Abstract:

Introduction:

• The purpose of this essay is to use topographic map interpretation methods to explore western South Dakota French Creek-Beaver Creek drainage divide area landform origins. Map interpretation methods can be used to unravel many geomorphic events leading up to formation of present-day drainage routes and development of other landform features. While each detailed topographic map feature provides detailed evidence to be explained, the solution must be consistent with explanations for adjacent area map evidence as well as solutions to big picture map evidence puzzles. I invite readers to improve upon my solutions or to propose alternate solutions that better explain evidence and are also consistent with adjacent map area and big picture evidence. Readers may do so either by making comments here or by writing and publishing their own essays and then by leaving a link to those essays in a comment here.

• This essay is also exploring a paradigm in which erosional landforms are interpreted as evidence left by immense glacial melt water floods. Implied in that interpretation is the immense floods were derived from a thick North American ice sheet that created a deep “hole” in the North American continent and also melted fast. The previously unexplored paradigm being tested in this and similar essays is a thick North American ice sheet, comparable in thickness to the present day Antarctic ice sheet, occupied approximately the North American region usually recognized to have been glaciated and through its weight and erosive actions created a “deep” North American “hole”, through its weight and deep erosion (and perhaps deposition) along major south-oriented melt water flow routes caused significant crustal warping and tectonic change, through its action of melting fast produced immense floods that flowed across the continent, and through its action of melting fast systematically opened up space in the ice sheet created “hole” so headward erosion of newly developed north-oriented drainage systems captured immense south-oriented melt water floods and diverted immense melt water floods north into space the ice sheet had once occupied.

• If this previously unexplored paradigm is correct the geographic region explored by this essay should contain evidence of immense floods that were captured by headward erosion of new valley systems so as to cause the floods to flow in a different direction. Ability of this previously unexplored paradigm to explain French Creek-Beaver Creek drainage divide area landform evidence will be regarded as evidence supporting the “thick ice sheet that melted fast” paradigm.

French Creek-Beaver Creek drainage divide area general location map

Figure 1: French Creek-Beaver Creek drainage divide area general location map. National Geographic Society map digitally presented using National Geographic Society TOPO software.

Figure 1 provides a general location map for the French Creek-Beaver Creek drainage divide area. The map illustrates an area in western South Dakota. Immediately west of the figure 1 map area is the state of Wyoming. French Creek and Beaver Creek both originate in the Black Hills southwest of Rapid City, South Dakota and flow southeast to join the northeast-oriented Cheyenne River west and southwest of the Badlands National Park. French Creek is the unlabeled stream originating near Custer, South Dakota (near Jewel Cave National Park) and flowing through Fairburn to reach the northeast-oriented Cheyenne River. Beaver Creek is not shown on figure 1, but also originates near Custer and flows generally southeast through the Wind Cave National Park area to Buffalo Gap, South Dakota and then to the northeast-oriented Cheyenne River. French Creek and Beaver Creek are two of several streams flowing southeast from the Black Hills to join the northeast-oriented Cheyenne River east of the Black Hills. North of Boxelder Creek is Elk Creek, both of which are labeled in figure 1. Rapid Creek is not labeled, but it is the unlabeled southeast-oriented stream immediately south of Boxelder Creek and flows through Rochford, Silver City, Rapid City, and Farmingdale, South Dakota. Spring Creek is the unlabeled stream immediately south of Rapid Creek and flows through Hill City and near the Stratobowl. Battle Creek is the unlabeled stream immediately south of Spring Creek and flows through Keystone and Hermosa.

