Shoshone River-Greybull River drainage divide area landform origins in the Wyoming Bighorn Basin, USA

Authors


Abstract:

This essay uses topographic map evidence to interpret landform origins in the region between the Shoshone River and Greybull River in the Wyoming Bighorn Basin. The Shoshone River headwaters originate in the Absaroka Mountains and converge near Cody, Wyoming to form the northeast oriented Shoshone River, which flows across the northern Bighorn Basin to the north and north-northeast oriented Bighorn River. The Greybull River is located south of the Shoshone River and flows in a northeast direction into the Bighorn Basin and then turns to flow in an east-southeast and northeast direction to join the Bighorn River. Between the Shoshone and Greybull Rivers in the Bighorn Basin is northeast and east oriented Dry Creek, which also flows to the Bighorn River. The Shoshone River-Dry Creek and the Dry Creek-Greybull River drainage divides are crossed by through valleys linking southeast and south oriented tributary valley with north and northwest oriented tributary valleys. The through valleys crossing the Dry Creek-Greybull River drainage divide were eroded by south and southeast oriented flood flow channels prior to headward erosion of the Dry Creek valley and the through valleys crossing the Shoshone River-Dry Creek drainage divide were eroded by south and southeast oriented flood flow channels prior to Shoshone River valley headward erosion. Floodwaters were derived from the western margin of a thick North American ice sheet and were flowing in south and southeast directions from western Canada to and across the Bighorn Basin. The thick ice sheet was located in a deep “hole” and as ice sheet melting progressed deep northeast oriented valleys eroded headward from the deep “hole” across Montana to capture the south and southeast oriented melt water floods. Headward erosion of the deep northeast oriented Yellowstone River valley beheaded a south oriented flood flow channel on the present day north oriented Bighorn River alignment. Floodwaters on the north end of the beheaded flood flow channel reversed flow direction to create the north oriented Bighorn River drainage route. Northeast oriented Bighorn River tributary valleys, including the Greybull River, Dry Creek, and Shoshone River valleys, then eroded headward from the newly reversed flood flow channel to capture yet to be beheaded and reversed flood flow moving in a south direction west of the actively eroding Yellowstone River valley head. Headward erosion of the deep Yellowstone River valley eventually captured all south and southeast oriented flood flow moving to the Bighorn 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 Shoshone River-Greybull River drainage divide area landform origins in the Wyoming Bighorn Basin. 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 Shoshone River-Greybull River drainage divide area landform evidence in the Wyoming Bighorn Basin will be regarded as evidence supporting the “thick ice sheet that melted fast” paradigm.

Shoshone River-Greybull River drainage divide area location map

Figure 1: Shoshone River-Greybull 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 a location map for the Shoshone River-Greybull River drainage divide area in the Wyoming Bighorn Basin. The Montana-Wyoming state line is located along the north edge of figure 1. The Bighorn River flows in a north direction from Wind River Canyon south of Thermopolis (near south center edge of figure 1) to the north center edge of figure 1 (south of Thermopolis the Bighorn River is known as the Wind River, which can be seen flowing in a southeast direction across the southeast corner of figure 1 before making an abrupt turn to flow in a north direction through Wind River Canyon to the Bighorn Basin). North of figure 1 the Bighorn River turns to flow in a north-northeast direction to join the northeast oriented Yellowstone River. East of the Bighorn River are the Bighorn Mountains, which form the Bighorn Basin eastern boundary. South of the Bighorn Basin are the Owl Creek Mountains and west of the Bighorn Basin is the Absaroka Range. Shoshone River headwaters are located in the Absaroka Range and the North Fork Shoshone River flows in an east direction to join the northeast oriented South Fork Shoshone River at Buffalo Bill Reservoir and to form the northeast oriented Shoshone River, which then joins the north oriented Bighorn River. Dry Creek is a northeast and east oriented tributary joining the Bighorn River near Greybull, Wyoming. The Greybull River originates near Francs Peak, where the Absaroka Range and Owl Creek Mountains meet, and flows in a northwest, east, northeast, east-southeast, and northeast direction to join the Bighorn River also near the town of Greybull. The Shoshone River-Greybull River drainage divide area in the Bighorn Basin investigated in this essay is south of the Shoshone River, north of the Greybull River, west of the Bighorn River, and east of the highway between Cody and Meeteetse. A separate essay illustrates and describes the South Fork Shoshone River-Greybull River drainage divide area west of the highway between Cody and Meeteetse.

