A geomorphic history based on topographic map evidence

The Milk River-Missouri River drainage divide area east of Larb Creek is located in Valley County, Montana, USA. Although detailed topographic maps of the Milk River-Missouri 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 Milk River is a Missouri River tributary and is located north of the Missouri River. Larb Creek is a north-oriented Milk River tributary. South of Larb Creek is south oriented Timber Creek, which flows to the Missouri River. The Larb Creek and Timber Creek drainage basins are linked by a north-south oriented through valley.  The Milk River-Missouri River drainage divide area east of Larb Creek 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 Milk and Missouri River valleys captured all southeast-oriented flood flow.

Preface:

Introduction:

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

Milk River-Missouri River drainage divide area east of Larb Creek location map

Figure 1: Milk River-Missouri River drainage divide area east of Larb Creek 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 Milk River-Missouri River drainage divide area east of Larb Creek location map and illustrates a region in northeast Montana. The Missouri River flows east-southeast from the figure 1 west edge to  Fort Peck Lake before joining the southeast-oriented Milk River and flowing to Culbertson, Montana near the figure 1 east edge. The Milk River flows from the northwest corner area to Zurich, Harlem, Dodson, Wagner, Malta, Saco, Hinsdale, Vandalia, Tampico, and Glasgow and joins the Missouri River east of Nashua, Montana. The Milk River-Missouri River drainage divide area discussed here is located east of Larb Creek, which flows north and in figure 1 appears to join the Milk River near Saco. The unnamed south-oriented stream flowing from the Larb Creek headwaters area to the Missouri River is Timber Creek, which also serves as a western boundary for the drainage divide region discussed here. The Milk River-Missouri River drainage divide area west of the area discussed is addressed by looking at drainage divides between additional Milk River and Missouri River tributaries (Beaver Creek, Peoples Creek, Birch Creek, and Big Sandy Creek, among others). Based on evidence from the hundreds of 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 headward erosion of deep valleys eroded into a topographic surface at least as high as the figure 1 region highest elevations today. The east-oriented Missouri River valley eroded west to near the location of Nashua (where the Milk River joins the Missouri River) and the Milk River valley eroded northwest to capture southeast-oriented flood water and to divert flood flow to the newly eroded Missouri River valley east of Nashua. Northeast and north-oriented tributary valleys eroded headward from the newly eroded north-oriented Milk River valley and one such tributary valley was the valley now used by the northeast-oriented Missouri River located southwest of Nashua. The north-oriented Larb Creek valley was a north-oriented Milk River tributary valley that eroded south to capture southeast-oriented flood flow that had not yet been beheaded by Milk River valley headward erosion. The north-oriented Larb Creek valley eroded south along what is today the south-oriented Timber Creek valley to the present day Missouri River valley location, and perhaps southwest from there. However, flood flow spilled northeast from that location to erode the present day northeast-oriented Missouri River, beheading north-oriented flood flow to the Larb Creek valley. Flood waters on the south end of the beheaded north-oriented flood flow reversed flow direction and eroded the present day Timber Creek valley. The Missouri River-Big Dry Creek drainage divide area essay, the Big Dry Creek-Prairie Elk Creek drainage divide area essay, the Musselshell River-Yellowstone River drainage divide area in Musselshell and Yellowstone Counties essay, the Musselshell River-Yellowstone River drainage divide area in Treasure and Rosebud Counties essay, and in the Big Dry Creek-Yellowstone River drainage divide area essay describe drainage divide areas located near the Milk River-Missouri River drainage divide area discussed here and can be found under appropriate river names on the sidebar category list (use MT Missouri River for the Missouri River in Montana).

