A geomorphic history based on topographic map evidence

The Missouri River-Arrow Creek drainage divide area in the Highwood Mountains region discussed here is located in Montana, USA. Although detailed topographic maps of the Missouri River-Arrow 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 Missouri River-Arrow 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 drainage divide ended when headward erosion of the deep Missouri 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 Missouri River-Arrow Creek drainage divide area landform origins in the Highwood Mountains region, 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 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 did 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 Missouri River-Arrow Creek drainage divide area landform evidence will be regarded as evidence supporting the “thick ice sheet that melted fast” paradigm. This essay is included in the Missouri River drainage basin landform origins research project essay collection.

Missouri River-Arrow Creek drainage divide area location map

Figure 1: Missouri River-Arrow 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 Missouri River-Arrow Creek drainage divide area location map and illustrates a region in central Montana. The Missouri River flows northwest in the figure 1 southwest quadrant area through Canyon Ferry Lake and Holter Lake and then turns northeast from Wolf Creek to flow to Great Falls, Fort Benton, and Loma before turning southeast, east-northeast, and southeast to flow to Fort Peck Lake (located along the figure 1 east edge). The Judith River flows north from south of the Judith Basin to join the east-oriented Missouri River south of the Bears Paw Mountains. Wolf Creek is an important northeast oriented Judith River tributary. Arrow Creek is the unlabeled northeast and north-oriented Missouri River tributary located immediately west of Wolf Creek. Arrow Creek originates in the Highwood Mountains and flows southeast before turning east, northeast, and north to flow to the Missouri River. The Musselshell River flows from the Little Belt Mountains area (figure 1 southwest quadrant) to Martinsdale and then southeast to Harlowton, Ryegate, and Lavina. From Lavina the Musselshell River flows northeast to Roundup and Melstone, where it turns to flow north to join the Missouri River at Fort Peck Lake. The Missouri River-Arrow Creek drainage divide is primarily located in the Highwood Mountains. The Highwood Mountains are not labeled, but Highwood Baldy, the highest point in the Highwood Mountains is labeled and is located east of Great Falls. The essay also illustrates drainage divide evidence between the Highwood Mountains and the Little Belt Mountains.

• Landform evidence in this essay is interpreted in the context of an immense southeast-oriented flood that crossed the entire figure 1 map area. Prior to Missouri River valley headward erosion the deep Musselshell River valley eroded headward into the figure 1 map area to capture southeast-oriented flood waters that had been moving to the newly eroded deep Yellowstone River valley (located south of the figure 1 map area) and to divert the captured flood waters further to the north and northeast. Initially the Little Belt Mountains and Highwood Mountains were not obstacles to southeast-oriented flood flow. However, as flood waters eroded the figure 1 map area the mountains emerged as significant obstacles to flood erosion, especially after the deep east-oriented Missouri River valley eroded headward into the region north of the present day Judith Basin. At first southeast-oriented flood waters eroded valleys into the emerging Highwood and Little Belt Mountains. Later flood waters were captured by headward erosion of north and northeast oriented Missouri River tributary valleys. The northeast and north-oriented Arrow Creek valley and tributary valleys eroded south and southwest to capture southeast-oriented oriented flood flow moving across the Highwood Mountains area. Important to understanding what happened are Highwood and Belt Creeks, which today are northwest-oriented Missouri River tributaries (unlabeled in figure 1). Belt Creek flows northwest through Belt and Highwood Creek flows northwest through Highwood. The Belt and Highwood Creek valleys were initiated as southeast-oriented flood flow routes that supplied significant water to help erode the northeast and north-oriented Arrow Creek valley. Southeast-oriented flood flow in those southeast-oriented Highwood and Belt Creek valleys was reversed when headward erosion of the northeast-oriented Missouri River valley beheaded southeast-oriented flood flow routes across the Highwood Mountains region. Reversal of flow may have also been aided by Little Belt Mountains and Highwood Mountains uplift as flood waters were eroding the figure 1 map area. The Arrow Creek-Judith River drainage divide area essay, the North Fork Smith River-North Fork Musselshell River drainage divide area essay, and the Big Sandy Creek-Birch Creek drainage divide area essay describe drainage divide areas located near the Missouri River-Arrow Creek drainage divide areas discussed here. Essays can be found under appropriate river names on the sidebar category list (e.g. Judith River, Smith River, Musselshell River, and Milk River, with Big Sandy Creek being a Milk River tributary).

