Abstract:

This essay uses topographic map evidence to interpret landform origins in the Lodgepole Creek-South Platte River drainage divide area in Kimball and Cheyenne Counties, Nebraska and Sedgwick and Logan Counties, Colorado. Kimball and Cheyenne Counties are located along the south margin of the Nebraska panhandle and Sedgwick and Logan Counties are located in the northeast corner of Colorado. The South Platte River originates as a southeast oriented river in the Colorado Front Range and then turns to flow in a north-northeast, east, and northeast direction to the northeast corner of Colorado and then in an east-northeast and east direction to join the North Platte River and to form the Nebraska Platte River, which flows to the Missouri River. Lodgepole Creek originates near the west edge of the southeast Wyoming Laramie Mountains and flows in an east direction near the south margin of the Nebraska panhandle before turning in a southeast direction to join the northeast oriented South Platte River in the northeast corner of Colorado. Between Lodgepole Creek and the South Platte River are east, northeast, east, and northeast oriented Sidney Draw and east oriented Sand Draw, which drain to east and southeast oriented Lodgepole Creek. Sidney Draw flows along the crest of a southeast and south-facing escarpment, which forms the northeast wall of the broad northeast oriented South Platte River valley. Short northwest and southeast oriented tributaries join east oriented Lodgepole Creek, Sand Draw, and Sidney Draw and southeast and south oriented streams drain the southeast and south-facing escarpment into the northeast oriented South Platte River valley. These landforms are interpreted to have developed during immense melt water floods from the western margin of a thick North American ice sheet. Floodwaters flowed from western Canada to and across the upland surface now drained by Lodgepole Creek and its east oriented tributaries and then into what was at that time the actively eroding and deep northeast oriented South Platte River valley. Floodwaters flowed into what at that time was the newly eroded and deep northeast oriented South Platte River valley until headward erosion of the east, northeast, east, and northeast oriented Sidney Draw valley captured the floodwaters and diverted the flood flow to the newly eroded east and southeast oriented Lodgepole Creek valley, which had eroded headward from the newly eroded northeast oriented South Platte River valley. Headward erosion of the east oriented Sand Draw valley soon thereafter beheaded flood flow to the newly eroded Sidney Draw valley and headward erosion of the east oriented Lodgepole Creek valley soon thereafter beheaded flood flow to the newly eroded Sand Draw valley. South and southeast oriented flood flow to the Lodgepole Creek valley was beheaded by headward erosion of the deep southeast oriented North Platte River valley and its east 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 Lodgepole Creek-South Platte River drainage divide area landform origins in Cheyenne and Kimball Counties, Nebraska and Sedgwick and Logan 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 Lodgepole Creek-South Platte River drainage divide area landform evidence in Cheyenne and Kimball Counties, Nebraska and Sedgwick and Logan Counties, Colorado will be regarded as evidence supporting the “thick ice sheet that melted fast” paradigm.

Lodgepole Creek-South Platte River drainage divide area location map

Figure 1: Lodgepole Creek-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 Lodgepole Creek-South Platte River drainage divide area in Cheyenne and Kimball Counties, Nebraska and Sedgwick and Logan Counties, Colorado and illustrates a region in northeast Colorado in the south and west with western Nebraska to the north and east and with the southeast corner of Wyoming in the northwest corner of figure 1 and the northwest corner of Kansas in the southeast corner of figure 1. The South Platte River flows in a north-northeast direction from the south edge of figure 1 to Denver and Greeley and then in an east and northeast direction to the northeast corner of Colorado before flowing in an east direction to join the southeast and east oriented North Platte River and to form the Platte River, which flows to the east center edge of figure 1. Note the north oriented streams flowing to the northeast oriented South Platte River in the region east of Denver. Lodgepole Creek originates in the Laramie Mountains near the west edge of figure 1 in southern Wyoming and flows in roughly an east direction just north of the Colorado northern border before turning to join the South Platte River near Ovid, Colorado in the northeast corner of Colorado. Sedgwick and Logan Counties, Colorado are located in the northeast corner of Colorado and include the South Platte River valley downstream from Sterling, Colorado. Kimball and Cheyenne Counties, Nebraska are located just north of the Colorado border and include the Lodgepole Creek valley downstream from the Wyoming border to the town of Lodgepole. An unnamed southeast oriented South Platte River north of Sterling, Colorado and flowing through Sterling Reservoir is Cedar Creek. The Lodgepole Creek-South Platte River drainage divide area investigated in this essay is located south of Lodgepole Creek, north and east of Cedar Creek, and north and west of the South Platte River.

