Whitewater Creek-Milk River drainage divide area landform origins, north central Phillips County, Montana, USA

Abstract:

Topographic map interpretation methods are used to determine landform origins in the Whitewater Creek-Milk River drainage divide area located in north central Phillips County, Montana. The Milk River in the study region flows in east direction to Malta, Montana and then turns to flow in a north-northeast direction before turning to flow in a southeast direction near where it is joined by north, north-northeast, and southeast oriented Beaver Creek. Whitewater Creek is a south-southeast oriented tributary which joins the southeast-oriented Milk River just downstream from the elbow of capture (where the north-northeast oriented Milk River turns to flow in a southeast direction). The south-southeast oriented Whitewater Creek valley is linked by several north-south oriented through valleys with the north-northeast oriented Milk River valley. The north-northeast oriented Milk River valley has several significant southeast-oriented tributaries and through valleys extend east from the present day north-northeast oriented Milk River valley to the present day north and north-northeast oriented Beaver Creek valley. Study region landforms were eroded as deep valleys eroded headward into the region to capture massive south- and southeast-oriented melt water floods which had been moving to a major south-oriented flood flow channel on the present day north-oriented Beaver Creek alignment. Headward erosion of the deep southeast-oriented Milk River valley captured multiple south- and southeast-oriented flood flow routes in sequence from east to west and in the process beheaded the flood flow channels to the major south-oriented flood flow channel. Flood waters on north ends of beheaded flood flow channels reversed flow direction to erode what are today north-oriented valleys and valley segments. The sequence of these flood flow channel captures and flood flow reversals can be reconstructed out to determine internally consistent histories of deep valley erosion (and valley abandonment where valleys have since been abandoned).

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 Whitewater Creek-Milk River drainage divide area landform origins in north central Phillips 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 Whitewater Creek-Milk River drainage divide area landform evidence in north central Phillips County, Montana will be regarded as evidence supporting the “thick ice sheet that melted fast” paradigm (see menu at top of page for paradigm related essay). This essay is included in the Missouri River drainage basin landform origins research project essay collection.

Whitewater Creek-Milk River drainage divide area location map

Figure 1: Whitewater Creek-Milk 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 Whitewater Creek-Milk River drainage divide area in north central Phillips County, Montana and illustrates a region of north central Montana with southwest Saskatchewan and southeast Alberta north of the international border. The Missouri River flows in a generally east direction from the figure 1 west edge (near the figure 1 southern margin) to Fort Peck Lake and then to the figure 1 east edge. The Milk River flows in a southeast direction from the figure 1 west edge (near international border) to Havre, Montana and then to Malta, Montana. At Malta the Milk River makes a pronounced north-northeast jog and then flows in a southeast direction to join the Missouri River just downstream from Fort Peck Dam. Whitewater Creek is a southeast-oriented Milk River tributary which joins the southeast-oriented Milk River near Nelson Reservoir, a short distance downstream from where the north-northeast oriented Milk River turns to flow in a southeast direction (which is downstream from Malta). Whitewater Creek originates in southern Saskatchewan and crosses the international border almost directly north of Malta. South of Whitewater Creek is southeast-oriented Cottonwood Creek, which joins the north-northeast oriented Milk River segment midway between Malta and the mouth of Whitewater Creek. The Whitewater Creek-Milk River drainage divide area investigated in this essay is south and west of Whitewater Creek, generally north of the Milk River, and east of a north-south line through Wagner, Montana (just west of Malta). North and east of Whitewater Creek is the Frenchman Creek (or River), which originates in the Cypress Hills area (figure 1 northwest quadrant) and which flows in an east and east-southeast direction across southwest Saskatchewan before turning to flow in a south direction to join the Milk River near Saco, Montana. The Whitewater Creek-Frenchman River drainage divide area landform origins northeast Phillips County, Montana essay describes the region between Whitewater Creek and the Frenchman River (Creek) and south of the international border. Note also Beaver Creek which originates in the Little Rocky Mountains (near figure 1 south center) and flows in a northeast, east-southeast, north, and southeast direction to join the Milk River between Saco and Hinsdale. The Milk River-Missouri River drainage divide area landform origins between Beaver and Larb Creeks, the Peoples Creek-Beaver Creek drainage divide area landform origins and other essays listed under the sidebar Milk River category describe other nearby drainage divide areas.

