Abstract:

This essay uses topographic map evidence to interpret landform origins in the Colorado River-North St Vrain Creek drainage divide area along the east-west continental divide. The Colorado River flows in a south direction in the Kawuneeche Valley from the south side of La Poudre Pass to southwest corner of Rocky Mountain National Park and then turns to flow in a southwest direction to eventually reach the Pacific Ocean. The north, north-northwest, and northwest oriented Fraser River flows as a barbed tributary from the north side of Berthoud Pass to join the Colorado River at its elbow of capture near the southwest corner of Rocky Mountain National Park. The east-west continental divide is located along the crest of a high mountain ridge east of the deep and south oriented Colorado River valley. The north oriented Cache la Poudre River headwaters valley is linked by a through valley at Milner Pass (and also at La Poudre Pass further to the north) with the south oriented Colorado River valley (water in the Cache la Poudre River eventually reaches the Gulf of Mexico). East of the continental divide are headwaters of the east oriented Big Thompson River located near Milner Pass and south of the Big Thompson River are headwaters of east oriented North St Vrain Creek, Middle St Vrain Creek, and South St Vrain Creek and their tributaries. North-to-south oriented through valleys or passes link the Big Thompson River valley with the North St Vrain Creek valley and the North St Vrain Creek valley with the Middle St Vrain Creek valley. Valley orientations, passes or through valleys across present day drainage divides, barbed tributaries, and elbows of capture seen on topographic maps are 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 Colorado at a time when Colorado mountain ranges were beginning to emerge. The mountains 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 the region to capture the immense south oriented melt water floods. Floodwaters in the study region eroded south oriented flood flow channels on both sides of the present day east-west continental divide. Headward erosion of the deeper southwest oriented Colorado River valley captured the western flood flow channel while headward erosion in sequence of deep east oriented valleys from south oriented flood flow channels on the present day north oriented South Platte River alignment captured the south oriented flood flow channels east of the present day continental divide. Headward erosion of the deep east and southeast oriented Cache la Poudre River valley (north of Rocky Mountain National Park) beheaded and reversed flood flow to the south oriented Colorado River headwaters valley while headward erosion of the deep northeast oriented South Platte River valley from western Nebraska captured the east and southeast oriented Cache la Poudre River and beheaded and reversed flood flow channels on the Colorado Piedmont 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 Colorado River-North St Vrain Creek drainage divide area landform origins along the east-west continental divide. 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 Colorado River-North St Vrain Creek drainage divide area landform evidence along the east-west continental divide will be regarded as evidence supporting the “thick ice sheet that melted fast” paradigm.

Colorado River-North St Vrain Creek drainage divide area location map

Figure 1: Colorado River-North 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 Colorado River-North St Vrain Creek drainage divide area along the east-west continental divide 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 eastern margin of the Colorado Front Range extends in a north-to-south direction from the north center edge to the south center edge of figure 1. The Colorado Piedmont is located east of the Front Range. Rocky Mountain National Park is shown and labeled. The Colorado River originates near the northwest corner of Rocky National Park and flows in a south direction to the Rocky Mountain National Park southwest corner before turning in a west-southwest and southwest direction to flow to Bond near the southwest corner of figure 1. South and west of figure 1 the Colorado River eventually reaches the Pacific Ocean. An important Colorado River tributary in this essay, but not shown in figure 1, is the Fraser River, which flows in a north-northwest direction from near Berthoud Pass through the town of Fraser to join the south and southwest oriented Colorado River near Granby as a barbed tributary. The South Platte River flows in a north-northeast and north direction from the south edge of figure 1 (near Denver) to near Greeley where the South Platte River turns in a northeast and then southeast direction to flow to the east center edge of figure 1. East of figure 1 the South Platte River turns again to flow in a northeast direction into western Nebraska with water eventually reaching the Gulf of Mexico. The Big Thompson River originates in Rocky Mountain National Park and flows in a southeast, northeast, and east-southeast direction to reach the Colorado Piedmont and joins the South Platte River south of Greeley. St Vain Creek and St Vrain Creek tributaries are shown but not labeled in figure 1. North St Vrain Creek originates just north of the south edge of Rocky Mountain National Park and flows in an east, northeast, east, northeast, and southeast direction to Lyons where it joins northeast oriented South St Vrain Creek to form St Vrain Creek. St Vrain Creek flows in a southeast direction from Lyons to Longmont and then turns in an east and northeast direction to join the South Platte River. The east and northeast oriented St Vrain Creek tributary flowing through Boulder is Boulder Creek. The Colorado River-North St Vrain Creek drainage divide area along the east-west continental divide investigated in this essay is located in and near southwest corner of Rocky Mountain National Park.

