Abstract:

This essay uses topographic map evidence to interpret landform origins in the Crow Creek-South Platte River drainage divide area along the Wyoming-Colorado border. The South Platte River flows in a north-northeast direction along the east side of the Colorado Front Range before turning in an east-southeast, east, and northeast direction to flow into western Nebraska and to join the North Platte River to form the Nebraska Platte River. Crow Creek headwaters consist of several east oriented streams originating near the west edge of the Wyoming Laramie Mountains and converging in or just east of the Laramie Mountains to form Crow Creek, which after flowing in an east direction just north of the Wyoming-Colorado state line and the south-facing Chalk Bluffs escarpment turns to flow in a south and south-southwest direction to join the east-southeast oriented South Platte River. South of east oriented Crow Creek are other east oriented streams, which also turn abruptly to flow in south directions with water eventually reaching the South Platte River. West of the east oriented Crow Creek headwaters in the Laramie Mountains are headwaters of south oriented Dale Creek, which flows to the southeast oriented Cache la Poudre River and then to the east-southeast oriented South Platte River. West of the south oriented Dale Creek drainage route is the west flank of the Laramie Mountains and the Laramie Basin, which is today drained by the north and northeast oriented Laramie River to the southeast oriented North Platte River. Crow Creek-South Platte River drainage divide area landforms along the Wyoming-Colorado border are 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 Wyoming and Colorado at a time when the Laramie Mountains were just beginning to emerge. Floodwaters flowed from the present day Laramie Basin in an east oriented anastomosing channel complex across the emerging the Laramie Mountains to deep valleys eroding headward into western Nebraska. Headward erosion of a deeper south oriented anastomosing channel complex on the Colorado Piedmont (east of the emerging Front Range) started to capture the east oriented anastomosing channel complex. This capture process took place near the present day Wyoming-Colorado state line as headward erosion of deep south oriented flood flow channels captured east oriented flood flow channels and in the process created the south-facing Chalk Bluffs escarpment. As the capture was taking place headward erosion of the east-southeast, east, and northeast oriented South Platte River valley from western Nebraska captured the south oriented anastomosing channel complex and diverted floodwaters into western Nebraska. Floodwaters on north ends of beheaded flood flow channels reversed flow direction to create what are today the north oriented South Platte River drainage route and north oriented tributary drainage routes to the east-southeast, east, and northeast oriented South Platte River segment. The capture of the east oriented anastomosing channel complex was halted when headward erosion of the Dale Creek valley and of even deeper south oriented valleys in the Laramie Basin (now reversed to drain in north directions) and/or uplift of the Laramie Mountains beheaded the east oriented flood flow channels and ended east oriented flood flow near the present day Wyoming-Colorado border.

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 Crow Creek-South Platte River drainage divide area landform origins along the Wyoming-Colorado border. 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 Crow Creek-South Platte River drainage divide area landform evidence along the Wyoming-Colorado border will be regarded as evidence supporting the “thick ice sheet that melted fast” paradigm.

Crow Creek-South Platte River drainage divide area location map

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

Figure 1 provides a location map for the Crow Creek-South Platte River drainage divide area along the Wyoming-Colorado border and illustrates a region in northern Colorado in the south and the southeast corner of Wyoming to the north with western Nebraska in the northeast corner. The Laramie Mountains are located just east of Laramie, Wyoming and extend in a south direction into Colorado where they merge with the north to south oriented Front Range located west of Denver. The South Platte River flows in a north direction to Denver and then to Greeley, Colorado where it turns to flow in an east-southeast, east, and northeast direction to the east edge of figure 1 (north half). North oriented tributaries flow to the east-southeast, east, and northeast oriented South Platte River segment. The Cache la Poudre River originates in northern Rocky Mountain National Park and flows in a north, east, and southeast direction to join the South Platte River near Greeley (and near where the South Platte River changes from flowing in north direction to flowing in an east-southeast direction). The east and south oriented Cache la Poudre River tributary flowing through Halligan Reservoir is the North Fork Cache la Poudre River and the south oriented tributary flowing from Wyoming to Halligan Reservoir is Dale Creek. Crow Creek flow from near the Dale Creek headwaters in the Wyoming Laramie Mountains in an east and southeast direction to Cheyenne and then continues to flow in an east direction before turning to flow in a south and south-southwest direction to join the east-southeast oriented South Platte River a short distance east of Greeley. Between Dale Creek and the south oriented Crow Creek drainage routes there are several unlabeled south and south-southeast streams flowing from near the Wyoming-Colorado border to the South Platte River and/or to Crow Creek and/or the Cache la Poudre River. Also originating near the Dale Creek and Crow Creek headwaters in the Wyoming Laramie Mountains is Lodgepole Creek, which flows in an east direction into western Nebraska and then to the east edge of figure 1. East of figure 1 Lodgepole Creek turns to flow in a southeast direction to join the northeast oriented South Platte River. The Crow Creek-South Platte River drainage divide area investigated in this essay is located south and west of Crow Creek, east of Dale Creek and the North Fork Cache la Poudre River, and north of the South Platte River, although this essay focuses on the drainage divide area near the Wyoming-Colorado border.

