Abstract:

This essay uses topographic map evidence to interpret landform origins in the region between South Fork Powder River and Casper Creek in Natrona County, Wyoming. The South Fork Powder River and Middle Fork Casper Creek and their tributaries originate in the Rattlesnake Hills and flow in northeast directions parallel to each other before the Middle Fork Casper Creek turns in an east direction to join the south oriented North Fork Casper Creek and to form south-southeast Casper Creek. Casper Creek flows to the east and southeast oriented North Platte River while the South fork Powder River flows to the north oriented Powder River. Landforms along the South Fork Powder River-Casper Creek drainage divide are interpreted in the context of immense melt water floods from the western margin of a thick North American ice sheet and which were flowing in south and southeast directions from western Canada to and across Wyoming. Mountain ranges emerged as floodwaters deeply eroded surrounding regions and as ice sheet related crustal warping raised the mountain ranges relative to surrounding basins. Floodwaters crossing the South Powder River-Casper Creek drainage divide first flowed in a south direction from the Powder River Basin and in an east and southeast direction between the emerging Bighorn Mountains and the emerging Rattlesnake Hills to a south oriented flood flow channel on the present day north oriented North Platte River alignment between the Laramie Range and Rattlesnake Hills. Headward erosion of the southeast and east oriented North Platte River valley along the northeast side of the emerging Laramie Range captured the south oriented flood flow from the Powder River Basin and beheaded the south oriented flood flow channel between the Laramie Range west end and the Rattlesnake Hills. Floodwaters on the north end of the beheaded flood flow channel reversed flow direction to create the north oriented North Platte River drainage route between the Laramie Range and Rattlesnake Hills. At about the same time headward erosion of the deep northeast oriented Yellowstone River valley in Montana beheaded south oriented flood flow routes to the Powder River Basin. Floodwaters on north ends of beheaded flood flow routes reversed flow direction to create the north oriented Powder River drainage route. The northeast oriented South Fork Powder River valley then eroded headward from the newly reversed Powder River valley to capture the east oriented floodwaters moving between the emerging Bighorn Mountains and the emerging Rattlesnake Hills to the newly eroded east and southeast oriented North Platte River valley. Subsequently headward erosion of the deep northeast oriented Yellowstone River valley in Montana beheaded south oriented flood flow channels to the Bighorn and Wind River Basins. Floodwaters on north ends of the beheaded flood flow routes reversed flow direction to create the north oriented Bighorn River and Wind River drainage routes, which captured the east oriented flood flow that had been moving to the newly eroded South Fork Powder River valley. Floodwaters on west ends of the beheaded flood flow routes reversed flow direction to create west oriented Wind River tributary drainage routes.

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 South Fork Powder River-Casper Creek drainage divide area landform origins in Natrona County, Wyoming, USA. Map interpretation methods can be used to unravel many geomorphic events leading up to formation of present-day drainage routes and development of other landform features. While each detailed topographic map feature provides detailed evidence to be explained, the solution must be consistent with explanations for adjacent area map evidence as well as solutions to big picture map evidence puzzles. I invite readers to improve upon my solutions and/or to propose alternate solutions that better explain evidence and are also consistent with adjacent map area and big-picture evidence. Readers may do so either by making comments here or by writing and publishing their own essays and then by leaving a link to those essays in a comment here.

This essay is also exploring a new geomorphology paradigm in which erosional landforms are interpreted as evidence left by immense glacial melt water floods. Implied in that interpretation is the immense floods were derived from a thick North American ice sheet that created a deep “hole” in the North American continent and also melted fast. The previously unexplored paradigm being tested in this and other Missouri River drainage basin landform origins research project essays is a thick North American ice sheet, comparable in thickness to the Antarctic ice sheet, occupied the North American region usually recognized to have been glaciated, and through its weight and erosive actions created a deep North American “hole”. The southwestern rim of that deep “hole” is today preserved in the high Rocky Mountains. The ice sheet through its weight and deep erosion (and perhaps deposition along major south-oriented melt water flow routes) caused significant crustal warping and tectonic change, through its action of melting fast produced immense floods that flowed across the continent, and through its action of melting fast systematically opened up space in the ice sheet created “hole” so headward erosion of newly developed north-oriented drainage systems captured immense south-oriented melt water floods and diverted 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 South Fork Powder River-Casper Creek drainage divide area landform evidence in Natrona County, Wyoming will be regarded as evidence supporting the “thick ice sheet that melted fast” paradigm.

