A geomorphic history based on topographic map evidence

The Elkhorn River-Loup River drainage divide area between Shell Creek and Beaver Creek, Nebraska, was eroded by massive southeast-oriented floods, which before being beheaded by Elkhorn River headward erosion flowed to what was probably a newly eroded east-oriented Loup River-Platte River valley. Evidence supporting this interpretation includes the southeast-oriented Shell Creek and Beaver Creek orientations, orientations of Shell Creek and Beaver Creek tributaries, and shallow through valleys across present day drainage divides. The large east-oriented Loup River-Platte River valley is interpreted to have eroded headward into the region to capture the southeast-oriented flood flow. The Shell Creek and Beaver Creek valleys and their tributary valleys then eroded headward along what were probably anastomosing southeast-oriented flood flow channels. Headward erosion of the Elkhorn River valley and tributary next beheaded southeast-oriented flood flow to the actively eroding Shell Creek and Beaver Creek valleys. North-oriented Elkhorn River tributary valleys were eroded by reversals of flood flow on the north ends of beheaded southeast-oriented flood flow routes.

Preface:

• The purpose of this essay is to use topographic map interpretation methods to explore Elkhorn River-Loup River drainage divide area landform origins between Shell Creek and Beaver Creek, 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 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 Elkhorn River-Loup River drainage divide area landform origins evidence between Shell Creek and Beaver Creek, 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.

Elkhorn River-Loup River drainage divide area between Shell Creek and Beaver Creek location map

Figure 1: Elkhorn River-Loup River drainage divide area between Shell Creek and Beaver Creek location map (select and click on maps to enlarge). National Geographic Society map digitally presented using National Geographic Society TOPO software.

Figure 1 provides an Elkhorn River-Loup River drainage divide area between Shell Creek and Beaver Creek location map. With the exception of an area in the figure 1 northeast corner the figure 1 map area shows a region in eastern Nebraska. The Missouri River flows south-southeast in the figure 1 northeast corner.  The Platte River flows northeast from the figure 1 south center edge to Columbus and then in an east-northeast direction to North Bend. From North Bend the Platte River flows in an east direction to Fremont and then turns to flow in a south direction to the figure 1 southeast corner. At the figure 1 southeast corner the Platte River turns to flow east to join the south-southeast oriented Missouri River (east of the figure 1 map area). The Elkhorn River flows from near Bassett in the figure 1 northwest corner to Stuart, O’Neill, Clearwater, Neligh, Oakdale, Tilden, Norfolk, Stanton, Pilger, Wisner, West Point, and Hooper before joining the Platte River near Elkhorn in the figure 1 southeast corner. Shell Creek originates south of Tilden and flows in a southeast direction through Newman Grove and Lindsay to Platte Center near the edge of the Platte River valley. Near Platte Center Shell Creek turns to flow in an east direction to join the Platte River east of Schuyler. Beaver Creek originates southwest of Clearwater and flows in a southeast direction to Albion and St. Edward before joining the Loup River near Genoa. The Loup River originates west of the figure 1 map and flows in a southeast direction from the figure 1 west edge (south half) to Sargent, Comstock, Arcadia, and Loup City before turning to flow in a northeast direction near Boelus. The northeast oriented Loup River flows roughly parallel to the Platte River and joins the Platte River near Columbus. The Elkhorn River-Loup River drainage divide area of concern in this essay is located between Shell Creek and Beaver Creek. The Elkhorn River-Shell Creek drainage divide area in Antelope, Madison, Boone, and Platte Counties essay describes the region located immediately east of the Shell Creek-Beaver Creek region discussed and illustrated here. The Niobrara River-Elkhorn River drainage divide area essay discusses the region north of the region described here. Both essays can be found under Elkhorn River on the sidebar category list. Hundreds of Missouri River drainage basin landform origins research project essays published on this website provide significant evidence that immense southeast-oriented floods flowed across Nebraska and were captured by headward erosion the northeast and east oriented Platte River valley. Subsequently the southeast-oriented flood flow was captured by headward erosion of the Elkhorn River, which beheaded flow routes to the newly eroded Platte River valley.

Elkhorn River-Loup River drainage divide area between Shell Creek and Beaver Creek detailed location map

Figure 2: Elkhorn River-Loup River drainage divide area between Shell Creek and Beaver Creek detailed location map. United States Geological Survey map digitally presented using National Geographic Society TOPO software. 