Milk River-Missouri River drainage divide area east of Larb Creek detailed location map

Figure 2: Milk River-Missouri River drainage divide area east of Larb Creek 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 Milk River-Missouri River drainage divide area discussed in this essay. Phillips and Valley Counties are located in Montana. The Missouri River forms the county line in the figure 2 south half and flows northeast to join the southeast-oriented Milk River downstream from Fort Peck Lake in the figure 2 east center area. In Phillips County the Milk River flows east and northeast in the figure 2 north half and then turns southeast to join the Missouri River downstream from Nashua. Larb Creek flows north in western Valley County (very near the county line) and enters Phillips County in the Larb Hills area before joining east-oriented Beaver Creek near Beaverton. Beaver Creek then joins the southeast-oriented Milk River near Hinsdale. Timber Creek flows south along the same alignment as that used by north-oriented Larb Creek and joins the Missouri River as a barbed tributary near Phillips-Valley County line. Southeast-oriented Sutherland Creek is the only lengthy Missouri River tributary coming from the north between south-oriented Timber Creek and the southeast-oriented Milk River. The Milk River has three lengthy northeast or east-oriented tributaries; Willow Creek, Brazil Creek, and Antelope Creek, all of which have southeast-oriented headwaters. Southeast-oriented Willow Creek headwaters streams include Lone Tree Creek and Hard Pan Creek. The figure 2 drainage pattern can be explained in the context of large southeast-oriented flood moving across the entire figure 2 map area and headward erosion of the deep east-oriented Missouri River valley to area east of Nashua. From that point a northeast-oriented valley eroded southwest (along the present day Missouri River valley route) to capture southeast-oriented flood flow while a valley eroded northwest along the present day Milk River valley alignment. Another northeast-oriented valley eroded southwest from the actively eroding Milk River valley along what is today the northeast-oriented Willow Creek valley alignment. This northeast-oriented Willow Creek valley captured southeast-oriented flood flow moving to the newly eroded northeast-oriented Missouri River valley. As headward erosion of the Milk River valley progressed northwest the east-oriented Brazil Creek valley eroded west to capture southeast-oriented flood flow moving to the newly eroded Willow Creek valley. Next, as Milk River valley headward erosion progressed to the northwest, the east-oriented Antelope Creek valley eroded west to capture southeast-oriented flood flow moving to newly eroded Brazil Creek valley. As Milk River valley headward erosion progressed, the Beaver Creek-Larb Creek valley eroded west and south to capture southeast-oriented flood flow to the Antelope Creek, Brazil Creek, Willow Creek, and Missouri River valleys. Detailed maps below better tell the story.

Willow Creek-Missouri River drainage divide area

Figure 3: Willow Creek-Missouri River drainage divide area. United States Geological Survey map digitally presented using National Geographic Society TOPO software.

Figure 3 illustrates the Willow Creek-Missouri River drainage divide area west of Fort Peck Dam. The flooded northeast-oriented Missouri River channel upstream from Fort Peck Dam is located in the figure 3 southeast corner and a segment of the former downstream channel is can be seen north of the dam. Note short southeast-oriented Missouri River tributaries from the northwest. Willow Creek flows north from the figure 3 southwest corner and turns northeast before flowing north to the figure 3 north edge. Note southeast-oriented tributaries to Willow Creek from the west and northwest-oriented tributaries from the east. A close look at the Willow Creek-Missouri River drainage divide reveals through valleys linking headwaters of southeast-oriented Missouri River tributaries and headwaters of northwest-oriented Willow Creek tributaries. The northwest-southeast tributary orientation and the through valleys provide evidence southeast-oriented flood water once flowed across the entire figure 3 map area. Headward erosion of the northeast-oriented Missouri River valley first captured the southeast-oriented flood flow. Southeast-oriented tributary valleys were then eroded into the newly eroded Missouri River valley northwest wall. A short time later, before the southeast-oriented tributaries could erode deep and lengthy valleys, headward erosion of the north, northeast, and north-northwest oriented Willow Creek valley beheaded southeast-oriented flood flow routes to the newly eroded Missouri River valley. Flood waters on the northwest ends of beheaded flood flow routes reversed flow direction to flow northwest into the newly eroded Willow Creek valley. This reversal of flood flow eroded northwest-oriented Willow Creek tributary valleys, such as the northwest-oriented Mud Creek valley, and also created the present day Willow Creek-Missouri River drainage divide. The source of the southeast-oriented flood waters cannot be determined from evidence presented here. However, the hundreds of Missouri River drainage basin landform origins research project essays published on this website 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.

