A geomorphic history based on topographic map evidence

The South Loup River-Platte River drainage divide area in Logan, Lincoln, Custer, and Dawson Counties, Nebraska, was eroded by a massive southeast and south-southeast oriented flood flowing across the entire drainage divide area. Evidence for the flood flow is seen in present day valley alignments, large abandoned headcuts, through valleys across modern-day drainage divides, anastomosing channels, streamlined erosional residuals, barbed tributaries, and locations of present day channels in the large Platte River valley. Flood waters from the north and northwest converged with flood waters from further west in the large Platte River valley and were forced to flow along the valley’s north wall, while flood waters from further west flowed along the valley’s south wall. Flood flow to and across the South Loup River-Platte River drainage divide area was captured by headward erosion of the Middle Loup River valley and its tributary valleys to the north and northwest, which beheaded all flood flow routes to the South Loup River-Platte River drainage divide area.

Preface:

• The purpose of this essay is to use topographic map interpretation methods to explore South Loup River-Platte River drainage divide area landform origins in Logan, Lincoln, Custer, and Dawson Counties, 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 essay 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 South Loup River-Platte River drainage divide area landform origins in Logan, Lincoln, Custer, and Dawson Counties, Nebraska will be regarded as evidence supporting the “thick ice sheet that melted fast” paradigm. This essay is included in the Missouri River drainage basin landform origins research project essay collection.

South Loup River-Platte River drainage area location map

Figure 1: South Loup River-Platte River drainage 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 general location map for the South Loup River-Platte River drainage divide area in Logan, Lincoln, Custer, and Dawson Counties, Nebraska. Nebraska is the state occupying most of the figure 1 map area with Colorado south of Nebraska in the figure 1 southwest corner and Kansas south of Nebraska along the eastern three-fourths of the figure 1 south edge area. The southeast-oriented North Platte River flows from the figure 1 west edge to join the northeast-oriented South Platte River near North Platte and then to flow as the Platte River in a southeast direction past Gothenberg, Cozad, and Lexington to Kearney. At Kearney the Platte River turns to flow in a northeast direction to Grand Island and the figure 1 east edge. The South Loup River originates near Stapleton (located north of North Platte) and flows in a southeast direction to Callaway and Pleasanton before turning to flow in a northeast direction and to flow as the northeast-oriented Loup River to the figure 1 east edge. Between the southeast-oriented South Loup River and the southeast-oriented Platte River is the southeast-oriented Wood River, which originates south of Callaway and flows through Oconto, Eddyville, Summer, Miller, Amherst, and Riverdale before entering the Platte River valley near Kearney and then flowing in a northeast direction parallel to the Platte River and eventually joining the Platte River near Grand Island. North and west of the South Loup River headwaters area are the Nebraska Sand Hills, which is a large sand covered region where most surface drainage routes have been obscured. The Mud Creek-South Loup River drainage divide area in Custer, Sherman, and Buffalo Counties essay and the Middle Loup River-Mud Creek drainage divide area essay describe regions located immediately east and north of the South Loup River-Platte River drainage divide area discussed here and can be found under Loup River on the sidebar category list. Essays addressing landform evidence in the Niobrara River drainage basin (located north of the figure 1 map area) can be found under Niobrara River on the sidebar category list. These and other hundreds of other Missouri River drainage basin landform origins research project essays published on this website have built a strong case for an immense southeast-oriented flood flowing across the figure 1 map area. The large Platte River valley eroded headward across Nebraska to capture this large southeast-oriented flood, which probably originated with a rapidly melting ice sheet to the north and northwest. The newly eroded Platte River valley diverted flood waters east to what was then the newly eroded Missouri River valley (located east figure 1). Southeast-oriented flood flow probably converged in Nebraska with east-oriented flood flow coming from the Rocky Mountain region to west (flood waters from the Rocky Mountain were also derived from the rapidly melting ice sheet, but used a completely route to reach Nebraska). This convergence of flood waters caused flood waters to become ponded. The Nebraska Sand Hills region is probably formed on what originated as sandy deltas deposited where flood waters entered the ponded flood water regions. Finer grained sediment probably settled out further to the east.

South Loup River-Platte River drainage area detailed location map

Figure 2: South Loup River-Platte River drainage area detailed location map. United States Geological Survey map digitally presented using National Geographic Society TOPO software.

