Origin of North America east-west continental divide, Little Blackfoot River-Missouri River drainage divide area landform origins in Lewis and Clark and Powell Counties, Montana, USA

Authors


Abstract:

This essay uses topographic map evidence to interpret landform origins in the region between Little Blackfoot River and the Missouri River along the east-west continental divide in Lewis and Clark and Powell Counties, Montana. East of the continental divide the Missouri River flows in a north-northwest direction in eastern Lewis and Clark County before turning to flow in a northeast direction with water eventually reaching the Gulf of Mexico. Southeast, east, northeast, and north oriented Missouri River tributaries drain the east side of the continental divide, with some flowing as barbed tributaries to the north oriented Missouri River or to other Missouri River tributaries. West of the continental divide the Little Blackfoot River flows in what could be considered to be a north and then west direction to join north and northwest oriented Clark Fork with water eventually reaching the Pacific Ocean. The west side of the continental divide is drained by southwest and south-southwest oriented tributaries flowing to the Little Blackfoot River from the north and northwest and northwest oriented tributaries flowing to the Little Blackfoot River from the south. The continental divide is crossed by numerous named and unnamed passes or through valleys with the named passes including Mullan Pass, MacDonald Pass, and Priest Pass. The through valleys (or passes) across the continental and other regional drainage divides were eroded by former flood flow channels, which were once carved into a high level surface extending across the entire region. At that time Montana mountain ranges and deep valleys and basins did not exist and floodwaters could freely flow across the state. Floodwaters were derived from the western margin of a thick ice sheet, which was located in deep “hole” north and east of figure 1. The floodwaters flowed in a south and southeast direction from southwest Alberta and southeast British Columbia to and across the figure 1 map area. In time ice sheet melting opened up space along the south margin of the deep “hole” the ice sheet was occupying and deep northeast oriented valleys eroded headward across Montana to capture the immense south and southeast oriented melt water floods. At about the same time the deep Columbia River valley eroded headward from the Pacific Ocean, also capturing the immense south and southeast oriented melt water floods. North and northwest oriented tributary valleys were eroded when headward erosion of these much deeper valleys beheaded less deep south and southeast oriented flood flow channels and when ice sheet related crustal warping raised Montana and Wyoming mountain ranges. The east-west continental divide marks the boundary between where the south and southeast oriented melt water floods were captured by the deep east oriented valleys and where the south and southeast oriented melt water floods were captured by the deep west oriented valleys.

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 Little Blackfoot River-Missouri River drainage divide area landform origins along the east-west continental divide in Lewis and Clark and Powell Counties, Montana, USA. Map interpretation methods can be used to unravel many geomorphic events leading up to formation of present-day drainage routes and development of other landform features. While each detailed topographic map feature provides detailed evidence to be explained, the solution must be consistent with explanations for adjacent area map evidence as well as solutions to big picture map evidence puzzles. I invite readers to improve upon my solutions and/or to propose alternate solutions that better explain evidence and are also consistent with adjacent map area and big-picture evidence. Readers may do so either by making comments here or by writing and publishing their own essays and then by leaving a link to those essays in a comment here.

This essay is also exploring a new geomorphology paradigm in which erosional landforms are interpreted as evidence left by immense glacial melt water floods. Implied in that interpretation is the immense floods were derived from a thick North American ice sheet that created a deep “hole” in the North American continent and also melted fast. The previously unexplored paradigm being tested in this and other Missouri River drainage basin landform origins research project essays is a thick North American ice sheet, comparable in thickness to the Antarctic ice sheet, occupied the North American region usually recognized to have been glaciated, and through its weight and erosive actions created a deep North American “hole”. The southwestern rim of that deep “hole” is today preserved in the high Rocky Mountains. The ice sheet through its weight and deep erosion (and perhaps deposition along major south-oriented melt water flow routes) caused significant crustal warping and tectonic change, through its action of melting fast produced immense floods that flowed across the continent, and through its action of melting fast systematically opened up space in the ice sheet created “hole” so headward erosion of newly developed north-oriented drainage systems captured immense south-oriented melt water floods and diverted immense melt water floods north into space the ice sheet had once occupied.

If this previously unexplored paradigm is correct the geographic region explored by this essay should contain evidence of immense floods that were captured by headward erosion of new valley systems so as to cause the floods to flow in a different direction. Ability of this previously unexplored paradigm to explain Little Blackfoot River-Missouri River drainage divide area landform evidence in Powell and Lewis and Clark Counties, Montana will be regarded as evidence supporting the “thick ice sheet that melted fast” paradigm.

