Abstract:

This essay uses topographic map evidence to interpret landform origins in the Little Thompson River-St Vrain Creek drainage divide area in the Colorado Front Range. The Little Thompson River originates east of Rocky Mountain National Park and flows in a southeast, east-northeast, and southeast direction to the Colorado Piedmont and then in an east-northeast direction to join the Big Thompson River, which flows to the South Platte River. St Vrain Creek is located south of the Little Thompson River and is formed at the confluence of east, northeast, and southeast North St Vrain Creek and east and northeast oriented South St Vrain Creek and then flows in a southeast direction onto the Colorado Piedmont before turning in northeast direction to join the north, northeast, southeast, and northeast oriented South Platte River. Middle St Vrain Creek is a southeast, east, northeast, and east-southeast oriented South St Vrain Creek tributary. North-to-south oriented through valleys link the Little Thompson River valley with the St Vrain Creek and North St Vrain Creek valleys and also link the various St Vrain Creek tributary valleys. These north-to-south oriented through valleys are found both on the Colorado Piedmont and in the Colorado Front Range to the west. The north-to-south oriented through valleys are interpreted to have been eroded as south oriented flood flow channels prior to headward erosion of the east oriented St Vrain Creek valley and its tributary valleys, which was prior to headward erosion of the east oriented Little Thompson River valley. The east oriented valleys in the Colorado Front Range are interpreted to have eroded headward from south oriented flood flow channels on the Colorado Piedmont into an emerging Colorado Front Range across massive south oriented flood flow. Floodwaters are interpreted to have been derived from the western margin of a thick North American ice sheet and flowed from western Canada to and across the present day South Platte River drainage basin at a time when the Colorado Front Range and other regional mountain ranges were just beginning to emerge. The mountain ranges emerged as floodwaters flowed across them, as deep valleys eroded headward into the region to capture the immense south oriented flood flow, and as ice sheet related crustal warping raised the mountain masses and the entire study region. South oriented flood flow on the Colorado Piedmont was captured by headward erosion of the deep southeast and northeast oriented South Platte River valley from western Nebraska. Floodwaters on north ends of the beheaded flood flow channels reversed flow direction to flow in north directions to the deeper southeast and northeast oriented South Platte River valley and to create the present north oriented South Platte River and 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 Little Thompson River-St Vrain Creek 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 Little Thompson River-St Vrain Creek drainage divide area landform evidence in the Colorado Front Range will be regarded as evidence supporting the “thick ice sheet that melted fast” paradigm.

Little Thompson River-St Vrain Creek drainage divide area location map

Figure 1: Little Thompson River-St Vrain 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 Little Thompson River-St Vrain Creek drainage divide area in the Colorado Front Range and illustrates a region in north central Colorado. The west to east oriented Wyoming-Colorado border is located along the north edge of figure 1. The Colorado Front Range is the mountain area west of the cities of Fort Collins, Longmont, Boulder, and Denver. Rocky Mountain National Park is located near the west center edge of figure 1. The South Platte River flows in a north direction from south of Denver to near Greeley where it turns to flow in a northeast and then southeast direction (with a northeast jog) to Fort Morgan and then turns to flow in a northeast direction to the east edge of figure 1. East and north of figure 1 the South Platte River flows into western Nebraska. The Big Thompson River originates in Rocky Mountain National Park and flows in a southeast, northeast, east-southeast, and southeast direction to enter the South Platte River valley near Milliken and then turns in an east-northeast direction to join the northeast oriented South Platte River. The Little Thompson River is shown, but not labeled in figure 1 (and the headwaters are incorrectly drawn), but is the southeast and east-northeast oriented drainage route originating south of Estes Park and joining the Big Thompson River near Milliken. St Vrain Creek is south of the Little Thompson River and is also shown, but not labeled in figure 1. The St Vrain Creek headwaters of interest in this essay originate near the south margin of Rocky Mountain National Park and flow in east directions through the mountains to Longmont. From Longmont St Vrain Creek flows in an east and northeast direction to join the north, northeast, southeast, and northeast oriented South Platte River. North St Vrain Creek is the northernmost headwaters stream, Middle St Vrain Creek is to the south and South St Vrain Creek is further to the south. The St Vrain Creek tributary flowing through Boulder is Boulder Creek, which is not addressed in this essay. The Little Thompson River-St Vrain Creek drainage divide area investigated in this essay is located east of Rocky Mountain National Park, south of the Little Thompson River, north of Middle St Vrain Creek, and west of the South Platte River.

