Abstract:

Introduction:

• The purpose of this essay is to use topographic map interpretation methods to explore eastern Montana Big Dry Creek (Missouri River)-Yellowstone 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 Big Dry Creek (Missouri River)-Yellowstone River drainage divide area landform evidence will be regarded as evidence supporting the “thick ice sheet that melted fast” paradigm.

Big Dry Creek-Yellowstone River drainage divide area location map

Figure 1: Big Dry Creek-Yellowstone 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 Big Dry Creek-Yellowstone River drainage divide area location map and illustrates a region in eastern Montana. The Yellowstone River flows from Billings along the figure 1 south edge in a northeast direction to Glendive, located near the figure 1 east edge. The Missouri River flows east from the figure 1 west edge to Fort Peck Lake, which is a reservoir flooding the Missouri River valley. Downstream from Fort Peck Dam the Missouri River flows roughly in an east direction across the figure 1 northeast quadrant. Big Dry Creek originates in the figure 1 center and flows north, northeast, east, and north to the Missouri River at Fort Peck Lake, which extends south into the Big Dry Creek valley. Little Dry Creek is a major Big Dry Creek tributary and originates south of Big Dry Creek and flows east-northeast and northwest to join Big Dry Creek south of the flooded north-oriented Big Dry Creek valley. East of the north-oriented Little Dry Creek-Big Dry Creek valley is the northwest, northeast, and north-oriented Redwater River drainage basin which drains to the Missouri River near Poplar, Montana. Figure 1 illustrates numerous southeast and northwest-oriented Yellowstone River tributaries. Southeast-oriented Yellowstone River tributaries of importance in this essay are Cherry Creek (unnamed on figure 1, but flowing to the Yellowstone River near Terry), South Sunday Creek (flowing to the Yellowstone River at Miles City), Little Porcupine Creek (flowing to the Yellowstone west of Rosebud), and Big Porcupine Creek (flowing to the Yellowstone River west of Forsyth).

• 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 to the southwest. Such captures of yet to be beheaded flood flow often helped erode significant northwest-oriented tributary valleys. Based on the northwest-southeast orientation of tributary streams, landform evidence illustrated in this essay is interpreted in the context of an immense southeast-oriented flood flowing across the entire figure 1 map area and which was systematically captured and diverted further and further to the 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 Yellowstone River valley captured southeast-oriented flood flow and diverted the flood waters northeast, and subsequently headward erosion of the east-oriented Missouri River valley and north-oriented Big Dry Creek valley captured the same southeast-oriented flood flow and diverted the flood waters still further to the north and east. Detailed maps below provide evidence supporting this interpretation. The Powder River-O’Fallon Creek drainage divide area essay describes a region located southeast of the Big Dry Creek-Yellowstone River drainage divide area described here and can be found under Powder River on the sidebar category list. The northeast end of the Redwater River-Yellowstone River drainage divide area and at the southwest end of the Redwater River-Yellowstone River drainage divide area essays describe regions east of Big Dry Creek and can be found under Redwater River on the sidebar category list.

