A geomorphic history based on topographic map evidence

The Big Blue River-Big Nemaha River drainage divide area in southeast Nebraska was eroded by massive south and southeast oriented floods. Floods were probably from a rapidly melting ice sheet located north and northwest of the drainage divide area. Initially flood waters flowed across a topographic surface higher than the highest present day Big Blue River-Big Nemaha River drainage divide elevations. The Big Nemaha River valley and tributary valleys eroded northwest from what was then a newly eroded south-southeast oriented Missouri River valley to capture south-oriented flood waters west of the actively eroding Missouri River valley. At about the same time the Big Blue River valley eroded headward from the newly eroded east-oriented Kansas River-Missouri River valley to capture south oriented flood water further to the west. Headward erosion of Big Nemaha River tributary valleys beheaded some flood flow routes to the actively eroding Big Blue River valley. Headward erosion of the Missouri River valley and its tributary northeast and east oriented Platte River-Salt Creek valley then beheaded all south-oriented flood flow routes to the Big Nemaha River valley system, but was unable to capture south-southeast oriented flood flow in the Big Blue River valley.

Preface:

• The purpose of this essay is to use topographic map interpretation methods to explore Big Blue River-Big Nemaha River drainage divide area landform origins in southeastern Nebraska, 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 Missouri River drainage basin landform origins research project essays is a thick North American ice sheet, comparable in thickness to the Antarctic ice sheet, occupied the North American region usually recognized to have been glaciated, and through its weight and erosive actions created a deep North American “hole”. The southwestern rim of that deep “hole” is today preserved in the high Rocky Mountains. The ice sheet through its weight and deep erosion (and perhaps deposition along major south-oriented melt water flow routes) caused significant crustal warping and tectonic change, through its action of melting fast produced immense floods that flowed across the continent, and through its action of melting fast systematically opened up space in the ice sheet created “hole” so headward erosion of newly developed north-oriented drainage systems captured immense south-oriented melt water floods and diverted the 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 Big Blue River-Big Nemaha River drainage divide area landform origins in southeastern Nebraska will be regarded as evidence supporting the “thick ice sheet that melted fast” paradigm.

Big Blue River-Big Nemaha River drainage divide area location map

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

Figure 1 provides a location map for the Big Blue River-Big Nemaha River drainage divide area in southeast Nebraska. Nebraska is located in the figure 1 northwest area, Kansas is south of Nebraska, Iowa is located in the figure 1 northeast area and Missouri is located south of Iowa. The Missouri River flows in a south-southeast direction along the Nebraska and Kansas east borders from the figure 1 north edge to Kansas City. At Kansas City the Missouri River turns to flow in an east-northeast direction to the figure 1 east edge. West of Kansas City is the east-oriented Kansas River, which can be seen along the figure 1 south edge. In Nebraska the Platte River flows in a northeast direction from the figure 1 west edge to Columbus near the north edge. From Columbus the Platte River flows in an east direction to Fremont and then turns to flow in a south-southeast direction to Ashland. At Ashland the Platte River turns to flow in an east-northeast direction to the Missouri River. The Big Blue River originates near Marquette in the figure 1 northwest quadrant and flows in a northeast and then southeast direction to Ulysses (south of Columbus). At Ulysses the Big Blue River turns to flow in a south-southeast direction to Beatrice and into Kansas. Once in Kansas the Big Blue River flows in a south, south-southwest, and southeast direction before joining the east-oriented Kansas River near Manhattan. The Big Nemaha River is the unlabeled southeast-oriented river or stream in southeast Nebraska flowing through Sterling, Tecumseh, Table Rock, Humboldt, Dawson, and Falls City and which joins the Missouri River near Rulo, which is located near the Nebraska-Kansas border. Also important in this essay is northeast oriented Salt Creek, which flows from near Crete (located on the Big Blue River southwest of Lincoln, Nebraska) to Lincoln and then flows to join the Platte River near Ashland. The Little Nemaha River-Big Nemaha River drainage divide area and the Platte River-Missouri River drainage divide area address regions located north of the Big Blue River-Big Nemaha River drainage divide area and can be found listed under NE Missouri River on the sidebar category list. Other essays addressing regions include the Platte River-Wahoo Creek drainage divide area, the Platte River-Salt Creek drainage divide area, and the Platte River-Big Blue River drainage divide area essays and can be found under Platte River. Hundreds of Missouri River drainage basin landform origins research project essays published on this website present overwhelming evidence for immense south and southeast oriented floods which flowed across Nebraska at the time the Missouri River valley and its tributary valleys eroded headward into and across the figure 1 map area. Flood waters were probably derived from a rapidly melting thick North American ice sheet. Evidence illustrated and discussed in this essay supports the massive south- and southeast-oriented flood interpretation.

