Laramie River-Sybille Creek drainage divide area landform origins in the Laramie Mountains, USA

Authors

 

Abstract:

This essay uses topographic map evidence to interpret landform origins in the Laramie River–Sybille Creek drainage divide area in the Wyoming Laramie Mountains. The Laramie River flows in a north direction in the Laramie Basin on the west side of the Laramie Mountains and then turns to flow in an east and northeast direction across the Laramie Mountains before flowing in an east and northeast direction to join the southeast oriented North Platte River. Sybille Creek and Bluegrass Creek headwaters originate on the west side of the Laramie Mountains and after flowing for short distances in north directions turn to flow across the Laramie Mountains with Bluegrass Creek flowing in an east and southeast direction to join northeast, north-northeast, and north oriented Sybille Creek, which joins the east and northeast oriented Laramie River on the east side of the Laramie Mountains. North to south oriented through valleys on both sides of the Laramie Mountains and in the Laramie Mountains link the Laramie River, Bluegrass Creek, and Sybille Creek valleys. The through valleys, valley orientations, barbed tributaries, elbows of capture, and other similar evidence is interpreted in the context of immense melt water floods from the western margin of a thick North American ice sheet. Floodwaters flowed from western Canada to and across the Laramie Mountains at a time when the Laramie Mountains were just beginning to emerge. Floodwaters at first flowed in south directions in anastomosing complexes of flood flow channels along the present day crest of the Laramie Mountains as well as along the east and west sides of the emerging Laramie Mountains, although the south oriented anastomosing channel complex was later captured by headward erosion of an east and northeast oriented anastomosing channel complex eroding headward from the deep southeast oriented North Platte River valley. More specifically headward erosion of the deep east and northeast oriented Laramie River valley from the deep southeast oriented North Platte River valley beheaded flood flow channels along the west margin of the Laramie Mountains. Floodwaters on the north end of a beheaded flood flow channel reversed flow direction to create the north-northeast and north oriented Sybille Creek drainage route, which then beheaded and reversed flood flow channels on the west side of the emerging Laramie Mountains. Next headward erosion of the east, southeast, and east oriented Bluegrass Creek valley beheaded and reversed flood flow routes to the newly eroded Sybille Creek valley including flood flow routes west of the emerging Laramie Mountains. Headward erosion of the Laramie River valley next beheaded and reversed flood flow channels to the newly eroded Bluegrass Creek valley and then beheaded and reversed flood flow routes further to the west in the Laramie Basin and created the north oriented Laramie River drainage route 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 Laramie River-Sybille Creek drainage divide area landform origins in the Wyoming Laramie 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 Laramie River-Sybille Creek drainage divide area landform evidence in the Wyoming Laramie Mountains will be regarded as evidence supporting the “thick ice sheet that melted fast” paradigm.

Laramie River-Sybille Creek drainage divide area location map

Figure 1: Laramie River-Sybille Creek drainage divide area location map (select and click on maps to enlarge). National Geographic Society map digitally presented using National Geographic Society TOPO software.