The Lodgepole Creek and South Platte River drainage routes and tributary drainage routes developed during immense melt water floods from the western margin of a thick North American ice sheet. Floodwaters flowed from western Canada to and across the region seen in figure 1 at a time when Wyoming and Colorado mountain ranges were beginning to emerge. Mountain ranges emerged as floodwaters flowed across them and as floodwaters deeply eroded surrounding regions. At the same time ice sheet related crustal warping raised the mountain masses and also raised large regions of Colorado, Wyoming, and adjacent states. At that time south and southeast oriented floodwaters flowed across eastern Wyoming, western Nebraska, and northeast Colorado and were captured by headward erosion of the southeast oriented Arkansas River valley (south of figure 1). Headward erosion of the deep northeast oriented South Platte River valley across the south and southeast flood flow routes then captured the south and southeast oriented flood flow and diverted the floodwaters in a northeast direction to the newly eroded Platte River valley in Nebraska. Floodwaters on north ends of beheaded flood flow channels reversed flow direction to create north oriented South Platte River tributaries and headwaters drainage routes. These reversals of flood flow were greatly aided by ice sheet related crustal warping that was raising regions to the south of figure 1. Headward erosion of the east oriented Lodgepole Creek and tributary valleys from the newly eroded northeast oriented South Platte River valley next captured the south and southeast oriented flood flow, although the deep southeast oriented North Platte River valley and tributary valleys quickly beheaded flood flow routes to the newly eroded Lodgepole Creek and tributary valleys. At least some floodwaters in the Lodgepole Creek valley and the North Platte River valleys came from west of the what were then the emerging Laramie Mountains in Wyoming. Orientations of tributary valleys and other landform features illustrated in the more detailed maps shown in this essay support the interpretation given in this very brief introduction.

Detailed location map for Lodgepole Creek-South Platte River drainage divide area

Figure 2: Detailed location map Lodgepole Creek-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 Lodgepole Creek–South Platte River drainage divide area in Cheyenne and Kimball Counties, Nebraska and Sedgwick and Logan Counties, Colorado. County lines are shown and Kimball and Cheyenne Counties, Nebraska and Sedgwick and Logan Counties, Colorado, are labeled. The west to east oriented Nebraska-Colorado state line extends across the center of figure 2. The north to south oriented Wyoming-Nebraska state line is located along the west edge of the northwest quadrant of figure 2.  The South Platte River flows in a north-northeast direction from the south edge of figure 2 to Sterling, Colorado and then flows in a northeast direction to the east center edge of figure 2. The North Platte River flows in a southeast direction in the northeast corner of figure 2 and east of figure 2 joins the South Platte River to form the Nebraska Platte River. Named South Platte River tributaries of interest in this essay are east-northeast and southeast oriented Cottonwood Creek, which joins the South Platte River near Dorsey in western Sedgwick County; east and south-southeast oriented Spring Creek in northeast Logan County; and southeast oriented Cedar Creek, which flows through Sterling Reservoir. Lodgepole Creek flows from the west edge of figure 2 (north half) in an east, east-southeast, and east direction to Kimball, Sidney, and Lodgepole, Nebraska before turning in a southeast direction to join the South Platte River near Ovid, Colorado (a close look at figure 2 shows Lodgepole Creek ending in an irrigation canal). Cow Creek is a northeast, east, and northeast oriented tributary joining Lodgepole Creek near the east edge of Cheyenne County. Sidney Draw is a long east-northeast drainage route draining from the west edge of figure 2 (south of center) to join Lodgepole Creek just west of Sidney.  Sand Draw is the long east oriented Sidney Draw tributary located between Lodgepole Creek and Sidney Draw in Kimball County. Figure 2 shows a remarkable difference in the orientations of South Platte River tributaries from the north and west and in the orientations of Lodgepole Creek tributaries. The south-southeast and southeast oriented South Platte River tributaries, which are barbed tributaries, were formed as south and southeast oriented floodwaters flowed into the actively eroding and deep northeast oriented South Platte River valley. The east oriented Lodgepole Creek tributaries were formed as the south oriented floodwaters were captured by headward erosion of shallower east oriented valleys and diverted in an east direction to the deep South Platte River valley. Crustal warping, which was occurring at the time, may have played a role in the diversion of floodwaters in an east direction along the Lodgepole Creek and tributary drainage routes.

