A geomorphic history based on topographic map evidence

The Big Dry Creek-Little Dry Creek drainage divide area discussed here is located in eastern Montana, USA. Although detailed topographic maps of the Big Dry Creek-Little Dry 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 Big Dry Creek-Little Dry 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.

Preface:

Introduction:

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

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

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

Big Dry Creek-Little Dry Creek drainage divide area location map

Figure 1: Big Dry Creek-Little Dry 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 Big Dry Creek-Little Dry Creek drainage divide area location map and illustrates a region in eastern Montana. The Missouri River flows east-southeast from the figure 1 west edge to Fort Peck Lake and then northeast and east to Wolf Point, Poplar, Brockton, and Culbertson before flowing to the figure 1 east edge. The Yellowstone River flows northeast from the figure 1 map south edge (center east) to Custer, Miles City and Glendive and then to the figure 1 east edge. The Musselshell River flows northeast from Lavina, to Roundup, and Melstone and then turns north to Mosby and then continues north to join the Missouri River at Fort Peck Lake. Big Dry Creek originates east of Mosby and flows northeast to Jordan, Montana and after joining north-oriented Little Dry Creek flows north to join the Missouri River at Fort Peck Lake. Little Dry Creek also originates east of Mosby and flows east-northeast and northwest to join Big Dry Creek and then to flow north to join the Missouri River at Fort Peck Lake. Northeast-oriented Sand Creek is a Big Dry Creek tributary of importance here. Based on evidence from 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 and the north-oriented Big Dry Creek-Little Dry Creek valley eroded south and southwest to capture southeast-oriented flood water and to divert the flood flow to the northeast. First, the East-oriented Missouri River valley eroded west to the Fort Peck Dam location and the deep Big Dry Creek valley head eroded south to capture southeast-oriented flood waters and to divert flood waters to the north and northeast. As the Big Dry Creek valley eroded south it beheaded a southeast-oriented flood flow route on the present day northwest-oriented Little Dry Creek valley segment. Flood waters on the northwest end of that beheaded flood flow route reversed flow direction to flow northwest to the newly eroded north-oriented Big Dry Creek valley. The east and northeast oriented Little Dry Creek valley then eroded west and southwest from the newly reversed northwest-oriented Little Dry Creek valley segment. At about the same time the northeast oriented a northeast oriented valley began to erode southwest along the present day northeast oriented Sand Creek-Big Dry Creek valley route and the northeast and east-oriented Big Dry Creek valley eroded west and southwest from that newly eroded Sand Creek-Big Dry Creek valley. Each valley eroded west and southwest to capture the southeast-oriented flood flow and the valleys captured the flood flow in sequence, which means the east-northeast and northwest oriented Little Dry Creek valley captured the flood flow first, the northeast oriented Sand Creek-Big Dry Creek valley captured the flood flow second, and the northeast- and east-oriented Big Dry Creek valley captured the flood water third. Subsequently the Missouri River valley eroded west and southwest to behead southeast-oriented flood flow routes to the newly eroded Big Dry Creek valley. The Missouri River-Big Dry Creek drainage divide area essay, the Big Dry Creek-Prairie Elk Creek drainage divide area essay, and in the Big Dry Creek-Yellowstone River drainage divide area essay describe other drainage divides in the Big Dry Creek drainage basin and can be found under Big Dry Creek MT on the side category list.

