A geomorphic history based on topographic map evidence

The Mud Creek-South Loup River drainage divide area in Custer, Sherman, and Buffalo Counties was eroded by immense southeast-oriented floods , which initially flowed on a topographic surface at least as high as the highest drainage divide elevations today. Evidence supporting this flood erosion interpretation includes orientations of the Mud Creek, South Loup River, and their tributary valleys, large abandoned headcuts eroded into the southeast margins of upland remnants, through valleys crossing present drainage divides, and barbed tributaries providing evidence of flood flow reversals. Valleys in the Mud Creek-South Loup River drainage divide area eroded headward in a logical and consistent sequence that can be reconstructed by studying present day drainage divides. Southeast-oriented flood flow across the Mud Creek-South Loup River drainage divide area ended as headward erosion of the deep Mud Creek valley, the South Loup River valley, and their various tributary valleys captured the flood flow and headward erosion of the deep Middle Loup River-Dismal River valley to the north and west beheaded all flood flow routes to the drainage divide area.

• The purpose of this essay is to use topographic map interpretation methods to explore Mud Creek-South Loup River drainage divide area landform origins in Custer, Sherman, and Buffalo 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 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 Mud Creek-South Loup River drainage divide area landform origins in Custer, Sherman, and Buffalo 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.

Mud Creek-South Loup River drainage divide area location map

Figure 1: Mud Creek-South Loup 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 Mud Creek-South Loup River drainage divide area in Custer, Sherman, and Buffalo Counties, Nebraska. Figure 1 illustrates a large region in central Nebraska. The Platte River is formed at the confluence of the North Platte River and South Platte River at North Platte (located in the figure 1 west center) and from North Platte flows in a southeast direction to Kearney and then in a northeast direction to Columbus near the figure 1 east edge. The South Loup River originates near Stapleton (located north of North Platte) and flows to Arnold and then in a southeast direction to Pleasanton. At Pleasanton the South Loup River turns to flow in a northeast direction to join southeast-oriented Mud Creek (labeled Clear Creek on figure 1) near Ravenna and then to join the southeast-oriented Middle Loup River near Boelus. The combined South Loup River and Middle Loup River flow then continues in a northeast direction as the Loup River and joins the Platte River near Columbus. Mud Creek originates near Broken Bow in the figure 1 center area and flows in a southeast direction through Berwyn, Ansley, Mason City, Litchfield, and Hazard to join the northeast-oriented South Loup River near Ravenna. Clear Creek is a major southeast-oriented Mud Creek tributary. Other Loup River drainage divide area essays can be found under Loup River on the sidebar category list. Additional essays describing drainage divides in the region northwest of the Loup River drainage basin can be found under Niobrara River or other appropriate Missouri River tributary names on the sidebar category list. Hundreds of published Missouri River drainage basin landform origins research project essays published on this website have built a strong case for immense southeast-oriented floods moving across central Montana, northeast Wyoming, and western South Dakota and then into western and central Nebraska. Initially flood waters moved in a southeast direction across Nebraska, but the flood waters were captured by headward erosion of the large northeast-oriented Loup River-Platte River valley. While on figure 1 the Loup River and Platte River appear to be separate river until they join near Columbus, the two rivers actually flow from the Grand Island area to the Columbus area on opposite sides of the same large northeast-oriented valley. The Loup River flows along the valley’s northwest wall while the Platte River flows along the valley’s southeast wall. These river channel locations originated when southeast-oriented flood waters flowing through the present day Loup River drainage basin joined flood waters from west of the Loup River drainage basin in the large northeast-oriented valley. Flood waters from the west were forced to flow along the valley’s southeast wall while flood waters from the northwest were confined to the northwest wall area.

