Abstract:

This essay uses topographic map evidence to interpret landform origins in the region between north oriented Clarks Fork of the Yellowstone River and north oriented Pryor Creek in south central Montana. Pryor Creek is a northwest, north, and north-northeast oriented Yellowstone River tributary originating the Pryor Mountains, which are located south of Billings, Montana. The Clarks Fork of the Yellowstone River is a southeast and north-northeast oriented Yellowstone River tributary originating in the Beartooth Mountains and joining the Yellowstone River west of Billings, Montana. East of Pryor Creek is the north and north-northeast oriented Bighorn River, which flows across the Wyoming Bighorn Basin to join the northeast oriented Yellowstone River north and east of the Pryor Mountains. While the Clarks Fork Yellowstone River-Pryor Creek drainage divide area is today dominated by north oriented drainage routes, those drainage routes are located in valleys which were initiated as anastomosing south oriented flood flow channels prior to headward erosion of the deep northeast oriented Yellowstone River valley, which beheaded the south oriented flood flow channels in sequence from east to west. A maze of through valleys links the north oriented drainage routes and provides evidence of former south oriented flood flow channels. Floodwaters were derived from a rapidly melting thick North American ice sheet and were flowing in south and southeast directions from the ice sheet’s west margin in western Canada across Montana and into Wyoming. The ice sheet was located in a deep “hole” which was formed by deep glacial erosion and by ice sheet related crustal warping. Ice sheet related crustal warping was responsible for uplift of the Pryor Mountains and of other regional mountain ranges. The deep northeast oriented Yellowstone River valley eroded headward across the south and southeast ice marginal melt water floods from space in the deep “hole” the rapidly melting ice sheet had formerly occupied. Floodwaters on north ends of the beheaded flood flow channels reversed flow direction and captured yet to be beheaded south and southeast oriented flood flow from flood flow channels further to the west.  The massive flood flow reversals were aided by uplift of the Pryor Mountains and other areas as floodwaters flowed across the region.

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 Clarks Fork of the Yellowstone River-Pryor Creek drainage divide area landform origins in south central 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 Clarks Fork of the Yellowstone River-Pryor Creek drainage divide area landform evidence in south central Montana will be regarded as evidence supporting the “thick ice sheet that melted fast” paradigm.

Clarks Fork of the Yellowstone River-Pryor Creek drainage divide area location map

Figure 1: Clarks Fork of the Yellowstone River-Pryor 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 Clarks Fork of the Yellowstone River-Pryor Creek drainage divide area in south central Montana. Yellowstone National Park is the yellow shaded area in the southwest corner of figure 1 (west half). The Montana-Wyoming state line extends in a west to east direction along the north edge of Yellowstone National Park. The Beartooth Mountains are not labeled in figure 1, but extend eastward from the northeast corner of Yellowstone National Park along the Montana-Wyoming border to the north-northeast oriented Clarks Fork of the Yellowstone River segment east of Red Lodge, Montana. The Yellowstone River flows from the Yellowstone National Park area in Wyoming in a northwest direction and once in Montana turns to flow in a northeast direction to Livingston and Big Timber before turning to flow in an east-southeast direction to Columbus and then turning to flow in a northeast direction to Billings and the figure 1 northeast corner. The Clarks Fork of the Yellowstone River originates north of Cooke City, Montana (near northeast corner of Yellowstone National Park) and flows in a southeast direction into Wyoming before turning to flow in a northeast and north-northeast direction around the east end of the Beartooth Mountains to join the Yellowstone River near Laurel, Montana. Pryor Creek is located south of Billings and flows in a north-northeast direction through Pryor, Montana to join the Yellowstone River near Huntley. The Clarks Fork of the Yellowstone River –Pryor Creek drainage divide area illustrated and discussed in this essay is east of the north-northeast oriented Clarks Fork of the Yellowstone River segment north of Bridger, Montana, south of the Yellowstone River segment between Laurel and Huntley, and west and north of Pryor Creek.

