Abstract:

This essay uses topographic map evidence to interpret landform origins in the Sage Creek-Medicine Bow River drainage divide area in the Wyoming Shirley and Seminoe Mountains. Sage Creek is a west oriented drainage system flowing from the Shirley Mountains to the north oriented North Platte River north of Seminoe Canyon. The Medicine Bow River originates in the northern Medicine Bow Mountains and flows in a north and northeast direction before turning to flow in a northwest, west, and northwest direction to join the north oriented North Platte River south of Seminoe Canyon. Seminoe Canyon is a deep water gap where the North Platte River crosses the south-southeast oriented Seminoe Mountains. A deep southeast and south oriented through valley is located between the Seminoe Mountains and the Shirley Mountains on the east side Seminoe Canyon. Shallower north to south oriented through valleys cross the Shirley Mountains upland surface and link north oriented Sage Creek tributary valleys with south oriented valleys. West to east oriented through valleys also link south oriented Medicine Bow River tributary valleys. Immense south oriented floods are interpreted to have eroded the through valleys. Floodwaters flowed from the western margin of a thick North American ice sheet in western Canada to and across Wyoming at a time when Wyoming mountain ranges were beginning to emerge. At first floodwaters could cross what are today high mountain ranges and later floodwaters were channeled into deep valleys crossing the emerging mountain ranges and/or around the emerging mountain ranges. The North Platte River alignment west of the Shirley Mountains originated as south oriented diverging and converging flood flow channels while the northwest, west, and northwest oriented Medicine Bow River valley south of the Shirley Mountains probably originated as an east oriented flood flow channel moving floodwaters to a much deeper southeast oriented North Platte River valley located east of the emerging Laramie Mountains. Headward erosion of a deeper south oriented valley on the North Platte River alignment beheaded and reversed flood flow on the Medicine Bow River alignment to create the northwest, west, and northwest oriented Medicine Bow River drainage route seen today. The west oriented Sage Creek drainage route eroded headward from the deeper valley on the North Platte River alignment to capture south oriented flood flow. Headward erosion of the much deeper southeast oriented North Platte River valley around the northwest end of the Laramie Mountains in several distinct steps next beheaded and reversed south and southeast oriented flood flow channels on the present day north oriented North Platte River alignment. As each beheading and reversal took place floodwaters on the north end of the beheaded flood flow channel reversed flow direction to flow to the much deeper beheading valley and in this manner the present day north and southeast oriented North Platte River drainage route was created.

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 Sage Creek-Medicine Bow River drainage divide area landform origins in the Wyoming Shirley and Seminoe Mountains. 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 Sage Creek-Medicine Bow River drainage divide area landform evidence in the Wyoming Shirley and Seminoe Mountains will be regarded as evidence supporting the “thick ice sheet that melted fast” paradigm.

Sage Creek-Medicine Bow River drainage divide area location map

Figure 1: Sage Creek-Medicine Bow 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 Sage Creek-Medicine Bow River drainage divide area in the Wyoming Shirley and Seminoe Mountains and illustrates a region in south central Wyoming. The Shirley Mountains are near the center of figure 1 and the Seminoe Mountains are not shown, but are located near Seminoe Dam. The North Platte River flows in a north direction from Seminoe Reservoir to Pathfinder Reservoir and then in a north-northeast direction to Casper at the northwest end of the Laramie Mountains. From Casper the North Platte River flows in an east, south, and southeast direction on the north and east sides of the Laramie Mountains to the east edge of figure 1 (north of center). The Medicine Bow Mountains extend in a south-southeast direction from near highway 80 to the south center edge of figure 1 and the North Platte River flows in a north-northwest direction on the west side of the Medicine Bow Mountains before turning in a northeast direction to enter Seminoe Reservoir. The Medicine Bow River originates near the north end of the Medicine Bow Mountains and flows in a north direction to the town of Elk Mountain. From Elk Mountain the Medicine Bow River flows in a northeast and northwest direction to the town of Medicine Bow and then in a northwest, west, and northwest direction to join the North Platte River at Seminoe Reservoir. Muddy Creek originates in the Shirley Mountains and flows in an east, southeast, south, and west direction to join the west oriented Medicine Bow River near the town of Medicine Bow. Sage Creek is not labeled in figure 1, but a tributary originates north of the Muddy Creek headwaters and flows in a west and southwest direction to join west oriented Sage Creek, which then joins the North Platte River near the south end of Pathfinder Reservoir (Kortes Dam is misplaced in figure 1 and should be further south). The unlabeled north and northwest stream originating north of the Muddy Creek headwaters is Stinking Creek, which joins northwest oriented Bates Creek (also unlabeled) before joining the north-northeast oriented North Platte River north of the town of Alcova. The Laramie River flows from the south edge of figure 1 to Laramie (near the south edge of southeast quadrant of figure 1) and then in a north direction before turning in a northeast direction north of Wheatland Reservoir to flow across the Laramie Mountains and to the east edge of figure 1 (north of center). East of figure 1 the Laramie River joins the North Platte River. The region between the Medicine Bow Mountains and the Laramie Mountains is the Laramie Basin (not labeled in figure 1). The Sage Creek-Medicine Bow River drainage divide area investigated here is located in the western Shirley Mountains and is north of the Medicine Bow River, south of Sage Creek, and east of the North Platte River.

