A geomorphic history based on topographic map evidence

Abstract:

This essay provides an overview of more detailed essays describing North and South Dakota Grand River drainage basin landform origins. The detailed essays can be found under SD Grand River on this website’s sidebar category list. The Grand River drainage basin is located in southwest North Dakota and northwest South Dakota. To the west is the north oriented Little Missouri River drainage basin. To the north is the southeast and northeast-oriented Cannonball River drainage basin. To the south is the southeast and northeast-oriented Moreau River drainage basin. The Grand River drains in a southeast and east direction and joins the south-oriented Missouri River near Mobridge, South Dakota. Major tributaries from the north tend to be southeast oriented suggesting the Grand River valley and major tributary valleys eroded headward across multiple southeast-oriented flood flow channels, such as might be found in a large-scale southeast-oriented anastomosing channel complex. Evidence supporting this southeast-oriented flood interpretation includes northwest-southeast oriented through valleys eroded across drainage divides, large abandoned southeast and east-oriented headcuts, and northwest-oriented tributaries to northeast-oriented Grand River tributaries (where the northwest-oriented tributary valleys were eroded by flood flow reversals on northwest ends of beheaded flood flow channels). Flood waters responsible for eroding the Grand River drainage basin were derived from a rapidly melting North American ice sheet and flowed in a southeast direction along the decaying ice sheet’s southwest margin. Flood waters flowing across the Grand River drainage basin once flowed in an east or southeast direction across the location of the present day south-oriented Missouri River to a breach in the ice sheet’s southwest margin to join a large melt water river, which had carved an immense ice-walled and bedrock-floored canyon into the ice sheet’s surface. Originally flow in the ice-walled and bedrock-floored canyon was south-oriented, although late in its history the flow direction was reversed. Missouri River valley headward erosion captured flood flow crossing the Grand River drainage basin as the deep Missouri River valley eroded north along the decaying ice sheet’s southwest margin. Headward erosion of the Grand River valley and its tributary valleys deeply eroded the Grand River drainage basin area. It is impossible to determine how much erosion occurred because southeast-oriented flood waters flowed across what are today the Grand River drainage basin’s highest elevations. Flood flow across the Grand River drainage basin ended when the deep north and east-oriented Little Missouri River valley eroded headward from a deep ice sheet margin breach in central North Dakota and captured the southeast-oriented flood flow. Grand River drainage basin landforms have changed little since flood flow routes to the Grand River drainage basin were beheaded.

Figure 1: Southwest North Dakota and northwest South Dakota Grand River drainage basin location map. National Geographic Society map digitally presented using National Geographic Society TOPO software.

Grand River drainage basin drainage history

The Grand River drainage basin is located in northwest South Dakota and southwest North Dakota. The North Fork Grand River originates south of Rhame, North Dakota and flows in an east and southeast direction to join the South Fork Grand River near Shadehill, South Dakota. The South Fork Grand River originates west of Buffalo, South Dakota and flows in an east-northeast and northeast direction to join the North Fork Grand River near Shadehill. From Shadehill the Grand River flows in an east direction until it turns to flow in a southeast direction to join the south-oriented Missouri River near Mobridge, South Dakota. North of the Grand River drainage basin is the southeast and northeast-oriented Cannonball River drainage basin. South of the Grand River drainage basin is the southeast, east, and east-northeast oriented Moreau River drainage basin. West of the Grand River drainage basin is the north-oriented Little Missouri River drainage basin. In west-central North Dakota the north-oriented Little Missouri River turns to flow in an east direction to join the south-oriented Missouri River. The Grand River is one of several southeast and east-oriented tributaries flowing to the south-oriented Missouri River, which are located east of the narrow north-oriented Little Missouri River drainage basin. Most of the other southeast and east-oriented rivers in southwest North Dakota and northwest South Dakota turn to flow in northeast directions to enter the south-oriented Missouri River as barbed tributaries.

