Abstract:

This essay uses topographic map evidence to interpret landform origins in the North Platte River-South Platte River drainage divide area in Deuel, Garden, and Keith Counties, Nebraska. Deuel, Garden, and Keith Counties are located in western Nebraska west of where the northeast oriented South Platte River and the southeast oriented North Platte River meet to form Nebraska’s Platte River. As the North and South Platte Rivers approach each other both rivers turn to flow in east directions with a relatively narrow upland surface in between. In western Keith County shallow, but easy to recognize, north-northwest to south-southeast oriented through valleys cross the narrow upland surface and link south-southeast oriented South Platte River tributary valleys with north and north-northwest oriented North Platte River tributary valleys. Further west in Deuel and Garden Counties the upland surface widens and is drained in the north by east and north oriented Ash Hollow to the southeast oriented North Platte River and in the south by southeast oriented Walrath Draw to the northeast oriented South Platte River. West of the Ash Hollow headwaters is north-northeast and north oriented Rush Creek, which flows to the southeast oriented North Platte River as a barbed tributary. Short southeast oriented streams from the west flow to Rush Creek as barbed tributaries while short northwest and north-northwest tributaries flow to Rush Creek from the east. Tributary orientations, shallow through valleys, and linear ridges on the upland surface provide evidence of multiple south-southeast oriented flood flow channels that once moved floodwaters to the deep northeast and east oriented South Platte River valley at a time when the deep North Platte River valley did not exist. Headward erosion of the deep southeast oriented North Platte River valley and of the deep north oriented Ash Hollow valley and the north-northeast and north oriented Rush Creek valley from the newly eroded North Platte River valley captured the southeast oriented flood flow with floodwaters on northwest ends of beheaded flood flow routes reversing flow direction to flow to the much deeper North Platte River and Rush Creek valleys. Floodwaters were derived from the western margin of a thick North American ice sheet and were flowing from western Canada to and across western Nebraska. Headward erosion of the northeast and east oriented South Platte River valley captured the floodwaters while headward erosion of the southeast oriented North Platte River valley and its tributary valleys shortly thereafter beheaded flood flow channels to the newly eroded South Platte River valley and its southeast oriented tributary valleys.

Preface

The following interpretation of detailed topographic map evidence is one of a series of essays describing similar evidence for all major drainage divides contained within the Missouri River drainage basin and for all major drainage divides with adjacent drainage basins. The research project is interpreting evidence in the context of a previously unexplored deep glacial erosion paradigm, which is fundamentally different from most commonly accepted North American glacial history interpretations. Project essays are listed on the sidebar category list under their appropriate Missouri River tributary drainage basin, Missouri River segment drainage basin (by state), and/or state in which the Missouri River drainage basin is located.

Introduction

The purpose of this essay is to use topographic map interpretation methods to explore the North Platte River-South Platte River drainage divide area landform origins in Deuel, Garden, and Keith Counties, Nebraska. 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 North Platte River-South Platte River drainage divide area landform evidence in Deuel, Garden, and Keith Counties, Nebraska will be regarded as evidence supporting the “thick ice sheet that melted fast” paradigm.

North Platte River-South Platte River drainage divide area location map

Figure 1: North Platte River-South Platte 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 North Platte River-South Platte River drainage divide area in Deuel, Garden and Keith Counties, Nebraska and illustrates a region in western Nebraska with the northeast corner of Colorado to the southwest. The North Platte River flows in a southeast and east direction from the northwest corner of figure 1 to the east edge of figure 1. Lake McConaughy is the reservoir flooding the North Platte River valley in the east half of figure 1. Pumpkin Creek is an east and northeast oriented North Platte River tributary near the northwest corner of figure 1. The unnamed east-southeast and north-northeast oriented North Platte River tributary flowing through the town of Gurley is Rush Creek. The unnamed east and northeast oriented tributary joining the North Platte River between Lewellen and Lake McConaughy is Ash Hollow. The South Platte River flows in a northeast and east direction from the south edge of figure 1 (west half) to the east edge of figure 1 (slightly south of center) and joins the North Platte River east of figure 1 to form the Platte River, which then flows across Nebraska to join the Missouri River. Lodgepole Creek flows from the west center edge of figure 1 in an east-southeast, east, and southeast direction to join the South Platte River near the northeast corner of Colorado. The unnamed east and southeast oriented tributary joining the South Platte River between the towns of Julesburg, Colorado and Blue Springs, Nebraska is Walrath Creek. The North Platte River-South Platte River drainage divide area in Deuel, Garden, and Keith Counties, Nebraska investigated here is located west of Kingsley Dam (at east end of Lake McConaughy), south of the North Platte River, north of the South Platte River, and east of Rush Creek.

