A geomorphic history based on topographic map evidence

The Judith River-Musselshell River drainage divide area discussed here is located in Fergus County, Montana, USA. Although detailed topographic maps of the Fergus County Judith River-Musselshell 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 Fergus County Judith River-Musselshell 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 Fergus County drainage divide ended when headward erosion of the deep Missouri River valley and its tributary Judith River valley captured all southeast-oriented flood flow.

Introduction:

• The purpose of this essay is to use topographic map interpretation methods to explore Judith River-Musselshell River drainage divide area landform origins in Fergus County, 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 Fergus County Judith River-Musselshell River drainage divide area landform evidence will be regarded as evidence supporting the “thick ice sheet that melted fast” paradigm.

Fergus County Judith River-Musselshell River drainage divide area location map

Figure 1: Fergus County Judith River-Musselshell River drainage divide area location map (select and click on maps to enlarge).

• Figure 1 provides a Judith River-Musselshell River drainage divide area location map and illustrates a region in Montana. The Missouri River flows northeast in the figure 1 northwest corner to Fort Benton and Loma and then turns southeast, east-northeast and southeast to flow to Fort Peck Lake. The Judith River flows north from the south of the Judith Basin to join the east-oriented Missouri River. The Musselshell River flows from the Little Belt Mountains area (figure 1 west center) to Martinsdale and then southeast to Harlowton, Ryegate and Lavina. From Lavina the Musselshell River lows northeast to Roundup and Melstone where it turns to flow north to join the Missouri River at Fort Peck Lake. South of the southeast- and northeast-oriented Musselshell River is the Yellowstone River, which flows through Livingston, Big Timber, Billings, and Forsyth. The Judith River-Musselshell River drainage divide area of concern in this essay is the drainage divide between the north-oriented Judith River and the north-oriented Musselshell River, which is located between the Judith Mountains and the Big Snowy Mountains. Included in the drainage divide area are Judith Mountains areas. A different essay addresses the drainage divide between the Judith River and the northeast-oriented Musselshell River (located south of the Big Snowy Mountains and the essay can be found under Judith River or Musselshell River on the sidebar category list). Prior to Musselshell River valley headward erosion the deep Yellowstone River valley eroded headward into the figure 1 map area to capture southeast-oriented flood waters and to divert flood waters northeast. Southeast-oriented tributaries to the north-oriented Musselshell River valley segment, such as Box Elder Creek, originated as southeast-oriented flood flow routes to the newly eroded and deep northeast-oriented Yellowstone River valley. At that time the Big Snowy Mountains and Judith Mountains did not significantly interfere with flood water movements. However, as immense quantities of flood water moved to the newly eroded and deep northeast-oriented Yellowstone River valley (and subsequently to the newly eroded and deep north-oriented Musselshell River valley) the Big Snowy Mountains and Judith Mountains emerged as significant obstacles, and the southeast-oriented flood waters were progressively channeled around them to flow in an east-oriented direction. The Missouri River-Musselshell River valley was the next major deep valley to erode into the figure 1 map region. The deep Musselshell River valley eroded south and southwest to capture southeast-oriented flood waters that had been moving to the newly eroded deep Yellowstone River valley and to divert the captured flood waters still further to the north and northeast. Headward erosion of the east-oriented Missouri River and the north-oriented Judith River valley next beheaded and reversed southeast-oriented flood flow routes to the newly eroded north-oriented Musselshell River valley and diverted flood waters north to the newly eroded east-oriented Missouri River valley. The Armells Creek-Box Elder Creek drainage divide area essay, Missouri River-Musselshell River drainage divide area essay, McDonald Creek-Flatwillow Creek drainage divide area essay,  Flatwillow Creek-North Willow Creek and Willow Creek drainage divide area essay, and North Willow Creek-Musselshell River drainage divide area essay, all located near the Judith River-Musselshell River drainage divide areas discussed here (all of the mentioned essays can be found under Musselshell River on the sidebar category list).

