Abstract:

This essay uses topographic map evidence to interpret landform origins in the region between the Yellowstone River and the Boulder River at the north end of the Absaroka Range, which is located north of Yellowstone National Park in south central Montana. The Absaroka Range straddles the Montana-Wyoming state line in the Yellowstone National Park region. The Yellowstone River flows in a northwest, north, and northwest direction across Yellowstone National Park near the Absaroka Range west flank. Once in Montana the Yellowstone River turns to flow in a northeast and east-southeast direction around the Absaroka Range north end. The Boulder River drains the Absaroka Range north of Yellowstone National Park and flows in a north and northeast direction to join the Yellowstone River. The Yellowstone River-Boulder River drainage divide area for much of its distance consists of the Yellowstone-West Boulder River and the West Boulder River-Boulder River drainage divide areas, with the northeast oriented West Boulder River (a Boulder River tributary) being located between the Yellowstone River and the Boulder River.  Northwest-to-southeast oriented through valleys cross the Yellowstone-West Boulder River and West Boulder-Boulder River drainage divides and provide evidence of southeast oriented flood flow channels, which existed prior to headward erosion of much deeper north and northeast oriented valleys. Crustal warping responsible for Yellowstone Plateau and Absaroka Range uplift combined with headward erosion of the deep east and northeast oriented Yellowstone River valley caused flood flow reversals that resulted in headward erosion of the much deeper north and northeast oriented valleys in sequence from east to west. Floodwaters were derived from a rapidly melting thick North American ice sheet, which is interpreted to have caused the crustal warping. Subsequent to Absaroka Range emergence as a high mountain range valley alpine glaciers formed and further eroded some high elevation valley heads.

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 Yellowstone River-Boulder River 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 Yellowstone River-Boulder River 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.

Yellowstone River-Boulder River drainage divide area location map

Figure 1: Yellowstone River-Boulder 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 Yellowstone River-Boulder River drainage divide in the northern Absaroka Mountains and illustrates a region of south-central Montana with a strip of northwest Wyoming along the figure 1 south edge. The Absaroka Range is located slightly east of the northwest oriented Yellowstone River segment and extends from southern Montana across the Yellowstone National Park eastern margin in a south-southeast direction to beyond the figure 1 map area. Yellowstone National Park is the yellows shaded area straddling the south edge of figure 1 (west half). The Yellowstone River flows from the Yellowstone National Park area in northwest Wyoming in a northwest direction and then turns to flow in a north-northeast direction to Livingston, Montana. From Livingston the Yellowstone River flows in an east-northeast direction to Big Timber before turning to flow in an east-southeast direction to Columbus and then turning to flow in a northeast direction to Billings before reaching the figure 1 east center edge. The Boulder River is a north and north-northeast oriented tributary originating in the northern Absaroka Range (north of Yellowstone National Park) and joining the Yellowstone River near Big Timber. The unnamed tributary originating near Mt. Cowan and joining the Boulder River near McLeod is the West Boulder River. The unnamed northwest oriented tributary originating south of Mt. Cowan and joining the Yellowstone River near Pray is Mill Creek. The Yellowstone River-Boulder River drainage divide area illustrated and discussed here is located south and east of the Yellowstone River, north and east of Mill Creek, and west and north of the Boulder River.

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 and as crustal warping raised the Yellowstone Plateau area and Absaroka Range. At approximately the same time the deep Yellowstone River valley eroded headward from a deep “hole” in which a large North American ice sheet was rapidly melting to capture immense south and southeast oriented melt water floods flowing from western Canada across Montana. 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. 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 uplift of the Yellowstone Plateau and of the regional mountain ranges gradually channeled the huge south and southeast oriented melt water floods into valleys or basins between the rising mountains and plateau areas. One such flood flow channel was between the rising Gallatin, and Absaroka mountain ranges along the alignment now used by the northwest and north-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 deep northeast and east oriented Yellowstone River valley from the deep “hole” the melting ice sheet had once occupied. The deep Yellowstone River valley and its deep northeast oriented tributary valleys eroded headward across immense south and southeast oriented ice sheet marginal melt water floods and diverted the melt water floods into space in the deep “hole” being opened up by the ice sheet melting. Beheading of the large south oriented flood flow channel on the present day north oriented Yellowstone River alignment probably took place in the Livingston, Montana area and the entire Yellowstone River valley upstream from Livingston was probably eroded by a massive flood flow reversal as the ongoing Yellowstone Plateau and Absaroka Range uplift continued.

