Silver Bow Creek-Big Hole River drainage divide area landform origins along continental divide, Silver Bow County, Montana, USA

Authors


Abstract:

This essay uses topographic map evidence to interpret landform origins in the region between Silver Bow Creek and the Big Hole River along the east–west continental divide in Silver Bow County, Montana. The east-west continental divide crosses the study region in roughly a west to east direction with north oriented drainage north of the continental divide flowing to west and north oriented Silver Bow Creek, which flows to north and northwest oriented Clark Fork with water eventually reaching the Pacific Ocean. South and southwest oriented drainage south of the continental divide flows to the south oriented Big Hole River, which south of the study region makes a large U-turn to flow to the northeast oriented Jefferson River, which then flows to the north oriented Missouri River with water eventually reaching the Gulf of Mexico. Multiple through valleys or mountain passes cross the continental divide and link valleys of north oriented Silver Bow Creek tributaries with valleys of south oriented Big Hole River tributaries. The deepest of these through valleys is today used as a major transportation route and crosses the continental divide at Deer Lodge Pass, although numerous other less deep through valleys can be seen on topographic maps. The through valleys were eroded as south and southeast oriented flood flow channels at a time when the continental divide did not exist and Montana mountain ranges were just beginning to emerge. Floodwaters were derived from a thick North American ice sheet and were flowing from western Canada across Montana. The thick ice sheet was located in a deep “hole” and the ice sheet weight was causing crustal warping that raised Montana and Wyoming mountain ranges. Floodwaters flowed across what were emerging mountain ranges and carved deep south oriented valleys into them. The Deer Lodge Pass through valley was eroded as a deep south oriented flood flow channel. Headward erosion of the west-oriented Silver Bow Creek valley gradually beheaded many of the adjacent south oriented flood flow channels and concentrated flood flow in the much deeper Deer Lodge Pass flood flow channel. Headward erosion of deep southeast, northeast, and east oriented valleys, including headward erosion of the deep north oriented Missouri River valley from space in the deep “hole” being opened up by ice sheet melting, then captured south oriented flood flow east and south of the present day continental divide. Floodwaters on north ends of beheaded flood flow channels reversed flow directions to erode north oriented valleys including the north oriented Missouri River valley (east of the study region). The Big Hole River U-turn provides evidence of the flood flow reversal that took place when the newly reversed and then north oriented Missouri River valley captured south oriented flood flow from the south oriented Deer Lodge Pass flood flow channel. Finally, west and north of the present day continental divide south and southeast oriented flood flow channels were beheaded and reversed to erode the north and northwest oriented Clark Fork valley and to create the present day continental 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 Silver Bow Creek-Big Hole River drainage divide area landform origins along the continental divide in Silver Bow 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 Silver Bow Creek-Big Hole River drainage divide area landform evidence along the continental divide in Silver Bow County, Montana will be regarded as evidence supporting the “thick ice sheet that melted fast” paradigm.

Silver Bow Creek-Big Hole River drainage divide area location map

Figure 1: Silver Bow Creek-Big Hole 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 Silver Bow Creek-Big Hole River drainage divide along the continental divide in Silver Bow County, Montana and illustrates a region in southwestern Montana. The Missouri River is located in the east half of figure 1 and is formed at Three Forks (center east) at the confluence the north and northwest oriented Gallatin River, north oriented Madison River, and 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 (large reservoir flooding the Missouri River valley). North of figure 1 the Missouri River turns to flow 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 Jefferson River is formed at the confluence of Big Hole and Beaverhead Rivers near Twin Bridges. Note how the Big Hole River flows in a north direction west of the Pioneer Mountains and then turns to flow in an east-southeast direction to the town of Divide. From Divide the Big Hole River flows in a south-southeast and northeast direction to join the north-northeast oriented Beaverhead River. North of the south-southeast oriented Big Hole River segment are headwaters of north and northwest oriented Clark Fork, which flows from Warm Springs to Deer Lodge, Garrison, and Drummond to the figure 1 north edge. North and west of figure 1 Clark Fork eventually joins the Columbia River with water reaching the Pacific Ocean. The west and north oriented stream flowing from the city of Butte to Warm Springs to form north oriented Clark Fork is Silver Bow Creek. The Silver Bow Creek-Big Hole River drainage divide area investigated here is located between the west oriented Silver Bow Creek segment and the south-southeast and northeast oriented Big Hole River segments.

