Abstract:

This essay uses topographic map evidence to interpret landform origins in the Pawnee Creek-South Platte River drainage divide area in Weld, Morgan, and Logan Counties, Colorado. Pawnee Creek is an east and southeast oriented tributary to the northeast oriented South Platte River in northeast Colorado. Topographic map evidence shows drainage divides between Pawnee Creek tributary and headwaters valleys are crossed by shallow northwest to southeast oriented through valleys while the east oriented tributaries have short southeast tributaries from the north and north, northwest, or north-northwest tributaries from the south. The barbed tributaries, valley orientations, and shallow through valleys are interpreted to have originated as the Pawnee Creek valley and its tributary valleys eroded headward across southeast oriented flood flow with Pawnee Creek tributary and headwaters valleys being eroded in sequence from the southeast to the northwest. Floodwaters are interpreted to have been derived from the western margin of a thick North American ice sheet and were flowing from western Canada to and across northeast Colorado at a time when the much larger Missouri River drainage system was also developing as deep east oriented tributary valleys eroded headward in sequence from the southeast to the northwest. The north oriented South Platte River drainage route south and west of the Pawnee Creek drainage basin was created by a reversal of flood flow on the north ends of south oriented flood flow channels, which were beheaded by headward erosion of the much deeper northeast oriented South Platte River valley.

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 Pawnee Creek-South Platte River drainage divide area landform origins in Weld, Morgan, and Logan Counties, Colorado. 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 Pawnee Creek-South Platte River drainage divide area landform evidence in Weld, Morgan, and Logan Counties, Colorado will be regarded as evidence supporting the “thick ice sheet that melted fast” paradigm.

Pawnee Creek-South Platte River drainage divide area location map

Figure 1: Pawnee 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 Pawnee Creek-South Platte River drainage divide area in Weld, Morgan, and Logan Counties Colorado and illustrates the northeast corner of Colorado with the southeast corner of Wyoming and southwest corner of the Nebraska panhandle to the north. The east edge of the Colorado Front Rant, which merges with the Wyoming Laramie Mountains, can be seen along the west edge of figure 1. The South Platte River flows in a north direction to Denver (near southwest corner of figure 1) and then in a north-northeast direction to Greeley. Near Greeley the South Platte River flows in an east-southeast direction with a northeast jog to near Fort Morgan and then in a northeast direction to the east edge of figure 1 (near the Nebraska-Colorado border). East of figure 1 the South Platte River flows in an east direction to join the southeast oriented North Platte River and to form the Nebraska Platte River. East of Denver there are several north oriented South Platte River tributaries including Kiowa Creek, Bijou Creek, and Beaver Creek. Several south oriented tributaries, including Crow Creek, join the South Platte River near Greeley. Crow Creek originates in the Wyoming Laramie Mountains and flows in an east and southeast direction to Cheyenne. From Cheyenne Crow Creek flows in an east, south-southeast, south, and south-southwest direction to join the South Platte River east of Greeley. Pawnee Creek is a southeast oriented South Platte River tributary located east of the south oriented Crow Creek segment. Pawnee Creek originates near Pawnee Buttes and joins the South Platte River near Atwood. Note the difference in the orientations of South Platte River tributaries from the north on either side of South Platte River northeast-southeast jog near Weldona. East of the jog South Platte River tributaries from the north are oriented in southeast directions. West of the jog tributaries from the north are oriented in south and even south-southwest directions. This essay investigates the region between Pawnee Creek and the South Platte River, which is located just east of the South Platte River jog. My next essay will address the region west of the South Platte River jog. The Lodgepole Creek-South Platte River drainage divide area near the Wyoming-Nebraska-Colorado corner essay addresses the region immediately to the north of the region addressed in this essay and the Crow Creek-South Platte River drainage divide area along the Wyoming-Colorado border addresses the region to the northwest of the region described in this essay.