Detailed location map for Yellowstone River-Boulder River drainage divide area

Figure 2: Detailed location map Yellowstone River-Boulder 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 Yellowstone River –Boulder River drainage divide area in the northern Absaroka Mountains. County boundaries are shown and Sweet Grass County in the figure 2 east half is labeled. Park County is west of Sweet Grass County and the county west of Park County is Gallatin County. Stillwater County is east of Sweet Grass County. Big Timber is a town in Sweet Grass County and the Yellowstone River flows in a northeast direction from southeast corner of figure 2 to Big Timber and then flows in a southeast direction. The green shaded areas show regions of National Forest lands, which are generally located in mountainous regions. The Absaroka Range northern end is located in the green shaded area in eastern Park County and is labeled. East of the Absaroka Range ridge crest are the West and East Boulder Plateaus and the Lake Plateau. The Boulder River flows in a north direction near and across the Park County-Sweet Grass County line from the south edge of figure 2 to north of the green shaded area and then turns to flow in north-northeast direction to join the Yellowstone River near Big Timber. The West Boulder River flows on the west side of West Boulder Plateau in a north-northeast and northeast direction to join the Boulder River near McLeod. Note the northwest and north-northwest oriented tributaries joining the Yellowstone upstream from Big Timber. Labeled tributaries include Mission Creek, joining the Yellowstone River near Mission, northwest and southwest oriented Deep Creek, northwest and north oriented Elbow Creek, and west and northwest oriented Mill Creek. Flood flow channels in a large south or southeast oriented anastomosing channel complex established orientations of these tributaries at a time when present day mountain ranges were just emerging and prior to headward erosion of the deep Yellowstone River valley. Evidence for these flood flow channels is best seen in the Yellowstone River-West Boulder River drainage divide area, but can also be seen in the West Boulder River-Boulder River drainage divide area.

Yellowstone River-Boulder River drainage divide area north of the Absaroka Mountains

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

Figure 3 provides a topographic map of the Yellowstone River-Boulder River drainage divide area north of the Absaroka Mountains. Springdale is the small town in the northwest quadrant of figure 3. The Yellowstone River flows in a northeast direction from the west center edge of figure 3 to the north edge of figure 3 (east of center). McLeod is a small town just east of the south-center of figure 3. The northeast oriented West Boulder River joins the north-northeast oriented Boulder River near McLeod and the Boulder River then flows in a northeast direction to the east edge of figure 3 (north of center). Mendenhall Creek and its East Fork is a northwest oriented tributary joining the Yellowstone River near Springdale. Note how a through valley (or gap) links the northwest oriented East Fork and Mendenhall Creek valley with the northeast oriented West Boulder River valley. The contour interval for figure 3 is 50 meters and the elevation of the through valley crossing the East Fork Mendenhall Creek-West Boulder River drainage divide is between 1700 and 1750 meters. The hill to the northeast rises to 1825 meters and the hill to the southwest rises to 1872 meters, meaning the through valley is at least 75 meters deep. The through valley is what remains of a southeast oriented flood flow channel that existed prior to headward erosion of the deep northeast oriented Yellowstone River valley. Yellowstone River valley headward erosion beheaded the southeast oriented flood flow and floodwaters on the northwest end of the beheaded flood flow route reversed flow direction to erode the northwest oriented East Fork and Mendenhall Creek valleys. Valleys of northwest oriented segments of other Yellowstone River tributaries seen in figure 3 have similar histories.