Big Blue River-Big Nemaha River drainage divide area detailed location map

Figure 2: Big Blue River-Big Nemaha River drainage divide area detailed location map. United States Geological Survey map digitally presented using National Geographic Society TOPO software. 

Figure 2 provides a slightly more detailed location map for the Big Blue River-Big Nemaha River drainage divide area in southeast Nebraska. Lancaster, Otoe, Gage, Johnson, Nemaha, Pawnee, and Richardson are Nebraska county names and the county boundaries are shown. Atchison is a Missouri county and Fremont is an Iowa county. The Missouri River flows in a south and south-southeast direction along the Nebraska east border. The Nebraska-Kansas state line is located just north of the figure 2 south edge. The Big Blue River flows south along the figure 2 west edge and then southeast to Beatrice in the Gage County center. From Beatrice the Big Blue River flows in a southeast and south direction to the figure 2 south edge. The North Fork Big Nemaha River originates in southern Lancaster County and flows east to Firth. At Firth the North Fork Big Nemaha River turns to flow in a southeast direction to Adams in northeast Gage County and then to Sterling, Saint Mary, Tecumseh, and Elk Point in Johnson County and finally to near Table Rock in northeast Pawnee County and to Humboldt, Dawson, Salem, and Falls City in Richardson County. Big Blue River tributaries illustrated and discussed in this essay include Clatonia Creek, Indian Creek, Bear Creek, and Mud Creek in Gage County. Turkey Creek which flows to the South Fork Big Nemaha River in Pawnee and Richardson Counties is also discussed. The southeast-oriented Little Nemaha River is located in Otoe and Nemaha Counties and flows to the south-southeast oriented Missouri River. The Haines Branch Salt Creek flows in a northeast direction to join Salt Creek near Lincoln and then to flow in a northeast direction to join the Platte River near Ashland (see figure 1). Salt Creek originates in southwest Lancaster County and flows to Kramer, Sprague, and Roca before flowing north to Lincoln and then turning to flow in a northeast direction. Note how headward erosion of the northeast-oriented Salt Creek valley and tributary valleys have beheaded southeast-oriented flood flow routes that were moving flood waters to what were then the actively eroding Little Nemaha River and Big Nemaha River drainage basins. Evidence documenting the southeast-oriented flood flow and the beheading of the flood flow routes is contained in the Platte River-Missouri River drainage divide area and the Little Nemaha River-Big Nemaha River drainage divide area essays. Note also how the Big Blue River tributaries from the east are relatively short and tend to be south-oriented, although some are southwest-oriented. Not shown in figure 2 are long east-oriented Big Blue River tributaries from the west (see figure 1). This evidence is interpreted to mean the Big Blue River valley eroded headward along a south-southeast oriented flood flow channel west of southeast-oriented flood flow channels eroding the Big Nemaha River valley system.

Big Blue River-Salt Creek drainage divide area west of Lincoln

Figure 3: Big Blue River-Salt Creek drainage divide area west of Lincoln. United States Geological Survey map digitally presented using National Geographic Society TOPO software. 