Before looking at detailed maps of the Silver Bow Creek-Big Hole 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. 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 or deep valleys or basins in western Montana or in the region south of figure 1 and floodwaters could freely flow across locations that today would be blocked by high drainage divides. Montana, Wyoming, and other mountain ranges were formed by ice sheet related crustal warping and occurred as floodwaters flowed across them. 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 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 in Montana 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 eastern and central Montana. At the same time headward erosion of the south and west oriented Columbia River valley from the Pacific Ocean beheaded and reversed southeast oriented flood flow channels moving floodwaters across western 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 channels. 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 reversed and deepened during the massive upper Missouri River drainage basin flood flow reversal. Uplift of the Yellowstone Plateau and mountain ranges south of figure 1 probably contributed significantly to the massive flood flow reversal. Reversal of flood flow in the present day north oriented Jefferson River valley captured south oriented flood flow on the present day north oriented Clark Fork-Big Hole River alignment, which created the present day Big Hole River U-turn. The north oriented Big Hole River segment flows on the alignments of what began as south oriented flood flow channels. A similar situation occurred north and west of the continental divide where headward erosion of the deep south and west oriented Columbia River valley and tributary valleys (north and west of figure 1) beheaded and reversed southeast and south oriented flood flow channels to create the present day north and northwest oriented Clark Fork drainage system. The west oriented Silver Bow Creek valley probably eroded headward from a south oriented flood flow channel on the present day north oriented Clark Fork alignment.

Detailed location map for Silver Bow Creek-Big Hole River drainage divide area

Figure 2: Detailed location map Silver Bow Creek-Big Hole 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 Silver Bow Creek-Big Hole River drainage divide area along the continental divide in Silver Bow County, Montana and shows drainage routes not seen in figure 1. County boundaries are shown and Silver Bow County is labeled with Jefferson County being the unlabeled county in the northeast quadrant of figure 2. Green shaded areas are National Forest lands, which generally are located in mountainous regions. The east-west continental divide is labeled and is located along the Silver Bow County-Jefferson County boundary just east of Butte where the continental divide is oriented in a north to south direction. South of Butte, near the small town of Donald, the continental divide orientation changes and is shown as a dashed line extending in a meandering west direction to the west edge of figure 2 (south of center). Feely is a railroad siding name where the railroad and highway cross the continental divide (between the large words “SILVER” and BOW”). The south oriented stream originating at Feely is Divide Creek, which joins the southeast and south oriented Big Hole River at the town of Divide. South of figure 2 the Big Hole River makes a U-turn and joins the northeast oriented Beaverhead River to form the north-northeast and northeast oriented Jefferson River, which flows across the southeast corner of figure 2. Note southwest oriented tributaries joining the south oriented Big Hole River south of the town of Divide. Silver Bow Creek flows from Butte in a west direction before turning to flow in a north direction to the north edge of figure 2 (west half). Clark Fork is formed at the confluence of tributaries at Warm Springs (just north of figure 2) and flows in a north direction before turning to flow in a northwest direction. The north to south oriented highway and railroad at Feely are located in a deep north-south oriented pass (Deer Lodge Pass) across the continental divide and high mountains are on either side. Deer Lodge Pass was eroded by south and southeast oriented melt water flowing from southeast British Columbia to and across western Montana. South of Deer Lodge Pass the melt water floods initially flowed in a south and southeast direction into eastern Idaho and northwest Wyoming, although as ice sheet related crustal warping raised mountain barriers the flood waters were reversed to flow in a north direction to the newly reversed and then north oriented Missouri River valley, which accounts the Big Hole River U-turn.

