South Fork Musselshell River-Cottonwood Creek drainage divide area landform origins, Crazy Mountains, Montana, USA

· Crazy Mountains, Montana, Musselshell River
Authors

A geomorphic history based on topographic map evidence

Abstract:

The South Fork Musselshell River-Cottonwood Creek drainage divide area discussed here is located in Montana, USA and includes areas in the northern Crazy Mountains. Although detailed topographic maps of the South Fork Musselshell River-Cottonwood 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 South Fork Musselshell River-Cottonwood 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 South Fork Musselshell River-Cottonwood Creek drainage divide ended when headward erosion of the 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 South Fork Musselshell River-Cottonwood Creek drainage divide area landform origins, 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 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 the South Fork Musselshell River-Cottonwood Creek drainage divide area landform evidence will be regarded as evidence supporting the “thick ice sheet that melted fast” paradigm.

South Fork Musselshell River-Cottonwood Creek drainage divide area location map

Figure 1: South Fork Musselshell River-Cottonwood 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 location map for the South Fork Musselshell River-Cottonwood Creek drainage divide area. Figure 1 illustrates an area in south central Montana and northwest Wyoming. The South Fork Musselshell River begins north of the Crazy Mountains. The South Fork Musselshell River (not labeled on figure 1) flows in a northeast direction to join the North Fork Musselshell River near Martinsdale, and then to flow as the Musselshell River east-southeast and northeast to Roundup and Melstone. At Melstone the Musselshell River turns to flow north-northwest to join the east-oriented Missouri River (not visible in figure 1). The Missouri River originates at Three Forks (located near the figure 1 south edge (west half) and flows north and northwest through Canyon Ferry Lake (a large reservoir) and the Gates of the Rocky Mountains to Wolf Creek before turning to flow northeast. North of figure 1 the Missouri River turns to flow southeast and east-northeast and southeast and is located north of the figure 1 map area. The Yellowstone River flows northwest and northeast from Yellowstone National Park (the yellow area in northwest Wyoming) to Livingston and Big Timber, Montana and then southeast and northeast to Billings and Custer. Cottonwood Creek is the unlabeled stream originating at north end of the Crazy Mountains near Loco Peak and flowing north to join the South Fork Musselshell River near Martinsdale. The South Fork Musselshell River-Cottonwood Creek drainage divide area discussed here includes areas in the northern Crazy Mountains area.

  • Essays describing regions near the South Fork Musselshell River-Cottonwood Creek drainage divide area include the North Fork Smith River-North Fork Musselshell River and the South Fork Smith River and South Fork Musselshell River drainage divide area landform origins essays and have interpreted landform evidence in the context of immense southeast-oriented flood event (essays can be found under appropriate river names on the sidebar category list). Those essays suggest mountain ranges such as the Crazy Mountains did not present obstacles to the southeast-oriented flood movements and suggest the mountain ranges emerged as flood waters crossed the region. Such emergence could have occurred if the mountains were buried in easily eroded sediments and/or ice, which the flood waters removed, and/or if the mountain ranges were uplifted as flood waters eroded the region. South Fork Musselshell River-Cottonwood Creek drainage divide evidence is interpreted likewise (i.e., flood waters initially moved across a topographic surface where the present day Crazy Mountains were not obstacles to southeast-oriented flood flow).
  • Headward erosion of the deep Yellowstone River valley and subsequently the deep Musselshell River valley captured southeast-oriented flood flow as the Big Belt and Crazy Mountains began to emerge. Southeast oriented flood water was channeled between the Big Belt and Crazy Mountains as flood waters flowed south to what was then the newly eroded Yellowstone River valley. At the same time flood waters were channeled between the Castle Mountains (not labeled on figure 1, but Elk Peak, which is located north of the Crazy Mountains is the highest point in the Castle Mountains) and the Crazy Mountains as they flowed to the actively eroding Musselshell River valley. Headward erosion of the deep Missouri River valley then beheaded the major southeast-oriented flood flow moving flood waters southeast along the west flank of the Castle and Crazy Mountains. Flood waters on the northwest end of that beheaded flood flow route reversed flow direction to erode the northwest and north oriented Smith River valley. Reversed flood flow probably captured yet to be beheaded southeast-oriented flood flow moving on flood flow routes further to the south. With the aid of that captured flood water a significant north and northwest-oriented Smith River drainage basin evolved and the Smith River- Musselshell River drainage divide was created.