Wyoming drainage routes developed during immense melt water floods. Floodwaters from the western margin of a thick North American ice sheet flowed from western Canada to and across Wyoming at a time when Wyoming mountain ranges were beginning to emerge. At first floodwaters could flow across the emerging mountain ranges, but later floodwaters were channeled around the mountains or confined to deep valleys eroded the across the emerging mountain ranges. Wyoming mountain ranges emerged as ice sheet related crustal warping raised the mountain ranges and as floodwaters deeply eroded surrounding valleys and basins. The present day north oriented North Platte River drainage route west of the Laramie, Shirley, and Medicine Bow Mountains originated as south oriented flood flow channels. The south oriented flood flow channels were beheaded by headward erosion of the much deeper southeast oriented North Platte River valley, which eroded headward around the northwest end of the Laramie Mountains. Floodwaters on north ends of the beheaded flood flow channels reversed flow direction to flow to the much deeper east and southeast oriented North Platte River valley and to create in a series of steps the present day north, east, and southeast oriented North Platte River drainage route. Each step involved the beheading and reversal of a North Platte River segment, which then enabled a deep valley to erode headward across an emerging mountain ridge to behead and reverse a south or southeast oriented flood flow channel slightly further to the west or southwest. Present day dams on the North Platte River are located at some of the locations where deep valleys eroded headward to behead and reverse south and/or southeast oriented flood flow channels.

Floodwaters initially flowed in complexes of diverging and converging channels, which were constantly evolving as mountain ranges emerged and as deeper channels beheaded diverging flood flow channels. The present day northeast oriented Medicine Bow River drainage route and the northwest and west oriented Medicine Bow River drainage route originated as east oriented flood flow channels moving floodwaters to deep valleys being eroded across the emerging Laramie Mountains as floodwaters flowed to the much deep southeast oriented North Platte River valley, which was eroding headward on the east side of the Laramie Mountains. The west oriented Sage Creek drainage route and the east and southeast oriented Muddy Creek drainage route also may have originated as an east and southeast flood flow channel diverging from a south oriented flood flow channel on the present day north oriented North Platte River alignment to reach the much deeper southeast oriented North Platte River valley east of the Laramie Mountains. In time the southeast oriented North Platte River valley eroded headward around the northwest end of the Laramie Mountains and began to behead and reverse south oriented flood flow channels west of the Laramie Mountains. The North Platte River segment between Alcova and Casper was beheaded and reversed before segments upstream from Alcova (or south of Alcova) were beheaded and reversed. The reversal of flood flow on the North Platte River segment between Alcova and Casper also beheaded a south oriented flood flow channel on the present day north oriented Stinking Water Creek alignment to create the north oriented Stinking Water Creek drainage route. The newly formed north oriented Stinking Water Creek drainage route then captured some of the east and southeast oriented flood flow moving from the present day west oriented Sage Creek alignment to the Muddy Creek alignment and eroded a deep north oriented valley (Bates Hole-not labeled on figure 1). As seen in the topographic maps illustrated here this process was repeated again as flood flow on additional North Platte River segments was beheaded and reversed.