Cow Creek-South Platte River drainage divide area

Figure 3: Cow Creek-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 Cow Creek-South Platte River drainage divide area. The map contour interval for figure 3 is 10 meters. The South Platte River flows in a northeast direction across the southeast corner of figure 3. Elevations in the South Platte River valley near the town of Sedgwick are slightly less than 1100 meters. Lodgepole Creek flows in a southeast direction across the northeast corner of figure 3 and east of figure 3 joins the South Platte River. Elevations in the Lodgepole Creek valley near the town of Chappell are between 1120 and 1130 meters. Cow Creek flows in an east direction near the north edge of figure 3 from the northwest corner to the north center edge where Cow Creek turns in a north direction to join southeast oriented Lodgepole Creek (north of figure 3). Cottonwood Creek flows in an east and south-southeast direction from the west edge of figure 3 (north of center) to the Julesburg Reservoir and then to the northeast oriented South Platte River. East of the south-southeast oriented Cottonwood Creek valley are other south-southeast oriented South Platte River tributaries including Sedgwick Draw and Sand Draw. Both Sedgwick and Sand Draws, like Cottonwood Creek and Lodgepole Creek, have east oriented headwaters suggesting they eroded headward to capture east oriented flood flow and to divert the floodwaters into the deeper northeast oriented South Platte River valley. The Sedgwick Draw headwaters begin at an elevation of approximately 1230 meters, which is 140 meters higher than the South Platte River valley elevation where Sedgwick Draw joined the South Platte River prior to being diverted by irrigation canals. West of Cottonwood Creek the South Platte River tributaries are oriented in south directions as they flow down the South Platte River north valley wall. The South Platte River tributary valleys were probably eroded as the deep northeast oriented South Platte River valley eroded headward across southeast oriented flood flow moving to the much deeper South Platte River valley, which was eroding headward into the region and which was being diverted in southeast and south directions as the floodwaters entered the deep northeast oriented South Platte River valley in northeast Colorado. Prior to being captured by headward erosion of the deep South Platte River valley floodwaters probably moved in other directions. Evidence for other flood flow movements can probably be determined from flood deposited sediments, but probably cannot be determined from the topographic map evidence seen in figure 3.

