Silver Bow Creek-Jefferson River drainage divide area landform origins along continental divide, Silver Bow and Jefferson Counties, Montana, USA

Authors


Abstract:

This essay uses topographic map evidence to interpret landform origins in the region between Silver Bow Creek and the Jefferson River along the east–west continental divide in Silver Bow and Jefferson Counties, Montana. The continental divide in the north half of the study region is oriented in a north to south direction and serves as the Silver Bow-Jefferson County border with Silver Bow County being west of the continental divide. Further south in the study region the continental divide extends in more of an east to west direction across southern Silver Bow County. South and east of the continental divide are southeast oriented tributaries to the northeast oriented Jefferson River, which is one of the three rivers forming the north oriented Missouri River at Three Forks, Montana. West and north of the continental divide are north oriented tributaries to west and north oriented Silver Bow Creek, which is one of the streams forming north and northwest oriented Clark Fork. Multiple through valleys or mountain passes cross the continental divide and link valleys of Silver Bow Creek tributaries with valleys of southeast oriented Jefferson River tributaries. The deepest of these through valleys are today used as transportation routes and include Homestake Pass and Pipestone Pass, although there are numerous other less deep through valleys seen on detailed 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 valleys into them. 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, 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. Barbed tributaries provide further evidence of the flood flow captures and reversals. West of the continental divide the south and southeast oriented flood flow channels were beheaded and reversed by headward erosion of the west-oriented Silver Bow Creek valley and then of the north and northwest oriented Clark Fork valley, which created 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-Jefferson River drainage divide area landform origins along the continental divide in Silver Bow and Jefferson Counties, 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-Jefferson River drainage divide area landform evidence along the continental divide in Silver Bow and Jefferson Counties, Montana will be regarded as evidence supporting the “thick ice sheet that melted fast” paradigm.

Silver Bow Creek-Jefferson River drainage divide area location map

Figure 1: Silver Bow Creek-Jefferson 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-Jefferson River drainage divide along the continental divide in Silver Bow and Jefferson Counties, 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 (a large reservoir flooding the Missouri River valley) before flowing to north edge of figure 1. 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 the 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 joins the Columbia River with water eventually 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 north oriented tributary joining west oriented Silver Bow Creek at Butte is Blacktail Creek. The Silver Bow Creek-Jefferson River drainage divide area investigated in this essay is located west of the Jefferson River, south of Interstate highway 90, and east of a line between Butte and Twin Bridges.

Before looking at detailed maps of the Silver Bow Creek-Jefferson 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 to 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. 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 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 a 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. Headward erosion of the east oriented Jefferson River valley captured south oriented flood flow on the present day north oriented Clark Fork 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 seen in figure 1. The north oriented Blacktail Creek was eroded by reversals of flood flow on the north end of a beheaded south oriented flood flow channel.

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

Figure 2: Detailed location map Silver Bow Creek-Jefferson 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-Jefferson River drainage divide area along the continental divide in Silver Bow and Jefferson Counties, Montana and shows drainage routes not seen in figure 1. County boundaries are shown and Silver Bow County is labeled and Jefferson County is 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 the Jefferson County-Silver Bow County boundary just east of Butte, where it is oriented in a north to south direction. South of Butte, near the small town of Donald, the continental divide orientation changes and extends in a west direction to the west center edge of figure 2. Feely is a small town 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 from the south center edge of figure 2 to near Whitehall and Cardwell before flowing in a southeast and northeast direction to the east edge of figure 2 (south of center). Big Pipestone Creek is a southeast oriented tributary originating near Elk Park Pass (northeast of Butte) and joining the Jefferson River near Whitehall. Note other southeast oriented tributaries flowing to the northeast oriented Jefferson River segment. The north oriented (and unlabeled) stream originating at Feely is Sand Creek, which flows to west oriented Silver Bow Creek near the small town of Ramsay. Silver Bow Creek flows from Butte in a west direction before turning to flow in a north direction to Warm Springs near the north edge of figure 2 (west half). Blacktail Creek is the unlabeled north oriented stream flowing just from west of the small town of Donald to Butte, where Silver Bow Creek originates. Clark Fork is formed at the confluence of tributaries at Warm Springs and flows in a north direction to the north edge of figure 2 and north of figure 2 turns 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 across the continental divide.