The North and South Platte River drainage route and their tributary drainage routes developed during immense melt water floods from the western margin of a thick North American ice sheet at a time when mountain ranges west of figure 1 were just beginning to emerge. Floodwaters flowed from western Canada to and across the entire present day North and South Platte River drainage basin area as mountain ranges emerged. Mountain ranges emerged as floodwaters deeply eroded them and surrounding regions and as ice sheet related crustal warping raised the mountain masses and also raised large regions in Wyoming and Colorado. The Platte River valley (east of figure 1) eroded headward across Nebraska as it captured south and southeast oriented flood flow and the North and South Platte River valleys then eroded headward from that Platte River valley with the South Platte River valley eroding headward slightly in advance of the North Platte River valley. Headward erosion of the northeast and east oriented South Platte River valley captured the south and southeast oriented flood flow and diverted the floodwaters to the newly eroded Platte River valley. The Lodgepole Creek valley then eroded headward from the South Platte River valley and captured south and southeast oriented flood flow moving to the newly eroded South Platte River valley. Headward erosion of the western Walrath Creek valley may have captured flood flow moving to the newly eroded Lodgepole Creek valley (east end). The North Platte River valley also eroded headward from the Platte River valley and also beheaded flood flow routes to the newly eroded South Platte River valley. Headward erosion of the Ash Hollow valley captured southeast oriented flood flow moving west of the actively eroding North Platte River valley head as did headward erosion of the Rush Creek valley. Headward erosion of the North Platte River valley eventually beheaded all south and southeast oriented flood flow routes to the newly eroded Ash Hollow and Rush Creek valleys.

Detailed location map for North Platte River-South Platte River drainage divide area

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

Figure 2 provides a detailed location map for the North Platte River–South Platte River drainage divide area in Deuel, Garden, and Keith Counties, Nebraska. County lines are shown and Deuel and Keith Counties are labeled. Garden County is located directly north of Deuel County. The North Platte River flows in a southeast direction from the northwest corner of figure 2 to the east center edge of figure 2. The South Platte River flows in a northeast, east-northeast, and east direction from near the southwest corner of figure 2 to the east edge of figure 2 (slightly south of the North Platte River). East of figure 2 the North and South Platte Rivers flow parallel to each other for a significant distance before joining to form the Nebraska Platte River. South Platte River tributaries in Deuel and Keith Counties are generally oriented in southeast and south-southeast directions. Lodgepole Creek flows from the west edge of figure 2 (south of center) in an east, southeast, and south-southeast direction to join the South Platte River in northern Sedgwick County. Walrath Creek originates near the northwest corner of Deuel County and flows in an east-northeast and southeast direction to join the South Platte River in southeast Deuel County. Labeled South Platte River tributaries in Keith County are south-southeast oriented Chase Canyon and Brule Canyon., which are located south of Lake McConaughy. Ash Hollow drains in an east direction near the south margin of Garden County before turning in a north direction to join the North Platte River in the Ash Hollow State Historical Park. Rush Creek flows from the west edge of figure 2 (north of center) in a northeast and north direction to join the North Platte River in western Garden County.

Lake McConaughy-South Platte River drainage divide area

Figure 3: Lake McConaughy-South Platte River drainage divide area. United States Geological Survey map digitally presented using National Geographic Society TOPO software.