South Fork Musselshell River-Cottonwood Creek drainage divide area detailed location map

Figure 2: South Fork Musselshell River-Cottonwood Creek drainage divide area detailed location map. United States Geological Survey map digitally presented using National Geographic Society TOPO software. 

Figure 2 provides a somewhat more detailed map of the South Fork Musselshell River-Cottonwood Creek drainage divide area. Meagher County is located in the figure 2 northwest quadrant, Wheatland County is located in the figure 2 northeast area. The South Fork Musselshell River begins east of Reservation Mountain, which is located south of Loweth and flows northeast and joins the northeast oriented North Fork Musselshell River near Martinsdale to form the southeast oriented Musselshell River. Of most interest in this essay is the Bozeman Fork of the South Fork Musselshell River, which originates near Bald Ridge and which flows northwest and north to join the South Fork Musselshell River between Loweth and Lennep. Cottonwood Creek flows north from the Bald Ridge area to join the South Fork Musselshell River between Lennep and Martinsdale. This essay illustrates and discusses evidence suggesting southeast oriented flood waters crossed what are today high drainage divides between the Bozeman Fork and Cottonwood Creek and also between various Cottonwood Creek tributaries. Note the south-oriented drainage routes south and southeast of Ringling and west of the Crazy Mountains (e.g. Potter Creek). Those streams flow to the south-oriented Shields River, which joins the Yellowstone River near Livingston. The southwest-oriented stream at Ringling is Sixteenmile Creek, which flows to the figure 2 southwest corner area and then turns west to join the northwest-oriented Missouri River (west of figure 2). The northwest oriented Smith River (which flows to the figure 2 northwest corner) eventually joins the northeast oriented Missouri River (see figure 1). Drainage divides in the Bald Ridge area include divides between the west-oriented Sixteenmile Creek (flowing to the northwest-oriented Missouri River), south-oriented Shields River (flowing to the southeast and northeast oriented Yellowstone River), and the northeast-oriented South Fork Musselshell River (flowing to the southeast-, northeast- and north-northwest oriented Musselshell River and then to the east-oriented Missouri River).

  • The discussion in this essay begins north of the Crazy Mountains where both the Bozeman Fork of the South Fork Musselshell River and Cottonwood Creek join the South Fork Musselshell River. Next the essay moves into the Crazy Mountains to look at evidence along what are today high drainage divides. Drainage divides with Sixteenmile Creek and the south-oriented Shields River tributaries are illustrated and discussed. The essay concludes by looking at evidence along drainage divides between Cottonwood Creek tributaries. The entire figure 2 region was deeply eroded by an immense southeast-oriented flood at a time when flood waters initially could move on a topographic surface where the present day mountain ranges did not interfere with flood flow. As flood waters eroded the figure 2 map region the Crazy Mountains emerged (perhaps by a combination of deep erosion of the surrounding materials and of uplift occurring as flood waters eroded the region). Flood waters were channeled to flow southeast along the present day Smith River alignment to the present day Shields River drainage basin and then to what was then the newly eroded Yellowstone River valley. The deep Musselshell River valley eroded headward into the figure 2 map region with the South Fork eroding into the region south of the Castle Mountains. The South Fork Musselshell River-Cottonwood Creek drainage divide was created when headward erosion of the South Fork Musselshell River valley beheaded and reversed southeast-oriented flood flow moving across the northern Crazy Mountains. Flood waters on the north and northwest ends of the beheaded flood flow routes reversed flow direction to erode northwest and north-oriented South Fork Musselshell River tributary valleys and to create present day drainage divides.

North end of South Fork Musselshell River-Cottonwood Creek drainage divide area

Figure 3: North end of South Fork Musselshell River-Cottonwood Creek drainage divide area. United States Geological Survey map digitally presented using National Geographic Society TOPO software. 