• The Battle Creek-French Creek drainage divide area, Spring Creek-Battle Creek drainage divide area, Rapid Creek-Spring Creek drainage divide area, Boxelder Creek-Rapid Creek drainage divide area, Elk Creek-Boxelder Creek drainage divide area, Belle Fourche River-Elk Creek drainage divide area north of Elk Creek, Whitewood Creek-Bear Butte Creek and Spearfish Creek-Whitewood Creek essays describe drainage divide west and north of the French Creek-Battle Creek headwaters area and can be found under Black Hills region on the sidebar category list. This essay interprets French Creek-Beaver Creek drainage divide area landform origins in the context of an immense southeast oriented flood that flowed across the entire figure 1 map area and that was systematically captured by headward erosion of deep northeast-oriented valleys, which diverted flood waters further and further northeast and north. The source of the southeast-oriented flood water cannot be determined from evidence presented here. However,based on evidence from numerous other Missouri River drainage basin landform origins research project essays published on this website the floods occurred before and/or while the Black Hills area was being uplifted and can be traced headward to a North American ice sheet location. Rapid melting of a thick North American ice sheet located in a deep “hole” would explain the flood water source and also why deep valleys eroded west and southwest to capture southeast-oriented flood waters to divert flood waters further and further northeast and north into space in the deep “hole” the rapidly melting ice sheet had once occupied. In addition, presence of a thick North American ice sheet in a deep “hole” north and east of the Black Hills might explain crustal warping that uplifted the Black Hills dome during or even after an immense southeast-oriented flood. Uplift of the Black Hills dome may have been accelerated by crustal unloading as flood waters deeply eroded the Black Hills region and removed overlying rock layers.

French Creek-Beaver Creek drainage divide area detailed location map

Figure 2: French Creek-Beaver Creek drainage divide area detailed location map. United States Geological Survey map digitally presented using National Geographic Society TOPO software.

Figure 2 provides a slightly more detailed location map for the French Creek-Beaver Creek drainage divide area, where Beaver Creek is shown and more streams are labeled. Custer County and Fall River County are located in western South Dakota. Green areas represent Black Hills National Forest lands, which are generally located in the Black Hills upland region. The Custer State Park and Wind Cave National Park lands are shown in red (also along the figure 2 east edge the Badlands National Park area is shown in red). French Creek originates northwest of Custer, South Dakota and flows through Custer State Park to Fairburn and then to the Cheyenne River. Beaver Creek originates a short distance south of Custer and flows south and southeast through Wind Cave National Park to Buffalo Gap and then to the northeast oriented Cheyenne River. Two Cheyenne River tributaries located between French Creek and Beaver Creek and shown on figure 2 are important here. Those Cheyenne River tributaries are Lame Johnny Creek and Cottonwood Creek. Figure 2 shows several southeast oriented tributaries flowing from the Black Hills area to the northeast oriented Cheyenne River. Figure 1 illustrated additional southeast oriented streams flowing from the Black Hills to the Cheyenne River. Also figure 2 shows northwest-oriented tributaries to the northeast oriented Cheyenne River. Detailed maps below further illustrate this northwest-southeast tributary orientation. This predominance of southeast and northwest oriented tributaries to the northeast-oriented Cheyenne River is evidence the northeast- oriented Cheyenne River valley eroded headward across multiple southeast-oriented flood flow routes, such as might be found in a large-scale anastomosing channel complex. Headward erosion of a deep northeast-oriented valley across such a complex of southeast-oriented flood flow channels would have captured the southeast-oriented flood waters and enabled large and deep southeast-oriented tributary valleys to erode headward from the newly eroded and deep Cheyenne River valley wall. At the same time capture of the southeast-oriented flood flow would have beheaded southeast-oriented flood flow routes and flood waters on the northwest ends of those beheaded flood flow channels would have reversed flow direction to flow northwest into the newly eroded and deeper northeast-oriented Cheyenne River valley. Because the channels were anastomosing (meaning they were interconnected) reversed flow on beheaded flood flow routes often captured flood waters from yet to be beheaded flood flow routes further to the south or southwest. Capture of water from such yet to be beheaded flood flow routes frequently provided sufficient water to erode significant northwest-oriented tributary valleys. Prior to headward erosion of the deep northeast-oriented Cheyenne River valley flood waters were flowing to what was then the newly eroded northeast-oriented White River valley. The northeast-oriented White River valley is located in the figure 2 southeast corner. The Cheyenne River-White River drainage divide area essay describes landform origins southeast of the Cheyenne River and can be found under White River on the sidebar category list.

French Creek-Beaver Creek drainage divide area south of Custer, South Dakota

Figure 3: French Creek-Beaver Creek drainage divide area south of Custer, South Dakota. United States Geological Survey map digitally presented using National Geographic Society TOPO software.

