A geomorphic history based on topographic map evidence

The Arrow Creek-Judith River drainage divide area discussed here is located in Fergus and Judith Basin Counties, Montana, USA. Although detailed topographic maps of the Arrow Creek-Judith River 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 Arrow Creek-Judith River 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 Missouri River drainage basin landform origins 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 Arrow Creek-Judith River drainage divide area landform origins in Fergus and Judith Basin Counties, 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 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 Arrow Creek-Judith River 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 collection.

Arrow Creek-Judith River drainage divide area location map

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

Figure 1 provides an Arrow Creek-Judith River drainage divide area location map and illustrates a region in central Montana. The Missouri River flows northwest in the figure 1 southwest corner area through Canyon Ferry Lake and Holter Lake and then turns northeast from the figure 1 west center edge 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 the 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 tributaries originate in the Little Belt Mountains (near Big Baldy Mountain). Arrow Creek itself originates in the Highwood Mountains and flows southeast before turning east, northeast, and north to flow to the east-oriented 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 Arrow Creek-Judith River drainage divide area of concern in this essay encompasses the entire drainage divide area from the Missouri River valley in the north to the Little Belt Mountains in the south.  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 at least the Little Belt Mountains were not an obstacle to southeast-oriented flood flow into the western Musselshell River drainage basin. However, as flood waters eroded the figure 1 map area the Little Belt 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 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 Judith River valley and tributary valleys (and subsequently the Arrow Creek valley and tributary valleys) eroded south and southwest to capture southeast-oriented oriented flood flow being blocked by the Little Belt Mountains emergence. Important to understanding what happened is Belt Creek, which today is the northwest-oriented Missouri River tributary (unlabeled in figure 1) originating near Big Baldy Mountain and flowing by Monarch, Armington, and Belt. The Belt Creek valley was initiated as a southeast-oriented flood flow route that supplied significant water to help erode the northeast and north-oriented Arrow Creek and Wolf Creek valleys. Southeast-oriented flood flow in that early Belt Creek valley was reversed when headward erosion of the northeast-oriented Missouri River valley beheaded the southeast-oriented flood flow route. Reversal of flow may have also been aided by Little Belt Mountain uplift as flood waters were eroding the figure 1 map area. The North Fork Smith River-North Fork Musselshell River drainage divide area essay, the Judith River-Armells Creek drainage divide area essay, the Big Sandy Creek-Birch Creek drainage divide area essay, the Peoples Creek-Missouri River drainage divide area essay, and the Judith River-Musselshell River (Fergus County) drainage divide area essay describe drainage divides located near the Arrow Creek-Judith River drainage divide areas discussed here. Essays can be found under appropriate river names on the sidebar category list with Big Sandy Creek and Peoples Creek being Milk River tributaries and the Montana Missouri River segment being MT Missouri River.

Arrow Creek-Judith River drainage divide area detailed location map

Figure 2 illustrates a somewhat more detailed map of the Arrow Creek-Judith River drainage divide area discussed in this essay. Fergus and Judith Basin Counties are located in Montana. Chouteau County is the unnamed county north of Judith Basin County and Cascade County is the unnamed county west of Judith Basin County. The Missouri River flows northeast in the figure 2 northwest corner, southeast from the figure 2 north center edge and then east-northeast along the Chouteau-Fergus County boundary. Green areas are National Forest lands, which usually are located in mountainous areas. The large green area in the figure 2 southwest quadrant is located in the Little Belt Mountains area. The smaller green area in the figure 2 west center area is located in the Highwood Mountains. The Judith River and several of its major tributaries originate in the Little Belt Mountains and flow northeast and north to join the Missouri River near the point marked “Ferry” on the secondary red highway between Winifred and Iliad. This essay is particularly concerned with Wolf Creek, which is the westernmost of the major northeast oriented Judith River tributaries. Wolf Creek originates in the Little Belt Mountains between Big Baldy Mountain and Yogo Peak and flows northeast near Stanford and Denton to eventually join the northwest and north-oriented Judith River near where the Judith River joins the Missouri River. West of Wolf Creek is Arrow Creek and its various tributaries. Arrow Creek tributaries of concern here are Surprise Creek and Lone Tree Creek, both of which originate in the Little Belt Mountains and then flow northeast to join northeast oriented Arrow Creek. Arrow Creek serves as the northeast and north-oriented Chouteau County-Fergus County boundary line until north-oriented Arrow Creek joins the Missouri River in the figure 2 north center area. Also of concern here is Belt Creek, which originates in the Little Belt Mountains, southwest of Big Baldy Mountain, and flows north-northwest along the red highway through Neihart, Monarch, 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 near the figure 2 northwest corner. Evidence presented in this essay suggests the Belt Creek valley alignment originated as a southeast-oriented flood flow channel that moved significant volumes of flood water into the present day Little Belt Mountains, where that southeast-oriented flood flow was captured by headward erosion of the northeast oriented Judith River and Wolf Creek valleys and also by headward erosion of Arrow Creek tributary valleys. Capture of this southeast-oriented flood flow in what is now the Little Belt Mountains played a major role in eroding the northeast- and north-oriented Judith River, Wolf Creek, and Arrow Creek valleys.