Figure 3 illustrates the Big Blue River-Salt Creek drainage divide area west of Lincoln, Nebraska. Lincoln is the city located in the figure 3 northeast corner. Milford is the town located near the figure 3 west center edge. The Big Blue River flows in a south-southeast direction from the figure 3 northwest corner to Milford and then to the figure 3 south edge. The southeast and northeast oriented West Fork Big Blue River joins the Big Blue River in the figure 3 southwest corner area. East and northeast oriented streams flowing towards Lincoln are Salt Creek tributaries. The South Branch Middle Creek originates east of Milford and flows in a northeast direction to Pleasant Dale and south of Pawnee Lake joins southeast oriented Middle Creek, which then turns to flow in an east direction to Lincoln. East of the figure 3 map area Middle Creek joins northeast oriented Salt Creek, which joins the Platte River near Ashland. South of the South Branch is northeast and east oriented Holmes Branch, which flows to Conestoga Lake and then to the northeast-oriented Haines Branch, which joins Salt Creek at Lincoln. Haines Branch originates south of the figure 3 map area and flows in a north-northeast direction to join the Holmes Branch east of Conestoga Lake and then in a northeast direction to join Salt Creek at Lincoln. Cheese Creek is a southeast and northeast oriented Haines Branch tributary located between Holmes Branch and Haines Branch. Note how Salt Creek tributaries begin almost at the edge of the south-southeast oriented Big Blue River valley and how the Big Blue River in this figure 3 map area has virtually no tributaries from the east. What has happened here is the Salt Creek valley and its tributary valleys eroded headward (in a southwest direction) from the Platte River valley to capture southeast and south-southeast oriented flood flow moving to what was then the newly eroded Missouri River valley. At that time the east-oriented Platte River valley north and northwest of the figure 3 map area did not exist, although it was eroded shortly thereafter. The Haines Branch valley eroded headward first (in figure 3) with the Cheese Creek and Holmes Branch valleys eroding next in that sequence. The Middle Creek-South Branch valley was eroded last (in figure 3). The Salt Creek tributary valleys were not deep enough to capture south-southeast oriented flood flow in the slightly deeper Big Blue River channel or valley, which had eroded headward from the Kansas River, but were able to capture south-southeast oriented flood flow adjacent to the Big Blue River channel.

Haines Branch Salt Creek-Olive Branch Salt Creek drainage divide area

Figure 4: Haines Branch Salt Creek-Olive Branch Salt Creek drainage divide area. United States Geological Survey map digitally presented using National Geographic Society TOPO software. 

Figure 4 illustrates the Haines Branch Salt Creek-Olive Branch Salt Creek drainage divide area south and east of the figure 3 map area and includes overlap areas with figure 3.  Crete is the town located south of the figure 4 west center area. The Big Blue River flows in a south-southeast direction from the figure 4 northwest corner to the Crete west edge and then to the figure 4 south edge. Haines Branch Salt Creek is not labeled in figure 4, but is the north-northeast oriented stream flowing to the figure 4 north center edge. Cheese Creek can be seen to the west of Haines Branch and north-oriented Spring Creek is to the east. Kramer is the small town located near the figure 4 south center edge and the Olive Branch Salt Creek flows in a northeast direction from Kramer to Sprague (another small town) and then to the figure 4 east center edge. Note the north-oriented and southeast-oriented Olive Branch Salt Creek tributaries. The tributaries provide evidence the northeast-oriented Olive Branch Salt Creek valley eroded headward across multiple southeast and/or south-southeast oriented flood flow channels. The southeast-oriented tributary valleys were eroded headward along the captured southeast-oriented flood flow channels. The north-oriented tributary valleys were eroded by reversals of flood flow on the north ends of beheaded south-oriented flood channels. Flood waters on the north ends of the beheaded flood flow channels reversed flow direction to flow north to the newly eroded and deeper Olive Branch Salt Creek valley. Headward erosion of the Haines Branch valley next captured the southeast oriented flood flow and the north-oriented Haines Branch tributary valleys (including the north-oriented Haines Branch valley segment) were probably eroded by reversals of flood flow on the north ends of beheaded south-oriented flood flow routes. Headward erosion of the Cheese Creek valley next beheaded flood flow to what was then the actively eroding Haines Branch valley head and also to what was then the actively eroding Walnut Creek valley head. Walnut Creek is a south-southeast and southwest oriented Big Blue River tributary north of Crete. Note how Walnut Creek originates on a southeast-oriented upland surface, which has been beheaded by headward erosion of the Cheese Creek valley. Note also, that other than Walnut Creek there are no significant Big Blue River tributaries from the east in the figure 4 map area. Headward erosion of the northeast-oriented Salt Creek tributary valleys has captured all of the southeast-oriented flood flow channels east of the south-southeast oriented Big Blue River valley, suggesting south-southeast oriented flood flow moving on the Big Blue River alignment had eroded a deeper flood flow channel than the Salt Creek tributary valleys could capture.

