Clark Fork-Boulder River drainage divide area landform origins along continental divide north of Butte, Montana, USA

Authors


Abstract:

This essay uses topographic map evidence to interpret landform origins in the region between Clark Fork and the Boulder River along the east-west continental divide north of Butte, Montana. The east-west continental divide is located just east of Butte and makes a jog to the west north of Butte before jogging back to the east. Silver Bow Creek flows in a west direction from Butte to the Clark Fork, which flows in a north and northwest direction with water eventually reaching the Columbia River and the Pacific Ocean. South oriented Silver Bow Creek tributaries have headwaters located along the continental divide north of Butte. North of those south-oriented Silver Bow Creek headwaters and the continental divide are north oriented headwaters of the Boulder River, which after flowing in a north direction turns to flow in an east and south direction to join the east oriented Jefferson River, which flows to the north oriented Missouri River with water eventually reaching the south oriented Mississippi River and the Gulf of Mexico. North oriented Bison Creek originates at Elk Park Pass just east of Butte and the continental divide and flows to the east oriented Boulder River. North of the east-oriented Boulder River and the continental divide are north oriented headwaters of west oriented Little Blackfoot River, which flows to the north and northwest oriented Clark Fork.

Through valleys or mountain passes, including Elk Park Pass, link south-oriented Silver Bow Creek tributaries with north oriented Boulder River headwaters and tributary valleys and also link south oriented Boulder River tributary valleys with north oriented Little Blackfoot River headwaters and tributary valleys. The through valleys are interpreted to have been eroded by southeast and south oriented floodwaters, which were derived from a thick North American ice sheet and which were flowing from western Canada across Montana. The thick ice sheet was located in a deep “hole” and the ice sheet weight caused crustal warping that raised Montana and Wyoming mountain ranges. Floodwaters flowed across what were emerging mountain ranges and carved deep valleys into them. A major south-southeast oriented flood flow channel on what is today the north-northwest oriented Missouri River segment was reversed in flow direction when headward erosion of the much deeper northeast oriented Missouri River valley north of the study area beheaded the south-southeast oriented flood flow channel and diverted the flood flow to space in the deep “hole” being opened up by the ice sheet melting. The reversal of flood flow on the Missouri River alignment captured southeast oriented flood flow channels from the west creating what are today barbed tributaries and significant drainage U-turns. At the same time similar flood flow reversals were occurring west of Butte to create the present day north and northwest oriented Clark Fork drainage system. The massive flood flow reversals in the study region were probably greatly aided by ice sheet related crustal warping that raised mountain ranges in the Yellowstone Plateau area, which is located south of the study region and which gradually became a topographic barrier blocking the south oriented flood flow. Evidence in the study region shows crustal warping occurred as floodwaters flowed across rising mountain ridges with especially good evidence found at Elk Park Pass.

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 Clark Fork-Boulder River drainage divide area landform origins along the continental divide north of Butte, Montana, USA. 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 Clark Fork-Boulder River drainage divide area landform evidence along the continental divide north of Butte, Montana will be regarded as evidence supporting the “thick ice sheet that melted fast” paradigm.

Clark Fork-Boulder River drainage divide area location map

Figure 1: Clark Fork-Boulder 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 Clark Fork-Boulder River drainage divide area along the continental divide north of Butte, Montana and illustrates a region in western Montana. The Missouri River is located in the east half of figure 1 and is formed at Three Forks (in southeast quadrant of figure 1) at the confluence the north and northwest oriented Gallatin River, the north oriented Madison River (not labeled), and the northeast, east, and northeast oriented Jefferson River. From Three Forks the Missouri River flows in a north and north-northwest direction to Canyon Ferry Lake and Holter Lake (both reservoirs) and then turns to flow in a northeast direction to the north edge of figure 1. North and east of figure 1 the Missouri River flows in a northeast and 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 Boulder River originates north of Butte and flows in a north direction before turning to flow in an east direction to the towns of Basin and Boulder. From the town of Boulder the Boulder River flows in a southeast and south-southwest direction to join the Jefferson River near Cardwell. The west oriented stream at Butte is Silver Bow Creek, which flows to north and west-northwest oriented Clark Fork. Clark Fork flows in a north direction from near Opportunity to Warm Springs and Deer Lodge before turning near Garrison to flow in a west-northwest direction to the west edge of figure 1 near Missoula. West of figure 1 Clark Fork joins the Columbia River with water eventually reaching the Pacific Ocean. The unlabeled west oriented stream flowing from Elliston to Avon and then joining Clark Fork near Garrison is the Little Blackfoot River. The Clark Fork-Boulder River drainage divide north of Butte is the west-east continental divide. This essay investigates the Clark Fork-Boulder River drainage divide area north of Butte and south of the Little Blackfoot River headwaters (north and west of the town of Basin).

