A geomorphic history based on topographic map evidence

The Sarpy Creek-Rosebud Creek drainage divide area is located in Montana, USA. Although detailed topographic maps of the Sarpy Creek-Rosebud 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 Sarpy Creek-Rosebud Creek drainage divide area is interpreted to have been eroded during immense southeast-oriented flood events, the first of which flowed on a topographic surface at least as high as the highest points in the present-day drainage divide area. Flood erosion across the drainage divide ended when headward erosion of the deep Yellowstone River valley captured all southeast-oriented flood flow.

Introduction:

• The purpose of this essay is to use topographic map interpretation methods to explore Montana Sarpy Creek-Rosebud Creek 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 Sarpy Creek-Rosebud Creek drainage divide area landform evidence will be regarded as evidence supporting the “thick ice sheet that melted fast” paradigm.

Sarpy Creek-Rosebud Creek drainage divide area location map

Figure 1: Sarpy Creek-Rosebud 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 Sarpy Creek-Rosebud Creek drainage divide area location map and illustrates a region in eastern Montana. The state of Wyoming is located south of Montana. The Yellowstone River flows from Billings in a northeast direction to Glendive, located near the figure 1 northeast corner. Rosebud Creek originates in the Wolf Mountains area of Montana (just north of the Wyoming state line) and flows north, northeast, and northwest to join the Yellowstone River at Rosebud, Montana. Sarpy Creek originates west of Bushby, Montana and flows north to join the Yellowstone River between Hysham and Sanders. Between Sarpy Creek and Rosebud Creek is an unnamed north-northwest oriented Yellowstone River tributary, which on more detailed maps is named as Armells Creek. Figure 1 illustrates southeast and northwest-oriented Yellowstone River tributaries. The southeast and northwest-orientation of tributary valleys is evidence the northeast-oriented Yellowstone River valley eroded southwest across multiple southeast-oriented flood flow routes, such as might be found in a large-scale flood-formed anastomosing channel complex. Northwest-oriented tributary valleys were eroded by reversed flood flow on northwest ends of beheaded flood flow channels. Because channels were anastomosing (meaning they were interconnected) reversed flood flow on beheaded flood flow channels often captured yet to be beheaded southeast-oriented flood flow from flood flow channels further southwest. Such captures of yet to be beheaded flood flow helped erode significant northwest-oriented tributary valleys. Based on the northwest-southeast orientation of Yellowstone River tributary streams, landform evidence illustrated in this essay 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 further and further northeast by headward erosion of deep valleys eroded into a topographic surface at least as high as the figure 1 region highest elevations today. In the figure 1 map region headward erosion of the north-oriented Rosebud Creek valley first captured the southeast-oriented flood flow and diverted the flood waters to the northeast-oriented Yellowstone River valley and then headward erosion of the Armells Creek and Sarpy Creek valleys (in that sequence) captured many of the southeast-oriented flood flow routes moving water to the newly eroded Rosebud Creek valley. Detailed maps below provide evidence supporting this interpretation. The Big Dry Creek-Yellowstone River drainage divide are essay and the Musselshell River-Yellowstone River drainage divide area essay describe regions north of the Sarpy Creek-Rosebud Creek drainage divide discussed here. The Yellowstone River-Tongue River drainage divide area essay describes the region located east of the Sarpy Creek-Rosebud Creek drainage divide area.  THese essays can be found under Yellowstone River on the sidebar category list.

Sarpy Creek-Rosebud Creek drainage divide area detailed location map

Figure 2: Sarpy Creek-Rosebud Creek drainage divide area detailed location map. United States Geological Survey map digitally presented using National Geographic Society TOPO software.