Basin Creek-Moose Creek drainage divide area

Figure 3: Basin Creek-Moose 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 Basin Creek-Moose Creek drainage divide area. Deer Lodge Pass is located in the northwest corner region of figure 3 and will be better illustrated in figures 7 and 8 below. Basin Creek is the north oriented stream originating south of the center of figure 3 and flowing to the north center edge of figure 3. North of figure 3 Basin Creek flows to west and north oriented Silver Bow Creek, which then forms north and northwest oriented Clark Fork with water eventually reaching the Pacific Ocean. The continental divide extends in a southeast direction from Deer Lodge Pass near the northwest corner of figure 3 to the south end of the north oriented Basin Creek drainage basin (in south center area of figure 3) and then in a northeast direction to near the northeast corner of figure 3. North oriented drainage north of the continental divide flows to Silver Bow Creek and eventually to the Pacific Ocean. South oriented drainage south of the continental divide flows to the Big Hole River and east oriented drainage to the east edge of figure 3 flows to the Jefferson River, with water in both cases eventually reaching the Gulf of Mexico, The west-southwest oriented stream flowing from just south of the north oriented Basin Creek headwaters is Moose Creek, which flows to south edge of figure 3 (near southwest corner) and south and west of figure 3 Moose Creek joins the south oriented Big Hole River, which then makes a U-turn to join the northeast oriented Beaverhead River and to form the northeast oriented Jefferson River with water eventually reaching the Gulf of Mexico. Note how in section 31 the north oriented Basin Creek headwaters valley is linked by a through valley with the west-southwest oriented Moose Creek headwaters valley. The map contour interval for figure 3 is 50 meters and the through valley floor elevation at the drainage divide is between 2200 and 2250 meters, which is considerably higher than the Deer Lodge Pass elevation of between 1750 and 1800 meters. Yet the Basin Creek-Moose Creek through valley is surrounded by higher elevations on either side and is at least 150 meters deep. The through valley was eroded by south oriented flood flow, probably at a time when the deep Deer Lodge Pass valley to the west did not exist. Flood water erosion of the deep Deer Lodge Pass flood flow channel in time captured the south oriented flood flow moving in the Basin Creek-Moose Creek through valley causing a reversal of flow in the Basin Creek drainage basin. That reversal of flow was probably greatly aided by ice sheet related crustal warping that raised mountain ridges in the figure 3 map area as the floodwaters were flowing across the region.