Looking at the big picture erosion history the figure 1 drainage routes developed as immense south and southeast oriented melt water floods flowed across the region and crustal warping raised the Beartooth Mountains, Pryor Mountains, and Bighorn Mountains (in southeast corner of figure 1) at approximately the same time as the deep Yellowstone River valley eroded headward from a deep “hole” in which a large North American ice sheet was rapidly 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 Yellowstone River valley and its northeast oriented tributary valleys were eroded headward from the deep “hole” to capture immense south and southeast oriented ice marginal floods flowing from western Canada across Montana and into Wyoming. Initially mountain ranges in the figure 1 map area, including Beartooth, Pryor, and Bighorn Mountains, did not stand high above the surrounding regions and floodwaters could freely flow across the entire figure 1 map area. Ice sheet related crustal warping raised the Beartooth, Pryor, and Bighorn Mountains as the immense melt water floods flowed across the region. As the Beartooth, Pryor, and Bighorn Mountains were uplifted deep valleys or flood flow channels were carved between the rising mountain masses as floodwaters flowed south across the present day Bighorn Basin. The southeast oriented Clarks Fork of the Yellowstone River segment was carved headward into the rising mountain mass by the south and southeast oriented floodwaters. Headward erosion of the much deeper northeast oriented Yellowstone River valley from space in the deep “hole” being opened up by ice sheet melting beheaded and reversed the south oriented flood flow channels to erode the north oriented valleys seen today. South oriented flood flow channels moving floodwaters to the present day Bighorn Basin were beheaded and reversed one at a time and in sequence from east to west. Newly beheaded and reversed flood flow channels captured immense quantities of yet to be beheaded flood flow from flood flow channels west of the Yellowstone River valley head and with this captured flood flow were able to erode significant north oriented valleys.

In the case of the figure 1 headward erosion of the deep northeast oriented Yellowstone River valley beheaded and reversed south oriented flood flow that eroded the north oriented Bighorn River valley, which captured south and southeast oriented flood flow from further to the west. Some of the southeast oriented flood flow was moving across the present day Beartooth Mountains and was captured by headward erosion of the northeast oriented Shoshone River valley (which eroded headward from the actively eroding north oriented Bighorn River valley in Wyoming and which had been reversed by headward erosion of the much deeper northeast Yellowstone River valley). Subsequently continued headward erosion of the deep northeast oriented Yellowstone River valley beheaded and reversed south and southeast oriented flood flow to create the north-northeast oriented Pryor Creek valley. For a time headward erosion of the actively eroding Pryor Creek valley captured southeast oriented flood flow moving to the newly eroded northeast oriented Shoshone River valley. However, headward erosion of the deep Yellowstone River valley beheaded and reversed the south and southeast oriented flood flow so as to initiate headward erosion of the deep north-northeast oriented Clarks Fork of the Yellowstone River valley, which then captured all south and southeast oriented flood flow moving to the actively eroding Pryor Creek valley and to the newly eroded Shoshone River valley. Capture of the southeast oriented flood flow ended Pryor Creek valley headward erosion and resulted in the reversal of flood flow on some of the beheaded southeast oriented flood flow channels to erode what are today northwest oriented Clarks Fork of the Yellowstone River tributary valleys.

Detailed location map for Clarks Fork Yellowstone River-Pryor Creek drainage divide area

Figure 2: Detailed location map of the Clarks Fork Yellowstone River-Pryor 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 Clarks Fork Yellowstone River-Pryor Creek drainage divide area in south central Montana. The entire figure 2 map area is located in south central Montana with the Wyoming state line being located a short distance south of the figure 2 south edge. Green shaded areas are National Forest lands, which are generally located in mountainous regions. The green shaded area in the southwest corner region of figure 2 is located in the Beartooth Mountains. The smaller green shaded area in the southeast quadrant of figure 2 is located in the Pryor Mountains. The brown shaded in the east half of figure 2 is the Crow Indian Reservation with the Bighorn Canyon National Recreation Area being the brighter brown shaded area adjacent to and within the Crow Indian Reservation. The Bighorn Canyon Recreation Area is located along the north-northeast and northeast oriented Bighorn River, which flows across the southeast corner of figure 2.  County names and boundaries are shown and sections of Sweet Grass, Stillwater, Yellowstone, Carbon, and Big Horn Counties can be seen. The Yellowstone River flows in an east-southeast direction from the west edge of figure 2 (north half in Sweet Grass County to the Stillwater-Carbon County border and then flows in a northeast direction to Laurel, Billings, and the northeast corner region of figure 2 and is closely followed by Interstate highway 90 and the railroad labeled on figure 2 as Burlington Northern.  Clarks Fork of the Yellowstone River flows in a north-northeast direction from the south edge of figure 2 (slightly west of center) to join the Yellowstone River near Laurel. Two Bear Ridge is a labeled feature located east of the Clarks Fork and west of the Crow Indian Reservation. Five Mile Creek and its Middle and North Forks are labeled Clarks Fork tributaries located between Two Bear Ridge and the Crow Indian Reservation. South of Two Bear Ridge there is an unlabeled northwest oriented Clarks Fork tributary important to this essay. That unlabeled tributary is Bluewater Creek, which is better seen in figure 9 below. Pryor Creek originates in the Crow Indian Reservation a short distance north of the Pryor Mountains National Forest area and flows in a northwest, north, and north-northeast direction to join the Yellowstone River near Huntley (northeast of Billings). Pryor Creek tributaries from the west are not labeled but flow in southeast, east, and northeast directions. This Clarks Fork of the Yellowstone River-Pryor Creek drainage divide area essay begins with a brief look at the region between the Yellowstone River and Pryor Creek downstream from Laurel. In that region north-northwest oriented Spring Creek and northeast and northwest oriented Blue Creek flow to the northeast oriented Yellowstone River as barbed tributaries. Next the essay focuses on the region between the Clarks Fork of the Yellowstone River and the Pryor Creek headwaters, which are located in the Pryor Mountain region.

