Origin of North America east-west continental divide, Dearborn River-Blackfoot River drainage divide, Montana

Authors


Abstract:

This essay uses topographic map evidence to interpret the east-west continental divide origin along the Montana Dearborn River-Blackfoot River drainage divide. The Dearborn River-Blackfoot River drainage divide is oriented in what might be considered a southeast direction along the crests of high mountain ridges at the south end of the Lewis and Clark Mountain Range. The Dearborn River originates near the continental divide and flows in generally a southeast direction, parallel to the continental divide, through the mountains northeast of the drainage divide and eventually joins the northeast-oriented Missouri River with water finally reaching the Gulf of Mexico. Deep through valleys or mountain passes cross the continental divide and link north and east-oriented Dearborn River tributary valleys with west and south oriented Blackfoot River tributary valleys. The Blackfoot River originates near the continental divide and flows in a generally west direction with water eventually reaching the Pacific Ocean. The west-oriented Blackfoot River is joined by southeast-oriented tributaries flowing parallel to and near the continental divide and also by south oriented tributaries originating near the Dearborn River-Blackfoot River drainage divide. The topographic map evidence, including the through valleys, can be interpreted in the context of immense south- and southeast-oriented floods, which initially flowed on a high level erosion surface equivalent in elevation, if not higher, to the present day continental divide (although mountain uplift has probably since raised the entire Lewis and Clark Mountain region). Flood waters eroded a large-scale anastomosing complex of diverging and converging flood flow channels into this high level erosion surface as deep valleys eroded headward from both the east and the west to capture the immense south- and southeast-oriented flood flow. North-oriented valleys were eroded by reversals of flood flow on north ends of beheaded south-oriented flood flow routes. Flood waters were derived from a rapidly melting thick North American ice sheet, which was located in a deep “hole”, and were flowing in south and southeast directions from the ice sheet’s west margin in Canada to the north.

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 Missouri River 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 available at this site may be found by selecting desired Missouri River tributaries and/or states from this essay’s sidebar category list.

Introduction:

  • The purpose of this essay is to use topographic map interpretation methods to explore the east-west continental divide origin along the Dearborn River-Blackfoot River drainage divide in 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 leaving a comment here with a link to those essays.
  • 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 essays in the Missouri River drainage basin landform origins research project 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 the east-west continental divide origin along the Dearborn River-Blackfoot River drainage divide Montana will be regarded as evidence supporting the “thick ice sheet that melted fast” paradigm (see essay listed at header). This essay is included in the Missouri River drainage basin landform origins research project essay collection.

