North Platte River-Sweetwater River drainage divide area landform origins in the Rattlesnake Hills, Natrona County Wyoming, USA

Authors

Abstract:

This essay uses topographic map evidence to interpret landform origins in the region between North Platte River tributaries and the Sweetwater River in the Rattlesnake Hills in Natrona County, Wyoming. The North Platte River flows in a north and northeast direction between the Rattlesnake Hills to the west and the Laramie Mountains to the east and then turns to flow in an east and southeast direction along the Laramie Mountains north and northeast flank before flowing into Nebraska, The Sweetwater  River is an east and south oriented river located south of the northwest to southeast oriented Rattlesnake Hills and joins the north oriented North Platte River as a barbed tributary. The Rattlesnake Hills northeast flank is drained by northeast, east, and south oriented North Platte River tributaries. Through valleys or passes cross the drainage divide between the northeast, east, and south oriented North Platte River tributary valleys and south oriented Sweetwater River tributary valleys. These through valley or passes are interpreted to have been eroded by south oriented melt water floods flowing to what was at that time the actively eroding east and south oriented Sweetwater River valley, which was eroding headward from a south oriented flood flow channel on the present day north oriented North Platte River alignment. At that time the region north and east of the Rattlesnake Hills had not been eroded and the northeast, east, and south oriented North Platte River tributary valleys did not exist. Floodwaters were derived from the western margin of a thick North American ice sheet and were flowing in a south direction from western Canada to and across Wyoming. At least initially regional mountain ranges had not emerged and floodwaters could freely flow across what are today major mountain barriers. Mountain ranges emerged as floodwaters deeply eroded surrounding regions and as ice sheet related crustal warping raised the mountain ranges relative to adjacent areas. The Laramie Mountains emerged as deep south-oriented flood flow channels eroded headward both east and west of the emerging mountain range. Headward erosion of a succession of east and northeast oriented valleys from the south oriented flood flow channel between the Rattlesnake Hills and Laramie Mountains beheaded south oriented flood flow routes crossing the emerging Rattlesnake Hills and diverted floodwaters to the south oriented flood flow channel on the present day north oriented North Platte River alignment. Headward erosion of a deeper North Platte River valley along the northeast and north flanks of the emerging Laramie Mountains enabled the deeper valley to erode headward in a northeast direction west of the Laramie Mountains where it beheaded the south oriented flood flow channel between the Rattlesnake Hills and Laramie Mountains. 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 Mountains. Ice sheet related crustal warping that was raising Rocky Mountain ranges further to south probably greatly aided in the North Platte River flood flow reversal west of the Laramie Mountains.

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

North Platte River-Sweetwater River drainage divide area location map

Figure 1: North Platte River-Sweetwater 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 North Platte River-Sweetwater River drainage divide area in the Rattlesnake Hills in Natrona County, Wyoming and illustrates a region in central Wyoming. Casper is the largest city shown and is located north and east of the center of figure 1. The Laramie Mountains extend in a southeast and south direction from near Casper to the south edge of figure 1 (east half). The Rattlesnake Hills are located west of the Laramie Mountains northwest end and are oriented in a northwest to southeast direction. The Granite Mountains are located south and west of the Rattlesnake Hills. The North Platte River flows in a north direction from the south edge of figure 1 (slightly west of center) to Seminoe Reservoir, Pathfinder Reservoir, and Alcova Reservoir and then turns to flow in a northeast direction to Casper. From Casper the North Platte River turns to flow in an east, south, east, and southeast direction to the east edge of figure 1. East of figure 1 the North Platte River flows in a southeast direction to Nebraska where it joins the South Platte River to form the Platte River. Note how the north and northeast oriented North Platte River in the Alcova Reservoir area is flowing between the Rattlesnake Hills and the Laramie Mountains northwest end. Also note how the east, south, and southeast North Platte River route east of Casper is located near the north and northeast flanks of the Laramie Mountains. The Sweetwater River is not labeled in figure 1 but is the east oriented stream flowing from the west edge of figure 1 (slightly south of center) between the Granite Mountains and Green Mountains to Independence Rock and then making a turn to the south to join the north oriented North Platte River at Pathfinder Reservoir. Casper Creek and Poison Spider Creek are northeast, east, and south-southeast oriented North Platte River tributaries originating on the Rattlesnake Hills northeast flank. The South Fork Powder River originates near the Rattlesnake Hills northwest end and flows in a northeast direction to the town of Powder River and then in a north-northeast direction to the north center edge of figure 1. The North Platte River-Sweetwater River drainage divide area investigated in this essay is bounded on the east by the North Platte River, on the south by the Sweetwater River, on the north by the Casper Creek and Poison Spider Creek headwaters, and on the west by the South Fork Powder River headwaters.

