Big Hole River-Beaverhead River drainage divide area landform origins, south of Pioneer Mountains, Beaverhead County, Montana, USA

Authors


Abstract:

This essay uses topographic map evidence to interpret landform origins south of the Pioneer Mountains between the Big Hole River and Beaverhead River in Beaverhead County, Montana. The Big Hole River flows in a north direction along the Pioneer Mountains west flank and then makes a U-turn to flow in a southeast and south direction along the Pioneer Mountains north and east flanks before making another U-turn to flow in a northeast direction to join the north-northeast oriented Beaverhead River and to form the Jefferson River. South of the Pioneer Mountains and north and east of the Beaverhead Mountains and south and east of the north oriented Big Hole River headwaters are south and southeast oriented headwaters of Beaverhead River tributaries. Well-defined through valleys cross the Big Hole Divide and link the north oriented Big Hole River drainage basin with the valleys of the south and southeast oriented Beaverhead River tributaries. In addition both the north oriented Big Hole River and the north-northeast oriented Beaverhead River are joined by barbed tributaries, which originate as south oriented streams in the Pioneer Mountains. The through valleys and barbed tributaries provide evidence the entire region was once crossed by immense south and southeast oriented floods as the Pioneer Mountains were beginning to emerge. Floodwaters were derived from the west margin of a thick North American ice sheet located along the present day Canadian Rocky Mountain front. Crustal warping related to the thick ice sheet presence and deep flood water erosion of present day mountain core regions combined with deposition of flood transported debris in adjacent valleys and basins was responsible for the emergence of the present mountain ranges including the Pioneer and Beaverhead Mountains and the Big Hole Divide ridge. Emergence of the Pioneer Mountains, Beaverhead Mountains, and Big Hole Divide ridge combined with headward erosion of a deep southeast oriented flood flow channel along the Pioneer Mountains north flank resulted in the beheading and reversal of flood flow west of the Pioneer Mountains that created the present day north oriented Big Hole River drainage system in that region, which also created the Big Hole Divide.

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 Big Hole River-Beaverhead River drainage divide area landform origins south of the Pioneer Mountains in Beaverhead County, Montana 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 Big Hole River-Beaverhead River drainage divide area landform evidence south of the Pioneer Mountains in Beaverhead County, Montana will be regarded as evidence supporting the “thick ice sheet that melted fast” paradigm.

Big Hole River-Beaverhead River drainage divide area location map

Figure 1: Big Hole River-Beaverhead 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 Big Hole River-Beaverhead River drainage divide south of the Pioneer Mountains in Beaverhead County, Montana and illustrates in the east half a region in southwest Montana with Idaho west and south of Montana. The Pioneer Mountains are labeled and the Big Hole River flows in a north direction along the west side of the Pioneer Mountains then turns and flows in a south direction on the east side of the Pioneer Mountains before making another U-turn to flow in a northeast direction to join the north-northeast oriented Beaverhead River and to form the northeast and east oriented Jefferson River. The Beaverhead River is formed at an unlabeled reservoir south of the Pioneer Mountains where an east oriented tributary joins the north-northwest oriented Red Rock River. The Missouri River is formed near the town of Three Forks (located near northeast corner of figure 1) at the confluence of the Gallatin, Madison, and Jefferson River and flows in a north and north-northwest direction. North of figure 1 the Missouri River turns to flow in a northeast and then east direction to North Dakota where it turns to flow in a southeast and south direction with water eventually reaching the Gulf of Mexico. The Wise River is shown, but not labeled in figure 1 and flows in a north-northwest and north-northeast direction in the heart of the Pioneer Mountains to join the Big Hole River near the town of Wise River. The Beaverhead Mountains are located along the Montana-Idaho state line south and west of the Pioneer Mountains. The east-west continental divide follows the state line along the Beaverhead Mountains crest ridge. The Big Hole River-Beaverhead River drainage divide area investigated in this essay is located between the Beaverhead Mountains and the Pioneer Mountains and links the north oriented Big Hole River drainage system west of the Pioneer Mountains with south, southeast, and east oriented streams south of the Pioneer Mountains (not all are shown in figure 1), which flow to the north-northeast oriented Beaverhead River .