Before looking at detailed maps of the Clark Fork-Boulder River drainage divide area a brief look at the big picture erosion history is appropriate. Large volumes of south and southeast oriented floodwaters once flowed across the region shown by figure 1, including the present day north and west-northwest oriented Clark Fork drainage basin. 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 (at least initially) there were no high mountains in western Montana or in the region south of figure 1 and floodwaters could freely flow across locations that are today high mountain ranges. Western Canada, Montana, Wyoming, and other mountain ranges were formed by ice sheet related crustal warping and occurred as floodwaters flowed across the rising mountain masses. In addition deep flood water erosion of valleys and basins surrounding the rising mountain ranges contributed to the emergence of present day mountain ranges.

In time the ice sheet related crustal warping combined by deep glacial erosion under the ice sheet created a deep “hole” in which the thick ice sheet was located. Eventually as the ice sheet melted there came a time when elevations on the ice sheet surface (at least in the south) were lower than elevations along the deep “hole” southwest rim where the immense south and southeast oriented ice marginal melt water floods were flowing. Deep northeast oriented valleys then eroded headward from space in the deep “hole” being opened up by the ice sheet melting to capture the south and southeast oriented melt water floods in present day Montana. The northeast oriented Missouri River valley segment north of figure 1) and its east and northeast oriented tributary valleys eroded headward from the deep “hole” across the south and southeast oriented flood flow. Northwest oriented Missouri River tributary valleys and the north-northwest oriented Missouri River valley segment seen in figure 1 were eroded by reversals of flood flow on north and northwest ends of the beheaded flood flow channels. The present day north oriented Madison River, north and northwest oriented Gallatin River, and north oriented Jefferson River tributaries alignments were established initially as south oriented flood flow channels, which were beheaded, reversed, and significantly deepened during massive upper Missouri River drainage basin flood flow reversal. Uplift of the Yellowstone Plateau and mountain ranges south of figure 1 probably contributed to the massive flood flow reversal. The north and west-northwest oriented Clark Fork valley and associated tributary valleys were created by similar reversals of flood flow that diverted the south and southeast oriented floodwaters in north, northwest, and west directions.

Detailed location map for Clark Fork-Boulder River drainage divide area

Figure 2: Detailed location map Clark Fork-Boulder 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 Clark Fork-Boulder River drainage divide area along the continental divide north of Butte, Montana. County boundaries are shown and Deer Lodge, Silver Bow, Jefferson, and Broadwater Counties are labeled. Green shaded areas are National Forest lands, which generally are located in mountainous regions. Butte is located in Silver Bow County near the south center edge of figure 2. The east-west continental divide is labeled and extends in a south to north direction along the Silver Bow-Jefferson County line east and north of Butte. Silver Bow Creek is the unlabeled west oriented stream flowing from Butte and near the north to south oriented Deer Lodge Guide Meridian turns to join other streams to form the north oriented Clark Fork, which flows near Warm Springs and Deer Lodge before turning near Garrison to flow in a northwest direction to Drummond near the northwest corner of figure 2.  Note the northwest and west oriented Clark Fork tributaries from the east (Peterson Creek is the only such tributary named on figure 2). Browns Gulch is a south and southwest oriented stream flowing to west oriented Silver Bow Creek near Ramsey (west of Butte). The Little Blackfoot River originates between Cliff Mountain and Thunderbolt Mountain (near continental divide east of Deer Lodge) and flows in a north direction to near Elliston before turning to flow in a west-northwest direction to Avon and then in a southwest direction to join the Clark Fork near Garrison.