Detailed map of Mendenhall Creek-West Boulder River drainage divide area

Figure 4: Detailed topographic map of the Mendenhall Creek-West Boulder 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 Mendenhall Creek-West Boulder River drainage divide area seen in less detail in figure 3 above.  The West Boulder River is labeled “Boulder River” and flows in a west-northwest direction across sections 24, 19, 17, and 16 in the south half of figure 4. The East Fork of Mendenhall Creek flows from section 7 (“Lone Tree Section”) to section 6 and the north center edge of figure 4. North of figure 4 the East Fork and Mendenhall Creek flow in northwest and north directions to join the northeast oriented Yellowstone River. Note in the southeast corner of section 7 (“Lone Tree Section”) a through valley linking the north-northwest oriented East Fork valley with the west-northwest oriented West Boulder River valley. The contour interval for the figure 4 map is 20 feet and the through valley elevation at the drainage divide is between 5580 and 5600 feet. The drainage divide elevation to the northeast in the northeast corner of section 8 rises to 5988 feet while in section 23 to the southwest the elevation rises to 6141 feet, meaning the through valley is approximately 400 feet deep. The through valley is a water-eroded feature and was eroded by south-southeast oriented flood flow at a time when the deep the Yellowstone River valley (north of figure 4) did not exist. Floodwaters were flowing to what at that time was the newly eroded West Boulder River valley, which had eroded headward from the newly eroded Boulder River valley, which had eroded headward from what at that time was the actively eroding Yellowstone River valley head near Big Timber (see figures 1 and 2). Headward erosion of the deep northeast oriented Yellowstone River valley north of figure 4 subsequently beheaded the south-southeast oriented flood flow channel and floodwaters on the north end of the beheaded flood flow channel reversed flow direction to erode the northwest and north oriented East Fork and Mendenhall Creek valleys.

Mission Creek-West Boulder River drainage divide area

Figure 5: Mission Creek-West Boulder River drainage divide area. United States Geological Survey map digitally presented using National Geographic Society TOPO software.

Figure 5 illustrates the Mission Creek-West Boulder River drainage divide area south and west of figure 3 and includes overlap areas with figure 3. Mission Creek flows in a northeast and north direction near the west edge of the northwest quadrant of figure 5 and north of figure 5 flows in a north-northwest direction to join the Yellowstone River. The West Boulder River flows in a northeast direction from the southwest quadrant of figure 5 to join the north-northeast oriented Boulder River near the northeast corner of figure 5. The East Boulder River flows from the southeast corner of figure 5 in a northwest, north-northeast, and north-northwest direction and joins the Boulder River. Labeled high points along the Mission Creek-West Boulder River drainage divide include Mount Greeley and Shell Mountain. Between those high points is a southeast to northwest oriented through valley drained by Little Mission Creek and its tributaries. Little Mission Creek originates on Shell Mountain and flows in a northeast and north-northeast direction into the through valley and then turns to flow in a northwest direction to join Mission Creek. Note the unnamed northwest oriented Little Mission Creek tributaries flowing from the West Boulder Ridge, which serves as the Mission Creek-West Boulder River drainage divide. Also note the Ellis Basin, which is located between Mount Greeley and West Boulder Ridge. Figure 5 is located along the northeast margin of the Absaroka Range and the northwest to southeast oriented through valley is probably eroded along the strike of dipping strata, however the through valley is also a water eroded feature. The through valley was eroded by southeast oriented flood flow at a time when the deep Yellowstone River valley to the north did not exist. Headward erosion of the deep Yellowstone River valley (north of figure 5) beheaded the southeast oriented flood flow. Floodwaters on the northwest end of the beheaded flood flow route reversed flow direction to erode the northwest and north oriented valley.