Figure 2 provides a somewhat more detailed location map for the South Loup River-Platte River drainage divide area. Logan, Custer, Valley, Sherman, Lincoln, Dawson, and Buffalo are Nebraska county names and the county boundaries are shown. North Platte near the figure 2 west center edge is located in Lincoln County and the Platte River flows in a southeast direction from North Platte to Kearney in the figure 2 southeast corner. Stapleton is located in south central Logan County and is near the South Loup River point of origin. From Stapleton the South Loup River flows in a southeast direction to Arnold in western Custer County and then to Callaway. From Callaway the South Loup River flows in a southeast direction to the Buffalo County northwest corner and then to Pleasanton, which is located directly north of Kearney. An important Platte River tributary, the Wood River, originates near Callaway and flows in a southeast direction to Oconton, Eddyville and Summer (in northeast Dawson County), and Miller, Amherst, and Riverdale in Buffalo County and then flows parallel to the Platte River valley for a considerable distance before joining the Platte River east of the figure 2 map area. Platte River tributaries from the north in Lincoln County are rare, although Pawnee Creek flows in a south-southeast direction to the Platte River valley and then flows parallel to the Platte River before eventually joining the Platte River. South-oriented Platte River tributaries become more common near the Lincoln County east border and flow in a south or south-southeast direction from southwest Custer County into Dawson County to the Platte River valley and then like Pawnee Creek (and the Wood River) flow parallel to the Platte River for considerable distances before joining the Platte River. An unnamed (in figure 2) South Loup River tributary originates in southeast Logan County and flows in a southeast direction before turning to flow north to join the southeast oriented South Loup River near Arnold. Other South Loup River tributaries from the south are also north-oriented, and join the southeast oriented South Loup River as barbed tributaries. Drainage patterns in the figure 2 east half suggest there is northwest-southeast alignment of major drainage routes. This drainage alignment is probably related to southeast oriented flood flow channels, which eroded headward from what was then the newly eroded northeast-oriented Platte River valley east of Kearney (see figure 1). The southeast-oriented Platte River valley west of Kearney probably eroded headward as one of these flood eroded southeast-oriented valleys, but unlike the valleys further to the northeast, the southeast-oriented Platte River valley was able to capture significant southeast-oriented flood flow from areas west of the figure 2 map area. Presence of this significant flood flow from western sources forced southeast- and south-oriented flood water flowing into the newly eroded Platte River valley to flow along the Platte River valley’s north wall, while flood water from western sources flowed along the Platte River valley’s south wall.

Drainage divide area southeast of South Loup River headwaters

Figure 3: Drainage divide area southeast of South Loup River headwaters. United States Geological Survey map digitally presented using National Geographic Society TOPO software.

Figure 3 uses reduced size maps to illustrate the west end of the South Loup River-Platte River drainage divide area south of the South Loup River headwaters. The east-oriented South Loup River flows near the figure 3 north edge in the figure 3 north center area and then in a southeast direction in the figure 3 northeast corner. Stapleton is the town located in the South Loup River valley near the figure 3 north center edge and Arnold is the town located in the South Loup River valley in the figure 3 northeast quadrant. Note how the figure 3 west half appears to be covered with what are probably sand dunes and there is no obvious surface drainage. Without surface drainage routes it is difficult or impossible to reconstruct drainage histories. However, the figure 3 east half does have identifiable valleys, which can be used for drainage history reconstructions. Tallin Table is the upland surface in the figure 3 southeast quadrant. Note how the South Loup River and its tributary valleys have eroded a deep southeast-oriented valley or valley complex into the upland erosion surface (in the figure 3 northeast quadrant). Figure 4 below provides a more detailed map of the figure 3 northeast quadrant and the northeast quadrant will be discussed with figure 4. Tallin Table is the name given to the upland erosion surface in the figure 3 southeast quadrant. West of the figure 3 southeast quadrant elevations are generally about the same as elevations of the Tallin Table upland surface. East and northeast facing escarpments bounding Tallin Table near the figure 3 east edge are 50 meters or more in height. Kilmer Valley is the shallow northwest-oriented valley located on the northwest side of Tallin Table. Figure 3a below provides a slightly more detailed map of the figure 3 southeast quadrant area and the area immediately south and east. Figure 3a also illustrates how northwest-oriented Kilmer Valley is aligned with southeast-oriented valleys eroded headward into the Tallin Table southeast margin. Note in figure 3a how south-southeast oriented headwaters of West Buffalo Creek and East Buffalo Creek originate in south-southeast oriented valleys eroded headward into the Tallin Table south margin. Buffalo Creek is a Platte River tributary. East of the Buffalo Creek headwaters is the south-southeast oriented Sells Valley, which also drains to the Platte River. What has happened here is prior to headward erosion of the South Loup River valley southeast-oriented flood water flowed across the entire figure 3 and 3a map area on a topographic surface at least as high as the Tallin Table elevation today. Flood waters were flowing to what was then the newly eroded and deep Platte River valley. Flood waters eroded the Sells Valley, East Buffalo Creek valley, and West Buffalo Creek valley headward into the Tallin Table upland surface. At approximately the time headward erosion of the Sells Valley, and East and West Buffalo Creek valleys reached their present positions, headward erosion of the South Loup River valley beheaded the south-southeast oriented flood flow routes across the Tallin Table upland surface. Flood waters on the northwest end of the beheaded flood flow routes reversed flow direction to flow northwest to the newly eroded and deeper South Loup River valley and eroded the northwest-oriented Kilmer Valley.

