A geomorphic history based on topographic map evidence

This overview essay provides highlights from more detailed essays describing the Redwater River drainage basin, which is located in eastern Montana and is a northeast and north-oriented Missouri River tributary. The detailed essays can be found under Redwater River on this website’s sidebar category list. To the southeast of the Redwater River drainage basin is the northeast oriented Yellowstone River valley and its associated drainage basin. To the west of the Redwater River drainage basin is the north-oriented Big Dry Creek drainage basin which drains to the east-oriented Missouri River valley. Detailed essays describe drainage divides between Redwater River tributaries and drainage divides with adjacent drainage basins and provide evidence the Redwater River valley eroded headward to capture an immense southeast-oriented flood moving across the present day Redwater River drainage basin on a topographic surface at least as high as the highest Redwater River drainage divide elevations today. Flood waters were derived from a rapidly melting North American ice sheet and were moving in a southeast direction adjacent to the ice sheet southwest margin on the high-level topographic surface, which was a flood eroded erosion surface. Headward erosion of the deep Redwater River valley diverted the flood waters north and northeast into what is today a large abandoned northeast oriented valley leading to the northwest corner of North Dakota. The deep northeast and north-oriented Redwater River valley was one of several deep northeast oriented valleys that eroded headward from the deep “hole” that developed as the thick North American ice sheet melted and opened up the space it had once occupied. Flood flow into the Redwater River drainage basin ended when a climate change caused by the reversal of flood flow from south-oriented to north-oriented resulted in the freezing and blockage of north-oriented flood flow routes and enabled headward erosion of the Missouri River valley to capture the newly eroded northeast- and north-oriented drainage routes.

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

Eastern Montana Redwater River drainage basin drainage history

The Redwater River drainage basin is located in eastern Montana and is a northeast and north-oriented Missouri River tributary. To the southeast of the Redwater River drainage basin is the northeast-oriented Yellowstone River valley and its associated drainage basin. To the west of the Redwater River drainage basin is the north-oriented Big Dry Creek drainage basin and to the northwest is the Missouri River valley and its associated drainage basin. Redwater River tributaries from the southeast and east tend to be oriented in a northwest direction and tributaries from the northwest and west tend to be oriented in a southeast direction (see figure 2 below). The northwest-southeast orientation of Redwater River tributary valleys suggests the deep Redwater River valley eroded headward across multiple southeast-oriented flood flow channels, such as might be found in a large southeast-oriented anastomosing channel complex. The southeast-oriented tributary valleys were eroded headward along captured southeast-oriented flood flow channels. The northwest-oriented tributary valleys were eroded by reversals of flood flow on northwest ends of beheaded flood flow channels. The flood flow channels were beheaded in sequence from the northeast to the southwest. Because the flood flow channels were captured and beheaded in sequence, one at a time, and also because the flood flow channels were anastomosing (or interconnected) reversed flood flow in a newly beheaded flood flow channel could capture yet to be beheaded flood flow from adjacent flood flow channels located southwest of the actively eroding Redwater River valley head. Such captures of yet to be beheaded flood water helped erode the northwest-oriented tributary valleys and the northwest-facing Redwater River valley southeast wall.

Figure 2: Southwest end of northeast-oriented Redwater River drainage basin showing northwest-southeast orientation of Redwater River tributaries. Redwater River flows from Brockway to Circle and then to figure 2 north center edge. Northeast-oriented Yellowstone River is located in figure 2 southeast corner. United States Geological Survey map digitally presented using National Geographic Society TOPO software. 

The Redwater 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 Redwater 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. Highest points in the present day Redwater River drainage basin are probably well below the level of the pre-glacial surface.

• Events important to Redwater River drainage basin history began as the ice sheet was rapidly melting and had melted to the point 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 deeply eroding the region between the present day Pine Ridge Escarpment in South Dakota and the ice sheet’s southwest margin, which at that time was located north and east of today’s Redwater River drainage basin. Also at that time immense southeast and south-oriented supra-glacial melt water rivers were flowing across the ice sheet’s surface to the ice sheet’s southern margin and carving giant ice-walled and bedrock-floored canyons. A huge southeast and south-oriented ice-walled and bedrock-floored canyon was carved 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 southeast-oriented ice marginal floods from the much deeper ice-walled and bedrock floored canyon floor was the decaying and detached ice sheet southwest margin or ice barrier.