Figure 1 provides a location map for the Laramie River-Sybille Creek drainage divide area in the Wyoming Laramie Mountains and illustrates a region in eastern Wyoming. The Wyoming-Nebraska border is located along the east edge of figure 1. Casper is a city near the north edge of figure 1 and the Laramie Mountains extend from just south of Casper in a southeast and south direction to the south edge of figure 1. The Medicine Bow Mountains are located south of highway 80 in the southwest quadrant of figure 1. The Laramie Basin is located between the Medicine Bow Mountains and the Laramie Mountains. The North Platte River flows in a north direction (with some jogs to the northeast and northwest) from the south edge of figure 1 (on west side of Medicine Bow Mountains) to the northwest end of the Laramie Mountains near Casper and then turns to flow in an east and southeast direction around the Laramie Mountains to the east center edge of figure 1. The Laramie River flows in a northeast direction from the south center edge of figure 1 to the city of Laramie. From Laramie the Laramie River flows in a north direction to just north of Wheatland Reservoir where it turns to flow in an east and northeast direction across the Laramie Mountains and then in an east and northeast direction to join the southeast oriented North Platte River near Fort Laramie. Sybille Creek is the unlabeled northeast and north oriented stream located south and east of the Laramie River and flowing from Morton Pass to join the Laramie River west of Wheatland. Like the Laramie River Sybille Creek flows across the Laramie Mountains. The Medicine Bow River originates in the northern Medicine Bow Mountains and flows in a north direction to the town of Elk Mountain and then turns to flow in a northeast, north, and northwest direction to near the town of Medicine Bow. 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 on the west of the Shirley Mountains. Rock Creek is an unlabeled north, northeast, north, and west oriented stream flowing through the towns of McFadden and Rock River before joining the Medicine Bow River near the town of Medicine Bow. The Laramie River-Sybille Creek drainage divide area investigated in this essay is located south and east of the Laramie River and north and west of Sybille Creek and includes regions on both sides of the Laramie Mountains as well as regions in the Laramie Mountains.

The North Platte River and tributary drainage routes, including the Laramie River and its Sybille Creek tributary drainage routes, were developed during immense melt water floods from the western margin of a thick North American ice sheet. The floodwaters flowed from western Canada to and across Montana and Wyoming at a time when Wyoming mountain ranges, including the Laramie Mountains, were just beginning to emerge. At first floodwaters flowed in huge complexes of ever-changing anastomosing south oriented flood flow channels across and along what are today high mountain ranges. As mountain ranges emerged deeper flood flow channels captured floodwaters from shallower flood flow channels and floodwaters on ends of beheaded flood flow channels would often reverse flow direction to flow to the deeper beheading flood flow channel. Often these reversed flow channels would capture floodwaters from adjacent flood flow channels, which resulted in the headward erosion of valleys across divides separating the flood flow channels. Over time by this process floodwaters were channeled into deep valleys surrounding the emerging mountains or into deep valleys crossing the emerging mountain ranges. In the case of the Laramie River and Sybille Creek it is first important to understand the North Platte River drainage route history. As the Laramie Mountains began to emerge a deep southeast oriented North Platte River valley began to erode headward in the region east of the Laramie Mountains and Laramie River valley eroded headward from that actively eroding southeast oriented North Platte River valley head. Headward erosion of the deep Laramie River valley beheaded a south oriented flood flow channel on the east side of the Laramie Mountains and floodwaters reversed flow direction to create what is now the north oriented Sybille Creek drainage route segment. The northeast oriented Sybille Creek drainage route segment eroded headward from that reversed flood flow channel by capturing south oriented flood flow as it eroded headward across the emerging Laramie Mountains. Upon reaching the west side of the Laramie Mountains the Sybille Creek valley beheaded and reversed southeast and south oriented flood flow channels on the west side of the Laramie Mountains. Headward erosion of the deep Laramie River valley followed erosion of the Sybille Creek valley and beheaded flood flow routes to the newly eroded Sybille Creek valley and once west of the emerging Laramie Mountains captured the southeast and south oriented flood flow to the Sybille Creek valley head and then beheaded and reversed a major flood flow channel in the Laramie Basin to create what is today the north oriented Laramie River drainage route in the region between the Medicine Bow Mountains and the Laramie Mountains. Headward erosion of the deep North Platte River valley around the northwest end of the Laramie Mountains then beheaded and reversed flood flow channels west of the emerging Laramie Mountains. In a series of beheading and reversal steps the north oriented North Platte River drainage route was created west of the Laramie Mountains. The reversal of flood flow on the North Platte River alignment also resulted in the reversal of flood flow on southeast and east oriented flood flow channels between the Laramie Mountains and the Medicine Bow Mountains, which created west and northwest oriented North Platte River tributary drainage routes such as the Medicine Bow River drainage route segments.