Detailed location map for Sage Creek-Medicine Bow River drainage divide area

Figure 2: Detailed location map for Sage Creek-Medicine Bow 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 Sage Creek-Medicine Bow River drainage divide area in the Wyoming Shirley and Seminoe Mountains. The North Platte River flows in a northeast direction from near the southwest corner of figure 2 into Seminoe Reservoir and then in a north direction to Seminoe Dam. From Seminoe Dam the North Platte River continues to flow to the south end of Pathfinder Reservoir (not labeled in figure 2) and the north edge of figure 2 (west half). Seminoe Dam is located where the North Platte River crosses the Seminoe Mountains and Kortes Dam is located short distance downstream from Seminoe Dam. The Shirley Mountains are located east of the Seminoe Mountains. The South Fork Sage Creek originates in the northern Shirley Mountains and flows in a west and northwest direction to join the unlabeled west oriented Middle Fork and to form west oriented Sage Creek, which flows to the north oriented North Platte River at the south end of Pathfinder Reservoir. South of Sage Creek Lost Creek flows in a west-northwest direction before turning in a southwest direction to join the north oriented North Platte River. South and east of Lost Creek is Saylor Creek, which flows in a southwest and west direction from the Shirley Mountains to join the north oriented North Platte River at Seminoe Reservoir. The Medicine Bow River flows in a north-northeast and northwest direction to the town of Medicine Bow near the southeast corner of figure 2. From the town of Medicine Bow the Medicine Bow River flows in a northwest, west, and northwest direction to join the north oriented North Platte River at Seminoe Reservoir. Muddy Creek originates on the north side of the Shirley Mountains (east of the Sage Creek headwaters) and flows in an east, south, and west direction to join the northwest oriented Medicine Bow River south of the Freezeout Mountains. Difficulty Creek is a southeast and south oriented Medicine Bow River tributary located at the west end of the Freezeout Mountains. West of Difficulty Creek is south-southeast and south-southwest oriented Troublesome Creek, which flows to the west oriented Medicine Bow River. Still further west is southeast and southwest oriented Dry Creek and even further west Austin Creek flows in a southwest direction to enter the flooded Medicine Bow River valley at Seminoe Reservoir.

Sage Creek-Lost Creek drainage divide area

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

Figure 3 provides a topographic map of Sage Creek-Lost Creek drainage divide area. The map contour interval for figure 3 is 20 meters. The Seminoe Mountains extend in an east-southeast direction across the southwest quadrant of figure 3. The North Platte River valley south of the Seminoe Mountains is flooded by Seminoe Reservoir and Seminoe Dam is located where a northwest oriented North Platte River segment turns to flow in a deep north-northeast oriented valley across the Seminoe Mountains before flowing in a north direction to the south end of Pathfinder Reservoir and the north edge of figure 3 (west half). The Middle Fork Sage Creek flows from the east edge of figure 3 (near northeast corner) to join the northwest and north-northwest oriented South Fork (which flows from the east center edge of figure 3) and to form west oriented Sage Creek, which joins the North Platte River at the south end of Pathfinder Reservoir. The west end of the Shirley Mountains (not labeled in figure 3) is located in the east half of the southeast quadrant of figure 3. Lost Creek originates in the western Shirley Mountains and flows in a southwest, west, north, west, northwest, and southwest direction to join the north oriented North Platte River near the Kortes Dam Camp (Kortes Dam is located south of the Kortes Dam Camp near the north end the deep North Platte River valley through the Seminoe Mountains). Corral Creek is a south-southeast oriented stream flowing to the south edge of figure 3 (between the Seminoe Mountains and the Shirley Mountains) and south of figure 3 turns to flow in a southwest direction to join west oriented Saylor Creek, which flows to the north oriented North Platte River at Seminoe Reservoir. The deep North Platte River valley (or water gap) crossing the Seminoe Mountains is known as Seminoe Canyon and is just one of several deep valleys or water gaps the north oriented North Platte River flows through in Wyoming. To understand the Seminoe Mountains water gap you need to visualize the region with immense south oriented floods flowing across the region. At first floodwaters were flowing on an erosion surface at least as high as the highest points in Seminoe Mountains, which are generally 500-600 meters higher the North Platte River elevation in the water gap. The south oriented floodwaters eroded valleys across the Seminoe Mountains and eroded the south side of the Seminoe Mountains, but also eroded a deep east-southeast and south oriented valley around the east end of the emerging Seminoe Mountains on the present day Lost Creek alignment. Headward erosion of this deep valley around the east end of the Seminoe Mountains beheaded and reversed south oriented flood flow channels crossing the eastern Seminoe Mountains to create what are today north oriented Lost Creek tributary drainage routes. Headward erosion of the deep south oriented water gap valley was able to provide a more direct route to deep south oriented flood flow channels south of the Seminoe Mountains and in time was able to behead and reverse the east-southeast and south oriented flood flow channel around the east end of the Seminoe Mountains and to create the present day west, north, west, northwest, and southwest oriented Lost Creek drainage route. Today North Platte River tributaries have many south oriented tributaries and/or south oriented valley segments, which are relics of the south oriented flood flow channels that once crossed the region.

