Fish Creek-Sweet Grass Creek drainage divide area landform origins, Sweet Grass County, Montana, USA

Authors

Abstract:

The Fish Creek-Sweet Grass Creek drainage divide area discussed here is located in south central Montana, USA and this essay interprets landform origins using topographic map evidence. Fish Creek is an east-northeast oriented Musselshell River tributary and originates just east of the Crazy Mountains. Sweet Grass Creek originates in the Crazy Mountains and flows in a northeast direction almost to the Fish Creek headwaters and then turns to flow in a southeast and south direction to join the Yellowstone River. A complex of through valleys eroded across the Cayuse Hills links the Sweet Grass Creek valley with the Fish Creek tributary valleys and the valley of Big Coulee Creek, which is a northeast oriented Musselshell River tributary located south and east of Fish Creek. An erosional escarpment is located along the Cayuse Hills’ northeast flank and north and east of that escarpment the Musselshell River drainage basin is significantly lower than the Sweet Grass Creek valley floor. The through valleys and the erosional escarpment are interpreted to have been eroded by massive floods at the time the deep Musselshell River valley eroded headward into the region. Headward erosion of the Sweet Grass Creek valley from what was then a newly eroded Yellowstone River valley captured floodwaters, which had been moving across the present day Crazy Mountains to the actively eroding Musselshell River drainage basin.

Preface

The following interpretation of detailed topographic map evidence is one of a series of essays describing similar evidence for all major drainage divides contained within the Missouri River drainage basin and for all major drainage divides with adjacent drainage basins. The research project is interpreting evidence in the context of a previously unexplored deep glacial erosion paradigm, which is fundamentally different from most commonly accepted North American glacial history interpretations. 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 the Fish Creek-Sweet Grass Creek drainage divide area landform origins in Sweet Grass County, Montana, USA. Map interpretation methods can be used to unravel many geomorphic events leading up to formation of present-day drainage routes and development of other landform features. While each detailed topographic map feature provides detailed evidence to be explained, the solution must be consistent with explanations for adjacent area map evidence as well as solutions to big picture map evidence puzzles. I invite readers to improve upon my solutions and/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 new geomorphology 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 other Missouri River drainage basin landform origins research project essays is a thick North American ice sheet, comparable in thickness to the Antarctic ice sheet, occupied the North American region usually recognized to have been glaciated, and through its weight and erosive actions created a deep North American “hole”. The southwestern rim of that deep “hole” is today preserved in the high Rocky Mountains. The ice sheet 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 Fish Creek-Sweet Grass Creek drainage divide area landform evidence in Sweet Grass County, Montana will be regarded as evidence supporting the “thick ice sheet that melted fast” paradigm.

Fish Creek-Sweet Grass Creek drainage divide area location map

Figure 1: Fish Creek-Sweet Grass 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 location map for the Fish Creek-Sweet Grass Creek drainage divide in south-central Montana. The Crazy Mountains are located slightly south and west of the figure 1 center and are where Sweet Grass Creek originates. Sweet Grass Creek is labeled and flows in a northeast direction from the Crazy Mountains before turning to flow in a southeast and south direction to join the Yellowstone River near Greycliff. The Yellowstone River flows from the figure 1 south edge (west half) to Livingston and Big Timber before turning to flow in an east-southeast direction to Greycliff and Columbus and then turning to flow in a northeast direction to Laurel and Billings before reaching the figure 1 east edge (south of center). East of figure 1 the Yellowstone River continues to flow in a northeast direction and joins the east oriented Missouri River at the North Dakota border. North of the Crazy Mountains the Musselshell River is formed near Martinsdale at the confluence of its southeast oriented North Fork and northeast oriented South Fork and then flows to Harlowton, Lavina, Roundup and Delphia before reaching the figure 1 east edge (north of center). East of figure 1 the Musselshell River turns to flow in a north direction to join the east oriented Missouri River. The unnamed northeast oriented tributary north of Sweet Grass Creek and flowing from the Crazy Mountains to join the Musselshell River near Harlowton is the American Fork. The unnamed east-northeast oriented Musselshell River tributary north of Melville and between Sweet Grass Creek and the American Fork is Fish Creek, which joins the Musselshell River near Ryegate. The unnamed northeast oriented Musselshell River south of Fish Creek is Big Coulee Creek, which joins the Musselshell River near Lavina. The Fish Creek-Sweet Grass Creek drainage divide area this essay illustrates and discusses is the region located between Fish Creek and Sweet Grass Creek and includes the Big Coulee Creek headwaters area.

