A geomorphic history based on topographic map evidence

The Missouri River-Yellowstone River drainage divide area discussed here is located in northeastern Montana, USA and is northeast of the Redwater River-Yellowstone River drainage divide area. Although detailed topographic maps of the Missouri River-Yellowstone River drainage divide area have been available for more than fifty years detailed map evidence has not previously been used to interpret the region’s geomorphic history. The interpretation provided here is based entirely on topographic map evidence. The Missouri River-Yellowstone River drainage divide area is interpreted to have been eroded during immense southeast-oriented flood events, the first of which flowed on a topographic surface at least as high as the highest points in the present-day drainage divide area. Flood erosion across the drainage divide ended when headward erosion of the deep Redwater River and Missouri River valleys captured all southeast-oriented flood flow.

Introduction:

• The purpose of this essay is to use topographic map interpretation methods to explore northeast Montana Missouri River-Yellowstone River 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 Missouri River-Yellowstone River drainage divide area landform evidence will be regarded as evidence supporting the “thick ice sheet that melted fast” paradigm.

Missouri River-Yellowstone drainage divide area location map

Figure 1: Missouri River-Yellowstone drainage divide area location map (select and click on maps to enlarge). National Geographic Society map digitally presented using National Geographic Society TOPO software.

Figure 1 provides a Missouri River-Yellowstone River drainage divide area location map. The state west of the north-south green border line is Montana. East of the north-south purple border is North Dakota. The Yellowstone River flows from the figure 1 south center to join the east-oriented Missouri River southwest of Williston, North Dakota. Fort Peck Lake is a reservoir flooding the Missouri River valley and today downstream from Fort Peck Dam the Missouri River flows roughly in an east direction across the figure 1 top half. In northeast Montana a large valley extends from the Missouri River valley northeast from near Poplar through Medicine Lake and is sometimes considered to be a former Missouri River channel. That now abandoned northeast-oriented valley played a significant role in the evolution of present day Missouri River-Yellowstone River drainage divide area landforms. The Missouri River-Yellowstone River drainage divide area discussed here is located east of Poplar, Montana (on the Missouri River) and north of Sidney, Montana (on the Yellowstone River). Figure 1 illustrates numerous southeast and northwest-oriented Yellowstone River and Missouri River (and Redwater River) tributaries. This southeast and northwest-orientation of tributary valleys is evidence the northeast-oriented Yellowstone River valley eroded southwest across multiple southeast-oriented flood flow routes, such as might be found in a large-scale flood formed anastomosing channel complex, and subsequently the abandoned northeast-oriented valley (and the Redwater River valley) eroded headward across the same anastomosing channel complex (with the present day Missouri River valley east of Poplar being formed slightly later). Northwest-oriented tributary valleys were eroded by reversed flood flow on northwest ends of beheaded flood flow channels. Because channels were anastomosing (meaning they were interconnected) reversed flood flow on beheaded flood flow channels often captured yet to be beheaded southeast-oriented flood flow from flood flow channels further to the southwest. Such captures of yet to be beheaded flood flow often helped erode significant northwest-oriented tributary valleys. Based on the northwest-southeast orientation of tributary streams landform evidence illustrated here is interpreted in the context of an immense southeast-oriented flood flowing across the entire figure 1 map area and which was systematically captured and diverted further and further to the northeast by headward erosion of deep valleys eroded into a topographic surface at least as high as the figure 1 region highest elevations today. In the figure 1 map region headward erosion of the Yellowstone River valley captured southeast-oriented flood flow and diverted the flood waters northeast, and subsequently headward erosion of the abandoned northeast-oriented valley captured the same southeast-oriented flood flow. Detailed maps below provide evidence supporting this interpretation. The Yellowstone River-Little Missouri River drainage divide area essay and in the Yellowstone River-Beaver Creek drainage area essay describe regions located immediately east of the Missouri River-Yellowstone River drainage divide area described here and can be found under Little Missouri River or Yellowstone River on the sidebar category list. The Redwater River-Yellowstone River drainage divide area essay describes the region to the southwest of the drainage divide described here and can be found under Redwater River on the sidebar category list.