Today the Bighorn Basin drains in a north direction to the northeast oriented Yellowstone River, which eventually joins the Missouri River near the Montana-North Dakota border. However, the Bighorn River alignment was established by a south oriented flood flow channel before a flood flow reversal created the present day north oriented drainage routes. Floodwaters were derived from the western margin of a thick North American ice sheet and flowed in south and southeast directions from western Canada to and across the region seen in figure 1. At that time the Bighorn Mountains, Owl Creek Mountains, Absaroka Range, and other regional mountain ranges had not yet emerged and floodwaters could freely flow across what are today high mountain ranges. The thick ice sheet created a deep “hole” in the North American continent by a combination of deep glacial erosion and of crustal warping that gradually raised mountain ranges along the deep “hole” southwest rim and elsewhere. Mountain ranges seen in figure 1 were uplifted as floodwaters flowed across them and as deep valleys eroded headward into them to capture the massive south and southeast oriented flood flow. A south oriented flood flow channel eroded Wind River Canyon into the rising Owl Creek Mountains until the Bighorn Basin flood flow reversal took place. The flood flow reversal occurred when ice sheet melting progressed to the point that space in the southern end of the deep “hole” was opened up permitting deep northeast oriented valleys to erode headward across the south and southeast oriented melt water floods in eastern and central Montana. Headward erosion of the deep northeast oriented Yellowstone River valley beheaded a major south oriented flood flow channel supplying floodwaters to the south oriented flood flow channel on the present day north oriented Bighorn River alignment. Floodwaters on the north end of the beheaded flood flow channel reversed flow direction to create the north oriented Bighorn River drainage route. Deep northeast oriented valleys then eroded headward from the newly reversed flood flow channel to capture south and southeast oriented flood flow from west of the actively eroding Yellowstone River valley head. In addition the reversed flood flow channel also captured southeast oriented flood flow channels such as the southeast oriented Wind River headwaters. In time Yellowstone River valley headward erosion north of figure 1 captured all south and southeast oriented flood flow while Absaroka Range emergence created what is today a major topographic barrier.

Detailed location map for Shoshone River-Greybull River drainage divide area

Figure 2: Detailed location map Shoshone Rive-Greybull River 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 Shoshone River-Greybull River drainage divide area in the Wyoming Bighorn Basin. The green area in the northeast corner of figure 2 is National Forest land located in the Bighorn Mountains. The Bighorn River flows in a north direction from the south edge of figure 2 (near southeast corner) to the towns of Basin and Greybull and then to Bighorn Lake (Reservoir), which straddles the north edge of figure 2. The Shoshone River flows in a northeast direction from the west edge of figure 2 (south half) to the towns of Cody, Powell, and Lovell before joining the Bighorn River at Bighorn Lake. Figure 2 illustrates many irrigation canals, which should not be confused with natural drainage routes. Note north-northwest and north oriented tributaries flowing to the Shoshone River including Foster Gulch and Coon Creek. The Greybull River (labeled “River” in figure 2) flows in a northeast, east-southeast, and northeast direction from the south edge of figure 2 (west of center) to join the Bighorn River a short distance south of Greybull. Dry Creek is an east-northeast and east oriented stream located just north of the Greybull River and flows from the Dry Creek Basin (in southwest quadrant of figure 2) to join the Bighorn River just north of Greybull. Labeled Dry Creek tributaries include northeast oriented South Fork, northeast and east oriented Oregon Coulee, and southeast oriented Red Paint Draw. Note south-southeast oriented Dry Creek tributaries between the town on Emblem and the Bighorn River and south-southeast and east oriented Little Dry Creek, which joins the Bighorn River just north of Dry Creek. These south-southeast oriented streams are aligned with the north-northwest oriented Shoshone River tributaries and provide evidence of multiple south-southeast oriented flood flow channels that crossed what is now the Shoshone River-Dry Creek drainage divide prior to headward erosion of the northeast oriented Shoshone River valley. Note southwest oriented tributaries to the Bighorn River from the Bighorn Mountains. These barbed tributaries are also evidence of the south oriented flood flow routes that once crossed the region.

