Crow Creek-South Platte River drainage divide area landform origins in Weld and Morgan Counties, Colorado, USA

Authors

 

Abstract:

This essay uses topographic map evidence to interpret landform origins in the Crow Creek-South Platte River drainage divide area in Weld and Morgan Counties, Colorado. Before entering Weld County the South Platte River flows in a north direction east of the Colorado Front Range and once in Weld County the South Platte River turns flows in a northeast, southeast, northeast, southeast, and northeast direction into Morgan County and then continues to flow in a northeast and east direction to western Nebraska where it joins the southeast oriented North Platte River to form the Nebraska Platte River. Crow Creek flows in an east direction in southeast Wyoming before turning in a southeast, south, west, and southwest direction to join the South Platte River near the western point where the northeast oriented South Platte River turns to flow in a southeast direction. East of the eastern South Platte River northeast-southeast jog South Platte River tributaries from the north are oriented in southeast directions with southeast oriented Wildcat Creek being the westernmost of these southeast oriented tributaries. Between Crow Creek and Wildcat Creek South Platte River tributaries are oriented in south directions and Crow Creek has short northwest oriented tributaries. Valley orientations, barbed tributaries, streamlined erosional residuals, through valleys crossing drainage divides, and upland erosion surfaces in the Crow Creek-Wildcat Creek drainage divide area are interpreted to have developed during immense melt water floods from the western margin of a thick North American ice sheet. Initially floodwaters flowed in south directions, although directions of flood flow changed and were even reversed in some cases as ice sheet related crustal warping raised mountain ranges and plateaus and as deep valleys eroded headward into the region to capture the immense melt water floods. The northeast oriented South Platte River valley (east of the northeast-southeast jogs) eroded headward from western Nebraska across southeast oriented flood flow moving to what at that time was the actively eroding Republican River valley. The south and southwest oriented Crow Creek valley eroded headward from southwest and south oriented flood flow channels on the present day north and northeast oriented South Platte River and north oriented South Platte River tributary alignments and beheaded southeast oriented flood flow routes to the actively eroding South Platte River valley. The South Platte River northeast-southeast jogs were created when the South Platte River valley eroded headward along southeast oriented flood flow channels for short distances before turning to erode across southeast oriented flood flow. Headward erosion of the South Platte River valley captured south oriented flood flow on the Crow Creek alignment and diverted floodwaters into Nebraska. Floodwaters on north ends of the beheaded flood flow channels reversed flow direction to flow to the deeper South Platte River valley and created the north and northeast oriented South Platte River drainage route and north oriented South Platte River tributary drainage routes.

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

Crow Creek-South Platte River drainage divide area location map

Fig1 locmap

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 in Weld and Morgan Counties, Colorado and illustrates a region in northern Colorado in the south with the southeast corner of Wyoming in the northwest corner and southwest corner of the Nebraska panhandle in the northeast corner. The Colorado Front Range, which merges into the Wyoming Laramie Mountains, can be seen near the west edge of figure 1. The South Platte River originates in the Colorado Front Range (south of figure 1 and flows in a southeast direction before turning to flow in a north and north-northeast direction along the east margin of the Colorado Front Range to Denver (near south edge of figure 1). From Denver the South Platte River flows in a north and northeast direction to Greeley and then in a southeast-northeast, and southeast direction to Fort Morgan. From Fort Morgan the South Platte River flows in a northeast direction to the east edge of figure 1 (near Colorado-Nebraska state line) and east of figure 1 flows into western Nebraska to join the southeast oriented North Platte River and to form the Nebraska Platte River. Note the northeast-southeast jog the South Platte River makes just west of Fort Morgan. East of that jog South Platte River tributaries from the north are oriented in southeast directions while west of that jog South Platte River tributaries are oriented in south and even south-southwest directions. South Platte River tributaries from the south between the Fort Morgan area and Greeley are generally oriented in north directions and include Kiowa Creek, Bijou Creek, and Beaver Creek. Further to the east there are no South Platte River tributaries from the southeast shown in figure 1, suggesting the South Platte River has an asymmetric drainage divide with the southeast and east oriented streams flowing towards the east edge of figure 1. Crow Creek originates in the Wyoming Laramie Mountains (near northwest corner of figure 1) and flows in an east and southeast direction to Cheyenne, Wyoming and then in an east, southeast, south, and south-southwest direction to join the east-southeast oriented South Platte River a short distance east of Greeley. The Crow Creek-South Platte River drainage divide area investigated in this essay focuses on the drainage divide between Crow Creek and streams flowing to the South Platte River in the vicinity of the South Platte River’s northeast-southeast jog just west of Fort Morgan.