Bison Creek-Big Pipestone Creek drainage divide area

Figure 3: Bison Creek-Big Pipestone 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 Bison Creek-Big Pipestone Creek drainage divide area. The highway proceeding north from the east side of Butte crosses the east-west continental divide at Elk Park Pass between the small towns of Woodville and Columbia Gardens. The east-west continental divide in this map is the Jefferson-Silver Bow County line and is shown with a labeled dashed line which extends in a south direction from the north edge of figure 3 (west of the highway) to the south edge of figure 3 near Highview (slightly west of center) and follows the high ridge east of Butte. Blacktail Creek is the north oriented stream west of the continental divide flowing into Butte on the east side of the County Airport (in southwest quadrant of figure 3). Once in Butte Blacktail Creek turns to flow in a west direction and to become Silver Bow Creek with water eventually reaching the Pacific Ocean. Bison Creek is the north-northeast oriented stream originating near Elk Park Pass and flowing to the north edge of figure 3 (west of center) with water eventually reaching the Gulf of Mexico. Big Pipestone Creek is formed at the confluence of several tributaries at Delmoe Lake (east half of figure 3) and flows in a south-southeast direction to the south edge of figure 3 (near southeast corner). South and east of figure 3 Big Pipestone Creek flows to the Jefferson River. Among the streams flowing to Delmoe Lake are southeast oriented Honey Creek, which originates east of Elk Park Pass, and east-northeast oriented O’Neil Creek, which originates east of Butte. A close look at figure 3 reveals the southeast oriented Honey Creek valley is linked by a high level through valley with west oriented Bison Creek headwaters and the O’Neil Creek valley is also linked by a high level through valley with west oriented Blacktail Creek tributary valleys. The contour interval for figure 3 is 50 meters and the through valley at the Honey Creek northwest end has a floor elevation at least 350 meters higher than the Bison Creek valley floor to the northwest. The through valley linking O’Neil Creek with the Blacktail Creek valley has a floor elevation at least 500 meters higher than the Blacktail Creek valley elevation to the west. Yet the through valleys are at least 200 meters deep based on elevations of high points along the drainage divides. These through valleys are evidence of southeast and east oriented flood flow channels that once crossed the region and converged in the present day Delmoe Lake region prior to the existence of the deep Bison Creek and Blacktail Creek valleys. The floodwaters converged to flow in a southeast direction along the present day Big Pipestone Creek alignment to the Jefferson River alignment, although at that tome floodwaters on the Jefferson River alignment were probably still flowing in a south direction. Flood flow to the Big Pipestone Creek flood flow channel was beheaded when headward erosion of a much deeper south-oriented flood flow channel on the Blacktail Creek (and Bison Creek) alignment captured the flood flow. Next the flood flow was captured by headward erosion of a still deeper west oriented Silver Bow Creek valley, which diverted the floodwaters in a west direction and then in a south direction on the present day Sand Creek-Divide Creek alignment. Subsequently headward erosion of the deep east oriented Boulder River valley (north of figure 3) beheaded and reversed flood flow on the Bison Creek alignment to create the north-northeast oriented Bison Creek drainage route and Elk Park Pass. Reversal of flood flow that created the north and northwest oriented Clark Fork drainage basin probably was late in the sequence of events.

