Box Elder Creek-La Prele 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 Box Elder Creek-La Prele Creek drainage divide area in the Wyoming Laramie Mountains. Box Elder Creek and La Prele Creek flow in north-northeast directions from the southwest side of the Laramie Mountains through deep canyons to reach the east and south oriented North Platte River on the north side of the Laramie Mountains. The North Platte River flows in a north, east, south, and southeast direction around the northwest end of the Laramie Mountains to flow in a southeast direction on the east side of the Laramie Mountains. On the southwest side of the Laramie Mountains the La Prele and Box Elder Creek valleys are linked by through valleys with the south oriented Little Medicine Bow River valley and with the northwest oriented Bates Creek valley, which drains to the north oriented North Platte River west of the Laramie Mountains. The La Prele and Box Elder Creek drainage routes are interpreted in the context of immense south oriented melt water floods from the western margin of a thick North American ice sheet. Floodwaters flowed from western Canada to and across Wyoming at a time when Wyoming mountain ranges were beginning to emerge. The present day north oriented Box Elder Creek and La Prele Creek valleys across the Laramie Mountains originated as south oriented flood flow channels converging with a southeast oriented flood flow channel on the present day northwest oriented Bates Creek alignment to form a south oriented flood flow channel on the present day south oriented Little Medicine Bow River alignment. The south oriented flood flow channel was for a time captured further to the south by east and northeast oriented flood flow channels crossing the emerging Laramie Mountains in valleys, which eroded headward from a deep southeast oriented North Platte River valley, which was actively eroding headward in the region east of the Laramie Mountains. In time headward erosion of the deep North Platte River valley along the east and northeast side of the emerging Laramie Mountains beheaded south oriented flood flow channels on the La Prele Creek and Box Elder Creek alignments. Floodwaters on north ends of the beheaded flood flow channels reversed flow direction to create the north-northeast oriented La Prele Creek and Box Elder Creek drainage routes, which then captured southeast oriented flood flow still moving on the present day northwest oriented Bates Creek alignment. Headward erosion of the deep North Platte River valley around the northwest end of the Laramie Mountains then beheaded south oriented flood flow channels west of the Laramie Mountains and in multiple steps created the north oriented North Platte River drainage route west of the Laramie Mountains. The reversal of flood flow west of the Laramie Mountains also reversed flow directions on the Bates Creek alignment to create the northwest oriented Bates Creek drainage route seen today and also ended flood flow in the La Prele Creek and Box Elder Creek valleys. Flood flow capture and reversal events were probably greatly aided by ice sheet related crustal warping that was raising the Laramie Mountains and that was probably also raising the entire region as floodwaters crossed the region.

Preface

The following interpretation of detailed topographic map evidence is one of a series of essays describing similar evidence for all major drainage divides contained within the Missouri River drainage basin and for all major drainage divides with adjacent drainage basins. The research project is interpreting evidence in the context of a previously unexplored deep glacial erosion paradigm, which is fundamentally different from most commonly accepted North American glacial history interpretations. Project essays are listed on the sidebar category list under their appropriate Missouri River tributary drainage basin, Missouri River segment drainage basin (by state), and/or state in which the Missouri River drainage basin is located.

Introduction

The purpose of this essay is to use topographic map interpretation methods to explore the Box Elder Creek-La Prele 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 Box Elder Creek-La Prele 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.

Box Elder Creek-La Prele Creek drainage divide area location map

Figure 1: Box Elder Creek-La Prele 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 Box Elder Creek-La Prele Creek drainage divide area in the Wyoming Laramie Mountains and illustrates a region in east-central Wyoming. The Laramie Mountains extend in a southeast and south direction from near Casper to the south center edge of figure 1. The North Platte River flows in a north, north-northeast, northeast, east, south, and southeast direction around the northwest end of the Laramie Mountains from Seminoe Reservoir (near southwest corner of figure 1) to the east edge of figure 1 (south half). Box Elder Creek is a labeled north-northeast tributary to the east oriented North Platte River segment north of the Laramie Mountains. The unlabeled north-northeast oriented North Platte River tributary directly east of Box Elder Creek is La Prele Creek. While not obvious from figure 1 both Box Elder Creek and La Prele Creek originate on the southwest side of the Laramie Mountains and are located in deep valley as they flow across the Laramie Mountains to reach the east, south, and southeast oriented North Platte River. The unlabeled west, southwest, south-southeast, south, and west oriented stream south of the Box Elder Creek headwaters is the North Fork Little Medicine Bow River and the Little Medicine Bow River, which near the south edge of figure 1 joins the west and northwest oriented Medicine Bow River to flow to Seminoe Reservoir. The unlabeled northwest oriented North Platte River tributary originating west of the Box Elder Creek headwaters is Bates Creek. Other North Platte River tributaries of importance in this essay include the northeast and east-northeast oriented Laramie River and the south, east-northeast, and east oriented North Laramie River, both of which also flow in deep valleys across the Laramie Mountains. The Box Elder Creek-La Prele Creek drainage divide area investigated in this essay is primarily located east and south of Box Elder Creek, north and west of La Prele Creek, and south of the North Platte River.

