Abstract:

This essay uses topographic map evidence to interpret landform origins in the Horse Creek-Pumpkin Creek drainage divide area along the Wyoming-Nebraska border just east of the Goshen Hole basin. Horse Creek originates at the west edge of the Wyoming Laramie Mountains and flows in an east-northeast direction across the Laramie Mountains to near the Nebraska border before turning in a north direction to flow across the Goshen Hole basin east end and then turns in a northeast direction to flow to the southeast oriented North Platte River. Pumpkin Creek originates east of the north oriented Horse Creek segment and of Goshen Hole and flows in an east-southeast and east direction in a broad and deep valley to join the southeast oriented North Platte River. Two deep and parallel west-to-east oriented through valleys link Goshen Hole with the east-southeast and east oriented Pumpkin Creek valley. These and additional through valleys and valley orientations are interpreted in the context of immense floods responsible for eroding the North Platte River valley, Pumpkin Creek valley, and the east oriented Goshen Hole escarpment-surrounded basin. Floodwaters were derived from the western margin of a thick North American ice sheet and flowed from western Canada to and across the Wyoming-Nebraska region at a time when Wyoming mountain ranges were beginning to emerge. The deep North Platte River-Pumpkin Creek valley eroded headward across south and southeast oriented flood flow, which had been moving to the newly eroded northeast oriented South Platte River valley, and captured significant east oriented flood flow crossing the emerging Laramie Mountains. At the same time headward erosion of the southeast oriented North Platte River valley beheaded flood flow routes to the newly eroded Pumpkin Creek valley. West of the present day Wildcat Hills the actively eroding North Platte River valley captured east oriented flood flow from the actively eroding Goshen Hole basin, which initiated headward erosion of the north oriented Horse Creek valley and which captured east oriented flood flow, which had been moving to the newly eroded east oriented Pumpkin Creek valley. At about the same time headward erosion of the deep east oriented Goshen Hole basin was significantly slowed by erosion resistant bedrock and headward erosion of the north oriented Chugwater Creek valley and the east and northeast oriented Laramie River valley around the north and west sides of the erosion bedrock area captured the east oriented flood flow moving into the Goshen Hole basin.

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 Horse Creek-Pumpkin Creek drainage divide area landform origins along the Wyoming-Nebraska border and east of Goshen Hole. 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 Horse Creek-Pumpkin Creek drainage divide area landform evidence along the Wyoming and Nebraska border and east of Goshen Hole will be regarded as evidence supporting the “thick ice sheet that melted fast” paradigm.

Horse Creek-Pumpkin Creek drainage divide area location map

Figure 1: Horse Creek-Pumpkin Creek 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 Horse Creek-Pumpkin Creek drainage divide area along the Wyoming-Nebraska border and east of Goshen Hole and illustrates a region in southeastern Wyoming with a region in western Nebraska east of Wyoming and a thin strip of northern Colorado along the south edge. The Laramie Mountains extend in a south direction from the northwest corner of figure 1 to the south edge with the eastern margin of the Laramie Basin seen west of the Laramie Mountains in the Laramie, Wyoming region. The North Platte River flows in a southeast direction from the north edge of figure 1 (west half) to the east edge of figure 1 (south of center). The South Platte River flows in a northeast direction across the southeast corner of figure 1 and joins the North Platte River east of figure 1 to form the Platte River. The Laramie River flows in a north direction from Laramie, Wyoming to just north of Wheatland Reservoir and then turns to flow in an east and northeast direction across the Laramie Mountains and then in an east and northeast direction to join the southeast oriented North Platte River. Lodgepole Creek originates near the west margin of the Laramie Mountains (just east of Laramie, Wyoming) and flows in roughly an east direction to the east edge of figure 1 and east of figure 1 turns in a southeast direction to join the northeast oriented South Platte River. Horse Creek originates just north of the Lodgepole Creek headwaters and flows in a northeast, east-northeast, north, and northeast direction to join the southeast oriented North Platte River just east of the Wyoming-Nebraska border. Chugwater Creek originates in the Laramie Mountains (north of the Horse Creek headwaters) and flows in an east, northeast, and north direction to join the east and northeast oriented Laramie River. Goshen Hole is not labeled in figure 1 but is a deep east oriented escarpment-surrounded basin located between the north oriented Chugwater Creek segment and the north oriented Horse Creek segment. Pumpkin Creek originates on the Nebraska side of the Wyoming-Nebraska border (south of Lyman, Nebraska) and flows in a north and east direction to join the southeast oriented North Platte River near the town of Bridgeport, Nebraska. An unnamed east-southeast and northeast oriented stream is shown as a tributary to Pumpkin Creek and on more detailed maps in the east is northeast oriented Lawrence Fork and further west is southeast and northeast oriented Rocky Hollow. The Horse Creek-Pumpkin Creek drainage divide area investigated in this essay is located east of the north oriented Horse Creek segment, south of the North Platte River, and north of the Rocky Hollow-Lawrence Fork drainage route.

