Madison River-Henrys Fork drainage divide area landform origins along the continental divide and west of Yellowstone National Park, Montana and Idaho, USA

Authors

Abstract:

This essay uses topographic map evidence to interpret landform origins along the continental divide between the Madison River and Henrys Fork west of Yellowstone National Park. The Madison River flows in a west and northwest direction from Yellowstone National Park along the north edge of this essay’s study region and then turns to flow in a north direction to join the north and northeast oriented Missouri River with water eventually reaching the Gulf of Mexico. Henrys Fork originates in the Henrys Lake basin just south of the north oriented Madison River–Missouri River segment and flows in a south and southwest direction to join the southwest and west oriented Snake River with water eventually reaching the Pacific Ocean. Three deep passes with approximately equal floor elevations and many higher-level passes link the north oriented Madison River valley with the south oriented Henrys Fork valley. Raynolds Pass provides the most direct north-to-south oriented link between the north oriented Madison River valley and the south oriented Henrys Fork valley. Targhee Pass and Reas Pass provide northeast-to-southeast oriented links between the south oriented Henrys Fork valley and the north oriented South Fork Madison River valley, which drains to a northwest oriented Madison River valley segment east of Raynolds Pass. This essay interprets these three deep through valleys to have been eroded as diverging and converging flood flow channels. Floodwaters were derived from a melting thick North American ice sheet located north and east of the essay’s study region. Initially floodwaters flowed at elevations much higher than elevations of the through valley floors and crossed what are today some of the highest regional drainage divides. Headward erosion of deep south-oriented diverging and converging flood flow channels systematically captured the higher-level flood flow. Flood flow on the newly eroded and deep south-oriented diverging and converging flood flow channels was beheaded by headward erosion of a much deeper northeast oriented Missouri River valley segment (north of the study region) from space in the deep “hole” the melting ice sheet had occupied. Floodwaters on the north end of the beheaded flood flow channels reversed flow direction to create the north oriented Madison River drainage system and the north oriented Missouri River segment north of the Madison River. This massive flood flow reversal was probably greatly aided by ice sheet related crustal warping that raised mountain ranges in the study region.

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 Madison River-Henrys Fork drainage divide area landform origins along the continental divide west of Yellowstone National Park and 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 Madison River-Henrys Fork drainage divide area landform evidence along the continental divide west of Yellowstone National Park will be regarded as evidence supporting the “thick ice sheet that melted fast” paradigm.

Madison River-Henrys Fork drainage divide area location map

Figure 1: Madison River-Henrys Fork 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 Madison River-Henrys Fork drainage divide area along the continental divide west of Yellowstone National Park and illustrates in the north half a region in southwest and south central Montana with the northwest corner of Wyoming appearing in the southeast quadrant of figure 1 and an area in eastern Idaho located in the southwest quadrant of figure 1. The Montana-Idaho state line west of Yellowstone National Park is located on the east-west continental divide, which follows the crest of the Beaverhead and Centennial Mountains from the west edge of figure 1 to the Wyoming state line. Henrys Fork originates near Henrys Lake (near the point where Montana, Idaho, and Wyoming meet and just west of Targhee Pass) and flows in a south and southwest direction to the town of Island Pond and then to the south center edge of figure 1 and south of figure 1 joins the Snake River. The Snake River originates in Yellowstone National Park and flows in a south direction to Jackson Lake and the south edge of figure 1.  South of figure 1 the Snake River turns to flow in a northwest direction back into figure 1 to Lorenzo, Idaho and then is joined by southwest oriented Henrys Fork as it turns to flow in a south direction near Roberts, Idaho.  South of figure 1 (the second time) the Snake River then flows in a southwest and northwest direction across southern Idaho before turning to flow in a north direction west of figure 1 to join the Columbia River with water eventually reaching the Pacific Ocean. The Madison River originates along the Yellowstone National Park western margin in the region east of Henrys Lake and flows in a west and northwest direction to Hebgen Lake and to join its east and northeast oriented West Fork north of Henrys Lake before turning to flow in a north direction to Three Forks, Montana (near north edge of figure 1). At Three Forks the north oriented Madison River joins the north and northwest oriented Gallatin River and the northeast and east oriented Jefferson River to form the north oriented Missouri River. North of figure 1 the Missouri River turns to flow in a northeast and then east direction to North Dakota where it turns again to flow in a southeast and south direction with water eventually reaching the Gulf of Mexico. West of Henrys Lake are headwaters of the west oriented Red Rock River, which near Lima, Montana turns to flow in a north-northwest direction to the north-northeast oriented Beaverhead River, which then flows to the northeast and east oriented Jefferson River. The Madison River-Henrys Fork drainage divide area investigated in this essay is located north and east of Henrys Lake. The Red Rock River-Henrys Fork drainage divide area essay illustrated and discussed the region directly to the west along the west end of the Centennial Mountains.

