Abstract:

This essay uses topographic map evidence to interpret landform origins in the Cache la Poudre River-Buckhorn Creek drainage divide area in the northern Colorado Front Range. The South Fork Cache la Poudre River originates in Rocky Mountain National Park and flows in a northeast direction to join the east oriented Cache la Poudre River, which near the east flank of the mountains turns in a southeast direction as it flows onto the Colorado Piedmont before turning in an east direction to join the north, northeast, southeast, and northeast oriented South Platte River at the point where the South Platte River turns to flow in a southeast direction. Buckhorn Creek headwaters are east of the northeast oriented South Fork Cache la Poudre River drainage route and Buckhorn Creek flows in an east and south-southeast direction to join the east and southeast oriented Big Thompson River, which joins the north and northeast South Platte River as a barbed tributary. Through valleys cross the Cache la Poudre River-Buckhorn Creek and South Fork Cache la Poudre-Buckhorn Creek drainage divides in the Colorado Front Range and also cross the Cache la Poudre River-Big Thompson River drainage divide on the adjacent Colorado Piedmont. Valley orientations, through valleys, diverging and converging valleys, and barbed tributaries seen on topographic maps are interpreted to have 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 South Platte River basin at a time when the Colorado Front Range was beginning to emerge. Initially floodwaters flowed in south directions, but as the Front Range emerged and as deep valleys eroded headward into the region flood flow directions changed and were even reversed. The Big Thompson River and its south and southeast oriented tributary valleys eroded headward from a south oriented flood flow channel on the present day north oriented South Platte River alignment. Next headward erosion of east oriented Cache la Poudre River valley and its northeast oriented South Fork valley eroded headward across south and southeast oriented flood flow routes to actively eroding Buckhorn Creek valley and tributary valleys. Headward erosion of the deep South Platte River valley from western Nebraska next captured the east and southeast oriented Cache la Poudre River flood flow route and beheaded the south oriented flood flow channel along the east margin of the emerging Colorado Front Range. Floodwaters on the north end of the beheaded flood flow channel reversed flow direction to flow to the deeper South Platte River valley and to create the north, southeast, and northeast oriented South Platte River drainage route seen today. The reversal of flood flow also captured the southeast oriented Big Thompson River.

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 Cache la Poudre River-Buckhorn Creek drainage divide area landform origins in the northern Colorado Front Range. 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 Cache la Poudre River-Buckhorn Creek drainage divide area landform evidence in the northern Colorado Front Range will be regarded as evidence supporting the “thick ice sheet that melted fast” paradigm.

 

Cache la Poudre River-Buckhorn Creek drainage divide area location map

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

Figure 1 provides a location map for the Cache la Poudre River-Buckhorn Creek drainage divide area in the northern Colorado Front Range and illustrates a region in northern Colorado. The west to east oriented Colorado-Wyoming border is located along the north edge of figure 1. The Colorado Front Range is the mountain range west of Fort Collins, Boulder, and Denver while the Colorado Piedmont is the region east of the Front Range. Rocky Mountain National Park is shown and labeled. The South Platte River flows in a north-northeast, north, and northeast direction from Denver to Greeley and then turns to flow in a southeast direction with a jog to the northeast near the east edge of figure 1 (slightly south of center). East of figure 1 the South Platte River turns to flow in a northeast direction to join the southeast North Platte River in western Nebraska. The Cache la Poudre River originates in northern Rocky Mountain National Park and flows in a north direction before turning in an east and southeast direction to Fort Collins on the Colorado Piedmont and then flows in a southeast and east direction to join the South Platte River near Greeley (near the point where the South Platte River turns to flow in a southeast direction). Cache la Poudre River tributaries shown in figure 1 are from the north and flow in south directions to reach the Cache la Poudre River. The Big Thompson River originates in Rocky Mountain National Park (south of the Cache la Poudre River headwaters) and as shown in figure 1 flows in a southeast, northeast, and southeast direction to join the South Platte River south of Greeley. Big Thompson River tributaries shown in figure 1 are from the north and flow in southeast directions to reach the Big Thompson River. Buckhorn Creek is shown, but not labeled in figure 1, and is the east and southeast oriented Big Thompson River tributary flowing near the town of Masonville. The Cache la Poudre River-Buckhorn Creek drainage divide area investigated in this essay is located north and east of Buckhorn Creek and south and west of the Cache la Poudre River and includes the Cache la Poudre River-Big Thompson River drainage divide area on the Colorado Piedmont.