The South Platte River and tributary drainage routes 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 beginning to emerge. Floodwaters flowed from western Canada to and across the present day South Platte River drainage basin initially in south oriented complexes of diverging and converging flood flow channels. However, as ice sheet related crustal warping raised mountain and plateau areas and as deep east oriented valleys eroded headward into the region from the developing Missouri River drainage basin floodwaters were diverted in other directions and even reversed to flow in north directions. Present day drainage patterns generally reflect directions of flood flow at the time floodwaters finally drained from a region and varies from region to region. In the case of the South Platte River drainage basin the northeast oriented South Platte River valley downstream from the northeast-southeast jog (just west of Fort Morgan) eroded headward across southeast oriented flood flow, which was moving to the newly eroded Republican River valley (the Arikaree River in the southeast corner of figure 1 is a Republican River tributary). The southeast oriented South Platte River valley west of the northeast-southeast jog eroded headward across south oriented flood flow channels, which were probably flowing to the southeast oriented Arkansas River valley in southern Colorado, however prior to Arkansas River valley headward erosion floodwaters flowed to southeast and south oriented valleys further to the south. Headward erosion of the south oriented flood flow channels west of the South Platte River northeast-southeast jog was at that time in the process of capturing southeast and east oriented flood flow moving to the actively eroding Republican River valley and subsequently to the actively eroding South Platte River valley. Headward erosion of the much deeper South Platte River valley then eroded headward across the south oriented flood flow channels (changing the South Platte River valley direction of headward erosion as it encountered flood flow moving in different directions). Floodwaters on north ends of beheaded flood flow channels reversed flow direction to create north oriented South Platte River tributary drainage routes. Flood flow channels were beheaded in sequence from east to west and because flood flow channels diverged and converged so a newly beheaded and reversed flood flow channel could capture floodwaters from adjacent and yet to beheaded flood flow channels further to the west. In addition to north oriented South Platte River tributary drainage routes the north and north-northeast oriented South Platte River drainage route along the Colorado Front Range east flank was created by a flood flow reversal and captured significant south and southeast oriented flood flow from flood flow channels in the emerging Colorado Front Range further to the west. Today the Colorado Front Range is a high mountain range, but at the time the Front Range was still emerging and south and southeast oriented flood flow from the north and northwest could reach what are today southeast oriented South Platte River headwaters (south of figure 1).

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

Fig2 detlocmap

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 in Weld and Morgan Counties, Colorado. County boundaries are shown and Weld and Morgan Counties are labeled. Greeley is located near the southwest corner of figure 2. Fort Morgan is located just south of figure 2 (south of the “R” in the word “MORGAN”). The South Platte River flows in a northeast direction from the southwest corner of figure 2 along the southeast side of Greeley and then turns to flow in a southeast direction to near Masters (near the south center edge of figure 2). From Masters the South Platte River flows in a northeast direction to Goodrich and then turns to flow in a southeast direction and just north of Fort Morgan turns again to flow in a northeast direction to the east edge of figure 2. Tributaries joining the South Platte River east of Weldon (a town on the South Platte River in western Morgan County) are generally oriented in southeast directions. Wildcat Creek is a labeled southeast oriented tributary in Morgan County. East and southeast oriented streams in the northeast quadrant of figure 2 all flow in southeast directions east of figure 2 to join the northeast oriented South Platte River. Crow Creek flows from the north center edge of figure 2 (near the town of Grover) in a south direction and makes a jog to the west just north of Seven Cross Hill before flowing in a south, southwest, and south direction to join the southeast oriented South Platte River east of Greeley. Crow Creek tributaries from the west are numerous and are generally oriented in south-southeast directions while Crow Creek has almost no tributaries from the east. This asymmetric drainage divide suggests the Crow Creek valley eroded headward across multiple south-southeast oriented flood flow channels and diverted floodwaters in a southwest direction to southwest and south oriented flood flow channels on alignments of what are today the north and northeast oriented South Platte River and north oriented South Platte River tributary drainage routes. The southeast oriented South Platte River segment west of Fort Morgan was created by headward erosion of the South Platte River valley along a southeast oriented flood flow channel. The northeast oriented South Platte River segment between Masters and Goodrich was created by headward erosion of the South Platte River valley across southeast oriented flood flow. The southeast oriented South Platte River segment between Greeley and Masters was created by headward erosion of the South Platte River valley across southwest oriented flood flow. Just north of Seven Cross Hill Crow Creek turns in a southeast direction before turning to flow in a west direction. The southeast oriented turn is where the south oriented Crow Creek valley captured a southeast oriented flood flow channel and eroded headward along that flood flow channel for a sort distance before headward across southeast oriented flood flow.

