Montana Smith River drainage basin landform origins overview essay

Authors

This essay is an overview of a essays describing landform origins for drainage divides between Montana’s Smith River tributaries and between the Smith River drainage basin and adjacent drainage basins. The Smith River is a north-northwest oriented Missouri River tributary located in central Montana. The north-northwest oriented Smith River (and South Fork Smith River) valley is located between the Big Belt Mountains and Castle Mountains, is west of the Little Belt Mountains, and is linked by a through valley between the Big Belt Mountains and the Crazy Mountains to the south with the south-southeast oriented Shields River, which flows to the east-oriented Yellowstone River. The southwest-oriented North Fork Smith River valley is linked by a through valley between the Little Belt Mountains and Castle Mountains with the east-oriented Musselshell River while north-northwest oriented South Fork Smith River is linked by a through valley between the Castle Mountains and Crazy Mountains with the northeast-oriented South Fork Musselshell River. Topographic map evidence found along all Smith River drainage divide areas indicates the entire region, including the high mountain ranges, was crosses by immense south- and southeast-oriented floods, which were beheaded and reversed by headward erosion of what was then a much deeper Missouri River valley with crustal warping contributing to the flood flow reversal process. When flood waters first flowed across present day drainage divides the regional mountain ranges did not stand high as they do today and flood waters could freely flow across them. Flood waters are interpreted to have been derived from a rapidly melting thick North American ice sheet and were flowing from western Alberta and eastern British Columbia into and across Montana until captured by Missouri River valley and tributary valley headward erosion.

Introduction

  • This Smith River drainage basin landform origins overview essay is one of a series of essay collections in the Missouri River drainage basin landform origins research project. The research project essay series goal is to use topographic map evidence to describe the evolution of drainage divides separating each significant present day Missouri River tributary valley and also to describe the evolution of drainage divides separating the present day Missouri River drainage basin from adjacent drainage basins. Each essay collection in this series relates to a specific Missouri River tributary, tributary to a present day Missouri River tributary, or a present day Missouri River valley segment. Each essay illustrates and discusses detailed topographic map evidence describing the evolution of a secondary drainage divide separating specified Missouri River tributary valleys. The Missouri River drainage basin research project series is being developed one essay at a time and essay collections are added as significant tributaries are reached. Presently available essays in the Missouri River drainage basin landforms origins research project can be found be in the archives or by searching desired categories listed on this essay’s sidebar.
  • Detailed topographic map evidence illustrated and discussed in the individual Missouri River drainage basin landform origins research project essays and in related essay collection essays builds a strong case for (1) deep glacial erosion of the North American continent by a thick North American ice sheet that created and occupied a deep “hole”, (2) rapid melting of that thick North American ice sheet, (3) immense floods of south oriented melt water, (4) headward erosion of deep east, northeast and north-oriented valley systems to capture the south and southeast-oriented melt water floods and to divert the melt water further and further northeast into space the ice sheet had once occupied, (5) deep flood water erosion of the North American continent surface, and (6) crustal warping that resulted in the uplift of mountain ranges as flood waters were flowing across them and deeply eroding what are now high mountainous regions. This evidence is presented for review and discussion by qualified research geomorphologists and geologists. This Smith River drainage basin landform origins introductory essay provides an overview of the much more detailed Smith River drainage basin essays which can be found by selecting the Smith River category on this essay’s sidebar list.
  • Essays illustrating and describing Smith River drainage divide areas interpret Smith River drainage basin area landform origins in the context of immense south oriented melt water floods flowing from a rapidly melting thick North American ice sheet located in a deep “hole.” The deep “hole” evolved after ice sheet formation by deep glacial erosion (under the ice sheet) and by crustal warping related to the ice sheet’s tremendous weight. The Missouri River drainage basin in Montana and northern Wyoming is located on the deep “hole’s” southwest wall. The Canadian Rocky Mountains in western Alberta and eastern British Columbia evolved as the deep “hole’s” western rim. Crustal warping was responsible for raising mountain ranges in the Smith River drainage basin as immense south and southeast-oriented melt water floods flowed across them. Mountain range uplift contributed to massive flood flow reversals that resulted in the present day north-oriented Smith River drainage basin. Headward erosion of the deep northeast-oriented Missouri River valley across south-southeast oriented flood flow channels in the present day Smith River drainage basin triggered the massive flood flow reversal. Discussions in the detailed essays provide many more details about the original south-oriented flood flow channels and the massive flood flow reversal responsible for eroding the Smith River drainage basin.

