Otter Creek-Powder River drainage divide area landform origins, southeast Montana, USA

· Montana, Powder River, Tongue River
Authors

A geomorphic history based on topographic map evidence

Abstract:

The Otter Creek-Powder River drainage divide area is located in southeastern Montana, USA and Otter Creek is a Tongue River tributary. Although detailed topographic maps of the Otter Creek-Powder 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 Otter Creek-Powder River drainage divide area is interpreted to have been eroded during immense southeast-oriented flood events, the first of which flowed on a topographic surface at least as high as the highest points in the present-day drainage divide area. Flood erosion across the drainage divide ended when headward erosion of the deep Tongue River valley captured all southeast-oriented flood flow.

Preface:

The following interpretation of detailed topographic map evidence is provided as evidence in the Missouri River drainage basin landform origins research project, which is compiling similar evidence for all major drainage divides contained within the Missouri River drainage basin and for all major drainage divides with and within certain adjacent drainage basins. The research project is interpreting evidence in the context of a previously unexplored geomorphology paradigm, which is briefly described in the introduction below. Project essays are listed on the sidebar category list under their appropriate Missouri River tributary drainage basin, Missouri River segment drainage basin (by state), and/or state in which the Missouri River drainage basin is located.

Introduction:

  • The purpose of this essay is to use topographic map interpretation methods to explore southeastern Montana Otter Creek-Powder River drainage divide area landform origins. Map interpretation methods can be used to unravel many geomorphic events leading up to formation of present-day drainage routes and development of other landform features. While each detailed topographic map feature provides detailed evidence to be explained, the solution must be consistent with explanations for adjacent area map evidence as well as solutions to big picture map evidence puzzles. I invite readers to improve upon my solutions or to propose alternate solutions that better explain evidence and are also consistent with adjacent map area and big picture evidence. Readers may do so either by making comments here or by writing and publishing their own essays and then by leaving a link to those essays in a comment here.
  • This essay is also exploring a paradigm in which erosional landforms are interpreted as evidence left by immense glacial melt water floods. Implied in that interpretation is the immense floods were derived from a thick North American ice sheet that created a deep “hole” in the North American continent and also melted fast. The previously unexplored paradigm being tested in this and similar essays is a thick North American ice sheet, comparable in thickness to the present day Antarctic ice sheet, occupied approximately the North American region usually recognized to have been glaciated and through its weight and erosive actions created a “deep” North American “hole”, through its weight and deep erosion (and perhaps deposition) along major south-oriented melt water flow routes caused significant crustal warping and tectonic change, through its action of melting fast produced immense floods that flowed across the continent, and through its action of melting fast systematically opened up space in the ice sheet created “hole” so headward erosion of newly developed north-oriented drainage systems captured immense south-oriented melt water floods and diverted immense melt water floods north into space the ice sheet had once occupied.
  • If this previously unexplored paradigm is correct the geographic region explored by this essay should contain evidence of immense floods that were captured by headward erosion of new valley systems so as to cause the floods to flow in a different direction. Ability of this previously unexplored paradigm to explain Otter Creek-Powder River drainage divide area landform evidence will be regarded as evidence supporting the “thick ice sheet that melted fast” paradigm.