While difficult to imagine considering present day regional topography drainage routes in figure 1 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 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 the mountain masses and the entire region, and as deep valleys eroded headward into the region from both the east and the west to capture the massive south oriented flood flow. The north oriented South Platte River and tributary drainage routes on the Colorado Piedmont were formed by reversals of flood flow on what had been south oriented flood flow channels eroding headward from the southeast oriented Arkansas River valley (south of figure 1). The south oriented flood flow channels were captured by headward erosion of the deeper 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 to the deeper southeast and northeast oriented South Platte River valley and to create the north oriented South Platte River and tributary drainage routes seen today. East oriented valleys eroded headward from the south oriented flood flow channels on the Colorado Piedmont into the emerging Colorado Front Range to capture south oriented flood flow moving across the emerging mountain mass. These east oriented valleys eroded headward in sequence from south to north and from east to west, which means the North St Vrain Creek valley captured south oriented flood flow prior to headward erosion of the Big Thompson River valley, which then beheaded flood flow channels to the newly eroded North St Vrain Creek valley. As east oriented valleys eroded headward into the region the southwest oriented Colorado River valley eroded headward to the southwest corner of Rocky Mountain National Park to capture a major south oriented flood flow channel moving floodwaters from the present day north oriented Cache la Poudre River alignment to the present day north-northwest oriented Fraser River alignment and then across present day Berthoud Pass to a newly eroded east oriented valley (Clear Creek) located south of figure 1. Capture of that south oriented flood flow channel beheaded and reversed the south-southeast oriented flood flow channel on the present day north-northwest oriented Fraser River alignment to create the north-northwest oriented Fraser River drainage route. Uplift of the mountains was occurring as floodwaters flowed across the region and probably continued after all flood flow across the region had ended. After all flood flow across the region had ceased and after the mountains had been uplifted many of the newly uplifted and high mountain ranges were glaciated, which further modified the landscape.

Detailed location map for Colorado River-North St Vrain Creek drainage divide area

Figure 2: Detailed location map Colorado River-North 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 Colorado River-North St Vrain Creek drainage divide area along the east-west continental divide. The red-brown region is Rocky Mountain National Park. The east-west continental divide is a labeled dashed line extending from the north edge (west of center) to the south edge of figure 2 (west of center). Milner Pass is located on the continental divide near the north edge and Berthoud Pass is located near the south edge of figure 2. The Colorado River flows in a south direction from the north edge of figure 2 along the west side of Rocky Mountain National Park to Lake Granby and then turns to flow in a west-southwest and west direction to the west edge of figure 2 (south of center). The Fraser River originates near Berthoud Pass and flows in a north, north-northwest, and northwest direction to join the Colorado River as a barbed tributary near Granby. North Inlet Creek is a labeled northwest and southwest oriented Colorado River tributary in Rocky Mountain National Park and flows through Grand Lake and Shadow Mountain Lake to reach the Colorado River. Other Colorado River tributaries in Rocky Mountain National Park are not labeled, but can be seen flowing in southwest, west and south, and northwest directions from the continental divide. On the east side of the continental divide the Big Thompson River originates near Milner Pass and flows in a southeast, east, northeast, and east-southeast direction to Loveland near the northeast corner of figure 2 and east of figure 2 joins the South Platte River. North St Vrain Creek originates just north of the Rocky Mountain National Park south border and near the continental divide and flows in an east, northeast, and southeast direction to Lyons where it joins east and northeast oriented South St Vrain Creek to form southeast oriented St Vrain Creek, which east of Longmont turns to flow in a northeast direction to join the South Platte River. Middle St Vrain Creek originates just south of the Rocky Mountain National Park south boundary and near the continental divide and flows in a southeast, east, northeast, and east direction to join northeast oriented South St Vrain Creek. As seen in topographic maps illustrated below headward erosion the deep west-southwest oriented Colorado River valley captured a major south oriented flood flow channel that flowed on the west side of the present day continental divide between Milner Pass and Berthoud Pass while headward erosion of the deep east oriented North St Vrain Creek captured a major south oriented flood flow channel on the east side of the present day continental divide. The continental divide between Milner Pass and Berthoud Pass is today a high ridge between the valleys formed by those two deep and south-oriented flood flow channels and their tributary flood flow channels.

