Origin of North America east-west continental divide along Sun River-Flathead River drainage divide, Montana, USA

Authors

Abstract:

This essay interprets topographic map evidence to determine the origin of the east-west continental divide in the Montana Sun River-Flathead River drainage divide area. The Sun River is formed at the confluence of south-southeast and north-northwest tributaries and flows in an east direction to join the Missouri River at Great Falls, Montana with water eventually reaching the Gulf of Mexico. South-southeast and north-northwest oriented Sun River tributaries have headwaters originating along and/or flow near and roughly parallel to the present day east-west continental divide. Through valleys (or mountain passes) eroded across the continental divide and other high drainage divides link Sun River tributary valleys with the northwest and north-northwest oriented Middle Fork Flathead River and South Fork Flathead River drainage systems which flow to the south-oriented Flathead River with water eventually reaching the Pacific Ocean. Both east and west of the continental divide streams and rivers make U-turns, flow in opposite directions to join at common meeting points, have barbed tributaries, and show other evidence of flow reversals. Valley orientations, the through valleys, and flow reversal evidence provide evidence of dismemberment of multiple south-oriented flood flow channels which once flowed along and across the present day east-west continental divide. Flood waters are interpreted to have been derived from a rapidly melting thick North American ice sheet and flowed in a south and southeast direction from Canada along the western and southwestern rim of the deep “hole” in which the ice sheet was located. Mountain uplift occurred as flood waters flowed across the region and the east-west continental divide was created as deep valleys eroded headward into the region from both east and the west with southern valleys generally capturing the south-oriented flood flow prior to headward erosion of more northern valleys. On both sides of the continental divide north and northwest-oriented valleys were eroded by reversals of flood flow on north and northwest ends of beheaded southeast oriented flood flow channels. Evidence for massive flood flow reversals is present on both sides of the continental divide.

Preface

The following interpretation of detailed topographic map evidence is one of a series of essays describing similar evidence for all major drainage divides contained within the Missouri River drainage basin and for all major drainage divides with adjacent drainage basins. The research project is interpreting evidence in the context of a previously unexplored deep glacial erosion paradigm, which is fundamentally different from most commonly accepted North American glacial history interpretations. Project essays 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 North America east-west continental divide origin along the Sun River-Flathead River drainage divide located 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 then providing 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 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 North America east-west continental divide origin along the Sun River-Flathead River drainage divide in Montana will be regarded as evidence supporting the “thick ice sheet that melted fast” paradigm (see link to paradigm related essay at top of page). This essay is included in the Missouri River drainage basin landform origins research project essay collection.

