• The purpose of this essay is to use topographic map interpretation methods to explore the Platte River-Thompson River drainage divide area landform origins in Adair, Union, Ringgold, and Decatur Counties, Iowa, USA. Map interpretation methods can be used to unravel many geomorphic events leading up to formation of present-day drainage routes and development of other landform features. While each detailed topographic map feature provides detailed evidence to be explained, the solution must be consistent with explanations for adjacent area map evidence as well as solutions to big picture map evidence puzzles. I invite readers to improve upon my solutions and/or to propose alternate solutions that better explain evidence and are also consistent with adjacent map area and big picture evidence. Readers may do so either by making comments here or by writing and publishing their own essays and then by leaving a link to those essays in a comment here.

• This essay is also exploring a new geomorphology paradigm in which erosional landforms are interpreted as evidence left by immense glacial melt water floods. Implied in that interpretation is the immense floods were derived from a thick North American ice sheet that created a deep “hole” in the North American continent and also melted fast. The previously unexplored paradigm being tested in this and other essays in the Missouri River drainage basin landform origins research project is a thick North American ice sheet, comparable in thickness to the Antarctic ice sheet, occupied the North American region usually recognized to have been glaciated, and through its weight and erosive actions created a deep North American “hole”. The southwestern rim of that deep “hole” is today preserved in the high Rocky Mountains. The ice sheet through its weight and deep erosion (and perhaps deposition along major south-oriented melt water flow routes) caused significant crustal warping and tectonic change, through its action of melting fast produced immense floods that flowed across the continent, and through its action of melting fast systematically opened up space in the ice sheet created “hole” so headward erosion of newly developed north-oriented drainage systems captured immense south-oriented melt water floods and diverted immense melt water floods north into space the ice sheet had once occupied.

• If this previously unexplored paradigm is correct the geographic region explored by this essay should contain evidence of immense floods that were captured by headward erosion of new valley systems so as to cause the floods to flow in a different direction. Ability of this previously unexplored paradigm to explain Platte River-Thompson River drainage divide area landform evidence in Adair, Union, Ringgold, and Decatur 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.

• Figure 1 provides a location map for the Platte River-Thompson River drainage divide area in Adair, Union, Ringgold, and Decatur Counties, Iowa. The state of Iowa is labeled and Missouri is the state south of Iowa. In figure 1 the Missouri River flows in a south-southeast direction along the Iowa and Missouri western borders and the state of Nebraska is west of Iowa with Kansas being the state south of Nebraska. South of the figure 1 map area the Missouri River changes direction and flows in more of an east direction across the state of Missouri to reach the south oriented Mississippi River. The Des Moines River flows in a south-southeast direction from the figure 1 north center edge to Des Moines, Iowa and then turns to flow in a southeast direction to the Iowa-Missouri border (located at the figure 1 east edge). East of figure 1 the Des Moines River flows to the south-oriented Mississippi River, which in turn flows to the Gulf of Mexico. All other southeast oriented rivers and streams flowing to the figure 1 east edge are Mississippi River tributaries. Also note southeast and northeast-oriented Des Moines River tributaries in the Des Moines, Iowa area. Contrast orientations of the southeast-oriented Mississippi River tributaries and their tributaries with the orientations of the south-oriented Missouri River tributaries in western Iowa and northern Missouri (all south-oriented rivers and streams flowing to the figure 1 south edge are Missouri River tributaries). This essay uses topographic map evidence to interpret landform origins in the drainage divide area between two of those south-oriented Missouri River tributaries. The Thompson River originates near Greenfield, Iowa (located south and west from Des Moines) and flows in a south-southeast direction to Davis City (located just north of the Iowa-Missouri border) and then south to join the south- and southeast-oriented Grand River near Chillicothe, Missouri (located near the figure 1 south center edge). South of the figure 1 map area the Grand River flows to the Missouri River. The Platte River originates between Orient and Creston (both located south of Greenfield) and flows in a south, south-southwest, and south direction to join the Missouri River south of the Kansas-Missouri border along the figure 1 south edge (just south of the figure 1 south edge the Missouri turns to flow in a south-southwest direction before resuming its south-southeast direction while the Platte River flows in a south direction so the two rivers flow roughly parallel and adjacent to each other for a significant distance). Between the Platte River and the Thompson River is the south- and southeast-oriented Grand River, which originates near Afton, Iowa (located just east of Creston). West of the Platte River and Thompson River headwaters is the southwest and south oriented Nodaway River drainage basin, with the south-oriented Nodaway River flowing to the Missouri River a short distance upstream from the figure 1 south edge.