Mud Creek-South Loup River drainage divide area detailed location map

Figure 2: Mud Creek-South Loup River drainage divide 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 Mud Creek-South Loup River drainage divide area in Custer, Sherman, and Buffalo Counties. Custer, Valley, Greeley, Sherman, Howard, Dawson, and Buffalo are Nebraska County names and the county boundaries are shown. The Platte River is flowing in a southeast direction in the figure 2 southwest corner and is flowing in a northeast direction in the figure 2 southeast corner. The South Loup River flows to Arnold in west-central Custer County and then flows in southeast direction to Callaway and then to the Buffalo County northwest corner. In northern Buffalo County the South Loup River turns near Pleasanton to flow in an east-northeast direction to join southeast-oriented Mud Creek near Ravenna and then to flow to the Howard County southwest corner where it joins the southeast-oriented Middle Loup River and the combined flow becomes the northeast-oriented Loup River downstream from Boelus (Howard City). The North and South Branches of Mud Creek originate near Merna and flow in a southeast direction to join near Broken Bow (in central Custer Counter County). From Broken Bow Mud Creek flows in a southeast direction to Berwyn, Ansley, Mason City, Litchfield, Hazard, and Sweetwater before joining the South Loup River near Ravenna. West Table located between Arnold and Merna is an upland region illustrated in detail below. Ash Creek, Elk Creek, and the Black Hill Basin are other named features in figure 2 illustrated in detail in figures below. Note the southeast-orientation of major tributaries to the northeast-oriented Loup River valley. Also note the southeast-orientations of many of the tributaries to those major southeast-oriented Loup River tributaries. This predominance of southeast-oriented tributaries provides evidence that immense quantities of southeast-oriented flood water flowed across the figure 2 map region and eroded southeast-oriented tributary valleys headward from what was then the newly eroded and deep northeast-oriented Loup River-Platte River northwest valley wall. The southeast-oriented Mud Creek and South Loup River valleys and their tributary valleys were eroded headward at that time. Northeast-oriented Mud Creek tributary valleys probably eroded headward from the newly eroded Mud Creek valley to capture southeast-oriented flood water south and west of the actively eroding valley head. Northwest and north oriented Mud Creek tributary valleys probably were eroded by reversals of southeast-oriented flood flow on the north and northwest ends of south-oriented flood flow routes (or channels) beheaded by headward erosion of the deep Mud Creek valley. Flood waters on the north ends of these beheaded flood flow channels reversed flow direction to flow north to the newly eroded and deeper Mud Creek valley.

Northwest end of Mud Creek-South Loup River drainage divide area

Figure 3: Northwest end of Mud Creek-South Loup River drainage divide area. United States Geological Survey map digitally presented using National Geographic Society TOPO software.

Figure 3 uses reduced sized maps to illustrate the northwest end of the Mud Creek-South Loup River drainage divide area. Arnold is the town located in the figure 3 west center area. The southeast-oriented stream flowing from Arnold to the figure 3 south center edge is the South Loup River. Callaway is the town located in the South Loup River valley near the figure 3 south edge. Merna is the town located in the figure 3 northeast quadrant between Dale Valley and East Table. The North Branch and South Branch Mud Creek originate on the East Table upland west edge, with the South Branch Mud Creek flowing in southwest direction across the Dale Valley before turning to flow in a southeast direction to the figure 3 east edge and the North Branch Mud Creek flowing directly in a southeast direction to the figure 3 east edge. West Table is the upland region located between the southeast-oriented South Loup River valley and the southeast-oriented Mud Creek headwaters. Northwest of the Dale Valley (just north of the figure 3 map area) are southeast-oriented headwaters of a northeast-oriented Middle Loup River tributary. Headward erosion of that northeast-oriented Middle Loup River tributary valley beheaded southeast-oriented flood flow to the southeast-oriented Mud Creek valley. The size of the northwest-southeast oriented through valley located between West Table and East Table provides evidence as to the volume of southeast-oriented flood water that flowed across the figure 3 map area and also as to the amount of erosion the southeast-oriented flood waters accomplished.The southeast-oriented South Loup River was also eroded headward by the same southeast-oriented flood. In fact, the figure 3 map evidence is best explained if flood waters initially flowed in a southeast direction across the entire figure 3 map area on a topographic surface at least as high as the highest figure 3 elevations today. Flood waters eroded deep southeast-oriented valleys headward into the West Table area with southeast-oriented flood flow on the South Loup River, Mud Creek, and Powell Canyon alignments eroding deep valleys headward across the West Table upland region and southeast-oriented flood flow on other alignments eroding southeast-oriented headcuts into the West Table upland region. Headward erosion of deep east and southeast oriented Middle Loup River and tributary valleys in the region north and west of the figure 3 map area probably beheaded southeast-oriented flood flow to not only the actively eroding Mud Creek valley, but also to the South Loup River valley.  Figure 4 below provides a somewhat more detailed map of the West Table upland surface located northeast of Arnold.

