A geomorphic history based on topographic map evidence

The McDonald Creek-Flatwillow Creek drainage divide area discussed here is located in Fergus and Petroleum Counties, Montana, USA. Although detailed topographic maps of the McDonald Creek-Flatwillow Creek 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 McDonald Creek-Flatwillow Creek 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 Missouri River valley captured all southeast-oriented flood flow.

Introduction:

• The purpose of this essay is to use topographic map interpretation methods to explore McDonald Creek-Flatwillow Creek drainage divide area landform origins in Fergus and Petroleum Counties, Montana, USA. 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 McDonald Creek-Flatwillow Creek drainage divide area landform evidence will be regarded as evidence supporting the “thick ice sheet that melted fast” paradigm.

McDonald Creek-Flatwillow Creek drainage divide area location map

Figure 1: McDonald Creek-Flatwillow Creek 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 McDonald Creek-Flatwillow Creek drainage divide area location map and illustrates a region in Montana. The Missouri River flows southeast from the figure 1 northwest corner to Fort Peck Lake. The Musselshell River flows from the figure 1 west center (south half) edge to Harlowton, Ryegate, Lavina, Roundup, and Melstone and then turns north to flow to Mosby and to join the Missouri River at Fort Peck Lake. The Yellowstone River flows from Big Timber (along the figure 1 west edge near the figure 1 southwest corner) to Greycliff, Columbus, Laurel, Billings, Custer, Forsyth, Miles City, and Terry (located along the figure 1 east edge). McDonald Creek is the unnamed stream beginning east of Lewistown (located figure 1 west center) and flowing to Grassrange and Winnett to join southeast-oriented Box Elder Creek, which flows to the north-oriented Musselshell River. Flatwillow Creek is located directly south of McDonald Creek and originates at the east end of the Big Snowy Mountain region (located in the figure 1 west center area) and flows east, southeast, and northeast to join southeast-oriented Box Elder Creek, which flows to the north-oriented Musselshell River. Based on other Missouri River drainage basin landform origins research project essays published on this website landform evidence illustrated here is interpreted in the context of an immense southeast-oriented flood flowing across the figure 1 map area and which was systematically captured and diverted northeast by deep valleys that eroded headward into a topographic surface at least as high as the figure 1 region highest elevations today. Prior to Musselshell River valley headward erosion (although not much before) the deep Yellowstone River valley eroded southwest to capture southeast-oriented flood waters and to divert flood waters northeast. The Musselshell River valley was the next valley that eroded southwest to capture southeast-oriented flood water and to divert flood flow northeast. The northeast-oriented North Willow Creek valley then eroded southwest to behead and capture southeast-oriented flood flow routes moving flood waters to the newly eroded northeast-oriented Musselshell River valley. The southeast-oriented North Willow Creek valley segment eroded headward along a captured southeast-oriented flood flow route and the Willow Creek valley eroded headward along another southeast-oriented flood flow route. Next the Flatwillow Creek valley eroded southwest and northwest to capture southeast-oriented flood flow that had been moving to what was then the newly eroded North Willow Creek valley. Headward erosion of the McDonald Creek valley next captured the flood flow. The Flatwillow Creek-North Willow Creek and Willow Creek drainage divide area essay, the North Willow Creek-Musselshell River drainage divide area essay, the Musselshell River-Yellowstone River drainage divide area in Musselshell and Yellowstone Counties essay, and the Musselshell River-Yellowstone River drainage divide area in Treasure and Rosebud Counties essay describe drainage divide area located near the McDonald Creek-Flatwillow Creek drainage divide area discussed here and can be found under Musselshell River on the sidebar category list.

