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

Abstract:

Topographic map interpretation methods are used to determine landform origins in the Teton River-Missouri River drainage divide area located in Chouteau County, Montana. No effort has been made to introduce evidence from other sources. The Teton River originates in the Montana Rocky Mountains and flows in roughly an east direction onto the Montana plains to join the northeast-oriented Missouri River in Chouteau County. Topographic map evidence shows multiple south and southeast-oriented through valleys crossing the Teton River-Missouri River drainage divide, some of which appear to have been diverging and converging anastomosing flood flow channels. These through valleys are interpreted to have been eroded by massive south and southeast-oriented meltwater flood flow prior to headward erosion of the deep east-oriented Teton River valley. Headward erosion of the Teton River valley captured the south and southeast-oriented meltwater flood flow and diverted the flood waters more directly to what was then the newly eroded Missouri River valley. Flood waters are interpreted to have been derived from a rapidly melting North American ice sheet, which had been located in a deep “hole” and the Teton River-Missouri River drainage divide area is interpreted to have been located on the deep “hole’s” southwest wall. Flood water erosion deeply eroded the deep “hole’s” southwest wall, including the Teton River-Missouri River drainage divide area in Chouteau County, although there are no markers in the Chouteau County region to determine how much bedrock material was stripped from the region.

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 Teton River-Missouri 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 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 Teton River-Missouri 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 listed above this essay’s title). This essay is included in the Missouri River drainage basin landform origins research project essay collection.

Teton River-Missouri River drainage divide area location map

Figure 1: Teton River-Missouri River drainage divide area location map (select and click on maps to enlarge). National Geographic Society map digitally presented using National Geographic Society TOPO software.

Figure 1 provides a location map for the Teton River-Missouri River drainage divide area in Chouteau County, Montana and shows a region in northern Montana. The Canadian border is located along the figure 1 north edge. Glacier National Park is labeled and is located in the figure 1 northwest quadrant. The east-west continental divide extends in a south-southeast direction from the figure 1 north edge in Glacier National Park through Logan Pass and Marias Pass and then just east of the northwest-oriented Middle Fork Flathead River to the figure 1 south edge (slightly west of Helena). The northwest-oriented Middle Fork Flathead River and north-northwest oriented South Fork Flathead River flow to the south-oriented Flathead River, which flows through Flathead Lake, to join the northwest-oriented Clark Fork near Dixon (north and west of Missoula near figure 1 west edge) with water eventually reaching the Pacific Ocean. East of the continental divide (except for a very small region adjacent to the Canadian border in Glacier National Park (which drains to Hudson Bay) all drainage routes flow to the Missouri River with water eventually reaching the Gulf of Mexico. The Missouri River flows in a north-northwest direction from the figure 1 south edge (just east of Helena) to near Craig and then turns to flow in a northeast direction to Great Falls, Fort Benton, and Loma before turning south of Big Sandy to flow in a south-southeast and east direction to the figure 1 east center edge. Note north and north-northwest oriented Missouri River tributaries from the south including the Smith River which flows between the Big Belt Mountains and the Little Belt Mountains. Tributaries from the north and west tend to be oriented in east directions, although the Marias River turns to flow in a south direction to join the Missouri River near Loma. Major Missouri River tributaries originating along the continental divide and flowing in east directions onto the Montana plains (from south to north) include the Sun River, the Teton River, and the Marias River (with the Marias River being formed at the confluence of east-oriented Cut Bank Creek and the Two Medicine River). The Teton River begins along the continental divide west Bynum Reservoir and flows in a south-southeast direction before turning to flow in more of an east direction to Chouteau and then to join the Marias River just before joining the Missouri River near Loma. The Teton River-Missouri River drainage divide area in Chouteau County is located south of the Teton River, north of the Missouri River, and east of Benton Lake (located north of Great Falls). The Marias River-Teton River drainage divide area landform origins essay describes the region immediately to the north. Other regional essays can be found listed under the Teton River, Marias River, or Sun River categories (see sidebar).