The North Platte River and several other streams seen in figure 1 first flow in one direction and then turn to flow in a completely opposite direction. Major direction changes in the present day drainage routes occurred as the drainage routes evolved during massive south and southeast oriented melt water floods, which flowed across the entire region seen in figure 1. Floodwaters were derived from the western margin of a thick North American ice sheet and were flowing from western Canada to and across Wyoming. At least initially Wyoming and other regional mountain ranges had not emerged and floodwaters could freely flow across what are today major mountain barriers. The mountain ranges emerged as floodwaters deeply eroded surrounding regions and as ice sheet related crustal warping raised the mountain ranges relatively to the adjacent regions. Ice sheet related crustal warping and deep glacial erosion also created a deep “hole” in which the huge ice sheet was located. The North Platte River history began as south and southeast oriented flood channels eroded headward both east and west of the emerging Laramie Mountains. The south oriented flood flow channel west of the Laramie Mountains was located between the present day Rattlesnake Hills and Laramie Mountains and the east oriented Sweetwater River valley may have eroded headward from that south oriented flood flow channel to capture south oriented flood flow moving west of the emerging Rattlesnake Hills. The flood flow channel east of the emerging Laramie Mountains captured south and southeast oriented flood flow that had been flowing across the emerging mountain range and eroded headward east and north of the present day mountain range to eventually reach the Laramie Mountains northwest end where it then beheaded a shallower south oriented flood flow channel to the south oriented flood flow channel eroding headward west of the Laramie Mountains. Floodwaters on the north end of the beheaded flood flow reversed flow direction to flow to the much deeper east, south, and southeast oriented North Platte River valley north and east of the Laramie Mountains. Reversed flood flow between the Rattlesnake Hills and Laramie Mountains captured the east and south oriented Sweetwater River flood flow channel. Drainage routes in the Powder River Basin north and east of Casper were reversed when headward erosion of the deep northeast oriented Yellowstone River valley in Montana eroded headward across the south oriented flood flow routes crossing the Powder River Basin. Floodwaters on north ends of the beheaded flood flow routes reversed flow direction to create the north oriented Powder River drainage system and to divert the captured floodwaters into space at the south end of the deep “hole” the melting ice sheet was opening up. The following illustrations and discussions describe detailed evidence supporting this melt water flood origin interpretation and also provide evidence of some the many flood flow capture and flood flow reversals that took place.

Detailed location map for North Platte River-Sweetwater River drainage divide area

Figure 2: Detailed location map North Platte River-Sweetwater River drainage divide area. United States Geological Survey map digitally presented using National Geographic Society TOPO software.