Missouri River-Arrow Creek drainage divide area detailed location map

Figure 2: Missouri River-Arrow 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 Missouri River-Arrow Creek drainage divide area discussed in this essay. Cascade, Chouteau, Fergus and Judith Basin Counties are located in Montana. The Missouri River flows northeast from the figure 2 west edge to Great Falls and Fort Benton and then almost to the figure 2 north edge. At the figure 2 north edge the Missouri River turns to flow southeast and upon reaching the Chouteau County-Fergus County boundary to flow east to the figure 2 east edge. Green areas are National Forest lands, which usually are located in mountainous areas. The green area along the figure 2 south edge is located in the Little Belt Mountains. The smaller green area in the figure 2 center south area is located in the Highwood Mountains. Arrow Creek originates in the Highwood Mountains and flows southeast and then turns east, northeast, and north to flow to the Missouri River. The northeast oriented Chouteau County-Fergus County boundary line follows the Arrow Creek valley. Highwood Creek originates in the Highwood Mountains and flows northwest through Highwood to join the northeast-oriented Missouri River midway between Great Falls and Fort Benton. Also of concern here is Belt Creek, which originates in the Little Belt Mountains, south of the figure 2 south edge, and flows through Monarch (near the figure 2 south edge), Armington, and Belt and then for a short distance serves as the northwest-oriented Chouteau-Cascade County boundary line before joining the northeast oriented Missouri River northeast of Great Falls. Little Belt Creek is a Belt Creek tributary, which flows southwest from the Highwood Mountains before turning to flow northwest to join Belt Creek northwest of Belt. Evidence presented in this essay suggests the Highwood Creek and Belt Creek valley alignments originated as a southeast-oriented flood flow channels that were captured by headward erosion what was then an actively eroding northeast- and north-oriented Arrow Creek drainage basin. Evidence presented in this essay also demonstrates some of this southeast-oriented flood flow moved across the present day Highwood Mountains. Based on this evidence the Highwood Mountains are interpreted to have emerged as flood waters eroded the region. Emergence of the Highwood Mountains may have occurred as flood waters removed easily eroded sediments and/or ice that had buried the Highwood Mountains and/or as the Highwood Mountains were uplifted while flood waters eroded the region. In either case southeast-oriented flood flow to the northeast- and north-oriented Arrow Creek valley ended when headward erosion of the northeast-oriented Missouri River valley west of the Highwood Mountains captured the southeast-oriented flood flow routes.

Big Otter Creek-Lone Tree Creek drainage divide area

Figure 3: Big Otter Creek-Lone Tree Creek drainage divide area. United States Geological Survey map digitally presented using National Geographic Society TOPO software.

Figure 3 illustrates the Big Otter Creek-Lone Tree Creek drainage divide area along the Little Belt Mountains northeast flank. Little Otter Creek flows north and north-northwest to the figure 3 northwest corner and is a tributary of Big Otter Creek. Big Otter Creek originates between Irene Peak and Clendennin Mountain along the figure 3 south center edge area and flows north-northeast, north-northwest, northeast, and northwest through the figure 3 center area to the figure 3 north edge. North and west of figure 3 Big Otter Creek is northwest-oriented and flows to join northwest-oriented Belt Creek, which flows to join the northeast oriented Missouri River. East of Clendennin Mountain is northeast and north-oriented Lone Tree Creek, which flows to the figure 3 northeast corner and then to join northeast and north-oriented Arrow Creek. Northeast-oriented streams in the figure 3 northeast quadrant (east of the Big Otter Creek valley) are also Arrow Creek tributaries. In other words, the drainage divide between the northeast oriented Missouri River (west of the Highwood Mountains) and Arrow Creek (which flows to the east-oriented Missouri River east of the Highwood Mountains) extends north from Clendennin Mountain to Peterson Mountain and then north along the east edge of the Big Otter Creek valley. Figure 3 evidence demonstrates this drainage divide extends into the Little Belt Mountain area. Two saddles or through valleys notched into the high ridge between Clendennin Mountain and Peterson Mountain in the figure 3 south center area provide evidence southeast-oriented flood flow once moved on a topographic surface at least as high as that ridge. Headward erosion of the deep northeast oriented Lone Tree Creek valley first captured the southeast-oriented flood flow and subsequently headward erosion of what is today the Big Otter Creek captured the southeast-oriented flood flow (at that time the Big Otter Creek valley in the Little Belt Mountains area, between Limestone Butte and Peterson Mountain, may have drained northeast to the deep east-oriented Missouri River valley head, which was still located east of the present day Highwood Mountains and which was actively eroding headward to the west and northwest). Southeast-oriented flood flow into the newly eroded Big Otter Creek valley eroded a deep southeast-oriented valley along the Little Belt Mountains northeast flank. When headward erosion of the deep northeast-oriented Missouri River valley (west of the Highwood Mountains) beheaded that southeast-oriented flood flow route, flood waters on the northwest end of the beheaded flood flow route reversed flow direction. The newly reversed flood flow created the northwest-oriented Belt Creek drainage system, including the northwest-oriented Big Otter Creek valley (which captured the northeast- and north-oriented Big Otter Creek headwaters valley between Limestone Butte and Peterson Mountain. The Little Otter Creek history is probably similar.

