Abstract:

This essay uses topographic map evidence to interpret landform origins in the region between the Clarks Fork Yellowstone River and the Shoshone River in the Wyoming Beartooth and Absaroka Mountains. Clarks Fork Yellowstone River flows in a southeast direction almost to east edge of the Beartooth Mountains before it is joined by northeast oriented Sunlight Creek and north-northeast, east-northeast, and north oriented Dead Indian Creek and then turns to flow in a northeast and north-northeast direction to join the Yellowstone River. Sunlight Creek and Dead Indian Creek originate in the Absaroka Range on the north side of a high drainage divide with south and southeast oriented tributaries to the east oriented North Shoshone River, which flows to the northeast oriented Shoshone River, which in turn flows to the north-northeast oriented Bighorn River, which is another Yellowstone River tributary. East of the Absaroka Range a deep north-to-south oriented through valley links the north-northeast oriented Clarks Fork valley with a south-southeast oriented Shoshone River tributary valley and is interpreted to have been eroded by south-southeast oriented flood flow. 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 Big Horn Basin. High mountain passes or notches in the Absaroka Range link north oriented Clarks Fork tributary valleys with south oriented Shoshone River tributary valleys. These passes or notches are interpreted to have been eroded by earlier south oriented flood flow channels at a time when the Absaroka Range had not yet emerged as a high mountain range, although several passes or notches have since been altered by Absaroka Range glaciation and different interpretations are possible. Absaroka Range uplift is interpreted to have occurred as floodwaters flowed across the region and was probably related to the thick ice sheet presence north and east of the study region. Massive flood flow reversals in the Big Horn Basin are interpreted to have occurred when headward erosion of the deep northeast oriented Yellowstone River valley from space in the deep “hole” the melting ice sheet had occupied and that was being opened up by the ice sheet melting captured the south and southeast oriented ice marginal melt water floods. Floodwaters on north ends of the beheaded flood flow channels reversed flow direction to create north oriented Yellowstone River tributaries and captured southeast oriented flood flow channels from west of the actively eroding Yellowstone River valley head to create elbows of capture such as the Clarks Fork elbow of capture.

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 Clarks Fork Yellowstone River-Shoshone River drainage divide area landform origins in the Wyoming Beartooth and Absaroka 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 Clarks Fork Yellowstone River-Shoshone River drainage divide area landform evidence in the Wyoming Beartooth and Absaroka Mountains will be regarded as evidence supporting the “thick ice sheet that melted fast” paradigm.

Clarks Fork Yellowstone River-Shoshone River drainage divide area location map

Figure 1: Clarks Fork Yellowstone River-Shoshone River drainage divide area location map (select and click on maps to enlarge). National Geographic Society map digitally presented using National Geographic Society TOPO software.

Figure 1 provides a location map for the Clarks Fork Yellowstone River-Shoshone River drainage divide area in the Wyoming Beartooth and Absaroka Mountains. The Montana-Wyoming state line extends in a west-to-east direction across figure 1 and Yellowstone National Park is located in the northwest corner of Wyoming. The Yellowstone River flows from Yellowstone Lake in a northwest, northeast, north, northwest, north-northeast, and east-northeast to Big Timber, Montana. From Big Timber the Yellowstone River flows in an east-southeast and northeast direction to the north edge of figure 1 (near Huntley). North and east of figure 1 the Yellowstone River flows in a northeast direction to eventually join the Missouri River. Clarks Fork Yellowstone River originates near Cooke City, Montana (near northeast corner of Yellowstone National Park) and flows in a southeast, northeast, and north-northeast direction to join the Yellowstone River near Laurel, Montana. Sunlight Creek is a northeast oriented tributary joining Clarks Fork Yellowstone River near the elbow of capture where Clarks Fork turns to flow in a northeast and north-northeast direction. The North Fork Shoshone River originates east of Yellowstone Lake and Sylvan Pass and flows in an east direction to Buffalo Bill Reservoir where it is joined by the northeast oriented South Fork Shoshone River to form the northeast oriented Shoshone River, which then flows to the north and north-northeast oriented Bighorn River, which joins the Yellowstone River north and east of figure 1. The Beartooth Mountains are not labeled in figure 1, but straddle the Montana-Wyoming state line between Cooke City and Red Lodge, Montana. The Absaroka Range is a high labeled mountain range located west of the highway from Cody, Wyoming to Belfry, Montana. The highway is located in a deep north-to-south oriented through valley linking the north oriented Clarks Fork Yellowstone River valley with the northeast oriented Shoshone River valley. Otherwise the Clarks Fork Yellowstone River-Shoshone River drainage divide is in a region of high mountains. The Clarks Fork Yellowstone River-Shoshone River drainage divide area investigated in this essay is located east of Yellowstone National Park, south of Sunlight Creek, north of the North Fork Shoshone River, and west of the highway from Cody, Wyoming to Belfry, Montana.

