A geomorphic history based on topographic map evidence

This essay provides an overview of more detailed essays which use topographic map evidence to interpret the history of drainage divides within and surrounding the Tongue River drainage basin. Detailed essays can be found under Tongue River on this website’s sidebar category list. Detailed essays describing Tongue River drainage divide areas in southeast Montana and Wyoming’s Powder River basin have been published and remaining Tongue River drainage divide areas in the Bighorn Mountains will be published sometime in 2012 or early 2013. The Tongue River originates in northern Wyoming in the high Bighorn Mountains and from the Bighorn Mountain base flows in a northeast direction to and across southeast Montana before turning to flow for a short distance in a northwest direction (near Miles City, Montana) to join the northeast-oriented Yellowstone River as a barbed tributary. Tongue River headwaters, including headwaters of Goose Creek which is a major Tongue River tributary, drain a significant section of the high Bighorn Mountains. To the west of the Tongue River drainage basin is the north-oriented Bighorn River drainage basin, to the north is the north-oriented Little Bighorn River drainage basin, and to the east is the north and north-northeast oriented Powder River drainage basin, all of which are tributary to the northeast-oriented Yellowstone River. Topographic map evidence illustrated in detailed essays and in similar Missouri River drainage basin landform origins research project essays (published on this website) documents an immense southeast-oriented flood which crossed the entire Tongue River drainage basin, including the present day high Bighorn Mountains. Flood waters were derived from a rapidly melting thick North American ice sheet, which was located in a deep “hole” created by deep glacial erosion and crustal warping caused by the ice sheet’s tremendous weight. Prior to Tongue River drainage basin development ice-marginal southeast-oriented melt water floods flowed on a topographic surface now represented by some of the highest level Bighorn Mountains erosion surfaces. Ice sheet melting opened up space in the deep “hole” the decaying ice sheet had been occupying and deep northeast-oriented valleys eroded headward from the ice sheet’s southwest margin to capture the high-level southeast-oriented floods and to divert flood waters into the deep “hole”. Headward erosion of the deep Yellowstone River-Tongue River valley and tributary valleys captured the flood waters and diverted flood flow in a northeast direction so as to flow into space the rapidly melting ice sheet had once occupied. The Bighorn Mountains emerged as flood waters eroded the Tongue River drainage basin. The Bighorn Mountains emerged as flood waters deeply eroded surrounding regions and/or as ice sheet-triggered crustal warping uplifted present day mountain ranges.

Tongue River drainage basin location map

Figure 1: Tongue River drainage basin location map. National Geographic Society map digitally presented using National Geographic Society TOPO software.

Tongue River drainage basin drainage history

The Tongue River originates in northern Wyoming along the west edge of the high Bighorn Mountains crest, and from the Bighorn Mountains base flows in a northeast direction to and into Montana and almost to Miles City, Montana, where it turns to flow in a northwest direction to join the northeast-oriented Yellowstone River as a barbed tributary. The northeast-oriented Yellowstone River joins the east and southeast-oriented Missouri River with water eventually reaching the Gulf of Mexico. Major Tongue River tributaries originating in the high Bighorn Mountains are shown in figure 2 below and include the southeast, northeast, and north-northeast oriented North Tongue River, northwest and north-northwest oriented South Tongue River, north and northeast oriented Big Goose Creek, and north-northeast oriented Little Goose Creek. Note how several Tongue River tributaries and other streams in the high Bighorn Mountains are oriented in southeast or northwest directions. West of the Tongue River drainage basin in the Bighorn Mountains is the north-oriented Bighorn River drainage basin with the Bighorn River being located along the Bighorn Mountains base and approximately 1800 meters lower than elevations of mountain peaks forming the Bighorn River-Tongue River drainage divide. North of the Tongue River drainage basin in the high Bighorn Mountains is the north-oriented Little Bighorn River drainage basin. The Little Bighorn River is a Bighorn River tributary, with the Bighorn River flowing to the Yellowstone River. East of the Tongue River drainage basin in Wyoming and southern Montana is the north and north-northwest oriented Powder River drainage basin, with the Powder River flowing in a north, northeast, and north-northwest direction to also join the northeast-oriented Yellowstone River. East and north of the Bighorn Mountains base many Tongue River tributaries from the north and west are southeast oriented barbed tributaries while many tributaries from the south and east are northwest oriented. Hanging Woman Creek, Otter Creek, and Pumpkin Creek are north oriented Tongue River tributaries in Montana and also have southeast-oriented barbed tributaries from the west and northwest-oriented tributaries from the east and turn to flow in northwest or north-northwest directions before joining the Tongue River.