Big Dry Creek-Little Dry Creek drainage divide area detailed location map

Figure 2: Big Dry Creek-Little Dry 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 Big Dry Creek-Little Dry Creek drainage divide area discussed here. Garfield County is located in Montana. Big Dry Creek originates southwest of Edwards in the figure 2 west center area and flows northeast through Jordan, Montana to join north-oriented Little Dry Creek near the Garfield County line. Big Dry Creek, after joining Little Dry Creek, flows north to join the Missouri River at Fort Peck Lake (north of figure 2). Sand Creek is a major Big Dry Creek tributary and originates in the figure 2 southwest corner area and flows northeast to join Big Dry Creek east of Jordan. Little Dry Creek also originates in the figure 2 southwest quadrant and flows east-northeast and northeast to Cohagen and then east-northeast to near the Garfield County line and then turns northwest to flow to the north-oriented Big Dry Creek valley. This essay first illustrates evidence at the Big Dry Creek-Sand Creek drainage divide area located east of Jordan. Next the essay looks at evidence in the LS Creek (Big Dry Creek tributary)-Taylor Creek (Little Dry Creek tributary) drainage divide area before looking at evidence at several points along the Sand Creek-Little Dry Creek drainage divide area. The essay concludes by looking at evidence along the southwest end of the Big Dry Creek-Sand Creek drainage divide area. Figure 2 shows numerous southeast and northwest-oriented Big Dry Creek, Sand Creek, and Little Dry Creek tributaries. This southeast and northwest tributary alignment is evidence the Little Dry Creek, Sand Creek, and Big Dry Creek valleys eroded headward to capture southeast-oriented flood flow. The southeast-oriented tributary valleys were eroded by southeast-oriented flood flow moving into the newly eroded valleys and the northwest-oriented tributary valleys were eroded by reversals of flood flow on the northwest ends of beheaded southeast-oriented flood flow routes. Because flood waters move in and erode anastomosing (or inter-connected) channels reversed flood flow on a beheaded flood flow route could capture flood flow from yet to be beheaded flood flow routes. Such captures of yet to be beheaded flood flow could enable reversed flood flow routes to erode much deeper and larger northwest-oriented valleys than might otherwise be possible. Often evidence for such flow reversals and captures can be found on detailed topographic maps such as those illustrated below.

Big Dry Creek-Sand Creek drainage divide area near Jordan, Montana

Figure 3: Big Dry Creek-Sand Creek drainage divide area near Jordan, Montana. United States Geological Survey map digitally presented using National Geographic Society TOPO software. 

Figure 3 illustrates the Big Dry Creek-Sand Creek drainage divide area near Jordan, Montana. Big Dry Creek flows east across the figure 3 north half and passes through Jordan. Sand Creek flows northeast from the figure 3 south center area to the figure 3 east center edge and joins Big Dry Creek east of the figure 3 map area (see figure 4 below). Note numerous southeast-oriented Sand Creek and Big Dry Creek tributaries and north and northwest-oriented Big Dry Creek tributaries. Also note evidence of linkages between headwaters of southeast-oriented Sand Creek tributaries and headwaters of north and northwest-oriented Big Dry Creek tributaries. These linkages are usually in the form of shallow through valleys crossing the present day Big Dry Creek-Sand Creek drainage divide (and show up best on more detailed topographic such as in figure 4 below). The southeast-orientation of tributaries and linkages between the southeast-oriented tributary valleys and the north oriented tributary valleys provide evidence that multiple channels of southeast-oriented flood water once crossed the present day Big Dry Creek-Sand Creek drainage divide. At that time the east-oriented Big Dry Creek valley did not exist and flood waters were moving to what was then a newly eroded northeast-oriented Sand Creek valley. Flood waters then eroded the newly cut Sand Creek northwest valley wall and eroded the southeast-oriented tributary valleys into the newly eroded southeast-sloping erosion surface. Headward erosion of the east-oriented Big Dry Creek valley then captured the southeast-oriented flood flow. The Big Dry Creek valley head eroded from east to the west and beheaded southeast-oriented flood flow channels in that same order, from east to west. Because flood waters were moving in ever-changing anastomosing (interconnected) channels flood flow on the northwest ends of newly beheaded channels reversed flow direction to flow north or northwest to the newly eroded and deeper east-oriented Big Dry Creek valley. The reversed flood flow often captured yet to be beheaded flood flow from adjacent channels further to the west. The reversed flood flow (aided by captured yet to be beheaded flood waters) eroded the north and northwest-oriented Big Dry Creek tributary valleys.