Lost Creek-Saylor Creek drainage divide area

Figure 4: Lost Creek-Saylor Creek drainage divide area. United States Geological Survey map digitally presented using National Geographic Society TOPO software.

Figure 4 provides a topographic map of the Lost Creek-Saylor Creek drainage divide area south and east of figure 3 and includes an overlap area with figure 3. The map contour interval for figure 4 is 20 meters. The Shirley Mountains are located in the east half of figure 4 and the Seminoe Mountains extend in an east-southeast direction across the west half of figure 4. The flooded North Platte River valley in Seminoe Reservoir can be seen along the west edge of figure 4 south of the Seminoe Mountains. Lost Creek flows in a southwest, west, north, west, northwest, and southwest direction from the western Shirley Mountains to the west edge of figure 4 (north of the Seminoe Mountains) and joins the north oriented North Platte River west of figure 4. The South Fork Sage Creek flows in a west and north direction in the northeast quadrant of figure 4 and is joined by north-northwest and north oriented Beaver Creek. North of figure 4 the South Fork joins the west oriented Middle Fork to form west oriented Sage Creek, which then flows to the north oriented North Platte River. Saylor Creek originates in the western Shirley Mountains and flows in a south-southwest direction to the north side of Horseshoe Ridge and then flows in a west-northwest and west-southwest direction to enter Seminoe Reservoir and join the north oriented North Platte River. Corral Creek is a south-southeast and south oriented Saylor Creek tributary located between the Seminoe Mountains and the Shirley Mountains. Norbacher Canyon is a south-southwest oriented Corral Creek tributary located between the southwest-oriented Lost Creek headwaters and the south-southwest oriented Saylor Creek headwaters. The Lost Creek-Corral Creek through valley between the Seminoe Mountains and the Shirley Mountains is probably a structural valley, but it is also a water-eroded valley and was eroded by east-southeast and south oriented flood flow moving from the south oriented flood flow channel on the present day north oriented North Platte River alignment to the Saylor Creek valley. However, prior to headward erosion of the deeper west oriented Saylor Creek valley the floodwaters probably flowed in a southeast direction to the south oriented Austin Creek valley and then in a southwest direction to the northwest oriented Medicine Bow River valley. Prior to that time the floodwaters may have flowed to a southeast and east oriented flood flow channel on the present day west and northwest oriented Medicine Bow River alignment. Note the large numbers of south oriented drainage routes in this region, which is today drained by the north oriented North Platte River.

Detailed map of Lost Creek-Corral Creek drainage divide area

Figure 5: Detailed map of Lost Creek-Corral Creek drainage divide area. United States Geological Survey map digitally presented using National Geographic Society TOPO software.

Figure 5 illustrates a detailed topographic map of the Lost Creek-Corral Creek drainage divide area seen in less detail in figure 4. The map contour interval for figure 5 is 20 feet. The southeast end of the Seminoe Mountains extends from the west edge of figure 5 to near the south center edge of figure 5. The west end of the Shirley Mountains are located in the east half of figure 5. Lost Creek flows in a southwest, west, and north direction from the north edge of figure 5 (east half) to the north edge of figure 5 (west half) and north of figure 5 turns to flow in a west, northwest, and southwest direction to join the north oriented North Platte River. Saylor Creek flows in a south-southwest direction from the east edge of figure 5 (slightly north of center) to the south edge of figure 5 and south of figure 5 turns to flow in a west-northwest and west-southwest direction to join the north oriented North Platte River. Corral Creek flows in a south-southwest and south-southeast direction in section 12 and then flows in a south-southeast and south-southwest direction to the south edge of figure 5 (near Saylor Creek) and south of figure 5 joins Saylor Creek. Norbacher Canyon drains from the east edge of figure 5 (north of Saylor Creek) to join south oriented Corral Creek near the southeast corner of section 13. A through valley near the corner of sections 1, 2, 11, and 12 links the west and north oriented Lost Creek valley with the south oriented Corral Creek valley. At its deepest point the through valley floor elevation is between 7280 and 7300 feet. The Seminoe Mountains in section 16 rise to 8281 feet and the Shirley Mountains near the northeast corner of figure 5 rise to more than 8400 feet. These elevations suggest the Lost Creek-Corral Creek through valley is approximately 1000 feet deep. The through valley was eroded by southeast and south oriented flood flow flowing between the emerging Seminoe and Shirley Mountains. At first floodwaters were flowing on an erosion surface as high as the Seminoe Mountains today and were flowing in many diverging and converging flood flow channels across the emerging mountain mass and the south oriented floodwaters eroded the south side of the emerging mountain mass. For example, the south-southeast and southwest oriented Beaver Jimmy Creek valley and its south oriented tributary valleys near the corner of sections 14, 15, 22, and 23 were eroded by south oriented flood flow moving across the emerging mountain mass. Headward erosion of the much deeper southeast and south oriented Lost Creek-Corral Creek through valley beheaded the south oriented flood flow to the Beaver Jimmy Creek drainage system and also eroded the northeast side of the emerging Seminoe Mountains which enabled the mountain mass to emerge as we see it today. While crustal warping may have played a role in the emergence of the Seminoe Mountains floodwaters deeply eroded valleys on all sides of the emerging mountain mass.