North end of the Arrow Creek-Judith River drainage divide area

Figure 3: North end of the Arrow Creek-Judith River drainage divide area. United States Geological Survey map digitally presented using National Geographic Society TOPO software.

Figure 3 illustrates the north end of the Arrow Creek-Judith River drainage divide area. The Missouri River flows east-southeast and northeast along the figure 3 north center edge area. Arrow Creek flows north along the figure 3 west edge. The Judith River flows north along the figure 3 east edge. The Big Sag is a large through valley linking the north-oriented Arrow Creek valley with the north-oriented Judith River valley and provides evidence large quantities of water once flowed from the present day Arrow Creek valley to the north-oriented Judith River valley. The Big Sag is not the only through valley linking the north-oriented Arrow Creek valley with the north-oriented Judith River valley. The Little Sag valley, while not deeply eroded at the west end provides evidence large volumes of water once flowed east along that alignment from the present day north-oriented Arrow Creek valley area to the north-oriented Judith River valley. Near the figure 3 south edge the northeast-oriented Mutton Coulee valley provides evidence large volumes of water once flowed northeast from the Arrow Creek valley area to the north-oriented Judith River valley. Figure 3 evidence is interpreted here to have been eroded when the deep Missouri River valley eroded headward into the figure 3 map area to capture southeast oriented flood flow. The north-oriented Judith River valley then eroded south to capture southeast and east-oriented flood flow while the deep Missouri River valley eroded west-northwest along one of the flood flow routes. As the deep Judith River valley eroded south the Little Sag valley, the Big Sag valley, and the Mutton Coulee valleys eroded headward in sequence from the newly eroded north-oriented Judith River valley. Note how the Big Sag valley is northeast-oriented near the Arrow Creek valley, suggesting flood flow moving through the Big Sag valley was captured and diverted north by headward erosion of the deep north-oriented Arrow Creek valley. However, before that capture could occur, volumes of flood water had to be great enough that flood water not only moved east and northeast in multiple channels to the newly eroded north-oriented Judith River valley, but flood water also moved north to the newly east-southeast and northeast oriented Missouri River valley. The north-oriented flood water began to erode the north-oriented Arrow Creek valley and beheaded east-oriented flood flow to the Little Sag valley and eventually beheaded the Big Sag valley flood flow route and also the northeast-oriented flood flow route eroding the northeast-oriented Mutton Coulee valley. Figure 3 evidence requires that at one time large volumes of flood water were flowing in multiple anastomosing channels through the figure 3 map area to the newly eroded Missouri River valley.

Arrow Creek-Judith River drainage divide area southeast of Arrow Creek Bench

Figure 4: Arrow Creek-Judith River drainage divide area southeast of Arrow Creek Bench. United States Geological Survey map digitally presented using National Geographic Society TOPO software.