Big Dry Creek-Yellowstone River drainage divide area detailed location map

Figure 2: Big Dry Creek-Yellowstone 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 Big Dry Creek-Yellowstone River drainage divide area discussed here. Garfield, Custer, Dawson and Prairie Counties are located in Montana. West of Custer County is Rosebud County and west of Dawson County is McCone County. The Big Dry Creek-Yellowstone River drainage divide area discussed here is located primarily in southern Garfield County, northwest Prairie County, northwest Custer County, and northeast Rosebud County. The Yellowstone River flows northeast through Forsyth, Miles City and Terry to the figure 2 east edge. Big Dry Creek originates south of Edwards (figure 2 northwest corner area) and flows northeast, north, and east to Jordan and then east before turning north to flow to the figure 2 north center edge. South of Big Dry Creek is Little Dry Creek, which originates southeast of Edwards and flows east, northeast to Cohagen and then east before turning northwest to join north-oriented Big Dry Creek. Figure 2 shows numerous southeast-oriented Yellowstone River, Big Dry Creek, and Little Dry Creek tributaries. Also, nearly all Yellowstone River tributaries from the east are northwest-oriented and at least some Big Dry Creek and Little Dry Creek tributaries are northwest-oriented. This northwest-southeast drainage alignment is evidence the northeast-oriented Yellowstone River valley eroded southwest across an immense southeast-oriented flood to capture flood waters and to divert flood waters northeast. Further, the drainage alignment is evidence the north-oriented Little Dry Creek valley subsequently eroded south, west, and southwest to capture the same southeast-oriented flood flow and that subsequently the Big Dry Creek valley eroded west, and southwest to capture the same immense southeast-oriented flood and divert the flood waters to the Missouri River valley to the north. The southeast-oriented tributary valleys were eroded by southeast-oriented flood flow moving into the newly eroded and deep Yellowstone and Big Dry Creek and Little Dry Creek valleys. The northwest-oriented tributary valleys were eroded by reversed flood flow on the northwest ends of beheaded southeast-oriented flood flow routes. 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 would 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. For example, note northwest-oriented Crow Rock Creek (and its west-oriented Ash Creek and White’s Creek tributaries) flowing to the elbow of capture where Little Dry Creek turns northwest to flow to north-oriented Big Dry Creek. Headward erosion of the north-oriented Little Dry Creek-Big Dry Creek valley beheaded southeast-oriented flood flow on the Crow Rock Creek-Ash Creek (and White’s Creek) alignment that was flowing to the southeast-oriented Cherry Creek and other valleys. Figure 3 below illustrates what happened when flood flow on the northwest end of that beheaded southeast-oriented flood flow route was reversed to flow northwest to the newly eroded Little Dry Creek valley.

Ash Creek-Cherry Creek drainage divide area

Figure 3: Ash Creek-Cherry Creek drainage divide area. United States Geological Survey map digitally presented using National Geographic Society TOPO software. 

Figure 3 illustrates the Ash Creek-Cherry Creek drainage divide area identified in figure 2 above. Cherry Creek flows southeast to the figure 3 east edge. Other east-oriented drainage flowing to the figure 3 east edge flows to Cherry Creek, which flows southeast to the northeast-oriented Yellowstone River. Ash Creek flows northwest and southwest to Dinosaur Dam and the west to the figure 3 west edge. West of figure 3 Ash Creek flows to northwest-oriented Crow Rock Creek, which flows to Little Dry Creek and then to Big Dry Creek and finally to the east-oriented Missouri River. In the figure 3 southwest corner is northwest and west oriented White’s Creek, which also flows to northwest-oriented Crow Rock Creek and eventually to the east-oriented Missouri River. North of the figure 3 map area is the northwest-oriented Timber Creek drainage basin, which drains to Big Dry Creek. Note how today Cherry Creek is draining an escarpment-surrounded upland that slopes to the southeast. That escarpment-surrounded upland surface is all that remains of the southeast-oriented topographic surface eroded by southeast-oriented flood waters moving into what was then the newly eroded and deep northeast-oriented Yellowstone River valley. Headward erosion of the deep Missouri River valley westward across northern Montana and of the Big Dry Creek valley south from the newly eroded Missouri River valley then beheaded southeast-oriented flood flow on what is today the Timber Creek-North Fork Cherry Creek alignment, which up until that time had been eroding a major southeast-oriented flood flow channel. Flood waters on the northwest end of the beheaded flood flow channel reversed flow direction to erode the northwest-oriented Timber Creek valley and drainage basin. At that time flood waters moving southeast on what is today the Crow Rock Creek-Ash Creek (and also White’s Creek)-Cherry Creek alignments had not yet been beheaded by headward erosion of the north-oriented Big Dry Creek and Little Dry Creek valleys. Some of that continuing southeast-oriented flood flow was captured by reversed flow on the newly reversed Timber Creek route and flowed east on the Ash Creek route and then northeast into the Timber Creek valley along what are today southwest-oriented Ash Creek tributary valleys (see figure 3 northwest corner). Flood waters on the Ash Creek alignment and also on the White’s Creek alignment also flowed southeast to what is today the head of southeast-oriented Custer Creek, located southeast of the northwest-oriented White’s Creek headwaters located along the figure 3 south center edge. Southeast-oriented flood flow to the Ash Creek valley was next beheaded and reversed while southeast-oriented flood flow continued briefly on the White’s Creek route. Reversed flow on the Ash Creek route captured flood flow from the White’s Creek route and the captured flood waters moved north along what are today south-oriented White’s Creek tributary valleys. Reversal of flood flow on the White’s Creek route then completed formation of the Big Dry Creek (Missouri River)-Yellowstone River drainage divide in the figure 3 map area and little has changed since.