Before looking at detailed maps of the Big Hole River-Beaverhead River drainage divide area a brief look at the regional big picture erosion history will help in understanding the more detailed discussions below. Large volumes of south and southeast oriented floodwaters once flowed across the entire region shown by figure 1. Floodwaters were derived from the western margin of a rapidly 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. At that time the high mountain ranges and deep valleys and basins that exist today did not exist and floodwaters formed large anastomosing complexes of diverging and converging south oriented flood flow channels as they flowed freely across the region. The mountains ranges, river valleys, and basins emerged as crustal warping, which was related to the presence of a huge continental ice sheet north and east of figure 1 occurred. North oriented rivers in figure 1 are generally flowing in valleys that originated as south oriented flood flow channels. The north oriented drainage systems seen today formed during massive flood flow reversals that occurred as mountain ranges and high plateaus were being uplifted by ice sheet related crustal warping and as floodwaters flowed across the region. During these flood flow reversals south oriented flood flow along one route would be captured so as to flow in a north direction along an adjacent route. In addition, deep flood water erosion of valleys and probably deposition of flood transported debris in the basins surrounding the rising mountain ranges contributed to the emergence of present day mountain ranges.

The south oriented Big Hole River segment east of the Pioneer Mountains is one of the few river segments seen in figure 1 that is still flowing in a south direction. Before being captured by the massive flood flow reversal that took place in the figure 1 region the south oriented flood flow continued in a south direction to what is now the Snake River drainage basin in eastern Idaho. The north oriented Big Hole River segment west of the Pioneer Mountains and the north oriented Wise River in the Pioneer Mountains flow on the alignments of what began as south oriented flood flow channels, but which were reversed to create the north oriented Big Hole River valley west of the Pioneer Mountains and the north oriented Wise River valley in the Pioneer Mountains. Reversal of flood flow in the Big Hole River valley west of the Pioneer Mountains and in the Wise River valley in the Pioneer Mountains probably occurred when crustal uplift raised areas in the south relative to areas in the north and as a deep southeast oriented valley eroded headward from the south oriented flood flow channel east of what was then the emerging Pioneer Mountains. The northeast oriented Missouri River valley (north and east of figure 1) and its east and northeast oriented tributary valleys then eroded headward from a deep “hole” in which the decaying ice sheet was located. The north-northwest oriented Missouri River valley segment (seen in the figure 1) was eroded by reversals of flood flow on north and northwest ends of beheaded flood flow channels. Reversal of flood flow in the Jefferson/Beaverhead River valley captured south oriented flood flow on the present day south oriented Big Hole River alignment (east of the Pioneer Mountains), which created the present day Big Hole River U-turn east of the Pioneer Mountains. A similar massive flood flow reversal occurred south and west of the Beaverhead Mountains with the floodwaters being captured by headward erosion of deep valleys from the Pacific Ocean so as to create the present day east-west continental divide.