Detailed map of Blacktail Creek-O’Neil Creek drainage divide area

Figure 4: Detailed map of Blacktail Creek-O’Neil 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 Blacktail Creek-O’Neil Creek drainage divide area seen is less detail in figure 3. The east-west continental divide serves as the Jefferson-Silver Bow County line and is shown by a labeled dashed line extending from the north center edge to the south center edge of figure 4. Blacktail Creek flows in a northwest direction across the southwest corner of figure 4. Blacktail Creek tributaries from the east include southwest oriented Mode S Canyon, Brookside Canyon, and Reese Canyon. Note how these tributaries are oriented in southwest directions to join a north oriented stream. East of the continental divide O’Neil Creek originates in section 26 and flows in a southeast direction before turning to flow in an east-northeast direction to the east center edge of figure 4. An O’Neil Creek tributary originates in section 23 and flows in a southeast and east-southeast direction to join O’Neil Creek near the east edge of figure 4. Note how a through valley links that tributary’s headwaters valley with the south oriented O’Neil Creek headwaters valley. The map contour interval for figure 4 is 40 feet and the through valley floor elevation at the drainage divide is between 7600 and 7640 feet. Elevations to the east and west rise to more than 7800 feet, which means the through valley is at least 160 feet deep. Compared to the deep valley on the west side of the continental divide where elevations in Butte are less than 5500 feet this north to south oriented through valley appears to be a minor landscape feature. Yet the through valley was eroded by south oriented flood flow at a time when the deep valley to west did not exist (see discussion in figure 6 about through valley in section 35, which links the O’Neil Creek valley with the south-southeast oriented Homestake Creek valley to the south). Note in the southwest quadrant of section a through valley linking the O’Neil Creek headwaters valley with the Mode S Canyon and Brookside Canyon valleys. The through valley floor elevation at the continental divide is also between 7600 and 7640 feet while elevations along the continental divide near the south edge of figure 4 rise to 8225 feet and near the north edge of figure 4 the elevations rise to 8251 feet, suggesting the through valley is approximately 600 feet deep. In the west half of section 23 a slightly deeper through valley links the O’Neil Creek tributary valley with the Reese Canyon valley. These through valleys suggests a south oriented flood flow channel along the east side of the continental divide once flowed along several flood flow routes to a south oriented flood flow channel on the present day north oriented Blacktail Creek alignment. Headward erosion of the O’Neil Creek valley and then of its tributary valley from the southeast oriented Big Pipestone Creek valley then captured the south oriented flood flow channel along the present day continental divide and diverted the flood water in an east direction to the Big Pipestone Creek flood flow channel. Subsequently south oriented flood flow on the present day north oriented Bison Creek alignment deeply eroded the basin west of the continental divide (where Butte is located today).

Blacktail Creek-Homestake Creek drainage divide area

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

Figure 5 illustrates the Blacktail Creek-Homestake Creek drainage divide area east and south of figure 3 and includes a significant overlap area with figure 3. The east-west continental divide serves as the Jefferson-Silver Bow County line and extends from the north edge to the south edge in the west half of figure 5. West of the continental divide Blacktail Creek flows in a northeast direction from near the southeast corner of figure 5 to the highway switchbacks and then in a north direction through Thompson Park to Butte in the northwest corner of figure 5. Delmoe Lake is located near the north center edge of figure 5. Big Pipestone Creek flows in a southeast direction from Delmoe Lake to Pipestone Hot Springs and the east edge of figure 5 (south half). The northeast oriented stream joining Big Pipestone Creek at the east edge of figure 5 is Little Pipestone Creek, which will be seen in figure 7. Highview is a place name on the continental divide in the west center region of figure 5. The west oriented Big Pipestone Creek tributary originating near Highview is Homestake Creek. Highview is located at the east end of Homestake Pass, which serves as a major transportation route across the continental divide. The map contour interval for figure 5 is 50 meters and the Homestake Pass elevation at the continental divide is between 1950 and 2000 meters. Elevations along the continental divide to the north rise to more than 2500 meters while to south elevations greater than 2200 meters can be seen along the continental (higher elevations are found further to the south and west). These elevations suggest Homestake Pass is at least 200 meters deep and may have been much deeper when originally eroded. Homestake Pass was probably eroded by southeast and east oriented flood flow moving to the southeast oriented Big Pipestone Creek valley at a time when the deep north oriented Blacktail Creek valley did not exist. As seen in figures 7 and 8 the north oriented Blacktail Creek valley is linked by a through valley at Pipestone Pass with southeast oriented Little Pipestone Creek headwaters. Flood flow on the Blacktail Creek alignment was originally in a south and southeast direction and was captured by headward erosion of the northeast oriented Little Pipestone Creek valley. Later headward erosion of the deeper west oriented Silver Bow Creek valley beheaded and reversed flood flow on the Blacktail Creek alignment to create the deep north oriented Blacktail Creek valley seen today. Erosion of that much deeper north oriented Blacktail Creek valley beheaded flood flow to the Homestake Creek valley.

