Abstract:

This essay uses topographic map evidence to interpret landform origins in the Big Thompson River-Little Thompson River drainage divide area in the Colorado Front Range. The Big Thompson River originates in Rocky Mountain National Park and flows in a southeast, northeast, and east-southeast direction onto the Colorado Piedmont before turning in a southeast direction to enter the north and northeast oriented South Platte River valley, which further to the north turns in a southeast direction before finally turning in a northeast direction to reach western Nebraska. The Little Thompson River originates just east of Rocky Mountain National Park and a short distance south and east of the northeast oriented Big Thompson River and then flows in a southeast, east, and east-northeast direction onto the Colorado Piedmont to join the southeast oriented Big Thompson River just before the Big Thompson River enters the South Platte River valley. Through valleys, both in the Colorado Front Range and on the Colorado Piedmont to the east, link the Big Thompson and Little Thompson River valleys. Northwest oriented tributaries flow to northeast oriented Big Thompson River segments as barbed tributaries. Valley orientations, barbed tributaries, and through valleys are illustrated on topographic maps and interpreted in the context of immense melt water floods from the western margin of a thick North American ice sheet. Floodwaters flowed from western Canada to and across the Big Thompson River-Little Thompson River drainage divide at a time when the Colorado Front Range was beginning to emerge. Floodwaters in the emerging Front Range first flowed in anastomosing complexes of south oriented flood flow channels, which were captured by anastomosing complexes of southeast oriented flood flow channels, which were then captured in sequence by headward erosion of the east oriented Little Thompson and Big Thompson River valleys, which eroded headward from south oriented flood flow channels on the present day north oriented South Platte River alignment. Headward erosion of the deeper southeast and northeast oriented South Platte River valley from western Nebraska next beheaded the south oriented flood flow channels on the present day north oriented South Platte River alignment. Floodwaters on north ends of beheaded flood flow channels reversed flow direction to flow to the deeper southeast and northeast oriented South Platte River valley and to create the present day north, southeast, and northeast oriented South Platte River drainage route.

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 Big Thompson River-Little Thompson River drainage divide area landform origins in the 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 Big Thompson River-Little Thompson River drainage divide area landform evidence in the Colorado Front Range will be regarded as evidence supporting the “thick ice sheet that melted fast” paradigm.

Big Thompson River-Little Thompson River drainage divide area location map

Figure 1: Big Thompson River-Little Thompson 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 Big Thompson River-Little Thompson River drainage divide area in the Colorado Front Range and illustrates a region in north central Colorado. The west to east oriented Wyoming-Colorado state line is located along the north edge of figure 1. The Colorado Front Range is the mountain range west of the cities of Denver, Boulder, Loveland, and Fort Collins. Rocky Mountain National Park is shown and labeled near the west edge of figure 1. The South Platte River flows in a north direction from the south edge of figure 1 (south of Denver) to near Greeley where it turns to flow in a southeast, northeast, southeast, and northeast direction to the east edge of figure 1 (north of center). East of figure 1 the South Platte River flows in a northeast direction to enter western Nebraska. Note north oriented tributaries from the south to the southeast oriented South Platte River segment downstream from Greeley and south oriented tributaries from the north. The Big Thompson River originates in Rocky Mountain National Park and flows in a southeast and northeast direction to Estes Park and then in a northeast, east-southeast, east, and southeast direction to near Milliken where it turns to flow in an east-northeast direction to join a northeast oriented segment of the South Platte River. The Little Thompson River is shown in figure 1 (although the headwaters are not correctly drawn) and originates south and east Estes Park and then flows in a southeast and northeast direction to join the Big Thompson River near Milliken. The Big Thompson River-Little Thompson River drainage divide area investigated in this essay is south of the Big Thompson River, north of the Little Thompson River, and extends from the east boundary of Rocky Mountain Nation Park to the north and northeast oriented South Platte River near Milliken.