Fergus County Judith River-Musselshell River drainage divide area detailed location map

Figure 2: Fergus County Judith River-Musselshell River drainage divide area detailed location map.

• Figure 2 illustrates a somewhat more detailed map of the Judith River-Musselshell River drainage divide areas discussed here. Judith Basin and Fergus Counties are located in Montana. The east-oriented Missouri River is located north of the figure 2 map area. The Judith River flows northeast from the figure 2 southwest corner area through Utica, Hobson, and then flows near Ross Fork and Ware, before turning northwest and north-northeast to flow to the figure 2 north edge. The north-oriented Musselshell River is located east of the figure 2 map area. The Judith Mountains are located northeast of Lewistown. The South Moccasin Mountains are located northwest of Lewistown and the unlabeled North Moccasin Mountains are located near the “E” in FERGUS. The Big Snowy Mountains are located near the figure 2 south center edge and the Little Snowy Mountains are located east of the Big Snowy Mountains. Warm Spring Creek is an important Judith River tributary mentioned here and originates in the Judith Mountains and flows west and northwest to join the north-northeast oriented Judith River near the figure 2 north edge. The East Fork Big Spring Creek is another important Judith River tributary and originates in the Big Snowy Mountains (located near the figure 2 south center edge) and flows north to Heath. From Heath Big Spring Creek flows through Lewistown and Kingston to join the north-northwest and north-northeast oriented Judith River just west of the Moccasin Mountains. Cottonwood Creek is an important Big Spring Creek tributary, which also originates in the high Big Snowy Mountains, and which flows northwest to join Big Spring Creek near Hanover. The North Fork McDonald Creek is an important Musselshell River tributary and originates east of Heath and flows east to Forestgrove and then east-northeast to Grassrange before flowing to the figure 2 east edge. Flatwillow Creek and its tributary, Half Moon Creek, are north-oriented Musselshell River tributaries also mentioned in this essay. Half Moon Creek originates near the East Fork Big Spring Creek source area in the high Big Snowy Mountains and flows northeast to join the east-oriented North Fork Flatwillow Creek, which turns southeast to the flow to the figure 2 southeast corner. East of the figure 2 map area Flatwillow Creek turns to flow northeast and join east-oriented McDonald Creek. Evidence in detailed maps below illustrates flood waters originally flowed on a topographic surface at least as high as the highest Judith Mountains elevations today. Flood waters of concern in this essay originally were moving to what was then a newly eroded and deep northeast-oriented Yellowstone River valley (see figure 1). Headward erosion of the deep north-oriented Musselshell River valley at some point captured the southeast-oriented flood flow routes and diverted the flood waters north, although flood waters moving across the figure 2 map area continued to flow to the same southeast-oriented flood flow channels. As flood waters flowed across the figure 2 map area the Big Snowy Mountains, Little Snowy Mountains, Judith Mountains, South Moccasin Mountains, and North Moccasin Mountains emerged as major obstacles, which forced flood flow to move around them. Emergence of these isolated mountain areas could have occurred as flood waters deeply eroded the region and/or could have occurred because the isolated mountain areas were uplifted as flood waters deeply eroded the region.