Saylor Creek-Troublesome Creek drainage divide area

Figure 6: Saylor Creek-Troublesome 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 Saylor Creek-Troublesome Creek drainage divide area south and east of figure 4 and includes an overlap area with figure 4. The map contour interval for figure 6 is 20 meters. The Medicine Bow River flows in a west direction from the east edge of figure 6 (near southeast corner) to its flooded northwest oriented valley, which extends beyond the west edge of figure 6 (south of center) into Seminoe Reservoir and to the north oriented North Platte River. Troublesome Creek originates near the north edge of figure 6 (east half) and flows in a south, southeast, and south-southwest direction to join the west oriented Medicine Bow River near the southeast corner of figure 6. Austin Creek flows in a southwest, south, and west-southwest direction from the north center edge of figure 6 to enter the flooded Medicine Bow River valley near the west edge of figure 6. Saylor Creek flows in a south-southwest direction from the north edge of figure 6 (west of center) to the north side of Horseshoe Ridge and then turns to flow in a west-northwest and west-southwest direction to the west edge of figure 6 (north half) and west of figure 6 joins the north oriented North Platte River. The southwest and south oriented Austin Creek drainage route is probably a relic of a south oriented flood flow channel that converged with a south oriented flood flow channel on the present day north oriented North Platte River alignment west of figure 6. The southeast oriented Troublesome Creek valley segment may be a relic of a southeast oriented flood flow that at one time flowed to east oriented flood flow on the present day west oriented Medicine Bow River alignment. The east oriented flood flow moved across the north end of the Laramie Basin to valleys crossing the emerging Laramie Mountains and then to the much deeper southeast oriented North Platte River valley on the east side of the Laramie Mountains. It is possible south oriented flood flow from the south oriented flood flow channels on the present day north oriented North Platte River spilled in an east direction across the region seen in figure 6 especially some of the southeast and south oriented flood flow moving through the Lost Creek-Corral Creek through valley, which crosses the north edge of figure 6 (west half) north of the east end of Horseshoe Ridge. If so headward erosion of a deeper south oriented flood flow channel on the North Platte River alignment may have beheaded and reversed the east oriented flood flow to create the west oriented Saylor Creek drainage route and the west-southwest oriented Austin Creek drainage route. Headward erosion of that deeper south oriented flood flow channel on the North Platte River alignment also probably beheaded and reversed southeast and east oriented flood flow on the Medicine Bow River alignment to create the west and northwest oriented Medicine Bow River drainage route seen today.