Looking at the big picture erosion history of the figure 1 map area the drainage routes shown developed as the deep Yellowstone and Missouri-Musselshell River valleys eroded headward from a deep “hole” in which a large North American ice sheet was deeply melting. The deep “hole” was located north and east of the figure 1 map area, which is located along the deep “hole’s” deeply eroded southwest wall. The east and northeast oriented valleys eroded headward from the deep “hole” to capture immense south and southeast oriented ice marginal floods flowing from western Canada across Montana. At that time mountain ranges in the figure 1 map area did not stand high above the surrounding regions and floodwaters could freely flow across the entire figure 1 map area. The Yellowstone River valley was the first deep valley to erode headward across the figure 1 map area and southeast and south oriented Yellowstone River tributary valleys began to erode headward from newly eroded Yellowstone River valley north wall. The southeast and south oriented Sweet Grass Creek valley was one of these tributary valleys eroding headward from the newly eroded Yellowstone River valley.

Closely following Yellowstone River headward erosion was headward erosion of the deep Musselshell River valley and its northeast oriented tributary valleys from what was then the actively eroding Missouri River valley (north of figure 1) and capturing the southeast and south oriented flood flow routes to the newly eroded Yellowstone River valley and its actively eroding tributary valleys. Northeast oriented Musselshell River tributary valleys eroded headward in sequence with each tributary valley capturing south and southeast oriented flood flow to the newly eroded tributary valley to the southeast (e.g. Fish Creek valley captured flood flow to the newly eroded Big Coulee valley, American Fork valley headward erosion captured flood flow to the newly eroded Fish Creek, and Musselshell River valley headward erosion captured flood flow to the newly eroded American Fork valley. However as will be seen in the topographic maps below headward erosion of the southeast oriented Sweet Grass Creek valley beheaded the northeast oriented Fish Creek valley and diverted flood flow moving across the present day Crazy Mountains region which had been captured by Musselshell River-Fish Creek valley headward erosion back to the newly eroded Yellowstone River valley. Volumes of flood water involve were immense and the deep valleys eroding headward into the region as this example illustrates were constantly changing the flood flow routes as they captured flood flow moving to adjacent deep valleys. American Fork valley and Musselshell River valley headward erosion and Crazy Mountains (and other mountain range) uplift, which was occurring as floodwaters flow across the region, ended all flood flow to the Fish Creek-Sweet Grass Creek drainage divide area.

Detailed location map for Fish Creek-Sweet Grass Creek drainage divide area

Figure 2: Detailed location map for Fish Creek-Sweet Grass Creek drainage divide area. United States Geological Survey map digitally presented using National Geographic Society TOPO software.

Figure 2 provides a more detailed location map for the Fish Creek-Sweet Grass Creek drainage divide area. County boundaries are shown and Sweet Grass County is labeled. Wheatland County is north of Sweet Grass County. Big Timber is the town near the figure 2 south edge (in Sweet Grass County) and the Yellowstone River flows in a northeast direction to Big Timber and then flows in a southeast direction to the figure 2 south edge. The green shaded area (west half of figure 2) shows regions of National Forest land, which are generally located in mountainous regions. In this case the mountains are the Crazy Mountains. Sweet Grass Creek originates in the Crazy Mountains and flows in a northeast direction to near Porcupine Butte (in Sweet Grass County northwest corner area). Near Porcupine Butte Sweet Grass Creek turns to flow in a southeast and south direction to join the Yellowstone River near the figure 2 south edge. North of Porcupine Butte is the northeast oriented American Fork, which also originates in the Crazy Mountains and which flows to the figure 2 north center edge where it joins the east-southeast oriented Musselshell River. Fish Creek originates just north of Porcupine Butte and flows in an east-northeast direction, with a jog to the southeast, to join the Musselshell River near Ryegate in the figure 2 northeast corner region.  Note how Fish Creek has several well-developed northeast oriented tributaries while Sweet Grass Creek to the southwest does not have any southwest oriented tributaries shown. This asymmetric drainage divide will be better seen in the topographic maps below. The unnamed southeast oriented Sweet Grass Creek tributary near Melville is Cayuse Creek, which will be seen in the topographic maps. Big Coulee Creek originates in the easternmost region of Sweet Grass County and flows in a northeast direction to join the Musselshell River just east of figure 2. The topographic maps and discussion below relate to the Fish Creek-Sweet Grass Creek drainage divide area between the Porcupine Butte region and the Big Coulee Creek headwaters area.