Otter Creek-Powder River drainage divide area location map

Figure 1: Otter Creek-Powder River 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 an Otter Creek-Powder River drainage divide area location map and illustrates a region in southeastern Montana and northeastern Wyoming. The state of Montana is located in figure 1 north of the green border line and the state of Wyoming is south of the purple boundary line. The state of North Dakota is located in the figure 1 northeast corner and the state of South Dakota is located south of North Dakota. The Yellowstone River flows in a northeast direction from Custer to Miles City, Montana. The Tongue River flows northeast from southwest of Sheridan, Wyoming into Montana and then south of Miles City, Montana turns northwest to join the northeast oriented Yellowstone River as a barbed tributary. Otter Creek originates southeast of Otter, Montana and flows north and northwest to join the Tongue River at Ashland, Montana.  Pumpkin Creek is a major Tongue River tributary which originates near Sonnette, Montana and flows north-northeast before turning northwest to join the northwest-oriented Tongue River valley segment. The Powder River flows north in Wyoming (east of the Bighorn Mountains) and then turns northeast to flow to Broadus and Powderville, Montana before turning northwest to flow to the northeast oriented Yellowstone River near the figure 1 north edge. Landform evidence illustrated here is interpreted in the context of an immense southeast-oriented flood flowing across the entire figure 1 map area and which was systematically captured and diverted further and further to the northeast by headward erosion of deep valleys eroded into a topographic surface at least as high as the figure 1 region highest elevations today. In the figure 1 map region headward erosion of the northeast oriented Powder River valley captured the southeast-oriented flood flow and diverted the flood waters north to the northeast oriented Yellowstone River valley (located north of the figure 1). Headward erosion of the deep northeast oriented Yellowstone River and the northeast- and northwest-oriented Tongue River-Pumpkin Creek valley next captured the southeast-oriented flood flow. Soon thereafter headward erosion of the Tongue River-Otter Creek valley captured southeast-oriented flood to the newly eroded Pumpkin Creek valley and to the Powder River valley (south of the Pumpkin Creek valley head). Subsequently headward erosion of the deep Tongue River valley captured southeast-oriented flood flow to the newly eroded Otter Creek valley and ended flood flow across the Tongue River-Otter Creek drainage divide. The Tongue River-Pumpkin Creek drainage divide area essay, the Tongue River-Otter Creek drainage divide area essay, the Pumpkin Creek-Mizpah Creek drainage divide area essay, and the Mizpah Creek-Powder River drainage divide area essay describe regions located near the area discussed here and can be found under appropriate River name on the sidebar category list (where Pumpkin Creek is a Tongue River tributary and Mizpah Creek is a Powder River tributary.

Otter Creek-Powder River drainage divide area detailed location map

Figure 2: Otter Creek-Powder River 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 Otter Creek-Powder River drainage divide area discussed here. The west to east border line along the figure 2 south edge is the Montana-Wyoming state line. Powder River County is located in Montana. Big Horn County is located west of the Powder River County southwest corner, while Rosebud County is located north and east of Big Horn County and west of Powder River County. The Otter Creek drainage divide area discussed here is located in southwest Powder River County. The Tongue River flows northeast from the figure 2 southwest corner to Tongue River Reservoir (near Decker, Montana) and then northeast to Birney and Ashland, Montana before turning north to flow to the figure 2 north edge. The Powder River flows from the figure 2 south center edge northeast into Powder River County, Montana to Broadus and then to the figure 2 northeast corner. Otter Creek originates southeast of Otter, Montana, near where the northeast-oriented Powder River crosses the Wyoming-Montana state line and flows northwest to near Otter where it turns north to flow to the Tongue River at Ashland Montana. Figure 2 shows numerous southeast oriented Tongue River tributaries, southeast oriented and northwest oriented Powder River tributaries, and some southeast and northwest oriented Otter Creek tributaries. This northwest-southeast drainage alignment is evidence the northeast-oriented Powder River valley eroded southwest to capture multiple southeast-oriented flood flow routes such as might be found in a southeast-oriented anastomosing channel complex. Subsequently the northwest- and north-oriented Otter Creek valley eroded south across the same southeast-oriented flood to capture flood waters and to divert flood waters north. Further, the drainage alignment is evidence the northeast-oriented Tongue River valley subsequently eroded southwest to capture the same southeast-oriented flood flow. The southeast-oriented tributary valleys were eroded by southeast-oriented flood flow moving into the newly eroded and deep Powder River, Otter Creek and Tongue River valleys. The northwest-oriented tributary valleys were eroded by reversed flood flow on the northwest ends of beheaded southeast-oriented flood flow routes. Because flood waters move in and erode anastomosing (or interconnected) channels reversed flood flow on a beheaded flood flow route could capture flood flow from yet to be beheaded flood flow routes. Such captures of yet to be beheaded flood flow could enable the 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. Detailed maps below start with a look at the Otter Creek-Pumpkin Creek drainage divide area just north of the Otter Creek-Powder River drainage divide area. Subsequent detailed maps illustrate evidence along the Otter Creek-Powder River drainage divide proceeding from the northeast to the southwest.