East end of Big Dry Creek-Sand Creek drainage divide area

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

Figure 4 illustrates a more detailed map of the Big Dry Creek-Sand Creek drainage divide area located immediately east of the figure 3 map area. Big Dry Creek is located along the figure 4 north edge and flows east-southeast in the figure 4 northeast corner. Sand Creek flows north-northeast from the figure 4 southeast quadrant area along the figure 4 east edge to join Big Dry Creek near the figure 4 east edge. Note southeast-oriented Sand Creek tributaries draining towards Sand Creek or the figure 4 south edge. Also note northwest and north-oriented Big Dry Creek tributaries and how the north-oriented tributaries have northwest-oriented tributaries (e.g. see north-oriented Big Dry Creek tributary in figure 4 northwest quadrant). Further, note shallow through valleys linking headwaters of southeast-oriented Sand Creek tributaries with headwaters of northwest-oriented Big Dry Creek tributaries. These through valleys provide evidence southeast-oriented flood flow once moved across the Big Dry Creek-Sand Creek drainage divide to what was then the newly eroded northeast-oriented Sand Creek valley. Also the through valleys provide evidence the flood waters originally flowed on a topographic surface at least as high as the highest figure 4 elevations today. The northeast-oriented Sand Creek valley probably eroded headward into that high level topographic surface and the southeast-oriented flood waters then eroded the newly cut Sand Creek valley northwest wall. Southeast-oriented Sand Creek tributary valleys were eroded into that newly eroded southeast-facing Sand Creek valley northwest valley wall. Southeast-oriented flood flow to the newly eroded Sand Creek valley was then beheaded by headward erosion of the deep Big Dry Creek valley which eroded headward into the same high level topographic surface. Flood waters on the northwest ends of the beheaded flood flow routes reversed flow direction to flow north and northwest into the newly eroded and deeper Big Dry Creek valley. As previously stated, because flood waters were moving in anastomosing channels reversed flood flow on newly beheaded flood flow routes captured yet to beheaded flood flow from adjacent flood flow routes further to the west. With the help of such captured flood water the reversed flood flow eroded the north- and northwest-oriented Big Dry Creek tributary valleys and created the present day Big Dry Creek-Sand Creek drainage divide.

LS Creek-Taylor Creek drainage divide area

Figure 5: LS Creek-Taylor Creek drainage divide area. United States Geological Survey map digitally presented using National Geographic Society TOPO software. 

