Abstract:

This essay uses topographic map evidence to interpret landform origins in the Arikaree River-South Fork Republican River drainage divide area in Lincoln and Kit Carson Counties, Colorado. The Arikaree River and South Fork Republican River are tributaries to the Republican River and flow in east and northeast directions across Lincoln and Kit Carson Counties with the Arikaree River located north and west of the South Fork Republican River. Northeast oriented Arikaree River tributaries include Dugout Creek and Hackberry Creek with its Hell Creek tributary. Northeast oriented Buffalo Creek and Duck Creek turn in southeast directions to join the northeast oriented South Fork Republican River as barbed tributaries while further to the north a different Hell Creek flows in an east direction to join the South Fork Republican River. Northeast and east oriented trunk streams have short southeast oriented tributaries from the northwest and short north-northwest oriented tributaries from the southeast and there are shallow north-northwest to south-southeast oriented through valleys crossing the drainage divides. The shallow through valleys are interpreted to have been eroded by diverging and converging south-southeast oriented flood flow channels at a time when the deeper northeast oriented valleys were being eroded headward into the region with headward erosion of each northeast oriented valley beheading flood flow routes to the newly eroded northeast oriented valley immediately to the southeast. Floodwaters on north-northwest ends of beheaded flood flow channels reversed flow direction to flow to the deeper beheading valley and to create north-northwest oriented tributary drainage routes while south-southeast oriented flood flow moving into the newly eroded valleys eroded southeast oriented tributary valleys. Floodwaters are interpreted to have been derived from the western margin of a thick North American ice sheet and flowed from western Canada to and across eastern Colorado at a time when deep east oriented valleys were eroding headward (in sequence from south to north) from what at that time were the developing Mississippi and Missouri River drainage systems.

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 Arikaree River-South Fork Republican River drainage divide area landform origins in Lincoln and Kit Carson Counties, Colorado. 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 Arikaree River-South Fork Republican River drainage divide area landform evidence in Lincoln and Kit Carson Counties, Colorado will be regarded as evidence supporting the “thick ice sheet that melted fast” paradigm.

Arikaree River-South Fork Republican River drainage divide area location map

Figure 1: Arikaree River-South Fork Republican 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 Arikaree River-South Fork Republican River drainage divide area in Lincoln and Kit Carson Counties, Colorado and illustrates a region in eastern Colorado with small areas of northwest Kansas and southwest Nebraska along the east edge. Denver is located near the west center edge of figure 1. The South Platte River flows in a north-northeast direction from Denver to near Greeley where it turns to flow in a southeast and east direction to Fort Morgan before turning in a northeast direction to flow to the north center edge of figure 1. North of figure 1 the South Platte River flows into western Nebraska with water eventually reaching the Platte, Missouri, and Mississippi Rivers. North oriented South Platte River tributaries east of Denver include Kiowa, Bijou, and Beaver Creeks. The Arikaree River originates near the Beaver Creek headwaters (north of Limon, Colorado) and flows in a northeast direction to Haigler, Nebraska and east of figure 1 joins the Republican River with water eventually reaching the Kansas, Missouri, and Mississippi Rivers. The South Fork Republican River originates in the south center area of figure 1 (east of Hugo, Colorado) and flows in a northeast direction to the east center edge of figure 1. East of figure the South Fork Republican River flows into southern Nebraska where it joins the east oriented Republican River. South of the Arikaree River and South Fork Republican River headwaters is southeast oriented Big Sandy Creek, which south of figure 1 flows in a south direction to reach the east oriented Arkansas River, which eventually flows directly to the Mississippi River. The Arikaree River-South Fork Republican River drainage divide area in Lincoln and Kit Carson Counties, Colorado investigated in this essay is located south and east of the Arikaree River, north and west of the South Fork Republican River.

