Marias River-Teton River drainage divide area landform origins, Chouteau County, Montana, USA

Authors

Abstract:

Topographic map interpretation methods are used to determine landform origins in the Chouteau County, Montana Marias River-Teton River drainage divide area. The Teton and Marias Rivers originate along the eastern slopes of the Montana Rocky Mountain front and flow in roughly east directions onto the Montana plains and into Chouteau County before the Marias River makes an abrupt turn to flow in a south direction to join the Teton River and then join the Missouri River. The Marias River-Teton River drainage divide area in Chouteau County is today marked by the presence of buttes or other high areas standing 100 meters or more above broad lowlands drained by south and southeast oriented Teton River tributaries and by north and northeast oriented Marias River tributaries. Through valleys link the north and south oriented drainage routes and provide evidence of former south-oriented flood flow channels. Flood waters are interpreted to have been derived from a rapidly melting thick North American ice sheet, which had been located in a deep “hole”, and which at the time present day landscape features began to form were flowing to what was at that time an actively eroding deep Teton River valley, which was eroding headward across the region. Subsequently headward erosion of the deep east-oriented Marias River valley and its northeast-oriented tributary valleys beheaded and reversed the south-oriented flood flow routes in sequence from east to west to erode a north-oriented slope and north-oriented tributary valleys. Buttes and other upland remnants document prior to Marias River valley headward erosion south-oriented flood flow to the newly eroded Teton River valley stripped much of the region of more than 100 meters of bedrock material, although deeper erosion could have occurred.

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 Marias River-Teton River drainage divide area landform origins in Chouteau County, Montana, USA. Map interpretation methods can be used to unravel many geomorphic events leading up to formation of present-day drainage routes and development of other landform features. While each detailed topographic map feature provides detailed evidence to be explained, the solution must be consistent with explanations for adjacent area map evidence as well as solutions to big picture map evidence puzzles. I invite readers to improve upon my solutions and/or to propose alternate solutions that better explain evidence and are also consistent with adjacent map area and big picture evidence. Readers may do so either by making comments here or by writing and publishing their own essays and then by leaving a link to those essays in a comment here.
  • This essay is also exploring a new geomorphology paradigm in which erosional landforms are interpreted as evidence left by immense glacial melt water floods. Implied in that interpretation is the immense floods were derived from a thick North American ice sheet that created a deep “hole” in the North American continent and also melted fast. The previously unexplored paradigm being tested in this and other 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 Marias River-Teton River drainage divide area landform evidence in Chouteau County, Montana will be regarded as evidence supporting the “thick ice sheet that melted fast” paradigm (see paradigm related essay in menu at top of page). This essay is included in the Missouri River drainage basin landform origins research project essay collection.