Lodgepole Creek-Cow Creek drainage divide area

Figure 4: Lodgepole Creek-Cow 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 Lodgepole Creek-Cow Creek drainage divide area north and west of figure 3 and includes an overlap area with figure 3. The map contour interval for figure 4 is 10 meters. Lodgepole Creek flows from the west edge of figure 4, through Sidney, to the east edge of figure 4 (north half). East of figure 4 Lodgepole Creek turns to flow in a southeast direction to join the northeast oriented South Platte River. Cow Creek flows in a northeast and east direction from the southwest corner of figure 4 to the east center edge of figure 4. East of figure 4 Cow Creek flows in an east and northeast direction to join southeast oriented Lodgepole Creek. In the west half of figure 4 Cow Creek has no visible valley and is flowing on an upland surface with elevations greater than 1300 meters in the west and gradually sloping to less than 1250 meters in the east. This upland surface is approximately 150 meters higher than the South Platte River valley floor elevation to the south of figure 4. The Lodgepole Creek valley floor elevation is 1240 meters near Sidney and less than 1190 meters near the east edge of figure 4 and is approximately 50 meters lower than the elevation of the adjacent upland surface elevation. Numerous short northwest oriented tributary valleys have been eroded into the south wall of the Lodgepole Creek valley while short southeast oriented valleys have been eroded into the north valley wall. The orientation of these short tributaries suggests the 50-meter deep and east oriented Lodgepole Creek valley eroded headward across southeast or south-southeast oriented flood flow, which was probably moving to the actively eroding and much deeper northeast oriented South Platte River valley to the south of figure 4. The southeast oriented tributary valleys were eroded by southeast or south-southeast oriented flood flow moving into the newly eroded Lodgepole Creek valley while the northwest oriented tributary valleys were probably eroded by reversals of flood flow on northwest ends of beheaded flood flow routes with the reversed flood flow flowing in northwest and north-northwest directions to the newly eroded east oriented Lodgepole Creek valley. The Cow Creek drainage route was probably established as floodwaters south of the actively eroding Lodgepole Creek valley drained down the upland surface slope to the deeper southeast oriented Lodgepole Creek valley. The east oriented slope had probably been created as floodwaters flowed in east directions to the actively eroding Platte River valley and other valleys east of figure 4 and also as ice sheet related crustal warping raised regions in the west relative to regions in the east.

Lodgepole Creek-Sidney Draw drainage divide area

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

Figure 5 illustrates the Lodgepole Creek-Sidney Draw drainage divide area west and slightly north of figure 4 and there is an overlap area with figure 4. The map contour interval for figure 5 is 10 meters. The west edge of Sidney, Nebraska can be seen along the east edge of figure 5. Lodgepole Creek flows in an east, southeast, and east direction from the north edge of figure 5 (west of center) to the east center of figure 5 (near south edge of Sidney) and east of figure 5 flows in an east and then southeast direction to join the northeast oriented South Platte River. Sidney Draw drains in a northeast and east direction from the south edge of figure 5 (near southwest corner) to join Lodgepole Creek just west of Sidney. Sand Draw (not labeled in figure 5) drains in an east-southeast direction from the west edge of figure 5 (north of center) to join northeast and east oriented Sidney Draw. Sidney Draw is not shown as being drained by a continuous drainage route suggesting that today flow in it is intermittent at best and probably nonexistent much of the time. The Lodgepole Creek valley is again approximately 50 meters deep and the south wall of the east oriented Lodgepole Creek valley near the north edge of the northwest quadrant of figure 5 is again eroded by short north-northwest oriented tributary valleys. The Sand Draw valley is between 40 and 50 meters deep and has short southeast oriented tributary valleys eroded into its north wall and some short north or north-northwest oriented valleys eroded into its south wall. Sidney Draw has a wider valley (at least in figure 5) and has fewer tributaries from the southeast, but those few short tributaries are oriented in north-northwest directions. A close look at the drainage divide between Sand Draw and Sidney Draw reveals what may be shallow northwest to southeast oriented through valleys linking the two valleys. The Sidney Draw valley probably eroded headward across southeast or south-southeast oriented flood flow first with headward erosion of the Sand Draw valley then beheading flood flow to the newly eroded Sidney Draw valley. Headward erosion of the Lodgepole Creek valley next beheaded flood flow to the newly eroded Sand Draw valley. Apparently the Sidney Draw valley eroded headward enough in advance of the Sand Draw valley that the Sidney Draw valley was able to continue eroding headward for a considerable distance as seen in subsequent figures (and in figure 2). Likewise, the Sand Draw valley eroded headward enough in advance of the Lodgepole Creek valley that it was also able to erode headward for a considerable distance. Southeast and south-southeast oriented flood flow to the Lodgepole Creek valley was beheaded by headward erosion of the southeast oriented North Platte River valley and its tributary valleys, which were eroding headward far enough behind the Lodgepole Creek valley headward erosion that the Lodgepole Creek valley could erode headward into the emerging Laramie Mountains (in Wyoming).

Lodgepole Creek-Sand Draw east drainage divide area

Figure 6: Lodgepole Creek-Sand Draw east drainage divide area. United States Geological Survey map digitally presented using National Geographic Society TOPO software.

