Abstract:

The Floyd River-Little Sioux River drainage divide area in Woodbury and Monona Counties, Iowa is located in northwest Iowa and the Floyd River and Little Sioux River are south-southwest oriented Missouri River tributaries, with the Floyd River being located north and west of the Little Sioux River. The south-southeast oriented Missouri River is located along the Woodbury and Monona County western border. Landforms in the Woodbury and Monona County region were eroded by massive southeast-oriented melt water floods which flowed across the region as deep valleys eroded headward into and across the region. Flood waters were derived from a rapidly melting North American ice sheet. The ice sheet had been located in a deep “hole” and it is probable melt water floods removed considerable bedrock material from the Woodbury and Monona County region prior to development of the highest level erosion/deposition surface seen today. South-southwest oriented tributary valleys eroded headward from the deep south-southeast oriented Missouri River valley, which was eroded headward along a major south-southeast oriented flood flow route. At that time flood waters were flowing on what is today the highest level erosion/deposition surface in the Woodbury and Monona County region. Topographic map evidence for massive southeast-oriented flood flow across the region includes orientations of the Missouri River valley, orientations of tributaries to the south-southwest oriented Missouri River tributaries, and through valleys eroded across present day drainage divides. Interpretations in this essay are based entirely on topographic map evidence, samples of which are illustrated in the essay.

Preface:

• The purpose of this essay is to use topographic map interpretation methods to explore Floyd River-Little Sioux River drainage divide area landform origins in Woodbury and Monona 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 Floyd River-Little Sioux River drainage divide area landform evidence in Woodbury and Monona 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.

Location map for Floyd River-Little Sioux River drainage divide area in Woodbury and Monona Counties, Iowa

Figure 1: Location map for Floyd River-Little Sioux River drainage divide area in Woodbury and Monona Counties, Iowa. National Geographic Society map digitally presented using National Geographic Society TOPO software.

Figure 1 provides a regional map of northwest Iowa, southwest Minnesota, southeast South Dakota, and northeast Nebraska. The Missouri River flows along the South Dakota-Nebraska border from the figure 1 west edge to Sioux City, Iowa where it then flows in a south-southeast direction along the Nebraska-Iowa border. The Big Sioux River is the south-oriented river just west of the South Dakota-Minnesota border, which flows to Sioux Falls and then flows south along the South Dakota-Iowa border to join the Missouri River near Sioux City, Iowa. The James River is the south-southeast oriented river flowing from the figure 1 northwest corner to join the Missouri River near Yankton, South Dakota. The Des Moines River originates near the figure 1 north center edge and flows in a south-southeast direction to the figure 1 south edge (near southeast corner). The Des Moines River is a Mississippi River tributary and the Des Moines River drainage basin is not included in the Missouri River drainage basin. Note how Missouri River tributaries from the east are relatively short and are generally oriented in a south-southwest direction. While not visible in figure 1 the Missouri River drainage basin extends westward into western Wyoming and Montana. The Little Sioux River is a south-southwest oriented Missouri River tributary flowing through Cherokee, Iowa to join the Missouri River near Little Sioux, Iowa (near where Missouri River flows to the figure 1 south edge). The Floyd River is the unlabeled south-southwest oriented river flowing near Le Mars, Iowa to join the Missouri River at Sioux City, Iowa. Sioux City, Iowa is located in Woodbury County, Iowa and Monona County, Iowa is located directly south of Woodbury County and is east of the Missouri River. This essay focuses on drainage divide origins between the Floyd River and Missouri River and the south-southwest oriented Little Sioux River in the Woodbury and Monona County areas. Essays describing drainage divide origins for tributaries joining the Missouri River in Iowa are listed under IA Missouri River on the sidebar category list.