Wildcat Creek-South Platte River drainage divide area

Fig3 WildcatSPLatte

Figure 3: Wildcat Creek-South Platte River drainage divide area. United States Geological Survey map digitally presented using National Geographic Society TOPO software.

Figure 3 provides a topographic map of Wildcat Creek-South Platte River drainage divide area. The map contour interval for figure 3 is 10 meters. Fort Morgan is the town straddling the south center edge of figure 3. The South Platte River flows in a southeast direction from the west center edge of figure 3 to Fort Morgan and then turns to flow in a northeast direction to the east edge of figure 2 (south half). Elevations in the South Platte River valley near Fort Morgan are about 1300 meters. Wildcat Creek flows in a southeast direction from the north center edge of figure 3 to join the northeast oriented South Platte River near the east edge of figure 3. Box Canyon and Porter Canyon are two north and northeast oriented Wildcat Creek tributaries near the north center edge of figure 3. Elevations on Fry Hill (just west of Porter Canyon and near north edge of figure 3) exceed 1460 meters and are approximately 160 meters higher than the South Platte River valley floor at Fort Morgan. Aker Draw and Lamborn Draw are south and south-southwest oriented South Platte River tributaries near the west edge of figure 3. Unnamed southeast oriented South Platte River tributaries flow across the northeast corner of figure 3. While subtle there is a difference in the orientations of South Platte River tributaries in the east half of figure 3 and the orientations in the west half of figure 3. The north and northeast oriented Box Canyon and Porter Canyon valleys were eroded by reversals of flood flow as the deep southeast oriented Wildcat Creek valley eroded headward across south and south-southwest oriented flood flow. At that time the deep southeast oriented South Platte River valley in the west half of figure 3 was being eroded and south and south-southwest oriented flood flow was moving to the actively eroding South Platte River valley head. Headward erosion of the deep southeast oriented Wildcat Creek valley beheaded and reversed flood flow on the Box Canyon alignment first. The reversed flood flow captured south oriented flood flow still moving on the yet to be beheaded and reversed Porter Canyon alignment and the captured flood flow helped erode the deep northeast and north oriented Box Canyon valley. Headward erosion of the deep Wildcat Creek valley next beheaded and reversed flood flow on the Porter Canyon alignment and the process was repeated.

Detailed map of the Porter Canyon-Aker Draw drainage divide area

Fig4 detPorterCanyonAkerDraw

Figure 4: Detailed map of Porter Canyon-Aker Draw 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 Porter Canyon-Aker Draw drainage divide area south and east of figure 3 and seen in less detail in figure 3. The map contour interval for figure 4 is 10 feet. Wildcat Creek flows in a southeast direction across the northeast corner of figure 4. East and south of figure 4 Wildcat Creek flows in a southeast direction to join the northeast oriented South Platte River. Box Canyon originates in the east half of section 27 and drains in a southeast, northeast, and north-northeast direction to enter the southeast oriented Wildcat Creek valley as a barbed tributary. Porter Canyon originates near the north edge of section 27 and drains in a north, northeast, and north-northeast direction to also enter the southeast oriented Wildcat Creek valley as a barbed tributary. Aker Draw originates near the northeast corner of section 19 and drains in a south-southwest direction to the southwest corner of figure 4. South and west of figure 4 Aker Draw drains to the southeast oriented South Platte River. Fry Hill is located near the northwest corner of section 21. A south-southwest and west oriented Aker Draw tributary originates near Fry Hill and joins Aker Draw in section 31 near the southwest corner of figure 4. Fry Hill is located on an upland erosion surface, which today is the Wildcat Creek-Aker Draw drainage divide (and Wildcat Creek-South Platte River drainage divide in the southeast quadrant of figure 4). The upland erosion surface was eroded by headward erosion of the deep southeast oriented Wildcat Creek valley and its tributary valleys and also by the deep south-southwest oriented Aker Draw and tributary valleys (and south oriented South Platte River tributary valleys in the southeast quadrant of figure 4), but remnants of the earlier erosion surface still survive along the drainage divide. A high point in the west half of section is labeled “Newton” has an elevation of 4774 feet. The Fry Hill elevation is at least 4810 feet. Between these two high points drainage divide elevations decreases to between 4700 and 4710 feet suggesting the presence of a northeast to southeast oriented through valley or former flood flow channel that once crossed the upland surface (prior to headward erosion of the deep southeast oriented Wildcat Creek valley). A shallower through valley in the north half of section 27 links the north oriented Porter Canyon headwaters valley with the southeast oriented Box Canyon headwaters valley. Prior to the reversal of flood flow on the Porter Canyon alignment floodwaters flowed in a southeast direction into the newly beheaded and reversed Box Canyon drainage route. Floodwaters that eroded the north and northeast oriented Porter Canyon valley apparently flowed in a southeast and east direction around the south side of Fry Hill and were subsequently captured by headward erosion of the deep south-southwest and southwest oriented Aker Draw tributary valley.

