Mill Creek-Hellroaring Creek drainage divide area landform origins in the northern Absaroka Range, Montana, USA

Authors


Abstract:

This essay uses topographic map evidence to interpret landform origins in the region between the Mill Creek and Hellroaring Creek in the northern Absaroka Range, which is located just north of Yellowstone National Park in south central Montana. The Yellowstone River flows in a northwest direction as it leaves Yellowstone National Park and Wyoming to enter Montana as the Yellowstone River  flows along the Absaroka Range west flank before turning to flow in a northeast direction along the Absaroka Range northwest flank. Mill Creek is a west and northwest oriented stream originating in the Absaroka Range and flowing to the northeast oriented Yellowstone River segment in southern Montana. Hellroaring Creek is a south oriented stream originating near the Mill Creek headwaters in the Absaroka Range and flowing to the northwest oriented Yellowstone River segment in northern Wyoming. Through valleys, which today might better be described as mountain passes or notches in high mountain ridges, cross most drainage divides in the Mill Creek-Hellroaring Creek drainage divide area and provide evidence of multiple flood flow channels such as might be found in a large-scale anastomosing channel complex. South and southeast oriented floodwaters are interpreted to have crossed the region prior to and during Absaroka Range uplift and are interpreted to have been derived from a rapidly melting thick North American ice sheet, which was located in a deep “hole.” Headward erosion of what was a very deep east and northeast oriented Yellowstone River valley (north of this essay’s study area) combined with ongoing Absaroka Range and Yellowstone Plateau uplift is interpreted to have captured the south and southeast oriented flood flow and also to have caused massive flood flow reversals resulting in numerous present day northwest, north, and northeast oriented Yellowstone River and north oriented Yellowstone River tributaries.

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 Mill Creek-Hellroaring Creek drainage divide area landform origins in the northern Absaroka Mountains, 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 Mill Creek-Hellroaring Creek drainage divide area landform evidence in the northern Absaroka Mountains, Montana will be regarded as evidence supporting the “thick ice sheet that melted fast” paradigm.

Mill Creek-Hellroaring Creek drainage divide area location map

Figure 1: Mill Creek-Hellroaring 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 Mill Creek-Hellroaring Creek drainage divide area in the northern Absaroka Mountains and illustrates a region of south-central Montana with northwest Wyoming in the southeast quadrant of figure 1 and a strip of Idaho seen along the south edge of the southwest quadrant. Yellowstone National Park is the yellow shaded area in northwest Wyoming. The Absaroka Range extends from southern Montana across the Yellowstone National Park eastern margin in south-southeast direction. The Yellowstone River flows from the Yellowstone National Park area in northwest Wyoming in a northwest direction and then in southern Montana turns to flow in a northeast direction to Livingston and Big Timber, Montana. From Big Timber the Yellowstone River flows in an east-southeast direction to the east edge of figure 1. Mill Creek is shown in figure 1, but is not labeled and is the west and northwest oriented tributary flowing to the northeast oriented Yellowstone River near Pray, Montana (south of Livingston). Hellroaring Creek is not shown in figure 1, but originates in the same region as Mill Creek and flows in a south direction to join the Yellowstone River in northern Yellowstone National Park near where the northwest oriented Lamar River joins the north oriented Yellowstone River, which then turns to flow in a northwest direction. The Mill Creek-Hellroaring Creek drainage divide area investigated here is located south of Mill Creek, east of the Yellowstone River and west of Hellroaring Creek. Figure 2 provides a more detailed location map, which shows Hellroaring Creek.