Dearborn River-Blackfoot River drainage divide area location map

Figure 1: Dearborn River-Blackfoot 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 Montana Dearborn River-Blackfoot River drainage divide and shows a large region in western and central Montana with a small region in Idaho located in the figure 1 southwest corner. The green shaded region straddling the figure 1 north edge (west half) is the south half of Glacier National Park. The east-west continental divide is not marked or labeled on figure 1, but extends in a south-southeast direction through Glacier National Park from the figure 1 north edge to Marias Pass and then along or near the Lewis and Clark Range crest to the figure 1 south edge (west of Helena). Figure 1 regions in Montana west of the continental divide drain to the north and northwest-oriented Clark Fork, which flows to the figure 1 west center edge with water eventually reaching the Pacific Ocean. Figure 1 regions east of the continental divide drain to the Missouri River, which flows in a north-northwest direction from the figure 1 south edge (just west of Big Belt Mountains) to near Wolf Creek where it turns to flow in a northeast direction through Great Falls, Fort Benton, and Loma to the figure 1 east edge, with water eventually reaching the Gulf of Mexico. Note how tributaries to the northeast-oriented Missouri River segment, including the upstream Missouri River segment and the Smith River, are oriented in north-northwest directions. Tributaries to the northeast-oriented Missouri River segment from the west include (from south to north) the Dearborn River, Sun River, Teton River, and Marias River, all of which originate along the east-west continental divide. As mentioned the continental divide is located along or near the crest of the north-northwest to south-southeast oriented Lewis and Clark Range. West of the east-oriented Missouri River tributary headwaters are headwaters of the northwest-oriented Middle Fork Flathead River and the north-northwest oriented South Fork Flathead River and the west-oriented Blackfoot River. The west-oriented Blackfoot River headwaters are located west of the Dearborn River headwaters near the south end of the Lewis and Clark Range. This essay focuses on the Dearborn River-Blackfoot River drainage divide, which is an east-west continental divide segment. Links to essays describing other continental divide segments can be found under east-west continental divide on the sidebar category list and links to essays describing Dearborn River drainage divide areas can be found by selecting the Dearborn River category from the sidebar category list .
  • The east-west continental divide is one of the best known North American geographical features, yet prior to the Missouri River drainage basin landform origins research project a detailed study of topographic map evidence has never been published to explain the east-west continental divide origin. Detailed topographic maps of most United States east-west continental divide segments have been available for more than 50 years and contain a wealth of information pertinent to the east-west continental divide origin. Numerous landscape features such as mountain passes, valley orientations, through valleys, barbed tributaries, and elbows of capture can be used to reconstruct drainage histories, which in turn can be used to interpret the east-west continental divide origin. Perhaps the most remarkable finding is the topographic map evidence documents immense south and southeast-oriented floods, which were captured by headward erosion of deep valleys from both the east and west to carve the present day east-west continental divide. Using erosional landforms depicted on the topographic maps these huge floods can be traced headward to what was probably a rapidly melting thick North American ice sheet, which was located in a deep “hole.” The deep “hole’s” western rim was the Rocky Mountains in Alberta and British Columbia and the deep “hole’s” southwest wall is today the Montana and northern Wyoming Missouri River drainage basin. Probably the deep “hole” did not exist when the ice sheet originally formed, but was created by deep glacial erosion (under the ice sheet) and by crustal warping of non glaciated regions caused by the ice sheet’s great weight. Topographic map evidence suggests ice sheet related crustal warping raised the Rocky Mountains, other North American mountain ranges, and high plateau areas as gigantic melt water floods flowed across them. Further, the topographic map evidence suggests present day drainage systems evolved as deep valleys systematically eroded headward from adjacent ocean basins to capture the immense south-oriented flood flow.
  • Of particular importance to the figure 1 map area were events that occurred when crustal warping and ice sheet melting had created a situation where the ice sheet (at least its southwest margin) no longer stood high above the adjacent Montana and northern Wyoming bedrock surface. Massive south and southeast oriented melt water floods were flowing across Montana and northern Wyoming and were being diverted in northeast directions by ice sheet related uplift of the Rocky Mountains. At the same time a giant southeast and south-oriented supra-glacial melt water river was carving a deep southeast and south-oriented ice-walled canyon into the decaying ice sheet surface. This huge ice-walled canyon was located in present day Saskatchewan, North Dakota, and South Dakota and in time became an ice-walled and bedrock-floored canyon and detached the ice sheet’s southwest margin. Today the northeast and east-facing Missouri Escarpment in Saskatchewan, North Dakota, and South Dakota is what remains of that giant canyon’s southwest and west wall. Deep northeast and east-oriented valleys eroded headward from that giant southeast- and south-oriented ice-walled canyon into adjacent non glaciated areas of Montana and northern Wyoming to capture the massive southeast-oriented ice-marginal melt water floods. Headward erosion of each new valley beheaded southeast-oriented flood flow routes to the newly eroded valley immediately to the south or southeast. In figure 1 headward erosion of the deep northeast-oriented Missouri River valley beheaded flood flow routes to actively eroding valleys south of the figure 1 map area. Flood waters on north ends of the beheaded flood flow routes reversed flow direction to erode what are today north and northwest oriented tributary valleys including the north-northwest oriented Missouri River valley segment seen in figure 1. West of the continental divide the same process occurred and the northwest-oriented Middle Fork Flathead River valley and the north-northwest oriented South Fork Flathead River were eroded by reversals of flood flow on north ends of beheaded southeast-oriented flood flow routes. The continental divide in the figure 1 map area was carved, probably as the Lewis and Clark Range was being uplifted, while immense southeast-oriented melt water floods flowed across the region and as deep valleys were being eroded headward into the region. The flood water movements were complex and volumes of water involved were immense, but the topographic map evidence can be used to decipher the flood history as headward erosion of deep valleys captured the flood flow.

Detailed location map for Dearborn River-Blackfoot River drainage divide area

Figure 2: Detailed location map for Dearborn River-Blackfoot River drainage divide area. United States Geological Survey map digitally presented using National Geographic Society TOPO software.

 