Today the region in figure 1 is dominated by north oriented drainage systems, however most north and northwest oriented drainage routes originated as south and southeast oriented flood flow channels, which were subsequently reversed to produce north oriented drainage systems. The south and southeast oriented floodwaters were derived from the western margin of a thick North American ice sheet and were flowing from western Canada to and across the region seen in figure 1. Deep glacial erosion under the thick ice sheet and ice sheet related crustal warping along ice sheet margins and elsewhere created a deep “hole” in which the ice sheet was located. The region seen in figure 1 is located on the deeply eroded deep “hole” southwest rim. The southwest rim evolved as immense melt water floods flowed along and across it, which means initially the high mountains and deep valleys did not exist and floodwaters were free to flow in south and southeast directions across figure 1 including across regions where high mountains exist today. The southeast oriented Clarks Fork headwaters valley was eroded by southeast oriented flood flow moving to south oriented flood flow channels in Wyoming’s Bighorn Basin. A massive reversal of flood flow occurred when ice sheet melting began to open up space in the south end of the deep “hole” in which the ice sheet was located and the northeast and east oriented Yellowstone River valley eroded headward from that space (which initially drained in a south direction east of figure 1). Headward erosion of the deep Yellowstone River valley was across south and southeast oriented flood flow channels and captured the flood flow channels in sequence from east to west and diverted floodwaters into the deep “hole”. Floodwaters on north and northwest ends of beheaded flood flow channels reversed flow direction to create north oriented drainage routes (now north oriented Yellowstone River tributaries). Because the Yellowstone River valley headward erosion beheaded flood flow channels in sequence from east to west newly reversed flood flow channels were able to capture south and southeast oriented flood flow from flood flow channels west of the actively eroding Yellowstone River valley head. A southeast oriented flood flow channel on the Clarks Fork headwaters alignment was captured by reversed flow in what had been a south oriented flood flow channel east of the Absaroka Range and Beartooth Mountains and west of the Pryor Mountains, which formed the elbow of capture where the Clarks Fork today turns from flowing in a southeast direction to flowing in a northeast direction. The North Fork Shoshone River captured southeast oriented flood flow, which had been moving across the northeast corner of Yellowstone National Park before the Yellowstone River valley headward beheaded and reversed that flood flow.

Detailed location map for Clarks Fork Yellowstone River-Shoshone River drainage divide area