Otter Creek-Pumpkin Creek drainage divide area

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

Figure 3 illustrates the Otter Creek-Pumpkin Creek drainage divide area immediately north of the Otter Creek-Powder River drainage divide area. Pumpkin Creek flows northwest from the figure 3 south edge (east half) and then turns northeast to flow to the figure 3 north edge (east half). Otter Creek is located west of the figure 3 map area, although west and northwest oriented streams in the figure 3 west half are Otter Creek tributaries. Note how tributaries to the northeast-oriented Pumpkin Creek valley segment are southeast-oriented and many Otter Creek tributaries are northwest oriented. Also note the northwest orientation of the Pumpkin Creek valley in the figure 3 southeast quadrant. Further note shallow through valleys eroded into the Otter Creek-Pumpkin Creek drainage divide which link Otter Creek tributary valleys with Pumpkin Creek tributary valleys. For example, in the figure 3 south center the drainage divide ridge in the Threemile Buttes area is crossed by multiple through valleys linking the northwest-oriented Threemile Creek valley with headwaters of both Skinner Gulch and Doonan Gulch, both draining to Pumpkin Creek. The southeast-oriented Pumpkin Creek tributaries and northwest-oriented Pumpkin Creek valley segment suggest the northeast-oriented Pumpkin Creek valley eroded headward across multiple southeast-oriented flood flow routes such as might be found in a southeast-oriented anastomosing channel complex. The northwest-oriented Pumpkin Creek valley segment was eroded by reversed flood flow on the northwest end of a beheaded southeast-oriented flood flow route. Because flood flow channels were anastomosing (or interconnected) reversed flow in one channel could often capture yet to beheaded flood flow in adjacent channels. Such captures enabled reversed flood flow to sometimes erode significant valleys. The through valleys are evidence flood waters once used multiple channels to cross the present day Otter Creek-Pumpkin Creek drainage divide and also indicate the presence of a southeast-oriented anastomosing channel complex. Figure 3 evidence suggests southeast-oriented flood flow once moved across the entire figure 3 map area on a topographic surface at least as high as the highest figure 3 elevations today. The deep northeast-oriented Pumpkin Creek valley eroded headward into the figure 3 map area and captured southeast-oriented flood flow as well as reversed flood flow on the northwest ends of major southeast-oriented flood flow routes. Subsequently headward erosion of the north-oriented Otter Creek valley (west of figure 3) beheaded and reversed flood flow routes to the newly eroded Pumpkin Creek valley and the resulting reversal of flood flow eroded the northwest- and west-oriented Otter Creek tributary valleys and created the present day Otter Creek-Pumpkin Creek drainage divide.

Otter Creek and Pumpkin Creek-Cache Creek drainage divide area

Figure 4: Otter Creek and Pumpkin Creek-Cache Creek drainage divide area. United States Geological Survey map digitally presented using National Geographic Society TOPO software.

Figure 4 illustrates the Pumpkin Creek-Cache Creek and the Otter Creek-Cache Creek drainage divide area immediately south of the figure 3 map area and includes overlap areas with figure 3. Pumpkin Creek originates near Sonnette and flows northeast and then turns northwest to flow to the figure 4 north edge. Northwest-oriented streams in the figure 4 southwest corner flow to north-oriented Otter Creek located west of the figure 4 map area. Southeast-oriented-oriented streams flow to east, northeast and southeast-oriented Cache Creek, which flows to the figure 4 southeast corner area. In the figure 4 northeast corner area are headwaters of Mizpah Creek, which flows north to eventually join the Powder River. Note the northwest-oriented tributaries to the northeast-oriented Pumpkin Creek valley segment and also to north-oriented Otter Creek and southeast-oriented tributaries to Cache Creek. Also note how southeast-oriented Cache Creek tributary valleys are linked to the northwest-oriented Otter Creek and Pumpkin Creek tributary valleys. Shallow through valleys cross the present day Otter Creek-Cache Creek and Pumpkin Creek-Cache Creek drainage divide and provide evidence of multiple channels of southeast-oriented flood flow to what was then the actively eroding east, northeast, and southeast-oriented Cache Creek valley, which drains to northeast-oriented Powder River valley (located southeast of figure 4). Headward erosion of the Pumpkin Creek valley beheaded the southeast-oriented flood flow to the actively eroding Cache Creek drainage basin causing flood waters to reverse direction and to create the northwest-oriented Pumpkin Creek tributary valleys and the northwest-oriented Pumpkin Creek valley segment as well as the present day Pumpkin Creek-Cache Creek drainage divide. At approximately the same time headward erosion of the Otter Creek valley (west of figure 4) beheaded and reversed southeast-oriented flood flow (south of Pumpkin Creek) to the actively eroding Cache Creek drainage basin and created northwest-oriented Otter Creek tributary valleys and the present day Otter Creek-Cache Creek drainage divide.