Crow Rock Creek-Custer Creek drainage divide area

Figure 4: Crow Rock Creek-Custer Creek drainage divide area. United States Geological Survey map digitally presented using National Geographic Society TOPO software. 

Figure 4 illustrates the region south and slightly west of the figure 3 map area and includes overlap areas with figure 3. West-oriented White’s Creek is located along the figure 4 north edge and flows to northwest-oriented Crow Rock Creek near Crow Rock in the figure 4 northwest corner. Crow Rock Creek originates in the figure 4 south center and flows to the northwest corner. Southeast-oriented Custer Creek originates just west of Little Sheep Mountain in the figure 4 northeast corner. Note how northwest-oriented White’s Creek headwaters are linked by through valleys with southeast-oriented Custer Creek headwaters. These shallow through valleys provide evidence water once flowed southeast across the present day Big Dry Creek (Missouri River)- Yellowstone River drainage divide and that the drainage divide was created by a reversal of flow in what is today the White’s Creek valley. Between White’s Creek and Crow Rock Creek is northwest-oriented Hay Creek, which also joins northwest-oriented Crow Rock Creek near Crow Rock and west of Custer Creek is southeast-oriented Finley Creek, which flows to the figure 4 southeast corner. Note how southeast-oriented Finley Creek is linked to northwest-oriented White’s Creek tributaries and also to northwest-oriented Hay Creek headwaters. These linkages provide evidence the southeast-oriented Finley Creek valley was a channel in a southeast-oriented anastomosing channel complex that was dismembered to cause reversals of flood flow on the northwest-oriented White’s Creek tributary valleys and also on the northwest-oriented Hay Creek valley. Following the northwest-oriented valleys downstream to determine what caused the flood flow reversals leads to the north-oriented Little Dry Creek-Big Dry Creek valley and the deep east-oriented Missouri River valley. In other words, the drainage history recorded by figure 4 evidence begins with erosion of a southeast-oriented erosion surface leading into what was then a newly eroded and deep Yellowstone River valley. The deep Yellowstone River valley had eroded southwest to capture an immense southeast-oriented flood and to divert the flood waters northeast. Southeast-oriented flood flow continued and was carving an anastomosing channel complex as it eroded the newly formed northwest Yellowstone River valley wall. Headward erosion of the east-oriented Missouri River valley and north-oriented Big Dry Creek-Little Dry Creek valley to the north and northwest then captured the flood flow and diverted the flood waters north and east. Flood waters on the northwest ends of beheaded flood flow routes reversed flow direction to flow northwest to the newly eroded Missouri River valley. Because flood waters were moving in anastomosing channels (meaning the channels were interconnected) and because the channels were beheaded in sequence from east to west and from north to south, reversed flood flow in one channel often captured flood waters from yet to be beheaded channels and the captured flood waters helped erode significant northwest-oriented valleys.

Uall Creek-Grimes Creek drainage divide area

Figure 5: Uall Creek-Grimes Creek drainage divide area. United States Geological Survey map digitally presented using National Geographic Society TOPO software. 

