Abstract:

This essay uses topographic map evidence to interpret landform origins in the region between Casper Creek and the North Platte River in Natrona County, Wyoming. The North Platte River flows in a north and northeast direction to the northwest end of the Laramie Mountains and then turns to flow in an east and southeast direction along the Laramie Mountains north and northeast flanks before flowing into Nebraska. The Middle Fork Casper Creek originates in the Rattlesnake Hills west of the Laramie Mountains and west of the northeast oriented North Platte River segment and flows in a northeast and east direction to join southeast oriented North Fork Casper Creek and to form south-southeast oriented Casper Creek, which then flows to the east oriented North Platte River north of the Laramie Mountains. Poison Spider Creek originates in the Rattlesnake Hills near the Middle Fork Casper Creek headwaters and flows in a northeast, east, and southeast direction to join the northeast oriented North Platte River as a barbed tributary. The Middle Fork Casper Creek, Poison Spider Creek, and other regional streams have eroded water gaps and wind gaps across hogback ridges and other structures while North Platte River has eroded deep water gaps across northwest extensions of Laramie Mountains structures. Through valleys link various stream valleys and provide evidence of previous water routes. Valley orientations, through valleys, water gaps and wind gaps, and barbed tributaries are interpreted to have formed during immense melt water floods, which deeply eroded the region as the Laramie Mountains and Rattlesnake Hills emerged. Floodwaters were derived from the western margin of a thick North American ice sheet and were flowing from western Canada to and across Wyoming. Emergence of the regional mountain ranges occurred as floodwaters deeply eroded surrounding regions and as ice sheet related crustal warping raised the mountain ranges relative to the adjacent basins. North oriented North Platte River segments originated as deep south oriented flood flow channels eroded headward between the emerging Laramie Mountains and the emerging Rattlesnake Hills. Headward erosion of a deeper southeast oriented flood flow channel along the northeast flank of the emerging Laramie Mountains proceeded around the north end of the Laramie Mountains where it captured flood flow moving to the south oriented flood flow channels west of the Laramie Mountains. Floodwaters on north ends of the beheaded flood flow channels reversed flow direction to create the north oriented North Platte River drainage route west of the Laramie Mountains. The deep North Platte River valley also captured flood flow from west of the emerging Bighorn Mountains and the captured flood flow moved in east and northeast directions to reach the newly eroded North Platte River valley. About the same time a flood flow reversal in the Powder River Basin to the north of the Laramie Mountains occurred when ice sheet melting opened up space in the deep “hole” the ice sheet had occupied and east and northeast oriented flood flow moving to the newly eroded North Platte River valley was also captured and diverted in a northeast direction to the newly formed north oriented Powder River drainage route. Headward erosion of the east oriented Casper Creek valley from the south-southeast oriented Casper Creek valley captured some northeast oriented flood flow routes to the Powder River valley and diverted floodwaters to the North Platte River valley. Flood flow reversals further to the west and emergence of mountain ranges ended all flood flow to the study region.

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 Casper Creek-North Platte River 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 Casper Creek-North Platte River drainage divide area landform evidence in Natrona County, Wyoming will be regarded as evidence supporting the “thick ice sheet that melted fast” paradigm.

Casper Creek-North Platte River drainage divide area location map

Figure 1: Casper Creek-North 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 Casper Creek-North Platte River drainage divide area in Natrona County, Wyoming and illustrates a region in central Wyoming. Casper is the largest city shown and is located south and east of the center of figure 1. The North Platte River flows in a northwest, northeast, and north direction from the south center edge of figure 1 to Seminoe Reservoir and then to Pathfinder Reservoir. From Pathfinder Dam the North Platte River flows in a north-northeast and northeast direction to the northwest end of the Laramie Mountains at Casper. At Casper the North Platte River turns to flow in an east and then southeast direction along the east side of the Laramie Mountains to the east edge of figure 1. East of figure 1 the North Platte River flows into Nebraska where it joins the South Platte River to form the east oriented Platte River. The Rattlesnake Hills are located near the center of figure 1 and are west of the north-northeast oriented North Platte River segment. Casper Creek originates in the Rattlesnake Hills and flows in a northeast, east, and south-southeast direction to join the North Platte River on the west edge of Casper. Poison Spider Creek originates in Rattlesnake Hills near the Casper Creek headwaters and flows in a northeast, east, and south-southeast direction to join the north-northeast oriented North Platte River as a barbed tributary. North of Casper Creek is the north-northeast oriented South Fork Powder River, which east of Kaycee joins the southeast oriented North Fork Powder River and 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 and joins the northeast oriented Yellowstone River. The North and Middle Forks of the Powder River originate in the southern Bighorn Mountains. East of the Bighorn Mountains is the Powder River Basin and west of the Powder River Basin is the Bighorn Basin. The Bighorn Basin is drained by the north oriented Bighorn River, which originates as the southeast oriented Wind River. The Wind River flows in a southeast direction from the figure 1 west edge (north half) between the Owl Creek Mountains and Wind River Range to Riverton in the Wind River Basin. At Riverton the Wind River turns to flow in a northeast and then north direction through Wind River Canyon (at east end of Owl Creek Mountains and between Boysen Reservoir and Thermopolis) to enter the Bighorn Basin and to become the Bighorn River. The Casper Creek-North Platte River drainage divide area investigated in this essay is located near the center of figure 1 and is south and east of Casper Creek and north and west of the North Platte River.