Figure 2: Detailed location map Clarks Fork Yellowstone River-Shoshone River 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 Clarks Fork Yellowstone River-Shoshone River drainage divide area in the Wyoming Beartooth and Absaroka Mountains. The Montana-Wyoming state line follows the north edge of figure 2. Red-brown colored areas along the west edge of figure 2 represent regions in Yellowstone National Park. The Yellowstone National Park boundary is for much of the distance shown located along a high crest ridge of the Absaroka Range, which forms the drainage divide between the north and northwest oriented Yellowstone River drainage basin to west and Clarks Fork Yellowstone River and Shoshone River drainage basins to the east. The Beartooth Mountains are located east of Yellowstone National Park and the Absaroka Range near the north edge of figure 2. Clarks Fork Yellowstone River originates a short distance north of figure 2 and in figure 2 flows in a southeast direction from the north edge (near highway 212) and then in a southeast, east, and southeast direction (near highway 296) before turning to flow in a northeast and north-northeast direction to the north edge of figure 2 (near highway 120). Sunlight Creek flows in a northeast direction to join Clarks Fork Yellowstone River near the elbow of capture where Clarks Fork turns from flowing in a southeast direction to flowing in a northeast direction. Gravelbar Creek is a north-northeast oriented Sunlight Creek tributary and Dead Indian Creek is a north-northeast, east-northeast, and north oriented stream also joining Clarks Fork near the elbow of capture near where Sunlight Creek joins Clarks Fork. The North Fork Shoshone River originates near Sunlight Peak (near the Sunliight Creek headwaters) and flows in a southwest and south direction to Pahaska (in the southwest quadrant of figure 2) and then in an east-southeast and east direction to Buffalo Bill Reservoir where it is joined by the northeast oriented South Fork Shoshone River to form the northeast oriented Shoshone River, which flows to the east center edge of figure 2. North Fork Shoshone River tributaries include south-southeast oriented Sweetwater Creek and Big Creek, east-southeast and south-southeast oriented Trout Creek, and southeast oriented Rattlesnake Creek. While not determinable from figure 2 the drainage divide between north oriented Sunlight and Dead Indian Creeks and the south oriented North Fork Shoshone River tributaries is generally located in high mountains and forms what is today a major topographic barrier. Highway 120 north of Cody, Wyoming is located in a deep north-to-south oriented through valley and the higher elevation north and northwest oriented Yellowstone River valley in Yellowstone National Park west of figure 2  mark the east and west boundaries of this high topographic barrier.

Sulphur Creek-Sweetwater Creek drainage divide area

Figure 3: Sulphur Creek-Sweetwater 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 Sulphur Creek-Sweetwater Creek drainage divide area. Sunlight Creek flows from near the northwest corner of figure 3 in a southeast, east, east-southeast, and northeast direction to the north edge of figure 3 (east half) and north of figure 3 joins southeast oriented Clarks Fork Yellowstone River, which then flows in a northeast and north-northeast direction to join the Yellowstone River. Dead Indian Peak is located in the east center area of figure 3 and Sunlight Peak is the high mountain located west of the center of figure 3. The northeast oriented Sunlight Creek tributary originating on the northeast side of Sunlight Peak is Sulphur Creek. The southwest and west-oriented stream located west of Sunlight Peak and flowing to the west center edge of figure 3 is the North Fork Shoshone River, which west of figure 3 turns to flow in a southwest and then south direction before turning to flow in a southeast and east direction south of figure 3. The southwest oriented stream flowing to near the southwest corner of figure 3 is Grinnell Creek, which joins the southeast oriented North Fork Shoshone River south and west of figure 3. Sweetwater Creek originates on the southeast side of Sunlight Peak and flows in a south-southeast direction to the south edge of figure 3 (east of center) and south of figure 3 joins the east oriented North Fork Shoshone River. Turret Creek is a south-southeast and south oriented Sweetwater Creek tributary. Today a high mountain ridge forms the Sunlight Creek-North Fork Shoshone River drainage divide between Sunlight Peak and Dead Indian Peak and forms what appears to be an insurmountable topographic barrier. However, a close look at the ridge top reveals notches, gaps, or passes linking north oriented Sunlight Creek tributary valleys with south oriented North Fork Shoshone River tributary valleys. The map contour interval for figure 3 is 50 meters and some of these notches, gaps, or passes are defined by 4 or more contour lines on a side suggesting they are at least 150 meters deep. For example between Sunlight Peak and Mount Pleasant (east of Sunlight Peak) a north-to-south oriented gap, notch, or pass links the north-northeast oriented Sulphur Creek valley with the south-southeast oriented Sweetwater Creek valley. The pass elevation is between 3150 and 3200 meters. Mount Pleasant to the east rises to 3403 meters and Sunlight Peak to the west rises to 3634 meters suggesting the pass may be as much as 200 meters deep. While almost insignificant compared to the depths of the adjacent valleys the pass is evidence of a former valley, which had been eroded into a surface as high, if not higher, than highest elevations in figure 3 today (although the Absaroka Range has probably been uplifted and eroded significantly since that valley was formed). The north-to-south oriented valley was probably eroded as a south or south-southeast oriented flood flow channel prior to headward erosion of much deeper flood flow channels both east and west of figure 3 and also prior to headward erosion of the deep Sunlight Creek and Sulphur Creek valleys to the north.