Drainage routes in the Crow Creek-South Platte River drainage divide area and adjacent regions developed during immense melt water floods from the western margin of a thick North American ice sheet at a time when Wyoming and Colorado mountain ranges were just beginning to emerge. Floodwaters initially flowed from western Canada in south directions to and across the region seen in figure 1, although flood flow directions changed as mountain ranges emerged and deep valleys eroded headward into the region. Drainage routes seen today generally reflect flood flow directions at the time floodwaters ceased to flow in the present day valleys, which varied from region to region. North of the Wyoming border and north of figure 1 are east oriented drainage routes (including the Lodgepole and Crow Creek drainage routes) flowing from the west edge of the Laramie Mountains across southeast Wyoming to join the northeast oriented South Platte River or the southeast oriented North Platte River. These east oriented drainage routes originated as an east oriented complex of ever-changing anastomosing flood flow channels flowing from the present day Laramie Basin area (west of the Wyoming Laramie Mountains) across what were at that time the emerging Laramie Mountains to the much deeper northeast oriented South Platte River and southeast oriented North Platte River valley heads, which were eroding headward from the deep and newly eroded Platte River valley in western Nebraska. Most of these east oriented flood flow channels were beheaded by uplift of the Laramie Mountains and/or by deep erosion that lowered the Laramie Basin floor west of the Laramie Mountains and today the east oriented North and South Platte River tributary drainage routes beginning near the west edge of Laramie Mountains and flowing into western Nebraska (including the Crow Creek and Lodgepole Creek drainage routes) are located in the former east oriented flood flow channels.

At about the same time as east oriented floodwaters were flowing across the emerging Laramie Mountains to the actively eroding and deep North and South Platte River valley heads in western Nebraska a deeper south oriented complex of anastomosing flood flow channels was eroding headward in the region east of the emerging Front Range in Colorado. At one time the south oriented flood flow channels flowed to the southeast oriented Arkansas River valley, but prior to headward erosion of the Arkansas River valley the south oriented flood flow drained to southeast and south oriented valleys further to the south. Headward erosion of these deeper south oriented flood flow channels to the present day Wyoming-Colorado border region resulted in the capture of some of the southern east oriented flood flow channels. The Crow Creek elbow of capture where east oriented Crow Creek turns to flow in a south direction illustrates one such capture location. Other capture locations are seen on more detailed maps illustrated in this essay. The south oriented anastomosing channel complex was captured by headward erosion of the deeper east-southeast, east, and northeast oriented South Platte River valley. Floodwaters on north ends of the beheaded flood flow channels reversed flow direction to flow in a north direction to the deeper South Platte River valley. Because flood flow channels were beheaded in sequence from east to west and because the flood flow channels were anastomosing (diverging and converging) the newly beheaded and reversed flood flow channels could capture floodwaters still moving in a south direction west of the actively eroding South Platte River valley head. These captures of yet to be beheaded flood flow enabled reversed flood flow to create significant north and north-northeast oriented drainage routes. The north-northeast oriented South Platte River drainage route south of Denver captured significant south oriented flood flow from west of the emerging Front Range, which accounts for the southeast and north-northeast oriented South Platte River drainage route south of figure 1 (and not seen in this essay).