Detailed location map for Big Hole River-Beaverhead River drainage divide area

Figure 2: Detailed location map for Big Hole River-Beaverhead 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 Big Hole River-Beaverhead River drainage divide area south of the Pioneer Mountains in Beaverhead County, Montana and shows drainage routes not seen in figure 1. Green shaded areas are National Forest lands, which generally are located in mountainous regions. The green shaded area in the north center area of figure 2 is located in the Pioneer Mountains. The east-west continental divide along the Beaverhead Mountains crest ridge extends in a south-southeast direction across the southwest corner of figure 2. The Big Hole River originates west of Selway Mountain near the continental divide in the southwest quadrant of figure 2 and flows in a north direction to the north edge of figure 2. Governor Creek is the north and northwest oriented Big Hole River tributary located between the Big Hole Divide and the Big Hole River. Big Hole Pass is a labeled mountain pass in the gap between the two green shaded areas. Bull Creek is a south and west oriented Governor Creek tributary west of Big Hole Pass. North of figure 2 the Big Hole River turns to flow in a northeast and southeast direction around the north end of the Pioneer Mountains and then flows in a south direction back into figure 1 along the east flank of the Pioneer Mountains before making a U-turn (seen in the northeast quadrant of figure 2) to join the north-northeast oriented Beaverhead River near the northeast corner of figure 2. The Beaverhead River is formed at the confluence of tributaries at Clark Canyon Reservoir seen along the south edge of figure 2. Horse Prairie Creek is a north and east oriented stream flowing to Clark Canyon Reservoir and Bloody Dick Creek and Painter Creek are south-southeast oriented tributaries flowing to the east oriented Horse Prairie Creek segment. Grasshopper Creek originates near Torrey Mountain in the Pioneer Mountains (in north center area of figure 2) and flows in a northwest and then south and southeast direction to join the north-northeast oriented Beaverhead River as a barbed tributary. The unlabeled north-northwest oriented stream originating near Torrey Mountain and flowing to the north edge of figure 2 is the Wise River, which joins the Big Hole River north of the Pioneer Mountains and north of figure 2. The Big Hole River-Beaverhead River drainage divide area investigated in this essay is generally located in the region labeled as the Big Hole Divide on figure 2, although also includes the Wise River-Grasshopper Creek drainage divide area in the Pioneer Mountains.

Wise River-Grasshopper Creek drainage divide area

Figure 3: Wise River-Grasshopper 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 Wise River-Grasshopper Creek drainage divide area in the Pioneer Mountains. The Wise River is formed at the confluence of tributaries east of Saymore Mountain (north center area of figure 3) and flows in a north-northwest direction to near Big Point along the north center edge of figure 3. North of figure 3 the Wise River flows in a north-northeast direction to join the southeast oriented Big Hole River along the Pioneer Mountains north flank. Mono Creek is a northeast oriented Wise River tributary located south and east of Saymore Mountain and Sheldon Creek is a northwest oriented Mono Creek tributary joining Mono Creek in Mono Park. Parallel to Sheldon Creek and just to the south is northwest oriented St Louis Gulch, which instead of draining to northeast oriented Mono Creek turns to drain in a south direction to join south-southeast oriented Shoestring Creek near Elkhorn Springs and to form south oriented Grasshopper Creek, which flows to the south center edge of figure 3. South of figure 3 Grasshopper Creek flows in a south and southeast direction to eventually join the north-northeast Beaverhead River south and east of the Pioneer Mountains. The Mono Park area between Saymore Mountain to the northwest and Cornet Mountain to the southeast is a major through valley linking the north oriented Wise River valley with the south oriented Grasshopper Creek valley. The map contour interval for figure 3 is 50 meters and the Mono Park elevation at the drainage divide is between 2300 and 2350 meters. Elevations on Saymore Mountain rise to 2710 meters and elevations on Cornet Mountain rise to more than 3100 meters suggesting the Mono Park through valley is at least 350 meters deep. The through valley was eroded by south oriented floodwaters flowing across the Pioneer Mountains at a time when the Pioneer Mountains were beginning to emerge as a high mountain range. At that time the deep northeast and southeast oriented Big Hole River valley along the north flank of the Pioneer Mountains did not exist and floodwaters were flowing freely in a south direction across what is today a high mountain range. Uplift of the Pioneer Mountains and headward erosion of the deep Big Hole River valley along the north flank of the emerging Pioneer Mountains caused a reversal of flood flow in the north end of the south oriented flood flow channel that resulted in the formation of the north oriented Wise River drainage system.