Detailed map of Sulphur Creek-Sweetwater Creek drainage divide area

Figure 4: Detailed map of Sulphur Creek-Sweetwater 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 Sulphur Creek-Sweetwater Creek drainage divide area seen in less detail in figure 3. Sulphur Creek flows from the northeast corner of section 33 in a south, east-southeast, and northeast direction to the north edge of figure 4 (east half) and joins Sunlight Creek north of figure 4. Valley glaciers have altered landforms seen in figure 4 and small ice fields still remain. While the glacial landforms are interesting the valley glaciers formed in preexisting valleys and the primary concern of this essay is with the origin of those preexisting valleys. Sweetwater Creek originates in section 5 (near the west edge of the southwest quadrant of figure 4) and flows in an east and southeast direction to the south center edge of figure 4. Note the south oriented Sweetwater Creek tributary in section 3. The Sulphur Creek-Sweetwater Creek drainage divide for much of its distance is an arête with glacially carved cirques and valley walls on both sides. Study of the arête top reveals various notches or gaps such as the notch or gap north of the south oriented Sweetwater Creek tributary in section 3. The map contour interval for figure 4 is 40 feet and the notch elevation at the drainage divide is between 10,400 and 10,440 feet. Sunlight Peak to the west rises to 11,922 feet and an unnamed peak in the southeast corner of section 26 (in the northeast quadrant of figure 4) rises to 11,524 feet. These elevations suggest the notch may be as much as 1180 feet deep. The adjacent valleys are much deeper and it is difficult to determine how much, if any, of the notch’s depth is due to glacial erosion. However, assuming the notch is not the result of glacial erosion then it was eroded by a south oriented flood flow channel carved into a surface as high, if not higher, than the Sulphur Creek-Sweetwater Creek drainage divide today. At that time there was no deep Sulphur Creek valley north of the drainage divide nor was there a deep Sunlight Creek valley north of figure 4. Probably at that time the Absaroka Range was just beginning to emerge as a mountain range and south and southeast oriented floodwaters could flow across what is today a high mountain range. The glaciation occurred after flood flow across the region had ended and probably after the Absaroka Range had emerged as a high mountain range.

Gravelbar Creek-Big Creek drainage divide area

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

Figure 5 illustrates the Gravelbar Creek-Big Creek drainage divide area east of figure 3 and includes a significant overlap area with figure 3. Dead Indian Peak is located near the center of figure 5. Sunlight Creek flows in an east-southeast and northeast direction from the west edge of figure 5 (near northwest corner) to the north edge of figure 5 (west of center) and north of figure 5 joins southeast oriented Clarks Fork at the point where the Clarks Fork turns to flow in a northeast direction. Sulphur Creek is a south and north-northeast oriented tributary joining Sunlight Creek near where Sunlight Creek turns to flow in a northeast direction. Jaguar Creek is the named north oriented Sunlight Creek tributary east of Suphur Creek. Gravelbar Creek originates on the west side of Dead Indian Peak and flows in a north-northwest, north-northeast, and north direction to the north center edge of figure 5 and joins Sunlight Creek north of figure 5. Dead Indian Creek originates on the east side of Dead Indian Peak and flows in a north-northeast and east-northeast direction to the east edge of figure 5 (near northeast corner) and north and east of figure 5 turns to flow in a north direction to join Clarks Fork near where Sunlight Creek joins Clarks Fork. Big Creek originates on the south side of Dead Indian Peak and flows in a south and south-southeast direction to the south edge of figure 5 (east of center) and south of figure 5 joins the east oriented North Fork Shoshone River. Again, the Clarks Fork-North Fork Shoshone River drainage divide forms a high mountain ridge, which today is a massive topographic barrier. However, a close at the ridge top reveals notches or passes linking north oriented valleys with south oriented valleys. For example just east of Dead Indian Peak a north-to-south oriented pass or notch links the north oriented Dead Indian Creek headwaters valley with the a south oriented Big Creek tributary valley. The map contour interval for figure 5 is 50 meters and the pass elevation is between 3350 and 3400 meters. Dead Indian Peak rises to 3723 meters and the unnamed peak to the east rises to more than 3700 meters suggesting the pass is as much as 300 meters deep. A similar northwest-to-southeast oriented pass or notch just west of Dead Indian Peak links the northwest oriented Gravelbar Creek headwaters valley with the southeast oriented Big Creek headwaters valley. These passes are probably remnants of south and southeast oriented flood flow channels that were eroded into a surface equivalent if elevation, if not higher, to the highest elevations seen in figure 5 today. Since that time the Absaroka Range has emerged as a high mountain range and has been glaciated further altering the region.