The Whitewater Creek-Milk River drainage divide area in north central Phillips County, Montana had a complex erosion history, which to properly understand requires the rapid melting of a thick North American ice sheet, which was located in a deep “hole”. By deep “hole” I mean the ice sheet had formed on a topographic surface now preserved, if it is preserved at all, on the highest level Rocky Mountain erosion surfaces. Those high level Rocky Mountain erosion surfaces were probably uplifted by ice sheet caused crustal warping, but what is important is massive melt water floods flowed in southeast directions on those erosion surfaces along the ice sheet’s southwest margin and as the ice sheet melted were captured by deep east and northeast-oriented valleys which eroded headward from the developing “hole” where the melting ice had been. East of Rocky Mountain outliers, such as the Little Rocky Mountains and Bears Paw Mountains seen in figure 1, the deep east and northeast-oriented valleys generally captured south, south-southeast, or southeast oriented melt water floods and diverted the flood waters onto the ice sheet surface or into deep ice-walled canyons eroded by supra glacial rivers into the decaying ice sheet’s surface. However, the presence of mountains consisting of more erosion resistant rocks created more complex flood flow patterns, which are encountered in the Malta, Montana region. The deep east-oriented Missouri River valley eroded headward from a deep ice-walled and bedrock-floored canyon, the southwest wall of which today is the northeast-facing Missouri Escarpment in northwest North Dakota, and the southeast-oriented Milk River valley and Whitewater Creek valley were eroded headward along and across massive south, south-southeast, and southeast oriented ice-marginal flood flow until reaching the Nelson Reservoir area slightly north and east of Malta.

In the region between Malta and Nelson Reservoir the actively eroding and north-northeast oriented Milk River valley eroded headward across what were several well-developed southeast-oriented flood flow channels moving flood water to a major south oriented flood flow channel located along the route of the present day north-oriented Beaver Creek segment seen in figure 1. A deep and well-defined through valley links the north-oriented Beaver Creek valley with the “V” in Fort Peck Lake (located near figure 1 south center edge) and the north-oriented Musselshell River, which joins the Missouri River at the south end of the “V” (not shown in figure 1). This south oriented flood flow channel had probably eroded headward from the Yellowstone River valley, which was eroding headward from the same ice-walled and bedrock-floored canyon slightly in advance of the Missouri River and Milk River valleys. Headward erosion of the deep Missouri River valley probably captured the south-oriented flood flow channel slightly in advance of the Milk River valley capture further to the north. Flood waters on the north end of the flood flow channel beheaded by deep Missouri River valley headward erosion reversed flow direction and the deep Musselshell River valley then eroded headward to capture southeast-oriented flood flow, which had been moving to the newly eroded Yellowstone River valley. Milk River valley headward erosion next captured the south- and southeast-oriented flood flow channels feeding this major south-oriented flood flow channel and flood waters on north end of the beheaded flood flow channel reversed flow direction to erode the north-oriented Beaver Creek valley segment.