Drainage routes in the North and South Platte River drainage basins 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 Wyoming, Nebraska, and Colorado at a time when Montana, Wyoming, and Colorado mountain ranges were beginning to emerge. The mountain ranges emerged as floodwaters flowed across them and deeply eroded surrounding regions and as ice sheet related crustal warping raised the mountain masses and also raised large regions in Wyoming and Colorado. The South Platte River valley eroded headward across south and southeast oriented flood flow routes and then the east oriented Lodgepole Creek valley eroded headward across the same flood flow channels and beheaded the flood flow routes to the newly eroded South Platte River valley. Next headward erosion of the northeast oriented Lawrence Fork-Pumpkin Creek valley captured southeast oriented flood flow that had been moving the newly eroded Lodgepole Creek valley. Headward erosion of the east oriented Pumpkin Creek valley then beheaded southeast oriented flood flow routes to the newly eroded Lawrence Fork (and Rocky Hollow) valley and headward erosion of the southeast oriented North Platte River valley beheaded flood flow routes to the newly eroded Pumpkin Creek valley. Headward erosion of the north and northeast oriented Horse Creek valley next beheaded east oriented flood flow routes to the newly eroded Pumpkin Creek valley. These east oriented drainage routes were crossing the emerging Laramie Mountains in east and northeast oriented valleys now draining to the Laramie River. The deep east oriented Goshen Hole escarpment-surrounded basin was being eroded headward from the Pumpkin Creek headwaters area by large volumes of east oriented  flood flow crossing the Laramie Mountains in the region west of the Goshen Hole basin, however headward erosion of the deep Goshen Hole basin was blocked by erosion resistant bedrock, which enabled the north oriented Chugwater Creek valley to erode headward from the newly eroded Laramie River valley and to capture the east oriented flood flow that had been moving into the Goshen Hole basin. Headward erosion of the deep Laramie River valley and tributary valleys across the emerging Laramie Mountains then captured floodwaters west of the Laramie Mountains and triggered a flood flow reversal west of the Laramie Mountains to create the north oriented Laramie River drainage route there. As these events were taking place floodwaters deeply eroded the Laramie Basin on the west side of the Laramie Mountains while ice sheet related raised the Laramie Mountains, both of which actions beheaded east oriented flood flow to the Lodgepole Creek, Horse Creek, and Chugwater Creek valleys.