Little Blackfoot River-Missouri River drainage divide area location map

Figure 1: Little Blackfoot River-Missouri 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 Little Blackfoot River-Missouri River drainage divide area along the east-west continental divide in Lewis and Clark and Powell Counties, Montana and illustrates a region in central and western Montana. The Missouri River is formed at the confluence of major tributaries near Three Forks, Montana (near south edge of figure 1-east of center) and flows in a north and north-northwest direction to Holter Lake and then in a northeast direction to Great Falls and the north edge of figure 1 (east half).  North and east of figure 1 the Missouri River turns to flow in an 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 unnamed north-north-northeast and northeast oriented tributary located west and north of Helena and flowing to Lake Helena is Tenmile Creek, which is an important stream in this essay. Clark Fork (of the Columbia River) flows in a north and west-northwest direction through or near Warm Springs, Deer Lodge, Garrison, Gold Creek, and Drummond before reaching the west center edge of figure 1 and west of figure 1 flows to the Columbia River, which flows to the Pacific Ocean. North of the west-northwest oriented Clark Fork segment is west oriented Blackfoot River, which flows near Lincoln and Ovando before reaching the west edge of figure 1 and which joins the Clark Fork west of figure 1. The Little Blackfoot River is not labeled, but is the west oriented Clark Fork tributary flowing near Elliston and Avon before joining the Clark Fork near Garrison. The Little Blackfoot River-Missouri River drainage divide area investigated in this essay extends from the Blackfoot River drainage basin southward along the east-west continental divide to the south end of the Little Blackfoot River-Tenmile Creek drainage divide. Water today east of the drainage divide flows to the Gulf of Mexico while water west of the continental drainage divide flows to the Pacific Ocean.

Before interpreting the detailed maps of the Little Blackfoot River-Missouri River drainage divide area a brief discussion of the big picture erosion history is needed. Large volumes of south and southeast oriented floodwaters once flowed across the region shown by figure 1.  The 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 southwestern Alberta and southeastern British Columbia to and across the figure 1 region. At that time (at least initially) there were no high mountains in western and central Montana and floodwaters could freely flow across locations that are today high mountain ranges. Western Canada, Montana, Wyoming, and other mountain ranges were formed by ice sheet related crustal warping that occurred as floodwaters flowed across the rising mountain masses. In addition, deep flood water erosion of valleys and basins surrounding the rising mountain masses 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’s” southwest rim where the immense south and southeast oriented ice marginal melt water floods were flowing. Deep northeast oriented valleys then eroded headward from space in the deep “hole” being opened up by the melting ice sheet to capture the south and southeast oriented melt water floods. The northeast oriented Missouri River valley segment seen in figure 1 (downstream from Holter Lake) 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 east-west continental divide in figure 1 represents the western limit of the region affected by headward erosion of deep northeast oriented valleys from the deep “hole.” West of the continental divide the southeast and south oriented flood flow was beheaded by headward erosion of the deep Columbia River valley and its tributary valleys (west and north of figure 1). The west-northwest oriented Clark Fork valley was eroded by a massive reversal of flood flow on the northwest end of a major beheaded east-southeast oriented flood flow channel. That reversal of flood flow also caused reversals of flood flow that eroded the west oriented Blackfoot River and Little Blackfoot River valleys and the north oriented Clark Fork headwaters valley. Previous to the Clark Fork flood flow reversal floodwaters were flowing in southeast and east directions across the west half of figure 1 to what is today the Missouri River drainage basin. For a time the floodwaters from western Montana were flowing to south oriented flood flow channels on the alignments of what are today north oriented Missouri River tributaries or on the alignment of the present day north and north-northwest oriented Missouri River segment. As seen in the detailed topographic maps illustrated in this essay the reversal of flood flow that created the north and north-northwest oriented Missouri River segment seen today also captured east oriented flood flow from west of the continental divide. The flood flow reversal that created the northwest oriented Clark Fork drainage system reversed the flood flow across the present day continental divide and eroded west oriented valleys such as the Blackfoot River and Little Blackfoot River valleys. The massive flood flow reversals were probably greatly aided by crustal warping that was raising mountain ranges, which developed barriers blocking the south and southeast oriented flood flow channels.