Figure 2: Drainage map for Tongue River headwaters area in the high Bighorn Mountains. United States Geological Survey map digitally presented using National Geographic Society TOPO software. 

Note in figure 2 a northwest-southeast drainage alignment for many of the secondary Tongue River tributaries and also for headwaters of major tributaries. This northwest-southeast drainage alignment is much more obvious on more detailed maps and is present in regions north and east of the Bighorn Mountains and also in the high Bighorn Mountains. This northwest-southeast drainage alignment is illustrated in much greater detail in the detailed essays and represents a landform feature that must be explained. Each of the Tongue River drainage basin landform origins detailed essays includes nine or more detailed maps including at least eight topographic maps of specific Tongue River drainage basin drainage divide areas. The detailed essays illustrate and describe all southeast Montana Tongue River drainage divide areas and most Wyoming Tongue River drainage divide areas located north and east of the Bighorn Mountain base. Detailed essays for Tongue River drainage basin drainage divides in the Bighorn Mountains have yet to be published, although are scheduled to be published during 2012 or in early 2013. Topographic map evidence presented in this overview essay and in the published detailed essays, as well as in other Missouri River drainage basin landform origins research project published essays (all found on this website) strongly suggests immense southeast-oriented floods crossed the entire Tongue River drainage basin, including areas located in what are today the high Bighorn Mountains, although at the time floods crossed the region the Bighorn Mountains did not stand high above surrounding areas as they do today.

Figure 3: North Tongue River headwaters in high Bighorn Mountains. United States Geological Survey map digitally presented using National Geographic Society TOPO software. 

What evidence indicates immense southeast-oriented floods flowed across what are today the high Bighorn Mountains? Figure 3 illustrates the North Tongue River headwaters near Little Bald Mountain. Note how the North Tongue River begins as a southeast-oriented stream and turns to flow in a northeast direction. Note also southeast-oriented Hideout Creek, which is a North Tongue River tributary and northwest-oriented Spring Creek and northwest and north oriented Bull Creek, which are also North Tongue River tributaries. Note how the southeast-oriented North Tongue River valley is linked by a deep through valley with the south-southwest oriented South Beaver Creek valley. South of figure 3 Beaver Creek flows in a south-southeast direction to join west-oriented Shell Creek, which flows to the north oriented Bighorn River. Elevation of the pass where the highway crosses from the Bighorn River drainage basin to the Tongue River drainage basin is between 2800 and 2820 meters. The elevation where Beaver Creek joins Shell Creek at the Bighorn Mountain base is between 1240 and 1260 meters, which demonstrates a drop of more than 1550 meters on the Bighorn Mountains west slope. Anyone looking at the Bighorn Mountains west slope today would probably be tempted to say there is no way a flood eroded the through valley linking the South Beaver Creek valley with the southeast-oriented North Tongue River headwaters valley. Yet the through valley exists and is more than 200 meters deep. It is a water eroded feature and the water came from somewhere. Further, a close look at figure 3 drainage divides reveals many other through valleys crossing high Bighorn Mountains ridges, some of which link north and northwest-oriented North Tongue River tributary valleys with south-oriented Shell Creek tributary valleys and some of which link the North Tongue River valley with north-oriented valleys draining to the north-oriented Little Bighorn River. These through valleys are all water eroded landforms and the water came from somewhere. Topographic map evidence suggests these through valleys were eroded as anastomosing flood flow channels by immense southeast-oriented floods, which implies at the time flood waters crossed what are today the high Bighorn Mountains the Bighorn Mountains did not stand high above the surrounding region.