Detailed location map for Horse Creek-Pumpkin Creek drainage divide area

Figure 2: Detailed location map Horse Creek-Pumpkin Creek 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 Horse Creek-Pumpkin Creek drainage divide area along the Wyoming-Nebraska border and east of Goshen Hole. The north to south oriented dashed line at the west edge of Scotts Bluff and Banner Counties is the Wyoming-Nebraska state line with Wyoming located west of the line. The North Platte River flows in a southeast direction from the north edge of figure 2 (west half) to the east center edge of figure 2. Horse Creek flows in an east direction from the west edge of figure 2 (south half) to near the town of Tremain and then turns to flow in a north-northwest direction to the towns of La Grange and Hawk Springs before flowing in a north direction almost to the town of Huntley where it turns to flow in a southeast and then northeast direction to join the southeast oriented North Platte River near the north edge of figure 2. Owl Creek and Kiowa Creek are northwest oriented Horse Creek tributaries and are located in western Scotts Bluff County, Nebraska and originate at the northwest end of the Wildcat Hills. Pumpkin Creek is formed at the confluence of tributaries south of the Wildcat Hills and flows in an east, east-southeast, and east direction to the east edge of figure 2 and joins the southeast oriented North Platte River just east of figure 2. Pumpkin Creek has several north and northeast oriented tributaries including Willow Creek and Indian Springs Creek. Rocky Hollow originates in southwest Banner County and drains in an east-southeast direction before turning to join northeast oriented Lawrence Fork, which then joins east oriented Pumpkin Creek in western Morrill County (east of Banner County). Lawrence Fork has several east-southeast oriented tributaries in addition to east-southeast oriented Rocky Hollow. East-southeast oriented streams south of Rocky Hollow flow to east oriented Lodgepole Creek, which then flows to the northeast oriented South Platte River. Headward erosion of the northeast oriented Rocky Hollow and Lawrence Fork valley beheaded flow routes to what was then the newly eroded Lodgepole Creek valley. Next headward erosion of the east and east-southeast oriented Pumpkin Creek valley and its north and northeast oriented tributary valleys (in sequence from east to west) beheaded flood flow routes to the newly eroded Rocky Hollow and Lawrence Fork valley. Headward erosion of the north oriented Horse Creek valley then beheaded flood flow routes to the newly eroded Pumpkin Creek valley. Floodwaters on northwest ends of beheaded flood flow routes reversed flow direction to create the northwest oriented Owl Creek and Kiowa Creek drainage routes.

Owl Creek- Gering Drain drainage divide area

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

Figure 3 provides a topographic map of Owl Creek-Gering Drain drainage divide area. The map contour interval for figure 3 is 10 meters. The city of Scottsbluff, Nebraska is located in the northeast corner of figure 3 and the city of Gerhing is south of Scottsbluff. The North Platte River flows in a southeast direction across the northeast corner of figure 3 and is located between the cities of Scottsbluff and Gerhing. The northwest end of the Wildcat Hills is located in the southwest quadrant of figure 3. Owl Creek originates in the west center area of figure 3 and flows in a northwest direction to the west edge of figure 3 (near northwest corner).  West and north of figure 3 Owl Creek turns to flow in a north direction and joins northeast oriented Horse Creek shortly before Horse Creek joins the southeast oriented North Platte River. Kiowa Creek originates in the Wildcat Hills and flows in a northwest, north, and northwest direction to the west center edge of figure 3. West of figure 3 Kiowa Creek turns to flow in a north direction to join Owl Creek. Bobcat Canyon is a northwest oriented drainage route near the southwest corner of figure 3. These northwest oriented drainage routes all qualify as barbed tributaries because they flow in northwest directions before joining the southeast oriented North Platte River. Irrigation canals obscure natural drainage routes in the southeast quadrant of figure 3, but an east and east-northeast slope leads to the southeast oriented North Platte River valley located east of figure 3. Roubadeau Pass in the west center area of figure 3 links the northwest oriented Owl Creek valley with a southeast oriented valley to the east. The Roubadeau Pass floor elevation is between 1380 and 1390 meters. The butte to the north rises to at least 1480 meters while elevations in the Wildcat Hills to the south rise to at least 1495 meters. These elevations suggest Roubadeau Pass is at least 90 meters deep. Roubadeau Pass was eroded by southeast oriented flood flow as the deep southeast oriented North Platte River valley was eroding headward into the region. The North Platte River valley floor elevation near Scottsbluff is approximately 1180 meters, which suggests a 300-meter deep valley was eroding headward into the region. At the time Roubadeau Pass was eroded the deep north and northeast oriented Horse Creek valley west of figure 3 did not exist, nor did the deep Goshen Hole basin west of the north oriented Horse Creek valley exist. Headward erosion of the deep North Platte River valley and its northeast oriented Horse Creek tributary valley beheaded the southeast oriented flood flow route across Roubadeau Pass. Floodwaters on the northwest end of the beheaded flood flow route reversed flow direction to create the northwest oriented Owl Creek drainage route.