Detailed map of Basin Creek-Moose Creek drainage divide area

Figure 4: Detailed map of Basin Creek-Moose 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 Basin Creek-Moose Creek drainage divide area seen is less detail in figure 3. The Middle Fork Moose Creek originates in section 31 and flows in a southwest direction to near the southwest corner of figure 4. The south-southeast and south oriented stream near the west edge of figure 4 is the North Fork Moose Creek, which is better illustrated in figures 5 and 6 below. The North and Middle Forks Moose Creek join near the southwest corner of figure 4 and Moose Creek then flows in a southwest direction to join the south oriented Big Hole River with water eventually reaching the Gulf of Mexico. Basin Creek originates in the north half of section 31 and flows in a north direction to the north edge of figure 4 (just east of center) and north of figure 4 Basin Creek joins west and north oriented Silver Bow Creek with water eventually reaching the Pacific Ocean. Fish Creek originates in the north half of section 32 and flows in an east direction to east edge of figure 4 (north of center) and east of figure 4 turns to flow in a southeast direction to join the northeast oriented Jefferson River with water eventually reaching the Gulf of Mexico. The continental divide is shown with a faint dashed line extending across the north half of section 25 and then in a south direction to the west center edge of section 31 before turning in an east direction to the center of section 32. From the center of section 32 the continental divide is shown with a darker and labeled dashed line extending in a north direction to the north edge of figure 4. Note how multiple through valleys link the north oriented Basin Creek headwaters valley with southwest oriented Moose Creek valley and with the east oriented Fish Creek valley. The deepest of the through valleys are found near the corner of sections 25, 30, 31, and 36 and have floor elevations at the drainage divide of between 7200 and 7240 feet (the map contour interval for figure 4 is 40 feet). These through valleys link the north oriented Basin Creek valley with the valley of a west, southwest, south, and west oriented North Fork Moose Creek tributary. The through valley in section 31 has a floor elevation at the drainage divide of between 7280 and 7320 feet and links the north oriented Basin Creek valley with the southwest oriented Middle Fork Moose Creek valley. Elevations in section 25 to the northwest rise to 7752 feet while the ridge to the southeast rises even higher suggesting the deepest through valleys may be more than 500 feet deep. Higher level west to east oriented through valleys along the line between sections 31 and 32 link the north oriented Basin Creek valley and the southwest oriented Middle Fork Moose Creek with the east oriented Fish Creek valley. The floor elevation of the northern through valley is between 7760 and 7800 feet with southern through valley floor elevation slightly higher at between 7800 and 7840 feet. The north-south oriented ridge the through valleys (or present day wind gaps) cross rises to 8151 feet in section 30 to the north and to more than 8800 feet near the south edge of figure 4. These elevations suggest the through valleys are 350 feet or more deep. All of these through valleys were eroded as flood flow channels while deeper valleys used by present day streams eroded headward in the region.

Bear Gulch-Moose Creek drainage divide area

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

Figure 5 illustrates the Bear Gulch-Moose Creek drainage divide area slightly west and north of figure 3 and overlaps much of the area seen in figure 3. Deer Lodge Pass is located in the northwest quadrant of figure 5 and the north to south oriented highway and railroad near the west edge of figure 5 cross the continental just south of Feely Hill. The continental divide extends in a southeast direction from the west edge of figure 5 (north half see word “DIVIDE”) across the deep north to south oriented through valley and then follows the words “CONTINENTAL DIVIDE” to the Basin Creek-Moose Creek through valley in section 31 (near south center edge of figure 5). The continental divide then extends in a north and northeast direction to the east edge of figure 5 (just north of center). Figure 5 shows south-southeast and south oriented North Fork Moose Creek, which joins southwest oriented Middle Fork Moose Creek (just west of the south center edge of figure 5) and its relationship with adjoining drainage basins. East of the south oriented North Fork Moose Creek is the north oriented Basin Creek valley with Basin Creek turning to flow in a northeast direction near the north edge of figure 5 (east of center). Bear Gulch is a south and east oriented Basin Creek tributary located noted north of the south-southeast oriented North Fork Moose Creek valley. West of Bear Gulch is west oriented Curly Gulch, which drains to south-southwest oriented Divide Creek, which flows from the Deer Lodge Pass area to the southwest corner of figure 5 and then to the south oriented Big Hole River. Note the north-northwest oriented Curly Gulch headwaters valley on the same alignment as the south-southeast oriented North Fork Moose Creek valley and the through valley linking the two opposing drainage routes. The map contour interval for figure 5 is 50 meters and the through valley floor elevation at the continental divide is between 2100 and 2150 meters (still much higher than the 1750-1800 meter elevation at Deer Lodge Pass). Locally elevations on either side of the through valley rise to more than 2250 meters, although much higher elevations can be found in either direction. Regardless of whether this through valley is considered a local valley or simply one of several channels on the floor of what was once a much broader and deeper through valley, this through valley is a water eroded feature and was eroded prior to erosion of the much deeper Deer Lodge Pass through valley to the west. The north-northwest oriented Curly Gulch headwaters valley was eroded by a reversal of flood flow when headward erosion of the deeper west oriented Curly Gulch valley from the deeper south oriented Divide Creek valley (which eroded headward into the region) beheaded the south-southeast flood flow channel to the North Fork Moose Creek valley. Similar, but slightly higher through valleys link the south and east oriented Bear Gulch valley with the south-southeast oriented North Fork Moose Creek valley and provide evidence of multiple converging and diverging flood flow channels that once crossed what is today the east-west continental divide.