A brief look at the big picture erosion history will help understand discussions related to detailed maps shown below. Large volumes of south and southeast oriented floodwaters once flowed across the region shown by figure 1. Floodwaters were derived from the western margin of a melting thick North American ice sheet and were flowing in a south and southeast direction from southwest Alberta and southeast British Columbia to and across the figure 1 region. North oriented rivers in figure 1, including the north oriented Madison River and Missouri River are generally flowing in valleys that originated as south oriented flood flow channels. When floodwaters first flowed across the region the mountain ranges, deep river valleys, and basins between the mountains did not exist and floodwaters could freely flow across the region. Mountain ranges emerged as floodwaters flowed across the region and initially floodwaters flowed across what are today high mountain ranges including mountain ranges, which today form the east-west continental divide. North-to-south oriented through valleys were eroded across the present day east-west continental divide in the study region by south and southeast oriented flood flow. The Madison River originated as a south oriented flood flow channel to the south oriented Henrys Fork valley, which was subsequently reversed to form the north oriented Madison River drainage route seen today. The flood flow reversal was probably indirectly caused by crustal warping that occurred as melt water floods flowed across the region with the crustal warping being related to thick ice sheet presence north and east of figure 1, although the direct cause of the flood flow reversal was headward erosion of a deep northeast oriented valley across Montana (north of figure 1), which beheaded south oriented flood flow channels supplying floodwaters to the south oriented Madison River flood flow channel. The deep northeast oriented valley eroded headward from space in the deep “hole” the melting ice sheet had occupied and was capturing the south and southeast oriented ice-marginal melt water floods and diverting the floodwaters into the deep “hole” the ice sheet had formed. This northeast oriented valley was much deeper than the beheaded flood flow channel and floodwaters on north end of the beheaded flood flow channel reversed flow direction to create the north oriented Madison River and other drainage routes seen in figure 1.

Detailed location map for Madison River-Henrys Fork drainage divide area

Figure 2: Detailed location map Madison River-Henrys Fork drainage divide area. United States Geological Survey map digitally presented using National Geographic Society TOPO software.

Figure 2 provides a more detailed location map for the Madison River-Henrys Fork drainage divide area along the continental divide west of Yellowstone National Park and shows drainage routes not seen in figure 1. The Yellowstone National Park boundary is labeled near the east edge of figure 2 and the Wyoming state line is just east of the Park boundary. West of Yellowstone National Park the continental divide serves as the Montana-Idaho state line and is shown with a well-marked dashed line extending from the west edge of figure 2 (south half) along the Centennial Mountains crest ridge to near Henrys Lake and then north around Henrys Lake and then continues in a southeast direction to near the south edge of edge of figure 2 (in Yellowstone National Park). Green shaded areas are National Forest lands, which generally are located in mountainous regions. The Madison River flows from Madison Junction in Yellowstone National Park in a west and northwest direction to Hebgen Lake. From Hebgen Lake the Madison River flows in a west direction through Earthquake Lake to the town of Cliff Lake and turns to flow in north-northwest direction to the north edge of figure 2 (west of center). The South Fork Madison River originates along the continental divide south of the town of West Yellowstone and flows in a north direction to join the Madison River at Hegben Lake. The West Fork Madison River originates north of the Red Rock Lakes Wilderness and flows in a southwest, southeast, east, southeast, and northeast direction to join the Madison River north of the town of Cliff Lake. Henrys Fork originates at Henrys Lake and flows in a southeast, west, and southwest direction to Island Pond Reservoir. Note other unlabeled streams in the Henrys Lake region flowing from near the continental divide to the north oriented Madison River and to south oriented Henrys Fork. These other streams are seen in more detail in the topographic maps illustrated below. Raynolds Pass north of Henrys Lake is where the south oriented flood flow channel on the present day Madison River-Henrys Fork alignment crossed the present day continental divide. The deep south oriented Madison River-Henrys Fork flood flow channel eroded headward from the deep southwest and west oriented Snake River valley, which was actively eroding headward across south oriented flood flow as the Centennial Mountains and other regional mountain ranges were emerging.