Detailed map of Roubadeau Pass drainage divide area

Figure 4: Detailed map of Roubadeau Pass 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 Roubadeau Pass drainage divide area seen in less detail in figure 3. The map contour interval for figure 4 is 20 feet. Owl Creek flows from the south edge of figure 4 (west of center) in a north-northwest and northwest direction to the west edge of figure 4 (north half) and west and north of figure 4 flows to northeast oriented Horse Creek, which then flows to the southeast oriented North Platte River. Roubadeau Pass is located in the southwest corner of section 5 and the southeast corner of section 6 and links a west oriented Owl Creek tributary valley with a southeast oriented stream valley. Roubadeau Pass at its deepest point in the southwest corner of section 5 has an elevation of between 4460 and 4480 feet. Elevations in the northwest quadrant of section 33 to the northeast rise to 4897 feet while elevations in section 17 to the south rise to 4808 (and to 4907 feet south of figure 4). These elevations suggest Roudbadeau Pass is at least 400 feet deep. Roubadeau Pass was eroded by southeast oriented flood flow moving from north and west of figure 4 to the actively eroding southeast oriented North Platte River valley east of figure 4. At that time elevation west of figure 4 were at least as high as the Roubadeau Pass elevation and probably as high, if not higher, than elevations of the tops of the highest buttes seen in figure 4 and at that time the deep North Platte River valley head was still eroding headward in the region north of figure 4. Initially floodwaters flowed in southeast directions on an erosion surface at least as high as the tops of the buttes seen in figure 4. Rifle Sight Pass is located in the northwest corner of section 2 (near east edge of figure 4) and links a north-northwest oriented drainage route with a south-southeast oriented drainage route. The Rifle Sight Pass elevation is between 4320 and 4340 feet. East of Rifle Sight Pass and east of figure 4 elevations on the drainage divide rise to 4730 feet suggesting Rifle Sight Pass is also approximately 400 feet. A south-southeast oriented flood flow channel eroded the Rifle Sight Pass valley prior to or at about the same time as the Roubadeau Pass through valley was being eroded. Headward erosion of the deep southeast oriented North Platte River valley then captured the south-southeast oriented flood flow and the captured floodwaters eroded the north-facing basin on the north side of Rifle Sight Pass.