Sun River-Flathead River drainage divide area location map

Figure 1: Sun River-Flathead 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 east-west continental divide between the east-oriented Sun River and the west-oriented Flathead River in northwest Montana. The Canadian border is located along the figure 1 north edge and the Idaho-Montana state line crosses the figure 1 southwest corner. Glacier National Park is the green area near the figure 1 north center edge. The east-west continental divide extends in a south-southeast direction from the figure 1 north edge through Logan Pass and Marias Pass in Glacier National Park and then along or near the Lewis and Clark Range crest to the figure 1 south edge (west of Helena). East of the continental divide all regions drain to the Missouri River with water eventually reaching the Gulf of Mexico (with the exception of the Saint Mary Lake region east of Glacier National Park where water eventually reaches Hudson Bay). West of the continental divide all rivers eventually flow to the Columbia River and the Pacific Ocean. Of particular importance to this essay is the Missouri River which flows in a north-northwest direction from the figure 1 south edge (just east of Helena in the figure 1 southeast corner) to Wolf Creek where it turns to flow in a northeast direction to Great Falls and the figure 1 east center edge. The Sun River originates near the north end of the Lewis and Clark Range (along the continental divide) and flows in a south-southeast direction to Gibson Reservoir where it turns to flow in an east direction to join the Missouri River at Great Falls. Other Sun River drainage basin drainage divide area essays are listed under the Sun River category (see sidebar category list). North of the Sun River drainage basin is the east-oriented Teton River drainage basin and essays related to Ten River drainage divide areas are listed under the Teton River category. North of the south-southeast oriented Sun River headwaters are headwaters of the northwest-oriented Middle Fork Flathead River which flows to the south-oriented Flathead River (which flows through Flathead Lake). West of the south-southeast oriented Sun River headwaters is the north-northwest oriented South Fork Flathead River, which also flows to the south-oriented Flathead River. West of the north-northwest oriented South Fork Flathead River is the north-northwest oriented Swan River, which flows to Flathead Lake where it joins the south-oriented Flathead River. These north-oriented and barbed tributaries to the south-oriented Flathead River provide important clues to the origin of the east-west continental divide.
  • Today it is difficult to imagine the high east-west continental divide in the figure 1 map area was eroded by immense south and southeast-oriented melt water floods derived from a rapidly melting thick North American ice sheet. The ice sheet was located in a deep “hole” and the Canadian Rocky Mountains to the north of figure 1 are located along what was the deep “hole’s” western rim. At the time the ice sheet formed the deep “hole” did not exist, which meant the ice sheet stood high above the surrounding non glaciated regions, including the area now occupied by the Canadian Rocky Mountains (and the Montana Rocky Mountains seen in figure 1). Crustal warping caused by the ice sheet’s great weight probably was responsible for uplifting the Rocky Mountains and other non glaciated continental areas. This uplift occurred as giant ice-marginal melt water floods flowed in south and southeast directions from Canada into and across the figure 1 map area. In time uplift of the Rocky Mountains and other non glaciated continental regions combined with ice sheet melting created a different melt water flood flow pattern. East of the present day continental divide this new melt water flood flow pattern was governed by the development of huge south-oriented ice-walled canyons being carved into the decaying ice sheet surface by immense south-oriented supra-glacial melt water rivers.
  • Of importance to figure 1 was a giant southeast and south oriented ice-walled canyon in present day Saskatchewan, North Dakota, and South Dakota. In time this large southeast and south oriented ice-walled canyon became an ice-walled and bedrock-floored canyon and detached the ice sheet’s southwest margin. Deep east and northeast-oriented valleys eroded headward from this giant south oriented ice-walled canyon into the adjacent non glaciated regions of Montana and northern Wyoming to capture the immense south and southeast-oriented melt water floods flowing in those regions. The east oriented Missouri River valley (east of the figure 1 map area) was one such valley and beheaded south-and southeast-oriented melt water flood flow to the east- and northeast-oriented Yellowstone River valley which had previously eroded headward from the same ice-walled canyon to capture the south and southeast-oriented melt water flood flow. Headward erosion of the northeast-oriented Missouri River valley seen in figure 1 beheaded south-southeast flood flow channels and flood waters on the north-northwest ends of those beheaded flood flow channels reversed flow direction to erode the north-northwest oriented Missouri River headwaters valley such as the Smith River valley seen in figure 1 (southeast quadrant). Probably the massive flood flow reversals involved were aided by continuing uplift of mountains to the south. At the same time the east-oriented Sun River valley eroded headward to capture the south- and southeast-oriented flood flow while Teton River valley headward erosion subsequently beheaded flood flow to the newly eroded Sun River valley. Headward erosion of the deep east-oriented Sun River and Teton River valleys into the rising mountain mass to capture the immense south- and southeast-oriented melt water flood flow (flowing along what are today the crests of the mountain ranges) carved the east side of the present day east-west continental divide.
  • West of the continental divide a somewhat different process was taking place. Headward erosion of the deep Columbia River valley captured south and southeast-oriented flood flow and in doing so beheaded a major southeast-oriented flood flow channel on the present day northwest-oriented Clark Fork alignment (Clark Fork flows in a northwest direction through Missoula to the figure 1 west edge, just north of center). Flood waters on the northwest end of the beheaded flood flow channel reversed flow direction to erode a much deeper northwest-oriented Clark Fork valley. This flood flow reversal also captured south-oriented flood flow in a south-oriented flood flow channel on the Flathead River alignment and the much deeper valley then eroded headward along that flood flow channel. The much deeper valley beheaded diverging south-southeast and southeast oriented flood flow channels on the Swan River, South Fork Flathead River, and Middle Fork Flathead River alignments. Flood waters on north ends of those beheaded south-oriented flood flow channels reversed flow direction to erode the north-northwest and northwest oriented Swan River, South Fork Flathead River, and Middle Fork Flathead River valleys. As will be seen in the topographic maps illustrated below prior to the massive flood flow reversals at least some south-oriented flood flow in the Middle Fork Flathead River and the South Fork Flathead River flood flow channels crossed what is today the east-west continental divide and flowed to what was then the actively eroding Sun River valley. Probably mountain uplift which was occurring as flood waters flowed across the figure 1 map area greatly aided the flood flow reversals and also contributed to the erosion of the deep valleys seen today. Headward erosion of the much deeper south-oriented Flathead River valley (after reversal of the Clark Fork flood flow channel) along the newly reversed Middle Fork Flathead River and South Fork Flathead River valleys and their tributary valleys carved the west side of the present day east-west continental divide and ended all flood flow across the continental divide.