The South Platte River drainage route, like all other Missouri River drainage routes, 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 the present day South Platte River drainage basin at a time when Wyoming and Colorado mountain ranges were just beginning to emerge. Floodwaters initially flowed in large complexes of anastomosing flood flow channels in south directions, but were subsequently diverted to flow in other directions as ice sheet related crustal warping raised mountain ranges and plateau areas and as deep valleys eroded headward to capture the massive flood flow. Present day drainage routes generally reflect flood flow directions at the time the final floodwaters drained from a region. The northeast oriented South Platte River valley downstream from the northeast-southeast jog (or Fort Morgan area) eroded headward across southeast and east-southeast oriented flood flow moving to the what was at that time the actively eroding Republican River valley east of figure 1 (the Arikaree River in the southeast corner of figure 1 is a Republican River tributary). The east-southeast oriented South Platte River valley west of the Fort Morgan area eroded headward across south oriented flood flow channels moving floodwaters along the east margin of what was at that time the emerging Colorado Front Range. Floodwaters at that time were probably flowing to the southeast oriented Arkansas River valley in southern Colorado (although prior to headward erosion of the Arkansas River valley floodwaters flowed to southeast and south oriented valleys further to the south). Headward erosion of the east-southeast oriented South Platte River valley segment beheaded south oriented flood flow channels in sequence from east to west. Floodwaters on north ends of 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 flood flow channels were anastomosing (diverging and converging) reversed flood flow on a newly beheaded and reversed flood flow channel could capture floodwaters from yet to be beheaded flood flow channels further to the west. Such captures enabled newly beheaded and flood flow channels to create significant north oriented South Platte River tributary drainage routes. The north oriented South Platte River drainage route south of Greeley was also created by a reversal of flood flow and the southeast oriented South Platte River headwaters (south of figure 1) illustrate how a how a reversed flood flow channel could capture floodwaters from yet to be beheaded flood flow channels further to the west (in the case of the South Platte River headwaters the yet to be beheaded flood flow channels were located in what was at that time the emerging Colorado Front Range, which has since emerged as a high mountain range).

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

Figure 2: Detailed location map for Pawnee 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 Pawnee Creek-South Platte River drainage divide area in Weld, Morgan, and Logan Counties, Colorado. The west to east oriented Wyoming-Colorado state line is located near the north edge of figure 2. Cheyenne, Wyoming is the city located near the northwest corner of figure 2 and Greeley, Colorado is located north of the southwest corner of figure 2. Fort Morgan, Colorado is located just north of the south center edge of figure 2 and Sterling, Colorado is located in the east center area of figure 2. County boundaries are shown and Weld, Morgan, and Logan Counties are labeled. The South Platte River flows in a north-northeast and northeast direction from the southwest corner of figure 2 to the south side of Greeley where the South Platte River turns to flow in an east-southeast direction to near the Weld-Morgan County boundary. Near the county line the South Platte River turns in a northeast direction before turning to flow in a southeast direction to Fort Morgan. From Fort Morgan the South Platte River flows in a northeast direction to the east edge of figure 2 (north of center). Crow Creek flows from Cheyenne in an east and southeast direction to near Hereford (just south of the state line) and then in a south and south-southwest direction to join the South Platte River a short distance east of Greeley. North Pawnee Creek originates in the north center area of figure 2 (east of Crow Creek and south of the state line) and flows in a southeast direction to join east-northeast and east oriented South Pawnee Creek and to form southeast oriented Pawnee Creek, which flows to the northeast oriented South Platte River as a barbed tributary near Atwood (south of Sterling). South Pawnee Creek originates west of Raymer, Colorado and flows in an east-northeast and east direction to join North Pawnee Creek. Wild Horse Creek is a south, southeast, and east-southeast oriented South Pawnee Creek tributary and Igo Creek is a southeast and east-southeast oriented North Pawnee Creek tributary. South of the South Pawnee Creek headwaters are headwaters of southeast oriented Wildcat Creek, which joins the South Platte River a short distance downstream from Fort Morgan. South Platte River tributaries (from the north) downstream from Pawnee Creek are oriented in southeast directions suggesting headward erosion of the South Platte River valley captured southeast oriented flood flow. The southeast oriented flood flow to the newly eroded South Platte River valley was subsequently beheaded by headward erosion of northeast and east oriented Lodgepole Creek tributary valleys near the Wyoming-Colorado border. The east oriented Lodgepole Creek valley is located just north of figure 2 and eroded headward from the South Platte River valley located east and north of figure 2. Crow Creek tributaries from the west are generally oriented in south-southeast directions suggesting headward erosion of the south oriented Crow Creek valley captured south-southeast oriented flood flow. The Pawnee Creek-South Platte River drainage divide area, which includes drainage divide between Pawnee Creek tributaries, was crossed by southeast oriented floodwaters as the Pawnee Creek and tributary valleys eroded headward to capture the flood flow.