Figure 6 provides a topographic map of the Lodgepole Creek-Sand Draw east drainage divide area north and west of figure 5 and includes an overlap area with figure 5 figure 5. The map contour interval for figure 6 is 10 meters. Lodgepole Creek flows in an east and east-southeast direction from the west edge of figure 6 (near northwest corner) to the east edge of figure 6 (north half). Sand Draw drains in an east and east-southeast direction from the west edge of figure 6 (south of center) to the east edge of figure 6 (near southeast corner). Again the Lodgepole Creek valley is approximately 50 meters deep and the Sand Draw valley is slightly shallower. Again the upland surface slopes in an east direction with elevations of 1450 meters found near the west center edge of figure 6 and elevations of less than 1390 meters found on the Lodgepole Creek-Sand Draw drainage divide near the east edge of figure 6. Both Lodgepole Creek and Sand Draw have short southeast and south-southeast oriented tributaries from the north and short north and north-northwest oriented tributaries from the south. A longer northeast and north oriented tributary joins Sand Draw near the Bar J Lazy V Airport in the south center area of figure 6. Northeast and north oriented tributaries flow to both Sand Draw and Lodgepole Creek near the west edge of figure 6. Shallow through valleys cross the Lodgepole Creek-Sand Draw drainage divide although they are generally defined by a single 10-meter contour line on each side. Some evidence in the west half of figure 6 suggests the through valleys may be oriented in a northwest to southeast direction. Prior to headward erosion of the deep east oriented Lodgepole Creek valley floodwaters did cross the present day Lodgepole Creek-Sand Draw drainage divide to enter what was probably an actively eroding east and east-southeast oriented Sand Draw valley. However most floodwaters flowing into the Sand Draw valley were not concentrated into flood flow channels and were flowing more as sheets of water and did not flow long enough to deeply erode what is now the Lodgepole Creek-Sand Draw drainage divide. This suggests the possibility that the Sidney Draw, Sand Draw, and Lodgepole Creek valleys, while formed in the sequence previously suggested, rapidly became channels in an east oriented anastomosing channel complex, with the channels converging east of figure 6 (in the region seen in figure 5). As such this complex of east oriented flood flow channels captured what may have been south and southeast oriented flood flow moving to the actively eroding and much deeper South Platte River valley, but may also have had significant source of floodwaters west of the regions seen in this essay.

Lodgepole Creek-Sand Draw west drainage divide area

Figure 7: Lodgepole Creek-Sand Draw west drainage divide area. United States Geological Survey map digitally presented using National Geographic Society TOPO software.

Figure 7 illustrates the Lodgepole Creek-Sand Draw west drainage divide area west and slightly north of figure 6 and there is an overlap area with figure 6. The map contour interval for figure 7 is 10 meters. Lodgepole Creek flows in an east, east-northeast, and east direction from the west edge of figure 7 (north half) to the east edge of figure 7 (north half). The Lodgepole Creek valley is slightly more than 50 meters deep. Lodgepole Creek tributaries from the north are generally oriented in southeast directions while tributaries from the south are oriented in north and northwest directions. Sand Draw drains in an east, east-northeast, and east direction from the southwest corner of figure 7 (west half) to the east edge of figure 7 (south half). The Sand Draw valley is approximately 40 meters deep. Sand Draw tributaries from the north are oriented in southeast and east-southeast directions. Tributaries from the south are oriented in northeast and north directions. The short southeast oriented tributary valleys draining to the east oriented Lodgepole Creek and Sand Draw valleys were probably eroded by southeast oriented flood flow moving into those valleys. Headward erosion of the east oriented Sand Draw valley captured the flood flow first with headward erosion of the east oriented Lodgepole Creek valley beheading the southeast oriented flood flow to the newly eroded Sand Draw valley. Floodwaters on north and northwest ends of beheaded flood flow routes reversed flow direction to flow to the newly eroded Lodgepole Creek valley and to create short north and northwest oriented Lodgepole Creek tributaries. Because floodwaters were flowing in diverging and converging flood flow channels reversed flood flow on a newly beheaded and reversed flood flow channel could frequently capture flood flow from adjacent and yet to be beheaded flood flow channels further to the west. Such captures of flood flow helped erode the north oriented tributary valleys. Southeast oriented flood flow captured by headward erosion of the east oriented Sand Draw and Lodgepole Creek valleys had been previously captured by headward erosion of the Sidney Draw valley seen in figure 8, but previous to that time had been moving to much deeper southeast oriented South Platte River tributary valleys such as those seen in figures 9 and 10. Headward erosion of the east oriented Sidney Draw, Sand Draw, and Lodgepole Creek ended southeast oriented flood flow into the deep northeast oriented South Platte River valley, which is located to the south of figure 7.