Robb Draw-Pumpkin Creek drainage divide area

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

Figure 5 illustrates a reduced size topographic map of the Robb Draw-Pumpkin Creek drainage divide area south and west of figure 3 and includes an overlap area with figure 3. The map contour interval for figure 5 is 10 meters. The Wildcat Hills are located in the east half of figure 5. Roubadeau Pass is located north of the Wildcat Hills near the north edge of the northeast quadrant of figure 5. Kiowa Creek originates in the Wildcat Hills and flows in a northwest, west, and northwest direction to the north center edge of figure 5. North of figure 5 Kiowa Creek turns to flow in a north direction to join northwest and north oriented Owl Creek, which flows to northeast oriented Horse Creek, which then flows to the southeast oriented North Platte River. Pumpkin Creek originates south of the Wildcat Hills and flows in a southeast direction to the southeast corner area of figure 5. East of figure 5 Pumpkin Creek flows in an east-southeast and east direction to eventually join the southeast oriented North Platte River. Sixtysix Mountain is the butte straddling the west edge of the southwest quadrant of figure 5. Horse Creek flows in a north direction west of Sixtysix Mountain (and west of figure 5) before turning to flow in a northeast direction to join the southeast oriented North Platte River. The deep east-oriented Goshen Hole basin is located west and north of Sixtysix Mountain (see Chugwater Creek-Horse Creek drainage divide area in the Goshen Hole region essay). A major northwest to southeast oriented through valley between Sixtysix Mountain and the Wildcat Hills links the east oriented Goshen Hole basin with the Pumpkin Creek valley. The through valley floor elevation is between 1360 and 1370 meters. Elevations in the Wildcat Hills reach 1504 meters and elevations on Sixtysix Mountain reach 1587 meters suggesting the through valley is at least 134 meters deep. The through valley was eroded by southeast and east oriented flood flow moving from what was at that time the actively eroding Goshen Hole basin to the southeast and east oriented Pumpkin Creek valley and then to the southeast oriented North Platte River valley. At that time the north oriented Horse Creek valley west of figure 5 did not exist. Headward erosion of the north oriented Horse Creek valley west of figure 5 ended flood flow to the Pumpkin Creek valley and diverted floodwaters in a north and northeast direction into the newly eroded southeast oriented North Platte River valley. Subsequently headward erosion of the southeast oriented North Platte River valley,  its east and northeast oriented Laramie River tributary valley ,and its northeast and north oriented Chugwater Creek tributary valley ended all east oriented flood flow into the Goshen Hole basin, although east oriented flood flow from west of the Laramie Mountains may have continued to flow into the east-northeast and north oriented Horse Creek valley after that time.

Horse Creek-Bull Canyon drainage divide area

Figure 6: Horse Creek-Bull Canyon drainage divide area. United States Geological Survey map digitally presented using National Geographic Society TOPO software.

Figure 6 provides a reduced size topographic map of the Horse Creek-Bull Canyon drainage divide south and slightly west of figure 5 and includes an overlap area with figure 5. The map contour interval for figure 6 is 10 meters. Sixtysix Mountain is located near the north edge of the northwest quadrant of figure 6. The Goshen Hole basin is located west and northwest of Sixtysix Mountain. The upland straddling the south center edge of figure 6 is the upland or higher plains surrounding the deeper Goshen Hole basin. Horse Creek flows in a north-northeast and north direction from the south edge of figure 6 (west half) to the town of La Grange and then flows in a north-northwest direction to the northwest corner of figure 6. North of figure 6 Horse Creek flows in a north-northwest and north direction across the east end of the Goshen Hole basin then in a southeast and northeast direction to reach the southeast oriented North Platte River. Bull Canyon drains in a north direction from the south center edge of figure 6 before turning to drain in an east-northeast and east direction to the east center edge of figure 6. East of figure 6 Bull Canyon drains to east-southeast and east oriented Pumpkin Creek. A major west to east oriented through valley between Sixtysix Mountain and the high plains east of the Horse Creek valley links the Goshen Hole basin to the west and northwest with the east oriented Pumpkin Creek valley to the east. The through valley floor elevation is between 1390 and 1400 (at it lowest point just south of Sixtysix Mountain). Elevations on Sixtysix Mountain reach 1587 meters while elevations on the high plains surface to the south exceed 1600 meters suggesting the through valley is almost 200 meters deep. This deep through valley and the through valley between Sixtysix Mountain and the Wildcat Hills were eroded by diverging and converging flood flow channels draining what at that time was the actively eroding Goshen Hole basin. While not seen one or more additional flood flow channels drained the Goshen Hole basin in a northeast direction along the present day southeast and northeast oriented Horse Creek alignment to the actively eroding southeast oriented North Platte River valley. The northeast oriented flood flow channel or channels eventually captured the east oriented flood flow moving to the Pumpkin Creek valley by headward erosion of the slightly deeper north oriented Horse Creek valley. The Horse Creek valley north of La Grange is approximately 20 meters deeper than the Horse Creek-Pumpkin Creek drainage divide on the south side of Sixtysix Mountain suggesting that the east oriented Pumpkin Creek drainage route and the north oriented Horse Creek drainage route probably both received floodwaters from the Goshen Hole basin up until the time east oriented flood flow into the Goshen Hole Basin ended. The Horse Creek valley may have transported floodwaters from west of the Goshen Hole basin area after east oriented flood flow into the Goshen Hole ended and those residual floodwaters may have helped to erode the slightly deeper north oriented Horse Creek valley.