The Box Elder Creek and La Prele Creek drainage routes across the Laramie Mountains and the North Platte River drainage route around the northwest end of the Laramie Mountains developed during immense melt water floods from the western margin of a thick North American ice sheet. Floodwaters flowed from western Canada to and across Wyoming at a time when Wyoming mountain ranges, including the Laramie Mountains, were beginning to emerge. Mountain ranges emerged as floodwaters deeply eroded surrounding valleys, basins, and other areas and as ice sheet related crustal warping raised the mountain ranges and probably much of the region seen in figure 1. The present day north oriented North Platte River drainage route west of the Laramie Mountains originated as south oriented flood flow channels west of the emerging Laramie Mountains while the present day north oriented Box Elder Creek and La Prele Creek drainage routes originated as south oriented flood flow channels across the emerging Laramie Mountains. As the Laramie Mountains emerged the south oriented Box Elder Creek and La Prele Creek flood flow channels eroded deeper and deeper valleys into the emerging mountain mass. South oriented flood flow on the Box Elder Creek and La Prele Creek alignments converged with southeast oriented flood flow on the present day northwest oriented Bates Creek alignment to form a south oriented flood flow channel on the present day south oriented Little Medicine Bow River alignment, which then turned in an east direction to reach east and northeast oriented Laramie River tributary valleys eroding headward from a deep southeast oriented North Platte River valley located east of the emerging Laramie Mountains. The deep southeast oriented North Platte River valley proceeded to erode headward along the northeast and north flank of the emerging Laramie Mountains and captured south oriented flood flow routes in sequence from east to west. Floodwaters on north ends of the beheaded flood flow channels reversed flow direction to flow in north directions to the much deeper North Platte River valley and to create north oriented drainage routes. Reversals of flood flow on the La Prele Creek and Box Elder Creek alignments also captured southeast oriented flood flow moving on the present day northwest oriented Bates Creek alignment and diverted that flood flow in north-northeast directions to the deep North Platte River valley. Continued headward erosion of the deep North Platte River valley around the northwest end of the Laramie Mountains in time began to behead and reverse flood flow channels west of the Laramie Mountains. In a series of steps this beheading and reversal process created the present day north oriented North Platte River drainage route west of the Laramie Mountains and also created the northwest oriented Bates Creek drainage route, which ended flood flow to the newly formed north-northeast oriented La Prele Creek and Box Elder Creek drainage routes.