Detailed location map for Crow Creek-South Platte River drainage divide area

Figure 2: Detailed location map Crow Creek-South Platte 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 Crow Creek-South Platte River drainage divide area along the Wyoming-Colorado border. The Wyoming-Colorado border extends in a west to east direction across figure 2 (north of center). Green colored areas are National Forest lands. The green colored area in the northwest corner of figure 2 is in the Wyoming Laramie Mountains (the Sherman Mountains are a small mountain range within the larger Laramie Mountains). Crow Creek headwaters streams originate in the Sherman Mountains area near the northwest corner of figure 2 and include North Fork Crow Creek, Middle Crow Creek, and South Crow Creek, among others, and flow in east directions to converge near Silver Crown on the east side of the Laramie Mountains and west Cheyenne. Crow Creek flows in an east and southeast direction from near Silver Crown to Cheyenne and then in an east direction to Campstool and Arcota. Near Arcota Crow Creek turns in a southeast and south direction and then flows almost to the southeast corner of figure 2 before turning in a west and south direction around Seven Cross Hill to reach the south edge of figure 2 (near Briggsdale). South of figure 2 Crow Creek flows in a south-southwest direction to join the east-southeast oriented South Platte River. Porter Creek (flowing in Porter Draw) originates south of Cheyenne and flows in an east direction to Chalk Bluffs where it turns to flow in a southeast and south-southeast direction to join south-southeast oriented Little Crow Creek, which joins Crow Creek on the northwest side of Seven Cross Hill. Little Crow Creek headwaters are located south of the Porter Creek headwaters and north of the state line and are named Little Simpson Creek and Simpson Creek on more detailed maps. Willow Creek is a south-southeast oriented tributary joining Little Crow Creek at Heart Reservoir just north of Seven Cross Hill. Lone Tree Creek (as seen in figure 2) originates near Buford, south of the green colored area in the northwest corner of figure 2, and flows in a southeast and east direction on the south side of the highway to Borie where it turns to flow in an south-southeast direction to the south center edge of figure 2. South of figure 2 Lone Tree Creek flows to the east-southeast oriented South Platte River. Owl Creek is a south-southeast oriented stream originating south of Cheyenne and just south of the state line and flows to the south edge of figure 2 (east of Lone Tree Creek) and joins Lone Tree Creek south of figure 2. Dale Creek originates in the Sherman Mountains near the northwest corner of figure 2 and flows in a south, southeast, and south direction to join the North Fork Cache la Poudre River near Halligan Reservoir. The North Fork Cache la Poudre River then flows in a southeast and south direction to join the southeast oriented Cache la Poudre River, which flows to the south edge of figure 2 (just east of green colored area) and south of figure 2 joins the South Platte River near the point where the South Platte River turns from flowing in a north direction to flowing in an east-southeast direction. Figure 2 illustrates several elbows of capture where east oriented flood flow channels coming from the Laramie Mountains were captured by headward erosion of south oriented flood flow channels. These elbows of capture include the Lone Tree Creek, Porter Creek, Simpson Creek, and Crow Creek elbows of capture.

Dale Creek-Middle Crow Creek drainage divide area

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

Figure 3 provides a topographic map of Dale Creek-Middle Crow Creek drainage divide area. The map contour interval for figure 3 is 20 meters. The Sherman Mountains are located in the north center area of figure 3 and are located in the larger Wyoming Laramie Mountains. The western flank of the Laramie Mountains is seen near the west edge of figure 3 with the Laramie Basin located at the base of steep west-facing slope. The Laramie Basin is today drained by the north oriented Laramie River and its north oriented tributaries. Elevations in the Laramie Basin just west of figure 3 are approximately 2200 meters. High points in the Sherman Mountains exceed 2700 meters. Middle Crow Creek originates near the north edge of figure 3 between the highway and the Sherman Mountains and flows in a south-southeast direction before turning in an east direction to flow between Twin Mountain and Turtle Rock to the east edge of figure 3 (slightly north of center). South Crow Creek originates south and east of Turtle Rock and flows in an east direction to the east edge of figure 3 (south of center). East of figure 3 Middle Crow Creek, South Crow Creek, and other east oriented Crow Creek tributaries converge to form east, southeast, and east oriented Crow Creek, which eventually turns to flow in a south and south-southwest direction to join the east-southeast oriented South Platte River. Lone Tree Creek (not labeled in figure 3) originates south of Turtle Rock and just south of the highway and flows in a southeast direction on the south side of the highway to the east edge of figure 3 (near southeast corner). East of figure 3 Lone Tree Creek flows in an east direction before turning to flow in a south-southeast direction to join the east-southeast oriented South Platte River. Dale Creek originates west of the Sherman Mountains and just west of the highway and flows in a south direction to the south edge of figure 3 (west half). South of figure 3 Dale Creek flows in a south, southeast, and south direction to the southeast oriented North Fork Cache la Poudre River, which flows to south and southeast oriented Cache la Poudre River, which joins the South Platte River near the point where the South Platte River turns from flowing in a north direction to flowing in an east-southeast direction. The east oriented Crow Creek and Lone Tree Creek headwaters seen in figure 3 originated as diverging and converging flood flow channels in an east oriented anastomosing channel complex. At that time the Laramie Mountains were just beginning to emerge and elevations to west (in the present day Laramie Basin) were at least as high as elevations in the Laramie Mountains. The south oriented Dale Creek valley originated as a south oriented flood flow channel that eroded headward to capture east and southeast oriented flood flow moving to the Crow Creek and Lone Tree Creek headwaters valleys. An even deeper south oriented flood flow channel probably eroded headward into the Laramie Basin and beheaded flood flow routes to the newly formed Dale Creek valley. Ice sheet related crustal warping was raising the Laramie Mountains as floodwaters flowed across them and continued after floodwaters ceased to flow in an east direction across the region seen in figure 1. In time deep erosion in the Laramie Basin to the west and continued uplift of the Laramie Mountains (which were no longer being eroded in the Sherman Mountains region) created the regional relief seen today.