  • Figure 2 is a detailed location map for the Dearborn River-Blackfoot River drainage divide segment of the North America east-west continental divide. Green shaded areas are National Forest lands, which are generally located in mountainous regions. The east-west continental divide is marked with a dashed line and extends from the figure 2 north edge (west half) through Sugarloaf Mountain, Observation Pass, Trident Peaks, Scapegoat Mountain, Rogers Pass, and Granite Butte before reaching the figure 2 south center edge. The Missouri River flows in a north-northwest direction from the figure 2 southeast corner to near the town of Wolf Creek and then flows in a north-northeast direction to the figure 2 east center edge. The Dearborn River originates north of Scapegoat Mountain (in figure 2 northwest quadrant) and flows in an east and southeast direction parallel to and adjacent to the continental divide before making a jog to the northeast and then resuming its southeast direction (with some jogs to the northeast) to join the north-northeast oriented Missouri River near the figure 2 east center edge. The Middle Fork Dearborn River originates at Rogers Pass and flows in a north-northeast direction to join the southeast oriented Dearborn River (highway 200 follows the Middle Fork Dearborn River from Rogers Pass to the Dearborn River). The South Fork Dearborn River is located east and south of the Middle Fork and originates along the continental divide and flows in a north and north-northeast oriented direction to join the Dearborn River. South of Rogers Pass (and the continental divide) are west and southwest oriented headwaters of the west-oriented Blackfoot River, which flows the figure 2 west edge (south half) with water eventually reaching the Pacific Ocean. The south-oriented Blackfoot River tributary west of Rogers Pass is Alice Creek and the southeast- and south-oriented Blackfoot River tributary west of Alice Creek is Landers Fork. The North Fork Blackfoot River originates in the Scapegoat Wilderness (just south of continental divide in figure 2 northwest quadrant) and flows in a southwest and south-southwest direction to join the Blackfoot River near Ovando in the figure 2 southwest quadrant.
  • As can be seen in figure 2 the east-west continental divide is not a north-south oriented line, but instead has segments oriented in various different directions. For example Rogers Pass crosses a short west to east oriented continental divide segment. North of Rogers Pass are headwaters of a north-northeast oriented Dearborn River tributary while to the south are headwaters of a south-southwest oriented Blackfoot River tributary. Rogers Pass is a through valley crossing the continental divide and while it is deeper than other passes across the Dearborn River-Blackfoot River drainage divide investigated in this essay, it is also typical of other passes across the continental divide. In the case of Rogers Pass it was eroded as a south oriented flood flow channel prior to headward erosion of the much deeper Dearborn River valley to the north. Flood waters at that time were probably moving to what was then the actively eroding Blackfoot River valley, which was eroding headward across massive south and southeast-oriented flood flow. The south-southwest oriented North Fork Blackfoot River valley, south-southeast oriented Landers Fork valley, and south-oriented Alice Creek valley (among others) were eroded by south-oriented flood flow moving to the newly eroded and much deeper west-oriented Blackfoot River valley. Headward erosion of the much deeper Dearborn River valley (north and east of the present day continental divide) beheaded the south-oriented flood flow channel crossing Rogers Pass. Flood waters on the north end of the beheaded flood flow channel reversed flow direction to erode a much deeper north-northeast oriented Middle Fork Dearborn River valley. Erosion of the north-northeast oriented Middle Fork Dearborn River valley was probably aided by capture of south- and southeast-oriented flood flow still moving west of the actively eroding Dearborn River valley head and also by uplift of the region that was occurring as flood waters flowed across the figure 2 map area. The east-west continental divide was carved in the figure 2 map area as the southeast-oriented Dearborn River valley continued to erode headward and behead south-oriented flood flow routes to what were then actively eroding south- and southeast-oriented Blackfoot River tributary valleys carving the continental divide south and southwest slope. Headward erosion of the deep Dearborn River valley and its deep tributary valleys, some of which were eroded by flood flow reversals, carved the continental divide north and northeast slope.

Middle Fork Dearborn River-Blackfoot River drainage divide area

Figure 3: Middle Fork Dearborn River-Blackfoot River drainage divide area. United States Geological Survey map digitally presented using National Geographic Society TOPO software.

 