Detailed location map for Little Blackfoot River-Missouri River drainage divide area

Figure 2: Detailed location map Little Blackfoot River-Missouri 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 Little Blackfoot River-Missouri River drainage divide area along the east-west continental divide in Lewis and Clark and Powell Counties, Montana. County boundaries are shown and Powell and Lewis and Clark Counties are labeled. Green shaded areas are National Forest lands, which generally are located in mountainous regions. Helena is the largest city in figure 2 and is located in the southeast quadrant of figure 2 near the south edge of Lewis and Clark County. Canyon Ferry Lake in the southeast quadrant of figure 2 floods the north-northwest oriented Missouri River valley with the Missouri River flowing in a north-northwest direction from the south edge of figure 2 to Holter Dam and then turning to flow in a northeast direction to the north edge of figure 2. Lake Helena is located north of East Helena and is slightly west of the Missouri River. Tenmile Creek originates near the southern tip of Lewis and Clark County (just north of south center edge of figure 2) and flows in a north and northeast direction to Lake Helena with the water then flowing to the Missouri River. Prickly Pear Creek is the north oriented stream joining Tenmile Creek near Lake Helena and Silver Creek is an east and southeast oriented stream also flowing to Lake Helena. The east-west continental is shown as a dashed line and is labeled (slightly north of the center of figure 2) and extends from the north edge to the south edge of figure 2 (roughly across the center of figure 2). In places the continental divide defines county boundaries while in other places the continental divide is east of the Powell-Lewis and Clark County line. The Blackfoot River is the major west oriented river in the northwest quadrant of figure 2. Nevada Creek is northwest oriented Blackfoot River tributary originating in the Avon Valley with southwest oriented headwaters. South of the Avon Valley (south and west of the center of figure 2) is the Little Blackfoot River, which originates near the south center edge of figure 2 (just west of where Tenmile Creek originates) and which flows in a north, west-northwest, and southwest direction to join the northwest oriented Clark Fork near Garrison. The Clark Fork flows in a north direction from the south edge of figure 2 (west half) to Deer Lodge and Garrison and then turns to flow in a west-northwest direction to Drummond and the west edge of figure 2 (south of center).

Nevada Creek-South Fork Little Prickly Pear Creek drainage divide area

Figure 3: Nevada Creek-South Fork Little Prickly Pear 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 Nevada Creek-South Fork Little Prickly Pear Creek drainage divide area and is located on the Blackfoot River-Missouri River drainage divide and is north of the Little Blackfoot River-Missouri River drainage divide. The east-west continental divide is shown with a dashed line and extends southward from the north center edge of figure 3 to Black Mountain and then in an east-southeast direction across the southeast quadrant of figure 3 to the east edge. Little Prickly Pear Creek drains the area east and north of the continental divide to the east edge of figure 3 (north half) and then in an east and north-northeast direction to the Missouri River. Nevada Creek originates along the west side of the continental divide just south of the north center edge of figure 3 and flows in a southwest and west direction to the west center edge of figure 3.  The Avon Valley is located along the west margin of the southwest quadrant of figure 3 and Halfway Creek is the northwest oriented stream draining the north half of the Avon Valley to the west edge of figure 3 and then to Nevada Creek, which then turns to flow in a northwest direction to join the west oriented Blackfoot River. South-southwest oriented streams originating in the region west of Black Mountain and flowing to the south edge of figure 3 (west half) flow to south oriented Sixmile Creek, which then flows to the west oriented Little Blackfoot River. The continental divide in figure 3 appears to be a high mountain ridge separating two independent drainage basins, although a close look reveals shallow through valleys (which today appear to be mountain passes) linking the east oriented valleys with the west oriented valleys. The map contour interval for figure 3 is 50 meters. Just north of Black Mountain is a through valley linking the south-southwest oriented Threemile Creek valley with the east-northeast oriented Deadman Creek valley and further to the north is a slightly deeper through valley linking the Threemile Creek valley with the east-northeast oriented South Fork Little Prickly Pear Creek valley. The Threemile Creek-Deadman Creek through valley floor elevation at the drainage divide is between 2300 and 2350 meters and the Threemile Creek-South Fork Little Prickly Pear Creek through valley floor elevation at the drainage divide is between 2250 and 2300 meters. Black Mountain to the south of the through valleys rises to 2547 meters and Nevada Mountain to the north rises to more than 2500 meters suggesting the through valleys may be as much as 150 meters deep. The through valleys are water eroded features and were eroded as flood flow channels which once crossed what is now the east-west continental divide. Figure 4 provides a more detailed map to better illustrate the Nevada Mountain and Black Mountain region.