Wildcat Creek-Cottonwood Draw drainage divide area

Fig5 WildcatCottonwoodDraw

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

Figure 5 illustrates the Wildcat Creek-Cottonwood Draw drainage divide area north and west of figure 3 and there is an overlap area with figure 3. The map contour interval for figure 5 is 10 meters. Fry Hill is located near the southeast corner of figure 5. Jackson Reservoir in the southwest quadrant of figure 5 is located north of the eastern South Platte River jog where the northeast oriented river segment turns to flow in a southeast direction. Wildcat Creek flows in a southeast direction from the north center edge of figure 5 to the east edge of figure 5 (south half) and east and south of figure 5 joins the northeast oriented South Platte River. Jackson Hills is the upland erosion surface extending in a southeast direction from the north edge of figure 5 to the Fry Hill area near the southeast corner of figure 5. The upland erosion surface is also present in the northeast corner of figure 5 on the northeast side of the southeast oriented Wildcat Creek valley. A southwest-facing escarpment extending from the north edge of figure 5 (west half) to the southeast corner of figure 5 is drained by south and south-southwest oriented tributaries headed towards the southeast oriented South Platte River (south of figure 5). Many of these south oriented streams end as surface drainage routes before they reach the South Platte River. Two Cottonwood Draws can be seen in figure 5. The first Cottonwood Draw drains in a south direction from the southwest-facing escarpment slope to the south edge of figure 5 (east of Jackson Reservoir). The second Cottonwood Draw drains in a south-southeast direction from the west edge of figure 5 toward Jackson Reservoir, but ends as a surface drainage route. The southwest-facing escarpment probably was eroded as the northeast wall of a southeast oriented flood flow channel, which was subsequently captured by a southwest oriented flood flow channel on the present day northeast oriented South Platte River alignment (in the northeast-southeast jog). The southwest oriented flood flow channel was then beheaded and reversed by headward erosion of the deeper southeast oriented South Platte River valley (again in the northeast-southeast jog) to create the northeast-southeast jog in the South Platte River west of Fort Morgan. Southeast oriented flood flow in the southeast oriented flood flow channel was beheaded at about that time by headward erosion of the south-southwest oriented Crow Creek valley (see figure 7).

Detailed map of Wildcat Creek-Cottonwood Draw drainage divide area

Fig6 detWildcatCottonwoodDraw

Figure 6: Detailed map of Wildcat Creek-Cottonwood Draw 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 Wildcat Creek-Cottonwood Draw drainage divide area seen in less detail in figure 5. The map contour interval for figure 6 is 10 feet. Wildcat Creek flows in a southeast direction from the north edge of figure 6 (east of center) to the east edge of figure 6 (north of center). East and south of figure 6 Wildcat Creek flows to the northeast oriented South Platte River. South oriented streams draining to the south edge of figure 6 are headwaters of south oriented Cottonwood Draw, which south of figure 6 drains to the South Platte River at northern point in the eastern South Platte River northeast-southeast jog. The low relief upland surface between the southeast oriented Wildcat Creek valley and the south oriented Cottonwood Draw headwaters valleys is the Jackson Hills seen in figure 5. While no deep valleys cross the Jackson Hills upland there are shallow through valleys and what may be streamlined erosional residuals. In addition there are shallow depressions usually defined by a single 10-foot contour line. The depressions may be wind eroded deflation basins and it possible some of the small streamlined hills are wind deposited sand dunes. However, the relatively smooth upland surface was eroded by south, south-southeast, and/or southeast oriented flood flow, which was being captured by headward erosion of the deep southeast oriented Wildcat Creek valley which was eroding headward from the northeast oriented South Platte River valley and by headward erosion of south oriented valleys from what initially was probably a southwest oriented flood flow channel on the present day northeast oriented South Platte River alignment (in the eastern South Platte River northeast-southeast jog), although which was later beheaded and reversed to become the northeast oriented South Platte River segment in the eastern South Platte River northeast-southeast jog. Flood flow across the Jackson Hills upland surface was beheaded by headward erosion of the deeper southwest oriented Crow Creek valley west of figure 6 (see figures 7 and 8).