Detailed location map for Sun River-Flathead River drainage divide area

Figure 2: Detailed location map for Sun River-Flathead 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 east-west continental divide in the Montana Sun River-Flathead River drainage area. Flathead Lake straddles the figure 2 west edge and the south-oriented Flathead River is located west of the figure 2 map area. East of Flathead Lake is the north and north-northwest oriented Swan River, which flows to Swan Lake and then to the north end of Flathead Lake where it joins the south-oriented Flathead River. Flathead Lake and the Swan River drainage basin are located in Lake County, Montana. East of the north-oriented Swan River drainage basin is the north-northwest oriented South Fork Flathead River, which flows to Hungry Horse Reservoir located in the figure 2 northwest quadrant. North and west of the figure 2 map area the South Fork Flathead River joins the south-oriented Flathead River. The South Fork Flathead River drainage basin is located in Flathead County, with the Swan River-Flathead River drainage divide serving as the Lake County-Flathead County line. Note how in the region near the words “Bob Marshall Wilderness” the north-oriented South Fork Flathead River is joined by the south-oriented White River. North of the south-oriented White River headwaters are north- and northwest-oriented tributaries and headwaters of west-oriented Spotted Bear River, which also flows to the north-oriented South Fork Flathead River. West of Hungry Horse Reservoir is the northwest-oriented Middle Fork Flathead River, which north and west of the figure 2 map area also joins the south-oriented Flathead River. Note how the northwest-oriented Middle Fork Flathead River also has south-oriented tributaries. The North Fork Sun River originates south of the northwest-oriented Middle Fork Flathead River headwaters (just west of the words “Lewis and Clark Range”) and flows in a south-southeast direction to join the north-oriented South Fork Sun River west of Gibson Reservoir and then to flow in an east direction along the Teton County south border to the figure 1 east edge (south half). The south-southeast oriented North Fork Sun River flows along the Teton County west border with a northwest arm of Lewis and Clark County (name not seen in figure 2) forming the west half of the North Fork Sun River drainage basin. The Lewis and Clark County-Flathead County border is defined by the east-west continental divide which in the south is the Sun River-Flathead River drainage divide. Further north the continental divide serves as the Teton County-Flathead County border and is the Teton River-Flathead River drainage divide. Note how the south-oriented North Fork Sun River headwaters are aligned with a northwest-oriented Middle Fork Flathead River tributary. While not seen in figure 2 a deep through valley links the two opposing drainage routes and is known as Sun River Pass. Also note how the north-oriented Spotted Bear River headwaters are linked with east-northeast oriented Rock Creek by Spotted Bear Pass (across the continental divide), with Rock Creek flowing to the North Fork Sun River. These and other passes across the present day east-west continental divide provide evidence of what were once deep anastomosing melt water flood flow channels, which once crossed the modern-day continental divide.

