Tongue River-Shell Creek drainage divide area landform origins in the Wyoming Bighorn Mountains, USA

Authors

Abstract:

This essay uses topographic map evidence to interpret landform origins in the region between the Tongue River and Shell Creek in the Wyoming Bighorn Mountains. The Tongue River and Shell Creek originate in same region of the high Bighorn Mountains, but flow to opposite sides of the Bighorn Mountains. The Tongue River flows in an east direction to the Bighorn Mountains east side and then in a northeast and north direction to join the northeast oriented Yellowstone River. Shell Creek flows in a northwest and west-southwest direction to join the north oriented Bighorn River on the Bighorn Mountains west side with the Bighorn River also flowing to the northeast oriented Yellowstone River. Through valleys or mountain passes cross the Bighorn Mountains crest ridge and link the Tongue River and Shell Creek drainage basins. The through valleys are evidence of multiple south oriented flood flow channels that once crossed the Bighorn Mountains. At that time the Bighorn Mountains did not stand high above surrounding regions as they do today and floodwaters could freely flow across what is today a high mountain range. Floodwaters are interpreted to have been derived from the western margin of a thick North American ice sheet and were flowing from western Canada to and across the Bighorn Mountains region. The Bighorn Mountains emerged as floodwaters flowed across them with floodwaters first being captured by south oriented flood flow channels eroding headward into the Powder River Basin to the east and into the Bighorn Basin to the west. In addition to deep erosion of regions surrounding them the Bighorn Mountains were uplifted by crustal warping as the ice sheet created a deep “hole” in which it became located. Headward erosion of the deep northeast oriented Yellowstone River valley across Montana from space at the south end of the deep “hole” being opened up by ice sheet melting captured south and southeast oriented flood flow channels in sequence from east to west. Reversals of flood flow occurred on north ends of beheaded flood flow channels and created the present day north oriented Tongue River and Bighorn River drainage systems. The north oriented Tongue River drainage system was created first and captured south and southeast oriented flood flow still crossing the emerging Bighorn Mountains. Headward erosion of the deep Yellowstone River valley to the point where it beheaded and reversed flood flow in the Bighorn Basin ended all flood flow across the Bighorn Mountains. Crustal warping since that time has probably significantly raised the Bighorn Mountains, although the reversed drainage routes still reflect orientations established when floodwaters crossed the region.

Introduction

The purpose of this essay is to use topographic map interpretation methods to explore the Tongue River-Shell Creek drainage divide area landform origins in the Wyoming Bighorn Mountains. 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 Tongue River-Shell Creek drainage divide area landform evidence in the Wyoming Bighorn Mountains will be regarded as evidence supporting the “thick ice sheet that melted fast” paradigm.

Tongue River-Shell Creek drainage divide area location map

Figure 1: Tongue River-Shell 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 Tongue River-Shell Creek drainage divide area in the Wyoming Bighorn Mountains and illustrates a region in north central Wyoming and south central Montana. The west to east oriented Montana-Wyoming state line is located in the center of figure 1 with Montana north of Wyoming. The Bighorn River flows in a north-northwest direction from the south edge of figure 1 (west half) to the Montana border and then turns to flow in a north-northeast direction to the north edge of figure 1 (west of center). North of figure 1 the Bighorn River flows to the northeast oriented Yellowstone River. The Bighorn Mountains are located east of the Bighorn River and extend from north of the state line to the south center edge of figure 1. The Little Bighorn River originates in the Bighorn Mountains (south of the state line) and flows in a northeast direction to Wyola, Montana and then in a north and north-northwest direction to join the Bighorn River near Hardin, Montana. Shell Creek is shown, but is not labeled in figure 1 and originates in the Bighorn Mountains (south of Dome Peak) and flows in a northwest and west-southwest direction to the town of Shell, Wyoming and then to join the Bighorn River near the town of Greybull, Wyoming. The Tongue River (unlabeled in figure 1) originates in the Bighorn Mountains south of the Little Bighorn River headwaters and flows in an east-northeast direction to Ranchester and Acme, Wyoming to join the north, northeast, and north oriented Goose Creek (unlabeled in figure 1). The Tongue River then flows in a northeast direction to Ashland, Montana where it turns to flow in a north direction to the north edge of figure 1 (east half). North of figure 1 the Tongue River flows to the northeast oriented Yellowstone River. East of the Tongue River is the north and northeast oriented Powder River, which flows from the south edge of figure 1 (east half) to the east edge of figure 1 (north half) and north and east of figure 1 joins the northeast oriented Yellowstone River. The Tongue River-Shell Creek drainage divide area in the Bighorn Mountains investigated in this essay is located north of Shell Creek, west of Goose Creek, and south of the North Tongue River.