Brazil Creek-Willow Creek drainage divide area

Figure 4: Brazil Creek-Willow Creek drainage divide area. United States Geological Survey map digitally presented using National Geographic Society TOPO software.

Figure 4 illustrates the Brazil Creek-Willow Creek drainage divide area northwest of the figure 3 map area and includes overlap areas with figure 3. The southeast-oriented Milk River is located in the figure 4 northeast corner. East-oriented Brazil Creek flows along the figure 4 north edge and joins the southeast-oriented Milk River north of the figure 4 northeast corner. Little Brazil Creek flows southeast from the figure 4 north center area and then turns northeast and north to join Brazil Creek north of the figure 4 northeast corner. Willow Creek flows northeast in the figure 4 southeast corner and then turns north-northwest before turning east-northeast to join the southeast-oriented Milk River east of the figure 4 map area. Note the predominance of southeast-oriented tributaries to the northeast-oriented Willow Creek valley segment. The Willow Creek valley eroded west-southwest from the newly eroded southeast-oriented Milk River valley to capture southeast-oriented flood flow moving to what was then the newly eroded northeast-oriented Missouri River valley (seen in figure 3). Reversed flood flow on beheaded southeast-oriented flood flow routes probably was responsible for eroding the north-northwest oriented Willow Creek valley segment and the Willow Creek valley then eroded southwest from the figure 4 southeast corner area to capture additional southeast-oriented flood flow. Southeast-oriented flood waters then eroded southeast-oriented tributary valleys headward from the newly eroded northeast-oriented Willow Creek valley segment. These tributary valleys included the present day Coyote Creek, Sage Hen Creek, and Miller Coulee valleys. Next headward erosion of the east-oriented Brazil Creek valley and the northeast-oriented Little Brazil Creek valleys beheaded southeast-oriented flood flow routes to the newly eroded Willow Creek valley and the actively eroding southeast-oriented Willow Creek tributary valleys. Southeast-oriented Little Brazil Creek headwaters provide evidence the northeast-oriented Little Brazil Creek valley captured a southeast-oriented flood flow channel. The northwest-oriented Brazil Creek tributary located in the figure 4 northwest corner area provides evidence flood waters on the northwest end of a beheaded southeast-oriented flood flow route reversed flow direction to flow northwest into the newly eroded Brazil Creek valley and in the process eroded the northwest-oriented tributary valley and also helped create the present day Brazil Creek-Willow Creek drainage divide.

Antelope Creek-Brazil Creek drainage divide area

Figure 5 illustrates the Antelope Creek-Brazil Creek drainage divide area northwest of the figure 4 map area and includes overlap areas with figure 4. The southeast-oriented North and South Forks of Brazil Creek join southeast of the VR-2 Reservoir and Brazil Creek flows northeast and east to the figure 5 east edge and then to the southeast-oriented Milk River. To the north in the figure 5 north center area southeast-oriented South Fork Antelope Creek joins southeast-oriented North Fork Antelope Creek and then Antelope Creek flows east-northeast and east-southeast to the figure 5 east edge (in northeast corner area) and then to the southeast-oriented Milk River. Northwest-oriented drainage located along the figure 5 west edge flows to north-oriented Larb Creek located west of the figure 5 map area (see figure 7 below). Note the through valley linking the southeast-oriented Brazil Creek headwaters (south of VR-2 Reservoir) with southeast-oriented headwaters of a Willow Creek tributary (Little Beaver Creek-headwaters of southeast-oriented North Fork Little Beaver Creek area are located further west in the figure 5 southwest quadrant). The through valley linking southeast-oriented Brazil Creek headwaters with the southeast-oriented Little Beaver Creek valley provides evidence headward erosion of the east-oriented Brazil Creek valley captured southeast-oriented flood flow that had been moving to what was then the newly eroded Willow Creek valley. Subsequently headward erosion of the east-oriented Antelope Creek valley beheaded southeast-oriented flood flow routes to the newly eroded Brazil Creek valley. Shortly thereafter headward erosion of north-oriented Larb Creek valley (west of figure 5) beheaded southeast-oriented flood flow routes to the newly eroded Antelope Creek, Brazil Creek, and Willow Creek valleys. Flood waters on the northwest ends of the beheaded flood flow routes reversed flow direction to flow northwest into the newly eroded northeast and north-oriented Larb Creek valley.