Bowl Creek-Fool Creek drainage divide area

Figure 3: Bowl Creek-Fool Creek drainage divide area. United States Geological Survey map digitally presented using National Geographic Society TOPO software.
  • Figure 3 illustrates the Bowl Creek-Fool Creek drainage divide area at the northwest end of the Sun River drainage basin. The continental divide is labeled and extends from near the figure 3 southwest corner along the Flathead County (north)-Lewis and Clark County (south) boundary to the Teton County border at Sun River Pass. From Sun River Pass the continental divide also serves as the Flathead County (west)-Teton County (east) boundary. Fool Creek flows in a south direction from Sun River Pass and joins east-oriented Open Creek and south-southwest oriented McDonald Creek to form the south-oriented North Fork Sun River. North of Sun River Pass is southwest and northwest-oriented Bowl Creek which flows to the west and north-northwest oriented Middle Fork Flathead River. Note how north of Sun River Pass and Bowl Creek is the valley of north-northwest oriented South Fork Trail Creek and Trail Creek, which drains as a barbed tributary to a south-oriented Middle Fork Flathead River tributary (Strawberry Creek, name not shown in figure 3). Sun River Pass and the Trail Creek-Bowl Creek through valley are drainage divides in what was once a south-oriented drainage route. The south-oriented drainage route was dismembered first by headward erosion of the deep Bowl Creek valley (from the actively eroding north-northwest oriented Middle Fork Flathead River valley) and second by headward erosion of deep Strawberry Creek valley, also from what was then the actively eroding north-northwest oriented Middle Fork Flathead River valley. In addition to Sun River Pass crossing the continental divide there are several other figure 3 well-defined passes crossing the continental divide. Most are not labeled and have relatively high elevations (compared to adjacent valleys), although just south of the headwaters of Bowl Creek and Trail Creek (both originate as north-northwest oriented streams near the same place) is Teton Pass. South of Teton Pass are south-southeast-oriented headwaters of the east-oriented West Fork Teton River, which flows to the south-southeast oriented Teton River seen near the figure 3 east edge. Sun River Pass, Teton Pass, and other north-south oriented through valleys (or passes) crossing the continental divide and other figure 3 drainage divides provide evidence of multiple diverging and converging south-oriented flood flow channels crossing the figure 3 map area, such as might be found in a large-scale anastomosing channel complex. Today the figure 3 map area is a region of high mountain peaks and ridges separated by deep valleys and the concept of a south-oriented flood formed anastomosing channel complex seems alien to the casual observer. However, at the time flood waters first flowed across the figure 3 map area there were no deep valleys or intervening high ridges and maybe no mountain peaks. Instead flood waters flowed across an erosional surface equivalent in elevation to the high figure 3 ridges today (if not higher). Deep valleys were formed as flood waters were captured by headward erosion of the deep east-oriented Sun River valley (south of figure 3) and headward erosion of the deep east-oriented Teton River valley (to the figure 3 southeast corner region). Subsequently headward erosion of the deep south-oriented Flathead River valley (north and west of figure 3) beheaded south-southeast oriented flood flow to the North Fork Sun River valley and flood waters on the north and northwest end of the beheaded flood flow channel reversed flow direction to erode the northwest-oriented Middle Fork Flathead River valley and the northwest-oriented Bowl Creek valley segment and to create the drainage divide at Sun River Pass.

Detailed map of Bowl Creek-Fool Creek drainage divide area

Figure 4: Detailed map of Bowl Creek-Fool 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 Bowl Creek-Fool Creek drainage divide area seen in less detail in figure 3 above. Sun River Pass is located in the section 2 northeast quadrant where Flathead, Teton, and Lewis and Clark Counties meet. Bowl Creek flows in a southwest direction from the figure 4 northeast corner to the section 36 south edge and then turns to flow in a northwest direction across section 35 to the figure 4 north edge. North of figure 4 Bowl Creek joins the northwest-oriented Middle Fork Flathead River (which flows to the south-oriented Flathead River with water eventually reaching the Pacific Ocean). Basin Creek is the east-northeast and north oriented tributary flowing from the figure 4 west edge (south of center) to  join Bowl Creek near the figure 5 north edge. Fool Creek is the east-northeast and south-oriented stream flowing from section 10 to drain the south end of the north-south oriented through valley at Sun River Pass. South of the figure 4 map area Fool Creek flows to the south-oriented North Fork Sun River, which flows to east-oriented Sun River with water eventually reaching the Gulf of Mexico. The Sun River Pass through valley  has a floor elevation of between 6160 and 6200 feet (the contour interval in figure 4 is 40 feet). Porphyry Reef to the east rises to 7780 feet while the unnamed mountain peak in the figure 4 southwest corner rises to more than 8000 feet. In other words the Sun River Pass through valley floor is at 1500 feet lower than surrounding mountain peaks. Sun River Pass, like other similar passes, is eroded across the continental divide and other present day mountain region drainage divides and is a water eroded feature and was eroded by large volumes of water that crossed the  east-west continental divide. To my knowledge the geologic literature completely ignores this evidence that at one time immense volumes of water once flowed across the continental divide, yet the evidence is real and must be explained. As already described the Sun River Pass through valley was eroded by a major south-southeast oriented flood flow channel, which was a component of a south-oriented anastomosing channel complex. Evidence for diverging and converging flood flow channels can be seen in figure 4. For example in the section 2 southwest quadrant (south and west of Sun River Pass) is a northwest-southeast oriented through valley linking the Basin Creek valley with the Fool Creek valley. Also in section 4 and 33 is a north-south oriented through valley linking a north-oriented Bowl Creek tributary valley with the Basin Creek valley. These additional through valleys and others can be used reconstruct what were at one time south-oriented anastomosing flood channels crossing the figure 4 map area. Headward erosion of deep valleys along some of the channels beheaded flood flow to diverging flood flow channels and in some cases triggered significant flood flow reversals. But, each of the through valleys was eroded by tremendous volumes of flood water, which gradually produced the mountain landscape seen today.