Powell Canyon-Pine Canyon drainage divide area

Figure 4: Powell Canyon-Pine Canyon drainage divide area. United States Geological Survey map digitally presented using National Geographic Society TOPO software.

Figure 4 provides a more detailed map of the Powell Canyon and Pine Canyon region located northeast of Arnold, which was seen in less detail in figure 3 above. Arnold is the town located in the figure 4 southwest corner. The southeast-oriented South Loup River flows across the figure 4 southwest corner. Pleasant Hill is the small town or place-name located in the figure 4 center area and is located on top of the West Table upland surface. Note how the northwest-southeast oriented Upper Powell Canyon-Lower Powell Canyon through valley separates the main West Table upland surface from a northwest-southeast oriented series of isolated upland remnants. These upland remnants include Judkins Table along the figure 4 west edge and Davenport Table located southwest of Lower Powell Canyon. The Powell Canyon valley is a northwest-southeast oriented through valley, which has been eroded across what appears to be the west side of the West Table upland surface and roughly parallels the southeast-oriented South Loup River valley to the southwest. Northwest of the Powell Canyon valley (and of the figure 4 map area) is the east-oriented Dismal River valley, which drains to the southeast-oriented Middle Loup River (see figure 1), although there is an intervening sand dune region. Headward erosion of the Middle Loup River-Dismal River valley appears to have beheaded southeast-oriented flood flow to the newly eroded Powell Canyon valley (and also to the South Loup River valley-see figure 1).  East of Lower Powell Canyon is south-southeast oriented Pine Canyon, which heads in the West Table upland region. Immediately north of the Pine Canyon head is the north-northwest, north, and northeast oriented Dry Creek valley. North of the figure 4 map area Dry Creek appears to be lost in a sand dune region, although it is headed toward northeast-oriented Victoria Creek, which flows to the Middle Loup River. The shallow Dry Creek-Pine Canyon through valley near the Pine Canyon head provides evidence flood water once flowed in a southeast direction across West Table to what was then the actively eroding southeast-oriented Pine Canyon headcut. Headward erosion of the deep Middle Loup River valley and its northeast-oriented Victoria Creek-Dry Creek tributary valley beheaded the southeast-oriented flood flow. Flood waters on the north end of the beheaded flood flow route (and on top of West Table) reversed flow direction to flow north to the newly eroded northeast-oriented Dry Creek-Victoria Creek valley. The fact flood waters were still moving across West Table at that time means the region north and northwest of West Table had not yet been eroded by headward erosion of the Middle Loup River-Dismal River and tributary valleys. Finally there is an interesting depression located on the West Table upland surface east of the Pine Canyon head. A close look at the West Table surface in figure 4 and in more detailed maps reveals other smaller depressions. Because a massive southeast oriented flood flowed across the West Table upland the depression is probably in some way related to the flood water movements and erosive and deposition actions, although based on the figure 4 evidence I can not say more.

Mud Creek-Ash Creek drainage divide area

Figure 5: Mud Creek-Ash Creek drainage divide area. United States Geological Survey map digitally presented using National Geographic Society TOPO software.

