A geomorphic history based on topographic map evidence

The Powder River-O’Fallon Creek drainage divide area discussed here is located in eastern Montana, USA. Although detailed topographic maps of the Powder River-O’Fallon 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 Powder River-O’Fallon 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 ended when headward erosion of the northeast-oriented Yellowstone River valley captured all southeast-oriented flood flow.

Introduction:

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

Powder River-O’Fallon Creek drainage divide area location map

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

Figure 1 provides a location map for the Powder River-O’Fallon Creek drainage divide area. The Powder River flows northeast from the figure 1 south edge center through Broadus and Powderville, Montana and then turns to flow north-northwest to the northeast-oriented Yellowstone River west of Terry, Montana. West of the Powder River drainage basin is the north-oriented Tongue River drainage basin, with the Tongue River flowing to the northeast-oriented Yellowstone River near Miles City, Montana. O’Fallon Creek originates east of the Powder River near Ekalaka, Montana and flows northwest, north, and northwest to reach the northeast-oriented Yellowstone River east of Terry, Montana. Northwest-oriented O’Fallon Creek tributaries are shown in figure 1 and a separate essay discusses the northeast oriented O’Fallon Creek-Little Beaver Creek drainage divide (found under Little Missouri River on sidebar category list). East of the O’Fallon Creek drainage basin is the north- and northeast-oriented Little Missouri River drainage basin with the Little Missouri River flowing across the Montana southeast corner and the South Dakota northwest corner to reach the North Dakota badlands. East of the north-oriented Little Missouri River are southeast-oriented headwaters of east-oriented streams, which today flow to the south-oriented Missouri River (not shown in figure 1). Evidence to be presented here suggests southeast-oriented floods flowing on a topographic surface higher than any present-day Powder River-O’Fallon Creek drainage divide elevations once crossed the Powder River-O’Fallon Creek drainage divide. These southeast-oriented floods were then captured by headward erosion of the deep Yellowstone River valley first causing a reversal of flow so flood waters flowed northwest into the newly eroded and deep Yellowstone River valley to create the northwest-oriented O’Fallon Creek drainage basin and second causing a reversal of flood flow that eroded the deep Powder River valley headward and in the process beheaded all southeast-oriented flood flow routes across the present day Powder River-O’Fallon Creek drainage divide. Note the Powder River elbow of capture north of Powderville where the northeast oriented Powder River turns to flow north-northwest. That elbow of capture will be significant in the following discussion, especially related to figures 9 and 10 below.

Detailed Powder River-O’Fallon Creek drainage divide area location map

Figure 2: Detailed Powder River-O’Fallon Creek drainage divide area location map. United States Geological Survey map digitally presented using National Geographic Society TOPO software.

Figure 2 provides a more detailed location map for the Powder River-O’Fallon Creek drainage divide area. West of the O’Fallon Creek drainage basin the Powder River has north-northwest-orientation and most Powder River tributaries flowing from the Powder River-O’Fallon Creek drainage divide are northwest-oriented. O’Fallon Creek tributaries from the east are also northwest-oriented, as is the much of the O’Fallon Creek course. O’Fallon Creek tributaries flowing from the Powder River-O’Fallon Creek drainage divide are often northeast-oriented although there are southeast-oriented tributaries and even northwest-oriented tributaries. Most Yellowstone River tributaries from the northwest flow in a southeast-oriented direction. The predominance of southeast-oriented and northwest-oriented drainage routes (or barbed tributaries) to what is today the northeast-oriented Yellowstone River is evidence that headward erosion of the Yellowstone River valley beheaded and reversed multiple southeast-oriented flow routes such as might be found in a southeast-oriented flood formed anastomosing channel complex. Detailed maps presented below will provide evidence for such an interpretation along the Powder River-O’Fallon Creek drainage divide, although on some of the detailed maps the evidence will suggest a northwest-oriented flood flow direction. The northwest-oriented flood flow direction developed as a reversal of flood flow on the northwest ends of southeast-oriented flood flow routes beheaded by headward erosion of the deep Yellowstone River valley. Both the north-northwest-oriented Powder River valley and northwest-oriented) O’Fallon Creek drainage basin were eroded by such reversals of southeast-oriented flood flow. The essay begins with a look at the Powder River-O’Fallon drainage divide in the present day Yellowstone River valley and then will proceed south along the drainage divide to the Powder River-O’Fallon Creek drainage divide south end.