Otter Creek-Powder River drainage divide area near Diamond Butte

Figure 5: Otter Creek-Powder River drainage divide area near Diamond Butte. United States Geological Survey map digitally presented using National Geographic Society TOPO software.

Figure 5 illustrates the Otter Creek-Powder River drainage divide area southwest of the figure 4 map area and includes overlap areas with figure 4. The northeast-oriented Powder River is located in the figure 5 southeast corner. East-oriented Cache Creek is located in the figure 5 northeast corner. Diamond Butte is located in the figure 5 southwest quadrant (northeast section). The North Fork Taylor Creek near Diamond Butte flows to northwest oriented Taylor Creek and then to north-oriented Otter Creek and the southeast-oriented Willie Bull Prong near Diamond Butte flows to southeast-oriented Bloom Creek, which flows to the northeast-oriented Powder River. Figure 6 below provides a detailed map of the Otter Creek-Powder River drainage divide in the Diamond Butte area. Figure 5 evidence shows multiple northwest oriented Otter Creek tributaries flowing to the figure 5 west and north edges and multiple southeast-oriented Powder River tributaries flowing to the northeast-oriented Powder River. Figure 5 evidence also shows multiple shallow through valleys crossing the present day Otter Creek-Powder River drainage divide. The northwest and southeast orientations of the Otter Creek and Powder River tributaries and the multiple through valleys linking the northwest-oriented Otter Creek tributaries with the southeast-oriented Powder River tributaries provide evidence the deep northeast-oriented Powder River valley eroded southwest across multiple southeast-oriented flood flow routes and subsequently the north-oriented Otter Creek valley eroded south to capture southeast-oriented flood flow routes that had been eroding southeast-oriented Powder River tributary valleys into the figure 5 map area. Flood waters on the northwest ends of the southeast-oriented flood flow routes beheaded by headward erosion of the north-oriented Otter Creek valley reversed flow direction to flow northwest to the newly eroded Otter Creek valley, to erode northwest-oriented Otter Creek tributary valleys, and to create the present day Otter Creek-Powder River drainage divide. Prior to headward erosion of the deep Powder River valley flood waters were flowing southeast on a topographic surface at least as high as the highest figure 5 elevations today.

Detailed map of Otter Creek-Powder River drainage divide area near Diamond Butte

Figure 6: Detailed map of Otter Creek-Powder River drainage divide area near Diamond Butte. United States Geological Survey map digitally presented using National Geographic Society TOPO software.