Almost all drainage routes seen in figure 1 are today oriented in north directions, however many of the north oriented drainage routes are located on alignments of earlier south oriented flood flow channels. The floodwaters were derived from the western margin of a thick North American ice sheet and were flowing from western Canada to and across Montana and Wyoming. At that time mountain ranges in Montana and Wyoming had not emerged and south and southeast oriented floodwaters could freely flow across what are today high mountain regions. Emergence of the mountain ranges occurred as floodwaters deeply eroded the region and as ice sheet crustal warping created the southwest rim of a deep “hole” in which the ice sheet was located. The region seen in figure 1 could be considered to be a deeply eroded and warped segment of the deep “hole’s” southwest rim. The Powder Basin east of the Bighorn Mountains began to emerge as south and southeast oriented flood flow channels eroded headward into the region. Headward erosion of south oriented flood flow channels west of the emerging Bighorn Mountains also began to excavate the Bighorn Basin. The south and southeast oriented flood flow channels were beheaded by headward erosion of the deep northeast oriented Yellowstone River valley across Montana to the north of figure 1 from space at the deep “hole” south end being opened up by the ice sheet melting and which was initially drained in a south direction on flood flow channels east of figure 1. Headward erosion of the Yellowstone River valley beheaded the 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 Yellowstone River tributary drainage routes. Northeast oriented valleys eroded headward from these newly formed north oriented drainage routes to capture south and southeast oriented flood flow moving west of the actively eroding Yellowstone River valley head. The northeast oriented Powder River valley and tributary valleys captured the flood flow first. Later the northeast oriented Tongue River valley and tributary valleys captured the south oriented flood flow, which was still moving across the emerging Bighorn Mountains. Subsequently the north-northeast oriented Bighorn River valley beheaded all flood flow routes crossing the emerging Bighorn Mountains and in the east half of the emerging Bighorn Basin. Floodwaters on the north ends of flood flow routes in the Bighorn Basin reversed flow direction to create the north-northwest oriented Bighorn River drainage route seen in figure 1. Bighorn Mountains uplift probably continued after flood flow across the region ended and today the high Bighorn Mountains form a massive barrier between the Bighorn and Powder River Basins.

Detailed location map for Tongue River-Shell Creek drainage divide area

Figure 2: Detailed location map Tongue River-Shell Creek 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 Tongue River-Shell Creek drainage divide area in the Wyoming Bighorn Mountains. The Montana-Wyoming state line is located along the north edge of figure 2. The green colored area is National Forest land located in the Bighorn Mountains. The Bighorn Basin is located west of the Bighorn Mountains and the Powder River Basin is located east of the Bighorn Mountains. The dashed county line follows the crest of the Bighorn Mountains, which also serves as a major drainage divide, and extends from the state line (west half of figure 2) to the south edge of figure 2 (east half).  The Bighorn River flows in a north direction from the south edge of figure 2 to Greybull and then in a north-northwest direction to Bighorn Lake along the west edge of figure 2. Shell Creek originates near the Bighorn Mountains drainage divide or county line (a short distance north of the south edge of figure 2) and flows in a northwest direction before turning to flow in a west-southwest direction to join the Bighorn River near Greybull (Shell Creek is the west-southwest oriented stream at the town of Shell, which is east of Greybull). Note south and southwest oriented Shell Creek tributaries originating at or near the Bighorn Mountains drainage divide (or county line). These south oriented tributaries are located in what is today a north oriented drainage system and are evidence of south oriented flood flow channels that preceded the reversals of flood flow that created the north oriented drainage systems.Burgess Junction is a highway junction in the Bighorn Mountains west of Sheridan. The North Tongue River originates along the Bighorn Mountains drainage divide (or county line) and flows in an east-southeast, northeast, and east direction to join the northwest and north oriented South Tongue River in the region north and east of Burgess Junction and to form the Tongue River. Once formed the Tongue River flows in an east and northeast direction to Ranchester and then in an east and northeast direction to the northeast corner of figure 2. Note north oriented Tongue River tributaries originating along or near the Bighorn Mountains drainage divide (or county line). Goose Creek is a north oriented Tongue River tributary formed near Sheridan at the confluence of northeast oriented Big Goose Creek and north-northeast oriented Little Goose Creek. Big Goose Creek is formed at the confluence of its north and northeast oriented West Fork and of its north oriented East Fork. Edelman Creek is a north-northeast tributary to East Fork Big Goose Creek, which originates near the Shell Creek headwaters. Slightly north of the North Tongue River headwaters are headwaters of the Little Bighorn River, which flows in a north and northeast direction to the north edge of figure 2 (west of center) and joins the Bighorn River north of figure 2.