• The Platte River-Thompson River drainage divide area in Adair, Union, Ringgold, and Decatur Counties, Iowa represents the region between the Platte River and the Thompson River north of the Iowa-Missouri state line and includes drainage divides between the Platte River and Grand River and between the Grand River and Thompson River in addition to drainage divides between their tributaries. Note how the Platte River and Grand River in southern Iowa and northern Missouri flow adjacent to and parallel to each other for a considerable distance before ultimately turning slightly to eventually the join the Missouri River in quite different locations. Study of the Nodaway River drainage system reveals many south, south-southwest, and southwest oriented tributaries flowing parallel and adjacent to each other before finally converging to form the south-oriented Nodaway River. The Thompson River and Grand River drainage systems are similar with tributaries flowing parallel to the Thompson and Grand Rivers before finally converging to flow to the Missouri River. Study of the figure 1 map reveals other similar south-oriented drainage systems flowing to the Missouri River and southeast-oriented drainage systems flowing to the Mississippi River. These drainage systems with parallel and elongate converging drainage routes provide evidence of former anastomosing channel complexes. Anastomosing channel complexes are formed when immense floods cross a region and overwhelm whatever drainage system existed before. Flood waters eroded systems of diverging and converging channels into the underlying landscape. While flood flow continues these diverging and converging channel complexes are constantly evolving as deep erosion of one channel beheads flood flow moving to an adjacent channel. Further the ever-changing channel complexes can evolve into a well-defined drainage network as deep valleys erode headward into the channel complex region, which is what happened in the figure 1 map area.

• Topographic maps with more detail than figure 1, some samples of which are shown below, illustrate additional evidence supporting this flood origin interpretation. Further, study of drainage divides throughout the entire Missouri River drainage basin, as is being done by this Missouri River drainage basin landform origins research project, provides still more evidence including data required to trace flood flow routes across the region. In brief the entire figure 1 map area was eroded by immense south-oriented floods as the deep valleys, which form today’s drainage system, eroded headward into the region. Flood waters were derived from a rapidly melting thick North American ice sheet the southern margin of which, at the time present day valley systems were eroded, was located north of the figure 1 map area. The ice sheet had been comparable in size to the modern Antarctic Ice Sheet, if not larger, and had been located in a deep “hole”. The deep “hole” had been formed by deep glacial erosion and also by crustal warping caused by the ice sheet’s tremendous weight. The figure 1 map region was located along the deep “hole’s” southern rim and was deeply eroded by immense south-oriented melt water floods flowing to the Gulf of Mexico. How much material flood waters stripped from the figure 1 map area and regions to the south may never be determined, although it could measure into the hundreds of meters. Further, the ice sheet’s maximum southern advance may never be determined because flood water erosion and deposition has probably destroyed all evidence of whatever end moraines may have been formed. With that said it should be understood flood waters completely altered whatever drainage system existed prior to the ice sheet formation. Present day drainage systems evolved as the deep Mississippi River valley eroded headward from the Gulf of Mexico and as deep tributary valleys eroded headward from the actively eroding Mississippi River valley.