Figure 6 illustrates a detailed map of the Otter Creek-Powder River drainage divide area north and south of Diamond Butte (the area is illustrated in less detail in figure 5 above). Diamond Butte is located in the figure 6 center. As illustrated in figure 5 northwest-oriented drainage in the figure 6 northwest quadrant flows to northwest-oriented North Fork Taylor Creek, which flows to northwest-oriented Taylor Creek and then to the north-oriented Otter Creek. Also as illustrated in figure 5 above southeast-oriented drainage in the Diamond Butte area flows to southeast-oriented Willie Bull Prong, which flows to southeast-oriented Bloom Creek and then to the northeast-oriented Powder River. Figure 6 illustrates the multiple through valleys crossing the present day Otter Creek-Powder River drainage divide. These through valleys provide evidence multiple channels of southeast-oriented flood flow moved across the present day drainage divide. Further, the through valleys provide evidence that flood waters originally flowed on a topographic surface at least as high as the top of Diamond Butte and that flood waters eroded the landscape we see today. Flood waters first flowed southeast to what was then the newly eroded northeast-oriented Powder River valley. Headward erosion of southeast-oriented drainage systems then eroded into the region southeast of the present day Otter Creek-Powder River drainage divide. Subsequently headward erosion of the deep north-oriented Otter Creek valley to the west of the figure 6 map area captured the flood flow. Flood waters on the northwest ends of the beheaded flood flow routes reversed flow direction to flow northwest to the newly eroded north-oriented Otter Creek valley. Because flood flow channels were anastomosing (or interconnected) reversed flood flow on a beheaded flood flow channel could easily capture yet to be beheaded flood flow from adjacent channels. Such captures of yet to be beheaded flood flow enabled the reversed flow flood waters to erode northwest-oriented valleys and to create a drainage divide where northwest-oriented valleys to Otter Creek are comparable in size (and sometimes even larger than) southeast-oriented valleys to the northeast-oriented Powder River.

Indian Creek-Powder River drainage divide area

Figure 7: Indian Creek-Powder River drainage divide area. United States Geological Survey map digitally presented using National Geographic Society TOPO software.

Figure 7 illustrates the Otter Creek-Powder River drainage divide area south and somewhat west of the figure 5 map area and includes overlap areas with figure 5. The northeast-oriented Powder River is located in the figure 7 southeast corner and has multiple southeast-oriented tributaries. North-northwest oriented Otter Creek flows from the figure 7 southwest corner to the figure 7 west center edge. West and north of figure 7 Otter Creek turns to flow north before turning northwest to flow to the Tongue River. Northwest-oriented streams in the figure 7 west half are all Otter Creek tributaries. Northwest-oriented Indian Creek flows through the figure 7 center area to the figure 7 northwest corner area. The Indian Creek-Spring Creek drainage divide area is illustrated in detail in figure 8 below. Note how Powder River tributaries are short and have not eroded deep southeast-oriented valleys headward into the Powder River valley northwest wall. Instead, it is the northwest-oriented Otter Creek tributaries and headwaters that have eroded the valleys southeast almost to the edge of the deep northeast-oriented Powder River. This evidence suggests headward erosion of the north-oriented Otter Creek valley beheaded southeast-oriented flood flow to the newly eroded northeast-oriented Powder River valley almost as fast as the Powder River valley was being eroded. Southeast-oriented flood flow moving into the newly eroded and deep Powder River valley did not have time to erode valleys headward from the Powder River valley northwest wall. Before such southeast-oriented valleys could be eroded the southeast-oriented flood flow routes were beheaded and reversed by headward erosion of the deep Otter Creek valley.

Detailed map of Indian Creek-Powder River drainage divide area

Figure 8: Detailed map of Indian Creek-Powder River drainage divide area. United States Geological Survey map digitally presented using National Geographic Society TOPO software.

Figure 8 illustrates the Indian Creek-Spring Creek drainage divide area illustrated in less detail in figure 7 above. Northwest-oriented Indian Creek flows toward the figure 8 northwest corner area. Southeast-oriented Spring Creek flows toward the figure 8 southeast corner. Headwaters of southeast-oriented Plum Creek are located in the figure 8 northeast corner. Note how the Otter Creek-Powder River drainage divide here is an asymmetric drainage divide with much steeper slopes on the Powder River drainage basin side and gentler slopes on the Otter Creek drainage basin side. Also note the multiple shallow through valleys crossing the drainage divide. The through valleys provide evidence that prior to reversal of flood flow in the present day northwest-oriented Indian Creek drainage system flood waters were flowing southeast to what was then the newly eroded Powder River valley. Headward erosion of the north-oriented Otter Creek valley then beheaded and reversed flood flow in the present day Indian Creek drainage basin and the reversed flood waters eroded the northwest-oriented Indian Creek and Indian Creek tributary valleys and also created te present day Indian Creek-Powder River drainage divide. The source of the immense southeast-oriented flood cannot be determined from evidence presented here. However, the Missouri River drainage basin landform origins research project essays when taken as a group can be used to trace flood waters headward toward the flood source. A logical flood water source would be rapid melting of a thick North American ice sheet located in a deep “hole”, where the deep “hole” was located approximately in the North American region usually recognized to have been glaciated. Such a flood water source would also explain why deep valleys were eroding headward to capture the immense south-oriented flood and to divert the flood waters further and further to the northeast into space in the deep North American “hole” the rapidly melting ice sheet had once occupied.