Detailed map of Big Otter Creek-Chambers Coulee drainage divide area

Figure 4: Detailed map of Big Otter Creek-Chambers Coulee drainage divide area. United States Geological Survey map digitally presented using National Geographic Society TOPO software.

Figure 4 provides a detailed map of the Big Otter Creek-Chambers Coulee drainage divide area seen in less detail in figure 3 above. Big Otter Creek flows north-northeast, north-northwest, and northeast in the figure 4 west half. Big Otter Creek north and west of the figure 4 map area flows northwest to northwest-oriented Belt Creek. Northeast oriented drainage in the figure 4 southeast quadrant flows to northeast oriented Shannon Creek, which flows from the figure 4 east edge (center south) to join northeast-oriented Lone Tree Creek (see figure 3). The north flank of Peterson Mountain is located in the figure 4 south center and southeast quadrant areas. At least some of the ridges appear to be hogbacks associated with Little Belt Mountains structures. Arch Coulee drains north-northeast from Peterson Mountain to northwest and north-oriented Chambers Coulee. North of figure 4 Chambers Coulee turns to drain northeast to McCarthy Creek (see figure 3), which flows to east, northeast, and north-oriented Arrow Creek. Note the well-defined through valley linking the Big Otter Creek valley with the Chambers Coulee valley. That through valley, while probably located between two hogback ridges, provides evidence water once flowed between the present day Belt Creek drainage basin and the present day Arrow Creek drainage basin. Also note the through valley linking Chambers Coulee with the Shannon Creek headwaters area. That through valley, while also probably related to the dipping beds, provides evidence water once flowed between the present day Chambers Coulee valley and the present day Shannon Creek valley. Combined the two through valleys suggest water once flowed across the Big Otter Creek-Lone Tree Creek drainage divide area north of Peterson Mountain. At the time water flowed across the present day drainage divides the figure 4 topography probably was quite different from what it is today. Present day valleys were being eroded headward by flood waters moving on a topographic surface that has since been removed by flood water erosion and/or by uplift of Little Belt Mountains structures.

Big Otter Creek-Arrow Creek drainage divide area near Spion Kop

Figure 5: Big Otter Creek-Arrow Creek drainage divide area near Spion Kop. United States Geological Survey map digitally presented using National Geographic Society TOPO software.