Montana Smith River drainage basin location map

Figure 1: Montana Smith River drainage basin 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 Smith River drainage basin location map and illustrates a large region in central Montana. The Big Belt Mountains are located in the figure 1 west center and the Little Belt Mountains are located just north of the figure 1 center. The Missouri River is formed at Three Fork (in figure 1 southwest quadrant south of Big Belt Mountains) at the confluence of the north-oriented Gallatin River, north-oriented Madison River, and northeast and east-oriented Jefferson River, and flows in a north and north-northwest direction to Holter Lake and then turns to flow in a northeast direction to Great Falls and the figure 1 north edge (west of center). White Sulphur Springs is a town located east of the Big Belt Mountains and south of the Little Belt Mountains. The Smith River is formed just west of White Sulphur Spring at the confluence of its southwest-oriented North Fork and its north-northwest oriented South Fork. From the White Sulphur Springs area the Smith River flows in a north-northwest direction to join the Missouri River near the town Ulm (near Great Falls). Elk Peak near White Sulphur Springs is located in the Castle Mountains (not labeled in figure 1). Note how the South Fork Smith River flows in a south direction before making a U-turn to flow in a north-northwest direction between the Big Belt Mountains and the Castle Mountains. Ringling is a town just south of the South Fork Smith River U-turn. The west-southwest oriented stream flowing through Ringling is Sixteenmile Creek (not labeled in figure 1), which is a Missouri River tributary. The south-southeast oriented stream south of Ringling is Potter Creek (not labeled in figure 1) which joins the Shields River (also not labeled) at Wilsall with the Shields River then flowing in a south-southeast direction to join the Yellowstone River downstream from Livingston. The Yellowstone River flows in a north-northeast direction from the figure 1 south edge (just west of center) to Livingston and then in an east and east-northeast direction to the figure 1 east edge (south of center). East of figure 1 the Yellowstone River flows in a northeast direction to join the Missouri River. East of the Castle Mountains is the town of Martinsdale. The Musselshell River is formed at Martinsdale at the confluence of its south and southeast-oriented North Fork and its northeast-oriented South Fork. From Martinsdale the Musselshell River flows in an east and east-northeast direction to the figure 1 east edge (just north of center). East of figure 1 the Musselshell River makes an abrupt turn to flow in a north direction to join the Missouri River. Note how the North Fork Musselshell River and North Fork Smith River both originate at approximately the same place along the Little Belt Mountains south margin and flow parallel to each other before diverging to flow in completely different directions. The Judith Basin is north of the Little Belt Mountains and is drained by the north-oriented Judith River and its tributaries flowing to the figure 1 north edge (east of center) and is north of the south-oriented North Fork Smith and Musselshell River headwaters. Also note how the South Fork Musselshell River and South Fork Smith River both originate along the Castle Mountains south margin and flow in south directions near each other before diverging and flowing in completely different directions.
  • Drainage routes in the figure 1 map area evolved during immense south and southeast-oriented floods which flowed across the figure 1 map area at a time when the present day mountain ranges were just beginning to emerge. Initially, at least, flood waters flowed across all of the figure 1 mountain ranges and eroded deep flood flow channels into those rising mountain masses. As the present day high mountain ranges emerged the flood waters were channeled into what became major flood flow channels between the rising mountain ranges. The Smith River linkages with the Yellowstone River and the Musselshell River  provide evidence of those south and southeast-oriented flood flow channels. A large through valley links the north-northwest oriented Smith River valley with the south-southeast oriented Shields River valley and before being dismembered and reversed by headward erosion of the much deeper Missouri River valley that Smith River-Shields River through valley was a major south-southeast oriented flood flow channel eroded headward from what was then the newly eroded east-oriented Yellowstone River valley. The southwest-oriented North Fork Smith River valley and the northeast-oriented South Fork Musselshell River valley were initially eroded headward by south-oriented flood water flowing to this major south-oriented flood flow channel. Headward erosion of a much deeper east-oriented Musselshell River valley beheaded and reversed the southwest-oriented flood flow between the Castle Mountains and Crazy Mountains to erode the northeast-oriented South Fork Musselshell River valley. At about the same time headward erosion of the deep Musselshell River valley captured south-oriented flood flow moving across the Little Belt Mountains just east of the south- and southwest-oriented North Fork Smith River headwaters valley and for a time may have captured at least some of the south-oriented flood flow moving on the south-oriented Smith River flood flow channel. Headward erosion of the west-southwest oriented Sixteenmile Creek valley from what was probably a south-oriented flood flow channel on the present day north and north-northwest oriented Missouri River alignment began the Smith River-Shields River flood flow channel dismemberment process, which was probably aided by crustal warping raising elevations along the middle of the flood flow channel route. Headward erosion of the deep northeast-oriented Missouri River valley next beheaded the south-southeast-oriented flood flow channel on the Smith River alignment and flood waters on the north end of the beheaded flood flow channel reversed flow direction to erode the north-northwest oriented Smith River valley and to create the Smith River-Musselshell River drainage divide and the Smith River-Sixteenmile Creek drainage divide. Continued headward erosion of the deep northeast-oriented Missouri River valley then beheaded and reversed the major south-oriented flood flow channel on the present day north and north-northwest oriented Missouri River alignment which caused a major flood flow reversal that not only eroded the north and north-northwest oriented Missouri River valley, but also eroded the north-oriented Gallatin, Madison, and Jefferson River valleys and their tributary valleys.