  • Figure 3 illustrates the Middle Fork Dearborn River-Blackfoot River drainage divide area near Rogers Pass. Rogers Pass is near the figure 3 center and is where highway 200 (the red highway) crosses the east-west continental divide. The continental divide is marked with a dashed line and is labeled and extends in a southeast direction from the figure 3 north edge (west half, near Lewis and Clark Pass) to Green Mountain, Cadotte Pass, Rogers Pass, and then to the figure 3 south edge (east half). The Middle Fork Dearborn River is the north-northeast oriented stream flowing from Rogers Pass to the figure 3 north edge (east of center) near highway 200. The north and north-northeast oriented stream flowing from the figure 3 southeast quadrant (just east of the continental divide) to the figure 3 north edge (just west of the northeast corner) is the South Fork Dearborn River. The south-southwest oriented stream flowing from Rogers Pass is Pass Creek, which joins the west and southwest-oriented Blackfoot River in the figure 3 southwest quadrant. Cadotte Creek is the south-southwest oriented Blackfoot River tributary originating at the south side of Cadotte Pass. The south-southwest and south-southeast oriented Blackfoot River tributary flowing from the Alice Creek Basin (near north edge of figure 3 northwest quadrant) to join Blackfoot River near figure 3 south edge) is Alice Creek. The figure 3 map contour interval is 50 meters and the Rogers Pass elevation at the drainage divide is between 1750 and 1800 meters. Spot elevations along the continental divide to the southeast rise to more than 2180 meters while Green Mountain and Red Mountain to the northwest have elevations in excess of 2200 meters. In other words Rogers Pass is approximately 400 meters deep and is a deep valley eroded across the continental divide. Passes like Rogers Pass, and even much shallower passes, are water eroded features and were eroded at a time when water flowed freely across the continental divide. Cadotte Pass is a shallower pass across the continental divide and is located just a short distance west of Rogers Pass. The Cadotte Pass elevation at the continental divide is between 1800 and 1850 meters. Cadotte Pass is also a water eroded feature and like Rogers Pass links a south-oriented Blackfoot River tributary valley with a northeast-oriented Middle Fork Dearborn River headwaters valley. These two passes across the continental can be best explained in the context of two diverging south-oriented flood flow channels (such as might be found in an anastomosing channel complex) moving flood waters to what was at that time the actively eroding Blackfoot River valley. The south-oriented flood flow was beheaded by headward erosion of the much deeper southeast-oriented Dearborn River valley north of the figure 3 map area. Flood waters on the northwest ends of the beheaded flood flow channels reversed flow direction to erode the deeper north-northeast oriented Middle Fork Dearborn River valley and its northeast-oriented tributary valley.

Detailed map of Middle Fork Dearborn River-Pass Creek drainage divide area

Figure 4: Detailed map of Middle Fork Dearborn-Pass 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 Middle Fork Dearborn River-Pass Creek drainage divide area seen in less detail in figure 3 above. The east-west continental divide extends from the figure 4 north edge (west half, near Cadotte Pass) in a southeast direction to the figure 4 southeast corner. Rogers Pass is located near the figure 4 center. The Middle Fork Dearborn River originates just north of Rogers Pass and flows in a north-northeast direction to the figure 4 north edge (east of center) with water eventually reaching the Gulf of Mexico. Pass Creek originates just south of Rogers Pass and flows in a south direction to the figure 4 south center edge with water eventually reaching the Pacific Ocean. The figure 4 map contour interval is 40 feet and the spot elevation at Rogers Pass reads 5630 feet. The continental divide in the northwest corner of section 10 just east of Rogers Pass rises to 7000 feet while to the west in southwest corner of section 4 the continental divide rises to more than 6280 feet. Cadotte Pass near the figure 4 northwest corner has an elevation of between 6040 and 6080 feet and the continental divide near the south border of section 32 rises to 6499 feet. At first glance these elevations suggest the Rogers Pass through valley may only be 650 feet deep and the Cadotte Pass through valley may only be 320 feet deep. However following the continental north and west of the figure 4 map area leads to Green Mountain which has an elevation of 7458 feet and following the continental divide south and east of figure 4 leads to elevations greater than 7200 feet. Using these more distant continental divide elevations the Rogers Pass through valley may be as much as 1400 feet deep and the Cadotte Pass through valley may be more than 1100 feet deep and the Rogers Pass and Cadotte Pass through valleys may have originated as channels eroded into the floor of a much broader and larger through valley eroded between the higher continental divide points.
  • Why is the continental divide ridge lower between the higher elevations (northwest and southeast from figure 4)? The Rogers Pass and Cadotte Pass through valleys obviously are water eroded valleys and are best explained in the context of diverging and converging south-oriented flood flow channels. Prior to the erosion of those deep south-oriented flood flow channels flood waters flowed on an erosion surface equal in elevation to the continental divide elevations seen in figure 4, if not on a surface equal in elevation to the higher continental divide elevations to the southwest and southeast of figure 4. A south-oriented flood capable of eroding the south-oriented and deep Rogers Pass and Cadotte Pass valleys into the underlying erosion surface would also be capable of creating the erosion surface by stripping hundreds of feet of bedrock rock material from the region. If so the southwest side of the continental divide in figure 4 was eroded by the south-oriented flood flow, while the northeast side was eroded by reversals of flood flow caused by headward erosion of the much deeper Dearborn River valley north of the figure 4 map area. Dearborn River valley headward erosion beheaded the south-oriented flood flow routes in sequence from east to west, which meant flood waters still moving south to the west of the actively eroding Dearborn River valley head could be captured by newly reversed flood flow routes to erode deep north-oriented Dearborn River tributary valleys.

Dearborn River-Landers Fork (Blackfoot River) drainage divide area

Figure 5: Dearborn River-Landers Fork (Blackfoot River) drainage divide area. United States Geological Survey map digitally presented using National Geographic Society TOPO software.

