A geomorphic history based on topographic map evidence
Yellowstone River drainage basin map
Figure 1: Yellowstone River drainage basin map (select and click on map to enlarge). National Geographic Society map digitally presented using National Geographic Society TOPO software.
Yellowstone River drainage basin drainage history
The Yellowstone River drainage basin is primarily located in Wyoming and Montana, although the northeast oriented Yellowstone River does enter North Dakota to join the east and southeast oriented Missouri River. Southwest of the Yellowstone River drainage basin in northwest Wyoming is the west-oriented Snake River drainage basin and the east-west continental divide is located between the Yellowstone and Snake River drainage basins. West, north, and east of the Missouri River drainage basin is the north, east, and southeast oriented Missouri River drainage basin, of which the Yellowstone River drainage basin is a component. South of the Yellowstone River drainage basin in central Wyoming is the east-oriented North Platte River drainage basin, with the North Platte River flowing to the Platte River, which in turn flows to the south-oriented Missouri River. Major Yellowstone River tributaries are north oriented and include the northeast and northwest-oriented Powder River, the north-northeast oriented Tongue River, and the north-oriented Bighorn River, which obtains much of its water from southeast oriented tributaries including the Wind River. Tributaries from the north are significantly shorter and today the Yellowstone River drainage basin is primarily a north- or northeast-oriented drainage basin flowing to what is today a southeast- and south-oriented river system.
- Looking at the Yellowstone River drainage system today one is tempted to suggest the Yellowstone River drainage basin originated in pre-glacial time and was blocked in northeast Montana and/or northwest North Dakota by a continental ice sheet margin, which caused northeast-oriented Yellowstone River water (and water from other northeast-oriented rivers) to spill over drainage divides along the ice sheet margin to erode the present day Missouri River valley. While there is topographic map evidence to suggest the northeast-oriented Yellowstone River valley and other northeast-oriented river valleys were blocked by a continental ice sheet margin the evidence does not support the pre-glacial origin interpretation. However, evidence illustrated and described in the detailed essays for the Yellowstone River and adjacent river drainage basins strongly suggests the deep northeast-oriented Yellowstone River valley in eastern Montana and its north-oriented tributary valleys in southeast Montana and northeast Wyoming were eroded headward across immense southeast-oriented floods. These large southeast-oriented floods were derived from a rapidly melting North American ice sheet and were flowing along the decaying ice sheet’s southwest margin. In other words, the Yellowstone River drainage basin as seen today did not exist in pre-glacial times, but instead was eroded by giant melt water floods as the ice sheet rapidly melted.
Figure 2: Yellowstone River, Bighorn River, and Powder River headwaters in northwest and north central Wyoming. National Geographic Society map digitally presented using National Geographic Society TOPO software.
The Yellowstone River drainage basin landform origins collection does not yet include detailed essays describing drainage divides surrounding the northwest-oriented Yellowstone River headwaters in northwest Wyoming, the north-oriented Bighorn River and southeast-oriented Wind River drainage basins in Wyoming, the Tongue River headwaters in the Bighorn Mountains, or the Powder River headwaters in and south of the Bighorn Mountains, however, when those detailed essays are published they will provide significant topographic map evidence suggesting immense southeast-oriented floods once crossed the present day Yellowstone Plateau, Absaroka Mountains, Owl Creek Mountains, Wind River Mountains, and Bighorn Mountains. Today the mountain ranges stand high above the surrounding basins and it is difficult to imagine how large southeast-oriented melt water floods from a continental ice sheet could have flowed have flowed across them. For example, Cloud Peak in the Bighorn Mountains has an elevation of 4012 meters on figure 2 and elevations in the Bighorn Basin to the west (in the Bighorn River valley) are less than 1200 meters. Further, evidence demonstrates flood water flowed across what is now the east-west continental divide, which today is difficult to visualize, yet the topographic map evidence for floods is overwhelming. For example, Two Ocean Pass located south of Yellowstone Nation Park in figure 2 and illustrated in figure 3 below is a deep through valley linking the present day Yellowstone River drainage basin (which drains to the Gulf of Mexico) with the Snake River drainage basin (which drains to the Pacific Ocean). In figure 3 below Atlantic Creek flows to the figure 3 northeast corner and then to the northwest-oriented Yellowstone River with the water eventually reaching the Gulf of Mexico and Pacific Creek flows to the figure 3 southwest corner with the water eventually reaching the west-oriented Snake River and eventually the Pacific Ocean. Note how northeast-oriented Atlantic Creek and southwest-oriented Pacific Creek are linked by a 2000-foot deep through valley. Similar through valleys, although not always as deep or as neatly defined as Two Ocean Pass, cross drainage divides throughout the Yellowstone River drainage basin and also all drainage divides between the Yellowstone River drainage basin and adjacent drainage basins. Obviously present day topography did not exist when flood waters flowed across the region, but the through valleys exist and they are erosional features which demand an explanation.