Figure 5 illustrates the Uall Creek-Grimes Creek drainage divide area east of Angela and is located southwest of the figure 4 map area and includes overlap areas with figure 4. Northwest-oriented Crow Rock Creek is located in the figure 5 northeast quadrant. Uall Creek is the northwest-oriented “Creek” in the east half of the figure 5 northwest quadrant. South-oriented Dry House Creek and Dirty Woman Creek begin in the figure 5 northwest quadrant and flow south to join in the southeast quadrant and then flow to the figure 5 south edge. Further east Grimes Creek flows southeast, south, southwest, and south to the figure 5 south edge. Sand Creek flows southeast to the figure 5 southeast corner. Southeast-oriented Sand Creek originates in an abandoned southeast-oriented headcut that illustrates how flood waters were eroding a southeast-oriented anastomosing channel complex into what was then the newly eroded and deep northeast-oriented Yellowstone River valley. During major flood events anastomosing channel complexes can be ever-changing as one channel erodes deeper and captures flood flow from an adjacent channel and that is exactly what happened here. Deeper erosion on the Grimes Creek channel (which flows south to join the southeast-oriented North Sunday Creek valley) enabled the Grimes Creek channel to capture southeast-oriented flood flow moving to the Sand Creek channel. Captured flood flow then eroded a deep channel southwest to the deeper Grimes Creek channel and in the process beheaded all flood flow routes to what had been the actively eroding southeast-oriented Sand Creek headcut. The southeast-oriented flood flow the Grimes Creek channel captured was moving southeast on what is today the northwest-oriented Uall Creek valley. Flood flow in the Uall Creek valley was reversed to flow northwest when headward erosion of the deep east-oriented Missouri River valley and its north-oriented Big Dry Creek-Little Dry Creek tributary valley beheaded the southeast-oriented Uall Creek valley flood flow route. Flood waters on the northwest end of the Uall Creek valley route then reversed flow direction to flow northwest to the deeper and newly eroded Little Dry Creek valley.

Thompson Creek-North Sunday Creek drainage divide area

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

Figure 6 illustrates the Thompson Creek-North Sunday Creek drainage divide area west and north of the figure 5 map area and includes overlap areas with figure 5. South-oriented Dirty Woman Creek is located in the figure 6 southeast corner. North and northwest oriented Uall Creek is located in the figure 6 northeast corner. Rock Springs Creek flows south from Rock Springs to the figure 6 south edge. North Sunday Creek flows southeast from the figure 6 center to the figure 6 south edge and then to the northeast-oriented Yellowstone River. The West Fork of North Sunday Creek is located along the figure 6 south edge. Rock Springs Creek and Dirty Woman Creek (which flows to Dry House Creek) are North Sunday Creek tributaries. Thompson Creek flows north along the figure 6 west edge and eventually reaches east and north-oriented Little Dry Creek and then Big Dry Creek and finally the east oriented Missouri River. Northwest-oriented Red Butte Creek flows to the figure 6 north edge (next to the highway) and then joins north-oriented Thompson Creek. The Missouri River (Thompson Creek)-Yellowstone River (North Sunday Creek) drainage divide in figure 6 was created when the east oriented Little Dry Creek valley eroded west from the north-oriented Little Dry Creek-Big Dry Creek valley to capture southeast-oriented flood flow. Headward erosion of the deep Little Dry Creek valley enabled the north-oriented Thompson Creek valley to erode south to capture southeast-oriented flood flow and to divert the flood waters north to the newly eroded and deep east and north-oriented Little Dry Creek valley. Headward erosion of the Thompson Creek valley beheaded flood flow routes to what was then the actively eroding southeast-oriented North Sunday Creek drainage basin. Flood waters on the northwest ends of the beheaded flood flow routes reversed flow direction to erode northwest-oriented Thompson Creek tributary valleys. The Pine Springs Creek valley and Bickel Coulee represent two such northwest-oriented tributary valleys.