Figure 2 illustrates a somewhat more detailed map of the Sarpy Creek-Rosebud Creek drainage divide area discussed here. Treasure, Big Horn and Rosebud Counties are located in Montana. The Sarpy Creek-Rosebud Creek drainage divide area discussed here is located in Treasure, Big Horn County and Rosebud Counties and is south of the Yellowstone River. Rosebud Creek flows northeast from Busby in the Northern Cheyenne Indian Reservation (located in the figure 2 south center) and then turns to flow north to the Yellowstone River at Rosebud. Sarpy Creek originates northwest of Busby and flows northwest and north into Treasure County and then north to the Yellowstone River between Hysham and Sanders. Figure 2 shows many southeast-oriented Rosebud Creek tributaries, especially to the northeast-oriented Rosebud Creek valley segment. This southeast drainage alignment is evidence the northeast-oriented Rosebud Creek valley eroded southwest to capture southeast-oriented flood flow. The southeast-oriented tributary valleys were eroded by southeast-oriented flood flow moving into the newly eroded Rosebud Creek valley. Northwest-oriented tributary valleys were eroded by reversals of flood flow on the northwest ends of beheaded southeast-oriented flood flow routes. Subsequently the Sarpy Creek valley eroded south across the same southeast-oriented flood flow routes to capture flood waters that were moving to the newly eroded Rosebud Creek valley and the northwest-oriented Sarpy Creek headwaters valley was eroded by a reversal of flood flow on the northwest end of a beheaded southeast-oriented flood flow channel. Because flood waters move in and erode anastomosing (or interconnected) 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 Yellowstone River-Rosebud Creek drainage divide area east of Forsyth, Montana and progress south along the Armells Creek-Rosebud Creek drainage divide. Next detailed maps look at the Sarpy Creek-Armells Creek drainage divide and then conclude by looking at the south end of the Sarpy Creek-Rosebud Creek drainage divide area near Busby.

Yellowstone River-Rosebud Creek drainage divide area southeast of Forsyth, Montana

Figure 3: Yellowstone River-Rosebud Creek drainage divide area southeast of Forsyth, Montana. United States Geological Survey map digitally presented using National Geographic Society TOPO software.

Figure 3 illustrates the Yellowstone River-Rosebud Creek drainage divide area southeast of Forsyth, Montana. The east-northeast oriented Yellowstone River flows across the figure 3 north half. Rosebud Creek flows north in the figure 3 east half to join the Yellowstone River west of Rosebud. Note several northwest-oriented Rosebud Creek tributaries from the east and several barbed southeast-oriented tributaries from the west. East of Rosebud Creek north-northeast and northwest oriented Butte Creek flows to join the Yellowstone River as a barbed tributary at Rosebud. Slaughterhouse Creek is the named northwest-oriented tributary flowing to the east-northeast oriented Yellowstone River as a barbed tributary at Forsyth. An unnamed northwest-oriented stream located east of Slaughterhouse Creek is another barbed Yellowstone River tributary. Also note shallow through valleys linking northwest-oriented Slaughterhouse Creek headwaters with headwaters of southeast-oriented Rosebud Creek tributaries. The northwest-oriented barbed tributaries flowing to the east-northeast oriented Yellowstone River provide evidence the Yellowstone River valley eroded headward across multiple channels of southeast-oriented flood flow such as might be found in a southeast-oriented anastomosing channel complex. Flood waters on the northwest ends of beheaded southeast-oriented flood flow channels reversed flow direction to flow northwest into the newly eroded and deeper Yellowstone River valley. At the same time northeast and north-oriented valleys, such as the Rosebud Creek valley, eroded south to capture yet to be beheaded southeast-oriented flood flow routes. For example, when the actively eroding and deep east-northeast oriented Yellowstone River valley head was located at the present day junction of Rosebud Creek and the Yellowstone River there was no Yellowstone River valley further to west and flood flow on the Slaughterhouse Creek alignment could flow southeast into the what was then the actively eroding north-oriented Rosebud Creek valley. Through valleys linking Slaughterhouse Creek headwaters with Rosebud Creek tributary valleys provide evidence multiple channels of flood water did flow southeast into what was then the newly eroded Rosebud Creek valley. Headward erosion of the deep Yellowstone River then beheaded the southeast-oriented flood flow. Flood waters on the northwest end of the beheaded flood flow route reversed direction to flow to the newly eroded Yellowstone River valley, to erode the northwest-oriented Slaughterhouse Creek valley, and to create the Yellowstone River-Rosebud Creek drainage divide.