Detailed map of Mono Creek-Grasshopper Creek drainage divide area

Figure 4: Detailed map of Mono Creek-Grasshopper 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 Mono Creek-Grasshopper Creek drainage divide area seen is less detail in figure 3. Mono Creek flows in a north-northeast direction from Mono Park in the north half of section 8 (west of center of figure 4) to the north center edge of figure 4 and north of figure 4 joins the north oriented Wise River. Sheldon Creek is the northwest oriented stream flowing from the northwest corner of section 15 to Mono Creek at Mono Park. South of Sheldon Creek is northwest oriented St Louis Gulch, which drains to Harrison Park in section 17 and to south oriented Grasshopper Creek, which flows to the south edge of figure 4 (west of center). The map contour interval for figure 4 is 40 feet and the lowest elevations on the Mono Creek-Grasshopper Creek drainage divide are between 7720 and 7760 feet. Saymore Mountain near the northwest corner of figure 4 rises to 8890 feet. Elevations on the north slope of Cornet Mountain seen near the southeast corner of figure 4 rise to more than 9500 feet and Cornet Mountain, which is just south of the southeast corner of figure 4, rises to 10, 217 feet suggesting the Mono Creek-Grasshopper Creek through valley is at least 1100 feet deep. As described in the figure 3 discussion the through valley is evidence of what was once a major south oriented flood flow channel eroded across the emerging Pioneer Mountains. Floodwaters were flowing in a south direction from a melting thick ice sheet’s western margin located along what is today the Canadian Rocky Mountain front in southwest Alberta and southeast British Columbia. The Pioneer Mountains were being uplifted by ice sheet related crustal warping, which may have been further influenced by deep flood erosion of the rising Pioneer Mountain core area and by deposition of flood transported debris in adjacent basins and valleys. Pioneer Mountain uplift combined with headward erosion of the deep Big Hole River valley along the Pioneer Mountains north flank eventually ended the south oriented flood flow on the present day Wise River-Grasshopper Creek alignment. Subsequently, after flood flow across the region had ended and after the Pioneer Mountains had emerged as a high mountain range, alpine glaciers formed in the high Pioneer Mountains and further modified the landscape.

Bull Creek-Grasshopper Creek drainage divide area

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

Figure 5 illustrates the Bull Creek-Grasshopper Creek drainage divide area south and west of figure 3 and is located along the south flank of the Pioneer Mountains so there is no overlap area with figure 3. The Big Hole Divide is labeled and extends in a north south direction across the center of figure 5. Big Hole Pass is located near the center of figure 5 and is a major pass linking the north oriented Big Hole River drainage basin west of the Big Hole Divide with the south oriented Grasshopper Creek drainage basin east of the Big Hole Divide. Grasshopper Creek flows in a south direction near the east edge of figure 5. Divide Creek is the southeast oriented Grasshopper Creek tributary draining the Big Hole Pass area. West of Big Hole Pass is south oriented Bull Creek, which makes a U-turn at the south end of Butch Hill to flow in a northwest direction to join north and northwest oriented Governor Creek, which west of figure 5 joins the north oriented Big Hole River. The south and west oriented stream in the northwest corner of figure 5 is Warm Springs Creek, which west of figure 5 joins the north oriented Big Hole River as a barbed tributary. The map contour interval for figure 5 is 50 meters and the Big Hole Pass elevation is between 2250 and 2300 meters. Elevations along the Big Hole Divide north of Big Hole Pass rise to more than 2650 meters near the north edge of figure 5. South of Big Hole Pass elevations rise to 2882 meters at Tash Peak suggesting the Big Hole Pass depth is at least 350 meters deep. Big Hole Pass is a water-eroded feature and was eroded by southeast oriented flood flow moving from the present day north oriented Big Hole River drainage basin west of the Big Hole Divide to the south oriented Grasshopper Creek drainage basin east of the Big Hole Divide. The Big Hole Divide was created when crustal warping probably raised the Big Hole Divide ridge area and perhaps the region west of the Big Hole Divide at the same time as headward erosion of a deep southeast and south oriented flood flow channel on the alignment of the present day southeast and south oriented Big Hole River segment north and east of the Pioneer Mountains beheaded south oriented flood flow routes supplying floodwaters to flood flow channels on the present day north oriented Big Hole River segment west of the Pioneer Mountains. Floodwaters on the north end of the beheaded flood flow channels reversed flow direction to form the north and northeast oriented Big Hole River drainage system west of the Pioneer Mountains, which captured south oriented drainage routes on south oriented flood flow channels in the Pioneer Mountains to create barbed tributaries and U-turns as seen in the figure 5 northwest quadrant.