Detailed map of Threemile Creek-Deadman Creek drainage divide area

Figure 4: Detailed map of Threemile Creek-Deadman 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 Threemile Creek-Deadman Creek drainage divide area seen in less detail in figure 3. The map contour interval for figure 4 is 40 feet. Nevada Mountain is located in the northwest quadrant of figure 4 and reaches an elevation of 8293 feet. Black Mountain is located near the south center edge of figure 4 and is shown as reaching an elevation 8330 feet. The east-west continental divide is labeled and is the dashed line extending from the north center edge of figure 4 to the Nevada Mountain east flank and then to the Black Mountain east flank. The South Fork Little Prickly Pear Creek drains the region east of the continental divide in the northeast quadrant of figure 4 to the northeast corner with water eventually reaching the Missouri River. Deadman Creek drains areas in the southeast quadrant of figure 4 east of the continental divide in a northeast direction to the east edge of figure 4 and then to Little Prickly Pear Creek and eventually to the Missouri River. Threemile Creek is the south-southwest oriented stream originating south of Nevada Mountain and flowing to the south edge of figure 3 with water eventually reaching the Little Blackfoot River. Note how in the southwest quadrant of section 32 a through valley links a west oriented Threemile Creek tributary valley with an east oriented Deadman Creek tributary valley. The through valley floor elevation at the drainage divide is shown as being 7627 feet, which is more than 700 feet lower than the top of adjacent Black Mountain. Further north in the south half of section 30 a through valley links the Threemile Creek valley with the South Fork Little Prickly Pear Creek valley. The floor elevation of this second through valley at the drainage divide is between 7480 and 7520 feet, which is more than 700 feet lower than the tops of nearby Nevada and Black Mountains. Floodwater movements, which eroded the through valleys, appear to have been complex with water first moving in a southeast direction across the region. At that time the deep south-southwest oriented Threemile Creek valley did not exist. Headward erosion of the deep south-southwest oriented Threemile Creek valley captured the southeast oriented floodwater and diverted the floodwaters to a south oriented flood flow channel in the Avon Valley. Headward erosion of the deep south-southwest oriented Threemile Creek valley also captured floodwaters from east of the continental divide, but headward erosion of the deep northeast oriented South Fork Little Prickly Pear Creek valley beheaded and reversed those south-southwest oriented floodwaters to erode the north-northeast oriented South Fork Little Prickly Pear Creek headwaters valley.

Uncle George Creek-Austin Creek drainage divide area near Mullan Pass

Figure 5: Uncle George Creek-Austin Creek drainage divide area near Mullan Pass. United States Geological Survey map digitally presented using National Geographic Society TOPO software.

Figure 5 illustrates the Uncle George Creek-Austin Creek drainage divide area near Mullan Pass south and east of figure 3 and includes an overlap area with figure 3. The east-west continental divide is can be seen near the north edge of the east half of the northwest quadrant of figure 5 and extends in an east direction from Meyers Hill to Roundtop Mountain and then to near Bald Butte. From near Bald Butte the continental divide extends in a south direction to Greenhorn Mountain, Mullan Pass, Priest Pass and the south edge of figure 5 (east half). East of Greenhorn Mountain is southeast oriented Skelly Gulch. South and west of Skelly Gulch are the southeast oriented headwaters of Greenhorn Creek, which turn to flow in an east-northeast direction to the east edge of figure 5 (south of center). East of figure 5 Skelly Gulch joins Greenhorn Creek and Greenhorn Creek joins Tenmile Creek, which flows to Lake Helena and then the Missouri River. South and west of the southeast oriented Greenhorn Creek headwaters is southeast and east oriented Austin Creek, which originates near Mullan Pass and which flows to Greenhorn Creek. South and west of the continental divide is southeast, south, south-southeast, and south-southwest oriented Hope Creek, which originates near Meyer Hill and which flows to the south edge of figure 5 (east of center) and then to the west oriented Little Blackfoot River south of figure 5. Uncle George Creek is the south oriented Hope Creek tributary west of Mullan Pass. The Avon Valley is the lowland in the southwest corner of figure 5 and the south-southwest oriented streams flowing to Avon Valley flow to the Little Blackfoot River. Mullan Pass is a significant through valley eroded across the continental divide. The map contour interval for figure 5 is 50 meters. The Mullan Pass elevation at the drainage divide is between 1750 and 1800 meters. Greenhorn Mountain to the north rises to 2288 meters and the Radio Tower on the continental divide near the south edge of figure 5 is on a hill at least 2200 meters high.  These elevations suggest Mullan Pass may be more than 400 meters deep. The Mullan Pass through valley is a water-eroded feature and numerous similar, but somewhat less deep through valleys can be seen crossing the continental divide and other drainage divides in figure 5. These through valleys provide evidence of flood flow channels that once crossed the region. Floodwaters initially flowed in a southeast direction across the region, but were captured by headward erosion of the south oriented Hope Creek valley and its tributary valleys. Probably the last flood flow through Mullan Pass was in a southwest direction toward the newly eroded Hope Creek valley, which was beheaded by headward erosion of the much deeper Austin Creek valley.