Antelope Creek-Henrys Lake drainage divide area

Figure 3: Antelope Creek-Henrys Lake drainage divide area. United States Geological Survey map digitally presented using National Geographic Society TOPO software.

Figure 3 provides a topographic map of the Antelope Creek-Henrys Lake drainage divide area. The east-west continental divide serves as the Montana-Idaho state line and extends in a north and north-northeast direction from the south center edge of figure 3 (near Red Rock Mountain) to the north edge of figure 3 (near Raynolds Pass) with Idaho being south and east of the continental divide and Montana being north and west. In this region areas in Montana drain to the Missouri River with water eventually reaching the Gulf of Mexico and areas in Idaho drain to Henrys Fork and the Snake River with water eventually reaching the Pacific Ocean. The high mountains seen along the south edge of figure 3 are the Centennial Mountains. Henrys Lake is located in the east half of figure 3 and Henrys Fork flows in a southeast direction from Henrys Lake to near the southeast corner of figure 3. Duck Creek is an east and northeast oriented stream flowing from near Red Rock Pass (on continental divide north of Red Rock Mountain) to Henrys Lake. Note the unlabeled south-southeast oriented stream flowing from near Raynolds Pass to Henrys Lake. North of Raynolds Pass is a valley extending northward to the west and north oriented Madison River, which is north of figure 3 and which flows to the north oriented Missouri River. Raynolds Pass is a major through valley linking the north oriented Madison River valley with the south oriented Henrys Fork valley and will be better seen in figure 5 below. The north oriented stream just west of the continental divide and flowing from Saddle Mountain (near center of figure 3) to Antelope Basin and then to the north edge of figure 3 (just west of center) is Antelope Creek, which north of figure 3 flows to Cliff Lake (see figure 5). While Cliff Lake has no surface drainage today it is located in a well-defined valley extending north from Cliff Lake to Wade Lake and then to the West Fork Madison River so for purposes of this essay Antelope Creek is considered to be a Madison River tributary. Anthill Creek is a northwest oriented Antelope Creek tributary and also originates near the continental divide east of Antelope Creek. West of Red Rock Pass and north of the Centennial Mountains is the Alaska Basin, which is the east end of the Centennial Valley. Red Rock Creek flows along the north edge of the Alaska Basin to the west edge of figure 3 (south half) and west of figure 3 flows to the west and north-northwest oriented Red Rock River with water eventually reaching the Missouri River. Red Rock Pass and Squaw Pass to the north of it are major passes across the continental divide linking the Red Rock River valley with the south oriented Henrys Fork valley and are further discussed in the Red Rock River-Henrys Fork drainage divide area essay, although they were eroded by east oriented flood flow moving to the south oriented flood flow channel on the present day Madison River-Henrys Fork alignment. While Raynolds Pass, Red Rock Pass, and Squaw Pass have names, and are labeled in figure 3, other through valleys also cross the continental divide. For example a shallow through valley or pass links the northwest oriented Anthill Creek valley with the southeast and east oriented Kelly Creek valley with Kelly Creek flowing to Henrys Lake. The map contour interval for figure 3 is 50 and the Anthill Creek-Kelly Creek through valley has an elevation at the continental divide of between 2400 and 2450 meters. Elevations rise to more than 2500 meters on either side of the through valley or pass and suggest the through valley is at least 50 meters deep and may be even deeper. The through valley was eroded as a southeast oriented flood flow channel with floodwaters coming from the present day north oriented Madison River valley. Floodwaters in this case were reversed by headward erosion of the deeper northeast oriented West Fork Madison River valley north of figure 3, which beheaded the south and southeast oriented flood flow channel on the Antelope Creek-Anthill Creek alignment. Floodwaters on the north end of the beheaded flood flow channel reversed flow direction to create the north oriented Antelope Creek-Anthill Creek drainage route.