• Drainage routes in the figure 1 map area were eroded by massive southeast-oriented melt water floods. The floods were flowing from a rapidly melting North American ice sheet, the southern margin of which was located in or near the figure 1 north half. Melt water flood erosion and deposition probably has destroyed most if not all evidence of the ice sheet margin location, although on detailed topographic maps areas where decaying ice sheet remnants were located can often be identified. At least some of the immense south-oriented melt water floods were flowing from the mouths of giant south-oriented ice-walled canyons carved into the decaying ice sheet’s surface. The south-oriented Big Sioux River flows along the floor of one such ice-walled canyon, although the supra-glacial melt water river supplying flood waters to that ice-walled canyon was captured north of the figure 1 map area and the south-oriented melt water floods were diverted in a southeast direction along the present day Minnesota River alignment. Before being beheaded south-oriented supra-glacial melt water flood flow floods moving through the Big Sioux ice-walled canyon flowed south across the figure 1 map area and initiated the south-southeast oriented Missouri River valley. Flood waters moving south across western Iowa were captured by headward erosion of this deeper south-southeast oriented Missouri River valley and proceeded to erode south-southwest oriented valleys headward in sequence as the deep Missouri River valley eroded headward into the figure 1 map area. Headward erosion of the Little Sioux River valley was initiated prior to Floyd River valley headward erosion. At the same time headward erosion of south-southeast oriented Des Moines River valley (from the Mississippi River valley) was capturing south-oriented flood flow to what were then the actively eroding south-southwest oriented Missouri River tributary valleys.

• The south-oriented James River flows along the floor of what was a much deeper and larger ice-walled canyon, which was not captured by headward erosion of the deep southeast oriented Minnesota River ice-walled canyon (although the south-oriented James River ice-walled canyon and the southeast oriented Minnesota River ice-walled canyon did intersect in southeast North Dakota). The east and northeast facing Missouri Escarpment is what remains of what became a giant southeast and south-oriented ice-walled and bedrock-floored canyon, which is named in some of my essays as the “Midcontinent Trench”. Immense southeast and south-oriented melt water floods, which can probably be traced headward into Saskatchewan and eastern Alberta, flowed to the ice sheet margin near the present day east-oriented Missouri River valley in southeast South Dakota. At first flood waters flowed south across eastern Nebraska, but later were captured by the south-southeast oriented Missouri River valley, which had been eroded by earlier flood waters moving south from the Big Sioux River ice-walled canyon. This capture resulted in headward erosion of the Missouri River valley to the James River ice-walled canyon mouth. The large Missouri River valley located downstream from the Yankton, South Dakota area was eroded by huge melt water floods flowing from the “Midcontinent Trench” ice-walled and bedrock-floored canyon. Further information describing evidence for the ice-walled canyons can be found in essays listed under James River and Big Sioux River on the sidebar category list..

Detailed location map for Floyd River-Little Sioux River drainage divide area in Woodbury and Monona Counties, Iowa

Figure 2: Detailed location map for Floyd River-Little Sioux River drainage divide area in Woodbury and Monona Counties, Iowa. United States Geological Survey map digitally presented using National Geographic Society TOPO software.

Figure 2 provides a somewhat more detailed map of the Floyd River-Little Sioux River drainage divide area in Woodbury and Monona Counties, Iowa. The Missouri River flows in a southeast and south-southeast direction from the figure 2 northwest corner area to the figure 2 south center edge. East of the Missouri River is the state of Iowa and west of the Missouri River is the state of Nebraska. County boundaries and names are shown. Sioux City, Iowa is the city located in the Woodbury County northwest corner. The Floyd River flows in a south-southwest direction from the figure 2 north edge to join the Missouri River at Sioux City. Note how the Floyd River has almost no tributaries from the east (at least in the figure 2 map area). The Little Sioux River flows in a south-southwest direction from the figure 2 north edge (east half) to the Woodbury County northeast corner and then across eastern Woodbury County to enter north central Monona County. Once in Monona County the Little Sioux River flows in almost a south direction to join the Missouri River just south of the Monona County southern border and near the figure 2 south center edge. South and east of the Little Sioux River in Monona County is the south-southwest Soldier River, which flows directly to the Missouri River. While the Little Sioux River does have tributaries from the east those tributaries are generally short. Little Sioux River tributaries from the west are much better developed. The West Fork Little Sioux River flows in a southwest direction to the Woodbury County north center area and then turns to flow in a south direction to join the Little Sioux River in central Monona County. [Many drainage routes in the Missouri River valley area are labeled ditches and may not reflect drainage routes as they were originally eroded. In other words, the West Fork Little Sioux River valley may have originally eroded headward from the Missouri River valley independent of Little Sioux River valley headward erosion and may have become a Little Sioux River tributary at a later time.] Between the West Fork Little Sioux River and the Little Sioux River is south-oriented Wolf Creek and the East Fork Wolf Creek. West of the West Fork Little Sioux River and east of the Floyd River is south-oriented Big Whisky Creek and its south-oriented Elliott Creek tributary (with south-oriented Muddy Creek being an Elliott Creek tributary. Note how each of the south and south-southwest oriented rivers and creeks has a relatively narrow drainage basin and how outside of the Missouri River valley region the Floyd River-Little Sioux River drainage divide area consists of several drainage divides separating several south and south-southwest oriented drainage basins.