South Fork Sage Creek-Muddy Creek drainage divide area

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

Figure 7 illustrates the South Fork Sage Creek-Muddy Creek drainage divide area east of figure 4 and includes an overlap area with figure 4. The map contour interval for figure 7 is 20 meters. The Lost Creek-Corral Creek through valley is located near the west edge of the southwest quadrant of figure 7. Saylor Creek flows in a south-southwest and west direction to the southwest corner of figure 7 and west of figure 7 joins the north oriented North Platte River. The South Fork Sage Creek originates near the “H” in “SHIRLEY” and flows in a northeast, northwest, west-northwest, and north direction to the north edge of figure 7 (west half) and joins the Middle Fork north of figure 7 to form west oriented Sage Creek, which then flows to the north oriented North Platte River. Beaver Creek is a north-northwest oriented South Fork Sage Creek tributary located in the west center area of figure 7. Muddy Creek is formed at the confluence of northeast and east oriented Quealy Creek, north-northeast and east-northeast oriented Lisenby Creek, and north-northeast oriented Sullivan Creek and then flows in an east direction to the east edge of figure 7 (near northeast corner). East of figure 7 Muddy Creek flows in an east, southeast, and south direction to join the southwest and west oriented Little Medicine Bow River, which then joins the northwest, west, and northwest oriented Medicine Bow River to flow to the north oriented North Platte River. The east and northeast facing escarpment extending from the north edge of figure 7 (east half) to the east edge of figure 7 (south of center) marks the boundary between the Shirley Mountains to the west and the Shirley Basin to the east. The escarpment is at least to some extent a water-eroded escarpment, although the erosion history is probably complex. Before headward erosion of the deep east oriented Muddy Creek valley south oriented flood flow moved across the region on an erosion surface as high or higher than the present day Shirley Mountains (although the Shirley Mountains and entire region may have been uplifted since that time). Evidence for the south oriented flood flow is found in shallow through valleys crossing the Shirley Mountains and linking north oriented valleys with south oriented valleys. For example the north oriented Beaver Creek valley is linked by through valleys with the south-southwest oriented Saylor Creek and Norbacher Canyon valleys. The through valleys are defined by at least five contour lines on each side suggesting the through valleys are approximately 100 meters deep. Study of the Shirley Mountains upland surface reveals other similar through valleys, which provide evidence of south-southwest oriented flood flow channels probably moving floodwaters to a deeper south oriented flood flow channel on the present day north oriented North Platte River alignment. Headward erosion of the deep east oriented Muddy Creek valley beheaded and reversed the flood flow channels crossing the southeast end of the Shirley Mountains to create the north-northeast oriented Muddy Creek tributary drainage routes. This beheading and reversal process probably occurred one flood flow channel at a time, which meant reversed flood flow channels could capture flood flow from yet to be beheaded flood flow channels further to the west.

Detailed map of Beaver Creek-Saylor Creek drainage divide area

Figure 8: Detailed map of Beaver Creek-Saylor 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 Beaver Creek-Saylor Creek drainage divide area seen is less detail in figure 7. The map contour interval for figure 8 is 20 feet. Beaver Creek flows from the north side of Button Meadows in a north-northwest direction to the north center edge of figure 8 and north of figure 8 joins west-northwest and north oriented South Fork Sage Creek, which flows to west oriented Sage Creek and then to the north oriented North Platte River. Balsam Draw is a southeast and north-northeast oriented Beaver Creek tributary located in sections 33 and 4 in the north center area of figure 8. Saylor Creek originates in section 4 and flows in a south-southwest direction to the south edge of figure 8 (west half) and south and west of figure 8 joins the north oriented North Platte River. Johnson Canyon is a west oriented drainage route extending from Button Meadows to south-southwest oriented Saylor Creek. A north-northeast to south-southwest oriented through valley in section 4 links the north-northeast oriented Balsam Draw valley with the south-southwest oriented Saylor Creek valley. The through valley floor elevation is 8096 feet. Elevations in the southeast quadrant of section 32 to the northwest rise to more than 8420 feet and elevations in section to the southeast rise to at least 8443 feet. These elevations suggest the through valley is more than 300 feet deep. The through valley is a water-eroded valley and was eroded by south-southwest oriented flood flow moving across what is now the Shirley Mountains upland surface. Another broader through valley is found north of Button Meadows and links the north-northwest oriented Beaver Creek valley with the east oriented Johnson Canyon valley. The through valley floor elevation is between 8340 and 8360 feet. Elevations near the west edge of section 10 rise to 8617 feet while elevations in section 2 to the northeast rise to more than 8880 feet. These elevations suggest the through valley at Button Meadows is approximately 250 feet deep. Ever changing diverging and converging south oriented flood flow channels eroded these and other through valleys seen in figure 8. Headward erosion of the much deeper east oriented Muddy Creek valley east of the Shirley Mountains and headward erosion of a much deeper south oriented flood flow channel on the present day north oriented North Platte River alignment captured the south oriented flood flow and diverted floodwaters in new directions. But, at least for a time floodwaters flowed in south directions across the present day Shirley Mountains upland surface.