South Fork Powder River-Casper Creek drainage divide area location map

Figure 1: South Fork Powder River-Casper 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 South Fork Powder River-Casper Creek drainage divide area in Natrona County, Wyoming. Casper is the largest city shown and is located in the southeast quadrant of figure 1 at the Laramie Range northwest end. The North Platte River flows in a north direction from Seminoe Reservoir near the south center edge of figure 1 to Pathfinder Reservoir and then turns to flow in a north-northeast direction to Casper. From Casper the North Platte River flows in an east and southeast direction to near the southeast corner of figure 1. East and south of figure 1 the North Platte River joins the South Platte River to form the east oriented Platte River, which flows to the Missouri River along the Nebraska-Iowa border. Casper Creek is a northeast, east, and south oriented tributary originating in the Rattlesnake Hills (in south center area of figure 1) and joining the North Platte River near Casper. Just north of the Casper Creek headwaters and at the northwest end of the Rattlesnake Hills are headwaters of the northeast and north-northeast oriented South Fork Powder River, which east of Kaycee joins the southeast oriented North Fork Powder River and the northeast oriented Middle Fork Powder River to form the east and north oriented Powder River. North of figure 1 the Powder River flows into Montana where it joins the northeast oriented Yellowstone River. The North Fork Powder River and the Middle Fork Powder River originate in the southern Bighorn Mountains, which are located in the north center region of figure 1. East of the Bighorn Mountains is the Powder River Basin. West of the Bighorn Mountains is the Bighorn Basin. The Bighorn Basin is drained by the north oriented Bighorn River, which north of figure 1 flows into Montana to join the northeast oriented Yellowstone River. The Bighorn River originates as the southeast oriented Wind River west of figure 1. The Wind River flows in a southeast direction from the west center edge of figure 1 between the Owl Creek Mountains and the Wind River Range to Riverton in the Wind River Basin. At Riverton the Wind River turns to flow in a northeast and north direction through Wind River Canyon (eroded across the east end of the Owl Creek Mountains) to near Thermopolis where the river name changes to become the Bighorn River. The South Fork Powder River-Casper Creek drainage divide area investigated in this essay is located south and east of the South Fork Powder River and north and west of northeast and east oriented Casper Creek segments.

Drainage routes in Wyoming developed during immense south and southeast oriented melt water floods that were subsequently reversed to flow in north and northeast directions to space in a deep “hole” the melting ice sheet had occupied. At least initially Wyoming and other regional mountain ranges had not emerged and floodwaters could easily flow across what are today major mountain barriers. Floodwaters flowed from the western margin of a thick North American ice sheet from western Canada to and across Wyoming. Mountain ranges emerged as floodwaters deeply eroded regions surrounding them and as ice sheet related crustal warping raised the mountain ranges relative to the intervening basins. Deep south and southeast oriented flood flow channels eroded headward on both sides of the emerging Laramie Range with a southeast oriented flood flow channel on the east and southeast oriented North Platte River alignment capturing south oriented flood flow from the Powder River Basin to the north and east oriented  flood flow moving between the emerging Bighorn Mountains and Rattlesnake Hills to a south oriented flood flow channel on the present day north oriented North Platte River alignment between the emerging Laramie Range and Rattlesnake Hills. The northeast oriented North Platte River valley segment (west of Casper) and northeast oriented North Platte River tributary valleys (Casper Creek and Poison Spider Creek valleys) eroded headward in sequence (from east to west) to capture east oriented flood flow moving between the emerging Bighorn Mountains and the emerging Rattlesnake Hills and south oriented flood flow from the Powder River Basin and beheaded the south oriented flood flow channel on the present day north oriented North Platte River alignment between the emerging Laramie Range and the emerging Rattlesnake Hills. Floodwaters on the north end of the beheaded flood flow channel reversed flow direction to create the north oriented North Platte River drainage route west of the Laramie Range. The flood flow reversal was probably greatly aided by ice sheet related crustal warping that was raising mountain ranges south of figure 1.