McDonald Creek-Flatwillow Creek drainage divide area detailed location map

Figure 2: McDonald Creek-Flatwillow Creek 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 McDonald Creek-Flatwillow Creek drainage divide area discussed in this essay. Fergus, Petroleum, and Musselshell Counties are located in Montana. The Musselshell River flows northeast from the figure 2 south center edge in Musselshell County to Delphia, Musselshell, and Melstone, before flowing north-northwest and north-northeast along the county line to the figure 2 north edge. The North Fork McDonald Creek originates east of Lewistown and flows east to join the South Fork McDonald Creek north of Grassrange, and then to flow east to Winnett and then continues east to join the southeast-oriented Box Elder Creek, which flows to the north-oriented Musselshell River. The South Fork McDonald Creek, which is the Fork of concern in this essay, begins southwest of Forestgrove and flows north, northeast, east, and northeast to join the North Fork north of Grassrange. Flatwillow Creek originates in the eastern Big Snowy Mountains and flows north of the Little Snowy Mountains before turning southeast and then northeast and east to join southeast-oriented Box Elder Creek, which flows to the north-oriented Musselshell River. Elk Creek is a major Flatwillow Creek tributary of interest in this essay and the South Fork flows northeast before joining the North Fork and forming southeast-oriented Elk Creek, which joins Flatwillow Creek at Petrolia Lake. Southeast and northeast oriented Spring Creek and Pike Creek are other Flatwillow Creek tributaries illustrated and discussed here. Figure 2 shows a number of southeast-oriented streams or segments of streams. This predominance of southeast-oriented drainage is interpreted as evidence the McDonald Creek-Flatwillow Creek drainage divide area was eroded by an immense southeast-oriented flood which crossed the figure 2 map area. Flood waters originally were moving to what was probably a newly eroded northeast- and north-oriented Musselshell River valley. Headward erosion of the North Willow Creek then captured the flood waters and diverted the flood flow more directly to the Musselshell River valley. Next headward erosion of the Flatwillow Creek valley captured the flood flow and beheaded flood flow routes to the newly eroded North Willow Creek valley. Soon thereafter headward erosion of the McDonald Creek valley captured the southeast-oriented flood flow and headward erosion of the South Fork McDonald Creek valley beheaded all flood flow routes to the newly eroded Flatwillow Creek valley. Detailed maps below illustrate evidence supporting this interpretation of McDonald Creek-Flatwillow Creek drainage divide landform origins.

East end of the McDonald Creek-Flatwillow Creek drainage divide area

Figure 3: East end of the McDonald Creek-Flatwillow Creek drainage divide area. United States Geological Survey map digitally presented using National Geographic Society TOPO software. 

Figure 3 illustrates the east end of the McDonald Creek-Flatwillow Creek drainage divide area east of Winnett, Montana. McDonald Creek flows east through Winnett to join southeast-oriented Box Elder Creek. Flatwillow Creek flows northeast from the figure 3 south edge to Petrolia Lake and then flows east to join southeast-oriented Box Elder Creek near the figure 3 east edge. Elk Creek flows northeast from the figure 3 southwest corner to Petrolia Lake, where it joins Flatwillow Creek to flow to southeast-oriented Box Elder Creek. Note the large number of southeast-oriented drainage routes. For example, the northeast oriented Elk Creek valley has several southeast-oriented tributaries, the east-oriented McDonald Creek valley in the Winnett area also has several southeast-oriented tributaries, Box Elder Creek is southeast-oriented, and Box Elder Creek has southeast-oriented tributaries, such as Gorman Coulee in the figure 3 northeast quadrant. Also note northwest-oriented Flatwillow Creek tributaries in the Petrolia Lake area. The predominance of southeast-oriented drainage routes and the northwest-oriented tributaries to an east-oriented stream are evidence the figure 3 map area was eroded by a large southeast-oriented flood, which was systematically captured and diverted east by headward erosion of the northeast and east-oriented Flatwillow Creek valley, headward erosion of the northeast oriented Elk Creek valley, and headward erosion of the Box Elder Creek-McDonald Creek valley. The southeast-oriented flood waters originally flowed on a topographic surface at least as high as the highest figure 3 elevations today. It is possible flood erosion of the figure 3 map area was much deeper than the depth of present day valleys indicates. Flood waters were coming from a source area northwest of the figure 3 map area and were probably flowing to what was then a newly eroded northeast and north oriented Musselshell River valley and/or to newly eroded northeast-oriented Musselshell River tributary valleys.