Detailed map of Little Blacktail Creek-Homestake Creek drainage divide area

Figure 6: Detailed map of Little Blacktail Creek-Homestake 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 Little Blacktail Creek-Homestake Creek drainage divide area seen in less detail in figure 5. The Jefferson County-Silver Bow County line is located along the east-west continental divide and is shown by a labeled dashed line extending from the north edge of figure 6 (west half) to the south edge of figure 6 (just west of center). Highview is located in the southwest quadrant of section 13 and Homestake (at the west end of Homestake Pass) is located in the east half of section 13. Between Highview and Homestake is Homestake Pass, which serves as a major transportation route across the continental divide. Homestake Creek flows in a south, southeast, and east direction from the north center edge of figure 6 to the east edge of figure 6 (south of center). A Homestake Creek tributary flows in a southeast direction to the town Homestake and then in an east-southeast direction to join Homestake Creek in the north half of section 20. The northwest oriented stream in the southwest quadrant of figure 6 (west of the continental divide) is Little Blacktail Creek, which west of figure 6 flows to north oriented Blacktail Creek. The map contour interval for figure 6 is 40 feet and the Homestake Pass elevation at the continental divide appears to be between 6320 and 6360 feet (the Bench Mark with an elevation of 6331 feet may be at the pass). Elevations greater than 8000 feet can be found along the continental just north of figure 6 while elevations greater than 7400 feet can be found along the continental divide south of figure 6 (southof Pipestone Pass seen in figure 8 elevations are greater than 7600 feet). These elevations suggest Homestake Pass is as much as 1000 feet deep or even deeper. Yet, elevations of less than 5600 feet are found in the Little Blacktail Creek valley along the west edge of figure 6, which suggest at least 800 feet of material has been removed from the basin west of Homestake Pass since the last east and southeast oriented flood water flowed across Homestake Pass. North of figure 6 Homestake Creek originates just south of the O’Neil Creek headwaters seen in figure 4 and then flows in a south-southeast direction just east of the continental divide to the region seen in figure 6. A through valley seen in section 35 of figure 4 links the south oriented O’Neil Creek headwaters with the south oriented Homestake Creek headwaters and provides evidence of a south-southeast oriented flood flow channel (east of the continental divide) that was captured by headward erosion of the east-northeast oriented Homestake Creek valley.

Blacktail Creek-Little Pipestone Creek drainage divide area

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

Figure 7 illustrates the Blacktail Creek-Little Pipestone Creek drainage divide area south and west of figure 5 and includes a significant overlap area with figure 5. Homestake Pass is located near the north center edge of figure 7. The Jefferson County-Silver Bow County line, which is located along the continental divide is marked with a labeled dashed line extending from Homestake Pass southward to the highway near the center of figure 7. At that location is another deep pass across the continental divide (Pipestone Pass) and the county line and continental divide also diverge. West and south of Pipestone Pass the continental divide is not marked but follows the divide between north-oriented drainage (in west half of figure 7) and east oriented Fish Creek, (which flows to the southeast corner of figure 7) and west oriented drainage (which flows to the southwest corner of figure 7). The north oriented drainage in the west half of figure 7 flows to west oriented Silver Bow Creek, which flows to the north and northwest oriented Clark Fork. Fish Creek flows to the Jefferson River while the west oriented drainage in the southwest corner of figure 7 flows to Big Hole River, which then flows to the Jefferson River. Blacktail Creek originates south and west of Pipestone Pass and flows in a north-northwest and northeast direction to the switchbacks on the highway and then in north-northwest direction (adjacent to the highway) to the north edge of figure 7. A northwest oriented Blacktail Creek tributary originates near Pipestone Pass and joins Blacktail Creek near the highway switchbacks. Little Pipestone Creek flows in a southeast and east-northeast direction from Pipestone Pass to the east edge of figure 7 (the highway follows Little Pipestone Creek) and joins Big Pipestone Creek east of figure 7. The map contour interval for figure 7 is 50 meters and the Pipestone Pass elevation is between 1950 and 2000 meters. Elevations on either side of the pass rise to more than 2400 meters suggesting the pass is at least 400 meters deep. Note how the Pipestone Pass and Homestake Pass elevations are similar. Before a reversal of flood flow that created the north oriented Blacktail Creek drainage route the deep Pipestone and Homestake Pass flood flow channels were eroded as diverging (and converging?) flood flow channels. The reversal of flood flow that created the north oriented Blacktail Creek drainage route ended all flood flow across both of the passes. Basin Creek is the north oriented stream west of Blacktail Creek and near the west edge of figure 7 and will be better seen in figures 9 and 10 below.