Missouri River-Yellowstone drainage divide area detailed location map

Figure 2: Missouri River-Yellowstone drainage divide area detailed location map. United States Geological Survey map digitally presented using National Geographic Society TOPO software. 

Figure 2 illustrates a somewhat more detailed map of the Missouri River-Yellowstone River drainage divide area discussed here. The red shaded area in the figure 2 northwest quadrant is the Fort Peck Indian Reservation. McCone, Richland, and Dawson Counties are located in Montana. The Montana-North Dakota border is the north-south border line near the figure 2 east edge. The Missouri River-Yellowstone River drainage divide area discussed here is located primarily in Richland County. The Yellowstone River flows northeast through Savage and Sidney, Montana to join the Missouri River in the figure 2 northeast corner. The Redwater River flows northeast from the figure 2 southwest corner area through Brockway, and Circle, Montana  and then flows north (with some jogs) to join the Missouri River near Poplar, Montana. Figure 2 shows many more southeast-oriented Yellowstone River tributaries than figure 1. Also, while outside the Redwater River-Yellowstone River drainage divide area there are numerous southeast-oriented and northwest-oriented Redwater River tributaries and nearly all Yellowstone River tributaries from the east are northwest-oriented. This northwest-southeast drainage alignment is evidence the northeast oriented Yellowstone River valley eroded southwest across an immense southeast-oriented flood to capture the flood waters and to divert the flood waters northeast. Further, the drainage alignment is evidence the northeast and north-oriented Redwater River valley eroded south and southwest across the same immense southeast-oriented flood to capture flood waters moving to the newly eroded Yellowstone River valley and to divert the flood waters still further to the northeast and north. This essay interprets evidence to mean the Redwater River valley eroded south from what is today a large abandoned valley extending northeast from Poplar, Montana that had eroded southwest to capture the southeast-oriented flood flow. Southeast-oriented tributary valleys were eroded by southeast-oriented flood flow moving into the newly eroded and deep Yellowstone River valley. The northwest-oriented tributary valleys were eroded by reversed flood flow on the northwest ends of beheaded southeast-oriented flood flow routes. Because flood waters move in and erode anastomosing (or interconnected) channels reversed flood flow on a beheaded flood flow route could capture flood flow from yet to be beheaded flood flow routes. Such captures of yet to be beheaded flood flow enabled the reversed flood flow to erode much deeper and larger northwest-oriented valleys than might otherwise be possible.

Drainage divide area at Missouri River-Yellowstone River confluence

Figure 3: Drainage divide area at Missouri River-Yellowstone River confluence. United States Geological Survey map digitally presented using National Geographic Society TOPO software. 

Figure 3 illustrates the Missouri River-Yellowstone River confluence area and the Missouri River-Yellowstone River drainage divide immediately southwest of the confluence area. The Yellowstone River flows from the figure 3 southeast corner along the figure 3 east edge to join the Missouri River just south of Buford, North Dakota. The Missouri River flows in a somewhat meandering valley from the figure 3 northwest corner to join the Yellowstone River in the figure 3 east center area. In the Missouri River-Yellowstone River drainage divide area immediately west and south of the confluence area note the southeast-oriented orientation of Yellowstone River tributaries and the northwest-orientation of Otis Creek, which is the only major Missouri River tributary shown. The orientations of headwaters of the Yellowstone River and Missouri River tributaries provide important clues as to the how the figure 3 region was eroded. Note how northwest-oriented Otis Creek headwaters originate at the edge of the Missouri River valley as a southeast-oriented stream near Antelope Butte and then make a U-turn to flow southwest and then northwest to the southeast-oriented Missouri River (in other words making almost a complete circle). Also note how northwest-oriented Otis Creek is linked by a through valley with southeast-oriented Fourmile Creek, which flows to the north-oriented Yellowstone River. Further note how Fourmile Creek headwaters also make a U-turn, this time from flowing northwest to flowing southeast and how the northwest-oriented Fourmile Creek valley segment is linked by a through valley with headwaters of a southeast-oriented Yellowstone River tributary. This evidence and similar evidence indicates the entire figure 3 map area was eroded by southeast-oriented flood flow moving to what must have been a newly eroded north-oriented Yellowstone River valley and headward erosion of the deep southeast-oriented Missouri River valley (and also of the southeast-oriented Fourmile Creek valley) subsequently captured the southeast-oriented flood flow, causing reversals of flood flow on the northwest ends of beheaded southeast-oriented flood flow routes. In the case of the Missouri River, the northwest-oriented Otis Creek valley was eroded by reversed southeast-oriented flood flow flowing northwest to the newly eroded Missouri River valley. In the case of Fourmile Creek, the northwest-oriented Fourmile Creek valley segment was eroded by reversed flood flow that had been captured by Fourmile Creek valley headward erosion. The north-northeast oriented Fourmile Creek headwaters south of the northwest-oriented Fourmile Creek valley segment provide evidence the Fourmile Creek valley captured southeast-oriented flood flow further to the south and southwest.