Horse Creek-Long Canyon drainage divide area

Figure 7: Horse Creek-Long Canyon drainage divide area. United States Geological Survey map digitally presented using National Geographic Society TOPO software.

Figure 7 illustrates the Horse Creek-Long Canyon drainage divide area south of figure 6 and also includes an overlap area with figure 6. The map contour interval for figure 7 is 10 meters. Horse Creek flows in an east direction from the west center edge of figure 7 and then turns to flow in a north direction to the north edge of figure 7 (near northwest corner). North of figure 7 Horse Creek flows in a north-northwest, north, southeast, and northeast direction to join the southeast oriented North Platte River. West of figure 7 Horse Creek flows in an east-northeast direction from the west edge of the Laramie Mountains. Bull Canyon originates east of the center of figure 7 and drains in a north direction to the north edge of figure 7 (east of center). North of figure 7 Bull Canyon drains in a northeast and east direction to join east oriented Pumpkin Creek, which then flows to the southeast oriented North Platte River. Long Canyon originates in the southeast quadrant of figure 7 and drains in an east-northeast and north direction to the north edge of figure 7 (near northeast corner). North and east of figure 7 Long Canyon drains to east oriented Bull Canyon, which drains to east oriented Pumpkin Creek. The east-southeast and east oriented stream in the southeast quadrant of figure 7 located south of Long Canyon and flowing to the east edge of figure 7 (near southeast corner) is the headwaters of east-southeast oriented Rocky Hollow, which drains to east and northeast oriented Lawrence Fork, which in turn flows to east oriented Pumpkin Creek. A southeast oriented stream near the south edge of figure 7 and just east of the south center edge of figure 7 is the headwaters of a southeast oriented Lodgepole Creek tributary, with east and southeast oriented Lodgepole Creek flowing to the northeast oriented South Platte River. Headward erosion of the north oriented Horse Creek valley captured east-northeast oriented flood flow from west of figure 7 (and perhaps from west of the Laramie Mountains) that had been flowing to the east, northeast, and north oriented Long Canyon valley and then to the Pumpkin Creek valley and diverted the floodwaters in a north direction to the North Platte River. Headward erosion of the north oriented Horse Creek valley also beheaded southeast oriented flood flow to the east oriented Lodgepole Creek valley (and the northeast oriented South Platte River valley) while headward erosion of the east and northeast oriented Long Canyon valley beheaded southeast oriented flood flow moving to the east-southeast and northeast Rocky Hollow valley (see figure 8), which flowed to the east and northeast oriented Lawrence Fork valley (see figure 9). In other words the landscape in figure 7 was carved by floodwaters first moving in southeast directions to the northeast oriented South Platte River valley, which were then captured by headward erosion of the much deeper east oriented Pumpkin Creek valley and tributary valleys (from the southeast oriented North Platte River valley), and which were later captured by headward erosion of the north oriented Horse Creek valley from the southeast oriented North Platte River valley. Prior to these events there may have been earlier flood flow movement directions, although landform evidence for such movements has been removed.