Detailed map of Blacktail Creek-Little Pipestone Creek drainage divide area

Figure 8: Detailed map of Blacktail Creek-Little Pipestone 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 Blacktail Creek-Little Pipestone Creek drainage divide area seen in less detail in figure 7. The continental divide is shown by a labeled dashed line and extends from the south edge of figure 8 (near section 14-15 border) to the north edge of figure 8 (along county line). Blacktail Creek flows in a north-northwest direction from the south edge of figure 8 (near east edge of section 16 near southwest corner of figure 8) to Thompson Park along the west center edge of figure 8. From the west center edge of figure 8 Blacktail Creek flows in a northeast direction to the Thompson Park area in section 3 where it turns to flow in a north-northwest direction to the north edge of figure 8. Little Pipestone Creek originates in the west half of section 1 and flows in a south-southwest direction to the northeast quadrant of section 11 where it turns to flow in a southeast direction to the south edge of figure 8 (near line between sections 13 and 18 near southeast corner of figure 8). Pipestone Pass is located in the northwest quadrant of section 11 near the center of figure 8 and links a northwest oriented Blacktail Creek tributary valley with the southeast oriented Little Pipestone Creek valley. The map contour interval for figure 8 is 40 feet and the Pipestone Pass elevation is given as 6453 feet (about 100 feet higher than Homestake Pass to the north). Elevations rise along the continental divide near the south edge of figure 8 to more than 7600 feet and to more than 7400 feet near the north edge of figure 8 (north of Homestake Pass elevations rise to more than 8000 feet). Pipestone Pass, like Homestake Pass, is a water-eroded feature and was eroded by southeast oriented flood flow prior to the reversal of flow in the present day north oriented Blacktail Creek drainage basin. At that time elevations north and west of figure 8 were higher than the floor of Pipestone Pass and floodwaters could freely flow in a southeast direction to the actively eroding southeast oriented Little Pipestone Creek valley segment seen in figure 8. Other much shallower through valleys (or mountain passes) can be seen crossing the continental divide in figure 8. These shallower through valleys (or mountain passes) provide evidence of a time before erosion of the deep Pipestone Pass valley when southeast oriented floodwaters flowed across the region seen in figure 8. At that time the high mountain ridge formed by the continental divide today did not exist and floodwaters freely flowed across the region. Ice sheet related crustal warping probably was responsible for uplift of the high mountain ridge, which occurred as floodwaters flowed across the region and eroded the deep Pipestone Pass flood flow channel, which was one of the final southeast oriented flood flow channel prior to the reversal of flood flow that created the Blacktail Creek drainage basin.