Detailed location map for Box Elder Creek-La Prele Creek drainage divide area

Figure 2: Detailed location map Box Elder Creek-La Prele 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 Box Elder Creek-La Prele Creek drainage divide area in the Wyoming Laramie Mountains. Green colored areas are National Forest lands, which in figure 2 are located in the Laramie Mountains. Casper is the city near the northwest corner of figure 2. The North Platte River flows in an east direction from Casper to near the northeast corner of figure 2 and then turns in a south and southeast direction to flow to the east center edge of figure 2. La Prele Creek originates near the south center edge of figure 2 and flows in a north-northeast direction to join the east, south, and southeast oriented North Platte River as a barbed tributary near the town of Orpha (near northeast corner of figure 2). Rabbit Creek is a north oriented La Prele Creek tributary in the south center area of figure 2. [East of Rabbit Creek figure 2 shows another north oriented La Prele Creek tributary and names it La Prele Creek. The southern end of that drainage route does not exist and the north end should be named Little La Prele Creek.] Red Canyon Creek is a northeast oriented La Prele Creek tributary originating east of the town of Boxelder (slightly south of the center of figure 2). Box Elder Creek originates in the Laramie Mountains west of the La Prele Creek headwaters and flows in a southwest direction before turning to flow in a north-northeast, north, north-northeast, and northeast direction to join the east, south, and southeast oriented North Platte River near the town of Careyhurst. East Box Elder Creek is a north oriented Box Elder Creek tributary in the south center area of figure 2. Little Box Elder Creek is a north, northeast, and northwest oriented tributary joining Box Elder Creek near the North Platte River. Deer Creek is a south, southwest, north, and north-northeast oriented stream west of Box Elder Creek, which also flows across the Laramie Mountains to join the east, south, and southeast oriented North Platte River near the town Glenrock. Rock Creek is a southwest oriented stream originating south of the north oriented East Box Elder Creek headwaters. Rock Creek flows to the west and southwest oriented North Fork Little Medicine Bow River, which south of figure 2 flows to the south and west oriented Little Medicine Bow River, which flows to the west and northwest oriented Medicine Bow River, which flows to the north, north-northeast, and northeast oriented North Platte River located west of the Laramie Mountains and which flows around the northwest end of the Laramie Mountains to reach the east oriented North Platte River segment seen at Casper in northwest corner of figure 2. Bates Creek Reservoir is located near the southwest corner of figure 2. Bates Creek flows in a west-northwest direction to Bates Creek Reservoir and then flows in a northwest, southwest, and northwest direction to the west edge of figure 2 (south half). West of figure 2 Bates Creek flows in a northwest direction to join the north-northeast and northeast oriented North Platte River before the North Platte River flows around the northwest end of the Laramie Mountains.

Box Elder Creek-North Fork Little Medicine Bow River drainage divide area

Figure 3: Box Elder Creek-North Fork Little Medicine Bow River drainage divide area. United States Geological Survey map digitally presented using National Geographic Society TOPO software.

Figure 3 provides a topographic map of the Box Elder Creek-North Fork Little Medicine Bow River drainage divide area. The map contour interval for figure 3 is 20 meters. The Cloverdale Basin is located near the southeast corner of figure 3. La Prele Creek originates near the Cloverdale Basin and flows in a north-northeast direction to the east edge of figure 3 (slightly north of center). East and north of figure 3 La Prele Creek flows in a north-northeast direction across the Laramie Mountains to join the east, south, and southeast oriented North Platte River. The La Prele Creek valley near the east edge of figure 3 is almost 400 meters deep and is eroded into the Laramie Mountains. The North Fork Little Medicine Bow River originates near the Cloverdale Basin and flows in a west-southwest and west-northwest direction before turning to flow in a south-southwest direction to the south edge of figure 3 (west half). South of figure 3 the North Fork flows to the south and west oriented Little Medicine Bow River, which flows to the west and northwest oriented Medicine Bow River, which then flows to the north oriented North Platte River, which then flows around the northwest end of the Laramie Mountains. Twin Peaks are located in the east center area of figure 3. East Box Elder Creek originates near Twin Peaks and flows for a short distance in a west direction before turning to flow in a north direction to the north edge of figure 3 (east half). North of figure 3 East Box Elder Creek flows to north-northeast oriented Box Elder Creek. The East Box Elder Creek valley between Cherry Mountain and Buffalo Peak is more than 300 meters deep. Box Elder Creek originates west of the East Box Elder Creek headwaters and flows in a southwest direction before turning to flow in a north-northeast direction to the north edge of figure 3 (east of center). North of figure 3 Box Elder Creek flows in a north-northeast direction to join the east, south, and southeast oriented North Platte River. The Box Elder Creek valley across the Laramie Mountains and seen in figure 3 is almost 400 meters deep. West of the southwest quadrant of figure 3 are headwaters of northwest oriented Bates Creek, which flows to the north oriented North Platte River before the North Platte River flows around the northwest end of the Laramie Mountains. As can be seen in figure 3 La Prele Creek, Box Elder Creek, and East Box Elder Creek have eroded deep north oriented valleys across the Laramie Mountains when south and west oriented drainage routes originate in the same region (on the southwest side of the Laramie Mountains). The La Prele Creek, Box Elder Creek, and East Box Elder Creek valleys originated as south oriented flood flow channels, which converged with a southeast oriented flood flow channel on the present day Bates Creek alignment to form a south oriented flood flow channel on the present day Little Medicine Bow River alignment. Headward erosion of the deep southeast oriented North Platte River valley beheaded and reversed flood flow in the La Prele and Box Elder Creek valleys to create north oriented drainage routes, which captured southeast oriented flood flow from the Bates Creek alignment. Continued headward erosion of the deep North Platte River valley around the northwest end of the Laramie Mountains then beheaded and reversed flood flow on the Bates Creek alignment and ended flood flow in the region seen in figure 3.