Detailed map of Bull Creek-Divide Creek drainage divide area

Figure 6: Detailed map of Bull Creek-Divide 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 Bull Creek-Divide Creek drainage divide area seen in less detail in figure 5. The Big Hole Divide extends in a north south direction across figure 6 just west of center. Bull Creek flows in a south and southwest direction from the north edge of figure 6 (near northwest corner) to the west edge of figure 6 (south of center). West of figure 6 Bull Creek turns to flow in a northwest direction to join north and northwest oriented Governor Creek, which then flows to the north oriented Big Hole River. Big Hole Pass is located in section 7 (west of center of figure 6) and is drained to the east by a tributary to southeast and east-southeast oriented Divide Creek, which east of figure 6 flows to south oriented Grasshopper Creek. The map contour interval for most of figure 6 is 40 feet, although the contour interval is 20 feet near the west edge of figure 6. Big Hole Pass has an elevation of between 7400 and 7440 feet. Elevations along the Big Hole Divide near the north edge of figure 6 are greater than 8240 feet and rise to more than 8800 feet north of figure 6. Elevations along the divide near the south edge of figure 6 exceed 8200 feet, although south of figure 6 the elevations rise to 9348 feet. These elevations suggest Big Hole Pass is a through valley eroded across the Big Hole Divide and is at least 1400 deep. As already described in the figure 5 discussion the Big Hole Pass through valley was eroded as a southeast oriented flood flow channel moving southeast oriented flood flow from west of the emerging Pioneer Mountains to join the deeper south oriented Grasshopper Creek flood flow channel on the east side of the Big Hole Divide. South and southeast oriented flood flow moving across the Big Hole Divide at Big Hole Pass probably used the Bull Creek valley alignment north of figure 6. West of Big Hole Pass that south oriented flood flow channel probably diverged, with one channel using the Big Hole Pass valley to reach the south oriented flood flow channel on the Grasshopper Creek alignment while the other flood flow channel continued in a south direction along the present day north oriented Governor Creek alignment. Uplift of the Big Hole Divide ridge and of the Governor Creek headwaters area caused a reversal of flood flow on the Governors Creek and Big Hole River alignments that resulted in the north oriented drainage systems seen today and headward erosion of the deeper valleys, including the deeper Bull Creek valley, that ended flood flow across the Big Hole Divide.

Governor Creek-Grasshopper Creek drainage divide area

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

Figure 7 illustrates the Governor Creek-Grasshopper Creek drainage divide area south of figure 5 and includes an overlap area with figure 5. The map contour interval for figure 7 is 50 meters. The Big Hole Divide is the high-forested ridge extending in a north-to-south direction near the center of figure 7. Grasshopper Creek flows in a south-southeast direction from the north edge of figure 7 (by highway) to the east center edge of figure 7. Buffalo Creek is the northeast oriented stream flowing across the southeast quadrant of figure 7 and joins Grasshopper Creek east of figure 7. Note how Buffalo Creek headwaters in the high-forested ridge area are oriented in south, southeast, and east-southeast directions indicating the northeast oriented Buffalo Creek valley captured south oriented flood flow. North of the Buffalo Creek headwaters is south and east oriented Brays Canyon Creek, which flows to Buffalo Creek east of the high-forested ridge. Note how the south oriented Brays Canyon Creek headwaters segment is linked by a through valley with the south oriented Right Fork of Buffalo Creek providing evidence of a dismembered south oriented flood flow channel, which was captured first by headward erosion of the deeper Buffalo Creek valley and then captured further to the north by headward erosion of the deep Brays Canyon Creek valley. Note also how the Pack Trail in Brays Canyon proceeds in a northwest direction over the Big Hole Divide to the North Fork Fox Creek with Fox Creek flowing in a west-northwest direction to north oriented Governors Creek, which flows to the north edge of figure 7 (near northwest corner). The Pack Trail is located in a through valley crossing the Big Hole Divide. The through valley is defined by at least three contour lines on each side suggesting it is at least 100 meters deep. While not as deep as Big Hole Pass the Fox Creek-Brays Canyon through valley is evidence of a southeast oriented flood flow channel that once crossed the Big Hole Divide. At the time floodwaters flowed in the Fox Creek-Brays Canyon flood flow channel the deep Big Hole Pass through valley to the north had not been eroded to the depth seen today, although it was probably in the process of being eroded by one of multiple diverging and converging flood flow channels crossing what is now the Big Hole Divide. Study of the Big Hole Divide in figure 7 reveals other through valleys linking southeast oriented headwaters valleys of streams east of the divide with northwest oriented headwaters valleys of streams west of the divide.