 

  • Figure 5 illustrates the Dearborn River-Landers Fork drainage divide area located north and west of the figure 3 map area and includes overlap areas with figure 3. The east-west continental divide is marked with a dashed line, is labeled, and extends in a southeast direction from the figure 5 north edge (near northeast corner) to the figure 5 south edge (east half). Rogers Pass is located where highway 200 crosses the continental divide near the figure 5 south edge. The Dearborn River flows in a southeast direction in the figure 5 northeast corner and the Middle Fork Dearborn River flows in a north-northeast direction from Rogers Pass to join the Dearborn River near the figure 5 northeast corner. The southeast-oriented streams flowing across the figure 5 southwest corner region include Landers Fork of the Blackfoot River and southeast-oriented tributaries to Landers Fork. Today the Landers Fork tributaries are independent streams flowing in separate valleys, although as can be seen in the figure 5 southwest corner the valleys are linked by a network of through valleys suggesting a one time southeast-oriented anastomosing channel complex. The anastomosing channel complex is at a much lower elevation than the continental divide and would have been eroded by massive southeast-oriented flood flow, probably after headward erosion of the deep Blackfoot River valley and its deep south-oriented tributary valleys had already eroded much of the continental divide southwest side. However, the Landers Fork anastomosing channel complex provides evidence of a large southeast-oriented valley that was eroded by massive southeast-oriented flood flow on the southwest side of the continental divide, probably at the same the deep southeast-oriented Dearborn River was being eroded headward by massive southeast-oriented flood flow on the northeast side of the continental divide.
  • As already mentioned headward erosion of the deep Dearborn River valley was beheading and reversing south-oriented flood flow routes to the newly eroded west-oriented Blackfoot River valley, which was eroding the continental divide northeast side. Lewis and Clark Pass is located near the figure 5 center and the Alice Creek Basin is located just west of Lewis and Clark Pass. Red Mountain is a high point on the continental divide just north of Lewis and Clark Pass. The north and west-northwest oriented stream originating just north of the Alice Creek Basin (and the continental divide) is the East Fork Falls Creek, which joins northeast-oriented West Fork Falls Creek near the figure 5 north edge to form north-oriented Falls Creek. There is a saddle in the continental divide between Red Mountain and Burned Point to the west which provides evidence of what was once a high elevation south-oriented flood flow channel on the East Fork Falls Creek-Alice Creek alignment, which probably helped erode the south-oriented Alice Creek valley.
  • The question might be asked, where did the water come from that eroded the north oriented East Fork Falls Creek valley, which is today a deep valley with some deep east-oriented headwaters? The east-oriented headwaters valleys provide some clues and figure 6 below shows a detailed topographic map of the region to better illustrate the valleys. Before looking at the detailed topographic map a big picture view is need. Note the north and northwest-oriented West Fork Falls Creek tributaries originating on the northwest side of Blowout Mountain and along the continental west of Burned Point. Some of the north and northwest-oriented West Fork Falls Creek tributaries are linked by high elevation through valleys with the east-oriented East Fork Falls Creek headwaters valleys. At the time the deep north-oriented East Fork Falls Creek valley was eroded there was no deep West Fork Falls Creek valley. Instead there was a high level erosion surface, as high as the present day continental divide, and south-oriented flood waters were flowing across that high level erosion surface to what was then a newly reversed and north-oriented East Fork Falls Creek flood flow channel, which had been beheaded and reversed by headward erosion of east-southeast oriented Middle Fork Dearborn River tributary valleys. Dearborn River valley headward erosion next beheaded and reversed south-oriented flood flow on the Falls Creek alignment (which had also been captured by headward erosion of the east-southeast oriented Middle Fork Dearborn River tributary valleys). The resulting flood flow reversal resulted in erosion of the deep north and west-northwest oriented East Fork Falls Creek valley. Headward erosion of the deep northeast-oriented West Fork Falls Creek valley next captured the high level southeast-oriented flood flow and flood waters on northwest ends of the beheaded flood flow routes reversed flow direction to erode the north- and northwest-oriented West Fork Falls Creek tributary valleys.