Yellowstone River-Pryor Creek drainage divide area

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

Figure 3 provides a topographic map of the Yellowstone River-Pryor Creek drainage divide area near Billings, Montana. Billings is the city located in the northwest quadrant of figure 3. The Yellowstone River flows in a northeast direction along the southeast side of Billings. Butte Creek is a labeled northwest oriented tributary flowing from the center region of figure 3 to join the northeast oriented Yellowstone River as a barbed tributary (just east of Billings). In the southwest quadrant of figure 3 Blue Creek (not labeled in figure 3) flows in a northeast and then northwest direction to join the Yellowstone River as a barbed tributary (just south of Billings). Note labeled northeast oriented Basin and Little Basin Creeks, which flow as tributaries to the northwest oriented Blue Creek segment. In the east half of figure 3 Pryor Creek flows in a northeast and north direction from the south edge of figure 3 (east of center) to near the northeast corner of figure 3. Note in the southeast corner area of figure 3 the northwest oriented tributaries flowing to northeast oriented Pryor Creek as barbed tributaries. Also note southeast oriented streams flowing to Pryor Creek as barbed tributaries from the west and northwest. The map contour interval for figure 3 is 20 meters and a close look at the Yellowstone River-Pryor Creek drainage divide reveals shallow northwest to southeast oriented through valleys linking northwest oriented Yellowstone River tributaries with southeast oriented Pryor Creek tributaries. Two such through valleys link the northwest oriented Butte Creek valley with valleys of east and southeast oriented streams flowing to northeast oriented Pryor Creek. The through valley floor elevations at the drainage divides are between 1100 and 1120 meters. A spot elevation immediately south of the southern through valley reads 1166 meters and elevations north of the northern through valley rise to more than 1200 meters (south of figure 3 elevations rise significantly higher than 1200 meters). These elevations suggest the through valleys are at least 80 meters deep and may have been deeper when eroded. These and similar through valleys are evidence of southeast oriented flood flow channels that crossed the region prior to headward erosion of the deeper northeast oriented Yellowstone River valley. Headward erosion of the northeast oriented Pryor Creek valley first captured the southeast oriented flood flow and diverted the flood flow to what was then the actively eroding Yellowstone River valley head, which was located north and east of figure 3. Floodwaters on northwest ends of the beheaded flood flow channels reversed flow direction to erode the northwest oriented Pryor Creek tributary valleys. Headward erosion of the Yellowstone River valley next captured the southeast oriented flood flow and floodwaters on northwest ends of the beheaded flood flow channels reversed flow direction to erode the northwest oriented Butte Creek valley.