The Missouri River drainage basin landform origins research project, of which this essay is a component, is the first known study to systematically use detailed topographic map evidence to interpret landform origins in a large drainage basin. Topographic map evidence encountered suggests a fundamentally different landform origin history than is commonly published in the geologic literature. Project essays, including this essay, present the topographic map evidence as suggested by the topographic map evidence and no effort is being made to compare that interpretation with previously published and fundamentally different interpretations. The interpretation used in the project essays describes landform origins in the context of immense melt water floods, which originated during the rapid melt down of a thick North American ice sheet. The ice sheet was comparable in geographic area and thickness to the present day Antarctic Ice Sheet and was located in a deep “hole.” The deep “hole” evolved after the ice sheet had been formed by deep glacial erosion under the ice sheet itself and by crustal warping of continental regions surrounding the ice sheet mass. The upper Missouri River drainage basin in Montana and northern Wyoming (and the Saskatchewan River drainage basin in southwest Alberta) are today what remain of the deeply eroded deep “hole’s” southwest and west wall. The deep “hole’s” western and southwest rim roughly followed the crests of present day Rocky Mountain ranges in Canada and western Montana. When ice sheet melting began the Rocky Mountains did not stand high as they do today, nor were they deeply eroded as they are today, and immense ice-marginal melt water floods could freely flow from the ice sheet’s western margin in Canada along the present day continental divide in south and southeast directions into Montana and then further south and southeast into Wyoming and Colorado and even New Mexico. Uplift of the Rocky Mountains occurred as massive south and southeast-oriented melt water floods were flowing across the region and proceeded from the south to the north. Uplift of the Rocky Mountains systematically blocked southern flood flow routes and caused of diversions of the immense melt water floods both to the east and to the west as headward erosion of deep valleys from both the east and the west captured the melt water floods and created the present day east-west continental divide. In time Rocky Mountain uplift and ice sheet melting proceeded to the point where the ice sheet surface was lower in elevation than the rising mountain areas along this south and southeast-oriented ice-marginal melt water flood flow route. Deep east- and northeast-oriented valleys then began to erode headward from space being opened up by ice sheet melting in the deep “hole” to divert the immense ice-marginal melt water floods to giant south-oriented ice-walled canyons being carved into the decaying ice sheet’s surface.

Of particular importance to the Missouri River drainage basin was a giant southeast and south oriented ice-walled canyon in present day Saskatchewan, North Dakota, and South Dakota which eventually became an ice-walled and bedrock-floored canyon and which 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 north, northeast, and east-oriented valleys eroded headward from that giant ice-walled canyon in sequence (from the southeast to the northeast) to capture the immense south and southeast-oriented ice-marginal melt water floods. The Missouri River valley in Montana was the last of the deep valleys to erode headward in the United States (the South and North Saskatchewan River valleys later eroded from the canyon in Canada) and not only captured south and southeast-oriented melt water floods flowing between the rising Rocky Mountain front and the ice sheet margin, but also captured significant south and southeast-oriented melt water flood flow from Canada which had become trapped between rising Rocky Mountain ranges and which had flowed into southwest Montana. The north-northwest oriented Missouri River valley segment seen in figure 1 was eroded by a massive reversal of flood flow on the north end of a beheaded south-southeast oriented flood flow channel, which captured south and southeast-oriented flood waters moving west of the east-west continental divide on the present day north oriented Middle and South Forks Flathead River, the south oriented Flathead River, and the northwest-oriented Clark Fork alignments. Headward erosion of the deep Columbia River valley (west of the figure 1 map area) subsequently beheaded the south oriented melt water flood flow routes to southwest Montana and flood waters on north ends of beheaded flood routes reversed flow direction to create the present day north- and northwest-oriented valleys and in time to erode the west side of the continental divide (although the process was much more complicated than described in this brief overview). At the same time deep east-oriented valleys were eroding headward from the newly eroded Missouri River valley to capture the south- and southeast-oriented melt water floods and to erode the east side of the continental divide. Headward erosion of the east-oriented Sun River valley captured the south-oriented flood flow prior to headward erosion of the deep Teton River valley, which beheaded flood flow to the newly eroded Sun River valley. Marias River valley headward erosion and headward erosion of Marias River tributary valleys next beheaded south- and southeast-oriented flood flow to the newly eroded Teton River valley. In this essay we will look at evidence suggesting Teton River valley headward erosion beheaded south- and southeast-oriented flood flow to what was then the newly eroded northeast-oriented Missouri River valley.