Drainage routes in the Big Thompson River-Little Thompson River drainage divide area and in the entire South Platte River drainage basin were 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 drainage basin at a time when the Colorado Front Range was beginning to emerge. At first floodwaters flowed in south directions both east of the emerging mountains and within the emerging mountain area. The north oriented South Platte River drainage route and north oriented South Platte River tributary drainage routes on the present day Colorado Piedmont are located on alignments what were once south oriented flood flow channels. Southeast and later east and northeast oriented valleys eroded headward from these south oriented flood flow channels in sequence from south to north to capture south oriented flood flow moving across the emerging mountain region. Headward erosion of each east oriented valley captured flood flow moving to the newly eroded east oriented valley immediately to the south. The east oriented valleys at times eroded headward in northeast directions across southeast oriented flood flow and also eroded headward along southeast oriented flood flow channels. Floodwaters on north ends of beheaded flood flow channels reversed flow direction to flow in north directions to the deeper beheading valley. The mountains were emerging as floodwaters flowed across them and floodwaters eroded deeper and deeper valleys into the emerging mountain masses. Emergence of the mountains was due to ice sheet related crustal warping in addition to deep erosion of surrounding areas. South oriented flood flow channels on the present day Colorado Piedmont moved floodwaters to the southeast oriented Arkansas River valley and prior to headward erosion of the Arkansas River valley to other southeast and south oriented valleys located further to the south. Headward erosion of the deep southeast and northeast oriented South Platte River valley from western Nebraska captured the south oriented flood flow channels on the Colorado Piedmont 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 southeast and northeast oriented South Platte River valley. Because flood flow channels were anastomosing (diverging and converging) reversed flood flow channels could capture floodwaters from yet to be beheaded flood flow channels further to the west. Such captures helped create significant north oriented South Platte River drainage routes and the present day north oriented South Platte River drainage route. Southeast oriented South Platte River headwaters (south of figure 1) provide evidence of such flood flow captures.

Detailed location map for Big Thompson River-Little Thompson River drainage divide area

Figure 2: Detailed location map Big Thompson River-Little Thompson 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 Big Thompson River-Little Thompson River drainage divide area in the Colorado Front Range. The red-brown region along the western margin of figure 2 is the eastern margin of Rocky Mountain National Park. Green colored areas are National Forest lands and are located in the Colorado Front Range. The Colorado Front Range eastern flank is located just west of the cities of Longmont and Fort Collins. Greeley is the city straddling the east edge of figure 2. The South Platte River flows in a north direction from the south edge of figure 2 (east half) to Maddux and Platteville and then turns in a northeast direction to cross the east edge of figure 2 near La Salle. The Big Thompson River flows in an east and northeast direction from the west center edge of figure 2 to Estes Park (on east edge of Rocky Mountain National Park) and then in a northeast direction to Drake. From Drake the Big Thompson River flows in an east-southeast direction to Loveland and then in an east and southeast direction to near Milliken where the Big Thompson River turns in an east-northeast direction to join the northeast oriented South Platte River. The Little Thompson River originates in the green colored area south and east of Estes Park and flows in a southeast direction toward Pinewood Springs and then turns in an east-northeast, east-southeast, and east-northeast direction to join the Big Thompson River near Johnstown (just west of Milliken). A labeled body of water located in the Big Thompson River-Little Thompson River drainage divide area is Carter Lake Reservoir, which is located between north-to-south oriented hogback ridges along the Colorado Front Range eastern flank. The region west of Carter Lake Reservoir consists of high mountains while the region east of Carter Lake Reservoir is located on the low relief Colorado Piedmont. Dry Creek is the unlabeled east and northeast oriented Big Thompson River tributary located north of Carter Lake Reservoir.

