Mill Creek-Big Hole River drainage divide area landform origins along continental divide, Silver Bow and Deer Lodge Counties, Montana, USA

Authors


Abstract:

This essay uses topographic map evidence to interpret landform origins in the region between Mill Creek and the Big Hole River along the east–west continental divide in Silver Bow and Deer Lodge Counties, 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 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 Clark Fork tributaries, including east-southeast and northeast oriented Mill Creek, with valleys of south oriented Big Hole River tributaries. The deepest of these through valleys is today used as transportation route and crosses the continental divide at Deer Lodge Pass, although numerous less deep through valleys can be seen on detailed topographic maps in the study region, which is west of Deer Lodge Pass. Headward erosion of east oriented Clark Fork tributary valleys captured south oriented flood flow west of the deep north-to-south oriented Deer Lodge Pass through valley and first diverted the floodwaters to a south oriented flood flow channel on that deep Deer Lodge Pass through valley alignment. However, the flood flow reversal that formed the north and northwest oriented Clark Fork drainage system subsequently reoriented these east oriented valleys to flow to the north oriented Clark Fork headwaters. 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.

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 Mill Creek-Big Hole River drainage divide area landform origins along the continental divide in Silver Bow and Deer Lodge 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 Mill Creek-Big Hole River drainage divide area landform evidence along the continental divide in Silver Bow and Deer Lodge Counties, Montana will be regarded as evidence supporting the “thick ice sheet that melted fast” paradigm.

Mill Creek-Big Hole River drainage divide area location map

Figure 1: Mill 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 Mill Creek-Big Hole River drainage divide along the continental divide in Silver Bow and Deer Lodge Counties, Montana and illustrates a region in southwest 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 (not labeled in figure 1), 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) and then to the 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 northwest corner of figure 1. North and west of figure 1 Clark Fork eventually joins the Columbia River with water reaching the Pacific Ocean. Mill Creek is not shown on figure 1, but is an east-southeast and east-northeast stream south of Anaconda and which joins the north oriented drainage to Clark Fork near the town of Opportunity. The Mill Creek-Big Hole River drainage divide area investigated here is located between Mill Creek segment and the east-southeast Big Hole River segment upstream from the town of Divide and is west of Interstate highway 15.

Before looking at detailed maps of the Mill 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 with 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 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 east oriented Mill Creek valley probably eroded headward from a south oriented flood flow channel on the alignments of present day north oriented Clark Fork segment and the south oriented Big Hole River segment, although that south oriented flood flow channel was subsequently beheaded and reversed to create the north oriented Clark Fork headwaters drainage system and the present day continental divide.

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

Figure 2: Detailed location map Mill 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 Mill Creek-Big Hole River drainage divide area along the continental divide in Silver Bow and Deer Lodge Counties, Montana and shows drainage routes not seen in figure 1. County boundaries are shown and Silver Bow County and Deer Lodge Counties are labeled. Green shaded areas are National Forest lands, which generally are located in mountainous regions. The east-west continental divide is shown with a dashed line extending from the west edge of figure 2 (just north of center) to near the Deer Lodge-Silver Bow County line near the center of figure 2. After making a southward jog along the county line the continental divide extends in a generally east direction to Burnt Mountain and the small town of Feely. From Feely the continental divide makes a large jog to the southeast before turning to follow the Silver Bow County east boundary in a north direction to the north edge of figure 2. North and west of the continental divide the region drains to north and northwest Clark Fork, with water eventually reaching the Pacific Ocean. Several tributaries join near Warm Springs (located near the north center edge of figure 2) to form north and northwest oriented Clark Fork (not seen in figure 2). Mill Creek is a stream in the northwest quadrant of figure 2 and just south of Anaconda, which flows just north of the continental divide in an east-southeast direction before turning to flow in a northeast direction to the town of Opportunity and then to join north oriented streams flowing to form Clark Fork.  The Big Hole River flows in a northeast direction along the Deer Lodge County southern boundary from near the southwest corner of figure 2 to the Silver Bow County line and then follows the Silver Bow County southern boundary in an east-southeast direction to the south edge of figure 2 (near the town of Divide). 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 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. The north to south oriented highway and railroad at Feely are located in a deep north-south oriented pass (Deer Lodge Pass) which crosses 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 floodwaters were reversed to flow in a north direction to the newly reversed Missouri River, which accounts the Big Hole River U-turn. Uplift of mountains north of the Big Hole River eventually formed a barrier that force a reversal of south oriented flood flow moving in the present day Deer Lodge Pass through valley. The massive flood flow reversal created the north and northwest oriented Clark Fork drainage system and the east-west continental divide.