Detailed map of East Box Elder Creek-Rock Creek drainage divide area

Figure 4: Detailed map of East Box Elder Creek-Rock 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 East Box Elder Creek-Rock Creek drainage divide area seen in less detail in figure 3. The map contour interval for figure 4 is 20 feet. East Box Elder Creek originates in section 18 and flows in a west direction to the west margin of section 18 where it turns to flow in a north direction to the north edge of figure 4 (east of center). North of figure 4 East Box Elder Creek flows in a north direction to join north-northeast oriented Box Elder Creek, which then flows to the east, south, and southeast oriented North Platte River.  Rock Creek originates in the south half of section 13 and flows in a south-southwest direction to the south edge of figure 4. South of figure 4 Rock Creek flows to the west and south-southwest oriented North Fork Little Medicine Bow River, which then flows to the south and west oriented Little Medicine Bow River, which then flows to the north, north-northeast, and northeast oriented North Platte River, which then flows in an east, south, and southeast direction around the northwest end of the Laramie Mountains. A well-defined through valley in section 13 links the north oriented East Box Elder Creek valley with the south-southwest oriented Rock Creek valley. The through valley floor elevation is between 8460 and 8480 feet. Elevations near the northwest corner of figure 4 rise to more than 9100 feet while elevations at Twin Peaks near the east center edge of figure 4 also exceed 9100 feet. These elevations suggest the through valley is at least 600 feet deep. The through valley was originally eroded by south oriented flood flow moving to a south oriented flood flow channel on the present day south oriented Little Medicine Bow River alignment. Headward erosion of the deep southeast oriented North Platte River valley beheaded and reversed the south oriented flood flow to create the north oriented East Box Elder Creek drainage route and to create the East Box Elder Creek-Rock Creek drainage divide. It is possible there were additional flood flow movements, although those movements cannot be easily determined from evidence seen in figure 4.

East Box Elder Creek-Horseshoe Bend Creek drainage divide area

Figure 5: East Box Elder Creek-Horseshoe Bend Creek drainage divide area. United States Geological Survey map digitally presented using National Geographic Society TOPO software.

Figure 5 illustrates the East Box Elder Creek-Horseshoe Bend Creek drainage divide area north and east of figure 3 and there is an overlap area with figure 3. The map contour interval for figure 5 is 20 meters. Box Elder Creek flows in a north-northeast direction from the southwest corner of figure 5 to the town of Boxelder and then in a north direction to the north edge of figure 5 (west of center). North of figure 5 Box Elder Creek flows in a north-northeast direction to join the east, south, and southeast oriented North Platte River. Box Elder Creek crosses the 2000-meter contour line shortly before it crosses the north edge of figure 5. East Box Elder Creek flows in a north direction from the south edge of figure 5 (west half) to join Box Elder Creek near the town of Boxelder. La Prele Creek flows in a north-northeast direction from the south edge of figure 5 (east of center) to the northeast corner of figure 5. North and east of figure 5 La Prele Creek flows to the east, south, and southeast oriented North Platte River. La Prele Creek crosses the 1740-meter contour just east of Moss Agate Hill (near northeast corner of figure 5). Peterson Mountain is a labeled high point in the south half of figure 5 and is located east of East Box Elder Creek. Horseshoe Bend Creek originates east of Peterson Mountain and flows in an east-southeast and northeast direction to join northeast and southeast oriented Dry Fork, which joins north-northeast oriented La Prele Creek at mouth of La Prele Gorge. The La Prele Creek valley north of La Prele Gorge is almost 300 meters deep and is much deeper than the Box Elder Creek valley to the west. The deep northeast and southeast oriented Dry Fork valley and southeast oriented Perry Creek valley just to the north suggest at least some of the floodwaters that eroded the deeper La Prele Creek valley came from the west. What has happened here is headward erosion of the deep southeast oriented North Platte River valley beheaded and reversed flood flow on the La Prele Creek alignment while floodwaters were still flowing in a south direction on the Box Elder Creek and East Box Elder Creek alignments. Reversed flood flow on the La Prele Creek alignment captured some of the south oriented flood flow on the East Box Elder Creek alignment and some the floodwaters may have flowed in through valleys south of Peterson Mountain to the Horseshoe Creek alignment and then to the newly reversed La Prele Creek drainage route. Captured south oriented floodwaters from the Box Elder Creek alignment helped erode the much deeper north-northeast oriented La Prele Creek valley north of La Prele Gorge.