Figure 2 provides a detailed location map for the North Platte River-Sweetwater River drainage divide area in the Rattlesnake Hills in Natrona County, Wyoming and shows a region in central Wyoming. Pathfinder Reservoir straddles the south center edge area of figure 2. The North Platte River flows from the eastern end of Pathfinder Reservoir in an east and north direction to Alcova Reservoir and then flows in a north-northeast direction, although with north and east jogs, to Casper where the North Platte River turns to flow in an east direction to flow to the east edge of figure 2. East of figure 2 the North Platte River turns to flow in more of a southeast direction near the Laramie Mountains northeast flank and then to flow into Nebraska and the east oriented Platte River. Casper Mountain (labeled in small letters) is located south of Casper and could be considered the Laramie Mountains northwest end. The Sweetwater River flows in an east direction from the southwest corner of figure 2 along and across the south edge of figure 2 to Independence Rock and Pathfinder Reservoir. Most of the Pathfinder Reservoir area seen in figure 2 is flooding the Sweetwater River valley. Note how the Sweetwater River turns to flow in a south direction to join the north oriented North Platte River as a barbed tributary. The Rattlesnake Hills are labeled and extend in a northwest to southeast direction across the west center area of figure 2. Dry Creek is a southeast, south, and southeast oriented stream flowing along the southwest side of the Rattlesnake Hills to join the Sweetwater River near the west end of Pathfinder Reservoir. Cottonwood Creek is a southeast and south-southwest oriented Dry Creek tributary. Further to the east-southeast oriented Horse Creek flows to southwest oriented Fish Creek, which joins the Sweetwater River at Pathfinder Reservoir. North Platte River tributaries of interest east of the Rattlesnake Hills include Eagle Creek, which flows in a southwest, south, and east direction to join the north oriented North Platte River at Alcova. Poison Spring Creek originates near the Rattlesnake Hills east end and flows in a northeast, east-northeast, and south direction to join the North Platte River as a barbed tributary. Poison Spider Creek originates in the Rattlesnake Hills and flows in a northeast, east, and south-southeast direction to join the north oriented North Platte River as a barbed tributary. The Middle Fork Casper Creek originates near Garfield Peak in the Rattlesnake Hills and flows in a northeast direction to the town of Natrona where it turns to flow in an east direction to the town of Illco where it joins southeast oriented North Fork Casper Creek and forms south-southeast oriented Casper Creek, which joins the east oriented North Platte River at Mills (just west of Casper). North and west of Garfield Peak are northeast oriented South Fork Powder River headwaters with the South Fork Powder River flowing to the town of Powder River and then in a north and north-northeast direction to join the north oriented Powder River (north of figure 2). Evidence of a massive flood flow reversal can be seen in figure 2 in the form of the south oriented Sweetwater River, Poison Spring Creek, and Poison Spider Creek drainage routes as they join the north oriented North Platte River as barbed tributaries.