Marias River-Teton River drainage divide area location map

Figure 1: Marias River-Teton 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 is a location map for the Marias River-Teton River drainage divide area located in Chouteau County of north central Montana. The United States-Canada border is located near the figure 1 north edge with Saskatchewan in the figure 1 northeast corner and Alberta being the province north of Montana for the remainder of the figure 1 map area. The Missouri River flows in a north and northeast direction from the figure 1 south center edge to Great Falls and Loma before turning to flow in south-southeast and east-northeast direction around the Bears Paw Mountains. The Teton River is an east-oriented tributary joining the northeast-oriented Missouri River near Loma. The Marias River is an east, south, and south-southeast oriented river also joining the Missouri River near Loma (the two rivers actually join at Loma just before joining the Missouri River). The Marias River-Teton River drainage divide area in Chouteau County is located along the eastern end of the Marias River-Teon River drainage divide area and includes the region east of Tiber Dam, south and west of the Marias River, and north of the Teton River. Note on figure 1 how both the Marias River and Teton River headwaters originate on the eastern slopes of the Rocky Mountains and then flow out onto the Montana plains (mountains shown in the figure 1 east half are isolated mountain ranges rising above the surrounding plains). North of the Marias River is the east-oriented Milk River, which originates in Montana east of Glacier National Park and then which flows across southern Alberta before turning to flow in a southeast direction into Montana to join the Missouri River east of the figure 1 map area. Big Sandy Creek is a northeast-oriented tributary, which joins the Milk River near Havre, Montana. The Marias River-Big Sandy Creek drainage divide area landform origins, Chouteau County essay describes the region east of the south-oriented Marias River segment. The Cottonwood Creek-Sage Creek drainage divide area landforms origins Liberty and Hill Counties essay describes the region directly north of Chouteau County. Marias River drainage basin drainage divide area essay can be found by selecting Marias River from the sidebar category list.
  • The Marias River-Teton River drainage divide area in Chouteau County is located on the plains east of the Rocky Mountains, although outlier mountain ranges rise 1000 meters or more above the plains north, east, and south of the Chouteau County Marias River-Teton River drainage divide area. Evidence presented in this essay does not show the high mountain elevations surrounding the study region in all directions, although does suggest the Chouteau County Marias River-Teton River drainage divide area was deeply eroded by massive south oriented floods. These immense south-oriented floods were derived from a rapidly melting thick North American ice sheet, which had been located in a deep “hole.” The deep “hole” had been formed by deep glacial erosion and by crustal warping caused by the ice sheet’s great weight. At the time the ice sheet formed the Rocky Mountains and various Rocky Mountain outlier ranges did not stand high above the surrounding surface. As ice sheet melting began huge south- and southeast oriented melt water floods flowed across and along what are now crests of high mountain ranges with one of the major melt water flood flow routes roughly paralleling the present east-west continental divide. Rocky Mountain uplift then systematically dismembered this giant southeast and south oriented melt water flood flow river beginning in the south and proceeding to the north and northwest. As the Rocky Mountains rose the massive melt water floods were diverted both to the east and the west and eroded what are today major river valleys, which head in the high Rocky Mountains. In time ice sheet melting (combined with Rocky Mountain and other regional uplift) resulted in a situation where the immense southeast- and south-oriented floods were flowing on a bedrock surface higher than the decaying ice sheet surface elevation. Large supra glacial melt water rivers then began to carve giant ice walled canyons into the ice sheet surface and east and northeast oriented tributary valleys eroded headward from these ice-walled canyons to capture the massive higher elevation ice-marginal melt water floods. Of particular importance to the Missouri River drainage basin in Montana and northern Wyoming was a giant ice-walled canyon in Saskatchewan, North Dakota, and South Dakota, which eventually became an ice-walled and bedrock-floored canyon and which detached the decaying ice sheet’s southwest margin. Today the northeast and east-facing Missouri Escarpment in Saskatchewan, North Dakota, and South Dakota is what remains of this giant ice-walled and bedrock-floored canyon’s southwest and west wall.
  • The upper Missouri River drainage basin in Montana and northern Wyoming and the Saskatchewan River drainage basin in southwest Alberta represent the eroded remnants of the deep “hole’s” southwest wall with the crests of the Montana and Canadian Rocky Mountains representing segments of the rim surrounding the deep “hole”, although the mountain crests have probably been deeply eroded by melt water flood erosion and probably are not remnants of the surface on which the ice sheet formed. In the case of the Missouri River drainage basin, tributaries from the west generally were eroded headward in sequence from south to north and from east to west, which means the Teton River valley eroded headward across Chouteau County prior to headward erosion of the east-oriented Marias River valley to the north. Marias River valley headward erosion beheaded south-oriented flood flow routes to the newly eroded Teton River valley (and/or to actively eroding south-oriented Teton River tributary valleys) and flood waters on north ends of beheaded flood flow routes reversed flow direction to erode north-oriented Marias River tributary valleys. Milk River valley headward erosion across southern Alberta subsequently beheaded south-oriented flood flow routes to the newly eroded Marias River valley (and/or to actively eroding south-oriented Marias River tributary valleys). Each of these valleys as it eroded headward across the region probably was several hundred meters deep, although as each deep valley eroded headward across the region the immense south-oriented floods flowing into the newly eroded deep valley significantly lowered the region to the north. For example the Marias River-Teton River drainage divide area was significantly lowered prior to headward erosion of the east-oriented Marias River valley segment, which then caused massive flood flow reversals, which in turn further eroded the Marias River-Teton River drainage divide area. How much erosion took place is difficult to determine, although hills and buttes in the drainage divide area provide markers which can be used to determine minimal erosion depths. Erosion of the Chouteau County Marias River-Teton River drainage divide area occurred very late during the ice sheet’s rapid melt down history and it is probable the region was deeply eroded several times prior to the erosion events interpreted from the present day landscape features.