Fish Creek-Sweet Grass Creek drainage divide area west of Porcupine Butte

Figure 3: Fish Creek-Sweet Grass Creek drainage divide area west of Porcupine Butte. United States Geological Survey map digitally presented using National Geographic Society TOPO software.

Figure 3 provides a topographic map of the Fish Creek headwaters area near Porcupine Butte. The American Fork (Musselshell River) flows from the Crazy Mountains (seen along the figure 3 west margin) from the figure 3 southwest quadrant, in a northeast direction to the figure 3 northeast corner. Porcupine Butte is labeled and is located in the figure 3 southeast quadrant. Sweet Grass Creek flows in a north-northeast direction from the figure 3 south edge (west of center and then turns to flow in an east and southeast direction along the Porcupine Butte south flank to near the figure 3 southeast corner.  Fish Creek originates along the Porcupine Butte northwest flank and flows in a northeast and then east direction just north of Porcupine to the figure 3 east center edge. Note how a through valley links Sweet Grass Creek with the Fish Creek headwaters along the Porcupine Butte west flank. The figure 3 map contour interval is 50 meters. The through valley provides evidence of a former flood flow through route linking the Sweet Grass Creek valley with the Fish Creek valley and suggests headward erosion of the Sweet Grass Creek valley beheaded northeast oriented flood flow moving to the Fish Creek valley. The northeast oriented flood flow was coming from west of the present day Crazy Mountains where Musselshell River valley headward erosion had not yet captured south and southeast oriented floodwaters. This interpretation implies the Crazy Mountains were still emerging as a mountain range and did not at that time have the elevations they have today.

Detailed map of Fish Creek-Sweet Grass Creek drainage divide area west of Porcupine Butte

Figure 4: Detailed map of Fish Creek-Sweet Grass Creek drainage divide area west of Porcupine Butte. United States Geological Survey map digitally presented using National Geographic Society TOPO software.

Figure 4 provides a detailed topographic map of the Fish Creek-Sweet Grass Creek drainage divide area west of Porcupine Butte. Sweet Grass Creek flows in a north-northeast direction from the figure 4 southwest corner and then turns to flow in an east and east-southeast direction to the figure 4 south edge (east of center). Porcupine Butte is labeled and is located in the figure 4 east half. Fish Creek originates in section 9 at the base of the Porcupine Butte northeast flank and flows in a northeast and east direction to the figure 4 east edge (just south of northeast corner). The American Fork (Musselshell River) can be seen flowing in a northeast direction across the figure 4 northwest corner. Note how in the northwest quadrant of section 19 (in figure 4 southwest quadrant) a road is located in a northeast oriented through valley linking the north-northeast oriented Sweet Grass Creek valley with the Fish Creek headwaters valley and also with a large north-oriented valley extending to the American Fork valley. Apparently at one time huge volumes of flood water flowed from the north-northeast oriented Sweet Grass Creek valley (which originates in the Crazy Mountains) to both the American Fork valley and the Fish Creek valley. At least some of the flood water also flowed in an east-southeast direction to the actively eroding Sweet Grass Creek valley, which was able to erode headward and to capture the north and northeast oriented flood water moving to the American Fork and Fish Creek valleys. Note also near the corner of section 10, 11, 14, and 15 through valleys eroded across Porcupine Butte. Those through valleys were eroded by southeast oriented floodwaters prior to headward erosion of the deep Fish Creek and American Fork valleys from the actively eroding Musselshell River valley head.