Detailed map of Gravelbar Creek-Big Creek drainage divide area

Figure 6: Detailed map of Gravelbar Creek-Big 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 Gravelbar Creek-Big Creek drainage divide area seen in less detail in figure 5. Dead Indian Peak is located in the northeast quadrant of section 3 (near center of figure 6). Gravelbar Creek flows in a northwest and north-northwest direction from the west side of Dead Indian Peak to the north edge of figure 6 (west of center). Dead Indian Creek originates in the north half of section 2 east of Dead Indian Peak and flows in a north-northeast direction across section 15 to the north edge of figure 6 (east half). Big Creek originates in the south half of section 3 (south of Dead Indian Peak) and flows in a south, east, and south-southeast direction to the south edge of figure 6 (east half). A south oriented Big Creek tributary originates in the southeast quadrant of section 2 (south of the Dead Indian Creek headwaters) and joins Big Creek south of figure 6. Dead Indian Peak appears to be a horn with cirques at the heads of the surrounding valleys. While there is good evidence of glacial erosion in those surrounding valleys the valleys existed before the glaciers formed. The concern in this essay is with how the valleys were originally formed and not with the glacial history, which occurred at a later time. The drainage divide in section 2 separating the north oriented Dead Indian Creek valley from the south oriented Big Creek tributary valley is an arête, but also shows an impressive notch linking the two opposing valleys. The map contour interval for figure 6 is 40 feet and the notch floor elevation is between 10,960 and 11,000 feet. Dead Indian Peak reaches an elevation of 12,216 feet and the unnamed peak in section 1 to the east rises to more than 12,200 feet suggesting the notch is approximately 1200 feet deep. While it is difficult to determine how much of the notch depth is due to glacial erosion and how much of the depth reflects a former flood flow channel, the notch is evidence of a south oriented flood flow channel that was carved into a surface equivalent in elevation, if not higher, to the highest points seen in figure 6 today. A similar, but somewhat higher elevation notch in the northwest quadrant of section 3 links the north-northwest oriented Gravelbar Creek valley with the south-southeast oriented Big Creek valley and is also probably evidence of former south-southeast oriented flood flow channel. At the time floodwaters flowed across the region the Absaroka Range had not emerged as a high mountain range and deep valleys north and west of figure 6 had yet to be eroded so floodwaters were able to flow across the region.

Dead Indian Creek-Rattlesnake Creek drainage divide area

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

Figure 7 illustrates the Dead Indian Creek-Rattlesnake Creek drainage divide area north and east of figure 5 and includes an overlap area with figure 5. Trout Peak is a high point in the southwest quadrant of figure 7 and Pat O’Hara Mountain is the high mountain in the east half of figure 7. Dead Indian Creek flows in an east-northeast and north direction from the west center edge of figure 7 to the north edge of figure 7 (west of center) and joins Clarks Fork north of figure 7. Rattlesnake Creek originates near the west end of Pat O’Hara Mountain and flows in a southwest direction along the Palisades, which are located on the southwest side of Rattlesnake Mountain. South and east of figure 7 Rattlesnake Creek flows to the east oriented North Fork Shoshone River (at Buffalo Bill Reservoir). Note the pass near the center of figure 7 linking the southeast oriented Rattlesnake Creek valley with a north oriented Dead Indian Creek tributary valley. The map contour interval for figure 7 is 50 meters and the pass elevation is between 2650 and 2700 meters. Pat O’Hara Mountain to the east rises to 3038 meters and Trout Peak to the southwest rises to more than 3700 meters suggesting the pass is at least 330 meters deep. Unlike regions further to the west the drainage divide in this region does not appear to have been altered by glacial erosion. The pass is a remnant of south or southeast oriented flood flow channel that moved floodwaters from the Clarks Fork drainage basin to what to what at that time were south oriented flood flow channels in the present day north oriented Big Horn Basin to the southeast of figure 7. Headward erosion of a much deeper Clarks Fork valley north of figure 7 beheaded the south oriented flood flow channel. Floodwaters on the north end of the beheaded flood flow channel then reversed flow direction to create the north oriented Dead Indian Creek drainage route and the east-northeast oriented Dead Indian Creek valley segment eroded headward to capture south and southeast oriented flood flow channels further to the west. This captured flood flow enabled flood flow on the Dead Indian Creek alignment to erode the deep valley seen in figure 7 today. This interpretation requires the region north and west of figure 7 to have been as high or higher than the Dead Indian Creek-North Fork Shoshone River drainage divide, although the entire region has probably been uplifted since.