Detailed map of East Box Elder Creek-Horseshoe Bend Creek drainage divide area

Figure 6: Detailed map of East Box Elder Creek-Horseshoe Bend 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 East Box Elder Creek-Horseshoe Bend Creek drainage divide area seen in less detail in figure 5. The map contour interval for figure 6 is 40 feet. East Box Elder Creek flows in a north, northwest, north, and northeast direction from the south edge of figure 6 (near southwest corner) to the north edge of figure 6 (near northwest corner) and north of figure 6 joins north-northeast oriented Box Elder Creek, which then flows to the east, south, and southeast oriented North Platte River. Elk Run Creek is the north and northwest oriented East Box Elder Creek tributary flowing from Elk Lake in the southwest quadrant of figure 6. Horseshoe Bend Creek originates in section 16 and flows in a south, southeast, and east direction to the east center edge of figure 6. East of figure 6 Horseshoe Bend Creek flows in a northeast direction to join northeast and southeast oriented Dry Fork, which then joins north-northeast oriented La Prele Creek. A southeast oriented Horseshoe Bend Creek tributary flows across section 15 and joins Horseshoe Bend Creek near the east center edge of figure 6. An east and northeast oriented stream flows across section 21 to join Horseshoe Bend Creek in the northwest corner of section 22. A through valley in the southwest quadrant of section 21 links the northeast oriented Horseshoe Bend Creek tributary valley with a west oriented Elk Run Creek tributary valley. The through valley floor elevation is shown as 7738 feet. Peterson Mountain to the north rises 8238 feet. Elevations near the south center edge of figure 6 rise to 8235 feet. These elevations suggest the through valley is approximately 500 feet deep. While not deep compared to the much deeper Box Elder Creek and La Prele Creek valleys the through valley is evidence of what was once a flood flow channel possibly linking what was at that time a south oriented flood flow channel on East Box Elder Creek alignment with a reversed flood flow channel on the La Prele Creek alignment, although flood flow in the through valley could have occurred before the reversal of flood flow on the La Prele Creek alignment. The through valley floor elevation is approximately 300 feet higher than the East Box Elder Creek valley to the west, which suggests floodwaters lowered the East Box Elder Creek by 300 feet after the time floodwaters stopped using the through valley to reach the La Prele Creek valley. There are numerous similar through valleys in the Laramie Mountains and they tell a story of ever-changing diverging and converging flood flow channels as floodwaters first moved in south directions and then as floodwaters were systematically beheaded and reversed by headward erosion of the much deeper North Platte River valley.

Box Elder Creek-La Prele Creek drainage divide area

Figure 7: Box Elder Creek-La Prele Creek drainage divide area. United States Geological Survey map digitally presented using National Geographic Society TOPO software.