The north oriented North Platte River drainage route between the Rattlesnake Hills and Laramie Mountains originated as south oriented flood flow channels at a time when the Rattlesnake Hills, Laramie Mountains, and other regional mountain ranges were just beginning to emerge. Floodwaters were derived from the western margin of a thick North American ice sheet and were flowing 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 mountain ranges relative to adjacent basins and valleys. Ice sheet related crustal warping combined with deep glacial erosion also created a deep “hole” in which the massive ice sheet was located. Headward erosion of the deep southeast oriented North Platte River valley along the northeast side of the emerging Laramie Mountains eventually reached the Laramie Mountains northwest end and captured the south oriented flood flow moving from the Powder River Basin and Wind River Basin to the south oriented flood flow channels between the emerging Laramie Mountains and the emerging Rattlesnake Hills. Floodwaters on north ends of the beheaded flood channels reversed flow direction to create the north and north-northeast oriented North Platte River drainage route west of the Laramie Mountains. Headward erosion of the east-northeast and east oriented Sweetwater River valley south of the Rattlesnake Hills captured significant south oriented flood flow west of the newly reversed flood flow channel and delivered that captured flood flow to the newly reversed North Platte River drainage route. About the same time the deep northeast oriented Yellowstone River valley eroded headward across Montana (north of figure 1) to capture the south and southeast oriented flood flow moving to Wyoming. The deep Yellowstone River valley eroded headward from space at the south end of the deep “hole” the melting ice sheet was opening up and that was draining in a south direction east of figure 1. Yellowstone River valley headward erosion beheaded flood flow routes to Wyoming in sequence from east to west. Flood flow routes to the Powder River Basin were beheaded before flood flow routes crossing the emerging Bighorn Mountains and Bighorn Basin were beheaded. Floodwaters on north ends of the beheaded flood flow channels to the Powder River Basin reversed flood flow direction to create the north oriented Powder River drainage route, which captured southeast oriented still moving across the emerging Bighorn Mountains (see southeast oriented North Fork Powder River). The north-northeast oriented South Fork Powder River valley eroded headward from the deep north oriented Powder River valley to capture east and southeast oriented flood flow moving between the emerging Bighorn Mountains and the Rattlesnake Hills to the newly formed North Platte River drainage route. Headward erosion of the Poison Spider Creek valley and then of the Casper Creek valley captured some, but not all of the northeast oriented flood flow moving to the newly formed South Fork Powder River drainage route and diverted the captured floodwaters to the newly formed North Platte River drainage route. Headward erosion of the Yellowstone River valley subsequently beheaded all flood flow routes to the Bighorn Basin. Floodwaters on north ends of beheaded flood flow routes reversed flow direction to create the north oriented Bighorn River drainage route, which captured south and southeast oriented flood flow from further to the west (see Wind River and other southeast oriented Bighorn River tributaries). Ice sheet related crustal warping that was raising mountain ranges probably greatly aided in the massive central Wyoming flood flow capture and reversal events.