Colorado River-Big Thompson River drainage divide area

Figure 3: Colorado River-Big Thompson River drainage divide area. United States Geological Survey map digitally presented using National Geographic Society TOPO software.

Figure 3 provides a topographic map of Colorado River-Big Thompson River drainage divide area. The map contour interval for figure 3 is 50 meters. The east-west continental divide extends in a south-southeast direction from the north edge of figure 3 (west half) to the south edge of figure 3 (east of center). The Colorado River flows in a south direction near the west edge of figure 3 and south of figure 3 turns in a southwest direction with water eventually reaching the Pacific Ocean. North of figure 3 the Colorado River originates just south of La Poudre Pass. A northeast oriented tributary to the north, east, and southeast oriented Cache la Poudre River drains the north side of La Poudre Pass. Milner Pass is located on the continental divide in the northwest quadrant of figure 3 and links the northeast oriented Cache la Poudre River headwaters valley with the south-southwest oriented Beaver Creek valley. North of figure 3 the Cache la Poudre River turns to flow in a north direction and north of Rocky Mountain National Park turns to flow in an east and southeast direction to join the southeast and northeast oriented South Platte River with water eventually reaching the Gulf of Mexico. Forest Canyon Pass is located a short east and north of Milner Pass and links the northeast oriented Cache la Poudre River headwaters valley with the southeast oriented Big Thompson River headwaters valley (Forest Canyon). In the southeast quadrant of figure 3 the Big Thompson River turns to flow in an east direction to the east edge of figure 3 (south half). East of the figure 3 the Big Thompson River flows in a northeast and east-southeast direction to join the South Platte River. Sprague Pass is located on the continental divide north of the south center edge of figure 3 and links the east-northeast oriented Spruce Creek valley (draining to the Big Thompson River) with the southwest, west, and south oriented Tonahutu Creek valley (draining to the Colorado River). Each pass seen in figure 3 was eroded by large volumes of water, which flowed across present-day drainage divides including the present day east-west continental divide. Valley orientations in figure 3 suggest headward erosion of a southwest oriented valley on the present day southwest oriented Beaver Creek and northeast oriented Cache la Poudre River headwaters alignments beheaded a southeast oriented flood flow channel on the southeast oriented Forest Canyon or Big Thompson River headwaters alignment. The southwest oriented valley was eroded by a south and southwest oriented flood flow channel that diverged from a southwest and south oriented flood flow channel on the present day northeast oriented Cache la Poudre River tributary and south oriented Colorado River alignment with the two south oriented flood flow channels converging near the present Beaver Creek confluence with the Colorado River. Headward erosion of the east oriented Cache la Poudre River valley (north of figure 3) then beheaded the south oriented flood flow channel north of Rocky Mountain National Park and floodwaters on north ends of the beheaded diverging flood flow channels reversed flow direction to create the northeast and north oriented Cache la Poudre River headwaters drainage route and the northeast oriented Cache la Poudre River tributary drainage route north of La Poudre Pass (and north of figure 3).