Sadie Creek-Cayuse Creek drainage divide area

Figure 5: Sadie Creek-Cayuse Creek drainage divide areaUnited States Geological Survey map digitally presented using National Geographic Society TOPO software.

Figure 5 illustrates the Sadie Creek-Cayuse Creek drainage divide area east of Porcupine Butte. Sweet Grass Creek (unlabeled) flows in a southeast direction across the figure 5 southwest corner (just west of Melville). Cayuse Creek flows in a southeast direction from the figure 5 west center edge to the figure 5 south edge (west of center) and south of figure 5 joins Sweet Grass Creek. Fish Creek flows in an east-southeast direction from the figure 5 west edge (just south of Wheatland-Sweet Grass County line) and then turns to flow in a northeast direction to near the figure 5 north center edge and then in an east direction along the figure 5 north margin before turning to flow north of figure 5. Sadie Creek is a northeast oriented Fish Creek tributary flowing across the figure 5 north center region. Note how Sadie Creek flows across an east-facing escarpment just before joining Fish Creek. The figure 5 map contour interval is 20 meters and in places the escarpment is more than 100 meters high.  East of Sadie Creek north oriented Gougley Creek and northeast oriented Spring Creek drain a northeast oriented escarpment surrounded basin to Fish Creek. The Cayuse Hills are located along the Fish Creek-Sweet Creek drainage divide in the figure 5 southeast quadrant and reach elevations greater than 1620 meters.  Note north of Melville the hill with the radio tower which reaches an elevation of 1713 meters. Between the radio tower and the Cayuse Hills is a north-south oriented through valley used by the highway linking the Sweet Grass Creek valley with the Sadie Creek valley. The through valley floor elevation at the drainage divide is between 1580 and 1600 meters. The through valley was probably eroded by south oriented flood flow prior to headward erosion of the Fish Creek valley. Fish Creek valley headward erosion beheaded the south oriented flood flow and flood waters on the north end of the beheaded flood flow route reversed flow direction to erode northeast oriented Sadie Creek valley and its north oriented unnamed tributary valley.

Detailed map of Fish Creek-Cayuse Creek drainage divide area

Figure 6: Detailed map of Fish Creek-Cayuse Creek drainage divide area. United States Geological Survey map digitally presented using National Geographic Society TOPO software.

Figure 6 provides a detailed topographic map of the Fish Creek-Cayuse Creek drainage divide area just west of the Sadie Creek headwaters, which was seen in less detail in figure 5 above. Cayuse Creek is labeled and flows in a southeast direction across the figure 6 southwest corner region. Fish Creek is also labeled and flows in a southeast and then northeast direction near the figure 6 north-center margin (this Fish Creek elbow of capture is seen in figure 5). Sadie Creek is also labeled and can be seen flowing in a northeast direction near the figure 6 east edge a short distance south of the figure 6 northeast corner. The hill labeled “Cayuse” is the figure 6 southeast quadrant is the hill with the radio seen in figure 5 (the radio tower is located just north of the “E” in “Cayuse” and the hilltop elevation is shown as 5621 feet—the figure 6 map contour interval is 20 feet). Note how just north of that radio tower hill there is a through valley linking the northeast oriented Sadie Creek headwaters valley with a southwest oriented Cayuse Creek tributary valley. The through valley floor elevation at the drainage divide is between 5380 and 5400 feet and elevations rise to 5490 on a hill a short distance to the northwest. In other words the through valley is at least 90 feet deep and represents a former northeast oriented flood flow route to what was at that time the actively eroding northeast oriented Sadie Creek valley. Headward erosion of a deeper southeast oriented Sweet Grass Creek-Cayuse Creek valley beheaded the northeast oriented flood flow and flood waters on the southwest end of the beheaded flood flow route reversed flow direction to erode the southwest oriented Cayuse Creek tributary valley. Other through valleys can be found in the figure 6 map area and probably indicate that the region was eroded by a constantly complex of anastomosing flood flow channels as headward erosion of the deep Sweet Grass Creek valley and the even deeper Fish Creek valleys captured the flood flow.