Figure 4: South Tongue River-Shell Creek drainage divide area at Granite Pass. United States Geological Survey map digitally presented using National Geographic Society TOPO software. 

Figure 4 illustrates more evidence that immense floods flowed across the high Bighorn Mountains and crossed what is today the Tongue River-Bighorn River drainage divide. The north-oriented river flowing to the figure 4 north center edge is the South Tongue River. Prospect Creek flows in a northeast direction from Granite Pass to join the north-northeast oriented West Fork of the South Tongue River. Granite Creek is the south and south-southwest oriented stream on the south side of Granite Pass and flows to northwest oriented Shell Creek, which is located in Shell Canyon (in figure 4 southwest corner). West of the figure 4 map area Shell Creek turns to flow in west direction to join the north-oriented Bighorn River. Granite Pass is labeled as having an elevation of 2753 meters. The spot elevation in Shell Canyon near the figure 4 southwest corner reads 1982 meters, indicating a drop of almost 800 meters in the short distance shown. Cedar Mountain to west of Granite Pass rise to 2991 meters while Dome Peak to the east rises to 3300 meters. Granite Pass is a water eroded valley at least 240 meters deep and the water that eroded the valley came from somewhere. Just as interesting as Granite Pass are passes linking northwest and west-oriented tributaries to the north-northwest oriented East Fork South Tongue River with southeast and east-oriented headwaters of streams flowing to the figure 4 east edge. Those streams flowing to figure 4 east edge are tributaries to north-oriented Big Goose Creek, which is a Tongue River tributary (see figure 2). North of Lookout Mountain a through valley links northwest-oriented Sucker Creek with an east-oriented tributary to northeast-oriented Quartz Creek. South of Lookout Mountain a through valleys links northwest-oriented Graves Creek with southeast-oriented Sawmill Creek. A slight distance further south another through valley links the northwest-oriented Mohawk Creek valley with the southeast-oriented Sawmill Creek valley. And just a short distance further south another through valley links the west-oriented East Fork South Tongue River valley with the valley of an east-oriented Sawmill Creek tributary valley. And still another through valley, although at a higher level, is located at Rock Chuck Pass. These through valleys provide evidence of a southeast-oriented anastomosing channel complex that was eroded into what is today the high Bighorn Mountains surface. Again, at the time flood waters crossed the Bighorn Mountains the Bighorn Mountains did not stand high above the surrounding region.

• Why would immense southeast-oriented floods be flowing across what are now the high Bighorn Mountains and how could those southeast-oriented flood waters flow across what are today high mountain elevations? The Tongue River drainage basin history began with development of a North American ice sheet comparable in size to the present day Antarctic Ice Sheet, if not larger. The ice sheet was thick, probably several kilometers thick, and was located in a deep “hole”, which the ice sheet had formed by a combination of deep glacial erosion and crustal warping caused by the ice sheet weight. When at its maximum size the ice sheet stood high above the pre-glacial surface, but also had roots that extended well below the pre-glacial surface, which no longer exists. The Tongue River drainage basin location was probably located south and west of ice sheet’s southwest margin, although evidence for the ice sheet’s southwest margin has probably been removed by deep melt water flood erosion. The pre-glacial surface under the ice sheet was completely destroyed by deep glacial erosion and the pre-glacial surface adjacent to the ice sheet and elsewhere on the North American continent was deeply eroded by deep melt water flood erosion and was also probably significantly altered by crustal warping caused by the thick North American ice sheet presence.