Spotted Bear River-Rock Creek drainage divide area

Figure 5: Spotted Bear River-Rock Creek drainage divide area. United States Geological Survey map digitally presented using National Geographic Society TOPO software.
  • Figure 5 illustrates the Spotted Bear River-Rock Creek drainage divide area south and somewhat west of the figure 3 map area (there is no overlap with figure 3). The North Fork Sun River flows in a south and south-southeast direction along the figure 5 east edge. Rock Creek is a northeast-oriented tributary flowing from south of Spotted Bear Pass in the figure 5 southwest quadrant to join the North Fork Sun River near the figure 5 east center edge. The east-west continental divide extends southward direction from the figure 5 north center edge along the high ridge to Redhead Peak and then jogs to the west through Spotted Bear Pass before resuming its southward direction along the high ridge in the figure 5 southwest quadrant. North of Spotted Bear Pass is an unnamed north oriented tributary to Hoop Creek, which flows to the northwest and west oriented Spotted Bear River, which in turn flows to the north-northwest oriented South Fork Flathead River. Spotted Bear Pass is a deep north-south through valley eroded across the present day continental divide. The figure 5 map contour interval is 50 meters and the Spotted Bear Pass elevation at the continental divide is between 2050 and 2100 meters, which is more than 200 meters higher than floors of Rock Creek valley and Hoop Creek valley on opposite sides of the Pass. However, Redhead Peak rises to 2680 meters and a spot elevation of 2509 meters can be seen on the ridge to west (near south edge) and these adjacent ridge elevations suggest Spotted Bear Pass is at least 400 meters lower than the adjacent ridge elevations. Again Spotted Bear Pass is a water eroded feature and was eroded by south-oriented flood flow moving to what was then the actively eroding Rock Creek valley (which had eroded headward from the North Fork Sun River valley). The south-oriented stream west of the continental divide in the figure 5 southwest corner are headwaters of the south-oriented White River, which south and west of the figure 5 map area makes a U-turn to join the north-northwest oriented South Fork Flathead River. Note Larch Hill Pass on the continental divide west of Spotted Bear Pass. Larch Hill Pass links a northwest oriented tributary to Juliet Creek with the Rock Creek headwaters. South-oriented Juliet Creek flows to the south-oriented White River and has north-oriented headwaters north of Larch Hill. Note how the Juliet Creek headwaters valley is linked by through valleys with both the east-oriented Hoop Creek headwaters valley and the north-oriented Wall Creek valley (with Wall Creek flowing to the north-, northwest-, and west-oriented Spotted Bear River). These mentioned through valleys (or mountain passes) are all water eroded features and were eroded by the south-oriented flood formed anastomosing channel complex as deep valleys began to erode headward into the figure 5 map area. Prior to headward erosion of the deep valleys flood waters flowed in south and southeast directions on an erosion surface at least as the high figure 5 mountain ridges today. Headward erosion of deep valleys into the figure 5 map area, probably aided by uplift of the figure 5 map region, systematically dismembered the south-oriented flood flow channels in sequence from south to north to produce the drainage pattern seen today.