The South Platte River and its tributary drainage routes, including tributary drainage routes in the present day Colorado Front Range, 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 Colorado and Wyoming mountain ranges were beginning to emerge. The mountain ranges emerged as floodwaters flowed across them, as ice sheet related crustal warping raised the mountain masses, and as floodwaters deeply eroded surrounding regions. Initially floodwaters flowed in south directions, but were later diverted in other directions and even reversed as crustal warping raised mountain ranges and plateau areas and as deep valley eroded headward into the region to capture the massive flood flow. The present day north oriented South Platte River drainage route (south of Greeley) and north oriented South Platte River tributaries (in southeast corner of figure 1) are located on alignments of what were once south oriented flood flow channels with floodwaters flowing to the southeast oriented Arkansas River valley in southern Colorado (south of figure 1) prior to headward erosion of the Arkansas River valley to south and southeast oriented valleys further to the south). Headward erosion of what at that time was the deep southeast and northeast oriented South Platte River valley from western Nebraska captured the south oriented flood flow channels in sequence from east to west. 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 and reversed in sequence from east to west and because flood flow channels were anastomosing (diverging and converging) newly beheaded and reversed flood flow channels could capture south oriented flood flow from yet to be beheaded flood flow channels further to the west. Such captures helped create significant north oriented South Platte River tributary drainage routes and the north oriented South Platte River drainage route. Southeast oriented South Platte River headwaters (south of Denver and south of figure 1) are evidence reversed flow on the present day north oriented South Platte River drainage route captured south and southeast oriented flood flow still flowing in the emerging Colorado Front Range. At that time south and southeast oriented floodwaters were flowing through and across what was an emerging mountain mass.

The Big Thompson River valley eroded headward from the south oriented flood flow channel on the present day north oriented South Platte River alignment prior to Cache la Poudre River valley headward erosion and captured south and southeast oriented flood flow moving through and across the emerging Colorado Front Range. The east and southeast oriented Buckhorn Creek valley eroded headward from the newly eroded Big Thompson River valley to capture south and southeast oriented flood flow moving towards the newly eroded Big Thompson River valley. The Cache La Poudre River valley initially eroded headward from the south oriented flood flow channel on the present day north oriented South Platte River alignment and captured south and southeast oriented flood flow moving to the newly eroded Big Thompson River valley and its south and southeast oriented tributary valleys. The north oriented Cache la Poudre River headwaters drainage route was created by a reversal of flood flow on a beheaded south oriented flood flow channel. Headward erosion of the deep southeast and northeast oriented South Platte River valley beheaded and reversed flood flow on the present day north oriented South Platte River alignment while floodwaters were still flowing in the Cache la Poudre River valley. The capture of south oriented flood flow channels near Greeley by the deep southeast and northeast oriented South Platte River valley also captured the southeast oriented Cache la Poudre River route west of Greeley and diverted the Cache la Poudre River flow in an east direction to the newly eroded and deep southeast and northeast oriented South Platte River valley. Evidence for these flood flow captures is seen today along drainage divides in the Colorado Piedmont and also in the high Colorado Front Range suggesting the Front Range did not stand high above the Piedmont when floodwaters flowed across the region.

Detailed location map for Cache la Poudre River-Buckhorn Creek drainage divide area