Detailed map of Uncle George Creek-Austin Creek drainage divide area near Mullan Pass

Figure 6: Detailed map of Uncle George Creek-Austin Creek drainage divide area near Mullan Pass. United States Geological Survey map digitally presented using National Geographic Society TOPO software.

Figure 6 provides a detailed topographic map of the Uncle George Creek-Austin Creek drainage divide area near Mullan Pass seen in less detail in figure 5. The continental divide is a labeled dashed line that extends from the north edge of figure 6 (west of center) to the south edge of figure 6 (near center). Mullan Pass is also labeled and is located in the southeast quadrant of section 2. Austin Creek flows in a southeast direction from the northeast quadrant of section 2 to the southeast corner of section 1 and then turns to flow in an east-northeast direction to join southeast and east oriented Greenhorn Creek with water eventually reaching the Missouri River. West of Mullan Pass Uncle George Creek originates near the north edge of section 6 and flows in a south direction through section 3 into section 10 where it turns to flow in south-southwest direction to the south edge of figure 6. The map contour interval for figure 6 is 40 feet. The spot elevation at Mullan Pass reads 5902 feet. The continental divide north of Mullan Pass rises to 6288 feet at the north edge of figure 6 and to 7506 feet at Greenhorn Mountain (north of figure 6).  Near the south edge of figure 6 the continental divide elevation reaches 6293 feet, and further south on the unnamed mountain with the communication towers the elevation is 7215 feet. Based on these elevations Mullan Pass is at least 1300 feet deep. Priest Pass is located in section 13 and has an elevation at the drainage divide of between 5960 and 6000 feet. Both Priest Pass and Mullan Pass are located between the two mentioned high points north and south of figure 6, which indicates they are deeper channels eroded into the floor of what was once a much larger valley. The deeper channels and the broader valley were eroded initially by large volumes of southeast oriented flood water moving from west of the present day continental divide to south oriented flood flow channels along the alignments of what are today north oriented Missouri River tributary valleys. As previously mentioned the final flood flow through Mullan Pass was probably in a southwest direction to the newly eroded south oriented Uncle George Creek valley, which had eroded headward from a south oriented flood flow channel on what is today the north oriented Little Blackfoot River headwaters valley.

Little Blackfoot River-Tenmile Creek drainage divide area near MacDonald Pass

Figure 7: Little Blackfoot River-Tenmile Creek drainage divide area near MacDonald Pass. United States Geological Survey map digitally presented using National Geographic Society TOPO software.