Figure 3a: Kilmer Valley-Buffalo Creek drainage divide area on Tallin Table. United States Geological Survey map digitally presented using National Geographic Society TOPO software.

South Loup River-Sand Creek drainage divide area northwest of Arnold

Figure 4: South Loup River-Sand Creek drainage divide area northwest of Arnold. United States Geological Survey map digitally presented using National Geographic Society TOPO software.

Figure 4 illustrates the South Loup River-Sand Creek drainage divide area seen in less detail in the figure 3 northeast quadrant above. Hoagland is the small town (or place-name) near the figure 4 north center edge. The South Loup River flows in an east and northeast direction from the figure 4 west edge to Hoagland and then turns to flow in a southeast direction to Arnold near the figure 4 east edge. The southeast and north oriented tributary joining the South Loup River near Arnold is Sand Creek (this is the first of several different Sand Creeks illustrated in this essay). Note southeast-oriented Mills Valley north of Arnold and the north-south oriented Judkins Table upland surface just east of the Mills Valley. What has happened here is prior to headward erosion of the deep southeast-oriented South Loup River valley southeast-oriented flood waters flowed across the entire figure 4 map area. A large and deep southeast-oriented valley eroded headward into the figure 4 southeast corner, with headward erosion being fed by multiple southeast-oriented flood flow routes. The primary flood flow route was along the alignment now used by the southeast-oriented South Loup River valley in the figure 4 northeast quadrant. Another significant southeast-oriented flood flow route was along the alignment of the present day southeast-oriented Sand Creek valley, although flood water was flowing in a southeast direction across the region in an anastomosing (interconnected) channel complex that crossed the entire figure 4 map area. Headward erosion of the South Loup River valley channel beheaded southeast-oriented flood flow in the Arnold area and flood waters on the north end of the beheaded flood flow route reversed flow direction to flow north. The reversed flood water captured yet to be southeast-oriented flood water from the northwest and eroded the north-oriented Sand Creek valley south to capture southeast-oriented flood flow on the southeast-oriented Sand Creek alignment. At the same time the South Loup River valley was eroding headward along its southeast-oriented flood flow channel. When headward erosion of the South Loup River valley reached the figure 4 north center edge the valley continued to erode to the northwest and that valley is the southeast-oriented North Fork of the South Loup River (not seen in figure 4). At the same time a tributary valley eroded southwest and west to capture southeast-oriented flood flow moving to the southwest of the present day southeast-oriented North Fork valley. That tributary valley was so successful in capturing southeast-oriented flood flow that it became the main South Loup River headwaters valley. Among the flood flow routes captured was the southeast-oriented flood flow route to the Sand Creek valley.

South Loup River-Sand Creek drainage divide area northwest of Callaway

Figure 5: South Loup River-Sand Creek drainage divide area northwest of Callaway. United States Geological Survey map digitally presented using National Geographic Society TOPO software.