The Republican (and Kansas), South Platte (and Platte), and Arkansas River drainage routes and their tributary drainage routes developed during immense melt water floods from the western margin of a thick North American ice sheet. Floodwaters flowing across the region seen in figure 1 flowed from western Canada as deep east oriented valleys eroded headward into Colorado from the developing Mississippi-Missouri River system. Headward erosion of the deep east oriented Arkansas River valley (south of figure 1) captured the south oriented flood flow and diverted the floodwaters in an east direction. Headward erosion of the deep east oriented valleys caused floodwaters in eastern Colorado and western Nebraska and Kansas to flow in southeast directions, which caused subsequent deep valleys to erode headward in southwest directions across the southeast oriented flood flow. Headward erosion of the east oriented Smoky Hill River valley (from the newly eroded Kansas-Missouri River valley) next captured the south oriented flood flow and beheaded south and southeast oriented flood flow routes to the newly eroded Arkansas River valley, with the east-northeast oriented North Fork Smoky Hill River valley eroding headward into eastern Colorado (in southeast corner of figure 1). Headward erosion of the east oriented Republican River valley captured the south and southeast oriented flood flow and beheaded flood flow routes to the newly eroded Smoky Hill River and Smoky Hill River tributary valleys in Kansas. The northeast oriented South Fork Republican River then eroded headward across south and southeast oriented flood flow, which had been moving to the newly eroded North Fork Smoky Hill River valley, and diverted the floodwaters to the newly eroded Republican River valley. Headward erosion of the northeast oriented Arikaree River valley next captured the south and southeast oriented flood flow and diverted floodwaters more directly to the newly eroded Republican River valley. Headward erosion of the deep southeast, east, and northeast oriented South Platte River valley from western Nebraska into northeast Colorado next captured the southeast and south oriented flood flow and beheaded flood flow routes west of the actively eroding Arikaree and South Fork Republican River valleys. Floodwaters on north ends of the beheaded flood flow routes reversed flow direction to create north oriented South Platte River tributary drainage routes and the north-northeast oriented South Platte River drainage route, which are located on the present day Colorado Piedmont.

Detailed location map for Arikaree River-South Fork Republican River drainage divide area

Figure 2: Detailed location map Arikaree River-South Fork Republican 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 Arikaree River-South Fork Republican River drainage divide area in Lincoln and Kit Carson Counties, Colorado. County lines are shown and Lincoln and Kit Carson Counties are labeled. Limon is located near the west center edge of figure 2. Big Sandy Creek flows in a southeast direction from Limon to Hugo, Clifford, Boyero, and the south edge of figure 2 (west half). South of figure 2 Big Sandy Creek flows in a southeast and south direction to join the east oriented Arkansas River, which eventually flows directly to the Mississippi River. The Arikaree River originates north of Limon (just west of figure 1) and flows in an east, northeast, east, and northeast direction to the north center edge of figure 2. North of figure 2 the Arikaree River flows in a northeast direction and eventually joins the east oriented Republican River with water then flowing to the Kansas, Missouri, and Mississippi Rivers. Northeast oriented Arikaree River tributaries east of Limon include the South Fork Arikaree River and Hell Creek with its Hackberry Creek tributary. The Hell Creek originating near Genoa is a northeast oriented Arikaree River tributary. The South Fork Republican River originates in eastern Lincoln County (east of Hugo) and flows in a northeast direction to the east edge of figure 2 (near northeast corner). East and north of figure 2 the South Fork Republican River flows in a northeast direction to join the east oriented Republican River. An unlabeled northeast and east-southeast oriented South Fork Republican River tributary originating south of Bovina and joining the South Fork Republican River north of Seibert is Buffalo Creek. The shorter unlabeled northeast and east-southeast tributary east and south of Buffalo Creek is Duck Creek. A second Hell Creek flows in a northeast and east direction across northern Kit Carson County and joins the South Fork Republican River near Tuttle. Drainage routes in the Arikaree River-South Fork Republican River drainage divide area seen in figure 2 are primarily oriented in northeast and east directions and were created in sequence from the southeast to the northwest by headward erosion of northeast and east oriented valleys across south and southeast oriented flood flow. Headward erosion of each northeast or east oriented valley beheaded flood flow routes to what at that time was the newly eroded valley immediately to the east or southeast. Southeast oriented drainage routes seen in the southwest corner of figure 2 flow to southeast and south oriented Big Sandy Creek and probably were created by headward erosion of southeast oriented valleys along southeast oriented flood flow channels. South-southeast oriented drainage routes near the south edge of the southeast quadrant of figure 2 flow to the east-northeast oriented North Fork Smoky Hill River and were eroded headward along south-southeast oriented flood flow channels. Headward erosion of northeast oriented South Fork Republican River tributary valleys captured the south-southeast oriented flood flow and ended flood flow to what at that time was the newly eroded North Fork Smoky Hill River valley.