• Why do rivers in southwest North Dakota and northwest South Dakota flow in southeast, east, and northeast directions to join the south-oriented Missouri River while just to the west of their headwaters is the north-oriented Little Missouri River? A popular hypothesis is the north-oriented Little Missouri River and the northeast-oriented Missouri River tributaries further to east are relics of a north-oriented pre-glacial drainage system. According to this hypothesis an ice sheet margin blocked the north-oriented rivers and the south-oriented Missouri River valley was eroded along the ice sheet margin to drain the blocked drainage. Evidence supporting this pre-glacial drainage system hypothesis includes the presence of valleys east and north of the present day Missouri River valley, in which the pre-glacial north-oriented rivers are hypothesized to have flowed. While this commonly accepted hypothesis has been repeatedly published it fails to explain much of the regional topographic map evidence and it also defies common sense logic. For example, the pre-glacial north-oriented drainage system hypothesis does not explain the southeast-oriented headwaters of almost every east-oriented Missouri River tributary. Further, the hypothesis does not explain the origin of the asymmetric drainage divide between the north-oriented Little Missouri River and the various east-oriented Missouri River tributaries. In addition the hypothesis defies common sense logic by assuming valleys eroded into easily eroded bedrock could survive glacial erosion as they were located underneath a large ice sheet and could be also be preserved from destruction by melt water flooding when that ice sheet melted.

Figure 2: Little Missouri River-North Fork Grand River drainage divide area. United States Geological Survey map digitally presented using National Geographic Society TOPO software.

If the pre-glacial north-oriented drainage system hypothesis is not correct then how and when was the Grand River drainage basin eroded? Figure 2 provides important clues as to what really happened. The north-oriented Little Missouri River is located near the figure 2 west edge. Note how Little Missouri River tributaries from the east are all northwest-oriented. The southeast-oriented North Fork Grand River is located in the figure 2 southeast quadrant and southeast-oriented streams in the figure 2 east half are North Fork Grand River tributaries. Note how northwest-oriented Little Missouri River tributary valleys are linked by northwest-southeast-oriented through valleys with valleys of the southeast-oriented North Fork Grand River and its southeast-oriented tributaries. The northwest-southeast valley orientations and through valleys provide evidence of multiple southeast-oriented flood flow channels that once crossed the figure 2 region. The flood flow channels were probably anastomosing channels and were components of an immense southeast-oriented anastomosing channel complex that covered much of southwest North Dakota and northwest South Dakota. Flood waters were flowing along the southwest margin of what was then a rapidly melting North American ice sheet. The ice sheet had been thick, probably several kilometers thick, and had been 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 it was at its maximum size the ice sheet had stood high above the pre-glacial surface, but also had roots that extended well below the pre-glacial surface. At the time flood waters eroded the Grand River drainage basin most of the thick ice sheet had melted, and at least in North and South Dakota what was left were the decaying ice sheet roots, which had been located below the pre-glacial surface.

• Flood waters flowing in a southeast direction along the ice sheet’s southwest margin deeply eroded the pre-glacial surface and the southwest North Dakota and northwest South Dakota surface seen today has no resemblance to that pre-glacial surface. Events on the decaying ice sheet’s surface played an important role in the Grand River drainage basin evolution. Immense melt water rivers flowed across the ice sheet surface to the ice sheet southern margin and carved what became giant ice-walled and bedrock-floored canyons. A huge southeast and south-oriented ice-walled and bedrock-floored canyon was located east of the present day Missouri River valley in North and South Dakota and the Missouri Escarpment is what remains of that giant canyon’s west and southwest wall. The floor of that huge ice-walled and bedrock-floored canyon was significantly lower in elevation than the bedrock surface south and west of the decaying ice sheet and separating the immense ice marginal floods from the much deeper ice-walled and bedrock floored canyon floor was the decaying and detached ice sheet southwest margin. While not in the Grand River drainage basin, the elevation difference still exists today and elevations at the Missouri Escarpment base are significantly lower than elevations of the surface into which the Missouri River valley has been eroded.