Detailed map of Beaver Creek-Timber Creek drainage divide area

Figure 4: Detailed map of Beaver Creek-Timber 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 Beaver Creek-Timber Creek drainage divide area seen in less detail in figure 3. The map contour interval for figure 4 is 40 feet. The east-west continental divide is shown with a labeled dashed extending from the north edge (west of center) to the south edge of figure 4 (east of center). The Colorado River flows in a south direction in a deep valley near the west edge of figure 4. South and west of figure 4 the Colorado River turns to flow in more of a southwest direction with water eventually reaching the Pacific Ocean. Poudre Lake is located in the north center area of figure 4. The Cache la Poudre River originates at Poudre Lake and flows in a northeast direction to the north edge of figure 4 (east of center). North of figure 4 the Cache la Poudre River turns to flow in a north direction before turning in an east and southeast direction to flow to the southeast and northeast oriented South Platte River with water eventually reaching the Gulf of Mexico. Milner Pass is located at the south end of Poudre Lake. Beaver Creek drains the south side of Milner Pass and flows in a north-northwest, south-southwest, and southwest direction to join the south oriented Colorado River. The Milner Pass elevation is 10,758 feet. Specimen Mountain is located on the continental divide just north of figure 4 and reaches an elevation 12,489 feet. Mount Ida is located on the continental divide just south of the south edge of figure 4 and reaches an elevation of more than 12,840 feet. These elevations suggest Milner Pass is approximately 1700 feet deep. Milner Pass is a water-eroded pass and was eroded by southwest oriented flood flow moving from the present day northeast and north oriented Cache la Poudre River valley to the south oriented Colorado River valley. The south and southwest oriented flood flow channel was beheaded and reversed by headward erosion of the east and southeast oriented Cache la Poudre River valley north of Rocky Mountain National Park (see figure 1). Other passes or through valleys can be seen in figure 4. In addition to Forest Canyon Pass (east and north of Poudre Lake) there is an interesting north-to-south oriented through valley or pass on the east side of Jackstraw Mountain linking the north oriented Beaver Creek headwaters valley with the northwest and southwest oriented Timber Creek valley, which south of figure 4 turns again in a northwest direction to join the south oriented Colorado River as a barbed tributary near the southwest corner of figure 4. The pass or through valley floor elevation is between 11,160 and 11,200 feet. Jackstraw Mountain rises to 11,704 feet suggesting the pass or through valley is more than 500 feet deep. The through valley or pass was also eroded by diverging and converging south oriented flood flow channels at a time when the deep Colorado River valley to the west had yet to be eroded. Headward erosion of the deep south oriented Colorado River valley beheaded a diverging southeast oriented flood flow channel on the present day northwest oriented Timber Creek alignment (figure 6 below shows the entire Timber Creek drainage route).