Figure 4 illustrates the Arrow Creek-Judith River drainage divide area south of the figure 3 map area and there is no overlap area. Arrow Creek is the northeast-oriented stream in the figure 4 northwest quadrant that serves as the Chouteau County-Fergus County boundary. Southeast of Arrow Creek Bench is northeast-oriented Coffee Creek, which joins Arrow Creek just north of the figure 4 map area. Southeast of Coffee Creek is Alton Bench in the south and Everson Bench in the north. Multiple southeast oriented streams flow from Alton Bench and Everson Bench to north-northeast oriented Wolf Creek, which joins the Judith River north and east of the figure 4 map area. The northeast-oriented Judith River is located in the figure 4 southeast corner area. Note how Wolf Creek has multiple southeast and northwest-oriented tributaries. Coffee Creek also has northwest-oriented tributaries and east and southeast oriented tributaries. Arrow Creek in the figure 4 northwest corner has southeast oriented tributaries while the Judith River in the figure 4 southeast corner also has southeast-oriented tributaries. This predominance of southeast- and northwest-oriented tributaries provides evidence the Judith River, Wolf Creek, Coffee Creek, and Arrow Creek valleys eroded headward across southeast-oriented flood flow. The Judith River valley eroded southwest first and was followed by headward erosion of the Wolf Creek valley, which captured the southeast-oriented flood flow routes moving flood waters to the newly eroded Judith River valley. Next the Coffee Creek valley eroded headward to capture southeast-oriented flood flow to the newly eroded Wolf Creek valley. Finally the Arrow Creek valley eroded headward to capture southeast-oriented flood flow to the newly eroded Coffee Creek valley. The southeast-oriented tributary valleys were eroded headward along southeast-oriented flood flow routes captured by each respective valley as it eroded headward across the figure 4 map area. The various benches are erosion surfaces eroded by the southeast-oriented flood water and provide evidence large volumes of flood waters moved across each of the present day drainage divides. Northwest-oriented tributary valleys were eroded by reversals of flood waters on the northwest ends of beheaded southeast-oriented flood flow routes. The flood flow reversals not only eroded the northwest-oriented tributary valleys, but also created the present day drainage divides. The northeast-orientation of the major valleys suggests a major flood water source was also located to the southwest.

Coffee Creek-Wolf Creek drainage divide area near Denton

Figure 5: Coffee Creek-Wolf Creek drainage divide area near Denton. United States Geological Survey map digitally presented using National Geographic Society TOPO software.

Figure 5 illustrates the Coffee Creek-Wolf Creek drainage divide area south and west of the figure 4 map area and includes overlap areas with figure 4. Coffee Creek is the unlabeled northeast-oriented stream in the figure 5 northwest corner and eventually joins Arrow Creek. Wolf Creek flows east-northeast from the figure 5 west edge through Denton and in the figure 5 center east area turns north-northeast to flow to the figure 5 north edge and eventually to join the Judith River. Coyote Creek is the northeast-oriented Wolf Creek tributary joining Wolf Creek west of Denton. Dry Wolf Creek is the north-northeast oriented Wolf Creek joining Wolf Creek at the Wolf Creek elbow of capture (where Wolf Creek turns to flow north-northeast). [Note, the Dry Wolf Creek in figure 5 is different from the Dry Wolf Creek seen in figures 7, 8, and 9 below.] The Judith River flows northwest and north from the figure 5 southeast corner before turning northeast to flow to the figure 5 east edge. Alton Bench serves as the Coffee Creek-Wolf Creek drainage divide. A close look at Alton Bench reveals multiple shallow through valleys linking southeast-oriented Wolf Creek tributary valleys with the northeast-oriented Coffee Creek valley. These shallow through valleys and the southeast-oriented Wolf Creek tributaries provide evidence the Wolf Creek valley eroded headward to capture to multiple southeast-oriented flood flow routes such as might be found in an anastomosing channel complex. Next headward erosion of the northeast-oriented Coffee Creek valley beheaded the southeast-oriented flood flow routes and diverted the flood water northeast and north to the Arrow Creek valley. The Wolf Creek-Judith River drainage divide is today (in the figure 5 map area) a ridge, which also is crossed by multiple shallow through valleys linking the north-northeast oriented Dry Wolf Creek and Wolf Creek valleys with the north- and northeast-oriented Judith River valley. These shallow through valleys provide evidence the Judith River valley eroded headward prior to headward erosion of the Wolf Creek and Dry Wolf Creek valleys to capture the southeast-oriented flood flow. Following Judith River valley headward erosion into the region the Wolf Creek and Dry Wolf Creek valleys eroded headward into the region. North and northeast-oriented valley depths suggests significant flood flow was captured from regions south and southwest of the figure 5 map area. Sources of that flood water are illustrated in figures below.