Figure 2 is a somewhat more detailed location map for the Elkhorn River-Loup River drainage divide area between Shell Creek and Beaver Creek. Antelope, Pierce, Wayne, Wheeler, Madison, Stanton, Greeley, Boone, Nance, Platte, and Colfax are Nebraska county names and county boundaries are shown. The Elkhorn River flows in a southeast direction across Antelope County and in an east-southeast direction across northern Madison County. East of Norfolk, in Stanton County, the Elkhorn River turns to flow southeast to Stanton and then to flow northeast to Pilger, and finally to flow southeast to the figure 2 east edge. The Platte River flows in an east-northeast direction along the southern boundaries of Platte and Colfax Counties (in the figure 2 southeast corner area). The Loup River flows in a northeast direction from the figure 2 south center border into Nance County and then in Platte County turns to flow southeast to join the Platte River near Columbus. Shell Creek originates in northeast Boone County and flows in a southeast direction across the Madison County southwest corner and into Platte County, where north of Columbus it turns to flow east to the figure 2 east edge. Beaver Creek originates in northeast Wheeler County and flows in a southeast direction across Boone County and into Nance County, where it joins the east-northeast oriented Loup River near Genoa. In western Platte County, between Shell Creek and Beaver Creek, is south-southeast and south oriented Looking Glass Creek. Clearwater Creek, which originates in northeast Wheeler County and flows in a northeast direction in Antelope County to join the Elkhorn River near Clearwater, and Cedar Creek, which originates near Raeville in northern Boone County and flows north to join the Elkhorn River near Oakdale, are two Elkhorn River tributaries of importance below. Note how drainage route orientations in figure 2 vary. Near the figure 2 south edge (east half) there are multiple east-northeast and east oriented channels, which are located on the floor of the broad east-northeast and east oriented Platte River valley. The Loup River and Shell Creek channels are generally located along the north edge of that broad Platte River valley. North of the east-oriented Loup River and Shell Creek channel segments are long southeast-oriented Platte River tributaries (treating Shell Creek and all Loup River tributaries as Platte River tributaries). South of the Elkhorn River are a number of north and northeast oriented Elkhorn River tributaries, although these tributaries are generally shorter than the southeast-oriented Platte River tributaries immediately to the south. The figure 2 drainage pattern originated when a massive southeast-oriented flood flowed across the entire figure 2 map area. Headward erosion of the broad east-northeast and east oriented Platte River valley then captured the southeast-oriented flood flow and diverted the flood water east. Large volumes of flood water from western source areas combined with captured southeast-oriented flood flow to create anastomosing east-oriented flood flow channels. Next headward erosion of the Elkhorn River valley and its northeast-oriented tributary valleys beheaded the southeast-oriented flood flow routes in sequence, from east to west. Flood waters on the north ends of the beheaded flood flow routes reversed flow direction to erode the north-oriented Elkhorn River tributary valleys.

Clearwater Creek-Beaver Creek drainage divide area

Figure 3: Clearwater Creek-Beaver Creek drainage divide area. United States Geological Survey map digitally presented using National Geographic Society TOPO software. 

Figure 3 illustrates the Clearwater Creek-Beaver Creek drainage divide in northeast Wheeler County. Clearwater Creek originates in the figure 3 northwest quadrant and flows in an east-southeast direction into the figure 3 north center area, where it turns to flow northeast and east-northeast to the figure 3 corner area. Note the southeast-oriented tributaries to the northeast-oriented Beaver Creek segment in the figure 3 north center area. Also note the north-northwest oriented Beaver Creek segment tributaries in the figure 3 northeast quadrant.  As seen in figure 2 northeast of the figure 3 map area Clearwater Creek flows in a northeast direction to join the southeast-oriented Elkhorn River near Clearwater. Beaver Creek originates in the figure 3 southwest quadrant and flows in a east-southeast direction to the figure 3 south center area and then makes a jog to the northeast before turning to flow in a southeast direction to the figure 3 south edge. As seen in figure 2 south of the figure 3 map area Beaver Creek continues to flow in a southeast direction until it reaches the east-northeast oriented Loup River. Much of the figure 3 map area lacks a drainage pattern and appears to be covered with what might be sand dunes. If so the sand dunes might be evidence that southeast-oriented flood waters were temporarily ponded in the region and deposited sediments in this region. It is also possible the sand has blown in from areas further to the west. In either case the figure 3 map area provides limited evidence from which the drainage history can be reconstructed and by itself can not be used to interpret flood flow movements, or even if the region was eroded by southeast-oriented flood waters. However, all figure 3 map evidence is consistent with what might be expected if the Beaver Creek valley eroded headward to capture southeast-oriented flood flow and if the Clearwater Creek valley eroded headward from what was then the actively eroding Elkhorn River valley head to capture southeast-oriented flood flow moving to the newly eroded Beaver Creek valley. These valleys could have eroded headward into a region where flood waters had previously been ponded and deposited sediment and then subsequently wind activity buried all but the major drainage routes (where there is sufficient flow to keep the channels open). While from figure 3 evidence alone other explanations are possible, no figure 3 evidence is contrary to the southeast-oriented flood interpretation.