North Inlet Creek-East Inlet Creek drainage divide area

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

Figure 5 illustrates the North Inlet Creek-East Inlet Creek drainage divide area south of figure 3 and there is an overlap area with figure 3. The map contour interval for figure 5 is 50 meters. The east-west continental divide follows the crest of the highest mountains and is shown with a dashed line extending from the north center edge of figure 5 to the south edge of figure 5 (east half). The Colorado River flows in a south direction in the Kawuneeche Valley near the west edge of figure 5. Grand Lake is the town in the southwest quadrant of figure 5 and is located on the shores of Grand and Shadow Mountain Lakes. Named Colorado River tributaries from the east include southwest oriented Onahu Creek; southeast, southwest, west, and south oriented Tonahutu Creek; northwest and southwest oriented North Inlet Creek; and west-northwest oriented East Inlet Creek. Drainage divides between these west oriented Colorado River tributaries are crossed by through valleys (or passes) providing evidence of former south oriented flood flow channels. For example near the center of figure 5 a north-to-south oriented through valley or pass between Mount Paterson and Snowdrift Peak links the Tonahutu Creek valley with the North Inlet valley. The through valley or pass elevation is between 3300 and 3350 meters. Mount Paterson rises to 3482 meters suggesting the through valley or pass is at least 132 meters deep. Another through valley or pass (in the southeast quadrant of figure 5) links north and northwest oriented North Inlet Creek headwaters valley with the west-northwest oriented East Inlet Creek valley. The through valley or pass floor elevation is between 2950 and 3000 meters. Andrews Peak to the west rises to 3850 meters and Mount Alice to the east rises to 4087 meters suggesting the through valley or pass is at least 550 meters deep. Grand Pass crosses the continental divide south of Mount Alice and links the west-northwest oriented East Inlet Creek valley with the southeast oriented North St Vrain Creek valley. These north-to-south oriented through valleys or passes provide evidence of diverging and converging flood flow channels on the west side of the emerging continental divide. Grand Pass is at least 200 meters deep and provides evidence of an east and southeast oriented flood flow channel that was probably beheaded by headward or deeper south oriented flood flow channels on the west side of the continental divide. Sprague Pass is located on the continental divide a short distance south of the north edge of figure 5 and links the southeast, southwest, west, and south oriented Tonahutu Creek valley with the east-northeast oriented Sprague Creek valley, which drains to the southeast and east-northeast oriented Big Thompson River, which flows to the northeast corner of figure 5. The Sprague Pass through valley may provide evidence of a southeast and east-northeast oriented flood flow channel that was captured by headward erosion of a much deeper southwest, west, and south oriented flood flow channel. Whatever sequence of flood flow captures is recorded in the Sprague Pass area the south and southeast oriented floodwaters once flowed on an erosion surface now preserved, if it is preserved at all, by elevations on the present day east-west continental divide.

Detailed map of Timber Creek-Onahu Creek drainage divide area

Figure 6: Detailed map of Timber Creek-Onahu 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 Timber Creek-Onahu Creek drainage divide area seen in less detail in figure 3 and partially seen along the north edge of figure 5. Figure 6 is also south of figure 4 and includes an overlap area with figure 4. The map contour interval for figure 6 is 40 feet. The east-west continental divide extends in a south-southeast direction along the crest of the high mountains from the north edge of figure 6 (east half) to the east center edge of figure 6. The Colorado River flows in a south direction in the deep Kawuneeche Valley (near the west edge of figure 4) and crosses the 8800-foot contour line in the southwest quadrant of figure 6. While not seen in figure 6 the east-west continental divide is also located west of figure 6 (the continental divide extends in a west and then north direction on the west side of the south oriented Colorado River headwaters to La Poudre Pass and then in a south and south-southeast direction on the east side of the south oriented Colorado River headwaters). Mountains west of the Kawuneeche Valley rise to more than 12,000 feet and Mount Ida in the northwest quadrant of figure 6 rises to more than 12,840 feet, which means the Kawuneeche Valley is more than 3200 feet deep. Timber Lake is located on the west side of Mount Ida and Timber Creek flows in a northwest, southwest, and northwest direction from Timber Lake to join the south oriented Colorado River as a barbed tributary. Jackstraw Mountain is north of the southwest-northwest Timber Creek jog and the Beaver Creek-Timber Creek through valley seen in figure 4 enters the Timber Creek valley at the north end of the Timber Creek northwest-southeast jog. Long Meadows is located in a south-southeast oriented through valley linking the south end Timber Creek southwest-northwest jog with the southwest oriented Onahu Creek valley. The Long Meadows through valley floor elevation is between 10,400 and 10,440 feet. Elevations in the southeast corner of section 30 to the west rise to 10,965 feet suggesting the Long Meadows through valley is almost 500 feet deep. A southeast oriented flood flow channel that diverged from a south oriented flood flow channel on the Colorado River alignment eroded the Long Meadows through valley. The floodwaters moved in a southeast direction on the present day northwest oriented Timber Creek alignment and then in a south-southeast direction on the Long Meadows valley alignment and were captured by headward erosion of the southwest Onahu Creek valley from the south oriented Colorado River valley. The southeast and southwest oriented flood flow channel provides evidence of diverging and converging flood channels as the deep Kawuneeche Valley was being eroded. Headward erosion of a much deeper south oriented flood flow channel on the present day Colorado River alignment beheaded the diverging southeast and southwest oriented flood flow channel. Floodwaters on the northwest end of the beheaded flood flow channel reversed flow direction and captured southwest oriented flood flow moving on the present day southwest oriented Timber Creek alignment. Other through valleys seen in figure 6 can be used to decipher additional flood flow capture and reversal events.

