Abstract:

This essay uses topographic map evidence to illustrate and discuss landform origins in the Floyd River-Little Sioux River northern drainage area located in northwest Iowa. A separate essay illustrates and discusses landform origins in the Floyd River-Little Sioux River drainage divide area in Woodbury and Monona Counties. The Floyd River and Little Sioux River are south-southwest and southwest oriented tributaries to the south-southeast oriented Missouri River. The Little Sioux River is located east and south of the Floyd River and also originates north of the Floyd River headwaters. East of the northern Little Sioux River drainage basin is the Des Moines River drainage basin, with the Des Moines River being a southeast-oriented Mississippi River tributary. West and north of the northern Floyd River drainage basin is the Rock River-Big Sioux River drainage basin, with the Big Sioux River flowing in a south direction to the Missouri River and the Rock River flowing in a south and southwest direction to the Big Sioux River. The northern Floyd River and Little Sioux River valleys and their tributary valleys eroded headward along and across large south- and southeast-oriented melt water floods from a rapidly melting North American ice sheet at a time when the ice sheet’s southern margin was located somewhere in the northern Little Sioux River and Des Moines River drainage basin areas, although probably north of the Floyd River headwaters area. The northern Little Sioux River and Des Moines River valleys probably originated as parallel south-oriented ice-walled canyons carved by supra glacial melt water rivers into the decaying ice sheet’s surface with flow from the western ice-walled canyon being captured by headward erosion of the southwest-oriented Little Sioux River valley from what was then the newly eroded Missouri River valley and flow from the eastern ice-walled canyon being captured by headward erosion of the southeast-oriented Des Moines River valley from the Mississippi River valley.

Preface:

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

Location map for Floyd River-Little Sioux River northern drainage divide area in northwest Iowa

Figure 1: Location map for Floyd River-Little Sioux River northern drainage divide area in northwest Iowa (select and click on maps to enlarge).

• Figure 1 provides a regional map of northwest Iowa with southwest Minnesota to the north, southeast South Dakota to the west and northeast Nebraska in the figure 1 southwest corner. The Missouri River flows in a southeast direction across the figure 1 southwest quadrant from Yankton, South Dakota to Sioux City, Iowa and then in a south direction to the figure 1 south edge. The Big Sioux River flows in a south direction from the figure 1 north edge to Sioux Falls, South Dakota and then flows along the Iowa-South Dakota border to join the Missouri River near Sioux City, Iowa. The unlabeled south and southwest oriented Big Sioux River tributary flowing through Luverne, Minnesota (in the Minnesota southwest corner) to Rock Rapids, Iowa and joining the Big Sioux River near Hudson, South Dakota is the Rock River. Big Sioux River drainage basin (including the Rock River drainage basin) landform origins essays can be found listed under Big Sioux River on the sidebar category list. The Floyd River is the unlabeled south-southwest oriented stream flowing from near Boyden, Iowa (near Iowa northwest corner) to Sioux City where it joins the south-oriented Missouri River. East of the Floyd River is the south, southwest, and south-southwest oriented Little Sioux River, which is labeled on figure 1 and which joins the Missouri River south of figure 1. The Little Sioux River originates in southern Minnesota (north of Spirit Lake, Iowa and flows in a south direction to Spirit Lake, Spencer, and Sioux Rapids, Iowa before turning to flow in a southwest and south-southwest direction to Cherokee and Anton, Iowa before flowing to the figure 1 south edge. The Floyd River-Little Sioux River drainage divide area in Woodbury and Monona Counties, Iowa essay illustrates and discusses landform origins in the southern half of the Floyd River-Little Sioux River drainage divide area and is listed under Iowa on the sidebar category list. This essay illustrates and discusses topographic map evidence related to landform origins north Woodbury County (Sioux City is in Woodbury County). East of the Little Sioux River (along the Minnesota-Iowa border) is the south-southeast oriented Des Moines River. The Des Moines River flows independently to the Mississippi River and, unlike the Little Sioux River drainage basin, the Des Moines River drainage basin is not included in the Missouri River drainage basin.