• Events important to Tongue River drainage basin history began as the ice sheet was rapidly melting and had melted to the point that in the south it no longer stood high above the surrounding non-glaciated surface, which had probably already been significantly lowered by deep melt water erosion. Immense melt water floods were flowing in a southeast direction along the ice sheet’s southwest margin and were just beginning to deeply erode the region between the Rocky Mountains and the ice sheet’s southwest margin, which at that time was located north and east of today’s Tongue River drainage basin. At that time the Rocky Mountains did not stand high above the ice sheet surface, or for that matter above the surface located between the Rocky Mountains and the ice sheet southwest margin. Initially immense floods of melt water flowing from the rapidly melting ice sheet flowed across and along what is now the east-west continental divide. Flood waters flowing into northern Wyoming were probably derived from immense southeast and south-oriented supra-glacial melt water rivers which had carved giant ice-walled and ice-floored (later bedrock-floored) canyons into the decaying ice sheet surface and which flowed to the ice sheet’s southwest margin in present day Alberta and then across the east-west continental divide into a gigantic southeast-oriented river which was flowing along the alignment of the present day northwest-southeast oriented Rocky Mountain Trench. Until headward erosion of deep valleys from the Pacific Ocean systematically captured this immense southeast-oriented melt water river the deep Rocky Mountain Trench valley did not exist and flood waters flowed in a southeast direction across western Montana to the present day Yellowstone Plateau area and then in a southeast direction across Wyoming. Tongue River drainage basin drainage history began as deep northeast-oriented valleys eroded headward from the deep “hole” the decaying ice sheet had once occupied to capture this gigantic southeast-oriented melt water river and to divert the flood waters into ice sheet’s deep “hole”.

• How did the deep “hole” the ice sheet had been occupying open up so as to permit headward erosion of the deep northeast-oriented Yellowstone River-Tongue River valley? Remember, the ice sheet was thick and had deep roots. The ice sheet roots may have extended more than a kilometer below the pre-glacial surface on which the ice sheet had formed. The deep “hole” had probably been formed by a combination of deep glacial erosion of the pre-glacial surface underlying the ice sheet and of crustal warping caused by the weight of an ice sheet several kilometers thick. The crustal warping, which almost certainly did not occur instantaneously, probably also affected regions elsewhere on the continent and may have contributed to uplift of the Rocky Mountains and other North American mountain ranges and high plateau areas as flood waters flowed across them. In other words, not only was the rapidly decaying ice sheet located in a deep “hole” that was opening up as the ice sheet melted, but delayed crustal warping caused by the ice weight was raising mountain ranges and high plateaus regions south and west of the ice sheet margin. The combination of these two events created a situation where the gigantic southeast-oriented melt water river flowing across and along what is now the east-west continental divide was systematically captured by headward erosion of deep northeast-oriented valleys, which were eroding headward from the decaying ice sheet location.

• In the case of the Yellowstone River-Tongue River valley (and other major northeast-oriented valleys in Montana, Wyoming, and North and South Dakota) it eroded headward from a huge southeast and south-oriented ice-walled and ice-floored (later bedrock-floored) canyon which was carved by an immense southeast and south oriented supra-glacial melt water river north and east of the ice sheet southwest margin. The Missouri Escarpment in North and South Dakota and in Saskatchewan is today what remains of that giant canyon’s west and southwest wall. The ice floor of that giant southeast and south-oriented ice-walled canyon was significantly lower in elevation than the bedrock surface south and west of the decaying ice sheet margin and the huge melt water river flowing in that southeast and south-oriented ice-walled canyon represented the region’s major drainage route, which captured the immense southeast-oriented ice-marginal floods by eroding deep northeast-oriented tributary valleys headward across the ice sheet’s southwest margin and then headward into the adjacent bedrock surface. These deep northeast-oriented valleys diverted the immense southeast-oriented ice-marginal floods into space the ice sheet had once occupied. Melting of what had been the thick ice sheet roots progressively lowered both the ice sheet surface, the ice-walled canyon floor, and the surrounding bedrock surface, creating a situation where new and even deeper northeast-oriented valleys repeatedly eroded headward to capture the immense southeast-oriented ice-marginal melt water floods. The deep northeast-oriented Yellowstone River-Powder River, Yellowstone River-Tongue River, Yellowstone River-Bighorn River valleys we see today were probably eroded very late in the ice sheet melt down history and were probably preceded by several earlier, but similar northeast-oriented valleys which also diverted massive southeast-oriented ice-marginal floods onto the decaying ice sheet surface. Valleys were eroded headward in sequence, with valleys located in the east being eroded headward first.