Drainage routes in Colorado and adjacent states developed during immense south oriented melt water floods from the western margin of a thick North American ice sheet. Floodwaters flowed from western Canada to and across Colorado at a time when Colorado mountain ranges were beginning to emerge. Colorado mountain ranges emerged as floodwaters flowed across them, as ice sheet related crustal warping raised mountain masses and the entire region, and as deep valleys eroded headward into Colorado to capture the massive melt water floods. Initially floodwaters flowed in south directions across the Colorado Front Range and Colorado Piedmont (east of the mountains), but directions of flood flow changed and even reversed in some case cases as crustal warping raised the region and mountains within the region and as deep valleys eroded headward into the region. The present day north oriented South Platte River drainage route (south of Greeley) and north oriented South Platte River tributary drainage routes in the southeast quadrant of figure 1 are located on alignments of what at one time were south oriented flood flow channels. Prior to headward erosion of the southeast and northeast oriented South Platte River valley from western Nebraska the south oriented flood flow east of the emerging Colorado Front Range was flowing to the southeast oriented Arkansas River valley (south of figure 1). East oriented valleys eroded headward from these south oriented flood flow channels on the present day Colorado Piedmont to capture south oriented flood flow moving across the emerging Colorado Front Range. Headward erosion of these valleys occurred in sequence from south to north with headward erosion of each new valley beheading flood flow routes to the newly eroded valley immediately to the south. Sometimes the east oriented valleys eroded in northeast directions across southeast oriented flood flow and at other times the east oriented valleys eroded headward along southeast oriented flood flow channels. North and northwest oriented valley segments and tributary routes were created by reversals of flood flow on north and northwest ends of beheaded south and southeast oriented flood flow channels. 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 present day Colorado Piedmont. Floodwaters on north ends of the beheaded flood flow channels reversed flow direction to flow to the deeper South Platte River valley and create north oriented South Platte River tributary drainage routes and the north oriented South Platte River drainage route. Because flood flow channels were beheaded in sequence from east to west and because flood flow channels were diverging and converging newly reversed flood flow channels could capture floodwaters from yet to be beheaded flood flow channels further to the west. Such captures of flood flow helped create significant north oriented drainage routes, including the present day north oriented South Platte River drainage route.

Detailed location map for Little Thompson River-St Vrain Creek drainage divide area

Figure 2: Detailed location map Little Thompson River-St Vrain 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 Little Thompson River-St Vrain Creek drainage divide area in the Colorado Front Range. The red-brown region along the western margin of figure 2 is Rocky Mountain National Park. Green colored area in the west half of figure 2 are National Forest lands located in the Colorado Front Range. The Colorado Piedmont is located in the east half of figure 2. The black dashed line extending from the west center edge of figure 2 to the south edge of figure 2 (near southwest corner) is the east-west continental divide. East of the continental divide drainage eventually reaches the Gulf of Mexico and west of the continental water flows to the Colorado River and eventually reaches the Pacific Ocean. The South Platte River flows in a north and northeast direction from the south edge of figure 2 (near southeast corner) to the east center edge of figure 2. East of figure 2 the South Platte River turns to flow in a southeast direction before turning to flow in a northeast direction to reach western Nebraska. The Big Thompson River flows in a southeast, east, and northeast direction from the west edge of figure 2 (north of center) to Estes Park and then in a northeast direction to Drake. From Drake the Big Thompson River flows in an east-southeast direction to the south edge of Loveland and then in an east and southeast direction to near Milliken where it turns in an east-northeast direction to join the South Platte River near the east center edge of figure 2. The Little Thompson River originates a short distance south and east of Estes Park and flows in a southeast direction almost to Pinewood Springs before turning to flow in an east-northeast, southeast, and east-northeast direction to join the Big Thompson River near Milliken. North St Vrain Creek originates along the continental divide just north of the southern boundary of Rocky Mountain National Park and flows in an east, east-northeast, and southeast direction to Lyons, where it joins northeast oriented South St Vrain Creek to form St Vrain Creek. St Vrain Creek then flows in a southeast direction to Longmont where it turns to flow in an east and then northeast direction to join the South Platte River near the east center edge of figure 2. Middle St Vrain Creek originates near the continental divide just south of the Rocky Mountain National Park southern boundary and flows in a southeast, east, and northeast direction to Raymond and then in a northeast and east direction to join northeast oriented South St Vrain Creek. South St Vrain Creek flows in an east and northeast direction to join North St Vrain Creek at Lyons and to form southeast, east, and northeast oriented St Vrain Creek. Highway number 7, which extends south from Estes Park just east of Rocky Mountain National Park,follows an unlabeled north oriented Big Thompson River tributary (Fish Creek) and then an unlabeled south oriented North St Vrain Creek tributary (Tahosa Creek). Note the large number of southeast oriented drainage routes or drainage route segments flowing from the Colorado Front Range onto the Colorado Piedmont to join the north oriented South Platte River.