Sand Creek-Divide Creek drainage divide area

Figure 3: Sand Creek-Divide 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 Sand Creek-Divide Creek drainage divide area at Deer Lodge Pass. The continental divide is labeled, but there is no dashed line, and extends from near the northwest corner of figure 3 to near the center of figure 3 and then in a southeast direction to the southeast quadrant of figure 3 before turning in a northeast direction to the east edge of figure 3 (south half). Deer Lodge Pass is located near the center of figure 3 and the north oriented stream flowing from the Deer Lodge Pass area to the north center edge of figure 3 is Sand Creek with water eventually reaching Clark Fork and the Pacific Ocean. Divide Creek is the south-southwest oriented stream flowing from near Deer Lodge Pass to the south edge of figure 3 (west of center) and south of figure 3 joins the south oriented Big Hole River, which then makes a giant U-turn to flow in a northeast direction to the north oriented Missouri River with water eventually reaching the Gulf of Mexico. The North Fork Divide Creek originates near the northwest corner of figure 3 and flows in a southeast and east direction along the southwest side of the continental divide to the Deer Lodge Pass region where it joins southwest oriented East Fork Divide Creek and then turns to flow in a south-southwest direction as Divide Creek. The map contour interval for figure 3 is 50 meters and the Deer Lodge Pass elevation at the continental divide is between 1750 and 1800 meters. Elevations near the southeast corner of figure 3 rise to more than 2300 meters and elevations west of Deer Lodge Pass rise much higher (more than 2800 meters near the southwest corner of figure 3). Proceeding along the continental divide east of figure 3 elevations rise to more than 2800 meters. Depending on which elevations are used Deer Lodge Pass is a north-to-south oriented water-eroded through valley 500 to 1000 meters deep and may be even deeper. Deer Lodge Pass is the deepest of numerous north-to-south oriented through valleys eroded across the continental divide in this region. The through valleys were eroded as south oriented flood flow channels at a time when the high west to east oriented mountains they cross did not exist. The mountains were uplifted as the floodwaters were flowing across them and over time the floodwaters became concentrated in the Deer Lodge Pass flood flow channel. Eventually the mountain uplift forced a reversal of flood flow that created the north and northwest oriented Clark Fork drainage system, including the north oriented Sand Creek drainage route and tributaries seen in figure 3.