Sand Draw-Bighorn River drainage divide area

Figure 3: Sand Draw-Bighorn River drainage divide area. United States Geological Survey map digitally presented using National Geographic Society TOPO software.

Figure 3 provides a topographic map of the Sand Draw-Bighorn River drainage divide area. The Bighorn River flows in a north direction along and across the east edge of figure 3. Note in the northeast quadrant of figure 3 how the Bighorn River has eroded a water gap across the southeast end of northwest-to-southeast oriented Little Sheep Mountain (“Mountain” in figure 3), which probably is an anticlinal structure. A much deeper water gap has been eroded across the larger Sheep Mountain structure south of figure 3. These water gaps provide evidence the Bighorn River route was established at a time when either the structures were buried in material that has since been removed or that crustal warping raised the structures after the Bighorn River route had been established. The Bighorn River route was established as a south oriented flood flow channel, although it was later reversed to become a north oriented flood flow channel. Evidence of diverging and converging flood flow channels can be seen along the road east of the Bighorn River from Red Flat to the north edge of figure 3. Sand Draw (“Draw” in figure 3) drains in a north-northwest direction from near the center of figure 3 (near highway) to the north edge of figure 3 (west of center) and then to the Shoshone River. Note how north-northwest oriented Sand Draw and other north-northwest drainage routes are linked by through valleys with south-southeast oriented headwaters of a southeast, north, and southeast oriented stream flowing to the north oriented Bighorn River as a barbed tributary (south of Spence Dome Oil Field). The map contour interval for figure 3 is 20 meters and some of the through valleys are defined by as many as four contour lines on a side suggesting the through valleys may be as much as 60 meters deep. Some through valleys may be defined by dipping beds associated with regional geologic structures, but the through valleys are also water-eroded features. South-southeast oriented flood flow moved across the Sand Draw-Bighorn River drainage divide before Shoshone River valley headward erosion north of figure 3 beheaded the south-southeast oriented flood flow. Note how many Bighorn River tributaries seen in figure 3 join the Bighorn River as barbed tributaries. These barbed tributaries are at least to some extent relics of the converging south oriented flood flow channels that once crossed the region, although a case can be made for structural control as well.

Detailed map of Sand Draw-Bighorn River drainage divide area

Figure 4: Detailed map of Sand Draw-Bighorn River drainage divide area. United States Geological Survey map digitally presented using National Geographic Society TOPO software.

Figure 4 provides a detailed topographic map of the Sand Draw-Bighorn River drainage divide area seen in less detail in figure 3. The Bighorn River flows in a north-northwest direction near the east edge of figure 4. East Sand Draw drains in a north-northwest direction to the north edge of figure 4 (near northwest corner). North of figure 4 East Sand Draw drains to north-northwest oriented Sand Draw, which then drains to the northeast oriented Shoshone River. Note how East Sand Draw is linked by a well-defined north-to-south oriented through valley with a south-southeast, southeast, and south oriented stream valley, which south and east of figure 4 drains to the north oriented Bighorn River as a barbed tributary. The map contour interval for figure 4 is 20 feet and the through valley floor elevation (at the drainage divide) is between 4360 and 4380 feet. Elevations along the through valley west side rise to 4627 feet and on the east side to more than 4500 feet suggesting the through valley is at least 120 feet deep. While probably defined by the regional geologic structures the through valley also is a water-eroded feature and was eroded by south-southeast oriented flood flow prior to headward erosion of the northeast oriented Shoshone River valley north of figure 4. Other north-northwest to south-southeast oriented through valleys cross the region in figure 4 and provide evidence of diverging and converging flood flow channels such as are found in a flood eroded anastomosing channel complex. Flood flow across this region was in a south direction until headward erosion of the Shoshone River beheaded the flood flow channels. At that time floodwaters on north-northwest ends of beheaded flood flow channels reversed flow direction to create north-northwest oriented Shoshone River tributary drainage routes. Shoshone River valley headward erosion probably occurred shortly after the reversal of flood flow that created the north oriented Bighorn River drainage route.