Figure 5 illustrates the Mud Creek-Ash Creek drainage divide area located south and east of the figure 4 map area and includes overlap areas with figure 3. Broken Bow is the town located in the figure 5 northeast corner. The South Branch Mud Creek flows from the figure 5 north center edge area to Broken Bow and joins the southeast-oriented North Branch Mud Creek (flowing southeast in the “Valley” located northeast of Broken Bow) to form southeast-oriented Mud Creek, which follows the highway to the figure 5 east edge. The upland located in the figure 5 northwest corner is West Table. The southeast-oriented South Loup River can just barely be seen in the figure 5 southwest corner. Spring Creek is the southeast-oriented stream located northeast of the South Loup River and flowing from the figure 5 west center edge to the figure 5 south edge (west half), Custer Canyon originates near the east edge of the West Table upland in the figure 5 northwest quadrant and drains to Spring Creek near the figure 5 south edge. Yellow Dog Canyon, which heads at the south end of a West Table southeast projection, is a major Custer Canyon tributary valley. Between Spring Creek and Yellow Dog Canyon is a southeast-oriented stream draining from southeast-oriented Turner Valley. Turner Valley, like Pine Canyon seen in figure 4, is on the floor of an abandoned headcut eroded by southeast-oriented flood waters into the West Table south margin. East the south-oriented Custer Canyon is northwest-southeast oriented Ryno Table and east of Ryno Table is the south-southeast oriented Ash Creek valley. Ash Creek headwaters originate on the east edge of the West Table upland (just east of the Custer Canyon headwaters) and also in the Union Valley area. Note how northeast-oriented Mud Creek tributaries have beheaded south-oriented through valleys leading to the Ash Creek headwaters. Presence of these through valleys and the northeast-oriented Mud Creek tributary valleys provides evidence headward erosion of the Mud Creek valley and its tributary valleys beheaded south-oriented flood flow to what was then the actively eroding Ash Creek valley. The figure 5 evidence, like the figure 3 and 4 evidence, suggests flood flow originally flowed on a topographic surface at least as high as the West Table upland surface elevation, if not higher. Headward erosion of what was then a deep southeast-oriented South Loup River valley and its tributary valleys (including the Ash Creek valley) then began to erode the region. Next headward erosion of what was then a deep southeast-oriented Mud Creek valley and its tributary valleys beheaded flood flow to the newly eroded Ash Creek valley. Figures 3, 4, and 5 suggests that immense quantities of sediment were removed from this Mud Creek-South Loup River drainage divide region, suggesting the region is underlain by easily eroded materials.

North-oriented barbed tributaries flowing to southeast-oriented Mud Creek

Figure 6 provides a detailed map of north-oriented (barbed) tributaries to southeast-oriented Mud Creek in the region southeast of Broken Bow. Broken Bow is the town in the figure 6 northwest corner and Mud Creek flows in a southeast direction from Broken Bow to the figure 6 east edge (south half). What is interesting about the figure 6 map area is the presence of north oriented tributaries flowing to southeast-oriented Mud Creek. Note for example the north-northwest oriented valley located along the section 25-26 border near the figure 6 south edge. That valley continues in a north-northwest direction to the east edge of section 23 and then turns to drain in a northeast direction across the northern part of section 24 to section 10 and Mud Creek. What has happened here is the entire figure 6 region was eroded by south-southeast oriented flood flow. When the southeast-oriented Mud Creek valley eroded headward into the figure 6 map region the northeast-oriented tributary valley eroded headward from the actively eroding Mud Creek valley to capture southeast-oriented flood flow west of the Mud Creek valley head. Figure 6 contains evidence the northeast-oriented tributary valley did capture southeast-oriented flood flow in the form of multiple south and south-southeast oriented through valleys linking the Mud Creek valley with the northeast-oriented tributary valley (in sections 13 and 14). Also the north-northwest oriented valley along the sections 25-26 border was eroded by a reversal of flood flow on the north end of a south-southeast oriented flood flow channel. The south-southeast oriented flood flow channel was beheaded by headward erosion of the northeast-oriented tributary valley and flood waters on the north end of that behead flood flow channel reversed flow direction to flow north to the newly eroded and deeper northeast-oriented Mud Creek tributary valley. Reversed flood flow in that channel captured yet to be beheaded flood flow from south-southeast and southeast oriented flood flow channels further to the west and with the aid of that captured yet to be beheaded flood flow eroded the north-northwest oriented tributary valley. Figure 7 below illustrates the region south of figure 6 to show how yet to be captured flood flow reached reversed flood flow in the north-northwest oriented Mud Creek tributary valley.

