Big Sandy Creek-Beaver Creek drainage divide area landform origins in Hill and Chouteau Counties, Montana, USA

Authors

A geomorphic history based on topographic map evidence

Abstract:

The Big Sandy-Beaver Creek drainage divide area is located in Hill and Chouteau Counties, Montana, USA and includes high Bear Paw Mountain regions. Although detailed topographic maps of the Big Sandy Creek-Beaver Creek drainage divide area have been available for more than fifty years detailed map evidence has not previously been used to interpret the region’s geomorphic history. The interpretation provided here is based entirely on topographic map evidence. The Big Sandy Creek-Beaver Creek drainage divide area is interpreted to have been eroded during immense southeast-oriented flood events, the first of which flowed on a topographic surface at least as high as the highest points in the present-day drainage divide area. Flood erosion across the high drainage divide ended when headward erosion of the Milk River valley captured all southeast-oriented flood flow.

Preface:

The following interpretation of detailed topographic map evidence is provided as evidence in the Missouri River drainage basin landform origins research project, which is compiling similar evidence for all major drainage divides contained within the Missouri River drainage basin and for all major drainage divides with and within certain adjacent drainage basins. The research project is interpreting evidence in the context of a previously unexplored geomorphology paradigm, which is briefly described in the introduction below. Project essays are listed on the sidebar category list under their appropriate Missouri River tributary drainage basin, Missouri River segment drainage basin (by state), and/or state in which the Missouri River drainage basin is located.

Introduction:

  • The purpose of this essay is to use topographic map interpretation methods to explore Big Sandy Creek-Beaver Creek drainage divide area landform origins in Hill and Chouteau Counties, Montana. 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 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 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 similar essays is a thick North American ice sheet, comparable in thickness to the present day Antarctic ice sheet, occupied approximately the North American region usually recognized to have been glaciated and through its weight and erosive actions created a “deep” North American “hole”, 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 Big Sandy Creek and Beaver Creek drainage divide area landform evidence in Hill and Chouteau Counties, Montana will be regarded as evidence supporting the “thick ice sheet that melted fast” paradigm.

Big Sandy Creek-Beaver Creek drainage divide area location map

Figure 1: Big Sandy Creek-Beaver Creek 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 Big Sandy Creek-Beaver Creek drainage divide area location map. Figure 1 illustrates a region in north central Montana and the US-Canada border is located along the figure 1 north edge. The Missouri River flows northeast from the figure 1 southwest corner and south of the town of Big Sandy turns southeast, then east-northeast, and finally southeast to flow to Fort Peck Lake, which continues to the figure 1 east edge. The lake is a large reservoir impounded behind Fort Peck Dam, which is located east of the figure 1 map area. The Milk River flows southeast from Canada (in the figure 1 northwest corner) to Fresno Reservoir, Havre, Chinook, Harlem, and Dodson. Big Sandy Creek originates in the Bear Paw Mountains and flows west, southwest, northwest, north, and northeast to join the Milk River just west of Havre. Beaver Creek (unnamed in figure 1) originates in the Bear Paw Mountains and flows north and north-northwest to also join the east-oriented Milk River just west of Havre. The Big Sandy Creek-Beaver Creek drainage divide area discussed here is located in the high Bear Paw Mountains and on the Bear Paw Mountains west flank. The Beaver Creek-Birch Creek drainage divide area essay describes the region located immediately east of the Big Sandy Creek-Beaver Creek drainage divide area and the Milk River-Peoples Creek drainage divide area and the Peoples Creek-Missouri River drainage divide area essays describe other drainage divide areas located in the Bear Paw Mountain region. Essays can be located under Milk River or MT Missouri River on the sidebar category list. Evidence presented other Milk River drainage basin drainage divide area essays demonstrated several present day north-oriented Milk River tributary valleys in the Bear Paw Mountains initially had been eroded by south-oriented flood flow, which was subsequently reversed to flow north when headward erosion of the deep east-oriented Milk River valley beheaded and reversed south-oriented flood flow routes. Based on evidence from the hundreds of Missouri River drainage basin landform origins research project essays published on this website and evidence observable on detailed topographic maps shown below, landform evidence illustrated in this essay is interpreted in the context of an immense southeast and south-oriented flood that moved large volumes of flood waters across the figure 1 map area, including high Bear Paw Mountains to what was at that time the newly eroded Missouri River valley. The south-oriented flood flow routes were then systematically beheaded by Milk River valley headward erosion. As the Milk River valley eroded northwest and west it captured southeast-oriented flood water moving on a topographic surface at least as high as the topographic surface now preserved in the high Bear Paw Mountains. Flood waters on the ends of beheaded south-oriented flood flow routes reversed flow direction and eroded the present day north-oriented Milk River tributary valleys. Detailed maps below show how reversed flow in the present day north-oriented valleys captured south-oriented flood waters from adjacent yet to be beheaded (by deep Milk River valley headward erosion) south-oriented flood flow routes.