Little Thompson River-South Platte River drainage divide area

Figure 3: Little Thompson River-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 Little Thompson River-South Platte River drainage divide area. The map contour interval for figure 3 is 10 meters except near the west edge where the contour interval is 50 meters. The South Platte River flows in a north and northeast direction from the south center edge of figure 3 to the east edge of figure 3 (near northeast corner). East and north of figure the South Platte River turns to flow in a southeast direction before turning in a northeast direction to flow into western Nebraska. The Big Thompson River flows in a southeast direction from the north edge of figure 3 (west of center) and once it enters the South Platte River valley near Milliken turns to flow in an east-northeast direction to join the South Platte River near the northeast corner of figure 3. The Little Thompson River flows in an east-northeast direction from the west edge of figure 3 (slightly south of center) to join the Big Thompson River near Millikan. The Big Thompson River enters the South Platte River valley as a barbed tributary, which suggests the Big Thompson River drainage route was established at a time when water was flowing in a south direction on the present day north oriented South Platte River alignment. Also supporting this interpretation are short south-southeast oriented Big Thompson River tributaries just east of the southeast oriented Big Thompson River segment. Also in the southwest quadrant of figure 3 three short southeast oriented streams flow towards the north oriented South Platte River. Wildcat Mound is a high point west of the South Platte River and south of Milliken. West of Wildcat Mound is a north oriented stream and a shallow north-to-south oriented through valley linking the southeast oriented Big Thompson River valley with the north oriented South Platte River segment to the south. While only defined by one 10-meter contour line on the east side this through valley is evidence of the route south oriented flood flow from the Big Thompson River valley used when moving to a south oriented flood flow channel on the present day north oriented South Platte River alignment. South oriented flood flow on the South Platte River alignment was beheaded by headward erosion of the deeper southeast and northeast oriented South Platte River valley from western Nebraska. Floodwaters on the north end of the beheaded (south oriented) flood flow channel reversed flow direction to flow in a north and northeast direction to the deeper southeast and northeast oriented South Platte River valley and to create the north and northeast oriented South Platte River drainage route seen in figure 3. The reversal of flood flow on the South Platte River alignment also captured the southeast oriented Big Thompson River, which created the Big Thompson River elbow of capture seen near Milliken.

Detailed map of Little Thompson River-South Platte River drainage divide area

Figure 4: Detailed map of Little Thompson River-South Platte River 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 Little Thompson River-South Platte River drainage divide area seen in less detail in figure 5. The map contour interval for figure 4 is 10 feet. The South Platte River flows in a north and northeast direction across the southeast corner of figure 4. East and north of figure 4 the South Platte River flows in a northeast and southeast direction before finally turning in a northeast direction to flow into western Nebraska. The Little Thompson River flows in an east-northeast direction from the west edge of figure 4 (near northwest corner) to the north center edge of figure 4. North of figure 4 the Little Thompson River joins the southeast oriented Big Thompson River near the point where the Big Thompson River turns to flow in an east-northeast direction to join the northeast oriented South Platte River. A through valley in section 27 (east half of figure 4) links a north oriented valley now drained by the north oriented Hillsboro Ditch with the north oriented South Platte River valley to the south. Wildcat Mound in sections 22 and 23 defines the through valley’s east wall. The high point on Wildcat Mound has an elevation of 4943 feet. Elevations on the through valley floor are between 4880 and 4890 feet suggesting the through valley is at least 53 feet deep. The through valley was probably eroded by south oriented flood flow moving from the southeast oriented Big Thompson River alignment to south oriented flood flow on the present day north oriented South Platte River alignment. At that time the south oriented flood flow channel floor elevation on the South Platte River alignment was approximately at the level of the section 27 through valley floor elevation. Flood flow on the South Platte River alignment was beheaded by headward erosion of the deeper southeast and northeast oriented South Platte River valley from western Nebraska. Floodwaters on the north end of the beheaded flood flow route reversed flow direction to flow to the deeper southeast and northeast oriented South Platte River valley and to create the north and northeast oriented South Platte River drainage route seen in figure 4. The reversed flood flow, which captured floodwaters still moving in south directions further to the west, eroded the deep South Platte River valley seen in figure 4. Today the floor of the South Platte River valley has an elevation of between 4720 and 4730 feet, which means the South Platte River valley floor elevation has been lowered by approximately 150 feet since the time of the flood flow reversal. At least some of this erosion took place rapidly after the flood flow reversal.  The north oriented valley now drained by Hillsboro Ditch was eroded by reversed or north oriented flood flow moving from the newly reversed flood flow on the South Platte River alignment to the south end of the Big Thompson River valley, which was lowered in elevation by the reversed flood flow before reversed flood flow eroded the deep South Platte River valley segment seen in figure 4.

Big Thompson River-Little Thompson River drainage divide area

Figure 5: Big Thompson River-Little Thompson River drainage divide area. United States Geological Survey map digitally presented using National Geographic Society TOPO software.