• Mississippi River tributary valleys eroded headward from the actively eroding south oriented valley both to the west and to the east. Of concern in this Missouri River drainage basin landform origins research project are tributary valleys which eroded headward toward the west. These tributaries eroded headward in sequence from the south to the north. For example, headward erosion of the Arkansas River valley occurred prior to headward erosion of the (White River valley (in Arkansas), which occurred prior to headward erosion of the Missouri River valley, which in turn occurred prior to headward erosion of the Des Moines River valley. Headward erosion of each successive east and southeast oriented Mississippi River tributary valley (and east oriented tributary valley to that tributary valley) beheaded south oriented flood flow to the newly eroded tributary valley located immediately to south. Often flood waters on north ends of beheaded flood flow routes (or channels) reversed flow direction to erode north-oriented tributary valleys (which are today barbed tributaries). At the same time south oriented flood flow eroded south-oriented tributary valleys headward from the newly eroded east and southeast-oriented deep tributary valleys. Headward erosion of these deep valleys systems also caused south-oriented flood waters to change direction and to flow in a southeast direction toward the actively eroding deep valley systems. The difference in tributary orientations observed along the figure 1 Des Moines River-Missouri River drainage divide resulted when headward erosion of the deep Mississippi River-Des Moines River valley captured south-oriented flood flow moving to actively eroding south-oriented Missouri River tributary valleys and created a southeast-oriented anastomosing channel complex which was captured by development of a south- southwest oriented anastomosing channel complex.

• Figure 2 provides a somewhat more detailed location map for the Platte River-Thompson River drainage divide area in Adair, Union, Ringgold, and Decatur Counties, Iowa. County boundaries and names are shown. The west to east oriented Iowa-Missouri state line is located a short distance north of the figure 2 south edge. The Thompson River originates near Greenfield in Adair County and flows in an east direction before turning to flow in a south-southeast direction across the Madison County southwest corner and eastern Union County to the Decatur County northwest corner. Once in Decatur County the Thompson River turns to flow in more of a south direction to the Missouri state line and the figure 2 south edge. Thompson River tributaries tend to have elongate and narrow south-southeast and south oriented drainage basins parallel to the Thompson River and include Twelvemile Creek and Threemile Creek in Union County. The Platte River originates near Green Valley Lake in northwest Union County and flows in a south-southwest, south-southeast, south, and south-southwest direction across the Union-Adams County border, western Ringgold County, the Taylor County southeast corner, and the Worth County, Missouri northwest corner to the figure 2 south edge. The Platte River has a narrow drainage basin with most tributaries being south-southwest, southwest, or south oriented and flowing roughly parallel to the Platte River before joining the Platte River. Between the Platte River and the Thompson River is the south, south-southwest, south, and south-southwest oriented Grand River, which originates in south central Union County and which flows to Diagonal in western Ringgold County and then which flows adjacent to and parallel with the Platte River to the figure 2 south edge. As previously mentioned the Platte River and Grand River are both south-oriented Missouri River tributaries, however south of the figure 2 map area the Grand River turns to flow in a southeast direction to join the Missouri River (and the south-oriented Thompson River is a Grand River tributary) and the Platte River flows in a south direction to eventually join the Missouri River at a point significantly upstream from where the Grand River enters the Missouri River. Again note how Grand River tributaries are south and south-southwest oriented and tend to have elongate narrow drainage basins. Shanghai Creek in southern Adair County is the northernmost East Nodaway River tributary while the Middle Nodaway River originates north and west of Greenfield in Adair County and flows in a south-southeast and southwest direction to the Adair County southwest corner and the figure 2 west edge. West of the figure 2 map area the Nodaway River branches join to form the south-oriented Nodaway River, which joins the Missouri River significantly upstream from where the Platte River joins the Missouri River. Between the Platte River and the Nodaway River in south central Adams County and Taylor County are south-southwest and south oriented headwaters of the One Hundred and Two River, which south of the figure 2 map area joins the south-oriented Platte River. As already noted all observed drainage basins in the figure 2 map area are elongate and narrow and roughly parallel with each other, although in the study region the Thompson River drainage basin has a south-southeast orientation while drainage basins to the west have more of a south or south-southwest orientation.