Fish Creek-North Platte River drainage divide area  

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

Figure 3 provides a topographic map of Fish Creek-North Platte River drainage divide area. The map contour interval for figure 3 is 20 meters. Alcova Reservoir straddles the south edge of figure 3 (slightly east of center) and the North Platte River flows in a northeast direction from Alcova Dam to the east center edge of figure 3 and then in a north direction to the northeast corner of figure 3. Several southeast oriented streams join the northeast oriented North Platte River as barbed tributaries in the region downstream from Alcova. From south to north these streams include Eagle Creek, Blue Gulch, Mowry Draw, Hogback Draw, S Gulch, Schrader Gulch, and Lone Tree Gulch. With the exception of Eagle Creek these streams originate on the east side of a high north to south oriented hogback ridge. The west-southwest oriented slope in the west half of figure 3 appears to form the hogback dip slope. The North Platte River has eroded a 400-meter deep valley across whatever structure formed this hogback ridge. The southeast oriented barbed tributaries suggest the valley was eroded by south oriented flood flow, not by a north oriented drainage route. A close look at the Eagle Creek drainage route shows Eagle Creek originates as southwest oriented stream flowing down the hogback ridge dip slope, which flows to a south-southeast and east-southeast oriented valley. Further north Blue Gulch originates as a south oriented drainage route west of Flat Top before turning to drain in a southeast direction to join the northeast oriented North Platte River as a barbed tributary. In the west half of figure 3 Fish Creek flows in a south and southwest direction to the west center edge of figure 3 and west of figure 3 joins south oriented Horse Creek to flow to the flooded east and south oriented Sweetwater Creek valley at Pathfinder Reservoir. Shell Creek is the southwest and south oriented Fish Creek tributary near the northwest corner of figure 3. While Fish Creek, Shell Creek, and the southwest oriented Eagle Creek headwaters are flowing on the dip slope surface Eagle Creek turns to flow across the structure and Fish Creek joins the east and south oriented Sweetwater River, which also flows across the structure. These barbed tributaries flowing across the structure provide convincing evidence the present day north oriented North Platte River valley was oriented in a south direction at the time the drainage routes in figure 3 were formed. Large volumes of south oriented flood flow were required to erode the deep North Platte River valley. The flow direction in the North Platte River valley was reversed when headward erosion of the deeper southeast and east oriented North Platte River valley along the Laramie Mountains northeast and north flanks beheaded a south oriented flood flow channel supplying floodwaters to the south oriented flood flow channel responsible for eroding the deep valley seen in figure 3. 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 Mountains. Ice sheet related crustal warping that was raising regional mountain ranges and other geologic structures in regions south of figure 3 probably greatly aided in the flood reversal. Also, while in my simplified discussions only one flood flow reversal is mentioned the flood flow reversal actually took place in multiple steps, which can traced by looking at the various jogs the north oriented North Platte River route makes.

Detailed map of Eagle Creek-Blue Gulch drainage divide area

Figure 4: Detailed map of Eagle Creek-Blue Gulch 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 Eagle Creek-Blue Gulch drainage divide area. The map contour interval for figure 4 is 20 feet. Eagle Creek flows in a southwest direction across the northwest corner of figure 4 and then turns to flow in a south direction near the west edge of figure 4 before turning to flow in a southeast direction into section 17. In section 17 Eagle Creek turns again to flow in an east and southeast direction to the south edge of figure 4 (east half) and south and east of figure 4 Eagle Creek joins the northeast oriented North Platte River as a barbed tributary. Note the multiple southwest oriented Eagle Creek tributaries flowing down the dip slope surface. Blue Gulch flows from section 34 (west of Flat Top) in a south direction to the section 3 northeast corner and then turns to flow in a southeast direction to flow to the east edge of figure 4 (south half) and east of figure 4 joins the northeast oriented North Platte River as a barbed tributary. The southwest oriented Eagle Creek headwaters and tributaries are flowing down the southwest dipping hogback dip slope surface, but Eagle Creek makes an abrupt turn to erode a deep water gap across the dipping strata to reach the North Platte River valley. Large volumes of water were required to erode the Eagle Creek water gap and those large volumes of water are best explained in the context of massive south oriented floods as a deep south oriented was eroded to the east of figure 4 on the present day north oriented North Platte River alignment. Initially floodwaters crossed the top of the high southwest dipping hogback ridge to reach the south and east oriented Eagle Creek valley and also eroded the south oriented Blue Gulch headwaters valley west of Flat Top in section 34. At that time the floodwaters were still eroding deep south-oriented flood flow channel on the present day north oriented North Platte River valley alignment and the region north of figure 4 was at least as high as the top of the hogback ridge. Headward erosion of the south oriented flood flow channel valley and the east and southeast oriented Lone Tree Gulch valley from it (north of figure 4) beheaded the south oriented flood flow to the actively eroding Blue Gulch valley. Flood flow on the north oriented North Platte River valley alignment was subsequently beheaded and reversed at some point after the deep North Platte River valley seen in figure 3 had been eroded and the North Platte River valley was probably deepened by north oriented flood flow after the flood flow reversal. The north oriented flood flow in addition to being a reversal of trapped floodwaters that had already flowed in a south direction and that were being blocked by crustal warping raising mountains to the south probably was captured south oriented flood flow from further to the west that the east oriented Sweetwater River valley had captured.