Warm Spring Creek-Musselshell River drainage divide area in Judith Mountains

• Figure 3 illustrates the Warm Spring Creek-Musselshell River drainage divide area in the Judith Mountains. Warm Spring Creek originates near Maiden in the figure 3 center area and flows northwest and west to the figure 3 west edge. Chippewa Creek and Fords Creek are southeast-oriented Musselshell River tributaries located in the figure 3 east half. Chippewa Creek originates near Giltedge and flows southeast to the figure 3 southeast corner and its water (after flowing southeast, east and southeast) eventually flows to the north-oriented Musselshell River. Maiden Canyon is located southeast of Maiden and drains southeast and east to southeast-oriented Fords Creek, and its water (also after flowing southeast, east, and southeast) eventually reaches the north-oriented Musselshell River. A close look at figure 3 reveals a number of through valleys linking northwest and west-oriented Warm Spring Creek and tributary valleys with the southeast-oriented Chippewa Creek and Fords Creek valleys. One such through valley links southeast-oriented Maiden Canyon with the Warm Spring Creek headwaters at Maiden. Southeast of Maiden, between Pekay Peak and Sheep Mountain, is a much higher level through valley linking the Warm Spring Creek headwaters with a southeast-oriented Chippewa Creek tributary. Similar through valleys are located throughout the Judith Mountains. These through valleys were eroded by southeast-oriented flood waters that once flowed across the Judith Mountains. Flood waters originally flowed on a topographic surface as high as the highest Judith Mountain elevations today. That topographic surface may have been created by easily eroded sediments and/or ice in which the Judith Mountains were buried and flood waters removed the surrounding material. Another possibility is the Judith Mountains were uplifted as flood waters flowed across the figure 3 map area. Some combination of these two possibilities is probable. Whichever possibility is correct, deep southeast-oriented valleys eroded headward along southeast-oriented flood flow routes into the figure 3 map area until the actively eroding headcuts encountered the Judith Mountains resistant rock mass. Flood waters moving in anastomosing channels next eroded multiple narrow deep valleys across the Judith Mountains resistant rock mass, with deeper valleys capturing flood waters from shallower flood flow routes. However, flood waters also eroded deep valleys around the Judith Mountains northeast and southwest ends. Those deep valleys eroded west and north along the Judith Mountains north and west flanks respectively and beheaded flood flow routes moving flood waters across the Judith Mountains (see Armells Creek-Box Elder Creek drainage divide area essay).  As this deep erosion occurred the Judith Mountains emerged as an even greater obstacle to southeast-oriented flood flow. Headward erosion of the deep north oriented Judith River valley to the west and northwest next beheaded remaining southeast-oriented flood flow routes moving flood waters across the Judith Mountains to the southeast-oriented Musselshell River tributaries. Flood waters on the west and northwest ends of the beheaded flood flow routes reversed flow direction to erode the northwest and west-oriented Warm Spring Creek valley and to create the Warm Spring Creek-Musselshell River drainage divide.

Detailed map of Warm Spring Creek-Musselshell River drainage divide area in the Judith Mountains

Figure 4: Detailed map of Warm Spring Creek-Musselshell River drainage divide area in the Judith Mountains.

• Figure 4 provides a detailed of the Judith River-Musselshell River drainage divide area east of Maiden in the Judith Mountains. Figure 3 above illustrates the figure 4 map area in less detail. Warm Spring Creek originates southeast of Maiden Peak and flows in a southwest-oriented valley to Maiden. At Maiden Warm Spring Creek turns to flow west-northwest to the figure 4 west edge and then west and northwest to the Judith River. East of Maiden is Gold Hill, and east of Gold Hill is north-south oriented through valley. The south end of that through valley is connected to southeast-oriented Maiden Gulch, which drains to Fords Creek. Fords Creek is a southeast-oriented Musselshell River tributary. The north end of the through valley is linked with the southwest-oriented Warm Spring Creek headwaters valley. The through valley and the southwest-oriented Warm Spring Creek headwaters valley are together linked by a somewhat higher level through valley with the south and east-southeast oriented Collar Gulch valley. Collar Gulch also drains to Fords Creek. East of Maiden is a through valley linking west-northwest oriented Warm Spring Creek with southeast-oriented Maiden Canyon. Southeast of Maiden, between Pekay Peak and Sheep Mountain is a much higher level through valley (many people would call it a mountain pass). That high level through valley links the west-northwest oriented Warm Spring Creek valley with a southeast-oriented Chippewa Creek tributary. Chippewa Creek is also a southeast-oriented Musselshell River tributary. These and other through valleys provide evidence large volumes of water once flowed in multiple channels through the heart of the Judith Mountains. The channels were components of a large southeast-oriented ever-changing anastomosing channel complex, where deeper channels captured flood waters from channels unable to erode as deeply. North and east of the figure 4 map area are much deeper and straighter through valleys, which are illustrated and described in the Armells Creek-Box Elder Creek drainage divide area essay. Flood waters originally flowed on a topographic surface at least as high as the highest figure 4 elevations today, and sculpted the figure 4 landscape before flood flow ceased. Southeast-oriented flood flow across the figure 4 map area ended when headward erosion of the deep Judith River valley beheaded southeast-oriented flood flow routes moving flood waters to and across the Judith Mountains region. Flood waters on the northwest and west ends of the beheaded flood flow routes reversed flow direction to flow northwest and west to the newly eroded Judith River valley. Reversed flood flow, with the aid of flood waters captured from yet to be beheaded flood flow routes, eroded the west- and northwest-oriented Warm Spring Creek valley and created the Judith River-Musselshell River drainage divide.