North Inlet Creek-North St Vrain Creek drainage divide area

Figure 7: North Inlet Creek-North St Vrain Creek drainage divide area. United States Geological Survey map digitally presented using National Geographic Society TOPO software.

Figure 7 illustrates the North Inlet Creek-North St Vrain Creek drainage divide area east and slightly south of figure 5 and includes an overlap area with figure 5. The map contour interval for figure 7 is 50 meters. The east-west continental divide is shown by a dashed line along the high mountain crests extending from the north edge (west half) to the south edge of figure 7 (west half). North Inlet Creek flows in a northwest and southwest direction to the west center edge of figure 7 and west of figure 7 flows to Grand and Shadow Mountain Lakes and then to the south oriented Colorado River. Boulder-Grand Pass is located on the continental divide near the south edge of figure 7. East Inlet Creek flows in a west-northwest direction from near Boulder-Grand Pass to the west edge of figure 7 and west of figure 7 also flows to Grand and Shadow Mountain Lakes. North St Vrain Creek originates east of Boulder-Grand Pass and flows in a southeast, east-northeast, and east direction to the east edge of figure 7 (south half). East of figure 7 North St Vrain Creek flows in an east, northeast, and southeast direction to join southeast oriented St Vrain Creek. Andrews Pass is located on the continental divide in the northwest quadrant of figure 7. Glacier Creek flows in a northeast direction from near Andrews Pass to the north edge of figure 7 (east of center). North of figure 7 Glacier Creek joins the east, northeast, and east-southeast oriented Big Thompson River. Wind River Pass is located in the northeast quadrant of figure 7 and is used by the north-to-south oriented highway in the east half of figure 7. The north-northeast oriented stream originating near Wind River Pass is Fish Creek, which north of figure 7 flows to the Big Thompson River. The north-northwest oriented stream originating near Wind River Pass is Aspen Brook and also flows to the Big Thompson River. The south-southeast oriented stream originating near Wind River Pass is Tahosa Creek, which joins southeast oriented Cabin Creek, which east of figure 7 joins North St Vrain Creek. Wind River Pass has an elevation of between 2750 and 2800 meters. Twin Sisters Peaks to the east rises to 3483 meters and mountains to the west rise to more than 4000 meters suggesting Wind River Pass is approximately 700 meters deep. Wind River Pass provided a major south oriented flood flow channel route on the east side of the present day continental divide while the Colorado River-Fraser River alignment provided a major south oriented flood flow channel route on the west side of the present day continental divide. With deep south oriented flood flow channels on both sides floodwaters no longer crossed the what is today the high mountain ridge between Milner Pass and Berthoud Pass, but instead eroded deep valleys on either side. The high mountain ridge between these two major south oriented flood flow channel routes then became the east-west continental divide when headward erosion of the deep southwest oriented Colorado River valley captured the western south oriented flood flow and beheaded and reversed flood flow on the present day Fraser River alignment to create the north-northwest oriented Fraser River drainage route. Crustal warping has probably further uplifted the mountains since floodwaters ceased to flow across the region, although deep valleys provide evidence considerable uplift occurred as floodwaters flowed across the region.