Big Nemaha River-Indian Creek drainage divide area

Figure 5: Big Nemaha River-Indian Creek drainage divide area. United States Geological Survey map digitally presented using National Geographic Society TOPO software. 

Figure 5 illustrates the Big Nemaha River-Indian Creek drainage divide area south and east of the figure 4 map area and does not include overlap areas with figure 4. Clatonia is the small town located in the figure 5 west center area. Clatonia Creek is the southwest-oriented stream flowing through Clatonia to the figure 5 southwest corner area where it joins the Big Blue River. The south-southeast oriented Big Blue River can just barely be seen in the figure 5 southwest corner. Cortland is the small town in the figure 5 north center area. The southeast-oriented stream originating west of Cortland is Indian Creek, which flows south from the Cortland area to Pickrell near the figure 5 south center edge and then to join the Big Blue River south of the figure 5 map area (see figure 6). Firth is the small town near the north edge in the figure 5 northeast quadrant. The North Fork Big Nemaha River flows in a southeast direction from Firth to the figure 5 east edge. Upstream from Firth the North Fork Big Nemaha River can be seen flowing east along the figure 5 north edge (north of Cortland. Note how headward erosion of the North Fork Big Nemaha River valley has beheaded south-oriented flood flow routes to what was at one time the actively eroding south-and southeast-oriented Indian Creek valley. Also note how headward erosion of the Clatonia Creek valley has beheaded southeast-oriented flood flow routes to what was the actively eroding southeast-oriented Indian Creek valley. Figure 5 evidence suggests the Big Blue River valley and its tributary valleys eroded headward into the figure 5 map area first, with headward erosion of the Indian Creek valley occurring slightly before Clatonia Creek valley headward erosion. Next headward erosion of the Big Nemaha River valley beheaded flood flow to the what was then the actively eroding Indian Creek valley. Headward erosion of the Big Nemaha River valley did not proceed further north or west because south- and southeast-oriented flood flow to the actively eroding Big Nemaha River valley was beheaded by headward erosion of the Salt Creek tributary valleys as seen in previous figures.

Bear Creek-Mud Creek drainage divide area northeast from Beatrice

Figure 6: Bear Creek-Mud Creek drainage divide area northeast from Beatrice. United States Geological Survey map digitally presented using National Geographic Society TOPO software. 