Little Thompson River-St Vrain Creek drainage divide area

Figure 3: Little Thompson River-St Vrain Creek 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-St Vrain Creek drainage divide area on the Colorado Piedmont. The map contour interval for figure 3 is 50 meters except near the east edge where the contour interval is 10 meters. The Little Thompson River flows in an east and east-northeast direction from the west edge of figure 3 (north of Rabbit Mountain) to the north center edge of figure 3. North and east of figure 3 the Little Thompson River flows in an east-northeast direction to join the east-northeast oriented Big Thompson River, which flows to the northeast, southeast and northeast oriented South Platte River. St Vrain Creek flows in a southeast direction from the west edge of figure 3 (south of Rabbit Mountain) to near the south center edge of figure 3 and then turns to flow in an east-northeast direction to the east edge of figure 3. East of figure 3 St Vrain Creek turns to flow in a northeast direction to join the South Platte River. Rabbit Mountain is located along the east flank of the Colorado Front Range and the region east of Rabbit Mountain is the Colorado Piedmont. West of figure 3 the Little Thompson River flows in a southeast direction to reach the Colorado Piedmont (see figure 5) and St Vrain Creek flows in a southeast direction as it emerges onto the Colorado Piedmont. The southeast orientations of the Little Thompson River and St Vrain Creek valleys as they emerge onto the Colorado Piedmont are evidence the valleys eroded headward from south oriented flood flow channels on the Colorado Piedmont and drainage on the Colorado Piedmont has since been reversed to flow in a north direction. The Little Thompson River and St Vrain Creek drainage routes on the Colorado Piedmont eroded headward from reversed flood flow on the present day South Platte River alignment and captured the southeast oriented flood flow emerging from the what at that time was the emerging Colorado Front Range west of figure 3. The 50-meter contour interval does not show most landforms on the low relief Colorado Piedmont surface. Figure 4 provides a more detailed topographic map of the region north of Longmont to illustrate topographic map evidence for former north-to-south oriented flood flow channels on the Colorado Piedmont.