East Fork Armells Creek-Rosebud Creek drainage divide area at South Fork Creek

Figure 4: East Fork Armells Creek-Rosebud Creek drainage divide area at South Fork Creek. United States Geological Survey map digitally presented using National Geographic Society TOPO software.

Figure 4 illustrates East Fork Armells Creek-Rosebud Creek drainage divide south of the figure 3 map area. Rosebud Creek flows north-northwest in the figure 4 northeast corner. The East Fork Armells Creek is located adjacent to the highway and railroad in the figure 4 west half and flows to the figure 4 northwest corner. Note how several East Fork Armells Creek tributaries from the east begin as northwest-oriented streams and then turn west or even southwest to join northwest-oriented East Fork Armells Creek. As previously mentioned northwest-oriented valleys provide evidence of reversed flood flow on the northwest ends of beheaded southeast-oriented flood flow channels. Multiple east and southeast-oriented tributaries provide evidence the northeast-oriented South Fork Creek valley eroded southwest across multiple southeast-oriented flood flow routes to capture southeast-oriented flood water and to divert the flood flow northeast to what was then the newly eroded north-oriented Rosebud Creek valley. Through valleys link headwaters of southeast-oriented South Fork Creek tributaries with northwest-oriented headwaters of East Fork Armells Creek tributaries. Subsequently the East Fork Armells Creek valley alignment may have been determined by southeast-oriented flood flow and southwest-oriented valleys may have originated as south-oriented tributary valleys captured southeast-oriented flood flow from adjacent channels, although the timing of the beheading and flow reversals could be different. Northwest-oriented headwaters of those southwest-oriented tributaries provide evidence of reversed flood flow on northwest ends of beheaded southeast-oriented flood flow channels. Headward erosion of the north-oriented Armells Creek valley north and west of figure 4 beheaded southeast-oriented flood flow on the East Fork Armells Creek alignment and caused a major flood flow reversal. The flood flow reversal then eroded the present day northwest-oriented East Fork Armells Creek drainage basin and was probably aided by the capture of yet to be beheaded southeast-oriented flood flow from flood flow channels further to the south.

East Fork Armells Creek-Rosebud Creek drainage divide area southwest of Colstrip, Montana

Figure 5: East Fork Armells Creek-Rosebud Creek drainage divide area southwest of Colstrip, Montana. United States Geological Survey map digitally presented using National Geographic Society TOPO software.

Figure 5 illustrates the East Fork Armells Creek-Rosebud Creek drainage divide area south and west of the figure 4 map area. Northeast-oriented Rosebud Creek is located in the figure 5 southeast corner. The east Fork Armells Creek flows east and east-northeast across the figure 5 north half and at Colstrip turns to flow northwest as seen in figure 4. Rosebud Creek tributaries from the northwest are southeast-oriented suggesting the northeast-oriented Rosebud Creek valley eroded southwest to capture multiple southeast-oriented flood flow channels such as might be found in a southeast-oriented anastomosing channel complex. The length of the southeast-oriented Rosebud Creek tributaries suggests southeast-oriented flood flow moving into the newly eroded Rosebud Creek was able to erode tributary valleys headward from the Rosebud Creek northwest valley wall. The east and east-northeast oriented East Armells Creek valley then eroded west-southwest and west from the Colstrip area to capture the southeast-oriented flood flow and to divert the flood waters to the what at that time was the newly eroded northwest-oriented Armells Creek valley. Through valleys linking the east- and east-northeast oriented East Fork Armells Creek valley with the valleys of the southeast-oriented Rosebud Creek tributaries provide evidence flood waters once moved southeast across what is now the East Fork Armells Creek-Rosebud Creek drainage divide. The source of the flood waters cannot be determined from evidence presented here, although the Missouri River drainage basin landform origins research project essays (published on this website) 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 located in a deep “hole” occupying approximately the North American locations usually thought to have been glaciated. Such a source would not only explain the immense southeast-oriented floods, but would also explain why deep valleys were eroding headward to capture an immense south-oriented flood and to divert flood waters northeast into space in the deep “hole” the rapidly melting ice sheet had once occupied.