Detailed map of through valleys crossing present day drainage divides

Figure 7 illustrates the region south and slightly west of the figure 6 map area and includes overlap areas with figure 6. The north-northwest oriented Mud Creek tributary seen in figure 6 flows from section 1 in the figure 7 southeast corner to section 36 and then along the border between sections 25 and 26 in the figure 7 northeast quadrant.  West of that north-northwest tributary valley there is a north-northeast oriented Mud Creek tributary valley located in the figure 7 north center area and another north-northwest oriented Mud Creek tributary valley used by the highway in section 28 (in the figure 7 northwest quadrant). Note how at the corner of sections 33, 34, 27, and 28 there is a through valley linking the western north-northwest oriented tributary valley with the north-northeast oriented tributary valley. That through valley provides evidence yet to be beheaded south-southeast oriented flood flow in the western valley was captured by north-oriented flood flow in the north-northeast oriented valley. Also note how an unimproved road south and southeast of that section corner uses a through valley linking the western north-northwest oriented through valley with headwaters of a south-southeast oriented stream (which is a South Loup River tributary). That through valley provides evidence the western north-northwest oriented through valley originated as a south-southeast-oriented flood flow channel moving flood water to a newly eroded south-southeast oriented South Loup tributary valley. Then study the valleys in southeast quarter of section 34. Note how there are northeast-oriented through valleys linking what was a south-southeast oriented flood flow with the eastern north-northeast oriented Mud Creek tributary valley. Those through valleys provide evidence yet to be beheaded south-southeast oriented flood flow was captured by reversed flow in the eastern north-northwest oriented valley and flowed to what was then the newly eroded Mud Creek valley. A careful study of the figures 6 and 7 map areas reveals many other such through valleys providing evidence of multiple captures. Remember, at the time of the captures the deeper valleys had yet to be eroded and the deeper valleys were eroded headward until flood flow to them ended.

Elk Creek-South Loup River drainage divide area

Figure 8 illustrates the Elk Creek-South Loup River drainage divide area located south and east of the previous figures. Mason City is the town located in the figure 8 northeast corner and is located in the southeast-oriented Mud Creek valley. Burr Oak is the smaller town located in the figure 8 southwest corner and is located in the southeast-oriented South Loup River valley. Deer Creek flows in a south direction near the figure 8 west edge to join the South Loup River near Burr Oak. East of Deer Creek are the south-oriented West and East Box Elder Creek, which combine near the figure 8 south edge to form south-oriented Box Elder Creek. East of Box Elder Creek near the figure 8 south center edge is south-southeast oriented Flat Bottom Creek and east of Flat Bottom Creek is south-southeast oriented Cat Creek. Flowing in a southeast direction across the headwaters of Box Elder, Flat Bottom, and Cat Creeks is Elk Creek, which then turns flow in a south direction to the figure 8 south edge. In the figure 8 northeast quadrant note north-northeast oriented Happy Hollow and north-northeast-oriented Lazy Hollow, both of which drain to the southeast-oriented Mud Creek. Close study of the Happy Hollow-Lazy Hollow drainage divide reveals northwest-southeast-oriented through valleys providing evidence that reversed flood flow in the Lazy Hollow valley captured yet to be beheaded south-oriented flood flow moving across what later became the north-oriented Happy Hollow valley. Also, close study of the Elk Creek-Cat Creek and Elk Creek-Box Elder Creek drainage divide areas reveals headward erosion of the Elk Creek valley beheaded south-oriented flood flow routes to the Cat Creek and Box Elder Creek valleys in that sequence. Further, study of the East Box Elder Creek-Flat Bottom Creek drainage divide reveals headward erosion of he Box Elder Creek valley captured south-southeast oriented flood flow that had been moving to the Flat Bottom Creek valley. In other words, Figure 8 region drainage history can be reconstructed in a logical and consistent manner, by assuming valleys eroded headward to capture a massive south-southeast oriented flood that was moving across the entire figure 8 map region.

Oak Creek-Pleasant Valley drainage divide area

Figure 9: Oak Creek-Pleasant Valley drainage divide area. United States Geological Survey map digitally presented using National Geographic Society TOPO software.