Further complicating the situation was west of the actively Milk River and Missouri River valleys elevations were much higher than they are today and massive southeast-oriented ice-marginal melt water floods were flowing on those high level surfaces. As deep valleys eroded headward into the figure 1 region those higher elevation southeast-oriented flood waters were diverted to flow towards the actively eroding deep valley heads. These water movements generally lowered the regional landscape, however as already mentioned the Rocky Mountain outliers are composed of much more erosion resistant materials than the surrounding regions. The presence of these erosion resistant masses worked to create more complex water movements where flood waters would flow in a southeast direction on the west side of a mountain mass and then turn to flow in a northeast direction towards deep southeast oriented valleys located north and east of the mountain mass. In this essay we will see evidence for northeast-oriented flood flow, which probably moved between the Bears Paw Mountains and Little Rocky Mountains to the actively southeast-oriented Milk River tributary valleys. Headward erosion of the deep Missouri River valley soon ended this northeast-oriented flood movement, although the northeast-oriented flood flow occurred as the Milk River valley and some of its southeast-oriented tributary valleys were being eroded headward in the Whitewater Creek-Milk River drainage divide area. To fully understand these flood water movements it is necessary to view a much larger region than is being shown in this essay or any of the other essays in this series. My major goal in this essay is to convince you the Whitewater Creek-Milk River drainage divide area was eroded by immense floods.

Detailed location map for Whitewater Creek-Milk River drainage divide area

Figure 2: Detailed location map for Whitewater Creek-Milk 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 Whitewater Creek-Milk River drainage divide area in north central Phillips County, Montana and shows northern Phillips County with Valley County to the east and Blaine County to the west (county boundaries are shown). The west to east oriented United State-Canada international boundary is located just north of the figure 2 north edge. The Milk River flows in an east direction from the figure 2 southwest corner area to Malta (just west of figure 2 south center edge) and then turns to flow in a north-northeast direction to north of the Hewitt National Wildlife Refuge before turning to flow in a southeast direction to the figure 2 southeast corner area. The south-oriented tributary joining the Milk River near the Phillips-Valley County line (near southeast corner) is Frenchman Creek (also known as Frenchman River). The south-southeast oriented tributary joining the Milk River near the intersection of 8th Auxiliary Guide Meridian and the 8th Standard Parallel is Whitewater Creek, which flows through the town of Whitewater. Southeast-oriented tributaries joining the north-northeast oriented Milk River segment from north to south are Little Cottonwood Creek, Cottonwood Creek, and Assiniboine Creek. East of the north-northeast oriented Milk River segment Nelson Reservoir floods a southeast and northeast-oriented Milk River tributary valley and Lake Bowdoin fills another low region. The north-northeast oriented stream east of Lake Bowdoin which turns east of Nelson Reservoir to flow to Saco before joining the Milk River is Beaver Creek and south of the figure 2 map area drains the north end of a large north-south oriented through valley linking the Milk River valley with the Missouri River valley (and the north-oriented Musselshell River valley which today drains to the Missouri River). The south-southeast oriented Whitewater Creek valley and the southeast-oriented Little Cottonwood Creek, Cottonwood Creek, and Assiniboine Creek valleys were probably initiated as flood flow channels which eroded headward from a major south-oriented flood flow channel on the present day north-oriented Beaver Creek alignment. Headward erosion of the deep Milk River valley then captured the south-southeast oriented Whitewater Creek flood flow channel and flood waters on the north end of the beheaded flood flow channel reversed flow direction to erode what is now the north-oriented valley segment flooded by Nelson Reservoir. The southeast-oriented valley segment flooded by Nelson Reservoir is where the reversed flood flow captured the southeast-oriented Little Cottonwood Creek and Cottonwood Creek flood flow channels. The Milk River valley however then eroded headward across the southeast-oriented flood flow channels, capturing the Little Cottonwood Creek, Cottonwood Creek, and Assiniboine Creek flood flow channels and beheading flood flow routes to the newly eroded Nelson Reservoir valley and also to the south-oriented flood flow channel on the Beaver Creek alignment. A reversal of flood flow on the north end of what was the south-oriented Beaver Creek flood flow channel created the north-oriented Beaver Creek valley and also left low areas between the newly eroded north-northeast oriented Milk River valley and the newly reversed north-northeast oriented Beaver Creek valley, which represented the former southeast-oriented Assiniboine Creek flood flow channel and which today are filled by Lake Bowdoin and adjacent lakes.