Missouri River-Little Sioux River drainage divide area

Figure 3: Missouri River-Little Sioux River drainage divide area. United States Geological Survey map digitally presented using National Geographic Society TOPO software.

Figure 3 is a reduced size topographic map of the Missouri River-Little Sioux River drainage divide area south of Sioux City, Iowa. The Missouri River flows in a south direction near the figure 3 west edge and is located in a large south-southeast oriented valley. The large Missouri River valley was eroded by huge melt water floods emerging from the mouth of the previously described “Midcontinent Trench” ice-walled and bedrock-floored canyon. The south-southwest oriented Little Sioux River is located near the figure 3 east edge and joins the Missouri River south of the figure 3 map area. South-oriented valleys west of the Little Sioux River (near the figure 3 north edge) are East Fork Wolf Creek, Wolf Creek, West Fork Little Sioux River (flowing from figure 3 north center edge), Elliott Creek, and Big Whisky Creek. Note how all figure 3 valleys have been eroded into a higher level surface, which probably was an erosion/deposition surface formed by southeast-oriented flood waters. The Missouri River drainage basin landform origins research project, which includes this essay, is presenting topographic map evidence suggesting immense south-oriented melt water floods flowed from a rapidly melting thick North American ice sheet, which was located in a deep “hole”. The deep “hole” was created by deep glacial erosion under the ice sheet itself and by crustal warping caused by the ice sheet’s tremendous weight. As already mentioned, ice sheet margin evidence has probably been destroyed by melt water flood erosion and deposition, although at the time immense melt water floods flowed across the figure 3 map area it can reasonably be said the ice sheet margin was located north of the figure 3 map area. If at one time the ice sheet actually did cover the figure 3 map area deep glacial erosion probably removed significant bedrock thicknesses. Whether the ice sheet covered the figure 3 map area or not, the immense south-oriented melt water floods almost certainly significantly lowered the figure 3 map area surface prior to headward erosion of the deep valleys seen today. How much the figure 3 surface was lowered before the deep south-oriented Missouri River valley eroded headward into the region is probably impossible to determine. However, at that time south-oriented flood waters were flowing across a surface at least as high as the highest figure 3 elevations today. The deep Missouri River valley then eroded headward across the figure 3 map area towards the mouths of the large ice-walled canyons. At the same time the south and south-southwest oriented Missouri River tributary valleys eroded headward from the newly eroded Missouri River valley. Little Sioux River valley headward erosion was first and was followed by Wolf Creek valley headward erosion, West Fork Little Sioux River valley headward erosion, and Big Whisky Creek-Elliott Creek headward erosion in that order.

Detailed map of Lum Hollow Creek-Little Sioux River drainage divide area

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

Figure 4 is a reduction of a detailed topographic map of the Lum Creek-Little Sioux River drainage divide area north and west of Smithland. The edge of the large south-southeast oriented Missouri River valley can be seen in the figure 4 southwest corner. Smithland is located just north of the Woodbury-Monona County line (just south of the figure 4 map area) and next to the south-oriented Little Sioux River (located along the figure 4 east edge). Smoky Hollow is the southeast-oriented valley draining to the Little Sioux River at Smithland. Lum Hollow Creek is the southwest and west oriented stream located in the figure 4 northwest quadrant. Moose Creek is the west-northwest oriented Lum Hollow Creek tributary with a highway located in its valley. The highway continues across the Lum Hollow Creek-Little Sioux River drainage divide and follows the Smokey Hollow valley to Smithland. Note how the highway crosses the drainage divide in what is a through valley. The map contour interval is 20 feet and the elevation at the drainage divide is marked as 1339 feet. Follow the drainage divide south into section 21 and elevations rise to more than 1420 feet. Follow the drainage divide north into section 15 and elevations rise to more than 1440 feet. In other words, the highway is located in a water eroded valley, which at one time was approximately 100 feet deep. Draining the south half of section 21 is south-, southwest and west oriented Cottonwood Hollow, which drains to the Missouri River valley in the figure 4 southwest corner. Note how another through valley in sections 27 and 28 links the Cottonwood Hollow drainage basin with the Little Sioux River drainage basin (the highway going straight west from Smithland is located in this second through valley). Also note in section 21 another through valley linking the Moose Creek valley with the Cottonwood Hollow valley. Close study of the figure 4 map area reveals numerous other through valleys crossing the present day drainage divides. These through valleys are all water eroded features and were eroded prior to headward erosion of the deep valleys seen today and/or as the deep valleys were eroding headward into the region. The large number of through valleys suggests they were eroded by anastomosing southeast-oriented flood flow channels. Note also how headward erosion of the Cottonwood Creek valley would have beheaded flood flow routes to what would have been the newly eroded Little Sioux River valley. And also note how Lum Hollow Creek valley headward erosion beheaded flood flow to both the newly eroded Little Sioux River valley and the newly eroded Cottonwood Hollow valley. The Moose Creek valley was eroded by a reversal of flood flow which had been moving to those two previously mentioned valleys. Lum Hollow Creek valley headward erosion beheaded and reversed all flood routes to what was then the actively eroding Cottonwood Hollow valley, but apparently the Little Sioux River valley had already eroded far enough north that Lum Hollow Creek headward erosion was not able to behead all flow to that valley.