Detailed location map for Casper Creek-North Platte River drainage divide area

Figure 2: Detailed location map Casper Creek-North Platte River 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 Casper Creek-North Platte River drainage divide area in Natrona County, Wyoming and shows a region in central Wyoming. The North Platte River flows in a north-northeast and northeast direction from Alcova Reservoir (near the south edge of figure 2) to Casper and then turns to flow in an east direction to the east center edge of figure 2. East of figure 2 the North Platte River flows in a southeast direction to western Nebraska where it joins the South Platte River to form the east oriented Platte River. Casper Mountain (labeled in small print) is located south of Casper and could be considered the Laramie Mountains northwest end. The Rattlesnake Hills extend in a southeast direction from near the west center edge of figure 2 . The Ervay Basin is located north of the Rattlesnake Hills northwest end (near west edge of figure 2). The South Fork Powder River originates in the Ervay Basin and flows in a north-northeast and east-northeast direction to the town of Powder River and the turns to flow in a north and north-northeast direction to the north edge of figure 2. North of figure 2 the South Fork Powder River flows to the north oriented Powder River, which then flows into Montana to join the northeast oriented Yellowstone River. Wallace Creek is a northeast oriented South Fork Powder River tributary originating in the Rattlesnake Hills. The Middle Fork Casper Creek originates in the Rattlesnake Hills (near Garfield Peak) and flows in a northeast direction adjacent to and parallel to Wallace Creek and east of the town of Powder River turns to flow in an east direction to the towns of Natrona, Petrie, Bucknum, and Illco. At Illco the Middle Fork Casper Creek is joined by southeast oriented North Fork Casper Creek to form south-southeast oriented Casper Creek, which flows to the east oriented North Platte River at the west edge of the city of Casper. The South Fork Casper Creek is located east of the northeast oriented Middle Fork Casper Creek segment and south of the east oriented Middle Fork Casper Creek segment and flows in an east-northeast, northeast, and east direction to join south-southeast oriented Casper Creek near the town of Bishop. Poison Spider Creek headwaters are located near the Middle Fork Casper Creek headwaters in the Rattlesnake Hills with Poison Spider Creek flowing in a northeast and east direction to Emigrant Gap Ridge where Poison Spider Creek turns to flow in a south-southeast direction to join the northeast oriented North Platte River as a barbed tributary. Other south oriented barbed tributaries to the north oriented North Platte River can be seen near Alcova Reservoir. Also south oriented tributaries to the east oriented Sweetwater River are located south of Rattlesnake Hills. These south oriented streams and stream segments  are relics of south oriented flood flow channels that existed before the massive flood flow captures and flood flow reversals that created present day drainage routes.

Casper Creek-Poison Spider Creek drainage divide area  south

Figure 3: Casper Creek-Poison Spider 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 the Casper Creek-Poison Spider Creek drainage divide area. The map contour interval for figure 3 is 20 meters. Casper is the city straddling the east center edge of figure 3. The North Platte River meanders in an east-northeast direction from the south edge of figure 3 (west half) to the east edge of figure 3 (at north edge of Casper). Casper Creek flows in a south-southeast direction from the north edge of figure 3 (just east of airport) to join the North Platte River near the town of Mills. Poison Spider Creek flows in a southeast and south-southeast direction from the west center edge of figure to join the North Platte River as a barbed tributary near the south edge of figure 3. The north edge of Casper Mountain can just barely be seen in the southeast corner of figure 3. Casper Mountain is at the northwest end of the Laramie Mountains. Emigrant Gap Ridge extends in a southeast–to-northwest direction from south center edge of figure 3 to the northwest corner of figure 3 and could possibly be considered a low elevation extension of the much higher Laramie Mountains. Emigrant Gap is located in the west center region of figure 3 and is a wind gap cut into the northwest-to-southeast oriented ridge. The elevation of the Emigrant Gap floor is between 1700 and 1720 meters. Emigrant Gap Ridge to the southeast rises to more than 1840 meters and to the northwest to 1811 meters suggesting the Emigrant Gap depth is approximately 100 meters. Perhaps just as intriguing is the North Platte River water gap eroded across Emigrant Gap Ridge in the south center area of figure 3. The river elevation in the water gap area is less than 1580 meters. Emigrant Gap Ridge to the northwest of the water gap rises to more 1840 meters and elevations on Casper Mountain to the southeast of the water gap (and south of figure 3) rise to 2475 meters. Using the Emigrant Gap Ridge elevation the water gap is at least 260 meters deep. Both the water gap and the wind gap are water-eroded features and the erosion began at a time when Emigrant Gap Ridge did not stand high above surrounding regions. Emigrant Gap Ridge was either buried by bedrock materials that have since been removed or Emigrant Gap Ridge was raised as water eroded the gaps, or some combination of these two possibilities occurred. Probably the gaps were initiated by south oriented flood flow from the Powder River Basin that was flowing to a south oriented flood flow channel on the present day north oriented North Platte River alignment south of figure 3. The south-southeast oriented Poison Spider Creek valley was probably eroded headward along the southwest flank of the emerging Emigrant Gap Ridge by floodwaters flowing to that south oriented flood flow channel on the present day north oriented North Platte River alignment. The flood flow was then captured by headward erosion of the much deeper east and southeast oriented North Platte River valley, which had eroded headward along the northeast side of the Laramie Mountains to capture the south oriented flood flow flowing across the Powder River Basin. Flood flow through the water gap was reversed to create the present day north and northeast oriented North Platte River drainage route and southwest oriented flood flow through Emigrant Gap ended.