South Crow Creek-Duck Creek drainage divide area

Figure 4: South Crow Creek-Duck 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 South Crow Creek-Duck 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 Wyoming-Colorado state line is located along the south edge of figure 4. South Crow Creek flows in an east direction from the northwest corner of figure 4 to the north edge of figure 4 (east half) and north of figure 4 joins Middle Crow Creek to form east, southeast, and east oriented Crow Creek, which eventually turns to flow in a south and south-southwest direction to join the east-southeast oriented South Platte River. South Fork Crow Creek originates between the towns of Buford and Granite (just north of highway) and flows in an east and northeast direction to the north edge of figure 4 (east half) and north of figure 4 joins east oriented Crow Creek. Lone Tree Creek flows from the west edge of figure 4 (north half) in an east and east-southeast direction to the east center edge of figure 4. East of figure 4 Lone Tree Creek flows in an east direction before turning to flow in a south-southeast direction to join the east-southeast oriented South Platte River. The South Fork Crow Creek-Lone Tree Creek drainage divide near the town of Granite is known as the Gangplank and provide a low gradient transportation route across the Laramie Mountains. Duck Creek originates in the west center area of figure 4 and flows in an east-southeast direction to the east edge of figure 4 (south half). East of figure 4 Duck Creek flows to south-southeast oriented Lone Tree Creek. Sand Creek originates south of Duck Creek (west of center of figure 4) and flows in a southeast and south direction to the south edge of figure 4 (slightly west of center). South of figure 4 Sand Creek flows to south oriented streams with water eventually reaching the southeast oriented Cache la Poudre River, which flows to the South Platte River near the point where the South Platte River turns from flowing a north direction to flowing in an east-southeast direction. Spottlewood Creek originates just south of Duck Creek (in south center area of figure 4) and flows in a southeast direction to the south edge of figure 4 (east half). South of figure 4 Spottlewood Creek flows to south oriented streams with water eventually reaching the southeast oriented Cache la Poudre River. The east and southeast oriented streams flowing across figure 4 and/or originating in figure 4 are flowing in valleys that originated as diverging and converging east oriented flood flow channels in an east oriented anastomosing channel complex. Headward erosion of deeper south oriented valleys from a south oriented anastomosing channel complex captured the east and southeast oriented flood flow channels and diverted the floodwaters in a south direction to south oriented flood flow on alignments of the present day south and north oriented South Platte River tributaries. Deadman Creek is the south oriented stream near the southwest corner of figure 4 and is a tributary to south and southeast oriented Dale Creek, with water eventually reaching the southeast oriented Cache la Poudre River.

Crow Creek-Lone Tree Creek drainage divide area

Figure 5: Crow Creek-Lone Tree Creek drainage divide area. United States Geological Survey map digitally presented using National Geographic Society TOPO software.