Arikaree River-Hackberry Creek drainage divide area

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

Figure 3 provides a topographic map of Arikaree River-Hackberry Creek drainage divide area. The map contour interval for figure 3 is 10 meters. The south oriented stream in the southwest corner of figure 3 flows to southeast oriented Big Sandy Creek and northeast rim of the deep Big Sandy Creek valley can be seen crossing the southwest corner of figure 3. South of figure 3 Big Sandy Creek flows in a southeast and south direction to join the east oriented Arkansas River, which eventually flows directly to the Mississippi River. The Arikaree River flows in a northeast direction across the northwest corner of figure 3. North of figure 3 the Arikaree River flows in an east and then northeast direction and eventually joins the east oriented Republican River with water eventually reaching the Kansas, Missouri, and Mississippi Rivers. Lickdab Creek flows in an east and northeast direction from the west center edge of figure 3 to the north center edge of figure 3. North of figure 3 Lickdab Creek joins the Arikaree River. Dugout Creek originates near the west edge of the southwest quadrant of figure 3 and flows in an east-southeast, north-northeast, east, and northeast direction to the north edge of figure 3 (near northeast corner) and north and east of figure 3 joins north-northeast oriented Hackberry Creek, which then joins the Arikaree River. Hell Creek originates near the Big Sandy Creek valley rim in the southwest quadrant of figure 3 and flows in an east-southeast direction before turning in a northeast, southeast, and northeast direction to flow to the east edge of figure 3. East north of figure 3 Hell Creek joins the Arikaree River. Hackberry Creek flows in a northeast direction from the south edge of figure 3 (east half) to the east center edge of figure 3. East and north of figure 3 Hackberry Creek flows in a north-northeast direction to join Hell Creek. Elevations in figure 3 decease in an east or east-northeast direction from approximately 1750 meters near the Radio Tower in the southwest corner of figure 3 to less than 1590 meters in the northeast corner of figure 3. A close look at figure 3 reveals several southeast oriented tributaries flowing to the northeast oriented trunk streams. Further some shallow north-northwest to south-southeast oriented through valleys can be seen crossing a few of the drainage divides (these are defined by a single contour line on each side). These features hint at southeast oriented flood flow channels that once crossed the region. However, the evidence in figure 3 by itself is not convincing and further evidence is required. Figure 4 provides a detailed topographic map of a Dugout Creek-Hell Creek drainage divide area to see if more convincing evidence exists.