Detailed map of Bear Gulch-North Fork Moose Creek drainage divide area

Figure 6: Detailed map of Bear Gulch-North Fork Moose 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 Bear Gulch-North Fork Moose Creek drainage divide area seen in less detail in figure 5. Basin Creek flows in a north-northwest direction in the northeast corner of figure 6 and Basin Creek Reservoir floods the Basin Creek valley. North of figure 6 Basin Creek flows to Silver Bow Creek with water eventually reaching the Pacific Ocean. Bear Gulch is the south and southeast oriented stream in section 10 and flows in an east-northeast direction in section 11 to join Basin Creek at Basin Creek Reservoir. Burton Park is the name of the non-forested region straddling the south center edge of figure 6. The North Fork Moose Creek originates in the southeast quadrant of section 16 and flows in a south-southeast direction through Burton Park. South of figure 6 Moose Creek flows to the Big Hole River with water eventually reaching the Gulf of Mexico. Curly Gulch originates in the northeast quadrant of section 16 and drains in a north-northwest direction to section 9 and then turns to drain in a west direction across section 8 to the west edge of figure 6 (north half). West of figure 6 Curly Gulch drains to south oriented Divide Creek and the Big Hole River. Note the continental divide extending from the north center edge of figure 6 to near the southeast corner of figure 6 (marked with a labeled dashed line). Note also the through valley linking the north-northwest oriented Curly Gulch headwaters valley with the south-southeast oriented North Fork Moose Creek valley. The map contour interval for figure 6 is 40 feet and the through valley floor elevation at the drainage divide is between 7000 and 7040 feet. The highest elevation in section 16 to the west is more than 7400 feet while elevations greater than 7500 feet can be found in section 15 to the east. Based on these local elevations the through valley is at least 360 feet deep and provides evidence of a south-southeast oriented flood flow channel that was adjacent to the present day east-west continental divide (note, at this location water on the west side of the east-west continental divide seen in figure 6 flows to the Atlantic Ocean while water on the east side flows to the Pacific Ocean). As an additional note, while the through valley was originally eroded as a south-southeast oriented flood flow channel, during the flood flow reversal that eroded the north-northwest oriented Curly Gulch headwaters valley it is probable that considerable north oriented flood flow used the valley. Before leaving figure 6 observe the through valleys in the southeast quadrant of section 15 linking the east-oriented Bear Gulch valley with the south oriented North Fork Moose Creek valley. These through valleys provide evidence of south oriented flood flow channels that once crossed what is today the east-west continental divide.