• Figure 3 provides a reduced size topographic map to illustrate the East Nodaway River-Platte River drainage divide area north of Creston, Iowa. Creston is the large town located near the figure 3 south edge. Green Valley Lake is the reservoir located north of Creston and is flooding the south oriented Platte River valley. The Platte River originates near Spalding, which is a very small town north of Green Valley Lake. The south-southeast oriented stream flowing across the figure 3 northeast corner is Threemile Creek and Twelvemile Creek is the south-southeast oriented stream just west of Threemile Creek. Threemile Creek and Twelvemile Creek are Thompson River tributaries. The south, west, south, southwest, south, and southwest oriented stream flowing from the figure 3 north center edge to the figure 3 southwest corner is the East Nodaway River. The southwest-oriented East Fork flows from the figure 3 north center area and joins the East Nodaway River in the figure 3 southwest quadrant. Nevinsville is the small town located in the Adams County northeast corner. The south-oriented East Nodaway River tributary located west of Nevinsville is Shanghai Creek. Note how Shanghai Creek, the East Nodaway River, and the East Fork East Nodaway River all have northwest-oriented barbed tributaries. North of Creston a southwest-oriented Platte River tributary also has a northwest-oriented tributary. These northwest-oriented streams flowing to what are today south-oriented drainage systems are located in valleys eroded by reversals of flood flow on northwest ends of beheaded southeast and/or south-southeast oriented flood flow routes. The southeast-oriented flood flow was captured in sequence from east to west by headward erosion of south, south-southwest, and southwest oriented deep valleys associated with what were then the developing Platte and Nodaway River drainage systems. Headward erosion of the southwest-oriented Platte River tributary valley north of Creston beheaded and reversed flood flow to a southeast-oriented Platte River tributary valley east of Creston. Headward erosion of the East Fork (East Nodaway River) valley beheaded and reversed south- and southeast-oriented flood flow to what was then the newly eroded Platte River valley. Next headward erosion of the deep East Nodaway River valley beheaded and reversed southeast-oriented flood flow to the newly eroded East Fork valley and also to the what was then the actively eroding Platte River valley head near Spalding. Headward erosion of the deep Shanghai Creek valley next beheaded and reversed southeast-oriented flood flow routes to the newly eroded East Nodaway River valley. Had the deep Platte River and Nodaway River headwaters and tributary valleys not eroded headward into the figure 3 map area the southeast and south-southeast oriented flood flow probably would have eroded additional south-southeast oriented Thompson River tributary valleys into the region (similar to the present day Twelvemile Creek and Threemile Creek valleys).