Detailed location map for Marias River-Teton River drainage divide area

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

 

  • Figure 2 provides a detailed location map for the Marias River-Teton River drainage divide area in Chouteau County. County boundaries are shown and Chouteau County is labeled (in figure 2 southeast region). Hill County is north of Chouteau County in the figure 2 northeast corner, Liberty County is in the figure 2 north center, and Toole County is in the figure 2 northwest corner. Teton County is in the figure 2 southwest corner and Pondera County is between Toole County and Teton County. The northern tip of Cascade County can be seen along the figure 2 south edge between Chouteau and Teton Counties. The Missouri River flows in a northeast direction from the figure 2 south center edge (along the Cascade-Chouteau County border and then into Chouteau County to Fort Benton, Loma, and Virgelle before turning to flow in a south-southeast direction to the figure 2 east edge (north of southeast corner). The Teton River flows in roughly an east direction from the figure 2 west edge (south half) across northern Teton County and into Chouteau County almost to Fort Benton and then flows in a northeast direction parallel to the adjacent Missouri River and joins the Marias River at Loma, just before joining the Missouri River. The Marias River flows from the figure 2 west edge (near northwest corner) in roughly an east direction along the Toole County-Pondera County border and then to Lake Elwell (or Tiber Reservoir). From Tiber Dam the Marias River continues across southern Liberty County into the Hill County southwest corner and then turns at an elbow of capture to flow in a south-southwest and southeast direction to join the Teton River at Loma and then to flow to the northeast oriented Missouri River. Major Marias River tributaries originating in or flowing through Chouteau County include north oriented Dead Indian Coulee, north and northeast oriented Dug Out Coulee, northeast- and north-oriented Basin Coulee, and northeast- and east-oriented Pondera Coulee. Chip Creek is a southeast-oriented tributary, which originates near Goose Bill Butte and which flows parallel to the southeast oriented Marias River segment before joining an east-northeast oriented stream and flowing to join the Marias River. South and southeast oriented Teton River tributaries in Chouteau County are unnamed and generally shorter than the north-oriented Marias River tributaries. The hypothesis presented in this essay is the deep east-oriented Teton River valley eroded headward across Chouteau County prior to headward erosion of the east-oriented Marias River valley segment to the north. The southeast-oriented Teton River tributaries are probably relics of southeast-oriented flood flow routes beheaded by headward erosion of the deep east oriented Marias River valley and its northeast oriented tributary valleys. The south oriented Marias River segment was probably eroded by headward erosion of a south-oriented flood flow route from the deep Missouri-Teton River valley, which captured what had been an east-oriented valley eroded headward from the deep Milk River valley (evidence for an abandoned east oriented valley east of the Marias River elbow of capture is shown in the Cottonwood Creek-Sage Creek drainage divide area landform origins in Liberty and Hill Counties, Montana essay). North oriented Marias River tributary valley segments were probably eroded by reversals of south-oriented flood flow routes beheaded by headward erosion of the deep Marias River valley or its northeast-oriented tributary valleys.

Dead Indian Coulee-Chimney Rock Coulee drainage divide area

Figure 3: Dead Indian Coulee-Chimney Rock Coulee drainage divide area.United States Geological Survey map digitally presented using National Geographic Society TOPO software.

 