Detailed location map for Laramie River-Sybille Creek drainage divide area

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

Figure 2 provides a detailed location map for the Laramie River-Sybille Creek drainage divide area in the Wyoming Laramie Mountains. The Laramie Mountains extend in a north to south direction across the center of figure 2. The Laramie Basin is located west of the Laramie Mountains and near the west margin of figure 2 while the Great Plains are located east of the Laramie Mountains and near the east margin of figure 2. The Laramie River flows in a north-northeast direction from the southwest corner of figure 2 and after flowing west of Wheatland Reservoir Number 2 turns to flow in an east and northeast direction across the Laramie Mountains and then on the east side of the Laramie Mountains where it turns to flow in an east direction near the north edge of figure 2 to the northeast corner of figure 2. East and north of figure 2 the Laramie River turns to flow in a northeast direction to join the southeast oriented North Platte River. North, Middle, and South Sybille Creeks flow in northeast, north-northeast, and north directions from the south edge of figure 2 (west of center) and converge to form north-northeast and north oriented Sybille Creek, which joins the Laramie River on the east side of the Laramie Mountains at the point where the Laramie River turns to flow in an east direction near the north edge of figure 2. [North Sybille Creek is erroneously labeled North Sulphur Creek in figure 2.] Bluegrass Creek is formed at the confluence of north oriented tributaries and then flows in a northeast, east, southeast, and east direction to join north-northeast and north oriented Sybille Creek. Halleck Creek is a northeast oriented tributary to the southeast oriented Bluegrass Creek drainage route segment. Slate Creek is a northeast and north oriented Laramie River tributary originating near Government Peak (slightly north of the center of figure 2). The north oriented North Sybille, Middle Sybille, and South Sybille Creek drainage routes were created by reversals of flood flow on north ends of flood flow channels beheaded by headward erosion of the deeper northeast oriented Sybille Creek valley. North and north-northeast oriented Bluegrass Creek headwaters drainage routes were created by reversals of flood flow on north ends of flood flow channels beheaded by headward erosion of the deeper Bluegrass Creek valley, which also beheaded flood flow routes to the newly eroded Sybille Creek valley. The north-northeast oriented Laramie River drainage route west of the Laramie Mountains was created by a reversal of flood flow on the north ends of flood flow channels beheaded by the deeper east and northeast oriented Laramie River valley, which also beheaded flood flow routes to the newly eroded Bluegrass Creek valley.

Laramie River-Sybille Creek drainage divide area east end

Figure 3: Laramie River-Sybille Creek drainage divide area east end. United States Geological Survey map digitally presented using National Geographic Society TOPO software.

Figure 3 provides a topographic map of Laramie River-Sybille Creek drainage divide area east end. The map contour interval for figure 3 is 20 meters. The Laramie River flows in a north-northeast direction from the west edge of figure 3 (south half) on the west side of Moonshine Peak to the west center area of figure 3 and then turns to flow in an east and northeast direction to the north edge of figure 3 (east half). North of figure 3 the Laramie River flows in an east and northeast direction to join the southeast oriented North Platte River. The Laramie River canyon west of Moonshine Peak is approximately 400 meters deep and was initially eroded as a south oriented flood flow channel prior to being beheaded and reversed by headward erosion of what was then a much deeper east and northeast oriented Laramie River valley. Sybille Creek flows in a north-northeast and north direction from the south edge of figure 3 (east half) to the north edge of figure 3 (east half) and north of figure 3 joins the east and northeast oriented Laramie River. The north oriented Sybille Creek valley in figure 3 is located east of the Laramie Mountains and the Sybille Creek drainage route was created by a reversal of flood flow on the north end of a flood flow channel beheaded by headward erosion of the deeper east and northeast oriented Laramie River valley. The Cooney Hills and South Cooney Hills are located in the southeast quadrant of figure 3. A north oriented Laramie River tributary valley is located between the Cooney Hills and Laramie Mountains and is linked by a through valley with a southeast oriented tributary valley. The southeast oriented stream flows to north oriented Sybille Creek as a barbed tributary and provides evidence of the south oriented flood flow channels that once crossed the region. The through valley located between the Cooney Hills and the South Cooney Hills has a floor elevation of between 1600 and 1620 meters. The South Cooney Hills rise to 1803 meters and the Cooney Hills to the north rise to more than 1780 meters suggesting the through valley is at least 160 meters deep. The floor of the through valley south and west of the South Cooney Hills has a floor elevation of between 1620 and 1640 meters and is also at least 160 meters deep. These through valleys were eroded by diverging south oriented flood flow channels that then converged with a south oriented flood flow channel on the present day north oriented Sybille Creek alignment. Present day elevations of the different former south oriented flood flow channels seen in figure 3 can be explained in the context of deep erosion as floodwaters eroded the east side of the emerging Laramie Mountains with crustal warping raising the Laramie Mountains as floodwaters flowed across them.