Detailed map of Seven Springs Creek-Divide Creek drainage divide area

Figure 4: Detailed map of Seven Springs Creek-Divide 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 Seven Springs Creek-Divide Creek drainage divide area seen is less detail in figure 3. The east-west continental divide is shown with a labeled dashed line and extends in a south-southeast direction across section 28 (near west edge of figure 4) and then in an east direction across the north halves of sections 34, 35, and 36 before turning in a northeast direction to section 30 and the east edge of figure 4 (north half). Seven Springs Creek is the northwest stream originating near the continental divide and flowing across section 25 and then to the north center edge of figure 4. North of figure 4 Seven Springs and other tributaries form north oriented Sand Creek with water flowing to north and northwest oriented Clark Fork and eventually reaching the Pacific Ocean. The East Fork Divide Creek flows in a southwest direction from the east edge of figure 4 (north of center) along the southeast side of the continental divide to join the southeast oriented North Fork Divide Creek near the south edge of figure 4 (near the highway). Feely is a railroad siding in section 35 and is located at Deer Lodge Pass. The map contour interval for figure 4 is 40 feet and the elevation where the railroad crosses the continental divide is shown as 5801 feet. While not seen in figure 4 elevations of mountains west of Deer Lodge Pass exceed 9000 feet. East of the figure 4 there is a region where the continental divide elevations rise to about 7500 feet, although further to the east and north the continental divide elevations rise to more than 8000 feet. Depending on which elevations are used Deer Lodge Pass is 1700 to 2200 or more feet deep. The Silver Bow Creek-Big Hole River drainage divide area along the continental divide in Silver Bow County, Montana essay illustrates and discusses the region east of Deer Lodge Pass, which has multiple north to south oriented through valleys, although with floors at much higher elevations than the floor of Deer Lodge Pass. Topographic maps shown in this essay (below) illustrate the region west of Deer Lodge Pass and also show north to south oriented through valleys with floors much higher than the Deer Lodge Pass through valley floor. As already described at one time there were numerous diverging and converging south oriented flood flow channels crossing what is now the east-west continental divide in the Deer Lodge Pass region. At that time the mountains did not exist, but the mountains emerged as the flood flow moved across the region. In time the flood flow became concentrated in the Deer Lodge Pass flood flow channel, which was the deepest and most successful of the south oriented flood flow channels. However, eventually the mountain uplift succeeded in forming a barrier that forced a massive flood flow reversal, which formed the present day north and northwest oriented Clark Fork drainage system and created the present day continental divide.

Norton Creek-North Fork Divide Creek drainage divide area

Figure 5: Norton Creek-North Fork Divide Creek drainage divide area. United States Geological Survey map digitally presented using National Geographic Society TOPO software.

Figure 5 illustrates the Norton Creek-North Fork Divide Creek drainage divide area west and north of figure 3 and includes a significant overlap area with figure 3. The east-west continental divide is follows the labeled dashed county line extending in an east direction from the west center edge of figure 5 to the point where the county line makes an abrupt turn to follow Fleecer Ridge. At that point the continental divide continues in a poorly marked east and southeast direction to Deer Lodge Pass (near south edge of figure 5) and then to the south edge of figure 5. Sand Creek flows in a north direction from Deer Lodge Pass to join west and north oriented Silver Bow Creek near the north edge of figure 5 at the town of Silver Bow. North of figure 5 Silver Bow Creek flows in a north direction to join other streams and to form north and northwest oriented Clark Fork with water eventually reaching the Pacific Ocean. German Gulch is a northeast and north oriented Silver Bow Creek tributary seen in the northwest quadrant of figure 5 and joins Silver Bow Creek north of figure 5. Beefstraight Creek is an east-southeast oriented German Gulch tributary flowing from near the northwest corner of figure 5. Norton Creek is a north-northwest oriented tributary joining German Gulch near the point where Beefstraight Creek joins German Gulch. The North Fork Divide Creek originates on the east side of Fleecer Ridge and flows in a southeast and east direction to Deer Lodge Pass, where it joins southwest oriented East Fork Divide Creek to form south oriented Divide Creek, which flows to the south oriented Big Hole River with water eventually reaching the Gulf of Mexico. Note how the north oriented Norton Creek headwaters valley is linked by a north-to-south oriented through valley with the valley of a south oriented North Fork Divide Creek tributary. The map contour interval for figure 5 is 50 meters and the through valley floor elevation is between 2000 and 2050 meters (or approximately 200 meters high than the floor of Deer Lodge Pass to the east). Elevations on the ridge east of the through valley rise to at least 2200 meters and to the west elevations rise to more than 2500 meters suggesting the through valley is at least 150 meters deep. The through valley is one of several higher level through valleys eroded across the west-to-east oriented east-west continental divide in this region and was eroded as a south oriented flood flow channel prior to being beheaded and reversed to erode the north oriented Norton Creek-German Gulch valley. Probably the south oriented flood flow channel was first beheaded and reversed by headward erosion of an east oriented valley on the Beefstraight Creek alignment from what was then a somewhat deeper south oriented Deer Lodge Pass through valley. Later the reversal of flood flow that created the north and northwest oriented Clark Fork drainage system eroded the even deeper north oriented German Gulch valley, which resulted in capture of east-southeast oriented flood flow on the present day east-southeast oriented Beefstraight Creek alignment.