Beaver Creek-Antelope Creek drainage divide area

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

Figure 6 illustrates Beaver Creek-Antelope Creek drainage divide area north and west of the figure 5 map area and does not include overlap areas with previous figures. The southeast-oriented Milk River is located in the figure 6 northeast quadrant. Note the size of the southeast-oriented Milk River valley. East-oriented Beaver Creek flows along the figure 6 north edge and joins the Milk River north of Hinsdale. North-oriented Larb Creek flows to the figure 6 southwest corner area and then flows north along the figure 6 west edge to join Beaver Creek in the figure 6 northwest corner. Southeast-oriented drainage in the figure 6 southeast quadrant flows to east-oriented Antelope Creek and includes the southeast-oriented North Fork Antelope Creek (see figure 5 above). Note how the southeast-oriented erosion surface drained by Antelope Creek headwaters stands higher than the surrounding valley floors. This higher level erosion surface was eroded by southeast-oriented flood waters that were captured by headward erosion of the east-oriented Antelope Creek valley seen in figure 5. The deep southeast-oriented Milk River valley and the deep east-oriented Beaver Creek valley eroded headward into this higher level Antelope Creek erosion surface (how much erosion flood waters accomplished before creating the Antelope Creek erosion surface cannot be determined from evidence presented in this essay). The Larb Creek valley then eroded south and southwest from the east-oriented Beaver Creek valley to capture southeast-oriented flood flow routes to the Antelope Creek, Brazil Creek, Willow Creek, and Missouri River valleys. It is possible the north-oriented Larb Creek valley segment was eroded by reversed flood flow on the northwest ends of beheaded southeast-oriented flood flow routes. The reversed flood flow would have moved north to the newly eroded and much deeper Beaver Creek-Milk River valley. Mc Nab Coulee in the figure 6 west center area provides some support for this reversed flood flow interpretation. Note how Mc Nab Coulee headwaters are south-oriented and Mc Nab Coulee then drains southwest to the flow to north-oriented Larb Creek, which in turn flows to east-oriented Beaver Creek, which flows in the east-oriented valley that beheaded southeast-oriented flood flow to Mc Nab Coulee.

Larb Creek-North Fork Lone Tree Creek drainage divide area

Figure 7: Larb Creek-North Fork Lone Tree Creek drainage divide area. United States Geological Survey map digitally presented using National Geographic Society TOPO software.

Figure 7 illustrates the Larb Creek-North Fork Lone Tree Creek drainage divide west of the figure 5 map area and includes overlap areas with figure 5. North and northeast oriented Larb Creek is located in the figure 7 west edge area. Note the predominance of northwest-oriented tributaries to north and northeast oriented Larb Creek. The southeast-oriented South and North Forks Brazil Creek join in the figure 7 northeast corner to form northeast and east-oriented Brazil Creek. Southeast-oriented North Fork Lone Tree Creek flows to the figure 7 southeast corner area and joins southeast-oriented Lone Tree Creek southeast of the figure 7 map area. Lone Tree Creek flows to northeast and north-oriented Willow Creek. Northeast of the North Fork Lone Tree Creek is southeast-oriented Little Beaver Creek, which flows to the figure 7 east edge and then to join southeast-oriented Beaver Creek. Beaver Creek flows to northeast and north-oriented Willow Creek. Note the northwest-southeast oriented through valley linking northwest-oriented Road Coulee with the southeast-oriented North Fork Lone Tree Creek. This through valley and other similar less obvious through valleys provide evidence multiple channels of southeast-oriented flood waters once moved across the figure 7 map area to the northeast and north-oriented Willow Creek valley. Headward erosion of the northeast and north-oriented Larb Creek valley captured the southeast-oriented flood flow and diverted the flood waters north to what was then the newly eroded southeast-oriented Milk River valley. Flood waters on the northwest ends of the beheaded southeast-oriented flood flow routes reversed flow direction to flow northwest into the newly eroded northeast and north-oriented Larb Creek valley. The reversed flood flow eroded the northwest-oriented Larb Creek tributary valleys and also created the present day Larb Creek-Willow Creek drainage divide.