Figure 5 illustrates the Big Thompson River-Little Thompson River drainage divide area west and slightly north of figure 3 and there is an overlap area with figure 3. The map contour interval for figure 5 is 50 meters except near the east edge where the contour interval is 10 meters. The east flank of the Colorado Front Range can be seen in the west half of figure 5 and the Colorado Piedmont is the region of low relief located east of the Front Range. Lakes seen in figure 5 are reservoirs used by the regional irrigation systems, which obtain water from rivers and streams in the mountains to the west. The Big Thompson River flows through The Narrows near the northwest corner of figure 5 and then in an east-southeast direction to the south side of Loveland before turning in an east-northeast direction to flow to the east edge of figure 5 (north half). East of figure 5 the Big Thompson River turns to flow in a southeast direction to enter the northeast oriented South Platte River valley and then turns in an east-northeast direction to join the northeast oriented South Platte River, which then turns to flow in a southeast direction before turning in a northeast direction to flow into western Nebraska. The Little Thompson River flows in an east-northeast, east, and east-northeast direction from the south center edge of figure 5 to the east edge of figure 5 (near southeast corner). East of figure 5 the Little Thompson River flows in an east-northeast direction to join the Big Thompson River near the point where the Big Thompson River enters the South Platte River valley. The 50-meter contour interval does not show enough detail to determine much in the Colorado Piedmont region east of the Colorado Front Range, however in the west half of figure 5 several north-to-south oriented through valleys can be seen. Hogback ridges bound the through valleys and the through valley orientations are defined by those ridges, although the through valleys are also water-eroded valleys and were eroded by south oriented flood flow. Carter Lake Reservoir is a large lake located between north-to-south oriented hogback ridges. West of Carter Lake Reservoir is an easier to observe through valley drained in the north by north oriented Chimney Hollow to Flatiron Reservoir, which drains to a northeast oriented Dry Creek, which flows to the Big Thompson River. The south end of the through valley west of Carter Reservoir is drained by a south oriented Dry Creek, which flows to the southeast, east, and east-northeast oriented Little Thompson River (south of the southwest corner of figure 5). The through valley floor elevation is between 1750 and 1800 meters. Elevations on the hogback ridge to the east rise to 1898 meters suggesting the through valley is at least 100 meters deep. The through valley is just one of several such north-to-south oriented through valleys eroded by south oriented flood flow prior to headward erosion of the east oriented Big Thompson River valley to the north. Headward erosion of the northeast oriented Dry Creek valley from the Big Thompson River valley first beheaded and reversed flood flow in the through valley to create the north oriented Chimney Hollow drainage route. Headward erosion of the east oriented Big Thompson River valley next beheaded south oriented flood flow to the newly eroded Dry Creek valley. This brief description is simplistic and a more complete description would have floodwaters flowing in ever-changing diverging and converging flood flow channels, which were captured in sequence by headward erosion of deeper valleys.

Detailed map of Chimney Hollow-Dry Creek drainage divide area

Figure 6: Detailed map of Chimney Hollow-Dry 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 Chimney Hollow-Dry Creek drainage divide area seen in less detail in figure 5. The map contour interval for figure 6 is 40 feet. Carter Lake Reservoir is located in the central area of figure 6 and is surrounded by north-to-south oriented hogback ridges forming the east flank of the Colorado Front Range. Dams impounding Carter Lake Reservoir are in the southwest corner of section 35, west half of section 10, and straddle the border between sections 2 and 3 in the north center of figure 6. Prior to construction of the Carter Lake Reservoir dams drainage from the Carter Lake Reservoir location appears to have flowed in southeast directions to southeast oriented Dry Creek, which flows to the east edge of figure 6 (south half). East and south of figure 6 Dry Creek flows to the east oriented Little Thompson River. Dry Creek and other drainage routes east of Carter Lake Reservoir eroded water gaps across north-to-south oriented hogback ridges. The water gaps are evidence drainage routes were established when valleys between the ridges did not exist. If the valleys had existed the drainage would have flowed in the valleys. Either the drainage routes originated on an erosion surface that has since been removed or the ridges were uplifted as water flowed across them. In either case it would be impossible to create the water gaps and also erode the north-to-south oriented through valleys unless water was moving in both valleys at the same time. The drainage routes seen east of Carter Reservoir had to be eroded by a complex of diverging and converging flood flow channels with floodwaters moving in a south and/or southeast direction. West of Carter Reservoir is the Chimney Hollow-Dry Creek through valley seen in less detail in figure 5. Chimney Hollow drains the north end of the through valley in a north direction and north of figure 6 drains to a northeast oriented Dry Creek, which then flows to the Big Thompson River. The through valley south end is drained by a south oriented Dry Creek, which flows to the southeast, east, and east-northeast oriented Little Thompson River south of figure 6. The through valley floor elevation at the drainage divide is between 5800 and 5840 feet. The hogback ridge between the through valley and Carter Lake Reservoir rises to 6227 feet suggesting the through valley is approximately 400 feet deep. The through valley was eroded by south oriented flood flow moving to a southeast oriented Little Thompson River valley segment. Floodwaters flowing in the present day north-to-south oriented valleys were captured by east oriented valleys eroding headward from south oriented flood flow channels east of the emerging mountain front