Poison Spring Creek-Fish Creek drainage divide area

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

Figure 5 illustrates the Poison Spring Creek-Fish Creek drainage divide area and is located north and west of figure 3 and there is an overlap area with figure 3. The map contour interval for figure 5 is 20 meters. The north and northeast oriented North Platte River valley can just barely near the southeast corner of figure 5. Lone Tree Gulch drains in an east direction north of Flat Top in the southeast quadrant of figure 5 and east of figure 5 turns to flow in a southeast direction to join the northeast oriented North Platte River as a barbed tributary. Further north in the east half of figure 5 are east-northeast oriented Willow Creek and east-northeast oriented Poison Spring Creek. East of figure 5 Willow Creek joins Poison Spring Creek and Poison Spring Creek then turns to flow in a south direction to join the north oriented North Platte River as a barbed tributary. South of the Poison Spring Creek headwaters near the center of figure 5 are south oriented headwaters of Fish Creek, which after flowing in a south direction turns to flow in a southwest direction to the southwest corner of figure 5. At the southwest corner of figure 5 Fish Creek joins south oriented Horse Creek, which flows to the east and south oriented Sweetwater River located south of figure 5. The Poison Spring Creek-Fish Creek drainage divide could be considered to be located on the southeast end of the Rattlesnake Hills uplift, although is lower than the Rattlesnake Hills to the northwest. Note how a north to south oriented through valley or pass links the east-northeast oriented Poison Spring Creek and Willow Creek valleys with the south oriented Fish Creek headwaters valley. The through valley or pass floor elevation is between 1960 and 1980 meters. The drainage divide ridge to the southeast rises to 2057 meters to the northwest rises to more than 2100 meters suggesting the through valley is at least 77 meters deep. While not as spectacular as the North Platte River valley to the east the through valley is a water-eroded feature and was eroded by south oriented flood flow prior to headward erosion of the east-northeast oriented Willow Creek and Poison Spring Creek valleys. Headward erosion of those east-northeast valleys beheaded south oriented flood flow routes to the Fish Creek valley. While in the context of present day topography it is difficult to visualize, prior to erosion of the east-northeast Willows Creek and Poison Spring Creek valleys the region north of the drainage divide was at least as high if not higher than the drainage divide elevation (although crustal warping since that time has probably altered regional elevations). In the northwest quadrant of figure 5 the West Fork Meadow Creek flows in a north-northeast direction to the north edge of figure 5 and north of figure 5 flows to east and south oriented Poison Spider Creek.

Detailed map of Poison Spring Creek-Fish Creek drainage divide area

Figure 6: Detailed map of Poison Spring Creek-Fish Creek area. United States Geological Survey map digitally presented using National Geographic Society TOPO software.