Missouri River-Yellowstone River drainage divide northwest of Fairview

Figure 4 provides a bigger picture view of the Missouri River-Yellowstone River drainage divide area west and south of the Missouri River-Yellowstone River confluence area and includes the figure 3 map area, which was shown in more detail. The town in the figure 4 southeast corner is Fairview, which straddles the Montana-North Dakota border. The southeast-oriented Missouri River flows from the figure 4 northwest corner to join the north-oriented Yellowstone River near the figure 4 east center edge. The northwest-oriented Missouri River tributary flowing to join the Missouri River in the figure 4 northwest corner is Hardscrabble Creek. Note how in the Hardscrabble Creek headwaters area the Hardscrabble Creek tributaries have eroded valleys around several erosional residual masses. Those interconnected northwest-oriented valleys are evidence of a northwest-oriented anastomosing channel complex flowing to what is now the southeast-oriented Missouri River valley. In the figure 4 northeast quadrant a large meandering valley leads south from the figure 4 north edge to the southeast-oriented Missouri River valley (figure 6 below better illustrates that valley). Note the narrow Missouri River valley immediately downstream (and also upstream) from this south-oriented valley. The narrow Missouri River valley indicates the southeast-oriented Missouri River valley eroded across what probably was a pre-existing drainage divide. This evidence supports the interpretation that an earlier large northeast-oriented valley eroded southwest to the Poplar, Montana area (with the Redwater River valley being a southwest extension of that initial deep northeast-oriented valley) and the present day east and southeast-oriented Missouri River valley east of Poplar initially did not exist. Probably the northwest-oriented Hardscrabble Creek drainage basin was eroded by reversed flood waters on the northwest ends of southeast-oriented flood flow routes that had been beheaded by headward erosion of the deep northeast-oriented valley (which is today the dry valley extending northeast from Poplar, Montana illustrated in figure 5 below). However, existence of the southeast-oriented Missouri River valley across the figure 4 map area provides evidence the drainage divide between the Redwater River-abandoned northeast valley and the Yellowstone River valley was breached along the present day Missouri River valley route at about the same time as flood waters were being reversed by headward erosion of the deep northeast-oriented Redwater River-abandoned northeast-oriented valley. Once the drainage divide was breached at least for a time flood waters probably flowed in all valleys, which were then components of a gigantic northeast-oriented anastomosing channel complex.