Detailed map of Norton Creek-North Fork Divide Creek drainage divide area

Figure 6: Detailed map of Norton Creek-North Fork Divide Creek drainage divide area. United States Geological Survey map digitally presented using National Geographic Society TOPO software.

Figure 6 provides a detailed topographic map of the Norton Creek-North Fork Divide Creek drainage divide area seen in less detail in figure 5. The continental divide is shown with a labeled dashed line and extends from the west edge of figure 6 (slightly north of center and near Burnt Mountain) to the east edge of figure 6 (south of center). Norton Creek originates just north of the continental divide near the corner of sections 7, 12, 13, and 18 (near center of figure 6) and flows in a north-northeast and north-northwest direction to the north edge of figure 6 (west of center). The North Fork Divide Creek originates near the northwest corner of section 14 and flows in a southeast direction to the south center edge of figure 6. A south oriented tributary joins the North Fork Divide Creek near the south center edge of figure 6 and is linked by a through valley with the north oriented Norton Creek headwaters valley. The map contour interval for figure 6 is 40 feet and the through valley floor elevation at the drainage divide is between 6600 and 6640 feet (compared to 5801 feet at Deer Lodge Pass to the east). Elevations along the continental divide in the east half of section 18 (east of the through valley) reach 7246 feet while the elevation at Burnt Mountain to the west is 8383 feet. Using the eastern elevation as the reference point the through valley is at least 600 feet deep. The through valley is a water-eroded feature and was eroded as one of several diverging and converging south oriented flood flow channels. Headward erosion of the deeper Deer Lodge Pass flood flow channel to the east captured the south oriented flood flow on the present day Norton Creek-North Fork Divide Creek alignment north of figure 6. That capture resulted in a reversal of flood flow that eroded the north oriented Norton Creek valley. Subsequently a much more massive flood flow reversal occurred that created the north and northwest oriented Clark Fork drainage system. Ice sheet related crustal warping that was raising the mountain region seen in figure 6 probably played a major role in the flood flow reversals.

German Gulch-Jerry Creek drainage divide area

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

Figure 7 illustrates the German Gulch-Jerry Creek drainage divide area west of figure 5 and includes a significant overlap area with figure 5. The continental Divide follows the northeast oriented Deer Lodge County-Silver Bow County line from near the southwest corner to the west center area of figure 7 and then extends in more of an east direction to the Selway Meadows area (near center of figure 7) and to the north end of Fleecer Ridge (Burnt Mountain on the detail map seen in figure 6) and then continues in a southeast direction to near the southeast corner of figure 7. South of the continental divide drainage routes flow to the Big Hole River, which is located south of figure 7. Jerry Creek originates just south of Selway Meadows (on the south side of the continental divide) and flows in a south direction to the south center edge of figure 7. Long Tom Creek is the south-southeast oriented stream originating near the Deer Lodge and Silver Bow County names along the continental divide (in the west center area of figure 7) and flowing to join Jerry Creek near the south center edge of figure 7. Note how multiple north-to-south oriented through valleys (which perhaps look more like saddles or mountain passes) cross the continental divide. The map contour interval for figure 7 is 50 meters and these north-to-south oriented through valleys are defined by one to four contour lines on a side. These through valleys link valleys of north oriented drainage routes with valleys of south oriented drainage routes. Floors of these through valleys are 600 or more meters higher than the floor of the Deer Lodge Pass through valley to the east and are also several hundred meters higher than the floor of the Norton Creek-North Fork Divide Creek through valley seen in figures 5 and 6. The through valleys seen in figure 7 were eroded by diverging and converging south oriented flood flow channels at a time when floodwaters were freely flowing across the entire region. At that time the mountains seen in figure 7 did not form an insurmountable barrier to south oriented flood flow as they do today. The mountains were probably beginning to rise (due to ice sheet related crustal warping) and as the mountains rose the flood flow channels eroded deeper and deeper into the rising mountain mass. In time some channels were more successful than others and were able to capture flow from the adjacent channels, which beheaded and reversed flow on the north ends of those adjacent channels. Capture of flow from adjacent flood flow channels provided greater water volumes, which helped erode still deeper valleys across the rising mountain mass. In time the Deer Lodge Pass flood flow channel captured all of the south oriented flood flow with a major drainage divide being formed between north oriented drainage routes on the north ends of the beheaded and reversed flood flow channels and the south oriented drainage routes south of where the flood flow reversals took place. Subsequently south oriented flood flow in the Deer Lodge Pass through valley was beheaded and reversed to create the north and northwest oriented Clark Fork drainage system.