Figure 6 provides a detailed topographic map of the Poison Spring Creek area seen in less detail in figure 5. The map contour interval for figure 6 is 20 feet. Poison Spring Creek originates in the southwest quadrant of section 31 (in northwest quadrant of figure 6) and flows in a southeast direction into the northeast quadrant of section 6 and then turns to flow in an east-northeast direction to the north edge of figure 6 (east half) and north and east of figure 6 turns to flow in a south direction to join the north and northeast oriented North Platte River as a barbed tributary. Willow Creek originates in the south half of section 6 and flows in an east-southeast direction to near Young Ranch in the northwest quadrant of section 9 where it turns to flow in an east-northeast and northeast direction and the Oregon Trail Road then follows it to the east edge of figure 6 (north half) and east and north of figure 6 it joins east-northeast oriented Poison Spring Creek. Fish Creek headwaters are located near the west edge of the southwest quadrant of section 6 and in the southeast quadrant of section 1 and Fish Creek then flows in a south direction to the south edge of figure 6 (west half). South of figure 6 Fish Creek turns to flow in a southwest direction to join south oriented Horse Creek, which flows to the east and south oriented Sweetwater River. Shell Creek flows in an east-southeast direction from the west edge of figure 6 (near northwest corner) into section 36 and then turns to flow in a south-southwest and south direction near the west edge of figure 6 to join Fish Creek south of figure 6. A through valley or pass in section 7 links the east-northeast oriented Willow Creek valley with the south oriented Fish Creek headwaters valley. The through valley or pass floor elevation is between 6460 and 6480 feet. Elevations along the drainage divide to the southeast rise to the south edge of figure 6 and south of figure 6 reach 6781 feet. Elevations near the northwest corner of figure 6 are greater than 6900 feet. These elevations suggest the through valley or pass is at least 300 feet deep. This 300-foot deep through valley or pass was eroded by south oriented flood flow moving from north of figure 6 to an east and south oriented flood channel on the present day Sweetwater River alignment. At that time the east-northeast oriented Willow Creek and Poison Creek valleys did not exist. The southeast oriented Poison Spring Creek and east-southeast oriented Shell Creek headwaters valleys suggest flood flow was moving in a southeast or east-southeast direction along what is now the drainage divide between the east-northeast oriented North Platte River tributaries and the south oriented Sweetwater River tributaries.

Cabin Creek-Horse Creek drainage divide area

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

Figure 7 illustrates the Cabin Creek-Horse Creek drainage divide area west and slightly north of figure 5 and includes a small overlap area with figure 5. The map contour interval for figure 7 is 20 meters. Sagehen Hill and Saddle Rock are located near the east end of the Rattlesnake Hills in the west half of figure 7. The Rattlesnake Hills uplift continues in an eastern direction (although with somewhat lower elevations) to Horse Heaven in the east center area of figure 7 and then eastward direction to the North Platte River as seen in previous figures. Horse Creek originates in the area between Saddle Rock and Buffalo Head and flows in a southeast direction to the south edge of figure 7. South of figure 7 Horse Creek turns to flow in more of a south direction to join the east and south oriented Sweetwater River. Poison Spider Creek originates in the Rattlesnake Hills (in northwest quadrant of figure 7) and flows through Eagles Nest Canyon in a north-northeast direction to the north edge of figure 7 and north of figure 7 turns to flow in an east and south-southeast direction to join the northeast oriented North Platte River as a barbed tributary. Soap Creek is a northeast oriented stream flowing to the north center edge of figure 7 and north of figure 7 joins Poison Spider Creek. Cabin Creek originates east of Sagehen Hill and flows in a northeast direction to the north edge of figure 7 (east half) and north of figure 7 joins Soap Creek, which then flows to Poison Spider Creek. Between Buffalo Head and Horse Heaven there is a deep north to south oriented through valley or pass linking the northeast oriented Cabin Creek valley with a south-southeast oriented Horse Creek tributary valley. The through valley floor elevation is shown as being 2063 meters. Elevations on Horse Heaven to the east rise to more than 2240 meters and Sagehen Hill to the west rises to more than 2340 meters. These elevations suggest the through valley or pass is approximately 180 meters deep. The through valley or pass is a water-eroded feature and was eroded by south oriented flood flow moving to the east and south oriented Sweetwater River valley south of figure 7. At that time the Sweetwater River was flowing to a south oriented flood flow channel on the present day north oriented North Platte River alignment. Also at that time the region north of the through valley was at least as high if not higher than the through valley floor elevation. Headward erosion of the northeast oriented Cabin Creek valley (and probably the parallel Soap Creek and Poison Spider Creek valleys) captured the south oriented flood flow and diverted floodwaters to the east and south-southeast oriented Poison Spider Creek valley. This sequence of events is consistent with headward erosion of a deep south-oriented flood flow channel on the present day north oriented North Platte River alignment. However, the reversal of flood flow on the North Platte River alignment probably occurred shortly after the Poison Spider Creek valley eroded headward from the south oriented flood flow channel (on the North Platte River alignment). In other words it is possible that by the time the Poison Spider Creek valley reached the region in figure 7 the reversal of flood flow on the North Platte River alignment had already occurred.