Detailed map of Laramie River-Sybille Creek drainage divide area

Figure 4: Detailed map of Laramie River-Sybille Creek 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 Laramie River-Sybille Creek drainage divide area seen in less detail in figure 3. The map contour interval for figure 4 is 20 feet. The east margin of the Laramie Mountains is located in the west half of figure 4 and the South Cooney Hills are labeled in the northeast quadrant of figure 4. Northeast, north-northeast, and north oriented Sybille Creek flows from the south center edge of figure 4 to the northeast corner of figure 4. North of figure 4 Sybille Creek joins the east and northeast oriented Laramie River. The north oriented stream flowing to the north center edge of figure 4 in section 19 west of the South Cooney Hills is a tributary to the northeast and east oriented Laramie River north of figure 4. A southeast and east oriented stream flows from sections 35 and 26 in the southwest quadrant of figure 4 to join north-northeast oriented Sybille Creek in section 4. A north to south oriented through valley links the north oriented Laramie River tributary valley with the southeast oriented Sybille Creek tributary valley. The through valley floor elevation by the irrigation canal tunnel in the northeast corner of section 36 is 5379 feet. The South Cooney Hills rise to 5915 feet and elevations in the Laramie Mountains to the west rise much higher suggesting the through valley is approximately 450 feet deep. While the through valley orientation is probably defined by the regional geologic structures the through valley is also a water-eroded valley and was eroded by south oriented flood flow prior to headward erosion of the deeper northeast, east, and northeast oriented Laramie River valley to the north. The north oriented Sybille Creek valley east of the Cooney Hills was also initiated as a south oriented flood flow channel prior to headward erosion of the deep northeast, east, and northeast oriented Laramie River valley. Headward erosion of the deep northeast, east, and northeast oriented Laramie River valley beheaded the south oriented flood flow channels along the east flank of the emerging Laramie Mountains in sequence from east to west. Floodwaters on north end of the beheaded flood flow channel east of the Cooney Hills reversed flow directions to flow in a north direction to the much deeper Laramie River valley and create the north oriented Sybille Creek drainage route east of the Cooney Hills. The reversal of flood flow east of the Cooney Hills captured south oriented floodwaters still moving west of the Cooney Hills and the captured floodwaters made a U-turn around the south end of South Cooney Hills to flow to the newly reversed Sybille Creek drainage route. Headward erosion of the deep Laramie River valley next beheaded and reversed the flood flow channel west of the Cooney Hills and created the north oriented Laramie River tributary drainage route west of the South Cooney Hills. .

Laramie River-Halleck Creek drainage divide area

Figure 5: Laramie River-Halleck Creek drainage divide area. United States Geological Survey map digitally presented using National Geographic Society TOPO software.

