A geomorphic history based on topographic map evidence

The Powder River-Little Powder River drainage divide area discussed here is located in Montana’s southeast corner and is immediately north of the Wyoming state line. Although detailed topographic maps of this Powder River-Little Powder River drainage divide area have been available for more than fifty years detailed map evidence has not previously been used to interpret the region’s geomorphic history. The interpretation provided here is based entirely on topographic map evidence. This Powder River-Little Powder River drainage divide area is interpreted to have been eroded during immense southeast-oriented flood events, the first of which flowed on a topographic surface at least as high as the highest points in the present-day drainage divide area. Flood erosion ended when headward erosion of the northeast-oriented Powder River valley captured all southeast-oriented flood flow.

Introduction:

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

Location map for Montana’s Powder River-Little Powder drainage divide area

Figure 1: Location map for Montana’s Powder River-Little Powder River drainage divide area (select and click on maps to enlarge). National Geographic Society map digitally presented using National Geographic Society TOPO software.

Figure 1 provides a general location map for Montana’s Powder River-Little Powder River drainage divide area. The Powder River begins in central Wyoming and flows northeast into Montana where it turns north-northwest to flow to the northeast oriented Yellowstone River. The Little Powder River begins in northeast Wyoming, south of the figure 1 map area, and flows north to join the Powder River near Broadus, Montana. East of the Powder River drainage is the northeast and north-oriented Little Missouri River drainage basin with the Little Missouri River flowing from northeast Wyoming across Montana’s southeast corner and then across South Dakota’s northwest corner to reach North Dakota. In northeast Wyoming east of the northeast-oriented Little Missouri River is the northeast-oriented Belle Fourche River, which flows almost to the Montana state line and then turns to flow in a southeast direction into South Dakota. West of the Powder River drainage basin in the Tongue River drainage basin, where the Tongue River after flowing northeast from Wyoming into Montana and almost to the northeast-oriented Yellowstone River, turns to flow northwest to join the northeast-oriented Yellowstone River. Landform evidence illustrated and discussed here will be interpreted to have been formed during an immense southeast-oriented flood or series of flood events. Evidence presented here is not adequate to determine the flood water source, although by using many of the essays published on this website flood waters can be traced headward to a North American ice sheet location. Rapid melting of a large North American ice sheet would be a logical flood water source. The sequence of major flood erosion events interpreted here begins with southeast-oriented flood water moving across Montana’s Powder River-Little Powder River drainage divide. Next headward erosion of the north-oriented Little Powder River valley captured those southeast-oriented flood waters and diverted them north. Then probably in rapid succession the northeast-oriented Powder River valley eroded southwest to behead and capture all southeast-oriented flood flow routes crossing the present day Montana Powder-Little Powder River drainage divide. Flood water already on the northwest ends of beheaded southeast-oriented flood flow routes reversed flow direction to flow northwest to the newly eroded northeast-oriented Powder River valley and by doing so eroded northwest-oriented Powder River tributary valleys and also created the Powder River-Little Powder River drainage divide. As detailed map evidence will demonstrate reversed flow on the northwest-ends of beheaded flood flow routes often captured flood waters from yet to be beheaded flood flow routes further to the southwest. This captured flood water enabled the reversed flood flow to erode significant northwest-oriented Powder River tributary valleys.

Detailed location map for Montana Powder River-Little Powder River drainage divide area

Figure 2: Detailed location map for Montana Powder River-Little Powder River drainage divide area. United States Geological Survey map digitally presented using National Geographic Society TOPO software. 

Figure 2 provides a more detailed location map for Montana’s Powder River-Little Powder River drainage divide area. The Wyoming-Montana state line is the west to east line just south of Bay Horse, Montana (figure 2 south center). The northeast-oriented Powder River flows from the figure 2 southwest corner to the figure 2 north center. The Little Powder River flows north from the figure 2 south center to join the northeast-oriented Powder River near Broadus, Montana. Figure 2 shows prominent northwest-oriented tributaries flowing from the Powder River-Little Powder River drainage divide to the northeast-oriented Powder River. Named tributaries from the northeast to the southwest are First Creek, Baking Powder Creek, Butte Creek, Buttermilk Creek, Bay Horse Creek, Three Bar Creek, Buffalo Creek, Dry Creek, and Bitter Creek. Buffalo Creek, Dry Creek, and Bitter Creek are discussed in a separate essay because they begin along Wyoming’s Powder River-Little Powder River drainage divide (found under Powder River on the sidebar category list). Little Powder River tributaries flowing from the Powder River-Little Powder River drainage divide are shorter and most are southeast-oriented, although Bowers Creek and its North Fork are named on figure 2 and Bowers Creek flows in an east-northeast direction. Little Powder River tributaries from the east tend to be northwest-oriented and Powder River tributaries from west tend to be southeast-oriented. This pronounced northwest-southeast oriented drainage alignment of Little Powder River and Powder River tributaries is evidence the Little Powder River valley eroded south to behead and capture multiple southeast-oriented flood flow routes, probably flowing in what was then an immense southeast-oriented anastomosing channel complex, and subsequently the Powder River valley eroded southwest to behead and capture those same southeast-oriented flood flow routes, with flood water already on the northwest ends of beheaded flood flow routes reversing flow direction to erode northwest-oriented tributary valleys.