Detailed map of Dead Indian Creek–Rattlesnake Creek drainage divide area

Figure 8: Detailed map of Dead Indian Creek-Rattlesnake 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 Dead Indian Creek-Rattlesnake Creek drainage divide seen in less detail in figure 7. Pat O’Hara Mountain is located near the northeast corner of figure 8 with the highest elevation being located just east of figure 8. Dead Indian Creek flows in an east-northeast direction across the northwest corner of figure 8 and north of the north center edge of figure 8 turns to flow in a north direction to join Clarks Fork near the elbow of capture where Clarks Forks turns from flowing in a southeast direction to flowing in a northeast direction. Rattlesnake Creek originates in section 20 and flows in a south-southeast direction to the south edge of figure 8 (east half) and south of figure 8 joins the east oriented North Fork Shoshone River at Buffalo Bill Reservoir. Note in section 20 a pass linking a north and north-northwest oriented Dead Indian Creek tributary valley (draining to the north center edge of figure 8) with the south-southeast oriented Rattlesnake Creek valley. The map contour interval for figure 8 is 40 feet and the pass floor elevation is between 8880 and 8920 feet. Pat O’Hara Mountain just east of figure 8 rises to 9971 feet and elevations along the drainage divide just west of figure 8 rise to more than 11,000 feet. These elevations suggest the pass could be more than 1000 feet deep. This pass is definitely a water-eroded valley and was eroded by south-southeast oriented flood flow moving from the southeast oriented Clarks Fork valley and what is today the northeast oriented Clarks Fork valley segment to south oriented flood flow channels in the present day north oriented Big Horn Basin east of figure 8. Headward erosion of the deep northeast oriented Yellowstone River valley in Montana from space in the deep “hole” the melting ice sheet had occupied beheaded south oriented flood flow channels in the Big Horn Basin. Floodwaters on north ends of the beheaded flood flow channels reversed flow direction to create the north oriented Big Horn River drainage route and subsequently the northeast and north-northeast Clarks Fork drainage route, which captured a southeast oriented flow channel on the Clarks Fork headwaters alignment to create the Clarks Fork elbow of capture. Headward erosion of the much deeper Yellowstone River valley knick point along the newly formed Clarks Fork drainage route beheaded the south oriented flood flow channel on the present day north oriented Dead Indian Creek alignment. Floodwaters on the north end of that beheaded flood flow channel reversed flow direction to create the north oriented Dead Indian Creek tributary drainage route and to create the Dead Indian Creek-Rattlesnake Creek drainage divide seen in figure 8.

Skull Creek-Cottonwood Creek drainage divide area

Figure 9: Skull Creek-Cottonwood Creek drainage divide. United States Geological Survey map digitally presented using National Geographic Society TOPO software.