Detailed map of East Fork Wolf Creek-Little Sioux River drainage divide area

Figure 5: Detailed map of East Fork Wolf Creek-Little Sioux River drainage divide area. United States Geological Survey map digitally presented using National Geographic Society TOPO software.

Figure 5 provides a detailed topographic map of the East Fork Wolf Creek-Little Sioux River drainage divide area located between Anthon and Oto, Iowa in eastern Woodbury County. The south-oriented Little Sioux River valley is located along the figure 5 east edge. The East Fork Wolf Creek flows in a south direction from the figure 5 north center edge through sections 2 and 11 and into section 14 where it turns to flow in west direction into sections 15 and 16 before turning again to flow in a southwest direction to section 21 and the figure 5 south edge (near southwest corner). The southwest-oriented stream in the figure 5 northwest quadrant is an unnamed tributary of the East Branch of south-oriented Wolf Creek. Note northwest-oriented East Fork Wolf Creek tributaries from the east and south-southeast oriented tributaries from the north and west. The northwest-oriented East Fork Wolf Creek tributaries were eroded by reversals of flood flow on beheaded southeast-oriented flood flow routes at the time the deep East Fork Wolf Creek valley eroded headward across the figure 5 map area. Note through valleys crossing all of the figure 5 map area drainage divides. For example in the section 12 southeast corner a northwest-southeast oriented through valley crosses the East Fork Wolf Creek-Little Sioux River drainage divide. The map contour interval is again 20 feet. The through valley floor elevation is between 1240 and 1260 feet. Following the drainage divide north into section 1 reveals elevations greater than 1360 feet. Following the drainage divide south into section 13 reveals elevations greater than 1340 feet. The through valley was at least 80 feet deep when eroded and probably was even deeper. Many similar through valleys cross the figure 5 drainage divides and provide evidence of multiple southeast-oriented anastomosing flood flow channels eroded into what was once a high level erosion surface by the immense melt water floods. Headward erosion of deep south-oriented valleys into the figure 5 map area captured the southeast-oriented flood flow and in the process diverted flood waters in new directions, including causing reversals of flood flow to erode north-oriented valleys such as the valley seen in sections 23 and 24.

Detailed map of East Branch Wolf Creek-East Fork Wolf Creek drainage divide area

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

Figure 6 is a detailed topographic map of the East Branch Wolf Creek-East Fork Wolf Creek drainage divide area north and west of the figure 5 map area. The East Branch Wolf Creek flows in a south direction in the figure 6 west half. The East Fork Wolf Creek flows in a south direction in the figure 6 east half. Note how tributaries to both south-oriented streams are oriented in southeast directions. Note how the drainage divide between the two south-oriented streams is crossed by multiple northwest-southeast oriented through valleys. The through valleys here are shallower than through valleys seen in figures 4 and 5 and are generally defined by only two or three of the 20-foot contour lines. However, the through valleys exist and are evidence of multiple southeast-oriented flood flow channels, which crossed the figure 6 map region prior to headward erosion of the deep south-oriented valleys. The southeast-oriented flood flow was probably moving to what was then the actively eroding south-oriented Little Sioux River valley located east and south of the figure 6 map area. Headward erosion of the deep south-oriented East Fork Wolf Creek valley then captured the southeast-oriented flood flow. Northwest and west oriented East Fork Wolf Creek tributary valleys were eroded by reversals of flood flow on northwest and west ends of beheaded flood flow routes. Headward erosion of the deep south-oriented East Branch Wolf Creek valley next captured the southeast-oriented flood flow and beheaded the flood flow routes to what were then actively eroding southeast-oriented East Fork Wolf Creek tributary valleys. Reversals of flood flow on west and northwest ends of beheaded flood flow channels eroded northwest- and west-oriented East Branch Wolf Creek tributary valleys. This process was repeated over and over again as south-oriented valleys eroded headward across the southeast-oriented flood flow.