Figure 5. Tongue River-Hanging Woman Creek drainage divide area south of Birney, Montana.  United States Geological Survey map digitally presented using National Geographic Society TOPO software. 

What evidence suggests immense southeast-oriented floods crossed the Tongue River drainage basin north and east of the Bighorn Mountains? Figure 5 illustrates the Tongue River-Hanging Woman Creek drainage divide area south of Birney, Montana (see figure 1 for location). The northeast oriented river flowing from the figure 5 southwest corner to Birney is the Tongue River and the major north-oriented tributary joining the Tongue River at Birney is Hanging Woman Creek). Note how Tongue River tributaries from the west and north are southeast-oriented and enter the northeast oriented Tongue River as barbed tributaries. Also note how Tongue River and Hanging Woman Creek tributaries from the south and east are northwest-oriented. This northwest-southeast orientation of tributary valleys is evidence the present day Tongue River and Hanging Woman Creek valleys eroded headward across a massive southeast-oriented flood, with the Hanging Woman Creek valley capturing the flood flow first and headward erosion of the Tongue River valley then beheading flood flow routes to the newly eroded north-oriented Hanging Woman Creek valley. Flood waters were flowing on topographic surface at least as high as the highest figure 5 elevations today and were probably flowing in what was then a southeast-oriented anastomosing channel complex. Headward erosion of the deep northeast oriented Tongue River valley (and its north-oriented Hanging Woman Creek tributary valley) across this southeast-oriented anastomosing channel complex captured the flood waters and diverted the flood flow in a northeast direction to the deep “hole” the melting ice sheet had once occupied. Tongue River valley (and Hanging Woman Creek valley) headward erosion beheaded the flood flow channels one at a time in sequence from the northeast to the southwest (or in the case of Hanging Woman Creek from north to south). Flood waters on northwest ends of newly beheaded flood flow channels reversed flow direction to erode what are today northwest-oriented tributary valleys. Because the flood flow channels were beheaded one at a time and also because the flood flow channels were anastomosing (or interconnected) reversed flood flow in a newly beheaded channel could capture southeast-oriented flood flow from channels further to the southwest. Such captures of flood water from yet to be beheaded flood flow channels provided the water volumes needed to erode significant northwest-oriented tributary valleys. Flood flow to the newly eroded Tongue River valley was subsequently beheaded by headward erosion of the northeast and north-northwest oriented Rosebud Creek valley which is Yellowstone River tributary valley (see figure 1). Further evidence of former southeast-oriented flood flow channels is found in shallow through valleys, which today link valleys of northwest-oriented Tongue River tributaries with east-oriented Hanging Woman Creek tributary valleys.

• Published Tongue River, Yellowstone River, Powder River, and Bighorn River drainage basin landform origins essays on this website use several hundred topographic maps to illustrate and describe evidence the deep Yellowstone River-Tongue River valley (and Tongue River tributary valleys) eroded headward from the Yellowstone River-Tongue River confluence region across southeast Montana to the present day Bighorn Mountains base and systematically captured southeast-oriented flood waters and diverted the flood flow into the deep “hole” the rapidly melting ice sheet had previously occupied. Published essays can be under appropriate river names on this website’s sidebar category list.

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.