Raymer Creek-Sand Creek drainage divide area

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

Figure 3 provides a topographic map of Raymer Creek-Sand Creek drainage divide area. The map contour interval for figure 3 is 10 meters. The South Platte River flows in a northeast direction across the southeast corner of figure 3. Pawnee Creek flows in a southeast direction from the north edge of figure 3 (west of center) to the east edge of figure 3 (south of center) and east of figure 3 joins the northeast oriented South Platte River as a barbed tributary. Raymer Creek flows in a northeast, southeast, east, and north-northeast direction across the northwest corner of figure 3 and north of figure 3 joins southeast oriented Pawnee Creek. Note north and northwest oriented Raymer Creek tributaries and the southeast oriented tributaries near the northwest corner of figure 3. Sand Creek originates in the west center area of figure 3 and flows in a southeast direction to Willard and then in an east and north and northeast direction to join southeast oriented Pawnee Creek as a barbed tributary. Two southeast oriented tributaries join Sand Creek east of Willard. A shallow northwest to southeast oriented through valley in the northwest quadrant of figure 3 links a northwest and north oriented Raymer Creek tributary valley with the southeast oriented Sand Creek headwaters valley. The through valley was eroded by southeast oriented flood flow moving to the actively eroding southeast oriented Sand Creek valley prior to headward erosion of the Raymer Creek valley. Headward erosion of the Raymer Creek valley beheaded the southeast oriented flood flow route ending flood flow to the Sand Creek valley. The northwest and north oriented Raymer Creek tributary drainage route was created by a reversal of flood flow on the northwest end of the beheaded flood flow route. The Sand Creek drainage route was also created by a reversal of flood flow on the north end of a flood flow route beheaded and reversed by headward erosion of the deeper southeast oriented Pawnee Creek valley. Floodwaters on the north end of the beheaded flood flow route reversed flow to flow to the deeper Pawnee Creek valley. The southeast and east oriented Sand Creek valley then eroded headward from the newly formed north oriented Sand Creek drainage route to capture south and southeast oriented flood flow west of the actively eroding Pawnee Creek valley head. The Raymer Creek valley eroded headward from the actively eroding Pawnee Creek valley and subsequently beheaded flood flow routes to the actively eroding Sand Creek valley. The sequence in which valleys were beheaded is important in deciphering drainage route histories.

Detailed map of Raymer Creek-Sand Creek drainage divide area

Figure 4: Detailed map of Raymer Creek-Sand 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 Raymer Creek-Sand Creek drainage divide area seen in less detail in figure 3. The map contour interval for figure 4 is 10 feet. Sand Creek originates in section 16 (in south center area of figure 4) and flows in a southeast direction near the railroad tracks (now abandoned) to the south edge of figure 4. South and east of figure 4 Sand Creek flows in a southeast, east, north, and northeast direction to join southeast oriented Pawnee Creek, which then joins the northeast oriented South Platte River. The northwest oriented stream in section 31 (near northwest corner of figure 4) flows to Raymer Creek at a point where Raymer Creek turns from flowing in a south direction to flowing in a northeast direction. Further east (and north of figure 4) Raymer Creek flows in a southeast, east, northeast, and east direction to join southeast oriented Pawnee Creek. The north oriented stream originating section 5 is also a tributary to Raymer Creek. Several landforms in figure 4 were streamlined in northwest to southeast directions as south and southeast oriented floodwaters flowed across the region (prior to headward erosion of the Raymer Creek valley). A northwest to southeast oriented hill crosses the southwest quadrant of section 5. Another northwest to southeast oriented hill crosses the southwest corner of section 10 and still other streamlined hills can be found. These streamlined hills suggest diverging and converging flood flow channels crossed the region with floodwaters flowing in a south and southeast direction. Prior to headward erosion of the Sand Creek valley floodwaters continued in a southeast direction toward the South Platte River valley. Headward erosion of the Raymer Creek valley (north of figure 4) captured the south and southeast oriented flood flow and diverted floodwaters to the newly eroded southeast oriented Pawnee Creek valley.