Powder River-O’Fallon Creek drainage divide at Yellowstone River

Figure 3: Powder River-O’Fallon Creek drainage divide at Yellowstone River. United States Geological Survey map digitally presented using National Geographic Society TOPO software.

Figure 3 illustrates the north end of the Powder River-O’Fallon Creek drainage divide near Terry, Montana, where both the northwest-oriented Powder River and northwest-oriented O’Fallon Creek are barbed tributaries flowing to the northeast-oriented Yellowstone River. Note how the Yellowstone River today flows in an inner valley eroded into a higher level topographic surface defined by Broadview Bench and Fallon Flat and how the Powder River and O’Fallon Creek have also eroded inner valleys into that higher level topographic surface. Northwest-oriented Conns Coulee, Spring Creek, Ash Creek, and Plum Coulee have eroded valleys headward into the Broadview Bench and Fallon Flat topographic surface indicating northwest-oriented flood flow once moved from the Powder River and O’Fallon Creek drainage basins to the northeast-oriented Yellowstone River valley, although northeast-oriented flood flow from further southwest in the Yellowstone River valley probably also played a role in shaping the Broadview Bench and Fallon Flat topographic surface. Note how Whitney Creek tributaries have eroded southwest and west to behead and capture northwest-oriented flood flow that was moving over the Broadview Bench surface to the Ash Creek and Spring Creek headwaters. The fact that northwest-oriented Powder River, O’Fallon Creek, Conns Coulee, Spring Creek, Ash Creek, and Plum Coulee all enter the northeast-oriented Yellowstone River valley as barbed tributaries is evidence the Yellowstone River valley eroded headward across multiple flood flow routes. Figure 3 evidence is not adequate to determine the flood flow initially flowed southeast, although the evidence does indicate the flood flow was moving to the northwest at the time the northwest-oriented valleys were eroded.

Coal Creek-Whitney Creek drainage divide area

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

Figure 4 illustrates the Powder River-O’Fallon Creek drainage divide region immediately south of the figure 3 map area (there is a thin strip of overlap). The major Powder River tributaries are northwest-oriented Tenmile Creek (figure 4 northwest corner), northwest-oriented Coal Creek, and northwest-oriented Snow Creek (figure 4 southwest corner). These northwest-oriented streams have eroded deep valleys into a higher level topographic surface that is probably a southern extension of the Broadview Bench surface. O’Fallon Creek flows northwest across the figure 4 northeast corner. Whitney Creek is the northeast-oriented stream beginning at the figure 4 south edge and then turning to flow northwest to the figure 4 north edge and is an O’Fallon Creek tributary. Little Whitney Creek is the northeast-oriented Whitney Creek tributary located in the figure 4 center. Note how Little Whitney Creek headwaters are northwest oriented, which is evidence the Little Whitney Creek valley eroded southwest to capture multiple northwest-oriented flood flow routes carrying water to the northwest-oriented Tenmile Creek valley and the northwest-oriented Powder River. The northeast-oriented Whitney Creek valley segment subsequently eroded southwest to capture multiple northwest-oriented flood flow routes moving to the northwest-oriented Coal Creek valley, although figure 5 evidence will better demonstrate Whitney Creek northwest-oriented headwaters. Figure 4 evidence documents northwest-oriented flood flow moving in multiple channels to the northwest-oriented Powder River valley that was systematically captured and diverted to the more northeasterly northwest-oriented O’Fallon Creek valley. Why the O’Fallon Creek valley was able to capture northwest-oriented flood flow to the Powder River valley is not apparent, although it could be related to headward erosion of the deep Yellowstone River valley (southeast-oriented flood flow on the O’Fallon Creek alignment would be beheaded and reversed first). Figure 4 evidence like the figure 3 evidence provides no clues as to the flood water source, nor is there adequate information to determine the northwest-oriented flood flow developed as a reversal of earlier southeast-oriented flood flow.