Detailed map of Emigrant Gap Ridge water gap area

Figure 4: Detailed map of Emigrant Gap Ridge water gap area. United States Geological Survey map digitally presented using National Geographic Society TOPO software.

Figure 4 provides a detailed topographic map of the Emigrant Gap Ridge water gap area. The map contour interval for figure 4 is 20 feet. The North Platte River flows in a northeast direction from the southwest corner of figure 4 to the east edge of figure 4 (north half). Emigrant Gap Ridge is northwest-to-southeast oriented ridge extending from the northwest corner of figure 4 to the south center edge area of figure 4. South of Emigrant Gap Ridge and seen along the south edge of the southeast quadrant of figure 4 are much higher elevations at the northwest end of the Laramie Mountains. The Emigrant Gap Ridge water gap is located in sections 25, 30, 31, and 36 and is where the North Platte River has eroded a deep valley across Emigrant Gap Ridge. The river elevation in the water gap is less than 5180 feet. Elevations in section 23 (near northwest corner of figure 4) rise to 6023 feet while much higher elevations are found south and east of figure 4. These elevations suggest the water gap is at least 840 feet deep. To erode the water gap Emigrant Gap Ridge was either raised at least 840 feet after the river course was established or at least 840 of erosion has occurred upstream from the Emigrant Gap Ridge (or some combination of the two possibilities has occurred). Whichever interpretation is correct the figure 4 evidence suggests large volumes of water flowed through the water gap to erode the incised meanders. Note how the deepest part of the water gap is oriented in a north-northeast direction and the North Platte River valley immediately downstream is oriented in more of an east direction. I suspect this deepest part of the water gap was initiated as a south-southwest oriented flood flow channel to a south oriented flood flow channel on the present day north oriented North Plate River alignment south and west of figure 4. Headward erosion of the much deeper southeast and east oriented North Platte River valley (which eroded headward along the east side of the Laramie Mountains) beheaded the south-southwest oriented flood flow channel in region of sections 19, 20, 29, and 30. Floodwaters on the north end of the beheaded flood flow channel then reversed flow direction to flow toward the much deeper east oriented North Platte River valley and in doing so captured floodwaters flowing in a south-southeast flood flow channel on the Poison Spider Creek alignment and caused a major reversal of the flood flow channel on the present day north oriented North Platte River alignment south and west of figure 4.

Poison Spider Creek-Iron Creek drainage divide area

Figure 5: Poison Spider Creek-Iron Creek drainage divide area. United States Geological Survey map digitally presented using National Geographic Society TOPO software.