The Boulder River originates on the north side of the continental divide just north of the south oriented Browns Gulch headwaters and flows in a north direction to near Blizzard Hill (just east of the Peterson Creek headwaters) and then turns to flow in an east direction to the towns of Basin and Boulder before turning to flow in a southeast and south-southwest direction to join the Jefferson River (not seen in figure 2). Bison Creek originates near Elk Park Pass across the continental divide from Butte and flows in a north-northeast direction to join the Boulder River west of the town of Basin. The Little Boulder River originates near Haystack Mountain and flows in a south direction toward Whitetail Reservoir, but makes an abrupt U-turn to flow in a northeast direction to join the Boulder River near the town of Boulder. Whitetail Creek flows in a south-southeast direction from Whitetail Reservoir to join the Jefferson River near the town of Whitetail (not seen in figure 2). Little Whitetail Creek originates south of the town of Boulder and flows in a south direction west of Bull Mountain to join Whitetail Creek north of the town of Whitetail.

The remarkable U-turns made by the various drainage routes in the Clark Fork-Boulder River drainage divide along the continental divide north of Butte provide evidence of one time south and southeast oriented flood flow channels that were beheaded and reversed by headward erosion of deep east and northeast oriented valleys from the east and by headward erosion of deep west and northwest oriented valleys from the west. The north oriented Clark Fork segment seen in figure 2 is located along the alignment of what was once a major south oriented flood flow channel, which was reversed by crustal warping and headward erosion of the much deeper northwest oriented Clark Fork valley to become a north oriented drainage route. South oriented streams, such as Browns Gulch document how headward erosion of the deep west oriented Silver Bow Creek valley captured south oriented flood flow channels (north oriented Silver Bow Creek tributary valleys were eroded by reversals of flood flow on north ends of beheaded flood flow channels). The north oriented Boulder River and Bison Creek drainage routes were formed by reversals along what had been south oriented flood flow channels. The north-northwest oriented Missouri River segment and north and northwest oriented Gallatin, Madison, and Jefferson River segments are also located on alignments of south oriented flood flow channels, which were reversed by crustal warping that raised the Yellowstone Plateau region south of figure 2 and also by headward erosion of the deep northeast oriented Missouri River valley from space in the deep “hole” the melting ice sheet had formerly occupied. Headward erosion of east, northeast, and southeast oriented Jefferson River segments captured south oriented flood flow channels on the alignments of present day south-southeast oriented Whitetail Creek, south oriented Little Whitetail Creek and the southeast and south-southwest oriented Boulder River.

Little Blackfoot River-Thunderbolt Creek drainage divide area

Figure 3: Little Blackfoot River-Thunderbolt 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 Little Blackfoot River-Thunderbolt Creek drainage divide area. The east-west continental divide is shown with a labeled dashed line along the Jefferson County west border and extends from the north edge of figure 3 (east of center) to the south edge of figure 3 (west of center). Northwest oriented streams flowing to the west edge of figure 3 flow to the north oriented Clark Fork segment, which is located west of figure 3. The Boulder River flows in a northeast direction from the south center edge of figure 3 before turning to flow in an east direction to the east edge of figure 3 (near southeast corner). Note south oriented tributaries flowing from near the continental divide to the east oriented Boulder River. From west to east these tributaries include Indian Creek, Rock Creek, and Thunderbolt Creek, which originates at Cottonwood Lake. North of Cottonwood Lake, and north of the continental divide, are north oriented headwaters of the Little Blackfoot River, which flows to the north edge of figure 3 near Blackfoot Meadows. Note how there is a north to south oriented through valley (or mountain pass) between Electric Peak and Thunderbolt Mountain linking the north oriented Little Blackfoot River valley with the south oriented Thunderbolt Creek valley. The map contour interval for figure 3 is 50 meters and the through valley floor elevation at the drainage divide is between 2250 and 2300 meters. Electric Peak reaches an elevation greater than 2500 meters while Thunderbolt Mountain is even higher. In other words the through valley is at least 200 meters deep and is evidence of a south oriented flood flow channel that once crossed what is today the east-west continental divide. The floodwaters came from west of the present day continental divide and were captured by headward erosion of the deep east oriented Boulder River valley, which eroded headward from flood flow channels east of the present day continental divide. Headward erosion of the deep west oriented Little Blackfoot River valley north of figure 3 beheaded the south oriented flood flow to the east oriented Boulder River valley. Floodwaters on the north end of the beheaded flood flow channel reversed flow direction to erode the north oriented Little Blackfoot River headwaters valley. Other shallower through valleys (or mountain passes) can be seen in figure 3 linking northwest oriented Clark Fork tributary valleys with south oriented Boulder River tributary valleys.