Hound Creek-Smith River drainage divide area

Figure 2: Hound Creek-Smith River drainage divide area. United States Geological Survey map digitally presented using National Geographic Society TOPO software. 
  • Looking now at some examples of the topographic map evidence for the initial south oriented flood flow in what is today a north oriented drainage basin figure 2 illustrates the Hound Creek-Smith River drainage divide area north of the Big Belt Mountains. The Smith River meanders in a north direction near the figure 2 east edge. Trout Creek is the north and northeast-oriented tributary flowing from the figure 2 south center edge through the small town of Millegan to join the Smith River in the figure 2 northeast quadrant. Mud Gulch is an east and southeast-oriented Smith River tributary in the figure 2 southeast quadrant. Note how the north and northeast-oriented Trout Creek valley is linked by through valleys with the Mud Gulch valley. The figure 2 map contour interval is 50 meters and some of the through valleys are defined by four or more contour lines on either side indicating depths of more than 200 meters. The through valley are water eroded features and were eroded by southeast-oriented flood flow moving to what was at one time a south oriented flood flow channel on the Smith River alignment. At that time the northeast-oriented Trout Creek valley did not exist. Headward erosion of the northeast-oriented Trout Creek valley beheaded southeast and east oriented flood flow routes to the east and southeast-oriented Mud Gulch valley. Hound Creek flows in a north-northeast and north direction from the figure 2 west edge (just south of center) to the figure 2 north edge (west half). Pine Coulee is the northwest, north, and west-northwest oriented Hound Creek tributary in the figure 2 southwest quadrant. North of Pine Coulee is northwest and north oriented Government Creek, which flows to Hound Creek west of Conway Ridge. West-northwest oriented Porcupine Creek is a Hound Creek tributary located north of Conway Ridge. Note how Porcupine Creek headwaters are linked by a through valley (or pass) with the northeast-oriented Trout Creek valley. The through valley is today a notch in an otherwise high ridge, but is a water eroded feature and is evidence of a southeast-oriented flood flow channel that crossed the region prior to headward erosion of the deep Hound Creek valley. An even deeper through valley can be seen linking the west-oriented East Fork Government Creek valley with the east-oriented Coal Creek valley, which drains to the northeast-oriented Trout Creek valley at Millegan. Still another through valley links the northwest-oriented Pine Coulee headwaters valley with the north- and northeast-oriented Trout Creek headwaters valley (near figure 2 south edge). These through valleys and other similar through valleys were eroded by south and southeast-oriented flood flow that was captured by headward erosion of the north- and northeast-oriented Trout Creek valley when flood flow in what had been the south oriented Smith River flood flow channel was beheaded and reversed north of the figure 2 map area by headward erosion of the much deeper northeast-oriented Missouri River valley. Because headward erosion of the deep Missouri River valley beheaded and reversed south- and southeast-oriented flood flow channels in sequence from east to west flood waters west and south of the actively eroding Missouri River valley head were still moving in south directions after flood waters in the newly beheaded Smith River flood flow channel began to reverse their flow direction.