Figure 5 illustrates the Laramie River-Halleck Creek drainage divide area 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. The Laramie River flows in an east-southeast, northeast, east-southeast, and north-northeast direction from the west edge of figure 5 (north half) to the north edge of figure 5 (east of center) and north of figure 5 turns to flow in an east and then northeast direction. The east-southeast oriented drainage route near the west edge of figure 5 includes incised meanders where the Laramie River reverses flow direction for a short distance to flow in a northwest direction before turning to join a south or southeast oriented tributary stream. Such reversals of flow direction were created when headward erosion of the deep Laramie River valley captured south or southeast oriented flood flow channels and then eroded headward for a short distance along the reversed flood flow drainage route created on the beheaded flood flow channel alignment. The deep north-northeast oriented Laramie River valley west of Moonshine Peak was probably initiated as a south and south-southwest oriented flood flow channel that was beheaded and reversed by headward erosion of the deep east and northeast oriented Laramie River valley north of figure 5. Sybille Creek flows in a north-northeast direction across the southeast corner of figure 5. Bluegrass Creek flows in a north-northeast direction from the south edge of figure 5 (near southwest corner) and before reaching the Laramie River turns to flow in an east direction to the center of figure 5 and then turns to flow in southeast and east direction to join north-northeast oriented Sybille Creek near the southeast corner of figure 5. Halleck Creek flows in a northeast and east-northeast direction from the south edge of figure 5 through Halleck Canyon to join southeast and east oriented Bluegrass Creek and to flow to Sybille Creek. The Laramie River, Bluegrass Creek, and Halleck are all flowing across the north to south oriented Laramie Mountains in figure 5. Valleys depths vary depending on where and how they are measured, although all valleys range from 200 to 400 meters in depth if not deeper. Slate Creek originates on the south side of Government Peak (in northeast quadrant of figure 5) and flows in a northeast direction to the north edge of figure 5 (near northeast corner). North of figure 5 Slate Creek turns to flow in a north direction to join the east and northeast oriented Laramie River. A deep through valley between Government Peak and Squaw Mountain links the northeast oriented Slate Creek valley with a south and southeast oriented Sybille Creek tributary valley, which drains to north-northeast oriented Sybille Creek as a barbed tributary near the east edge of figure 5. The through valley floor elevation is between 1880 and 1900 meters. Squaw Mountain rises to more than 2160 meters and Government Peak rises to more than 2180 meters. These elevations suggest the through valley is almost 300 meters deep. The through valley was eroded by a southwest and south oriented flood flow channel that probably diverged from the south oriented flood flow channels between the Laramie Mountains and the Cooney Hills and then converged with a southeast oriented flood flow channel, which then converged with a south oriented flood flow channel on the present day north oriented Sybille Creek alignment. Headward erosion of the deep east and northeast oriented Laramie River valley beheaded and reversed the flood flow channel, which for a time captured flood flow from west of Moonshine Peak before headward erosion of the deep Laramie River valley beheaded and reversed that flood flow channel as well to create the north-northeast Laramie River valley segment seen in figure 5.

Detailed map of Slate Creek-Sybille Creek drainage divide area

Figure 6: Detailed map of Slate Creek-Sybille Creek drainage divide area. United States Geological Survey map digitally presented using National Geographic Society TOPO software.

Figure 6 provides a detailed topographic map of the Slate Creek-Sybille Creek drainage divide area seen in less detail in figure 5. The map contour interval for figure 6 is 20 feet. Government Peak is located near the northwest corner of figure 6 and rises to 7248 feet. Squaw Mountain is the mountain mass in the southeast quadrant of figure 6 and in section 32 reaches an elevation of 7102 feet. Slate Creek originates in section 25 as a south oriented stream and then makes a U-turn to flow in a northeast direction across section 30 and then to the north edge of figure 6 (east half). North of figure 6 Slate Creek turns to flow in a north direction to join the east and northeast oriented Laramie River. The east oriented stream flowing across the south margin of section 25 and then turning to flow in a south-southeast and south direction to the south edge of figure 6 (west of center) is an unnamed south and southeast oriented Sybille Creek tributary, which joins north oriented Sybille Creek as a barbed tributary. A through valley near the southeast corner of section 25 links the Slate Creek U-turn valley with the south and southeast oriented Sybille Creek tributary valley. The through valley floor elevation is between 6160 and 6180 feet suggesting the through valley is more than 900 feet deep. The through valley was eroded by a diverging and converging south oriented flood flow channel prior to headward erosion of the deep Laramie River valley to the north of figure 6. The south oriented flood flow channel diverged and converged with flood flow channels along the eastern margin of the Laramie Mountains, which included flood flow channels between the Laramie Mountains and the Cooney Hills and also flood flow channels on the present day Sybille Creek alignment. The present day elevation differences along these former flood flow channel routes is the result of much deeper flood flow erosion east of the Laramie Mountains and probably also of crustal warping that raised the Laramie Mountains as floodwaters were flowing across them. The south oriented Slate Creek headwaters valley suggests the northeast oriented Slate Creek valley (which eroded headward from the south end of a beheaded and reversed flood flow channel) captured south oriented flood flow moving across the high level through valley just east of Government Peak. For that to happen topography of the Laramie Mountains must have looked very different than it does today at the time the deep Laramie River valley eroded headward across the emerging Laramie Mountains.