Figure 5 illustrates the Crow Creek-Lone Tree Creek drainage divide area east and slightly north of figure 4 and there is a small overlap area with figure 3. The map contour interval for figure 5 is 10 meters except near the west edge where the contour interval is 20 meters. Crow Creek flows from near the northwest corner of figure 5 to near the north center edge of figure 4 and then turns to flow in a southeast and east direction to flow through Cheyenne to the east edge of figure 5 (north of center). East of figure 5 Crow Creek flows in an east direction before turning to flow in a south and south-southwest direction to join the east-southeast, east, and northeast oriented South Platte River. Several east and northeast oriented tributaries flow from the west edge of figure 5 to join the southeast oriented Crow Creek segment. These tributaries provide more of diverging and converging flood flow channels that once crossed the region. Lone Tree Creek flows in an east direction from the west edge of figure 5 (south half) and then turns to flow in a southeast direction to the south center edge of figure 5. South of figure 5 Lone Tree Creek flows in a south and south-southeast direction to join the east-southeast, east, and northeast oriented South Platte River. Goose Creek is an east oriented Lone Tree Creek tributary near the south edge of figure 5 (west half). Goose Creek provides additional evidence of east oriented flood flow channels captured by headward erosion of the south oriented Lone Tree Creek valley. The east oriented stream in the southeast corner of figure 5 is the headwaters of Porter Creek. East of figure 5 Porter Draw drains in an east direction before turning in a south-southeast direction to join south-southeast oriented Little Crow Creek, which the joins south-southwest oriented Crow Creek to flow to east-southeast, east, and northeast oriented South Platte River. The Porter Creek headwaters probably are on the alignment of what was once the eastern continuation of the east oriented Lone Tree Creek flood flow channel. Headward erosion of the deeper south oriented Lone Tree Creek flood flow channel captured the east oriented flood flow and diverted the floodwaters in a south direction and beheaded the east oriented Port Creek (Porter Draw) valley. In summary the evidence seen in figure 5 is showing one step in how a south oriented anastomosing channel complex was beginning to capture an east oriented anastomosing channel complex.

Crow Creek-Porter Draw drainage divide area

Figure 6: Crow Creek-Porter Draw drainage divide area. United States Geological Survey map digitally presented using National Geographic Society TOPO software.

Figure 6 provides a topographic map of the Crow Creek-Porter Draw drainage divide area east and slightly south of figure 5 and includes an overlap area with figure 5. The map contour interval for figure 6 is 10 meters. Cheyenne, Wyoming is located in the northwest corner of figure 6. Crow Creek flows in an east direction from the south edge of Cheyenne to the east edge of figure 6 (north half-east of the small town of Campstool). Porter Creek in Porter Draw flows in an east direction from the west edge of figure 6 (south half) to the east edge of figure 6 (south half). Remember Porter Creek originated east of where Lone Tree Creek turned from flowing in an east direction to flowing in a south direction and that Porter Draw is probably the beheaded eastern continuation of the east oriented Lone Tree Creek valley. Simpson Creek originates near the southwest corner of figure 6 and flows in an east-southeast direction to the south edge of figure 6 (west of center). South of figure 6 Simpson Creek flows in an east direction before turning to flow in a southeast direction to join south-southeast and south oriented Little Crow Creek, which flows to south-southwest oriented Crow Creek, which in turn flows to the east-southeast, east, and northeast oriented North Platte River. Little Simpson Creek originates in the southwest quadrant of figure 6 and flows in an east, southeast, and east direction to the south edge of figure 6 and south of figure 6 turns in a southeast direction to join southeast oriented Simpson Creek. Bull Canyon is the east-southeast oriented drainage route between Porter Draw and Little Simpson Creek. East of figure 6 Bull Canyon turns in a south direction to join southeast oriented Simpson Creek. The unnamed east oriented stream immediately north of Porter Draw and flowing to the east edge of figure 6 (south half) is a Porter Creek tributary. The two unnamed east oriented streams flowing to the east center edge of figure 6 are Crow Creek tributaries. Drainage routes seen in figure 6 are primarily oriented in east directions and are relics of the east oriented anastomosing channel complex that once crossed the region. These east oriented flood flow channels were captured east (and also west) of figure 6 by headward erosion of the deeper south oriented valleys in an evolving south oriented anastomosing channel complex to create the present day elbows of capture (where east oriented drainage routes turn to flow in south directions).