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

Figure 2 provides a detailed location map for the Cache la Poudre River-Buckhorn Creek drainage divide area in the northern Colorado Front Range. Green colored areas are National Forest lands and are located in the Front Range. The red-brown area in the southwest corner of figure 2 is Rocky Mountain National Park. The Cache la Poudre River flows in an east direction from the west edge of figure 2 (north half) to the towns of Rustic and Poudre Park and then to the east edge of green colored area where it turns to flow in a southeast direction to the northeast edge of Fort Collins and then in a south-southeast direction to Windsor where the Cache la Poudre River turns to flow in an east direction to the east edge of figure 2 (south half). East of figure 2 the Cache la Poudre River joins the southeast and northeast oriented South Platte River. The South Fork Cache la Poudre River originates just south of the north margin of Rocky Mountain National Park (near west edge of figure 2) and flows in a northeast direction to join the east oriented Cache la Poudre River west of Poudre Park. Horsetooth Reservoir is located between Lory State Park and Fort Collins and is located between north-to-south oriented hogback ridges along the east flank of the Colorado Front Range. The Big Thompson River flows in a southeast, east, and northeast direction in the southwest corner of figure 2 to Estes Park and then in a northeast and east direction to Loveland. East of Loveland the Big Thompson River turns to flow in a southeast direction to the south edge of figure 2 (east half). South of figure 2 the Big Thompson River joins the north and northeast South Platte River as a barbed tributary. Note in the southeast corner of figure 2 how the south-southeast oriented Cache la Poudre River segment between Fort Collins and Windsor is on approximately the same alignment as the southeast oriented Big Thompson River segment east of Loveland.  Buckhorn Creek originates in the west center area of figure 2 (north and east of the Rocky Mountain National Park northeast corner) and flows in an east and south-southeast direction to join the Big Thompson River west of Loveland (north of the south center edge of figure 2). Redstone Creek is a southeast, south-southeast, and southwest oriented Buckhorn Creek tributary west of Lory State Park. Other Big Thompson River tributaries shown in figure 2 are oriented in southeast directions and suggest headward erosion of the Big Thompson River valley captured multiple southeast oriented flood flow channels. Headward erosion of the northeast oriented South Fork Cache la Poudre River valley captured southeast oriented flood flow moving to the actively eroding Buckhorn Creek valley and tributary valleys. North oriented South Fork and Cache la Poudre River tributary drainage routes were created by reversals of flood flow on north ends of beheaded flood flow channels. The predominance of south oriented drainage routes in what is today the north oriented South Platte River drainage basin is evidence a major reversal of drainage direction took place in the South Platte River drainage basin.

South Fork Cache la Poudre River-Box Prairie Creek drainage divide area

Figure 3:South Fork Cache la Poudre River-Box Prairie Creek drainage divide area. United States Geological Survey map digitally presented using National Geographic Society TOPO software.

Figure 3 provides a topographic map of South Fork Cache la Poudre River-Box Prairie Creek drainage divide area. The map contour interval for figure 3 is 50 meters. The Cache la Poudre River flows in an east direction from the northwest corner of figure 3 to the east edge of figure 3 (near northeast corner). East of figure 3 the Cache la Poudre River flows in an east, southeast, south-southeast, and east direction to join the southeast and northeast oriented South Platte River. The South Fork Cache la Poudre River flows in a north-northeast and northeast direction from the west edge of figure 3 (near southwest corner) to join the Cache la Poudre River near the north center edge of figure 3. Pennock Pass is a labeled pass in the southwest quadrant of figure 3 and links a west oriented stream with east oriented Box Prairie Creek, which flows to the town of Box Prairie and then to east oriented Buckhorn Creek, which then flows to the east edge of figure 3 (near southeast corner). East and south of figure 3 Buckhorn Creek flows in a south-southeast direction to join the east and southeast oriented Big Thompson River, which then flows to the north and northeast oriented South Platte River. North of the town of Box Prairie is West White Pine Mountain and east of West White Pine Mountain is East White Pine Mountain. Pendergrass Creek originates on the north side of the gap between the two mountains and flows in a north direction to join the northeast oriented South Fork Cache la Poudre River south of Mount McConnell. The gap between the two mountains links the north oriented Pendergrass Creek valley with a south and southeast oriented Buckhorn Creek tributary valley. The gap or pass floor elevation is between 2900 and 2950 meters or approximately 175 meters lower than the adjacent mountain tops. The gap or pass is what remains of a water-eroded valley and is evidence of a former drainage route. Other passes or through valleys can be seen in figure 3 including Pennock Pass and a northwest to southeast oriented between West White Pine Mountain and Pennock Pass. Still another impressive through valley is in the northeast quadrant of figure 3 and links a north-northwest oriented Cache la Poudre River tributary valley with the south-southeast oriented Stove Prairie Creek valley which drains to Buckhorn Creek near the southeast corner of figure 3. These and other through valleys seen in figure 3 (with the exception of the Pennock Pass through valley) were eroded by south and southeast oriented flood flow channels prior to headward erosion of deep east oriented Cache la Poudre River valley. The south and southeast oriented flood flow was flowing to what at that time was the actively eroding east oriented Buckhorn Creek valley and its east oriented Box Prairie Creek tributary valley. Floodwaters were flowing in diverging and converging flood flow channels. Headward erosion of the deep east oriented Cache la Poudre River valley and the northeast oriented South Fork Cache la Poudre River valley beheaded and reversed the south and southeast oriented flood flow channels to the actively eroding Buckhorn Creek and tributary valleys to create north and northwest oriented Cache la Poudre River and South Fork Cache la Poudre River tributary drainage routes. The west oriented stream west of Pennock Pass was created when headward erosion of the deep north-northeast oriented South Fork Cache la Poudre River valley and a north oriented tributary valley (which were eroding headward as a reversed flood flow routes) beheaded an east oriented flood flow channel moving floodwaters to what was at that time the actively eroding east oriented Box Prairie Creek valley.