Warm Spring Creek-Big Spring Creek drainage divide area west of Judith Mountains

Figure 5: Warm Spring Creek-Big Spring Creek drainage divide area west of Judith Mountains.

• Figure 5 illustrates the Warm Spring Creek-Big Spring Creek drainage divide area west of the Judith Mountain and west of the figure 3 map area. Figure 5 includes overlap areas with figure 3. The southwest end of the Judith Mountains is located along the figure 5 east edge (south half). The South Moccasin Mountains are located in the figure 5 center and the North Moccasin Mountains are located in the figure 5 north center edge area. The Judith River flows north-northeast from the figure 5 southwest corner and then turns to flow north-northwest to the figure 5 northwest corner. Big Springs Creek flows from the figure 5 south edge along the South Moccasin Mountains southwest flank and joins the Judith River in the figure 5 west center area. Warm Spring Creek flows west from Judith Mountains and then northwest between the South and North Moccasin Mountains to join the Judith River just northwest of the figure 5 northwest corner. Note the large north-south through valley between the South Moccasin Mountains and the Judith Mountains, which links the present day west and northwest-oriented Warm Spring Creek valley with the northwest-oriented Big Spring Creek valley. Also note the Warm Spring Creek valley eroded between the South Moccasin Mountains and the North Moccasin Mountains. Today that valley is used by northwest-oriented Warm Spring Creek, but it was eroded by southeast-oriented flood flow moving to join an immense flood of southeast-oriented water moving along the Big Spring Creek alignment to a large west-east oriented through valley between the Judith Mountains and the Big Snowy Mountains (illustrated in figure 6 below) and probably to what was then the newly eroded deep Yellowstone River valley, until headward erosion of the north-oriented Musselshell River valley captured the flood flow and diverted the flood waters north. The north-south valley between the South Moccasin Mountains and Judith Mountains was also eroded by southeast-oriented flood flow moving to the large west to east oriented through valley between the Judith Mountains and the Big Snowy Mountains. In the figure 5 northeast quadrant is a southwest-northeast oriented through valley linking the west- and northwest-oriented Warm Spring Creek valley with the northeast-oriented Armells Creek valley (Hilger is on the drainage divide and Armels Creek is not shown in figure 5). That southwest-northeast oriented through valley probably also moved large volumes of flood waters southwest along the Judith Mountains northwest flank to the north-south through valley and then east around the Judith Mountains south end.

Judith River-Musselshell River drainage divide area between Judith Mountains and Big Snowy Mountains