• Landforms in the figure 1 map area were eroded by massive south-oriented melt water floods which flowed across the entire figure map area prior to headward erosion of present day river valleys. Flood waters were derived from a rapidly melting North American ice sheet, the southern margin of which during events important to this essay was probably located near the Minnesota-Iowa border. The ice sheet had been thick and had been located in deep”hole” created by deep glacial erosion and by crustal warping caused by the ice sheet’s great weight. To what extent the ice sheet once extended south of the Minnesota-Iowa border area is difficult to determine (especially from topographic map evidence alone) because subsequent melt water flood erosion and deposition has significantly altered landscapes along all melt water flood flow routes. Evidence for the ice sheet margin near the Minnesota-Iowa border at the time of events important to this discussion can be seen on figure 1 in the form of lakes in the northern Little Sioux River drainage basin (near the Minnesota-Iowa border). These lakes are much better shown on more detailed maps illustrated below and provide evidence of glacial deposition around decaying ice sheet remnants. In other words, the figure 1 map evidence suggests the presence of a decaying ice sheet located in the Little Sioux River headwaters area. Essays listed under Big Sioux River on the sidebar category list present evidence suggesting the Big Sioux River location originated as an ice-walled canyon carved into the decaying ice sheet surface. A much larger and deeper south-oriented ice-walled canyon was located west of the Big Sioux River along the route of the present day James River, which joins the Missouri River at Yankton, South Dakota. Immense south-oriented melt water floods flowing from those two ice-walled canyons were responsible for eroding the deep (and large) south-oriented Missouri River valley headward into the figure 1 map area. It is possible the Little Sioux River valley eroded headward from the newly eroded Missouri River valley to capture flood waters from similar, but much smaller and less extensive ice-walled canyons carved into the decaying ice sheet surface.

Detailed location map for Floyd River-Little Sioux River northern drainage divide area

• Figure 2 provides a more detailed location map for Floyd River-Little Sioux River northern drainage divide area in northwest Iowa. Iowa county names and boundaries are shown. The Minnesota-Iowa boundary is located north of Lyon, Osceola, Dickinson, and Emmet Counties. The south-oriented Big Sioux River can be seen along the figure 2 west edge and forms the Iowa-South Dakota border. The Rock River flows in a south direction from the figure 2 north edge into central Lyon County and then turns to flow in a south-southwest direction to join the Big Sioux River near Hudson, South Dakota (located near figure 2 west center edge). The Floyd River originates in the O’Brien County northwest corner and flows across western Sioux County in a south-southwest direction to Le Mars in Plymouth County and then to the figure 2 south edge. Note how for most of its distance the Floyd River is oriented in a south-southwest direction and has a relatively narrow drainage basin. Except in the headwaters area most tributaries are generally oriented in south-southwest directions and flow parallel to the Floyd River. In the headwaters area in north central O’Brien County the Floyd River flows in a south, northwest, and west direction before turning to flow in a south-southwest direction. North of the Floyd River headwaters are headwaters of west-oriented Rock River tributaries and further north are headwaters of southeast-oriented Ocheyedan River tributaries, both of which appear to originate in regions near lakes shown in and north of Osceola County, suggesting water that eroded the present day drainage routes was derived from a melting ice sheet located in and north of Osceola County.

• The Little Sioux River flows from the figure 2 north edge in a south and southeast direction to Spirit Lake in Dickinson County and then meanders in a south direction to Spencer in Clay County and Sioux Rapids in northern Buena Vista County. From Sioux Rapids the Little Sioux River flows in a west-northwest direction into the O’Brien County southeast corner and then turns to flow in a south-southwest direction to Cherokee in Cherokee County and to the figure 2 south center edge. A Little Sioux River tributary of importance in the following discussion is the southeast-oriented Ocheyedan River, which flows to the Osceola County southeast corner and then into Clay County to join the Little Sioux River at Spencer. Southeast-oriented Willow Creek in southern Clay County, south-southeast oriented Waterman Creek in eastern O’Brien County, south- and southeast-oriented Mill Creek in O’Brien and Cherokee Counties, and the West Fork Little Sioux River (which originates in northwest Cherokee County and which flows to the figure 2 south edge) are other significant Little Sioux River tributaries. East of the Little Sioux River the south-southeast oriented Des Moines River flows from the figure 2 north edge into and across western Emmet County and then across central Palo Alto County. Both the Little Sioux River and the Des Moines River originate north of the figure 2 map area and flow through the lake dotted regions in Dickinson, Emmet, Clay, and Palo Alto Counties. Both rivers probably originated as supra-glacial melt water flow routes, which had carved deep ice-walled canyons into the decaying ice sheet surface. The southeast oriented Des Moines River valley eroded headward across south-oriented melt water floods to capture melt water flood flow from the south-southeast oriented Des Moines River ice-walled canyon while the south-southwest oriented Little Sioux River valley eroded headward across south- and southeast-oriented flood flow to capture flow from the Little Sioux River ice-walled canyon.