Big Sandy Creek-Beaver Creek drainage divide area detailed location map

Figure 2: Big Sandy Creek-Beaver Creek drainage divide area detailed location map. United States Geological Survey map digitally presented using National Geographic Society TOPO software. 

Figure 2 illustrates a somewhat more detailed map of the Big Sandy Creek-Beaver Creek drainage divide area discussed in this essay. Green boundary lines are county lines. Hill County is located in the figure 2 northwest area, Chouteau County is located in the figure 2 southwest area, and Blaine County is located in the figure 2 east area. The red shaded area is the Rocky Boys Indian Reservation. The Milk River flows southeast from the figure 2 north edge to Fresno Reservoir and Havre and then east to Chinook and the figure 2 east edge. The Missouri River flows northeast and south in the figure 2 southwest quadrant. Big Sandy Creek originates in the southern Rocky Boys Indian Reservation near Baldy Mountain and flows northwest, southwest, and northwest to Big Sandy and then north and northeast to join the Milk River west of Havre. Beaver Creek flows north and northwest from near Baldy Mountain in the Bear Paw Mountains to join the east-oriented Milk River as a barbed tributary. As previously mentioned this essay interprets Big Sandy Creek-Beaver Creek drainage divide evidence in the context of an immense southeast and south oriented flood, which crossed the figure 2 map area. Headward erosion of the south and east-oriented Missouri River valley first captured the southeast and south oriented flood flow. Southwest-oriented Big Sandy Creek tributaries (including the southwest-oriented Big Sandy Creek valley) eroded headward from the south oriented Missouri River valley that eroded north from the east-oriented Missouri River valley towards the town of Big Sandy.  Soon thereafter headward erosion of the Milk River valley from the east to the west systematically beheaded south oriented flood flow routes to the newly eroded Missouri River valley. including the south-oriented Missouri River, which probably had eroded north into the present day Big Sandy Creek drainage basin. Flood waters on the north ends of the beheaded flood flow routes reversed flow direction to flow north to the newly eroded (and at that time deeper) Milk River valley. Because flood waters were moving in anastomosing (or interconnected channels) flood waters on a newly beheaded and reversed flood flow routes captured  flood waters from yet to be beheaded south- and southeast oriented flood flow routes further to the west. With the aid of such captures the newly reversed flood flow eroded the Bear Paw Mountain north and west slopes and the north and west-oriented Milk River and Big Sandy Creek tributary valleys. Evidence requires flood waters to have flowed on a topographic surface at least as high as the highest Bear Paw Mountain elevations today, although it is possible the Bear Paw Mountains were uplifted while flood erosion was taking place. An alternate possibility is the Bear Paw Mountains were surrounded by sedimentary rocks and/or ice, which flood water erosion removed.

Southeast corner of Big Sandy Creek-Beaver Creek drainage divide area

Figure 3: Southeast corner of Big Sandy Creek-Beaver Creek drainage divide area. United States Geological Survey map digitally presented using National Geographic Society TOPO software. 