Figure 5 illustrates the LS Creek-Taylor Creek drainage divide area located south and east of the figures 3 and 4 map areas. LS Creek flows northwest and north from the figure 5 west center edge area to the figure 5 northwest corner area. Northwest-oriented Spring Draw is the labeled LS Creek tributary located in the figure 5 northwest quadrant. East of LS Creek in the figure 5 northwest corner area is northwest-oriented Ada Creek. Both LS Creek and Ada Creek flow to east-oriented Big Dry Creek. Little Dry Creek flows northwest from the figure 5 east center edge into the figure 5 northeast quadrant, where it is joined by northeast and southeast oriented Big Wild Horse Creek. South of Big Wild Horse Creek is southeast and northeast oriented Little Wild Horse Creek and continuing south is northeast and southeast-oriented Spring Creek. Continuing south into the figure 5 south half is east-oriented Taylor Creek, which joins northwest-oriented Little Dry Creek east of the figure 5 map area. Note northwest-southeast oriented through valleys linking northwest-oriented Spring Draw (draining to LS Creek) and a southeast-oriented Taylor Creek tributary and also with headwaters of northeast and southeast-oriented Spring Creek. Also note through valleys crossing the drainage divides between east-oriented Little Dry Creek tributaries. Figure 5a below illustrates a detailed map of a Big Wild Horse Creek, Little Wild Horse Creek, and Spring Creek drainage divide area to better show through valleys crossing the drainage divides. Note how the large through valley in the figure 5a center area is northwest to southeast oriented providing evidence headward erosion of the northeast-oriented Big Wild Horse Creek valley captured southeast-oriented flood flow to the southeast-oriented Spring Creek valley. Figure 5 and 5a evidence can best be explained in the context of southeast-oriented flood flow moving across the entire figure 5 map area on a topographic surface at least as high as the highest present day figure 5 elevations today. Headward erosion of the north-oriented Big Dry Creek valley north of figure 5 then beheaded southeast-oriented flood flow on the present day northwest-oriented Little Dry Creek valley segment. Flood waters on the northwest end of the beheaded flood flow route reversed flow direction to flow northwest to the newly eroded and deeper north-oriented Big Dry Creek valley. East-oriented tributary valleys then eroded west from the newly reversed flood flow route to capture southeast-oriented flood flow from yet to be beheaded flood flow routes further to the west. The east-oriented Little Dry Creek valley south of figure 5 eroded west first. Next east-oriented Taylor Creek valley eroded west, and then the Spring Creek, Little Wild Horse Creek, and Big Wild Horse Creek valleys in that order. Finally the Big Dry Creek valley north of figure 5 eroded west and beheaded southeast-oriented flood flow to newly developed Little Dry Creek drainage basin causing reversals of flow on the northwest ends of the beheaded southeast-oriented flood flow routes.

Figure 5a: Detailed map of Big Wild Horse Creek-Spring Creek drainage divide area. United States Geological Survey map digitally presented using National Geographic Society TOPO software. 

Langs Fork-Skunk Arroyo drainage divide area

Figure 6: Langs Fork-Skunk Arroyo drainage divide area. United States Geological Survey map digitally presented using National Geographic Society TOPO software. 

Figure 6 illustrates the Langs Fork-Skunk Arroyo drainage divide area south and west of the figure 5 map area and includes overlap areas with figure 5. East-oriented Taylor Creek is located in the figure 6 northeast quadrant. Southeast-oriented Skunk Arroyo drains to the figure 6 southeast corner. West of Skunk Arroyo is southeast-oriented Duck Creek. West of Duck Creek is southeast-oriented Hay Creek and west of Hay Creek (along the highway) is southeast-oriented Red Horse Creek. Skunk Arroyo, Duck Creek, Hay Creek, and Red Horse Creek all flow to east and northwest-oriented Little Dry Creek. Lone Tree Creek flows north-northwest to the figure 6 northwest corner. Lone Tree Creek flows to join northeast-oriented Sand Creek at approximately the location where Sand Creek crosses the figure 3 east edge. East of Lone Tree Creek is north-northwest oriented Langs Fork (of Big Dry Creek) and east of Langs Fork is north-northwest LS Creek. Langs Fork and LS Creek both flow to east and north oriented Big Dry Creek downstream from where Sand Creek joins Big Dry Creek. Figure 6 evidence illustrates multiple through valleys linking headwaters of north-northwest oriented Big Dry Creek tributaries with headwaters of southeast-oriented Little Dry Creek tributaries. These through valleys combined with the northwest-southeast drainage alignment provide evidence that southeast-oriented flood waters once flowed in multiple channels across the present day Big Dry Creek-Little Dry Creek drainage divide. Flood flow originally moved on a topographic surface at least as high as the highest figure 6 elevations today. Headward erosion of the east-oriented Little Dry Creek valley south of the figure 6 map area first captured the southeast-oriented flood flow and diverted the captured flood waters east and then northwest to the newly eroded north-oriented Big Dry Creek valley. Headward erosion of the east-oriented Big Dry Creek (and northeast-oriented Sand Creek) valley north of the figure 6 map next beheaded the southeast-oriented flood flow channels in sequence from east to west. Flood waters on the northwest ends of the beheaded southeast-oriented flood flow routes reversed flow direction to flow north-northwest to the newly eroded east-oriented Big Dry Creek valley. The reversed flood flow eroded the north-northwest oriented Big Dry Creek (and Sand Creek) tributary valleys and created the present day Big Dry Creek-Little Dry Creek drainage divide.