Figure 9 illustrates the Oak Creek-Pleasant Valley drainage divide area located south and east of the figure 8 map area and includes a small overlap area with figure 8 (northwest corner of figure 9 overlaps with southeast corner of figure 8). The south-southeast stream in the figure 9 northeast corner area is Mud Creek and Hazard is the town located in the Mud Creek valley. The southeast-oriented stream in the figure 9 southwest quadrant is the South Loup River. Elk Creek flows in a south direction along the figure 9 west edge. Black Hill Basin is an interesting feature located in the figure 9 northwest quadrant and figure 10 below provides a more detailed map of the Black Hill Basin area. South of Black Hill Basin is south-oriented Black Hill, which flows to the southeast-oriented South Loup River. In the figure 9 southeast quadrant is southeast-oriented Dry Creek, which is the stream flowing through Pleasant Valley. The northeast-and southeast-oriented Mud Creek tributary immediately west of Hazard is Spring Creek. Further west in the figure 9 northeast quadrant is northeast-oriented Oak Creek, which flows to the figure 9 north edge and then to Mud Creek north of he figure 9 map area. Close study of the Oak Creek-Dry Creek (Pleasant Valley) drainage divide reveals multiple through valleys suggesting headward erosion of the northeast-oriented Oak Creek valley beheaded south and south-southeast oriented flood flow routes to what was then the actively eroding Dry Creek (Pleasant Valley) valley. Also, close study of the Oak Creek-Spring Creek drainage divide reveals through valleys linking northwest-oriented Oak Creek tributaries with southeast-oriented Spring Creek tributaries. These through valleys and the tributary orientations suggests headward erosion of the northeast-oriented Oak Creek valley beheaded southeast-oriented flood flow to what was then the newly eroded Spring Creek valley. In the figure 9 northwest quadrant the Black Hill Basin area appears to a basin at the southeast end of an eroded upland surface, which is drained to the south by Black Hill Creek. Drainage in the Black Hill basin area is not continuous, but what drainage routes are shown are southeast-oriented and appear to have been beheaded by headward erosion of the Elk Creek valley. If so, southeast-oriented drainage routes in the Black Hill Basin area are evidence the Elk Creek valley eroded headward into a topographic surface at least as high as the Black Hill highest points.

Detailed map of the Elk Creek-Black Hill Basin drainage divide area

Figure 10: Detailed map of the Elk Creek-Black Hill Basin drainage divide area. United States Geological Survey map digitally presented using National Geographic Society TOPO software.

Figure 10 provides a detailed map of the Elk Creek-Black Hill Basin drainage divide area seen in less detail in figure 9 above. Elk Creek is the south-oriented stream flowing near and across the figure 10 west edge. Black Hill Basin is located in the figure 10 center area and has a southeast-oriented drainage system draining from section 6, 7, and 8 into the main basin centered in section 17. While there is a shallow closed basin area in section 17, the Black Hill Basin appears to be able to drain to the south via a southwest-oriented valley in the section 16 southwest corner and the section 17 southeast corner to south-oriented Black Hill Creek in section 20. Black Hill Basin appears to be almost completely surrounded with a rim of hills rising as much as 100 feet above the basin floor and also above the surrounding region. Black Hill Basin internal topography suggests it was eroded by southeast-oriented flood water prior to headward erosion of the south-oriented Elk Creek valley and perhaps prior to headward erosion of most surrounding figure 10 valleys. If so, the Black Hill Basin may be a relic of an earlier flood eroded topographic surface that developed prior to headward erosion of the deep southeast-oriented South Loup River and Mud Creek valleys (and their tributary valleys). The earlier flood flow eroded topographic surface would have been formed prior to headward erosion of the deep northeast-oriented Loup River-Platte River valley to the south. Headward erosion of that deep northeast-oriented valley significantly lowered base level and enabled present day southeast-oriented Loup River tributary valleys to erode headward into what is now the Mud Creek-South Loup River drainage divide area. Black Hill Basin history may be further complicated by the presence of significant flood deposited sediments from that earlier flood stage. Evidence presented in this and other essays suggests the immense southeast-oriented floods, which flowed across the Mud Creek-South Loup River drainage divide area, converged with a large east-oriented flood and that there may have been a ponding of flood waters. The presence of the Nebraska Sand Hills region immediately to the west and the north of the drainage divide region studied here suggests flood waters may have deposited large sandy deltas in the ponded flood water region and it is possible finer grained sediments settled out further east and south. If so, the Black Hill Basin area could be covered by such finer grained flood deposited material, which was subsequently eroded by southeast-oriented flood waters prior to deeper erosion of the surrounding region.

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.