Crow Creek-Sanborn Draw drainage divide area

Fig7 CrowSanbornDraw

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

Figure 7 uses a reduced size topographic map to illustrate the Crow Creek-Sanborn Draw drainage divide area west 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 a south and southwest direction from the north edge of figure 7 (west half) to the west edge of figure 7 (south half). West and south of figure 7 Crow Creek joins the South Platte River. Sanborn Draw originates slightly north and west of the center of figure 7 and drains in a south direction to the south edge of figure 7 (slightly west of center). South of figure 7 Sanborn Draw drains to Riverside Reservoir, which is located north of an east oriented South Platte River segment. The upland in the northeast quadrant of figure 7 is a continuation of the Jackson Hills upland seen in figure 5 and north of figure 7 merges into Seven Cross Hill with Crow Creek flowing in a west and south direction around the northwest end of Seven Cross Hill. Greasewood Flats is located at the base of the northwest end of the southwest-facing escarpment seen in figure 5 (on southwest side of Jackson Hills) and is actually a shallow southeast oriented through valley defined by three 10-meter contour lines. Perhaps easier to visualize is the northwest to southeast oriented through valley crossing the Crow Creek-Sanborn Draw drainage divide. Point of Rocks is a labeled high point in the southwest quadrant of figure 7 and reaches an elevation of more than 1520 meters. Elevations along the Crow Creek-Sanborn Draw drainage divide north of Point of Rocks drop to less than 1500 meters and then rise to more than 1520 meters on Seven Cross Hill near the north edge of figure 7. These elevations suggest a 20 meter deep or deeper southeast oriented flood flow channel eroded the drainage divide. Initially floodwaters flowed in a southeast direction toward the southeast corner of figure 7, but were captured by headward erosion of south oriented valleys. For example, headward erosion of south oriented Sanborn Draw captured the southeast oriented flood flow and diverted floodwaters in a south direction. Headward erosion of the southwest oriented Crow Creek valley next captured the southeast oriented flood flow and diverted floodwaters in a southwest direction. Floodwaters on northwest ends of beheaded flood flow routes reversed flow direction to create northwest oriented tributary drainage routes to southwest oriented Crow Creek. Coal Creek is the south-southeast oriented stream flowing from the northwest corner of figure 7 to join Crow Creek near Cornish and provides further evidence that headward erosion of the southwest oriented Crow Creek valley captured south-southeast oriented flood flow.

Detailed map of Crow Creek-Sanborn Draw drainage divide area

Fig8 detCrowSanbornDraw

Figure 8: Detailed map of Crow Creek-Sanborn Draw 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 Crow Creek-Sanborn Draw drainage divide area seen in less detail in figure 7. The map contour interval for figure 8 is 10 feet. Crow Creek can just barely be seen flowing in a southwest direction across the northwest corner of figure 8. West and south of figure 8 Crow Creek flows to the South Platte River. Northwest oriented streams in the west half of figure 8 flow to Crow Creek as barbed tributaries. South and southeast oriented streams in the east half of figure 8 are tributaries to south oriented Sanborn Draw. South of figure 8 Sanborn Draw drains to Riverside Reservoir, which is located just north of an east oriented South Platte River segment. Point of Rocks is a labeled high point in section 17 near the south edge of figure 8 (west half) and reaches an elevation of 4975 feet. North of section 17 the Crow Creek-Sanborn Draw drainage divide elevation decreases to between 4910 and 4920 feet in section 32. Elevations along the drainage divide remain below 4950 feet to the north edge of figure 8, but north of figure 8 rise to more than 5040 feet on Seven Cross Hill. These elevations suggest there is a broad northwest to southeast oriented through valley between Point of Rocks and Seven Cross Hill, which at its deepest points is at least 55 feet deep. Multiple shallower northwest-to-southeast oriented through valleys are eroded into the floor of that broader through valley. The shallower through valleys are defined by two or more contour lines on a side and suggest floodwaters flowed in diverging and converging flood flow channels. At the time floodwaters flowed in a southeast direction across figure 8 the southwest oriented Crow Creek valley did not exist. Headward erosion of the southwest oriented Crow Creek valley captured the southeast oriented flood flow. Floodwaters on northwest ends of beheaded flood flow channels reversed flow direction to flow in northwest directions to the deeper southwest oriented Crow Creek valley and to create northwest oriented Crow Creek tributary drainage routes.