Figure 3 illustrates the southeast corner of the Big Sandy Creek-Beaver Creek drainage divide area, which is located in the high Bear Paw Mountains. Unlikely as it may seem this high Bear Paw Mountain region was eroded by an immense southeast and south-oriented flood flowing on a topographic surface at least as high as the highest figure 3 elevations today. At that time present day topography did not exist and the Bear Paw Mountains did not stand high above the surrounding region. The present day Bear Paw Mountains elevation above surrounding regions was created by either by deep erosion of surrounding regions and/or by Bear Paw Mountains uplift during the immense southeast and south-oriented flood. The West Fork of Beaver Creek is located in the figure 3 southeast quadrant and is joined along the figure 3 east edge by northwest-oriented East Fork Beaver Creek to form north-oriented Beaver Creek, which flows along the figure 3 east edge area to the figure 3 north edge and then to the east-oriented Milk River. Big Sandy Creek headwaters are located in the figure 3 south center area (just west of West Fork Beaver Creek headwaters) and Big Sandy Creek now flows northwest, southwest, and northwest across the figure 3 south center area and southwest quadrant. The Beaver Creek-Birch Creek drainage divide area essay illustrated evidence south and east of this figure 3 map area which showed through valleys linking the northwest-oriented East Fork Beaver Creek valley with the south-oriented Birch Creek valley (which flows to an east-oriented Missouri River valley segment) and the northeast-oriented West Fork Beaver Creek valley with the southwest-oriented Eagle Creek valley (which flows to a south-oriented Missouri River valley segment). Evidence presented in that drainage divide essay describes how south-oriented flood waters flowing in the Beaver Creek valley were first captured by headward erosion the south-oriented Birch Creek valley from the newly eroded and deep east-oriented Missouri River valley head and then as the Missouri River valley head eroded west, northwest, and north how south-oriented flood flow in the Beaver Creek valley was captured by headward erosion of the southwest-oriented Eagle Creek valley, which had eroded headward from what was at that time the newly eroded and deep south-oriented Missouri River valley head. Finally that essay presents evidence to show how headward erosion of the Milk River valley to the north of the figure 3 map area systematically beheaded and reversed south-oriented flood flow routes and how newly beheaded and reversed flood flow routes captured yet to be beheaded south-oriented flood flow from south-oriented flood flow routes further to the west. When headward erosion of the deep Milk River beheaded south-oriented flood flow in the figure 3 Beaver Creek valley segment, reversed flow in the Beaver Creek valley captured yet to be beheaded flood flow still moving further to the west. Some of that captured flood water moved east along the present day Big Sandy Creek headwaters valley to the West Fork Beaver Creek and then north in the Beaver Creek valley to what was then the newly eroded and deep Milk River valley.

Boxelder Creek-Beaver Creek drainage divide area

Figure 4: Boxelder Creek-Beaver Creek drainage divide area. United States Geological Survey map digitally presented using National Geographic Society TOPO software. 