Figure 3: Two Ocean Pass south of Yellowstone Park in northwest Wyoming links northeast-oriented Atlantic Creek, water in which eventually reaches the Gulf of Mexico, with southwest-oriented Pacific Creek, water in which eventually reaches the Pacific Ocean. United States Geological Survey map digitally presented using National Geographic Society TOPO software.
Why would immense southeast-oriented floods be flowing across what are now high Wyoming mountain ranges and how could those southeast-oriented flood waters flow across the high mountain elevations? The Yellowstone 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. Most or all of the Yellowstone 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 Yellowstone 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 Yellowstone 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. Yellowstone River drainage basin drainage history is the history of how 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 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 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, Missouri River, Musselshell River, and Little Missouri River valleys (and other northeast-oriented 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.
Figure 4: Yellowstone River confluence with Missouri River along Montana-North Dakota border. National Geographic Society map digitally presented using National Geographic Society TOPO software.
Figure 4 illustrates the Yellowstone River-Missouri River confluence region located along the Montana-Wyoming border. The Missouri River in northwest North Dakota is flowing approximately along the north-south continental divide, with Missouri River water eventually reaching the Gulf of Mexico and water in the southeast oriented Souris (or Mouse) River to the north and east (in figure 4 northeast corner) eventually reaching Hudson Bay. The Souris River valley floor is generally lower in elevation than the Missouri River. Between the Missouri River valley and the Souris River is a poorly drained region known as the Missouri Coteau, which has a landscape suggesting the region was once covered by a slowly melting ice sheet, which deposited significant debris as it melted. North and east of this Missouri Coteau region is the northeast-facing Missouri Escarpment slope, which drains to the southeast oriented Souris River and/or its southeast and east oriented tributaries. Topographic map features on the Missouri Escarpment slope and in the lowland drained by the Souris River along the Missouri Escarpment base are completely different from features on the Missouri Coteau and, while not devoid of glacial features, lack many of the glacial features found in the Missouri Coteau region, suggesting glacial deposits are much thinner. The Missouri Escarpment and Missouri Coteau are located outside of the present day Yellowstone River drainage basin and for that reason detailed essays describing them must be found under ND Missouri on the sidebar category list. However, understanding northwest North Dakota drainage history is important in understanding Yellowstone River valley history.
- As the ice sheet melted, especially along its southwest margin in North and South Dakota, northeast Montana, and southern Saskatchewan, the large southeast oriented ice-marginal floods (and the headward erosion of deep northeast-oriented valleys from the ever-lowering southeast and south-oriented ice-walled canyon floor) gradually lowered elevations in the region south and west of the decaying ice sheet’s southwest margin and north and east of the emerging Rocky Mountain ranges. The Rocky Mountain ranges were emerging as flood waters deeply eroded the regions around them and also probably as delayed crustal warping triggered by the immense ice sheet weight selectively uplifted areas where deep flood water erosion had occurred and perhaps lowered areas where flood waters had deposited sediments (it is impossible to tell from topographic maps what rock types underlie basin areas between the mountain regions). As the ice sheet’s southwest margin continued to decay, the southeast-oriented ice marginal floods, which were flowing at a higher elevation than the deep ice-walled and bedrock-floored canyon floor to the northeast and east, began to breach the ice barrier and to flow into the giant ice-walled and bedrock-floored canyon. Evidence for those breaches is today located along the Missouri Escarpment where deep valleys have been eroded into the Missouri Escarpment slope.
- One such breach was located in the region north of Williston, North Dakota and in figure 4 extended from the Missouri Escarpment base near Crosby, North Dakota in a south and southwest direction. Figure 4 illustrates the Yellowstone River confluence with the Missouri River and note how the southeast oriented Missouri River turns at its junction with the Yellowstone River to flow in a northeast direction to the mouth of south-oriented Little Muddy River near Williston. The northeast-oriented Yellowstone River valley we see today probably was eroded headward from the ice sheet breach which was responsible for eroding what is today the large Little Muddy River valley, which at the time it was eroded was probably a deep ice-walled canyon sliced into the decaying ice sheet’s southwest margin. Between the Little Muddy River and Crosby the large valley is partially filled with what on topographic maps appear to be glacial deposits. The deep southeast and south-oriented ice-walled canyon from which the northeast-oriented Yellowstone River valley eroded was for most of its history the route of a gigantic southeast oriented melt water river. However, late in its history, as the ice sheet was in its final stages of decay, the large southeast and south oriented melt water river in that deep ice-walled canyon was captured and diverted north and east as new and lower outlets to the present day Saint Lawrence River drainage basin and later to what is now Hudson Bay had opened up. These diversions of what had been south-oriented oriented melt water floods to flow to northern outlets created a north-oriented drainage network on the floors of ice-walled and bedrock-floored canyons separating the decaying ice sheet remnants.