Abandoned valley northeast of Poplar, Montana

Figure 5 illustrates the present day Missouri River valley at the northwest end of the Missouri River-Yellowstone River drainage divide area discussed here. Poplar, Montana is the town located near the Missouri River along the figure 5 west edge. Brockton is the town located on the Missouri River midway between the figure 5 west and east edges. Northwest-oriented Charlie Creek flows to the Missouri River at Brockton (Charlie Creek headwaters are seen in figure 9 below). While technically outside the present day Missouri River-Yellowstone River drainage divide area the large dry valley extending northeast from Poplar played a significant role in the development of the present day Missouri River-Yellowstone River drainage divide area landforms. The south-oriented Poplar River flows south along the dry valley’s west edge to join the Missouri River at Poplar. Further east in the figure 5 northeast quadrant Big Muddy Creek flows southwest along the dry valley’s southeast edge and then turns southeast to flow in a large southeast-oriented valley to the east oriented Missouri River valley. Opposite that large southeast-oriented valley is northwest-oriented Hardscrabble Creek, where it flows to the east oriented Missouri River. The sequence of valley formation in figure 5 begins with southeast-oriented flood water moving across a topographic surface at least as high as the highest figure 5 elevations today and probably moving to a newly eroded deep Yellowstone River valley as seen in figure 4 above (the east oriented Missouri River valley did not exist at that time and the Yellowstone River valley had eroded south and southwest to the Williston, North Dakota area and then southwest along what is now a northeast-oriented Missouri River valley segment to the figure 4 map area). Headward erosion of what is now the deep northeast-oriented dry valley extending northeast from Poplar captured the southeast-oriented flood flow and diverted the flood waters further to the northeast (although that valley and the former Yellowstone River valley north of Williston probably converged in northwest North Dakota or southern Saskatchewan). Flood waters on the northwest ends of beheaded southeast-oriented flood flow routes reversed flow direction to erode northwest-oriented valleys into the newly eroded and deep northeast-oriented valley. Because flood waters were moving in anastomosing (or interconnected) channels, reversed flow routes often captured significant flow from yet to be beheaded flow routes further to the southwest. Reversed flow on what is today the northwest-oriented Hardscrabble Creek alignment captured significant yet to be beheaded flood flow and eroded a deep northwest-oriented valley into the newly eroded deep northeast-oriented valley (extending northeast from Poplar). For reasons not apparent from topographic map evidence, although perhaps due to a surge of flood flow or some blockage of flood flow in the northeast-oriented valley, flood waters then breached the drainage divide between the newly eroded deep northeast-oriented valley and the deep Yellowstone River valley to erode the present day east and southeast-oriented Missouri River valley and what is today a parallel east and southeast oriented valley illustrated in figure 6 below.

Abandoned valley east of Culbertson, Montana

Figure 6 illustrates the Missouri River valley immediately east of the figure 5 map area and also illustrates a previously mentioned through valley parallel to the Missouri River valley. Northwest-oriented Hardscrabble Creek is located in the figure 6 southwest corner. Otis Creek is the northwest-oriented Missouri River tributary in the figure 6 southeast quadrant that turns northeast just before joining the Missouri River. The large dry valley extending east from Culbertson deserve mention. The west end is drained by Clover Creek, which flows west to the east-oriented Missouri River valley. The primary Clover tributary is southeast oriented Shell Creek, which joins Clover Creek at Lanark. The east end of the dry valley is drained by southeast oriented Shotgun Creek, which flows to southwest-oriented Little Muddy Creek, which in turn flows to the southeast oriented Missouri River valley at Lakeside. North of figure 6 southeast-oriented Shotgun Creek begins along a partially breached south wall of the large northeast-oriented valley seen in figure 5. This evidence suggests the Shotgun Creek valley at one time was a reversed flood flow route when headward erosion of the large northeast-oriented valley beheaded a southeast-oriented flood flow route. The northeast-oriented dry valley segment was probably eroded by captured yet to be beheaded southeast-oriented flood flow moving to reversed flow on the Shotgun Creek alignment. That captured flood flow moved east and southeast- along the dry valley alignment (and also along the present day Missouri River valley alignment upstream from Culbertson). At the same time the present day southeast-oriented Missouri River valley between Culbertson and the Otis Creek mouth was eroded headward on the alignment of the southeast-oriented flood flow channel responsible for initiating the alignments of the southeast-oriented Fourmile Creek valley and the northwest-oriented Otis Creek valley. The southeast-oriented Missouri River valley southeast from Lakeside (see figure 4 above) originated as a southeast-oriented valley eroded by southeast-oriented flood flow into the west wall of the newly eroded northeast-oriented Yellowstone River valley. The southwest-oriented Little Muddy Creek valley probably eroded northeast to capture southeast-oriented flood flow and divert flood flow to the southeast-oriented valley being eroded headward from the Yellowstone River valley west wall (although other interpretations are possible). Then when the northeast-oriented valley-Yellowstone River drainage divide was breached an additional breach at the Shotgun Creek headwaters area along the northeast-oriented valley south edge began to develop. Probably large amounts of flood waters did flow south along the present day Shotgun Creek valley and then southwest along the Little Muddy Creek route. For a time flood waters were probably moving simultaneously in all of the larger valleys, which were acting as anastomosing channels.