West Fork Armells Creek-East Fork Armells Creek drainage divide area

Figure 6 illustrates the West Fork Armells Creek-East Fork Armells Creek drainage divide area located south and west of the figure 4 map area and north of the figure 5 map area and includes overlap areas with both figure 4 and 5. The East Fork Armells Creek flows east and east-northeast along the figure 6 south edge to Colstrip where it makes an abrupt turn to flow north-northwest along the figure 6 east edge. The West Fork Armells Creek originates as an east oriented stream southwest of Castle Rock, but quickly turns northeast and then north-northwest to flow to the figure 6 north edge where it joins northeast-oriented Trail Creek. Stocker Creek also originates southwest of Castle Rock and flows northeast right next to the West Fork Armells Creek, but continues to flow northeast to join north-northwest oriented East Fork Armells Creek. Further north northeast-oriented Corral Creek flows to the East Fork Armells Creek, while still further north near the figure 6 north center edge East Cromo Creek flows northwest to the figure 6 north edge and then to northeast-oriented West Fork Armells Creek. The north-northwest oriented West Fork Armells Creek valley in figure 6 has northwest-oriented tributaries from the east and northeast-oriented tributaries from the west. Events recorded by figure 6 evidence begin with headward erosion of the east and east-northeast oriented East Fork Armells Creek valley across multiple southeast-oriented flood flow channels moving to what was then the newly eroded northeast-oriented Rosebud Creek valley. Flood waters were moving on a topographic surface at least as high as the highest figure 6 elevations today and deep valleys were being eroded into that topographic surface. Headward erosion of the northeast-oriented Stocker Creek valley next captured the southeast-oriented flood flow and diverted the water more directly to the newly eroded north-northwest-oriented East Fork Armells Creek valley. Next headward erosion of the northeast-oriented Corral Creek valley captured some of the flood flow and diverted the flood waters to the East Fork Armells Creek. Then headward erosion of the northeast-oriented West Fork Armells Creek-Trail Creek valley captured the southeast-oriented flood flow. Flood waters on northwest ends of the beheaded flood flow routes (south of the northeast-oriented West Fork Armells Creek-Trail Creek valley) reversed flow direction and flowed north to the newly eroded West Fork Armells Creek-Trail Creek valley. Reversed flood flow eroded the northwest-oriented East Cromo Creek valley and the north-northwest oriented West Fork Armells Creek valley. The east- and northeast-oriented West Fork Armells Creek headwaters valley then eroded southwest and west to capture yet to be beheaded southeast-oriented flood flow, however headward erosion of northeast-oriented West Fork Armells Creek tributary valleys (such as the Donley Creek and Black Hank Creek valleys) rapidly beheaded that southeast-oriented flow.

North end of Sarpy Creek-Armells Creek drainage divide area

Figure 7: North end of Sarpy Creek-Armells Creek drainage divide area. United States Geological Survey map digitally presented using National Geographic Society TOPO software.

Figure 7 illustrates the Sarpy Creek-Armells Creek drainage divide area at the Yellowstone River. Armells Creek flows north along the figure 7 east edge to join the Yellowstone River in the figure 7 northeast corner area. North-northwest oriented Sarpy Creek can be seen in the figure 7 southwest corner and flows north just west of the figure 7 west edge. North-oriented Reservation Creek flows north from the figure 7 south edge to join the Yellowstone River in the Howard Valley area. Deveny Coulee in the figure 7 northwest quadrant drains to the Yellowstone River as a barbed tributary. Several unnamed northwest oriented Yellowstone River tributaries are also located in the figure 7 northwest quadrant. These northwest oriented Yellowstone River tributaries provide evidence the Yellowstone River valley beheaded multiple southeast-oriented flood flow routes and flood waters on the northwest ends of the beheaded flood flow routes reversed flow direction to flow northwest and to erode northwest-oriented Yellowstone River tributary valleys. North-northwest oriented Sarpy Creek has northwest-oriented tributaries seen in figure 7. These include northwest-oriented Swede Creek and northwest- and west-oriented Corral Creek. These northwest-oriented Sarpy Creek tributaries provide evidence headward erosion of the north-northwest oriented Sarpy Creek valley beheaded southeast-oriented flood flow routes and caused reversals of flood flow on the northwest ends of those flood flow routes. Further east the evidence is somewhat more complex, but evidence for south-oriented flood flow can be found. For example,  Hay Creek is a north, northeast, and north-oriented Yellowstone River tributary located in the figure 7 north center area. Hay Creek headwaters are linked by a through valley with northeast-oriented Cache Coulee, which drains to north-oriented Reservation Creek. The through valley provides evidence south-oriented flood flow to the Cache Coulee valley was beheaded by headward erosion of the northeast-oriented Hay Creek valley, which caused a reversal of flood flow that eroded the north-oriented Hay Creek headwaters valley segment.