Figure 6 illustrates the Bear Creek-Mud Creek drainage divide area south and east of the figure 5 map area and includes overlap areas with figure 5. Beatrice is the city in the figure 6 southwest corner and the Big Blue River is located immediately southwest of Beatrice (but is not seen in figure 6). Indian Creek flows along the figure 6 west edge from the northwest corner to Beatrice and joins the Big Blue River just west of Beatrice. Pickrell is the small town located in the figure 6 northwest corner (near the west edge). Bear Creek is the northwest, west, and southwest oriented stream flowing from the figure 6 north center edge area to Beatrice and joins the Big Blue River south of Beatrice (and south of the figure 6 map area). Filley is the small town located in the figure 6 southeast quadrant. The southwest-oriented stream flowing from Filley to the figure 6 south center edge is Mud Creek. North and west of Mud Creek in the figure 6 south center area is southwest-oriented Cedar Creek. East and northeast oriented drainage along the figure 6 east edge flows to the southeast-oriented North Fork Big Nemaha River. As seen in figure 5, south of the northeast-oriented Salt Creek tributary valleys the Big Blue River does have tributary valleys from the east. These tributary valleys are generally southwest oriented and eroded headward from what was then the newly eroded Big Blue River valley to capture south and southeast oriented flood flow moving parallel to the newly eroded Big Blue River valley. Evidence for the south and southeast oriented flood flow channels is seen in the south and southeast oriented and north and northwest oriented tributary valleys to the larger southwest-oriented Big Blue River tributaries and also in shallow north-south and northwest-southeast oriented through valleys crossing drainage divides between the southwest-oriented Big Blue River tributaries. Some of the shallow through valleys can be seen in figure 6, although more detailed maps show the through valleys better. Figure 6a below is a more detailed map of the Cedar Creek-Mud Creek drainage divide area near Filley. Three shallow through valleys cross the Cedar Creek-Mud Creek drainage divide in section 20 (in figure 6a). More similar through valleys can be seen in sections 19, 30, and 25. While these through valleys are not spectacular they exist and they are evidence of south and southeast oriented flood flow channels that crossed the figure 6 map area prior to headward erosion of deeper southwest-oriented Big Blue River tributary valleys.

Figure 6a: Detailed map of Cedar Creek-Mud Creek drainage divide area near Filley. United States Geological Survey map digitally presented using National Geographic Society TOPO software. 

Mud Creek-Adamson Creek drainage divide area

Figure 7: Mud Creek-Adamson Creek drainage divide area. United States Geological Survey map digitally presented using National Geographic Society TOPO software. 

Figure 7 illustrates the Mud Creek-Adamson Creek drainage divide area south and east of the figure 6 map area and includes overlap areas with figure 6. Filley is the town located in the figure 7 northwest quadrant and Mud Creek flows in a southwest direction from Filley to the figure 7 west edge. Southeast from Filley is Virginia, another small town, and southeast from Virginia is southeast oriented Adamson Creek, which flows to the figure 7 south center edge area. Note the northwest-oriented Mud Creek tributary flowing from near Virginia to join Mud Creek near Filley and also the north-oriented Mud Creek headwaters valley located just west of the Gage County border (and northeast from Virginia). The northwest-oriented Mud Creek tributary valley and the north oriented Mud Creek headwaters valley were eroded by reversals of southeast and south oriented flood flow on northwest and north ends of southeast and south oriented flood flow channels beheaded by Mud Creek valley headward erosion. Figure 8 below provides a detailed map of the Mud Creek-Adamson Creek drainage divide area. Lewiston is the town located east of Virginia in the Pawnee County northwest corner. Mayberry is the small town located in the figure 7 southeast corner area. North of Lewiston is east, northeast, and southeast oriented Turkey Creek, which is seen again in figure 9 below and Turkey Creek eventually flows to the Big Nemaha River. The southeast oriented stream at Mayberry is Rock Creek, which flows to southeast oriented Turkey Creek east of the figure 7 map area. Note the north-south oriented through valleys linking the Turkey Creek valley with the south-oriented Rock Creek tributary valley just north of Mayberry. The through valleys are evidence of south-oriented flood flow channels that moved flood waters to the actively eroding Rock Creek valley prior to headward erosion of the Turkey Creek valley. The Sampson Branch is the southeast oriented Turkey Creek tributary in the figure 7 northeast quadrant. West of the Sampson Branch headwaters is north-oriented Lost Branch, which flows to southeast and northeast oriented Yankee Creek, which flows to the southeast-oriented Big Nemaha River. The Sampson Branch headwaters and the Lost Branch valley are linked by through valleys providing evidence the Lost Branch valley was initiated as a south-oriented flood flow route and then reversed when it was beheaded by Yankee Creek valley headward erosion. Shallow through valleys also link the north-oriented Lost Branch valley with southeast-oriented tributaries to the east-oriented Turkey Creek valley, providing additional evidence of south-oriented flood flow.