Pawnee Creek-Raymer Creek drainage divide area

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

Figure 5 illustrates a topographic map of the Pawnee Creek-Raymer Creek drainage divide area north and west of figure 3 and includes an overlap area with figure 3. The map contour interval for figure 5 is 10 meters. North Pawnee Creek flows in a southeast direction from the northwest corner of figure 5 to join northeast and east oriented South Pawnee Creek and to form east oriented Pawnee Creek, which flows almost to the east edge of figure 5 before turning in a south-southeast direction to flow to the east edge of figure 5 (south of center). East and south of figure 5 Pawnee Creek flows in a southeast direction to join the northeast oriented South Platte River. Raymer Creek is the Pawnee Creek tributary located in a the southeast quadrant of figure 5 and in addition to north and northwest oriented tributaries seen in figure 3 Raymer Creek also has south-southeast oriented headwaters and tributaries seen here in figure 5. Pawnee Creek and South Pawnee Creek tributaries from the south are generally oriented in northwest and north-northwest directions and join Pawnee Creek and South Pawnee Creek as barbed tributaries. These northwest and north-northwest oriented and barbed tributaries to an east and southeast oriented stream are evidence the Pawnee Creek valley and South Pawnee Creek valleys eroded headward across multiple southeast and/or south-southeast oriented flood flow routes. The flood flow routes were captured in sequence from east to west and floodwaters on northwest ends of beheaded flood flow routes reversed flow direction to flow to the newly eroded Pawnee Creek or South Pawnee Creek valley. Southeast and south-southeast oriented tributaries from the north also flow to Pawnee Creek. Cottonwood Creek is the southeast oriented Pawnee Creek tributary flowing from the north center edge of figure 5. Spring Creek is the south and south-southeast oriented “Creek” near the northeast corner of figure 5. These southeast and south-southeast oriented tributary drainage routes were created by southeast and south-southeast oriented flood flow moving into the newly eroded Pawnee Creek valley.

Detailed map of South Pawnee Creek-Raymer Creek drainage divide area

Figure 6: Detailed map of South Pawnee Creek-Raymer 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 South Pawnee Creek-Raymer Creek drainage divide area seen in less detail in figure 5. The map contour interval for figure 6 is 10 feet. Shaded regions in the west half of figure 6 are located in Pawnee National Grasslands. Pawnee Creek flows in an east direction north of figure 6 and then turns to flow in a southeast direction across the northeast corner of figure 6. Raymer Creek originates in section 24 (west half of figure 6) and flows in a south-southeast, northeast, southeast, east, northeast, and east direction to the east center edge of figure 6. East of figure 6 Raymer Creek joins southeast oriented Pawnee Creek, which flows to the northeast oriented South Platte River. Several depressions can be seen on the upland surfaces in figure 6. These depressions may indicate sinkholes formed in some type of soluble bedrock material, although topographic map evidence is not adequate to say for sure. Narrow ridges surround the depressions in section 18, which suggests the possibility of some sort of excavation, although other origins are also possible. Without additional evidence I cannot determine what the ridge are. In addition to the south-southeast oriented Raymer Creek headwaters south-southeast and southeast oriented Raymer Creek tributaries are located in sections 30, 19, 20, and 21 as well as in section 15 and 16. These south-southeast and southeast oriented drainage routes to the Raymer Creek valley and the southeast oriented Raymer Creek headwaters provide evidence the east, northeast, and east oriented Raymer Creek valley eroded headward across southeast oriented flood flow. The southeast oriented Raymer Creek valley segment was eroded as the  valley eroded headward along a southeast oriented flood flow route. The south-southeast and southeast oriented headwaters and tributary drainage routes were created by south-southeast and southeast oriented flood flow moving into the Raymer Creek valley. The north-northeast oriented valley in section 12 (in northwest quadrant of figure 6) eroded headward from what at that time was the actively eroding east oriented Pawnee Creek valley north of figure 6 to capture south-southeast oriented flood flow west of the Pawnee Creek valley head.  The north-northwest oriented tributaries to that valley were created by reversals of flood flow on north-northwest ends of beheaded flood flow routes. Likewise the north oriented drainage route in section 11 (near northwest corner of figure 6) was created by a reversal of flood flow beheaded by headward erosion of the east oriented Pawnee Creek valley. Shallow through valleys can be seen in figure 6 linking the north oriented Pawnee Creek tributary valleys with the south oriented Raymer Creek tributary and headwaters valleys. One or two contour lines on a side define these shallow through valleys and provide further evidence of south-southeast oriented flood flow across the Pawnee Creek-Raymer Creek drainage divide.