Detailed map of Anthill Creek-Kelly Creek drainage divide area

Figure 4: Detailed map of Anthill Creek-Kelly 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 Anthill Creek-Kelly Creek drainage divide area seen is less detail in figure 3. The east-west continental divide serves as the state and county line and extends from the south edge of figure 4 (west half) to the north edge of figure 4 (east of center). In this figure the region east of the continental divide drains to Henrys Fork with water eventually reaching the Pacific Ocean. Areas west of the continental drain to Antelope Creek, which in this essay is considered to be in the Madison River drainage basin, where water eventually reaches the Gulf of Mexico. Saddle Mountain is located in section 32 in the northwest quadrant of figure 4. The northwest and north oriented stream west of Saddle Mountain is Antelope Creek. The northwest oriented stream east of Saddle Mountain is Anthill Creek, which joins Antelope Creek just north of figure 4. East and south of the continental divide the south oriented stream flowing to the south edge of figure 4 (west of center) is the North Fork Duck Creek. Further east the stream flowing in a southeast direction across section 11 in the southeast quadrant of figure 4 is Kelly Creek. Note how a through valley links the south oriented North Fork Duck Creek valley with the northwest and north oriented Antelope Creek valley. The map contour interval for figure 4 is 40 feet and the through valley floor elevation at the drainage is between 7840 and 7880 feet. Immediately to the south the continental divide rises to more than 8560 feet while Saddle Mountain to the north rises to 8281 feet suggesting the through valley is at least 400 feet deep. The floor elevation of the through valley linking the northwest oriented Anthill Creek valley with the southeast oriented Kelly Creek valley is between 7920 and 7960 feet. Elevations further to the northeast on the continental divide rise to 8377 feet suggesting the through valley is also at least 400 feet deep. Note how Saddle Mountain is located on a northwest-to-southeast oriented streamlined ridge between the two through valleys. The streamlined ridge is an erosional residual between two diverging, but southeast oriented flood flow channels. The southeast oriented flood flow was reversed when a much deeper northeast oriented valley north and west of figure 4 beheaded the southeast oriented flood flow routes. Floodwaters on the northwest ends of the beheaded flood flow routes reversed flow direction to create the northwest oriented Antelope and Anthill Creek drainage routes seen today and also to create the Antelope Creek-Henrys Fork drainage divide.

Horn Creek-Henrys Lake drainage divide area

Figure 5: Horn Creek-Henrys Lake drainage divide area. United States Geological Survey map digitally presented using National Geographic Society TOPO software.

Figure 5 illustrates the Horn Creek-Henrys Lake drainage divide area north and slightly east of figure 3 and includes a significant overlap area with figure 3. The east-west continental divide serves as the state line and extends from the south edge of figure 5 (west of center) to Raynolds Pass and then to the northeast quadrant of figure 5 before turning in southeast direction to the east center edge of figure 5. Areas south of the continental divide drain to Henrys Fork with water eventually reaching the Pacific Ocean. Regions north of the continental divide drain to the Missouri River with water eventually reaching the Gulf of Mexico. Henrys Lake straddles the south edge of figure 5 and south of figure 5 drains to south oriented Henrys Fork. Raynolds Pass is located north of Henrys Lake and north of Raynolds Pass is northwest and southwest oriented Horn Creek, which flows to Cliff Lake. Cliff Lake is located in an elongate valley, which today does not serve as a continuous drainage route. However, to the north the valley extends to the West Fork Madison River valley and to the southwest the valley extends to the Centennial Valley suggesting the Cliff Lake through valley once served to move east oriented flood flow from the present day west and north-northwest oriented Red Rock River alignment to the north oriented Madison River valley. The map contour interval for figure 5 is 50 meters and the drainage divide between Hidden Lake and Elk Lake (near west center edge of figure 5) has an elevation of between 2100 and 2150 meters. Raynolds Pass near the center of figure 5 has a slightly lower elevation at the drainage divide of between 2050 and 2100 meters. East of the northwest oriented Horn Creek segment is north-northwest oriented Mile Creek, which flows to the north center edge of figure 5 and then to the west and north oriented Madison River. Note how there is continuous through valley extending from Henrys Lake northward across Raynold Pass to the north oriented Miles Creek valley. This large north-to-south oriented through valley was formed as a major south oriented flood flow channel moving floodwaters to what was then the actively eroding Henrys Fork and Snake River valley. Headward erosion of a deep northeast oriented valley (now the northeast oriented Missouri River valley in central Montana) beheaded the south oriented flood flow channel on the Madison River-Henrys Fork alignment. Floodwaters on the north end of the beheaded flood flow channel reversed flow direction to create the north oriented Madison River-Missouri River drainage route seen today. The flood flow reversal also captured the east oriented flood flow channel on the present day west oriented Red Rock River-Red Rock Creek alignment. The captured east oriented flood flow flowed in a northeast direction in the Elk Lake-Hidden Lake-Cliff Lake valley seen near the west edge of figure 5. Headward erosion of the deep east and northeast oriented Jefferson River valley next beheaded the south oriented flood flow route supplying floodwaters to the south and east oriented flood flow channel on the Red Rock River alignment. The resulting flood flow reversal created the west and north-northwest oriented Red Rock River drainage route. Note north of Henrys Lake is Black Mountain and a short distance north and east of Black Mountain are headwaters of north-northwest oriented Mile Creek and of southeast oriented West Fork Targhee Creek with Targhee Creek flowing in a southeast and southwest direction to Henrys Lake. A 350-meters deep northwest-to-southeast oriented through valley links the north-northwest Miles Creek valley with the southeast oriented West Targhee Creek valley and provides evidence floodwaters once flowed on a surface as high, if not higher, than the through valley floor elevation of between 2800 and 2850 meters.