Detailed map of Fox Creek-Brays Canyon Creek drainage divide area

Figure 8: Detailed map of Fox Creek-Brays Canyon 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 Fox Creek-Brays Canyon Creek drainage divide area seen in less detail in figure 7. The Big Hole Divide is the high mountain ridge extending in a north-to-south direction across the center of figure 8. The South Fork Fox Creek originates in the northwest corner of section 20 flows in a northwest direction to join the northwest and west-southwest oriented North Fork Fox Creek to form northwest oriented Fox Creek, which flows to the west edge of figure 8 (north of center). The North Fork Fox Creek originates in section 8 and is linked by a through valley across the Big Hole Divide to the south oriented headwaters of Brays Canyon Creek, which flows to the south center edge of figure 8. A trail is shown in the through valley. The map contour interval for figure 8 is 40 feet and the through valley floor elevation at the drainage divide is between 8680 and 8720 feet. Tash Peak to the north rises to 9291 feet and an elevation of 9116 feet on the Big Hole Divide ridge is located near the south edge of figure 8. These elevations suggest the through valley is more than 400 feet deep. A slightly deeper through valley in the southeast quadrant of section 8 links the North Fork Fox Creek valley with southeast oriented Right Fork Swamp Creek. In the north half of section 8 a slightly higher through valley links a North Fork Fox Creek tributary valley with an east oriented tributary valley to the southeast oriented Left Fork Swamp Creek valley. The through valleys were eroded by southeast oriented flood flow moving to the south oriented Brays Canyon Creek valley and to the southeast oriented Left and Right Forks of Swamp Creek. What we are seeing in section 8 is evidence these flood flow channels diverged from each other, with the Left and Right Forks of Swamp Creek then converging further to the east. This pattern of diverging and converging flood flow channels is common in large-scale complexes of anastomosing channels. At that time the deep north oriented Governors Creek valley to the west and northwest did not exist and floodwaters were flowing in a south direction in what is now the north oriented Big Hole River drainage basin west of the Pioneer Mountains. The high Big Hole Divide ridge was emerging as floodwaters flowed across it. Emergence of the high mountain ridge was probably accomplished by a combination of crustal warping and of deep flood erosion of the surrounding valleys and basin regions, both by south and southeast oriented floodwaters and later by north oriented floodwaters west of the Big Hole Divide ridge when the direction of flood flow west of the Pioneer Mountains was reversed.

Big Hole River-Bloody Dick Creek drainage divide area

Figure 9: Big Hole River-Bloody Dick Creek drainage divide area. United States Geological Survey map digitally presented using National Geographic Society TOPO software.