Figure 5 illustrates the South Loup River-Sand Creek drainage divide area northwest of Callaway and southeast of the figure 4 map area (the Sand Creeks in figure 5 are different Sand Creeks than the Sand Creek in figure 4). Figure 5 includes overlap areas with figure 3a above (the southwest corner of figure 5 overlaps with the figure 3a northeast corner). Callaway is the town in the figure 5 southeast corner area and is located in southeast oriented South Loup River valley and northeast and east oriented Sand Creek joins the South Loup River at Callaway. The South Loup River flows in a southeast direction from the figure 5 north edge (west half) to Finchville and then makes a jog to the northeast before continuing in a southeast direction to Callaway. South of Finchville is the north-northwest oriented Rye Valley and several north-oriented tributaries flow to the southeast, northeast, southeast oriented South Loup River near Finchville. One of the north-oriented tributaries is still another Sand Creek (suggesting there is a lot of sand in the figures 3, 4, and 5 map areas). Between the north-northwest oriented Rye Valley and the southeast-oriented South Loup River is northwest-southeast oriented Murphy Table. Note two northwest-oriented streams flowing from the Murphy Table southwest margin to Rye Valley, which drains to the north to the South Loup River valley. Also note the east-oriented Sand Creek valley located immediately to the southeast of both Rye Valley and Murphy Table. There is a large northwest-southeast oriented through valley linking the southeast-oriented South Loup River valley upstream from Finchville with the east-oriented Sand Creek valley. That northwest-southeast oriented through valley is evidence that multiple anastomosing flood flow channels eroded the figure 5 map region. West of that through valley is another through valley, which can be better seen in figure 3a above. The north-oriented Sand Creek valley, which drains to the South Loup River near Finchville is linked by a through valley to the south-southeast oriented Sells Valley seen in figure 3a (Sells Valley drains to Stump Ditch, which flows directly south to the Platte River valley). These multiple through valleys suggest large quantities of south-oriented flood flow were captured and diverted to the southeast by headward erosion of the southeast-oriented South Loup River valley. Figure 6 illustrates still another large through valley just south of Callaway.

South Loup River-Wood River drainage divide area south of Callaway

Figure 6: South Loup River-Wood River drainage divide area south of Callaway. United States Geological Survey map digitally presented using National Geographic Society TOPO software.

Figure 6 illustrates the South Loup River-Wood River drainage divide area south of Callaway and is located south and east of the figure 5 map area and includes overlap areas with figure 5. Callaway is located near the figure 6 north center edge. The South Loup River makes a jog to the east at Callaway and then flows in a southeast direction to the figure 6 east center edge. The southeast-oriented highway from Callaway to Oconto (located in the figure 6 southeast corner) flows in a northwest-southeast oriented through valley drained in the figure 6 southeast quadrant by the southeast-oriented Wood River. The northwest end of the through valley is drained by north-oriented Cottonwood Creek, which originates in the figure 6 center area and flows in a northeast direction before turning to flow north to join the South Loup River as a barbed tributary near Callaway. Note how the northeast-oriented Cottonwood Creek segment has southeast-oriented tributaries from the northwest and northwest-oriented tributaries from the southeast. This northwest-southeast tributary alignment is evidence the northeast-oriented Cottonwood Creek valley eroded headward across multiple southeast-oriented flood flow channels. Flood waters on the northwest ends of beheaded flood flow channels reversed flow direction to flow in a northwest direction to the newly eroded Cottonwood Creek valley. The north-oriented Cottonwood Creek segment at the north end of the South Loup River-Wood River through valley probably originated as a reversal of flood flow when headward erosion of the deeper South Loup River valley beheaded southeast-oriented flood flow to what was then the actively eroding Wood River valley. The South Loup River valley-Wood River through valley is further evidence of a large-scale anastomosing channel complex that existed as headward erosion of the present day valley systems took place. Flood waters originally flowed on a topographic surface at least as high as the highest figure 6 elevations today and flood waters deeply eroded the figure 6 map regions as deep valleys eroded headward into the region.

Wild Horse Valley area north of Gothenberg

Figure 7: Wild Horse Valley area north of Gothenberg. United States Geological Survey map digitally presented using National Geographic Society TOPO software.