• Figure 6 uses reduced size maps to illustrate the Judith River-Musselshell River drainage divide in the large west to east oriented through valley between the Judith Mountains in the north and the Big and Little Snowy Mountains in the south. Flat Mountain, which is at the southern end of the Judith Mountains is located north of the highway in the figure 6 north center area. The north flank of the Big Snowy Mountains is located along the figure 6 south edge in the figure 6 southwest quadrant. The Little Snowy Mountains are located just south of the figure 6 south edge in the figure 6 southeast quadrant. Lewistown is the city located in the figure 6 northwest quadrant. The East Fork Big Spring Creek flows north from the Big Snowy Mountains in the figure 6 south center to Heath, and then turns northwest to joins Big Spring Creek and flow through Lewistown and to the figure 6 north edge. Cottonwood Creek in the major north-northeast and northwest oriented stream west of the East Fork Big Spring Creek and flowing from the Big Snowy Mountains to the figure 6 west edge (north half) and then to join Big Spring Creek (see figure 5 above). The South Fork McDonald Creek originates a short distance southeast of Heath (see figures 7 and 8 below) and flows almost directly east from the Heath area to the figure 6 east edge, and eventually joins southeast oriented Box Elder Creek and Flatwillow Creek to flow to the north-oriented Musselshell River. Immediately south Flat Mountain is an east oriented abandoned headcut, which now serves as the headwaters area for east-southeast oriented North Fork McDonald Creek, which joins the South Fork east of the figure 6 map area. The North Fork Flatwillow Creek originates in the figure 6 south center edge area, very near the north-oriented East Fork Big Spring Creek (see figure 9 below) and flows east, northeast, east, and southeast to the figure 6 east edge (southeast corner area). The McDonald Creek-Flatwillow Creek drainage divide area has been illustrated and described in a different essay. While it may be difficult to image the figure 6 map area was eroded by an immense flood, it was eroded by southeast and east-oriented flood waters, first moving to a newly eroded and deep Yellowstone River valley and later moving to what was then the actively eroding north-oriented Musselshell River valley. The through valley developed as either deep erosion of surrounding material and/or uplift raised the Big and Little Snowy Mountains in the south and the Judith Mountains in the north. Flood flow through this giant through valley ended when headward erosion of the deep Missouri River-Judith River valley systematically beheaded and reversed flood flow routes supplying east- and southeast-oriented flood waters moving to the McDonald Creek and Flatwillow Creek valleys. The north- and northwest-oriented Big Spring drainage basin was largely eroded by reversed flood flow captured by headward erosion of the deep Judith River valley.

Big Spring Creek-Musselshell River drainage divide area south of Judith Mountains

Figure 7: Big Spring Creek-Musselshell River drainage divide area south of Judith Mountains.

• Figure 7 illustrates the Big Spring Creek-Musselshell River drainage divide area immediately south of the Judith Mountains. The figure 7 map area was illustrated in less detail in figure 6 above. The East Fork Big Spring Creek flows north-northeast from the figure 7 south edge to Heath and then northwest and west to join northwest-oriented Big Spring Creek, which flows to Lewistown (located along the figure 7 west edge) and then to the north-oriented Judith River (see figure 5). Flat Mountain is located at the Judith Mountains south end and is located in the figure 7 north center edge area. Immediately south of Flat Mountain is an east-oriented basin where east-southeast oriented North Fork McDonald Creek originates. That east-oriented basin is an abandoned headcut, which was eroded by east-oriented flood waters moving south along the Judith Mountains west flank and then east around the Judith Mountains south end to flow to the north-oriented Musselshell River valley (and previous to that to the Yellowstone River valley). East of Heath is a west to east oriented through valley linking the East Fork Big Spring Creek valley with the east-oriented South Fork McDonald Creek valley. The South Fork McDonald Creek joins the North Fork east of the figure 7 map area to form McDonald Creek and as previously mentioned to flow east and southeast to the north-oriented Musselshell River. The through valley provides evidence flood waters once flowed east across the present day drainage divide from the present day Big Spring Creek drainage basin to the McDonald Creek drainage basin. In other words, the northwest-oriented East Fork Big Spring valley segment northwest of Heath was originally eroded by southeast-oriented flood water moving to the McDonald Creek drainage basin and the Musselshell River. Like most, if not all of the north- and northwest-oriented Judith River tributary valley segments shown in figure 7, the direction of flood flow in the East Fork Big Spring Creek valley northwest of Heath was reversed when Judith River valley headward erosion beheaded southeast-oriented flood flow routes to the McDonald Creek drainage basin. Flood waters on the west and northwest ends of those beheaded flood flow routes reversed flow direction to flow west, northwest, and north to the newly eroded Judith River valley. Headward erosion of the Judith River valley beheaded flood flow routes systematically from north to south, and reversed flood flow on newly beheaded flood flow routes then captured yet to be beheaded flood flow from flood flow routes further to the south. These captures of yet to be beheaded flood flow helped erode significant reversed flood flow valleys and also aided in creating the present day Judith River-Musselshell River drainage divide.