Wild Horse Creek-South Pawnee Creek drainage divide area

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

Figure 7 illustrates the Wild Horse Creek-South Pawnee Creek drainage divide area west and slightly south of figure 5 and there is an overlap area with figure 5. The map contour interval for figure 7 is 10 meters. Buckingham is the small town located in the southwest quadrant of figure 7 and Raymer is the slightly larger town located in the southeast quadrant of figure 7. South Pawnee Creek originates south of Buckingham and then flows in a northeast direction until it is north of Raymer and then turns to flow in more of an east direction to the east edge of figure 7. Wild Horse Creek flows from the northwest corner of figure 7 in a southeast, east, and east-southeast direction to join South Pawnee Creek north of Raymer. The southeast oriented stream located east of Raymer and flowing to the east edge of figure 7 (near southeast corner) ends south and east of figure 7 in a depression, but is headed towards the northeast oriented South Platte River. Wild Horse Creek and South Pawnee Creek tributaries from the north are oriented in southeast directions suggesting the east oriented South Pawnee Creek and Wild Horse Creek valley segments eroded headward across southeast oriented flood flow. Tributaries from the south are short and are oriented in north and north-northwest directions and were created by reversals of flood flow on north and northwest ends of beheaded flood flow routes. Shallow northwest to southeast oriented through valleys defined by one or two 10-meter contour lines on each side can be seen crossing the Wild Horse Creek-South Pawnee Creek drainage divide. These through valleys can be seen by following the drainage divide in a southwest direction from the Wild Horse Creek-South Pawnee Creek confluence to and beyond Buckingham. These northwest to southeast oriented through valleys provide evidence of multiple shallow southeast oriented flood flow channels that once crossed the drainage divide.

Detailed map of Wild Horse Creek-South Pawnee Creek south drainage divide area

Figure 8: Detailed map of Wild Horse Creek-South Pawnee 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 Wild Horse Creek-South Pawnee Creek drainage divide area seen is less detail in figure 7. The map contour interval for figure 8 is 10 feet. The small town of Buckingham is located in section 33 near the south edge of figure 8. South Pawnee Creek flows in a northeast and east direction near the southeast corner of figure 8. Wild Horse Creek flows in a southeast, east, and southeast direction from the north edge of figure 8 (west of center) to the east edge of figure 8 (north half). East of figure 8 Wild Horse Creek joins South Pawnee Creek, which then joins North Pawnee Creek to form east and southeast oriented Pawnee Creek. A stream flows in an east-southeast direction from the west edge of figure 8 to section 20 and then turns in an east-northeast direction to the south margin of section 16 where it turns to flow in a southeast, northwest and north-northeast direction to join Wild Horse Creek in the northeast corner of section 14. Two northwest to southeast oriented through valleys in section 15 link the southeast oriented Wild Horse Creek valley with the southeast segment of this Wild Horse Creek tributary. The eastern through valley has a floor elevation of between 4810 and 4820 feet while the western through valley floor elevation is between 4820 and 4830 feet. Elevations in the southeast corner of section 15 rise to more than 4850 feet as do elevations near the east margin of section 16. These elevations suggest the eastern through valley is at least 30 feet deep and the western through valley is at least 20 feet deep. To the southeast in sections 24 and 25 a northwest to southeast oriented through valley crosses the drainage divide between the Wild Horse Creek tributary and South Pawnee Creek. The through valley floor elevation is between 4830 and 4840 feet. Elevations in the northwest quadrant of section 24 rise to 4891 feet and elevations in section 26 rise to more than 4900 feet. These elevations suggest the through valley crossing the Wild Horse Creek-South Pawnee Creek drainage divide is at least 51 feet deep. Additional northwest to southeast oriented through valleys cross the drainage divides. These through valleys were eroded by southeast oriented flood flow prior to headward erosion of the southeast and east oriented Wild Horse Creek valley. Headward erosion of the Wild Horse Creek valley captured the southeast oriented flood flow and floodwaters on north and northwest ends of beheaded flood flow routes reversed flow direction to create north and northwest oriented Wild Horse Creek tributary drainage routes.