Troublesome Creek-Difficulty Creek drainage divide area

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

Figure 9 illustrates the Troublesome Creek-Difficulty Creek drainage divide area east and slightly south of figure 6 and there is an overlap area with figure 6. The map contour interval for figure 9 is 20 meters. The Medicine Bow River flows in a north, west-northwest, and west direction from the southeast corner of figure 9 to the west edge of figure 9 (south half). West of figure 9 the Medicine Bow River flows in a west and northwest direction to join the north oriented North Platte River. Troublesome Creek flows in a south, southeast, and south-southwest direction from the north edge of figure 9 (near northwest corner) to join the Medicine Bow River near the west edge of figure 9. Difficulty Creek flows in a south, southeast, and south-southwest direction to join the Medicine Bow River south of the center of figure 9. Dry Creek is a south, southeast, and south oriented Medicine Bow River tributary located near the center of figure 9 and just west of Difficulty Creek. A west to east oriented through valley links the southeast oriented Troublesome Creek valley segment with the southeast oriented Dry Creek valley segment. The through valley is better seen in figure 10 and may have been eroded by east and southeast oriented flood flow at a time when a deep east oriented valley was eroding headward into the region along the present day northwest oriented Medicine Bow River alignment. At that time the floodwaters were moving in an east direction to flow across the northern Laramie Basin and the emerging Laramie Mountains to the much deeper southeast oriented North Platte River valley located east of the Laramie Mountains. East and southeast oriented flood flow on the Medicine Bow River alignment was beheaded and reversed probably by headward erosion of a deeper south oriented flood flow channel on the present day north oriented North Platte River alignment west of figure 9. The reversal of flood flow in the Medicine Bow River valley resulted in the erosion of a deeper west oriented valley on the Medicine Bow River alignment and it is also possible the Troublesome Creek-Dry Creek through valley was eroded by west oriented flood flow moving to the south oriented flood flow channel on the North Platte River alignment. In either case the through valley was eroded by a diverging and converging flood flow channel at the time the adjacent Medicine Bow River valley was also being eroded.

Detailed map of Troublesome Creek-Difficulty Creek drainage divide area

Figure 10: Detailed map of Troublesome Creek-Difficulty 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 Troublesome Creek-Difficulty Creek drainage divide area seen in less detail in figure 9. The map contour interval for figure 10 is 20 feet. The Medicine Bow River flows in a west-northwest and west-southwest direction from near the southeast corner of figure 10 to near the southwest corner of figure 10. Troublesome Creek flows in a southeast direction from the west edge of figure 10 (north half) into section 15 where it turns to flow in a south-southwest direction to the west edge of figure 10 (south half) and joins the Medicine Bow River west of figure 10. Mud Springs Draw drains in a south and south-southwest direction from the north edge of figure 10 (west half) to join Troublesome Creek in section 15. Difficulty Creek flows in a south-southwest direction from the east edge of figure 10 (north half) to join the Medicine Bow River near the southeast corner of section 30. Dry Creek flows from the west margin of section 7 in a south direction across section 18 and then in a southeast direction across section 19 before turning in a south-southwest direction to join the Medicine Bow River in section 30. A through valley in the southeast corner of section 13 and the northeast corner of section 24 links a west oriented Troublesome Creek tributary valley with the southeast oriented Dry Creek valley. The through valley floor elevation is between 6660 and 6680 feet. Elevations in section 26 rise to 6876 feet suggesting the through valley is approximately 200 feet deep. The through valley is a relatively minor feature in the context of the Shirley Mountains to the north, but it is evidence of diverging and converging flood flow channels at the time the Medicine Bow River valley was eroded. Diverging and converging south and south-southwest oriented flood flow channels eroded the valleys surrounding Beer Mug Mountain near the east edge of figure 10. Difficulty Creek flows in a south-southwest direction on the east side of Beer Mug Mountain and a west and south-southwest oriented through valley north and west of Beer Mug Mountain links the Difficulty Creek valley with the Dry Creek valley. The through valley floor elevation north of Beer Mug Mountain is between 6860 and 6880 feet. Beer Mug Mountain rises to at least 7260 feet and ridges to the north (and seen in figure 10) rise to more than 7140 feet with higher elevations found further to the north. These elevations suggest the through valley north of Beer Mug Mountain is at least 260 feet deep and is probably as much as 380 feet deep. At least some of the present day drainage route and through valley orientations were determined by regional geologic structures, but all of the valleys were eroded by water.

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.