Detailed map of Little Thompson River-St Vrain Creek drainage divide area

Figure 4: Detailed map of Little Thompson River-St Vrain 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 Little Thompson River-St Vrain Creek drainage divide area seen in less detail in figure 3. The map contour interval for figure 4 is 10 feet except near the northwest corner where the contour interval is 40 feet (with some dotted lines at 20 feet intervals). Longmont is the city straddling the south edge of figure 4. Lakes seen in figure 4 appear to be reservoirs used in the regional irrigation systems. Table Top Mountain in the west center area of figure 4 is an erosional residual east of Rabbit Mountain (seen in figures 3 and 5) and provides evidence 200 or more feet of surrounding bedrock material has been stripped from the Colorado Piedmont surface. The Little Thompson River flows in an east and east-northeast direction from the west edge of figure 4 (near northwest corner) to the north edge of figure 4 (west half). North of figure 4 the Little Thompson River flows in an east-northeast direction to join the east-northeast oriented Big Thompson River, which then joins the northeast, southeast, and northeast oriented South Platte River. St Vrain Creek can just barely be seen flowing in a southeast direction across the southwest corner of figure 4. South and east of figure 4 St Vrain Creek flows in a southeast direction before turning in an east-northeast and then northeast direction to join the north oriented South Platte River. Terry Lake is located in sections 9 and 16 north of Longmont and is located in what was once a north-to-south oriented flood flow channel used by southeast oriented flood flow emerging from the southeast oriented Little Thompson River valley west of figure 4 (see figure 5) and flowing in a south direction to the St Vrain Creek valley. The hill in section 4 near the north edge of figure 4 reaches an elevation of 5235 feet while elevations on the Little Thompson River-St Vrain Creek drainage divide west of Highland No. 2 Reservoir in section 6 are between 5160 and 5180 feet. These elevations suggest there is 55-foot deep or deeper north-to-south oriented through valley. Divide Reservoir and Ish Reservoir are located in an even deeper north-to-south oriented through valley east of Terry Lake. This deeper through valley has a floor elevation of between 5130 and 5140 feet. The hill on the county line between sections 12 and 7 to the east rises to more than 5220 feet suggesting this through valley is at least 80 feet deep. These north-to-south oriented through valleys were eroded by south oriented flood flow prior to the flood flow reversal on the Colorado Piedmont. When the flood flow reversal took place northeast oriented valleys eroded headward into the region to capture the south oriented flood flow. The north and northeast oriented drainage route east of Ish Reservoir is located in one of those northeast oriented valleys that captured the south oriented flood flow. The north oriented headwaters drainage route east of Divide Reservoir was created by a reversal of flood flow on the north end of the beheaded flood flow channel.

North St Vrain Creek-South St Vrain Creek drainage divide area

Figure 5: North St Vrain Creek-South St Vrain Creek drainage divide area. United States Geological Survey map digitally presented using National Geographic Society TOPO software.

Figure 5 illustrates the North St Vrain Creek-South St Vrain Creek drainage divide area west of figure 3 and there is an overlap area with figure 3. The map contour interval for figure 5 is 50 meters. Rabbit Mountain is located near the east center edge of figure 5. North-to-south oriented ridges in the east half of figure 5 are hogback ridges along the east flank of the Colorado Front Range, which is seen to the west. The Little Thompson River flows in a southeast direction from the north edge of figure 5 (west half-next to highway) almost to the town of Pinewood Springs and then turns to meander in an east-northeast, southeast, and east direction to the east edge of figure 5 (north half). The West Fork Little Thompson River flows in an east-northeast and northeast direction from the west edge of figure 5 (north of center) to join the southeast oriented Little Thompson River near Moose Mountain. North St Vrain Creek flows in an east direction from the west edge of figure 5 (south of center) to Button Rock Reservoir and then in a northeast direction before turning in a south and southeast direction to Lyons and then to flow as St Vrain Creek to the east edge of figure 5 (near southeast corner). South St Vrain Creek flows in a northeast direction from the south edge of figure 5 (west half) to join southeast oriented North St Vrain Creek at Lyons. Middle St Vrain Creek flows in a northeast and east-southeast direction from near the southwest corner of figure 5 to join South St Vrain Creek east of Riverside. Numerous north-to-south oriented through valleys link the various east oriented drainage routes. Some of these north-to-south oriented through valleys are strike valleys between the steeply dipping hogback ridges and valley orientations are determined by underlying geologic structures. However, each through valley is a water-eroded valley and was eroded by south oriented flood flow in what was probably a huge south oriented anastomosing channel complex. At that time the Colorado Front Range was emerging and floodwaters were eroding deeper and deeper valleys into the emerging mountain mass. Headward erosion of the east oriented valleys captured the south oriented flood flow in sequence from south to north and from east to west and diverted floodwaters to what were initially south oriented flood flow channels on the Colorado Piedmont to the east of figure 5, although the flood flow reversal on the Colorado Piedmont probably occurred while south oriented flood flow was still moving into and across the emerging Colorado Front Range. Figure 6 illustrates a detailed map of through valleys in the West Fork Little Thompson River-North St Vrain Creek drainage divide area.