Blacksnake Creek-Rae Creek drainage divide area

Figure 4: Blacksnake Creek-Rae Creek drainage divide area.United States Geological Survey map digitally presented using National Geographic Society TOPO software. 

Figure 4 illustrates the Blacksnake Creek-Rae Creek drainage divide area southeast of the figure 3 map area. Beaver Creek flows in a southeast direction across the figure 4 southwest quadrant. Rae Creek flows in a south-southeast direction from the figure 4 center area to Petersburg and then south to join Beaver Creek south of the figure 4 map area. North of the Rae Creek headwaters is north-oriented Blacksnake Creek. Blacksnake Creek flows in a northeast direction in the figure 4 north center edge area. Notice the multiple through valleys linking the north-oriented Blacksnake Creek headwaters area with the south-oriented Rae Creek headwaters area. The through valleys provide evidence multiple channels of south-oriented flood water flowed from the present day Blacksnake Creek drainage basin to what was then the actively eroding Rae Creek drainage basin. Figure 5 below illustrates the Blacknake Creek-Rae Creek through valley area in more detail. Headward erosion of a an east-oriented valley north of the figure 4 map area beheaded the south-oriented flood flow channels, which resulted in a reversal of flow that eroded the north-oriented Blacksnake Creek valley and created the Blacksnake Creek-Rae Creek drainage divide. Figure 4a below illustrates the Blacksnake Creek course north of the figure 4 map area. Note in figure 4a how Blacksnake Creek flows in a northeast direction to Elgin and then flows in a north-northwest direction, then turns to flow east, south-southwest, and finally southeast to join north-oriented Cedar Creek, which flows to the Elkhorn River near Oakdale in the figure 4a northeast corner. Returning to figure 4 north-oriented Cedar Creek headwaters are located in the figure 4 northeast quadrant. Notice the through valleys linking the north-oriented Cedar Creek valley with the south-oriented Rae Creek valley. Figure 6 below illustrates those through valleys in more detail. Note in both figures 4 and 4a how Cedar Creek has northwest oriented tributaries and southeast-oriented tributaries, including Blacksnake Creek. The northwest and southeast oriented tributaries are evidence the Cedar Creek valley eroded headward across multiple southeast-oriented flood flow routes. The southeast-oriented tributary valleys were eroded headward from the newly eroded Cedar Creek valley wall along the captured southeast-oriented flood flow routes. The northwest-oriented tributary valleys were eroded by reversals of flood flow on the northwest ends of beheaded flood flow routes. The complex Blacksnake Creek valley route was created by a combination of headward erosion along a southeast-oriented flood flow route, a reversal of flow on what was originally a northeast-oriented valley, headward erosion to the west, reversal of flow on a beheaded southeast-oriented flow route, and headward erosion of a northeast-oriented valley. It is possible the complex Blacksnake Creek valley route was created while flood water still moving south in the Cedar Creek valley to the south-oriented and actively eroding Rae Creek and Beaver Creek valleys, with the south-oriented Cedar Creek flood flow channel being beheaded and reversed by Elkhorn River valley headward erosion after the Blacksnake Creek-Rae Creek drainage divide had been created.

Figure 4a. Blacksnake Creek north of the figure 4 map area. United States Geological Survey map digitally presented using National Geographic Society TOPO software. 

Detailed map of Blacksnake Creek-Rae Creek drainage divide area

Figure 5: Detailed map of Blacksnake Creek-Rae Creek drainage divide area. United States Geological Survey map digitally presented using National Geographic Society TOPO software. 