Big Thompson River-North Fork Little Thompson River drainage divide area

Figure 7: Big Thompson River-North Fork Little Thompson River drainage divide area. United States Geological Survey map digitally presented using National Geographic Society TOPO software.

Figure 7 illustrates the Big Thompson River-North Fork Little Thompson River drainage divide area west and slightly north of figure 5 and includes an overlap area with figure 5. The map contour interval for figure 7 is 50 meters. The Big Thompson River flows in an east-northeast and northeast direction from the west edge of figure 7 (north of center) to Drake (near north edge of figure 7) and then in an east-southeast direction to The Narrows where it makes a jog to the northeast before flowing to the east edge of figure 7 (near northeast corner). Rabbit Gulch and an unnamed tributary east of Rabbit Gulch flow in northwest directions to join the northeast oriented Big Thompson River as barbed tributaries. Muggins Gulch drains in a southeast direction across the southwest quadrant of figure 7 and is the headwaters of the Little Thompson River. The North Fork Little Thompson River originates in the west center region of figure 7 (between Sugarloaf Mountain and Panorama Peak) and flows in an east direction to near the center of figure 7 and then turns to flow in a south direction to the south center edge of figure 7. South of figure 7 the North Fork joins the east, southeast, and east-northeast oriented Little Thompson River. Northwest-to-southeast oriented through valleys link the northeast oriented Big Thompson River segment with the east and south oriented North Fork Little Thompson River valley. For example, the northwest oriented Rabbit Gulch valley is linked by a through valley between Sugarloaf Mountain and Pole Hill with a southeast oriented valley draining to the east oriented North Fork. Further east is an even more intriguing through valley extending from Waltonia in the Big Thompson River valley to the south oriented North Fork Little Thompson River valley. The north end of this through valley is drained by an unnamed northwest oriented Big Thompson River tributary and the south oriented North Fork Little Thompson River valley drains the through valley’s south end. In between are southeast oriented headwaters of Quillan Gulch, which instead of draining to the south oriented North Fork Little Thompson River turns in an east direction to join northeast and southeast oriented Cottonwood Creek, which then drains to northeast oriented Dry Creek, which east of figure 7 joins the Big Thompson River. Another northwest-to-southeast oriented through valley (to the east) links a north oriented Big Thompson River tributary valley with the southeast oriented Saddle Notch Gulch valley, which also drains to Cottonwood Creek. These through valleys are more than 250 meters deep and were eroded by southeast and south oriented flood flow prior to headward erosion of the northeast oriented Big Thompson River valley. Headward erosion of Cottonwood Creek valley first captured the southeast oriented flood flow east of Pole Hill while headward erosion of the east oriented North Fork Little Thompson River valley first captured southeast oriented flood flow west of Pole Hill. Next headward erosion of the deep northeast oriented Big Thompson River valley beheaded the southeast oriented flood flow channels in sequence from east to west and floodwaters on northwest ends of beheaded flood flow channels reversed flow direction to create northwest oriented Big Thompson River tributary drainage routes.