Benton Gulch-Cement Gulch drainage divide area

Figure 3: Benton Gulch-Cement Gulch drainage divide area. United States Geological Survey map digitally presented using National Geographic Society TOPO software. 
  • Do similar through valleys cross drainage divides in the Big Belt Mountains south of the figure 2 map area? Figure 3 provides an answer and illustrates the Benton Gulch-Cement Gulch drainage divide in the Big Belt Mountains. The lake in the figure 3 southwest corner is Canyon Ferry Lake, which floods the north-northwest oriented Missouri River valley. Note how most tributaries flowing to the north oriented Missouri River are barbed tributaries and are oriented in south and southwest directions. From west to east the major Missouri River tributaries in figure 3 include Hellgate Gulch, Avalanche Creek, White Gulch, and Confederate Gulch. The Broadwater County-Meagher County boundary is shown with a dashed line and is labeled and extends in a south, southeast, and south direction from the figure 3 north edge (east of center) to the figure 3 south edge (east half). The county boundary is located on the Missouri River-Smith River drainage divide with Broadwater County being in the Missouri River drainage basin and Meagher County being in the Smith River drainage basin. Benton Gulch is a north and northeast-oriented Smith River tributary located in the figure 3 northeast quadrant and drains to the figure 3 north edge (east half). South of the north-oriented Benton Gulch headwaters is south-southeast oriented Cement Gulch, which drains to southwest and south-southwest oriented Confederate Gulch. Note how the north-oriented Benton Gulch headwaters valley is linked by a north-south oriented through valley with the south-oriented Cement Gulch valley. The figure 3 map contour interval is again 50 meters. The through valley floor elevation at the drainage divide is between 1850 and 1900 meters. Elevations on either side of the through valley rise to more than 2050 meters meaning the through valley is at least 150 meters deep and may be even deeper. The through is a water eroded feature and was eroded by south-oriented flood flow moving from what is today the north-oriented Smith River drainage basin to what is today the north-oriented Missouri River drainage basin. At that time flood waters were flowing in a south direction in both drainage basins and the Benton Gulch-Cement Gulch through valley was eroded by a south-oriented flood flow channel diverging from flood flow channels east of what was then the rising Big Belt Mountains mass to converge with south-oriented flood flow channels west of the rising Big Belt Mountains mass. Uplift of the Big Belt Mountains mass eventually ended the diverging south-oriented flood flow and flood waters on the north end of the Benton Gulch-Cement Gulch flood flow channel reversed flow direction to erode the north- and northeast-oriented Benton Gulch valley. Other less deep through valleys can be seen in figure 3. Note in particular an east-west through valley linking the north-oriented Benton Gulch headwaters valley with the south-oriented White Gulch headwaters valley (a short distance north and west of the Benton Gulch-Cement Gulch through valley). This higher level through valley provides evidence of multiple diverging and converging flood flow channels such as might be found in an anastomosing channel complex.