  • Figure 3 illustrates the Dead Indian Coulee-Chimney Rock Coulee drainage divide area near Goose Bill Butte and west of the south-oriented Marias River segment. The south-oriented Marias River is seen near the figure 3 east edge. Note southeast-oriented Sheep Coulee draining to the Marias River in the figure 3 northeast quadrant. Goose Bill Butte is located east of the figure 3 center and rises to an elevation of 1149 meters (the map contour interval is 20 meters). Dead Indian Coulee originates west of Goose Bill Butte and drains in a north direction to the figure 3 north edge (just west of center) and north of figure 3 joins the east oriented Marias River segment, which is located north of the figure 3 map area. Note how the southeast-oriented Sheep Coulee valley has eroded what looks like a water gap across a high ridge, has north-oriented headwaters, and is linked to the north-oriented Dead Indian Coulee valley by what could be considered a through valley. The drainage divide between the north-oriented Dead Indian Coulee valley and the southeast-oriented Sheep Coulee valley has an elevation of between 940 and 960 meters. The ridge the Sheep Coulee valley has eroded its valley across rises to more than 1040 meters north of Sheep Coulee and to more than 1020 meters immediately to the south of Sheep Coulee (with Goose Bill Butte rising to 1149 meters). The Sheep Coulee water gap is evidence of a southeast-oriented flood flow route at a time prior to the reversal of south-oriented flood flow on the Dead Indian Coulee alignment. Headward erosion of the deep Marias River valley north of the figure 3 map area beheaded and reversed flood flow on the Dead Indian Coulee alignment so as to erode the north-oriented Dead Indian Coulee valley and to create the Dead Indian Coulee-Sheep Coulee drainage divide. Chimney Rock Coulee is a south-oriented stream originating west and slightly south of Goose Bill Butte and draining to the figure 3 south edge (west of center) while East Dugout Coulee is a north-oriented stream draining to the figure 3 northwest corner region (and then to the east-oriented Marias River north of figure 3). Note how a northwest-oriented East Dugout Coulee tributary is linked by a through valley with the south-oriented Chimney Rock Coulee valley. South of the figure 3 map area Chimney Rock Coulee drains to south-oriented Dry Fork Coulee which drains to the Teton River. The through valley (plus the alignments of Chimney Rock Coulee and Dead Indian Coulee) provide evidence of former south-oriented flood flow routes to what was an actively eroding south-oriented Teton River tributary valley prior to headward erosion of the east-oriented Marias River valley north of the figure 3 map area. Headward erosion of the deep Marias River valley beheaded south-oriented flood flow to the Chimney Rock Coulee valley and flood waters on the north ends of beheaded flood flow routes reversed flow direction to erode the north-oriented Dead Indian Coulee and East Dugout Coulee valleys. Prior to the flood flow reversal flood waters deeply eroded the figure 3 map area. Elevations along the East Dugout Coulee-Chimney Rock drainage divide area are between 980 and 1000 meters while Goose Bill Butte, which rises to 1149 meters, is a marker indicating at least 150 meters of bedrock material was stripped from the region by the south-oriented flood flow.

Detailed map of Dead Indian Coulee-Chimney Rock Coulee drainage divide area

Figure 4: Detailed map of Dead Indian Coulee-Chimney Rock Coulee 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 Dead Indian Coulee-Chimney Rock Coulee drainage divide area seen in less detail in figure 3 above. Chimney Rock Coulee is labeled and drains to the figure 4 south edge (just east of center). South of the figure 4 map area water in Chimney Rock Coulee eventually reaches the east-oriented Teton River. North-oriented drainage in the figure 4 northeast quadrant represents headwaters of north-oriented Dead Indian Coulee. East Dugout Coulee drains in a north-northeast direction across the figure 4 northwest corner and a northwest-oriented tributary originates in section 36 and joins East Dugout Coulee in the northwest quadrant of section 27. North of figure 4 water in Dead Indian Coulee and East Dugout Coulee reaches the east-oriented Marias River. Note how the northwest-oriented East Dugout Coulee tributary valley is linked in section 36 with the south-oriented Chimney Rock Coulee valley. The map contour interval is 10 feet and the through valley floor elevation at the drainage divide is between 3250 and 3260 feet. Elevations greater than 3400 feet can be seen in the figure 4 southwest quadrant (e.g. southeast corner of section 3) and a spot elevation of 3392 feet can be seen near the north edge of section 4 in the figure 4 southeast quadrant. These elevations suggest the section 36 through valley was approximately 150 feet deep or deeper when eroded. A slightly higher level through valley links the north-oriented Dead Indian Coulee headwaters valley in section 30 (figure 4 northeast quadrant) with the south oriented Chimney Rock Coulee valley in the section 36 southeast quadrant. The floor of this higher level through valley has an elevation at the drainage divide of between 3280 and 3290 feet. These two through valleys provide evidence of diverging and converging south-oriented flood flow channels such as might be found in a large-scale anastomosing channel complex. The south-oriented anastomosing channel complex would have been carved by immense south-oriented flood flow moving across the figure 4 map region to what was then the actively eroding Teton River valley. At that time there was no Marias River valley to the north and flood waters were flowing on a surface at least as high as the highest Marias River-Teton River drainage divide area elevations today. Flood flow channels eroded headward into that high level surface as flood waters gradually stripped bedrock material from the region. Headward erosion of the deep east-oriented Marias River valley across the region north of the figure 4 map area beheaded the south-oriented flood flow channels in sequence and flood waters on north ends of beheaded flood flow channels reversed flow direction to erode north-oriented valleys.