Detailed map of Horn Creek-Henrys Lake drainage divide area

Figure 6: Detailed map of Horn Creek-Henrys Lake 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 Horn Creek-Henrys Fork drainage divide area seen in less detail in figure 5. The east-west continental divide serves as the state line and extends from the south edge of 6 (west of center) to Raynolds Pass and then to the east edge of figure 6 (north of center). Areas north and west of the continental divide drain to the north oriented Madison River with water eventually reaching the Gulf of Mexico. South and east of the continental divide drainage is to Henrys Lake with water eventually reaching the Pacific Ocean. Antelope Creek is the north oriented stream in the Antelope Basin near the west edge of the southwest quadrant of figure 6. Raynolds Pass is the labeled pass where the highway crosses the continental divide. The map contour interval for figure 6 is 40 feet and the Raynolds Pass elevation at the continental divide is 6836 feet. South of figure 6 the continental divide reaches an elevation of 8377 feet and still further south in the Centennial Mountains elevations rise to 10,181 feet at Mount Jefferson. East of figure 6 on Black Mountain the continental divide elevation reaches 10,327 feet. Depending on which elevations are chosen the Raynolds Pass depth could be considered to be anywhere from 1500 to 3200 feet deep. Raynolds Pass is a water-eroded feature and the pass seen in figure 6 was eroded by immense south oriented flood flow moving on the Missouri River-Madison River-Henrys Fork alignment. The deeper broad valley between Mount Jefferson and Black Mountain was also eroded by immense south and east oriented flood flow moving on the present day west and north-northwest oriented Red Rock River alignment. As described previously the south oriented flood flow channel on the Missouri River-Madison River-Henrys Fork alignment was beheaded by headward erosion of the much deeper northeast oriented Missouri River valley further to the north. That much deeper Missouri River valley was eroding headward from space in a deep “hole” the melting ice sheet had once occupied. Floodwaters on the north end of the beheaded flood flow channel reversed flow direction to create the present day north oriented Madison River-Missouri River drainage route and to create a drainage divide at Raynolds Pass. Subsequently headward erosion of the much deeper Jefferson River valley beheaded and reversed south oriented flood flow routes supplying floodwaters to the south-southeast and east oriented flood flow channel on the Red Rock River alignment. The resulting flood flow reversal created the west and north-northwest oriented Red Rock River drainage route and ended all flood flow to the region illustrated and discussed in this essay.

Hebgen Lake-Henrys Lake drainage divide area

Figure 7: Hebgen Lake-Henrys Lake drainage divide area. United States Geological Survey map digitally presented using National Geographic Society TOPO software.