Antelope Creek-Dead Beaver Creek drainage divide area

Figure 7: Antelope Creek-Dead Beaver Creek drainage divide area. United States Geological Survey map digitally presented using National Geographic Society TOPO software.

Figure 7 illustrates the Antelope Creek-Dead Beaver Creek drainage divide area south and east of the figure 5 map area and includes overlap areas with figure 5. Sweet Grass Creek flows in a southeast direction across the figure 7 southwest quadrant. The Cayuse Hills extend as a northwest to southeast ridge of hills from the figure 7 northwest quadrant to the southeast quadrant. Northeast oriented drainage routes east and north of the Cayuse Hills are Fish Creek tributaries, with Cherry Creek (which is labeled) flowing to the figure 7 northeast corner. Antelope Creek flows in a northeast direction to the figure 8 north edge (east of center). While not visible in figure 7 the Antelope Creek headwaters are located west of the Cherry Creek headwaters (see figure 8 for a more detailed map). Note the east and northeast-facing escarpment along the Cayuse Hills east and northeast flank. Dead Beaver Creek is a southwest, southeast and south oriented Sweet Grass Creek tributary originating just west of the word “CAYUSE”.  The east oriented Cherry Creek headwaters and north oriented Antelope Creek headwaters are linked by a through valley with a southwest oriented Dead Beaver Creek tributary (an east-west oriented road intersects with a north oriented road and south oriented road near the through valley location). The figure 7 map contour interval in 20 meters and the through valley elevation at the drainage divide is between 1540 and 1560 meters. Elevations greater than 1600 meters can be found along the Cayuse Hills on either side, although southwest to northeast oriented through valleys can be found between those higher elevations. The multiple through valleys suggest multiple northeast oriented flowed to the actively eroding Fish Creek drainage basin before Sweet Grass Creek-Dead Beaver Creek valley headward erosion beheaded and reversed the flood flow to erode present day southwest oriented Dead Beaver Creek and Sweet Grass Creek tributary valleys.

Detailed map of Antelope Creek-Dead Beaver Creek drainage divide area

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

Figure 8 provides a detailed topographic map of the Antelope Creek-Dead Beaver Creek drainage divide area seen in less detail in figure 7 above. Dead Beaver Creek is labeled and originates near the north edge in the figure 8 northwest quadrant and flows in a southwest direction almost to the figure 8 west edge and then turns to flow in a southeast and south direction to the figure 8 south edge (west half). Antelope Creek is also labeled and flows in a north direction in the figure 8 northeast quadrant to the figure 8 north edge. Cherry Creek headwaters are located just north of the road crossing the figure 8 east center edge. The figure 8 contour interval is 20 feet and the southwest oriented Dead Beaver Creek headwaters originate at an elevation greater than 5300 feet. The southwest to northeast oriented through valley linking a southwest oriented Dead Beaver Creek tributary valley with the north oriented Antelope Creek valley has an elevation of between 4980 and 5000 feet at the drainage divide. Further south other slightly higher elevation southwest to northeast oriented through valley link the Dead Beaver Creek valley with the Cherry Creek valley. These multiple through valleys provide evidence of multiple northeast oriented flood flow channels to what was at one time the actively eroding  Fish Creek drainage basin. Headward erosion of the Sweet Grass Creek-Dead Beaver Creek valley captured the northeast oriented flow and diverted the floodwaters in a south direction to what was then the newly eroded Yellowstone River valley.

South Fork Big Coulee Creek-Sweet Grass Creek drainage divide area

Figure 9: South Fork Big Coulee Creek-Sweet Grass Creek drainage divide area. United States Geological Survey map digitally presented using National Geographic Society TOPO software.