Detailed map of Big Thompson River-Quillan Gulch drainage divide area

Figure 8: Detailed map of Big Thompson River-Quillan Gulch 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 Big Thompson River-Quillan Gulch drainage divide area seen in less detail in figure 7. The map contour interval for figure 8 is 40 feet. The Big Thompson River flows in an east and northeast direction from the west edge of figure 8 (north half) to the north center edge of figure 8. Tributaries from the north are oriented in southeast and south-southeast directions while tributaries from the south are oriented in northwest and north directions. Rabbit Gulch is a northwest oriented Big Thompson River tributary located in the west half of figure 8 and is linked with a southeast oriented Rabbit Gulch draining to the south edge of figure 8 (west half) and then to the east and south oriented North Fork Little Thompson River. A northwest-to-southeast oriented through valley links the two opposing Rabbit Gulches. The through valley floor elevation is 8330 feet. Pole Hill to the east rises to 8683 feet and Sugarloaf Mountain to the west rises to more than 8920 feet suggesting the through valley is at least 350 feet deep. Near the center of figure 8 an even deeper northwest-to-southeast oriented through valley links a northwest oriented Big Thompson River tributary valley (draining to the Big Thompson River at Waltonia) with south-southeast and east oriented Quillan Gulch, which drains to the east edge of figure 8 (near southeast corner). The through valley floor elevation is 7342 feet. East of the through valley elevations rise to 8310 feet and west of the through valley elevations rise to more than 8600 feet suggesting the through valley is almost 1000 feet deep. The through valley continues in a south-southeast direction south of the Quillan Gulch elbow of capture (in section 26 near south edge of figure 8). Just south of the Quillan Gulch elbow of capture there is a low drainage divide (not meriting a single 40-foot contour line) and then a steep south oriented valley draining to the south oriented North Fork Little Thompson River valley (south of figure 8). The low drainage divide has an elevation of between 7040 and 7080 feet. While not seen in figure 8 ridges to the east rise to more than 7380 feet suggesting the Quillan Gulch-North Fork Little Thompson River through valley is at least 300 feet deep. Still another northwest-to-southeast oriented through valley is located east of Waltonia and links a northwest and north oriented Big Thompson River tributary valley with the southeast oriented Saddle Notch Gulch valley. This Saddle Notch Gulch through valley could be as much as 1000 feet deep (depending on where measurements are made). These and other northwest-to-southeast oriented through valleys were eroded by southeast oriented flood flow channels prior to headward erosion of the northeast oriented Big Thompson River valley. A close look at figure 8 also shows evidence for north-to-south oriented through valleys, which were beheaded by headward erosion of the southeast oriented flood flow channels. For example Saddle Notch in the east center area of figure 8 was eroded by a south oriented flood flow channel prior to headward erosion of the southeast oriented Saddle Notch Gulch valley.

Big Thompson River-Muggins Gulch drainage divide area

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

Figure 9 illustrates the Big Thompson River-Muggins Gulch drainage divide area west and slightly south of figure 7 and there is a large overlap area with figure 7. The map contour interval for figure 9 is 50 meters. The Big Thompson River flows in a northeast direction from the west edge of figure 9 (north half) to Estes Lake (in Estes Park) and then to the north center edge of figure 9. Little Thompson River headwaters, which flow in Muggins Gulch, originate east and south of Estes Lake and flows in a southeast and south-southeast direction before turning to flow in northeast and southeast direction to the east edge of figure 9 (near southeast corner). A northwest-to-southeast oriented through valley south of Mount Pisgah links the northeast oriented Big Thompson River valley at Estes Park with the southeast oriented Muggins Gulch valley. The through valley floor elevation is between 2400 and 2450 meters. Mount Pisgah rises to 2630 meters and elevation to the southwest rise even higher suggesting the through valley is at least 280 meters deep. The through valley is only one of many through valleys seen in figure 9. The North Fork Little Thompson River originates between Sugarloaf Mountain and Panorama Peak in the north center area of figure 9 and flows in an east and south direction to join the Little Thompson River near the east edge of figure 9. The east oriented North Fork Little Thompson River headwaters valley is linked by a through valley at The Notch with the northwest oriented Solitude Creek valley and then with a west oriented valley draining to Estes Lake. A maze of north-to south oriented through valleys can be seen in the southwest quadrant of figure 9 and link north oriented Big Thompson River tributary valleys with valleys of south oriented St Vrain Creek tributaries (St Vain Creek is an east oriented drainage route south of figure 9). Of special note is Wind River Pass near the southwest corner of figure 9, which links the north-northeast oriented Fish Creek valley with the south-southeast oriented Tahosa Creek valley. The Wind River Pass elevation is between 2750 and 2800 meters. Twin Sisters Peaks to the east rise to 3483 meters and mountains west of figure 9 rise to more than 4000 meters. These elevations suggest Wind River Pass is almost 700 meters deep. Wind River Pass was eroded by south oriented flood flow, which was beheaded and reversed by headward erosion of the southeast oriented Muggins Gulch valley, which was then beheaded by headward erosion of the northeast oriented Big Thompson River valley.  The erosion of these deep valleys, the flood flow captures, and the flood flow reversals were taking place as floodwaters flowed across an emerging mountain range.