• Figure 4 provides a more detailed topographic map of the East Nodaway River-Platte River drainage divide area seen in less detail in figure 3 above. Nevinsville is the town located near the figure 4 west center edge. Spalding is located just east of the figure 4 east center edge. The Platte River originates near Spalding and flows in a south direction along the figure 4 east edge to the southeast corner (the north end of Green Valley Lake can be seen in the southeast corner). The East Nodaway River flows in a southwest and northwest direction from the figure 4 north edge into sections 33 and 32 and then back north of figure 4. The East Nodaway River then reenters figure 4 as a south and south-southwest oriented stream in section 36 and flows to the figure 4 west edge south of Nevinsville in section 14. The East Fork (East Nodaway River) originates in section 4 (figure 4 northeast quadrant) and flows in a south and southwest direction to the figure 4 south edge (west of center).  Note the north oriented tributary joining the East Fork in the section 17 northeast corner. While most figure 4 barbed tributaries are not as obvious as that section 17 tributary a study of the figure 4 map area reveals numerous northwest-oriented tributaries to both the East Nodaway River and the East Fork. Close study of figure 4 drainage divides also reveals some shallow through valleys linking northwest-oriented tributary valleys with south and southeast oriented tributary (and/or headwaters) valleys. Relief along the drainage divides in this region is very low and the through valleys are defined by a single 10-foot contour line on each side. For example in sections 13 and 14 in the figure 4 southwest corner shallow through valleys can be seen linking a west-oriented East Nodaway River tributary valley with south-oriented East Fork tributary valleys. A broad shallow through valley in the section 12 southeast corner links a northwest-oriented East Nodaway River tributary valley with a south-oriented East Fork tributary valley.  Near the corner of sections 32, 33, 4, and 5 several shallow through valleys link north and northwest-oriented East Nodaway River tributary valleys with the south-oriented Platte River valley head. All of these through valleys provide evidence of south- and southeast-oriented flood flow routes which were beheaded and reversed by headward erosion of the deep valleys to the north or northwest. The northwest-oriented East Nodaway River valley segment in section 32 probably was eroded by a reversal of flood flow on the northwest end of a southeast-oriented flood flow route to what was then the actively eroding Platte River valley head. Once the southeast-oriented flood flow route was beheaded and reversed headward erosion of the deep south-oriented Platte River valley ended and the Platte River valley has changed little since.

• Figure 5 provides a topographic map of the Thompson River-Twelvemile Creek drainage divide area located east and slightly north of the figure 3 map area and includes overlap areas with figure 3. Orient, Iowa is the town located in the northwest corner and Spalding is located in the figure 5 west center area. The Platte River originates near Spalding and flows in a south direction through Green Valley Lake to the figure 5 south edge (near southeast corner). The south-southeast oriented stream originating north of Spalding and flowing to the figure 5 south center edge is Twelvemile Creek and Twelvemile Lake is a reservoir flooding the Twelvemile Creek valley near the south edge. The east-northeast and south-southeast oriented stream originating north of the Twelvemile Creek headwaters near Orient and flowing adjacent to and parallel with Twelvemile Creek to the figure 5 south edge (east half) is Threemile Creek. Twomile Creek is the south-southeast and south oriented stream flowing to the figure 5 south edge just east of Threemile Creek. The Thompson River flows in a south-southeast direction from the figure 5 north edge (east half) to the east edge (south half). South and east of the figure 5 map area Twomile Creek joins Threemile Creek which then joins the Thompson River and further south Twelvemile Creek joins the Thompson River. West Branch Creek flows in a southeast direction from the figure 5 north center edge and then in an east direction before turning to flow in a southeast direction to join the south-southeast oriented Thompson River (near the Madison-Union County line and figure 5 east edge). Note how the various south-southeast and southeast oriented streams have north and northeast oriented tributaries. These barbed tributaries are flowing in valleys eroded by reversals of flood flow on what were originally south-oriented flood flow routes. For example a north-oriented tributary flows to Twelvemile Creek at the north end of Twelvemile Lake (near figure 5 south center edge) and West Branch Creek has several north-oriented tributaries. A close look at the West Branch Creek-Threemile Creek drainage divide reveals shallow through valleys linking north-oriented West Branch Creek tributary valleys with south-oriented Threemile Creek tributary valleys. These through valleys are defined by one 10-meter contour line on each side and provide evidence of south-oriented flood flow routes to what was then the actively eroding Threemile Creek valley prior to headward erosion of the deep West Branch Creek valley. Relief along drainage divides in this region is very low and through valleys are best seen on more detailed topographic maps and even then are subtle. Figure 6 below provides a detailed topographic map of the West Branch Creek-Twomile Creek drainage divide area to better illustrate through valleys crossing that divide.