Blacktail Creek-Fish Creek drainage divide area

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

Figure 9 illustrates the Blacktail Creek-Fish Creek drainage divide area south and slightly west of figure 7 and includes a significant overlap area with figure 7. The continental divide is labeled (but there is no dashed line) in the northwest quadrant of figure 9 and extends in a southeast direction from the northwest corner of figure 9 to section 31 at the south end of north oriented Basin Creek (in west center area of figure 9). Basin Creek is a north oriented Silver Bow Creek tributary in the northwest quadrant of figure 9. Just south of the north oriented Basin Creek headwaters are headwaters of west and west-southwest oriented Moose Creek, which west of figure 9 flows to the south oriented Big Hole River, with the Big Hole River then making a U-turn to join the northeast oriented Jefferson River. East of section 31 are north oriented headwaters of Fish Creek, which after flowing in a north direction turns to flow in a generally east direction to the east center edge of figure 9 and east of figure 9 turns to flow in a southeast direction to join the northeast oriented Jefferson River. Blacktail Creek originates just north of the center of figure 9 and flows in an east-southeast, north-northwest, and northeast direction to the highway switchbacks near the north center edge of figure 9. North of figure 9 Blacktail Creek flows in a north direction to Silver Bow Creek. Little Pipestone Creek flows in a southeast and east-northeast direction along the highway seen in the northeast quadrant of figure 9. Note how in section 31 the north oriented Basin Creek valley is linked by a deep through valley with the southwest oriented Moose Creek valley. The map contour interval for figure 9 is 50 meters and the through valley floor elevation at the continental divide is between 2200 and 2250 meters. East of the through valley elevations exceed 2450 meters while to the west the highest elevations seen in figure 9 exceed 2350 meters, although west of figure 9 and west of a much deeper and broader north to south oriented through valley (or pass across the continental divide) elevations greater than 2800 meters can be found. Based on the local elevations seen in figure 9 the section 31 through valley is at least 100 meters deep, although south oriented flood flow may have eroded a much broader and deeper through valley than can be seen using the figure 9 evidence. In either case the through valley is a water-eroded feature and was eroded by south oriented flood flow prior to the flood flow reversal that created the present day north oriented Basin Creek drainage route. The flood flow reversal was probably greatly aided by ice sheet related crustal warping that was raising the present day continental divide mountain ridge. Uplift of the mountain ridge was occurring as south oriented flood water was flowing across it. At first erosion eroded the south oriented valley as fast as the uplift occurred, but in time headward erosion of the much deeper west oriented Silver Bow Creek valley to the north of figure 9 was able to behead and reverse the south oriented flood flow to create the present day north oriented Basin Creek drainage basin.

Detailed map of Basin Creek-Fish Creek drainage divide area

Figure 10: Detailed map of Basin Creek-Fish 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 Basin Creek-Fish Creek drainage divide area seen in less detail in figure 9. The continental divide is shown with a labeled dashed line extending along the ridge top in a meandering direction from the south edge of figure 10 (west half) to near the northeast corner of figure 10. Basin Creek flows in a north direction near the west edge of figure 10 and north of figure 10 joins west and north oriented Silver Bow Creek. Blacktail Creek originates in section 20 (on north side of continental divide) and flows in an east-southeast direction into section 21 before turning to flow in a north direction to the north edge of figure 10 and north of figure 10 to west and north oriented Silver Bow Creek. Fish Creek flows in a northeast direction from the south edge of figure 10 (in section 32-west of center along south edge of figure 10) and then near the corner of sections 27, 28, 32, and 33 turns to flow in a southeast direction to the south edge of figure 10. South and east of figure 10 Fish Creek flows in an east and southeast direction to join the northeast oriented Jefferson River. Note how the north oriented Basin Creek valley is linked by a northwest to southeast oriented through valley across the continental divide with the east oriented Fish Creek valley (an aqueduct makes use of the through valley). The map contour interval for figure 10 is 40 feet and the through valley floor elevation at the drainage divide is shown as being 7505 feet. The continental divide in section 20 rises to 8018 feet and near the east edge of section 30 it rises to 8151 feet meaning the through valley is more than 500 feet deep. The through valley is a water-eroded feature and was eroded by southeast oriented flood flow prior to headward of the much deeper Basin Creek valley, which before being reversed to flow in a north direction was a south oriented flood flow channel. Another interesting through valley seen in figure 10 links the Blacktail Creek headwaters valley with southeast oriented Horse Creek valley, with Horse Creek joining Fish Creek near the point where Fish Creek turns to flow in a southeast direction. This second through valley is located along the line between section 21 and section 28 and has a floor elevation at the continental divide of between 7560 and 7600 feet. Limekiln Hill to the east rises to 8085 feet while as previously mentioned the continental divide in section 30 to the west rises to 8151 feet. This Blacktail Creek-Horse Creek through valley is almost 500 feet deep if not deeper and is also a water-eroded feature and may have been eroded by southeast oriented flood flow from the Basin Creek drainage basin (prior to the Basin Creek flood flow reversal) that was captured by reversed flow on the Blacktail Creek valley segment seen in figure 10. These captures were complex and each capture probably only affected a local segment of a present day drainage system (e.g. further north and east the captured flood water may have moved in southeast direction again to Little Pipestone Creek and at that time did not flow further north to Silver Bow Creek as Blacktail Creek does today).

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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