Detailed map of Big Spring Creek-South Fork McDonald Creek drainage divide area near Heath

Figure 8: Detailed map of Big Spring Creek-South Fork McDonald Creek drainage divide area near Heath.

• Figure 8 provides an even more detailed map of East Fork Big Spring Creek-South Fork McDonald Creek drainage divide area east of Heath. North-northeast and northwest oriented East Fork Big Spring Creek is located in the figure 8 west half and flows to the figure 8 northwest corner. The South Fork McDonald Creek flows northeast in the figure 8 east center area. Several through valleys in the figure 8 map area link the north-oriented East Fork Big Spring Creek valley with the east-oriented South Fork McDonald Creek valley. The deepest through valleys is used by the railroad (now abandoned) and is the west to east oriented through valley located east of Heath. Another through valley is located in the figure 8 south center edge area. A much higher level and shallower through valley is located on the upland surface between the first two through valleys. And a fourth shallow and high level through valley is located in the figure 8 north center edge. Recognizing the higher level through valleys is important, because the figure 8 drainage history is not simple. The higher level through valleys probably reflect flood flow routes used before the East Fork Big Spring Creek valley was reversed to become a northwest-oriented flood flow route. The reversal probably occurred when flood waters were still flowing on a topographic surface reflected by the elevations of those higher level through valley floors. As previously mentioned headward erosion of the Judith River valley was from north to south and southeast-oriented flood flow routes were beheaded one by one. In other words, while northern flood flow routes were reversed and flowing northwest to the newly eroded and deep Judith River valley, southeast-oriented flood flow continued to move uninterrupted further to the south. The reversed flood flow routes systematically captured the yet to be beheaded southeast-oriented flood waters and the captured flood waters eroded north-oriented valleys as they moved to the newly reversed flood flow routes. Significant quantities of such yet to be beheaded flood water moved north into the figure 8 area first to the northeast and east-oriented South Fork McDonald Creek valley and then was captured by headward erosion of the newly reversed north-northeast and northwest oriented East Fork Big Spring Creek valley. For a brief time, north-oriented flood flow dominated the figure 8 map area and flood waters moved west from the South Fork McDonald Creek valley into the newly reversed and rapidly eroding northwest-oriented East Fork Big Spring Creek valley.

East Fork Big Spring Creek-North Fork Flatwillow Creek drainage divide area

Figure 9: East Fork Big Spring Creek-North Fork Flatwillow Creek drainage divide area.