• Figure 6 provides a detailed topographic map of the West Branch Creek-Twomile Creek drainage divide area seen in less detail in the figure 5 map above. Note the west to east oriented Madison-Union County line just south of the figure 6 north edge. The Thompson River flows in a south-southeast direction from the figure 6 north edge (east half) to the figure 6 southeast corner. West Branch Creek is located north of the Madison-Union County line and flows from the figure 6 north center area to join the Thompson River. Note the northeast and north-northeast oriented West Branch Creek tributary flowing through section 9 and how that tributary has north-oriented tributaries. The southeast and south-southeast oriented stream flowing to the section 16 southeast corner and then to the figure 6 south center edge is Twomile Creek (not labeled in figure 6). Note the south-oriented tributary to Twomile Creek with the small reservoir in the section 16 northeast quadrant. Observe how that south-oriented tributary valley is linked by a shallow through valley with the north-oriented West Branch Creek valley in section 9. Also note other shallow through valleys linking the south-oriented Twomile Creek valley with north-oriented West Branch Creek tributary valleys. For example in section 8 a shallow through valley links the southeast-oriented Twomile Creek headwaters valley with a north-oriented West Branch Creek tributary valley. The through valleys while defined by single 20-foot contour lines on each side provide evidence of multiple south-oriented flood flow channels prior to headward erosion of the deep West Branch Creek valley. These multiple south-oriented flood flow routes suggest the presence of multiple diverging and converging flood flow channels typical of a flood formed anastomosing channel complex. Headward erosion of the deep Thompson River valley and its tributary valleys captured these south-oriented flood flow channels in sequence from the south to the north. In the figure 6 map area headward erosion of the deep West Branch Creek valley and its tributary valleys captured south- and southeast-oriented flood flow channels moving flood waters to what were then the actively eroding Twomile Creek valley and its tributary valleys. Flood waters on north ends of the beheaded flood flow routes reversed flow direction to erode the north-oriented West Branch Creek tributary valleys.

• Figure 7 illustrates the Twelvemile Creek-Grand River drainage divide area south of the figure 5 map area (there is no overlap). Afton, Iowa is the town near the figure 7 north center edge. Twelvemile Creek makes an east-oriented jog along the figure 7 north center edge and then turns to flow in a south-southeast direction just west of Afton to the figure 7 east edge (near southeast corner). The Thompson River flows in a south and southeast direction from the figure 7 north edge (near northeast corner) to the figure 7 east center edge. Threemile Creek is the southeast oriented tributary joining the Thompson River just north of Talmage near the figure 7 northeast corner and Star Branch is the southeast and east-oriented tributary joining the Thompson River just south of Talmage. Note how a north-northeast oriented Star Branch tributary is linked by a shallow through valley with a south-southeast oriented Twelvemile Creek tributary valley. Also make note of the northeast-oriented Twelvemile Creek tributaries located south of Afton (Indian Creek is the labeled southeast and northeast-oriented tributary). The south-oriented stream just west of Indian Creek (which has a jog to the west) is the headwaters of the Grand River. The south- and southwest-oriented stream west of the Grand River (the stream flowing through the word “HIGHLAND”) is the East Platte River. Note how the East Platte River and the Grand River both originate directly south of the east-oriented Twelvemile Creek jog. Remember, the Platte River and the Grand River join the Missouri River at significantly different locations and Twelvemile Creek is a Thompson River tributary and the Thompson River is a Grand River tributary. What this evidence is saying is headward erosion of the deep Twelvemile Creek valley (from the deep Thompson River valley) beheaded a diverging south-oriented flood flow channel supplying flood waters to both the actively eroding East Platte River valley and the actively eroding Grand River valley. What appears to have happened in this region is the south and south-southwest oriented Grand River and East Platte River eroded headward into the region to capture south- and southeast-oriented flood flow, but headward erosion of the deep Thompson River valley and its Twelvemile Creek tributary valley was able to behead flood flow routes from the north while headward erosion of the Platte River valley (and tributary valleys) west of the figure 7 map area beheaded flood flow from the northwest. The result was headward erosion of the Grand River valley and the East Platte River valley ended and those valleys as seen in the figure 7 map area have changed little since.