Detailed map of Aspen Brook-Tahosa Creek drainage divide area

Figure 8: Detailed map of Aspen Brook-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 Aspen Brook-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 the southwest corner of section 14. Fish Creek flows in a north-northeast direction from Lily Lake to the north edge of figure 8 (east half) and north of figure 8 joins the northeast and east-southeast oriented Big Thompson River. Aspen Brook is the north-northwest oriented stream just west of Lily Lake and flows to the north center edge of figure 8. North of figure 8 Aspen Brook also flows to the east oriented Big Thompson River. Wind River Pass is south of Lily Lake on the boundary between sections 22 and 23. The south and south-southeast oriented stream originating on the south side of Wind River Pass is Tahosa Creek, which flows to the south edge of figure 8 (slightly east of center). South of figure 8 Tahosa Creek joins southeast oriented Cabin Creek, which flows to east, east-northeast, and southeast oriented North St Vrain Creek. Wind River Pass has an elevation of 9,130 feet. Twin Sisters Peaks to the east reaches an elevation of 11,413 feet and Battle Mountain near the southwest corner of figure 8 exceeds 12,000 feet in elevation. These elevations suggest Wind River Pass is almost 2300 feet deep. Note how the north-northeast oriented Fish Creek valley and the north-northwest oriented Aspen Brook diverge just north of Wind River Pass. To understand how Wind River Pass was eroded it is necessary to think of present day drainage north of Wind River Pass as being reversed. The north-northwest oriented Aspen Brook valley was eroded as a south-southeast oriented flood flow channel that converged with a south-southwest oriented flood flow channel on the present day north-northeast oriented Fish Creek alignment. These south oriented flood flow channels converged so they could flow across an emerging mountain ridge. As the mountain ridge emerged the combined floodwaters eroded the Wind River Pass valley deeper and deeper until headward erosion of the east oriented Big Thompson River valley north of figure 8 beheaded and reversed the flood flow north of Wind River Pass. Storm Pass between Battle Mountain and Estes Cone (in the southwest quadrant of figure 8) provides evidence of what at one time was a separate diverging and converging flood flow channel, but which was probably abandoned in favor of the deeper Wind River Pass valley. Evidence for diverging and converging south oriented flood flow channels in figure 8 suggests the entire region was crossed by a south oriented anastomosing channel complex, which was captured by headward erosion of deeper east oriented valleys, which eroded headward from south oriented flood flow channels on the present day Colorado Piedmont to the east of figure 8.