Igo Creek-South Pawnee Creek drainage divide area

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

Figure 9 illustrates the Igo Creek-South Pawnee Creek drainage divide area north and east of figure 7 and there is a large overlap area with figure 7. The map contour interval for figure 9 is 10 meters. South Pawnee Creek flows in a north-northeast, east, northeast, and east direction from the south center edge of figure 9 to the east edge of figure 9 (south half). North Pawnee Creek flows in a south and southeast direction from the north center edge of figure 9 to the east edge of figure 9 (south of center) and east of figure 9 joins South Pawnee Creek to form east and southeast oriented Pawnee Creek, which flows to the northeast oriented South Platte River. Wild Horse Creek flows in an east-southeast direction from the west edge of figure 9 (south half) to join north-northeast oriented South Pawnee Creek just south of the south center edge of figure 9. Igo Creek flows in a south-southeast and east-southeast direction from near the northwest corner of figure 9 to join southeast oriented North Pawnee Creek in the east half of figure 9. Cottonwood Creek is the southeast oriented stream near the northeast corner of figure 9 and east of figure 9 joins Pawnee Creek. Multiple shallow northwest-to-southeast oriented through valleys link the Igo Creek valley with southeast oriented Wild Horse Creek and South Pawnee Creek tributary valleys. One to four contour on each side define the through valleys and the streamlined erosional residuals located between the through valleys. The through valleys and erosional residuals were eroded by diverging and converging southeast oriented flood flow channels prior to headward erosion of the east-southeast oriented Igo Creek valley. Headward erosion of the east-southeast oriented Igo Creek valley captured the southeast oriented flood flow and ended flood flow to the Wild Horse Creek and South Pawneee Creek valleys seen in figure 9. The process seen in figure 9 and in earlier figures illustrates how the Pawnee Creek drainage system developed from the southeast to the northwest as Pawnee Creek tributary valleys captured southeast oriented flood flow and beheaded flood flow routes to newly eroded Pawnee Creek tributary valleys immediately to the southeast.

Detailed map of Igo Creek-South Pawnee Creek drainage divide area

Figure 10: Detailed map of Igo Creek-South Pawnee 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 Igo Creek-South Pawnee Creek drainage divide area seen in less detail in figure 9. The map contour interval for figure 10 is 10 feet. Igo Creek flows in an east-southeast direction from the north edge of figure 10 (west of center) to the east edge of figure 10 (north half). Southeast oriented streams in the east half of figure 10 flow to east oriented South Pawnee Creek while the south-southeast oriented stream in the west half of figure 10 flows to east-southeast oriented Wild Horse Creek, which then flows to South Pawnee Creek (see figure 9). A north to south oriented through valley along the boundary between sections 13 and 18 (near north center edge of figure 10) links the east-southeast oriented Igo Creek valley with the valley of a southeast oriented South Pawnee Creek tributary. The through valley floor elevation is between 4860 and 4870 feet. Elevations on the northwest to southeast oriented hill in the east half of section 19 to the southeast rise to more than 4930 feet while elevations in the northwest corner of figure 10 rise to more than 5000 feet. These elevations suggest the north to south oriented through valley is at least 60 feet deep. Similar through valleys can be found elsewhere in figure 10 and provide evidence of diverging and converging south oriented flood flow channels that once crossed the present day Igo Creek-South Pawnee Creek drainage divide (prior to headward erosion of the Igo Creek valley). Northwest to southeast oriented erosional residuals seen in figure 10 are located between these former diverging and converged flood flow channels and are further evidence of the southeast oriented flood flow. Headward erosion of the east-southeast oriented Igo Creek valley captured the southeast oriented flood flow and created the present day Igo Creek-South Pawnee Creek drainage divide.

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.