Detailed map of Thompson Creek tributary valleys

Figure 7 provides a detailed map of Thompson Creek tributary valleys north of Clear Water Reservoir seen in less detail in figure 6 above. Note how the north-oriented Thompson Creek valley has eroded south to capture multiple southeast-oriented flood channels, such as would be expected in a southeast-oriented anastomosing channel complex. Captured flood waters were diverted from flowing southeast to the northeast-oriented Yellowstone River valley to flowing north to the newly eroded east and north-oriented Little Dry Creek-Big Dry Creek valley and then east in the newly eroded Missouri River valley. Flood waters on the northwest ends of beheaded southeast-oriented flood flow routes reversed flow direction to flow northwest into the newly eroded north-oriented Thompson Creek valley. Figure 6 illustrates a north-northeast oriented Bickel Coulee valley segment east of the figure 7 map area. That north-northeast oriented Bickel Coulee valley segment was eroded by yet to be beheaded flood waters moving north to flow northwest in the beheaded and reversed Bickel Coulee valley. Headward erosion of the Thompson Creek valley subsequently beheaded the southeast-oriented flood flow routes that had been supplying captured flood waters to that north-oriented Bickel Coulee valley segment. Note how shallow through valleys cross drainage divides between the southeast-oriented Thompson Creek tributary valleys. Those through valleys crossing the tributary valley drainage divides are evidence of the ever-changing channel pattern of the southeast-oriented flood eroded anastomosing channel complex dismembered by Thompson Creek valley headward erosion. The through valleys also provide evidence as to how the anastomosing channels were interconnected so reversed flood flow on one channel could easily capture yet to be reversed flood flow from an adjacent channel.

Little Dry Creek-Little Porcupine Creek drainage divide area

Figure 8 illustrates the Little Dry Creek headwaters area and the Little Dry Creek-Little Porcupine Creek drainage divide area. There is no overlap with previous figures. Little Dry Creek originates near the figure 8 north edge west of Blazier Ridge and then flows east and northeast to the figure 8 north edge. Little Porcupine Creek originates south of Blazier Ridge in the figure 8 center area and then flows southeast to the figure 8 southeast corner area and then southeast and south to the Yellowstone River valley. Other southeast-oriented streams in the figure 8 southeast quadrant are Little Porcupine Creek tributaries. Big Porcupine Creek originates in the figure 8 northwest quadrant near Crown Butte and flows south to the figure 8 south edge. Southwest-oriented Acorn Creek originates just west of where Little Porcupine Creek originates and diverges from Little Porcupine Creek to flow to Porcupine Creek, which independently from Little Porcupine Creek flows south and southeast to the Yellowstone River. The divergence of the Little Porcupine Creek and Acorn Creek valleys is further evidence of the anastomosing flood flow channels eroding the northwest wall of what was then the newly eroded and deep Yellowstone River valley. Note how through valleys link the northeast-oriented Little Dry Creek valley with the southeast-oriented Little Porcupine Creek headwaters area. Those through valleys are evidence water once flowed south in those valleys and flow was reversed to create north-oriented Little Dry Creek tributary valleys after headward erosion of the deeper Little Dry Creek valley beheaded the south-oriented flood flow routes. Southeast-oriented flood flow in this figure 8 map area was eroding deep valleys headward into what must be some type of resistant rock layer (note the falls marked by Hole in the Rock near the Garfield-Rosebud County line at the figure 8 west edge). While the underlying geology here is different from areas further east, the figure 8 area was eroded by southeast-oriented flood waters moving to the Yellowstone River valley. Subsequently headward erosion of the northeast-oriented Little Dry Creek valley captured flood waters moving to had been up to that time the actively eroding southeast-oriented Little Porcupine Creek drainage basin. South and southeast-oriented flood flow to the Big Porcupine Creek valley was beheaded by headward erosion of Big Dry Creek tributary valleys north of the figure 8 map area.

