys with north and northwest oriented East Nishnabotna River tributary valleys. Further note how northwest-oriented Mill Creek headwaters and tributary valleys are linked by through valleys to headwaters valleys of Rock Creek and the other southwest-oriented Missouri River tributary valleys. The map contour interval is ten meters and most of the through valleys are defined by a single contour line on each side, although a few are defined by two contour lines on each side. Again, through valleys are better seen on more detailed topographic maps and figure 8 below provides a detailed topographic map of the East Nishnabotna River-Mill Creek drainage divide area.

Detailed map of East Nishnabotna River-Mill Creek drainage divide area

Figure 8: Detailed map of East Nishnabotna River-Mill 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 East Nishnabotna River-Mill Creek drainage divide area seen in less detail in figure 7 above. Mill Creek flows in a southwest direction to the figure 8 south edge (west half) and is labeled. Note the northwest-oriented Mill Creek tributaries and headwaters. North and northwest oriented streams flowing to the figure 8 north edge are East Nishnabotna River tributaries. The northwest and west-northwest oriented streams flowing to the figure 8 west edge are headwaters of an unnamed north-oriented East Nishnabotna River tributary located east of Ledgewood Creek. Note how the north oriented East Nishnabotna River tributary valleys are linked by shallow through valleys with valleys of south and southeast-oriented Mill Creek tributaries. For example in the section 32 southwest quadrant a through valley links headwaters of an East Nishnabotna River tributary with headwaters of a southeast oriented Mill Creek tributary. The map contour interval is ten feet and the through valley floor elevation is between 1120 and 1130 feet. Hills on either side of the through valley rise to at least 1170 feet. Two similar through valleys are located further north and east in section 32. A deeper north-south oriented through valley is located in section 28 and has a floor elevation of between 1110 and 1120 feet. Again hills on either side rise to more than 1170 feet. More shallow through valleys are found in the section 27 northwest corner and southern half of section 22. Still another northeast-southwest oriented through valley is crossed by the road following the section line between section 23 and section 26 in the figure 8 northeast quadrant. The northeast-southwest through valley links the southwest-oriented Mill Creek valley segment with the valley of a north-oriented East Nishnabotna River tributary and has a floor elevation of between 1110 and 1120. These through valleys provide evidence headward erosion of the southwest-oriented Mill Creek valley captured south and southeast oriented flood flow channels before East Nishnabotna River valley headward erosion beheaded and reversed those flood flow routes. The multiple through valleys and multiple barbed tributaries to both southwest oriented Mill Creek and the southwest-oriented East Nishnabotna River provide evidence of multiple flood flow channels such as might be expected in a south and/or southeast oriented anastomosing channel complex being captured by headward erosion of the deep south oriented Nishnabotna River and tributary valleys.

East Nishnabotna River-West Nodaway River drainage divide area

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

Figure 9 provides a topographic map of the East Nishnabotna River-West Nodaway River drainage divide area located east and somewhat north of the figure 5 map area. Shenandoah, Iowa is the town located in the figure 9 southwest corner. Clarinda is the town located in the southeast corner. The west to east oriented Montgomery-Page County line is located just south of the figure 9 north edge. The west edge of the south-oriented West Nodaway River valley is located near the figure 9 east edge and the West Nodaway River channel can be seen adjacent to the east edge. The south-southwest oriented East Nishnabotna River flows from the figure 9 north edge (west half) to the west edge (just north of Shenandoah). Between the East Nishnabotna River and the West Nodaway River three south-southwest oriented streams flow from the north edge to the south edge. The westernmost of those three streams is West Tarkio Creek, the center stream is the Tarkio River, and the easternmost stream is East Tarkio Creek. Snake Creek is a southwest-oriented East Tarkio Creek tributary located between East Tarkio Creek and Clarinda and joins East Tarkio Creek south of the figure 9 map area. As seen in figures 1 and 2 the Nishnabotna River, Tarkio River, and Nodaway River all flow independently to the Missouri River valley. Note how drainage basins for the various south and south-southwest oriented rivers and streams crossing the figure 9 map area are narrow. Also observe northwest-oriented (barbed) tributaries to the south-southwest oriented East Nishnabotna River and southeast-oriented tributaries to most of the south and south-southwest oriented rivers. Study of the figure 9 map area drainage divides again reveals numerous through valleys crossing those drainage divides. The map contour interval is ten meters and the through valleys are generally defined by a single contour line on each side. Some of the easiest through valleys to see on the figure 9 map link northwest-oriented East Nishnabotna River tributary valleys with southeast-oriented West Tarkio Creek tributary valleys. Figure 10 below provides a detailed topographic map of the East Nishnabotna River-West Tarkio Creek drainage divide area located north and east of Shenandoah. The figure 9 map evidence can be used to determine the sequence of valley headward erosion. The West Nodaway River valley eroded headward across the figure 9 map area first and was followed by headward erosion of the East Tarkio Creek valley, which was followed by Tarkio River valley headward erosion. West Tarkio Creek valley headward erosion followed Tarkio River valley headward erosion and was followed by East Nishnabotna River valley headward erosion. Probably all valleys were being eroded at the same time with the easternmost valleys being slightly in advance of the western valleys.

Detailed map of East Nishnabotna River-West Tarkio Creek drainage divide area

Figure 10: Detailed map of East Nishnabotna River-West Tarkio Creek 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 East Nishnabotna River-West Tarkio Creek drainage divide area east and north of Shenandoah. Shenandoah is located in the figure 10 southwest quadrant on the east edge of the south-southwest oriented East Nishnabotna River valley. West Tarkio Creek flows in a southwest direction across the figure 10 southeast corner. Fourmile Creek is the named northwest-oriented East Nishnabotna River tributary located in the figure 10 southwest quadrant. Note other northwest and north oriented East Nishnabotna River (barbed) tributaries further north in the figure 10 map area and also flowing to the figure 10 north center edge. Note also how West Tarkio Creek tributaries in the figure 10 east half are generally oriented in a south or southeast direction, although north and northwest-oriented tributary valleys can be seen in the figure 10 southeast corner. Figure 10 drainage divides are crossed by numerous shallow through valleys, which provide evidence of former diverging and converging flood flow channels. A through valley located in the section 23 east half links a north-northwest oriented East Nishnabotna River tributary valley with a south-southeast oriented West Tarkio Creek tributary valley. The map contour interval is ten feet and the through valley floor elevation is between 1130 and 1140 feet. Hills on either side rise to elevations greater than 1180 feet. The through valley and tributary orientations provide evidence of a south-southeast oriented flood flow channel moving water from what is now the deep East Nishnabotna River valley area to what is now the deep West Tarkio Creek valley. The south-southeast oriented flood flow channel was probably one of many diverging and converging channels in what was probably an immense south-oriented anastomosing channel complex. Headward erosion of the deep West Tarkio Creek valley captured the south-southeast flood flow first, although before the through valley could be eroded deeper headward erosion of the deep East Nishnabotna River beheaded and reversed the south-southeast oriented flood flow to erode the north-northwest oriented East Nishnabotna River tributary valley. A somewhat deeper through valley in section 13 has a very similar history and provides evidence of multiple diverging and converging flood flow channels. The floor elevation of the section 13 through valley is between 1120 and 1130 feet and hills on either side rise to more than 1180 feet. Study of the figure 10 map area reveals additional through 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.