• In time the ice sheet’s southwest margin had decayed sufficiently that ice marginal floods could breach the ice barrier and flow into the giant ice-walled and bedrock-floored canyon. At about the same time south-oriented flood flow on the canyon’s floor was captured and diverted north and east as new and lower outlets to the present day Saint Lawrence drainage basin and later to what is now Hudson Bay opened up. Breaches in the decaying ice sheet southwest margin ice barrier triggered the headward erosion of deep northeast and north-oriented valleys which began to capture the southeast-oriented flood flow. The Little Missouri River valley eroded west from an ice margin breach in central North Dakota and then eroded south across the entire southeast-oriented flood flow route between the decaying ice sheet margin and the Black Hills. But previously deep northeast-oriented valleys had eroded headward from more southerly breaches and had captured selected segments of the southeast-oriented flood flow. Note how the Cheyenne and Moreau Rivers in South Dakota flow in northeast directions to reach the south-oriented Missouri River. Note also in North Dakota how the Cannonball, Heart, and Knife Rivers flow in northeast directions to reach the south-oriented Missouri. The Grand River flows in a southeast direction to reach the Missouri River, but probably joined with the Moreau River to flow through an ice sheet margin breach prior to Missouri River valley headward erosion.

Figure 3: East and northeast-oriented South Fork Grand River flowing into Shadehill Reservoir where the South Fork Grand River joins the North Fork Grand River to form the east and southeast-oriented Grand River. United States Geological Survey map digitally presented using National Geographic Society TOPO software.

Returning to the present day Grand River drainage basin, evidence for southeast oriented flood flow is located almost every where one looks. Figure 3 illustrates the east and northeast-oriented South Fork Grand River as it flows from the figure 3 southwest corner into Shadehill Reservoir, which north of the figure 3 map area is where the South and North Fork Forks meet to form the east and southeast oriented Grand River. Note how the South Fork Grand River tributaries from the north and west are southeast oriented and the tributaries from the east and south are northwest-oriented. The drainage alignment is a relic of the multiple southeast-oriented flood flow channels that crossed the figure 3 map area prior to headward erosion of the deep east and northeast-oriented South Fork Grand River valley. Headward erosion of the northeast-oriented South Fork Grand River valley segment captured the southeast-oriented flood flow channels in sequence from the northeast to the southwest. Flood waters from north and west of the newly eroded South Fork Grand River valley eroded the southeast-oriented tributary valleys and were subsequently beheaded by headward erosion of the southeast- and east-oriented North Fork Grand River valley north and west of the figure 3 map area. Flood waters on northwest ends of beheaded flood flow channels reversed flow direction to erode the northwest oriented tributary valleys. Because flood flow channels were beheaded in sequence from the northeast to the southwest and because flood flow channels were anastomosing, reversed flow in a newly beheaded flood flow channel could capture yet to be beheaded flood flow from adjacent channels.

Figure 4: Bull Creek valley eroded across the Cave Hills. Bull Creek is a southeast-oriented South Fork Grand River tributary and separates the North Cave Hills from the South Cave Hills. United States Geological Survey map digitally presented using National Geographic Society TOPO software. 

How deeply did the flood water erode the Grand River drainage basin? Figure 4 illustrates the large southeast-oriented Bull Creek valley eroded between the North Cave Hills to the north and east and the South Cave Hills located to the south and west. Bull Creek is a South Fork Grand River tributary and originates near the drainage divide with the north oriented Little Missouri River. Middle Creek is a southeast-oriented Bull Creek tributary and is further illustrated in figure 5 below. The Cave Hills are not the highest points in the Grand River drainage basin, Table Mountain located north of the figure 4 northwest corner area and illustrated in figure 5 is significantly higher. High points in the region are isolated buttes similar to the Cave Hills. The figure 4 map contour interval is 20 meters and both the North and South Cave Hills rise to elevations greater than 1040 meters. Bull Creek as it flows between the North and South Cave Hills is at an elevation of less 900 meters. In other words, headward erosion of the southeast-oriented Bull Creek valley eroded at least 140 meters of material from between the North and South Cave Hills and flood water erosion removed a similar amount of material from the entire region surrounding the Cave Hills. Flood waters eroded the surface which now forms the top of the Cave Hills and there is no way to determine how much material was removed from region before flood waters lowered the regional surface to the level of the present day Cave Hills tops.