A major flood flow reversal in the Powder River Basin next resulted in headward erosion of the north-northeast oriented South Fork Powder River valley, which captured east oriented flood flow moving between the emerging Bighorn Mountains and emerging Rattlesnake Hills. The flood flow reversal was caused by headward erosion of the deep northeast oriented Yellowstone River valley in Montana (north of figure 1). The Yellowstone River valley eroded headward from space at the south end of the deep “hole” the melting ice sheet was opening up and which initially drained in a south direction east of figure 1. Headward erosion of the deep northeast oriented Yellowstone River valley captured the south and southeast oriented floods in Montana and diverted floodwaters to the south end of the deep “hole”. Flood flow routes to Wyoming were beheaded in sequence from east to west. Floodwaters on north ends of the beheaded flood flow reversed flow direction to erode deeper north oriented drainage routes. These deeper north oriented drainage routes then eroded northeast and north-northeast oriented tributaries headward to capture south and southeast oriented flood flow still moving west of the actively eroding Yellowstone River valley head. Floodwaters in the Powder River Basin were beheaded and reversed to create the north oriented Powder River drainage system, which captured southeast and south oriented flood flow still moving across the emerging Bighorn Mountains (see southeast oriented North Fork Powder River) and south and southeast oriented flood flow moving into the present day Wind River Basin and then in an east direction between the emerging Bighorn Mountains and Rattlesnake Hills to the newly formed North Platte River drainage system. Headward erosion of the deep Yellowstone River valley in Montana subsequently beheaded and reversed flood flow routes in the Bighorn Basin to create the north oriented Bighorn River. The deeper north oriented Bighorn River valley then captured southeast oriented flood flow still moving further to the west including the southeast oriented flood flow moving to the Wind River Basin. This capture of southeast oriented flood flow in the Wind River Basin resulted in deep erosion of the Wind River Basin, which in turn beheaded and reversed the east oriented flood flow routes to the newly eroded South Fork Powder River valley and created west oriented Wind River tributary drainage routes.

Detailed location map for South Fork Powder River-Casper Creek drainage divide area

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

Figure 2 provides a more detailed location map for the South Fork Powder River-Casper Creek drainage divide area in Natrona County, Wyoming and shows a region in central Wyoming. The North Platte River flows in a northeast direction from the south edge of figure 2 to Casper and then in an east direction to the east edge of figure 2. East of figure 2 the North Platte River turns to flow in a southeast direction with water eventually reaching the Missouri River in eastern Nebraska. The Rattlesnake Hills are located in the southwest corner of figure 2 and the Bighorn Mountains are located north of the northwest quadrant of figure 2. Poison Spider Creek originates in the Rattlesnake Hills and flows in an east direction to near Emigrant Gap Ridge where it turns to flow in a south-southeast direction to the northeast oriented North Platte River as a barbed tributary. The Middle Fork Casper Creek originates in the Rattlesnake Hills (near Garfield Peak and just west of the Poison Spider Creek headwaters) and flows in a northeast direction to Natrona where it turns to flow in an east direction to Illco. At Illco the Middle Fork Casper Creek joins the southeast oriented North Fork Casper to form south-southeast oriented Casper Creek, which joins the North Platte River just west of Casper. The South Fork Powder River originates in the Ervay Basin (near west edge of figure 3 at northwest end of Rattlesnake Hills) and flows in a northeast and east-northeast direction to the town of Powder River. From the town of Powder River the South Fork Powder River flows in a north-northeast and northeast direction to the north edge of figure 2. North of the figure 2 the South Fork Powder River joins the southeast oriented North Fork Powder River and northeast oriented Middle Fork Powder River to form the north oriented Powder River, which flows to Montana and the northeast oriented Yellowstone River. Wallace Creek is the northeast oriented South Fork Powder River located between the Casper Creek and South Fork Powder River headwaters in the Rattlesnake Hills region. Anderson Draw is a north oriented tributary to the South Fork Powder River north of Natrona. The unnamed north oriented South Fork Powder tributary originating west of the town of Merino is Cloud Creek. The northwest end of the Laramie Mountains is located south and east of Casper and while not illustrated in detail in this essay the North Platte River has eroded a 300-meter deep water gap across the northwest end of the Laramie Range near the town Goose Egg. Emigrant Gap Ridge could be considered a low relief northwest extension of the Laramie Mountains uplift with Emigrant Gap being a 100-meter deep wind gap eroded across it.

Wallace Creek-Middle Fork Casper Creek drainage divide area  south

Figure 3: Wallace Creek-Middle Fork Casper Creek drainage divide area south. United States Geological Survey map digitally presented using National Geographic Society TOPO software.