• Figure 8 provides a detailed topographic map of the Indian Creek-Grand River drainage divide area seen in less detail in figure 7 above. Arispe is the small town straddling the figure 8 south center edge. The southwest edge of the southeast-oriented Twelvemile Creek valley can be seen in the figure 8 northeast corner.  The Grand River flows in a south-southeast direction from section 36 (near figure 8 northwest corner) to section 7 and then makes a jog in a west direction to the section 12 southwest corner before resuming its south-oriented flow direction. Note north oriented tributaries joining the west-oriented Grand River segment and a west-oriented tributary to that segment. Indian Creek originates just north of the figure 8 map area and flows in a south-southeast direction across the section 36 northeast corner and the section 31 southwest corner to section 6. Once in section 6 Indian Creek changes direction to flow in a northeast direction to the figure 8 north edge (in section 33) and joins Twelvemile Creek just north of the figure 8 map area. Observe how Indian Creek has north and northwest-oriented tributaries from the south. Shallow through valleys cross the Indian Creek-Grand River drainage divide in the section 7 northeast quadrant and section 8 northwest quadrant and provide evidence of south-oriented flood flow channels to the once actively eroding Grand River valley. At that time a south-southeast oriented flood flow channel and a southwest-oriented flood flow channel converged near the Indian Creek elbow of capture and then flowed in a south and southwest direction to the actively eroding Grand River valley and its west-oriented tributary valley. Headward erosion of the deep Twelvemile Creek valley north and east of the figure 8 map area then beheaded the southwest-oriented flood flow channel and flood waters on the northeast end of the beheaded flood flow channel reversed flow direction to erode the deep northeast-oriented Indian Creek valley. Headward erosion of the deep northeast-oriented Indian Creek valley captured the south-southeast oriented flood flow channel to create the Indian Creek elbow of capture and the deep Indian Creek valley eroded headward along that south-southeast oriented flood flow channel. A similar north-south oriented shallow through valley can be seen near the figure 8 west center edge and links an east-oriented Grand River tributary valley with a south-oriented Grand River tributary valley.

• Figure 9 illustrates the Platte River-Grand River drainage divide area south and west of the figure 7 map area (there are no overlap areas). The west to east oriented Iowa-Missouri state line is located a short distance north of the figure 9 south edge (Worth County is located in Missouri). The Platte River flows in a south-southwest direction from the figure 9 north center edge to the figure 9 southwest corner. Maloy is the town located in the Platte River valley in the figure 9 north center area and Blockton is the Platte River valley town located in the west center area. Note southeast-oriented Platte River tributaries from the north and west. Most Platte River tributaries from the east and south are short, although a close look reveals some northwest-oriented tributaries. For example north of Blockton a south and west oriented Platte River tributary valley is linked by shallow through valleys with two northwest-oriented Platte River tributary valleys. The Grand River flows in a south-southeast direction from the figure 9 north edge (east half) parallel to the Platte River to the figure 9 south edge (west half). Observe how Grand River tributaries from the north and west are oriented in southeast and south directions. Also observe how many of those south- and southeast-oriented Grand River tributaries are linked by shallow through valleys with the Platte River valley. For example south of Blockton a northwest-oriented Platte River tributary valley is linked by a shallow through valley with a south-oriented Grand River tributary valley. Further note northwest-oriented Grand River tributaries from the south and east. The Middle Fork Grand River flows in a south-southwest direction from the figure 9 east edge (north half) to the figure 9 south edge (east half). Again note how Middle Fork Grand River tributaries from the north and west are oriented in south and southeast directions and are linked by shallow through valleys with northwest-oriented Grand River tributary valleys. Mitchells Run and Fiddlers Creek are two labeled south-southeast oriented tributaries joining the Middle Fork Grand River in the figure 9 east center area. Note how in the Delphos area Mitchells Run and Fiddlers Creek are linked by multiple shallow through valleys with the south-southeast oriented Grand River valley. Fletchall Creek is a south-southwest oriented Middle Fork Grand River tributary (joining the Middle Fork just south of the figure 9 map area). Note how near the figure 9 east center edge the Fletchall Creek valley is linked by a shallow through valley with a north-oriented Middle Fork Grand River tributary. The south-southwest oriented stream flowing across the figure 9 southeast corner is the East Fork Grand River, which is better seen in figure 10 below. Remember when looking at figure 9 the Platte River and the Grand River are separate Missouri River tributaries, with the Platte River flowing in a south-southwest and south direction from the figure 9 map area to join the Missouri River while the Grand River turns to flow in a southeast direction to join the Missouri River. What has happened in the figure 9 map area is headward erosion of the deep southeast-oriented Grand River valley captured the east half of a south-southwest-oriented anastomosing channel complex, while the Platte River channel represents the easternmost channel not captured by Grand River valley headward erosion. The northwest-southeast oriented through valleys and tributary orientations suggest the south-southwest oriented anastomosing channel complex had previously captured a southeast or south-southeast oriented anastomosing channel complex.