Figure 3 illustrates the French Creek-Beaver Creek drainage divide area south of Custer, South Dakota. The dark green area along the figure 3 east edge is Custer State Park. French Creek flows southeast from the figure 3 northwest corner and then east through Custer to Stockade Lake, where it turns southeast again to flow to Blue Bell and then to the figure 3 east center edge. Beaver Creek originates near the landing strip south of Custer and flows south to Nihart and the figure 3 south edge. Fourmile Creek is the southwest-oriented stream flowing to the figure 3 southwest corner. Fourmile Creek drains eventually to the Cheyenne River south of the Black Hills near Edgemont, South Dakota. Haven Canyon and other southeast-oriented drainage in the figure 3 southeast quadrant drains to southeast-oriented Beaver Creek. Flynn Creek in the figure 3 southeast quadrant flows southeast and then northeast to join the southeast-oriented South Fork Lame Johnny Creek (east of figure 3-Lame Johnny Creek flows to the Cheyenne River and is located between French Creek and Beaver Creek). Note how through valleys link the various independent drainage basins. Figure 4 below illustrates in more detail through valleys linking the Fourmile Creek valley with the French Creek valley and also with the Beaver Creek valley. Figure 5 below illustrates in more detail through valleys linking French Creek valley and Beaver Creek valley south of Custer. Figure 6 below illustrates in more detail through valleys linking the French Creek valley with the South Fork Lame Johnny Creek valley near Blue Bell. Figure 7 below illustrates through valleys located east of the figure 3 map area linking the French Creek valley with the North Fork Lame Johnny Creek valley and also with the Swint Creek valley, which drains eventually to French Creek. Figure 8 below illustrates through valleys also east of the figure 3 map area linking the Swint Creek valley with the Lame Johnny Creek valley. And, figure 9 below illustrates through valleys east of the figure 3 map area linking the South Fork French Creek valley with the Cottonwood Creek valley, which drains directly to the Cheyenne River. Before leaving figure 3 note through valleys near Cicero Peak in the figure 3 southeast quadrant linking the southeast-oriented Haven Canyon valley (draining to Beaver Creek) with the Flynn Creek valley (draining to the Lame Johnny Creek valley) with the northeast-oriented Glen Erin Creek valley (draining to the French Creek valley), among others. These through valleys provide evidence of a former southeast-oriented anastomosing channel complex that was systematically dismembered by headward erosion of the Beaver Creek valley system, the Lame Johnny Creek valley system, the French Creek valley system, and the Fourmile Creek valley system, approximately in that order.

French Creek-Beaver Creek drainage divide area southwest of Custer

Figure 4: French Creek-Beaver Creek drainage divide area southwest of Custer. United States Geological Survey map digitally presented using National Geographic Society TOPO software.

Figure 4 illustrates the French Creek-Beaver Creek drainage divide area southwest of Custer and also a segment of the Fourmile Creek-Beaver Creek drainage divide area. French Creek flows southeast in the figure 4 northwest quadrant and then turns northeast to flow to Custer and the figure 4 north edge. A Beaver Creek tributary originates in the figure 4 south center (south of Spar Spring) and flows southeast to join a south-oriented tributary by the highway and railroad near the figure 4 south edge. Fourmile Creek originates in the figure 4 southwest quadrant and flows northwest to the campground and then southwest to Fourmile along the figure 4 west edge. Sidney Creek originates south of Custer in the figure 4 northeast corner and flows southeast and east of figure 4 joins a north-oriented tributary and flows north to French Creek. The north-oriented Sidney Creek tributary originates in the figure 4 southeast corner and flows east before turning north to flow along the figure 4 east edge. Note the northwest-southeast orientation of many of the valleys or valley segments and also how all of the drainage basins are linked by through valleys. What has happened here is at one time an immense southeast-oriented flood flowed across the entire figure 4 map area on a topographic surface at least as high as the highest figure 4 elevations today. Headward erosion of the deep French Creek valley to the area east of Custer (where Sidney Creek joins French Creek, which is northeast of figure 4) enabled the north-oriented Sidney Creek valley segment and the north-oriented Sidney Creek tributary valley to erode south to capture southeast-oriented flood flow moving on what are today the southeast-oriented Sidney Creek valley route and the southeast-oriented Beaver Creek headwaters valley route. Headward erosion of the south-oriented Beaver Creek tributary valley captured southeast-oriented flood flow to the north-oriented Sidney Creek tributary valley. Headward erosion of the French Creek valley southwest of Custer beheaded the flood flow route to the southeast-oriented Sidney Creek valley and also at least some of the southeast-oriented flood flow to the newly eroded Beaver Creek valley and in the process captured flood flow moving southeast along what is now the southeast-oriented French Creek valley in the figure 4 northwest quadrant. Headward erosion of the southwest-oriented Fourmile Creek valley then beheaded all southeast-oriented flood flow to the Beaver Creek valley and diverted the water southwest and south.