Figure 7 illustrates the Wild Horse Valley and Platte River valley south of the figure 3a map area and includes overlap areas with figure 3a. The southeast-oriented Platte River flows in a large valley from the figure 7 west edge to the figure 7 south edge. Gothenberg is the town located near where the Platte River crosses the figure 7 south edge. Note the south-southeast oriented stream flowing from near the figure 7 west edge (north half) to the Platte River valley and then flowing in a southeast direction once it enters the Platte River valley. That tributary stream is Pawnee Creek and illustrates how most Platte River tributaries from the north turn to flow parallel to the Platte River before finally joining the Platte River. Figure 9 below further illustrates this phenomena, which will be discussed in the figure 9 discussion. Wild Horse Valley is the south-southeast oriented valley draining from the figure 7 north center and center area toward the Platte River valley and was eroded headward by southeast-oriented flood flow eroding the valley headward from what was then the newly eroded Platte River valley north wall. Immediately east of Wild Horse is Odencranze Table and east of Odencranze Table is the Cottonwood Valley. The Cottonwood Valley is drained by West Buffalo Creek and Buffalo Creek while east of West Buffalo Creek is the Pancake Valley drained by East Buffalo Creek. The south margin of Tallin Table can be seen near the figure 7 north edge just north of the West and East Buffalo Creek valley heads. Further east in the figure 7 map area is the south-southeast oriented Sells Valley, which is linked by a through valley to the north-oriented Sand Creek seen in figure 5 above. Note how south-southeast oriented Buffalo Creek and other Platte River tributaries do not flow directly to the Platte River, but turn to flow in southeast directions upon entering the Platte River valley. Multiple south-southeast oriented Platte River tributary valleys that eroded headward into what was an upland topographic surface to the north provide evidence of massive quantities of south-southeast oriented flood flow to the newly eroded and deep Platte River valley prior to headward erosion of the deep South Loup River valley to the north. Headward erosion of the South Loup River valley beheaded south-southeast oriented flood flow to these Platte River tributary valleys.

Wood River-Buffalo Creek drainage divide area southwest of Oconto

Figure 8: Wood River-Buffalo Creek drainage divide area southwest of Oconto. United States Geological Survey map digitally presented using National Geographic Society TOPO software.

Figure 8 illustrates the Wood River-Buffalo Creek drainage divide area southeast of the figure 6 map area and includes overlap areas with figure 6 (Note the Buffalo Creek in figure 8 is a different Buffalo Creek than the Buffalo Creek in figures 3a and 7). The Wood River flows in a southeast direction from the figure 8 north center edge area to the figure 8 southeast corner. Oconto is the town located in the Wood River valley in the figure 8 northeast quadrant. Redfern Table is the upland surface located in the figure 8 northwest quadrant. Southeast of Redfern Table are headwaters of south-southeast oriented Buffalo Creek, which flows to the figure 8 south center edge. Note how a northeast-oriented Wood River tributary originates just north of the Buffalo Creek headwaters and a close look at figure 8 reveals through valleys linking northwest-oriented tributaries to that northeast-oriented Wood River tributary with the south-southeast oriented Buffalo Creek headwaters. Also a close look at figure 8 reveals northwest-southeast oriented erosional residuals in the Buffalo Creek headwaters area and an anastomosing channel complex defining those erosional residuals. Figure 8a below provides a more detailed map of that Buffalo Creek headwaters area to better illustrate this evidence of a massive south-southeast oriented flood flow and flood erosion in the Buffalo Creek headwaters area. Figure 8a below illustrates the Redfern Table southeast margin and the Buffalo Creek headwaters area seen in less detail in figure 8 above. South-southeast oriented Buffalo Creek is located in the figure 8a south center area and south-oriented drainage to the figure 8 south edge flows to Buffalo Creek. North-oriented drainage in sections 5, 4, and 3 along the figure 8a north edge flows to the northeast-oriented Wood River tributary seen in figure 8. Note how there are through valleys linking the north-oriented drainage routes with the south-oriented Buffalo Creek headwaters. The through valleys provide evidence of multiple south-oriented flood flow channels, which were beheaded by headward erosion of the northeast-oriented Wood River tributary valley (which eroded headward from what was then the newly eroded and deep southeast-oriented Wood River valley). Also note how Buffalo Creek headwaters valleys have eroded headward into the Redfern Table upland surface. These headcuts eroded into the Redfern Table surface provide evidence flood waters flowed across the Redfern Table upland surface to what was then the actively eroding deep Buffalo Creek valley. Also note in the figure 8 south center area northwest-southeast oriented streamlined erosional residuals in the Buffao Creek headwaters area and the anastomosing complex of channels separating those erosional residuals. The streamlined erosional residuals and the anastomosing channels are further evidence of the flood flow that eroded the region.

Figure 8a: Through valleys, erosional residuals, and anastomosing channels in Buffalo Creek headwaters area. United States Geological Survey map digitally presented using National Geographic Society TOPO software.

Wood River-Platte River drainage divide area northeast of Lexington

Figure 9: Wood River-Platte River drainage divide area northeast of Lexington. United States Geological Survey map digitally presented using National Geographic Society TOPO software.