Figure 5 provides a detailed map of the Blacksnake Creek-Rae Creek drainage divide area seen in less detail in figure 4 above. The west to east oriented Antelope-Boone County line runs across the figure 5 center and can be used as a reference line. The south-oriented drainage basin in the figure 5 southeast quadrant is the Rae Creek drainage basin. Rae Creek originates near the section 33-section 4 border along the county line and flows south through section 4 to the figure 5 south edge. Blacksnake Creek originates in section 33 and flows north to section 28. Note how the Rae Creek valley is the deeper valley, providing evidence flood flow came from the north to erode the south-oriented Rae Creek valley headward. Note the presence of other north-south through valleys, although at higher elevations. Those other through valleys provide evidence that south-oriented flood water originally flowed across a topographic surface at least as high as the highest figure 5 elevations today. Deeper through valleys represent the final south-oriented flood flow routes immediately before the Blacksnake Creek headwaters reversed flow direction to flow north to the Elkhorn River valley. As seen in figure 4a the Blacksnake Creek valley downstream from the figure 5 map area is complex suggesting it was eroded in stages and this headwaters area reversal of flow probably occurred before the final stage of the figure 5 drainage route evolution. Also as seen in figure 4 and in figure 6 below there are deeper north-south oriented through valleys linking the north-oriented Cedar Creek valley and the south-oriented Rae Creek valley just east of the figure 5 map area. These deeper through valleys suggest south-oriented flood water continued to flow to the south-oriented Rae Creek drainage basin after the Blacksnake Creek-Rae Creek drainage divide had been created. Drainage complexities such as these suggest there was considerable shifting of flood flow routes as new valleys eroded headward and changed the regional landscape. My goal in this discussion is to suggest how to unravel this complex puzzle, not to solve every twist and turn of the valleys (although such a detailed solution is possible should anyone care to take the time to work it out).

Detailed map of Cedar Creek-Rae Creek drainage divide area

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

Figure 6 provides a detailed map of the Cedar Creek-Rae Creek drainage divide area near Raeville seen in less detail in figure 4 above. The figure 6 map area is located east and slightly south of the figure 5 map area (the figure 6 north edge roughly corresponds with the west to east oriented Antelope-Boone County line). The north-oriented drainage routes north and east of Raeville are Cedar Creek headwaters. Figure 4a above illustrated the Cedar Creek route north of the figure 6 map area and where Cedar Creek joins the Elkhorn River valley. The south-southwest oriented drainage in the figure 6 south center area flows to south-oriented Rae Creek. Note the multiple through valleys linking the north-oriented Cedar Creek drainage basin with the south-oriented Rae Creek drainage basin. These through valleys are much larger and deeper than the Blacksnake Creek-Rae Creek through valleys seen in figure 5. For example the through valley used by the now abandoned railroad line is approximately 40-50 feet deeper than the lowest Blacksnake Creek-Rae Creek through valley floor seen in figure 5. Presence of these larger and deeper through valleys just west of the Blacksnake Creek-Rae Creek drainage divide area and the complex Blacksnake Creek route suggests the  Blacksnake Creek-Rae Creek drainage divide was created while large volumes of flood water were still moving south from the Cedar Creek valley to the Rae Creek valley. In other words, reversed flood flow in the Blacksnake Creek headwaters area was beheaded and reversed by headward erosion of a south-oriented Cedar Creek tributary valley prior to the time south-oriented flood flow in the Cedar Creek valley was beheaded and reversed, so as to flow north to the what would have been the newly eroded and deeper Elkhorn River valley. The size of the north-oriented Cedar Creek headwaters valleys suggests there were large quantities of water present in the region at the time south-oriented flood waters were reversed to flow north. Flood waters originally flowed across a topographic surface at least as high the highest figure 6 elevations today and it is possible much of the figure 6 was still covered by flood water when the flood flow reversal occurred.