Figure 3 provides a topographic map of Wallace Creek-Middle Fork Casper Creek drainage divide area south. The map contour interval for figure 3 is 20 meters. The Rattlesnake Hills are located in the southwest corner of figure 3 and Garfield Peak is the labeled high point with an elevation of 2613 meters. Elevations near the northeast corner of figure 3 are less than 1900 meters. The Woodland Basin is located west of Garfield Peak. Wallace Creek flows through the Woodland Basin in a north direction and then continues to the north edge of figure 3 (west half). North of figure 3 Wallace Creek joins the South Fork Powder River with water eventually reaching the Yellowstone River in Montana. Snider Basin is located east of Garfield Peak. The Middle Fork Casper Creek flows in a northeast direction through Snider Basin and then with some northward jogs continues in a northeast direction to the north edge of figure 3 and north and east of figure 3 joins the North Fork Casper Creek to flow in a south-southeast direction as Casper Creek to the North Platte River with water flowing to the Platte River in Nebraska. Poison Spider Creek flows in a northeast direction across the southeast quadrant of figure 3 and east of figure 3 flows in an east and south-southeast direction to join the northeast oriented North Platte River as a barbed tributary. While water in Wallace Creek and in the Middle Fork Casper Creek eventually ends up in the Missouri River water in the two different streams travels on fundamentally different routes to reach southeastern Nebraska. Even a quick glance at figure 3 shows the two streams originate in almost the same place and are linked by through valleys crossing the drainage divide between them. In other words, the two stream valleys originated at approximately the same time and under the same conditions and then something occurred north and east of figure 3 to cause the streams to flow in different directions. The northwest to southeast oriented through valley linking the Wallace Creek valley with the Middle Fork Casper Creek valley provides a clue and the south-southeast oriented Poison Spider Creek segment (east of figure 3) provides another clue. As the Rattlesnake Mountains emerged large volumes of southeast oriented floodwaters flowed across the region seen in figure 3. The floodwaters were flowing to a south oriented flood flow channel on the present day north oriented North Platte River segment west of the Laramie Mountains (and south and east of figure 3-see figure 1). The east (and northeast) oriented Poison Spider Creek valley eroded headward to capture the southeast oriented flood flow. Next the flood flow reversal in the Powder River Basin (north and east of figure 3) enabled deep northeast oriented valleys to erode headward from the newly reversed and deeper Powder River valley to capture the southeast oriented flood flow. The Middle Fork Casper Creek valley eroded headward across the flood flow first and diverted  floodwaters in a northeast and north direction to the deep “hole” the melting ice sheet was opening up. Next headward erosion of the Wallace Creek valley captured the southeast oriented flood flow and beheaded flood flow to the newly eroded Middle Fork Casper Creek valley. Still later the South Fork Powder River valley north and west of figure 3 beheaded flood flow routes to the newly eroded Wallace Creek valley. Flood flow in the Middle Fork Casper Creek valley was captured east and north of figure 3 by headward erosion of a deeper valley from the North Platte River valley, although the North Platte River valley was not able to capture flood flow moving in the Wallace Creek and South Fork Powder River valleys.

Detailed map of Wallace Creek-Middle Fork Casper Creek drainage divide area south

Figure 4: Detailed map of Wallace Creek-Middle Fork Casper Creek drainage divide area south. United States Geological Survey map digitally presented using National Geographic Society TOPO software.