Crow Creek-South Platte River drainage divide area

Fig9 CrowSPlatte

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

Figure 9 illustrates the Crow Creek-South Platte River drainage divide area south and west of figure 7 and there is an overlap area with figure 7. The map contour interval for figure 9 is 10 meters. The South Platte River flows in a southeast direction across the southwest corner of figure 9. Crow Creek flows in a southwest and south direction from the north edge of figure 9 (west of center) to join the South Platte River north of the town of Kuner. Sanborn Draw drains in a south direction from near the northeast corner of figure 9 to the east center edge of figure 9. East and south of figure 9 Sanborn Draw drains to Riverside Reservoir, which is located north of an east oriented South Platte River segment, just west of the eastern South Platte River northeast-southeast jog. Point of Rocks is the labeled high point in the northeast quadrant of figure 9. Shallow northwest-to-southeast oriented through valleys can be seen crossing the drainage divide south and west of Point of Rocks. Generally these through valleys are defined by one 10-meter contour line on each side. The through valleys combined with evidence for the deeper through valleys seen north and east of Point of Rocks provide evidence of southeast oriented flood flow moving across the region in figure 9 prior to headward erosion of the southwest oriented Crow Creek valley. While not seen in figure 9 the southwest oriented Crow Creek valley (before it turns in a south direction) is headed towards the present day northeast oriented South Platte River valley segment west of Greeley (see figure 10). Headward erosion of the southwest oriented Crow Creek valley probably was from a southwest and south oriented flood flow channel on the present day north and northeast oriented South Platte River alignment south of Greeley (see figure 1). Headward erosion of the deep southeast oriented South Platte River valley captured the flood flow on the newly eroded southwest oriented Crow Creek flood flow route and beheaded the southwest and south oriented flood flow channel on the present day north and northeast oriented South Platte River alignment. Floodwaters on the northeast and north ends of the beheaded flood flow channel reversed flow direction to create the north, northeast, and southeast oriented South Platte River drainage route near Greeley.

Lone Tree Creek-Crow Creek drainage divide area

Fig10 LoneTreeCrow

Figure 10: Lone Tree Creek-Crow 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-Crow Creek drainage divide west and slightly south of figure 9 and includes an overlap area with figure 9. The map contour interval for figure 10 is 10 meters. Greeley is the city near the west center margin of figure 10. The South Platte River flows in a northeast direction from near the southwest corner of figure 10 to Scout Island (near center of figure 10) and then turns to flow in a southeast direction to the east edge of figure 10 (near southeast corner).  The Cache la Poudre River flows from the west edge of figure 10 (north of Greeley) along the north edge of Greeley in an east-southeast direction to join the South Platte River near Scout Island. Crow Creek flows in a west direction from near the northeast corner of figure 10 and west of Barnesville turns to flow in a south direction to join the southeast oriented South Platte River just north of the town of Kuner. Lone Tree Creek flows in a south direction from the north center edge of figure 10 to join the South Platte River at its elbow of capture (where it turns from flowing in a northeast direction to flowing in a southeast direction). Sand Creek is a south oriented stream flowing from the north edge of figure 10 (west half) to join the east oriented Cache la Poudre River near the County Municipal Airport (just west of Scout Island). The northeast oriented “Creek” and South Platte River tributary south of Kuner is Box Elder Creek, which south of figure 10 flows in a north direction. The South Platte River elbow of capture seen in figure 10 is where headward erosion of the deep southeast oriented South Platte River valley captured south flood flow channels that had been flowing in a south direction along the alignments of the present day north and northeast oriented South Platte River and its north oriented tributary drainage routes. The Cache la Poudre River originates in the high mountains west of figure 10 and prior to being captured by headward erosion of the deeper southeast oriented South Platte River valley probably turned in a southeast direction west of Greeley on an alignment now used by a southeast oriented Big Thompson River segment, which joins the north and northeast oriented South Platte River as a barbed tributary (south of Greeley) near the point where the north oriented South Platte River turns to flow in a northeast direction, although a different essay illustrates and discusses the Cache la Poudre River-Big Thompson River drainage divide area.

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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