Detailed map of Camp Creek-East Fork Falls Creek drainage divide area

Figure 6: Detailed map of Camp Creek-East Fork Falls 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 Camp Creek-East Fork Falls Creek drainage divide area seen in less detail in figure 5 above. The east-west continental divide is labeled and marked and follows the high ridge extending from the figure 6 west center edge to the figure 6 east edge (north half). Areas north of the continental divide drain to the Dearborn River with water eventually reaching the Gulf of Mexico. Areas south of the continental divide drain to the Blackfoot River with water eventually reaching the Pacific Ocean. The East Fork Falls Creek originates between Blowout Mountain and the continental divide and flows in an  east and north-northeast direction to the figure 6 northeast corner. Camp Creek originates north of the continental divide in the figure 6 center region and flows in a north-northwest direction to the figure 6 north edge (west half) and joins northeast-oriented West Fork Falls Creek north of the figure 6 map area. West of Camp Creek is north-oriented Middle Fork Camp Creek, which originates along the continental divide and which joins Camp Creek north of the figure 6 map area. Note how in the south half of section 34 (just north of continental divide near figure 6 center) there is a west to east oriented through valley linking the north-northwest oriented Camp Creek valley with the northernmost of the two east-oriented East Fork Falls Creek headwaters valleys. The through valley provides evidence of an east-oriented flood flow channel that moved yet to be beheaded and reversed flood flow from west of the beheaded and reversed East Falls Creek flood flow channel to that newly reversed East Fork Falls Creek flood flow channel. Such captured flood flow provided the water volumes required to erode the deep north-oriented East Fork Falls Creek valley. Note also a northwest-southeast oriented through valley across Burned Point in the section 3 northeast corner. That through valley links the northern East Falls Creek headwaters valleys with the southern East Falls Creek headwaters valley. Further note near the section 3 center (south of the continental divide) a west to east oriented through valley linking the southeast-oriented Alice Creek headwaters valley (which drains to the Blackfoot River) with the southern East Fork Falls Creek headwaters valley (a western extension of the through valley can be seen in the section 9 northwest corner). These two through valleys provide evidence of flood flow routes to the deep southern East Fork Falls Creek headwaters valley. The west to east oriented through valley provides evidence of an east-oriented flood flow route to the north-oriented East Fork Falls Creek valley that was located south of the continental divide. In fact, the continental divide ridge west of section 3 was probably formed as the divide between two east-oriented and deep flood flow channels to what was then a newly beheaded and reversed flood flow channel on the East Fork Falls Creek alignment. Headward erosion of the deep southeast-oriented Alice Creek valley captured the east-oriented flood flow channel south of the present day continental divide and diverted the flood flow to the Blackfoot River valley.

West Fork Falls Creek-Bighorn Creek drainage divide area

Figure 7: West Fork Falls Creek-Bighorn Creek drainage divide area. United States Geological Survey map digitally presented using National Geographic Society TOPO software.

 

  • Figure 7 illustrates the West Falls Creek-Bighorn Creek drainage divide area west and north of the figure 5 map area and includes overlap areas with figure 5. The continental divide is again marked with a dashed line and labeled and extends along a high ridge from the figure 7 west edge (north half) to the figure 7 south edge (near southeast corner). The Dearborn River flows in an east-southeast direction from the figure 7 north edge (west half, just east of Grassy Hills) and after flowing through Devils Glen (in figure 7 north center area) turns to flow in a northeast direction to the figure 7 north edge. Lewis and Clark Pass in located near the figure 7 southeast corner and the Alice Creek Basin is located directly west from Lewis and Clark Pass. North of the Alice Creek Basin (and the continental divide) are headwaters of north and west-northwest oriented East Fork Falls Creek, which joins northeast-oriented West Fork Falls Creek east of Monitor Mountain to form north-oriented Falls Creek, which flows the Dearborn River north of the figure 7 map area. West Fork Falls Creek headwaters originate on the east side of a north-south oriented continental divide segment and flow in an east-southeast direction to join the north-oriented Middle Fork and to flow in a northeast direction to join the west-northwest oriented East Fork Falls Creek. Note how the West Fork Falls Creek headwaters valley is linked by an unnamed pass across the continental divide. West of the pass are north-northwest and southwest-oriented headwaters of south oriented Bighorn Creek, which flows to southeast-oriented Landers Fork (Blackfoot River) near the figure 7 south edge. Also north of the south oriented Bighorn Creek valley are through valleys linking the Bighorn Creek valley with north-oriented Dearborn River tributaries. These passes provide evidence of east-oriented flood flow routes west of the actively eroding Dearborn River valley head used to reach the newly beheaded and north-oriented Falls Creek valley as flood waters eroded the continental divide northeast side. Headward erosion of the deep south-oriented Bighorn Creek valley captured the south- and east-oriented flood flow and diverted the flood waters to the south as headward erosion of Blackfoot River tributary valleys eroded the continental divide southwest side. Not all deep valleys, on both the east and west sides of the east-west continental divide, have deep through valleys at their valley heads. Instead there are saddles along the adjacent high ridges, which provide evidence of flood flow channels which supplied the flood waters to erode the deep valleys seen today. Elevations of the saddle floors is such that flood waters must have been flowing on an erosion surface almost as high if not higher than the highest figure 7 elevations today. In other words, prior to headward erosion of the deep Dearborn River valley and its tributary valleys from the east and of the deep Blackfoot River valley and its tributary valleys from the west the entire figure 7 map area was underlain by an erosion carved surface over which south- and southeast-oriented flood waters could freely move. Headward erosion of the deep valleys from opposite sides of the continental divide (and probably aided by regional uplift) not only carved the east-west continental divide, but also produced the rugged mountain topography seen today.