Shell Creek-Edelman Creek drainage divide area

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

Figure 3 provides a topographic map of the Shell Creek-Edelman Creek drainage divide area and is located in the high Bighorn Mountains. The dashed line extending from the north center edge of figure 3 to near the southeast corner of figure 3 is the county line, which is defined by the Tongue River-Bighorn River drainage divide. Emerald Lake is located near the center of figure 3. Shell Creek originates at Emerald Lake and flows in a northwest direction to the north edge of figure 3 (west half) and eventually enters the Bighorn Basin and joins the Bighorn River. North of Emerald Lake is Edelman Pass and north of Edelman Pass are headwaters of north-northeast oriented Edelman Creek, which joins the north oriented East Fork Big Goose Creek in the northeast quadrant of figure 3. North oriented Big Goose Creek originates just north of Geneva Pass with water eventually flowing to the east side of the Bighorn Mountains and to the Tongue River. South of Geneva Pass are south oriented headwaters of southwest oriented Paint Rock Creek, which flows to the south edge of figure 3 (west of center) and which eventually joins the northwest oriented Nowood River, which flows to the Bighorn River. South and west of Emerald Lake are headwaters of southwest oriented Medicine Lodge Creek, which flows to the south edge of figure 3 (near southwest corner) and eventually joins Paint Rock Creek. Note the unnamed pass linking the southwest oriented Medicine Lodge Creek valley with the Emerald Lake basin. The named and unnamed passes seen in figure 3 are water-eroded features and cross drainage divides along and near the Bighorn Mountains crest ridge. Large volumes of water flowing from one side of the Bighorn Mountains crest ridge to the other side eroded these passes. The map contour interval for figure 3 is 20 meters and Edelman Pass for example has an elevation of between 3120 and 3140 meters and is at least 240 meters deep. Where was the water that eroded Edelman Pass coming from and where was the water going? Probably the pass was initiated by a south oriented flood flow channel on the present day north-northeast oriented Edelman Creek alignment that converged with a southeast oriented flood flow channel on the present day northwest oriented Shell Creek alignment at the present day location of Emerald Lake. These early flood flow channels were flowing on a surface as high, if not higher, than the mountain ridge southeast of Emerald Lake and the floodwaters probably flowed across that ridge. Headward erosion of the Paint Rock valley captured the floodwaters first and next headward erosion of the Medicine Lodge Creek valley captured the flood flow and beheaded the flood flow to the Paint Rock Creek valley, which was still being eroded by south oriented flood flow on the present day north oriented East Fork Goose Creek alignment. Next a reversal of flood flow on the East Fork Big Goose Creek alignment ended south oriented flood flow across Geneva Pass and reversed the direction of flood flow on the Edelman Creek alignment and captured the southeast oriented flood flow on the Shell Creek alignment. Subsequently flood flow on the northwest oriented Shell Creek alignment was beheaded and reversed to create the northwest oriented Shell Creek drainage route and to end flood flow across Edelman Pass. These flood flow movements and reversals took place as the Bighorn Mountains were emerging and as headward erosion of deep valleys in the Powder River Basin to the east and the Bighorn Basin to west systematically captured the south and southeast oriented flood flow that had been crossing the region seen in figure 3.