Sarpy Creek-West Fork Armells Creek drainage divide area

Figure 8: Sarpy Creek-West Fork Armells Creek drainage divide area. United States Geological Survey map digitally presented using National Geographic Society TOPO software.

Figure 8 illustrates the Sarpy Creek-West Fork Armells Creek drainage divide area south of the figure 7 map area and west of the figure 6 map area and includes overlap areas with figure 6. North-oriented Sarpy Creek is located along the figure 8 west edge. Northeast-oriented Trail Creek originates in the figure 8 southeast quadrant near the county line and flows northeast through the figure 8 east center area to the figure 8 east edge and then to join the West Fork Amells Creek as seen in figure 6. Sarpy Creek tributaries from the east are predominately northwest-oriented (remember this area is directly northwest of area seen in figure 5 where the East Fork Armells Creek had beheaded multiple southeast-oriented flood flow routes to the northeast-oriented Rosebud Creek valley). Note how northwest-oriented Sarpy Creek tributary valleys are linked to northeast-oriented West Fork Armells Creek tributary valleys. For example, the northwest-oriented South Fork Beaver Creek headwaters are linked by a through valley across the present day drainage divide with headwaters of northeast-oriented Middle Fork of Trail Creek. Other through valleys can be seen in figure 8, although more detailed maps show the through valleys much better. What has happened in this area (figures 5, 6, and 8) is southeast-oriented flood flow moving on a topographic surface at least as high as the highest regional elevations today was captured by headward erosion of the deep northeast-oriented Rosebud Creek valley. Next the deep East Fork Armells Creek valley eroded south and west to capture the flood flow and then northeast-oriented East Fork Armells Creek tributary valleys eroded southwest to capture some of the southeast-oriented flood flow. Next headward erosion of the northeast-oriented West Fork Armells Creek valley and its various tributary valleys captured the southeast-oriented flood flow. Finally headward erosion of the deep north-oriented Sarpy Creek valley captured the southeast-oriented flood flow and flood waters on the northwest ends of the beheaded southeast-oriented flood flow routes reversed flow direction to erode the northwest-oriented Sarpy Creek tributary valleys and create the present day Sarpy Creek-West Fork Armells Creek drainage divide.

East Fork Sarpy Creek-Armells Creek and Rosebud Creek drainage divide area

Figure 9: East Fork Sarpy Creek-Armells Creek and Rosebud Creek drainage divide area. United States Geological Survey map digitally presented using National Geographic Society TOPO software.