Figure 9 illustrates the Big Hole River-Bloody Dick Creek drainage divide area south and west of figure 7 and includes an overlap area with figure 7. The east-west continental divide is shown with a dashed line along the crest of the Beaverhead Mountains and extends in roughly a south-southeast direction from the west edge of figure 9 (north of center) to the south edge of figure 9 (west half). The Big Hole River is formed at Skinner Meadows in the northwest quadrant of figure 9 and flows in a north-northeast direction to the north edge of figure 9 (west of center). Darkhorse Creek is an east-northeast tributary flowing from near the continental divide to the Big Hole River at Skinner Meadows. South of Skinner Meadows is a through valley linking the north oriented Big Hole River valley with the south-southeast oriented Bloody Dick Creek valley ,with Bloody Dick Creek flowing to the south center edge of figure 9. Bloody Dick Creek originates as a northeast oriented stream near Goldstone Pass (across the continental divide) and flows towards Skinner Meadows before making an abrupt turn to flow in a south-southeast direction. The map contour interval for figure 9 is 50 meters and the Big Hole River-Bloody Dick Creek through valley floor elevation at the drainage divide is between 2300 and 2350 meters, which is only slightly higher than the Big Hole Pass floor elevation to the north. Based on the elevation of Black Mountain to the east the through valley is at least 350 meters deep. The Big Hole Divide extends along the Darkhorse Creek-Bloody Dick Creek drainage divide to Black Mountain and then around the north end of the south oriented Selway Creek drainage basin to Bloody Dick Peak and Painter Peak in the east center edge area of figure 9. Selway Creek is the south oriented stream formed at the confluence of Ore Creek and Hidden Creek just south of the Big Hole Divide and joining Bloody Dick Creek near the south center edge of figure 9. North oriented streams north of the Big Hole Divide in the northeast quadrant of figure 9 flow to north oriented Governors Creek, which eventually joins the north oriented Big Hole River. Note the north-to-south oriented through valley linking the north oriented Governors Creek drainage basin with the south oriented Selway Creek drainage basin. The through valley floor elevation at the drainage divide is also between 2300 and 2350 meters, which means it is at least 350 meters deep. Painter Peak rises to 2926 meters and elevations along the continental divide rise to more than 3000 meters suggesting the through valleys may be as much as 450 meters deep. Based on elevations of the two major through valleys in figure 9 and of Big Hole Pass and of the Wise River-Grasshopper Creek through valleys further to the north it is probable than south and southeast oriented floodwaters were flowing in all these through valleys up until the massive reversal of flood flow west of the Pioneer Mountains occurred.

Detailed map of Englebaugh Creek-Ore Creek drainage divide area

Figure 10: Detailed map of Englebaugh Creek-Ore 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 Englebaugh Creek-Ore Creek drainage divide area seen in less detail in figure 9. The map contour interval for figure 10 is 40 feet. Black Mountain is located near the southwest corner of figure 10 and rises to 9190 feet. Bloody Dick Peak and Painter Peak are located east of figure 10 and rise to more than 9800 feet. Ore Creek originates at Mud Lake in section 33 (in southwest quadrant of figure 10) and flows in an east and south direction to the south edge of figure 10 (east of center) and south of figure 10 joins south oriented Selway Creek, which flows to south-southeast oriented Bloody Dick Creek. Governor Creek flows in a north-northwest direction from the east edge of figure 10 (south of center) and near the northeast corner of figure 10 turns to flow in a northeast direction. Indian Creek originates in section 35 and flows in a southeast direction before turning to flow in a northeast direction to join Governor Creek in section 19. Note in the north half of section 35 how the southeast oriented Indian Creek headwaters are flowing on the hillside adjacent to the parallel and deeper Ore Creek valley. The elevation at the drainage divide is between 7720 and 7760 feet. Headward erosion of the northeast oriented Indian Creek valley was able to capture southeast oriented flood flow moving to the deeper Ore Creek valley, but was not deep enough to capture floodwaters flowing in the deeper Ore Creek valley. Just to the west in section 27 are northwest oriented headwaters of the East Fork of north oriented Englebaugh Creek, which flows to the north edge of figure 10 and joins the north oriented Big Hole River north of figure 10. The Saginaw Road crosses the through valley linking the north oriented Englebaugh Creek valley with the southeast and south oriented Ore Creek valley. The through valley floor elevation at the drainage divide is between 7880 and 7920 feet. These elevations suggest the much larger through valley linking the north oriented Big Hole River valley with the south oriented Selway Creek valley is at least 1250 feet deep. The through valley is a water-eroded valley and was eroded by south oriented flood flow prior to the massive flood flow reversal west of the Pioneer Mountains that created the present day north oriented Big Hole River headwaters.

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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