North Fork Shell Creek-Shell Creek drainage divide area

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

Figure 7 illustrates the North Fork Shell Creek-Shell Creek drainage divide area located east and somewhat south of the figure 6 map area. Shell Creek flows in a southeast direction in the figure 7 south center area. North Fork Shell Creek flows in a northeast direction in the figure 7 northwest quadrant and then turns to flow in a southeast direction in the figure 7 northeast quadrant. East of the figure 7 map area North Fork Shell Creek flows in a south-southeast direction to join southeast-oriented Shell Creek. North of the North Fork Shell Creek valley are through valleys linking the North Fork Shell Creek valley with north-oriented Elkhorn River tributaries, including northwest-oriented Cedar Creek tributaries. A close look at the figure 7 drainage divide between the North Fork Shell Creek valley and the southeast-oriented Shell Creek valley reveals numerous shallow through valleys. For example, starting in section 23 in the figure 7 west center area, two shallow through valleys link a northwest-oriented North Fork Shell Creek tributary with the Shell Creek valley head. And just to the south in the section 26 northeast corner is another through valley linking the Shell Creek headwaters valley with the head of a southeast-oriented Shell Creek tributary valley. Continuing east along the North Fork Shell Creek-Shell Creek drainage divide from section 23 there is another through valley along the section 23-section 24 boundary and at least 5 shallow through valleys in section 24 alone (although some appear to be very minor notches). Continuing into section 19 there are still more such through valleys crossing the drainage divide. In fact, a study of drainage divides separating each and every one of the figure 7 deeper valleys reveals the presence of such shallow through valleys. These through valleys are evidence of a south- or southeast-oriented anastomosing channels that were eroded into the regional landscape prior to headward erosion of the present day Shell Creek, North Fork Shell Creek, and their tributary valleys. The sequence of headward erosion of the valleys can be determined. For example headward erosion of the North Fork Shell Creek valley eroded west and southwest across the figure 7 north half after the Shell Creek valley had eroded headward into the figure 7 south center area. Headward erosion of the North Fork Shell valley beheaded south-oriented flood flow routes to the what was then the actively eroding Shell Creek valley system. Flood waters on the north ends of the beheaded flood flow routes reversed flow direction to flow north and eroded the short north-oriented North Fork Shell Creek tributary valleys seen today.

Shell Creek-Looking Glass Creek drainage divide area

Figure 8: Shell Creek-Looking Glass Creek drainage divide area. United States Geological Survey map digitally presented using National Geographic Society TOPO software. 

Figure 8 illustrates the Shell Creek-Looking Glass Creek drainage divide area located south of the figure 7 map area. Albion is the town located in the figure 8 west center edge are. Beaver Creek is the southeast-oriented stream flowing from Albion to the figure 8 south edge. O’Neil Valley is the south oriented valley draining to Beaver Creek east of Albion. East of O’Niel Valley is south-southeast oriented Vorhees Creek, which joins Beaver Creek near the figure 7 south edge. Newman Grove is the small town located in the figure 8 northeast corner area. Shell Creek is the southeast stream flowing near Newman Grove in the figure 8 northeast corner. Looking Glass Creek is the south-southeast-oriented stream flowing to the figure 8 southeast corner. South of figure 8 Looking Glass Creek flows directly to the Loup River (see figure 10 below). Note the unnamed northeast-oriented Shell Creek tributary flowing to Shell Creek at Newman Grove (the abandoned railroad line follows the tributary valley). Note how that unnamed tributary has northwest-oriented tributaries and how those northwest-oriented tributary valleys are linked to the south-southeast oriented Looking Glass Creek headwaters (and also to an unnamed south- and southwest-oriented Beaver Creek tributary valley). Figure 9 below provides a more detailed map of the northeast-oriented Shell Creek tributary-Looking Glass Creek drainage divide area and illustrates shallow northwest-southeast oriented through valleys crossing that drainage divide. The multiple south- and southeast-oriented figure 8 drainage routes provides evidence the figure 8 map area was eroded by south-southeast oriented flood water, with the present day Shell Creek and Beaver Creek valleys eroding headward to capture those south- southeast oriented flood flow routes. The unnamed northeast-oriented Shell Creek tributary valley eroded southwest to capture south-southeast oriented flood flow to what was then the actively eroding Looking Glass Creek valley. Flood waters on the northwest ends of the beheaded flood flow route reversed flow direction to flow northwest and north to the newly eroded northeast-oriented tributary valley and in doing so eroded the northwest-oriented tributary valleys.