Detailed map of Little Blackfoot River-Thunderbolt Creek drainage divide area

Figure 4: Detailed map of Little Blackfoot River-Thunderbolt 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 Little Blackfoot River-Thunderbolt Creek drainage divide area seen is less detail in figure 3. The east-west continental divide follows the labeled Powell County-Jefferson County border, which extends from near the southwest corner of figure 4 to Electric Peak and then to the east edge of figure 4 (south half). Cottonwood Lake is located in section 28 and is where south oriented Thunderbolt Creek originates. The Little Blackfoot River originates in section 22 and flows in a north-northeast direction to the northeast corner of figure 4. A Little Blackfoot River tributary originates in section 21 and flows in a northeast direction to join the Little Blackfoot River just north of the northeast corner of figure 4. Note the well-defined through valley linking the north oriented Little Blackfoot River valley with the south oriented Thunderbolt Creek valley. The map contour interval for figure 4 is 40 feet and the through valley floor elevation at the lowest point on the drainage divide is between 7440 and 7480 feet. Elevations in section 29 to the west rise to 8359 feet while the Thunderbolt bench mark (B.M.) along the east edge of figure 4 has an elevation of 8597 feet, which means the through valley is at least 870 feet deep. This through valley is a water eroded valley and was eroded by south oriented flood flow moving to the east oriented Boulder River valley south of figure 4. Headward erosion of the deep west oriented Little Blackfoot River valley north of figure 4 beheaded the south oriented flood flow and floodwaters on the north end of the beheaded flood flow channel reversed flow direction to erode the north oriented Little Blackfoot River valley. This is an overly simplified interpretation of what happened as there are many other through valleys seen in figure 4. For example near the corner of sections 16, 17, 20, and 21 is a through valley linking the northeast oriented Little Blackfoot River tributary valley with the west oriented Middle Fork of Cottonwood Creek, which flows to the west edge of figure 4 (near northwest corner) and then in a northwest direction to join the north oriented Clark Fork (near Deer Lodge).  Another through valley is in section 30 links a north oriented tributary valley to the Middle Fork Cottonwood Creek with the south oriented Rock Creek valley. Still other through valleys can be found crossing the continental divide and other drainage divides in figure 4. These through valleys document a complex pattern of flood flow routes as headward erosion of deep valleys from both the east and the west beheaded and reversed flood flow channels to create the present day valley pattern and drainage system, including the east-west continental divide.

Clark Fork-Boulder River drainage divide area

Figure 5: Clark Fork-Boulder River drainage divide area. United States Geological Survey map digitally presented using National Geographic Society TOPO software.

Figure 5 illustrates the Clark Fork-Boulder River drainage divide area south and west of figure 3 and includes an overlap area with figure 3. The east-west continental divide is located along the Jefferson County west border and is shown with a dashed line extending from the north edge of figure 5 (east of center) to the south center edge of figure 5. The South Fork Boulder River originates just east of the continental divide near the south edge of figure 5 and flows in a north, east, and north direction to join the northeast oriented West Fork and to form the north-northeast and northeast oriented Boulder River, which flows through Lockhart Meadows before turning to flow to the east center edge of figure 5. Clark Fork flows in a north direction from the southwest corner of figure 5 to the north edge of figure 5 (near northwest corner). Note northwest oriented Clark Fork tributaries originating near the continental divide. The South Fork of Dry Cottonwood Creek for example originates near the south edge of figure 5 just west of the continental divide and then flows in a northwest direction to join the west oriented North Fork Dry Cottonwood Creek and to form northwest oriented Dry Cottonwood Creek. Note how the west oriented North Fork Dry Cottonwood Creek valley is linked by a deep through valley with a northeast oriented Boulder River tributary valley. The map contour interval for figure 5 is 50 meters and the through valley floor elevation at the drainage divide is between 2050 and 2100 meters. The continental divide both north and south of the through valley rises to more than 2250 meters meaning the through valley is at least 150 meters deep. Further north along the continental divide is Champion Pass, which is south of Blizzard Hill. Champion Pass links the east-southeast oriented Powderhorn Creek valley with the north oriented Dieders Fork valley, which drains to northwest oriented Peterson Creek. Champion Pass at the drainage divide has an elevation of between 2100 and 2150 meters and is at least 100 meters deep. These and other through valleys seen crossing the continental divide in figure 5 provide evidence of additional southeast oriented flood flow channels, which were captured by headward erosion of the deep northeast and east oriented Boulder River valley. At the time these through valleys were eroded the deep north oriented Clark Fork valley did not exist, although there probably was a south oriented flood flow channel on the Clark Fork alignment, but the water was flowing at an elevation at least as high as the through valleys crossing the present day continental divide.