North Fork Smith River-North Fork Musselshell River drainage divide area

Figure 4: North Fork Smith River-North Fork Musselshell River drainage divide area. United States Geological Survey map digitally presented using National Geographic Society TOPO software. 
  • Figure 4 illustrates the North Fork Smith River-North Fork Musselshell River divide area along the Little Belt Mountains south margin and is located north and east of the figure 3 map area. The Judith Basin-Meagher County boundary is shown with a dashed line and is labeled and extends in a southeast direction from the figure 4 north edge (west half) to the figure 4 east edge (north of southeast corner). North and east of the county line is the Judith River drainage basin, with the Judith River (not seen in figure 4) being a north-oriented Missouri River tributary. The northeast-oriented stream flowing to the figure 4 northeast corner is the Lost Fork Judith River. The east oriented stream flowing to the figure 4 east edge (south of center) is the South Fork Judith River, which east of the figure 4 map area turns to flow in a northeast and north-northeast direction to join other tributaries and to form the north-northeast and north oriented Judith River. The south-southeast, south-southwest, and west oriented stream in the figure 4 northwest corner region is Sheep Creek. West of figure 4 Sheep Creek flows to the north-northwest oriented Smith River. North and slightly west of the figure 4 northwest corner the south-oriented Sheep Creek headwaters are linked by a through valley at Kings Hill Pass with north-oriented headwaters of north-northwest oriented Belt Creek, which flows to the northeast-oriented Missouri River (it is the unlabeled stream in figure 1 flowing through the town Belt). The south-, southwest, and south-oriented stream flowing to the figure 4 southwest corner is the North Fork Smith River which south and west of the figure 4 map area flows in a southwest direction to join the north-northwest oriented South Fork Smith River as a barbed tributary and to form the north-northwest oriented Smith River. The south-oriented stream just east of the South Fork Smith River and flowing to the figure 4 south center edge is the North Fork Musselshell River, which south of figure 4 turns to flow in a southeast direction to join the northeast-oriented South Fork Musselshell River and to form the east and north-oriented Musselshell River. South of figure 4 the North Fork Smith River and North Fork Musselshell River are linked by a large west to east oriented through valley between the Little Belt Mountains and the Castle Mountains.
  • What makes figure 4 interesting are through valleys linking the south-oriented North Fork Smith River valley with the south-oriented North Fork Musselshell River valley and then with the northeast-oriented Lost Fork Judith River valley. Also at the  west end of Lost Fork Ridge a much higher level through valley links the northwest-oriented South Fork Sheep Creek valley with the south-oriented North Fork Smith Valley. These through valleys record flood flow movements that at one time resulted in south-southeast oriented flood flow on the Belt Creek alignment flowing across the figure 4 map area in an east direction to what was then the northeast-oriented Lost Fork Judith River valley. Remember, headward erosion of the deep Missouri River valley beheaded and reversed flood flow in the Judith River drainage basin before flood flow further to the west was beheaded and reversed. Headward erosion of the south-oriented North Fork Musselshell River valley then captured the flood flow with headward erosion of the south-oriented North Fork Smith River valley next capturing the flood flow at about the same time as headward erosion of the west-oriented Sheep Creek valley captured the flood flow. Headward erosion of the deep Missouri River valley north of the figure 4 map area then beheaded the south-southeast oriented flood flow on the Belt Creek alignment and flood waters on the north-northwest ends of the beheaded flood flow channel reversed flow direction to erode the north-northwest oriented Belt Creek valley and to create the Belt Creek-Sheep Creek drainage divide. Probably these immense flood flow reversals and associate drainage route captures were aided by Little Belt Mountains region uplift that was occurring as flood waters flowed across the region.

South Fork Smith River-South Fork Musselshell River drainage divide area

Figure 5: South Fork Smith River-South Fork Musselshell River drainage divide area. United States Geological Survey map digitally presented using National Geographic Society TOPO software. 
  • South of the figure 4 map area and south of the Castle Mountains are some more interesting linkages between the Smith River and the Musselshell River. Figure 5 illustrates the South Fork Smith River-South Fork Musselshell River drainage divide area along the Castle Mountains south margin and just north of the Crazy Mountains (not seen in figure 5). The South Fork Smith River originates in a southeast-facing basin near the figure 5 center and flows in a southeast direction and then turns to flow in a southwest direction before turning to flow in a northwest direction to the town of Moss Agate and the figure 5 west edge (south of northwest corner). Agate Creek is a southwest-oriented tributary joining the northwest-oriented South Fork Smith River at Moss Agate. The South Fork Musselshell River flows in a north direction on the east side of Rimrock Ridge from the figure 5 south edge (east half) and then turns to flow in a northeast direction through the town of Bruno to the figure 5 east edge (north half). Note how the South Fork Musselshell River has several southeast-oriented tributaries originating in the Castle Mountains including Sourdough Creek, Warm Springs Creek, and Alabaugh Creek. Note how the town of Loweth is located in a through valley linking the South Fork Smith River valley with the east-oriented Sourdough Creek valley. Also note how the southeast-oriented Warm Springs Creek valley is linked by a through valley with the southwest oriented Agate Creek valley. The remarkable South Fork Smith River U-turn seen in figure 5 is evidence of southeast-oriented flood flow at a time when the deep northwest-oriented South Fork Smith River valley did not exist. The southeast-facing basin in which the South Fork Smith River originates is a southeast-facing abandoned headcut eroded by southeast-oriented flood flow from the northwest. The figure 5 map contour interval is 50 meters and today the northwest-oriented South Fork Smith River valley is approximately 300 meters lower than the abandoned headcut rim, which means the northwest-oriented South Fork Smith River valley floor was lowered by at least 300 meters since the southeast-oriented South Fork Smith River valley segment was eroded. Probably much of that valley floor lowering occurred as flood waters flowed to the south of the figure 5 map area by using the broad and deep valley crossing the figure 5 south center edge and seen further south in figure 6 below. The south-oriented flood flow for much of the time was flowing between the rising Crazy Mountains to the east and the rising Bridger Range to the west to what was then the newly eroded east-oriented Yellowstone River valley (the Bridger Range is not labeled in figure 1, but is located south of the Big Belt Mountains). Figure 6 illustrates the region directly south of figure 5 map area and the discussion will continue there.