Figure 4 provides a detailed topographic map of the Wallace Creek-Middle Fork Casper Creek drainage divide area south. The map contour interval for figure 4 is 20 feet. Wallace Creek flows in a north-northeast and northwest direction from the west edge of figure 4 (south half) to near the northwest corner of figure 4 and north of figure 4 joins the South Fork Powder River with water eventually reaching the Yellowstone River in Montana. The Middle Fork Casper Creek flows in a north direction from the south edge of figure 4 (east half) into section 19 where it turns to flow in a northeast direction to the east edge of figure 4 (north half) with water eventually reaching the North Platte River, which flows to the Platte River in Nebraska. McClanahan Lake in section 13 is located in a northwest-to-southeast oriented through valley linking the Wallace Creek valley with the Middle Fork Casper Creek valley. McClanahan Draw is a northeast oriented Middle Fork Casper Creek tributary so the Wallace Creek-Middle Fork Casper Creek drainage divide is located in the northeast corner of section 14. The through valley floor elevation at the drainage divide is between 6380 and 6400 feet. The hogback ridge in the southeast quadrant of section 11 exceeds 6520 feet and a ridge just north of figure 4 exceeds 6640 feet. Elevations in the Rattlesnake Hills to the southwest of the through valley rise much higher than 6640 feet suggesting the through valley is at least 240 feet deep. While the through valley probably follows the underlying geologic structure the through valley is also a water-eroded valley and was eroded by southeast oriented flood flow moving to the northeast oriented Middle Fork Casper Creek valley prior to being captured by headward erosion of the Wallace Creek valley. At that time the region was probably awash with southeast oriented flood flow moving to a south oriented flood flow channel on the present day north oriented North Platte River alignment and which was being captured by headward erosion of deeper northeast oriented valleys eroding headward from the newly reversed and north oriented Powder River drainage route. This was probably a situation where a southeast oriented anastomosing channel complex was captured by headward erosion of a northeast oriented anastomosing channel complex. Headward erosion of a southeast oriented anastomosing channel complex from the actively southeast oriented North Platte River valley on the north and northeast side of the Laramie next captured the southeast oriented channels in the northeast oriented anastomosing channel complex, although most of the northeast oriented channels continued to drain to the north oriented Powder River drainage route.

Wallace Creek-Middle Fork Casper Creek drainage divide area north

Figure 5: Wallace Creek-Middle Fork Casper Creek drainage divide area north. United States Geological Survey map digitally presented using National Geographic Society TOPO software.

Figure 5 illustrates the Wallace Creek-Middle Fork Casper Creek drainage divide area north and is located north and slightly east of figure 34 and there is an overlap area with figure 3. The map contour interval for figure 5 is 20 meters. The South Fork Powder River flows in a northeast direction across the northwest corner of figure 5. North and east of figure 5 the South Fork Powder River flows to the north oriented Powder River with water eventually reaching the northeast oriented Yellowstone River in Montana. Wallace Creek flows in a north direction from the south edge of figure 5 (near southwest corner) and then turns to flow in a northeast direction to the north edge of figure 5 (east half). North of figure 5 Wallace Creek joins the South Fork Powder River. The Middle Fork Casper Creek flows in a northeast direction from the south center edge of figure 5 to the east edge of figure 5 (north of center). East of figure 5 the Middle Fork Casper Creek turns to flow in an east direction to join the North Fork Casper Creek and then to flow in a south-southeast direction to the east and southeast oriented North Platte River with water eventually reaching the east oriented Platte River in Nebraska. Drainage divides between these northeast oriented streams are defined by only one or two 20-meter contour lines suggesting the valleys are relatively shallow. Broad Mesa and other drainage divide surfaces were probably eroded by massive southeast and/or east oriented floods moving to a south oriented flood flow channel on the present day north oriented North Platte River alignment west of the Laramie Mountains and/or to what was at that time the actively eroding southeast oriented North Platte River valley, which was eroding headward towards the Casper area. The southeast and/or east oriented floodwaters were captured by headward erosion of slightly deeper northeast oriented valleys, which eroded headward from the north oriented Powder River valley. Flood flow to the Powder River Basin (north and east of figure 5) had been beheaded by headward erosion of the much deeper northeast oriented Yellowstone River valley, which had eroded headward from space at the south end of the deep “hole” the melting ice sheet had opened up and which was draining in a south direction further to the east. The deep southeast oriented North Platte River valley and the deep north oriented Powder River competed with each to capture the southeast and east oriented flood flow. In the end headward erosion of the northeast oriented South Fork Powder River valley beheaded all southeast and east oriented flood flow routes flowing to the actively eroding North Platte River valley in the region north of the Rattlesnake Hills, although before doing so the deep North Platte River valley captured flood flow in the Middle Fork Casper Creek valley and also beheaded and reversed south oriented flood flow on the present day north oriented North Platte River alignment. Reversed flood flow on the present day north oriented North Platte River alignment captured significant flood flow moving west and south of the Rattlesnake Mountains so significant flood flow continued to move in the North Platte River valley after headward erosion of the South Fork Powder River valley beheaded flood flow routes in this region.

South Fork Powder River-Middle Fork Casper Creek drainage divide area

Figure 6: South Fork Powder River-Middle Fork Casper Creek drainage divide area. United States Geological Survey map digitally presented using National Geographic Society TOPO software.