Figure 7 illustrates the Little Blackfoot River-Tenmile Creek drainage divide area near Macdonald Pass and is located south of figure 5 and includes an overlap area with figure 5. The continental divide is located in the east half of figure 7 and extends from the north edge to the south edge. Mullan Pass is located on the continental divide near the north edge of figure 7. The west to east red highway crosses the continental divide at MacDonald Pass. The Little Blackfoot River flows in a north-northeast, north-northwest, and west-northwest direction from the south edge of figure 7 (just west of center) to the west center edge of figure 7. Uncle George Creek flows in a south-southwest direction from near Mullan Pass to join southeast, south-southwest, and southwest oriented Dog Creek, which joins the Little Blackfoot River as a barbed tributary near the elbow of capture where the Little Blackfoot River turns from flowing in a north-northwest direction to flowing in a west-northwest direction. The elbow of capture reflects the Little Blackfoot River valley origin as a southeast and south oriented flood flow channel. Flood flow in the channel was beheaded  and reversed when headward erosion of the deep Columbia River beheaded and reversed southeast flood flow to the Clark Fork valley. Also contributing to the reversal of flood flow in the Little Blackfoot River valley was uplift of mountain ranges in the Little Blackfoot River headwaters area. In the southeast quadrant of figure 7 and east of the continental divide is north and northeast oriented Tenmile Creek, which flows from the south edge (east half) to the east center edge of figure 7. The north oriented Tenmile Creek headwaters valley was initiated as a south oriented flood flow channel and was later beheaded and reversed by headward erosion of the much deeper northeast oriented Tenmile Creek valley (from the deep Missouri River valley). MacDonald Pass is a major through valley crossing the continental divide. MacDonald Creek is the west oriented stream flowing to the Little Blackfoot River (via Dog Creek) from MacDonald Pass. Walker Creek is the north and northeast oriented Tenmile Creek tributary draining the east slope of MacDonald Pass. The map contour interval for figure 7 is 50 meters and the MacDonald Pass elevation at the drainage divide is between 1900 and 1950 meters. To the north and south the continental divide elevations rise to more than 2200 meters making the MacDonald Pass through valley at least 250 meters deep. The Macdonald Pass through valley is a water eroded feature and provides further evidence that large volumes of flood water once crossed what is today the east-west continental divide.

Detailed map of MacDonald Creek-Walker Creek drainage divide area near MacDonald Pass

Figure 8: Detailed map of MacDonald Creek-Walker Creek drainage divide area near MacDonald Pass. United States Geological Survey map digitally presented using National Geographic Society TOPO software.

Figure 8 provides a detailed topographic map of the MacDonald Creek-Walker Creek drainage divide area near MacDonald Pass, which was seen in less detail in figure 7. The map contour interval for figure 8 is 40 feet. The east-west continental divide is the labeled dashed line extending from the figure 8 north center edge to the south center edge. MacDonald Pass is located in section 2 and has an elevation where the highway crosses the drainage divide of between 6280 and 6320 feet. MacDonald Creek drains the MacDonald Pass west slope while Walker Creek drains the east slope. South of MacDonald Pass in section 13 there is an unnamed pass with an elevation at the drainage divide approximately the same as at MacDonald Pass. The east slope of this unnamed pass is drained by the north oriented Walker Creek headwaters while the west slope is drained by a tributary to Mike Renig Gulch. The continental divide north of figure 8 rises to 7215 feet before gradually dipping down to Priest Pass and then north of Mullan Pass rises to more than 7500 feet at Black Mountain (see figure 3). South of figure 8 the continental divide rises to more than 7600 feet. Between the high elevations mentioned there are several low areas such as Mullan Pass, Priest Pass, MacDonald Pass, and the unnamed section 13 pass. These low areas are well-defined water-eroded through valleys that were abandoned when deeper valleys eroded headward on both sides of the present day continental divide to capture floodwaters that had been eroding the through valleys. These multiple through valleys document the one time presence of multiple channels such as would be found in an anastomosing channel complex. Floodwaters probably flowed in both directions (both east and west) across at least some of the passes although the overall direction of flow was to the south until massive flood flow reversals occurred on both sides of the continental divide. The massive flood flow reversals were caused by ice sheet related crustal warping that raised mountain ranges and also by headward erosion of deep valleys that beheaded and reversed the south and southeast oriented flood flow channels in sequence as the deep valleys eroded headward from both the east and the west toward the present day continental divide. The north oriented Tenmile Creek, Walker Creek, and Mike Renig Gulch valley segments seen in figure 8 were eroded by reversals of flood flow on the north ends of much shallower south oriented flood flow channels, which were beheaded and reversed by headward erosion of the what were then the much deeper northeast oriented Tenmile Creek valley segment (for the north oriented Tenmile and Walker Creek valley segments) and the west oriented Mike Renig Gulch valley segment (for the north oriented Mike Renig Gulch valley segment).