Detailed map of Big Thompson River-Muggins Gulch drainage divide area

Figure 10: Detailed map of Big Thompson River-Muggins Gulch 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 Big Thompson River-Muggins Gulch drainage divide area seen in less detail in figure 9. The map contour interval for figure 10 is 40 feet. Estes Park and Lake Estes are located near the northwest corner of figure 10. The Big Thompson River flows in an east direction from the west edge of figure 10 to Lake Estes and then in a northeast direction to the north edge of figure 10 (west half). Fish Creek flows in an east, north, and north-northeast direction from the west edge of figure 10 (near southwest corner) to join the Big Thompson River at Lake Estes. South of figure 10 the north oriented Fish Creek valley is linked by Wind River Pass with the south oriented Tahosa Creek valley, which drains to east oriented St Vrain Creek. Mount Pisgah is located east and south of Lake Estes. South of Mount Pisgah is a northwest-to-southeast oriented through valley linking a northwest oriented Big Thompson River tributary valley with the southeast oriented Muggins Gulch valley, which is drained by southeast oriented Little Thompson River headwaters. The through valley floor elevation is 8037 feet. Mount Pisgah rises to 8630 feet and an unnamed mountain in section 33 to the south rises to 8820 feet suggesting the through valley is approximately 600 feet deep, although by using the Panorama Peak elevation of 9284 feet (near east edge of the southeast quadrant of figure 10) and the Kruger Rock elevation of 9355 feet (in the southwest quadrant of figure 10) a case could be made the through valley is 1250 feet deep. Shallower northwest-to-southeast oriented through valleys in the southwest corner of section 33 and the northwest quadrant of section 5 link northwest oriented Fish Creek tributary valleys with southeast oriented headwaters streams flowing to southeast oriented Big Gulch, which is also a Little Thompson River headwaters drainage route. The North Fork Little Thompson River originates in section 25 and flows in an east direction to the east edge of figure 10 (north of center). East of figure 10 the North Fork turns in a south direction to join the Little Thompson River. A deep west-to-east oriented through valley in the southwest corner of section 25 links the east oriented North Fork Little Thompson Creek valley with the north oriented Solitude Creek valley (which drains to north-northeast oriented Noels Draw and then to the Big Thompson River) and with a west oriented Big Thompson River tributary valley. These and other through valleys seen in figure 10 document multiple southeast oriented flood flow channels of the type found in a southeast oriented anastomosing channel complex that was captured first by headward erosion of the east oriented Little Thompson River valley and which was subsequently beheaded by headward erosion of the northeast oriented Big Thompson River valley.

Additional information and sources of maps studied

This essay has provided only a sample of the detailed topographic map evidence supporting the flood erosion interpretation. Many additional illustrations could be provided. Readers are encouraged to look at mosaics of detailed topographic maps to see the abundance of available data. Maps used in this study were created and published by the United States Geologic Survey and can be obtained directly from the United States Geological Survey and/or from dealers offering United States Geological Survey maps. Hard copy maps can also be observed at United States Geological Survey map depositories, which are located throughout the United States and elsewhere. Illustrations used here were created using National Geographic Society TOPO software and digital map data. TOPO software and map data can be obtained from the National Geographic Society and/or dealers offering National Geographic Society digital map data.