Detailed map of West Fork Little Thompson River-North St Vrain Creek drainage divide area

Figure 6: Detailed map of West Fork Little Thompson River-North St Vrain 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 West Fork Little Thompson River-North St Vrain Creek drainage divide area seen in less detail in figure 5. The map contour interval for figure 6 is 40 feet. The West Fork Little Thompson River flows in an east-northeast direction (with some incised meanders) from the west edge of figure 6 (north of center) to the north center edge of figure 6 and north of figure 6 joins the south-southeast, east-northeast, and southeast oriented Little Thompson River, which once on the Colorado Piedmont turns in an east-northeast direction. North St Vrain Creek flows in an east direction from near the southwest corner of figure 6 to the west side of Cook Mountain where it turns to flow in a south and northeast direction around the south end of Cook Mountain to Button Rock Reservoir. North St Vrain Creek flows from Button Rock Reservoir in a northeast direction to the east edge of figure 6. East of figure 6 North St Vrain Creek flows in a northeast, south, and southeast direction to join South St Vrain Creek and to form southeast oriented St Vrain Creek, which once on the Colorado Piedmont turns to flow in an east-northeast and northeast direction. Two deep north-to-south oriented through valleys (in the center of figure 6) link the West Fork Little Thompson River valley with the east oriented North St Vrain Creek valley. Rattlesnake Gulch drains the eastern through valley south end and Coulson Gulch drains the western through valley south end. The eastern through valley floor elevation at the drainage divide in the northeast quadrant of section 1 is between 7600 and 7640 feet. The western through valley floor elevation on the border between sections 1 and 2 is between 7640 and 7680 feet. Button Rock Mountain to the east rises to 8450 feet and elevations in the northeast corner of section 10 to the west rise to 8572 feet suggesting the through valleys are more than 750 feet deep. Today these through valley link south oriented North St Vrain Creek tributary valleys with north oriented West Fork Little Thompson River tributary valleys. The through valleys are water-eroded valleys and were eroded by diverging south oriented flood flow channels prior to headward erosion of the east-northeast oriented West Fork Little Thompson River valley. The south oriented floodwaters were captured by headward erosion of the east oriented North St Vrain Creek valley and the deep south oriented Rattlesnake Gulch and Coulson Gulch valleys eroded headward along the south oriented flood flow channels. Headward erosion of the deeper east-northeast oriented West Fork Little Thompson River valley next beheaded the south oriented flood flow channels. Floodwaters on north ends of the beheaded flood flow channels reversed flow direction to flow to the deeper West Fork Little Thompson River valley and to create north oriented West Fork Little Thompson River tributary drainage routes.

Fish Creek-Tahosa Creek drainage divide area

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

Figure 7 illustrates the Fish Creek-Tahosa Creek drainage divide area west and north of figure 5 and includes an overlap area with figure 5. The map contour interval for figure 7 is 50 meters. Estes Park and Lake Estes are near the north center edge of figure 7. The Big Thompson River flows in an east direction from the west edge of figure 7 (north half) through Moraine Park and then in a northeast direction to Lake Estes before flowing in a northeast direction to the north edge of figure 7 (east of center). North of figure 7 the Big Thompson River turns to flow in an east-southeast direction to reach the Colorado Piedmont. Muggins Gulch is located adjacent to the highway extending in a southeast direction from Estes Park. Muggins Gulch is a southeast oriented headwaters drainage route for the Little Thompson River, which turns to flow to the east edge of figure 7 (north of Pinewood Springs). East of figure 7 the Little Thompson River flows in an east-northeast and southeast direction to reach the Colorado Piedmont. The southeast oriented highway is located in a northwest-to-southeast oriented through valley linking southeast oriented Big Thompson River tributary valleys (north of the Big Thompson River) with the southeast oriented Muggins Gulch (or Little Thompson River) valley. The through valley is approximately 250 meters deep and was eroded by southeast oriented flood flow moving to the southeast oriented Muggins Gulch valley prior to headward erosion of the northeast oriented Big Thompson River valley. Further west another highway extends south from Estes Park to the south edge of figure 7 (west of center) and crosses the Big Thompson River-North St Vrain Creek drainage divide at Wind River Pass. North of Wind River Pass the highway makes use of the north oriented Fish Creek valley while south of Wind River Pass the highway makes use of the south-southeast oriented Tahosa Creek valley. Wind River Pass has an elevation of between 2750 and 2800 meters. Twin Sisters Peaks to the east rises to 3483 meters and elevations near the southwest corner of figure 7 rise to more than 4300 meters. These elevations suggest Wind River Pass is at least 700 meters deep. Wind River Pass was eroded by south oriented flood flow prior to headward erosion of the northeast oriented Big Thompson River valley. Headward erosion of the northeast oriented Big Thompson River valley beheaded the south oriented flood flow and floodwaters on the north end of the beheaded flood flow channel reversed flow direction to create the north oriented Fish Creek drainage route. The reversal of flood flow was probably aided by crustal warping that was raising the Wind River Pass region as floodwaters flowed across it.