Figure 5 illustrates the Poison Spider Creek-Iron Creek drainage divide area and is located south and west of figure 3 and there is an overlap area with figure 3. The map contour interval for figure 5 is 20 meters. Emigrant Gap Ridge is located in the northeast corner region of figure 5 and Emigrant Gap can be seen near the north edge of figure 5. The North Platte River makes a large meander and then flows in a northeast, north, east, and northeast direction from the south edge of figure 5 (east half) to the Emigrant Gap Ridge water gap just north of the east center edge of figure 5. Poison Spider Creek flows in an east direction from the near the northwest corner of figure 5 to near Emigrant Gap Ridge and then turns to flow in a south-southeast direction to join the North Platte River near Bessemer Bend as a barbed tributary. South of Bessemer Bend the North Platte River is oriented in a north direction as it flows through the deep Bessemer Narrows water gap eroded between Coal Mountain to the east and Bessemer Mountain to the west. The river elevation in the Bessemer Narrows water gap is less than 1600 meters. Bessemer Mountain rises to 1945 meters while Coal Mountain rises much higher suggesting the water gap is at least 345 meters deep. The Bessemer Narrows water gap was probably initiated as a south oriented flood flow channel that was beheaded and reversed when headward erosion of the east oriented North Platte River valley beheaded the flood flow channel at the north end of the Emigrant Gap Ridge water gap seen in figures 3 and 4. Perhaps more intriguing is the much broader gap between Bessemer Mountain and Oil Mountain. Today east and east-northeast oriented Iron Creek flows through this broad water gap. Iron Creek as seen in figure 5 has no large drainage basin and did not erode this broad valley. South of Iron Creek is east-northeast, east, and southeast oriented Poison Spring Creek. Note how the broad valley is actually a north-to-south oriented through valley crossed today by the Poison Spider Creek valley, Iron Creek valley, and the Poison Spring Creek valley. This through valley may have originated as a south oriented flood flow channel moving floodwaters to the south oriented flood flow channel on the North Platte River alignment south of figure 5. The south oriented flood flow was captured by the reversal of flood flow that occurred when headward erosion of the much deeper east oriented North Platte River valley beheaded a south-southwest oriented flood flow channel as seen in figures 3 and 4. The Poison Spring Creek valley and then the Iron Creek valley eroded headward from the newly reversed flood flow channel to capture the south oriented flood flow. Next the east oriented Poison Spider Creek valley eroded headward from the south oriented flood flow channel to capture the south oriented flood flow in the region west of Oil Mountain. Soon thereafter headward erosion of the east and northeast oriented Middle Fork Casper Creek valley north of figure 5 captured the south oriented flood flow and ended all south, southeast, and east oriented flood flow to the region seen in figure 5.

Detailed map of Bessemer Narrows water gap area

Figure 6: Detailed map of Bessemer Narrows water gap area. United States Geological Survey map digitally presented using National Geographic Society TOPO software.

Figure 6 provides a detailed topographic map of the Bessemer Narrows water gap area seen in less detail in figure 5. The map contour interval for figure 6 is 20 feet. The North Platte River meanders into and out of the southwest corner region of figure 6 and then flows in a northeast direction from the south center edge of figure 6 to the north oriented Bessemer Narrows water gap and next makes a northeast jog before turning to flow in a northwest and north direction around Bessemer Bend to the north edge of figure 6. Poison Spring Creek flows in an east-southeast and south direction from the west edge of figure 6 (south half) to join the North Platte River south of figure 6 (west half). The North Platte River crosses the 5200-foot contour line just before entering the Bessemer Narrows water gap. Red Butte on Bessemer Mountain has an elevation of 6372 feet and elevations on Coal Mountain are much higher suggesting the Bessemer Narrows water gap is at least 1172 feet deep. This deep water gap is rather intriguing because in the northwest quadrant of figure 6 a through valley links the Iron Creek valley (north of figure 6) with the Poison Spring Creek valley (an irrigation canal west of figure 6 and seen in figure 5 makes use of the through valley). The through valley floor elevation is slightly higher than 5400 feet or only about 200 feet higher than the Bessemer Narrows water gap floor elevation. The through valley appears to be oriented in a south-southwest direction and there does not appear to be evidence that large volumes of south-southwest oriented flood flow in the through valley made a U-turn to flow in a north-northeast direction to the Bessemer Narrows water gap. While not seen in figures 5 and 6 south of the southwest corner of figure 6 is a north oriented North Platte River valley segment seen in figures 1 and 2. The through valley probably supplied  flood flow to a south oriented flood flow channel on that north oriented North Platte River segment alignment. Reversals of flood flow in the flood flow channel on the Emigrant Gap Ridge water gap and the Bessemer Narrows water gap alignment probably resulted in headward erosion of east oriented tributary valleys north of region seen in figure 6 that beheaded the south oriented flood flow in the through valley before large volumes of flood water made a U-turn around the south side of Bessemer Mountain.