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

Figure 2: Detailed location map for Teton River-Missouri 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 Teton River-Missouri River drainage divide area in Chouteau County. County boundaries and Chouteau, Teton, and Cascade County names are shown. The Missouri River flows in a northeast direction from the figure 2 south edge (west half) to the figure 2 east edge (just south of the northeast corner). Note north and northwest-oriented tributaries located south of the northeast-oriented Missouri River. The north and northwest-oriented tributary valleys were eroded by reversals of south and southeast-oriented flood flow channels triggered by headward erosion of the deep Missouri River valley. The Teton River flows in a southeast direction from the figure 2 west edge (north half) to the town of Chouteau and then turns to flow in a northeast directions to Collins where it turns to flow in more of an east direction to join the Missouri River near Loma. Between Fort Benton and Loma the Teton River roughly parallels the Missouri River and at one point the two rivers almost meet. Teton River tributaries from the north in Chouteau County are oriented in south and southeast directions and were eroded by south and southeast-oriented flood flow moving to what was then the newly eroded Teton River valley. Note north-oriented Teton River tributaries in western Chouteau County including Alkali Coulee, Sheep Coulee, and Timber Coulee. The north-oriented coulee valleys were eroded by reversals of south oriented flood flow channels as the deep Teton River valley eroded headward across the region. The flood flow channels were moving flood waters to south- and southeast-oriented Missouri River tributaries, many of which are not shown in figure 2. Huntley Coulee is an east, northeast, and southeast-oriented Missouri River tributary appearing to drain Benton Lake, which has an east-southeast oriented inlet (Lake Creek). Prior to headward erosion of the Teton River valley the Lake Creek-Benton Lake valley region may have been a developing east-oriented Missouri River tributary route, which never fully developed when Teton River valley headward erosion beheaded all south-oriented flood flow routes to it. Figure 2 does not show topography so we need to move to the topographic maps, which will start in the east near Loma and then proceed westward to the Chouteau County-Teton County line.

Teton River-Marias River drainage divide area

Figure 3: Teton River-Marias River drainage divide area. United States Geological Survey map digitally presented using National Geographic Society TOPO software.

Figure 3 illustrates the Teton River-Marias River drainage divide area at the east end of the Teton River-Missouri River drainage divide area. Fort Benton is the town near the figure 3 south center edge. The Marias River flows in a south, east, and southeast direction in the figure 3 northeast corner. The Missouri River flows in a northeast direction from the figure 3 south edge near Fort Benton to Evans Bend where it turns to flow in a northwest direction to flow to the Crocon du Nez and then turns to flow in an east-southeast direction to the figure 3 east edge (south half). East of the figure 3 map area the Missouri River resumes its northeast direction of flow as seen in figures 1 and 2. Crocon du N is a narrow cliff separating the Missouri River valley from the Teton River valley just to the northwest. The Teton River flows in a south-southeast direction from the figure 3 west edge (just south of center) and then turns to flow in a northeast direction to join the Marias River at the figure 3 east edge. Note how the northeast-oriented Teton River segment is flowing along the southeast base of a southwest to northeast oriented ridge (named Vimy Ridge at the northeast end). West of the figure 3 map area the Teton River flows in an east-northeast direction along the northwest side of the southwest extension of the same ridge and the south-southeast oriented Teton River segment seen in the figure 3 southwest quadrant is where the Teton River has cut a valley across the ridge before continuing its east-northeast and northeast flow direction. The deep south-southeast oriented Teton River valley across the ridge could be considered to be a water gap. The water gap becomes even interesting when the Dry Fork Coulee is observed. Dry Fork Coulee drains in a south direction from the figure 3 north edge (near northwest corner) toward the Teton River water gap, but before reaching the Teton River turns to drain in an east-northeast, south-southeast, and east-northeast direction to the Marias River. A through valley links the Teton River valley (on the northwest side of the water gap) with the east-northeast oriented Dry Fork Coulee valley. The figure 3 map contour interval is 20 meters and the through valley floor elevation at the Teton River-Dry Fork Coulee drainage divide is between 880 and 900 meters. The ridge to the south on Chinaman Hill rises to at least 945 meters (see spot elevation) while elevations greater than 960 meters can be seen near the figure 3 north edge. In other words the through valley is at least 45 meters deep and is a water eroded valley that at one time moved Teton River water in an east-northeast and northeast direction to the Marias River valley. The present day south-southeast oriented Teton River valley through the water gap could only be eroded if volumes of water moving across the region were so great that flood waters were also moving in south-southeast directions as well in the east-northeast direction. The south-southeast oriented valley was eroded deep enough that it eventually beheaded the east-northeast oriented flood flow to the Marias River. The same type of argument can be made for the origin of the roughly parallel Teton River and Missouri River valleys in the figure 3 map area. Volumes of flood waters moving in an east-northeast and northeast direction at one time were so great that multiple flood channels were eroded to move the water.