East end of McDonald Creek-Elk Creek drainage divide area

Figure 4: East end of McDonald Creek-Elk Creek drainage divide area. United States Geological Survey map digitally presented using National Geographic Society TOPO software. 

Figure 4 illustrates the east end of the McDonald Creek-Elk Creek drainage divide area west of Winnett. located west of the figure 3 map area and containing overlap areas with figure 3. McDonald Creek flows in an east-southeast direction from the figure 4 northwest quadrant to Winnett in the figure 4 east center edge area. Elk Creek flows southeast from the figure 4 west center area to the figure 4 southeast corner and then to join Flatwillow Creek as seen in figure 3. In the figure 4 southwest corner is the southeast-oriented North Fork Yellow Water Creek and Yellow Water Creek is located along the figure 4 south edge. South of figure 4 Yellow Water Creek flows southeast and then northeast to join Elk Creek near the figure 4 southeast corner. Note the predominance of southeast-oriented tributaries to McDonald Creek and Elk Creek. These southeast-oriented tributaries provide evidence the Elk Creek valley eroded headward to capture multiple southeast-oriented flood flow routes such as might be found in a southeast-oriented anastomosing channel complex. Further, these southeast-oriented tributaries provide evidence the McDonald Creek valley eroded headward to behead flood flow channels moving flood waters to the newly eroded Elk Creek valley and to divert the flood waters more directly to the east. Flood waters originally flowed on a topographic surface at least as high as the highest figure 4 elevations today. The Elk Creek valley and the McDonald Creek valleys were eroded into that topographic surface as were the valleys of their various tributaries. Flood waters moving across the region to those actively eroding valleys were responsible for lowering the topographic surface to the level seen today. Figure 4 evidence is inadequate to determine how much material has been removed from the figure 4 map area. Flood waters flowed over and eroded the highest present day figure 4 elevations.

McDonald Creek-Elk Creek drainage divide area south of Grassrange

Figure 5: McDonald Creek-Elk Creek drainage divide area south of Grassrange. United States Geological Survey map digitally presented using National Geographic Society TOPO software. 

Figure 5 illustrates the McDonald Creek-Elk Creek drainage divide area southeast of Grassrange and is located west of the figure 4 map area and includes overlap areas with figure 4. The South Fork McDonald Creek flows northeast from the figure 5 west center edge to Grassrange and then north to join the east-oriented North Fork McDonald Creek and to form northeast and southeast-oriented McDonald Creek, which flows to the figure 5 east edge. Elk Creek flows northeast and north in the figure 5 south center area and then turns northeast and east-southeast to flow to the figure 5 east center edge. The North Fork Yellow Water Creek flows southeast from the Button Butte area to join east-oriented Yellow Water Creek in the figure 5 southeast corner. Note how southeast-oriented headwaters of North Fork Yellow Water Creek are linked by a through valley (or saddle) with a west and northwest-oriented Elk Creek tributary. That high level through valley provides evidence southeast-oriented flood waters once flowed on a topographic surface at least as high as the floor of the through valley and probably as the top of Button Butte. Southeast-oriented flood waters eroded the Button Butte upland east-facing slope as the deep Elk Creek and Yellow Water Creek valleys eroded headward or west along southeast-oriented flood flow routes. Apparently the Button Butte upland mass is composed of erosion resistant rock and headward erosion of Yellow Water Creek valley was slower than headward erosion of the Elk Creek valley, which eroded around the erosion resistant rock mass and beheaded the flood flow routes moving southeast-oriented flood flow to the Yellow Water Creek valley. The northeast oriented North Fork Elk Creek valley, located northwest of the northeast oriented Elk Creek valley segment, then eroded headward to capture southeast-oriented flood flow to the newly eroded northeast oriented Elk Creek valley. Next headward erosion of the deep northeast- and north-oriented South Fork McDonald Creek valley beheaded flood flow routes to the North Fork Elk Creek valley and the Elk Creek valley. Flood waters on the northwest ends of the beheaded southeast-oriented flood flow routes reversed flow direction to erode northwest-oriented South Fork McDonald Creek tributary valleys, such as the northwest-oriented Dry Fork valley. Figure 6 below provides a more detailed map of drainage divides in the figure 5 southwest corner area.