Locate Creek-Whitney Creek drainage divide area

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

Figure 5 illustrates the Powder River-O’Fallon Creek drainage divide region south of the figure 4 map area and there is considerable overlap. Northwest-oriented Coal Creek flows to the figure 5 northwest corner. Midway between Coal Creek and the highway is northwest-oriented Snow Creek and northwest-oriented Locate Creek flows from the figure 5 south edge center to the highway and then west-northwest to the Powder River (west of figure 5). Archdale Creek is the west-oriented Locate Creek tributary paralleling the highway. Northeast-oriented Whitney Creek begins in the figure 5 center and flows to the figure 5 north edge. Note northwest-oriented Whitney Creek tributaries, which provide evidence Whitney Creek eroded southwest to capture multiple northwest-oriented flood flow routes to the northwest-oriented Coal Creek valley and the Powder River. Ash Creek and its Dry Creek tributary flow to the figure 5 northeast corner and then to northwest-oriented O’Fallon Creek. South of Ash Creek along the Figure 5 east edge are east-oriented Station Creek, North and South Forks of Cottonwood Creek, and southeast-oriented Spring Creek (figure 5 southeast corner), all flowing to north and northwest-oriented O’Fallon Creek. South of the Cottonwood Creek-O’Fallon Creek confluence O’Fallon Creek is north-oriented and at least some O’Fallon Creek tributaries from the west are southeast-oriented. North of the southeast-oriented Spring Creek headwaters are southeast-oriented headwaters of Scroggin Creek, another southeast-oriented O’Fallon Creek tributary. Southeast-oriented O’Fallon Creek tributaries may be evidence of the initial southeast-oriented flood flow direction that headward erosion of the deep Yellowstone River valley reversed to create the northwest-oriented flood flow documented by earlier figure evidence, although it is possible the Scroggin Creek and Spring Creek orientations developed as reversals of northwest-oriented flood flow. Note how southeast-oriented Spring Creek and Scroggin Creek headwaters are aligned with northwest-oriented Archdale Creek and Locate Creek headwaters.

Locate Creek-Hay Creek drainage divide area

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

Figure 6 illustrates the Powder River-O’Fallon Creek drainage divide region south of the figure 5 map area with considerable overlap. O’Fallon Creek flows north along the figure 6 east edge. Locate Creek flows northwest to the figure 6 northwest corner. Sheep Creek is the northwest-oriented Powder River tributary flowing across the figure 6 southwest corner. Note southeast-oriented Scroggin Creek and Spring Creek flowing as barbed tributaries to north-oriented O’Fallon Creek and evidence of southeast-oriented tributaries flowing to east-oriented Hay Creek and Miles City Creek further to the south. Note how southeast-oriented Hay Creek tributaries are aligned with northwest-oriented Locate Creek. The southeast-oriented drainage may be evidence of the initial southeast-oriented flood flow direction that prevailed prior to headward erosion of the deep northeast-oriented Yellowstone River valley and that the north-oriented O’Fallon Creek valley eroded headward to capture southeast-oriented flood flow moving on the yet to be beheaded northwest-oriented Powder River-Locate Creek alignment. It is also possible southeast-oriented O’Fallon Creek tributaries were formed as reversals of northwest-oriented flood flow. Headward erosion of the deep Yellowstone River valley caused a reversal of flood flow on northwest ends of beheaded southeast-oriented flood flow routes and headward erosion of the north-oriented O’Fallon Creek valley could also have caused a reversal of flood flow on southeast ends of beheaded northwest-oriented flood flow routes. In the case of the Yellowstone River valley headward erosion reversed flood flow captured flood flow still moving on yet to be beheaded southeast-oriented flood flow further to the southwest (the Yellowstone River valley was eroding to the southwest and flood flow routes were beheaded in sequence, with those in the east being beheaded before those in the west). Headward erosion of the Powder River valley (once beheaded and reversed) captured many yet to beheaded flood flow routes and as a result significant northwest-oriented flood flow was available to erode the northwest-oriented Powder River and O’Fallon Creek valleys. Note how shallow through valleys link headwaters of the northwest-oriented Powder River tributaries with southeast-oriented headwaters of the east-oriented O’Fallon Creek tributaries. These through valleys are evidence multiple flood flow routes once crossed the present day Powder River-O’Fallon Creek drainage divide. In this case the last flood flow to cross the present day drainage divide may have been northwest-oriented and may have been flowing to the northwest-oriented Powder River valley and may have been captured by O’Fallon Creek valley headward erosion.