Detailed map of Bighorn Creek-West Fork Falls Creek drainage divide area

Figure 8: Detailed map of Bighorn Creek-West Fork Falls 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 Bighorn Creek-West Fork Falls Creek drainage divide area seen in less detail in figure 7 above. The east-west continental divide is labeled and follows a high ridge from the figure 8 northwest corner to the figure 8 south center edge. Areas north and east of the continental divide drain to the Dearborn River with water eventually reaching the Gulf of Mexico. Areas south and west of the continental divide drain to the Blackfoot River with water eventually reaching the Pacific Ocean. Bighorn Creek is the labeled figure 8 north-northwest and southwest oriented stream south and west of the continental divide and south of the figure 8 map area flows in more of a south direction. West Fork Falls Creek is the major east-oriented stream in the figure 8 southeast quadrant and is linked with the Bighorn Creek valley by a deep west-northwest to east-southeast oriented through valley across the continental divide in the section 22 northeast quadrant. The through valley floor elevation at the continental divide is between 6920 and 6960 feet (the figure 8 map contour interval is 40 feet). The unnamed peak immediately to the north rises to more 7960 feet while an unnamed peak along the figure 8 south center edge reaches 8655 feet (north and west of the figure 8 map area the continental divide rises to 8677 feet). These elevations suggest the section 22 northeast quadrant through valley is at least 1000 feet deep and may have been eroded into an erosion surface at least as high the 7960 foot peak today. The higher peak elevations suggest the erosion surface at one time may have been equivalent to or higher than tops of the 8600 plus foot high peaks today. The figure 8 map area was probably significantly uplifted as flood waters flowed across the region and after flood flow ceased so present day elevations should not be considered to be the same as elevations when flood waters flowed across the region. Through valleys west and north of the deep south-oriented Bighorn Creek valley show where converging flood flow channels from the north and west met to first supply vast quantities of flood waters to the actively eroding West Fork Falls Creek valley and subsequently to the actively eroding and deeper south-oriented Bighorn Creek, which beheaded east-oriented flood flow to the West Fork Falls Creek valley and in the process created the present day east-west continental divide in sections 22, 15, and 16.

Dearborn River-North Fork Blackfoot River drainage divide area

Figure 9: Dearborn River-North Fork Blackfoot River drainage divide area. United States Geological Survey map digitally presented using National Geographic Society TOPO software.

 

  • Figure 9 illustrates the Dearborn River-North Fork Blackfoot River drainage divide area north and west of the figure 7 map area and includes overlap areas with figure 7. The east-west continental divide is marked with a dashed line, is labeled, and extends roughly in a southeast direction from near the figure 9 northwest corner to near the figure 9 southeast corner. Areas north and east of the continental divide drain to the Missouri River with water eventually reaching the Gulf of Mexico. Areas south and west of the continental divide drain to the Blackfoot River with water eventually reaching the Pacific Ocean. The Dearborn River originates just east of Scapegoat Mountain (in figure 9 northwest quadrant along continental divide) and flows in an east-northeast direction, with a southeast-oriented jog, to the figure 9 north center edge where it joined by a southeast-oriented tributary. At the figure 9 north center edge the Dearborn River turns to flow in southeast direction to the figure 9 east center edge. The southeast-oriented Dearborn River tributary at the figure 9 north center edge is north of the figure 9 map area and is linked by a through valley with a northwest-oriented Sun River tributary. The east-southeast and northeast oriented stream flowing from Elk Pass is Elk Creek, which is another Sun River tributary. Elk Pass is the drainage divide between east-southeast oriented Elk Creek headwaters and northwest-oriented Smith Creek headwaters, with Smith Creek being a northeast-oriented Sun River tributary. Elk Pass is a deep northwest-southeast oriented through valley linking two streams flowing in opposite directions, just as Straight Creek Pass (north of the figure 9 map area) links a northwest-oriented Sun River tributary valley with a southeast-oriented Dearborn River tributary valley. These through valleys (and others) provide evidence of multiple southeast-oriented flood flow channels which were dismembered by headward erosion of deep southeast-oriented valleys which were beheaded and reversed by headward erosion of the deeper east-oriented Sun River valley and its northeast-oriented tributary valleys in the north.
  • South and west of the continental divide the south-southwest oriented North Fork Blackfoot River flows to the figure 9 southwest corner and is joined in the figure 9 west center region by southeast and south-oriented El Dorado Creek and north and northwest-oriented North Cooney Creek (among others). The stream located in the valley labeled “Tobacco Valley” is the North Fork Blackfoot River. Note the southeast-northwest alignment of segments of these and other drainage routes south and west of the continental divide, which also parallels the northwest-southeast orientation of many drainage route segments north and east of the continental divide. Also note how a deep through valley (or mountain pass) across the continental divide links the west-southwest-oriented Tobacco Valley with a southeast oriented tributary to the east-northeast oriented Whitetail Creek valley (a pack trail is located in the through valley). The through valley was eroded by east-oriented flood flow from west and north of the figure 9 map area which was moving to what was then the actively eroding and much deeper Dearborn River valley and also flowing to diverging southeast- and south-oriented flood flow channels further to the east and south. Headward erosion of the much deeper south-oriented North Fork Blackfoot River valley captured the east- and southeast-oriented flood flow and flood waters on the west and northwest ends of the beheaded flood flow channels reversed flow direction to erode the west-southwest oriented Tobacco Valley and the north and northwest-oriented North Cooney Creek valley. Again this flood origin interpretation only works if vast quantities of flood waters were initially freely flowing on an erosion surface as high as the highest figure 9 map elevations today and headward erosion of the deep valleys captured the southeast- and south-oriented flood waters in a sequence that permitted yet to be beheaded flood flow to be captured by beheaded and reversed flood flow channels to erode deep north and northwest-oriented valleys (which means flood movement descriptions given in this essay are greatly simplified and the actual flood flow movements were much more complex than described here).