Little Sioux River route near Spirit Lake, Iowa

Figure 3: Little Sioux River route near Spirit Lake, Iowa.

• Figure 3 uses a reduced size topographic map to illustrate the south-oriented Little Sioux River route west of Spirit Lake, Iowa. The west-east oriented Minnesota-Iowa border is located just south of the figure 3 north edge. The town of Spirit Lake, Iowa is located in the figure 3 east center area and is south of Spirit Lake. South of Spirit Lake is East Okoboji Lake and west of East Okoboji Lake is West Okoboji Lake. Note the numerous other smaller lakes in the figure 3 east half. Silver Lake is the largest lake in the figure 3 east half. The Little Sioux River flows in a south-southwest and then south-southeast direction from the figure 3 north center edge to the figure 3 south center edge and is joined by the south-oriented West Fork Little Sioux River  west of the figure 3  center area. Note how the Little Sioux River flows between Silver Lake and the concentration of lakes in the Spirit Lake region. The lakes probably represent locations of ice sheet remnants around which glacially transported and melt water flood transported debris was deposited. The ice sheet remnants then melted leaving depressions where they had been located. The Little Sioux River location between the lakes suggests the Little Sioux River route was initiated as a south-oriented ice-walled canyon in the decaying ice sheet surface. Melt water floods flowing on the ice-walled canyon’s floor probably moved and deposited debris which had been contained in the melting ice sheet along the canyon floor and also proceeded to hasten ice sheet melting adjacent to and along the canyon route. Areas further from the south-oriented ice-walled canyon probably melted more slowly and were not subjected to the same amount of deposition of melt water flood transported glacial debris. While inspection of more detailed topographic maps and also of field evidence is needed to further develop this interpretation, the figure 3 map evidence definitely suggests the Little Sioux River route was established at a time when ice was still present in the figure 3 map area.

Little Sioux River-Des Moines River drainage divide area east of Spencer, Iowa

Figure 4: Little Sioux River-Des Moines River drainage divide area east of Spencer, Iowa. 

• Figure 4 provides a reduced size topographic map of the Little Sioux River-Des Moines River drainage divide area between Spencer and Emmetsburg, Iowa and is located south of the figure 3 map area. The Little Sioux River flows in a south direction from the figure 4 north edge (west half) to the southwest quadrant and then turns to flow in a south direction to the south edge where it is joined by southeast-oriented Willow Creek. Spencer, Iowa is the larger town located just west of the south oriented Little Sioux River. The Des Moines River flows in a south-southeast direction from the figure 4 north edge (east half) to the figure 4 east edge (just north of southeast corner). Emmetsburg is the larger town located just east of the Des Moines River. Ruthven is the town located between Spencer and Emmetsburg and south of Lost Island Lake. Note how the region between the Little Sioux River and the Des Moines River is characterized by low hills, lakes, and poorly drained areas such as might be expected in a glacial moraine area. The topographic map evidence suggests decaying ice sheet remnants were present in what is now the Little Sioux River-Des Moines River drainage divide area at the time the Little Sioux River and Des Moines River routes were established. If so, at that time the Little Sioux River and Des Moines River were probably flowing in south-oriented ice-walled and bedrock-floored canyons which had been carved into the decaying ice sheet’s surface by large south-oriented supra-glacial melt water rivers. What makes this Little Sioux River-Des Moines River drainage divide area different from other south-oriented melt water river drainage divide areas is south-oriented melt water flow on the Des Moines River alignment was captured by headward erosion of a deep southeast-oriented valley from the south-oriented Mississippi River valley while south-oriented melt water flow on the Little Sioux River alignment was captured by headward erosion of a deep south-southwest and southwest oriented valley from what was then the newly eroded Missouri River valley. Headward erosion of the deep southeast-oriented Des Moines River valley and the deep south-southwest and southwest oriented Little Sioux River valley to this figure 4 map area in northern Iowa implies immense south- and southeast-oriented melt water floods were flowing across the entire state of Iowa (until being captured by headward erosion of the Des Moines River and Little Sioux River valleys).

Ocheyedan River-Floyd River drainage divide area

Figure 5: Ocheyedan River-Floyd River drainage divide area. 