Figure 7 illustrates the Hebgen Lake-Henrys Lake drainage divide area east and slightly north of figure 5 and includes a significant overlap area with figure 5. The east-west continental divide serves as the state line and is shown with a dashed line extending across the northwest corner of figure 7 from Black Mountain to the north edge of figure 7 and then a short distance further east from north edge of figure 7 in a southeast and south direction to the south center edge of figure 7. South and west of the continental divide streams drain to Henrys Fork, which drains in a southeast direction from Henrys Lake. North and east of the continental divide streams drain to the northwest and north oriented Madison River. The lake labeled Madison Arm in the northeast quadrant of figure 7 is Hebgen Lake and is flooding the west-northwest oriented Madison River valley. The South Fork Madison River flows in a north, northwest, and north-northwest direction from the south edge of figure 7 to enter the Madison Arm of Hebgen Lake near the north edge of figure 7. Denny Creek is a north-northeast oriented South Fork Madison River tributary in the north half of figure 7. Note the Denny Creek southeast oriented West Fork and north-northeast oriented East Fork. A short distance south and west of where the West and East Forks of Denny Creek meet is Targhee Pass, which links the north-northeast oriented Denny Creek valley with the southwest oriented Howard Creek valley. The map contour interval for figure 7 is 50 meters and the Targhee Pass elevation at the continental divide is between 2150 and 2200 meters. Elevations along the continental divide to the north rise to 3100 meters at Bald Peak and to the south to 2556 meters suggesting Targhee Pass is at least 350 meters deep. Targhee Pass is a water-eroded through valley, which was eroded by southwest oriented flood flow moving to converge with the south oriented flood flow on the Madison River-Henrys Fork alignment. The converging flood flow channels in the Henrys Lake area provide evidence of an immense south oriented anastomosing channel complex that once crossed the region. The southwest oriented flood flow across Targhee Pass was beheaded and reversed by headward erosion of the much deeper Madison River valley. While evidence seen in figure 7 is not adequate to determine the orientation of flow in that initial deep Madison River valley it is possible the valley was first oriented in an east-southeast direction and was subsequently reversed to create the west-northwest oriented Madison River drainage route seen today. Regardless of which direction the initial deep Madison River valley was oriented in the deep valley beheaded diverging south oriented flood flow channels on the present day north oriented South Fork Madison River alignment and the present day Denny Creek-Howard Creek alignment. Floodwaters on the north ends of the beheaded flood flow channels reversed flow direction to create the north oriented South Fork Madison River and Denny Creek drainage routes seen today and also to create the drainage divide at Targhee Pass.

Detailed map of Denny Creek-Howard Creek drainage divide area

Figure 8: Denny Creek-Howard 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 Denny Creek-Howard Creek drainage divide area seen in less detail in figure 7. The east-west continental divide serves as the state and county line and extends from the north edge of figure 8 (west of center) to the south edge of figure 8 (slightly west of center). East of the continental divide Denny Creek is formed at the confluence of its south-southeast oriented West Fork and of its north-northeast oriented East Fork near the Lionhead Resort in the northeast quadrant of figure 8 and then flows in a northeast direction to the northeast corner of figure 8. North and east of figure 8 Denny Creek joins the north oriented South Fork Madison River. West of the continental divide Howard Creek originates in section 32 and flows in a northwest and southwest direction to the south edge of figure 8. Targhee Creek is the south-southeast and south-southwest oriented stream located on the west side of the valley in which Howard Creek is flowing (near the southwest corner of figure 8). South and west of figure 8 Targhee Creek and Howard Creek drain to Henrys Lake and south oriented Henrys Fork. Targhee Pass is located in the deep northeast-to-southwest oriented through valley linking the northeast oriented Denny Creek valley with the southwest oriented Howard Creek valley. The map contour interval for figure 8 is 40 feet and the Targhee Pass elevation is shown as being 7072 feet. Elevations on the continental divide near the south edge of figure 8 rise to 8386 feet while elevations near the north edge of figure 8 rise to more than 8200 feet and north of figure 8 rise to more than 10,000 feet. These elevations suggest Targhee Pass is at least 1300 feet deep. The 1300-foot deep Targhee Pass through valley was eroded into an emerging mountain mass by a southwest oriented flood flow channel. The reversal of flood flow that created the drainage divide and the northeast oriented Denny Creek valley was directly caused by headward erosion of the deep Madison River valley to the north. However, erosion of that deep Madison River valley was probably made possible by crustal warping that was raising the mountain ridge seen in figure 8. The crustal warping was probably related to the presence of a thick North American ice sheet in the region north and east of this essay’s study region, which is usually considered to be the region of North America covered by continental ice sheets. The immense south oriented floods that eroded the deep south oriented flood flow channels such as seen in figure 8 were derived from that thick North American ice sheet.

South Fork Madison River-Henrys Fork drainage divide area

Figure 9: South Fork Madison River-Henrys Fork drainage divide area. United States Geological Survey map digitally presented using National Geographic Society TOPO software.