Crow Creek-Muddy Creek drainage divide area

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

Figure 7 illustrates the Crow Creek-Muddy Creek drainage divide area east and north of figure 5 and includes an overlap area with figure 6. The map contour interval for figure 7 is 10 meters. Crow Creek flows in an east and southeast direction from the west edge of figure 7 to the south center edge of figure 7. South of figure 7 Crow Creek flows in a south and south-southwest direction to join the east-southeast, east, and northeast oriented South Platte River. Muddy Creek is the east oriented stream flowing to the east center edge of figure 7 and has several east oriented tributaries flowing from the west edge of figure 7 (north of Crow Creek). East of figure 7 Muddy Creek turns to flow in a north-northeast direction to join east oriented Lodgepole Creek, which eventually turns in a southeast direction to join the northeast oriented South Platte River. Prior to being captured by headward erosion of a deeper south oriented flood flow channel on the present day south oriented Crow Creek alignment the east oriented Crow Creek flood flow channel continued in an east direction to converge with the east oriented Muddy Creek flood flow channel and to flow into what is today western Nebraska. Headward erosion of a deep south oriented flood flow channel captured the east oriented Crow Creek flood flow channel and diverted the floodwaters in a south direction. Headward erosion of the deep east-southeast, east, and northeast oriented South Platte River valley (south of figure 7) then captured the south oriented flood flow channel and diverted the floodwaters to western Nebraska and to the what was then the newly eroded Nebraska Platte River valley. Floodwaters on the north end of the beheaded flood flow channel reversed flow direction to flow to deeper South Platte River valley and to create a north oriented South Platte River tributary drainage route (today north oriented Box Elder Creek-see figure 1).

Porter Draw-Simpson Creek drainage divide area

Figure 8: Porter Draw-Simpson Creek drainage divide area. United States Geological Survey map digitally presented using National Geographic Society TOPO software.

Figure 8 provides a topographic map of the Porter Draw-Simpson Creek drainage divide area south and west of figure 7 and includes an overlap area with figure 7. The map contour interval for figure 8 is 10 meters. The west to east oriented Wyoming-Colorado state line extends across the south half of figure 8. Crow Creek flows in a southeast, south, and southeast direction from the north edge of figure 8 (east half) to the east edge of figure 8 (south half). East of figure 8 Crow Creek flows in a south and south-southwest direction to join the east-southeast, east, and northeast oriented South Platte River. Porter Creek flows in Porter Draw and flows from the west edge of figure 8 (north of center) in an east-southeast, east, and southeast direction to the south edge of figure 8 (east half). South of figure 8 Porter Creek flows in a south and south-southeast direction to join south-southeast and south oriented Little Crow Creek, which eventually joins south-southwest oriented Crow Creek. Simpson Creek (“Creek” near west edge of figure 8) flows in an east and southeast direction from the west edge of figure 8 (south half) to the south center edge of figure 8. South of figure 8 Simpson Creek joins south-southeast and south oriented Little Crow Creek, which then flows to Crow Creek. Little Simpson Creek (“Simpson Creek” near west edge of figure 8) flows in an east and southeast direction from the west edge of figure 8 (south of center) to join Simpson Creek. Bull Canyon drains from the west center edge of figure 8 to join southeast oriented Simpson Creek in the south center area of figure 8. The southeast and south-facing escarpment where these east oriented streams turn to flow in southeast and south directions is Chalk Bluffs. Elevations in the Simpson Creek valley near the south center edge of figure 8 are less than 1650 meters while elevations on the upland surface near the west edge of figure 5 exceed 1850 meters. These elevations suggest Chalk Bluffs escarpment represents an elevation difference of approximately 200 meters. This 200-meters elevation difference represents the difference in elevation of the erosion/deposition surface on which the east oriented anastomosing channel complex was formed and the floors of the south oriented anastomosing channels that eroded headward to capture the east oriented flood flow channels. Headward erosion of deep south oriented flood flow channels probably ended because east oriented floodwaters were beheaded by uplift in the Laramie Mountains and/or by headward erosion of deep south oriented flood flow channels into the Laramie Basin.