Yellowstone River valley slope northwest of Sidney

Figure 7: Yellowstone River valley slope northwest of Sidney. United States Geological Survey map digitally presented using National Geographic Society TOPO software. 

Figure 7 illustrates the northwest wall of the northeast oriented Yellowstone River valley west of Sidney, Montana. Yellowstone River tributaries from the west are nearly all southeast-oriented and the configuration of valleys on the southeast-sloping Yellowstone River valley wall provides evidence the valley wall was eroded by flood waters moving in an ever-changing anastomosing channel complex. The named Yellowstone River tributaries from the northeast to the southwest are: North Fork First Hay Creek, First Hay Creek, North Fork Lone Tree Creek (which has  a through valley to southeast-oriented Brorson Creek), Lone Tree Creek, South Fork Lone Tree Creek, North Fork of Fox Creek, and Three Buttes Creek, which flows near the figure 7 west edge (southwest quadrant). Note how a Three Buttes Creek tributary flows south from the figure 7 northwest quadrant and has beheaded headwaters of Lone Tree Creek. Figure 9 below illustrates how the North Fork Lone Tree Creek beheaded that south-oriented Three Buttes Creek tributary. Also note through valleys linking the south-oriented Three Buttes Creek tributary valley with southeast-oriented Lone Tree Creek headwaters and the erosional residuals isolated by those various valleys. Also note isolated erosional residuals between North Fork Hay Creek and Hay Creek, southeast of North Fork Lone Tree Creek where it turns to join Lone Tree Creek, and between North Fork Lone Tree Creek and Lone Tree Creek. The entire slope is a maze of anastomosing channels, some used today by Yellowstone River tributaries and some today are dry valleys linking valleys in which there are streams. This maze of anastomosing valleys was eroded by southeast-oriented flood flow that eroded what was then the newly eroded and deep northeast oriented Yellowstone River valley northwest wall. Flood waters continued to erode the Yellowstone River northwest valley wall until flood flow was captured in the northwest and west by headward erosion of the deep northeast oriented valley seen in figure 5 and its southwest extension, which is today the northeast- and north-oriented Redwater River valley. The Missouri River-Yellowstone River drainage divide was not breached by any figure 7 southeast-oriented Yellowstone River tributary valleys and for that reason erosion of the present-day southeast-oriented Missouri River valley seen in figure 4 did not affect the figure 7 region.

Detailed map of Hardscrabble Creek headwaters

Figure 8 illustrates a detailed map of the Hardscrabble Creek headwaters area, which was seen in less detail in figure 4. Remember from the figure 5 discussion the northwest-oriented Hardscrabble Creek valley was eroded by reversed flood flow on a southeast-oriented flood flow route beheaded by headward erosion of what is today the large dry valley extending northeast from Poplar. Where did reversed flow flood waters come from that eroded the northwest-oriented Hardscrabble Creek valley? Figure 8 provides some clues. Note how Hardscrabble Creek originates as a southeast-oriented stream in the figure 8 center and then turns northeast and north to flow to the figure 8 north edge. North of figure 8 Hardscrabble Creek turns northwest. What has happened is southeast-oriented flood flow moving to what was then the newly eroded and deep northeast-oriented Yellowstone River valley was beheaded by headward erosion of the deep northeast-oriented abandoned valley seen in figure 5. Flood waters on what is today the northwest-oriented Hardscrabble Creek alignment reversed flow direction to flow northwest to the newly eroded and locally deeper northeast-oriented abandoned valley. Because the northeast-oriented abandoned valley was eroded headward reversed flood flow on the Hardscrabble Creek alignment captured yet to be beheaded flood flow from southeast-oriented flood flow routes further to the south and southwest. The north-oriented Hardscrabble Creek valley segment in figure 8 illustrates one route such captured flood waters took and the southeast-oriented Hardscrabble Creek headwaters valleys were eroded by yet to be beheaded southeast-oriented flood flow headward erosion of the north-oriented Hardscrabble Creek valley captured. Subsequently headward erosion of the deep northeast-oriented abandoned valley beheaded flood flow to the Hardscrabble Creek headwaters area and flood waters on the northwest ends of those beheaded flood flow routes reversed flow direction to erode northwest-oriented valleys in the figure 8 northwest quadrant and to create the drainage divide between those northwest-oriented valleys and the southeast-oriented Hardscrabble Creek headwaters valleys.