Detailed map of South Fork Cache la Poudre River-Box Prairie Creek drainage divide area

Figure 4: Detailed map of South Fork Cache la Poudre River-Box Prairie 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 South Fork Cache la Poudre River-Box Prairie Creek drainage divide area seen in less detail in figure 5. The map contour interval for figure 4 is 40 feet. The South Fork Cache la Poudre River flows in a north-northeast direction from the west edge of figure 4 (south half-section 11) to the north edge of figure 4 (west half) and north of figure 4 flows to the east, southeast, and east oriented Cache la Poudre River. The north oriented South Fork tributary flowing from the southwest corner of figure 4 is Pennock Creek. Pennock Pass is located in section 18 (southwest quadrant of figure 4) and links a west oriented Pennock Creek tributary valley with the east oriented Box Prairie Creek valley, which continues to the southeast corner of figure 4. Near the southeast corner of figure 4 Box Prairie Creek becomes east oriented Buckhorn Creek, which eventually turns in a south-southeast direction to join the east and southeast oriented Big Thompson River. Monument Gulch is a southeast oriented Box Prairie Creek tributary in section 8 and is linked by a pass or through valley with an unnamed north-northwest oriented South Fork Cache la Poudre River tributary valley. The through valley or pass floor elevation is between 8840 and 8880 feet. Elevations at the southwest corner of section 7 rise to 9495 feet and West White Pine Mountain rises to 10,305 feet. These elevations suggest the northwest-to-southeast oriented through valley is at least 615 feet deep. The through valley was eroded by southeast oriented flood flow prior to headward erosion of the north-northeast oriented South Fork Cache la Poudre River valley. Headward erosion of the South Fork valley beheaded the southeast oriented flood flow channel and floodwaters on the northwest end of the beheaded flood flow channel reversed flow direction to flow to the much deeper South Fork valley and to create the north-northwest oriented South Fork tributary drainage route. Pennock Pass has an elevation of 9143 feet and is at least 350 feet deep. Pennock Pass was eroded by east oriented flood flow moving to the actively eroding east oriented Box Prairie Creek valley. The gap between West and East White Pine Mountains in the east half of figure 4 links a south and southeast oriented Box Prairie Creek tributary valley with the north oriented Pendergrass Creek valley, which north of figure 4 drains to the northeast oriented South Fork Cache la Poudre River. The gap elevation is between 9600 and 9640 feet, approximately 600 feet lower in elevation than the adjacent mountain tops. The gap provides further evidence of a south oriented flood flow channel and also provides evidence floodwaters once flowed on an erosion surface as high or higher than the highest points seen in figure 4, which means floodwaters deeply eroded the region surrounding West and East White Pine Mountains.

Cache la Poudre River-Buckhorn Creek drainage divide area

Figure 5: Cache la Poudre River-Buckhorn Creek drainage divide area. United States Geological Survey map digitally presented using National Geographic Society TOPO software.