Figure 3 provides a topographic map of Lake McConaughy-South Platte River drainage divide area. The map contour interval for figure 3 is 10 meters. Lake McConaughy in the north half of figure 3 floods the southeast oriented North Platte River valley. The South Platte River flows in a east-northeast and east direction near the south edge of the southeast quadrant of figure 3. Ogallala is the town located on the north bank of the South Platte River. The South Platte River valley north wall is eroded by short south-southeast oriented tributary valleys. These south-southeast oriented tributary valleys were eroded by south-southeast oriented flood flow moving into the newly eroded South Platte River valley. At that time the deep North Platte River valley to the north did not exist and floodwaters were flowing in south-southeast directions across a continuous upland surface at least as high as the present day North Platte River-South Platte River drainage divide. Headward erosion of the deep southeast and east oriented North Platte River valley beheaded south oriented flood flow routes to the South Platte River valley in sequence from east to west. Floodwaters on north ends of beheaded flood flow channels reversed flow direction to flow to the much deeper southeast and east oriented North Platte River valley and in the process initiated the short north oriented North Platte River tributary valleys seen in figure 3. Because flood flow routes were beheaded and reversed in sequence from east to west reversed flood flow on a newly beheaded and reversed flood flow channel could capture floodwaters from yet to be beheaded flood flow channels further to the west. Such captures of floodwaters from further to the west sometimes enabled reversed flood flow drainage routes to develop significant north oriented drainage routes. Evidence seen in figure 3 shows south-southeast oriented floodwaters once flowed across the present day North Platte River-South Platte River drainage divide at a time when the North Platte River valley did not exist and that headward erosion of the deep North Platte River valley then beheaded the south-southeast oriented flood flow routes to the South Platte River valley.

Detailed map of Lake McConaughy-South Platte River drainage divide area

Figure 4: Detailed map of Lake McConaughy-South Platte River drainage divide area. United States Geological Survey map digitally presented using National Geographic Society TOPO software.

Figure 4 provides a detailed topographic map of the Lake McConaughy-South Platte River drainage divide area seen in less detail in figure 3. The map contour interval for figure 4 is 20 feet. South-southeast oriented drainage routes flowing to the south edge of figure 4  flow to the South Platte River (south of figure 4). North-northwest oriented drainage routes flowing to the north edge of figure 4 flow to the North Platte River (north of figure 4). The North Platte River-South Platte River drainage divide seen in figure 4 appears at first glance to be a relatively flat erosion surface, however a close look reveals shallow north-northwest to south-southeast oriented through valleys eroded into that surface. Perhaps it is easier to see the north-northwest to south-southeast oriented ridges between the through valleys. For example one such ridge is located near the corner of sections 13, 18, 19, and 24 in the northwest quadrant of figure 4 and achieves an elevation of 3530 feet. Elevations in the through valley to the southwest drop to less than 3400 feet although west of figure 4 elevations rise to more than more 3600 feet. Elevations east of the ridge decrease to about 3440 feet and then rise to 3520 feet at the corner of sections 16, 17, 20, and 21. These elevations suggest the north-northwest to south-southeast oriented through valley extending across the center of figure 4 is approximately 80 feet. The north-northwest to south-southeast through valley extending across the southwest corner of figure 4 may be as much 130 feet deep. These north-northwest to south-southeast oriented through valleys were eroded by diverging and converging south-southeast oriented flood flow channels moving floodwaters to the newly eroded South Platte River valley just before headward erosion of the deep North Platte River valley captured the flood flow. Headward erosion of the deep North Platte River valley beheaded the south-southeast oriented flood flow channels and floodwaters on northwest ends of the beheaded flood flow routes reversed flow direction to flow into the deep North Platte River valley and to create the north-northwest oriented North Platte River tributary drainage routes.

Chase Canyon-Brule Canyon drainage divide area

Figure 5: Chase Canyon-Brule Canyon drainage divide area. United States Geological Survey map digitally presented using National Geographic Society TOPO software.