Detailed map of Fish Creek-Tahosa Creek drainage divide area

Figure 8: Detailed map of Fish Creek-Tahosa 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 Fish Creek-Tahosa Creek drainage divide area seen in less detail in figure 7. The map contour interval for figure 8 is 40 feet. Lily Lake is located in section 14 in the northeast quadrant of figure 8. Fish Creek originates at Lily Lake and flows in a north-northeast direction to the north edge of figure 8 (east half). North of figure 8 Fish Creek flows to the northeast and east-southeast oriented Big Thompson River. The north-northwest oriented stream just west of Lily Lake in the east half of section 15 and flowing to the north center edge of figure 8 is Aspen Brook. North of figure 8 Aspen Brook also flows to the Big Thompson River. South of the Aspen Brook headwaters is Wind River Pass (located on the line between sections 22 and 23). Just south of Wind River Pass are headwaters of south and south-southeast oriented Tahosa Creek, which flows to the south edge of figure 8. South of figure 8 Tahosa Creek joins a southeast oriented tributary to east, northeast, and southeast oriented North St Vrain Creek. Wind River Pass has an elevation of 9130 feet. Twin Sisters Peaks to the east reach an elevation of 11,413 feet while Mount Lady Washington near the southwest corner of figure 8 reaches an elevation of 13,281 feet. Based on these elevations Wind River Pass is almost 2300 feet deep. Wind River Pass is a water-eroded feature, which means at one time large volumes of water flowed through it. The deep valley suggests large volumes of water eroded the valley deeper and deeper as the mountain ridge was uplifted around it. The water was flowing in a south direction prior to headward erosion of the Big Thompson River valley to the north of figure 8. The south oriented flow was first captured by headward erosion of the deep east, northeast, and southeast North St Vrain Creek valley (south of figure 8) and was subsequently beheaded by headward erosion of the deep northeast and east-southeast oriented Big Thompson River valley. Erosion of these deep valleys into a rising mountain mass could only be accomplished by immense volumes of floodwaters, which were flowing across the region as the mountains were being uplifted. The north-northeast and north-northwest oriented Fish Creek and Aspen Brook valleys north of Wind River Pass were eroded by south-southwest and south-southeast oriented flood flow channels that converged to flow through the deep Wind River Pass valley. These converging flood flow channels provide evidence of an anastomosing channel complex, which further supports the massive flood flow interpretation.

North St Vrain Creek-Middle St Vrain Creek drainage divide area

Figure 9: North St Vrain Creek-Middle St Vrain Creek drainage divide area. United States Geological Survey map digitally presented using National Geographic Society TOPO software.