- Why do glacial sediments now fill that former ice sheet margin breach valley? To answer that question think about what the immense south-oriented melt water floods were doing when they were captured and diverted north. Those massive south-oriented melt water floods had been flowing to the Gulf of Mexico and forcing warm Gulf of Mexico waters into the Atlantic Ocean, where the warm waters then moved north to warm Northern Hemisphere climates. When those immense south-oriented floods were captured so as to flow across what had been the ice sheet’s floor in northward directions the flood waters then began to displace what were cold waters, which then moved south into the Atlantic Ocean to cool the North Hemisphere climate. The resulting climatic change halted the ice sheet’s rapid melting and north-oriented flood waters located on the ice sheet floor began to freeze, with what for all practical purposes was a thin ice sheet beginning to form. Incorporated into that new thin ice sheet were the isolated and rejuvenated thick ice sheet remnants, including remnants of what had been the decaying ice sheet’s southwest margin ice barrier. The resulting thin ice sheet blocked the breaches through the ice sheet’s southwest margin, which had the effect of damming the newly eroded and deep northeast oriented valleys at the ice sheet’s southwest margin. Water spilled from one valley segment to another along the ice sheet margin, which resulted in headward erosion of the present day North Dakota and northeast Montana Missouri River valley. Unlike the previous thick ice sheet, the new thin ice sheet did not deeply erode the underlying landscape, although it did alter some surface features. Because the new thin ice sheet between former thick ice sheet remnants was formed by the freezing of north-oriented flood water, the frozen flood water areas tended to be wet based, which meant large slabs of ice could easily move and sometimes carry underlying slabs of frozen bedrock with them. Such movements of wet based frozen flood water, which also included frozen slabs of the underlying bedrock, combined with expansion of the rejuvenated thick ice sheet remnants along the ice sheet’s southwest margin, partially filled the northeast and east-oriented valleys, which had previously been eroded across the ice sheet’s southwest margin. The thin ice sheet did melt, with areas between the rejuvenated thick remnants melting first. The thick ice sheet remnants melted much more slowly and today in North Dakota include the Missouri Coteau and Turtle Mountain upland area.
Figure 5: Reduced sized topographic maps illustrating the Redwater River-Yellowstone River drainage divide located northwest of Glendive, Montana. Northwest-oriented streams in the figure 5 northwest corner flow to the northeast-oriented Redwater River, which flows to the Missouri River. Southeast-oriented streams in remaining sections of figure 5 flow to the northeast-oriented Yellowstone River. The northwest-southeast oriented highway is the highway between Circle and Glendive shown in figure 4. United States Geological Survey map digitally presented using National Geographic Society TOPO software.
Figure 5 provides a sample of topographic map evidence illustrated and discussed in the presently written Yellowstone River drainage basin landform origins detailed essays. Northwest-oriented streams in the figure 5 northwest corner flow to the northeast-oriented Redwater River, which is a Missouri River tributary (see figure 4). Southeast-oriented streams in the remainder of figure 5 flow to the northeast-oriented Yellowstone River (and are barbed tributaries). Note the aligned northwest-southeast oriented drainage that prevails across the entire region and on both sides of the drainage divide. Also note how shallow through valleys cross the drainage divide and link the northwest-oriented Redwater River tributary valleys with the southeast-oriented Yellowstone River tributary valleys. The northwest-southeast oriented drainage alignment is a relic of an immense flood eroded south-oriented anastomosing channel complex that was eroded into the northwest wall of the deep and newly eroded northeast-oriented Yellowstone River valley. At that time the deep northeast-oriented Redwater River valley to the northwest had not been eroded and flood waters were flowing on a topographic surface at least as high as the present day Redwater River-Yellowstone River drainage divide (which today represents the highest elevations in the region). Study of the southeast-oriented Yellowstone River tributary valleys reveals a network of northwest-southeast oriented through valleys eroded across the drainage divides separating them. Those through valleys provide further evidence of the former anastomosing channel complex carved by immense southeast-oriented flood waters into the newly eroded Yellowstone River valley northwest wall. Headward erosion of the deep northeast-oriented Redwater River valley captured the southeast-oriented flood waters and diverted the flood waters north to what was then a new and actively eroding Missouri River valley (not located on the present day Missouri River route), which had eroded headward from still another ice sheet margin breach. Flood waters on northwest ends of beheaded flood flow channels reversed flow direction to erode the northwest-oriented Redwater River tributary valleys. Published Powder River, Tongue River, and Bighorn River drainage basin landform origins detailed essays use several hundred topographic maps to illustrate and describe evidence the deep Yellowstone River valley (and Yellowstone River tributary valleys) eroded headward from the Yellowstone River-Missouri River confluence region to the Laurel, Montana area (which is located a short distance upstream from Billings) across immense southeast-oriented floods and systematically captured the flood waters and diverted the flood flow into the deep “hole” the rapidly melting ice sheet had previously occupied.
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.