North Fork Lone Creek-Three Buttes Creek drainage divide

Figure 9 illustrates the drainage divide between North Fork Lone Tree Creek and a south-oriented Three Buttes Creek tributary, both of which flow to the Yellowstone River and also the drainage divide between north-oriented Timber Creek (which is a Charlie Creek tributary) and northwest-oriented Charlie Creek, which flows to the Missouri River. Timber Creek flows north in the figure 9 north center and then turns northwest to flow to northwest-oriented Charlie Creek and then to the Missouri River. Northwest-oriented Charlie Creek is located in the figure 9 southwest quadrant. North Fork Lone Tree Creek originates in the figure 9 center and then flows southeast to the figure 9 east edge. A southeast oriented through valley links a southeast oriented North Fork Lone Tree Creek valley segment with southeast and southwest oriented headwaters of an unnamed Three Buttes Creek tributary in the figure 9 southeast quadrant. Note how headwaters of what north of figure 9 is northwest-oriented Timber Creek have eroded south to capture southeast-oriented flood flow from flood flow routes south and southwest of the northwest-oriented Timber Creek alignment. What is today the southwest-oriented Charlie Creek tributary valley that originates immediately southwest of the north-oriented Timber Creek valley was initiated as a northeast-oriented flow route for yet to be beheaded flood waters on the Charlie Creek alignment captured by reversed flood flow on the Timber Creek alignment. Probably the southeast-oriented flood flow the Timber Creek headwaters valley captured had been going to the south-oriented Three Buttes Creek tributary valley and the North Fork Lone Tree Creek valley (which was slightly deeper and was capturing the flow). Almost certainly flood waters were moving in ever-changing anastomosing channels and the drainage history here is much more complicated than I have described.

Anastomosing channel complex on Yellowstone River valley west wall

Figure 10 illustrates more of the previously seen anastomosing channel complex eroded into the Yellowstone River valley west wall. Fox Creek is the stream flowing southeast from Fox Lake next to Lambert in the figure 10 southwest corner. The southeast-oriented East Fork of Fox Creek is located north of Lambert and the southeast-oriented North Fork of Fox Creek is located in the figure 10 southeast quadrant. Three Buttes Creek flows southeast from the figure 10 northwest corner and joins the previously mentioned unnamed south-oriented tributary (seen in figures 9 and 7) and then makes an abrupt turn to flow west to join the southeast-oriented East Fork of Fox Creek. Prior to making its abrupt turn west Three Buttes Creek is headed for the southeast-oriented North Fork Fox Creek valley and a northwest-southeast oriented through valley links the southeast-oriented Three Buttes Creek valley segment with the southeast-oriented North Fork Fox Creek valley. Note also south of the highway a through valley linking an east-oriented North Fork Fox Creek tributary with a northwest- and south-oriented Fox Creek tributary. These valleys were all eroded by southeast-oriented flood waters flowing into the northeast-oriented Yellowstone River valley. The captures that resulted in this maze of anastomosing valleys are typical of captures expected in an ever-changing anastomosing channel complex, where as one channel erodes deeper it captures flood waters from adjacent channels and even causes flood waters to reverse flow direction so as to flow toward the deeper channel. The presence of this anastomosing channel complex on the Yellowstone River valley west wall is evidence supporting the interpretation the deep northeast-oriented Yellowstone River valley eroded southwest to capture an immense southeast-oriented flood and to divert the flood waters to the northeast and that subsequently headward erosion of deep northeast-oriented abandoned valley captured the southeast-oriented flood waters and diverted the flood flow still further to the northeast.

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.