Otter Creek-Powder River drainage divide area near state line

Figure 9: Otter Creek-Powder River drainage divide area near state line. United States Geological Survey map digitally presented using National Geographic Society TOPO software.

Figure 9 illustrates the Otter Creek-Powder River drainage divide area south of the figure 7 map area and includes overlap areas with figure 7. The west to east boundary line near the figure 9 south edge is the Montana-Wyoming state line. North-northwest oriented Otter Creek flows to the figure 9 northwest corner area. North- and northwest-oriented Otter Creek headwaters and tributaries originate almost on the lip of the deep northeast-oriented Powder River valley. The northeast-oriented Powder River flows from the figure 9 south (east half) edge to the figure 9 northeast corner. Tributaries to the Powder River from the west are southeast-oriented and have not eroded deep southeast-oriented valleys headward into the Powder River valley northwest wall. Figure 9 evidence suggests a major southeast or south-southeast oriented flood flow route that was supplying flood waters to the newly eroded northeast-oriented Powder River valley was beheaded and reversed to create the north-northwest oriented Otter Creek headwaters area seen here. The flood flow reversal must have taken place almost as fast the northeast-oriented Powder River valley was eroded. The southeast-oriented Powder River tributaries provide evidence southeast-oriented flood flow did enter the newly eroded Powder River valley. However the short length and shallow depth of the southeast-oriented Powder River tributary valleys provides evidence southeast-oriented flood flow to the Powder River valley ended almost as soon as the Powder River valley was eroded. The Otter Creek-Powder River drainage divide was created by a reversal of flood flow so flood waters flowed north-northwest to the north-oriented and what was then the newly eroded Otter Creek valley. Figure 10 below illustrates in detail the Otter Creek-Powder River drainage divide located in the figure 9 south center area.

Detailed map of Otter Creek-Powder River drainage divide area near state line

Figure 10: Detailed map of Otter Creek-Powder River drainage divide area near state line. United States Geological Survey map digitally presented using National Geographic Society TOPO software.

Figure 10 illustrates in detail the northwest-oriented Otter Creek headwaters area and the Otter Creek-Powder River drainage divide. Northwest-oriented Otter Creek flows to the figure 10 north edge (west half). Note how the Otter Creek valley and the valleys of northwest-oriented Otter Creek tributaries are eroded into a relatively smooth erosion surface. The erosion surface was eroded by southeast-oriented flood flow moving to the actively eroding northeast-oriented Powder River valley headcut. Small hills standing above the erosion surface plane provide evidence flood flow channels were eroded into what must have been a higher level topographic surface. Line Creek, located in the figure 10 east center area, illustrates how the deep northeast-oriented Powder River valley was eroded. Note how Line Creek has northwest-oriented headwaters and then turns northeast and east before turning southeast (east of figure 10, but clearly shown in figure 9) to flow to the northeast-oriented Powder River. The northwest-oriented headwaters valley was eroded by a reversal of southeast-oriented flood flow on a southeast-oriented flood flow route beheaded by headward erosion of the southeast-oriented Line Creek valley. Southeast-oriented flood flow to what was then the actively eroding Line Creek valley ended when headward erosion of the north-oriented Otter Creek valley beheaded the southeast-oriented flood flow route supplying water to what was then the actively eroding Line Creek valley. Flood waters on the northwest end of the beheaded flood flow route then reversed flow direction to flow northwest and eroded the northwest-oriented Otter Creek valley segment and also created the present day Otter Creek-Line Creek drainage divide.

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.

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