Detailed map of Dugout Creek-Hell Creek drainage divide area

Figure 4: Detailed map of Dugout Creek-Hell Creek 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 Dugout Creek-Hell Creek drainage divide area seen in less detail in figure 3. The map contour interval for figure 4 is 10 feet. Dugout Creek meanders in a northeast direction across the northeast quadrant of figure 4. Short southeast oriented tributaries join Dugout Creek from the northwest while short north-northwest oriented tributaries join Dugout Creek from the southeast. Hell Creek meanders across the southeast quadrant of figure 4. Short southeast oriented tributaries join Hell Creek from the northwest and short north-northwest oriented tributaries join Hell Creek from the southeast. North-northwest to south-southeast oriented ridges in sections 16,, 20, 21, and 29 define a series a north-northwest to south-southeast through valleys crossing the Dugout Creek-Hell Creek drainage divide. The deepest through valleys are defined by at least three 10-foot contour lines on each side and shallower through valleys are defined by a single contour line on one or both sides. Diverging and converging south-southeast oriented flood flow channels eroded the through valleys prior to headward erosion of the deeper northeast oriented Dugout Creek valley. Headward erosion of the northeast oriented Dugout Creek valley captured the south-southeast oriented flood flow and floodwaters on north-northwest ends of the beheaded flood flow channels reversed flow direction to flow to the deeper Dugout Creek valley and to create the north-northwest oriented Dugout Creek tributary drainage routes. North-northwest oriented Hell Creek tributary drainage routes had been created earlier by reversals of flood flow triggered by headward erosion of the northeast oriented Hell Creek valley.

Arikaree River-Buffalo Creek drainage divide area

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

Figure 5 illustrates a topographic map of the Arikaree River-Buffalo Creek drainage divide area east and slightly north of figure 3 and includes an overlap area with figure 3. The map contour interval for figure 5 is 10 meters. The Arikaree River flows in an east and then northeast direction from the west edge of figure 5 (near northwest corner) to the north edge of figure 5 (east of center). North and east of figure 5 the Arikaree River flows in a northeast direction and eventually joins the east oriented Republican River. Dugout Creek (unlabeled in figure 5) flows in a north-northeast direction from the west edge of figure 5 (south of center) to join the Arikaree River in the northwest quadrant of figure 5. Hell Creek flows in a northeast and north-northeast direction from the west edge of figure 5 (near southwest corner) to join the Arikaree River south of the north center edge of figure 5. Buffalo Creek flows in a north-northeast direction across the southeast corner of figure 5. East of figure 5 Buffalo Creek turns to flow in an east-southeast direction to join the northeast oriented South Fork Republican River, which eventually joins the east oriented Republican River. There are hints of through valleys crossing drainage divides in figure 5, but the evidence is not convincing. Figure 6 illustrated a detailed topographic map of the Arikaree River-Hell Creek drainage divide area (just west of where Hell Creek joins the Arikaree River) to further test the south-southeast oriented flood flow hypothesis.

Detailed map of Arikaree River-Hell Creek drainage divide area

Figure 6: Detailed map of Arikaree River-Hell Creek 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 Arikaree River-Hell Creek drainage divide area seen in less detail in figure 5. The map contour interval for figure 6 is 10 feet. The Arikaree River “flows” in an east direction from the west edge of figure 6 (north half) near the north edge of figure 6 before turning in an east-northeast direction to “flow” across the north edge of figure 6 (east half). North and east of figure 6 the Arikaree River “flows” in a northeast direction to eventually join the east oriented Republican River. Hell Creek meanders in a north-northeast and north direction from the south edge of figure 6 (east of center) to the north edge of figure 6 (near northeast corner) and north of figure 6 joins the Arikaree River. Both the Arikaree River and Hell Creek are shown as normally dry drainage routes with sandy beds. Evidence for north-northwest to south-southeast oriented through valleys crossing the Arikaree River-Hell Creek drainage divide is not as obvious as seen in figure 4, but does exist. For example in the southwest corner of section 18 a through valley links a north oriented Arikaree River tributary valley with the Hell Creek valley. The through valley is defined by two contour lines on each side and is at least ten feet deep. Another through valley in section 7 is defined by one contour line on the east side. A north oriented Arikaree River tributary valley in section 14 is linked by through valleys with an east, north, and north-northeast oriented Arikaree River tributary valley. Through valleys in section 14 are defined by one contour on each side. These and other through valleys seen in figure 6 provide evidence south-southeast oriented flood flow did cross the region prior to headward erosion of the deeper east and northeast oriented Arikaree River valley. The north oriented Arikaree River tributary drainage routes were created by reversals of flood flow on north ends of beheaded flood flow routes.