Long Canyon-Rocky Hollow drainage divide area

Figure 8: Long Canyon-Rocky Hollow 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 Long Canyon-Rocky Hollow drainage divide east and south of figure 7 and includes an overlap area with figure 7. The map contour interval for figure 8 is 10 meters. Pumpkin Creek flows in a southeast and east direction north of figure 8 and the north-facing escarpment in the north half of figure 8 is the south wall of the deep Pumpkin Creek valley. The escarpment height varies, but probably is more than 100 meters with the Pumpkin Creek elevation north of figure 8 being almost 200 meters lower than the elevations on the uplands south of the escarpment rim. Many streams draining the escarpment face are oriented in northwest directions and then turn to flow in north and northeast directions to join east oriented Pumpkin Creek. Long Canyon drains in a northeast and north direction across the northwest corner of figure 8 and north of figure 8 joins Bull Canyon to drain to east oriented Pumpkin Creek, which then flows to the southeast oriented North Platte River. Rocky Hollow drains in an east-southeast direction to the east edge of figure 8 (near southeast corner) and east of figure 8 flows in a northeast direction to join east and north-northeast oriented Lawrence Fork, which flows to east oriented Pumpkin Creek. Southeast oriented streams in the southwest quadrant of figure 8 are tributaries of east and southeast oriented Lodgepole Creek, which flows to the northeast-oriented South Platte River. Headward erosion of the deep east oriented Pumpkin Creek valley and its northeast oriented Long Canyon tributary valley beheaded southeast oriented flood flow channels supplying floodwaters to the east-southeast oriented Rocky Hollow headwaters and tributary valleys and also to southeast oriented Lodgepole Creek tributary valleys. Northwest oriented valleys draining the north-facing escarpment were formed by reversals of flood flow on northwest ends of flood flow channels beheaded by headward erosion of the much deeper east oriented Pumpkin Creek valley. Floodwaters on northwest ends of beheaded flood flow reversed flow direction to flow to the much deeper Pumpkin Creek valley and to create northwest oriented drainage routes.

Pumpkin Creek-Lawrence Fork drainage divide area

Figure 9: Pumpkin Creek-Lawrence Fork drainage divide area. United States Geological Survey map digitally presented using National Geographic Society TOPO software.

Figure 9 illustrates the Pumpkin Creek-Lawrence Fork drainage divide area east of figure 8 and there is an overlap area with figure 8. The map contour interval for figure 9 is 10 meters. The north-facing escarpment near the north edge of figure 9 is the south wall of the deep east oriented Pumpkin Creek valley. The Pumpkin Creek elevation north of figure 9 is approximately 200 meters lower than the elevation of the uplands south of the escarpment rim. Pumpkin Creek flows in an east direction north of figure 9 and eventually joins the southeast oriented North Platte River. Lawrence Fork flows in an east-southeast direction to Lone Pine Springs and then in an east direction to the east edge of figure 9 (south half). East of figure 9 Lawrence Fork turns to flow in a north-northeast direction to join east oriented Pumpkin Creek. Rocky Hollow drains in a northeast direction from the south edge of figure 9 (east of center) to join east oriented Lawrence Fork. South and west of figure 9 Rocky Hollow drains in an east-southeast direction before turning to drain in a northeast direction. Southeast oriented streams flowing across the southwest quadrant of figure 9 are Rocky Hollow tributaries. Bighorn Gulch originates in the north center area of figure 9 and drains in a deep east and north-northeast valley to the north center edge of figure 9 and north of figure 9 drains to east oriented Pumpkin Creek. Short northwest and southeast oriented tributary valleys provide evidence the deep north-northeast oriented Bighorn Gulch valley eroded headward across southeast oriented flood flow channels. The northwest oriented tributary valleys were eroded by reversals of flood flow on northwest ends of beheaded flood flow channels. Prior to headward erosion of the deep east oriented Pumpkin Creek valley north of figure 9, headward erosion of the northeast oriented Rocky Hollow valley captured east-southeast oriented flood flow channels flowing to east and southeast oriented Lodgepole Creek, which flows to the northeast oriented South Platte River. Headward erosion of the east-southeast and east oriented Lawrence Fork valley from the northeast oriented Rocky Hollow and north-northeast oriented Lawrence Fork valley (from what was then the actively eroding Pumpkin Creek valley, which was eroding headward from the actively eroding and southeast oriented North Platte River valley) then captured some southeast oriented flood flow channels and beheaded some flood flow routes to the newly eroded Rocky Hollow valley. Headward erosion of the Bighorn Gulch valley from the actively eroding and much deeper east oriented Pumpkin Creek valley next beheaded some flood flow channels to the newly eroded Lawrence Fork valley. Continued headward erosion of the deep east oriented Pumpkin Creek valley then beheaded southeast oriented flood flow routes to the actively eroding east-southeast oriented Rocky Hollow headwaters and tributary valleys and ended flood flow across uplands seen in figure 9.