Larb Creek-Hard Pan Creek drainage divide area

Figure 8: Larb Creek-Hard Pan Creek drainage divide area. United States Geological Survey map digitally presented using National Geographic Society TOPO software.

Figure 8 illustrates the Larb Creek-Hard Pan Creek drainage divide area south of the figure 7 map area. North-northeast oriented Larb Creek flows from the figure 8 west center edge area along the figure 8 west edge to the figure 8 north edge. South of where southeast-oriented Larb Creek headwaters enter the figure 8 map area is a south-oriented Timber Creek valley segment. The Larb Creek-Timber Creek through valley and drainage relationships are better shown in more detailed topographic maps, although the relationship can be seen in figure 8. Southeast-oriented Larb Creek headwaters in the figure 8 west center enter a north-south oriented through valley and turn north to flow as north-oriented Larb Creek. Also note how northwest and west-oriented Timber Creek headwaters enter the same north-south oriented through valley and turn south to flow south as Timber Creek. The north-south oriented through valley was originally a north-oriented valley eroded south from what was then the newly eroded east and southeast-oriented Milk River-Beaver Creek valley. The size of the valley suggests significant volumes of flood waters flowed north in the through valley. East of the north-south through valley in the figure 8 northeast quadrant southeast-oriented drainage to Triple Crossing Reservoir is flowing to east-northeast and southeast-oriented Lone Tree Creek, which flows to northeast and north-oriented Willow Creek. Hard Pan Creek in the figure 8 southeast corner also flows to northeast and north-oriented Willow Creek. Tony Coulee in the figure 8 south center edge area flows southeast to southeast-oriented Willow Creek headwaters (which are located along the figure 8 south edge just southwest of Tony Coulee). Figure 8 evidence can be explained by southeast-oriented flood waters flowing in multiple channels across the figure 8 map area to what was then the newly eroded and actively eroding Willow Creek valley system, which had eroded headward from the newly eroded southeast-oriented Milk River valley. Headward erosion of the north-oriented Larb Creek-Timber Creek through valley then captured the southeast-oriented flood flow and diverted the flood waters north to the east-oriented Beaver Creek and then to the southeast-oriented Milk River valley. Reversals of flood flow on the northwest ends of the beheaded southeast-oriented flood flow routes eroded the northwest-oriented tributaries to the north-oriented Larb Creek-Timber Creek valley and created the present day Larb Creek-Willow Creek drainage divide and Timber Creek-Willow Creek drainage divide. Subsequently headward erosion of the deep Missouri River valley south of the figure 8 map area beheaded north-oriented flood flow in the Larb Creek-Timber Creek valley. Flood waters on the south end of the beheaded north-oriented flood flow route reversed flow direction to flow south into the deeper Missouri River valley. The reversed flood waters the eroded the south-oriented Timber Creek valley and in the process created the present day Timber Creek-Larb Creek drainage divide.

Timber Creek-Sutherland Creek drainage divide area

Figure 9: Timber Creek-Sutherland Creek drainage divide area. United States Geological Survey map digitally presented using National Geographic Society TOPO software.