Detailed map of Butte Creek-Pryor Creek drainage divide area

Figure 4: Detailed map of Butte Creek-Pryor Creek 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 Butte Creek-Pryor Creek drainage divide area seen in less detail in figure 3. Pryor Creek flows in a northeast direction across the southeast corner of figure 4. Butte Creek originates in the south center area of figure 4 and flows in a northwest direction to the northwest corner of figure 4. Note the northeast oriented tributary flowing from section 31 to join Butte Creek in section 29 and the northwest oriented tributary to that northeast oriented tributary. The two through valleys seen in figure 3 are better illustrated in figure 4 with the northeastern through valley located in the southwest quadrant of section 27 and the southwestern through valley located in the north half of section 33. The through valleys link the northwest oriented Butte Creek valley with southeast oriented Pryor Creek tributary valleys. The map contour interval for figure 4 is 20 feet and the floor elevation for the northeastern through valley at the drainage divide is between 3620 and 3640 feet. The floor elevation of the southwestern through valley at the drainage divide is between 3640 and 3660 feet. The Radio Tower in the south half of section 21 has an elevation of more than 3960 feet while elevations greater than 3800 feet can be seen where the line between sections 32 and 33 crosses the south edge of figure 4. Continuing further the southwest of figure 4 along the Yellowstone River-Pryor Creek drainage divide elevations rise and are considerably higher than 3960 feet. Floors of the through valleys are 300 feet lower than the elevation at the base of the adjacent Radio Tower. These are water eroded through valleys and were eroded as southeast oriented flood flow channels at a time when the deep Yellowstone River valley to the northwest did not exist. Headward erosion of the deep northeast oriented Yellowstone River valley from space in the deep “hole” being opened by the thick ice sheet melting captured the southeast oriented flood flow and diverted the flood waters to the deep “hole” the rapidly melting ice sheet had occupied.

Cottonwood Creek-Fourth of July Creek drainage divide area

Figure 5: Cottonwood Creek-Fourth of July Creek drainage divide area. United States Geological Survey map digitally presented using National Geographic Society TOPO software.

Figure 5 illustrates the Cottonwood Creek-Fourth of July Creek drainage divide area south and west of figure 3 and does not include an overlap area with figure 3. Pryor is the small town near the southeast corner of figure 5 and Pryor Creek flows in a northeast direction across the southeast corner of figure 5 near Pryor. Fourth of July Creek originates south of Stratford Hill (in northeast quadrant of figure 5) and flows in an east-southeast direction to join Pryor Creek near the east edge of figure 5. Macheta Creek is a northeast, southeast, and east oriented Pryor Creek tributary south of Fourth of July Creek. Plum Creek is a northeast, southeast, and northeast oriented Pryor Creek tributary between Fourth of July Creek and Macheta Creek. Cottonwood Creek originates just west of the Fourth of July Creek headwaters and flows in west, southwest, and northwest direction (at the base of the south-facing escarpment) to the northwest corner of figure 5. North and west of figure 5 Cottonwood Creek joins the north oriented Clarks Fork Yellowstone River. Note the north oriented Cottonwood Creek tributaries from the south and the escarpment-surrounded basin drained by the west and southwest oriented Cottonwood Creek headwaters segments. The escarpments surrounding that basin are what remains of an abandoned headcut, which was eroded headward by south and southeast oriented flood flow moving into what at that time was a deeper south oriented flood flow channel. Water falling over the retreating cliff face moved in southwest and southeast directions, although more water flowed in a southwest direction to join south oriented flood flow channels on alignments of what are today north oriented Clarks Fork Yellowstone River tributaries seen in the southwest corner region of figure 5. Also note how the Cottonwood Creek valley narrows toward the northwest corner of figure 5, suggesting the northwest oriented Cottonwood Creek valley segment flows through a water gap, which has been eroded across a hogback ridge.  The water gap was eroded by southeast oriented flood flow prior to reversal of flood flow on the Clarks Fork Yellowstone River alignment. The southeast oriented flood flow was moving to south oriented flood flow channels including one on the present day north oriented Pryor Creek alignment (south of figure 5 and seen in figures 7 and 9). Some of the southeast oriented flood flow was captured by headward erosion of the northeast oriented Pryor Creek valley, which also caused a reversal of flood flow on the Pryor Creek alignment south of figure 5. Subsequently Yellowstone River valley headward erosion beheaded and reversed flood flow on the Clarks Fork of the Yellowstone River alignment, which in turn reversed flood flow on the northwest oriented Cottonwood Creek segment alignment and created the Cottonwood Creek-Fourth of July Creek drainage divide and which also reversed flood flow on the alignments of the Clarks Fork tributaries seen in the southwest corner of figure 5.