• As the ice sheet’s detached southwest margin continued to decay the southeast oriented ice marginal floods, which were flowing at a higher elevation than 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. The northwest-southeast oriented Missouri Escarpment is located north and east of the Redwater River drainage basin, meaning the deep southeast oriented ice-walled and bedrock-floored canyon was located north and east of the present day Redwater River drainage basin location. The deep northeast and north-oriented Redwater River valley was one of the deep valleys that eroded headward from a major ice sheet margin breach. Prior to Redwater River valley headward erosion the deep northeast-oriented Yellowstone River valley had eroded headward from a different ice sheet margin breach. And prior to Yellowstone River valley headward erosion the deep Little Missouri River valley had eroded headward from a still different ice sheet margin breach. The east-oriented Missouri River valley located north and west of the Redwater River drainage basin eroded headward from the same ice sheet margin breach as the deep Redwater River valley and captured southeast oriented flood flow channels supplying flood water to the newly eroded Redwater River valley. [Probably all valleys were being eroded simultaneously, with valleys to the southeast being eroded slightly in advance of valleys to the northwest, which beheading flood flow channels to the newly eroded valleys further to the southeast.] Today the ice sheet’s southwest margin ice barrier location is the Missouri Coteau, which in North and South Dakota is a 40-100 kilometer wide region of easy to recognize glacial moraine type landscape located between the southeast and south-oriented Missouri River to the southwest and south and the southeast and south oriented Missouri Escarpment to the northeast and east. Locations of breaches through the ice sheet’s southwest margin ice barrier can be located on topographic maps, although the deep valleys eroded across the Missouri Coteau area are now partially filled with glacial deposits.

• Why are the deep northeast and east-oriented valleys, which were eroded at the ice sheet margin breach locations, now filled with glacial deposits? To answer that question think about what the immense south-oriented melt water floods were doing when they were captured and diverted to flow in a north direction. 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 and created what for all practical purposes was a thin ice sheet. Incorporated into the 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 then spilled from one valley segment to another along the ice sheet margin, which resulted in headward erosion of the present day North Dakota 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 ice 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 ice sheet remnants melting first. The thick ice sheet remnants melted much more slowly and today in North  and South Dakota include the Missouri Coteau.

Figure 3: Southwest end of northeast-oriented Redwater River drainage basin. Northeast-oriented Redwater River is located in figure 3 north center area. Northwest-oriented streams in figure 3 west half flow to north-oriented Big Dry Creek, which flows to east-oriented Missouri River. Southeast-oriented streams in figure 3 east half flow to northeast-oriented Yellowstone River. United States Geological Survey map digitally presented using National Geographic Society TOPO software. 

Figure 3 uses reduced size topographic maps to illustrate the southwest end of the northeast-oriented Redwater River drainage basin. Big Sheep Mountain in the figure 3 east center area is one of the highest points on the Redwater River-Yellowstone River drainage divide. The Redwater River is the northeast-oriented stream flowing to the figure 3 north center edge. Note how major Redwater River headwaters area tributaries are northwest oriented with some east and southeast-tributaries. The northwest-oriented Redwater River tributary valleys were eroded by reversals of southeast-oriented flood flow channels which were beheaded by headward erosion of the deep northeast-oriented Redwater River valley. Southeast-oriented streams flowing to the figure 3 east edge are Yellowstone River tributaries. Note how the southeast-oriented tributary valleys are linked by shallow northwest-southeast oriented through valleys with the northwest-oriented Redwater River tributary valleys. Also note the northwest-oriented streams flowing to the figure 3 west edge, which are tributaries to north-oriented Big Dry Creek, which flows to the east-oriented Missouri River. The northwest-oriented Big Dry Creek tributary valleys were eroded by reversals of southeast-oriented flood flow in channels beheaded by headward erosion of the deep north-oriented Big Dry Creek valley. The north-oriented Big Dry Creek valley eroded headward from what was then the actively eroding and deep east-oriented Missouri River valley, which was also beheading southeast-oriented flood flow channels supplying flood waters to the newly eroded Redwater River valley. Note how in the figure 3 south center area northwest-oriented Timber Creek, which flows to north-oriented Big Dry Creek and the Missouri River, is linked by through valleys with southeast-oriented North Fork Cherry Creek and Cherry Creek, with Cherry Creek flowing to the northeast-oriented Yellowstone River. Headward erosion of the deep northeast-oriented Redwater River valley was not able to capture the southeast-oriented flood flow channel eroding the Cherry Creek valley headward. Headward erosion of the deep east-oriented Missouri River valley and the deep north-oriented Big Dry Creek valley beheaded and reversed all southeast-oriented flood flow routes to what had been the actively eroding Redwater River and Cherry Creek valleys, and the Redwater River valley has changed little since.