Sand Draw-Sidney Draw drainage divide area

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

Figure 8 provides a reduced size topographic map of the Sand Draw-Sidney Draw drainage divide area south and east of figure 7 and includes an overlap area with figure 7. The map contour interval for figure 8 is 10 meters. Sidney Draw drains in an east direction just north of the south edge of figure 8 and is located in a 30-40 meter deep valley. East of figure 8 Sidney Draw drains in an east and northeast direction to join east and southeast oriented Lodgepole Creek, which then joins the northeast oriented South Platte River. Sand Draw drains in an east, east-northeast, and east direction from the west edge of figure 8 (north half) to the east edge of figure 8 (near northeast corner) and is located in a 40-50 meter deep valley. East of figure 8 Sand Draw drains in an east and east-southeast direction to join Sidney Draw, which then joins east and southeast oriented Lodgepole Creek, which flows to the northeast oriented South Platte River. An unnamed northeast oriented tributary flows from the southwest quadrant of figure 8 to the east edge of figure 8 (north half) and joins Sand Draw east of figure 8. The regional slope is in an east-northeast direction with elevations near the southwest corner of figure 8 exceeding 1560 meters and elevations in the Sand Draw valley near the northeast corner of figure 8 being less than 1400 meters. This regional slope was probably created by flood flow erosion, although it may be related to the nature of underlying bedrock materials and crustal warping may have also contributed. Sidney Draw has short southeast oriented tributaries, which is consistent with the capture of southeast oriented flood flow and there is no evidence in figure 8 precluding flood flow across the region seen in figure 8, although the topographic map evidence for flood flow is limited at best. Something eroded the deep east oriented Sidney Draw and Sand Draw valleys across the region seen in figure 8 and something was responsible for creating the gently sloping erosion/deposition surface seen in figure 8. As seen in earlier figures and in figures 9 and 10 below southeast oriented flood flow that was captured by headward erosion of the east oriented Sidney Draw, Sand Draw, and Lodgepole Creek valleys is the interpretation that best fits the larger picture regional evidence.

Sidney Draw-George Creek drainage divide area

Figure 9: Sidney Draw-George Creek drainage divide area. United States Geological Survey map digitally presented using National Geographic Society TOPO software.