Detailed map of Cottonwood Creek-Fourth of July Creek drainage divide area

Figure 6: Detailed map of Cottonwood Creek-Fourth of July 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 Cottonwood Creek-Fourth of July Creek drainage divide area seen in less detail in figure 5. Stratford Hill is located in section 2 (northeast quadrant of figure 2). Fourth of July Creek flows from sections 10 and 11 (south of Stratford Hill) in an east-southeast direction to the east edge of figure 6 (south half). Cottonwood Creek originates in sections 2 and 3, north of the Fourth of July Creek headwaters, but south of Stratford Hill, and flows in a southwest, west, and southwest direction along the base of the south-facing escarpments to section 18 where it turns to flow in a northwest direction. Note the north oriented tributary that joins Cottonwood Creek as a barbed tributary at the elbow of capture where Cottonwood Creek turns from flowing in a southwest direction to flowing in a northwest direction. The north oriented tributary valley alignment was originated as a south oriented flood flow channel formed by the convergence of southeast and southwest oriented flood flow channels. The southeast oriented flood flow channel eroded the valley, which today is used by the northwest oriented Cottonwood Creek segment. The southwest oriented flood flow channel received its water from southeast oriented flood flow moving across the southeast and south-facing escarpment seen in sections 5, 32, and 33. Floodwaters flowing across the escarpment face (probably in the form of a massive waterfall) primarily flowed in a southwest direction to the south oriented flood flow channel originating in section 18, although some of the flood water flowed across the Cottonwood Creek-Fourth of July Creek drainage divide in a southeast direction to a south oriented flood flow channel on the present day north oriented Pryor Creek alignment (east and south of figure 6).  While floodwaters were still moving in a southeast direction to the Pryor Creek alignment, the direction of flood flow on the Pryor Creek alignment was reversed from flowing in a south direction to flowing in a north and northeast direction to the newly eroded and much deeper northeast oriented Yellowstone River valley. Subsequently southeast oriented flood flow on the present day northwest oriented Cottonwood Creek segment alignment was reversed to flow to the newly reversed Clarks Fork of the Yellowstone River flood flow channel north and west of figure 6. Reversal of flood flow on the Cottonwood Creek alignment also reversed flood flow on what had been the south oriented flood flow channel originating in section 18. Reversal of flood flow in that flood flow channel eroded a north oriented Cottonwood Creek tributary valley on that former south oriented flood flow channel alignment.

North Fork Five Mile Creek-Willow Creek drainage divide area

Figure 7: North Fork Five Mile Creek-Willow Creek drainage divide area. United States Geological Survey map digitally presented using National Geographic Society TOPO software.

Figure 7 illustrates the North Fork Five Mile Creek-Willow Creek drainage divide area south and slightly west of figure 5 and includes an overlap area with figure 5. West Pryor Mountain is the forested upland straddling the south edge of the southeast quadrant of figure 7. Clarks Fork of the Yellowstone River can be seen meandering in its north-northeast oriented valley in the northwest corner of figure 7. The Middle Fork of Five Mile Creek originates on West Pryor Mountain, and flows in a west, northwest, and north-northwest direction before joining north-northwest oriented Five Mile Creek, which then flows to the north edge of figure 7 and which joins Clarks Fork Yellowstone River north of figure 7. Note Two Bear Ridge west of north-northwest oriented Five Mile Creek and how there is a through valley at the south end of Two Bear Ridge linking the north-northwest oriented Five Mile Creek valley with the northwest oriented Bluewater Creek valley, which crosses the southwest corner of figure 7. The through valley was eroded by south oriented flood flow moving around the west margin of what was probably a rising West Pryor Mountain mass before the reversal of flood flow that created the north oriented drainage routes seen today. Pryor Creek flows in a north direction from near the southeast corner of figure 7 to the Chief Plenty Coups Memorial State Monument where it turns to flow in a northeast direction to the east edge of figure 7. Macheta Creek joins Pryor Creek near the Chief Plenty Coups Memorial. Willow Creek is a north and northeast oriented Macheta Creek tributary. Note how there is a shallow, but broad, through valley linking north oriented Willow Creek headwaters with north-northwest and west oriented North Fork Five Mile Creek. The through valley was probably eroded when the flood flow direction on the Pryor Creek alignment was reversed to create a north oriented flood flow channel to the newly eroded and much deeper Yellowstone River valley, but before south oriented flood flow on the Clarks Fork alignment had been beheaded and reversed by Yellowstone River valley headward erosion. During that time interval south oriented flow in the west half of figure 7 was captured by the newly reversed and then north oriented Pryor Creek flood flow channel and the captured floodwaters moved in an east direction across the present day Five Mile Creek-Willow Creek drainage divide. Capture of the south oriented flood flow provided the water volumes required to erode the deep north oriented Pryor Creek valley.