Figure 9 illustrates the East Fork Sarpy Creek-Armells Creek and the East Fork Sarpy Creek-Rosebud Creek drainage divide area south and east of the figure 8 map area and west of the figure 5 and 6 map areas and includes overlap areas with figures 5 and 6. The northwest-oriented Little Wolf Mountains ridge forms the present day Sarpy Creek-Armells Creek drainage divide and the northeast oriented Little Wolf Mountain ridge to the south forms the present day Sarpy Creek-Rosebud Creek drainage divide. Northeast-oriented East Fork Sarpy Creek flows from the figure 9 south edge to the figure 9 south center where it turns northwest to flow to the figure 9 northwest corner. Southeast-oriented drainage in the figure 9 southeast corner area flows to northeast oriented Rosebud Creek. The East Fork Armells Creek is located in the figure 9 northeast quadrant and northeast- and north-oriented drainage north of the East Fork Armells Creek flows to the West Fork Armells Creek. Northwest-oriented tributaries flowing to northwest-oriented East Fork Sarpy Creek are linked by through valleys with southeast-oriented tributaries flowing to northeast-oriented Rosebud Creek. The through valleys are saddles or notches eroded into the northeast-oriented Little Wolf Mountain ridge and provide evidence southeast-oriented flood flow once moved on a topographic surface at least as high as the Little Wolf Mountain ridge to what was then a newly eroded and deep northeast-oriented Rosebud Creek valley. Southeast-oriented Rosebud Creek tributary valleys were eroded headward into the deep Rosebud Creek valley northwest wall by southeast-oriented flood flow moving into the newly eroded valley. Subsequently headward erosion of the north-oriented Sarpy Creek valley beheaded the southeast-oriented flood flow and caused a major flood flow reversal along the present day northwest-oriented East Fork Sarpy Creek valley. Yet to beheaded flood flow routes south and west of the figure 9 map area were captured and the captured flood waters moved northeast along the present day northeast-oriented East Sarpy Creek valley segment. Northeast-oriented East Sarpy Creek tributaries also eroded southwest to capture yet to be beheaded flood flow routes. Subsequently headward erosion of the Sarpy Creek valley beheaded all southeast-oriented flow.

South end of Sarpy Creek-Rosebud Creek drainage divide area

Figure 10: South end of Sarpy Creek-Rosebud Creek drainage divide area. United States Geological Survey map digitally presented using National Geographic Society TOPO software.

Figure 10 illustrates the south end of the Sarpy Creek-Rosebud Creek drainage divide area and is located immediately south of the figure 9 map area. The Crow Indian Reservation is located west of the north-south boundary line located in the figure 10 west half and the Northern Cheyenne Indian Reservation is located east of the boundary line. Northeast-oriented Rosebud Creek is located in the figure 10 southeast corner. Busby, Montana is located south of the figure 10 map area. Northwest-oriented Sarpy Creek originates near the middle of the north-south Indian Reservation boundary line and flows to the figure 10 northwest corner area. At the east end of the figure 10 northeast quadrant (east of the Indian Reservation boundary line) are northwest-oriented headwaters of East Fork Sarpy Creek, which turn northeast to flow to the figure 10 north edge. The Little Wolf Mountains form the present day Sarpy Creek-Rosebud Creek drainage divide. Southeast of the drainage divide are southeast-oriented Rosebud Creek tributaries. Northwest and west of the drainage divide are northwest-oriented Sarpy Creek headwaters. What has happened here is southeast-oriented flood flow once moved across the figure 10 map area on a topographic surface at least as high as the highest Wolf Mountains elevations today to a deep and newly eroded northeast-oriented Rosebud Creek valley. Southeast-oriented Rosebud Creek tributary valleys were eroded headward into the newly eroded Rosebud Creek valley wall by the southeast-oriented flood flow. Headward erosion of the deep north-oriented Sarpy Creek valley northwest of the figure 10 map area then captured the southeast-oriented flood flow and diverted the flood waters north to what was then the newly eroded and deep east and northeast-oriented Yellowstone River valley. Flood waters on the northwest ends of the beheaded flood flow routes reversed flow direction to flow northwest to the newly eroded north-oriented Sarpy Creek valley. Southeast-oriented flood flow routes were beheaded in sequence from north to south. Because flood flow routes were anastomosing or interconnected reversed flood flow on a beheaded flood flow route could capture yet to be beheaded flood flow from routes further to the south. Such captures enabled the East Fork Sarpy Creek to erode a significant northwest-oriented valley and also enabled the northwest-oriented Sarpy Creek headwaters to erode a significant northwest-oriented valley. Northwest-oriented drainage in the figure 10 southwest corner flows to north-oriented Tullock Creek, which flows north to the west of Sarpy Creek to the Yellowstone River.

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.