Coon Creek-Dry Creek drainage divide area

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

Figure 5 illustrates the Coon Creek-Dry Creek drainage divide area south and west of figure 3 and includes a small overlap area with figure 3. Dry Creek flows in an east-northeast and east direction across the southeast corner of figure 5 and is joined by east oriented Horse Creek near the southeast corner of figure 5. Note in the southeast quadrant of figure 5 multiple south-southeast oriented streams flowing to east oriented Horse and Dry Creeks. Emblem Draw is the labeled south-southeast oriented Dry Creek tributary seen near the east center edge of figure 5. North of Emblem Draw is north and north-northwest oriented Foster Gulch (“Gulch” in figure 5), which north of figure 5 drains to the Shoshone River. West of Foster Gulch is north-northwest oriented Sand Draw (different from the Sand Draw in figures 3 and 4), which north of figure 5 turns to drain in a north direction to the Shoshone River. West of Sand Draw is north oriented Coon Creek, which originates in the south center region of figure 5 and which north of figure 5 flows to the Shoshone River. West of Coon Creek is north, northeast, and north oriented Whistle Creek. Note how northwest oriented Coon Creek tributaries are linked by shallow through valleys with southeast oriented Horse Creek tributaries. The map contour interval for figure 5 is 20 meters and the deeper through valley floor elevations are between 1380 and 1400 meters. Elevations to the north and east (and seen in figure 5) of the deeper through valleys rise to at least 1460 feet with much higher elevations being found on Little Sheep Mountain further to the east and north. Elevations greater than 1500 meters can be seen in figure 5 near the south edge (near the county line). The figure 5 elevations suggest the deeper through valleys may be as much as 60 meters deep and more distant elevations suggest the through valleys may be deeper. Whatever their depths the through valleys were eroded by southeast oriented flood flow moving to the east oriented Dry Creek valley at a time when the north oriented Coon Creek valley did not exist (and when the Shoshone River valley north and west of figure 5 did not exist). Headward erosion of the Shoshone River valley north of figure 5 beheaded a south oriented flood flow channel on the present day north oriented Coon Creek alignment. Floodwaters on the north end of the beheaded flood flow channel reversed flow direction to create the north oriented Coon Creek drainage route. Headward erosion of the northeast oriented Whistle Creek valley segment from a reversed flood flow channel on the north oriented Whistle Creek alignment next captured the southeast oriented flood flow channels. Note the southeast oriented Whistle Creek tributaries near the west edge of figure 5.

Detailed map of Foster Gulch-Emblem Draw drainage divide area

Figure 6: Detailed map of Foster Gulch-Emblem Draw 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 Foster Gulch-Emblem Draw drainage divide area seen in less detail in figure 5. Foster Gulch (“Gulch” in figure 6) drains in a north direction from section 35 (east of center of figure 6) to the north edge of figure 6 (east of center) and north of figure 6 drains to the Shoshone River. Sand Draw (different from the Sand Draw in figures 3 and 4) originates in section 33 (west of center of figure 6) and drains in a north-northeast and northwest direction to the north edge of figure 6 (near northwest corner) and north of figure 6 drains to the Shoshone River. Emblem Draw is located south of the Foster Gulch headwaters and drains in a south-southeast direction to the south edge of figure 6 (east of center) and south of figure 6 drains to Dry Creek. Note in section 35 a north-to-south oriented through valley linking the north oriented Foster Gulch valley with a south oriented Emblem Draw tributary valley. In section 34 a broader through valley links a north oriented Foster Gulch tributary valley with the south-southeast oriented Emblem Draw headwaters valley. The map contour interval for figure 6 is 20 feet and the through valley floor elevations are between 4580 and 4600 feet. Elevations rise to 4756 feet near the southwest corner of figure 6. Elevations rise to more than 4680 feet near the northeast corner of section 26. These elevations suggest the through valleys are at least 80 feet deep. The through valleys provide evidence of diverging and converging south oriented flood flow channels that once crossed the region. At that time the northeast oriented Shoshone River valley north of figure 6 did not exist. Headward erosion of the northeast oriented Shoshone River valley across south oriented flood flow channels captured the floodwaters and diverted the flood flow to what was then the newly reversed flood flow channel on the Bighorn River alignment. Floodwaters on north ends of beheaded flood flow channels reversed flow direction to create the north oriented Shoshone River tributary drainage routes.