Detailed map of North Fork Five Mile Creek –Willow Creek drainage divide area

Figure 8: Detailed map of North Fork Five Mile Creek-Willow Creek 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 North Fork Five Mile Creek-Willow Creek drainage divide seen in less detail in figure 7 above. The North Fork Five Mile Creek flows in a north-northwest direction in the figure 8 west half. Willow Creek flows in a north and northeast direction in the east half of figure 8. The map contour interval for figure 8 is 20 feet and the spot elevation near the south center edge of section 19 in figure 8 reads 4922 feet. South of figure 8 elevations rise on the north facing West Pryor Mountain slope and eventually exceed 6500 feet. North of section 19 on the line between sections 7 and 8 there is a hill with a spot elevation of 4972 feet. Between that hill and the south edge of figure 8 is a through valley linking the North Fork Five Mile Creek valley with the Willow Creek valley. A spot elevation on the through valley floor reads 4808 feet, which suggests the through valley is at least 164 feet deep. The through valley was eroded by south and southeast oriented flood flow in the west half of figure 8 moving in an east direction to the northeast oriented Willow Creek valley, which had eroded headward from what was at that time the newly reversed flood flow channel on the Pryor Creek alignment (which had been reversed to flow in a north direction). North of figure 8 elevations along the Clarks Fork-Pryor Creek drainage divide decrease even more to less than 4460 feet in the Cottonwood Creek-Fourth of July Creek drainage divide area seen in figure 6. The North Fork Five Mile Creek-Willow Creek through valley seen in figure 8 was eroded before the Cottonwood Creek-Fourth of July Creek through valley was eroded and was one of a sequence of through valleys eroded by south oriented floodwaters on the Clarks Fork alignment, which were captured by the newly reversed Pryor Creek flood flow channel and diverted to flow in a north and northeast direction to the actively eroding and deep Yellowstone River valley. In time Yellowstone River valley headward erosion beheaded the south and southeast oriented flood flow routes in the present day north oriented Clarks Fork valley. Flood waters on the north ends of the beheaded flood flow routes reversed flow direction to erode the north oriented Clarks Fork valley and the north oriented Clarks Fork tributary valleys, such as the North Fork Five Mile Creek valley.

Bluewater Creek-Pyror Creek drainage divide area at Pryor Gap

Figure 9: Bluewater Creek-Pryor Creek drainage divide are at Pryor Gap. United States Geological Survey map digitally presented using National Geographic Society TOPO software.

Figure 9 illustrates the Bluewater Creek-Pryor Creek drainage divide area at Pryor Gap and is located south of figure 7 and includes overlap areas with figure 7. The north oriented Clarks Fork of the Yellowstone River flows near the west edge of figure 9 to the northwest corner of figure 9. Bridger, Montana is the small town located near the west center edge of figure 9. Bowler Flats is located just north of the south center edge of figure 9 and the South Fork Bluewater Creek flows in a north-northwest direction from Bowler Flats to join the southwest and west oriented North Fork Five Mile Creek to form Bluewater Creek. Bluewater Creek then flows in a north-northwest, west, and northwest direction to join the Clarks Fork Yellowstone River just north of the northwest corner of figure 9. The upland region just south of the southeast quadrant of figure 9 is Big Pryor Mountain. The northwest oriented stream flowing to the east edge of figure 9 (just north of southeast corner), which turns to flow in a south direction to the south center edge of figure 9 (west of Big Pryor Mountain) is Sage Creek. South of figure 9 Sage Creek flows in a south-southeast direction to join the east-northeast oriented Shoshone River, which then joins the north oriented Bighorn River. The drainage divide between the north-northwest oriented Bluewater Creek valley and the south oriented Sage Creek is at Bowler Flats. The map contour interval is 50 meters and the Bowler Flats elevation is between 1450 and 1500 meters. West of Bowler Flats the Clarks Fork Yellowstone River is flowing in a north direction, while just a short distance to the east Sage Creek is flowing in a south direction. The south oriented Sage Creek valley segment is a former south oriented flood flow channel, which was captured by headward erosion of the deep Shoshone River valley, which eroded headward from the Bighorn River valley. The Bighorn River valley was initiated as a south oriented flood flow channel, but was subsequently beheaded and reversed by headward erosion of the much deeper northeast oriented Yellowstone River valley. The northwest oriented Sage Creek valley segment was eroded by a reversal of flood flow on what had originated as a southeast oriented flood flow channel to the south oriented flood flow channel on the Bighorn River alignment. West Pryor Mountain is located in the northeast quadrant of figure 9 and Pryor Gap is a prominent (and labeled) through valley on the southeast flank of West Pryor Mountain. Much of Pryor Gap is drained by Summit Creek, which flows in a northwest direction past Summit Creek Cave to enter the deep southwest to northeast oriented Pryor Gap valley. Once in the Pryor Gap valley Summit Creek is shown as splitting with some of the flow moving in a northeast direction to join north oriented Pryor Creek at the north end of the Pryor Gap valley with Pryor Creek then flowing in a north direction to the north edge of figure 9 (near northeast corner). The remaining Summit Creek water flows in a southwest direction to join Sage Creek and south oriented Section House Draw (at the point where Section House Draw joins Sage Creek and where Sage Creek turns from flowing in a northwest direction to flowing in a south direction). The through valley links the northeast oriented Pryor Creek valley with the south oriented Sage Creek valley and the through valley floor is such that Summit Creek water can flow in both directions. In other words, the deep Pryor Gap through valley links the north oriented Pryor Creek valley with the south oriented Sage Creek valley and also with the north-northwest oriented Bluewater Creek valley. What we are seeing is evidence of former diverging and converging south oriented flood flow channels, which were eroded into the rising Pryor Mountains region before the reversals of flood flow that created the north oriented Pryor Creek drainage system and the subsequent reversal of flood flow that created the north oriented Clarks Fork Yellowstone River drainage system.