• Figure 5 uses a reduced size topographic map to illustrate the Ocheyedan River-Floyd River drainage divide area located west of the figure 4 map area. Sibley, Iowa is the larger town located west of the figure 5 north center area. Sheldon is the larger town located near the south edge in the figure 5 southwest quadrant. Ashton is the smaller town located between Sibley and Sheldon. Sanborn is the smaller town located near the figure 5 south center edge and Hartley is the smaller located east of Sanborn. The Ocheyedan River flows in a south-southeast direction in the figure 5 east half from the north edge to the east edge (near southeast corner). East of the figure 5 map area the Ocheyedan River turns to flow in an east direction to join the south oriented Little Sioux River east of Spencer (see figure 4). The south-southeast oriented stream flowing to the figure 5 south edge just west of Hartley is Waterman Creek, which also flows to the Little Sioux River. The Floyd River originates north of Sanborn and flows in a south, northwest, west, and southwest direction to Sheldon and the figure 5 south edge. South of the figure 5 map area the Floyd River flows in a south-southwest direction to join the Missouri River. The south- and southwest-oriented stream flowing from the figure 5 north edge to Sibley, Ashton, and then the figure 5 west edge (just north of southwest corner) is Otter Creek. Otter Creek is a Rock River tributary, with the Rock River flowing to the south-oriented Big Sioux River (see figures 1 and 2). Note how a shallow northwest-southeast oriented through valley between Ashton and Sheldon links the southwest-oriented Otter Creek valley with the southwest-oriented Floyd River valley (see figure 6). The through valley provides evidence flood water once flowed in a southeast direction across the present day Otter Creek-Floyd River drainage divide. Note also how Floyd River headwaters are south-oriented and then turn to flow in a northwest direction. Note also the south-southwest oriented North Fork Floyd River, which also has northwest-oriented headwaters (in figure 5 south center area). Note the south-southeast and northwest-oriented Otter Creek tributary north of the North Fork Floyd River (joining Otter Creek just south of Sibley) and northwest-oriented Otter Creek tributaries in the Ashton area. The northwest-oriented stream valleys and valley segments were eroded by reversals of flood flow on beheaded southeast-oriented flood flow routes. The southeast-oriented flood flow was probably moving along the ice sheet’s southwest margin and was subsequently diverted in other directions as deep valleys eroded headward into the region. The figure 5 map evidence suggests south- and southeast-oriented flood flow to the actively eroding Floyd River valley and tributary valleys was beheaded by headward erosion of the Otter Creek valley and its tributary valleys. Map evidence, including evidence from north of the figure 5 map area, suggests figure 5 valleys were eroded at a time when the decaying ice sheet southern margin was located in or just north of the figure 5 map area, with large volumes of flood flow moving across the entire figure 5 map area.

Detailed map of Otter Creek-Floyd River drainage divide area

Figure 6: Detailed map of Otter Creek-Floyd River drainage divide area.

• Figure 6 provides a detailed topographic map of the Otter Creek-Floyd River drainage divide area at Ritter, located between Ashton and Sheldon and seen in the less detailed figure 5 map. Otter Creek flows in a southwest direction across the figure 6 northwest corner. The Floyd River meanders in a west-southwest direction in the figure 6 southeast corner area. Wolf Creek is the west-northwest and south-southwest stream flowing around Ritter to the figure 6 south edge (west half) and is a Floyd River tributary. Note how elevations in the figure 6 southwest corner area rise to at least 1460 feet (the map contour interval is 10 feet). Elevations in the figure 6 northeast corner rise to 1520 feet and just north of the northeast corner to more than 1530 feet. While contour lines in the figure 6 north half are faint and difficult to read the through valley floor west of Ritter, which links the Otter Creek valley with the Wolf Creek valley, has an elevation of between 1420 and 1430 feet. The through valley floor linking the Wolf Creek west-northwest oriented headwaters valley with the Floyd River valley has an elevation of between 1430 and 1440 feet. The Otter Creek-Wolf Creek through valley is at least 30-40 feet deep and may be deeper and the Wolf Creek-Floyd River through valley is at least 20-30 feet deep and may be deeper. These through valleys are water eroded features and were eroded by southeast-oriented flood flow which was probably first captured by Floyd River valley headward erosion. Headward erosion of the south-southwest oriented Wolf Creek valley from the newly eroded Floyd River valley next beheaded and reversed the southeast-oriented flood flow to erode the west-northwest oriented Wolf Creek headwaters valley. Southeast-oriented flood flow continued to move into the newly eroded Wolf Creek valley, which is why the Otter Creek-Wolf Creek through valley is slightly deeper than the Wolf Creek-Floyd River through valley. Headward erosion of the southwest-oriented Otter Creek valley next beheaded southeast-oriented flood flow to the newly eroded Wolf Creek valley. Continued Otter Creek valley headward erosion beheaded and reversed flood flow to what was then the actively eroding Floyd River valley and tributary valleys, and diverted all southeast-oriented flood flow to the newly eroded Rock River-Big Sioux River valley. This figure 6 map evidence illustrates how valleys eroded headward across massive southeast-oriented flood flow in sequence, to form the present day drainage network.