French Creek-Beaver Creek drainage divide area near Evergreen School

Figure 5: French Creek-Beaver Creek drainage divide area near Evergreen School. United States Geological Survey map digitally presented using National Geographic Society TOPO software.

Figure 5 illustrates the French Creek-Beaver Creek drainage divide area southeast of the figure 4 map area and includes overlap areas with figure 4. Beaver Creek is located in the figure 5 southwest quadrant just east of the State Sanatorium and the southeast and south-oriented Beaver Creek tributary follows the railroad west of the Sanatorium. The previously mentioned east and north-oriented Sidney Creek tributary originates in the figure 5 west center north of the Sanatorium and after flowing east and northeast flows north in the valley north of Evergreen School to the figure 5 north edge. Note how that east and north-oriented Sidney Creek tributary headwaters are linked by through valleys with the south-oriented Beaver Creek headwaters and also with the previously mentioned south-oriented Beaver Creek tributary valley. Also note the south-oriented stream originating near Evergreen School. That stream (West Pole Creek) turns southwest and joins Beaver Creek south of the figure 5 map area. Note also northeast, east and northeast-oriented Glen Erin Creek, which flows to French Creek northeast of the figure 5 map area. Note how in the figure 5 south center Glen Erin Creek headwaters are linked by a through valley with a southwest-oriented valley draining to West Pole Creek and south-oriented Beaver Creek. Numerous other such through valleys are located throughout the figure 5 map region. Some through valleys are saddles cut into high level ridges, but they still provide evidence of former valleys that once were eroded into the figure 5 landscape. Working out details for all such through valleys goes beyond what I am attempting to do with this essay. However details for through valleys linking the Sidney Creek tributary valley with the Beaver Creek valley and the Glen Erin Creek valley can be briefly described. As previously mentioned southeast-oriented flood flow crossed the entire figure 5 map area on a topographic surface at least as high as the highest figure 5 elevations today. Flood waters were probably moving towards actively eroding deep Beaver Creek valley system headcuts that were eroding headward into the figure 5 map region. At the same time deep French Creek valley system headcuts were also eroding headward into the figure 5 map region (specifically the northeast-oriented Glen Erin Creek valley). Headward erosion of the Glen Erin Creek valley captured significant southeast-oriented flood flow at several locations and diverted the water east and northeast and also northeast, east, and northeast. Headward erosion of the Beaver Creek and West Pole Creek valleys then beheaded flood flow to the Glen Erin Creek valley in the figure 5 south center while headward erosion of the north-oriented Sidney Creek tributary valley beheaded flow to the Glen Erin Creek valley further north. Next headward erosion of the south-oriented Beaver Creek tributary valley along the figure 5 west edge beheaded flood flow to the east and north-oriented Sidney Creek tributary valley.

French Creek-Lame Johnny Creek drainage divide area near Blue Bell

Figure 6: French Creek-Lame Johnny Creek drainage divide area near Blue Bell, South Dakota. United States Geological Survey map digitally presented using National Geographic Society TOPO software.

Figure 6 illustrates the French Creek-Lame Johnny Creek drainage divide area near Blue Bell, South Dakota. French Creek flows south into the figure 6 north center area and meanders across the north center and northeast areas to the figure 6 northeast corner. Flynn Creek flows northeast in the figure 6 south center and then turns southeast to eventually join the South Fork of Lame Johnny Creek southeast of the figure 6 map area. East of Flynn Creek the unlabeled stream flowing to the figure 6 southeast corner is the South Fork of Lame Johnny Creek. Figure 6 has some areas without well-defined drainage, suggesting the region may be underlain by limestone, but through valleys across regions lacking well-defined drainage can be readily identified. Perhaps the most notable of these through valleys extends north from the Flynn Creek elbow of capture (in the figure 6 south center) and then west to the Haselrodt Spring area, where it is connected by a through valley with the French Creek valley. This through valley and several through valleys located south of Blue Bell link the French Creek valley segment with the southeast-oriented Flynn Creek valley and the Lame Johnny Creek valley further to the southeast. Also a well-defined, but higher level through valley (now used by a road), links this French Creek-Flynn Creek through valley with the southeast-oriented South Fork Lame Johnny Creek valley. These and other through valleys located in the figure 6 map area provide evidence for an anastomosing southeast-oriented complex of channels that once crossed the region. Headward erosion of the southeast-oriented South Fork Lame Johnny Creek-Flynn Creek valley beheaded southeast-oriented flood flow moving to erode the southeast-oriented South Fork Lame Johnny Creek valley. Subsequently headward erosion of the French Creek valley beheaded southeast-oriented flood flow moving to what is today the French Creek-Flynn Creek through valley. Beheading of the flood flow occurred in sequence from east to west.