South Fork Smith River-Potter Creek drainage divide area

Figure 6: South Fork Smith River-Potter Creek drainage divide area. United States Geological Survey map digitally presented using National Geographic Society TOPO software. 
  • The final figure in this Smith River drainage basin landform origins essay collection overview essay illustrates the South Fork Smith River-Potter Creek drainage divide area south of the figure 5 map area and includes overlap areas with figure 5. The South Fork Smith River flows in a southwest and then northwest direction near the figure 6 north center edge (the V-shaped highway follows the river). Sixteenmile Creek flows in a west direction from the figure 6 east edge (south half) and then turns to flow in north-northwest direction in the valley west of the East Hogback before turning to flow in a west-southwest direction to the town of Ringling and then to the figure 6 west edge. West of figure 6 Sixteenmile Creek flows between the Big Belt Mountains to the north and the Bridger Range to the south to eventually reach the north-northwest oriented Missouri River. Note north-oriented tributaries flowing from the west half of the figure 6 south edge to join Sixteenmile Creek. Also note north-oriented Sixteenmile Creek tributaries flowing from the east half of the east half of the figure 6 south edge. Between these north-oriented Sixteenmile Creek tributaries and east of the figure 6 south center edge is an unlabeled south-oriented stream (just east of the highway). This south-oriented stream is Potter Creek, which south of the figure 6 map area flows to the Shields River, which then flows in a south-southeast direction to join the east-oriented Yellowstone River. In other words the figure 6 map is showing a segment of a major north-south oriented through valley now drained in the north by the north-northwest oriented Smith River and its tributaries, in the south by the south-southeast oriented Shields River and its tributaries, and in the middle by west-southwest oriented Sixteenmile Creek and its tributaries. At one time this large north-south oriented through valley served as a major south-oriented flood flow channel moving flood waters to what was then the newly eroded Yellowstone River valley. Dismemberment of the south-oriented flood flow channel probably occurred as crustal warping raised the through valley middle section (seen in figure 6) and as headward erosion of the west-southwest oriented Sixteenmile Creek valley beheaded and reversed the south-oriented flood flow to erode the north-oriented Sixtennmile Creek tributary valleys seen today and also to erode the north-northwest oriented Sixteenmile Creek valley segment seen today. At about the same time a combination of crustal uplift and headward erosion of the deep northeast-oriented Missouri River valley beheaded and reversed the south-southeast oriented flood flow north of the newly eroded Sixteenmile Creek valley. This reversal of flood flow captured the southeast and southwest-oriented South Fork Smith River headwaters to create the South Fork Smith River U-turn seen today.
  • The topographic maps illustrated and discussed in this Smith River drainage basin landform origins overview essay provide a sample of topographic map evidence illustrated and discussed in the much more detailed contained in this blog. Each of the essays includes a large region location map, a detailed location map, and eight topographic maps related to a specific Smith River drainage divide area with a discussion describing each map. The Smith River drainage basin is large drainage basin with a complex history and this overview essay and the nine more detailed essays provide a slightly larger sample of the topographic map evidence available. Future researchers working with more complete topographic map coverage will undoubtably be able to describe flood movements much more completely than described in these first attempts to determine the Smith River drainage basin erosional history.

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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