Detailed map of Shell Creek-Edelman Creek drainage divide area

Figure 4: Detailed map of Shell Creek-Edelman 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 Shell Creek-Edelman Creek drainage divide seen in less detail in figure 3. Emerald Lake is located at the corner of sections 22, 23, 26, and 27 in the northwest quadrant of figure 4. Shell Creek originates at Emerald Lake and flows in a northwest direction to the northwest corner of figure 4. Edelman Pass is located in southwest corner of section 23 and Edelman Creek originates north of Edelman Pass and flows in a northeast direction to the north edge of figure 4 (west of center). The map contour interval for figure 4 is 40 feet and the Edelman Pass elevation is between 10,280 and 10,320 feet. A spot elevation north of Edelman Pass reads 10,713 feet and just north of figure 4 the drainage divide elevation rises to 11,044 feet. Elevations east of Edelman Pass rise to 11,540 feet. These elevations suggest Edelman Pass is at least 700 feet deep. Note how the Edelman Pass elevation is only slightly higher than the Emerald Lake elevation of 10,250 feet. The Edelman Trail south and west of Emerald Lake crosses an unnamed pass between Emerald Lake and the southwest oriented Medicine Lodge Creek valley (not labeled in figure 4, but flows to west edge of figure 4-south half). The unnamed pass elevation is 10,465 feet and elevations to the west rise to 10,958 feet suggesting the pass is approximately 500 feet deep. These passes were eroded by south oriented flood flow, which initially flowed in a southeast direction on the present day northwest oriented Shell Creek alignment and in a southwest direction on the present day northeast oriented Edelman Creek alignment. Flood flow to the Medicine Lodge Creek valley was beheaded when flood flow on the Edelman Creek alignment was beheaded and reversed and captured the southeast oriented flood flow on the Shell Creek alignment. Flood flow to the newly reversed Edelman Creek alignment ended when the southeast oriented flood flow channel on the Shell Creek alignment was beheaded and reversed. Geneva Pass is located in the north half of section 31 and links the north oriented East Fork Goose Creek headwaters valley with the south oriented Paint Rock Creek headwaters valley. The Geneva Pass elevation is between 10,10,240 and 10,280 feet. Elevations east of figure 4 rise to 10,480 feet suggesting the Geneva Pass depth may be more than 1100 feet. The Geneva Pass through valley was eroded by south oriented flood flow moving to the Paint Rock Creek valley. South oriented flood flow on the present day north oriented East Fork Big Goose Creek alignment was beheaded and reversed to end flood flow across Geneva Pass. Obviously at the time floodwaters crossed the high Bighorn Mountains the Bighorn Mountains did not stand high above surrounding regions as they do today. Deep erosion of surrounding regions and crustal warping that raised the Bighorn Mountains was occurring as floodwaters crossed the region and has occurred since that time.

South Tongue River-Shell Creek drainage divide area

Figure 5: South Tongue River-Shell Creek drainage divide area. United States Geological Survey map digitally presented using National Geographic Society TOPO software.

Figure 5 provides a topographic map to illustrate the South Tongue River-Shell Creek drainage divide area west and north of figure 3 and includes a small overlap area with figure 3. The dashed county line is also the Tongue River-Shell Creek drainage divide and extends from the north edge of figure 5 (west half) to near the southeast corner of figure 5. Shell Creek flows in a northwest direction from the south edge of figure 5 (east of center) to Shell Canyon and the west edge of figure 5 (south of center). The map contour interval for figure 5 is 20 meters and Shell Canyon is more than 500 meters deep near the west edge of figure 5. Note how the two major south-oriented Shell Creek tributaries seen in figure 5 originate at passes across the Tongue River-Shell Creek drainage divide. The highway follows south-southwest oriented Granite Creek from Granite Pass into Shell Canyon and Willett Creek flows in a west-southwest and south-southwest direction south of Woodchuck Pass to join Shell Creek north of the south center edge of figure 5. The West Fork South Tongue River is located just east of the highway north of Granite Pass and flows to the north center edge of figure 5. The East Fork South Tongue River originates north of Dome Peak in the northeast quadrant of figure 5 and flows in a west and north-northwest direction to the north edge of figure 5 (east of center) and joins the West Fork north of figure 5 to form the north oriented South Tongue River. Granite Pass has an elevation of 2753 meters. Elevations west of Granite Pass rise to more than 2960 meters and elevations east of Granite Pass rise to more than 3100 meters. These elevations suggest Granite Pass is at least 200 meters deep and links the north oriented West Fork Tongue River valley with the south oriented Granite Creek valley. Granite Pass was eroded by south oriented flood flow moving across the present day Bighorn Mountains. Woodchuck Pass has an elevation of 2930 meters and Bruce Mountain to the west rises to more 3140 meters while Dome Peak to the east rises to 3300 meters. These elevations suggest Woodchuck Pass is also at least 200 meters deep. Woodchuck Pass links a north oriented East Fork South Tongue River tributary valley with a south oriented Willett Creek tributary valley and was also eroded by south oriented flood flow prior to the reversal of flood flow on the East Fork South Tongue River alignment. Obviously at the time south oriented floodwaters flowed across the Tongue River-Shell Creek drainage divide the regional topography looked very different from how it does today. Floodwaters deeply eroded the emerging Bighorn Mountains and surrounding Bighorn and Powder River Basins at the same time as crustal warping was raising the Bighorn Mountains and the Bighorn Mountains have probably been uplifted significantly since the flood flow ended.