Detailed map of German Gulch-Jerry Creek drainage divide area

Figure 8: Detailed map of German Gulch-Jerry 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 German Gulch-Jerry Creek drainage divide area seen in less detail in figure 7. The continental divide is marked in various ways and extends along the high ridge from the west edge of figure 8 (south half) to the east edge of figure 8 (just south of center). North of the continental divide Greenland Gulch originates near Selway Meadows in section 8 and then drains in a northeast and north-northeast direction to join northeast oriented German Gulch along the line between sections 33 and 34. Minnesota Gulch is the north-northeast oriented stream originating in section 13 (just north of continental divide in the southwest quadrant of figure 8) and draining to the north edge of figure 8 (west half). North of figure 8 Minnesota Gulch joins east-southeast oriented Beefstraight Creek, which as seen in previous figures flows to join the north oriented German Gulch segment. South of the continental divide in the southwest corner region of figure 8 are headwaters of south oriented Long Tom Creek and in the south center region of figure 8 are headwaters of south oriented Jerry Creek. Note how valleys of north oriented tributaries to Greenland Gulch are linked by through valleys with the south-oriented Jerry Creek valley and how the north-northeast oriented Minnesota Gulch valley is linked by a through valley with the south oriented Long Tom Creek valley. The south oriented flood flow channels were eroded at a time when floodwaters could freely flow in a south direction across the region. The flood flow channels were probably diverging and converging flood flow channels such as might be found in an anastomosing channel complex. The present day drainage divide was probably created when an east-southeast oriented valley eroded headward along the Beefstraight Creek alignment from the much deeper south oriented Deer Lodge Pass flood flow channel to capture the south oriented flood flow channels in this region. The northeast oriented German Gulch valley segment eroded headward from that east-southeast oriented valley and the northeast and north-northeast Greenland Gulch valley eroded headward from the northeast German Gulch valley segment. Headward erosion of these deep valleys occurred in sequence from south to north, which means the Greenland Gulch valley captured the south oriented flood flow first, the German Gulch valley captured the flood flow next, and the Beefstraight Creek valley captured the flood flow third. Floodwaters on north ends of the beheaded flood flow channels reversed flow direction to erode the north oriented valleys and to create a drainage divide where the present day east-west continental divide is located.