Sheep Creek-O’Fallon Creek drainage divide area

Figure 7: Sheep Creek-O’Fallon Creek drainage divide area. United States Geological Survey map digitally presented using National Geographic Society TOPO software.

Figure 7 illustrates the Powder River-O’Fallon Creek drainage divide region south of the figure 6 map area and again there is considerable overlap. Sheep Creek is the northwest-oriented Powder River tributary in the figure 7 northwest quadrant and Trail Creek is the northwest-oriented Powder River tributary in the figure 7 southwest corner. O’Fallon Creek flows along the figure 7 east edge. Miles City Creek is the east oriented O’Fallon Creek tributary linked to the southwest-oriented North Fork of northwest-oriented Sheep Creek. Mile Creek and Ash Creek are the east and east-northeast-oriented O’Fallon Creek tributaries linked to the north-oriented headwaters to northwest-oriented Sheep Creek. Note how a southeast-oriented Ash Creek tributary is aligned with the northwest-oriented Sheep Creek alignment. This may be evidence the north-oriented O’Fallon Creek eroded headward to capture yet to be beheaded southeast-oriented flood flow on the present day northwest-oriented Powder River-Sheep Creek alignment. If so, headward erosion of the deep Yellowstone River valley soon thereafter beheaded the southeast-oriented flood flow on the Powder River-Sheep Creek alignment, causing flood waters on the northwest end of the flood flow route to reverse flow direction and to erode the deep northwest-oriented Powder River-Sheep Creek valley. Again, it is also possible the north-oriented O’Fallon Creek valley eroded headward to capture northwest-oriented flood flow that had already been reversed by headward erosion of the deep Yellowstone River valley when it beheaded southeast-oriented flood flow on what is today the northwest-oriented Powder River alignment. If so, the O’Fallon Creek tributaries were formed by reversals of flood flow on the southeast ends of beheaded northwest-oriented flood flow routes. In either case the Powder River-O’Fallon Creek drainage divide was created by reversal of flood flow on the ends of multiple beheaded flood flow routes.

Trail Creek-O’Fallon Creek drainage divide area

Figure 8: Trail Creek-O’Fallon Creek drainage divide area. United States Geological Survey map digitally presented using National Geographic Society TOPO software.

Figure 8 illustrates the Powder River-O’Fallon Creek drainage divide region south of the figure 7 map area again with overlap. O’Fallon Creek flows north and northwest across the figure 8 west half. Named O’Fallon Creek tributaries from the west are (from north to south) Ranch Creek, Antelope Creek, Short Creek, Hay Creek, Dugout Creek, and Skunk Creek. Note how most of these tributaries are southeast-oriented. Note also northwest oriented Lily Creek flowing to north-oriented O’Fallon Creek (in the figure 8 southeast corner) and the (unnamed on figure 8) northwest oriented East Fork flowing to the north-oriented O’Fallon Creek in the figure 8 northeast corner. This southeast-northwest drainage alignment, combined with the northwest oriented Powder River tributary alignment, is evidence the O’Fallon Creek valley eroded headward to capture multiple southeast or northwest oriented flood flow routes. Trail Creek flows northwest to the figure 8 northwest corner to the Powder River and a Trail Creek tributary, Straight Creek, flows northwest just south of it. Note how shallow through valleys link the northwest-oriented Trail Creek and Straight Creek headwaters with the southeast oriented headwaters of the O’Fallon Creek tributaries. These through valleys are further evidence northwest- or southeast-oriented flood flow once crossed the present day Powder River-O’Fallon Creek drainage divide. In the figure 8 southwest corner northwest-oriented Alkali Creek flows to the Powder River and the Alkali Creek North Fork begins as a southeast-oriented stream and then turns southwest to join northwest-oriented Alkali Creek. The southeast-oriented North Fork headwaters are evidence of an initial southeast-oriented flood flow direction that was captured by headward erosion of the northwest-oriented Powder River-Alkali Creek valley. While much of the evidence is inconclusive as to which direction flood waters across the figure 8 map area initially moved, the southeast-oriented North Fork Alkali Creek headwaters provide the key that unlocks the initial southeast direction. In other words, the north-oriented O’Fallon Creek valley eroded south to capture yet to be beheaded and reversed southeast-oriented flood flow on an alignment corresponding with the present day northwest-oriented Powder River valley and the Powder River-O’Fallon Creek drainage divide was created when the deep Yellowstone River valley eroded headward to behead southeast-oriented flood flow on what is today the northwest-oriented Powder River valley alignment.