Weatherwax Coulee-Black Coulee drainage divide area

Figure 4: Weatherwax Coulee-Black Coulee drainage divide area. United States Geological Survey map digitally presented using National Geographic Society TOPO software.

Figure 4 illustrates the Weatherwax Coulee-Black Coulee drainage divide area west and somewhat south of the figure 3 map area. The Missouri River flows in a northeast and east-southeast direction in the figure 4 southeast quadrant. Bullhead Coulee is an east and south-southeast oriented Missouri River tributary. Antelope Coulee drains in a southeast direction in the figure 4 southwest quadrant and appears to drain to east and southeast-oriented Black Coulee, which joins the Missouri River near the figure 4 south edge. There is a continuous through valley linking the Antelope Coulee valley with the Black Coulee valley although today the Antelope Coulee drainage ends at the intermittent lake shown, which normally has no outlet. The through valley provides evidence of a former melt water flood flow channel. Huntley Coulee is the unlabeled east and southeast oriented stream in the figure 4 southwest corner and will be seen again in figures 8 and 9. The Teton River flows in an east-southeast direction from the figure 4 north edge (west of center) and then turns to flow in an east-northeast direction to the northeast corner where it turns to flow in a south-southeast direction across the figure 4 northeast corner. Weatherwax Coulee is a Teton River tributary draining in an east-northeast, and east direction from the figure 4 northwest quadrant to join the Teton River in the figure 4 northeast quadrant. Note north-oriented Weatherwax Coulee tributaries. Eightmile Coulee is an east-northeast oriented Teton River tributary near the figure 4 east center edge and joins the Teton River east of the figure 4 map area. Note the southwest to northeast oriented ridge between the Teton River valley and the Missouri River valley, which rises gradually to the southwest. The figure 4 map contour interval is again 20 meters and the ridge elevation is almost 100 meters higher than the Teton River valley floor elevation to the north and even higher than the deeper Missouri River valley floor elevation to the southeast. Note how west of the small town of Carter there is a north-south oriented through valley crossing the ridge and linking a north-oriented Weatherwax Coulee tributary valley with the east- and southeast-oriented Black Coulee valley. The through valley is defined by only one contour line on each side, but is otherwise well-defined. The through valley was eroded by south-oriented flood waters flowing to the Black Coulee valley prior to headward erosion of the east-oriented Weatherwax Coulee valley (and of the Teton River valley to the north). Headward erosion of the Weatherwax Coulee valley beheaded the south-oriented flood flow and flood waters on the north end of the beheaded flood flow channel reversed flow direction to erode the north-oriented Weatherwax Coulee tributary valley. A close look at the figure 4 map area reveals additional through valleys. For example near the south edge of the figure 4 southwest quadrant is a north-south oriented through valley linking the Antelope Coulee valley with the Huntley Coulee valley (just east of Floweree Lake). This through valley was also eroded by south-oriented flood flow prior to headward erosion of the Antelope Coulee-Black Coulee valley.

Detailed map of Weatherwax Coulee-Black Coulee drainage divide area

Figure 5: Detailed map of Weatherwax Coulee-Black Coulee drainage divide area. United States Geological Survey map digitally presented using National Geographic Society TOPO software.

Figure 5 provides a detailed topographic map of the Weatherwax Coulee-Black Coulee drainage divide area seen in less detail in figure 4 above. Carter is the small town located in the figure 5 east half. The Missouri River can just barely be seen in the figure 5 southeast corner. Black Coulee drains in an east direction near the south edge of the figure 5 southwest quadrant and then turns to flow in a southeast direction to the figure 5 south center edge and to join the Missouri River south of the figure 5 map area. The north-northeast oriented stream flowing to the figure 5 north center edge is a Weatherwax Coulee tributary. Note in the east halves of sections 6 and 7 a north-south oriented through valley eroded across the southwest to northwest oriented ridge crossing the figure 5 map area. Just east of the through valley the figure 5 contour interval is 20 feet, while the through valley and areas to the west are mapped using a 10 foot contour interval. The through valley floor elevation is between 3190 and 3200 feet and the ridge in section 5 rises to 3234 feet while the ridge to the southwest rises to more than 3270 feet. The through valley is at least 34 feet deep and is a water eroded feature and was eroded by south-oriented melt water flood flow. The ridge in section 5 appears to be a streamlined erosional residual providing further evidence of flood flow across the figure 5 map area. The south-oriented flood flow was moving to what was then the actively eroding Black Coulee valley, which had eroded headward from what was then the newly eroded Missouri River valley. At that time the Weatherwax Coulee and Teton River valleys did not exist and flood waters could freely move in a south direction to and across the figure 5 map area. Headward erosion of the Weatherwax Coulee valley from the actively eroding Teton River valley beheaded the south-oriented flood flow channel. Flood waters on the north end of the beheaded flood flow channel reversed flow direction to erode the north-northeast oriented Weatherwax Coulee tributary valley and the figure 5 landscape has changed little since. Subsequently Teton River valley headward erosion beheaded south-oriented flood flow to the newly eroded Weatherwax Coulee valley.