Figure 6 provides a topographic map of the South Fork Powder River-Middle Fork Casper Creek drainage divide area north and east of figure 5 and includes an overlap area with figure 5. The map contour interval for figure 6 is 20 meters. Pine Mountain is the upland located near the southeast corner of figure 6. Elevations at the top of Pine Mountain exceed 2000 meters. The Middle Fork Casper Creek flows in a northeast direction from the south center edge of figure 6 to the east edge of figure 6 (near the town of Sodium). East of figure 6 the Middle Fork Casper Creek turns to flow in an east direction to join southeast oriented North Fork Casper Creek and to form south-southeast oriented Casper Creek, which flows to the east and southeast oriented North Platte River. The South Fork Powder River flows in an east-northeast direction from the west edge of figure 6 (south half) to near the town of Powder River and then turns to meander in a northeast direction to the north edge of figure 6. North of figure 6 the South Fork Powder River flows to the north oriented Powder River. The relatively low relief erosion surface in the vicinity of the town of Powder River linking the South Fork Powder River valley with the Middle Fork Casper Creek valley is in fact the floor of a broad through valley with Pine Mountain being the southeast wall and the Bighorn Mountains (to the northwest of figure 6) being the northwest wall. Elevations along the South Fork Powder River-Middle Fork Casper Creek drainage divide near the town of Powder River are between 1740 and 1760 meters, suggesting the through valley is approximately 250 meters deep. Today the northwest side of the through valley is drained by the northeast oriented South Fork Powder River and the southeast side is drained by the northeast and east oriented Middle Fork Casper Creek. The through valley was probably initially eroded as a south oriented flood flow channel moving floodwaters to a south oriented flood flow channel on the present day north oriented North Platte River alignment. Flood flow in the through valley was subsequently beheaded and reversed by headward erosion of the deep northeast oriented Yellowstone River valley to create the north oriented Powder River drainage routes. At about the same time headward erosion of the south-southeast oriented Casper Creek valley from the newly eroded east and southeast oriented North Platte River captured flood flow along southeast margin of the through valley. The north oriented Powder River drainage system and the east and southeast oriented North Platte River drainage system competed with each other to capture the flood flow in this region and in the end created the northeast oriented South Fork Powder River and northeast and east oriented Middle Fork Casper Creek drainage routes as floodwaters finally drained from the region.

South Fork Powder River-North Fork Casper Creek drainage divide area

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

Figure 7 illustrates the South Fork Powder River-North Fork Casper Creek drainage divide area north and east of figure 6 and includes an overlap area with figure 6. The map contour interval for figure 7 is 20 meters. The South Fork Powder River meanders in a north direction near the west edge of figure 7 before turning to flow in a northeast direction across the northwest corner of figure 7. North of figure 7 the South Fork Powder River flows to the north oriented Powder River. Reynolds Reservoir is located near the east edge of figure 7 (north of center). The North Fork Casper Creek flows in an east direction near the south center edge of figure 7 and is joined by a south oriented tributary flowing from Reynolds Reservoir and then turns to flow in a south direction to Gowin-Kesecker Lake and then turns to flow in an east and southeast direction to join the east oriented Middle Fork Casper Creek (south of figure 7) to form the south-southeast oriented Casper Creek, which then flows to the east and southeast oriented North Platte River. The north oriented stream seen in the northeast corner of figure 7 is Cloud Creek, which north of figure 7 flows to the South Fork Powder River and which will be seen again in figures 9 and 10. Anderson Draw is the north oriented South Fork Powder River tributary draining to the north center edge of figure 7. The drainage divide between the South Fork Powder River and the North Fork Casper Creek in figure 7 is an asymmetric drainage divide with a steeper and more rugged slope on the South Fork Powder River side. I suspect this asymmetric drainage divide was eroded at the time the Powder River valley and the North Platte River valley were competing with each other for floodwaters. If correctly interpreted what is now the broad and relatively shallow south oriented North Fork Casper Creek valley eroded headward from the newly eroded North Platte River valley along the south oriented flood flow (at that time the North Platte River valley probably was not as deep as it is now). Next there was a major reversal of flood flow in the Powder River Basin to the north of figure 7 and the South Fork Powder River valley eroded headward across the south oriented flood flow routes to capture the flood flow and to divert the floodwaters to newly formed and deeper north oriented Powder River valley. The deeper northeast oriented South Fork Powder River valley beheaded south oriented flood flow channels to the North Platte River valley. Floodwaters on north ends of the beheaded reversed flow direction to flow in a north direction to the deeper South Fork Powder River valley. However instead of becoming concentrated in deep valleys the north oriented flood flow moving moved more as sheets of floodwater. These north oriented sheets of water eroded the South Fork Powder River southeast valley wall headward until all floodwaters in the region had drained to one of the two competing drainage systems.