Alkali Creek-O’Fallon Creek drainage divide area

Figure 9: Alkali Creek-O’Fallon Creek drainage divide area. United States Geological Survey map digitally presented using National Geographic Society TOPO software.

Figure 9 illustrates the Powder River-O’Fallon Creek drainage divide region south of the figure 8 map area with considerable overlap. The deep Powder River valley is located in the figure 9 southwest quadrant and this location is the approximate location of the Powder River elbow of capture mentioned in the figure 1 discussion. Downstream from this location the Powder River flows in a north-northwest and northwest direction to the northeast-oriented Yellowstone River. Upstream from this location the Powder River is a northeast-oriented river. In other words, the downstream Powder River alignment probably represents a reversal of flow on what was initiated as a southeast-oriented flood flow route. The north-oriented O’Fallon Creek valley, which eroded headward from previously reversed southeast-oriented flood flow routes (the deep Yellowstone River valley eroded from the northeast to the southwest and beheaded southeast-oriented flood flow routes in sequence from northeast to southwest), eroded south to capture yet to be beheaded southeast-oriented flood flow routes. For reasons that will become apparent in figure 10 what is today the northwest-oriented Powder River valley alignment had developed as a major southeast-oriented flood flow route. When the deep Yellowstone River valley beheaded that major southeast-oriented flood flow there was a reversal of flood flow that rapidly eroded a deep valley headward to the figure 9 location and then southwest. Headward erosion of that deep Powder River valley created the present day Powder River-O’Fallon Creek drainage divide and also was responsible for flood flow reversals that eroded the present day northwest-oriented Powder River tributary valleys.

Powder River-O’Fallon Creek drainage divide at Beaver Flats

Figure 10: Powder River-O’Fallon Creek drainage divide at Beaver Flats. United States Geological Survey map digitally presented using National Geographic Society TOPO software.

Figure 10 illustrates the Powder River-O’Fallon Creek-Little Beaver Creek drainage divide region and overlaps with figure 9. The deep Powder River valley is located along the figure 10 west edge. Northwest-oriented drainage north of the Beaver Flats erosion surface flows to O’Fallon Creek. Northeast and east-oriented drainage on the Beaver Flats erosion surface represents headwaters of northeast-oriented Little Beaver Creek, which flows to the north and east-oriented Little Missouri River. Prior to headward erosion of the deep Yellowstone River valley the northeast-oriented Little Beaver Creek eroded a deep valley headward to capture southeast-oriented flood flow moving across the entire region on a topographic surface now completely removed from the Powder River-O’Fallon Creek drainage divide area discussed here. Evidence of that higher level topographic surface is presented in the  O’Fallon Creek-Little Beaver Creek drainage divide and in the Little Beaver Creek-Boxelder Creek drainage divide essays (found under Little Missouri River on sidebar category list). That deep northeast-oriented Little Beaver Creek valley probably extended southwest from the figure 10 map area location and may even have eroded upstream along what is today the northeast-oriented Powder River alignment upstream from the figure 10 map location. It also is probable that southeast-oriented flood flow eroded a significant southeast-oriented valley headward from the figure 10 map location along the present day north-northwest-oriented Powder River alignment downstream from the figure 10 map location. Headward erosion of the deep Yellowstone River valley then began to interfere by first beheading southeast-oriented flood flow across the present day O’Fallon Creek drainage basin and causing a reversal of flood flow that captured significant flood flow from the northeast-oriented Little Beaver Creek valley and eroded the O’Fallon Creek drainage basin. Next headward erosion of the deep Yellowstone River valley beheaded southeast-oriented flood flow on the Powder River alignment and caused a massive reversal of flood flow that captured the probable southwest Little Beaver Creek valley extension (southwest of the figure 10 map location) creating the Powder River elbow of capture, eroding the deep Powder River valley, and creating the Powder River-O’Fallon Creek drainage divide.

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 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.