Figure 5 illustrates the Cache la Poudre River-Buckhorn Creek drainage divide area east of figure 3 and there is an overlap area with figure 3. The map contour interval for figure 5 is 50 meters. The Cache la Poudre River flows in (roughly) an east direction from the west edge of figure 5 (north half) to near the northeast corner of figure 5 and then turns to flow in a south and southeast direction to the east edge of figure 5 (north half). The South Fork Cache la Poudre River flows in a northeast direction from the west edge of figure 5 (just south of Mount McConnell) to join the Cache la Poudre River near the northwest corner of figure 5. Pendergrass Creek is the north oriented South Fork tributary flowing near the west center edge of figure 5. Poverty Gulch is a north-northwest and north-northeast oriented Cache la Poudre River tributary east of Pendergrass Creek. Box Prairie Creek flows in (roughly) an east direction from the west edge of figure 5 (near southwest corner) to east and east-southeast oriented Buckhorn Creek, which flows to the south edge of figure 5 (east of center). South of figure 5 Buckhorn Creek turns to flow in a south-southeast direction to join the east and southeast oriented Big Thompson River. Mount Ethel is located near the center of figure 5. Immediately west of Mount Ethel is a north-northwest to south-southeast oriented through valley linking the Cache la Poudre River valley with the Buckhorn Creek valley. The “town” of Stove Prairie is located in the through valley a short distance south of Mount Ethel. The south end of the through valley is drained by west and south-southeast oriented Stove Prairie Creek, which joins east-southeast and south-southeast oriented Buckhorn Creek near Deadman Hill. The through valley mid section is drained by west, north-northwest, northeast, and north oriented Stove Prairie Gulch, which drains to north oriented Young Gulch, which in turn drains to the east oriented Cache la Poudre River. The through valley north end is drained by an unnamed northeast and north-northwest oriented stream, which joins the east oriented Cache la Poudre River near Stove Prairie Landing. Study of the region seen in figure 5 reveals other through valleys although this Stove Prairie through valley is perhaps one of the easiest to observe. The Stove Prairie through valley was initially eroded by south-southeast oriented flood flow moving to the southeast oriented Buckhorn Creek valley, which had eroded headward from the east and southeast oriented Big Thompson River valley, which had eroded headward from a south oriented flood flow channel on the present day north oriented South Platte River alignment (south of Greeley). Flood flow across the region seen in figure 5 was flowing in diverging and converging south oriented flood flow channels, which were beheaded in sequence from east to west by headward erosion of the deep east oriented Cache la Poudre River valley. Floodwaters on one of the south oriented flood flow channels supplying floodwaters to the south-southeast oriented Stove Prairie through valley were reversed to create the north oriented Young Gulch and north-northwest, northeast, and north oriented Stove Prairie Gulch drainage route, which captured south and southeast oriented flood flow from yet to be beheaded flood flow channels further to the west (e.g. the north end of the Stove Prairie through valley and perhaps the Poverty Gulch valley). This captured flood made a U-turn to flow in an east and north direction to and in the newly reversed Young Gulch valley to reach the newly eroded Cache la Poudre River valley. Headward erosion of the deep Cache la Poudre River valley next beheaded and reversed the south-southeast oriented flood flow route at Stove Prairie Landing to create the unnamed north-northwest oriented Cache la Poudre River tributary drainage route (or the third drainage route now draining the former south-southeast oriented flood flow channel).