Berry Coulee-Antelope Flat drainage divide area

Figure 6: Berry Coulee-Antelope Flat drainage divide area. United States Geological Survey map digitally presented using National Geographic Society TOPO software.

Figure 6 illustrates the Berry Coulee-Antelope Flat drainage divide area west and slightly south of the figure 4 map area and includes overlap areas with figure 4. The Teton River flows in roughly an east direction from the figure 6 northwest corner region to the figure 6 east edge (north half). Timber Coulee is the north oriented Teton River tributary near the figure 6 west edge and the northeast-oriented Timber Coulee tributary (labeled “Coulee” in figure 6) is also named Timber Coulee and drains in a north-northeast direction west of the figure 6 southwest quadrant. Sheep Coulee is the north-oriented tributary joining the Teton River in the figure 6 north center. East of north, east, and north-oriented Sheep Coulee is northwest-oriented Wolf Coulee and north-northwest and northwest oriented Berry Coulee. These north- and northwest-oriented Teton River tributaries are flowing in valleys eroded by reversals of south and southeast-oriented flood flow which was beheaded and reversed by headward erosion of the deep Teton River valley. The south and southeast-oriented flood flow was moving to what at that time were the actively eroding Missouri River valley and its tributary valleys. Figure 10 illustrates Timber Coulee linkages with south-oriented Missouri River tributaries. Antelope Flat in the figure 6 southeast quadrant drains to Antelope Lake (in figure 6 southeast corner) and then to Antelope Coulee which was seen in figure 4. As seen in figure 4 Antelope Coulee is a discontinuous drainage route today although it is linked by a well-defined through valley with east and southeast-oriented Black Coulee, which drains to the Missouri River. Note how a shallow through valley links the north-oriented Berry Coulee headwaters with the southeast-oriented stream valley draining to Antelope Lake. This shallow northwest-southeast oriented through valley is rather interesting because today it appears to be on the side of a northeast-facing slope. Just to the northeast near the east edge of the figure 6 southeast quadrant is evidence of another shallow northwest-southeast oriented though valley on the side of the same northeast-facing slope. These through valleys suggest southeast-oriented flood water was eroding the northeast-facing slope surface with greater erosion to the northeast at the same time as the deep Teton River valley was eroding headward across the region (and beheading the southeast-oriented flood flow routes). Figure 7 below provides a detailed topographic map to better illustrate the northwest–southeast oriented through valleys.

Detailed map of Berry Coulee-Antelope Flat drainage divide area

Figure 7: Detailed map of Berry Coulee-Antelope Flat drainage divide area. United States Geological Survey map digitally presented using National Geographic Society TOPO software.