Detailed map of Cabin Creek-Horse Creek drainage divide area

Figure 8: Detailed map of Cabin Creek-Horse 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 Cabin Creek-Horse Creek drainage divide seen in less detail in figure 7. The map contour interval for figure 8 is 20 feet. Horse Heaven is located in the east center area of figure 8. The Rattlesnake Hills eastern end is labeled in the west half of figure 8. Cabin Creek flows in an east-northeast and northeast direction in the northwest quadrant of figure 8 to the north edge of figure 8 and north of figure 8 joins northeast oriented Soap Creek, which then joins east and south-southeast oriented Poison Spider Creek, which flows to the northeast oriented North Platte River as a barbed tributary. Horse Creek originates near the west center edge of figure 8 and flows in a southeast direction to the south edge of figure 8 (west half) and south of figure 8 turns to flow in more of a south direction to join the east and south oriented Sweetwater River, which flows to the north and northeast oriented North Platte River as a barbed tributary.  A through valley or pass near the northwest corner of section 30 links a north oriented Cabin Creek tributary valley with a south oriented Horse Creek tributary valley. The through valley floor elevation is between 6760 and 6780 feet. Horse Heaven to the east rises to 7414 feet. While not seen in figure 8 elevations in the Rattlesnake Hills just west of figure 8 are more than 7600 feet. These elevations suggest the through valley is at least 630 feet deep. The through valley is a water-eroded valley and was eroded by water flowing across the present day drainage divide. At that time the region north of the drainage divide had not been eroded and the deep Cabin Creek valley did not exist. South oriented flood flow moved across what were at that time the emerging Rattlesnake Hills to the actively eroding east and south oriented Sweetwater River valley south of figure 8. The Sweetwater River valley was eroding headward from a south oriented flood flow channel on the present day north oriented North Platte River alignment. Headward erosion of that deep south-oriented flood flow channel (north and east of figure 8) enabled the east oriented Poison Spider Creek valley and its tributary valleys (e.g. Cabin Creek valley) to erode headward north of the emerging Rattlesnake Hills and erode the region north and east of the Rattlesnake Hills and the south oriented flood flow channel to the Sweetwater River valley was captured and diverted in an east and south-southeast direction along the newly eroded Poison Spider Creek valley. As mentioned in the figure 7 discussion the reversal of flood flow on the present day north oriented North Platte River alignment probably took place about the same time the deep northeast oriented Cabin Creek valley eroded headward into the region seen in figure 8.