Whitewater Creek-Martin Lake drainage divide area

Figure 3: Whitewater Creek-Martin Lake drainage divide area. United States Geological Survey map digitally presented using National Geographic Society TOPO software.

Figure 3 illustrates the Whitewater Creek-Martin Lake drainage divide area near the international border. Whitewater Creek flows in a south-southeast direction from the figure 3 north center edge to the figure 3 southeast corner. Loring is a small town located near the figure 3 south center edge and Martin Lake is a swamp west of Loring. Note how Martin Lake and Loring are located in an east-southeast and east oriented through valley (referred here as the Martin Lake through valley) which turns in an east-northeast direction to join the Whitewater Creek valley near the figure 3 southeast corner. The Burlington Northern Railroad line is located on the Martin Lake through valley floor. Near the figure 3 west edge Horseshoe Lake is located along the Martin Lake through valley’s north side. Several well-defined south-oriented valleys drain to this east-oriented Martin Lake through valley. In the figure 3 southeast quadrant Dibble Creek flows in a south-oriented valley to the east-oriented Martin Lake through valley and then drains the Martin Lake through valley east end. East of the south-oriented Dibble Creek headwaters valley a well-defined through valley links southeast-oriented Lone Tree Coulee with the east-northeast oriented Martin Lake through valley segment (and extends further south as seen in figure 4). North of Martin Lake is another west and south-oriented through valley linking the Whitewater Creek valley with the east-oriented Martin Lake through valley, the west and south end of which is drained by south-oriented Lake Coulee. These through valleys provide evidence of what were once a maze of melt water flood flow channels probably which served as components of an anastomosing channel complex draining the region to the actively eroding Whitewater Creek valley. Probably much of the water flowing in the Martin Lake through valley was coming from west of the figure 3 map area. Water in the south-oriented through valleys was spilling across the upland between the present day south-southeast oriented Whitewater Creek valley and the Martin Lake through valley, which suggests the Whitewater Creek valley was still being eroded headward from the figure 3 southeast corner area and the Martin Lake through valley was eroded headward slightly in advance of the Whitewater Creek valley. Headward erosion of the deep south-southeast oriented Whitewater Creek valley beheaded flood flow to south-oriented Martin Lake through valley tributary valleys and those valleys were then left abandoned as they are today. The hummocky topography of the upland regions and the nature of the anastomosing valley complex in this region suggests ice may have been present in the region as the valleys were eroded headward across the figure 3 map area. If so the ice was not thick and the valleys were eroded as ice-walled and bedrock-floored valleys.

Martin Lake-Little Cottonwood Creek drainage divide area

Figure 4: Martin Lake-Little Cottonwood Lake drainage divide area. United States Geological Survey map digitally presented using National Geographic Society TOPO software.