Looking at the big picture erosion history of the figure 1 map area the drainage routes shown developed as immense south and southeast oriented melt water floods flowed across the region, which was approximately the same time as crustal warping raised the Yellowstone Plateau and Absaroka Range and the deep east and northeast oriented 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 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, including the Yellowstone Plateau and the Absaroka Range, did not stand high above the surrounding regions and floodwaters could freely flow across the entire figure 1 map area. Over time however uplift of the Yellowstone Plateau and of the regional mountain ranges channeled the huge south and southeast oriented melt water floods into valleys or basins between the rising mountains. One such flood flow channel was between the rising Gallatin, and Absaroka mountain ranges along the valley now used by the northwest and northeast oriented Yellowstone River. This large south oriented flood flow channel was eventually beheaded and reversed by continued crustal warping and by headward erosion of the much deeper northeast and east oriented Yellowstone River valley from the deep “hole”. Beheading of the south oriented flood flow channel on the present day north oriented Yellowstone River alignment probably took place where the Yellowstone River valley turns from flowing in a northwest direction to flowing in a northeast direction. The Yellowstone River drainage basin upstream from this elbow of capture was probably eroded by a massive flood flow reversal as the ongoing Yellowstone Plateau and Absaroka Range uplift continued.

Detailed location map for Mill Creek-Hellroaring Creek drainage divide area

Figure 2: Detailed location map Mill Creek-Hellroaring 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 Mill Creek-Hellroaring Creek drainage divide area in the northern Absaroka Mountains. The northern margin of Yellowstone National Park is the brown shaded area along the south margin of figure 2 with the Montana-Wyoming state line being the west to east oriented dashed line running through the northern margin of Yellowstone National Park. Green shaded areas are National Forest lands, which are generally located in mountainous regions. The Yellowstone River flows in a northwest direction from the south center edge of figure 2 (near Tower Junction) to Miner, Montana (near west center edge of figure 2) and then in a northeast direction to the north edge of figure 2 (west half). The mountainous region (green shaded area) east of the Yellowstone River includes the Absaroka Range, which is labeled. Mill Creek originates in the Absaroka Range near the center of figure 2 (north of Mount Wallace) and flows in a west and northwest direction to join the northeast oriented Yellowstone River in the northeast quadrant of figure 2. Hellroaring Creek also originates in the Mount Wallace region and flows in a south direction and joins the Yellowstone River in Yellowstone National Park north of Tower Junction. East of south oriented West Fork Hellroaring Creek are headwaters of the north oriented Boulder River, which north of figure 2 flows in a northeast direction to join the Yellowstone River near Big Timber (see figure 1).  Note how on the east side of the Absaroka Range the drainage in that region is north oriented while on the west side of the Absaroka Range the drainage is south oriented. Also note the large number of south oriented tributaries flowing to the north oriented Yellowstone River. These south oriented tributaries, or barbed tributaries, provide evidence their valleys were eroded at a time when drainage in the region was oriented in a south direction rather than in the north direction it is today.

Yellowstone River-Yellowstone River drainage divide area north of Yellowstone National Park

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

Figure 3 provides a topographic map of the Yellowstone River-Yellowstone River drainage divide area north of Yellowstone National Park, which provides a good staring point for this essay. The Yellowstone River is located in the west half of figure 3 and flows in a northwest direction to Miner and then in a north-northeast direction. Dome Mountain is the mountain located just east of Miner between the northwest and north-northeast oriented Yellowstone River segments. East of Dome Mountain is a north to south oriented through valley linking the north-northeast oriented Yellowstone River segment with the northwest oriented Yellowstone River segment. The south end of the through valley is drained by south oriented Joe Brown Creek, which flows to the north oriented Yellowstone River as a barbed tributary. The figure 3 map contour interval is 50 meters and the through valley floor elevation at the drainage divide is between 2150 and 2200 meters, Dome Mountain reaches an elevation of 2620 meters and mountains east of the through valley rise even higher. In other words this water-eroded through valley is at least 420 meters deep. South of Dome Mountain is Sphinx Mountain and north oriented Sphinx Creek. Note how Sphinx Creek and a north-northwest oriented Sphinx Creek tributary are linked by through valleys with southeast oriented Cottonwood Creek. These two through valley plus the through valley east of Dome Mountain and the barbed tributaries provide evidence of multiple south oriented flood flow channels that existed prior to the reversal of flow that resulted in the present day north oriented Yellowstone River. South oriented flood flow in the Yellowstone River valley was reversed by a combination of crustal warping that raised the Yellowstone Plateau area to the south and by headward erosion of the deep east and northeast oriented Yellowstone River valley from the deep “hole” a thick North American ice sheet had occupied. The deep east and northeast oriented Yellowstone River valley eroded headward to capture immense south and southeast oriented ice marginal flood flow, which was moving from western Canada across Montana and into Wyoming. North oriented Yellowstone River tributaries and the north oriented Yellowstone River in figure 3 were formed by massive flood flow reversals on north ends of beheaded flood flow channels. Crustal warping that raised the Yellowstone Plateau to the south was probably related to the thick ice sheet presence and probably continued for some time after the massive Yellowstone River flood flow reversal.