Detailed map of Stove Prairie Gulch-Stove Prairie Creek drainage divide area

Figure 6: Detailed map of Stove Prairie Gulch-Stove Prairie 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 Stove Prairie Gulch-Stove Prairie Creek drainage divide area seen in less detail in figure 5. The map contour interval for figure 6 is 40 feet. Mount Ethel is located in the northeast quadrant of figure 6 and rises to 8471 feet. East White Pine Mountain is located near the southwest corner of figure 6 and rises to 10,248 feet. Stove Prairie School is located in section 33 south of Mount Ethel and is located in the north-northwest to south-southeast oriented through valley observed in figure 5. Stove Prairie Creek originates near the east edge of figure 6 and flows in a west direction toward Stove Prairie School and then turns to flow in a south-southeast direction to the southeast corner of figure 6. South and east of figure 6 Stove Prairie Creek flows to south-southeast oriented Buckhorn Creek, which flows to the east and southeast Big Thompson River, which then flows to the north and northeast oriented South Platte River. Stove Prairie School is located at a drainage divide in the through valley and just north of Stove Prairie School the through valley is drained in a north-northwest direction by Harlan Gulch, which drains to north and northeast oriented Stove Prairie Gulch, which drains to the north edge of figure 6 (near northeast corner). North of figure 6 Stove Prairie Gulch drains to north oriented Young Gulch, which drains to the east oriented Cache la Poudre River. The Stove Prairie Gulch-Stove Prairie Creek drainage divide at Stove Prairie School has an elevation of 7326 feet, which is more than 1100 lower than the top of Mount Ethel and which suggests the through valley may be as much as 1100 feet deep. The through valley is a water-eroded valley and was eroded by southeast-southeast oriented flood flow moving to a south oriented flood flow channel on the alignment of the present day north oriented South Platte River (south of Greeley). Poverty Gulch is the north, northwest, and north oriented drainage route draining to the north edge of figure 6 (near northwest corner). The north oriented Poverty Gulch headwaters in the northeast corner of section 35 are linked by a through valley (or pass) with the southeast, south, and southeast oriented Twin Cabin Gulch valley, which drains to the south center edge of figure 6. South of figure 6 Twin Cabin Gulch drains to east and south-southeast oriented Buckhorn Creek. The Poverty Gulch-Twin Cabin Gulch through valley (or pass) is at least 480 feet deep and is evidence of a different south-southeast oriented flood flow channel. Numerous other through valleys or passes can be seen in figure 6 and provide evidence of an evolving network of diverging and converging flood flow channels as headward erosion of the deep east and south-southeast oriented Buckhorn Creek valley (south of figure 6) and headward erosion of the deep east oriented Cache la Poudre River valley (north of figure 6) captured the south-southeast oriented flood flow, which was deeply eroding the entire region.

Rist Canyon-Redstone Creek drainage divide area

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

Figure 7 illustrates the Rist Canyon-Redstone Creek drainage divide area south and east of figure 5 and includes an overlap area with figure 5. The map contour interval for figure 7 is 50 meters. The eastern flank of the Colorado Front Range extends from near the north center edge of figure 7 to near the south center edge of figure 7. Fort Collins is the city straddling the east edge of figure 7 and is located on the Colorado Piedmont. The Cache la Poudre River flows in a southeast direction from the north edge of figure 7 (slightly east of center) to the east center edge of figure 7. East of figure 7 the Cache la Poudre River flows in a southeast and east direction to join the southeast and northeast oriented South Platte River. Buckhorn Creek flows in an east and southeast direction from the west edge of figure 7 (south of center) to the south edge of figure 7 (west of center) and south of figure 7 joins the east and southeast oriented Big Thompson River, which then joins the north and northeast (and then southeast and northeast) oriented South Platte River. The Rist Canyon drainage route originates south of the picnic area east of Mount Ethel (near northwest corner) and drains in an east direction toward the southeast oriented Cache la Poudre River. Redstone Creek originates just east of Mount Ethel and flows in a southeast and south-southeast direction to the south center edge of figure 7. South of figure 7 Redstone Creek joins Buckhorn Creek. North-to-south oriented ridges such as those on either side of Horsetooth Reservoir are hogback ridges along the eastern flank of the Colorado Front Range, but also bound through valleys. While the through valleys are strike valleys (located along the strike of dipping strata) the through valleys are also water-eroded landforms and provide evidence of what were once south oriented flood flow channels. Horsetooth Reservoir is located in one such through valley, which at its drainage divide south of figure 7 has an elevation of 1658 meters. Keeping that elevation in mind the elevation of the Rist Canyon-Redstone Creek through valley drainage divide at the top (or west end) of Rist Canyon is between 2000 and 2050 meters. The Rist Canyon-Redstone Creek through valley is at least 250 meters deep, which suggests large volumes of flood flow were required to erode it. Further complicating the situation headward erosion of the east oriented Rist Canyon valley captured south-southeast and south oriented flood flow moving to the Redstone Creek valley, which converged (south of figure 7) with south oriented flood flow in the Horsetooth Reservoir through valley. There is a difference of almost 350 meters between the elevation of the Rist Canyon-Redstone Creek through valley elevation and Horsetooth Reservoir through valley elevation, yet both through valleys were eroded by south oriented flood flow at approximately the same time. How is it possible that floodwaters could be flowing at such different elevations? Probably at the time floodwaters flowed across the region the Colorado Front Range was emerging and the large elevation difference seen today did not exist. In addition the floodwaters were eroding the region from east to west as deep valleys eroded headward from the Gulf of Mexico to capture the south oriented flood flow.