Figure 5 illustrates the Big Otter Creek-Arrow Creek drainage divide area between the Little Belt Mountains and the Highwood Mountains. Figure 5 is located north of the figure 3 map area and includes overlap areas with figure 3. South Peak in the figure 5 north center is at the south end of the Highwood Mountains. Arrow Creek flows southeast in the figure 5 northeast quadrant (east of South Peak) to the figure 5 east center edge. Big Otter Creek flows northwest from the figure 5 south center edge to join north-oriented Little Otter Creek at Raynesford and then to flow northwest to the figure 5 west edge (west of figure 5 Big Otter Creek joins northwest-oriented Belt Creek). Note Williams Creek, which flows south and southwest from South Peak to near Spion Kop and then makes a sharp turn to flow west and southwest to join northwest-oriented Big Otter Creek near Raynesford. Also note just to the east of Williams Creek southeast-oriented Hay Creek, which flows south and southeast from South Peak to near Geyser (in the figure 5 southeast quadrant) and then turns to flow northeast to join Arrow Creek near the figure 5 east center edge. Further, note the through valley at Spion Kop linking the Williams Creek valley and the Hay Creek valley. This figure 5  map location provides evidence of a massive flood flow reversal. Southeast-oriented flood flow, which once flowed across the entire figure 5 map area was captured by headward erosion of the northeast and north-oriented Arrow Creek valley (which had eroded south and southwest from the deep Missouri River valley located east of the present day Highwood Mountains). When initially captured the southeast-oriented flood flow was moving across the present day Highwood Mountains area, suggesting the Highwood Mountains emerged as flood waters were eroding the region. Headward erosion of the deep northeast-oriented Missouri River valley (west of the present day Highwood Mountains) next beheaded the southeast-oriented flood flow routes across the figure 5 map area (in sequence from the northeast to the southwest). Flood waters on the northwest ends of the beheaded flood flow routes reversed flow direction to flow northwest to the newly eroded northeast-oriented Missouri River valley. In figure 5 the flood flow reversal affected the region south of the Highwood Mountains and the reversed flow flood waters eroded the northwest-oriented Big Otter Creek valley and created the present day Big Otter Creek-Arrow Creek drainage divide. Figure 6 below looks at this drainage divide in more detail.

Detailed map of Big Otter Creek-Arrow Creek drainage divide area near Spion Kop

Figure 6: Detailed map of Big Otter Creek-Arrow Creek drainage divide area near Spion Kop.United States Geological Survey map digitally presented using National Geographic Society TOPO software.

Figure 6 provides a more detailed map of the Big Otter Creek-Arrow Creek drainage divide area seen in less detail in figure 5 above. Big Otter Creek flows northwest in the figure 6 southwest quadrant to the figure 6 west edge. Sion Kop is located in the figure 6 north center edge area. West of Sion Kop Williams Creek flows south-southeast and then turns abruptly to flow southwest through the figure 6 northwest quadrant near the railroad tracks. East of Spion Kop southeast-oriented Hay Creek flows near the railroad track to the figure 6 east edge and then flows east to join Arrow Creek. The west to east oriented highway dividing the figure 6 north and south halves is located in a west to east oriented through valley linking the Big Otter Creek valley with the Hay Creek (and Arrow Creek) valley. Another through valley is located in the figure 6 north center area near Sion Kop where the railroad crosses the Williams Creek-Hay Creek drainage divide. One remarkable figure 6 landform is the large east-oriented basin located in the figure 6 east half. This basin is a large east-oriented abandoned headcut that was eroded by east-oriented flood flow moving between what were then the emerging Highwood Mountains to the north and the emerging Little Belt Mountains to the south. The flood water was moving east to what was then the newly eroded northeast and north-oriented Arrow Creek drainage basin (and possibly before that to what was then the newly eroded northeast and north-oriented Judith River drainage basin). At the time flood waters were eroding that headcut westward the northeast-oriented Missouri River valley west and northwest of the figure 6 map area did not exist. Subsequent headward erosion of that northeast-oriented Missouri River valley beheaded and reversed the major flood flow route moving flood waters into the figure 6 map area. Flood waters on the northwest ends of the newly beheaded flood flow route then reversed flow direction to flow northwest to the newly eroded and deeper Missouri River valley. The northwest-oriented Big Otter Creek drainage basin was created by that flood flow reversal. Also created by that flood flow reversal was the Big Otter Creek-Hay Creek (or Arrow Creek) drainage divide in figure 6, which resulted in abandonment of the east-oriented headcut.