Detailed map of Sage Creek-Pryor Creek drainage divide area at Pryor Gap

Figure 10: Detailed map of Sage Creek-Pryor Creek drainage divide area at Pryor Gap. United States Geological Survey map digitally presented using National Geographic Society TOPO software.

Figure 10 provides a detailed topographic map of the Sage Creek-Pryor Creek drainage divide area at Pryor Gap. Summit Creek flows in a northwest direction from the south edge of figure 10 (south of Summit Creek Cave in section 1 in southeast quadrant of figure 10) to enter the southwest to northeast oriented Pryor Gap through valley in section 34. Note how Summit Creek flow is split in section 34 with some of the flow turning to flow in a northeast direction across section 26 to the north edge of figure 10 and then to join north oriented Pryor Creek (north of figure 10). The remaining flow turns to flow in a southwest direction to across section 3 to the south edge of figure 10 and then to join south oriented Sage Creek (south of figure 10). The map contour interval for figure 10 is 40 feet and the spot elevations on the Pryor Gap valley floor along the road in section 34 read 5047 and 5034 feet. The high point near the north edge of figure 10 (west of center) reads 6325 feet while the high point north of Summit Creek Cave reads 6505 feet. Based on these elevations the Pryor Gap through valley is at least 1250 feet deep and may be deeper. The elevation where Summit Creek joins Sage Creek at the Pryor Gap southwest end (not seen in figure 10) is between 4920 and 4960 feet.  The elevation where the Summit Creek joins Pryor Creek at the Pryor Gap northeast end (not seen in figure 10) is between 4520 and 4560 feet.  The deeper northeast end suggests reversed, or north oriented flood flow on the Pryor Creek alignment for a time captured some of the south oriented flood flow moving on the South Fork Bluewater Creek alignment to the south oriented Sage Creek alignment and that the captured flood flow moved in a northeast direction through Pryor Gap. However, the Pryor Gap through valley was initiated as a southwest oriented flood flow channel, which converged with a south-southeast oriented flood flow channel on the South Fork Bluewater Creek alignment to a form a south oriented flood flow channel on the south oriented Sage Creek alignment (and perhaps for a time to supply flood water for a southeast oriented flood flow channel on the present day northwest oriented Sage Creek headwaters alignment. If so the southeast oriented flood moved to a flood flow channel on the south-southeast oriented Crooked Creek alignment, which then converged with south oriented flood flow on the present day north oriented Bighorn River alignment). There is a logic to the organization of drainage routes and the valleys seen in the Clarks Fork of the Yellowstone River-Pryor Creek drainage divide area, although that logic requires thinking in terms of immense south oriented floods, which were systematically reversed from east to west to flow in a north direction.

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.