Beaverhead River-Ruby River drainage divide area landform origins in the Ruby Range, Madison County, Montana, USA

· Beaverhead River, Montana, Ruby River
Authors


Abstract:

This essay uses topographic map evidence to interpret landform origins between the Beaverhead River and the Ruby River in the Ruby Range, Madison County, Montana. The Beaverhead River flows in a north-northeast direction west of the Ruby Range and north of the Ruby Range joins the Ruby River and south and northeast oriented Big Hole River to form the north-northeast, east, and northeast oriented Jefferson River. The Ruby River flows in a north direction east of the Ruby Range and turns to flow in a northwest direction north of Ruby Range to join the north-northeast oriented Beaverhead River. Beaverhead River tributaries originating in the Ruby Range are oriented in northwest directions while Ruby River tributaries originating in the Ruby Range are oriented in southeast directions. Barbed tributaries and drainage direction U-turns are common as are deep through valleys or passes across the high Ruby Range crest ridge. The through valleys (or passes) link northwest oriented Beaverhead River tributary valleys with southeast oriented Ruby River tributary valleys and were eroded by southeast oriented flood flow channels at a time when the Ruby Range was beginning to emerge. The southeast oriented floodwaters eroded deeper and deeper valleys into the emerging Ruby Range until being captured west of the Ruby Range by south oriented flood flow channels on the present day north oriented Beaverhead River alignment. Floodwaters on northwest ends of the beheaded flood flow reversed flow direction to create what is today the Beaverhead River-Ruby River drainage divide and what are today northwest oriented drainage routes. Floodwaters are interpreted to have been derived from the western margin of a thick North American ice sheet and were flowing in south and southeast directions from western Canada across western Montana to and across the study region. A major flood flow reversal occurred when north and east of the study region a deep northeast oriented valley eroded headward from space in the deep “hole” the melting ice sheet had occupied and captured a major south oriented flood flow channel supplying flood flow to the study region. The flood flow reversal was probably greatly aided by ice sheet related crustal warping that was raising mountain ranges in western Montana, including the Ruby Range. The flood flow reversal created the north oriented Ruby River and Beaverhead River drainage systems seen today.

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 Beaverhead River-Ruby River drainage divide area landform origins in the Ruby Range, Madison County, Montana and 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 Beaverhead River-Ruby River drainage divide area landform evidence in the Ruby Range, Madison County, Montana will be regarded as evidence supporting the “thick ice sheet that melted fast” paradigm.

Beaverhead River-Ruby River drainage divide area location map

Figure 1: Beaverhead River-Ruby 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 Beaverhead River-Ruby River drainage divide in the Ruby Range, Madison County, Montana and in the north half illustrates a region in southwest and south central Montana with the northwest corner of Wyoming and Yellowstone National Park in the southeast quadrant and an area of eastern Idaho located west of Yellowstone National Park. The Montana-Idaho state line west of Yellowstone National Park follows the east-west continental divide, which is located on the crest of the Beaverhead and Centennial Mountains from the west edge of figure 1 to the Wyoming state line. Upper Red Rock Lake is located north of the Centennial Mountains and drains in a west direction to Lower Red Rock Lake and then to the Red Rock River, which flows in a west direction to Lima, Montana where it turns to flow in a north-northwest direction to an unnamed reservoir (Clark Canyon Reservoir) where it joins other streams to form the north-northeast-oriented Beaverhead River. The Beaverhead River joins the north, southeast, south, and northeast oriented Big Hole River and north and northwest Ruby River (shown, but not labeled in figure 1) near Twin Bridges, Montana to form the north-northeast, east, and northeast oriented Jefferson River. The Jefferson River flows to Three Forks, Montana where it joins the north oriented Madison and Gallatin Rivers to form the north and north-northwest oriented Missouri River, which north of figure 1 turns to flow in a northeast and then east direction. The Ruby River is the unlabeled north and northwest drainage route originating near Hogback Mountain and flowing to the towns of Alder, Laurin, and Sheridan before joining the Beaverhead and Big Hole Rivers near Twin Bridges, Montana to form the north-northeast, east, and northeast oriented Jefferson River.  The Beaverhead River-Ruby River drainage divide area investigated in this essay is located in the Ruby Range north of Dillon, Montana, west and south of the Beaverhead River, and east and south of the Ruby River.