Figure 9 illustrates the North St Vrain Creek-Middle St Vrain Creek drainage divide area south and slightly east of figure 7 and there is an overlap area with figure 7. The map contour interval for figure 9 is 50 meters. North St Vrain Creek flows in a southeast, east-northeast, and east direction from the west center edge of figure 9 to Button Rock Reservoir and then in a northeast direction to the east edge of figure 9 (north half). East of figure 9 North St Vrain Creek flows in a northeast and southeast direction to join South St Vrain Creek and to form southeast oriented St Vrain Creek, which then flows onto the Colorado Piedmont before turning to flow in a northeast direction. Tahosa Creek flows in a south-southeast direction from the north edge of figure 9 (west half) to join southeast oriented Cabin Creek, which then flows to join east oriented North St Vrain Creek. South St Vrain Creek flows in a north and northeast direction from the south center edge of figure 9 to the east center edge of figure 9 and east of figure 9 joins southeast oriented North St Vrain Creek to form southeast oriented St. Vrain Creek. Middle St Vrain Creek flows in a southeast and east direction from the west edge of figure 9 (near southwest corner) to Peaceful Valley and then turns in a northeast direction to flow to Riverside before turning in an east-southeast direction to join northeast oriented South St Vrain Creek. Multiple north-to-south oriented through valleys cross the drainage divide between North St Vrain Creek and Middle St Vrain Creek and between North St Vrain Creek and South St Vrain Creek. Some of the deepest through valleys are located north of Riverside where northeast oriented Dry St Vrain Creek is located between North St Vrain Creek and Middle St Vrain Creek. The Dry St Vrain Creek-Middle St Vrain Creek drainage divide at its lowest point has an elevation of between 2300 and 2350 meters. The high point in section 36 immediately to the east is 2557 meters and elevations west of Riverside rise to more than 3000 meters suggesting the through valley is at least 200 meters deep. Further east a north-to-south oriented through valley can be seen immediately west of Coffintop Mountain and links the Button Rock Reservoir area with the northeast oriented South St Vrain Creek valley. This through valley has an elevation of between 2200 and 2250 meters. Coffintop Mountain rises to 2453 meters suggesting the through valley is also at least 200 meters. These and other north-to-south oriented through valleys seen in figure 9 are evidence of south oriented flood flow channels that crossed the region prior to headward erosion of the deep North St Vrain Creek valley and its northeast oriented Dry St Vrain Creek tributary valley.

Detailed map of North St Vrain Creek-Middle St Vrain Creek drainage divide area

Figure 10: Detailed map of North St Vrain Creek-Middle St Vrain Creek drainage divide area. United States Geological Survey map digitally presented using National Geographic Society TOPO software.

Figure 10 provides a detailed topographic map of the North St Vrain Creek-Middle St Vrain Creek drainage divide area seen in less detail in figure 9. The map contour interval for figure 10 is 40 feet. North St Vrain Creek flows in an east direction (with multiple northeast and southeast turns) from the west edge of figure 10 (near northwest corner) to Button Rock Reservoir near the northeast corner of figure 10. East and north of figure 10 North St Vrain Creek flows in a northeast and southeast direction. South St Vrain Creek flows in an east-northeast direction across the southeast corner of figure 10 and east of figure 10 flows in a northeast direction to join southeast oriented North St Vrain Creek and to form southeast oriented St Vrain Creek. Middle St Vrain Creek flows in a northeast direction from the south edge of figure 10 (west of center) to Riverside and then in an east-southeast direction to join east-northeast oriented South St Vrain Creek near the south edge of figure 10. Dry St Vrain Creek originates near the southwest corner of figure 10 and flows in a northeast direction to join North St Vrain Creek near the east edge of section 23. Numerous north-to-south oriented through valleys link the various east oriented St Vrain Creek tributary valleys. For example in the south half of section 22 a north-to-south oriented through valley on the west side of South Sheep Mountain links the North St Vrain Creek valley with a southeast oriented tributary to northeast oriented Dry St Vrain Creek. The through valley floor elevation is between 7720 and 7760 feet. South Sheep Mountain rises to 8171 feet and Big John Mountain to the west rises to more than 9080 feet suggesting the through valley is at least 400 feet deep. The through valley was eroded by south oriented flood flow, which initially had flowed to the Middle St Vrain Creek valley, but which was captured by headward erosion of the northeast oriented Dry St Vrain Creek valley, which had eroded headward from what at that time was the actively eroding North St Vrain Creek valley. Headward erosion of the much deeper North St Vrain Creek valley then captured the south oriented flood flow channel and ended flood flow in the through valley. The gap between Big John Mountain and Taylor Mountain to the west of the through valley was eroded by south oriented flood flow moving at a much higher elevation, which suggests floodwaters initially flowed on an erosion surface now largely removed.

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.