Shoshone River-Dry Creek drainage divide area

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

Figure 7 illustrates the Shoshone River-Dry Creek drainage divide area west and south of figure 5 and there is no overlap area with figure 5. The northeast oriented Shoshone River can just barely be seen in the northwest corner of figure 7. Sage Creek is a north oriented tributary flowing from near the southwest corner of figure 7 to join the Shoshone River near the northwest corner of figure 7. Dry Creek is a northwest, west, northwest, and north oriented Shoshone River tributary in the northwest quadrant of figure 7 (and is a different Dry Creek from the Dry Creek, which flows to the Bighorn River). East-northeast oriented Dry Creek (the Dry Creek which flows to the Bighorn River) can just barely be seen in the southeast corner of figure 7. The east oriented stream flowing from near Mud Springs to the east edge of figure 7 is the North Fork Dry Creek, which joins Dry Creek east of figure 7. The Dry Creek Basin (“Dry” in figure 7) is located in the southeast quadrant of figure 7 and is drained by Dry Creek. North of figure 7 (and unseen in figure 7) is the McCullough Peaks area where elevations almost reach 2000 meters (the map contour interval for figure 7 is 20 meters). Unlike Sheep Mountain and Little Sheep Mountain and hogbacks surrounding the Oregon Basin in which the Loch-Katrine Bird Reservation is located (in figure 7) McCullough Peaks appears to be an erosional residual of what may have been horizontal strata that once covered the entire region. South and west of figure 7 is the Meeteetse Rim where elevations exceed 200 meters. The highway north of the Loch-Katrine Bird Reservation crosses the Sage Creek-North Fork Dry Creek drainage divide at an elevation of 1601 meters and is located in a northwest-to-southeast oriented through valley almost 400 meters deep. The through valley was eroded by southeast oriented flood flow, which was first captured by headward erosion of the east oriented Dry Creek valley. At that time the northeast oriented Shoshone River valley north and west of figure 7 did not exist. Headward erosion of the northeast oriented Shoshone River valley subsequently captured the southeast oriented flood flow. Floodwaters on north ends of the beheaded flood flow channels reversed flow direction to create the north oriented Sage Creek drainage route and the northwest, west, and north oriented Dry Creek (north) drainage route.

Dry Creek–Greybull River (east) drainage divide area

Figure 8: Dry Creek-Greybull River (east) drainage divide area. United States Geological Survey map digitally presented using National Geographic Society TOPO software.

Figure 8 provides a topographic map of the Dry Creek-Greybull River drainage divide area south of figure 3 and there is no overlap area with figure 3. The north oriented Bighorn River can be seen near Greybull in the northeast corner of figure 8. Dry Creek flows in an east-southeast and east direction from the north edge of figure 8 (north of Emblem Bench) to join the Bighorn River near Greybull. The Greybull River flows in an east and northeast direction from near the southwest corner of figure 8 to join the Bighorn River just south of Greybull. Table Mountain straddles the west edge of figure 8 and is located on the Dry Creek-Greybull River drainage divide. East of Table Mountain Gould Butte and Three Sisters are buttes located along the drainage divide. Note how Greybull River tributaries from the drainage divide are generally oriented in southeast or south-southeast directions while Dry Creek tributaries from the drainage divide are generally oriented in north or north-northwest directions. Through valleys between the buttes and other high points along the drainage divide link north oriented Dry Creek tributary valleys with south oriented Greybull River tributary valleys. For example a through valley between Three Sisters and Gould Butte links a northwest oriented Dry Creek tributary valley with a southeast oriented Greybull River tributary valley. The map contour interval is 20 meters and that through valley floor elevation is between 1280 and 1300 meters. Three Sisters and Gould Butte each rise to at least 1340 meters suggesting the through valley is at least 40 meters deep. The northeast oriented Greybull River valley probably eroded headward from the newly reversed flood flow channel on the Bighorn River alignment to capture yet to be beheaded and reversed south and southeast oriented flood flow west of the Bighorn River flood flow channel. The through valleys were eroded by southeast oriented flood flow moving to the newly eroded northeast oriented Greybull River valley prior to headward erosion of the east oriented Dry Creek valley. Headward erosion of the Dry Creek valley beheaded the southeast oriented flood flow channels and floodwaters on northwest and north ends of beheaded flood flow routes reversed flow direction to create northwest and north oriented Dry Creek tributary drainage routes.