Middle Fork Casper Creek-Dry Creek drainage divide area

Figure 9: Middle Fork Casper Creek-Dry 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-Dry 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 extend in a northwest to southeast direction across the center of figure 9.  Garfield Peak is the labeled high point and is located in the north center region of figure 9. Snider Basin is located east of Garfield Peak and the Middle Fork Casper Creek flows through Snider Basin to the north edge of figure 9 (east half) and north and east of figure 9 the Middle Fork Casper Creek turns to flow in an east direction to flow to south-southeast oriented Casper Creek, which then flows to the east and southeast oriented North Platte River near Casper. The Woodward Basin is located west of Garfield Peak and Wallace Creek flows in a north-northeast, north, and north-northeast direction through the Woodward Basin to the north center edge of figure 9. North of figure 9 Wallace Creek flows to the northeast and north-northeast oriented South Fork Powder River with water eventually reaching the north oriented Powder River and the northeast oriented Yellowstone River. Dry Creek originates near the northwest corner of figure 9 on the west side of the Rattlesnake Hills and flows in a south, south-southeast, and southeast direction to the south edge of figure 9 (slightly west of center) and south of figure 9 joins the east and south oriented Sweetwater River. U T Pass is located near the center of figure 9 and links the northeast oriented Middle Fork Casper Creek valley with the south-southwest oriented U T Creek valley with U T Creek flowing to southeast oriented Dry Creek. U T Pass has an elevation of between 2200 and 2220 meters. The drainage divide immediately to the east rises to more than 2360 meters and to the west rises to more than 2400 meters suggesting the pass is at least 140 meters deep. While the straight U T Creek valley probably has been eroded along a fault line U T Pass is a water-eroded valley and was eroded by south oriented flood flow moving to the southeast oriented Dry Creek valley and then to the east and south oriented Sweetwater River valley at a time when the deep Middle Fork Casper Creek valley did not exist (and when the northeast oriented South Fork Powder River valley and its tributary valleys, including the Wallace Creek valley, did not exist). Headward erosion of the Middle Fork Casper Creek valley captured the south oriented flood flow that had been moving across U T Pass and diverted the floodwaters in a northeast direction. The deep northeast oriented Middle Fork Casper Creek valley also captured south oriented flood flow moving west of Garfield and that flood flow moved in an east direction south of Garfield Peak to the newly eroded Middle Fork Casper Creek valley. The captured flood flow helped erode the Snider Basin. Next headward erosion of the northeast oriented South Fork Powder River valley beheaded and reversed the south oriented flood flow route to the Woodward Basin. The reversed flood flow route created the Wallace Creek drainage route and captured south oriented flood flow from further to the west. In this manner the northeast flank of the Rattlesnake Hills was deeply eroded as northeast oriented drainage routes evolved.

Detailed map of Middle Fork Casper Creek-U T Creek drainage divide area

Figure 10: Detailed map of Middle Fork Casper Creek-U T 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-U T Creek drainage divide area seen in less detail in figure 9. The map contour interval for figure 10 is 20 feet. The Middle Fork Casper Creek originates in section 8 and flows in a northeast direction to the north center edge of figure 10. North of figure 10 the Middle Fork Casper Creek flows in a northeast and east direction to south-southeast oriented Casper Creek, which flows to join the east and southeast oriented North Platte River near Casper.  U T Pass is located near the corner of sections 9, 10, 15, and 16. U T Creek originates just south of U T Pass and flows in a south-southwest direction to the south edge of figure 10 (slightly west of center) and south of figure 10 flows to southeast oriented Dry Creek, which then flows to the east and south oriented Sweetwater River, which in turn flows to the north and northeast oriented North Platte River. The U T Pass elevation appears to be between 7580 and 7600 feet. Elevations in section 15 to the east exceed 8080 feet and elevations greater than 8100 feet can be found along the west edge of figure 10. These elevations suggest U T Pass is at least 500 feet deep. U T Pass is a water-eroded valley and was eroded by south oriented flood flow moving to the deep Sweetwater River valley, which was actively eroding headward south of figure 10. At that time the region north of the Rattlesnake Mountains had not been eroded and the Middle Fork Casper Creek valley did not exist. The region north of figure 10 was eroded in sequence from the east to the west by headward erosion of deep northeast oriented valleys. Headward erosion of each successive deep northeast oriented valley captured flood flow routes to the actively eroding Sweetwater River valley and to the northeast oriented valley immediately to the southeast and diverted the captured floodwaters in a northeast direction. For example, headward erosion of the deep northeast oriented Middle Fork Casper Creek valley beheaded flood flow routes to the previously eroded northeast oriented Poison Spider Creek valley (east of figure 10) and also to the south oriented flood flow routes to the actively eroding U T Creek valley and captured south oriented flood flow routes west of figure 10. Some of the captured floodwaters flowed in a southeast direction to the actively eroding Middle Fork Casper Creek valley across the pass seen in the northwest corner of figure 10.

Additional information and sources of maps studied

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

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