French Creek-Lame Johnny Creek drainage divide area in Custer State Park

Figure 7: French Creek-Lame Johnny Creek drainage divide area in Custer State Park. United States Geological Survey map digitally presented using National Geographic Society TOPO software.

Figure 7 illustrates the French Creek-Lame Johnny Creek drainage divide area east of the figure 6 map area and includes overlap areas with figure 6. French Creek flows across the figure 7 north half. Southeast-oriented headwaters of the South Fork of Lame Johnny Creek are located in the figure 7 southwest corner. The North Fork of Lame Johnny Creek originates near French Creek and flows southeast to the figure 7 south edge (near the southeast corner). Lame Johnny Creek as previously mentioned flows to the northeast-oriented Cheyenne River and is located between the southeast-oriented French Creek and Beaver Creek drainage basins. Further east, Swint Creek originates in the figure 7 east center and flows south-southeast to the figure 7 east edge (also near the southeast corner). Swint Creek is seen again in figure 8 below and eventually flows to join French Creek. As seen in figure 6 southeast-oriented South Fork Lame Johnny Creek is linked by a through valley with the French Creek-Flynn Creek through valley. Also in both figures 6 and 7 a higher level through valley can be seen directly linking the southeast-oriented South Fork Lame Johnny Creek valley with the French Creek valley. Further note the through valley linking the French Creek valley with the southeast-oriented North Fork Lame Johnny Creek valley. Also note the through valleys linking the Swint Creek valley with the French Creek valley. These through valleys, combined with the through valleys seen in figure 6, provide further evidence of a southeast-oriented anastomosing channel complex that was dismembered by headward erosion of the deep French Creek valley.

Swint Creek-Lame Johnny Creek drainage divide area

Figure 8: Swint Creek-Lame Johnny Creek drainage divide area. United States Geological Survey map digitally presented using National Geographic Society TOPO software.

Figure 8 illustrates the Swint Creek-Lame Johnny Creek drainage divide area southeast of the figure 7 map area (there is no overlap and a gap does exist between the two map areas). Swint Creek is located in the figure 8 north center and flows to French Creek, which can just barely be seen in the figure 8 northeast corner. The southeast oriented South Fork of Lame Johnny Creek is located in the figure 8 southwest corner and the southeast oriented North Fork is located just north of the South Fork. The two forks join in the figure 8 southwest quadrant to form southeast oriented Lame Johnny Creek. Numerous through valleys link the Swint Creek valley and the Lame Johnny Creek valley. While some of these through valleys are probably related to underlying geologic units the valleys were eroded by water and provide evidence of earlier drainage systems. Perhaps one of the best defined through valleys is located northwest of Dow Ridge. Today a short north-oriented Swint Creek tributary drains the north end of that through valley while a Lame Johnny Creek tributary flows southeast through a water gap to the east side of Dow Ridge and then south to southeast oriented Lame Johnny Creek. West of Dow Ridge a south-oriented Lame Johnny Creek tributary drains the south two-thirds of a north-south through valley linking the southeast-oriented tributary valley with the Lame Johnny Creek valley directly to the south. These through valleys and other through valleys like them provide further evidence of anastomosing flood flow channels that were dismembered by headward erosion of the deep Lame Johnny Creek valley systems and subsequent headward erosion of the deep Swint Creek valley. Headward erosion of the southeast and south oriented Lame Johnny Creek tributary valley (the stream that flows east of Dow Ridge) beheaded south-oriented flood flow moving in the south-oriented Lame Johnny Creek tributary valley west of Dow Ridge. Subsequently headward erosion of the deep Swint Creek valley beheaded southeast-oriented flood flow to what was then the actively eroding southeast- and south-oriented Lame Johnny Creek tributary valley (the one east of Dow Ridge) and reversed flow on the north end of that flood flow route eroded a north-oriented Swint Creek tributary valley.