South Fork Casper Creek-Poison Spider Creek drainage divide area

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

Figure 7 illustrates the South Fork Casper Creek-Poison Spider Creek drainage divide area north and west of figure 5 and includes an overlap area with figure 5. The map contour interval for figure 7 is 20 meters. Pine Mountain is the uplifted structure in the north center area of figure 7 and appears to be a northwest continuation of the geologic structures seen on the Oil Mountain and Bessemer Mountain alignment in figure 5. Poison Spider Creek flows in an east direction near the south edge of figure 7. East of figure 7 Poison Spider Creek turns to flow in a south-southeast direction along the Emigrant Ridge southwest flank to reach the northeast oriented North Platte River as a barbed tributary. The South Fork Casper Creek flows in an east and northeast direction from the west edge of figure 7 (slightly south of center) to the east edge of figure 7 (north half). East of figure 7 the South Fork Casper Creek has eroded a shallow water gap across Emigrant Ridge and then turns to flow in an east direction to join south-southeast oriented Casper Creek. Several through valleys link the South Fork Casper Creek valley with the Poison Spider Creek valley and their orientations suggest they were eroded as diverging and converging flood flow channels. Perhaps the most obvious of the through valleys extends from the South Fork Casper Creek valley at the center of figure 78 in a southeast direction to the Poison Spider Creek valley. The through valley floor elevation is between 1760 and 1780 meters. West of the through valley elevations also rise to more than 1860 meters. East and north of the through valley is a northwest to southeast oriented ridge with elevations rising to more than 1860 meters, which suggests the through valley is at least 80 meters deep. A second northwest-to-southeast oriented through valley is located west of the northwest-to-southeast oriented ridge and is bounded on the east by Emigrant Gap Ridge (not seen in figure 7). This second through valley has a floor elevation of between 1720 and 1740 meters. Elevations on Emigrant Gap ridge to the east rise to more than 1800 meters suggesting the through valley is at least 60 meters deep. A third through valley is oriented in a southwest to northeast direction and extends from the Poison Spider Creek valley near the southwest corner of figure 7 to the South Fork Casper Creek valley near the center of figure 7. The floor elevation of this third through valley is between 1800 and 1820 meters. Elevations both east and west of the through valley rise to more than 1860 meters suggesting the through valley is at least 40 meters deep. The through valleys are water-eroded features and provide evidence of an east oriented anastomosing channel complex that once crossed the region.

Detailed map of South Fork Casper Creek-Poison Spider Creek drainage divide area

Figure 8: Detailed map of South Fork Casper Creek-Poison Spider 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 Casper Creek-Poison Spider Creek drainage divide seen in less detail in figure 7 above. The map contour interval for figure 8 is 20 feet. The South Fork Casper Creek can be seen flowing in an east direction near the north edge of the northwest quadrant of figure 8. The Poison Spider Oil Field is located in the southeast quadrant of figure 8 and is located on a northwest to southeast oriented ridge. Poison Spider Creek flows in an east direction south of figure 8 and has eroded a water gap across the northwest to southeast oriented ridge. The southeast and south oriented stream flowing from section 32 to the south center edge of figure 8 is a Poison Spider Creek tributary and is draining the southeast end of a northwest to southeast oriented through valley, which links the South Fork Casper Creek valley with the Poison Spider Creek valley. The lowest point on South Fork Casper Creek-Poison Spider Creek drainage divide in the through valley is located in section 32 and has an elevation of between 5820 and 5840 feet. The high point on the ridge to the east has an elevation 6125 feet and slightly higher elevations can be seen on the ridge to the west. These elevations suggest the through valley is almost 300 feet deep. The through valley orientation probably follows the geologic structure orientation, however the through valley is also a water-eroded valley and was eroded by large volumes of water flowing from the present day east oriented South Fork Casper Creek valley to the present day east oriented Poison Spider Creek valley. A segment of a parallel northwest to southeast oriented through valley can be seen in the northeast corner region of figure 8. These through valleys can probably be best explained in the context of an anastomosing complex of flood flow channels that eroded a maze of diverging and converging valleys into the regional landscape. Headward erosion of the deep east and southeast oriented North Platte River valley then captured at least some of the flood flow channels enabling headward erosion of still deeper flood flow channels that beheaded shallower diverging flood flow channels to create the regional drainage system seen today.