Dugout Coulee-Teton River drainage divide area

Figure 5: Dugout Coulee-Teton River drainage divide area.United States Geological Survey map digitally presented using National Geographic Society TOPO software.

 

  • Figure 5 illustrates the Dugout Coulee-Teton River drainage divide area south and west of the figure 3 map area and includes overlap areas with figure 3. The Teton River can be seen flowing in roughly an east direction along the south edge of the figure 5 southwest quadrant. South-oriented Chimney Rock Coulee is located in the figure 5 northeast quadrant and drains to south-oriented Dry Fork Coulee, which drains to the Teton River just south and east of the figure 5 southeast corner. Note southeast-oriented Dry Fork Coulee and tributaries including the West Fork Dry Fork Coulee. Also note the southeast-oriented Teton River tributary in the figure 5 southwest quadrant. The southeast-oriented valleys may be relics of southeast-oriented flood flow routes which flowed across the region at the time the deep Teton River valley eroded headward across the region. Dugout Coulee originates on the north side of a high ridge west of the figure 5 center and drains in a north direction to the figure 5 north edge (west of center). The two roughly parallel north-oriented streams join just north of the figure 5 map area. Note how a narrow through valley crosses the high ridge and links the north-oriented Dugout Coulee valley with the south-oriented headwaters valley of an unnamed southeast-oriented Teton River tributary. The map contour interval is 20 meters and the through valley is defined by two contour lines. This north-south oriented through valley is evidence of a south-oriented flood flow route, which was beheaded and reversed to erode the north-oriented Dugout Coulee valley. Also note the much deeper and broader through valley around the west end of the ridge on which Dugout Coulee originates. This deeper through valley is defined by four contour lines on each side and its round about route suggests the high ridges seen in figure 5 are composed of more resistant bedrock materials. South-oriented flood flow on the Dugout Coulee alignment flowed not only in a south direction, but also in a southwest and then southeast direction to erode the deeper and broader through valley prior to being beheaded and reversed by headward erosion of the deep Marias River valley north of the figure 5 map area. High points in the figure 5 map area suggest flood waters originally flowed on a surface equivalent to the 1100 meter contour line today or higher and removed more than 100 meters of material from lower elevation figure 5 regions to produce the landscape seen today.

Detailed map of Dugout Coulee-Teton River drainage divide area

Figure 6: Detailed map of Dugout Coulee-Teton River 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 Dugout Coulee-Teton River drainage divide area seen in less detail in figure 5 above to better illustrate the described through valleys. Dugout Coulee is labeled and drains in a north direction from sections 26 and 27 to the figure 6 north edge (east half). North of the figure 6 map area Dugout Coulee drains to the east-oriented Marias River. The south-southeast oriented stream in section 32 (figure 6 southwest quadrant) is a tributary to a southeast-oriented Teton River tributary. The higher level and narrow through valley described in figure 5 is located in section 34 near the figure 6 south edge. The map contour interval is ten feet and the through valley floor elevation at the drainage divide is between 3530 and 3540 feet. An elevation of 3657 feet is marked in section 35 to the east while elevations rise above 3630 in section 28 to the west suggesting the through valley was approximately 100 feet deep when eroded, if not deeper. The much deeper and broader (and more round about) through valley extends in a southwest direction from section 21 into section 29 and then in a south-southeast direction along the Teton River tributary valley. The floor of this round about through valley at the drainage divide has an elevation of between 3380 and 3390 feet. Elevations rise to more than 3630 in section 28 to the east while elevations greater than 3500 feet can be seen at several points along the ridge to the northwest. In other words the through valley is more than 100 feet deep based on the ridge to the northwest, which appears to have been eroded by multiple southeast-oriented flood flow routes. However, elevations along the ridge to the east suggest the region was at one time covered by a surface equivalent to or higher in elevation than the highest points shown (e. g. 3657 feet) and the south-oriented flood waters originally flowed on that surface. If so the through valley in sections 21, 20, and 29 documents almost 200 feet of erosion by the south-oriented flood flow. There are no higher markers in the figure 6 map area so it is possible considerable bedrock material was stripped from the figure 6 map area prior to reaching the 3657 foot surface elevation from which the present day valleys may have been eroded.