Detailed map of Rist Canyon-Redstone Creek drainage divide area

Figure 8: Detailed map of Rist Canyon-Redstone 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 Rist Canyon-Redstone Creek drainage divide area seen in less detail in figure 7. The map contour interval for figure 8 is 40 feet. Redstone Creek flows from section 35 (near the northwest corner of figure 8) in a southeast, east, and southeast direction to the south edge of figure 8 (east half). South of figure 8 Redstone Creek flows in a south-southeast direction to join south-southeast oriented Buckhorn Creek, which then joins the east and southeast oriented Big Thompson River, which flows to the north and northeast oriented South Platte River. Lawrence Creek flows in an east direction across section 12 (near south edge of figure 8) and then turns in a southeast direction to join Redstone Creek near the south edge of figure 8. A south-southeast oriented tributary joins Lawrence Creek in section 7 and is linked by a through valley (in the southwest quadrant of section 6 and east center margin of section 1) with the southeast oriented Redstone Creek headwaters valley. Near the east center edge of section 1 the southeast oriented Redstone Creek valley splits into two diverging valleys with the present day Redstone Creek flowing in an east and southeast direction while the abandoned through valley route continues in a south-southeast direction before turning in a southeast direction to join the present day Redstone Creek route. Diverging and converging valleys of this type are typical in flood formed anastomosing channel complexes. What makes these diverging and converging valleys somewhat unique is they are located in a mountain region and the valleys are deep (the present day east oriented Redstone Creek valley segment is approximately 800 feet deep). The valley depths were probably achieved as the Colorado Front Range emerged around the diverging and converging flood flow channels. The Rist Canyon drainage route originates in section 26 (near northwest corner of figure 8) and flows in an east direction near the north edge of figure 8 to the east edge of figure 8 (near northeast corner). East of figure 8 Rist Canyon drains in an east direction toward the southeast oriented Cache la Poudre River. A through valley in section 32 links a north oriented Rist Canyon tributary valley with the valley of a south oriented Redstone Creek tributary. The through valley floor elevation at the road intersection is 6695 feet. Elevations in the northwest quadrant of section 4 to the southeast rise to 7660 feet and elevations in the northwest quadrant of section 32 to the west rise to 8032 feet.  These elevations suggest the north-to-south oriented through valley is almost 1000 feet deep. This deep north-to-south oriented through valley was eroded by south oriented flood flow moving to the south-southeast oriented Redstone Creek valley prior to headward erosion of the east oriented Rist Canyon valley. Headward erosion of the deep east oriented Rist Canyon valley captured the south oriented flood flow and diverted the floodwaters in an east direction to what was at that time the actively eroding southeast oriented Cache la Poudre River valley.

Cache la Poudre River-Big Thompson River drainage divide area

Figure 9: Cache la Poudre River-Big Thompson River drainage divide area. United States Geological Survey map digitally presented using National Geographic Society TOPO software.