Detailed map of Mud Creek-Adamson Creek drainage divide area

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

Figure 8 provides a detailed of the Mud Creek-Adamson Creek drainage divide near Virginia. Virginia is the town located in the figure 8 west center. West oriented drainage at Virgina is a Mud Creek tributary. The north oriented stream in section 1 in the figure 8 north center is the headwaters of north and southwest oriented Mud Creek, which flows to the south-southeast oriented Big Blue River. The southeast-oriented stream originating in section 14 near Virginia and flowing to the figure 8 south center edge is Adamson Creek. South of the figure 8 map area Adamson Creek flows in a southeast direction to join southwest-oriented Wolf Creek, which flows to the south-southeast oriented Big Blue River. Turkey Creek headwaters are located in section 7 and flow in a northeast direction to section 5 and the figure 8 east edge. Turkey Creek flows in several different directions before joining the southeast-oriented Big Nemaha River. Note the north-south oriented through valley in section 12 (in the figure 8 center) linking the north-oriented Mud Creek headwaters valley with a south-oriented Adamson Creek tributary valley. The through valley is evidence that prior to headward erosion of the southwest-oriented Mud Creek valley (north of the figure 8 map area) south-oriented flood flow moved from north of the figure 8 map area to what was then the actively eroding Adamson Creek valley. Headward erosion of the southwest-oriented Mud Creek valley beheaded the south-oriented flood flow channel. Flood waters on the north end of the beheaded flood flow channel then reversed flow direction to flow north to the newly eroded Mud Creek valley. Similar north-south oriented through valleys link the north-northeast oriented Turkey Creek headwaters valley with south oriented Adamson Creek tributary valleys. Through valleys are also evidence of south oriented flood flow channels to the actively eroding Adamson Creek valley prior to headward erosion of the northeast-oriented Turkey Creek valley. Prior to headward erosion of the Big Blue River and Big Nemaha River tributary valleys flood waters flowed across the figure 8 map area on a topographic surface at least as high as the highest figure 8 elevations today. Further, the figure 8 evidence suggests the Big Blue River and Big Nemaha River tributary valleys eroded headward into the figure 8 map area at approximately the same time, with the Adamson Creek eroding into the region first.

North Fork Big Nemaha River-South Fork Big Nemaha River drainage divide area

Figure 9: North Fork Big Nemaha River-South Fork Big Nemaha River drainage divide area. United States Geological Survey map digitally presented using National Geographic Society TOPO software. 

Figure 9 illustrates the North Fork Big Nemaha River-South Fork Big Nemaha River drainage divide area south and east of the figure 8 map area. The Nebraska-Kansas state line is located along the figure 9 south edge. Table Rock is the town located near the figure 9 north center edge. Humboldt is the town located in the figure 9 northeast corner. The North Fork Big Nemaha River flows from near Table Rock to Humboldt in the figure 9 northeast corner. Pawnee City is the somewhat larger town located northwest of the figure 9 center. The south-southeast oriented stream flowing from the figure 9 north edge through Pawnee City to the figure 9 south center edge is Turkey Creek (the same Turkey Creek seen in figures 7 and 8). South of figure 9 Turkey Creek turns to flow in an east direction to join the north-oriented South Fork Big Nemaha River, which flows in a northeast direction across the Pawnee County southeast corner and then northeast to the figure 9 east edge. East of figure 9 the South Fork Big Nemaha River joins the southeast oriented North Fork Big Nemaha River and the Big Nemaha River then flows east to join the south-oriented Missouri River. Du Bois is the small town located in the figure 9 southeast quadrant and in the Pawnee County southeast corner. Long Branch is the southeast oriented South Fork Big Nemaha River tributary flowing through Du Bois to join the northeast oriented South Fork Big Nemaha River. Taylor Branch is the northeast oriented stream flowing to join the southeast oriented North Fork Big Nemaha River near Table Rock. Note how there is a northwest-oriented tributary to the northeast-oriented Taylor Branch valley just north of Pawnee City. East of the Long Branch headwaters are headwaters of southeast, northeast, and north oriented Dry Branch, which flow to the North Fork Big Nemaha River. Note how the Dry Branch headwaters valley is also linked by a through valley to a north-oriented Taylor Branch tributary valley. Figure 10 below provides a more detailed map of the Taylor Branch-Long Branch drainage divide and Dry Branch headwaters area, but the through valleys linking the  present day opposing valleys can be seen in figure 9. Numerous similar through valleys can found in the figure 9 map area, although the through valleys are mush easier to see using more detailed maps. The through valleys and the present day valley orientations provide evidence of multiple southeast and south oriented flood flow channels that existed prior to headward erosion of the present day valleys. Valleys were eroded in sequence, generally from the south to the north. The South Fork Big Nemaha River valley system was eroded before the North Fork Big Nemaha River valley and tributary valleys beheaded the south-oriented flood flow.