Figure 7 provides a detailed topographic map of the Berry Coulee-Antelope Flat drainage divide area seen in less detail in figure 6. Berry Coulee is the north-northwest oriented deep valley seen in the figure 7 northwest quadrant. As seen in figure 6 north of the figure 6 map area Berry Coulee drains to the east oriented Teton River. South of the Berry Coulee headwaters is south and southeast-oriented Leepers Flat which links the north-oriented Berry Coulee valley with the southeast-oriented Antelope Flat valley. As seen in figure 4 drainage in the Antelope Flat valley is not continuous, but is linked by a through valley with east and southeast-oriented Black Coulee which drains to the Missouri River. Note how Leepers Flat is actually the floor of a through valley linking the north-oriented Berry Coulee valley with southeast-oriented Antelope Flat-Black Coulee through valley. The figure 7 map contour interval is 10 feet and the Leepers Flat elevation at the drainage divide is between 3280 and 3290 feet. Elevations to the east rise to more than 3340 feet while elevations to the west rise even higher suggesting the Leepers Flat through valley is at least 50 feet deep. The Leepers Flat through valley provides evidence of a south-oriented flood flow channel prior to headward erosion of the deep Teton River valley to the north. Headward erosion of the east-oriented Teton River 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 Berry Coulee valley. Also in figure 7 note in section 20 (in the southeast quadrant) a somewhat more subtle north-northwest to south-southeast oriented through valley along the base of what appears to be a low east-northeast facing escarpment. The through valley floor elevation is between 3200 and 3210 feet and elevations rise to at least 3240 feet to the east and even higher west of the 30-80 foot high escarpment. This lower elevation through valley also links north-oriented Teton River drainage with south-oriented Antelope Lake drainage (which is linked by a through valley with the east- and southeast-oriented Black Coulee valley, which drains to the Missouri River). Again the through valley provides evidence of a south-oriented flood flow channel, which existed prior to headward erosion of the deep Teton River valley. Teton River valley and a northeast-oriented tributary valley headward erosion beheaded and reversed the south-oriented flood flow channel to create the present day through valley.

Huntley Coulee-Portage Coulee drainage divide area

Figure 8: Huntley Coulee-Portage Coulee drainage divide area. United States Geological Survey map digitally presented using National Geographic Society TOPO software.

Figure 8 illustrates the Huntley Coulee-Portage Coulee drainage divide area south and east of the figure 6 map area and south and west of the figure 4 map area and includes overlap areas with figure 4. The Missouri River flows in a north-northeast direction from the figure 8 south edge (east half) to the figure 8 east edge (near northeast corner). Note northwest-oriented Missouri River tributaries from the east. The northwest-oriented tributary valleys were eroded by reversals of flood flow on northwest ends of beheaded southeast oriented flood flow routes. Missouri River tributaries from the west tend to be oriented in southeast and east directions. In the figure 8 northeast corner area is east and southeast oriented Black Coulee. Proceeding south there is southeast oriented Middle Coulee, southeast-oriented Huntley Coulee, southeast- and east-oriented Ryan Coulee, and southeast- and east-oriented Portage Coulee (near figure 8 south edge). Further west from the Missouri River valley Huntley Coulee drains in an east, northeast, southeast, and south direction before finally draining in a southeast direction to the north-northeast oriented Missouri River. Note how the Huntley Coulee valley is linked by shallow diverging and converging through valleys with the Portage Coulee valley and also with the Ryan Coulee valley. Low streamlined erosional residuals are located between this complex of former anastomosing south oriented flood flow channels. At the time the anastomosing channels were eroded the deep Teton River valley to the north of figure 8 did not exist and flood waters could freely move in a south and southeast direction to the figure 8 map area and then to what were actively eroding tributary valleys eroding headward from the newly eroded Missouri River. Headward erosion of the deep Teton River valley (north of the figure 8 map area) captured the south and southeast-oriented flood flow and diverted the flood waters more directly to the newly eroded Missouri River valley. Flood waters on north ends of beheaded flood flow channels reversed flow direction to erode north-oriented Teton River tributary valleys and to create the Teton River-Missouri River drainage divide. Looking at the figure 8 map area headward erosion of the Huntley Coulee valley beheaded south- and southeast-oriented flood flow routes to what were then the actively eroding Ryan Coulee and Portage Coulee valleys. Apparently the Huntley Coulee valley was not deep enough relative to the depths of the flood flow channels moving flood waters to the Ryan Coulee and Portage Coulee valleys and there were no significant reversals of flood flow on the north ends of the beheaded flood flow channels. Landforms in the figure 8 map area have remained unchanged since Teton River valley headward erosion beheaded flood flow channels crossing the figure 8 map area.

Detailed map of Huntley Coulee-Portage Coulee drainage divide area

Figure 9: Detailed map of Huntley Coulee-Portage Coulee drainage divide area. United States Geological Survey map digitally presented using National Geographic Society TOPO software.