Figure 4: Northeast-oriented Redwater River flows from Brockway (near west center edge) to Circle (near north edge). Northwest-facing escarpment marks Redwater River-Yellowstone River drainage divide with southeast-oriented streams in southeast quadrant flowing to the northeast-oriented Yellowstone River. United States Geological Survey map digitally presented using National Geographic Society TOPO software. 

Figure 4 above uses reduced size maps to illustrate the Redwater River valley north and east of the figure 3 map area. The Redwater River flows from the figure 4 west edge (south half) to Brockway and Circle before reaching the figure 4 north edge. Note how Redwater River tributaries from the northwest are southeast oriented and from the southeast are northwest-oriented. The northeast facing escarpment seen in the figure 4 east half is the location of the Redwater River-Yellowstone drainage divide. Southeast-oriented streams flowing to the figure 4 east edge and south edge (east half) are Yellowstone River tributaries. The southeast-oriented slope drained by those southeast-oriented Yellowstone River tributaries represents the erosion surface into which the deep northeast oriented Redwater River valley was eroded. Study of the southeast-oriented Yellowstone River valley northwest wall, or the slope now drained by the southeast-oriented Yellowstone River tributaries, reveals evidence those southeast-oriented tributary valleys were eroded as channels in what was at one time a large southeast-oriented anastomosing channel complex, which had been captured by headward erosion of the deep northeast oriented Yellowstone River valley. At that time the deep northeast-oriented-oriented Redwater River valley did not exist, nor did the deep east-oriented Missouri River valley (further to the north and west) exist. Headward erosion of the deep Redwater River valley beheaded the southeast-oriented anastomosing flood flow channels in sequence from the northeast to the southwest. Flood waters on northwest ends of beheaded flood flow channels reversed flow direction to erode the northwest-oriented Redwater River tributary valleys. Erosion of those northwest-oriented tributary valleys was aided by flood flow from yet to be beheaded flood flow channels located south and west of the actively eroding Redwater River valley head. Today, the northeast- and north-oriented Redwater River valley is an unusually large valley for a river the size of the present day Redwater River and the Redwater River could be considered a underfit stream and provides evidence the valley was eroded by a much larger volume of water than presently flows in the Redwater River. Orientations of Redwater River tributaries and of tributaries to adjacent drainage routes provide evidence the large volumes of water flowed in a southeast direction. Further, elevations of present day drainage divides surrounding the large Redwater River valley provide evidence the Redwater River valley eroded headward across a large southeast-oriented flood that originally flowed on a topographic surface at least as high as the highest points along present day Redwater River drainage basin drainage divides.

Figure 5: Large through valley eroded across Redwater River-Yellowstone River drainage divide near Enid, Montana. Northwest-oriented streams in west half flow to Redwater River. East and southeast-oriented streams in east half flow to northeast and north-northeast oriented Yellowstone River (east of figure 5). United States Geological Survey map digitally presented using National Geographic Society TOPO software. 

Figure 5 illustrates the Redwater River-Yellowstone River drainage divide area north of Enid, Montana. Fox Creek flows north to Enid and then in an east and southeast direction to the Yellowstone River. The East Fork Fox Creek flows in a southeast direction to the north of Fox Lake and east of figure 5 turns south to join Fox Creek. Also, east of figure 5 the southeast-oriented East Fork Fox Creek valley is linked by a through valley with the southeast-oriented North Fork Fox Creek valley. This through valley provides further evidence of the anastomosing channel complex that once existed. West of Enid is a large well-defined through valley linking the east and southeast-oriented Fox Creek valley with the northwest-oriented Redwater Creek valley, which drains to a northwest-oriented segment of the north-oriented Redwater River. The through valley provides evidence that large amounts of southeast-oriented flood water once crossed the Redwater River-Yellowstone River drainage divide at this location and eroded what is now a deep east-oriented through valley. The present day Redwater River-Yellowstone River drainage divide at this location was created when headward erosion of the deep Redwater River valley, northwest of the figure 5 map are, beheaded southeast-oriented flood flow moving through the present day west to east oriented through valley and caused a reversal of flood waters on the northwest end of the beheaded flood flow route. The reversed flood flow aided by flood flow from yet to be beheaded southeast-oriented flood flow routes further to the southeast eroded the northwest-oriented Redwater Creek valley. Note the nature of the Redwater River-Yellowstone River drainage divide north of the west to east oriented through valley. Southeast-oriented Yellowstone River tributaries are linked by higher level through valleys with northwest-oriented Redwater River tributaries, providing evidence flood water once flowed across the entire divide area. Headward erosion of the deep Redwater River valley to the northwest of figure 5 progressively beheaded the southeast-oriented flood flow routes (from the northeast to the southwest) and reversed flood flow to create the present day drainage divide and erode northwest-oriented tributary valleys.

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.