Figure 4 illustrates the Martin Lake-Little Cottonwood Creek drainage divide area south of the figure 3 map area and includes overlap areas with figure 3. Whitewater is the town located in the figure 4 northeast quadrant (near east edge) and Whitewater Creek flows in a south-southeast direction through Whitewater to the figure 4 east edge (south half). Loring is located west of the figure 4 north center edge and Martin Lake is just west of Loring. The Martin Lake through valley extends from Martin Lake along the figure 4 north edge to Dibble Creek, which then flows in an east and east-northeast direction to join Whitewater Creek just north of the figure 4 northeast corner. Note how a maze of south and southeast-oriented through valleys link the east end of the Martin Lake through valley (which is drained by Dibble Creek) with the south-southeast oriented Whitewater Creek valley. This maze of through valleys provides evidence of multiple south-oriented flood flow routes or channels and is a south-oriented anastomosing channel complex.The south- oriented stream flowing along the west edge of the figure 4 northwest quadrant and then turning to flow in a southeast direction across the figure 4 southwest quadrant is Little Cottonwood Creek, which south of the figure 4 map area flows to the Milk River. Note how a south- and southwest-oriented through valley links the Martin Lake through valley (at Martin Lake) with the southeast-oriented Little Cottonwood Creek valley. Near the figure 4 south margin to the east of Little Cottonwood Creek is southeast-oriented Austin Coulee, which south of the figure 4 map area turns to join Little Cottonwood Creek. And east of Austin Coulee is southeast-oriented Martins Coulee, which drains to the Milk River at the elbow of capture where the north-northeast oriented Milk River segment turns to flow in a southeast direction. North and east of Martins Coulee is Lush Coulee, which drains to Whitewater Creek near the figure 4 east edge (and Whitewater Creek joins the Milk River east and south of the figure 4 southeast corner. What has happened here is the southeast-oriented Milk River valley eroded headward toward the figure 4 southeast corner and captured and beheaded one or more of the south-southeast oriented flood flow channels moving flood waters to the south-oriented Beaver Creek through valley. Deep valleys then eroded headward along the captured flood flow channels on the present day Whitewater Creek and Lush Coulee alignments, while another valley eroded headward along the present day Martins Coulee alignment. Flood flow from the north to this latter valley was beheaded by headward erosion of the first valleys and their tributary valleys, however by eroding headward in a south-southwest direction the second valley was able to capture southeast-oriented flood flow from the northwest moving on what is today the Little Cottonwood Creek alignment. This southeast-oriented flood flow was also moving to the south-oriented Beaver Creek through valley. Headward erosion of the deep north-northeast oriented Milk River valley then proceeded to behead all southeast-oriented flood flow routes to the south-oriented Beaver Creek through valley.

Little Cottonwood Creek-Whitewater Creek drainage divide area

Figure 5: Little Cottonwood Creek-Whitewater Creek drainage divide area. United States Geological Survey map digitally presented using National Geographic Society TOPO software.

Figure 5 illustrates the Little Cottonwood Creek-Whitewater Creek drainage divide area slightly east and south of the figure 4 map area and includes significant overlap areas with figure 4. Whitewater is the town near the north edge of the figure 5 northeast quadrant. Whitewater Creek flows in a south-southeast direction from Whitewater to the figure 5 southeast corner area. Lush Coulee drains in a south and southeast direction along the west edge of the Whitewater Creek valley and eventually drains to Whitewater Creek. Between Lush Coulee and the present day Whitewater Creek valley are at least two additional through valleys draining to Austin Lake. These multiple through valleys provide evidence of anastomosing channels which eroded headward at the same time the present day Whitewater Creek valley eroded headward. South and west of the southeast-oriented Lush Coulee valley segment is southeast-oriented Martins Coulee. Martins Coulee drains to the north and southeast-oriented Milk River, which can be seen along the south edge of the figure 5 southeast quadrant. Note how the southeast-oriented Milk River segment and Martins Coulee segment are located on approximately the same alignment and are linked by through valleys with the Lush Coulee valley. This evidence suggests the Martins Coulee valley and at least segments of the Lush Coulee valley eroded headward from the southeast-oriented Milk River valley seen in figure 5. The north-oriented Milk River valley segment seen in figure 5 was eroded by a reversal of south-oriented flood flow, which had been moving south on the south-oriented Lush Coulee alignment. As previously stated the south-oriented flood flow was moving to what was then a south-oriented flood flow channel located on the present day Beaver Creek alignment. Little Cottonwood Creek flows from the figure 5 west center edge to the figure 5 south center edge and joins the north-oriented Milk River a short distance south of the figure 5 map area. Note how Austin Coulee flows in a southeast and south-southwest direction to join Little Cottonwood Creek near the figure 5 south center edge. A shallow through valley (defined by a single contour line) links the southeast-oriented Austin Coulee valley segment with the north-oriented Milk River valley segment and provides evidence flood waters originally flowed on a surface at least as high as the through valley floor and were captured by headward erosion of the deep Little Cottonwood Creek valley, which probably eroded headward from the deep Milk River valley (although along the alignment of a higher level flood flow channel).