Figure 9 provides a detailed topographic map of the Huntley Coulee-Portage Coulee drainage divide area seen in less detail in figure 8 above. Huntley Coulee drains in a northeast direction from the figure 9 west center toward Flick Lake, but then turns to drain in an east-southeast oriented direction before turning again in section 35 to drain in a northeast direction to the section 36 northwest corner. At the section 36 northwest corner Huntley Coulee turns to drain in a north-northwest and then north-northeast direction to the section 26 northeast corner and then drains in a northeast direction to the figure 9 north edge (east half). What is interesting about this unusual route is the east-southeast oriented through valley at the northwest end of the south-southeast oriented Portage Coulee valley (which drains to the figure 9 south center edge) and north of Flick Lake is a south-oriented through valley linked to north-oriented drainage routes. Further, in sections 26 and 24 the Huntley Coulee valley crosses at least two well-defined diverging and converging through valleys (and probably crosses somewhat more subtle through valleys further to the northeast). The southeast and south-southeast oriented through valleys seen in the figure 9 map area provide additional evidence of a former southeast and south-southeast oriented anastomosing channel complex crossing the Teton River-Missouri River drainage divide. The through valleys document former southeast and south-southeast oriented flood flow channels at a time when flood waters could freely move across the Teton River-Missouri River drainage divide. The figure 9 map contour interval is 10 feet and the through valleys are not deep, although they are deep enough to be well-defined. There is evidence of higher level through valleys such as in the southwest quadrant of section 4 (in figure 9 southwest quadrant) where a shallow northwest-southeast oriented through valley crosses one of the higher ridges in the figure 9 map area. This higher level through valley is evidence of an earlier and higher level southeast oriented flood flow channel which was eroded into a surface which was largely removed by subsequent flood flow erosion. Headward erosion of the Huntley Coulee valley was the last major drainage change in the figure 9 map area and probably occurred just before Teton River valley headward erosion beheaded all southeast- and south-oriented flood flow to the figure 9 map area. The important thing to remember is the figure 9 map evidence documents massive southeast and south-southeast oriented flood flow across the region prior to headward erosion of the Huntley Coulee valley.

Timber Coulee-Benton Lake drainage divide area

Figure 10: Timber Coulee-Benton Lake drainage divide area. United States Geological Survey map digitally presented using National Geographic Society TOPO software.

Figure 10 illustrates the Timber Coulee-Lake Benton drainage divide area south and west of the figure 4 map area and south of the figure 6 map area and includes overlap areas with both figures 4 and 6. Lake Benton is located near the figure 10 south center edge and appears to drain in an east-northeast direction to Huntley Coulee, which crosses the figure 10 east center edge, although a southeast-oriented outlet route exists south of the figure 10 map area (this southeast-oriented outlet route appears on detailed topographic maps to be man-made). As seen in figure 8 Huntley Coulee eventually drains to the Missouri River. Lake Creek is the east and east-southeast oriented Lake Benton inlet flowing from the figure 10 west edge (south of center). In the figure 10 northwest quadrant are two north-northeast oriented Timber Coulees, which join north of the figure 10 map area to form north-oriented Timber Coulee, which as seen in figure 6 drains to the Teton River. The north-oriented stream draining to the figure 10 north center edge is Sheep Coulee, which as seen in figure 6 also drains to the Teton River. The southeast-oriented Antelope Flat and Antelope Coulee through valley can be seen in the figure 10 northeast corner region and southeast-oriented through valleys linking the Huntley Coulee valley with the southeast-oriented Ryan Coulee and Portage Coulee valleys can be seen in the figure 10 southeast corner region. Note the well-defined through valleys linking the two north-northeast oriented Timber Coulee valleys with the east and east-southeast oriented Lake Creek valley. The figure 10 map contour interval is 20 meters and the western through valley floor elevation at the drainage divide is between 1140 and 1160 meters (the eastern through valley floor is shown as being between 1160 and 1180 meters). Elevations on either side of the western through valley rise to at least 1220 meters meaning the western through valley is at least 60 meters deep. The eastern through valley is not as deep, but is still an identifiable feature. Other somewhat less obvious through valleys link the north-oriented Sheep Coulee valley with the valleys of south-oriented Lake Creek tributaries. These through valleys are water eroded features and were initiated as south-oriented flood flow channels. At that time the deep Teton River valley to the north did not exist and flood waters could freely flow in a south direction to the broad east-oriented Lake Creek valley, which was probably eroding headward across the region (probably from the Missouri River valley south and east of the figure 10 southeast corner). The shallow Lake Benton basin may have scoured by flood water erosion although other origins are also possible. Again, the figure 10 map evidence documents south-oriented flood flow across the figure 10 map area prior to Teton River valley headward erosion.

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.