Sand Creek-Divide Creek drainage divide area

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

Figure 7 illustrates the Sand Creek-Divide Creek drainage divide area west and slightly north of figure 5 and includes a significant overlap area with figure 5. The continental divide is shown by a labeled dashed line that extends from just south of the northwest corner of figure 7 in a meandering southeast direction to near the southeast corner of figure 7. Deer Lodge Pass is located near the center of figure 7 and is where the deep non-forested north to south oriented valley used by a major north to south oriented highway and railroad crosses the continental divide (near Feely Hill). North oriented Sand Creek drains the north end of this deep through valley while Divide Creek drains the south end. The map contour interval for figure 7 is 50 meters and the through valley floor elevation at the continental divide is between 1750 and 1800 meters, which is considerably lower than elevations of through valleys seen in previous figures. Elevations seen in figure 7 to the east of the through valley rise to more than 2250 meters and much higher elevations are seen in figure 7 to the west. However, by going further east or further west much higher elevations are present, suggesting the through valley may be a deep channel in what was once a much broader and deeper north to south oriented through valley. Regardless of how it is interpreted the through valley is at least 450 meters deep and may be much deeper and while it may be related to regional structures it is also a water-eroded landscape feature. The Deer Lodge Pass through valley was eroded by massive south oriented flood water that became concentrated along this route as ice sheet related crustal warping raised mountain barriers to the east and west faster than flood water erosion could erode south oriented flood flow channels across them. The adjacent flood flow channels, both to the east and the west, were gradually abandoned with floodwaters being concentrated in the Deer Lodge Pass flood flow channel. The concentrated flood flow moving through the Deer Lodge Pass flood flow channel for a time was able to erode the flood flow channel faster than ice sheet related crustal warping could raise the present day continental divide, although in time the crustal warping succeeded in raising a barrier the floodwaters could not overcome. Development of this barrier combined with headward erosion of deeper valleys to the north and west of figure 7 caused a flood flow reversal that resulted in development of the north oriented Sand Creek drainage system, which drains to Silver Bow Creek and north and northwest oriented Clark Fork with water eventually reaching the Pacific Ocean. However, before that flood flow reversal took place the massive flood flow reversal that created the north oriented Missouri River drainage system east of figure 7 had captured the south oriented flood flow south of figure 7. That flood flow reversal and subsequent flood flow capture formed the present day Big Hole River U-turn seen south of figure 7.

Detailed map of Sand Creek-Divide Creek drainage divide area

Figure 8: Detailed map of Sand Creek-Divide 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 Sand Creek-Divide Creek drainage divide area seen in less detail in figure 7. The east-west continental divide is shown with a labeled dashed line extending from the west edge of figure 8 (north half) in a southeast direction across section 28 and then in east direction across the north halves of 33, 34, 35, and 36 before turning to extend in a northeast direction to the east edge of figure 8 (north half). Drainage north of the continental divide is to north oriented Sand Creek, which flows to Silver Bow Creek, which in turn flows to north and northwest oriented Clark Fork with water eventually reaching the Pacific Ocean. Drainage south of the continental divide is to south oriented Divide Creek, which flows to the south oriented Big Hole River, which further to the south makes a U-turn to flow to the northeast oriented Jefferson River, which flows to the north oriented Missouri River with water eventually reaching the Gulf of Mexico. Deer Lodge Pass is where the continental divide crosses the floor of the north to south oriented through valley linking the north oriented Sand Creek valley with the south oriented Divide Creek valley and is found near Feely, which is a railroad siding name just south of the continental divide in section 35. The map contour interval for figure 8 is 40 feet and the Deer Lodge Pass elevation where the railroad crosses the continental divide is shown as being 5801 feet. West of figure 8 and not seen in figure 8 are mountains rising to more than 9000 feet. Also not seen in figure 8 are elevations greater than 8000 feet along the continental east and north of figure 8, although for a considerable distance to the east and northeast the continental divide does not rise significantly above 7400 feet and is crossed by many lower through valleys such as those seen in the previous figures. The Deer Lodge Pass through valley is a remarkable erosional landform and deserves an explanation. The through valley was eroded by south oriented melt water flood flow, which over time was concentrated in the Deer Lodge Pass through valley. At the same time as south oriented flood flow was moving across the region ice sheet related crustal warping was raising the west to east oriented mountain ridge the through valley crosses. This was the most successful of multiple south oriented flood flow channels crossing that rising mountain ridge and was able to erode deeper than the other channels, which were gradually abandoned as the south oriented melt water flood flow was concentrated in this Deer Lodge Pass through valley. However, in time the rising mountain ridge won the battle and successfully formed a barrier that caused a flood flow reversal with floodwaters flowing in north and northwest direction to new and deeper valleys eroding headward from the Pacific Ocean.