Figure 9 illustrates the Sidney Draw-George Creek drainage divide area south and east of figure 8 and there is an overlap area with figure 8. The map contour interval for figure 9 is 10 meters. The west to east oriented Nebraska-Colorado state line is located in the north half of figure 9. Sidney Draw drains in an east, east-northeast, and east direction from the west edge of figure 9 (north half) to the east edge of figure 9 (north half) and east of figure 9 drains in an east and northeast direction to join east and southeast oriented Lodgepole Creek, which then flows to the northeast oriented South Platte River. The Sidney Draw valley is 40-50 meters deep and is eroded into an upland surface that slopes in an east direction with elevations greater than 1520 meters near the west edge of figure 9 and less than 1440 meters near the east edge of figure 9. Just south of the east oriented Sidney Draw valley is a south-facing escarpment drained by south and southeast oriented streams. While most of the streams appear to end before reaching the south edge of figure 9 the streams are flowing towards the northeast oriented South Platte River, which is located south of figure 9. Elevations near the southeast corner of figure 9 are less than 1290 meters suggesting the south-facing escarpment is approximately 150 meters high. George Creek is a southeast and south oriented stream flowing down the escarpment slope and is located near the center of figure 9. A close look at the Sidney Draw-George Creek drainage divide reveals a shallow through valley near a Caliche Pit linking the east oriented Sidney Draw valley with a south oriented George Creek tributary valley. The through valley is defined by at least two contour lines on a side suggesting it is more than ten meters deep. The through valley provides evidence south oriented floodwaters once flowed across the escarpment face and was beheaded by headward erosion of the slightly deeper Sidney Draw valley. Another through valley can be seen further to the west in Weld County and links the Sidney Draw valley at the point where it turns in a northeast direction with an unnamed south-southeast and southeast oriented stream valley. This second through valley is defined by three contour lines on each side and is at least 20 meters deep. The second through valley also provides evidence of a south oriented flood flow channel that crossed the escarpment face and that was captured by headward erosion of the slightly deeper east, northeast, and east oriented Sidney Draw valley. Sidney Draw tributaries from the north are oriented in southeast directions providing evidence the Sidney Draw valley eroded headward across southeast oriented flood flow moving to and across the escarpment face. The escarpment itself was eroded by something and the most logical explanation is it was eroded by south and southeast oriented flood flow moving into the newly eroded and much deeper northeast oriented South Platte River valley. Apparently the upland surface is underlain by erosion resistant materials, which prevented the south and southeast oriented flood flow from eroding deep valleys headward and which permitted headward erosion of the east oriented Sidney Draw valley to capture the south and southeast oriented flood flow.

Sidney Draw-Cedar Creek drainage divide area

Figure 10: Sidney Draw-Cedar Creek drainage divide area. United States Geological Survey map digitally presented using National Geographic Society TOPO software.

Figure 10 provides a detailed topographic map of the Sidney Draw-Cedar Creek south and west of figure 9 and includes an overlap area with figure 9. The map contour interval for figure 10 is 10 meters. The west to east oriented state line is located in the north half of figure 10. Sidney Draw drains in an east, northeast, east, northeast, and east direction from the west center edge of figure 10 to the east edge of figure 10 (near northeast corner). East of figure 10 Sidney Draw drains in an east and northeast direction to join east and southeast oriented Lodgepole Creek, which then flows to northeast oriented South Platte River. A southeast-facing escarpment extends from near the southwest corner of figure 10 to near the northeast corner of figure 10 and is the northwest wall of the northeast oriented South Platte River valley. South and southeast oriented streams flow down the escarpment face and are flowing toward the northeast oriented South Platte River, which is located south and east of figure 10. Named streams flowing to the south edge of figure 10 (from east to west) are Spring Draw, Cedar Creek, Twomile Creek, and Spring Creek. Shallow through valleys link headwaters of these south and southeast oriented South Platte River tributaries with the east, northeast, and east oriented Sidney Draw valley. Some of the through valleys are defined by two contour lines on a side suggesting they are more than ten meters deep. The few Sidney Draw tributaries from the north seen in figure 10 are oriented in southeast directions. The Sidney Draw valley is 30 to 40 meters deep and is eroded into an upland surface that is almost 1600 meters high near the west edge of figure 10 and that is less than 1500 meters high near the northeast corner of figure 10. Elevations near the southeast corner of figure 10 are less than 1350 meters suggesting the southeast-facing escarpment is at least 150 meters high. The southeast-facing escarpment was eroded by southeast oriented flood flow prior to headward erosion of the Sidney Draw, Sand Draw, and Lodgepole Creek valleys to the north and northwest. Floodwaters were flowing into what at that time was the newly eroded northeast oriented and deep South Platte River valley. Headward erosion of the east, northeast, and east oriented Sidney Draw valley captured the southeast oriented flood flow and ended flood flow across the escarpment face. Headward erosion of the Sand Draw valley soon thereafter ended southeast oriented flood flow to the newly eroded Sidney Draw valley and headward erosion of the east oriented Lodgepole Creek valley soon thereafter ended southeast oriented flood flow to the newly eroded Sand Draw valley, although it is possible some or all three of the east oriented valleys (especially the Lodgepole Creek valley) continued to receive floodwaters from west of the region studied in this essay.

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.