Surprise Creek-Coffee Creek drainage divide area

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

Figure 6 illustrates the Surprise Creek-Coffee Creek drainage divide area southwest of the figure 4 map area. Arrow Creek flows northeast across the figure 6 northwest corner. Surprise Creek flows north-northeast in the figure 6 west half from the figure 6 south edge to the north edge. The Meadow Creek valley is located in the figure 6 southeast corner (Meadow Creek is a northeast-oriented Wolf Creek tributary better seen in figure 7 below). Coffee Creek originates in the figure 6 center south area and flows in a large northeast-oriented valley to the figure 6 east edge. The Coffee Creek valley is a northeast-oriented abandoned headcut eroded by northeast-oriented flood flow prior to headward erosion of the north-northeast oriented Surprise Creek valley. The relatively smooth Arrow Creek Bench erosion surface and erosion surfaces west of Surprise Creek suggest the region was evenly eroded by sheets of flood water prior to headward erosion of the deep Coffee Creek and Meadow Creek valleys. The Coffee Creek and Meadow Creek valleys were eroded by northeast-oriented flood flow, which came from southwest of the present day north-northeast oriented Surprise Creek valley. Headward erosion of the north-northeast oriented Surprise Creek valley then captured the northeast-oriented flood flow. The sequence of drainage history events recorded by this figure 6 evidence is consistent with the interpretation that the Judith River and Arrow Creek valleys and their tributary valleys eroded headward from the newly eroded Missouri River valley in sequence to capture southeast-oriented flood flow. However, the flood flow in figure 6 appears to have been northeast-oriented, at least at the time the present day figure 6 landscape features were formed. Why would flood flow in the figure 6 map area be northeast-oriented if the general flood flow direction was southeast-oriented? Figures 8-10 below suggest some answers.

Surprise Creek-Wolf Creek drainage divide area

Figure 7 illustrates the Surprise Creek-Wolf Creek drainage divide area south and west of the figure 6 map area. Surprise Creek flows northeast in the figure 7 southwest corner to the Surprise Creek Colony and then flows north-northeast to the figure 7 north edge. The north-oriented Surprise Creek tributary in the figure 7 southwest quadrant is Sun Creek. Wolf Creek flows northeast from the figure 7 south edge (west of Stanford) to the figure 7 north edge. Meadow Creek flows north to Dover (located along railroad near the tunnel in figure 7 northwest quadrant) and then turns to flow northeast to the figure 7 north edge and to join Wolf Creek north of the figure 7 map area. Coyote Creek is the northeast-oriented stream flowing from the figure 7 south edge (east of Stanford) to the figure 7 northeast corner. Figure 7 evidence, like the figure 6 evidence, suggests the northeast-oriented Wolf Creek and Meadow Creek valleys (and possibly the northeast-oriented Coyote Creek valley) were eroded headward by northeast-oriented flood flow. Further the figure 7 evidence suggests headward erosion of the north-northeast and north oriented Surprise Creek and Sun Creek valleys captured northeast-oriented flood flow moving across the figure 7 map area to the Meadow Creek valley (and possibly to the Wolf Creek valley as well). If so, the Meadow Creek headwaters area near Dover are located in an abandoned northeast-oriented headcut, which was abandoned when headward erosion of the Surprise Creek valley captured the northeast-oriented flood flow and diverted the flood waters north-northeast. Again the question remains, if the primary flood flow direction was to the southeast, why was the flood flow in this region, at least at the time present day landforms were eroded, oriented in a northeast direction?

Otter Creek-Wolf Creek drainage divide area

Figure 8 illustrates the Otter Creek-Wolf Creek drainage divide area south and west of the figure 7 map area and includes overlap areas with figure 7. Surprise Creek flows northeast to the Surprise Creek Colony located near the figure 8 northeast corner. Northeast-oriented Sun Creek headwaters are located in the figure 8 east center edge area. Dry Wolf Creek flows northeast in the figure 8 southeast corner and joins Wolf Creek east of the figure 8 map area (this is different Dry Wolf Creek than the Dry Wolf Creek seen in figure 5 above). Note the northwest-southeast oriented through valley east of Granite Mountain (located in the figure 8 south center) linking southeast-oriented Surprise Creek headwaters with the northeast-oriented Dry Wolf Creek valley. Lone Tree Creek flows northeast across the figure 8 center area before turning north to flow to the figure 8 north edge. North of figure 8 Lone Tree Creek joins northeast-oriented Arrow Creek. Note northwest-oriented Lone Tree Creek headwaters, which are linked by a through valley near the figure 8 south center edge area to a southeast-oriented Dry Wolf Creek tributary. Shannon Creek in the figure 8 north center area is a northeast-oriented Lone Tree Creek tributary. In the figure 8 northwest quadrant Chambers Coulee and Jackson Coulee drain eventually to Arrow Creek. The unnamed stream immediately west of Chambers Coulee is Otter Creek, which north of the figure 8 map area flows northwest to join northwest-oriented Belt Creek, which flows to the northeast-oriented Missouri River (see figures 1 and 2). Note the through valley near The Arch (north of Peterson Mountain) linking Chambers Coulee headwaters with Shannon Creek headwaters and also the through valley linking Shannon Creek headwaters with the northeast-oriented Lone Tree Creek valley. Figure 8 evidence, located along the northeast edge of the Little Belt Mountains, suggests southeast-oriented flood flow was captured in sequence by the Dry Wolf Creek, Surprise Creek, Lone Tree Creek, Shannon Creek,and Chambers Coulee valleys, and then by a reversal of southeast-oriented flood flow in the Otter Creek valley. Also note northwest-oriented Lost Creek in the Otter Creek headwaters area in the figure 8 west center. Lost Creek headwaters are linked to two saddles in the ridge connecting Clendennin Mountain and Peterson Mountain. Those two saddles are evidence of former southeast-oriented valleys, which once carried southeast-oriented flood water to what was then the newly eroded northeast-oriented Lone Tree Creek valley. The northwest-oriented Lost Creek valley was eroded by reversed flood flow when reversed flood flow on the newly beheaded Otter Creek valley alignment (which captured significant yet to beheaded southeast-oriented flood from southwest of figure 8) eroded the deep Otter Creek valley. In other words, figure 8 evidence suggests significant amounts of the northeast-oriented flood flow responsible eroding the northeast-oriented Arrow Creek and Judith River tributary valleys was captured in the region which is today the Little Belt Mountains.

Belt Creek-Dry Wolf Creek drainage divide area

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

Figure 9 illustrates the Dry Wolf Creek headwaters area located south of the figure 8 map area and located in the heart of the Little Belt Mountains. Big Baldy Mountain is the high peak located in the western half of the figure 9 northeast quadrant. Dry Wolf Creek headwaters are located southeast of Big Baldy Mountain and flow northeast and north to the figure 9 north edge. A northwest-oriented Dry Wolf Creek headwaters tributary is linked by a high level through valley (or saddle) between Tepee Butte and Yogo Peak to south-and southeast-oriented Warm Springs Creek, which flows to the east and northeast-oriented Middle Fork Judith River. The east-oriented stream east of Yogo Peak is Yogo Creek, which also flows east and southeast to the Middle Fork Judith River. Northeast of Yogo Peak are more high level through valleys (or saddles) notched in the high ridge between Yogo Peak and Bandbox Mountain, which link northwest-oriented Dry Wolf Creek tributaries with southeast-oriented Yogo Creek tributaries. The northwest and north-northwest oriented stream located near the red highway in the figure 9 west half is Belt Creek, which flows northwest to eventually reach the northeast-oriented Missouri River (see figures 1 and 2). The west-oriented stream west of Tepee Butte, which flows to join northwest-oriented Belt Creek, is Jefferson Creek. Note how Jefferson Creek is linked by high level through valleys (or saddles) notched into the high ridge between Tepee Butte and Big Baldy Mountain to northeast-oriented Dry Wolf Creek headwaters.

• The high level through valleys (or saddles) notched into the high level ridges provide evidence of drainage routes that existed prior to development of the present day drainage system. In brief the figure 9 region was crossed by an immense southeast-oriented flood as the Little Belt Mountains were beginning to emerge as an upland region. Why would a mountain range emerge while being eroded by an immense flood? 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 mountains 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.

• However the Little Belt Mountains emerged southeast-oriented flood flow moving along the present day Belt Creek alignment entered the figure 9 map area and was captured by headward erosion of the Middle Fork Judith River valley and its various tributary valleys, including Warm Springs Creek and Yogo Creek. Later headward erosion of the Dry Wolf Creek valley also captured the southeast-oriented flood flow. At that time the deep Missouri River had eroded headward into the region illustrated in figure 3 and the Judith River valley and its tributary valleys had eroded headward into the figure 9 map area, but Missouri River headward erosion had not yet beheaded and reversed southeast-oriented flood flow on the Belt Creek alignment. When headward erosion of the deep Missouri River valley did behead southeast-oriented flood flow on the Belt Creek alignment there was a major flood flow reversal. Flood waters on the northwest end of the beheaded flood flow route reversed flow direction to flow northwest to the newly eroded and much deeper northeast-oriented Missouri River valley. This massive flood flow reversal was probably greatly aided by emergence of the Little Belt Mountains as a significant mountain region. Reversed flow flood waters also captured yet to be beheaded flood waters from flood flow routes further to the south and southwest and with the aid of such captured yet to be beheaded flood water were able to erode a significant northwest-oriented Belt Creek drainage basin and also to create the present day Belt Creek-Judith River drainage divide.

Belt Creek-Middle Fork Judith River drainage divide area

Figure 10: Belt Creek-Middle Fork Judith River drainage divide area. United States Geological Survey map digitally presented using National Geographic Society TOPO software.

Figure 10 illustrates the Belt Creek-Middle Fork Judith River drainage divide area southeast of the figure 9 map area and includes overlap areas with figure 9. Tepee Butte is located in the figure 10 north center area with Yogo Peak located northeast of Tepee Butte. Yogo Creek flows east-southeast from the Yogo Peak area to the figure 10 east edge and then southeast to join the Middle Fork Judith River. Warm Springs Creek flows south and southeast from near Yogo Peak to join the east-southeast oriented Middle Fork Judith River, which flows to the figure 10 east edge and east of figure 10 turns northeast to flow eventually to the Missouri River. The northeast-oriented Lost Fork (Judith River) is located in the figure 10 southeast corner. West-southwest oriented Jefferson Creek flows from the Tepee Butte area to join northwest-oriented Belt Creek in the figure 10 northwest quadrant. Belt Creek originates near Kings Hill Pass and flows northeast and northwest near the red highway to the figure 10 northwest corner. South-oriented drainage south of Kings Hill Pass is Sheep Creek, which south of figure 10 turns west and then northwest and eventually joins northwest-oriented Belt Creek. Through valleys illustrated and described in the North Fork Smith River-North Fork Musselshell River drainage divide area essay link the Sheep Creek valley with the southwest-oriented North Fork Smith River valley (which drains to the northwest-oriented Smith River valley) and to the southeast-oriented North Fork Musselshell River valley. To understand the figure 10 drainage history it is necessary to think in terms of an immense southeast-oriented flood flowing across the entire figure 10 map area to what was then a deep southeast-oriented valley eroding headward along the present day Musselshell River valley alignment (the Little Belt Mountains had not yet emerged as an obstacle to the flood flow). Headward erosion of the deep Judith River valley and its deep tributary valleys then eroded into the figure 10 map area to progressively capture increasing amounts of the immense southeast-oriented flood flow. About the time headward erosion of the Judith River tributary valleys had reached the stage seen in figure 10 southeast-oriented flood flow on the Belt Creek alignment was beheaded and reversed. Flood waters on the northwest end of the beheaded flood flow route (northwest of Kings Hill Pass) reversed flow direction to flow northwest to the newly eroded and much deeper Missouri River valley. This reversal was probably aided by emergence of the Little Belt Mountains at that time. However, southeast-oriented flood flow on the present day northwest-oriented Sheep Creek and Smith River alignments had not yet been beheaded and continued to flow into the figure 10 map area and was captured by reversed flow on the newly reversed Belt Creek alignment. This captured yet to be beheaded flood flow helped erode the northwest-oriented Belt Creek valley. The process was repeated when flood flow on the Sheep Creek alignment was reversed, and again when flood flow on the Smith River alignment was beheaded.

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.