Buffalo Creek-South Fork Republican River drainage divide area

Figure 7: Buffalo Creek-South Fork Republican River drainage divide area. United States Geological Survey map digitally presented using National Geographic Society TOPO software.

Figure 7 illustrates a topographic map of the Buffalo Creek-South Fork Republican River drainage divide area east and slightly south of figure 5 and there is an overlap area with figure 5. The map contour interval for figure 7 is 10 meters. Flager Reservoir is located near the south center edge of figure 7. The South Fork Republican River flows in a northeast direction from Flagler Reservoir to the east center edge of figure 7. East of figure 7 the South Fork Republican River flows in a northeast direction to join the east oriented Republican River. Tributaries to the South Fork Republican River from the northwest are oriented in southeast directions and join the South Fork Republican River as barbed tributaries suggesting headward erosion of the South Fork Republican River valley captured southeast oriented flood flow channels. Buffalo Creek flows in a northeast and east-southeast direction from the west edge of figure 7 (south half) to join the South Fork Republican River near the east edge of figure 7. Duck Creek flows in a northeast, east, and southeast direction to join the South Fork Republican River as a barbed tributary in the east center area of figure 7. The southeast oriented and barbed tributaries flowing to the northeast oriented South Fork Republican River provide good evidence for southeast oriented flood flow. Evidence for through valleys crossing drainage divides is not as obvious, but does exist. For example a north-northwest to south-southeast oriented through valley defined by at least two 10-meter contour lines on each side can be seen crossing the Buffalo Creek-Duck Creek drainage divide north of Flagler Reservoir. A through valley defined by one contour line on each side is located in section 36 on the northeast side of the town of Flagler and links a north-northwest oriented Duck Creek segment with the south-southeast oriented headwaters of a South Fork Republican River tributary. Further there are hints of short north-northwest and south-southeast oriented tributaries to the west end of the east-southeast oriented Buffalo Creek valley segment. Figure 8 provides a detailed topographic map of the Buffalo Creek-Duck Creek drainage divide area to better illustrate evidence for north-northwest to south-south-southeast through valleys crossing the drainage divide.

Detailed map of Duck Creek-South Fork Republican River drainage divide area

Figure 8: Detailed map of Duck Creek-South Fork Republican River drainage divide area. United States Geological Survey map digitally presented using National Geographic Society TOPO software.

Figure 8 provides a detailed topographic map of the Duck Creek-South Fork Republican River drainage divide area seen in less detail figure 7. The map contour interval for figure 8 is 10 feet. Buffalo Creek “flows” in a southeast and east direction from near the northwest corner of figure 8 to the east edge of figure 8 (north half). East of figure 8 Buffalo Creek turns to “flow” in an east-southeast and southeast direction to join the northeast oriented South Fork Republican River as a barbed tributary. Duck Creek meanders in an east direction near the south edge of figure 8 from the west edge to the east edge and east of figure 8 turns in a southeast direction to join the northeast oriented South Fork Republican River as a barbed tributary. North-northwest to south-southeast oriented through valleys cross the Buffalo Creek-Duck Creek drainage divide. The deepest through valley is located near the corner of sections 2, 3, 10, and 11 and is defined by five 10-foot contour lines on the east side suggesting it is at least 40 feet deep. A through valley in the east half of section 2 is defined by at least two contour lines on each side. Shallower through valleys defined by a single contour line on each side are seen in section 1. These through valleys provide evidence of multiple south-southeast oriented flood flow channels to the Duck Creek valley prior to headward erosion of Buffalo Creek valley. Headward erosion of the Buffalo Creek valley captured the south-southeast oriented flood flow and the southeast oriented Buffalo Creek valley segment in section 3 may have eroded headward along a southeast oriented flood flow route. Floodwaters on north ends of beheaded flood flow routes reversed flow direction to create the short north and north-northwest oriented Buffalo Creek tributary drainage routes.