Next look at the West Boulder River-Boulder River drainage divide located east of West Boulder Ridge and the Ellis Basin. Between Baker Mountain and the Mcleod Basin is a northwest to southeast oriented through valley. A deeper through valley crosses the drainage divide in the McLeod Basin area just south of Coal Mine Rim. These through valleys provide evidence of flood flow channels eroded prior to headward erosion of the deep West Boulder River valley. The higher elevation northwest to southeast oriented through valley was probably eroded at a time when flood waters were moving to a south oriented flood flow channel on the present day north oriented Boulder River alignment (south of figure 5). The deeper east-oriented through valley was probably eroded after headward erosion of the deep north-northeast oriented Boulder River valley captured the southeast oriented flood flow and diverted the floodwaters in a northeast direction to what was then the actively eroding Yellowstone River valley. This flood flow capture, which was probably greatly aided by Absaroka Range uplift which was occurring at the same time, caused a massive flood flow reversal to create the north oriented Boulder River drainage basin south of figure 5. Subsequently headward erosion of the deep northeast oriented West Boulder River valley captured the southeast oriented flood flow and ended flood flow across the West Boulder River-Boulder River drainage divide.

Deep Creek-Davis Creek drainage divide area

Figure 6: Deep Creek-Davis Creek drainage divide area. United States Geological Survey map digitally presented using National Geographic Society TOPO software.

Figure 6 illustrates the Deep Creek-Davis Creek drainage divide area south and west of figure 5 and includes overlap areas with figure 5. The large north-northeast oriented river seen along the western margin of figure 6 is the Yellowstone River. The Yellowstone River valley in this location is known as the Paradise Valley. Most Yellowstone River tributaries from the east are oriented in northwest directions and from south to north the labeled tributaries are Strawberry Creek, McDonald Creek and its tributary George Creek, Cascade Creek, Barry Creek, and Pool Creek. Next is Deep Creek, which flows in a southwest direction to join the north oriented Yellowstone River as a barbed tributary. Deep Creek does have a northwest oriented South Fork and the North Fork has northwest oriented headwaters. The northeast oriented river flowing from the south edge of figure 6 (east half) to the east edge of figure 6 (near northeast corner) is the West Boulder River. Most West Boulder River tributaries from the west are relatively short, although the longer northeast and east oriented tributary in the center of figure 6 is Davis Creek. Note how north of Mount McKnight (near the center of figure 6) a through valley (or mountain pass) links the northwest oriented South Fork Deep Creek valley with the northeast oriented Davis Creek valley. The contour interval for figure 6 is 50 meters and the through valley floor elevation at the drainage divide is between 2750 and 2800 meters. The drainage divide on either side of the through valley rises to more than 3100 meters meaning the through valley is at least 300 meters deep. This through valley is evidence of another southeast oriented flood flow channel that existed prior to erosion of the deep Yellowstone River valley to the west. A somewhat higher elevation through valley links the North Fork Deep Creek valley with the Davis Creek valley just south of Elephanthead Mountain. The multiple through valleys provide evidence of multiple southeast oriented flood flow channels such as might be found in a large-scale anastomosing channel complex. The deep through valleys also provide evidence floodwaters were eroding the valleys as the Absaroka Range was rising around them.

Detailed map of South Fork Deep Creek-Davis Creek drainage divide area

Figure 7: Detailed map of South Fork Deep Creek-Davis Creek drainage divide area. United States Geological Survey map digitally presented using National Geographic Society TOPO software.