Highwood Creek-Arrow Creek drainage divide area

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

Figure 7 illustrates the Highwood Creek-Arrow Creek drainage divide area in the Highwood Mountains. Highwood Creek drains northwest from the figure 7 center area to the figure 7 north edge. Arrow Creek drains south and southeast from the figure 7 center area to the figure 7 south edge. Southeast-oriented drainage in the figure 7 east half flows to Arrow Creek, which southeast and east of figure 7 turns to flow east, northeast and north to join the east-oriented Missouri River northeast of the figure 7 map area (see figures 1 and 2 above). The south, southwest, and west-oriented stream originating south of Highwood Baldy and flowing between Middle Peak and Comers Butte is Little Belt Creek, which west of figure 7 turns to flow northwest to join northwest and north-oriented Belt Creek. Note the prominent northwest-southeast oriented through valley linking the northwest-oriented Highwood Creek valley with the southeast-oriented Arrow Creek headwaters valley. That through valley provides evidence southeast-oriented flood flow once moved across the Highwood Mountains region. At the time flood waters flowed across the Highwood Mountains area there was no northeast-oriented Missouri River valley to the northeast. Even more intriguing is a much higher level through valley located east of the Highwood Creek-Arrow Creek through valley. That much higher level through valley links the northwest-oriented North Fork Highwood Creek valley with the southeast-oriented Martin Creek valley and is located immediately west of Arrow Peak. That high level through valley also provides evidence southeast-oriented flood flow moved across the Highwood Mountains region at a time when flood waters were moving on a much higher level topographic surface. That higher level topographic surface may have been created by easily eroded sediments and/or ice that had buried the Highwood Mountains and/or the Highwood Mountains may have been uplifted as flood waters eroded the figure 7 map area. In either case, the Highwood Mountains emerged as high mountains while flood waters eroded the figure 7 map area. And as the Highwood Mountains emerged southeast-oriented flood flow routes across the Highwood Mountains were one by one abandoned as the deeper Highwood Creek-Arrow Creek through valley first captured the southeast-oriented flood flow and the even deeper Big Otter Creek-Arrow Creek through valley south of the Highwood Mountains (seen in figures 5 and 6) then captured all flood flow moving across the Highwood Mountains region. Figures 8, 9, and 10 below provide detailed maps of some of the Highwood Mountains through valleys.

Detailed map of Highwood Creek-Arrow Creek drainage divide area

Figure 8: Detailed map of Highwood Creek-Arrow Creek drainage divide area.United States Geological Survey map digitally presented using National Geographic Society TOPO software.

Figure 8 provides a detailed map of the Highwood Creek-Arrow Creek through valley seen in less detail in figure 7 above. Highwood Creek flows north-northwest from the figure 8 center area to the figure 8 north edge and then flows northwest to the northeast-oriented Missouri River. Arrow Creek flows south from the figure 8 center area to the figure 8 south edge. As seen in figure 7 above this through valley is the deepest of the through valleys eroded across the present day Highwood Mountains. The through valley was eroded by southeast-oriented flood water moving from northwest of the figure 8 map area to the Arrow Creek drainage basin south and southeast of the figure 7 map area. Much of the erosion probably occurred at a time when the Highwood Mountains were only beginning to emerge as a high mountain region. Volumes of flood water required to erode a valley of this magnitude must have been immense. Why would a mountain region emerge as an immense flood was eroding the region? Emergence of the mountains may have been as flood waters removed easily eroded materials, such as easily eroded sediments and/or ice, from around the mountains, and/or as the mountains were uplifted. Why would a mountain range be uplifted while an immense southeast-oriented flood was rapidly eroding the adjacent region? While the source of the southeast-oriented flood waters described in this essay cannot be determined from evidence presented here, 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 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 flood waters further and further 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 mountain regions during an immense southeast-oriented flood. A thick North American ice sheet, in a deep “hole” created in part by the ice sheet’s weight, would probably cause crustal warping elsewhere on the continent, especially along ice sheet margins. Rapid erosion of significant amounts of overlying bedrock material might also trigger localized uplift.

Detailed map of Little Belt Creek-Arrow Creek drainage divide area

Figure 9: Detailed map of Little Belt Creek-Arrow Creek drainage divide area.United States Geological Survey map digitally presented using National Geographic Society TOPO software.