Detailed map of Shell Creek tributary-Looking Glass Creek drainage divide area

Figure 9 provides a detailed map of the Shell Creek tributary-Looking Glass Creek drainage divide seen in less detail in figure 8 above. Looking Glass Creek is labeled in the figure 9 southeast quadrant and flows from the figure 9 north center area to the figure 9 south edge. North and northwest oriented drainage near the north edge in the figure 9 northwest quadrant flows to the unnamed northeast-oriented Shell Creek tributary described in the figure 8 discussion above. Southeast-oriented drainage flowing to the figure 9 east edge represents the headwaters areas of southeast-oriented Shell Creek tributaries. Southeast-oriented streams in the figure 9 south center area are Looking Glass Creek tributaries. Note the shallow northwest-southeast oriented through valleys linking the north-oriented drainage in sections 7 and 8 with the Looking Glass Creek headwaters in sections 18 and 17. Those through valleys provide evidence of multiple southeast-oriented flood flow channels, such as might be found in a southeast-oriented anastomosing channel complex. Prior to being beheaded the flood flow channels were moving flood waters southeast into what was at that time the actively eroding Looking Glass Creek valley system. Headward erosion of the northeast-oriented Shell Creek tributary valley beheaded the southeast-oriented flood flow channels one channel at a time (from the east to the west). Flood waters on the north ends of the beheaded flood flow channels reversed flow direction to flow north or northwest to the newly eroded and deeper Shell Creek tributary valley. Because the flood flow channels were anastomosing (or interconnected) and because the channels were beheaded one channel at a time, reversed flow in a newly beheaded channel could capture yet to be beheaded flood flow from channels further to the west. Evidence for captures can be seen in shallow west to east oriented through valley seen in the south of sections 12 and 7 in the figure 9 northwest quadrant area. These captures of yet to be beheaded flood flow helped the large north-oriented valleys seen today. Note in the figure 9 southwest quadrant shallow through valleys providing evidence that headward erosion of the south-oriented valley located along the figure 9 west edge beheaded southeast-oriented flood flow routes to the southeast-oriented Looking Glass Creek tributary valleys. The south-oriented stream along the figure 9 west edge (south half) flows to Beaver Creek.

Beaver Creek and Shell Creek enter the Platte River valley

Figure 10: Beaver Creek and Shell Creek enter the Platte River valley. United States Geological Survey map digitally presented using National Geographic Society TOPO software. 

Figure 10 illustrates where Beaver Creek, Looking Glass Creek, and Shell Creek enter the large northeast oriented Platte River valley. The northeast oriented Platte River channel can just barely be seen in the figure 10 southeast corner. At this location the Platte River valley south of the Platte River channel is almost as wide as it is north of he Platte River channel. The northeast and east oriented river flowing in the figure 10 west half near the north edge of the Platte River valley is the Loup River. In the figure 10 east half the Loup River channel is turning to flow east and southeast to join the Platte River channel near Columbus, which is located a short distance east of the figure 10 map area. Shell Creek is located in the figure 10 northeast quadrant and flows southeast to near Platte Center (in the northeast corner) and east of the figure 10 map area flows along the north edge of the Platte River valley for a considerable distance before turning southeast to join the Platte River east of Schuyler (see figure 2). Beaver Creek is the southeast-oriented stream flowing from the figure 10 west edge to join the northeast oriented Loup River near Genoa. Looking Glass Creek is the south-oriented stream joining the Loup River east of Genoa. An irrigation canal is located along the Platte River valley north edge. North of the Platte River valley north edge all Elkhorn River-Loup River drainage divide area evidence between Shell Creek and Beaver Creek suggests the region was eroded by a massive southeast-oriented flood, with the southeast-oriented Shell Creek and Beaver Creek valleys (and other valleys) being eroded headward to capture the southeast oriented flood water. In figure 10 we see evidence of a large northeast and east oriented valley in which there are multiple river channels. This large valley apparently was eroded headward across the southeast-oriented flood and captured the southeast-oriented flood waters. Southeast-oriented flood flow moving into the east-oriented valley flowed along the north edge of the large northeast and east oriented Platte River valley while flood water from further west flowed in the valley center, which accounts for the present day Loup River and Platte River channel locations in the figure 10 west half (and also for the Shell Creek and Platte River channel locations east of the figure 10 map area). This arrangement suggests massive floods from two different source area (or at least which used two very different routes) joined together in the Platte River valley to flow east to what was probably at that time the newly eroded Missouri River valley.

Additional information and sources of maps studied

This essay has provided only a sample of the detailed topographic map evidence supporting the flood erosion interpretation. Many additional illustrations could be provided. Readers are encouraged to look at mosaics of detailed topographic maps to see the abundance of available data. Maps used in this study were created and published by the United States Geologic Survey and can be obtained directly from the United States Geological Survey and/or from dealers offering United States Geological Survey maps. Hard copy maps can also be observed at United States Geological Survey map depositories which are located throughout the United States and elsewhere. Illustrations used here were created using National Geographic Society TOPO software and digital map data. TOPO software and map data can be obtained from the National Geographic Society and/or dealers offering National Geographic Society digital map data.