Figure 5 illustrates the Chase Canyon-Brule Canyon drainage divide area west of figure 3 and there is an overlap area with figure 3. The map contour interval for figure 5 is 10 meters. Lake McConaughy, which floods the southeast oriented North Platte River valley can be seen the northeast corner of figure 5. South-southeast oriented streams flowing to the south edge of figure 5 are tributaries to the east-northeast oriented South Platte River, which is located south of figure 5. These south-southeast oriented drainage routes include Chase Canyon and Brule Canyon. North of Chase Canyon is north oriented Eagle Canyon, which drains to the North Platte River north of figure 5. A well-defined north-northwest to south-southeast oriented through valley links the north oriented Eagle Canyon valley with the south-southeast oriented Chase Canyon valley. The through valley floor elevation is between 1090 and 1100 meters. Elevations between Chase Canyon and Brule Canyon rise to more than 1120 meters and elevations west of Brule Canyon rise to more than 1130 meters. Elevations east of the Eagle Canyon-Chase Canyon through valley also rise to more than 1130 meters. These elevations suggest the Eagle Canyon-Chase Canyon through valley is at least 30 meters deep. A similar but shallower through valley links the south-southeast oriented Brule Canyon valley with a north oriented North Platte River tributary valley. In addition to the through valleys mentioned the landscape in figure 5 has been streamlined in a north-northwest to south-southeast direction.  The through valleys and the streamlining of the landscape are due to south-southeast oriented flood flow that once moved across the present day North Platte River-South Platte River drainage divide area to the South Platte River valley at a time when the North Platte River valley to the north of figure 5 did not exist. Headward erosion of the deep southeast oriented North Platte River valley captured the south-southeast oriented flood flow and beheaded the south-southeast oriented flood flow channels crossing the present day drainage divide. Floodwaters on north ends of beheaded flood flow channels reversed flow direction to flow to the deep North Platte River valley and in the process created the north oriented North Platte River tributary drainage routes.

Detailed map of Eagle Canyon-Chase Canyon drainage divide area

Figure 6: Detailed map of Eagle Canyon-Chase Canyon drainage divide area. United States Geological Survey map digitally presented using National Geographic Society TOPO software.

Figure 6 provides a detailed topographic map of the Eagle Canyon-Chase Canyon drainage divide area seen in less detail in figure 5. The map contour interval for figure 6 is 20 feet with some dotted contour lines at 10 foot intervals. The north oriented Eagle Canyon drainage route originates near the south edge of figure 6 (east half) and drains in a north-northwest direction across section 12 before turning to flow in a north direction to flow to the north edge of figure 6 (east half). North of figure 6 Eagle Canyon drains to the southeast oriented North Platte River. The north-northwest to south-southeast oriented Eagle Canyon-Chase Canyon through valley extends across section 17 to the south edge of figure 6 and south of figure 6 is drained by south-southeast oriented Chase Canyon, with water flowing to the east-northeast oriented South Platte River. The through valley floor elevation at the drainage divide (near south edge of figure 6) is between 3590 and 3600 feet. Elevations in section 7 immediately east of the through valley rise to more than 3710 feet (3740 feet east of figure 6) while elevations and elevations west of the through valley rise to more than 3740 feet. These elevations suggest the Eagle Canyon-Chase Canyon through valley is at least 110 feet deep and may be 130 feet deep. The Eagle Canyon-Chase Canyon through valley was eroded by a south-southeast oriented flood flow channel prior to headward erosion of the deep southeast oriented North Platte River valley to the north of figure 6. The south-southeast valley draining to the south center edge of figure 6 is Brule Canyon, which south of figure 6 also drains to the east-northeast oriented South Platte River. A through valley near the corner of sections 28, 29, 32, and 33 (near northwest corner of figure 6) links the south-southeast oriented Brule Canyon valley with north oriented North Platte River tributary valleys. The through valley floor elevation at the drainage divide is between 3780 and 3790 feet. Elevations east of the through valley rise to 3848 feet and north and west of figure 6 elevations rise to 3834 feet. These elevations suggest the through valley is only be 34 feet deep, although the valley and the deeper south-southeast oriented Brule Canyon valley provide evidence of a south-southeast oriented flood flow channel that existed prior to headward erosion of the southeast oriented North Platte River valley to the north. Headward erosion of the deep southeast oriented North Platte River valley north of figure 6 beheaded the south-southeast oriented Chase Canyon and Brule Canyon flood flow channels and floodwaters on north ends of the beheaded flood flow channels reversed flow direction to create north oriented North Platte River tributary drainage routes.