Detailed map of Hoop Creek-Rock Creek drainage divide area

Figure 6: Detailed map of Hoop Creek-Rock 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 Hoop Creek-Rock Creek drainage divide area seen in less detail in figure 5 above. The east-west continental divide serves as the Flathead County-Lewis and Clark County border and is well-marked. Rock Creek flows in an east-northeast direction across the figure 6 southeast corner with water eventually reaching the Gulf of Mexico. A southeast-oriented tributary originates at Mu Lake in the section 16 southeast corner and joins Rock Creek in the figure 6 southeast corner. Juliet Creek originates in the section 16 west half and flows in a north direction before turning to flow in a southwest direction to the figure 6 west edge (north half) with water flowing to the south-oriented White River and then to the north-northwest oriented South Fork Flathead River, which flows to south-oriented Flathead River, etc. with water eventually reaching the Pacific Ocean. The north-oriented stream originating north of Spotted Bear Pass is a Hoop Creek tributary with water north of the figure 6 map area flowing to the north-, northwest, and west-oriented Spotted Bear River and eventually reaching the Pacific Ocean. The figure 6 map contour interval is 40 feet and the Bench Mark at Spotted Bear Pass reads 6721 feet. Redhead Peak to the east rises to 8793 feet while the unnamed peak immediately to west rise to 7867 feet suggesting Spotted Bear Pass is at least 1140 feet deep. Spotted Bear Pass is approximately 700 feet higher than the Rock Creek valley in the figure 6 southeast corner. The Hoop Creek to the north is even deeper suggesting after the reversal of the north end of the flood flow channel across Spotted Bear Pass yet to be beheaded south-oriented flood waters from the west were able to enter the newly reversed flood flow channel. Note how there is an unnamed pass between the Juliet Creek valley in section 16 and an east-oriented tributary valley in section 15 to the north-oriented Hoop Creek tributary valley. This through valley is today represented by a narrow mountain ridge, although the elevation at the drainage divide is between 7640 and 7680 feet. To the north is a peak with an elevation of 7975 feet while to the south is a peak with an elevation of 7867 feet meaning the through valley is approximately 200 feet deep. Something eroded that valley and it was probably east-oriented flood flow moving to the newly reversed Hoop Creek tributary valley. While it takes very complex flood flow movements of this type and tremendous volumes of flood water it is possible to explain the various through valleys seen in figure 6 and also the various deep valleys which eroded headward into the figure 6 map area.

White River-West Fork South Fork Sun River drainage divide area

Figure 7: White River-West Fork South Fork Sun River drainage divide area. United States Geological Survey map digitally presented using National Geographic Society TOPO software.
  • Figure 7 illustrates the White River-West Fork South Fork Sun River drainage divide area south and somewhat west of the figure 5 map area (there is no overlap). The east-west continental divide extends in a north-south direction along the high ridge in the figure 7 east half, which also serves as a county boundary. The south-oriented stream east of the continental divide in the figure 7 northeast quadrant is the West Fork South Fork Sun River, which turns to flow in a southeast direction to the figure 7 east edge (south of center). East of the figure 7 map area the West Fork South Fork Sun River joins the north-oriented South Fork Sun River, which then joins the south-oriented North Fork Sun River to form the east-oriented Sun River. Note how in the figure 7 east center area north-oriented Ahorn Creek joins the south-oriented West Fork South Fork Sun River, which then turns to flow in a southeast direction. West of the continental divide  the same pattern of barbed tributaries and streams flowing in opposite directions to meet also prevails. The South Fork Flathead River flows in a north-northwest direction from the figure 7 south edge (west half) to the figure 7 west edge (near northwest corner). The White River flows in a south, west, and northwest direction from the figure 7 north edge (west of center) to join the north-northwest oriented South Fork Flathead River in the figure 7 west center. The South Fork White River originates between Flathead Alp and Junction Mountain (near figure 7 south edge, just west of the continental divide) and flows in a north-northwest direction to join the south-oriented White River near the point where the White River turns to flow in a southwest, west, and northwest direction to join the South Fork Flathead River. Note also that many South Fork Flathead River tributaries (from the east at least) are oriented in southwest directions. The unusual drainage features (barbed tributaries, elbows of capture, and streams flowing in opposite directions to meet), which are really not unusual, provide evidence of former south-oriented flood flow channels which were systematically captured by headward erosion of deep valleys, with flood waters on north ends of beheaded flood routes reversing flow direction to erode much deeper north-oriented valleys. East of the continental divide headward erosion of the deep east-oriented West Fork South Fork Sun River valley segment captured south-oriented flood flow on the south-oriented West Fork South Fork Sun River segment alignment. Flood waters on the north end of the beheaded flood flow channel reversed flow direction to erode a much deeper north-oriented Ahorn Creek valley. West of the continental divide the same thing happened as headward erosion of the west-oriented White River valley segment captured south-oriented flood flow on the south-oriented White River segment alignment. Flood waters on the north end of beheaded flood flow channel reversed flow direction to erode a much deeper north-oriented South Fork White River valley. Perhaps the most intriguing thing about these flood flow captures is they occurred on flood flow channels adjacent to the continental divide and at elevations almost as high as the continental divide, which means massive south-oriented flood flow was moving along and across the present day east-west continental divide.