Whitewater Creek-Cottonwood Creek drainage divide area

Figure 6: Whitewater Creek-Cottonwood Creek drainage divide area. United States Geological Survey map digitally presented using National Geographic Society TOPO software.

Figure 6 illustrates the Whitewater Creek-Cottonwood Creek drainage divide area south and west of the figure 5 map area and includes significant overlap areas with figure 5. The Milk River flows in a northeast direction from the figure 6 south center edge and then turns to flow in a south-southeast direction along the east edge of the figure 6 southeast quadrant. Whitewater Creek can just barely be seen in the figure 6 northeast corner and joins the Milk River east of the figure 6 map area. Little Cottonwood Creek flows in a southeast direction from the figure 6 northwest corner to join the Milk River in the figure 6 south center area. Cottonwood Creek is located in the figure 6 southwest quadrant and flows in a southeast and east-southeast direction from the figure 6 west edge (south half) to join the Milk River near the figure 6 south center edge. Martins Coulee is located in the figure 6 northeast quadrant and joins the Milk River near the elbow of capture where the northeast-oriented Milk River turns to flow in a south-southeast direction. Note how the region south and east of the Milk is today honeycombed with a maze of through valleys and lake filled depressions. These through valleys provide evidence of former southeast and south-oriented flood flow channels, which were beheaded when headward erosion of the deep southeast-oriented Milk River-Martins Coulee valley beheaded south- and southeast-oriented flood flow channels moving flood waters to what was then the south-oriented flood flow channel on the present day north-oriented Beaver Creek alignment. The northeast-oriented Milk River valley was eroded headward across the southeast-oriented flood flow moving to that south-oriented Beaver Creek through valley flood flow channel and captured the southeast-oriented flood flow from the northwest. The deep southeast-oriented Little Cottonwood Creek and Cottonwood Creek valleys eroded headward from the deep Milk River valley at that time. Floors of through valleys south and east of the northeast-oriented Milk River valley segment provide evidence of depths of south- and southeast-oriented flood flow channels just prior to being beheaded by Milk River valley headward erosion.

Cottonwood Creek-Assiniboine Creek drainage divide area

Figure 7: Cottonwood Creek-Assiniboine Creek drainage divide area. United States Geological Survey map digitally presented using National Geographic Society TOPO software.

Figure 7 illustrates the Cottonwood Creek-Assiniboine Creek drainage divide area south and west of the figure 6 map area and includes overlap areas with figure 6. The Milk River flows in a north-northeast direction from the figure 7 south edge (east of center) to the figure 7 northeast corner. In the figure 7 southeast quadrant Lone Tree Sag is a through valley linking the north-northeast oriented Milk River valley with the Nelson Reservoir valley (east of figure 7, but seen in figure 9). Cottonwood Creek flows in a southeast and east-southeast direction from the figure 7 north edge (west of center) to join the Milk River near Fanny Hill in the figure 7 northeast quadrant. Garland Creek is the north and east-southeast oriented tributary joining Cottonwood Creek near the figure 7 north center. The north-oriented Garland Creek headwaters valley was eroded by a reversal of south-oriented flood flow. Assinibione Creek is the east-southeast oriented Milk River tributary in the figure 7 southwest quadrant and joins the north-northeast Milk River south of the figure 7 south center region. Note how north-south oriented through valleys link the Garland Creek valley with the Assiniboine Creek valley. The through valleys were eroded by south-oriented flood flow prior to headward erosion of the deep Cottonwood Creek-Garland Creek valley. The north-northeast oriented Milk River valley, especially the north-oriented valley segment seen in the figure 7 east center region, was eroded by a reversal of south-oriented flood flow, which was beheaded by headward erosion of the deep southeast-oriented Milk River valley and its south-southeast-oriented Whitewater Creek and southeast-oriented Martins Coulee tributary valleys. The Lone Tree Sag is the west end of a through valley linking today the north-northeast oriented Milk River valley with the southeast-oriented Milk River valley to the east (see figure 9). Headward erosion of the deep north-northeast oriented Milk River valley beheaded east-oriented flood flow moving through the Lone Tree Sag through valley, although for a time flood waters flowed both in that east- and north-oriented through valley and in the present day Milk River valley. As previously stated headward erosion of the deep north-northeast oriented Milk River valley captured southeast-oriented flood flow moving to what was then a major south-oriented flood flow channel on what is today the north-oriented Beaver Creek alignment.