Mill Creek-California Creek drainage divide area

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

Figure 9 illustrates the Mill Creek-California Creek drainage divide area north and west of figure 7 and includes an overlap area with figure 7. The east-west continental divide is labeled and is shown with a dashed line and extends in an east and southeast direction from the west edge of figure 9 (north half) to the southeast quadrant of figure 9 and then extends in a south direction to the south edge of figure 9 (east half). North and north-northeast oriented streams west of Beals Hill in the southeast corner of figure 9 flow to east-southeast oriented Beefstraight Creek, which flows to the east edge of figure 9 (south half) and then to north oriented German Gulch with water eventually reaching Clark Fork and the Pacific Ocean. Mill Creek originates near Miller Lake (near northwest corner of figure 9) and flows in an east-southeast and east-northeast direction to near the northeast corner of figure 9. Note how the east-southeast oriented Mill Creek valley segment is adjacent to and parallel to the continental divide. On the south side of that continental divide segment are southeast oriented headwaters of Tenmile Creek, which joins other streams to form south oriented Deep Creek, which flows to the Big Hole River with water eventually reaching the north oriented Missouri River and then the Gulf of Mexico. East of Tenmile Creek and south of the continental divide are other south oriented Deep Creek tributaries. Grassy Mountain is near the center of figure 9 and the southwest oriented Deep Creek tributary between Grassy Mountain and the south edge of figure 9 is California Creek, which just north of the south center edge of figure 9 turns to flow in a south direction. West of Grassy Mountain are headwaters of south oriented Sixmile Creek, which joins California Creek near the south center edge of figure 9. Note how east of Grassy Mountain a north-to-south oriented through valley links a north oriented Mill Creek tributary valley with the south oriented California Creek valley. Also west of Grassy Mountain a north-to-south oriented through valley links the Mill Creek valley with the south oriented Sixmile Creek valley. The map contour interval for figure 9 is 50 meters. The Grassy Mountain elevation is shown as 2435 meters and the floor of the western through valley is 2306 meters meaning the western through valley is at least 129 meters deep. The floor of the eastern through valley is much deeper and has an elevation of between 2050 and 2100 meters. Sugarloaf Mountain to the east exceeds 2300 meters in height, which suggests the eastern through valley is at least 200 meters deep. These through valleys provide evidence of further north-to-south oriented flood flow channels that once crossed the region. Headward erosion of the east-northeast oriented Mill Creek valley captured the south oriented flood flow and diverted it to the much deep Deer Lodge Pass flood flow channel. The north oriented Mill Creek tributary valley located east of Grassy Mountain was eroded by a reversal of flood flow on the north end of a beheaded south oriented flood flow channel.

Detailed map of Mill Creek-California Creek drainage divide area

Figure 10: Detailed map of Mill Creek-California 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 Mill Creek-California Creek drainage divide area seen in less detail in figure 9. The continental divide is shown with a labeled dashed line and extends from the west edge of figure 10 (north half) in a southeast direction to the east edge of figure 9 (near southeast corner). Mill Creek flows in an east-southeast and northeast direction in the northwest corner area of figure 10. A north oriented Mill Creek tributary flows from section 8 to the north center edge of figure 10 and joins Mill Creek north of figure 10. South of the continental divide California Creek flows in a west direction in the southeast quadrant of figure 10 and then turns to flow in a southwest direction to the south center edge of figure 9.  A short distance north of the corner of sections 8, 9, 16, and 17 (near center of figure 10) is a north-to-south oriented through valley linking the north oriented Mill Creek tributary valley with a south oriented California Creek tributary valley. The map contour interval for figure 10 is 40 feet and the through valley floor elevation at the continental divide is 6772 feet. Grassy Mountain in the north half of section 7 reaches an elevation of 7990 feet. Sugarloaf Mountain in section 15 reaches an elevation 7756 feet, although south of figure 10 continental divide elevations rise to more than 8900 feet. West of figure 10 continental divide elevations rise to more than 10,000 feet. Depending on which elevations are used the through valley is anywhere from 1000 feet to 2000 feet deep. If the latter depth is considered then the through valley is really a deep channel eroded into the floor of much broader and larger north-to-south oriented valley. Another north-to-south oriented channel eroded into the floor of that much broader and larger can be seen in section 1 near the northwest corner of figure 10 and links the south-oriented Sixmile Creek valley with the east-southeast and east-northeast northeast oriented Mill Creek valley at the Mill Creek elbow capture. That western through valley floor elevation at the continental divide is 7565 feet, which is considerably higher than the floor of the through valley east of Grassy Mountain. Apparently this western through valley was not eroded as deep as the eastern through valley, which may be related to volumes of south oriented floodwater flowing in the two adjacent south oriented flood flow channels. Both south oriented flood flow channels were beheaded by headward erosion of the much deeper Mill Creek valley, probably with the aid of crustal warping that was raising the mountain range as south oriented flood water flowed across it.

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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