Figure 4 illustrates the Boxelder Creek-Beaver Creek drainage divide area north of the figure 3 map area. Beaver Creek flows north in the figure 4 east half and eventually reaches the east-oriented Milk River. Boxelder Creek flows northwest and west in the figure 4 southwest quadrant and northwest-oriented Wolf Creek is located in the figure 4 northwest quadrant. Boxelder Creek flows west, northwest, and west from the figure 4 map area to join north and northeast-oriented Big Sandy Creek at the western base of the Bear Paw Mountains near the town of Box Elder (see figure 2). Wolf Creek flows northwest and west to join west-oriented Boxelder Creek in the high Bear Paw Mountains. Note the northeast-oriented through valley linking Boxelder Creek with the north oriented Beaver Creek valley. The road from section 24 through sections 19 and  17 makes use of much of the through valley. Also note the through valley linking west-oriented Boxelder Creek with northwest-oriented Wolf Creek (this valley is better shown in figure 6 below). The road southeast of Haystack Mountain (located on the figure 4 west edge, north half) follows this second through valley. A close look at figure 4 evidence reveals other similar through valleys, although perhaps not as deep or as well-defined. This maze of through valleys provides evidence of an ever-changing complex of anastomosing flood flow channels eroded into the Bear Paw Mountain upland surface as southeast and south oriented flood waters were systematically captured by headward erosion of newly reversed north, northwest, and west-oriented valleys as headward the deep Milk River valley along the Bear Paw Mountain north flank and headward erosion of a deep northeast-oriented valley along the Bear Paw Mountain northwest flank (the present day northeast-oriented Big Sandy Creek valley) beheaded and reversed the southeast and south oriented flood flow routes. South-oriented flood flow in the Beaver Creek valley was beheaded and reversed before flood flow routes further west were beheaded and reversed. In other words south and southeast-oriented flood flow was still moving into the present day Boxelder Creek drainage basin at the time south-oriented flood flow in the Beaver Creek valley was beheaded and reversed. The newly reversed flow in the Beaver Creek valley captured south-oriented flood waters from the Boxelder Creek drainage basin and the captured flood waters moved northeast along the through valley in sections 24, 19 and 17.

Big Knife Coulee-Beaver Creek drainage divide area

Figure 5: Big Knife Coulee-Beaver Creek drainage divide area. United States Geological Survey map digitally presented using National Geographic Society TOPO software. 

Figure 5 illustrates the Big Knife Coulee-Beaver Creek drainage area northwest of the figure 4 map area. North-oriented Beaver Creek is located along the figure 5 east edge. Southwest-oriented Big Knife Coulee is located in the figure 5 southwest quadrant and southwest of figure 5 drains to Wolf Creek (see figure 6 below). Watsons Knob is the named hill located in the figure 5 center area near the Big Knife Coulee headwaters. Note a northwest-oriented through valley (Gravel Coulee) located between Wild Horse Ridge and Number One Mountain. Gravel Coulee drains northwest to join northeast-oriented Big Sandy Creek. Note also the through valleys north of Watsons Knob linking east-northeast oriented Shambo Coulee (which drains to Beaver Creek) with the Big Knife Coulee headwaters and the Gravel Coulee headwaters. Also note the east-oriented valley immediately east of Watsons Knob linking northwest-oriented Gravel Coulee and southwest-oriented Big Knife Coulee with the Beaver Creek valley. These through valleys and other similar through valleys were all eroded by southeast oriented flood waters that flowed across the figure 5 map area and were systematically dismembered and reversed as headward erosion of the deep east-oriented Milk River valley along the Bear Paw Mountain north flank and a northeast-oriented Milk River tributary valley along the Bear Paw Mountain northwest flank beheaded and reversed the southeast and south-oriented flood flow routes. Today it is difficult to imagine southeast-oriented flood waters moving from the northwest to the figure 5 map area. Through valley floors surrounding Watsons Knob area are more 1400 feet higher than the elevation where northwest-oriented Gravel Coulee joins northeast-oriented Big Sandy Creek. And northwest of Big Sandy Creek is a vast plain where present day elevations do not rise significantly. At the time flood waters across the figure 5 map area those topographic relationships did not exist. The northeast-oriented Big Sandy Creek valley did not exist, nor did the vast plain west and northwest of the Big Sandy Creek valley exist. Flood waters flowed on a topographic surface at least as high or higher than the highest figure 5 elevations today and flood waters removed the material surrounding the Bear Paw Mountains. It is possible some of the surrounding material was ice, although some of the surrounding was probably easily eroded sedimentary rock. It is also possible the Bear Paw Mountains were uplifted as flood waters eroded the region. And some combination of these possibilities is also possible, in fact probable. But, however it was done the figure 5 through valleys were eroded by immense volumes of water, some of which flowed southeast into the figure 5 map area.