Assiniboine Creek-Milk River drainage divide area

Figure 8: Assiniboine Creek-Milk River drainage divide area. United States Geological Survey map digitally presented using National Geographic Society TOPO software.

Figure 8 illustrates the Assiniboine Creek-Milk River drainage divide area south and west of the figure 7 map area and includes overlap areas with figure 7. Wagner is the small town near the figure 8 southwest corner and Malta is the larger town east of the figure 8 south center edge area. The Milk River flows in an east direction near the figure 8 south edge from Wagner to Malta and then turns to flow in a north-northeast direction to the figure 8 northeast corner. Exeter Creek flows in a south-southeast and southeast direction from the figure 8 west edge (north half) to join the east-oriented Milk River in the figure 8 southwest quadrant. Assininboine Creek flows in a southeast direction from the figure 8 north edge (west half) to join the north-northeast oriented Milk River just north of the figure 8 east center area. South of Assiniboine Creek is southeast, east, and east-northeast oriented Spring Coulee, which joins Assiniboine Creek at the point where Assiniboine Creek joins the Milk River. Note how the southeast-oriented Spring Coulee valley is linked by a through valley with the northeast-oriented Dry Fork valley, which drains to southeast-oriented Assiniboine Creek. The through valley is evidence headward erosion of the northeast-oriented Dry Fork valley beheaded a southeast-oriented flood flow channel on the Spring Coulee alignment. The southeast-oriented Milk River tributary valleys were eroded by southeast-oriented flood flow captured by headward erosion of the deep Milk River valley. Prior to Milk River valley headward erosion the southeast-oriented flood flow had been moving to the major south-oriented channel located on what is today the north-oriented Beaver Creek alignment. Headward erosion of the deep Milk River valley beheaded flood flow routes to that south-oriented flood flow channel. The railroad line east of Malta is located in a broad through valley eroded by east-oriented flood flow moving towards the present day Beaver Creek valley. Figure 10 illustrates regions east of figure 8.

Milk River-Nelson Reservoir drainage divide area

Figure 9: Milk River-Nelson Reservoir drainage divide area. United States Geological Survey map digitally presented using National Geographic Society TOPO software.