Willow Creek-Gray Creek drainage divide area

Figure 7: Willow Creek-Gray Creek drainage divide area.

• Figure 7 provides a reduced size topographic map of the Little Sioux River valley segments near Sioux Rapids, Iowa and located south and west of the figure 4 map area. The Little Sioux River flows in a south direction into the figure 7 northeast corner and then turns near Sioux Rapids to flow in a west and northwest direction to the figure 7 northwest corner, where it turns again to flow in a southwest and south-southwest direction to the Missouri River. The south-southeast oriented tributary joining the Little Sioux River in the figure 7 northwest corner is Waterman Creek. The north oriented tributary flowing from the figure 7 south center edge is Brooke Creek and the north and northwest oriented tributary immediately east of Brooke Creek is Fox Run. The south-oriented stream in the figure 7 southeast corner is the North Raccoon River, which south of the figure 7 map area flows in a south-southeast direction to join other Raccoon River tributaries to form the east-oriented Raccoon River, which then joins the southeast-oriented Des Moines River at Des Moines, Iowa with the Des Moines River flowing the Mississippi River. In other words the Missouri River-Mississippi River drainage divide is located between the Little Sioux River and North Raccoon River valleys. Note how a northwest-southeast oriented through valley links the northwest-oriented Fox Run valley with the valley of a southeast-oriented North Raccoon River tributary. The figure 7 map contour interval is 10 meters and the through valley is defined by at least two contour lines on each side. The through valley is a water eroded feature and provides evidence of a southeast-oriented flood flow channel to what was once the actively eroding North Raccoon River valley and which was beheaded and reversed by headward erosion of the deep southwest and south-southwest oriented Little Sioux River valley. The northwest-oriented Fox Run valley segment and the northwest-oriented Little Sioux River valley segment were eroded by the resulting flood flow reversal. Headward erosion of the Little Sioux River valley then beheaded south-oriented flood flow routes supplying flood waters to the actively eroding North Raccoon River valley (see other north-south through valleys in Sioux Rapids region).

Whiskey Creek-West Fork Little Sioux River drainage divide area

Figure 8: Whiskey Creek-West Fork Little Sioux River drainage divide area.

• Figure 8 provides a topographic map of the Whiskey Creek-West Fork Little Sioux River drainage divide area northwest of Cherokee, Iowa. Cherokee is located just south of the figure 8 southeast corner and the south-southwest oriented Little Sioux River can be seen in the southeast corner. Marcus is the town located in the figure 8 southwest quadrant. Cleghorn is the small town located north of the figure 8 south center edge. Mill Creek is the southeast-oriented tributary flowing from the figure 8 north center edge to join the south-southwest oriented Little Sioux River in the figure 8 southeast corner. Whiskey Creek is the north-northeast oriented Mill Creek tributary located in the figure 8 north center area. Headwaters of the south and south-southwest oriented West Fork Little Sioux River are located between Marcus and Cleghorn and flow to the figure 8 south edge. The West Fork Little Sioux River flows roughly parallel to the Little Sioux River to enter the large south-southeast oriented Missouri River valley and then joins the Little Sioux River as a tributary before the Little Sioux River joins the Missouri River (river channels have been altered by human activity in the Missouri River valley area and no longer are located in their natural positions). Note the north-south oriented through valley linking the north-northeast oriented Whiskey Creek valley with the south-oriented West Fork Little Sioux River headwaters valley. The figure 8 map evidence suggests Mill Creek valley headward erosion beheaded and reversed south-oriented flood flow to what was then the actively eroding West Fork Little Sioux River valley. Calumet is the town located in the figure 8 northeast corner. The south-oriented stream originating just south of Calumet and joining the Little Sioux River in the figure 8 southeast corner is Gray Creek. The southwest and south oriented Mill Creek tributary located just north of Calumet is Willow Creek (one of several Willow Creeks in the region). Note the broad north-south oriented through valley linking the Willow Creek valley with the Gray Creek valley. Through valleys mentioned here are defined by one 10-meter contour line, but they are water eroded features and provide evidence of former flood flow routes. In the case of the Calumet region headward erosion of the Willow Creek valley beheaded flood flow to the actively eroding Gray Creek valley.