Detailed map of Yellowstone River-Yellowstone River drainage divide area

Figure 4: Detailed topographic map of the Yellowstone River-Yellowstone 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 Yellowstone River-Yellowstone River drainage divide area seen in less detail in figure 3 above. Dome Mountain is located near the corner of sections 27, 28, 33 and 34 in the west half of figure 4. The Yellowstone River can just barely be seen flowing in a northwest direction in the southwest corner of figure 4. Joe Brown Creek originates in the southwest corner of section 26 and flows in a south direction through section 35 to the north oriented Yellowstone River (south of figure 4). Red Mountain is the high point in the northeast quadrant of figure 4 and is located in section 19 near its southern boundary. The map contour interval for figure 4 is 40 feet and Dome Mountain reaches an elevation of 8596 feet while Red Mountain reaches an elevation of 8883 feet. The spot elevation on the floor of the north to south oriented through valley between Dome Mountain and Red Mountain reads 7118 feet, which means the through valley is more than 1700 feet deep. The through valley was eroded by south oriented flood flow at a time when the Yellowstone River valley to the west probably had a comparable valley floor elevation. At that time south oriented floodwaters were flowing in multiple channels across the region. The reversal of flood flow in what had been a complex of south oriented flood flow channels occurred when headward erosion of the much deeper east and northeast oriented Yellowstone River valley beheaded the south and southeast oriented flood flow channels. Floodwaters on north and northwest ends of the beheaded flood flow channels reversed flow direction to erode deep north oriented valleys. In the case of the Yellowstone River flood flow channel the deeper valley floor in the southwest corner of figure 4 today has an elevation of about 5000 feet. In other words, since the time south oriented floodwaters ceased flowing between Dome Mountain and Red Mountain flood erosion and regional drainage erosion has lowered the Yellowstone River valley by approximately 2100 feet.

Monitor Creek-Bear Creek drainage divide area

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

Figure 5 illustrates the Monitor Creek-Bear Creek drainage divide area east and slightly south of figure 3 and includes overlap areas with figure 3. Monitor Peak is a high peak located just west of the center of figure 5. Monitor Creek originates on the Monitor Peak northeast flank and flows in a northeast direction to join the north oriented West Fork of Mill Creek, which north of figure 5 joins northwest oriented Mill Creek, which in turns flows to the northeast oriented Yellowstone River. Bear Creek (unlabeled in figure 5) originates a short distance east of Monitor Peak and flows in a south direction to the south center edge of figure 5. South of figure 5 Bear Creek flows to the northwest oriented Yellowstone River near Gardiner, Montana. Note the north to south oriented through valley linking the north oriented Monitor Creek valley with the south oriented Bear Creek valley. The map contour interval for figure 5 is 50 meters. The through valley floor elevation at the drainage divide is between 2650 and 2700 meters. Monitor Peak to the west rises to 3179 meters while a high point immediately east of the through valley has a spot elevation of 3076 meters meaning the through valley is approximately 400 meters deep. The through valley is a water-eroded feature and was eroded by south oriented flood flow at a time when south oriented floodwaters flowed across the region. At that time the deep Yellowstone River valley to the north did not exist and crustal warping had not yet raised the Absaroka Range or the Yellowstone Plateau area to the south. Study of the figure 5 map area reveals other similar through valleys linking the north oriented valleys with the south oriented valleys, suggesting multiple south oriented flood flow channels once crossed the region. Elevations of through valley floors vary suggesting floodwaters were flowing across a rising mountain mass and were gradually being captured by deeper flood flow channels as the mountains rose (as floodwaters were being channeled into the deepest channels).