Figure 9 illustrates the Milk River-Nelson Reservoir drainage divide area east of the figure 7 map area and includes overlap areas with figure 7. The Milk River flows in a north-northeast direction from near the figure 9 southwest corner to near the figure 9 north center edge and then turns to flow in a south-southeast and southeast direction to the figure 9 east center edge. Whitewater Creek flows in a south-southeast direction across the figure 9 northeast corner region and joins the Milk River a short distance east of the figure 9 map area. Nelson Reservoir is the large lake in the figure 9 southeast quadrant. Note how the west end of Nelson Reservoir is located in a southeast oriented valley while the Nelson Reservoir east end is located in a northeast and north-oriented valley. Also note how the north-oriented valley at the Nelson Reservoir east end is on the same alignment as a through valley (partially drained by Alkali Creek) linking the Whitewater Creek valley with the Milk River valley. Prior to headward erosion of the deep southeast-oriented Milk River valley a major south-oriented flood flow channel moved flood water south along the alignment of that north-south through valley and the north-oriented Nelson Reservoir valley segment to what was then the south-oriented flood flow channel on the present day north-oriented Beaver Creek alignment. Headward erosion of the deep southeast-oriented Milk River valley captured the south-oriented flood flow and reversed flood flow on the north end of the beheaded flood flow channel to the south. The reversed flood flow captured southeast-oriented flood flow channels (e.g. on the Little Cottonwood Creek and Cottonwood Creek alignments) to create a deep southeast, northeast, and north oriented valley (now filled by Nelson Reservoir). The deep east-oriented Lone Tree Sag valley was eroded by flood waters captured by southeast-oriented flood flow captured further to the southwest (e.g. on Assininboine Creek alignment) and then was beheaded by headward erosion of the deep north-northeast oriented Milk River valley, which was eroded by a reversal of flood flow on the north end of another beheaded south-oriented flood flow route. Nelson Reservoir is flooding the eastern end of what became a large abandoned valley linking the north-northeast oriented Milk River valley with the southeast-oriented Milk River valley. Evidence for other through valleys is found throughout the region suggesting flood movements were more complex than I have described, which means there is significant room for improvement of the simple flood flow interpretations provided in this essay.

Milk River-Beaver Creek drainage divide area

Figure 10: Milk River-Beaver Creek drainage divide area. United States Geological Survey map digitally presented using National Geographic Society TOPO software.

Figure 10 illustrates the Milk River-Beaver Creek drainage divide area south and west of the figure 9 map area and east of the figure 8 map area and includes overlap areas with both figures 8 and 9. Malta is the town near the figure 10 southwest corner. The Milk River flows in a north-northeast direction from Malta to the figure 10 north edge (west of center). Nelson Reservoir is located along the north edge of the figure 10 northeast quadrant and the south half of Lone Tree Sag can be seen along the figure 10 north center edge and links the north-northeast oriented Milk River valley with Nelson Reservoir. Sleeping Buffalo is a small community (resort) near the figure 10 northeast corner. Beaver Creek flows in a north and north-northeast direction from the figure 10 south edge (just west of the southeast corner) to the figure 10 east edge (south of Sleeping Buffalo). Note how north-oriented Beaver Creek emerges from a large north-oriented valley in the figure 10 southeast quadrant. While Beaver Creek headwaters are west of that north-oriented valley, the north-oriented Beaver Creek valley is the north end of a large through valley extending south to the Missouri River valley (see figure 1) and then continuing south in the form of the north-oriented Musselshell River valley. The north-oriented Musselshell River valley was eroded by reversals of flood flow on the north end of a south oriented flood flow channel moving flood water to what was then the actively eroding Yellowstone River valley. Headward erosion of the deep Missouri River valley captured the south-oriented flood flow channel and triggered the reversal of flood flow that eroded the deep north-oriented Musselshell River valley. Next headward erosion of the deep Milk River valley captured flood flow channels feeding the major south-oriented flood flow channel (as seen in this essay) and triggered the flood flow reversal on the north end of the beheaded flood flow channel to erode the north-oriented Beaver Creek valley. A broad through valley links the Milk River valley in the Malta region with the north-northeast oriented Beaver Creek valley and was once used by southeast and east-oriented flood water to reach first the south-oriented Beaver Creek flood flow channel and for a time after the flood flow reversal to reach the actively eroding and newly reversed north-oriented Beaver Creek valley. Note how the railroad line instead of following the Milk River valley proceeds eastward from Malta through the Lake Bowdoin region to the Beaver Creek valley and then follows Beaver Creek to the Milk River valley east of the figure 10 map area. The railroad is able to use this route without encountering any grades of significance because this was once a major flood flow route. The shallow Lake Bowdoin and other lakes in the region are filling low spots in this large flood eroded lowland.

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.