Figure 9 illustrates the Timber Creek-Sutherland Creek drainage divide area south of the figure 8 map area and there is a very narrow overlap area with figure 8. Timber Creek flows south into the figure 9 northwest corner area and then jogs southwest before turning south-southeast to flow to the figure 9 south edge. Northwest-oriented Square Creek joins southwest and south-southeast oriented Timber Creek in the figure 9 northwest corner area. Headwaters of northwest-oriented Square Creek are linked by a northwest-southeast oriented through valley with headwaters of southeast-oriented Sutherland Creek, which flows to the figure 9 southeast corner and then to the northeast-oriented Missouri River. Southeast and east-southeast oriented headwaters of Willow Creek are located in the figure 9 northeast quadrant. East-southeast and east oriented Desert Coulee is the southernmost of the named Willow Creek tributaries. The southwest-oriented jog in the Timber Creek valley is related to a northwest-southeast oriented through valley linking the north-south Larb Creek-Timber Creek through valley with the large north-south oriented Telegraph Creek (south-oriented) and Beaver Creek (north-oriented) through valley to the west of figure 9. The drainage divide between the Larb Creek-Timber Creek valley and the Beaver Creek-Telegraph Creek valley are discussed in the Beaver Creek-Larb Creek drainage divide area essay. What is important here is the northwest-southeast oriented through valley was initiated as a southeast-oriented flood flow route moving flood waters from northwest of the figure 9 map area across the figure 9 map area on the present day Square Creek-Sutherland Creek alignment. Flood waters were probably moving to what was then the actively eroding northeast-oriented Missouri River valley head. The Sutherland Creek valley and tributary valleys eroded northwest from that actively eroding northeast-oriented Missouri River valley head. Headward erosion of the north-oriented Larb Creek-Timber Creek through valley then captured the southeast-oriented flood flow and diverted the flood waters north to the Milk River valley. The northwest-oriented Square Creek valley was eroded by reversed flood flow on the northwest end of the beheaded southeast-oriented flood flow route. The south-southeast-oriented Timber Creek valley segment was probably originally eroded as a north-northwest oriented valley to capture additional southeast-oriented flood flow routes further to the south, although headward erosion of the northeast-oriented Missouri River captured it as seen in figure 10 below.

Timber Creek-Missouri River drainage divide area

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

Figure 10 illustrates the Timber Creek-Missouri River drainage divide area south of the figure 9 map area and includes overlap areas with figure 9. The flooded east oriented Missouri River valley is located along the figure 10 south edge. East of figure 10 the Missouri River valley develops a northeast orientation. South-southeast and south-southwest oriented Timber Creek flows along the figure 10 west edge to join the Missouri River as a barbed tributary. Timber Creek tributaries from the east are predominantly northwest-oriented and Missouri River tributaries (with the exception of Timber Creek) from the north are predominantly southeast-oriented. This drainage alignment is evidence the east oriented Missouri River valley eroded west to capture multiple southeast-oriented flood flow routes. The southeast-oriented Missouri River tributary valleys were then eroded northwest from what was then the newly eroded east oriented Missouri River valley. The northwest-oriented Timber Creek tributary valleys were eroded by reversals of flood waters on the northwest ends of beheaded southeast-oriented flood flow routes. The reversed flood flow eroded the northwest-oriented Timber Creek tributary valleys and also created the present day Timber Creek-Missouri River drainage divide. But, why does Timber Creek enter the Missouri River valley as a barbed tributary? As previously mentioned the Timber Creek valley was eroded headward as a north-oriented valley and probably reached the present day Timber Creek-Missouri River junction area at approximately the same time (or even slightly before) headward erosion of the east oriented Missouri River valley reached the same area. Just west of figure 10 the Missouri River valley is north-oriented for a short distance (see figure 10a below) and headward erosion of the north-oriented Larb Creek-Timber Creek through valley may have contributed to the erosion of that north-oriented Missouri River jog. If so, it is probable that for a short time the Larb Creek-Timber Creek valley to the Milk River valley and the east- and northeast-oriented Missouri River valley acted as separate channels in an east-oriented anastomosing channel complex moving captured southeast-oriented flood waters to what was then the newly eroded Missouri River valley downstream from the present day Fort Peck Dam area. However, the east- and northeast-oriented Missouri River valley had the much more direct route and was able to erode a deeper valley. The deeper Missouri River valley beheaded the north-oriented flood flow route to the Larb Creek-Timber Creek through valley and flood waters on the south end of the beheaded flood flow route reversed flow direction to flow south into the deeper Missouri River valley. The reversed flood flow eroded the south-oriented Timber Creek valley and created the present day Timber Creek-Larb Creek drainage divide (see figure 8a).

Figure 10a: Timber Creek relationship to Missouri River jog. United States Geological Survey map digitally presented using National Geographic Society TOPO software.

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.