• Figure 10 illustrates the East Fork Grand River-West Fork Big Creek drainage divide area located east of the figure 9 map area and includes overlap areas with figure 9. Note the west to east oriented Iowa-Missouri state line near the south edge (Worth and Harrison Counties are in Missouri). The Middle Fork Grand River flows in a south and south-southwest direction in the figure 10 northwest corner area. The East Fork Grand River flows in a south and south-southwest direction from the figure 10 north edge (just west of center) to the figure 10 southwest corner. South-southwest oriented Fletchall Creek is located between the Middle Fork Grand River and the East Fork Grand River. Lotts Creek is the south and south-southwest oriented stream flowing parallel to the East Fork from the figure 10 north center edge to the south edge (west half). Tuckers Creek is the south-southwest and west oriented tributary joining Lotts Creek just north of the figure 10 center. Long Branch is the north-northwest oriented barbed tributary joining Lotts Creek in the figure 10 south center area. The south-oriented stream near the figure 10 east edge is named Kuder Creek in the north and the West Fork Big Creek further to the south. South of the figure 10 map area the West Fork Big Creek flows to Big Creek which in turn flows to the southeast-oriented Grand River. Wolf Creek is the labeled south-oriented West Fork Big Creek tributary located between Lotts Creek and the West Fork Big Creek. Study of the figure 10 map area reveals several north- and northwest-oriented barbed tributaries and elbows of capture and also numerous shallow through valleys crossing drainage divides. For example near the figure 10 north center edge a shallow through valley links the south-southwest oriented Tuckers Creek valley with a northwest-oriented Lotts Creek tributary valley. Further south, just south of the elbow of capture where Tuckers Creek turns to flow in a west direction multiple shallow through valleys link the Tuckers Creek valley with the south-oriented Wolf Creek valley. Or, just north of Caledonia (a place-name near the figure 10 center) shallow through valleys link the East Fork Grand River valley with the Lotts Creek valley. The barbed tributaries, elbows of capture, and shallow through valleys all provide evidence of diverging and converging flood flow channels typical of anastomosing channel complexes. South-oriented valleys in the figure 10 east half probably eroded headward along and across south- and southeast-oriented flood flow channels moving flood waters toward actively eroding deep Grand River tributary valleys to the south and east. The south-southwest oriented channels in the figure 10 west half and in figure 9 probably initially eroded headward along and across south- and southeast-oriented flood flow channels from deep Missouri River tributary valleys to the south and west. However, present day south-southwest oriented Grand  River tributary valleys (including the Grand River valley) were captured by headward erosion of the deep southeast-oriented Grand River valley.

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.