Laramie River-Bluegrass Creek drainage divide area

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

Figure 7 illustrates the Laramie River-Bluegrass Creek drainage divide area west and slightly south of figure 5 and includes an overlap area with figure 5. The map contour interval for figure 7 is 20 meters. The Laramie Mountains are located in the east half of figure 7 and the eastern margin of the Laramie Basin is seen in the west half of figure 7. Wheatland Reservoir Number 2 is located in the west half of figure 7. The Laramie River flows in a north-northeast from the west edge of figure 7 (south half) to near the north edge of figure 7 and then turns to flow in an east direction with some incised meanders and jogs to eventually reach the east edge of figure 7 (near northeast corner). Bluegrass Ridge is located in the south center area of figure 7. West Bluegrass Creek flows in a north, northeast, and east direction from the south edge of figure 7 (west of center and west of Bluegrass Ridge) to join north-northeast oriented East Bluegrass Creek, which flows from the south center edge of figure 7 (and east of Bluegrass Ridge), and to form northeast and east oriented Bluegrass Creek, which the flows to the east edge of figure 7 (north half). East of figure 7 Bluegrass Creek turns to flow in a southeast and east direction to join north-northeast oriented Sybille Creek. Halleck Creek flows in a northeast and east direction in the southeast quadrant of figure 7 and east of figure 7 joins Bluegrass Creek. The Laramie River, Bluegrass Creek, and Halleck Creek all flow from the region seen in figure 7 on the west side of the Laramie Mountains in independent valleys across the Laramie Mountains and then converge in the Laramie River valley on the east side of the Laramie Mountains. These valleys plus other valleys crossing the Laramie Mountains both north and south of figure 7 were once flood flow channels in a large-scale east and northeast oriented anastomosing channel complex crossing what was at that time the emerging Laramie Mountains. Headward erosion of this east and northeast oriented anastomosing channel complex had systematically captured diverging and converging south oriented flood flow channels some of which flowed along the present day crest of the Laramie Mountains. The north oriented Bluegrass Creek and Laramie River drainage routes seen in figure 7 were formed by reversals of flood flow on north ends of beheaded flood flow routes. As the Laramie Mountains emerged southeast and south oriented flood flow channels formed along the west margin of the emerging Laramie Mountains. At that time mountain ranges in Colorado were still emerging and floodwaters could flow in a south direction into Colorado and probably to the actively eroding Colorado River valley. Headward erosion of the deep northeast and east oriented Bluegrass Creek valley captured south oriented flood flow west of the Laramie Mountains and floodwaters on north ends of the beheaded flood flow channels reversed flow direction to create the north oriented East and West oriented Bluegrass Creek drainage routes. Headward erosion of the deep Laramie River valley next captured south oriented flood flow routes to the newly eroded Bluegrass Creek valley. Floodwaters on the north ends of a beheaded flood flow route further to the west reversed flow direction to create the north oriented Laramie River drainage route. The reversal of flood flow on the present day north oriented Laramie River drainage route was greatly aided by crustal warping that raised mountain ranges in Colorado to the south of figure 7 and which was gradually blocking south oriented floodwaters flowing across the Laramie Basin. The deep Laramie River valley across the Laramie Mountains captured much of this reversed flood flow and diverted the captured floodwaters to the much deeper southeast oriented North Platte River valley east of the Laramie Mountains.