North Platte River-Ash Hollow drainage divide area

Figure 7: North Platte River-Ash Hollow drainage divide area. United States Geological Survey map digitally presented using National Geographic Society TOPO software.

Figure 7 illustrates the North Platte River-Ash Hollow drainage divide area north and west of figure 5 and there is no overlap area with figure 5. The map contour interval for figure 7 is 10 meters. The North Platte River flows in a southeast direction across the northeast corner of figure 7. Ash Hollow meanders in an east direction from the west edge of figure 7 (south of center) to the east edge of figure 7 (south of center) and east of figure 7 turns to drain in a north direction to join the southeast oriented North Platte River. The southwest wall of the North Platte River valley has been carved by short North Platte River tributary valleys. Some of these tributaries are oriented in northeast directions, but others are oriented in northwest directions and join the North Platte River as barbed tributaries. In addition to the northwest oriented tributaries there are shallow northwest to southeast oriented valleys and low northwest to southeast oriented ridges extending across the upland surface between the North Platte River and Ash Hollow and continuing south of Ash Hollow to the south edge of figure 7. The northwest oriented tributaries and the northwest to southeast oriented shallow valleys and low ridges are evidence the upland surface was crossed by southeast oriented flood flow prior to headward erosion of the deep southeast oriented North Platte River valley. Headward erosion of the North Platte River valley captured the southeast oriented flood flow and floodwaters on northwest ends of beheaded flood flow routes reversed flow direction to flow in north and northwest directions to the much deeper North Platte River valley. The northeast oriented North Platte River tributary valleys (e.g. northeast oriented tributary valley near Eagles Cliff located near north edge of the northwest quadrant of figure 7) eroded headward to capture southeast oriented flood flow moving west of the actively eroding North Platte River valley head. Note how northwest oriented tributaries flow to the north-northeast oriented North Platte River tributary near Eagles Cliff.

Ash Hollow-Walrath Draw drainage divide area

Figure 8: Ash Hollow-Walrath Draw drainage divide area. United States Geological Survey map digitally presented using National Geographic Society TOPO software.

Figure 8 provides a topographic map of the Ash Hollow-Walrath Draw drainage divide area south of figure 7 and includes an overlap area with figure 7. The map contour interval for figure 8 is 10 meters. Ash Hollow meanders in an east direction near the north edge of figure 8. East of figure 8 Ash Hollow turns to drain in a north direction to the southeast oriented North Platte River. Walrath Draw drains in a northeast direction from the west edge of figure 8 (north of center), but once in figure 8 quickly turns to drain in a southeast, east, and southeast direction to the south edge of figure 8. South of figure 8 Walrath Draw continues to drain in a southeast direction to join the northeast oriented South Platte River. A north-northwest to south-southeast oriented linear ridge can be seen in the east half of figure 8 and southeast oriented tributaries join Walrath Draw in the south center region of figure 8. The linear ridge and the southeast oriented Walrath Draw drainage route and tributary drainage routes were created by southeast and south-southeast oriented flood flow moving across the present day North Platte River-South Platte River drainage divide prior to headward erosion of the east oriented Ash Hollow valley, which was prior to headward erosion of the much deeper southeast oriented North Platte River valley. Headward erosion of the east oriented Ash Hollow valley probably occurred as headward erosion of the deeper southeast oriented North Platte River valley was beheading flood flow routes crossing the region in figure 8 and the east oriented Ash Hollow drainage route was probably created by floodwaters draining to a much deeper north oriented North Platte River tributary valley. At the same time the southeast oriented Walrath Draw drainage route was probably created as final floodwaters drained in a southeast direction to the deeper northeast oriented South Platte River valley.

Rush Creek-Ash Hollow drainage divide area

Figure 9: Rush Creek-Ash Hollow drainage divide area. United States Geological Survey map digitally presented using National Geographic Society TOPO software.