Detailed map of Woodchuck Creek-Willett Creek drainage divide area

Figure 6: Detailed map of Woodchuck Creek-Willett Creek drainage divide area. United States Geological Survey map digitally presented using National Geographic Society TOPO software.

Figure 6 illustrates a detailed topographic map of the Woodchuck Creek-Willett Creek drainage divide area seen in less detail in figure 5. Woodchuck Pass is near the center of figure 6. Woodchuck Creek originates in section 36, north and east of Woodchuck Pass, and flows in a north direction to the north edge of figure 6 (east of center). North of figure 6 Woodchuck Creek flows to the north oriented East Fork South Tongue River. Willett Creek originates in section 7 near the southeast corner of figure 6 and flows in a northwest, southwest, west, and west-southwest direction to the south edge of figure 6 in section 11 (south of Woodchuck Pass). A southwest and south oriented stream originates near Woodchuck Pass and flows to the south edge of figure 6 to join Willett Creek south of figure 6. South of figure 6 Willett Creek flows to the northwest oriented Shell Creek valley. The map contour interval for figure 6 is 40 feet and the Woodchuck Pass elevation is 9612 feet. Bruce Mountain to the northwest rises to 10,300 feet and Dome Peak to the east rises to 10,828 feet. These elevations suggest Woodchuck Pass is approximately 700 feet deep. Woodchuck Pass was eroded by south oriented flood flow moving on the present day north oriented East Fork Tongue River alignment to what was probably a southeast oriented flood flow channel on the present day northwest oriented Shell Creek alignment. South oriented flood flow channels crossing the present day Bighorn Mountains were beheaded and reversed in sequence from east to west, which means flood flow on the East Fork Big Goose Creek and Edelman Creek alignments seen in figures 3 and 4 was beheaded and reversed before flood flow on the East Fork South Tongue River alignment was beheaded and reversed. If correctly interpreted south oriented flood flow continued to the reach the southeast oriented flood flow channel on the Shell Creek alignment after flood flow on the Edelman Creek alignment had been reversed. This raises the question of when was flood flow on the Shell Creek alignment beheaded and reversed? The reversal of flood flow on the Shell Creek alignment probably occurred when the west-southwest oriented Shell Creek valley eroded headward from a deep south-oriented flood flow channel eroding headward into the Bighorn Basin. Erosion of Shell Creek Canyon required large volumes of water, which means the reversal of flood flow on the Shell Creek alignment occurred when floodwaters were still flowing across the Tongue River-Shell Creek drainage divide. Again these concepts are difficult to understand in the context of present day topography, but the topography at that time looked very different from how it looks today and was rapidly changing as floodwaters flowed across the region.

North Tongue River-Shell Creek drainage divide area

Figure 7: North Tongue River-Shell Creek drainage divide area. United States Geological Survey map digitally presented using National Geographic Society TOPO software.

Figure 7 provides a topographic map of the North Tongue River-Shell Creek drainage divide area west and north of figure 5 and includes an overlap area with figure 5. The dashed county line is the Tongue River-Shell Creek drainage divide and extends from near the northwest corner of figure 7 to the south edge of figure 7 (east half). The North Tongue River originates in the northwest quadrant of figure 7 and flows in an east-southeast and northeast direction to the north edge of figure 7 (east half). Some north oriented North Tongue River tributaries seen in figure 7 include Wallrock Creek, Trail Creek, Hidden Tepee Creek, Spring Creek, and Bull Creek (Trail Creek is seen again in figure 8). The West Fork South Tongue River flows in a north-northeast direction across the southeast corner of figure 7 and joins the East Fork east of figure 7 to form the north oriented South Tongue River, which flows in a north direction near the east edge of the northeast quadrant of figure 7 and which north of figure 7 joins the North Tongue River to form the Tongue River. Shell Creek flows in a northwest, west, and southwest direction south of figure 7 and south oriented streams flowing to the south edge of figure 7 are Shell Creek tributaries. The unlabeled south oriented Shell Creek tributary with a labeled East and West Fork is Horse Creek, which is seen in figure 8. The north oriented North Tongue River tributary valleys are linked by shallow through valleys with the valleys of the south oriented Shell Creek tributaries. The map contour interval for figure 7 is 20 meters and some of the through valleys are defined by four or more contour lines on a side. The multiple through valleys are evidence of multiple south oriented flood flow channels that once crossed the region and suggests the region was crossed by a large-scale south oriented anastomosing channel complex. Floodwaters were probably flowing initially to a southeast oriented flood flow channel eroding headward along the present day northwest oriented Shell Creek alignment, although the direction of flood flow on the Shell Creek alignment was probably reversed before the south oriented flood flow ended. Headward erosion of northeast and east-southeast oriented North Tongue River valley captured the south oriented flood flow channels in sequence from east to west and beheaded the flood flow channels to the Shell Creek flood flow channel and created the Tongue River-Shell Creek drainage divide seen in figure 7.