Divide Creek-Moose Creek drainage divide area

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

Figure 9 illustrates the Divide Creek-Moose Creek drainage divide area south of figure 7 and includes an overlap area with figure 7. The Big Hole River flows in a southeast and south direction from the west edge of figure 9 (north of center) to the south edge of figure 9 and serves as the Silver Bow-Beaverhead County line. Divide Creek flows in a south-southwest direction from the north edge of figure 9 (west of center) to join the south oriented Big Hole River (south of the town of Divide). Moose Creek flows in a southwest direction from near the east edge of figure 9 to join the south oriented Big Hole River near the south edge of figure 9. Note how the Divide Creek-Moose Creek drainage divide is crossed by multiple through valleys. Starting in the south Interstate Highway 15 makes use of one through valley south of the town of Divide. The map contour interval for figure 9 is 50 meters and the through valley floor elevation where the highway crosses the drainage divide is between 1700 and 1750 meters. Elevations on the hill immediately to the southwest of the through valley and just northeast of the Big Hole River rise to more than 1950 meters while elevations to the northeast of the through valley rise even higher. In other words the through valley is at least 200 meters deep. The through valley was eroded by a southeast oriented flood flow channel, which probably diverged and converged with a flood flow channel on the present day Big Hole River alignment. Continuing north from the first through valley another through valley is located just east of Selway Spring (east of the town of Divide) and is at least 100 meters deep. Still further north the west oriented Lime Gulch headwaters are linked by a through valley with an unnamed south oriented Moose Creek tributary. This third through valley is also at least 100 meters deep. These multiple through valleys provide evidence of what were multiple diverging and converging south and/or southeast oriented flood flow channels such as might be found in a south or southeast oriented anastomosing channel complex, which had been captured by headward erosion of the much deeper southwest oriented Moose Creek valley. Headward erosion of a deeper flood flow channel along the present day south oriented Big Hole River-Divide Creek alignment beheaded the southeast and east oriented flood flow channels moving floodwaters to the southwest oriented Moose Creek valley.

Detailed map of Lime Gulch-Moose Creek drainage divide area

Figure 10: Detailed map of Lime Gulch-Moose 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 Lime Gulch-Moose Creek drainage divide area seen in less detail in figure 9. Divide Creek flows in a south-southwest direction across the northwest corner of figure 10. Lime Gulch originates near the southeast corner of section 2 and drains in a northwest and west direction across sections 3 and 4 to join Divide Creek at the west edge of section 4. Moose Creek flows in a southwest and northwest direction from the east edge of figure 10 (south half) to the north edge of section 13 and then turns to flow in a south-southwest direction to the south edge of figure 10. A south oriented Moose Creek tributary originates in the southwest quadrant of section 1 and flows in a southwest and south direction to the northwest corner of section 12. From the northwest corner of section 12 the Moose Creek tributary flows in a south-southeast direction across section 12 to join Moose Creek, which then flows in a south-southwest direction to the south edge of figure 10 (east of center). Note how a through valley links the northwest oriented Lime Gulch headwaters valley with the south-southeast oriented Moose Creek tributary valley (at corner of sections 1, 2, 11, and 12). The map contour interval for figure 10 is 40 feet and the through valley floor elevation at the drainage divide is between 6280 and 6320 feet. Elevations in section 1 to the northeast rise to 7345 feet while elevations in section 14 to the southwest rise to 6870 feet suggesting the through valley may be 540 feet or more deep. The through valley is a water eroded feature and was eroded by southeast oriented flood flow moving to the south oriented Moose Creek tributary valley, which was eroding headward at that time. At that time the much deeper south oriented Divide Creek valley to the west did not exist, but was probably eroding headward along a shallower flood flow channel on the present day Divide Creek alignment. Headward erosion of that deeper south oriented Divide Creek valley beheaded and reversed the southeast oriented flood flow channel to the south oriented Moose Creek tributary valley, which resulted in the erosion of the west oriented Lime Gulch valley. Note the large gravel pit located in the southwest corner of figure 10. While the topographic evidence provides no information regarding the type of gravel found in that gravel pit it is possible gravel found in the Divide Creek valley may contain debris transported by the melt water floods from north of Deer Lodge Pass. If so such debris would confirm the hypothesis presented in this essay.

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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