Figure 9 illustrates the Skull Creek-Cottonwood Creek drainage divide area and is located east of figure 7 and includes overlap areas with figure 7. Pat O’Hara Mountain straddles the west center edge of figure 9. Rattlesnake Creek can just barely be seen flowing in a southeast direction across the southwest corner of figure 9. Rattlesnake Mountain extends in a northwest-to-southeast direction across the southwest corner of figure 9 and is north and east of Rattlesnake Creek. Pat O’Hara Creek flows in a northeast direction from Rattlesnake Mountain and then turns to flow in east direction along the Pat O’Hara Mountain south flank before turning to flow in a north and northwest direction around the Pat O’Hara Mountain east end and then turning to flow in northeast direction to the north edge of figure 9 (west of center). North of figure 9 Pat O’Hara Creek flows in a north and north-northeast direction to join north-northeast oriented Clarks Fork. Skull Creek originates near the east end of Pat O’Hara Mountain (just south of Pat O’Hara Creek) and flows in a south, east, northeast, and north-northwest direction to the north center edge of figure 9 and joins Pat O’Hara Creek north of figure 9. Cottonwood Creek originates east of Goff Lake and flows in an east direction before turning to flow in a south-southeast direction (along the highway) to the south edge of figure 9 (east half) and joins the northeast oriented Shoshone River south of figure 9. Note how the highway is located in a through valley linking the north-northwest oriented Skull Creek valley with the south-southeast oriented Cottonwood Creek valley. The map contour interval for figure 9 is 50 meters and the through valley elevation where the highway crosses the drainage divide is between 1800 and 1850 meters significantly lower than elevations along the Clarks Fork-Shoshone River drainage divide further to the west. Pat O’Hara Mountain to the west rises to 2835 meters in figure 9 (and higher further west) and Heart Mountain to the east rises to 2476 meters suggesting the through valley is at least 600 meters deep. Using Absaroka Range elevations west of figure 9 and Bighorn Mountains elevation on the east side of the Big Horn Basin (east of figure 9) a case could be made that the through valley is more than 1200 meters deep. Whatever its depth the through valley is deep and to some extent is a water-eroded valley. The through valley at the end of flood flow was eroded by south oriented flood flow moving to the newly eroded northeast oriented Shoshone River valley, which had eroded headward from a newly beheaded and reversed flood flow channel on the Bighorn River alignment. Prior to the reversal of flood flow on the Bighorn River alignment floodwaters in the through valley moved to a south oriented flood flow channel on the present day north oriented Bighorn River alignment. Flood flow in the through valley ended when Yellowstone River valley headward erosion progressed to a location where it beheaded and reversed the south oriented flood flow channel to create the northeast and north-northeast oriented Clarks Fork drainage route.

Detailed map of Skull Creek-Cottonwood Creek drainage divide area

Figure 10: Detailed map of Skull Creek-Cottonwood 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 Skull Creek-Cottonwood Creek drainage divide area seen in less detail in figure 9. Skull Creek flows in an east and northeast direction from the west center edge of figure 10 to the north center edge of figure 10 and north of figure 10 flows in a north-northwest direction to north oriented Pat O’Hara Creek, which in turn flows to north-northeast oriented Clarks Fork.  Cottonwood Creek originates in section 25 (east of Goff Lake) and flows in an east and southeast direction to the southeast corner of figure 10. South and east of figure 10 Cottonwood Creek joins the northeast oriented Shoshone River. The highway in the east half of figure 10 is located in a through valley linking the north-northwest oriented Skull Creek valley (north of figure 10) with the southeast oriented Cottonwood Creek valley in the southeast corner of figure 10. The map contour interval for figure 10 is 40 feet and the through valley floor elevation where the highway crosses the drainage divide is between 5920 and 5960 feet. Elevations in the northeast corner of figure 10 rise to 6873 feet and in the southwest corner of figure 10 rise to more than 7000 feet. Based on elevations seen in figure 10 the through valley is at least 1000 feet deep. As seen in figure 9 much higher elevations are found both east and west of figure 10 suggesting the through valley could be several thousand feet deep. The through valley as seen in figure 10 is a water-eroded valley and was eroded by south-southeast oriented flood flow prior to the reversal of flood flow in the present day north-northeast oriented Clarks Fork valley segment north of figure 10. Floodwaters just before that Clarks Fork flood flow reversal were moving to the newly eroded northeast oriented Shoshone River valley, which had eroded headward from what was then the newly beheaded and reversed flood flow channel on the present day north oriented Big Horn River alignment. Prior to headward erosion of the northeast oriented Shoshone River valley (and other Big Horn Basin northeast oriented valleys) the south-southeast oriented flood flow continued in south-southeast direction across the Big Horn Basin to a south oriented flood flow channel on the present day north oriented Big Horn River alignment.

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.