Figure 9 uses reduced size maps to illustrate the Wood River-Platte River drainage divide area southeast of the figure 8 map area. The southeast-oriented Platte River is located in the figure 9 southwest corner. Note how the Platte River channel is located near the southwest wall of a large southeast-oriented valley. Lexington is the town located in the Platte River valley in the figure 9 southwest quadrant. Elm Creek is the much smaller town located at the highway intersection near the figure 9 southeast corner. Overton is located on the highway between Lexington and Elm Creek. The Wood River flows from the figure 9 north center edge area in a southeast, east and southeast direction to the figure 9 east edge. Miller is the small town located in the Wood River valley north of Elm Creek and Summer is the town in the Wood River north of Overton. The Buffalo Creek seen in figures 8 and 8a flows south along the figure 9 west edge (north half) to enter the large southeast-oriented Platte River valley and then instead of flowing to the Platte River channel turns to flow in a southeast direction near the Platte River valley’s northeast wall. Buffalo Creek eventually turns to flow to the Platte River channel south of the figure 9 southeast corner. This phenomenon was observed in figure 7 above and can be observed for the entire Platte River valley route across Nebraska (see Loup River-Platte River drainage divide area between Kearney and Columbus essay for additional examples). What is happening here is the present day Platte River channel and the Buffalo Creek channel are reflecting flood flow routes that once existed in the large Platte River valley. The Platte River valley was eroded headward across Nebraska and into the Rocky Mountain region as a massive flood flow channel, which captured an immense southeast-oriented flood. Considerable flood water entered the Platte River valley west of the figure 9 map area and the massive southeast-oriented flood flow entering the Platte River channel in the figure 9 region was forced by flood flow from the west to flow along the valley’s north wall while the flood waters from the west were pushed to flow along the Platte River valley’s south wall. As more southeast-oriented flood flow entered the Platte River valley in a downstream direction flood waters that had been flowing along the valley’s north wall were pushed further and further into the main Platte River channel. Today those flood flow patterns are preserved in the Platte River channel location and the locations of the Platte River tributary channels entering from the north and northwest.

South Loup River-Wood River drainage divide in Park Valley area

Figure 10: South Loup River-Wood River drainage divide in Park Valley area. United States Geological Survey map digitally presented using National Geographic Society TOPO software.

Figure 10 illustrates the South Loup River-Wood River drainage divide area in the Park Valley area and is located north of the figure 9 northeast quadrant and includes overlap areas with figure 9. The Wood River flows in a southeast direction across the figure 10 southwest corner. Eddyville is the town located along the figure 10 west edge (south half) and Summer and Miller are located in the Wood River valley south of the figure 10 map area. The South Loup River flows in a southeast direction from the figure 10 north center edge area to the figure 10 east center area. Park Valley is an interesting northwest-southeast oriented basin located in the figure 10 drainage divide area. The Park Valley southeast end drains to a southeast-oriented Wood River tributary while the Park Valley northwest end is drained by a northwest and north oriented South Loup River tributary. Figure 10a below provides a more detailed map of the Park Valley basin. Note in section 7 of the figure 10a map that there is a closed depression in the Park Valley center area. The bottom of that closed depression is 20-30 feet lower than the surrounding Park Valley floor, while the Park Valley floor is generally 50-75 feet lower than the hills on either side. Park Valley was eroded by southeast-oriented flood flow moving to what was then the newly eroded southeast-oriented Wood River valley. Why the Park Valley basin was eroded the way it was probably requires knowledge not obtainable from a topographic map, although it appears as though flood waters flushed out easily eroded materials from the basin. It is possible these easily eroded materials were flood deposited sediments from an earlier flood stage, when flood may have been ponded in the region. However, why material was flushed out of the Park Valley basin and not from the surrounding region is difficult to determine, although a similar basin, The Black Hill Basin, is located in the adjacent Mud Creek-South Loup River drainage divide area. Headward erosion of the deep South Loup River valley beheaded southeast-oriented flood flow to the Park Valley basin and flood waters on the north end of the beheaded flood flow route reversed flow direction to drain the Park Valley northwest end in a north direction to the newly eroded South Loup River valley. At the same time the Park Valley southeast end drained to the southeast to the Wood River. The closed depression between the northwest- and southeast-oriented drainage routes is probably somehow related to the flood flow movements, although I do not have a good explanation for the that depression.

Figure 10a: Detailed map of South Loup River-Wood River drainage divide in Park Valley area. United States Geological Survey map digitally presented using National Geographic Society TOPO software.

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.