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

Figure 7: Detailed map of Camp Creek-West Fork Little Sioux River drainage divide area. United States Geological Survey map digitally presented using National Geographic Society TOPO software.

Figure 7 provides a detailed map of the Camp Creek-West Fork Little Sioux River drainage divide area located north and west of the figure 4 map area. The east edge of the large south-southeast oriented Missouri River valley extends from the figure 7 northwest corner area to the figure 7 south edge (west half). Camp Creek is the northwest-oriented Missouri River tributary flowing to the figure 7 northwest corner. Note other northwest-oriented Missouri River tributaries and/or tributaries with northwest-oriented valley segments. The northwest-oriented (and barbed) Missouri River tributary valleys were eroded by reversals of southeast oriented flood flow on northwest ends of flood flow routes beheaded by headward erosion of the deep south-oriented Missouri River valley. The West Fork Little Sioux River flows in a south direction in the figure 7 eastern quarter. Note how most West Fork Little Sioux River tributaries from the west are oriented in a southeast direction. Also note several northwest-oriented West Fork Little Sioux River tributaries from the east. The southeast and northwest-oriented West Fork Little Sioux River tributaries are evidence the deep south-oriented West Fork Little Sioux River valley eroded headward across multiple southeast-oriented flood flow routes. Also note how some of the southeast-oriented West Fork Little Sioux River tributary valleys are linked by shallow trough valleys with northwest-oriented Missouri River tributary valleys. The tributary valley orientations and the through valleys provide evidence the south-oriented West Fork Little Sioux River valley eroded headward prior to headward erosion of the deep south-southeast oriented Missouri River valley, which beheaded and reversed the southeast-oriented flood flow routes. Both the Missouri River valley and the West Fork Little Sioux River valley were probably enlarged and deepened by flood waters flowing from north of the figure 7 map area.

Floyd River-West Fork Little Sioux River drainage divide area

Figure 8: Floyd River-West Fork Little Sioux River drainage divide area. United States Geological Survey map digitally presented using National Geographic Society TOPO software.

Figure 8 is a reduced size topographic map of the Floyd River-West Fork Little Sioux River drainage divide area between Sioux City and Moville, Iowa. The southeast-oriented oriented Missouri River valley is located in the figure 8 southwest corner with the Missouri River meandering on the valley floor. Floyd River is the south-southwest oriented river joining the Missouri River at Sioux City in the figure 8 southwest corner area. The West Fork Little Sioux River flows in a south-southwest direction from the figure 8 east center edge to the figure 8 south edge (near southeast corner) with Moville being the town located in its valley. Mud Creek is the south-oriented tributary joining the West Fork Little Sioux River at Moville. Lawton is a small town located between Sioux City and Moville. The south-oriented stream flowing just west of Lawton is Elliot Creek. North of Lawton Elliott Creek is joined by south-oriented Muddy Creek. Between the Muddy-Elliot Creek and Floyd River valleys in the figure 8 north half is south-oriented Big Whisky Creek, which flows from the figure 8 north edge to the figure 8 south edge. Between Big Whisky Creek and Sioux City, in the figure 8 south half, is south-oriented Little Whisky Creek. The West Fork Little Sioux River, Elliott Creek, Big Whisky Creek, and Little Whisky Creek all enter the large Missouri River valley as independent streams. Note how the figure 8 drainage basins are narrow and how none of the south-oriented streams and rivers has extensive tributaries on either side. Study of drainage divides between the south-oriented Missouri River tributaries reveals numerous shallow northwest-southeast oriented through valleys. These through valleys are best seen on more detailed topographic maps and figures 9 and 10 below provide detailed topographic maps of a Floyd River-Little Whisky Creek drainage divide area and of a Big Whisky Creek-Muddy Creek drainage divide area. Figure 8 south-oriented valleys eroded headward along and across southeast-oriented flood flow routes, with the valleys originating at what was then the newly eroded south-southeast oriented Missouri River valley. Again the figure 8 south-oriented valleys eroded headward in sequence with the West Fork Little Sioux River valley eroding headward first. Headward erosion of Elliott Creek valley followed and Big Whisky Creek valley headward erosion was next. Floyd River valley headward erosion beheaded all flood flow routes to what was then the actively eroding Little Whisky Creek valley, which was capturing flood flow moving to the newly eroded Big Whisky Creek valley.