Detailed map of North Fork Dry Cottonwood Creek-West Fork Boulder River drainage divide area

Figure 6: Detailed map of North Fork Dry Cottonwood Creek-West Fork Boulder River 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 North Fork Dry Cottonwood Creek-West Fork Boulder River drainage divide area seen in less detail in figure 5. The east-west continental divide is the labeled dashed line extending from the north edge of figure 6 (west of center) to the south center edge of figure 6. The North Fork Dry Cottonwood Creek originates near the southeast corner of section 3 (near center of figure 6) and flows in a west-northwest direction to the west edge of figure 6 (north half). The Boulder River flows in a north and north-northeast direction from the south edge of figure 6 (near southeast corner) to the northeast corner of figure 6. The West Fork Boulder River originates in section 11 and flows in a northeast and east direction and joins the Boulder River near the north edge of section 12. Four Corners (near the corner of sections 2, 3, 10, and 11) is located on the floor of a through valley crossing the continental divide between the west-northwest oriented North Fork Dry Cottonwood Creek and the northeast and east oriented West Fork Boulder River. The map contour interval for figure 6 is 40 feet and the elevation at Four Corners is between 6800 and 6840 feet. The continental divide to the north in section 34 rises to 7495 feet while to the south in section 15 the continental divide rises to at least 7400 feet. Based on these elevations the Four Corners through valley is at least 560 feet deep. The through valley is a water-eroded feature and was eroded by southeast oriented flood flow moving to the Boulder River valley. Other much shallower through valleys (or mountain passes) can be seen crossing the continental divide in figure 6. These through valleys collectively provide evidence of multiple flood flow channels, which once crossed the region. At that time elevations west of the present day continental were such that floodwaters could freely flow to what was then the actively eroding Boulder River valley. Headward erosion of the deep Clark Fork valley west of figure 6 beheaded the southeast oriented flood flow. Floodwaters on the northwest ends of the beheaded flood flow channels reversed flow direction to erode northwest oriented Clark Fork tributary valleys (including the northwest oriented Dry Cottonwood Creek valley). It is possible the southeast oriented flood flow channels were beheaded and reversed by headward erosion of a deep south oriented flood flow channel on the Clark Fork alignment and that the Clark Fork reversal took place after the northwest oriented tributary valleys had been initiated.

Boulder River-Browns Gulch drainage divide area

Figure 7: Boulder River-Browns Gulch drainage divide area. United States Geological Survey map digitally presented using National Geographic Society TOPO software.

Figure 7 illustrates the Boulder River-Browns Gulch drainage divide area south and slightly east of figure 5 and includes an overlap area with figure 5. The east-west continental divide is labeled and is the dashed line extending from Champion Pass (along north edge of figure 7-west of center) to the south edge of figure 7 (east half) and serves as the Jefferson County west border. Note the location near the center of figure 7 where Jefferson, Silver Bow, and Deer Lodge Counties meet. The South Fork Boulder River originates along the north (east) side of the continental divide just east of that location and streams flowing south from the continental divide near that location flow to southwest and south oriented Browns Gulch. South of figure 7 Browns Gulch flows to west oriented Silver Bow Creek, which flows to the north and northwest oriented Clark Fork. Study of the continental divide east of where the three counties meet reveals through valleys (or mountain passes) linking the north oriented Boulder River headwaters and tributaries with the south oriented Brown Gulch headwaters and tributaries. West of where the three counties meet through valleys (or mountain passes) link south oriented Browns Gulch tributary valleys with north oriented tributaries to the northwest oriented South Fork Cottonwood Creek valley, with Cottonwood Creek flowing in a northwest direction to join the north and west-northwest oriented Clark Fork (west of figure 7). These multiple north to south oriented through valleys provide evidence of multiple south oriented flood flow channels that once crossed the region and suggests the presence of a south oriented anastomosing channel complex. Further east in figure 7 north-northeast oriented Bison Creek flows across the southeast corner of figure 7. Bison Creek is a Boulder River tributary originating along the continental divide near Butte and is better illustrated in figure 9.  West of Bison Creek, but still in the east half of figure 7 is north oriented Lowland Creek, which originates near the south edge of figure 7 and which then flows in a north direction past the Boy Scout Camp to eventually reach the north edge of figure 7 and north of figure 7 joins the east oriented Boulder River. Note the through valley linking the north oriented Lowland Creek valley with the north-northeast oriented Bison Creek valley (the road between the Boy Scout Camp and the small town of Trask is located in the through valley). The map contour interval for figure 7 is 50 meters and the through valley floor elevation at the drainage divide is between 2000 and 2050 meters. Elevations on Sheepshead Mountain to the north rise to more than 2350 meters and equally high elevation can be seen along the continental divide near the south edge of figure 7 suggesting the through valley is as much as 300 meters deep. The through valley is a water eroded feature and is evidence of the converging and diverging south oriented flood flow channels that once crossed the region. Headward erosion of the deep east oriented Boulder River valley (north of figure 7) beheaded the south oriented flood flow channels and floodwaters on the north ends of the flood flow channels reversed flow direction to erode the north oriented valleys seen today.