Figure 7 illustrates the Box Elder Creek-La Prele Creek drainage divide area north and east of figure 5 and includes an overlap area with figure 5. The map contour interval for figure 7 is 20 meters. Box Elder Creek flows in a north, northeast, northwest, northeast, and north direction from the southwest corner of figure 7 to the north edge of figure 7 (west half) and north of figure 7 flows in a northeast direction to join the east, south, and southeast oriented North Platte River. La Prele Creek flows in a north-northeast direction from the south edge of figure 7 (east of center) to La Prele Reservoir and then in a north direction to the north edge of figure 7. North of figure 7 La Prele Creek flows in a north-northeast direction to join the east oriented North Platte River just before the North Platte River turns to flow in a south and southeast direction. Windy Ridge is a labeled ridge located north of the center of figure 7. Little Box Elder Creek originates north of Windy Ridge and flows in a west-northwest and north-northeast direction to the north edge of figure 7 (west of center). North of figure 7 Little Box Elder Creek turns to flow in a northwest direction toward Box Elder Creek. Cottonwood Creek originates north and east of the northeast end of Windy Ridge and flows in a north-northeast direction to the north edge of figure 7 (west of center). North of figure 7 Cottonwood Creek turns to flow in a north-northwest direction toward Box Elder Creek. Buckshot Creek is a southeast and east oriented La Prele Creek tributary originating near the northeast end of Windy Ridge and Deadwood Creek is a southeast oriented La Prele Creek tributary south of Buckshot Creek. A northwest to southeast oriented through valley near the northeast end of Windy Ridge links the northeast oriented Cottonwood Creek headwaters valley with the southeast oriented Buckshot Creek headwaters valley. The through valley was eroded by southeast oriented flood flow moving to the La Prele Creek valley and provides of south oriented flood flow prior to the reversals of flood flow that created the present day north oriented drainage routes. Figure 7 illustrates deep north oriented canyons eroded across hogback ridges forming the northern margin of the Laramie Mountains upland region. Box Elder Canyon in the northwest quadrant of figure 7 is more than 200 meters deep and La Prele Creek has eroded a water gap almost as deep. Little Box Elder Creek and Cottonwood Creek also originate south of the hogback ridges and have eroded deep water gaps. These water gaps provide evidence the drainage routes were initiated at a time when the hogback ridges were not barriers to water movements as they are today. The water gaps were probably initiated by diverging and converging south oriented flood flow channels crossing what at that time was an emerging Laramie Mountains mass. Headward erosion of the deep North Platte River valley to the north beheaded and reversed the south oriented flood flow channels in sequence from east to west.

Detailed map of Cottonwood Creek-Buckshot Creek drainage divide area

Figure 8: Detailed map of Cottonwood Creek-Buckshot 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 Cottonwood Creek-Buckshot Creek drainage divide seen in less detail in figure 7. The map contour interval for figure 8 is 20 feet. Little Box Elder Creek originates near the southeast corner of section 21 and flows in a west-northwest direction almost to the west edge of figure 8 before turning to flow in a north-northeast direction to the north edge of figure 8 (near northeast corner). North of figure 8 Little Box Elder Creek flows to northwest oriented Cottonwood Creek, which is flowing toward north-northeast oriented Box Elder Creek. Cottonwood Creek originates in section 22 and flows in an east-northeast direction into section 23 and then in a northeast direction to the north edge of figure 8 (east half). North of figure 8 Cottonwood Creek turns to flow in a northwest direction toward northeast oriented Box Elder Creek. Buckshot Creek originates in the northeast corner of section 27 and flows in a southeast and east-northeast direction to the east edge of figure 8 (south half). East of figure 8 Buckshot Creek flows to north-northeast oriented La Prele Creek. A through valley near the corner of sections 21,22, 27, and 28 links the west-northwest oriented Little Box Elder Creek headwaters valley with the east-northeast oriented Cottonwood Creek headwaters valley. The through valley floor elevation is between 6300 and 6320 feet. Elevations in section 16 to the north rise to 6585 feet while elevations on Windy Ridge to the south rise to 6634 feet suggesting the through valley is at least 265 feet deep. A slightly deeper through valley in the north half of section 27 links the east-northeast oriented Cottonwood Creek headwaters valley with the southeast oriented Buckshot Creek headwaters valley. This second through valley has a floor elevation of between 6240 and 6260 feet suggesting this through valley is almost 300 feet deep. These two through valleys were eroded by floodwaters that moved in a south direction on the present day north oriented Little Box Elder Creek alignment and then in an east direction to a southeast oriented flood flow channel on the Buckshot Creek alignment and to a diverging east-northeast oriented flood flow channel on the Cottonwood Creek alignment. This interpretation is consistent with a reversals of flood flow on the La Prele and Cottonwood Creek alignments prior to a reversal of flood flow on the Little Box Elder Creek alignment, although it requires different drainage patterns north of figure 8 at that time (which makes sense because the region north of figure 8 has been deeply eroded since that time).The Spring Canyon Creek Road in sections 24 and 25 is located in a north to south oriented through valley linking the north oriented Spring Canyon Creek valley with the southeast and east-northeast oriented Buckshot Creek valley. North of figure 8 Spring Canyon Creek turns to flow in a northeast direction to join La Prele Creek. This third through valley floor elevation is 6169 feet. Elevations to the east rise to 6302 feet suggesting the through valley is at least 140 feet deep. This third through valley was probably eroded by south oriented flood flow prior to the reversal of flood flow on the La Prele Creek alignment.