Big Dry Creek-McGinnis Creek drainage divide area

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

Figure 9 illustrates the Big Dry Creek-McGinnis Creek drainage divide area located north and west of the figure 8 map area and includes overlap areas with figure 8. Southeast-oriented Little Porcupine Creek is located in the figure 9 southeast corner and to the north is Blazier Ridge where northeast-oriented Little Dry Creek flows to the figure 9 east edge. Northeast-oriented Sand Creek flows from the figure 9 center to the figure 9 north edge and joins Big Dry Creek north of the figure 9 map area. North oriented Big Dry Creek headwaters are located east and west of Manlove Butte in the figure 9 northwest corner. South-southeast oriented McGinnis Creek is located to the south in the figure 9 southeast quadrant. Note how the northeast-oriented Sand Creek valley has numerous southeast oriented tributary valleys and also has northwest-oriented tributary valleys. Those southeast and northwest oriented tributary valleys are evidence northeast oriented Sand Creek eroded southwest to capture multiple southeast oriented flood flow channels, such as might be found in a southeast-oriented anastomosing channel complex. The northwest-oriented tributary valley as previously mentioned were eroded by reversed flood flow on the northwest ends of beheaded southeast-oriented flood flow routes. For example, south-southeast oriented headwaters of south-oriented Big Porcupine Creek are linked by a northwest-southeast oriented through valley between School Butte and Crown Butte with a northwest-oriented Sand Creek tributary valley. Prior to headward erosion of the northeast-oriented Sand Creek valley flood waters were flowing southeast along the alignment of that present day northwest-oriented Sand Creek tributary valley to what was then the actively eroding Porcupine Creek valley. Flood flow along that route to the Big Porcupine Creek valley was beheaded by headward erosion of the Sand Creek valley, and flood waters on the northwest end of the beheaded flood flow route reversed direction to flow northwest to the newly eroded and deeper northeast-oriented Sand Creek valley. Further west the Big Dry Creek-McGinnis Creek drainage divide represents the west end of the Big Dry Creek-Yellowstone River drainage divide area discussed here. The north-oriented Big Dry Creek headwaters valley was initiated as a south-oriented flood flow route that was captured by headward erosion of the northeast-oriented Sand Creek valley (and was subsequently beheaded and reversed by headward erosion of the Big Dry Creek valley-see figures 1 and 2 above and 10 below).

Detailed map of Big Dry Creek-McGinnis Creek drainage divide area

Figure 10: Detailed map of Big Dry Creek-McGinnis Creek drainage divide area. United States Geological Survey map digitally presented using National Geographic Society TOPO software. 

Figure 10 provides a detailed map of the Big Dry Creek-McGinnis Creek-Sand Creek drainage divide area illustrated in less detail in figure 9 above. Big Dry Creek flows north to the figure 10 north center edge. Sand Creek flows east to the figure 10 east edge and then turns northeast as illustrated in figure 9. McGinnis Creek flows south-southeast to the figure 10 south edge and east of McGinnis Creek an unnamed south-oriented McGinnis Creek tributary flows south to the figure 10 south edge. Note now dry through valleys link these diverging drainage routes. Drainage history that can be reconstructed from this figure 10 evidence begins with southeast-oriented flood flow moving across a topographic surface at least as high as the highest figure 10 elevations today. Headward erosion of the McGinnis Creek tributary valley and the McGinnis Creek valley from the newly eroded northeast oriented Yellowstone River valley probably initiated the present day north-oriented Big Dry Creek valley, although at a much higher level than the valley is today. Next headward erosion of the deep east and northeast oriented Sand Creek valley eroded into the region and began to capture flood waters moving south on what is today the north-oriented Big Dry Creek valley, although the capture was not complete as flood waters were still probably also moving to the McGinnis Creek tributary valley and the McGinnis Creek valley. Before the Sand Creek capture could be completed headward erosion of the northeast and east oriented Big Dry Creek valley north of the figure 10 map area (see figures 1 and 2) beheaded south-oriented flood flow on the figure 10 Big Dry Creek valley. Flood waters on the north end of what had been a south-oriented flood flow route reversed flow direction to flow north to the newly eroded Big Dry Creek valley. For a short time southeast-oriented flood waters may have continued to flow into the figure 10 map area on  alignments of what are unnamed northwest-oriented valleys in the figure 10 northwest corner. However, those flood flow routes were soon beheaded and reversed and the figure 10 landscape has changed little since.

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.