Dry Creek-Greybull River (west) drainage divide area

Figure 9: Dry Creek-Greybull River (west) drainage divide area. United States Geological Survey map digitally presented using National Geographic Society TOPO software.

Figure 9 illustrates the Dry Creek-Greybull River (west) drainage divide area and is located west and slightly south of figure 8 and includes overlap areas with figure 8. Dry Creek flows in an east and east-northeast direction near the north edge of the northwest quadrant of figure 9. The Greybull River flows in a northeast, east-southeast, and east direction from the west edge of figure 9 (south half) to the east edge of figure 9 (south of center). YU Bench (“Bench” in figure 9) straddles the west edge of figure 9 and is located along the Dry Creek-Greybull River drainage divide. Table Mountain is located in the northeast corner of figure 9 and is also located along the Dry Creek-Greybull River drainage divide. Emblem Bench is located along the Dry Creek valley in the north center area of figure 9 and forms the Dry Creek-Greybull River drainage divide between YU Bench and Table Mountain. The map contour interval for figure 9 is 20 meters. Elevations on Emblem Bench near the west end of Table Mountain are less than 1380 meters and elevations on the west end of Table Mountain rise to 1440 meters. Emblem Bench elevations rise to the west and are more than 1460 meters near the east end of YU Bench while elevations on the east end of YU Bench exceed 1560 meters. These elevations suggest there may be a sloping through valley between YU Bench and Table Mountain linking the Dry Creek valley with the Greybull River valley, although the benches also have many characteristics associated with stream terraces. Depending on which elevations are used the sloping through valley could be as much as 100 meters deep. The sloping through valley was eroded by east or east-southeast oriented flood flow moving to what was then the newly eroded Greybull River valley. Headward erosion of the east-northeast oriented Dry Creek valley captured the flood flow leaving Emblem Bench as evidence of the former flood flow channel floor. The Table Mountain and YU Bench surfaces probably were formed at an earlier time in a similar manner as floodwaters deeply eroded sediments that had been filling the Bighorn Basin.

South Fork Dry Creek-Greybull River drainage divide area

Figure 10: South Fork Dry Creek-Greybull River drainage divide area. United States Geological Survey map digitally presented using National Geographic Society TOPO software.

Figure 10 provides a topographic map of the South Fork Dry Creek-Greybull River drainage divide area west and south of figure 9 and includes a small overlap area with figure 9. The Greybull River flows in a northeast direction from the south center edge of figure 10 to the east edge of figure 10 (north half). YU Bench is the smooth surfaced upland on the northwest side of the Greybull River valley extending to the northeast corner of figure 10. The northeast end of Meeteetse Rim (“RIM” in figure 10) can be seen on the northwest side of the Greybull River valley near the south edge of figure 10. The South Fork Dry Creek flows in an east, north, east, and northeast direction from the west edge of figure 10 (south of center) to the north edge of figure 10 (east of center). An east, northeast, and north oriented South Fork Dry Creek tributary flows from near the southwest corner of figure 10 to a water gap near the town of Bad Cabin and then to the South Fork. The water gap appears to be eroded across a hogback ridge, which suggests the presence of an underlying geologic structure. Note other water gaps and wind gaps eroded across that hogback ridge. The water gaps and wind gaps provide evidence that the stream valleys were eroded headward from a surface higher in elevation than the highest points on the hogback ridge. Note southeast oriented Greybull River tributary valleys located southwest of the YU Bench southwest end, which were eroded by southeast oriented flood flow moving to the newly eroded and deep northeast oriented Greybull River valley. The map contour interval for figure 10 is 20 meters and the Meeteetse Rim northeast end elevation is 100 meters higher than the YU Bench southwest end elevation. YU Bench is probably the floor of a broad southeast oriented flood flow channel captured by Greybull River valley headward erosion and subsequently beheaded by headward erosion of the South Fork Dry Creek valley and its tributary valleys. North and northwest oriented South Fork Dry Creek valley segments and tributary valley segments were probably eroded by reversals of flood flow on north and northwest ends of the beheaded flood flow routes.

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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