Basin Coulee-Teton River drainage divide area

Figure 7: Basin Coulee-Teton River drainage divide area.United States Geological Survey map digitally presented using National Geographic Society TOPO software.

 

  • Figure 7 illustrates the Basin Coulee-Teton River drainage divide area west and north of the figure 5 map area and includes overlap areas with figure 5. Dugout Coulee is labeled and drains in a north direction near the figure 7 east edge. North of the figure 7 map area Dugout Coulee drains to the east oriented Marias River. East-northeast and east-oriented North Fork is a Dugout Coulee tributary. Basin Coulee originates in the figure 7 southwest quadrant (north of West and East Knees) and drains in a north-northeast direction to the figure 7 north edge (west of center) and north of the figure 7 map area turns to drain in an east-northeast direction to join the east-oriented Marias River. West Knee and East Knee (buttes in the figure 7 southwest quadrant) are located along the Marias River-Teton River drainage divide, which continues eastward roughly along the figure 7 south edge. Drainage south of the figure 7 map area is to the east-oriented Teton River. The figure 7 map contour interval is 20 meters. West Knee rises to between 1160 and 1180 meters and is the highest point in the figure 7 map area. East Knee elevations rise to between 1120 and 1140 meters and the ridge north and west of Sample Flat rises to a similar elevation. Elevations on Sample Flat are less than 1000 meters while elevations in the north-northeast oriented Basin Coulee valley are also less than 1000 meters. West and East Knee and other figure 7 highland areas are erosional remnants left after south-oriented flood waters stripped much of the figure 7 map area of more than 100 meters of bedrock material. The erosional remnants may be composed of slightly more erosion resistant bedrock material than what was present in the surrounding lowland areas. Flood waters were flowing to what was at that time the actively eroding east-oriented Teton River valley, which is located south of the figure 7 map area. The Teton River valley at that time was more than 100 meters deep and flood waters were removing much of the valley’s north wall as they flowed into the newly eroded valley. Headward erosion of the east-oriented Marias River valley and its east- and northeast- oriented tributary valleys north of the figure 7 map area beheaded the south-oriented flood flow routes in sequence from east to west. Flood waters on north ends of the beheaded flood flow routes reversed flow direction to erode north-oriented valleys (such as the north-oriented Dugout Coulee and Basin Coulee valleys).

Detailed map of Basin Coulee-Teton River drainage divide area

Figure 8: Detailed map of Basin Coulee-Teton River 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 Basin Coulee-Teton River drainage divide area near West and East Knee, which was seen in less detail in figure 7 above. The figure 8 map contour interval is ten feet. West Knee is the high butte in the figure 8 southwest quadrant and has a high point of 3865 feet. East Knee is the two buttes in section 13 east of West Knee and has a high point of 3675 feet. Basin Coulee originates as an east and northeast oriented stream north of West Knee while a northwest-oriented tributary drains north of East Knee. North of the figure 8 map area Basin Coulee eventually drains to the east-oriented Marias River. South of West and East Knee the slope is to the south and drainage is to the east-oriented Teton River, which is located south of the figure 8 map area. Elevations along the drainage divide between West and East Knee at the lowest point are between 3410 and 3420 feet while east of East Knee near the figure 8 east edge elevations along the drainage divide are less than 3400 feet. The valley between West and East Knee is (as is the broad valley between East Knee and ridges further to the east) a through valley, which was eroded by massive south-oriented flood flow moving to what was at that time the actively eroding Teton River valley. At that time there was no Marias River valley to the north and flood waters could freely move across the figure 8 map area to the newly eroded Teton River valley. The Teton River valley was probably eroded headward into an upland surface as high as the highest figure 8 map elevations today and flood waters then eroded deep south-oriented flood flow channels headward from the newly eroded Teton River valley wall. These south-oriented flood flow channels stripped the bedrock surface leaving erosional remnants such as West and East Knee as markers of the upland surface that once existed. How much material was removed before the upland surface was lowered to the level of the present day West Knee top can not be determined because there are no higher elevations in the figure 8 map area. Headward erosion of the Marias River valley north of the figure 8 map area next beheaded the south-oriented flood flow and flood waters on the north ends of the beheaded flood flow routes reversed flow direction to erode the north-oriented Basin Coulee valley.

Flat Coulee-Teton River drainage divide area

Figure 9: Flat Coulee-Teton River drainage divide area.United States Geological Survey map digitally presented using National Geographic Society TOPO software.