Powder River-Little Powder River confluence area

Figure 3: Powder River-Little Powder River confluence area. United States Geological Survey map digitally presented using National Geographic Society TOPO software. 

Figure 3 illustrates the Powder River-Little Powder River confluence area and the Powder River-Little Powder River drainage divide area immediately south of the confluence area. Note the northwest-southeast oriented drainage alignment of Powder River and Little Powder River tributaries. This drainage alignment is evidence the Powder River and Little Powder River valleys were eroded southwest and south across multiple southeast-oriented flood flow routes, as might be expected in a southeast-oriented anastomosing channel complex. The Little Powder River valley must have eroded south slightly faster than Powder River valley could erode southwest and behead and capture southeast-oriented flood flow routes that were flowing to what was then the actively eroding Little Powder River valley. The northwest-oriented Phillipi Creek and Swede Creek valleys were eroded by reversals of flood flow on northwest ends of beheaded southeast-oriented flood flow routes. Through valleys at heads of Phillipi and Swede Creeks cross the Powder River-Little Powder River drainage divide and are linked to southeast-oriented Little Powder River tributaries. The northwest to southeast oriented highway makes use of a through valley crossing the drainage divide. The through valleys are evidence  multiple flow routes once crossed the drainage divide and were beheaded and captured by Powder River valley erosion. The north-northwest oriented Doyle Creek valley probably eroded south to capture yet to be beheaded southeast-oriented flood flow on flood flow routes southwest of the actively eroding Powder River valley head. Unnamed northwest-oriented Powder River tributaries are located between the north-oriented Doyle Creek valley and the northeast-oriented Powder River valley and were formed as reversals of flow on the northwest ends of the southeast-oriented flood flow routes that Doyle Creek valley erosion had captured.

Powder River-Little Powder River drainage divide area near Eldon Mountain

Figure 4: Powder River-Little Powder River drainage divide area near Eldon Mountain. United States Geological Survey map digitally presented using National Geographic Society TOPO software. 

Figure 4 illustrates the Powder River-Little Powder River drainage divide region immediately south of the figure 3 map area with a small overlap strip. Named northwest-oriented Powder River tributaries from northeast to southwest are Third Creek and its East Fork, Second Creek, First Creek, Bog Spring Creek, Dobe Creek, and Baking Powder Creek. Named Little Powder River tributaries from north to south are Antelope Creek, Spring Creek, Fighting Butte Creek, Hockey Creek, Plum Creek, Spring Creek, Doggie Creek, Allison Creek, and Spring Creek. Note how Powder River tributaries are northwest oriented and Little Powder River tributaries are southeast-oriented. Also note through valleys linking heads of northwest-oriented Powder River tributaries with heads of southeast-oriented Little Powder River tributaries. Through valleys are easier to identify on more detailed maps and the figure 5 detailed map illustrates through valleys connecting northwest-oriented Second Creek headwaters with southeast-oriented Spring Creek and east and southeast-oriented Doggie Creek headwaters. Eldon Mountain is the high point on the figure 4 Powder River-Little Powder River drainage divide segment and through valleys cross the Powder River-Little Powder River drainage divide both north and south of Eldon Mountain. Probably the southeast-oriented flood flow first moved across a topographic surface at least as high as Eldon Mountain and the southeast-oriented flood flow and headward erosion of the northeast and north-oriented Powder River and Little Powder River valleys was responsible for eroding that initial high level topographic surface to produce the figure 4 landscape surface that exists today. A flood capable of accomplishing that much erosion must have been immense and long-lived. While the flood source cannot be determined from map evidence presented here, the logical source would be rapid melting of a large North American ice sheet, especially a thick ice sheet that through its weight and deep ice erosion created a large North American continent “hole” and because of its weight and significant melt water flood erosion caused pronounced crustal warping that altered continent elevations far from the ice sheet location.

Detailed map of Second Creek-Doggie Creek drainage divide

Figure 5: Detailed map of Second Creek-Doggie Creek drainage divide. United States Geological Survey map digitally presented using National Geographic Society TOPO software. 