• Figure 9 illustrates the East Fork Big Spring Creek-North Fork Flatwillow Creek drainage divide area located south of the figure 7 map area and includes overlap areas with figure 7. The figure 9 map area is also shown in less detail in figure 6 above. The north flank of the Big Snowy Mountains is located in the figure 9 southwest quadrant along the figure 9 south edge. The Little Snowy Mountains are located south of the figure 9 southeast quadrant south edge. The North Fork Flatwillow Creek flows northeast and east in the figure 9 southeast quadrant. At the head of the east-oriented North Fork Flatwillow Creek valley is north and east-oriented Half Moon Creek, which originates in the high Big Snowy Mountains south of the figure 9 map area. Note how a through valley links the north-oriented Big Spring Creek valley with the Half Moon Creek-North Fork Flatwillow Creek valley. That through valley provides evidence large volumes of flood water once moved east from the present day Judith River drainage basin to the Flatwillow Creek drainage basin. North of North Fork Flatwillow Creek is east-oriented Mc Cartney Creek, which flows to the North Fork Flatwillow Creek. Note how Mc Cartney Creek headwaters are linked by a through valley with north-oriented Buffalo Creek, which flows to north-oriented East Fork Big Spring Creek. That through valley also provides evidence that East Fork Big Spring Creek valley headward captured flood water moving from the present day Judith River drainage basin to the Flatwillow Creek drainage basin. While these through valleys are related to dipping bedrock units along the Big Snowy Mountains north flank, they were eroded by east-oriented flood water moving along what is now the Big Snowy Mountains north flank. Based on present day elevations such flood movements appear impossible. However, at the time flood waters flowed across the figure 9 map area elevations were quite different. Either the Big Snowy Mountains were buried by easily eroded sedimentary rocks and/or ice or the Big Snowy Mountains had not been uplifted. In either case, the Big Mountains emerged as an immense flood eroded the present day Judith River-Musselshell River drainage divide area. How could a flood be large enough to uncover a mountain range and/or a mountain range be raised while flood waters were eroding it? While the source of the southeast-oriented flood waters described in this essay cannot be determined from evidence presented in this essay 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 flood waters further and further 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 mountains regions, such as the Big 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 deep erosion of overlying material might also trigger localized uplift.

Detailed map of Cottonwood Creek-Middle Fork Big Spring Creek drainage divide area

• Figure 10 provides a detailed map of the Cottonwood Creek-Middle Fork Big Spring Creek drainage divide area along the Big Snowy Mountains north flank. The Middle Fork Big Spring Creek is located in the figure 10 east half and flows north-northeast from the figure 10 south edge to the figure 10 north edge. The Middle Fork Big Spring Creek joins the East Fork Big Spring Creek northeast of the figure 10 map area (see figure 9). Cottonwood Creek flows north-northeast and north in the figure 10 west half. Cottonwood Creek and the East Fork Big Spring Creek originate in the high Big Snowy Mountains, and are linked by shallow through valleys (shallow notches eroded into the high ridge that today forms the highest Big Snowy Mountains elevations) with southeast and south-oriented tributaries to the northeast-oriented Musselshell River, located south of the Big Snowy Mountains. That high level Big Snowy Mountains drainage divide will be the subject of a different essay. My goal in this figure 10 discussion is to convince you southeast-oriented flood waters once flowed from the present day northwest-oriented Cottonwood Creek valley (see figure 6 above) to the Middle Fork Big Spring Creek valley and then north to the north-oriented East Fork Big Spring Creek valley into the figures 7 and 8 map areas. To do so you need to find Lyon Canyon, which is located in the figure 10 center area and drains northwest, north, and northwest to the figure 10 north edge. North of figure 10 Lyon Canyon joins Cottonwood Creek, which as seen in figure 6 becomes a northwest-oriented Big Spring Creek tributary. Note how in the figure 6 center area Lyon Canyon is linked by an east and northeast-oriented through valley with the north-northeast oriented Middle Fork Big Spring Creek valley. That through valley represents one of several such valleys eroded by yet to be beheaded and reversed southeast-oriented flood flow moving on the Cottonwood Creek alignment that was captured by reversed flood flow eroding the north-oriented East Fork Big Spring Creek valley. As previously mentioned southeast-oriented flood flow routes were beheaded and reversed in sequence from north to south. Flood flow on the northwest-oriented East Fork Big Spring Creek alignment was beheaded and reversed before flood flow on the Cottonwood Creek alignment was beheaded and reversed. Yet to be beheaded flood flow still moving southeast on the Cottonwood Creek alignment was captured by reversed flood flow in what was then the rapidly eroding north-oriented East Fork Big Spring Creek valley and those northeast-oriented tributary valleys were eroded by the captured flood waters moving from the Cottonwood Creek alignment to the actively eroding north-oriented Big Spring Creek valley. Such flood flow movements would be impossible with present day elevations, however at the time figure 10 valleys were eroded the Big Snowy Mountains were just beginning to emerge as a southeast-oriented flood flow obstacle.

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.