Detailed map of Boulder River-Browns Gulch drainage divide area

Figure 8: Detailed map of Boulder River-Browns Gulch 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 Boulder River-Browns Gulch drainage divide area seen in less detail in figure 7. The county boundaries are shown with dashed lines and the east-west continental divide follows the Jefferson County border with Jefferson County being on the east side of the divide. Jefferson, Silver Bow, and Deer Lodge Counties meet near the corner of sections 14, 15, 22, and 23 in the west half of figure 8. North of that corner the continental divide is oriented in a south to north direction while east of that corner the continental divide is oriented in a west to east direction. The South Fork Boulder River originates in section 14 and flows in a north and east direction into section 13 where it is joined by a north oriented tributary and turns to flow in a north direction to the north center edge of figure 8. South oriented streams originating in sections 23 and 24 are tributaries to Browns Gulch. Note how in sections 23 and 24 there are north to south oriented through valleys (or mountain passes) linking the north-oriented South Boulder River valley with the south oriented Browns Gulch tributary valleys. The map contour interval for figure 8 is 40 feet and the through valley in section 23 has a floor elevation at the drainage divide of between 7200 and 7240 feet while the floor elevation at the drainage divide for the through valley in section 24 is between 7160 and 7200 feet. The continental divide elevation where the three counties meet is more than 7480 feet and in section 18 to east is more than 7640 feet meaning the through valleys are at least 240 meters deep. Additional somewhat shallower through valleys can be seen crossing the continental divide in figure 8, such as the through valley (or mountain pass) near the corner of sections 13, 18, 19, and 24. Also through valleys (or mountain passes) cross the South Fork Cottonwood Creek-Browns Gulch drainage divide along the Deer Lodge-Silver Bow County line (east of where the three counties meet). Northwest oriented South Fork Cottonwood Creek originates in section 15 and flows to the west edge of figure 8 (north half). All of these through valleys were eroded as south and southeast oriented flood flow channels into a surface that was at least as high as the highest elevations in figure 8 today. Floodwaters were moving to what was then the actively eroding south oriented Browns Gulch valley and its tributary valleys. Headward erosion of the deep east oriented Boulder River  (north of figure 8) beheaded and reversed the south oriented flood flow channels east of the present day continental divide to erode the north oriented South Fork Boulder River valley and tributary valleys while headward erosion of the deep Clark Fork valley (west of figure 8) beheaded and reversed southeast oriented flood flow channels west of the present day continental divide so as to erode the northwest oriented South Fork Cottonwood Creek valley.

Bison Creek-Silver Bow Creek drainage divide area

Figure 9: Bison Creek-Silver Bow Creek drainage divide area. United States Geological Survey map digitally presented using National Geographic Society TOPO software.