Boxelder Creek-Wolf Creek drainage divide area

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

Figure 6 illustrates the Boxelder Creek-Wolf Creek drainage divide area west of the figure 4 map area and includes overlap areas with figures 4 and 5. Wolf Creek flows northwest, west, and northwest in the figure 6 north half. Southwest-oriented Big Knife Coulee joins northwest oriented Wolf Creek in the figure 6 northwest quadrant. Boxelder Creek flows west from the figure 6 southeast corner and then turns northwest, west, and northwest to flow to the figure 6 west edge and then west to join north and northeast-oriented Big Sandy Creek near Boxelder, Montana. Haystack Mountain is located in the figure 6 east center area. Figure 6 drainage today is northwest and west-oriented to the northeast-oriented Big Sandy Creek valley located along the Bear Paw Mountains northwest flank. Note through valleys linking the Wolf Creek valley with the Boxelder Creek valley. While the through valleys may reflect underlying geology they also are erosional features eroded by water. The through valleys provide evidence of what at one time were interconnected channels moving water across the figure 6 map area. At that time flood waters were coming from the northwest and the vast plain west and northwest of the Big Sandy Creek valley did not exist (and /or the Bear Paw Mountains had not yet been uplifted. Whatever was west and northwest of the present day Bear Paw Mountains region it provided a topographic surface at least as high as the present day Bear Paw Mountains and flood waters could freely move across the figure 6 map area. Flood waters were probably initially flowing to what was then a deep east-oriented Missouri River valley head, which was eroding headward to the south of the Bear Paw Mountains (see figure 1). However, at approximately the same time the deep Milk River valley north of the Bear Paw Mountains was systematically beheading and reversing south-oriented flood flow routes. As seen in figures 4 and 5 above through valleys link the Boxelder Creek headwaters and the Big Knife Coulee valley headwaters with the Beaver Creek valley. When flood flow in the Beaver Creek valley was beheaded and reversed southeast-oriented flood still moving across the figure 6 map area was captured and diverted north to the newly eroded Milk River valley. As headward erosion of the Missouri River valley to the south and southwest and the Milk River valley to the north and northwest progressed there probably was an ever-changing pattern of flood flow across the figure 6 map region and the entire Bear Paw Mountain upland region.

Boxelder Creek-Duck Creek drainage divide area

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

Figure 7 illustrates the Boxelder Creek-Duck Creek drainage divide area south of the figure 6 map area. Northwest, west, and northwest-oriented Boxelder Creek is located in the figure 7 northeast quadrant. Northwest-oriented Duck Creek flows from the figure 7 south center area and flows to the figure 7 west center edge. North-oriented Sundance Creek joins Boxelder Creek at Rocky Boy. North-northeast oriented Daychild Creek, also joins Boxelder Creek at Rocky Boy. Note the two parallel through valleys linking Daychild Creek headwaters with the northwest-oriented Duck Creek valley (roads are located in each, one road is shown with dashed lines). Those through valleys provide evidence flood water once flowed from the Duck Creek valley area northeast to the Daychild Creek valley and then probably northwest and west in the Boxelder Creek valley. If interpreted correctly this evidence means southeast-oriented flood flow on the Boxelder Creek alignment was beheaded and reversed while southeast-oriented flood flow continued to move uninterrupted on the Duck Creek alignment. Reversed flow on the Boxelder Creek alignment captured southeast-oriented flood flow from the Duck Creek alignment and the captured flood water moved northeast on the Daychild Creek alignment and eroded the northeast-oriented through valleys linking the Duck Creek valley with the Daychild Creek valley. Subsequently southeast-oriented flood flow on the Duck Creek alignment was beheaded and reversed. The reversed flood flow eroded the present day northwest-oriented Duck Creek valley. A valid question is where did enough northwest-oriented flood flow come from to erode the northwest-oriented Duck Creek valley, which has been eroded deeper than the floors of the two northeast-oriented through valleys? Figure 8 below illustrates several possible routes yet to be beheaded southeast-oriented flood flow at that time could have used to reach what was then the newly beheaded and reversed Duck Creek flood flow route.