Detailed map of South Fork Powder River-North Fork Casper Creek drainage divide area

Figure 8: Detailed map of South Fork Powder River-North Fork Casper Creek 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 South Fork Powder River-North Fork Casper Creek drainage divide seen in less detail in figure 7. The map contour interval for figure 8 is 20 feet. Anderson Draw originates in section 3 (in southwest quadrant of figure 8) and drains in a north direction to the north edge of figure 8 (west half). In sections 14 and 15 a southwest oriented tributary joins Anderson Draw as a barbed tributary. North of figure 8 Anderson Draw drains to the northeast oriented South Fork Powder River. The North Fork Casper Creek originates in section 36 (east of the Anderson Draw headwaters) and flows in an east-northeast direction across sections 31, 32,and 33 and then in section 34 turns to flow in a south-southeast direction to the east edge of figure 8 (near southeast corner). South and east of figure 8 the North Fork Casper Creek is joined by the Middle Fork Casper Creek to form south-southeast oriented Casper Creek, which flows to the east and southeast oriented North Platte River. Figure 8 provides a detailed look at the South Fork Powder River-North Fork Casper Creek drainage divide. The drainage divide has been much more intensely eroded on the South Fork Powder River (or Anderson Draw) side than on the North Fork Casper Creek side. Shallow through valleys are eroded across the drainage divide. For example in section 36 west of the North Fork Casper Creek headwaters a shallow through valley links the east-northeast oriented North Fork Casper Creek valley with the north oriented Anderson Draw headwaters valley. The through valley floor at the deepest point has an elevation of between 5740 and 5760 feet. South of the through valley in section 2 elevations rise to 5837 feet and north of the through valley in section 25 elevations rise to more than 5880 feet. These elevations suggest the through valley is at least 77 feet deep. The through valley is a water-eroded feature and appears to have been eroded by east oriented flood flow to the North Fork Casper Creek valley that was subsequently beheaded by headward erosion of the deeper north oriented Anderson Draw valley. If so the Anderson Draw valley was being eroded headward across east oriented flood to the North Fork Casper Creek valley and the rugged topography on the Anderson Draw side of the drainage divide was caused by captured floodwaters as they changed direction to enter the actively eroding north oriented Anderson Draw valley. The southwest oriented Anderson Draw tributary valley may have been eroded by floodwaters stranded east of the actively eroding Anderson Draw valley. This interpretation is somewhat different from the interpretation given for the evidence seen in figure 7 so figures 9 and 10 look at Cloud Creek-North Fork Casper Creek drainage divide slightly east of figures 7 and  8 to see if additional clues can be found.