Second Creek-Red Horse Creek drainage divide area

Figure 7: Second Creek-Red Horse Creek drainage divide area. United States Geological Survey map digitally presented using National Geographic Society TOPO software. 

Figure 7 illustrates the Second Creek-Red Horse Creek drainage divide area west of the figure 6 map area and includes overlap areas with figure 6. Red Horse Creek flows southeast along the highway to the figure 7 southeast corner. West of Red Horse Creek is southeast-oriented White Horse Creek and west of White Horse Creek are the southeast-oriented North and Middle Forks of Phillips Creek. Red Horse Creek, White Horse Creek and Phillips Creek all flow to east and northwest-oriented Little Dry Creek. Second Creek flows northwest along the highway to the figure 7 north edge. East of Second Creek is northwest oriented Lone Tree Creek and in the figure 7 northeast corner are headwaters of north-northwest oriented Langs Fork. Second Creek and Lone Tree Creek flow to northeast-oriented Sand Creek and Langs Fork flows to the east and north-oriented Big Dry Creek downstream from where Sand Creek and Big Dry Creek converge. West of Second Creek is northwest-oriented Long Branch, which also flows to northeast-oriented Sand Creek. Figure 7 evidence is similar to figure 6 evidence and is best explained by southeast-oriented flood waters flowing across the entire figure 7 map area on a topographic surface at least as high as the highest figure 7 elevations today. Headward erosion of the east-oriented Little Dry Creek valley south of the figure 7 map area captured the southeast-oriented flood flow and southeast-oriented tributary valleys eroded northwest from the newly eroded Little Dry Creek valley. Next headward erosion of east-oriented Big Dry Creek and northeast-oriented Sand Creek valley beheaded southeast-oriented flood flow routes to the newly eroded east-oriented Little Dry Creek valley. Flood waters on the northwest ends of beheaded southeast-oriented flood flow routes reversed flow direction to flow northwest and north to the newly eroded Sand Creek-Big Dry Creek valley. The reversed flood flow eroded the northwest and north-northwest oriented Sand Creek-Big Dry Creek tributary valleys and created the present day Sand Creek-Little Dry Creek and Big Dry Creek-Little Dry Creek drainage divides.

Sand Creek-Phillips Creek drainage divide area

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

Figure 8 illustrates the Sand Creek-Phillips Creek drainage divide area west of the figure 7 map area and includes overlap areas with figure 7. Northeast-oriented Sand Creek is located in the figure 8 northwest corner. Northwest-oriented Tepee Creek flows from the figure 8 west center area to join Sand Creek. Further east northwest-oriented Santo Arroyo Creek flows from the figure 8 center area to the figure 8 north edge and then to join Sand Creek north of the figure 8 map area. Southeast-oriented North Phillips Creek, Middle Phillips Creek, and Phillips Creek flow to the figure 8 east edge and then to join east-oriented Little Dry Creek southeast of the figure 8 map area. Other southeast-oriented drainage flowing to the figure 8 south edge also flows to the east-oriented Little Dry Creek south of the figure 8 map area. Through valleys link headwaters of northwest-oriented Sand Creek tributaries and southeast-oriented Little Dry Creek tributaries and along with the tributary orientations provide evidence southeast-oriented flood waters once crossed the present day Sand Creek-Little Dry Creek drainage divide. Figure 8 evidence is similar to the figure 7 evidence and can be explained in the same way. 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 used 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.