Figure 3 illustrates the north end of the South Fork Musselshell River-Cottonwood Creek drainage divide area between the Castle Mountains and the Crazy Mountains. The Castle Mountains uplift is visible in the figure 3 northwest corner. The north end of the Crazy Mountains uplift area is located in the figure 3 south center. The South Fork Musselshell River originates in the figure 3 southwest corner area between Reservation Mountain and Rimrock Reefs and flows north and northeast to Bruno, Lennep, and Groveland in the figure 3 northeast corner. The Bozeman Fork of the Musselshell River is located east of Rimrock Reefs and flows north and north-northwest from the figure 3 south edge to join the South Fork Musselshell River northeast of Bruno. Indian Creek is the major Bozeman Fork labeled west-northwest tributary. Cottonwood Creek flows northwest, northeast, and north from the figure 3 southeast corner area to join the South Fork Musselshell River at Groveland in the figure 3 northeast corner. Southwest and south-oriented drainage in the figure 3 southwest corner flows to west-oriented Sixteenmile Creek, which flows to the northwest oriented Missouri River. While not visible in maps shown in this essay, the area immediately west of the figure 3 southwest corner is a large north-south through valley, today drained at the north by the northwest oriented Smith River (which flows to the northeast-oriented Missouri River), in the middle by the west-oriented Sixteenmile Creek (which flows to the northwest-oriented Missouri River), and in the south by the south-oriented Shields River (which flows to the Yellowstone River). The South Fork Musselshell River flows eventually to the east-oriented Missouri River (see figure 1). For all practical purposes a four-way drainage divide is located in that through valley (the through valley is discussed in the South Fork Smith River-South Fork Musselshell River drainage divide area essay). A close look at figure 3 reveals northwest-oriented South Fork Musselshell River tributary valleys or tributary valley segments and also southeast-oriented tributaries from the north. This northwest-southeast tributary orientation is evidence a deep South Fork Musselshell River valley eroded headward across an immense southeast-oriented flood, where flood waters were moving on a topographic surface at least as high as the northwest-oriented tributary valley heads. The northwest- and north-oriented South Fork Musselshell River tributary valleys were eroded by reversals of flood flow on northwest and north ends of the beheaded southeast-oriented flood flow routes. Erosion of those valleys was aided by capture of yet to be beheaded southeast-oriented flood flow routes from flood flow routes further to the west. For example, the northwest-oriented Comb Creek valley was eroded by yet to be beheaded (by South Fork Musselshell River valley headward erosion) flood waters moving south on the Bozeman Fork alignment and then east on the Indian Creek alignment and then northeast on the Little Cottonwood Creek alignment. Figure 4 below provides a detailed map of the Indian Creek-Little Cottonwood Creek drainage divide area.

Indian Creek-Little Cottonwood Creek drainage divide area

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

Figure 4 provides a detailed map of the Indian Creek-Little Cottonwood Creek drainage divide area seen in less in figure 3 above. Comb Creek flows northeast to the figure 4 east center edge area and north-northwest to the figure 4 north edge. Indian Creek originates in section 36 and flows northwest and north into section 25 where it turns to flow west-northwest and west to the figure 4 west edge. Little Cottonwood Creek also originates in section 36 (northeast corner) and flows north-northeast and northeast to the figure 4 north edge. A prominent through valley in section 25 links the west-northwest oriented Indian Creek valley with a northeast-oriented Little Cottonwood Creek tributary valley. The through valley was eroded by water and is interpreted here to have been eroded by flood waters moving east-southeast in the Indian Creek valley to the northeast-oriented Little Cottonwood Creek valley. These yet to be beheaded (by headward erosion of the South Fork Musselshell River valley) southeast-oriented flood waters had been captured by reversal of flow on what was then a newly beheaded and reversed flood flow using the Comb Creek alignment (see figure 3 above). Figure 4 evidence suggests multiple capture events occurred prior to formation of the present day drainage network. For example, note northwest-oriented Deer Creek headwaters in section 24 and northwest-oriented Sawmill Creek headwaters in section 23. Also note the through valley in the section 24 south center linking the northwest-oriented Deer Creek and Sawmill Creek valleys with the northeast-oriented Little Cottonwood Creek valley. Then continue southeast from that through valley and note a through valley linking the northeast-oriented Little Cottonwood Creek valley with the northeast-oriented West Fork Comb Creek valley. Those present day high level through valleys provide evidence of a southeast-oriented flood flow route that once carried flood waters to the West Fork Comb Creek valley. A close look at figure 4 (and also at adjacent areas) reveals numerous such through valleys, all of which provide evidence of multiple southeast-oriented flood flow channels. Those southeast-oriented flood flow channels were systematically dismembers as deeper valleys eroded into what was then an emerging Crazy Mountains upland region. The Crazy Mountains upland region may have emerged as flood waters removed easily eroded sediments and/or ice from the surrounding region and/or as uplift raised the Crazy Mountains upland region.

South end of South Fork Musselshell River-Cottonwood Creek drainage divide area

Figure 5: South end of South Fork Musselshell River-Cottonwood Creek drainage divide area. United States Geological Survey map digitally presented using National Geographic Society TOPO software. 

Figure 5 illustrates the north end of the Crazy Mountains upland region and is located south of the figure 3 map area. The figure 5 map area includes overlap areas with figure 3. The Bozeman Fork of the South Fork Musselshell River is located in the figure 5 northwest quadrant and flows northwest between Bald Ridge and Box Canyon to the figure 5 northwest corner area. East of the northwest oriented Bozeman Fork in the figure 5 north center area is northwest and northeast oriented West Fork Cottonwood Creek, which joins the northwest, northeast, and north-oriented Middle Fork Cottonwood Creek and north-northeast and northwest oriented Loco Creek near the figure 5 north edge (center east). South of Bald Ridge are southwest oriented headwaters of Sixteenmile Creek, which flows west to join the northwest-oriented Missouri River (see figure 1). Also south of Bald Ridge (and linked to Sixteenmile Creek headwaters by a well-defined deep through valley is south oriented Smith Creek, which flows to the southwest and south-oriented Shields River, which flows to the Yellowstone River (see figure 1). West and southwest-oriented Shields River headwaters are located along the figure 5 south edge in the figure 5 southeast quadrant and south center area. While figure 5 appears to be about the last place one might look for evidence of a large-scale anastomosing channel complex a close look at figure 5 reveals numerous through valleys linking what are today deep and independent valleys. For example, the already mentioned through valley linking the west-oriented Sixteenmile Creek headwaters with the south-oriented Smith Creek (and Shields River) valley provides evidence flood water moving from the west once flowed through that valley and then south to what was then the newly eroded Yellowstone River valley. In the figure 5 south center area through valleys between Davey Peak and Target Rock and East of Target Rock provide evidence south-oriented flood water once moved in multiple channels from the present day Cottonwood Creek drainage basin to what is today the Shields River drainage basin. The presence of multiple channels suggests the presence of anastomosing channels. Remaining figures in this essay illustrate some of the many through valleys using more detailed maps.

  • The Crazy Mountains probably emerged as a significant flood flow obstacle as flood waters eroded the figure 5 map 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 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.

Bozeman Fork Musselshell River-West Fork Cottonwood Creek drainage divide area

Figure 6: Bozeman Fork Musselshell River-West Fork Cottonwood Creek drainage divide area. United States Geological Survey map digitally presented using National Geographic Society TOPO software. 

Figure 6 illustrates the Bozeman Fork Musselshell River drainage divide with the West Fork of Cottonwood Creek, which was seen in less detail in figure 5 above. The Bozeman Fork originates in the figure 6 center area in section 18 and flows northwest through section 13 to the figure 6 north edge. The West Fork Cottonwood Creek originates in section 19 and flows northeast through section 20 and 16 to the figure 6 east edge. The drainage divide becomes even more interesting if we notice in section 24 headwaters of southwest oriented Sixteenmile Creek, which flows west to the northwest-oriented Missouri River, and in section 19 headwaters of south-oriented Smith Creek, which flows south to the southwest and south-oriented Shields River (which flows to the east-oriented Yellowstone River). Further, a close look at figure 6 reveals shallow through valleys (or saddles) eroded into the high ridge that now serves as the drainage divide. For example, there is a shallow saddle linking the northwest-oriented Bozeman Fork valley with the south-oriented Smith Creek valley. There is also a shallow saddle linking the south-oriented Smith Creek valley with the northwest-oriented West Fork Cottonwood Creek valley. These shallow saddles provide clues that can be used in reconstructing the figure 6 drainage history. The reconstruction proposed here starts with southeast-oriented flood water flowing across the entire figure 6 map area on a topographic surface at least as high as the highest figure 6 elevations today. Obviously the figure 6 map area at that time did not stand high above the surrounding region as it does now. The present day high elevation developed as flood waters eroded the region and removed easily eroded sediments and/or ice from the surrounding region and/or the Crazy Mountains upland region was being uplifted. In either case the deep south-oriented Shields River valley eroded headward into the region to capture the southeast-oriented flood water at about the same time the deep West Fork Cottonwood Creek valley eroded headward into the region to also capture the southeast-oriented flood flow. For a time southeast-oriented flood waters using the Bozeman Fork alignment moved into section 19 and then northeast to erode the West Fork Cottonwood Creek valley. However, headward erosion of the south-oriented Smith Creek valley captured the flood flow, beheading the section 19 flood flow route to the West Fork Cottonwood Creek valley. Soon thereafter flood waters on the Bozeman Fork alignment were reversed (by events northwest of figure 6) and the reversed flood waters eroded the northwest-oriented Bozeman Fork valley. Probably the reversed flood waters captured significant yet to be beheaded flood flow from adjacent flood flow routes.

West Fork Cottonwood Creek-Middle Fork Cottonwood Creek drainage divide area

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

Figure 7 provides a detailed map of the West Fork Cottonwood Creek-Middle Fork Cottonwood Creek drainage divide area seen in less detail in figure 5 above. Figure 7 is east of figure 6 and includes overlap areas with figure 6. The West Fork Cottonwood Creek flows through section 20 to the figure 7 north center edge area. A large northwest-oriented West Fork tributary valley is located in section 21. The Middle Fork Cottonwood Creek flows northwest through Forest Lake (southeast corner area) and then turns to flow northeast through section 23 to the figure 7 northeast corner area. Bitter Creek flows west to south-oriented Smith Creek, which flows to the southwest and south-oriented Shields River. Note the through valleys linking the various drainage systems. For example, in the northeast corner of section 21 and the southeast corner of section 22 is a deep through valley eroded across the present day ridge separating the northwest-oriented West Fork Cottonwood Creek tributary valley from the northeast-oriented Middle Fork Cottonwood Creek valley. While today it is hard to image that valley as a major flood channel, it was probably eroded as such by southeast oriented flood water moving into what was then the newly eroded northeast-oriented Middle Fork Cottonwood Creek valley. Flood flow through that valley was beheaded by headward erosion of the northeast-oriented West Fork Cottonwood Creek valley and flood waters on the northwest end of the beheaded flood flow route reversed flow direction to erode the northwest-oriented West Fork tributary valley. Another interesting through valley is located near the south center edge of section 28 and links the West Fork Cottonwood Creek tributary valley with the Bitter Creek valley. Probably this valley was used by yet to be beheaded southeast and east-oriented flood water moving to what was then the newly reversed northwest-oriented West Fork Cottonwood Creek valley. Flood waters on the Bitter Creek alignment were reversed to flow west and south when headward erosion of the deep south-oriented Shields River valley entered the region and the south-oriented Smith Creek valley eroded headward from that south-oriented Shields River valley.

Middle Fork Cottonwood Creek-Loco Creek drainage divide area

Figure 8: Middle Fork Cottonwood Creek-Loco Creek drainage divide area. United States Geological Survey map digitally presented using National Geographic Society TOPO software. 

Figure 8 illustrates the Middle Fork Cottonwood Creek-Loco Creek drainage divide area north and east of the figure 7 map area and the figure 8 map area was seen in less detail in figure 5 above. Figure 8 includes overlap areas with figure 7 (see section 23 in figure 8 southwest corner). The Middle Fork Cottonwood Creek flows northeast and north-northeast from the figure 8 southwest corner area to the figure 8 north edge. Loco Creek flows northwest, north-northeast, and northwest from the figure 8 southeast quadrant to the figure 8 north center edge. The northeast-oriented West Fork Cottonwood Creek crosses the figure 8 northwest corner. The West Fork and Middle Forks of Cottonwood Creek and Loco Creek all meet to form Cottonwood Creek just north of the figure 8 map area (see figures 5 and 9). The figure 8 map area is further north than the figures 6 and 7 map areas is located on the margin of the Crazy Mountains uplift area. Northwest-southeast oriented ridges between major valleys are probably hogbacks, although valleys between those hogbacks are water eroded features. Those valleys provide evidence of multiple northwest-southeast oriented flood flow routes that were captured by headward erosion of the Loco Creek, Middle Fork, and West Fork valleys. The Loco Creek valley eroded headward across the region first. Northwest-oriented Loco Creek valley segments were probably eroded by reversals of flood flow on the northwest ends of beheaded flood flow routes. Through valleys in figure 8 provide evidence that reversed flow in the Loco Creek valley captured significant southeast-oriented flood flow moving across what is now the northeast-oriented Middle Fork Cottonwood Creek valley. Reversed flow in the Loco Creek valley also captured significant yet to be beheaded southeast-oriented flood flow from the south end of the Middle Fork Cottonwood Creek drainage basin (see figure 10 below). Headward erosion of the northeast-oriented Middle Fork Cottonwood Creek valley systematically beheaded the multiple flood flow routes to the newly reversed and actively eroding Loco Creek valley and eventually beheaded all of the flood flow routes to the Loco Creek valley. Subsequently the same process was repeated by headward erosion of the northeast-oriented West Fork Cottonwood Creek valley, which captured flood flow moving to the newly eroded Middle Fork Cottonwood Creek valley. Headward erosion of the deep Loco Creek, Middle Fork Cottonwood Creek, and West Fork Cottonwood Creek valleys was probably greatly aided by emergence of the Crazy Mountains upland region as flood waters were eroding the region. Emergence of the upland region may have occurred as flood waters removed easily eroded sediments and/or ice from the surrounding region and/or as the Crazy Mountains upland region was uplifted while flood waters eroded the region.

Cottonwood Creek-Lost Horse Creek drainage divide area

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

Figure 9 illustrates the Cottonwood Creek-Lost Horse Creek drainage divide area located north and east of the figure 8 map area and includes overlap areas with figure 8. Northwest-oriented Loco Creek, north oriented Middle Fork Cottonwood Creek, and northeast-oriented West Fork Cottonwood Creek meet in section 3 in the figure 9 southwest quadrant to form north and northeast-oriented Cottonwood Creek. Little Elk Creek flows north-northeast from section 10 in the figure 9 southeast quadrant and in the figure 9 east center area turns to flow north-northwest to section 27 and the figure 9 north edge. West of Little Elk Creek is Lost Horse Creek, which flows north across the section 10 northwest corner into section 3. In section 3 Lost Horse Creek turns to flow west into the north half of section 2 and then turns to flow north again through section 33 to section 28 and the figure 9 north edge. West of Lost Horse Creek along the figure 9 south edge is Spring Creek, which flows north through section 9 to join Lost Horse Creek in section 2. Figure 9 illustrates several well-defined northeast-oriented through valleys linking the northwest-oriented Loco Creek valley with the north-oriented Lost Horse Creek valley. These through valleys provide evidence of multiple northeast-oriented valleys that eroded headward to capture southeast-oriented flood flow, which were beheaded by headward erosion of the northwest-oriented Loco Creek valley. As previously mentioned the Loco Creek valley was probably eroded by reversed flood flow on the northwest end of a beheaded flood flow route and the beheading was done by headward erosion of the Cottonwood Creek valley. The figure 9 evidence suggests that flood flow reversal occurred as other northeast-oriented valleys were also eroding headward into the region. In other words, what was probably a southeast-oriented anastomosing channel complex of flood flow routes across what is today the northern Crazy Mountains was in the process of being captured by headward erosion of what was probably an anastomosing complex of northeast-oriented flood flow channels eroding southwest from what was then probably a newly eroded deep South Fork Musselshell River valley. In figure 9 the Little Elk Creek valley eroded headward first to capture the southeast-oriented flood flow. Next the Lost Horse Creek valley eroded headward to capture the southeast-oriented flood flow. The Cottonwood Creek-Loco Creek valley was next, with the Middle Fork Cottonwood Creek and the West Fork Cottonwood Creek valleys following in that order.

Middle Fork Cottonwood Creek-Loco Creek headwaters area

Figure 10: Middle Fork Cottonwood Creek-Loco Creek headwaters area. United States Geological Survey map digitally presented using National Geographic Society TOPO software. 

Figure 10 illustrates the Middle Fork Cottonwood Creek-Loco Creek headwaters area and is located east and south of the figure 7 map area (and includes overlap areas with figure 7). The Middle Fork Cottonwood Creek originates in section 6 (figure 10 south center area) and flows southwest before turning northwest to flow through Forest Lake to the figure 10 northwest corner area. Loco Creek originates in the southwest corner of section 32 and flows north along the section 31-section 32 boundary and then turns northeast in section 29 to flow to the figure 10 north edge. The southwest oriented stream originating in section 5 and flowing to the figure 10 south center edge area is Crandall Creek, which flows to the west oriented Shields River (located south of figure 10). Note the well-defined through valleys crossing what are today the ridges between the southwest oriented Middle Fork Cottonwood Creek valley and the north-oriented Loco Creek valley and the southwest-oriented Middle Fork Cottonwood Creek valley and the southwest-oriented Crandall Creek valley. Those through valleys further support the previously mentioned flood interpretation. Prior to being beheaded and reversed by headward erosion of the deep South Fork Musselshell River valley south-oriented flood flow was moving to what was probably a newly eroded deep west, southwest, and south-oriented Shields River valley. Flood waters were moving south on the Loco Creek valley alignment and also southeast on the Middle Fork Cottonwood Creek valley alignment to that newly eroded Shields River valley. Probably the Crazy Mountains upland region was beginning emerge and flood waters were eroding deep valleys into the emerging upland region. As previously mentioned headward erosion of the Cottonwood Creek valley first beheaded and reversed flood flow on the Loco Creek alignment. Southeast-oriented flood flow on what is today the northwest-oriented Middle Fork Cottonwood Creek valley alignment continued to flow to the Shields River valley and also was captured by reversed flow on the Loco Creek valley alignment. For a time flood waters were moving southeast in the Middle Fork alignment and then making a U-turn to flow north on the Loco Creek valley alignment. Subsequently headward erosion of the northeast-oriented Middle Fork Cottonwood Creek valley (see figures 7 and 8) beheaded the southeast-oriented Middle Fork flood flow route. Flood waters on the northwest of the beheaded flood flow route reversed flow direction to erode the northwest-oriented Middle Fork Cottonwood Creek valley segment. These captures and flood flow reversals were probably greatly aided by emergence of the Crazy Mountains upland region as flood waters were eroding the figure 10 region.

Additional information and sources of maps studied

This essay has provided only a sample of the detailed topographic map evidence supporting the flood erosion interpretation. Many additional illustrations could be provided. Readers are encouraged to look at mosaics of detailed topographic maps to see the abundance of available data. Maps used in this study were created and published by the United States Geologic Survey and can be obtained directly from the United States Geological Survey and/or from dealers offering United States Geological Survey maps. Hard copy maps can also be observed at United States Geological Survey map depositories which are located throughout the United States and elsewhere. Illustrations used here were created using National Geographic Society TOPO software and digital map data. TOPO software and map data can be obtained from the National Geographic Society and/or dealers offering National Geographic Society digital map data.

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