Blacktail Creek-Elk Creek drainage divide area

Figure 6: Blacktail Creek-Elk Creek drainage divide area. United States Geological Survey map digitally presented using National Geographic Society TOPO software. 

Figure 6 illustrates the Blacktail Creek-Elk Creek drainage divide area, most of which was shown in less detail in figure 5 above. Blacktail Creek flows northeast from the figure 6 west edge and then north to join northwest-oriented Dry Fork near the figure 6 north edge and then flow northwest to join northeast-oriented South Fork McDonald Creek just north of the figure 6 map area. Elk Creek flows northeast from the figure 6 south edge and then north and northeast to the figure 6 northeast corner area. Note how Elk Creek and Blacktail Creek tributaries from the east are usually northwest oriented and how several Elk Creek tributaries from the west are southeast-oriented. While underlying geologic structures almost certainly played a role in shaping figure 6 drainage routes, this northwest-southeast drainage orientation is evidence the Blacktail Creek-Elk Creek drainage divide area was eroded by southeast-oriented flood flow moving across the figure 6 map area. The deep northeast-oriented Elk Creek valley eroded into a high topographic surface that has now been completely removed and captured southeast-oriented flood flow moving across the figure 6 map area. Flood waters on  northwest ends of beheaded southeast-oriented flood flow routes reversed flow direction to erode northwest-oriented Elk Creek tributary valleys. Because the Elk Creek valley eroded headward and because flood flow routes were anastomosing or interconnected, reversed flood flow on newly beheaded flood flow routes captured flood waters from yet to be beheaded flood flow routes. Such captured flood waters helped erode the present day northwest-oriented Elk Creek tributary valleys. Southeast-oriented flood flow into the newly eroded northeast-oriented Elk Creek valley then eroded the east and southeast-oriented Elk Creek valley slope and tributary valleys. At approximately the same time the South Fork McDonald Creek-Blacktail Creek valley began to erode south and behead and reverse southeast-oriented flood flow routes moving flood waters to the newly eroded Elk Creek valley and Elk Creek tributary valleys. Flood waters on the northwest ends of the beheaded southeast-oriented flood flow routes reversed flow direction to erode northwest-oriented Blacktail Creek tributary valleys and to create the present day Blacktail Creek-Elk Creek drainage divide.