Figure 5 is detailed map illustrating the Powder River-Little Powder River drainage divide area where northwest-oriented Second Creek headwaters are linked by through valleys with the southeast oriented Spring  Creek and east-oriented Doggie Creek valleys. Northwest-oriented Second Creek flows from the figure 5 center to the figure 5 northwest corner. Spring Creek flows southeast to the figure 5 west center edge and Doggie Creek begins in the figure south center and flows northeast and east through the figure 5 southeast quadrant. Note well-defined west to east oriented through valleys linking the southeast oriented Spring Creek headwaters with northwest-oriented Second Creek headwaters. Also note two through valleys linking the east-oriented Doggie Creek valley with northwest-oriented Second Creek headwaters. These through valleys are evidence water once flowed southeast along the present day northwest-oriented Second Creek valley and split to flow in separate channels to the southeast oriented Spring Creek and east-oriented Doggie Creek valleys. These multiple valleys suggest southeast-oriented flow was moving in an anastomosing channel complex, which implies the southeast-oriented flow was associated with a major southeast-oriented flood. Through valleys linking other southeast- and northwest-oriented valleys can be observed on figure 5 and adjacent area detailed maps. These through valleys suggest the southeast-oriented flood waters flowed over the entire region and was not restricted to the present day Second Creek and Spring and Doggie Creek valleys.

Powder River-Little Powder River drainage divide area north of Bear Skull Mountain

Figure 6: Powder River-Little Powder River drainage divide area north of Bear Skull Mountain. United States Geological Survey map digitally presented using National Geographic Society TOPO software. 

Figure 6 illustrates the Powder River-Little Powder River drainage divide region south of the figure 4 map area and includes some overlap. Major northwest-oriented tributaries to the northeast-oriented Powder River are Baking Powder Creek and its North and South Forks and Butte Creek and its East Fork, Named east and southeast-oriented Little Powder River tributaries from north to south are Allison Creek, Spring Creek, Watt Creek, Little Bear Skull Creek, Bear Skull Creek, Rue Creek, and Hay Creek. Eldon Mountain is at the north end of the figure 6 Powder River-Little Powder River drainage divide segment and Bear Skull Mountain is at the south end. Through valleys link headwaters of northwest-oriented streams with headwaters of east and southeast-oriented streams. Bear Skull Creek, which begins as a north-oriented stream west of Bear Skull Mountain, provides evidence of the region’s drainage history. A through valley links the Bear Skull Creek valley elbow of capture with the northwest-oriented South Fork of Baking Powder Creek. Headwaters of the north-oriented Bear Skull Creek segment are linked by high level through valleys with headwaters of the northwest-oriented East Fork of northwest-oriented Butte Creek. Southeast-oriented Hay Creek originates just east of Bear Skull Mountain, which suggests flood waters that eroded the Hay Creek valley flowed over the Bear Skull Mountain top and then the north-oriented Bear Skull Creek valley segment eroded south to behead and capture southeast-oriented flood flow that had been moving to the Hay Creek valley. Subsequently Powder River valley headward erosion beheaded and captured the southeast-oriented flood flow causing flood flow already on the northwest ends of the beheaded flood flow routes to reverse flow direction and to create the present day Powder River-Little Powder River drainage divide and to erode the northwest-oriented valleys.

Detailed map of through valley at head of Little Bear Skull Creek

Figure 7: Detailed map of through valley at head of Little Bear Skull Creek. United States Geological Survey map digitally presented using National Geographic Society TOPO software. 

Figure 7 illustrates a detailed map of the northwest-oriented South Fork Baking Powder Creek drainage divide with east-oriented Little Bear Skull Creek and east-oriented Bear Skull Creek. This is an asymmetric drainage divide and evidence suggests it was eroded by southeast-oriented flood flow moving into the Little Powder River valley. Note how Little Bear Skull Creek begins in an escarpment-surrounded basin or abandoned headcut that has been eroded into the east-facing escarpment face. THis headcut was being eroded headward or west when the southeast-oriented flood waters were beheaded and captured by Powder River valley headward erosion. What is particularly interesting here are the multiple through valleys linking northwest-oriented South Fork Baking Powder Creek with east-oriented Little Powder River tributaries. These multiple through valleys are evidence southeast-oriented flood flow was using multiple anastomosing channels to flow across the region when the deep north-oriented Little Powder River valley eroded headward into the region. Also evidence here suggests most erosion of the northwest-oriented South Fork Baking Powder Creek valley was done at a time when flow in that valley was southeast-oriented. Today flow in that valley is northwest-oriented, which means the flow direction was reversed when the deep Powder River valley beheaded and captured the southeast-oriented flow. However, that beheading occurred rapidly after the deep Little Powder River valley eroded south so there was not enough time for the east-oriented tributary valleys to erode deep valleys headward into the present day Powder River-Little Powder River drainage divide area.

Detailed map of Bear Skull Mountain area

Figure 8: Detailed map of Bear Skull Mountain area.  United States Geological Survey map digitally presented using National Geographic Society TOPO software. 