Detailed map of Monitor Creek-Bear Creek drainage divide area

Figure 6: Detailed map of Monitor Creek-Bear 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 Monitor Creek-Bear Creek drainage divide area seen in less detail in figure 5 above.  Monitor Peak is located near the southeast corner of section 5 near the west edge of figure 6. Monitor Creek originates in section 4, just east of Monitor Peak, and flows in a northeast direction to the southeast corner of section 34 (near Lonesome Pond) and then turns to flow in more of a north direction. Bear Creek originates near the south margin of section 3 and flows in a south direction across section 10 to the south center edge of figure 6. The north to south oriented through valley linking the north oriented Monitor Creek valley with the south oriented Bear Creek valley is located in section 3. The map contour interval for figure 6 is 40 feet. The through valley floor elevation at the drainage divide is given by a spot elevation of 8804 feet. Monitor Peak reaches an elevation of 10,429 feet and the high point in section 2 (to the east of the through valley) has an elevation of 10,082 feet, which means the through valley is more than 1200 feet deep. An interesting question is: what eroded the deep northeast oriented Monitor Creek valley? North of Monitor Peak are headwaters of the north oriented North Fork Sixmile Creek, which north of figure 6 flows to northwest oriented Sixmile Creek. A high level through valley (or mountain pass) just north of Monitor Peak and used by a trail links the North Fork Sixmile Creek valley with the Monitor Creek valley. Apparently floodwaters on the Monitor Creek-Bear Creek alignment were beheaded and reversed prior to the beheading of floodwaters on the Sixmile Creek alignment, which would be consistent with headward erosion of the northeast oriented Yellowstone River valley segment seen in figures 1 and 2. Southeast oriented flood flow on the Sixmile Creek alignment moved across that high level through valley to the newly reversed Monitor Creek alignment and then made a U-turn to flow in a north and northwest direction on the Mill Creek alignment to what was then an actively eroding and very deep Yellowstone River valley. At that time the deep Sixmile Creek valley did not exist and the flood flow channel floor elevation north of Monitor Peak was at least as high the through valley floor elevation (although regional uplift was probably occurring and has probably occurred since). The deep north oriented North Fork Sixmile Creek valley was eroded by floodwaters captured from a yet to beheaded southeast oriented flood flow route still further to the west (unseen in figure 6).

Wallace Creek-Grizzly Creek drainage divide area

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

Figure 7 illustrates the Wallace Creek-Grizzly Creek drainage divide area east and north of the figure 6 map area and includes overlap areas with figure 6. Monitor Peak is located near the southwest corner of figure 7. Mill Creek originates near the northeast corner of figure 7 and flows in a west and northwest direction to the north center edge. Labeled north oriented tributaries flowing to Mill Creek from east to west include Lambert Creek, Colley Creek, and Wallace Creek, with the north oriented West Fork (and its Monitor Creek and Thompson Creek tributaries) joining Mill Creek north of figure 7. Wallace Creek originates just west of Mount Wallace and the East Fork Wallace Creek originates just east of Mount Wallace. Passage Creek is a north and north-northeast oriented Wallace Creek tributary and is located on the west side of Wallace Creek. Hellroaring Creek is the south oriented stream flowing near the east edge of figure 7 with its North Fork originating in North Fork Basin and the North Fork tributaries of Silver Creek and Clover Creek originating in Silver and Clover Basins. Grizzly Creek originates on the Mount Wallace south flank and flows in a southeast direction to join Hellroaring Creek south of the figure 7 map area. The unnamed southeast oriented stream west of Grizzly Creek is Horse Creek, which is another Hellroaring Creek tributary. Note the through valleys (or mountain passes) linking the north oriented Wallace Creek headwaters valleys with the southeast oriented Clover Creek, Grizzly Creek, and Horse Creek valleys. A somewhat higher elevation through valley (or mountain pass) links the north oriented Lambert Creek valley with the south oriented North Fork at North Fork Basin. The map contour interval for figure 7 is 50 meters and some of the through valleys are defined by five or more contour lines on each side. These 200-250 meter deep through valleys are water eroded features and were eroded as south and southeast oriented flood flow channels prior to headward erosion of the deep northeast oriented Yellowstone River valley (north and west of figure 7). Yellowstone River valley headward erosion beheaded the south and southeast oriented flood flow channels in sequence from east to west and created  massive flood flow reversals that eroded the west and northwest oriented Mill Creek drainage basin. The flood flow reversals were probably greatly aided by Absaroka Range uplift, which was occurring at the same time and which probably continued following the flood flow reversals.