Hell Creek-South Fork Republican River drainage divide area

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

Figure 9 illustrates a topographic map of the Hell Creek-South Fork Republican River drainage divide area north and east of figure 7 and there is an overlap area with figure 7. The map contour interval for figure 9 is 10 meters. The South Fork Republican River flows in an east-northeast and northeast direction from the south edge of figure 9 (west half) to the east edge of figure 9 (north of center) and east of figure 9 flows in a northeast direction to join the east oriented Republican River. Short southeast and south-southeast oriented tributaries join the South Fork Republican River from the north and short north and north-northwest oriented tributaries drain to the South Fork Republican River from the south. Hell Creek (this is a different Hell Creek from the Hell Creek seen in figures 3, 4, and 5) meanders in an east direction from the west edge of figure 9 (near northwest corner) to near the northeast corner of figure 9. East of figure 9 Hell Creek joins the northeast oriented South Fork Republican River. A few north-oriented Hell Creek tributaries are seen and include north-northwest oriented segments. Other than the South Fork Republican River valley, which is at most 40-50 meters deep, there is very little relief visible although there is a gentle east-northeast slope with elevations being greater than 1410 meters in the southwest quadrant of figure 9 and less than 1300 meters in the northeast corner (and in the South Fork Republican River valley near the east edge of figure 9). Other than orientations of the few short South Fork Republican River and Hell Creek tributaries seen in figure 9 there is no evidence to suggest southeast or south-southeast oriented flood flow crossed the region. Based on previous figures illustrated in this essay and evidence from adjacent drainage divide areas illustrated in other essays (e.g. South Fork Republican River-North Fork Smoky Hill River drainage divide area) we can assume floodwaters did cross the Hell Creek-South Fork Republican River drainage divide area seen in figure 9. Figure 10 provides a reduced size detailed topographic map of the Hell Creek-South Fork Republican River drainage divide area to further test this assumption.

Detailed map of Hell Creek-South Fork Republican River drainage divide area

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

Figure 10 provides a reduced size detailed topographic map of the Hell Creek-South Fork Republican River drainage divide area seen in less detail in figure 9. The map contour interval for figure 10 is 10 feet. The South Fork Republican River “flows” in a northeast direction across the southeast corner of figure 10. Short southeast and south-southeast oriented tributary valleys have eroded headward into the South Fork Republican River northwest valley wall and provide evidence the northeast oriented South Fork Republican River valley eroded headward across southeast and/or south-southeast oriented flood flow. Hell Creek meanders in an east and east-northeast direction from the west edge of figure 10 (near northwest corner) to near the northeast corner of figure 10. East and north of figure 10 Hell Creek joins the northeast oriented South Fork Republican River. A gentle east-northeast oriented slope is visible with elevations greater than 4500 feet near the west edge of the southwest quadrant and elevations of less than 4350 feet near the northeast corner. Other than stream valleys and the South Fork Republican River valley and the east-northeast oriented slope there is little relief visible in figure 10 except a very low north-northwest to south-southeast oriented ridge seen near the center of figure 10. A close look at the ridge reveals it is actually a series of shorter low ridges streamlined in a north-northwest to south-southeast direction. The ridge may be related to the underlying geology and may be where a resistant rock unit meets the surface. Regardless of the ridge origin there are shallow north-northwest to south-southeast through valleys on either side of the ridge. The through valleys are water-eroded valleys and were eroded by south-southeast oriented flood flow crossing the region, but if the ridge is related to a geologic structure the geologic structure it may have influenced the water flow direction. Orientation of the short southeast and south-southeast oriented South Fork Republican River tributaries is probably a safer determiner of the direction of flood flow across the Hell Creek-South Fork Republican River drainage divide area seen in 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.