Figure 8 is a detailed map of the Bear Skull Mountain area. Note how east and southeast-oriented Hay Creek originates in an escarpment surrounded basin on the Bear Skull Mountain east face. That escarpment-surrounded basin is an abandoned headcut formed when southeast-oriented flood water flowing on the East Fork Butte Creek alignment (see figure 6) and on a topographic surface at least as high as the Bear Skull Mountain eroded a deep Hay Creek valley headcut northwest and west. For some reason, probably a resistant rock mass, headward erosion of the deep Hay Creek valley was halted and east and southeast-oriented valleys being eroded north and south of the present day Bear Skull Mountain were able to erode west of Bear Skull Mountain to behead and capture southeast-oriented flood flow that had been eroding the deep Hay Creek valley. Note how southeast-oriented Badger Creek (figure 8 south center) has eroded west of Bear Skull Mountain and is linked by through valleys with west-oriented headwaters of northwest-oriented Butte Creek. But even more significant, the deep east-oriented Bear Skull Creek valley was able to erode south to behead and capture the southeast-oriented flood flow that was moving to the Hay Creek valley and in the process lowered the regional topographic surface so Bear Skull Mountain is today an isolated erosional remnant. The reason there is no clear-cut link today between northwest-oriented East Fork Butte Creek and Bear Skull Creek can be seen on figure 6. Headward erosion of the northeast-oriented Powder River valley beheaded flood flow moving southeast on the present day Baking Powder Creek route and flood water already on the northwest end of that flood flow route reversed flow direction to flow northwest to the newly eroded Powder River valley. That reversed flood flow captured southeast-oriented flood flow moving on the yet to be beheaded Butte Creek-East Fork alignment and that captured flood flow eroded northeast-oriented valleys linking northwest-oriented East Fork Butte Creek headwaters with northwest-oriented Baking Powder Creek headwaters.

Powder River-Little Powder River drainage divide area near Bay Horse

Figure 9: Powder River-Little Powder River drainage divide area near Bay Horse. United States Geological Survey map digitally presented using National Geographic Society TOPO software. 

Figure 9 illustrates the Powder River-Little Powder River drainage divide region south of the figure 6 map area and includes some overlap. The Montana-Wyoming state line is located just south of the figure 9 map area. Bay Horse Creek flows northwest to the figure 9 northwest corner. The North and South Forks of northwest-oriented Three Bar Creek are located in the figure 9 southwest corner. Northwest-oriented Butte Creek headwaters are located in the figure 9 north center. Bowers Creek flows east from the figure 9 south center to the figure 9 southeast corner. Named southeast-oriented Little Powder River tributaries from north to south are Hay Creek, Badger Creek, Blacktail Creek, Wild Bill Creek, Mitchell Creek, and North Fork Bowers Creek. Northwest-southeast oriented through valleys link northwest-oriented Butte Creek headwaters with southeast-oriented headwaters of Badger Creek, Blacktail Creek, Wild Bill Creek, North Fork Bowers Creek, and Mitchell Creek. These multiple through valleys are evidence of a small-scale southeast-oriented anastomosing channel complexes prior to beheading of southeast-oriented flood flow on the Butte Creek alignment, however larger northwest-oriented valleys appear to be components of a much larger scale southeast-oriented anastomosing channel complex as well. Headwaters of east-oriented Bowers Creek are linked by multiple through valleys to northwest-oriented Bay Horse Creek headwaters and higher level through valleys link Bowers Creek headwaters with headwaters of west-oriented North Fork flowing to northwest-oriented Three Bar Creek. In other words the east-oriented Bowers Creek valley is connecting valleys of what once were three different southeast-oriented flood flow channels in much the same way anastomosing channels are interconnected.

Detailed map of Bay Horse through valley area

Figure 10: Detailed map of Bay Horse through valley area. United States Geological Survey map digitally presented using National Geographic Society TOPO software. 

Figure 10 is a detailed map of through valleys connecting east-oriented Bowers Creek headwaters with northwest-oriented Bay Horse Creek headwaters. Note the presence of multiple valleys between the streamlined erosional residuals. Large volumes of water once flowed southeast from the Bay Horse Creek valley to the Bowers Creek valley and used multiple channels. These multiple channels are typical of anastomosing channels formed during large flood events. Flood flow through the Bay Horse region ceased when headward erosion of the northeast-oriented Powder River valley beheaded and captured the southeast-oriented flood flow. Flood flow already present on the northwest end of what was then the beheaded Bay Horse Creek-Bowers Creek flood flow route reversed flow direction to flow northwest to the newly eroded Powder River valley, to create the Powder River-Little Powder River drainage divide, and to erode the northwest-oriented Bay Horse Creek valley. Since then Bay Horse area landforms have remained largely unchanged.

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.