Detailed map of Wallace Creek-Grizzly Creek drainage divide area

Figure 8: Detailed map of Wallace Creek-Grizzly 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 Wallace Creek-Grizzly Creek drainage divide area seen in less detail in figure 7. The map contour interval for figure 8 is 40 feet and Mount Wallace, which is located in section 27, rises to 10, 697 feet. Wallace Creek originates in section 28 (west of Mount Wallace) and flows in a north direction through section 21 to the north edge of figure 8. Grizzly Creek originates in section 27 on the Mount Wallace south flank and flows in a south direction across section 34 to the south edge of figure 8. A through valley (or mountain pass) near the corner of sections 27, 28, 33, and 34 links the north oriented Wallace Creek valley with the south oriented Grizzly Creek valley. A trail makes use of the mountain pass (or through valley). Elevation of the mountain pass at the drainage divide is given as 9773 feet. The unnamed mountain peak to the west (in northwest quadrant of section 33) reaches 10,605 feet, meaning the through valley or mountain pass is approximately 800 feet deep. While today this through valley or mountain pass looks like a notch in a high mountain ridge at one time it was a 800-foot deep valley eroded into a landscape surface equivalent in elevation to the surrounding high mountain peaks (although the entire region has probably been uplifted since that time). The valley was eroded by south oriented flood water moving across what was probably a rising Absaroka Range, although at that time the Absaroka Range did not stand high above surrounding valleys and basins as it does today. Also, at that time there was no deep Yellowstone River valley to the north of figure 8. Immense melt water floods from the rapidly melting thick ice sheet in western Canada were free to flow across Montana and the Yellowstone Plateau region and probably deeply eroded the rising mountain range and plateau areas as they did so. Removal of significant bedrock thicknesses from the rising mountain ranges and plateau areas probably accelerated uplift of those regions and may also have contributed to crustal thinning and volcanic activity seen in some of those areas.

Boulder River-Hellroaring Creek drainage divide area

Figure 9: Boulder River-Hellroaring Creek drainage divide area. United States Geological Survey map digitally presented using National Geographic Society TOPO software.