Detailed map of Molly Creek-Indian Creek drainage divide area

Figure 8: Detailed map of Molly Creek-Indian Creek drainage divide area. United States Geological Survey map digitally presented using National Geographic Society TOPO software.
  • Figure 8 uses a detailed topographic map of the Molly Creek-Indian Creek drainage divide area seen in less detail in figure 7 above. The east-west continental divide follows the high mountain ridge from the figure 8 north edge to the south edge (near the figure 8 center) and is well-marked as it serves as both the county boundary and the boundary between ranger districts. The South Fork White River flows in a north-northwest direction from the figure 8 south edge (west half) to the figure 8 west edge (north of center). West and north of the figure 8 map area the South Fork White River joins the southwest, west and northwest oriented White River, which flows to the north-northwest oriented South Fork Flathead River with water eventually reaching the Pacific Ocean. Molly Creek is a southwest and west-southwest oriented tributary originating in section 15 along the continental divide (near figure 8 center) and flowing across the north margin of section 21 to join the north-northwest oriented South Fork White River. Indian Creek is located east of the continental divide and originates as a south-oriented stream in section 10 and turns to flow in an east and east-northeast direction to the figure 8 east edge. East of the figure 8 map area Indian Creek joins the north-oriented South Fork Sun River with water eventually reaching the Gulf of Mexico. Note in section 10 how the south-oriented Indian Creek headwaters are linked by a through valley (or mountain pass) with a north-oriented stream and valley. That north-oriented stream is Red Butte Creek, which north of the figure 8 map area turns to flow in a northeast direction to join the north-oriented South Fork Sun River. The through valley floor elevation is marked as 7295 feet (the figure 8 contour interval is 40 feet). Red Butte to the east is shown as reaching 8590 feet while Haystack Mountain to the west is shown as reaching 8376 feet. Based on these adjacent peak elevations the section 10 through valley may be as much as 1100 feet deep. This through valley was eroded as a south-oriented flood flow channel to what was then the actively eroding Indian Creek valley prior to headward erosion of the deep northeast-oriented Red Butte Creek valley (north of figure 8), Headward erosion of the deep northeast-oriented Red Butte Creek valley beheaded the south-oriented flood flow channel and flood waters on the north end of the beheaded flood flow channel reversed flow direction to erode the north-oriented Red Butte Creek valley segment seen in figure 8. Similar north-south oriented through valleys can be seen just west of the continental divide. For example, in section 15 the trail across White River Pass also crosses a north-south oriented through valley (or mountain pass) on its way to the Molly Creek valley. That north-south oriented through valley as well as White River Pass originated as flood eroded flood flow channels prior to headward erosion of the unnamed South Fork White River tributary valley west and north of White River Pass. At that time flood flow moved in an east direction (in the White River Pass through valley) to the actively eroding Indian Creek valley while flood water moved in a south direction to what was then the actively eroding Molly Creek valley. These and other through valleys provide evidence of south-oriented flood flow channels adjacent to and crossing the present day east-west continental divide.

Lost Fork Ahorn Creek-Camp Creek drainage divide area

Figure 9: Lost Fork Ahorn Creek-Camp Creek drainage divide area. United States Geological Survey map digitally presented using National Geographic Society TOPO software.
  • Figure 9 illustrates the Lost Fork Ahorn Creek-Camp Creek drainage divide area at Camp Creek Pass located south of the figure 7 map area. The east-west continental divide follows high mountain ridges from the figure 9 north center edge to the figure 9 southeast corner and serves a county boundary in the figure 9 north center region. The South Fork Flathead River flows in a northwest direction to the figure 9 west edge (north half) with water eventually reaching the Pacific Ocean and is formed at the confluence of northwest oriented Danaher Creek and northeast and north-oriented Youngs Creek in the figure 9 southwest quadrant. Camp Creek is a south-oriented Danaher Creek tributary originating near the figure 9 center on the south side of Camp Creek Pass. North of Camp Creek Pass are headwaters of north-oriented Lost Fork Ahorn Creek, which flows to the figure 9 north edge (east of center). North of figure 9 Lost Fork Ahorn Creek flows to north-oriented Ahorn Creek which in turns flows to the east-oriented West Fork South Fork Sun River, which then flows to the north-oriented South Fork Sun River. Camp Creek Pass is another through valley eroded across the continental divide and links a north-oriented Sun River tributary valley with a south-oriented South Fork Flathead River tributary valley. Remember the north-oriented South Fork Sun River meets the south-oriented North Fork Sun River to form the east-oriented Sun River. Also remember the south-oriented North Fork Sun River valley is linked by a through valley with a northwest-oriented Middle Fork Flathead River tributary valley. While not seen in this essay northwest- and north-oriented Danaher Creek is linked by an extremely well-defined through valley with the south-oriented Dry Fork Blackfoot River, which flows to the west-oriented Blackfoot River. These through valleys provide evidence of what were once diverging and converging south-oriented flood flow channels in a giant anastomosing channel complex, which eroded deep flood flow channels into a large region of what are today the Montana Rocky Mountains. These south-oriented flood flow channels were systematically dismembered by headward erosion of much deeper valleys from both the east and the west and probably by uplift of the mountain region as the much deeper valleys eroded headward into the region to capture the immense south-oriented melt water floods. Headward erosion of the deep east-oriented Sun River valley (north of figure 9) captured the south-oriented flood flow channel crossing Camp Creek Pass and flood waters on the north end of the beheaded flood flow reversed flow direction to erode the north-oriented South Fork Sun River valley and its tributary valleys. West of the continental divide headward erosion of the deep west-oriented Blackfoot River valley (south of the figure 9 map area) first captured the south-southeast oriented flood flow on the South Fork Flathead River-Danaher Creek alignment. Headward erosion of the deep south-oriented Flathead River valley (north and west of figure 9) then beheaded the south-southeast oriented flood flow channel. Flood waters on the north end of the beheaded flood flow channel (probably aided by uplift in the south) reversed flow direction to erode the north-northwest oriented South Fork Flathead River-Danaher Creek valley. The valleys shown in this and other figures used in this essay provide evidence of anastomosing south-oriented flood flow channels which were not only adjacent to and roughly parallel with the present day east-west continental divide, but which also crossed the present day east-west continental divide.