Figure 9 provides a detailed map of the Little Belt Creek-Arrow Creek drainage divide area located southwest of the figure 8 map area and includes overlap areas with figure 8 (and shows an area seen in less detail in figure 7 above). South and southeast-oriented Arrow Creek flows to the figure 9 southeast corner. Highwood Creek headwaters are located in the figure 9 northeast corner. The North Fork Little Belt Creek flows southwest in the figure 9 northwest corner and the northwest-oriented South Fork Little Belt Creek flows through the figure 9 west center area to join the southwest-oriented North Fork near the figure 9 west edge. The Middle Fork Little Belt Creek originates south of North Peak (near the figure 9 north edge) and flows northwest, southwest, and northwest to the southwest-oriented North Fork Little Belt Creek near the figure 9 northwest corner. The high ridge extending southwest from North Peak (near the figure 9 north edge) through Middle Peak to the figure 9 south edge is the present day Little Belt Creek-Arrow Creek drainage divide. A close look at that ridge reveals through valleys (or saddles) notched into the ridge. Generally these through valleys (or saddles) link northwest-oriented Little Belt Creek tributary valleys with southeast-oriented Arrow Creek tributary valleys. For example, one of the deeper through valleys (or saddles) is located between North Peak and Middle Peak. That through valley (or saddle) links the northwest-oriented Middle Fork Little Belt Creek valley with a southeast-oriented Arrow Creek headwaters valley. These high level through valleys (or saddles) provide evidence of multiple southeast-oriented flood flow routes once crossed the Highwood Mountains region. At the time flood waters crossed the figure 9 map area the Highwood Mountains did not stand high above the surrounding region. Either the surrounding region was buried in easily eroded sediments and/or ice flood waters removed or the Highwood Mountains were uplifted as flood waters eroded the region.

Detailed map of North Fork Highwood Creek-Martin Creek drainage divide area

Figure 10: Detailed map of North Fork Highwood Creek-Martin Creek drainage divide area.United States Geological Survey map digitally presented using National Geographic Society TOPO software.

Figure 10 provides a detailed map of the North Fork Highwood Creek-Martin Creek drainage divide area located north and east of the figure 8 map area and also seen in less detail in figure 7 above. Arrow Peak is located in the figure 10 south center area. The North Fork Highwood Creek originates north of Arrow Peak and flows northwest, west, and northwest to the figure 10 northwest edge. Martin Creek originates southeast of Arrow Peak and flows southeast in the figure 10 southeast quadrant to the figure 10 south edge. In the figure 10 northeast quadrant Cottonwood Creek flows east-southeast and east-northeast to the figure 10 east edge. Note the high level through valley (or saddle) notched into the high ridge just northeast of Arrow Peak. That through valley (or saddle) links the northwest-oriented North Fork Highwood Creek valley with the southeast-oriented Martin Creek. Note also the large escarpment surrounded basin in the figure 10 southeast quadrant, which today represents the Martin Creek drainage basin. That escarpment-surrounded basin is a large southeast-oriented abandoned headcut eroded at a time when immense volumes of flood water flowed southeast across the Highwood Mountains to what was then the deep Martin Creek valley (which may have eroded headward from what was then the deep northeast and north-oriented Arrow Creek valley,which had eroded south from what was then the newly eroded east-oriented Missouri River valley). The Cottonwood Creek valley was also eroded headward by southeast-oriented flood flow on the North Fork Highwood Creek alignment. Southeast-oriented flood flow on the North Fork Highwood Creek was subsequently beheaded and reversed by headward erosion of the northeast-oriented Missouri River valley (northwest of the figure 10 map area) to create the northwest-oriented North Fork Highwood Creek valley and the North Fork Highwood Creek-Martin Creek and North Fork Highwood Creek-Cottonwood Creek drainage divides.

• The figure 7 discussion suggested the immense quantities of flood water required to erode the Highwood Mountains region came from a rapidly melting North American ice sheet located in a deep “hole”. Why would such an ice sheet generate immense southeast-oriented floods that deeply eroded central and western Montana mountain ranges? The massive southeast-oriented floods and the deep erosion in central and western Montana mountain ranges makes sense if the deep “hole” was eroded into a topographic surface equivalent in elevation to the crests of highest Montana mountain ranges today. In other words, central and western Montana mountain ranges were located along the deep “hole” rim and initially melt water from the rapidly melting ice sheet flowed southeast along the ice sheet margin. As the ice sheet melted flood waters were captured by headward erosion of deep northeast-oriented valleys so as divert flood waters into space being opened up by the rapidly melting ice sheet. To visualize what happened think in terms of an Antarctica-sized ice sheet developing on a North American topographic surface at least as high as the high Rocky Mountain peneplain defined by high Rocky Mountain ridges today. The ice sheet through its weight and deep glacial erosion created a deep “hole” in that topographic surface. Then the ice sheet began to melt faster than it was being formed. Essays in this Missouri River drainage basin landform origins research project collectively build a strong case the Missouri River drainage basin landforms evolved during the resulting floods.

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.