Duck Creek-Big Sandy Creek drainage divide area

Figure 8: Duck Creek-Big Sandy Creek drainage divide area. United States Geological Survey map digitally presented using National Geographic Society TOPO software. 

Figure 8 illustrates the Duck Creek-Big Sandy Creek drainage divide area south and east of the figure 7 map area and includes overlap areas with figure 7. Figure 8 maps have been reduced to show a larger area. Big Sandy Creek flows northwest into the figure 8 south center edge area where it is joined by northwest, southwest, west, and south-oriented Muddy Creek, which flows from the figure 8 east edge. After joining south-oriented Muddy Creek the Big Sandy Creek valley turns southwest to flow down the Bear Paw Mountains west flank (see figure 9 below). Timber Creek flows south from the Assneyewin Ridge area to join Muddy Creek at its elbow of capture (where it turns to flow south) and flow to Big Sandy Creek. A road goes north from the figure 8 south edge along the Big Sandy Creek, Muddy Creek, and Timber Creek valleys and travels through a low mountain pass to a northwest-oriented stream that flows to the figure 8 north edge. That northwest-oriented stream is Duck Creek seen in figure 7. Note how Duck Creek is linked to the Muddy Creek and the Big Sandy Creek valleys by a deep through valley eroded between Centennial Mountain and Assneyewin Ridge. That through valley was eroded by southeast oriented flood waters moving from northwest of the Bear Paw Mountain upland region to somewhere southeast of the Bear Paw Mountain region. The through valley floor is approximately 1100 feet lower than the top of Centennial Mountain and 360 feet lower than the highest points on Assneyewin Ridge. To decipher the figure 8 evidence it is again necessary to think of topographic relationships as they existed at the time southeast oriented  flood water began to erode the figure 6 landform features we see today. At that time the Bear Paw Mountains did not stand high above the surrounding region and the Missouri River valley to the south, the Milk River valley to the north, and the Big Sandy Creek valley and the vast plain to the west, did not exist. The first event to change that topographic setting was headward erosion of the deep Missouri River valley west along the south side of the Bear Paw Mountains and then northwest and north as it reached the west end of the Bear Paw Mountains. The Bear Paw Mountains formed a barrier that south-oriented flood waters eroding the deep Missouri River valley westward could not breach, but once the west end of the Bear Paw Mountains was reached it was possible for the southeast and south-oriented flood waters to erode a deep valley headward (or north) from the newly eroded east-oriented and deep Missouri River valley along the Bear Paw Mountain west flank (see figure 1 above to see how Missouri River valley changes orientation). Figure 9 below illustrates how headward erosion of a deep south-oriented Missouri River valley (southwest of the Bear Paw Mountain upland region) next altered drainage patterns.

Big Sandy Creek-Godfrey Creek drainage divide area

Figure 9: Big Sandy Creek-Godfrey Creek drainage divide area. United States Geological Survey map digitally presented using National Geographic Society TOPO software. 

Figure 9 illustrates the Big Sandy Creek drainage basin located on the Bear Paw Mountains southwest flank and includes overlap areas with figure 8 above. The figure 9 maps have been reduced to show a larger area. Big Sandy Creek in the figure 9 northeast corner area flows northwest and is joined by southwest and northwest oriented Lost Canyon Creek and then turns to flow southwest down the Bear Paw Mountains west flank to the figure 9 southwest corner area. The southwest, west, southwest and west-oriented tributary joining Big Sandy Creek in the figure 9 southwest corner is Godfrey Creek. Figure 9 illustrates how headward erosion of the deep south-oriented Missouri River valley southwest of the Bear Paw Mountains captured southeast and south-oriented flood waters moving across the Bear Paw Mountains upland surface and diverted the flood waters southwest and west toward the new south-oriented Missouri River valley. At approximately the same time the deep east-oriented Milk River valley was being eroded north of the Bear Paw Mountains and a northeast-oriented tributary valley eroded southwest along the Bear Paw Mountain northwest flank (today the northeast-oriented Big Sandy Creek valley). At that time the Milk River valley was deeper and the northeast-oriented Milk River tributary valley was able to behead and reverse the north end of the south-oriented valley (that had eroded headward from the south-oriented Missouri River) and in the process captured the southwest and west-oriented tributaries flowing from the Bear Paw Mountains upland regions to that former south-oriented Missouri River valley segment. In other words, the Bear Paw Mountains were eroded by flood waters moving in several different directions. First by southeast-oriented flood flow moving to the east-oriented Missouri River valley when it was southeast of the Bear Paw Mountains, later by southwest-oriented flood flow moving to the south-oriented Missouri River valley eroding north along the Bear Paw Mountain west flank, and finally by reversed flood flow moving to the northeast-oriented Milk River tributary valley eroding southwest along the Bear Paw Mountain northwest flank. At that time the Milk River valley was deeper than the Missouri River valley and headward erosion of the northeast-oriented Milk River tributary valley produced another dramatic drainage change illustrated in figure 10 below.

Big Sandy Creek elbow of capture and Big Sandy Creek-Missouri River drainage divide area

Figure 10: Big Sandy Creek elbow of capture and Big Sandy Creek-Missouri River drainage divide area. United States Geological Survey map digitally presented using National Geographic Society TOPO software. 

Figure 10 illustrates the Big Sandy Creek-Missouri River drainage divide area at the Big Sandy Creek elbow of capture. The Missouri River is located in the figure 10 southwest quadrant and turns to flow south in the figure 10 south center. Southwest-oriented Big Sandy Creek is joined by west-southwest oriented Godfrey Creek in the figure 10 east center and then turns to flow northeast and north. After flowing north for a distance Big Sandy Creek flows northeast to the east-oriented Milk River. As described in the figure 9 discussion the southwest oriented Big Sandy Creek valley eroded headward from what was then an actively eroding south-oriented Missouri River valley. However, headward erosion of the Milk River valley and a northeast-oriented tributary valley along the Bear Paw Mountain northwest flank (which at that time was deeper than the Missouri River valley) captured the southwest and west-oriented streams flowing from the Bear Paw Mountain upland regions to south-oriented Missouri River valley. That capture included the southwest-oriented Big Sandy Creek valley. To some extent the Bear Paw Mountains region high elevation is the result of the erosion of deep valleys around it. Some of the present day elevation may also have resulted from localized uplift, which may have taken place as flood waters eroded the region. The source of the southeast-oriented flood waters cannot be determined from evidence presented in this essay. However, the hundreds of Missouri River drainage basin landform origins research project essays published on this website when taken as a group can be used to trace flood waters both up flood to source areas and down flood to see where flood waters were going. A logical flood water source would be rapid melting of a thick North American ice sheet located in a deep “hole” occupying approximately the North American location usually recognized to have been glaciated. The deep “hole” would have been created by deep glacial erosion and by crustal warping caused by the ice sheet weight. Such a flood water source would not only explain the immense southeast-oriented floods this essay series describes, but would also explain why deep valleys were eroding headward to capture the southeast-oriented flood waters and diverting the flood waters further and further to the northeast and north into space in the deep “hole” the rapidly melting thick ice sheet had once occupied. In addition, such a flood water source may explain uplift of the Bear Paw Mountains region during an immense southeast-oriented flood. A thick North American ice sheet in deep “hole” created in part due to the ice sheet’s weight would probably create crustal warping elsewhere on the continent, especially along ice sheet margins. Further, rapid erosion of significant volumes of overlying material might trigger localized uplifts of what are today high mountain regions, such as the Bear Paw Mountains.

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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