Detailed map of Trail Creek-Horse Creek drainage divide area

Figure 8: Detailed map of Trail Creek-Horse 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 Trail Creek-Horse Creek drainage divide area seen in less detail in figure 7. The dashed county line is the Tongue River-Shell Creek drainage divide and extends from near the northwest corner of figure 8 to and across the southeast corner of figure 8. Trail Creek flows in an east-southeast direction in section 29 and then turns to flow in a north-northeast direction in section 28 to the north edge of figure 8 (east half). North of figure 8 Trail Creek flows to the North Tongue River with water flowing to the east side of the Bighorn Mountains. Horse Creek originates in section 33 and flows in a southwest and south direction to the south center edge of figure 8. The West Fork Horse Creek originates near the south edge of section 30 and flows in a south-southeast direction to the south edge of figure 8 (in section PB 41) and joins Horse Creek south of figure 8. South of figure 8 Horse Creek flows to Shell Creek with water flowing to the west side of the Bighorn Mountains. In the southeast corner of section 29 and the northeast corner of section 32 a through valley links the north-northeast oriented Trail Creek valley with a south oriented tributary valley draining to the south-southeast oriented West Fork Horse Creek valley. The map contour interval for figure 8 is 40 feet and the through valley floor elevation is between 9440 and 9480 feet. Elevations along the drainage divide to the northwest rise to more than 10,000 feet near the northwest corner of figure 8. Elevations along the drainage divide in section 3 rise to 9697 feet, although if the drainage divide is followed far enough to the east of figure 8 elevations greater than 10,000 feet can be found. Depending on which elevations are used the Trail Creek-Horse Creek through valley could be considered to be anywhere from 200 to 500 feet deep. In the context of the deeper depth the through valley could be considered to be a deeper channel eroded into the floor of what was once a broad north to south oriented valley eroded across the region. The broader north to south oriented valley would have been eroded into an erosion surface at least as high, if not higher, than some of the highest elevations in the Bighorn Mountains today and the region surrounding the Bighorn Mountains would have been just as high. Obviously since that time the Bighorn Mountains have been uplifted and there has been deep erosion of the region surrounding the Bighorn Mountains. The deep erosion was probably primarily done by the massive melt water floods as they first moved in a south direction across the region and later as the floodwaters were captured and diverted in north and northeast directions to the space in the deep “hole” being opened up by the ice sheet melting.

Little Bighorn River-North Tongue River drainage divide area

Figure 9: Little Bighorn River-Tongue River drainage divide area. United States Geological Survey map digitally presented using National Geographic Society TOPO software.