South Fork French Creek-Cottonwood Creek drainage divide area

Figure 9: South Fork French Creek-Cottonwood Creek drainage divide area. United States Geological Survey map digitally presented using National Geographic Society TOPO software.

Figure 9 illustrates the South Fork French Creek-Cottonwood Creek drainage divide area southeast of the  figure 8 map area (there is no overlap area-figure 10 below provides a big picture view of valleys east of the Black Hills where the figure 9 map area is located). Cottonwood Creek flows southeast to the figure 9 south center edge and then southeast before turning northeast to join the northeast-oriented Cheyenne River (see figure 10 below). The South Fork French Creek flows southeast from the figure 9 north center to the figure 9 southeast corner and then southeast and northeast to join east and southeast-oriented French Creek, which also flows to the Cheyenne River. Note the maze of through valleys linking the South Fork French Creek valley with the southeast-oriented Cottonwood Creek valley. This anastomosing complex of dry valleys is evidence the region was eroded by southeast-oriented flood waters before headward erosion of the deep southeast-oriented French Creek valley captured the southeast-oriented flood flow and diverted the water to the French Creek valley. In the figure 9 west center are through valleys linking the South Fork French Creek valley with south-oriented valleys draining to the southeast-oriented Lame Johnny Creek valley. Headward erosion of the Cottonwood Creek valley beheaded south-oriented flood flow to some of those Lame Johnny Creek tributary valleys prior to headward erosion of the deep South Fork French Creek valley. Headward erosion of the deep French Creek valley subsequently beheaded southeast-oriented flood flow to the South Fork French Creek valley (north of the figure 9 and figure 10 map areas-see figure 2 for valley relationships).

French Creek-Beaver Creek drainage divide area west of Cheyenne River

Figure 10: French Creek-Beaver Creek drainage divide area west of Cheyenne River. United States Geological Survey map digitally presented using National Geographic Society TOPO software.

Figure 10 illustrates the French Creek-Beaver Creek drainage divide area between the Black Hills and the northeast-oriented Cheyenne River. The Cheyenne River is the northeast-oriented valley flowing from the figure 10 south (east half) edge to the figure 10 east edge (north half). French Creek is the southeast and northeast-oriented stream flowing in the figure 10 northeast quadrant to the figure 10 northeast corner (and then to the northeast-oriented Cheyenne River. Beaver Creek flows through Buffalo Gap, South Dakota in the figure 10 southwest corner and then southeast to the Cheyenne River. Lame Johnny Creek flows from the figure 10 northwest corner to join the Cheyenne River near the figure 10 south center edge. Cottonwood Creek originates in the figure 10 center (west) and flows southeast before turning northeast to join the northeast-oriented Cheyenne River in the figure 10 east center. The Cheyenne River-White River drainage divide essay describes the area east of the Cheyenne River valley. Flats and tables adjacent to the Cheyenne River valley are erosion surfaces developed prior to headward erosion of the present day northeast-oriented Cheyenne River valley. Prior to Cheyenne River valley headward erosion large volumes of flood water moved southeast in the various southeast-oriented valleys to what was then the actively eroding deep White River valley (southeast of figure 10-see White River drainage basin essays under White River on the sidebar category list for more details). Southeast-oriented flood waters flowed across the entire figure 10 map area and eroded the erosion surfaces now preserved in the form of flats and tables standing above the deeper Cheyenne River valley. Headward erosion of the deep northeast-oriented Cheyenne River valley then captured the southeast-oriented flood flow and diverted the flood waters northeast. Headward erosion of the deep Cheyenne River valley also lowered base level causing flood waters in the various valleys (and in what are today other Cheyenne River tributary valleys) to erode deeper inner valleys within their broad earlier valleys. Headward erosion of the deep Cheyenne River valley captured southeast-oriented flood flow moving to the White River valley, and flood waters on the northwest ends of those beheaded flood flow routes reversed flow direction to erode what are today northwest-oriented Cheyenne River tributary valleys. Erosion of those northwest-oriented valleys was aided by flood flow from not yet captured (by headward erosion of the deep Cheyenne River valley) southeast-oriented flood flow further to the south and southwest, which was captured and then flowed northeast along what is today the northeast-oriented White River valley, and some of which spilled to the northwest into the newly eroded northeast-oriented Cheyenne River valley.

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.