 

  • Figure 9 illustrates the Flat Coulee-Teton River drainage divide area south and west of the figure 7 map area and includes significant overlap areas with figure 7. East Knee is located just north of the figure 9 center and West Knee is located west of East Knee. Basin Coulee originates north of West Knee and drains in a northeast and north direction to the figure 9 north center edge (a northwest-oriented tributary is located north of East Knee). South-oriented drainage in the figure 9 southeast quadrant flows to the east oriented Teton River. Flat Coulee is located in a well-defined north-south oriented valley located near the figure 9 west edge. Note how the valley is draining to the figure 9 north edge and is also draining to the figure 9 south edge with the drainage divide just north of the figure 9 west center edge region. North of figure 9 Flat Coulee drains to northeast and east oriented Pondera Coulee, which drains to the Marias River. The east- and south-oriented stream in the figure 9 southwest corner is the Teton River and is joined by south-oriented Flat Coulee. The well-defined Flat Coulee through valley probably represents one of the deepest south-oriented flood flow channels to be beheaded and reversed by headward erosion of the northeast and east oriented Pondera Coulee valley (which eroded headward from the Marias River valley). South-oriented flood waters east of the Flat Coulee flood flow channel were beheaded and reversed at a time when flood water in the Flat Coulee valley was still flowing south to the newly eroded Teton River valley. Headward erosion of the Pondera Coulee valley beheaded the south-oriented flood flow channel and flood waters on the north end of the Flat Coulee flood flow channel reversed flow direction to erode the north-oriented Flat Coulee valley. Figure 9 also illustrates how south-oriented flood waters prior to being beheaded and reversed had stripped the landscape south of West and East Knee of more than 100 meters of bedrock material. West and East Knee as previously stated are erosional remnants providing markers to document a higher level upland surface which flood waters once flowed across and into which the deep Teton River valley was eroded. South-oriented flood flow to the newly eroded Teton River valley was responsible for stripping most of the figure 9 landscape.

Detailed map of Flat Coulee-Flat Coulee drainage divide area

Figure 10: Detailed map of Flat Coulee-Flat Coulee drainage divide area.United States Geological Survey map digitally presented using National Geographic Society TOPO software.

 

  • Figure 10 is a detailed topographic map of the Flat Coulee-Flat Coulee drainage divide area seen in less detail in figure 9 above. The north oriented Flat Coulee drains to the figure 10 northwest corner and north of figure 10 drains to northeast- and east-oriented Pondera Coulee, which drains to the Marias River. The south-oriented Flat Coulee drains to the figure 10 southwest corner and south of figure 10 drains to the Teton River. The drainage divide between the north- and south-oriented Flat Coulee drainage routes is located in sections 1 and the section 12 northwest corner. The map contour interval is 10 feet and the Flat Coulee through valley floor elevation at the drainage divide is between 3270 and 3280 feet. Elevations west of the figure 10 southwest quadrant rise to more than 3400 feet while elevations along the Flat Coulee east rim in the figure 10 southwest quadrant rise to more than 3400 feet. In other words the Flat Coulee through valley, just based on the valley rim elevations, is approximately 120 feet deep. However, as can be seen in the figure 10 southeast quadrant, West Knee rises to an elevation of 3865 feet and provides a marker to document much deeper regional erosion. The Flat Coulee through valley is a 120-foot deep south-oriented flood flow channel, which was eroded into a landscape surface which had already been lowered by at least 400 feet as south-oriented flood waters flowed across the region. Headward erosion of the deep east-oriented Marias River valley subsequently captured the south-oriented flood flow and caused major flood flow reversals, which eroded the north-oriented Flat Coulee valley. Elevations to the north decrease towards the east-oriented Marias River valley indicating the flood flow reversals and diversion of the reversed flood flow in an east direction further lowered the landscape to the north of the figure 10 map area. While many details of flood flow movements remain to be worked out the important thing to remember is the Marias River-Teton River drainage divide seen in figure 10 and in other figures in this essay was deeply eroded by south-oriented flood flow moving to the newly eroded Teton River valley at a time before the east-oriented Marias River valley existed. Evidence shown in figure 10 and in the other figures documents significant erosion and more than 100 meters (or hundreds of feet) of bedrock material were removed from the Marias River-Teton River drainage divide 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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