Figure 9 illustrates the Boulder River-Hellroaring Creek drainage divide area east of figure 7 and includes overlap areas with figure 7. Crow Mountain is a high peak located south of the south center edge of figure 9. Mill Creek originates near Crow Mountain and flows in a west and northwest direction to near the northwest corner of figure 9. North and west of figure 9 Mill Creek flows to the northeast oriented Yellowstone River south of Livingston, Montana (see figures 1 and 2). Hellroaring Creek (not labeled in figure 9) originates south of Crow Mountain and flows in a south and south-southwest direction to the south center edge of figure 9. South of figure 9 Hellroaring Creek joins the northwest oriented Yellowstone River north of Tower Junction, Wyoming. The Boulder River is the north oriented drainage route east of Crow Mountain and east of the Hellroaring Creek drainage basin and is located near the east edge of figure 9. North of figure 9 the Boulder River flows in a north and northeast direction to join the east oriented Yellowstone River near Big Timber, Montana (see figure 1). The high Absaroka Range ridge marks the Boulder River-Hellroaring Creek drainage divide and is labeled “RANGE” in figure 9. Extending in a southwest direction from the northwest to southeast oriented Absaroka Range ridge is the “Middle Ridge” and between Middle Ridge and Iron Mountain is the southwest oriented Middle Fork of Hellroarding Creek. While the main northwest to southeast oriented Absaroka Range ridge looks like an insurmountable barrier a close look reveals through valleys (or high mountain passes) link the northeast oriented Boulder River tributary valleys with the south and southwest oriented Hellroaring Creek headwaters and tributary valleys. The deepest of these through valleys links the northeast oriented Copper Creek valley with the southwest oriented Middle Fork Hellroaring Creek valley and is crossed by a trail. The map contour interval for figure 9 is 50 meters and the elevation where the trail crosses the drainage divide is between 2850 and 2900 meters. A spot elevation of 3162 meters can be seen on the Absaroka Range ridge to the north and a spot elevation of 3192 meters can be seen on the ridge to the south indicating the through valley is approximately 300 meters deep. Boulder Pass at the south end of the Boulder River valley is a similar through valley linking the north oriented Boulder River valley with the south oriented Buffalo Creek valley, which drains eventually to the northwest oriented Yellowstone River near Tower Junction, Wyoming. These through valleys and other similar through valleys provide evidence of multiple south oriented flood flow channels across the present day Absaroka Range prior to headward erosion of the deep east and northeast oriented Yellowstone River valley (north of figure 9) and prior to uplift of the Absaroka Range and of the Yellowstone Plateau (south of figure 9).

Detailed map of Copper Creek-Middle Fork Hellroaring Creek drainage divide area

Figure 10: Detailed map of Copper Creek-Middle Fork Hellroaring Creek drainage divide area. United States Geological Survey map digitally presented using National Geographic Society TOPO software.

Figure 10 illustrates the Mill Creek-Boulder River drainage divide area seen in less detail in figure 9. The East Branch Hellroaring Creek originates in the northwest quadrant of figure 10 in section 23 and flows in a northwest and west-southwest direction to the west edge of figure 10 to join south oriented Hellroaring Creek west of figure 10.  The Middle Fork Hellroaring Creek originates in section 25 and flows in a south and southwest direction to the south edge of figure 10 (west half) and joins south oriented Hellroaring Creek south and west of figure 10. The north oriented Boulder River is just barely be seen in the northeast corner of figure 10. Copper Creek originates in section 24 and flows in a northeast direction to join the north oriented Boulder River north of figure 10. Sheep Creek originates in section 30 and flows in a northeast and north direction and joins the Boulder River near the northeast corner of figure 10. The northwest to southeast oriented Boulder River-Hellroaring Creek drainage divide is also the high Absaroka Range ridge. While the ridge today appears to be a solid wall there are mountain passes or notches in the ridge that provide evidence of former valleys eroded by south oriented flood flow channels before deep valleys on either side of the present day high ridge were carved.  One such mountain pass or through valley is located near the corner of sections 19, 24, 25, and 30 and links the northeast oriented Copper Creek valley with the southwest oriented Middle Fork Hellroaring Creek valley. The map contour interval for figure 10 is 40 feet. The mountain pass, or through valley, elevation at the drainage divide is between 9440 and 9480 feet. Peaks, both north and south of the through valley or mountain pass, rise almost 900 feet higher. While today this mountain pass is notched into a high mountain ridge at one time it was a southwest oriented valley being carved into what was then the rising Absaroka Range by south oriented flood flow. Absaroka Range uplift combined with headward erosion of the deep east and northeast oriented Yellowstone River valley (north of figure 10) caused a massive flood flow reversal that created the north oriented Boulder River drainage basin and also that created the Boulder River-Hellroaring Creek drainage divide. Continued Absaroka Range uplift has probably significantly raised figure 10 elevations since that time.

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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