Figure 9 illustrates the South Fork Madison River-Henrys Fork drainage divide area south and slightly east of figure 7 and includes a significant overlap area with figure 7. West Yellowstone is the town located near the northeast corner of figure 9. The continental divide serves as the state and county border and extends from Targhee Pass at the north edge of figure 9 (west of center) to the south edge of figure 9 (east half). West of the continental divide Henrys Fork flows in a south-southeast direction from the south end of Henrys Lake to the south edge of figure 9 (west half). Howard Creek is the southwest oriented stream flowing from near Targhee Pass to the south end of Henrys Lake. Reas Pass Creek is a west oriented stream near the south edge of figure 9 flowing toward Henrys Fork. An old railroad grade is located in the Reas Pass Creek valley and extends in a northeast direction from Reas Pass Creek to Reas Pass on the continental divide. Just north of Reas Pass on the east side of the continental divide is an elbow of capture where southeast oriented South Fork Madison River headwaters turn abruptly to flow in a north direction to near the north edge of figure 9 where the South Fork Madison River turns to flow in a northwest direction to the north edge of figure 9. Reas Pass is located in another southwest oriented flood eroded through valley. The map contour interval for figure 9 is 50 meters and the Reas Pass elevation at the continental divide is between 2100 and 2150 meters, which is slightly lower than the Targhee Pass elevation and slightly higher than the Raynolds Pass elevation. All three passes have elevations very similar to each other suggesting they were being eroded at the same time by converging flood flow channels. North of Reas Pass Mount Two Top rises to 2655 meters and south of figure 9 the continental divide rises to more than 2600 meters suggesting the Reas Pass through valley is as much as 500 meters deep. The Reas Pass through valley was eroded as a south and southwest oriented flood flow channel that diverged from the southwest oriented flood flow channel eroding the Targhee Pass through valley and that continued in a south direction along the present day north oriented South Fork Madison River alignment to Reas Pass and then in a southwest direction to converge with the south oriented Henrys Fork valley or flood flow channel. This diverging and converging south oriented flood flow channel was beheaded and reversed when the south oriented South Fork Madison River flood flow channel was beheaded by headward erosion of the deeper Madison River valley in the Hegben Lake area seen in figure 7. The resulting flood flow reversal created the north oriented South Fork Madison River drainage route and the South Fork Madison River-Henrys Fork drainage divide seen in figure 9.

Detailed map of South Fork Madison River-Reas Pass Creek drainage divide area

Figure 10:Detailed map of South Fork Madison River-Reas Pass 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 South Fork Madison River-Reas Pass Creek drainage divide area seen in less detail in figure 9. The continental divide serves as the state line and extends from the north edge of figure 10 (west half) to the south edge of figure 10 (near southeast corner). North of the continental divide the South Fork Madison River flows in a southeast direction from the north edge of figure 10 (west of center) and then turns to flow in a north direction to the north edge of figure 10 (near northeast corner). Reas Pass is located on the continental divide a short distance south and west of the elbow of capture where the South Fork Madison River makes its abrupt change of direction. The map contour for figure 10 is 20 feet and the Reas Pass elevation at the continental divide is shown as being 6941 feet. Elevations in the northwest quadrant of figure 10 rise to more 8200 feet and the continental divide elevation near the south edge of figure 10 rises to more than 7760 feet suggesting that based on evidence seen in figure 10 Reas Pass is at least 820 feet deep. However, elevations rise much higher to the north of figure 10 and also to the southwest of figure 10, so it is possible the Reas Pass through valley is much deeper. There is a much steeper slope along the through valley southwest wall than along the northwest wall, which suggests the through valley may be located along the northwest edge of lava layers, although the topographic map evidence gives no clues as to the bedrock type. If so the Reas Pass location is geologically controlled, but that does not change the fact that Reas Pass is a water-eroded feature and was eroded as a southwest oriented flood flow channel. The southeast oriented South Fork Madison River headwaters valley orientation provides evidence of south and southeast oriented floodwaters that prior to erosion of the deep diverging and converging flood flow channels on the present day Targhee Pass, Reas Pass, and Raynolds Pass through valley alignments were flowing at much higher elevations and that were captured by headward erosion of the deeper south oriented flood flow channels forming the deep Raynolds Pass, Targhee Pass, and Reas Pass through valleys. In the case of the southeast oriented South Fork Madison River segment it was also captured by the flood flow reversal that created the north oriented South Fork Madison River drainage route and the Henrys Fork-South Fork Madison River drainage divide.

Additional information and sources of maps studied

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

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