Detailed map of North Fork Big Nemaha River-South Fork Big Nemaha River drainage divide area

Figure 10: Detailed map of North Fork Big Nemaha River-South Fork Big Nemaha River drainage divide area. United States Geological Survey map digitally presented using National Geographic Society TOPO software. 

Figure 10 provides a detailed map of the North Fork Big Nemaha River-South Fork Big Nemaha River drainage divide area east of Pawnee City, which was seen in less detail in figure 9 above. Turkey Creek is the south-southeast oriented stream flowing from the figure 10 west center edge (near Pawnee City) to the figure 10 south edge. Long Branch is the south-southeast oriented stream originating in section 30 and flowing across section 31 to the figure 10 south center edge. Long Branch as seen in figure 9 flows to the northeast oriented South Fork Big Nemaha River. Also originating in section 30, north of the Long Branch headwaters, is a north-northwest oriented Taylor Branch tributary. Taylor Branch as seen in figure 9 flows to the southeast oriented North Fork Big Nemaha River. Note the prominent north-south oriented through valley located in section 30 linking the two opposing valleys. The through valley provides evidence that south-oriented flood flow once flowed to what was the actively eroding Long Branch valley. Headward erosion of the North Fork Big Nemaha River valley and its northeast-oriented Taylor Branch tributary valley beheaded the south-southeast oriented flood flow channel to the Long Branch valley. Flood waters on the north end of the beheaded flood flow channel reversed direction to flow north to the newly eroded northeast-oriented Taylor Branch valley. Southeast-oriented Dry Branch headwaters are located in the figure 10 east center area. The through valleys provide evidence south-oriented flood flow moved to the newly eroded southeast, northeast, and north oriented Dry Branch valley before headward erosion of the North Fork Big Nemaha River valley and northeast oriented Taylor Branch valley beheaded the south oriented flood flow channels.  Through valleys linking a north oriented Taylor Branch tributary valley with the southeast oriented Dry Branch headwaters valley can be seen in sections 29 and 28 in the figure 10 northeast quadrant. South oriented flood flow moved to the southeast oriented Dry Branch headwaters valley until headward erosion of the Taylor Branch valley beheaded the south-oriented flood flow. Flood waters moved south to the southeast-oriented Dry Branch headwaters valley, which had been captured by headward erosion of the northeast-oriented Dry Branch valley segment, which had eroded from a reversed south-oriented flood flow channel, which had been beheaded by North Fork Big Nemaha River headward erosion. Subsequently North Fork Big Nemaha River valley and northeast oriented Taylor Branch valley headward erosion beheaded and reversed the south oriented flood flow to the Dry Branch valley. Sequences of events are logical and provide an internally consistent description of how the Big Nemaha River tributary valleys eroded headward to capture an immense south- and southeast-oriented flood.

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.