Cloud Creek-North Fork Casper Creek drainage divide area

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

Figure 9 illustrates the Cloud Creek-North Fork Casper Creek drainage divide area north and east of figure 7 and includes a large overlap area with figure 7. The map contour interval for figure 9 is 20 meters. The South Fork Powder River flows in a northeast direction from the west edge of figure 9 (north half) to the north edge of figure 9 (west half) and north of figure 9 joins the north oriented Powder River. Anderson Draw originates near the south edge of figure 9 (west half) and drains in a north direction in the west half of figure 9 to join the northeast oriented South Fork Powder River. The North Fork Casper Creek originates in section 36 just east of the Anderson Draw headwaters and flows in an east-northeast, southeast and south direction to the south center edge of figure 9. North of the south center edge of figure 9 is a south oriented North Fork Casper Creek tributary draining from Reynolds Reservoir. North of Reynolds Reservoir is the north rim of the south oriented North Fork Casper Creek drainage basin and the north oriented drainage basin on the other side is the Cloud Creek drainage basin. Cloud Creek originates just east of the center of figure 9 and flows in an east-northeast, north-northeast, northwest, and north direction to the north center edge of figure 9. North of figure 9 Cloud Creek flows to the north-northeast oriented South Fork Powder River. An old railroad grade is shown with a dashed black line east of Reynolds Reservoir. The old railroad grade crosses the Cloud Creek-North Fork Casper Creek drainage divide in a north-to-south oriented through valley linking the north oriented Cloud Creek valley with the south oriented North Fork Casper Creek valley. The through valley floor elevation is between 1700 and 1720 meters. Elevations east of the through valley and seen in figure 9 rise to more than 1740 meters and east of figure 9 rise to more than 1800 meters. Elevations west of the through valley (and seen in the west half of figure 9) rise to more than 1800 meters. These elevations suggest the through valley is a broad through valley extending from the west half of figure 9 to east of figure 9 that at its deepest points is at least 80 meters deep. This broad through valley provides evidence of a broad south oriented flood flow channel to the actively eroding east and southeast oriented North Platte River valley. The south oriented flood flow lowered the landscape as it stripped bedrock from the through valley floor, with at least 80 meters of erosion documented by the above described figure 9 evidence. Headward erosion of the deeper northeast oriented South Fork Powder River valley beheaded the south oriented flood flow channel. Floodwaters on the north end of the beheaded flood flow channel reversed flow direction to create the north oriented Cloud Creek drainage route. The new and deeper north oriented Cloud Creek valley then captured south oriented flood flow moving west of the actively eroding South Fork Powder River valley head. The captured floodwaters moved in an east-northeast direction to the north oriented Cloud Creek valley and created the east-northeast oriented Cloud Creek headwaters drainage route. Headward erosion of the South Fork Powder River valley next beheaded and reversed flood flow routes to the actively eroding east-northeast oriented Cloud Creek headwaters valley and created the north oriented Anderson Draw drainage route.

Detailed map of Cloud Creek-North Fork Casper Creek drainage divide area

Figure 10: Detailed map of Cloud Creek-North Fork Casper 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 Cloud Creek-North Fork Casper Creek drainage divide area seen in less detail in figure 9. The map contour interval for figure 10 is 20 feet. Reynolds Reservoir is located at corner of sections 23, 24, 25, and 26. South oriented drainage to and from Reynolds Reservoir flows to North Casper Creek with water eventually reaching the east and southeast oriented North Platte River. North of Reynolds Reservoir in section 13 are headwaters of north oriented tributaries to Cloud Creek. Cloud Creek flows in an east direction across the northwest corner of figure 9 before turning to flow in a northeast direction to the north edge of figure 9 (west half). North of figure 10 Cloud Creek turns to flow in a northwest and north direction to join the north-northeast oriented South Fork Powder River. An old railroad grade in sections 18 and 19 east of Reynolds Reservoir crosses the Cloud Creek-North Fork Casper Creek drainage divide using a through valley located at the corner of sections 13, 18, 19, and 24. The floor elevation of the through valley is between 5600 and 5620 feet. Proceeding west along the drainage divide elevations rise to the west edge of figure 10 with an elevation of 5907 feet being located one section west of figure 10. In the other direction elevations remain relatively low until four sections east of figure 10 at Statzer Point (a local butte) where elevations rise to 5902 feet. Assuming the 5900-foot high elevations define an erosion surface the south oriented floodwaters once flowed on the through valley used by the old railroad grade is approximately 300 feet deep and the distance across figure 10 and then to Statzer Point is approximately ten sections or ten miles. For that entire distance the drainage divide today is lower than 5900-foot elevation suggesting the floodwaters stripped the entire region of up to 300 feet of bedrock material in some areas. The drainage divide in the west half of figure 10 is somewhat different in that to the north are the east oriented Cloud Creek headwaters. The deep east oriented Cloud Creek headwaters valley eroded headward from the newly reversed Cloud Creek valley to capture south oriented flood flow still moving west of the actively eroding South Fork Powder River valley head. In doing so the east oriented Cloud Creek headwaters valley beheaded and reversed south oriented flood flow routes to actively eroding south oriented North Fork Casper Creek tributary valleys. Floodwaters on north ends of the beheaded flood flow routes were reversed to create the northwest, north, and northeast oriented Cloud Creek tributary routes seen in the northwest quadrant of figure 10. There were probably many additional flood flow movements, which with a more detailed study could be worked out. My goal in this essay is to simply describe the major flood flow movements and to demonstrate the drainage divide evidence is consistent with those major flood flow movements.

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.