Detailed map of Floyd River-Little Whisky Creek drainage divide area

Figure 9: Detailed map of Floyd River-Little Whisky Creek drainage divide area. United States Geological Survey map digitally presented using National Geographic Society TOPO software.

Figure 9 provides a detailed topographic map of the Floyd River-Little Whisky Creek drainage divide area located north and east of Sioux City. Little Whisky Creek flows in a south direction in the figure 9 southeast quadrant and has a narrow drainage basin. Tributaries from the west are oriented in a southeast direction and are generally short. The Little Whisky Creek-Big Whisky Creek drainage divide is located immediately east of the Little Whisky Creek and is crossed by northwest-southeast oriented through valleys, which are linked to the southeast oriented Big Whisky Creek tributaries flowing to the figure 9 east edge. The west-oriented stream originating near the figure 9 south center edge and flowing along the figure 9 south edge to Sioux City is Bacon Creek, which enters the Missouri River independently of the Floyd River. Note the south-southwest oriented Bacon Creek tributary flowing through Bacon Creek Park (sections 19 and 25) and the southeast and northwest-oriented tributaries to that tributary. The Floyd River flows in a south-southwest direction in the figure 9 northwest quadrant. Note how many Floyd River tributaries are oriented in a northwest direction or have significant northwest-oriented valley segments or northwest-oriented tributaries. Also note how these northwest-oriented Floyd River tributaries are linked by shallow northwest-southeast oriented through valleys with the south-oriented Little Whisky Creek valley and the valley of the south-southwest oriented Bacon Creek tributary. These northwest-oriented tributaries join the Floyd River as barbed tributaries and are evidence Floyd River valley headward erosion beheaded and reversed multiple southeast-oriented flood flow routes, such as might be found in a large southeast-oriented anastomosing channel complex. Flood waters on northwest ends of the beheaded flood flow routes reversed flow direction to erode the northwest-oriented tributary valleys. Because flood flow routes were beheaded in sequence from the south to the north and because flood flow routes were interconnected, reversed flood flow on a newly beheaded flood flow route could capture flood flow from adjacent and yet to be beheaded flood flow routes. These captures of yet to be beheaded flood flow not only provided water volumes required to erode the northwest-oriented tributary valleys, but also established flood flow movements in other directions, which are today recorded in tributary valley orientations.

Detailed map of Big Whisky Creek-Muddy Creek drainage divide area

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

Figure 10 provides a detailed map of the Big Whisky Creek-Muddy Creek drainage divide and the Muddy Creek-Elliott Creek drainage divide area located north and east of the figure 9 map area. Big Whisky Creek flows in a south and southwest direction near the figure 10 west edge. Elliott Creek flows in a south-southwest and south direction from the figure 10 northeast corner to the figure 10 south edge (east half). Muddy Creek is located west of Elliott Creek and flows in a south direction from the figure 10 north edge to the south edge and joins Elliott Creek south of the figure 10 map area. Note how tributaries from the west (to all three of the south-oriented streams) and to their west and southwest oriented tributaries are oriented in a southeast direction. Also note how all south-oriented streams and their west and southwest oriented tributaries also have northwest oriented tributaries. Further note how northwest-southeast oriented through valleys cross all of the drainage divides. The northwest- and southeast-oriented tributaries and through valleys provide evidence of multiple southeast-oriented flood flow channels that crossed the figure 10 map area prior to headward erosion of the deep south-oriented valleys. The map contour interval here is 10 feet and depths of the through valleys can be debated. For example, in the northwest corner of section (in figure 10 center area) the floor of a through valley has an elevation of between 1300 and 1310 feet. To the north in section 5 elevations rise to more than 1350 feet and to the south in section 18 elevations rise to more than 1360 feet. Between the section 5 and section 18 high points are several ups and downs suggesting the presence of several northwest-southeast oriented channels eroded into the floor of a much broader northwest-southeast oriented channel. Southeast-oriented flood flow across the figure 10 map area was first captured by Elliott Creek valley headward erosion. Next Muddy Creek valley headward erosion beheaded and reversed southeast-oriented flood flow routes to the newly eroded Elliott Creek valley. Big Whisky Creek valley headward erosion then beheaded and reversed southeast-oriented flood flow routes to the newly eroded Muddy Creek 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.