Detailed map of East Bluegrass Creek-Halleck Creek drainage divide area

Figure 8: Detailed map of East Bluegrass Creek-Halleck 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 East Bluegrass Creek-Halleck Creek drainage divide area seen in less detail in figure 7. The map contour interval for figure 8 is 20 feet. East Bluegrass Creek flows in a north-northwest and north-northeast direction from the south edge of figure 8 (west half) to the north edge of figure 8 (west of center) and north of figure 8 joins West Bluegrass Creek to form north-northeast, east, southeast, and east oriented Bluegrass Creek, which flows across the Laramie Mountains and to join north-northeast oriented Sybille Creek. Halleck Creek originates near the corner of sections 9, 10, 15, and 16 and then flows in a north direction before turning to flow in an east and then northeast direction through Halleck Canyon to the north edge of figure 8 (near northeast corner). North and east of figure 8 Halleck Creek flows in an east direction to eventually join Bluegrass Creek and to flow to north-northeast oriented Sybille Creek. Halleck Canyon near the northeast corner of figure 8 is more than 400 feet deep and is even deeper north and east of figure 8. A through valley in section 9 links a west oriented East Bluegrass Creek tributary valley with the east and northeast oriented Halleck Creek valley. The through valley floor elevation is between 7140 and 7160 feet. Elevations near the northeast corner of section 4 to the north rise to more than 7360 feet while comparable elevations are found near the south edge of the southeast quadrant of figure 8 suggesting the through valley is approximately 200 feet deep. East oriented flood flow to the actively eroding Halleck Creek valley was beheaded by headward erosion of the deep Bluegrass Creek valley to the north. Floodwaters on the north end of the beheaded flow channel reversed flow direction to create the north-northeast oriented East Bluegrass Creek drainage route and to behead the east oriented flood flow to the newly eroded Halleck Creek Canyon valley. Interestingly the Bluegrass Creek-Halleck Creek drainage divide elevation as the two streams flow across the Laramie Mountains decreases in elevation although much higher Laramie Mountains elevations can be found north of the Laramie River valley and south of the Sybille Creek drainage basin. The region between the Laramie River valley and the Sybille Creek drainage basin is an unusually low region along the Laramie Mountains crest and is crossed by multiple east, northeast, and north-northeast oriented valleys such as the Bluegrass Creek valley and the Halleck Creek valley. This low region across the Laramie Mountains was probably eroded as massive amounts of south and southeast oriented floodwaters flowing along the west side of the emerging Laramie Mountains flowed across the emerging Laramie Mountains to reach the much deeper North Platte River valley on the east side of the Laramie Mountains.