Detailed map of Lost Fork Ahorn Creek-Camp Creek drainage divide area

Figure 10: Detailed map of Lost Fork Ahorn Creek-Camp Creek drainage divide area. United States Geological Survey map digitally presented using National Geographic Society TOPO software.
  • Figure 10 uses a detailed topographic map to illustrate the Lost Fork Anhorn Creek-Camp Creek drainage divide area at Camp Creek Pass, which was seen in less detail in figure 9 above. The east-west continental divide follows high ridges from just west of the figure 10 north center edge to the figure 10 east edge (north half) and serves as the county boundary. Camp Creek Pass is located near the southwest corner of section 14 and is labeled. Lost Fork flows in a north-northeast direction through the Pearl Basin north of Camp Creek Pass. North of figure 10 Lost Fork Ahorn Creek flows to north-oriented Ahorn Creek with water eventually reaching the Gulf of Mexico. Camp Creek is the stream originating just south of Camp Creek Pass and flows in a south-southwest direction to the figure 10 south edge (just west of center). South of figure 10 Camp Creek flows to northwest-oriented Danaher Creek, which flows to the north-northwest oriented South Fork Flathead River with water eventually reaching the Pacific Ocean. Camp Creek Pass is today a deep through valley eroded across the east-west continental divide. The figure 10 map contour interval is 40 feet and the Camp Creek Pass elevation at the drainage divide is between 7160 and 7200 feet. The spot elevation on the continental divide near the north edge of section 10 to the west and north of Camp Creek Pass reads 8490 feet while Twin Peaks to the east is shown as reaching an elevation of 8719 feet. In other words the Camp Creek Pass floor elevation is at least 1200 feet lower than continental divide high points on either side. A 1200 foot deep valley eroded across the continental divide is evidence of a former water eroded valley. The Camp Creek Pass through valley was eroded by south-oriented flood flow moving to what was then a south-oriented flood flow channel on the present day north-northwest oriented Danaher Creek alignment. At that time flood waters were probably flowing to the actively eroding and much deeper Blackfoot River valley south of the figure 10 map area. As already described headward erosion of the deep south-oriented Flathead River valley beheaded the south-southeast oriented flood flow channel on the South Fork Flathead River-Danaher Creek alignment and flood waters on the north-northwest end of the beheaded flood flow channel reversed flow direction to erode the north-northwest oriented Danaher Creek-South Fork Flathead River valley. Probably about the same the deep east-oriented Sun River valley eroded headward into the region north of figure 10 and beheaded the south-oriented flood flow channel crossing present day Camp Creek Pass (at that time all flood flow channels north of Camp Creek Pass were at least as high as the Camp Creek Pass elevation). Flood waters on the north end of the beheaded flood flow channels reversed flow to erode the much deeper South Fork Sun River valley and its much deeper north-oriented tributary valleys, including the Lost Fork Ahorn Creek valley. Erosion of the deep valleys on both sides of the continental divide was probably aided by significant regional uplift which probably occurred as massive flood flow crossed the region.

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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