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 of figure 7 and there is an overlap area with figure 7. The map contour interval for figure 9 is 50 meters. The east-west continental divide follows the crest of the high mountains and is shown with a dashed line extending from the north edge of figure 9 (west of center) to the south edge of figure 9 (slightly west of center). The National Park-National Forest Boundary is shown with a labeled west-to-east oriented dashed line crossing the continental divide slightly north of the center of figure 9. Wild Basin is located south of the north center edge of figure 9. North St Vrain Creek flows in a southeast and east-northeast direction into Wild Basin and then flows in an east direction along the north edge to the northeast corner of figure 9. Rock Creek is an east-northeast and north-northeast oriented stream flowing from the east center area of figure 9 to join North St Vrain Creek near the northeast corner of figure 9. Cony Creek is an east and north-northeast oriented stream flowing from Cony Lake on the northeast side of the intersection where the National Park boundary crosses the continental divide to join North St Vrain Creek at the elbow of capture in Wild Basin where North St Vrain Creek turns to flow in a northeast direction. St Vrain Glaciers are located on the east side of the continental divide just south of the National Park boundary. Middle St Vrain Creek originates in the St Vrain Glaciers region and flows in a southeast, east, and northeast direction to the east center edge of figure 9. South St Vrain Creek flows in an east-northeast and northeast direction from the south edge of figure 9 (slightly east of center) to the east edge of figure 9 (south half). East of figure 9 Middle St Vrain Creek joins South St Vrain Creek and South St Vrain Creek then joins North St Vrain Creek to form southeast and northeast oriented St Vrain Creek. While not as obvious as passes seen in earlier figures several passes or through valleys cross drainage divides between the various east oriented St Vrain Creek tributaries (and also can be seen crossing drainage divides between west oriented Colorado River tributaries seen on the west side of the continental divide). One of the most obvious of these passes or through valleys is located in the east center region of figure 9 and links the north-northeast oriented Rock Creek valley with the east oriented Middle St Vrain Creek valley to the south. This through valley or pass has an elevation of between 3050 and 3100 meters. The hill or mountain to the east rises to 3226 meters suggesting the through valley or pass is at least 126 meters deep. The through valley or pass was eroded by south oriented flood flow prior to headward erosion of the North St Vrain Creek valley. Another through valley or pass of interest is located between St Vrain Mountain and Meadow Mountain and links the Cony Creek valley with the Rock Creek headwaters valley. This second through valley or pass has an elevation of between 3350 and 3400 meters and is approximately 150 meters deep. This second through valley was eroded by southeast oriented flood flow, which was captured by reversed flood flow on the Rock Creek alignment (after south oriented flood flow on the Rock Creek alignment had been beheaded and reversed by headward erosion of the east oriented North St Vrain Creek valley).

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

Figure 10: Detailed map of Rock 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 Rock 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. Cony Creek flows in a north-northeast direction across the northwest corner of figure 10. Middle St Vrain Creek flows in a southeast and east direction from the west edge of figure 10 (south half) to Peaceful Valley near the southeast corner of figure 10 and then turns in a northeast direction. St Vrain Mountain is located in the west center area of figure 10. Rock Creek originates on the west slope of St Vrain Mountain and flows in an east, east-northeast, and north-northeast direction to the north edge of figure 10 and north of figure 10 joins east oriented North St Vrain Creek. A north-to-south oriented through valley in the south center region of figure 10 links the north-northeast oriented Rock Creek valley with a south, west, and south oriented Middle St Vrain Creek tributary route. The through valley floor elevation is between 10,080 and 10,120 feet. Elevations to the east of the through valley rise to 10,583 feet suggesting the through valley is at least 460 feet deep. Another through valley is located between St Vrain Mountain and Meadow Mountain and links a north-northwest oriented Cony Creek tributary valley with an east oriented Rock Creek tributary valley. The through valley (or pass) floor elevation is between 11,200 and 11,240 feet. Meadow Mountain rises to 11,632 feet and St Vrain Mountain rises to 12,162 feet suggesting the through valley is approximately 400 feet deep. These and other passes or through valleys seen in figure 10 are evidence of former flood flow channels that once crossed the region. Initially floodwaters flowed in south directions to the newly eroded east oriented Middle St Vrain Creek valley. Headward erosion of the east oriented North St Vrain Creek valley north of figure 10 then beheaded the south oriented flood flow channels in sequence from east to west. Floodwaters on north ends of beheaded flood flow channels reversed flow direction to create north oriented North St Vrain Creek tributary drainage routes. Because flood flow channels were beheaded in sequence from east to west and because flood flow were anastomosing (diverging and converging) floodwaters on the Rock Creek alignment were beheaded and reversed while floodwaters were still flowing in a south direction between St Vrain Mountain and Meadow Mountain. Reversed flood flow on the Rock Creek alignment captured the south oriented flood flow moving between St Vrain Mountain and Meadow Mountain and diverted the floodwaters in an east and north-northeast direction to the newly eroded North St Vrain Creek valley. In time headward erosion of the North St Vrain Creek valley beheaded and reversed flood flow west of Meadow Mountain to create the north-northeast oriented Cony Creek drainage route and the north-northwest oriented Cony Creek tributary route west of Meadow Mountain.

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.