Detailed map of North Fork Blackfoot River-Whitetail Creek drainage divide area

Figure 10: Detailed map of North Fork Blackfoot River-Whitetail 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 North Fork Blackfoot River-Whitetail Creek drainage divide area seen in less detail in figure 9 above. The east-west continental divide is well-marked and labeled and extends in an east-southeast direction from the figure 10 northwest corner to the figure 10 north center area and then in a south and south-southwest direction to the figure 10 south edge (west of center) The North Fork Blackfoot River originates just south of the figure 10 map area and flows in a north-northeast direction along the continental divide west side into section 34 where it turns to flow in west-southwest direction to the figure 10 west center edge. As seen in figure 9 west of the figure 10 map area the North Fork Blackfoot River turns to flow in more of a south direction to join the west-oriented Blackfoot River with water eventually reaching the Pacific Ocean. The Dearborn River can just barely be seen in the figure 10 northeast corner and flows to the Missouri River with water eventually reaching the Gulf of Mexico. Whitetail Creek is an east and east-northeast oriented Dearborn River tributary located along the figure 10 southeast quadrant south edge. Lower Twin Creek originates in the section 35 northeast quadrant and flows in an east-northeast and northeast direction to join the southeast-oriented Dearborn River. Note the deep west to east oriented through valley in the east half of section 34 crossing the continental divide just west of Twin Lakes. West of the continental divide the through valley is linked to both the north-oriented and west-southwest oriented North Fork Blackfoot River valley segments and also to south-oriented North Fork Blackfoot River tributaries originating at much higher elevation passes or through valleys across the continental divide to the north. East of the Twin Lakes area the section 34 through valley is linked to a southeast-oriented Whitetail Creek tributary valley and also to the east- and northeast-oriented Lower Twin Creek valley. These valley linkages provide evidence of what were once diverging and converging flood flow routes that eroded deep flood flow channels across the what is now the east-west continental divide. Flood waters flowing through the deep section 34 through valley moved in an east direction, were derived from west and north of the figure 10 map area, and were flowing to what at that time was the actively eroding and much deeper Dearborn River valley. Headward erosion of the deep east-oriented flood flow channel across the present day continental divide beheaded a south-oriented flood flow route on the present day north-oriented North Fork Blackfoot River headwaters valley alignment. Erosion of that north-oriented North Fork Blackfoot River valley segment was caused by a reversal of flood waters to the much deeper east-oriented flood flow channel being eroded headward from the deep southeast-oriented Dearborn River valley. Subsequently headward erosion of the still deeper south- and southwest-oriented North Fork Blackfoot River valley beheaded the east-oriented flood flow channel across section 34. Flood waters on the west end of the beheaded flood flow channel reversed flow direction to erode a deeper west-southwest oriented North Fork Blackfoot River valley segment and to capture the north-oriented North Fork Blackfoot River valley segment. These captures created the east-west continental divide in the figure 10 map area.

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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