Figure 9 illustrates the South Fork Big Coulee Creek-Sweet Grass Creek drainage divide south and east of the figure 7 map area and includes an overlap area with figure 7. The South Fork Big Coulee Creek flows in a northeast direction to the figure 9 northeast corner. Big Coulee Creek is a Musselshell River tributary. Note how the South Fork Big Coulee Creek originates on the northwest side of West Bench near the top of the northeast facing Cayuse Hills escarpment. The northeast and east oriented stream originating immediately to the southeast on West Bench is Whitney Creek, which east of the figure 9 map area joins Sixshooter Creek which turns to flow in a southeast direction to the southeast oriented Lake Basin, which drains to the Yellowstone River. Note the northwest to southeast oriented through valley at Gibson  (at base of escarpment north of West Bench) linking the northeast oriented South Fork Big Coulee Creek valley with the Whitney Creek valley. The figure 9 map contour interval is 20 meters and the through valley floor elevation is between 1380 and 1400 meters. Not seen in figure 9 are headwaters of Sixshooter Creek, which are located in the through valley between the South Fork Big Coulee CReek and Whitney Creek. The hill east of Gibson reaches an elevation of 1473 meters, meaning the through valley is at least 73 meters deep. The through valley was eroded  by southeast oriented flood flow moving to the newly eroded Lake Basin and Yellowstone River valleys prior to headward erosion of the northeast oriented South Fork Big Coulee valley. This through valley provides evidence of southeast oriented flood to the Yellowstone River valley on the northeast side of the Cayuse Hills upland region prior to headward erosion of the deep Musselshell River drainage basin, which beheaded the southeast oriented flood flow and diverted floodwaters in a northeast direction. Sweet Grass Creek can be seen flowing in a south direction near the west edge of the figure 9 southwest quadrant. Southwest oriented streams flowing from the northwest to southeast oriented Cayuse Hills upland are Sweet Grass Creek tributaries. Headward erosion of the Yellowstone River valley and its tributary Sweet Grass Creek valley captured flood flow moving across the Cayuse Hills upland with the resulting flood flow reversals eroding the southwest oriented Sweet Grass Creek tributary valleys.

Detailed map of South Fork Big Coulee Creek-East Fork Sweet Grass Creek drainage divide area

Figure 10: Detailed map of South Fork Big Coulee Creek-Sixshooter Creek drainage divide area. United States Geological Survey map digitally presented using National Geographic Society TOPO software.

Figure 10 provides a detailed topographic map of the South Fork Big Coulee Creek-Sixshooter Creek drainage divide near Gibson at the base of the Cayuse Hills escarpment. The South Fork Big Coulee Creek is labeled and flows in a north direction (down the Cayuse Hills escarpment) in the figure 10 southwest quadrant to near Gibson and then turns to flow in a northeast direction to the figure 10 north center edge. Sixshooter Creek is also labeled and originates near the figure 10 south edge, a short distance east of the north oriented South Fork Big Coulee Creek segment, and flows in a north and northeast direction before turning to flow in an east direction across the figure 10 southeast quadrant to the figure 10 east edge. Whitney Creek is the unlabeled stream south of Knob Hill near the figure 10 southeast corner. East of figure 10 Whitney Creek joins Sixshooter Creek, which then flows to the Lake Basin, which drains to the Yellowstone River. The through valley just east of Gibson linking the South Fork Big Coulee Creek valley with the Sixshooter Creek valley crosses the Musselshell River-Yellowstone River drainage divide and was eroded by southeast oriented flood flow moving to the newly eroded Yellowstone River valley just prior to headward erosion of the deep northeast oriented South Fork Big Coulee Creek valley. The figure 10 map contour interval is 20 feet and the through valley floor elevation at the drainage divide is between 4540 and 4560 feet and the hill immediately to the north rises to 4842 feet with much higher elevations (as high as 5300 feet) being found on Sweet Grass Creek drainage divide to the south and west. In other words the through valley is today almost 300 feet deep although a case could be made that as much as 800 feet of bedrock material was stripped by southeast oriented floods moving across this region to the newly eroded Yellowstone River valley.

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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