West end of Elk Creek-Flatwillow Creek drainage divide area

Figure 7 illustrates the Elk Creek-Flatwillow Creek drainage divide area south of the figures 5 and 6 map areas. The North Fork Flatwillow Creek flows southeast from the figure 7 west center edge and is joined by northeast-oriented South Fork Flatwillow Creek northwest of Tyler. Flatwillow Creek then flows southeast to the figure 7 south edge and makes a northeast jog in the figure 7 southeast corner. Southeast-oriented Spring Creek begins north of Tyler and flows into the figure 7 southeast quadrant where it turns northeast to flow to join Pike Creek near the figure 7 east edge. Pike Creek in the figure 7 east half flows southeast, north, and southeast and has several southeast and southwest-oriented tributaries. Buck Creek is located south of Pike Creek and flows southeast, east and southeast to join Spring Creek. Figure 8 below provides a detailed map of a Pike Creek-Buck Creek drainage divide area. Elk Creek begins north of Spring Creek headwaters and first flows southeast before turning northeast to flow to the figure 7 north edge (near the red highway). Note how a shallow high level northeast-oriented through valley links the northeast-oriented Elk Creek valley with the northeast-oriented South Fork Flatwillow Creek valley. That shallow northeast-oriented through valley provides evidence headward erosion of the deep Flatwillow Creek valley beheaded a higher level northeast-oriented Elk Creek valley, which extended southwest into the Little Snowy Mountain region. In other words, the South Fork Flatwillow Creek valley was initially eroded as an extension of the northeast-oriented Elk Creek valley and then was captured by headward erosion of the Flatwillow Creek valley (the North and South Forks Flatwillow Creek are illustrated and discussed in the Flatwillow Creek-North Willow Creek and Willow Creek drainage divide area essay). Large quantities of southeast-oriented flood waters would have been required to erode the present day deep Flatwillow Creek valley headward to capture northeast-oriented South Fork Flatwillow Creek and also erode the upstream North Fork Flatwillow Creek valley. Note also southeast-oriented Spring Creek tributaries in the figure 7 center south region. Those tributary valleys were eroded by southeast-oriented flood waters that were beheaded by headward erosion of the northeast-oriented Elk Creek valley.

Detailed map of a Pike Creek-Buck Creek drainage divide area

Figure 8 illustrates a detailed map of the Pike Creek-Buck Creek drainage divide area seen in less detail in figure 7 above. Pike Creek flows southeast from the figure 8 northwest corner and makes an abrupt turn to flow north in the figure 8 north center area and then flow southeast in the figure 8 northeast corner area. Buck Creek flows southeast in the figure 8 west center area and then flows east-northeast to the figure 8 center where it turns southeast to flow to the figure 8 southeast corner area. Pike Creek in the figure 8 northeast quadrant flows around a southeast-dipping hogback, suggesting bedrock geology and geologic structures have definitely played a role in shaping figure 8 drainage patterns. However, the valleys were eroded by running water and it is possible to reconstruct at least some figure 8 drainage history. Note the northwest-southeast oriented through valley linking the southeast-oriented Pike Creek headwaters valley with the downstream southeast-oriented Buck Creek valley segment. That through valley provides evidence flood water once moved south between the two present day drainage routes. Also note the north-south through valley linking the north-oriented Pike Creek valley segment with the downstream southeast-oriented Buck Creek valley segment. That through valley provides evidence the present day north-oriented Pike Creek valley segment originally was a south-oriented flood flow route moving water to the southeast-oriented Buck Creek valley. Headward erosion of the downstream southeast-oriented Pike Creek valley segment beheaded and reversed south-oriented flood flow in that present day north-oriented Pike Creek valley segment. Reversed flow in that north-oriented Pike Creek valley then captured southeast-oriented flood flow from the upstream southeast-oriented Pike Creek valley segment and in the process beheaded the downstream southeast-oriented Buck Creek valley segment and created the present day Pike Creek-Buck Creek drainage divide. This drainage history requires the presence of large quantities of southeast-oriented flood waters moving across the figure 8 map area.