Figure 9 illustrates the Rush Creek-Ash Hollow drainage divide area west and slightly north of figure 7 and there is an overlap area with figure 7. The map contour interval for figure 9 is 10 meters. The southeast oriented North Platte River valley crosses the northeast corner of figure 9 with the North Platte River located north and east of figure 9. McCuligan Canyon is the north-northeast and north oriented North Platte River tributary in the northeast corner of figure 9 and was seen earlier in figure 7 (although the name was not visible). The southeast, east-northeast, and east-southeast oriented stream in the southeast quadrant of figure 9 is Ash Hollow, which east of figure 9 drains in an east and north direction to join the southeast oriented North Platte River. Several southeast oriented tributaries can be seen flowing to east oriented Ash Hollow. Rush Creek flows in a north-northeast and north direction from the west edge of figure 9 (south of center) to the north edge of figure 9 (west half). North of figure 9 Rush Creek flows in a north direction to join the southeast oriented North Platte River as a barbed tributary. Rush Creek tributaries from the northwest and west are oriented in southeast and south-southeast directions and join north oriented Rush Creek as barbed tributaries while Rush Creek tributaries from the east and southeast are oriented in northwest and north-northwest directions. The north-northeast oriented Rush Creek valley segment seen in figure 9 eroded headward across southeast or south-southeast oriented flood flow moving to the South Platte River valley and which was being captured by headward erosion of the east oriented Ash Hollow valley. Floodwaters on northwest ends of beheaded flood flow routes reversed flow direction to flow to the much deeper Rush Creek valley and to create the northwest and north-northwest oriented Rush Creek tributary drainage routes. Southeast oriented flood flow moving into the newly eroded Rush Creek valley created the southeast and south-southeast oriented Rush Creek tributary drainage routes, but was soon beheaded by headward erosion of the much deeper southeast oriented North Platte River valley.

Detailed map of Rush Creek barbed tributaries

Figure 10: Detailed map of Rush Creek barbed tributaries. United States Geological Survey map digitally presented using National Geographic Society TOPO software.

Figure 10 provides a detailed topographic map of the Rush Creek barbed tributaries seen in less detail in figure 9. The map contour interval for figure 10 is 20 feet. The north to south oriented dashed line near the west edge of figure 10 is the Cheyenne-Garden County line with Cheyenne County west of Garden County. Rush Creek flows in a north-northeast, northeast, north, and north-northeast direction from the southwest corner of figure 10 to the north center edge of figure 10. North of figure 10 Rush Creek flows in a north direction to join the southeast oriented North Platte River as a barbed tributary. Rush Creek tributaries from the east and southeast are oriented in northwest and north-northwest directions. Rush Creek tributaries from the west and northwest are oriented in south-southeast and southeast directions. For example a south-southeast oriented tributary flows from the west edge of figure 10 (north half) across section 28 to join north and northeast oriented Rush Creek near the south edge of section 28. A southeast oriented tributary joins Rush Creek at approximately the same location. A short south-southeast oriented tributary joins Rush Creek near the southwest corner of section 27. A southeast oriented tributary joins Rush Creek near the corner of section 22, 23, 26, and 27. Another short southeast oriented tributary flows across the northeast corner of section 22 to join Rush Creek near the border of sections 22 and 23. The northwest and north-northwest oriented tributaries from the east and southeast and the southeast and south-southeast oriented barbed tributaries from the west and northwest are evidence the deep north and north-northeast oriented Rush Creek valley eroded headward across southeast and/or south-southeast oriented flood flow channels. Floodwaters on northwest ends of beheaded flood flow routes reversed flow direction to flow in northwest or north-northwest directions to the much deeper north oriented Rush Creek valley and to create northwest and north-northwest oriented Rush Creek tributary drainage routes. Southeast and south-southeast oriented Rush Creek tributary valleys were eroded by southeast and south-southeast oriented flood flow moving into the newly eroded north oriented Rush Creek valley with the south and south-southeast oriented flood flow routes being beheaded by headward erosion of the deep southeast oriented North Platte River valley north and west of figure 10.

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.