Telegraph Creek-Tenmile Creek drainage divide area

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

Figure 9 illustrates the Telegraph Creek-Tenmile Creek drainage divide area south and slightly east of figure 7 and includes an overlap area with figure 7. The east-west continental divide is the labeled dashed line extending from the north edge to the south edge of figure 9 and is located just east of the center of figure 9. Tenmile Creek originates near the continental divide a short distance north of the south edge of figure 9 and flows in a north, northeast, north, north-northwest, and north-northeast direction to the north edge of figure 9 (east half). The Little Blackfoot River flows in a northeast direction from the west edge of figure 9 (just north of southwest corner) and then turns to flow in a north-northwest, north-northeast, and north-northwest direction to the north edge of figure 9 (west half).  Telegraph Creek is the north and north-northwest oriented tributary joining the Little Blackfoot River near the YMCA Camp in the northwest quadrant of figure 9 and originating just west of the continental divide from the Tenmile Creek headwaters. Mike Renig Gulch is the north and west oriented Little Blackfoot River tributary north of Telegraph Creek and joins the Little Blackfoot River near the north edge of figure 9. Note how a broad and somewhat shallow through valley (in the Bullion Parks area) across the continental divide links the Tenmile Creek headwaters and the Telegraph Creek headwaters. The map contour interval for figure 9 is 50 meters and the through valley at Bullion Parks has an elevation of between 2100 and 2150 meters. Much lower elevations can be found linking the Mike Renig Gulch valley with the Tenmile Creek valley so the Telegraph Creek-Tenmile Creek through valley at Bullion Parks is by no means the lowest through valley seen in figure 9. However, continental divide elevations south of figure 9 rise to more than 2400 meters and north of figure 9 at Black Mountain (seen in figure 3) elevation rise to more than 2500 meters suggesting the presence of a broad through valley linking the west oriented Little Blackfoot River-Clark Fork drainage basin with the north and east oriented Missouri River drainage basin. The numerous mountain passes seen in this area today were eroded as deeper channels in the floor of this broad through valley. The north oriented valleys in figure 9 were eroded during reversals of flood flow on what had been south oriented flood flow routes. The reversals of flood flow were caused by headward erosion of much deeper east and west oriented valleys, headward erosion of which created the present day continental divide. The continental divide was created when the much deeper valleys eroded headward from the east and from the west and beheaded and reversed the south and southeast oriented flood flow channels and diverted the floodwaters to either the Missouri River valley in the east or the Clark Fork valley in the west (both of which were initiated as south or southeast oriented flood flow channels).

Detailed map of Telegraph Creek-Tenmile Creek drainage divide area

Figure 10: Detailed map of Telegraph Creek-Tenmile 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 Telegraph Creek-Tenmile Creek drainage divide area seen in less detail in figure 9. The continental divide is the labeled dashed line extending from the north center edge of figure 10 to the south edge of figure 10 (west of center). Telegraph Creek originates in the south of section 15 and flows in a north direction to section 10 where it turns to flow in a north-northwest direction to the northwest corner of figure 10. O’Keefe Creek is the north-northwest oriented tributary originating in the southwest corner of section 14 and joining Telegraph Creek in section 10. Note how the north oriented Telegraph Creek and O’Keefe Creek valleys are linked by through valleys with south oriented valleys draining to the figure 10 south edge. The south oriented streams flow to west and northwest oriented Ontario Creek, which flows to the north and west-northwest oriented Little Blackfoot River. The through valleys provide evidence of south oriented flood flow channels that existed prior to the flood flow reversal that eroded the north and north-northwest oriented Telegraph Creek valley. Tenmile Creek originates near the south edge of figure 10 (just east of the continental divide) and flows in a north, northeast, east, and north-northeast direction to the northeast corner of figure 10. South of figure 10 a through valley links the Tenmile Creek valley with the west oriented Ontario Creek headwaters valley, which then turns to drain in a northwest direction to the Little Blackfoot River. A higher level and broader through valley near the corner of sections 11, 12, 13, and 14 links the north-northwest oriented Telegraph Creek valley with the north oriented Tenmile Creek valley. The through valleys linking present day north oriented drainage routes on opposites sides of the continental divide provide evidence the present day north oriented drainage routes were initiated as anastomosing, or diverging and converging, south oriented flood flow channels, which were beheaded and reversed by headward erosion of much deeper valleys eroding into the region from completely different directions. In the case of the Tenmile Creek valley it was beheaded and reversed by headward erosion of the northeast and east oriented Tenmile Creek valley north and east of figure 10 (see figure 2). In the case of the Telegraph Creek it was beheaded and reversed in the massive flood flow reversal responsible for the Clark Fork reversal in western Montana. Both flood flow reversals were probably aided by crustal warping that was raising Wyoming and Montana mountain ranges.

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.

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s

%d bloggers like this: