A geomorphic history based on topographic map evidence

The Big Sandy-Birch Creek drainage divide area is located in Chouteau County, Montana, USA and includes high Bear Paw Mountain regions. Although detailed topographic maps of the Big Sandy Creek-Birch 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-Birch 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.

Introduction:

• The purpose of this essay is to use topographic map interpretation methods to explore Big Sandy Creek-Birch Creek drainage divide area landform origins in Chouteau County, 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 Birch Creek drainage divide area landform evidence in Chouteau County, Montana will be regarded as evidence supporting the “thick ice sheet that melted fast” paradigm.

Big Sandy Creek-Birch Creek drainage divide area location map

Figure 1: Big Sandy Creek-Birch 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-Birch Creek drainage divide area location map. Figure 1 illustrates a region in north central Montana and the US-Canada border is located just north of the figure 1 north edge. The Missouri River flows northeast from Great Falls in the figure 1 southwest corner and south of the town of Big Sandy turns southeast, then east-northeast, and finally southeast to flow to the figure 1 east edge. 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. Birch Creek (unnamed in figure 1) originates in the Bear Paw Mountains near the Big Sandy Creek headwaters and flows south-southwest, southeast, and southwest to join the east-oriented Missouri River. The Big Sandy Creek-Birch Creek drainage divide area discussed here is located in the high Bear Paw Mountains and on the Bear Paw Mountains west and south flanks. The Big Sandy Creek-Beaver Creek drainage divide area essay, the Beaver Creek-Birch Creek drainage divide area essay describe drainage divide areas located immediately east of the Big Sandy Creek-Beaver Creek drainage divide area and the Milk River-Peoples Creek drainage divide area essay and Peoples Creek-Missouri River drainage divide area essay describe drainage divide areas located in the Bear Paw Mountains region. Essays can be found under Milk River on the sidebar category list. Evidence presented in these mentioned and 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 an actively eroding initial 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 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.

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

Figure 2: Big Sandy Creek-Birch 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-Birch Creek drainage divide area discussed in this essay. Green boundary lines are county lines. Chouteau County is located in Montana. The red shaded area is the Rocky Boys Indian Reservation. The east-oriented Milk River is located north of the figure 2 map area. The Missouri River flows northeast from the figure 2 west edge (south half) to just north of Virgelle and then turns south, southeast, and east-northeast to flow to figure 2 east edge. Big Sandy Creek originates in the southern Rocky Boys Indian Reservation near Baldy Mountain and flows northwest, southwest, and northwest to Big Sandy, Montana and then north and northeast to join the Milk River north of the figure 2 map area. Birch Creek also originates in the Baldy Mountain area and flows south, southeast, southwest, southeast, and south-southwest to join an east-oriented Missouri River segment in the figure 2 south center area. This essay also discusses Little Sandy Creek (which originates east of Studhorse Butte and flows south, northwest, and south to join the south-oriented Missouri River east of Virgelle) and Eagle Creek (which originates near Old Baldy Mountain and flows southwest to join the south-oriented Missouri River in the figure 2 west center area). As previously mentioned this essay interprets Big Sandy Creek-Birch 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 an initial 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 an initial south-oriented Missouri River valley that eroded north from the initial 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 initial Missouri River valley, including the south-oriented initial 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.

West end of Big Sandy Creek-Missouri River drainage divide area

Figure 3: West end of Big Sandy Creek-Missouri River drainage divide area. United States Geological Survey map digitally presented using National Geographic Society TOPO software. 

Figure 3 illustrates the west end of the Big Sandy Creek-Missouri River drainage divide area, which is included in the Big Sandy Creek-Birch Creek drainage divide area discussed in this essay. The Missouri River flows northeast from the figure 3 southwest corner area to the Coalbanks Landing State Recreation Area and then turns east and south-southeast to flow to the figure 3 south center edge. The Bear Paw Mountains are located in the figure 3 northeast area. Unfortunately the digital map set being used for these essay uses maps at this scale without contour lines to show high Bear Paw Mountains areas. Generally the northeast corner area is 700 meters or higher than the elevation at the town of Big Sandy in the figure 3 north center area. Big Sandy Creek originates east of the figure 3 northeast corner and flows in a southwest direction from the figure 3 northwest corner before turning north to flow through the town of Big Sandy to the figure 3 north edge. North of figure 3 map area Big Sandy Creek flows north and northeast to join the Milk River, which flows east along the Bear Paw Mountains north flank. Godfrey Creek is the major east-oriented tributary joining Big Sandy Creek southeast of the town of Big Sandy. South-southwest oriented Eagle Creek is located in the figure 3 east center edge area and turns southwest to join the south-oriented Missouri River just south of the figure 3 south edge. Little Sandy Creek originates in McNamara Butte area in the figure 3 east center edge area and flows west-northwest before turning south to join the Missouri River at the point where the Missouri River turns to flow south-southeast. To understand figure 3 evidence it is necessary to visualize the figure 3 map area before any of the present day drainage routes existed. At that time an immense southeast oriented flood flowed across the entire figure 3 map area including the present day high Bear Paw Mountain regions. Either the Bear Paw Mountains upland regions had not been uplifted and/or the surrounding region was covered with sediments and/or ice to the elevation of the present day Bear Paw Mountains uplands region or some combination of the two. The southeast oriented flood waters were moving to what was then an initial Missouri River valley head, which was eroding east along the Bear Paw Mountains region south flank (flood waters were unable to erode deep valleys across the Bear Paw Mountains region and for that reason the initial Missouri River valley eroded west). When that early east-oriented Missouri River valley reached the west end of the Bear Paw Mountains it was possible to erode a deep valley north along the Bear Paw Mountain west flank and flood waters started to do so. Flood waters still moving across the Bear Paw Mountains uplands were captured and diverted southwest to that actively eroding south-oriented initial Missouri River valley. As this was happening headward erosion of the east-oriented Milk River valley north of the Bear Paw Mountains was beheading and reversing southeast and south oriented flood flow routes to the newly eroded initial Missouri River valley. When the Milk River valley reached the west end of the Bear Paw Mountains a northeast-oriented tributary valley eroded southwest along the Bear Paw Mountains northwest flank. At that time the Milk River valley was deeper than the initial Missouri River valley and the northeast-oriented Milk River tributary valley beheaded and reversed the north end of the south-oriented initial Missouri River valley, which created the present day Big Sandy Creek elbow of capture. Since that time vast quantities of flood water from west and south of the figure 3 map area have greatly altered the initial Missouri River valley and the north and northeast-oriented Big Sandy Creek valley segments. This essay focuses on events related to higher elevations and drainage divides and does not attempt to decipher flood history within the Missouri River valley.

Missouri River-Birch Creek drainage divide area

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

Figure 4 illustrates the Missouri River valley downstream from the figure 3 map area and includes overlap areas with figure 3. The Missouri River today flows south-southeast, south, southeast from the figure 4 northwest corner to the figure 4 south center and then easterly to the figure 4 east edge. Sand Creek flows south-southwest from the figure 4 northeast corner area to join south-, southeast, south, and southwest-oriented Birch Creek, which joins the Missouri River in the figure 4 southeast corner. Birch Creek, upstream from where it joins Sand Creek, is south-southeast oriented and then, upstream from where it joins south-southeast oriented Little Birch Creek, is southwest-oriented. Headwaters of southwest-oriented Chip Creek are located near the point where southwest-oriented Birch Creek joins south-southeast oriented Birch Creek. Chip Creek flows southwest to the figure 4 center area and then turns southeast in large northwest-southeast oriented through valley to join the Missouri River a short distance west of where Birch Creek joins the Missouri River. Flowing northwest in that same northwest-southeast oriented through valley is Spring Coulee, which joins southwest-oriented Eagle Creek to flow west to the Missouri River at the point where it turns from flowing south-southeast to flowing south. Birch Creek and Eagle Creek originate in the high Bear Paw Mountains north of the figure 4 map area. The initial Missouri River valley was much shallower than the present day Missouri River valley and was eroded headward by south-oriented flood waters that flowed across the high Bear Paw Mountains to the north. Flood waters were unable to erode deep valleys across the erosion resistant Bear Paw Mountains and as a result the initial Missouri River valley south of the Bear Paw Mountains is east-oriented. When the actively eroding initial Missouri River valley head reached the Bear Paw Mountains west end the initial Missouri River valley head was able to erode northwest and north along the incoming flood flow routes. At that time the initial Missouri River valley was not as deep as it is now and the various benches provide evidence of subsequent stages of Missouri River valley history. Vast quantities of flood waters from west, southwest, and south of the figure 3 map area flowed through the figure 4 map area and eroded deeper valleys into the floor of the initial Missouri River valley, which had eroded headward into the region.

North end of Big Sandy Creek-Birch Creek drainage divide area

Figure 5: North end of Big Sandy Creek-Birch Creek drainage divide area. United States Geological Survey map digitally presented using National Geographic Society TOPO software. 

Figure 5 illustrates the Big Sandy Creek, Eagle Creek, and West Fork Birch Creek headwaters area in the high Bear Paw Mountains north of the figure 4 map area. Baldy Mountain is the mountain located in figure 5 center area. North of Baldy Mountain is northeast-oriented West Fork Beaver Creek and northeast of Baldy Mountain is northwest-oriented East Fork Beaver Creek. The West and East Forks Beaver Creek meet north of Baldy Mountain to form north-oriented Beaver Creek, which flows to the figure 5 north edge and eventually to the east-oriented Milk River. In the figure 5 northwest corner area are west-northwest oriented Big Sandy Creek headwaters, which as seen in figure 3 eventually turn southwest to flow down the Bear Paw Mountains west slope and then turn north and northeast to join the east-oriented Milk River. Immediately west of Baldy Mountain and flowing southwest along the northwest side of Pecora Ridge are headwaters of southwest-oriented Eagle Creek, which as seen in figure 4 flows to the south-oriented Missouri River located southwest of the figure 5 map area. East of Baldy Mountain near the figure 5 east edge are headwaters of south-southeast oriented West Fork Birch Creek, which as seen in figure 4 flows to the east-oriented Missouri River located south of the figure 5 map area. What is remarkable about the figure 5 evidence are the through valleys linking these various diverse drainage routes. What is today the north-oriented Beaver Creek valley originated as a south-oriented flood flow route moving flood waters to what was then the actively eroding Missouri River valley head. At the time the initial Missouri River valley was eroding west (in the region south of figure 5) vast quantities of flood water moved southeast on the East Fork Beaver Creek valley to the West-Fork Birch Creek valley and then south to that initial Missouri River valley. It is also possible that southeast-oriented flood waters also moved into the figure 5 map area along the present day west-oriented Big Sandy Creek valley route. When the initial Missouri River valley head began to erode north large quantities of flood waters moved southwest on the West Fork Beaver Creek valley to the southwest-oriented Eagle Creek valley. South-oriented flood flow from the Beaver Creek valley was subsequently beheaded and reversed by headward erosion of the deep Milk River valley to the north. Next southeast-oriented flood flow in the northwest-oriented Big Sandy Creek valley was beheaded and reversed as the Milk River valley eroded west and the present day northeast-oriented Big Sandy Creek valley eroded southwest along the Bear Paw Mountains northwest flank.

Little Sandy Creek-Eagle Creek drainage divide area big picture view

Figure 6: Little Sandy Creek-Eagle Creek drainage divide area big picture view. United States Geological Survey map digitally presented using National Geographic Society TOPO software. 

Figure 6 illustrates a big picture view of the Little Sandy Creek drainage basin. Little Sandy Creek originates in the figure 6 east center area almost at the edge of the south-southeast oriented Little Eagle Creek valley (see figure 8 below for detailed map of that drainage divide) and the flows west-northwest and northwest to the figure 6 northwest corner area where it turns south to flow to the south-oriented Missouri River (see figure 3). South of Little Sandy Creek is Alkali Coulee which also flows northwest before turning south to flow to the south-oriented Missouri River. North of Little Sandy Creek is east-oriented Godfrey Creek, which north of Rattlesnake Butte and Studhorse Butte is joined by southwest oriented Big Sandy Creek (not named in figure 6), which turns to flow northwest and north to the figure 6 north edge. The northwest-oriented Little Sandy Creek and Alkali Coulee alignments were initiated by southeast-oriented flood waters flowing to what was then the actively eroding initial east-oriented Missouri River valley head. As the Missouri River valley eroded west and then north it beheaded those southeast-oriented flow routes. Flood waters on the northwest ends of the beheaded flow routes reversed flow direction to flow northwest to what was then a south-oriented valley eroding north from the present day south-southeast oriented Missouri River valley segment (see figure 3). Northwest-oriented (or reversed) flood flow on the Little Sandy Creek and Alkali Coulee alignments was probably supplemented by yet to be beheaded flood flow moving south into the area (especially near the Eagle Creek drainage divide area, see figure 8 below). The Little Sandy Creek and Alkali Coulee elbows of capture provide evidence the Missouri River valley did erode north toward the present day town of Big Sandy (and probably further) and did capture flood flow still moving across the high Bear Paw Mountains regions, which means headward erosion of the deep Milk River valley had not yet beheaded and reversed all southeast-oriented flood flow routes moving flood waters to the high Bear Paw Mountains. Figures below illustrate evidence along present day drainage divides at higher elevations, which probably were not altered by subsequent Missouri River valley flood events.

Through valleys in the Rattlesnake Butte and Studhorse Butte area

Figure 7: Through valleys in the Rattlesnake Butte and Studhorse Butte area. United States Geological Survey map digitally presented using National Geographic Society TOPO software. 

Figure 7 illustrates through valleys linking the present day west-oriented Godfrey Creek and Little Sandy Creek valleys in the Rattlesnake Butte and Studhorse Butte area. The figure 7 map area is shown in less detail in figure 6 above. As previously mentioned flood waters originally flowed southeast across the figure 7 map area, probably moving to what was then the east-oriented initial Missouri River valley, which was eroding headward into the region south of the present day Bear Paw Mountains. That initial Missouri River valley was eroding headward into a topographic surface much higher than the topographic surface that exists today (flood waters significantly lower topography surrounding the Bear Paw Mountains). While it is difficult to determine how much material was removed from the figure 7 surface, buttes and hills provide markers from which minimal estimates can be made. In figure 7 note the valley eroded between Rattlesnake Butte and Studhorse Butte and also the saddle eroded into Ryan Butte. Those valleys were eroded by south and southeast-oriented flood water moving across the figure 7 map area in what were then flood eroded channels on what was then the prevailing topographic surface. The floor of the Ryan Butte saddle is approximately 1000 feet higher than the floor of the Godfrey Creek valley to the north. The floor of the valley between Rattlesnake Butte and Studhorse Butte is much lower, but still documents several hundred feet of regional erosion. Erosion of the magnitude recorded by these markers required immense quantities of flood waters. The flood waters first moved southeast and later were reversed to flow west. It is possible the reversal of flood flow was greatly aided by Bear Paw Mountains localized uplift.

Little Sandy Creek-Eagle Creek drainage divide area detailed map

Figure 8 illustrates the Little Sandy Creek-Eagle Creek drainage divide area seen in less detail in figure 6 above. Little Sandy Creek originates north of McNamara Ridge and flows west-southwest to the figure 8 west edge. Little Eagle Creek flows south-southeast from the figure 8 north edge to the McNamara Ridge northeast end and then joins south-southwest and south oriented Eagle Creek, which flows to the figure 8 south edge. Southwest and south-oriented Dog Creek is located in the figure 8 southeast quadrant. Note the through valleys linking Eagle Creek and Dog Creek. Figure 9 below illustrates additional through valleys linking the two drainage basins further to the north. The through valleys provide evidence of multiple southeast-oriented flood flow channels crossing what is today the drainage divide between Eagle Creek and Dog Creek, which is an Eagle Creek tributary. The multiple channels are remnants of what was probably a southeast-oriented anastomosing channel complex eroded by southeast-oriented flood waters into the Bear Paw Mountains south flank. The through valley linking the Little Sandy Creek headwaters with the Little Eagle Creek headwaters valley suggests reversed flood flow in the Little Sandy Creek valley partially captured flood flow moving south in the Little Eagle Creek valley and diverted the captured flood flow west, northwest, and south to the Missouri River valley as seen in figure 6 above. Flood waters that eroded the anastomosing valley complex (and that were captured by reversed flow in the Little Sandy Creek valley) came from the north and northwest, which means the water moved over what are today high Bear Paw Mountains uplands. This would only be possible if the region north and northwest of the present day Bear Paw Mountains was at least as high as the Bear Paw Mountains upland regions are today. In other words, the deep Milk River valley and northeast-oriented Big Sandy Creek valley (along the Bear Paw Mountains northwest flank) had not yet eroded into the region and the region north and west of the Bear Paw Mountains was considerably higher than it is now. Since that time the Milk River and northeast-oriented Big Sandy Creek valley eroded west and southwest into the region north of the Bear Paw Mountains and the sedimentary rock and/or ice that provided the high level topographic surface further to the north and west was removed by flood water erosion, and perhaps Bear Paw Mountains localized uplift has changed the regional topography by raising the Bear Paw Mountains area.

Eagle Creek-Dog Creek drainage divide area

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

Figure 9 illustrates the Eagle Creek-Dog Creek drainage divide area northeast of the figure 8 map area. Note through valleys around the hills northwest of Sawmill Butte. Water eroded valleys separate those hills and provide evidence of anastomosing channels in the Eagle Creek drainage basin. Also note the northwest-southeast oriented valley northeast of Sawmill Butte (now used by an unimproved road) linking the southwest oriented Eagle Creek valley with the southwest and south-oriented Dog Creek valley. That northwest-southeast oriented through valley provides evidence water once flowed southeast across the present day Eagle Creek-Dog Creek drainage divide. A close look at figure 9 reveals additional though valleys, although many are more subtle. Figure 9 evidence suggests the southwest-oriented Eagle Creek valley eroded headward across multiple southeast oriented flood flow channels, captured the southeast oriented flood waters, and diverted the flow to the south-oriented Missouri River valley. Again, southeast and south oriented flood flow crossing the Eagle Creek drainage basin is difficult to imagine based on present day topography. However, at the time flood waters eroded the figure 9 map area regional topography was different. To some extent the Bear Paw Mountains region elevation is the result of the erosion of deep valleys around it. 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 overlying material might trigger localized uplifts of what are today high mountain regions, such as the Bear Paw Mountains.

Dog Creek-Birch Creek drainage divide area

Figure 10 illustrates the Dog Creek-Little Birch Creek and the Little Birch Creek-Birch Creek drainage divide east of the figure 9 map area and includes overlap areas with figure 9. The East and West Forks Birch Creek join in the figure 10 northeast corner and Birch Creek flows south near the figure 10 east edge. Little Birch Creek flows south from the figure 10 north center edge and in the figure 10 center area makes a jog to the southwest to flow west of Tiger Ridge to the figure 10 south edge. Between Little Birch Creek and Birch Creek is south-southeast oriented Connely Creek, which joins Birch Creek south of Warwick. Dog Creek flows south near the figure 10 west edge. Figure 10 illustrates numerous through valleys eroded across the present day north-south oriented drainage divides providing evidence south-oriented valleys captured water from a previous southeast oriented anastomosing channel complex. For example, north of Tiger Ridge are three northwest-southeast oriented through valleys linking the Little Birch Creek valley with the Birch Creek valley. North of those through valleys is the through valley used by the road linking the Little Birch Creek valley with the south-southeast oriented Connely Creek valley. Further west, just south of the road, are additional northwest-southeast oriented through valleys linking the Dog Creek valley with the south-oriented Little Birch Creek valley. The southeast oriented anastomosing channel complex was probably eroded into a topographic surface at least as high as the highest figure 10 elevations today. Flood flow directions in the figure 10 map area were probably altered when headward erosion of the deep east-oriented Missouri River valley reached the region south of the figure 10 map area. As the actively eroding initial Missouri River valley head eroded west, because flood waters could not erode deep valleys across the Bear Paw Mountains, flood flow directions probably followed the actively eroding valley head location. Flood waters that eroded the southeast oriented through valleys and flood waters that eroded the present day south-oriented valleys flowed across what are today high Bear Paw Mountains upland regions. Once southeast- and south-oriented flood flow routes across present day high Bear Paw Mountains regions were beheaded and reversed, flood flow across the figure 10 map area ceased and figure 10 map area drainage features have not significantly changed since.

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.