Figure 9 illustrates the Little Bighorn River-North Tongue River drainage divide area north of figure 7 and includes an overlap area with figure 7. Burgess Junction is a labeled highway intersection along the south edge of the southeast quadrant of figure 9. The North Tongue River flows in a north-northeast direction from the south edge of figure 9 (just west of Burgess Junction) to join northeast and southeast oriented Fool Creek and its south oriented Camp Creek tributary and then to turn in a southeast direction to join the north oriented South Tongue River and then to flow to the east edge of figure 9 (south half). The South Tongue River flows in a north direction from the south edge of figure 9 (east of Burgess Junction) to join the southeast oriented North Tongue River and to form the Tongue River, which then flows to the east edge of figure 9. The Little Bighorn River flows in a north-northeast direction across the northwest corner of figure 9. The northwest oriented stream originating near where Camp Creek joins Fool Creek at the Fool Creek elbow of capture is the Dry Fork Little Bighorn River and flows to the north edge of figure 9 (west of center) and joins the Little Bighorn River north of figure 9. Note how the northwest oriented Dry Fork Little Bighorn River flows on almost the same alignment as southeast oriented Fool Creek and North Tongue River segments to the southeast and how the drainage routes flowing today in opposite directions are linked by a through valley. The map contour interval for figure 9 is 20 meters and the through valley elevation at the drainage divide is 2280 meters. Elevations north of the through valley rise to more 2600 meters while elevations at Twin Buttes to the south of the through valley rise to at least 2500 meters. These elevations suggest the through valley is at least 220 meters deep. The through valley is evidence of a southeast oriented flood flow channel on the alignment of the present day northwest oriented Dry Fork Little Bighorn River valley. The southeast oriented flood flow was probably moving to what was at that time the actively eroding east oriented Tongue River valley and was coming from north and west of the present day Bighorn Mountains. If so, at that time the Bighorn Mountains did not stand high above regions to the north and west as they do today. Probably the east oriented Tongue River valley on the Bighorn Mountains upland surface had eroded headward from a south oriented flood flow channel that had eroded headward into the Powder River basin. Headward erosion of the deep Yellowstone River valley and its north-northeast oriented tributary Tongue River valley north and east of figure 9 beheaded south oriented flood flow channels east of the emerging Bighorn Mountains and captured the east oriented Tongue River flood flow moving from the emerging Bighorn Mountains. Subsequently headward erosion of the northeast oriented Yellowstone River valley beheaded and reversed flood flow to create the north-northeast oriented Little Bighorn River drainage route, which beheaded and reversed flood flow on the Dry Fork Little Bighorn River alignment.

Detailed map of Dry Fork Little Bighorn River-North Tongue River drainage divide area

Figure 10: Detailed map of Dry Fork Little Bighorn River-North Tongue River 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 Dry Fork Little Bighorn River-North Tongue River drainage divide area seen in less detail in figure 9. The North Tongue River flows in a north-northeast and southeast direction from the south edge of figure 10 (east half) to the southeast corner of figure 10. Fool Creek flows in an east-northeast, east, and southeast direction from near the southwest corner of figure 10 to join the southeast oriented North Tongue River at the elbow of capture (in section 17 where the North Tongue River turns to flow in a southeast direction). Camp Creek is a south-southwest and south-southeast oriented Fool Creek tributary flowing through section 7 to join southeast oriented Fool Creek near the east edge of section 18. The Dry Fork (Little Bighorn River) originates in the southwest quadrant of section 7 and flows in a northwest direction to the northwest corner of figure 10. North and west of figure 10 Dry Fork joins the north-northeast oriented Little Bighorn River. The northwest oriented Dry Fork valley alignment and the southeast oriented North Tongue River valley alignment appear to be structurally controlled and to follow the strike of dipping strata, however the valleys are water-eroded valleys. A through valley near the south center edge of section 7 links the northwest oriented Dry Fork valley with the southeast oriented Camp Creek and southeast oriented Fool Creek and North Tongue River valleys. The map contour interval for figure 10 is 40 feet and the through valley floor elevation at the Dry Fork-Camp Creek drainage divide is shown as being 7480 feet. Elevations north of the through valley rise and reach 8548 feet just north of figure 10. Elevations south of the through valley also rise to 8235 feet at Twin Buttes just south of figure 10. These elevations suggest the through valley is at least 650 feet deep. The through valley is also a water-eroded valley and was eroded by southeast oriented flood flow moving from the present day northwest oriented Dry Fork alignment to the southeast oriented North Tongue River valley, which was probably being actively eroded headward into the what was then an emerging Bighorn Mountains mass. Subsequently headward erosion of the deep north-northeast oriented Little Bighorn River valley north of west of figure 10 beheaded the southeast oriented flood flow channel. Floodwaters on the northwest end of the beheaded flood flow channel reversed flow direction to create the northwest oriented Dry Fork drainage route. Enough floodwaters may have been flowing across the Bighorn Mountains west of figure 10 that the reversed flood flow on the Dry Fork alignment may have been able to capture significant volumes of floodwaters moving in an east direction from the west, which would explain the  deep northwest oriented Dry Fork valley.

Additional information and sources of maps studied

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

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