Middle Fork Casper Creek-Poison Spider Creek drainage divide area

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

Figure 9 illustrates the Middle Fork Casper Creek-Poison Spider Creek drainage divide area south and west of figure 7 and includes an overlap area with figure 7. The map contour interval for figure 9 is 20 meters. The Rattlesnake Hills northeast flank can be seen in the southwest corner of figure 9. The Middle Fork Casper Creek originates a short distance west of the southwest corner of figure 9 and flows in a northeast and north-northeast direction from the west edge of figure 9 (in the Rattlesnake Hills area) to the north edge of figure 9 (west of center). Poison Spider Creek flows in a northeast direction in Eagles Nest Canyon (in the Rattlesnake Hills area) and then in a northeast and east-northeast direction to the east edge of figure 9 (north of center). The South Fork Casper Creek originates west of the center of figure 9 and flows in a northeast direction almost to the north edge of figure 9 and then turns to flow in an east direction to near the northeast corner of figure 9. West of figure 9 are northeast oriented headwaters of Wallace Creek, which flows to the northeast and north-northeast oriented South Fork Powder River. The Middle Fork Casper Creek and South Fork Casper Creek originate in the same general region and flow along diverging routes, which ultimately converge where Casper Creek joins the North Platte River. At one time large volumes of water flowed from the Rattlesnake Hills area in a northeast direction to what was probably a deep north oriented valley that was eroding headward from the Powder River Basin (more specifically the South Fork Powder River valley). At that time the Rattlesnake Hills had not emerged and did not stand high above surrounding regions and the floodwaters probably moved across what is today a major topographic barrier. While the flood flow was probably initially captured by headward erosion of the deep north-northeast oriented South Fork Powder River valley, headward erosion of the deeper North Platte River valley east and north of the Laramie Range reached the region at about the same time and headward erosion of the south-southeast oriented Casper Creek valley captured some of the flood flow channels, which had been moving floodwaters to the South Fork Powder River valley. Flood flow on the Poison Spider Creek alignment was probably first captured by headward erosion of a south oriented flood flow channel west of the Laramie Mountains, but then that south oriented flood flow channel was beheaded and reversed to flow to the deeper east and southeast oriented North Platte River valley at the Laramie Mountains northwest end. The region east and north of the Rattlesnake Mountains was deeply eroded by flood flow moving across it and it is possible crustal warping was raising the Rattlesnake Mountains as floodwaters flowed across them. Emergence of the Rattlesnake Mountains combined with flood flow reversals west of figure 9 ended all flood flow across the region seen in figure 9.

Detailed map of Middle Fork Casper Creek-Poison Spider Creek drainage divide area

Figure 10: Detailed map of Middle Fork Casper Creek-Poison Spider 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 Middle Fork Casper Creek-Poison Spider Creek drainage divide area seen in less detail in figure 9. The map contour interval for figure 10 is 20 feet. The northeast edge of the northwest to southeast oriented Rattlesnake Hills can be seen in the southwest corner of figure 10. The South Fork Casper Creek (“Creek” in figure 10) flows in a northeast and north direction from the west center edge of figure 10 to the north edge of figure 10 (in section 19 near northwest corner). North of figure 10 the South Fork Casper Creek turns to flow in a northeast and east direction to join south-southeast oriented Casper Creek, which then flows to the east and southeast oriented North Platte River. Stinking Water Creek flows in a north-northeast direction from near the southwest corner of figure 10 to the north edge of figure 10 (in section 20) and joins the South Fork Casper Creek north of figure 10. Poison Spider Creek flows in a north-northeast and northeast direction from the south center edge of figure 10 to the east edge of figure 10 (north half) and east of figure 10 turns to flow in an east and south-southeast direction to join the northeast oriented North Platte River as a barbed tributary. Through valleys link the South Fork Casper Creek valley with the Stinking Water Creek valley and also with the Poison Spider Creek valley. For example in the northeast corner of section 31 a road is located in a northwest to southeast oriented through valley linking the South Fork Casper Creek valley with the Stinking Water Creek valley. The through valley floor elevation is between 6460 and 6480 feet. Elevations in the northeast corner of section 30 to the north rise to 6556 feet and much higher elevations are located to the south of the through valley.  These elevations suggest the through valley is at least 76 feet deep. A much deeper through valley is located in section 28 and links the Stinking Water Creek valley with the Poison Spider Creek valley. The through valley floor elevation is between 6520 and 6540 feet. Elevations in section 27 on the northeast side of the through valley rise to more than 6760 feet suggesting the through valley is at least 220 feet deep. Study of the region in figure 10 reveals many other through valleys of varying depths and orientations. While many of the through valley follow the orientations of the local geologic structures some through valley appear to cross the geologic structure orientations. The through valleys provide evidence of an anastomosing complex of flood flow channels that eroded the region north and east of the Rattlesnake Hills.

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.