Detailed map of Whiskey Creek-West Fork Little Sioux River drainage divide area

Figure 9: Detailed map of Whiskey Creek-West Fork Little Sioux River drainage divide area. 

• Figure 9 provides a detailed map of the Whiskey Creek-West Fork Little Sioux River drainage divide area seen in less detail in figure 8 above. The figure 9 map contour interval is 10-feet. The West Fork Little Sioux River originates as an east-southeast oriented stream in section 22 (in figure 9 southwest corner) and flows across section 23 and into section 24 where it turns to flow in a south direction to the figure 9 south edge. Whiskey Creek originates as an east, southeast, and east-southeast-oriented stream just north of the east-southeast oriented West Fork Little Sioux River headwaters and flows across section 13 to section 18 where it turns to flow in a north-northeast direction to join south-southeast oriented Mill Creek as a barbed tributary. The floor of the through valley linking the north-northeast oriented Whiskey Creek valley with the south-oriented West Fork Little Sioux River valley has an elevation of between 1420 and 1430 feet. Note in the section 18 southeast corner and section 20 northwest corner elevations rising to at least 1460 feet. Also note along the figure 9 west edge elevations rising to more than 1470 feet. The through valley width, from high points on either side appears to be at least 2 sections, where each section is one mile square. This north-south oriented through valley, while shallow, is a significant erosional feature and illustrates how south-oriented flood flow eroded the Floyd River-Little Sioux River drainage divide area. Flood waters moved in a south direction across the through valley floor to the actively eroding south-oriented West Fork Little Sioux River valley until headward erosion of the south-southeast oriented Mill Creek valley from the newly eroded south-southwest oriented Little Sioux River valley beheaded and reversed the south-oriented flood flow. Reversal of flood flow on the north end of the beheaded flood flow route eroded the north-northeast oriented Whiskey Creek valley, created the Whiskey Creek-West Fork Little Sioux River drainage divide, and ended all flood flow to the West Fork Little Sioux River valley. The figure 9 map area landscape has changed little since.

Plymouth Creek-Mud Creek drainage divide area

Figure 10: Plymouth Creek-Mud Creek drainage divide area.

• Figure 10 illustrates the Plymouth Creek-Mud Creek drainage divide area and the Deep Creek-Johns Creek drainage divide area west and slightly south of the figure 8 map area. Le Mars is the larger town located in the figure 10 northwest quadrant. The south-southwest oriented river flowing just west of Le Mars is the Floyd River. Deep Creek is the west-southwest and west oriented tributary joining the Floyd River at Le Mars. Plymouth Creek is a southwest and west oriented tributary joining the Floyd River near the figure 10 west edge. O’Leary is a place-name north of the figure 10 south center edge. The unnamed south-oriented stream just west of O’Leary is Mud Creek, which is a West Fork Little Sioux River tributary. Remsen is the town on Deep Creek located in the figure 10 northeast corner. The south-southwest and south oriented stream originating south of Remsen and flowing to the figure 10 south edge (east half) is Johns Creek in the north (and Clear Creek further to the south). South of the figure 10 map area Johns Creek (or Clear Creek-the map keep using both names) joins the West Fork Little Sioux River. The Floyd River-West Fork Little Sioux River drainage divide extends diagonally across the figure 10 map area from the southwest corner to the northeast corner. Close study of the drainage divide reveals several north-south oriented through valleys eroded across the drainage divide. The through valleys are defined by one 10-meter contour line and provide evidence of multiple south-oriented flood flow channels such as might be found in a south-oriented anastomosing channel complex. Headward erosion of the west- and southwest-oriented Plymouth Creek valley beheaded and reversed south-oriented flood flow channels in the figure 10 west half. Next headward erosion of the Floyd River valley and its west-oriented Deep Creek tributary valley beheaded and reversed the south-oriented flood flow channels all across the figure 10 map area, including those to what was then the actively eroding Plymouth Creek valley. Headward erosion of the Floyd River valley and its tributary valleys beheaded all flood flow routes to the newly eroded West Fork Little Sioux River drainage basin and that drainage basin has changed little since.

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.