Sand Creek-Little Dry Creek drainage divide area

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

Figure 9 illustrates the Sand Creek-Little Dry Creek drainage divide area southwest of the figure 8 map area and includes overlap areas with figure 8. In the figure 9 southeast quadrant Little Dry Creek flows northeast from the figure 9 south center edge and then turns east to flow to the figure 9 east edge. Sand Creek flows east and northeast in the figure 9 northwest quadrant and is joined by northwest-oriented Basin Creek. Headwaters of northwest-oriented Tepee Creek are located in the figure 9 north center. Named Little Dry Creek tributaries from east to west are southeast-oriented Tinsley Coulee, Wolf Creek, Badger Creek, and Wildcat Creek. Note through valleys linking headwaters of northwest-oriented Sand Creek (and Basin Creek) tributaries with headwaters of southeast-oriented Little Dry Creek tributaries. These through valleys along with the northwest-southeast tributary alignment provide evidence southeast-oriented flood waters once flowed across the present day Sand Creek (and Basin Creek)-Little Dry Creek drainage divide. Through valleys have been cut adjacent to present day hills (e.g. Black Buttes and Fig Mountain in the figure 9 center area), which suggests flood waters originally flowed on a topographic surface at least as high as the highest figure 9 elevations today. Headward erosion of what was then a deep Little Dry Creek valley captured the southeast-oriented flood flow and diverted the captured flood waters east and northwest to the newly eroded north-oriented Big Dry Creek valley. Subsequently headward erosion of the Sand Creek-Basin Creek valley beheaded the southeast-oriented flood flow to the newly eroded Little Dry Creek valley and diverted the flood waters northeast and east to the north-oriented Big Dry Creek valley. The Sand Creek valley then eroded southwest and west from the newly eroded Basin Creek valley to capture southeast-oriented flood flow moving to the newly eroded north-oriented Basin Creek valley.

Big Dry Creek-Sand Creek drainage divide area

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

Figure 10 illustrates the Big Dry Creek-Sand Creek drainage divide area northwest of the figure 9 map area and includes overlap areas with figure 9. Big Dry Creek flows northeast, north and northeast from the figure 10 west edge to the figure 10 north edge. Sand Creek flows northeast, east and northeast from the figure 10 south edge to the figure 10 east edge. North-northwest oriented Basin Creek flows from the figure 10 southeast corner to join Sand Creek. Note southeast-oriented Sand Creek tributaries and northwest and north oriented Big Dry Creek tributaries. A close look at figure 10 reveals through valleys linking headwaters of southeast-oriented Sand Creek tributaries with headwaters of northwest-oriented Big Dry Creek tributaries. The northwest-southeast tributary alignment and through valleys provide evidence southeast-oriented flood flow once crossed the present day Big Dry Creek-Sand Creek drainage divide. The multiple through valleys and tributaries suggest flood waters were eroding an ever-changing complex of southeast-oriented anastomosing channels. Again flood waters initially flowed on a topographic surface at least as high as the highest figure 10 elevations today. As seen in figure 9 headward erosion of the Little Dry Creek valley first captured southeast-oriented flood flow and diverted flood waters east and northwest to the north-oriented Big Dry Creek valley. Prior to Little Dry Creek valley headward erosion flood waters moved in a southeast direction to what was then the newly eroded northeast oriented Yellowstone River valley (see Big Dry Creek (Missouri River)-Yellowstone River drainage divide area essay). Next headward erosion of the northeast oriented Sand Creek valley captured the flood flow and diverted flood waters more directly to the north-oriented Big Dry Creek valley. Finally headward erosion of the northeast and east oriented Big Dry Creek valley captured the southeast-oriented flood flow and diverted flood waters on a more northern route to the north-oriented Big Dry Creek valley. Following Big Dry Creek headward erosion flood waters to the newly eroded Big Dry Creek valley were beheaded by Missouri River and Musselshell River valley headward erosion (see Missouri River and Musselshell River-Big Dry Creek drainage divide area essay).

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.