South Fork McDonald Creek-North Fork Flatwillow Creek drainage divide area

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

Figure 9 illustrates the South Fork McDonald Creek-North Fork Flatwillow Creek drainage divide area south and southeast of Forestgrove and includes overlap areas with figures 5 and 6. The South Fork McDonald Creek flows across the figure 9 top half near the north edge. Northwest-oriented Dry Fork flows to north-oriented Blacktail Creek in the figure 9 northeast corner. Southeast-oriented Potter Creek joins the North Fork Flatwillow Creek near the figure 9 south center edge. Figure 9 is located north of the Little Snowy Mountains and what appear to be northeast dipping hogbacks are probably associated with the Little Snowy Mountain uplift to the south. Potter Creek headwaters are linked by a deep through valley with headwaters of north-northwest and north-northeast oriented Surenough Creek, which joins McDonald Creek at Forestgrove. West of the Surenough Creek headwaters is an extension of the through valley, which links the southeast-oriented Potter Creek valley with the northeast-oriented Tyler Creek valley, which drains to Surenough Creek in the figure 9 northwest quadrant (southwest of Forestgrove). A close look at figure 9 evidence reveals additional through valleys linking headwaters of northeast-oriented South Fork McDonald Creek tributaries. For example northeast-oriented Bear Creek headwaters are linked by a through valley with headwaters of north-northeast oriented Rose Canyon and northeast-oriented Atherton Creek headwaters. These through valleys provide evidence of multiple southeast-oriented drainage routes across the figure 9 map area before headward erosion of the present day northeast and north-northeast oriented South Fork McDonald Creek tributary valleys. Headward erosion of these northeast and north-northeast oriented South Fork McDonald Creek valleys to capture southeast-oriented flood flow would be greatly aided by uplift of the Little Snowy Mountains as flood waters were flowing southeast across the figure 9 map area. In fact this figure 9 evidence cannot be easily explained without uplift occurring as flood waters were eroding the region. Deep flood water erosion of the region may have helped trigger the Little Snowy Mountain regional uplift.

Surenough Creek-Potter Creek drainage divide area

Figure 10: Surenough Creek-Potter Creek drainage divide area. United States Geological Survey map digitally presented using National Geographic Society TOPO software. 

Figure 10 illustrates a detailed map of the through valley linking north-northwest and north-northeast oriented Surenough Creek headwaters with southeast-oriented Potter Creek headwaters. The figure 10 map area is shown in less detail in figure 9 above. Potter Creek flows southeast to southeast-oriented North Fork Flatwillow Creek. As seen in figure 9 above the northwest-southeast oriented through valley extends west from the figure 10 map area, providing evidence headward erosion of the deep Surenough Creek valley beheaded a deep southeast-oriented valley. The through valley linking Surenough Creek headwaters with Potter Creek headwaters is approximately 400 feet deep (depending on where measurements are made). Probably at one time this deep valley was one channel in a southeast-oriented anastomosing channel complex, where flood waters were moving south from the east-oriented South Fork McDonald Creek valley in the Surenough Creek valley to the Potter Creek-Flatwillow Creek valley, while flood waters were also continuing to flood east in the South Fork McDonald Creek valley. At that time Little Snowy Mountain uplift may have been underway and elevations were not what they are today. Uplift of the Little Snowy Mountains raised the Surenough Creek valley south end causing a reversal of flood flow in the Surenough Creek valley and creating the present day Surenough Creek-Potter Creek drainage divide. The source of the southeast-oriented flood waters described in this essay cannot be determined from evidence presented here. However, essays in this Missouri River drainage basin landform origins research project series when taken as a group can be used to trace flood waters both up flood to source areas and down flood to see where flood waters were going. A logical flood water source would be rapid melting of a thick North American ice sheet located in a deep “hole” occupying approximately the North American location usually recognized to have been glaciated. The deep “hole” would have been created by deep glacial erosion and by crustal warping caused by the ice sheet weight. Such a flood water source would not only explain the immense southeast-oriented floods this essay series describes, but would also explain why deep valleys were eroding headward to capture the southeast-oriented flood waters and diverting the flood waters further and further to the northeast and north into space in the deep “hole” the rapidly melting thick ice sheet had once occupied. In addition, such a flood water source may explain uplift of the mountains regions, such as the Little Snowy Mountains, during an immense southeast-oriented flood. A thick North American ice sheet in deep “hole” created in part due to the ice sheet’s weight would probably create crustal warping elsewhere on the continent, especially along ice sheet margins. Rapid erosion of overlying material might trigger localized uplifts of geologic structures such as those observed in this figure 9 region north of the Little Snowy Mountains.

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.