Figure 9 illustrates the Cache la Poudre River–Big Thompson River drainage divide area south and east of figure 7 and there is a small overlap area with figure 7. The map contour interval for figure 9 is 50 meters except near the east edge where the contour interval is 10 meters. The Cache la Poudre River flows in a southeast direction across the northeast corner of figure 9 and east of figure 9 turns in a east direction to join the north, northeast, southeast, and northeast oriented South Platte River near the point where the South Platte River turns to flow in a southeast direction. The Big Thompson River flows in an east-southeast direction from the west edge of figure 9 (south half) to the south edge of Loveland and then flows in an east-northeast and southeast direction to the southeast corner of figure 9. South and east of figure 9 the Big Thompson River flows in a southeast direction to join the South Platte River near the point where it changes from flowing in a north direction to flowing in a northeast direction. Buckhorn Creek flows in a south-southeast direction from the west edge of figure 9 (near northwest corner) to join the Big Thompson River west of the Devils Backbone. Redstone Creek flows in a south and southwest direction from the north edge of figure 9 (near northwest corner) to join Buckhorn Creek near Masonville. The town of Horsetooth Heights is located at the south end of Horsetooth Reservoir, which was seen in figure 7. North-to-south south oriented ridges in the west half of figure 9 are hogback ridges along the east flank of the Colorado Front Range. Through valleys defined by those ridges are water-eroded features and were eroded by south oriented flood flow as the Colorado Front Range was emerging. Emergence of the Colorado Front Range occurred as floodwaters flowed across the region and was probably caused by ice sheet crustal warping (including the effects of the removal by floodwaters of great thickness of bedrock from the emerging mountain mass) and also by deep erosion by floodwaters of the Colorado Piedmont to the east (and seen in figure 9). While the 50-meter contour interval does not provide much detail there is no high drainage divide between the southeast-oriented Cache la Poudre River and the Big Thompson River once the rivers reach the Colorado Piedmont. Valleys of both rivers in the mountains to the west eroded headward from a deep south oriented flood flow channel on the present day north oriented South Platte River alignment (south and east of figure 9). That south oriented flood flow channel probably crossed the region seen in figure 9 and was beheaded by the deeper southeast and northeast oriented South Platte River valley, which eroded headward from western Nebraska. Floodwaters on the north end of the beheaded flood flow channel reversed flow direction to create the north and northeast oriented South Platte River drainage route (south of Greeley and seen in figures 1 and 10).

Cache la Poudre River-South Platte River drainage divide area

Figure 10: Cache la Poudre River-South Platte River drainage divide area. United States Geological Survey map digitally presented using National Geographic Society TOPO software.

Figure 10 provides a topographic map of the Cache la Poudre River-South Platte River drainage divide area south and east of figure 9 and there is a small overlap area with figure 9. The map contour interval for figure 10 is 10 meters. The South Platte River flows in a north and northeast direction from the south center edge of figure 10 to the east edge of figure 10 (south of center). East of figure 10 the South Platte River turns to flow in a southeast direction before turning to flow in a northeast direction into western Nebraska. The Big Thompson River flows in a southeast direction from the west center edge of figure 10 to enter the South Platte River valley near Milliken. After entering the South Platte River valley the Big Thompson River turns to flow in a northeast direction to join the northeast oriented South Platte River. The Cache la Poudre River flows in a southeast and east direction from the north edge of figure 10 (west half) to the northeast edge of Greeley and then turns in a south-southeast direction to the east edge of figure 10 (north half). East of figure 10 the Cache la Poudre River turns to flow in an east direction to join the South Platte River near the point where the South Platte River turns to flow in a southeast direction. The southeast oriented Big Thompson River valley enters the north and northeast oriented South Platte River valley as a barbed tributary, which is evidence the Big Thompson River valley eroded headward from a south oriented flood flow channel on the present day north oriented South Platte River alignment (south of figure 10). The Cache la Poudre River-Big Thompson River drainage divide near the town of Gove (near Oklahoma Reservoir in northwest quadrant of figure 10) is lower in elevation than the drainage divide further to the east. The railroad at Gove crosses the drainage divide at an elevation of between 1450 and 1460 meters. East of Gove the drainage divide elevation rises to more than 1490 meters suggesting there is a north-to-south oriented through valley near Gove linking the southeast oriented Cache la Poudre River valley with the southeast oriented Big Thompson River valley. Other north-to-south oriented through valleys are located further to the west), but could not be seen in figure 9 with the 50-meter contour interval. These north to south oriented through valleys are evidence floodwaters from the southeast Cache la Poudre River alignment once continued in a south and southeast direction to a south oriented flood flow channel on the present day north oriented South Platte River alignment. Headward erosion of the deep southeast and northeast oriented South Platte River valley from western Nebraska to the Greeley area captured the southeast oriented flood flow on the Cache la Poudre River alignment, but did not capture the flood flow on the Big Thompson River until floodwaters on the present day north oriented South Platte River alignment (south of figure 10) had been beheaded and reversed.

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.