Bluegrass Creek-Sybille Creek drainage divide area

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

Figure 9 illustrates the Bluegrass Creek-Sybille Creek drainage divide area south and slightly west of figure 7 and there is an overlap area with figure 7. The map contour interval for figure 9 is 20 meters. The south end of Wheatland Reservoir Number 2 crosses the northwest corner of figure 9 and is flooding the Laramie River valley, which then extends in a north direction before turning in an east direction to cross the Laramie Mountains. Morton Pass is located north of the south center edge of figure 9 and is where the northeast oriented highway enters the Laramie Mountains. Plumbago Creek (north Sybille Creek in figure 10) is the north oriented stream west of Morton Pass and north of Morton Pass turns in an east direction to join northeast and north oriented Long Canyon to form northeast oriented North Sybille Creek. The highway follows the North Sybille Creek valley to the east edge of figure 9. Middle Sybille Creek flows in a north-northeast direction from the south edge of figure 9 (near southeast corner) to the east center edge of figure 9 and east of figure 9 joins North Sybille Creek, which after joining north oriented South Sybille Creek forms north-northeast and north oriented Sybille Creek, which then joins the east and northeast oriented Laramie River. Streams flowing to the north center edge of figure 9 and labeled “East” and “West” are East and West Bluegrass Creek, which originate north of the Plumbago Creek (or North Sybille Creek) elbow of capture. Prior to Bluegrass Creek headward erosion headward erosion of the northeast oriented North Sybille Creek valley (probably from a beheaded and reversed flood flow channel on the present day north oriented South Sybille Creek-Sybille Creek alignment) captured south oriented flood flow moving along the west margin of the emerging Laramie Mountains. Floodwaters on the north end of the beheaded flood flow channel reversed flow direction to create the north oriented Plumbago Creek drainage route. Other north oriented North Sybille Creek tributary drainage routes were also created by reversals of flood flow on north ends of beheaded flood flow channels. Headward erosion of the Bluegrass Creek valley (north of figure 9) beheaded and reversed the south oriented flood flow channels west of the emerging Laramie Mountains to create the north oriented East and West Bluegrass Creek drainage routes and to end south oriented flood flow to the North Sybille Creek headwaters.

Detailed map of West Bluegrass Creek-North Sybille Creek drainage divide area

Figure 10: Detailed map of West Bluegrass Creek-North Sybille 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 West Bluegrass Creek-North Sybille Creek drainage divide area seen is less detail in figure 9. The map contour interval for figure 10 is 20 feet. North Sybille Creek (Plumbago Creek in figure 9) flows in a north direction from the south center edge of figure 10 into the southeast corner of section 13 and then turns to flow in an east and northeast direction to the east center edge of figure 10. The northeast oriented highway crossing the southeast quadrant of figure 10 makes use of the northeast oriented North Sybille Creek valley. East of figure 10 North Sybille Creek flows in a northeast direction to join north oriented South Sybille Creek and to form north-northeast and north oriented Sybille Creek, which flows to the east and northeast oriented Laramie River. West Bluegrass Creek originates near the west center edge of figure 10 and flows in east, north, and northeast direction to the north center edge of figure 10. North of figure 10 West Bluegrass Creek flows in a north and then northeast direction to join north-northeast oriented East Bluegrass Creek and to form north-northeast, east, southeast, and east oriented Bluegrass Creek, which joins north-northeast and north oriented Sybille Creek. Pine Ridge is a labeled (hogback?) ridge in the north center area of figure 10. An unimproved north to south oriented road just east of Pine Ridge is located in a north to south oriented through valley linking a northwest oriented West Bluegrass Creek tributary valley with a south oriented North Sybille Creek tributary valley. The through valley floor elevation is between 7240 and 7260 feet. Elevations in section 11 to the west rise to more than 7500 feet and elevations in section 7 to the east also rise to more than 7500 feet suggesting the through valley is at least 240 feet deep. The through valley orientation is probably determined by the local geologic structures, but the through valley is also a water-eroded valley and was eroded by south oriented flood flow moving along the west margin of what at that time were the emerging Laramie Mountains. Headward erosion of the northeast oriented North Sybille Creek valley captured the south oriented flood flow and diverted the floodwaters in a northeast, north-northeast, and north direction to the east and northeast oriented Laramie River valley and then to the deep southeast oriented North Platte River valley. Headward erosion of the Bluegrass Creek valley north of figure 10 next captured the south oriented flood flow. Floodwaters on the north end of the beheaded flood flow channel reversed flow direction and the reversed flow direction to flow to the deeper Bluegrass Creek valley and to create the north oriented West Bluegrass Creek drainage route. The reversed flood flow captured flood flow still moving in a south direction on the present day north oriented Laramie River alignment (west of figure 10) and this captured flood flow moved in an east direction to create the present day east oriented West Bluegrass Creek headwaters drainage route. Headward erosion of the deep east and northeast oriented Laramie River valley next beheaded and reversed the flood flow channel west of figure 10 to create the north oriented Laramie River drainage route on the west side of the Laramie Mountains.

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.

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s

%d bloggers like this: