Yellowstone River-Bighorn River drainage divide area landform origins, south central Montana, USA

· Bighorn River, Montana, Yellowstone River
Authors

A geomorphic history based on topographic map evidence

Abstract:

The Montana Yellowstone River-Bighorn River drainage divide area discussed here is located north of Williams Coulee, which drains southeast to the Bighorn River, and east of Fly Creek, which drains northwest to the Yellowstone River. Although detailed topographic maps of the Yellowstone River-Bighorn 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 Yellowstone River-Bighorn 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 Yellowstone 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 Montana Yellowstone River-Bighorn River drainage divide area landform origins. 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 Yellowstone River-Bighorn River drainage divide area landform evidence will be regarded as evidence supporting the “thick ice sheet that melted fast” paradigm.

Yellowstone River-Bighorn River drainage divide area location map

Figure 1: Yellowstone River-Bighorn 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 a Yellowstone River-Bighorn River drainage divide area location map and illustrates a region in southern Montana and northern Wyoming. The Yellowstone River flows from Billings in a northeast direction to Miles City and then to the figure 1 northeast corner. The Bighorn River originates in Wyoming south of the figure 1 map area and enters the figure 1 map area at Worland, Wyoming. After flowing north-northwest to the Montana state line the Bighorn River turns to flow northeast through the Bighorn Canyon National Recreation Area and then north-northeast to join the northeast-oriented Yellowstone River at Bighorn, Montana. The Yellowstone River-Bighorn River drainage divide area discussed here is located almost entirely north and east of a line extending northwest from Hardin, Montana to Pompeys Pillar, Montana. Based on evidence from hundreds of Missouri River drainage basin landform origins research project essays published on this website landform evidence illustrated here is interpreted in the context of an immense southeast-oriented flood flowing across the figure 1 map area and which was systematically captured and diverted northeast by headward erosion of deep valleys eroded into a topographic surface at least as high as the figure 1 region highest elevations today. The northeast-oriented Yellowstone River valley was one of the deep valleys that eroded southwest to capture the southeast-oriented flood water and to divert the flood flow northeast. North-oriented Yellowstone River tributary valleys, including the Bighorn River valley, eroded south and southwest from the actively eroding Yellowstone River valley head to capture yet to be beheaded flood flow south and southwest of the deep Yellowstone River valley head. Headward erosion of the north-northeast oriented Bighorn River valley first captured the southeast-oriented flood flow and diverted the flood waters to what was then the actively eroding Yellowstone River valley head. As the deep Yellowstone River valley head eroded southwest it captured the southeast-oriented flood waters moving to the newly eroded Bighorn River valley. Flood waters on the northwest ends of the beheaded flood flow routes reversed flow direction to flow northwest to the newly eroded Yellowstone River valley. Detailed maps below provide evidence supporting this interpretation. This essay only addresses Yellowstone River-Bighorn River drainage divide area evidence northeast of the Fly Creek-Williams Coulee through valley illustrated in detailed maps below. The Bighorn River-Tullock Creek drainage divide area essay describes the drainage divide area located east of the drainage divide area discussed here and the Rosebud and Treasure County Musselshell River-Yellowstone River drainage divide area essay describes the drainage divide located northeast of the drainage divide area discussed here. Essays can be found under appropriate river names on the sidebar category list.

Yellowstone River-Bighorn River drainage divide area detailed location map

Figure 2: Yellowstone River-Bighorn River 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 Yellowstone River-Bighorn River drainage divide area discussed here. Yellowstone, Treasure and Big Horn Counties are located in Montana. The northeast oriented Yellowstone River flows from the figure 2 west edge (south half) through Billings to Ballantine, Pompeys Pillar, Custer and Bighorn, Montana before turning east in the figure 2 northeast corner. The north-northeast oriented Bighorn River flows from the figure 2 south edge (center) through the Crow Indian Reservation to Hardin and then north-northeast to join the northeast oriented Yellowstone River at Bighorn. The Yellowstone River-Bighorn River drainage divide area discussed here is the Pine Ridge area located northeast of the railroad which extends northwest from Hardin to Ballantine. Figure 2 shows numerous southeast-oriented Yellowstone River tributaries and Bighorn River tributaries (especially in the region southeast of Pine Ridge). Figure 2 also shows northwest-oriented tributaries to northeast and other north oriented major drainage routes. This southeast and northwest drainage alignment is evidence the northeast oriented Yellowstone River valley (and the north-northeast oriented Bighorn River valley) eroded headward to capture southeast-oriented flood flow. The southeast-oriented tributary valleys were eroded by southeast-oriented flood flow moving into the newly eroded valleys and the northwest-oriented tributary valleys were eroded by reversals of flood flow on the northwest ends of beheaded southeast-oriented flood flow routes. Because flood waters move in and erode anastomosing (or inter-connected) channels reversed flood flow on a beheaded flood flow route could capture flood flow from yet to be beheaded flood flow routes. Such captures of yet to be beheaded flood flow could enable the reversed flood flow routes to erode much deeper and larger northwest-oriented valleys than might otherwise be possible. Often evidence for such flow reversals and captures can be found on detailed topographic maps. Detailed maps below start with the northeast end of the Yellowstone River-Bighorn River drainage divide area, where the Bighorn River joins the Yellowstone River, and then progress southwest along the drainage divide area in the Pine Ridge area and conclude by looking at the Fly Creek drainage basin, which marks the western extent of the Yellowstone River-Bighorn River drainage divide area discussed here. Immediately west of the Fly Creek drainage basin north end is the north-oriented Arrow Creek drainage basin and west of the Fly Creek drainage basin south end is the north-oriented Pryor Creek drainage basin. This essay concludes with a look at the Pryor Creek-Fly Creek drainage divide area.

Northeast end of Yellowstone River-Bighorn River drainage divide area

Figure 3: Northeast end of Yellowstone River-Bighorn River drainage divide area. United States Geological Survey map digitally presented using National Geographic Society TOPO software.

Figure 3 illustrates the northeast end of the Yellowstone River-Bighorn River drainage divide area. The northeast-oriented Yellowstone River flows from the figure 3 west edge (south half) to the figure 3 north edge (east half). The Bighorn River flows north-northeast from the figure 3 south edge to join the Yellowstone River near Bighorn, Montana, which is located near the figure 3 north edge. With the exception of the Bighorn River most Yellowstone River tributaries from the south and shown in figure 3 are northwest oriented and most tributaries from the north are southeast oriented. Most Bighorn River tributaries from the west are southeast oriented or have southeast oriented valley segments and most Bighorn River tributaries from the east are northwest oriented. The southeast and northwest-orientations of the Yellowstone River and Bighorn River tributaries is evidence the deep Yellowstone River and Bighorn River valleys eroded headward across multiple channels of southeast-oriented flood flow such as might be found in a southeast-oriented anastomosing channel complex. Shallow through valleys notched into the Yellowstone River-Bighorn River drainage divide link headwaters of northwest-oriented Yellowstone River tributaries with headwaters of southeast-oriented Bighorn River tributaries. Northwest-oriented tributary valleys were eroded by reversals of flood flow on the northwest ends of beheaded southeast-oriented flood flow channels. Because flood waters were moving in anastomosing (or interconnected) channels reversed flow in one channel could capture yet to be beheaded flood flow from adjacent channels. Such captures of yet to be beheaded flood flow sometimes enabled reversed flow channels to erode significant northwest-oriented valleys, such as the northwest-oriented Tullock Creek valley extending from the figure 3 east edge center to where the Bighorn River and Yellowstone River meet near Bighorn, Montana. Figure 3 evidence suggests the north-northeast oriented Bighorn River valley eroded south-southwest slightly in advance of Yellowstone River valley headward erosion to the southwest. Headward erosion of the deep northeast-oriented Yellowstone River captured all of the southeast-oriented flood flow, beheading the flood flow routes to newly eroded north-northeast oriented Bighorn River valley.

Northeast end of Yellowstone River-Bighorn River drainage divide area at Pine Ridge

Figure 4: Northeast end of Yellowstone River-Bighorn River drainage divide area at Pine Ridge. United States Geological Survey map digitally presented using National Geographic Society TOPO software.

Figure 4 illustrates the northeast end of the Yellowstone River-Bighorn River drainage divide area at Pine Ridge south and west of the figure 3 map area and includes overlap areas with figure 3. The northeast-oriented Yellowstone River is located in the figure 3 northwest corner. The north-northeast oriented Bighorn River is located in the figure 4 southeast corner. Pine Ridge is the drainage divide between the Yellowstone River and the Bighorn River. Yellowstone River tributaries from the south are predominantly northwest oriented and their valleys were eroded by reversals of flood flow on the northwest ends of beheaded southeast-oriented flood flow routes. Bighorn River tributaries from the west are predominantly southeast oriented and their valleys were eroded by southeast-oriented flood flow moving into what was then the newly eroded Bighorn River valley. The north-northeast oriented Bighorn River valley eroded south-southwest slightly in advance of headward erosion of the deep Yellowstone River valley to the northwest. Southeast-oriented tributaries provide evidence that southeast-oriented flood flow did enter the newly eroded north-northeast oriented Bighorn River valley. However, the southeast-oriented tributary valleys are not deep or lengthy, which suggests southeast-oriented flood flow was beheaded and diverted elsewhere soon after formation of the deep north-northeast oriented Bighorn River valley. A close look at the drainage divide reveals multiple shallow through valleys notched into the ridge, which link northwest-oriented Yellowstone River tributaries with the southeast-oriented Bighorn River tributaries. The through valleys provide additional evidence that southeast oriented flood waters once moved on a topographic at least as high as the present day drainage divide to what was at that time the newly eroded and deep north-northeast oriented Bighorn River valley (and the figure 4 northeast-oriented Yellowstone River valley did not yet exist). Headward erosion of the deep northeast-oriented Yellowstone River valley then captured the southeast-oriented flood flow and reversals of flood flow on northwest ends of beheaded southeast-oriented flood flow routes eroded northwest-oriented Yellowstone River tributary valleys.

Yellowstone River-Bighorn River drainage divide area southeast of Pine Ridge

Figure 5: Yellowstone River-Bighorn River drainage divide area southeast of Pine Ridge. United States Geological Survey map digitally presented using National Geographic Society TOPO software.

Figure 5 illustrates the Yellowstone River-Bighorn River drainage divide south of the figure 4 map area and includes overlap areas with figure 4. The north-oriented Bighorn River is located along the figure 5 east edge. Note multiple southeast-oriented tributaries to the north-oriented Bighorn River. These southeast-oriented (or barbed) tributaries provide evidence the north-oriented Bighorn River valley eroded headward to capture southeast-oriented flood flow. Northwest-oriented streams in the figure 5 northwest corner area are Yellowstone River tributaries. Northeast-oriented Pine Ridge is the Yellowstone River-Bighorn River drainage divide. A close look at the Pine Ridge drainage divide reveals shallow through valleys linking headwaters of northwest-oriented Yellowstone River tributaries with headwaters of southeast-oriented Bighorn River tributaries. Figure 5 evidence can be best explained in the context of a southeast-oriented flood moving across the entire figure 5 map area on a topographic surface at least as high as the highest figure 5 elevations today. Headward erosion of the deep north-oriented Bighorn River valley then captured the southeast-oriented flood flow and diverted the flood waters north and northeast. Flood waters on the northwest ends of beheaded flood flow routes reversed flow direction to erode northwest oriented Bighorn River tributary valleys (see Bighorn River tributary orientations from the east located along the figure 5 east edge). Subsequently headward erosion of the deep Yellowstone River valley captured southeast-oriented flood flow to the newly eroded north-oriented Bighorn River valley. Flood waters on the northwest ends of the beheaded southeast-oriented flood flow routes reversed flow direction to erode northwest-oriented Yellowstone River tributary valleys. Some of these reversed flow channels captured flood waters from yet to be beheaded flood flow routes further to the southwest. Such captured (yet to be beheaded) flood waters sometimes eroded northeast-oriented headwaters valleys to the northwest-oriented reversed flow tributary valleys. An example of such a northeast-oriented headwaters valley is located in the section 36 area located just west of the word “Ridge”.

Yellowstone River-Bighorn River drainage divide area northwest of Pine Ridge

Figure 6: Yellowstone River-Bighorn River drainage divide area northwest of Pine Ridge. United States Geological Survey map digitally presented using National Geographic Society TOPO software.

Figure 6 illustrates Yellowstone River northwest-oriented tributaries west of the figure 5 map area and includes overlap areas with figure 5. The northeast-oriented Yellowstone River is located in the figure 6 northeast corner. Fly Creek is the northwest-oriented Yellowstone River tributary located adjacent to the railroad and highway in the figure 6 southwest corner. Fly Creek represents the western drainage basin discussed in this Yellowstone River-Bighorn River drainage divide essay and is featured in additional figures below. Northwest-oriented Yellowstone River tributary valleys were eroded by reversals of flood flow on northwest ends of beheaded southeast-oriented flood flow routes. Northeast-oriented Pine Ridge is located in the figure 6 southeast corner area. Southeast-oriented drainage in the figure 6 southeast corner flows to the north-oriented Bighorn River (see figure 5). The source of the southeast-oriented flood waters cannot be determined from evidence presented here. However, the hundreds of Missouri River drainage basin landform origins research project essays when taken as a group can be used to trace flood waters toward their source. A logical flood water source would be rapid melting of a thick North American ice sheet, where the thick ice sheet was located in a deep ice sheet created “hole” in the North American continent corresponding approximately with the North American region usually recognized to have been glaciated. Such a flood water source would not only explain the immense southeast-oriented floods required to erode landscape features described in this and other similar essays, but would also explain why deep valleys were eroding headward to capture the immense southeast-oriented floods and to divert the flood waters further and further to the northeast. If correct, flood waters were being diverted northeast into space in the deep “hole” the rapidly melting ice sheet had once occupied. At the same time evidence in this essay and other Missouri River drainage basin research project essay also shows flood waters were deeply eroding the deep “hole’s” southwest wall. While not pertinent to the Yellowstone River-Bighorn River drainage divide area at least for a period of time flood waters entering the deep “hole”  made another U-turn and flowed south, before being captured and diverted further north to eventually flow north across the deep “hole” floor.

Fly Creek-Williams Coulee drainage divide area southwest of Pine Ridge

Figure 7: Fly Creek-Williams Coulee drainage divide area southwest of Pine Ridge. United States Geological Survey map digitally presented using National Geographic Society TOPO software.

Figure 7 illustrates the Fly Creek-Williams Coulee drainage divide south of figures 5 and 6 and includes overlap areas with figures 5 and 6. Southeast-oriented Williams Coulee is located in the figure 7 southeast corner and drains to the north-northeast oriented Bighorn River (see figure 8 below). Fly Creek flows north from the figure 7 south edge (center west) and in the figure 7 north half follows the railroad to the figure 7 north edge (near Corinth) and then flows north-northwest and north to join the northeast-oriented Yellowstone River west of Pompeys Pillar. A prominent northwest-southeast oriented through valley at Toluca, Montana links the north-oriented Fly Creek valley with southeast-oriented Williams Coulee. The through valley is a major transportation route and provides evidence large quantities of flood water once flowed south along the present day north-oriented Fly Creek alignment and then southeast along the present day Williams Coulee alignment. Depth of the through valley suggests it was eroded after headward erosion of the deep north-northeast oriented Bighorn River valley captured southeast-oriented flood waters, but before headward erosion of the deep northeast-oriented Yellowstone River valley beheaded the southeast-oriented flood flow. Headward erosion of the deep northeast-oriented Yellowstone River valley did subsequently behead the southeast-oriented flood flow and caused a reversal of flood waters on the northwest ends of the beheaded flood flow routes. That reversal of flood flow eroded the north-oriented Fly Creek valley and was aided by capture of significant amounts of yet to be beheaded flood flow from southeast-oriented flood flow routes further to the southwest. Evidence for the captures of that yet to be beheaded southeast-oriented flood flow is provided in figures 9 and 10 below.

Williams Coulee drainage route to Bighorn River

Figure 8: Williams Coulee drainage route to Bighorn River. United States Geological Survey map digitally presented using National Geographic Society TOPO software.

Figure 8 illustrates the Williams Coulee drainage basin downstream from Toluca and the north-northeast oriented Bighorn River valley southeast of the figure 7 map area and also includes overlap areas with figure 7. The north-northeast oriented Bighorn River is located in the figure 8 east half. Southeast-oriented Williams Coulee flows from the figure 8 west edge (center) to join the Bighorn River near Hardin, Montana. South of Williams Coulee is southeast-oriented Leggins Creek and the northeast-oriented North Fork of Leggins Creek. The Williams Coulee-Leggins Creek drainage divide provides evidence the southeast-oriented flood flow moving into what was then the newly eroded north-northeast oriented Bighorn River valley was moving in an ever-changing southeast-oriented anastomosing channel complex. Note how southeast-oriented Leggins Creek tributaries (northwest of the North Fork) originate along an asymmetric drainage divide with southeast-oriented Williams Coulee. The evidence shows headward erosion of the deeper Williams Coulee valley  beheaded southeast-oriented flood flow to the Leggins Creek valley. The evidence also indicates that at one time flood waters were moving from what is now the Williams Coulee drainage basin to what is now the Leggins Creek drainage basin, and at least for a period of time flood waters were also moving southeast along the present day Williams Coulee route. Figure 8 evidence also shows a large erosional residual standing downstream from where the flood waters split, which indicates the southeast-oriented flood waters were moving in separate, but interconnected channels (which describes an anastomosing channel complex). Flood waters then eroded the Williams Coulee valley deeper, which beheaded flood flow to the Leggins Creek valley, which is also how an ever-changing anastomosing channel complex evolves over time.

Pryor Creek-Fly Creek drainage divide area west of Toluca

Figure 9: Pryor Creek-Fly Creek drainage divide area west of Toluca. United States Geological Survey map digitally presented using National Geographic Society TOPO software.

Figure 9 illustrates the Pryor Creek-Fly Creek drainage divide west of the large Toluca through valley shown in figure 6 and includes overlap areas with figure 6. Fly Creek flows north in the figure 9 east half. Named Fly Creek tributaries from the west (starting in the north) are southeast-oriented Spring Creek, east-oriented Alkali Creek, southeast-oriented North Telegraph Creek, and east-northeast oriented Telegraph Creek. The north-northeast drainage in the figure 9 northwest corner area is the head of north-oriented Arrow Creek. West-oriented drainage by the highway (near Indian Arrow) is northwest-oriented Indian Creek, which flows to north-oriented Pryor Creek (see figure 2). Northwest-oriented Broken Leg Creek is south of Indian Creek and northwest-oriented Alkali Creek is south of Broken Leg Creek (and is in the figure 9 southwest corner area). Note the southeast-facing escarpment bounding the present day Fly Creek drainage basin. That southeast-facing escarpment is an abandoned headcut, which was being eroded by large volumes of southeast-oriented flood waters moving to the newly eroded north-northeast-oriented Bighorn River valley. The flood waters were literally stripping the landscape as they flowed across the figure 9 map area. Flood flow was coming from northwest of the present day Yellowstone River valley, which means the northeast-oriented Yellowstone River valley (immediately northwest of the figure 9 map area) did not exist when the headcut was being actively eroded. Headcut erosion of the southeast-oriented headcut ceased when the deep northeast-oriented Yellowstone River valley eroded southwest and beheaded the southeast-oriented flood flow. Flood waters on the northwest ends of the beheaded southeast-oriented flood flow routes then reversed flow direction to move northwest and north to the newly eroded Yellowstone River valley. The reversed flood waters eroded the north-oriented Pryor Creek valley and the northwest-oriented Indian Creek, Broken Leg Creek, and Alkali Creek tributary valleys. Abandoned headcuts such as this figure 9 abandoned headcut can be found throughout the Rocky Mountain and Northern Great Plains regions and once located on detailed topographic maps can be used to quickly plot flood flow movements without going through the detailed analysis I doing with these Missouri River drainage basin research project essays.

Pryor Creek-Fly Creek drainage divide area southwest of Toluca

Figure 10: Pryor Creek-Fly Creek drainage divide area southwest of Toluca. United States Geological Survey map digitally presented using National Geographic Society TOPO software.

Figure 10 illustrates the Pryor Creek-Fly Creek drainage divide area south and west of the figure 9 map area and includes overlap areas with figure 9. Fly Creek originates as northeast-oriented stream (just north of the first “R” in RESERVATION) and flows to the figure 10 east edge before turning north as seen in figure 9. Northeast and east-southeast oriented Big Woody Creek is located south of Fly Creek and flows to the north oriented Bighorn River. The East Fork of Pryor Creek and several tributaries flow northeast from the figure 10 southwest corner area and then turn north before flowing northwest to the figure 10 northwest corner and then to north oriented Pryor Creek. The figure 10 map area illustrates what was developing as another large through valley linking the northeast-oriented Yellowstone River valley with the north-northeast oriented Bighorn River valley. Large volumes of southeast-oriented flood flow were moving southeast to erode what was then a deep southeast-oriented Big Woody Creek valley headward from what was then the newly eroded north-northeast oriented Bighorn River valley. What was then a deep northeast-oriented Fly Creek valley next eroded headward into the region to capture southeast-oriented flood flow moving to the actively eroding Big Woody Creek valley. It is possible the northeast-oriented Fly Creek valley eroded headward from what was then an actively eroding southeast-oriented Leggins Creek or Williams Coulee valley and was later captured by reversed flood flow when headward erosion of the Yellowstone River valley beheaded flood flow on the north-oriented Fly Creek valley alignment. Regardless of exact timing, headward erosion of the northeast-oriented Fly Creek valley was halted when headward erosion of the deep Yellowstone River valley beheaded the southeast-oriented flood flow to the figure 10 map area. Flood waters on the northwest ends of the beheaded flood flow routes then reversed flow direction to flow northwest and north to the newly eroded Yellowstone River valley. The northwest-oriented East Fork Pyror Creek valley was eroded by such reversed flood flow. The north- and northeast-oriented East Fork Pryor Creek and tributary valleys eroded headward to capture yet to beheaded southeast-oriented flood flow on flood flow routes further to the south and southwest (remember the Yellowstone River valley eroded headward from the northeast to the southwest and southeast-oriented flood flow west of the Yellowstone River valley head would be moving south of the actively eroding valley head).

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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