Figure 7 provides a detailed topographic map of the South Fork Deep Creek-Davis Creek drainage divide area seen in less detail in figure 6. Davis Creek flows in a north-northeast direction from section 13 along the south edge of figure 7 to the northeast corner of figure 7. The South Fork Deep Creek originates in section 14 and flows in a north direction into section 11 where it turns to flow in a northwest direction to the west edge of figure 7. Note in the northeast corner of section 11 the through valley (or mountain pass) between the northwest oriented South Fork Deep Creek valley segment and the Davis Creek valley.  The contour interval for the figure 7 map is 40 feet and the through valley floor elevation at the drainage divide is between 9080 and 9120 feet. Mount McKnight to the south rises to 10310 feet and a spot elevation of 10280 feet is located near the northeast corner of section 1 (in northeast quadrant of figure 7). These elevations suggest the through valley is an 1100-foot deep water-eroded feature and was eroded by southeast oriented flood flow moving first to the northeast oriented West Boulder River valley (east of figure 7) and which was later captured by headward erosion of the deep north-northeast oriented Davis Creek valley (which eroded headward from the newly eroded West Boulder River valley). Subsequently headward erosion of the deep Yellowstone River valley (west of figure 7) beheaded and reversed the southeast oriented flood flow to create northwest oriented South Fork Deep Creek. These flood flow captures and reversals occurred as the Absaroka Range was being uplifted, which contributed to the deep valleys seen today. Absaroka Range uplift continued after flood flow across the region ended and alpine glaciers eventually formed in the high valley heads to produce the glacially carved landscape features seen today. Alpine glaciation occurred after immense floods responsible for eroding the present day drainage route valleys ended.

West Boulder River-Boulder River drainage divide area

Figure 8: West Boulder River-Boulder River drainage divide area. United States Geological Survey map digitally presented using National Geographic Society TOPO software.

Figure 8 illustrates the West Boulder River-Boulder River drainage divide area south and east of figure 6 and includes overlap areas with figure 6. The Boulder River flows in a north direction near the east edge of figure 8. The West Boulder River is formed at the confluence of its East Fork and West Fork in the southwest quadrant of figure 8 and then flows in a north-northeast direction to the north center edge of figure 8. The West Boulder Plateau forms the West Boulder River-Boulder River drainage divide. A close look at the drainage divide reveals through valleys linking northeast oriented Boulder River tributary valleys with the northwest oriented West Boulder River tributary valleys. One interesting through valley is located near the center of figure 8 and is crossed by the trail from the Falls Creek valley (a northwest oriented West Boulder River tributary) to the Great Falls Creek valley (a northeast oriented Boulder River tributary). The map contour interval for figure 8 is 50 meters. The trail elevation at the drainage divide is between 3050 and 3100 meters. West Boulder Plateau elevations to the north rise to 3244 meters while elevations to the south rise to 3285 meters. In other words the through valley is at least 144 meters deep if not deeper and provides evidence of a southeast oriented flood flow channel that was captured by headward erosion of the deep northeast oriented Great Falls Creek valley from what was probably a newly reversed and actively eroding north oriented Boulder River valley. At that time the deep north-northeast oriented West Boulder River valley had not yet beheaded and reversed southeast-oriented flood flow on the Falls Creek alignment, although it did so a short time later. Note how the north and northwest oriented Falls Creek valley is linked by a deep through valley (near Kaufman Lake) with the west and northwest oriented East Fork, which flows to the north-northeast oriented West Boulder River. The floor of that through valley has an elevation at the drainage divide of between 2850 and 2900 meters and elevations to the north rise to 3175 meters while elevations to the south rise to 3237 meters. This southern through valley provides evidence of the route used by flood flow to reach the actively eroding north oriented Falls Creek valley before West Boulder River headward erosion beheaded and reversed the southeast oriented flood flow route on the present day northwest oriented East Fork West Boulder River alignment.

Detailed map of the East Fork West Boulder River-Speculator Creek drainage divide area

Figure 9: Detailed map of the East Fork West Boulder River-Speculator Creek drainage divide area. United States Geological Survey map digitally presented using National Geographic Society TOPO software.