La Prele Creek-North Platte River drainage divide area

Figure 9: La Prele Creek-North Platte River drainage divide area. United States Geological Survey map digitally presented using National Geographic Society TOPO software.

Figure 9 illustrates the La Prele Creek-North Platte River drainage divide area north and east of figure 7 and there is an overlap area with figure 7. The map contour interval for figure 9 is 20 meters. Douglas is the city near the east edge of figure 9. The North Platte River flows in east direction from near the northwest corner of figure 9 into the east half of figure 9 and then turns to flow in a south and south-southeast direction to the south edge of figure 9 (near southeast corner). La Prele Creek flows in a north and north-northeast direction from the south edge of figure 9 (near southwest corner) to join the North Platte River just east of the north center edge of figure 9. La Prele Creek flows to the North Platte River as a barbed tributary. Fivemile Creek is a northeast and east oriented tributary joining the south oriented North Platte River in the east center area of figure 9. Alkali Gulch is a north-northeast and north oriented North Platte River west of La Prele Creek. A west to east oriented through valley extends from the Alkali Gulch valley across the La Prele Creek valley to the valley of an east oriented Fivemile Creek tributary. This through valley is defined by two or more contour lines suggesting it is probably 40 meters deep, if not deeper. The through valley probably was eroded by an east oriented flood flow channel (parallel to an east oriented flood flow channel on the present day North Platte River alignment) in what at that time was an anastomosing channel complex. If so somewhat complex flood flow movements occurred as the deep south-southeast oriented North Platte River valley eroded headward into the region. East oriented flood flow channels along the northern margin of the emerging Laramie Mountains moved floodwaters to the actively eroding south oriented North Platte River valley. Headward erosion of these east oriented flood flow channels probably beheaded and reversed flood flow on the La Prele Creek alignment before headward erosion of the deep east oriented North Platte River valley,. As seen in earlier figures the reversal of flood flow on the La Prele Creek alignment captured flood flow from south and west of the Laramie Mountains so after headward erosion of the deep east oriented North Platte River valley north-northeast oriented flood flow probably moved on the present day La Prele Creek alignment to the newly eroded North Platte River valley.

Detailed map La Prele Creek-Fivemile Creek drainage divide area

Figure 10: Detailed map of La Prele Creek-Fivemile 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 La Prele Creek-Fivemile Creek drainage divide area seen in less detail in figure 9. The map contour interval for figure 10 is 20 feet. La Prele Creek flows in a north-northeast direction from the west center edge of figure 10 to the north edge of figure 10 (west half). North of Figure 10 La Prele Creek flows to the east and south oriented North Platte River. Fivemile Creek flows in a northeast direction across the southeast corner of figure 10 and east of figure 10 turns to flow in an east direction to join the south oriented North Platte River. A stream originates in the east half of section 32 and flows in an east direction across sections 33, 34, and 35 to the east edge of figure 10 and joins Fivemile Creek east of figure 10. A southeast oriented tributary to the east oriented Fivemile Creek tributary originates in the south half of section 28. Through valleys link the north-northeast oriented La Prele Creek valley with the east oriented Fivemile Creek tributary valley. The deepest through valley is in section 28 at the head of the southeast oriented tributary to the east oriented Fivemile Creek tributary. The section 32 through valley has a floor elevation of between 5020 and 5040 feet. Just north of figure 10 elevations rise to 5259 feet and south of figure 10 elevations rise much higher suggesting the through valley is at least 200 feet deep. Through valleys near the corner of sections 28, 29, 32, and 33 and in section 32 have floor elevations of 5075 feet and are slightly less than 200 feet deep. These three through valleys were probably eroded as deeper channels in the floor of a much broader west-northwest to east-southeast flood flow channel, which in this region was captured by headward erosion of the deeper north-northeast oriented La Prele Creek valley. The La Prele Creek valley in this region was eroded by north-northeast oriented flood flow moving across the Laramie Mountains in the deep La Prele Creek valley, but is at a much lower elevation and was probably eroded at a much later time when the deep North Platte River valley was actively eroding headward across the region north of figure 10. Headward erosion of a deeper north-northeast oriented La Prele Creek valley across east oriented flood flow channels along the north margin of the Laramie Mountains captured the east oriented flood flow and diverted the floodwaters to the deeper North Platte River valley.

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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