Geary Creek-Willow Creek drainage divide area

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

Figure 9 illustrates the Geary Creek-Willow Creek drainage divide area south and west of figure 8 and there is an overlap area with figure 8. Figure 9 is also located south and slightly east of figure 6. The map contour interval for figure 9 is 10 meters. The west to east oriented Wyoming-Colorado state line is located near the north edge of figure 9. Figure 9 provides a good view of the south-facing Chalk Bluffs escarpment. Elevations in the southeast corner of figure 9 are less than 1650 meters while elevations in the Simpson Mesa area near the northwest corner of figure 9 exceed 1850 meters. Simpson Creek flows in an east direction from the west edge of figure 9 (near northwest corner) into the northeast quadrant of figure 9 and then turns to flow in a southeast direction to the east edge of figure 9 (north of center). East of figure 9 Simpson Creek joins south-southeast and south oriented Little Crow Creek to flow to Crow Creek, which then flows to the east-southeast, east, and northeast oriented South Platte River. Geary Creek originates on top of Chalk Bluffs and flows in an east and northeast direction before turning to flow in a southeast direction to the east edge of figure 9 (near southeast corner). South and east of figure 9 Geary Creek joins south oriented Little Crow Creek. Willow Creek headwaters are near the top of Chalk Bluffs (near the center of figure 9) and after flowing for a short distance in an east direction turn flow in a south-southeast direction down the Chalk Bluffs escarpment face and to the south edge of figure 9 (east of center). South of figure 9 Willow Creek flows to south oriented Little Crow Creek. The West Fork Willow Creek flows in a southeast direction to the south center edge of figure 9. South oriented streams west of West Fork Willow Creek flow to south oriented Owl Creek, which joins south oriented Lone Tree Creek to flow to the east-southeast, east, and northeast oriented South Platte River. Figure 9 illustrates how headward erosion of south oriented valleys or flood flow channels in a south oriented anastomosing channel complex captured east oriented flood flow channels in an east oriented anastomosing channel complex. The south oriented anastomosing channel complex was eroding an erosion surface approximately 200 meters lower in elevation than the erosion/deposition surface on which the east oriented flood flow channels were located. Headward erosion of the deep south oriented valleys into the east oriented anastomosing channel complex ended when floodwaters moving to the east oriented anastomosing channel complex were beheaded by Laramie Mountains uplift and/or by headward erosion of deep south oriented flood flow channel into the Laramie Basin on the west side of what were then the emerging Laramie Mountains.

Lone Tree Creek-Simpson Creek drainage divide area

Figure 10: Lone Tree Creek-Simpson Creek drainage divide area. United States Geological Survey map digitally presented using National Geographic Society TOPO software.

Figure 10 provides a topographic map of the Lone Tree Creek-Simpson Creek drainage divide area west of figure 9 and includes an overlap area with figure 9. Figure 10 is also located south and slightly east of figure 5. The map contour interval for figure 10 is 10 meters. The west to east oriented Wyoming-Colorado state line is located in the north half of figure 10. Lone Tree Creek (not labeled in figure 10) flows in a south, south-southwest, and south-southeast direction from the north edge of figure 10 (west of center and near highway and railroad) to the south center edge of figure 10. South of figure 10 Lone Tree Creek flows in a south-southeast and south direction to join the east-southeast, east, and northeast oriented South Platte River. Simpson Mesa is located near the east edge of figure 10 (north of center). Simpson Creek is the east-southeast oriented stream originating east of Athol and flowing to the east edge of figure 10 (on north side of Simpson Mesa). Most other streams seen in figure 10 either join Lone Tree Creek in figure 10 or flow in south directions to join Lone Tree Creek south of figure 10. Figure 10 illustrates how headward erosion of the deep south oriented Lone Tree Creek valley and tributary valleys beheaded east oriented flood flow to the east oriented Simpson Creek valley. The Simpson Creek headwaters east of Athol are at an elevation greater than 1910 meters. The Lone Tree Creek valley floor elevation at the state line is less than 1840 meters or more than 70 meters lower than the Simpson Creek headwaters elevation. The Union Pacific Railroad line just south of the state line is located in a southwest oriented dry valley draining to south oriented Lone Tree Creek. The dry valley was eroded as a south oriented flood flow channel just prior to headward erosion of the deeper Lone Tree Creek valley to the west, which then beheaded flood flow routes to the dry valley. East and southeast oriented Lone Tree Creek tributaries in the northwest quadrant of figure 10 illustrate how headward erosion of the deep south oriented Lone Tree Creek valley captured east oriented flood flow channels coming from the Laramie Mountains to the west. Duck Creek, which was seen in figure 4, flows in an east and southeast direction near the north edge of figure 10 to join south oriented Lone Tree Creek.

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.