Figure 5: Detailed topographic map of the Middle Creek headwaters area at Table Mountain. Middle Creek is a southeast-oriented Bull Creek tributary, with Bull Creek flowing to the South Fork Grand River. United States Geological Survey map digitally presented using National Geographic Society TOPO software.

Did southeast-oriented flood waters flow across even higher elevations than the Cave Hills upland surface? Figure 4 illustrated Middle Creek, which is a southeast-oriented Bull Creek tributary. Middle Creek originates at the base of Table Mountain which is located just north of the figure 4 map area. In meters highest points on Table Mountain are higher than 1500 meters. The more detailed topographic map shown in figure 5 has a 10 foot contour interval and the highest points on Table Mountain exceed 3600 feet in elevation. The southeast-oriented stream originating along the Table Mountain southeast margin and flowing between Dead Horse Butte and Mt. McKinley is Middle Creek, which south and east of figure 5 joins southeast-oriented Bull Creek. Note how Middle Creek originates in what could be considered a southeast-oriented escarpment-surrounded basin. The southeast-oriented escarpment-surrounded basin is a large abandoned headcut eroded when southeast-oriented flood waters flowed across the Table Mountain upland surface and eroded what was then the deep southeast-oriented Middle Creek valley headward into what was then a high level topographic surface, at least as high as the top of Table Mountain today. A resistant cap rock probably protected the Table Mountain upland surface from further erosion, although deep flood water erosion lowered surrounding region to produce the regional landscape seen today. Grand River drainage basin landform origins detailed essays provide more detail in how the Table Mountain, Cave Hills, and other Grand River drainage basin regions were eroded in addition to documenting additional flood eroded landform features.

Figure 6: Little Missouri River-South Fork Grand River drainage divide at “The Jumpoff”. United States Geological Survey map digitally presented using National Geographic Society TOPO software.

Is it possible the Grand River drainage basin was eroded by a series of smaller melt water floods occurring over long periods of time rather than by massive southeast-oriented ice marginal melt water floods? Figure 6 illustrates the Little Missouri River-South Fork Grand River drainage divide area at “The Jumpoff”, and is located near the Little Missouri River-Grand River drainage divide south end. Figure 2 illustrated the Little Missouri River-North Fork Grand River drainage divide area near the Little Missouri River-Grand River drainage divide north end. Evidence for southeast-oriented flood flow can be found all along the entire Little Missouri River-Grand River drainage divide and also along Little Missouri River drainage divides with other east-oriented tributaries located north and south of the Grand River drainage basin. The Little Missouri River valley eroded headward across southeast-oriented flood flow which extended from the decaying ice sheet’s southwest margin to the Black Hills. Note how in figure 6 Little Missouri River tributaries from the east are northwest-oriented and South Fork Grand River tributaries from the north and west are southeast-oriented. Also note how in figure 6 the Little Missouri River-South Fork Grand River drainage divide is at the crest of “The Jumpoff” escarpment, which encloses an east-oriented escarpment-surround basin in which the South Fork Grand River originates. “The Jumpoff” escarpment is another, and much larger, abandoned headcut, which was formed by massive amounts of southeast-oriented flood water flowing into what then the actively eroding east-oriented South Fork Grand River valley. “The Jumpoff” illustrates how immense sheets of southeast-oriented flood water stripped layers of material from the regional surface. This stripping process was probably repeated over and over again as what had been the pre-glacial surface between the ice sheet southwest margin and the Black Hills was deeply eroded to produce the landscape seen today. Headward erosion of the north oriented Little Missouri River valley beheaded the massive southeast-oriented flood flow to what had been the actively South Fork Grand River valley and diverted the flood water north and east to a breach in the ice sheet’s southwest margin ice barrier and into the complex of ice-walled and bedrock-floored valleys, which had been carved by supra-glacial rivers into the decaying ice sheet’s surface. Southeast-oriented flood flow to the north oriented Little Missouri River valley was subsequently beheaded by headward erosion of the deep north and northeast oriented Yellowstone-Powder River valley, which eroded headward from a still different breach through the ice sheet’s detached and decaying southwest margin ice barrier.

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.