Figure 9 provides a detailed topographic map of the East Fork West Boulder River-Speculator Creek drainage divide area seen in less detail in figure 8 above. The East Fork West Boulder River is labeled “East Fork” and is seen in the northwest quadrant of figure 9 and flows to the north-northeast oriented West Boulder River north and west of figure 9. Speculator Creek is located in the northeast quadrant of figure 9 and flows in an east-northeast and east direction to join the north-oriented Boulder River east of figure 9. Kaufman Lake is located south of the north center edge of figure 9 and drains in a north direction to north and northwest oriented Falls Creek, which is a West Boulder River tributary. The East Fork Mill Creek is located in section 33 in the southwest quadrant of figure 9 and south of figure 9 turns to flow in a west direction to northwest oriented Mill Creek, which flows to the Yellowstone River. The unnamed south-southeast oriented stream in section 34 is Fourmile Creek (southeast quadrant of figure 9), which south of figure 9 turns to flow in an east direction to the north oriented Boulder River. Alpine glaciers have eroded valley heads in this high mountain region, but a close look at the drainage divides also reveals through valleys (or mountain passes) linking the diverging drainage routes. Previously noted was the through valley between Kaufman Lake and the East Fork West Boulder River. Other through valleys include a through valley in section 28 linking the north oriented East Fork West Boulder River tributary valley with the valley of an unnamed south-southwest East Fork Mill Creek tributary and a through valley in the southeast corner of section 22 linking the Kaufman Lake valley with the east oriented Speculator Creek valley. While today these through valleys (and others like them) appear to be merely notches in high mountain ridges the through valleys (or notches) provide evidence of former flood flow channels, which were eroded into the Absaroka Range at a time when south and southeast oriented floodwaters could freely flow across the region. At that time the Absaroka Range did not stand high above surrounding regions and was being eroded by the immense melt water flood flow as fast as crustal warping could raise the mountain mass. However, eventually crustal warping proceeded faster than the floodwaters could erode the rising mountain mass and headward erosion of deep valleys from the deep “hole” the melting ice sheet had occupied captured the south and southeast oriented flood flow and in doing so beheaded and reversed  flood flow routes. Valley orientations and through valleys (notches in high mountain ridges) provide evidence of the former flood flow routes.

Mill Creek-Boulder River drainage divide area

Figure 10: Mill Creek-Boulder River 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 south of the figure 8 map area and there is no overlap area with figure 8. The Boulder River flows in a north direction near the east edge of figure 10. Meatrack Creek is a northeast oriented tributary originating near the Pyramid (a named mountain peak south of north center edge of figure 10) and joining the Boulder River just north of the northeast corner of figure 10. Mill Creek originates near Crow Mountain (near center of figure 10) and flows in a west and west-northwest direction to the west edge of figure 10 (north of center) and west of figure 10 turns to flow in a northwest direction to join the north oriented Yellowstone River (see figure 2). Note how Mill Creek has several significant north oriented tributaries from the south. The East Fork of Mill Creek can be seen near the north edge of the northwest quadrant of figure 10. While the Mill Creek-Boulder River drainage divide in the high Absaroka Range appears to be the last place one would look for evidence of a former flood flow capture event, the evidence is present if one takes the time to look. Note how through valleys (mountain passes or notches in high mountain ridges) link the northeast oriented Meatrack Creek valley with the west oriented Mill Creek valley between the Pyramid and Crow Mountain. The map contour interval for figure 10 is 50 meters and the through valley floor elevations at the drainage divide are between 2950 and 3000 meters. The Pyramid rises to 3271 meters and Crow Mountain rises to 3270 meters meaning the through valleys could be 270 meters or more deep. The through valleys provide evidence of a south, southeast, east, northeast, and north oriented flood flow route to the north oriented Boulder River valley, which was supplying flood water to the newly eroded Yellowstone River north and east of figure 10. At that time the deep Yellowstone River valley north of figure 10 had not yet been eroded far enough west to behead south oriented flood flow moving along what is today the north oriented Yellowstone River alignment south of Livingston, Montana. Also at that time the Absaroka Range had not risen to a point that it blocked southeast and east oriented flood flow across what is today a high mountain range.

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.