North Platte River-Pumpkin Creek drainage divide area

Figure 10: North Platte River-Pumpkin Creek drainage divide area. United States Geological Survey map digitally presented using National Geographic Society TOPO software.

Figure 10 provides a reduced size topographic map of the North Platte River-Pumpkin Creek drainage divide area north and east of figure 9 and includes a small overlap area with figure 9. The map contour interval for figure 10 is 10 meters. The North Platte River flows in an east-southeast direction across the northeast corner of figure 10. Pumpkin Creek flows in an east-southeast, northeast, and east direction from the west edge of figure 10 (slightly north of center) to the east edge of figure 10 (slightly south of center). East of figure 10 Pumpkin Creek flows in an east direction to join the east-southeast oriented North Platte River. The deeply eroded ridge between the North Platte River valley and the Pumpkin Creek valley is an eastern extension of the Wildcat Hills seen in earlier figures. The high point on the ridge just west of the north to south oriented Banner-Morrill County line is 1422 meters and further east (just west of Redington Gap) a high point elevation of 1382 meters is shown. Elevations in the North Platte River valley near the northeast corner of figure 10 are less than 1140 meters and Pumpkin Creek crosses the 1150-meter contour line near the east edge of figure 10. These elevations suggest the North Platte River and Pumpkin Creek valleys are approximately 250 meters deep and that the Pumpkin Creek valley is almost as deep as the North Platte River valley. What has happened here is two deep valleys eroded headward across south-southeast and southeast oriented flood flow with the Pumpkin Creek valley eroding headward slightly in advance of the North Platte River valley. South-southeast oriented flood flow channels to the newly eroded east oriented Pumpkin Creek valley were beheaded and reversed to create the northwest and north-northwest oriented North Platte River tributary drainage routes seen in figure 10. North to south oriented gaps crossing the high ridge (e.g. Hubbard Gap and Redington Gap) were eroded by south and/or southeast oriented flood flow channels prior to being beheaded by headward erosion of the much deeper southeast oriented North Platte River valley. The Pumpkin Creek valley eroded headward into the present day Goshen Hole basin as seen in earlier figures, while the North Platte River valley eroded headward into the region north of Goshen Hole. Headward erosion of the Pumpkin Creek valley was significantly slowed at the west end of Goshen Hole by erosion resistant strata, while North Platte River tributary valleys (north and northeast oriented Horse Creek valley were able to first capture east oriented flood flow at the east end of the Goshen Hole basin and later (the north oriented Chugwater Creek valley and the east and northeast oriented Laramie River valley) to erode headward around north and west sides of the erosion resistant and to behead east oriented flood flow routes to the east oriented Goshen Hole valley. Had the headward erosion of the Goshen Hole valley not been slowed by erosion resistant bedrock at the west end of the Goshen Hole basin today the Laramie River would flow through Goshen Hole and in an east direction in the Pumpkin Creek valley rather than turning to flow around the north side of Goshen Hole to reach the southeast oriented North Platte River valley.

Additional information and sources of maps studied

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