Figure 9 illustrates the Bison Creek-Silver Bow Creek drainage divide area south of figure 7 and includes an overlap area with figure 7. The continental divide is the labeled dashed line serving as the Jefferson-Silver Bow County line and extending from the north edge of figure 9 (east of center) to the south edge of figure 9 (east half). Elk Park Pass is the labeled deep pass crossing the continental divide and is located in the southeast quadrant of figure 9 north and east of Butte. Bison Creek is the north-northeast oriented stream flowing in the large north-northeast oriented valley from near Elk Park Pass to the north edge of figure 9 (near northeast corner). North and east of figure 9 Bison Creek joins the east, south-southeast, south-southwest oriented Boulder River with water eventually reaching the north oriented Missouri River before ending up in the Gulf of Mexico. The west oriented stream flowing from Butte to the west edge of figure 9 (south half) is Silver Bow Creek and west of figure 9 Silver Bow Creek flows to the north and west-northwest oriented Clark Fork with water eventually reaching the Pacific Ocean. Browns Gulch is a Silver Bow Creek tributary flowing in a southwest, south and southwest direction from the north edge of figure 9 to the west edge of figure 9 (south half) and joins Silver Bow Creek just west of figure 9. Note how north of Silver Bow Creek drainage in the region west of the continental divide is in a south direction while east of the continental divide drainage is in a north direction. Elk Park Pass is a remarkable landform that deserves some attention. The map contour interval for figure 9 is 50 meters and the Elk Park Pass floor elevation at the drainage divide is between 1900 and 1950 meters. Elevations along the continental divide to the northwest of Elk Park Pass rise to more than 2350 meters and to the southeast of Elk Park Pass elevations rise to more than 2450 meters. In other words Elk Park Pass is at least 400 meters deep and links the north-northeast oriented Bison Creek valley with the west oriented Silver Bow Creek valley. While possibly located along a zone of geologic weakness Elk Park Pass is a water-eroded feature and was eroded by massive south oriented flood flow crossing the region. Floodwaters were moving in a south direction to the west oriented Silver Bow Creek valley. At that time flood flow on the present day north oriented Clark Fork alignment probably had not been beheaded and reversed and may have still been flowing in a south direction to what is today the Beaverhead River drainage basin south of the Clark Fork headwaters. Today the Beaverhead River is a north oriented tributary to the Jefferson River, which flows to the north oriented Missouri River.

Detailed map of Bison Creek-Silver Bow Creek drainage divide area

Figure 10: Detailed map of Bison Creek-Silver Bow 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 Bison Creek-Silver Bow Creek drainage divide area seen in less detail in figure 9. The city of Butte, Montana is located in the southwest quadrant of figure 10. The Berkley Pit is a man-made hole, which was dug during a large-scale mining operation. Elk Park Pass is located in the northeast quadrant of figure 10 with the southwest end of the pass being drained by Woodville Canyon to west oriented Silver Bow Creek. North of Elk Park Pass are headwaters of north-northeast oriented Bison Creek, which flows to the east and south oriented Boulder River (north and east of figure 10). Note how the valley north of Elk Park Pass is broad and relatively flat floored compared to the narrow and steep Woodville Canyon to the south. The difference between the valleys on opposite sides of the pass suggests floodwaters eroding Elk Park Pass were flowing in a south direction. Also the broad and relatively flat-floored valley north of the pass suggests crustal warping was occurring as floodwaters flowed across the region and the mountain ridge crossed by Elk Park Pass was being uplifted as the floodwaters were eroding a deep water gap at the location of present day Elk Park Pass. Apparently floodwaters were not able to erode the south oriented valley as fast as the mountain ridge was being uplifted and the rising mountain ridge gradually formed a dam, which caused the south oriented floodwaters to deposit debris on the floor of the valley north of Elk Park Pass. Eventually uplift of the mountain ridge combined with headward erosion of the deep east oriented Boulder River valley north and east of figure 10 resulted in a reversal of flood flow north of the Elk Park Pass location and the formation of the present day drainage divide. However, before that flood flow reversal took place the south oriented flood water was able to erode what is today a deep wind gap through the rising mountain ridge. The map contour interval for figure 10 is 40 feet and the floor of Elk Park Pass at the drainage divide is between 6360 and 6400 feet. The spot elevation at East Ridge on Rampart Mountain to the west of Elk Park Pass reads 7765 feet while the continental divide east and south of Elk Park Pass rises to more than 8000 feet. These elevations suggest the south oriented flood flow eroded a water gap at least 1365 feet deep into the rising mountain ridge before the rising mountain ridge won the contest and the south oriented flood flow was reversed so as to flow in a north direction.

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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