A brief look at the big picture erosion history will help understand discussions related to detailed maps shown below. Large volumes of south and southeast oriented floodwaters once flowed across the region shown by figure 1. Floodwaters were derived from the western margin of a melting thick North American ice sheet and were flowing in a south and southeast direction from western Canada to and across the figure 1 region. North oriented rivers in figure 1, including the north oriented Missouri River, the north and north-northwest oriented Ruby River and the north-northeast oriented Beaverhead and Jefferson Rivers are flowing in valleys that originated as south oriented flood flow channels. The west oriented Red Rock River alignment was at one time used by an east oriented flood flow channel. When floodwaters first flowed across the region the present day mountain ranges did not exist and floodwaters could freely flow in south and southeast directions across the region. The mountain ranges emerged as floodwaters flowed across the region and initially floodwaters flowed across what are today high mountains including the Ruby Range and mountain ranges which today form the east-west continental divide. More successful, or deeper, flood flow channels moving floodwaters across mountain ranges first captured floodwaters from adjacent less successful flood flow channels and later floodwaters were captured by flood flow channels moving floodwaters between the emerging mountain ranges. Through valleys or mountain passes crossing present-day drainage divides today provide evidence of the former flood flow channels. South-southeast oriented flood flow channels between the Beaverhead River and the north and northwest oriented Ruby River were beheaded by headward erosion of a deep south-oriented flood flow channel on the present day north-northeast Beaverhead River alignment. Floodwaters on north and northwest ends of the beheaded flood flow channels reversed flow direction to create what are today north and northwest oriented drainage routes including the north and northwest oriented Ruby River.

The flood flow reversal that created the present day north-northeast oriented Beaverhead River and north-northwest oriented Red Rock River drainage routes was probably indirectly caused by crustal warping that occurred as melt water floods flowed across the region with the crustal warping being related to thick ice sheet presence north and east of figure 1, although the direct cause was headward erosion of a deep northeast oriented valley across Montana (north of figure 1), which beheaded south oriented flood flow channels supplying floodwaters to a south oriented flood flow channel on the present-day north oriented Missouri River alignment. At Three Forks, Montana this south oriented flood flow channel split into several diverging south oriented flood flow channels. The deep northeast oriented valley (now northeast oriented Missouri River valley north of figure 1 was eroding headward from space in the deep “hole” the melting ice sheet had occupied and was capturing the south and southeast oriented ice-marginal melt water flood flow and diverting the captured floodwaters into space being opened up in the deep “hole” where the melting the ice sheet had been located. This northeast oriented valley was much deeper than the beheaded south oriented flood flow channel on the present day Missouri River alignment and floodwaters on the north end of the beheaded flood flow channel reversed flow direction to create the north oriented Missouri River drainage route seen north of Three Forks in figure 1.The reversal of flow in the Missouri River flood flow channel also reversed flood flow in flood flow channels on the Gallatin and Madison River alignments to create the north oriented Madison and Gallatin River drainage routes seen today. Headward erosion of the deep northeast and east Jefferson River valley from this reversed Missouri River flood flow channel next beheaded south oriented flood flow channels further to the west and floodwaters on the north ends of those beheaded flood flow channels reversed flow direction to create north oriented drainage routes, including the north-northeast oriented Beaverhead and Jefferson River drainage routes and north-northwest oriented Red Rock River drainage route (which then reversed the east oriented flood flow north of the Centennial Mountains to create the west oriented Red Rock River headwaters drainage route seen in figure 1).

Detailed location map for Beaverhead River-Ruby River drainage divide area

Figure 2: Detailed location map Beaverhead River-Ruby 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 Beaverhead River-Ruby River drainage divide area in Madison County, Montana and shows drainage routes not seen in figure 1. Green shaded areas are National Forest lands, which generally are located in mountainous regions. The county boundary is shown and Madison and Beaverhead Counties are labeled. Clark Canyon Reservoir is located near the southwest corner of figure 2. The north oriented river near the east edge of figure 2 is the Madison River, which north of figure 2 joins the Gallatin and Jefferson Rivers to form the north oriented Missouri River. The Beaverhead River is formed by tributaries at Clark Canyon Reservoir and flows in a north-northeast direction to the north edge of figure 2 (near Twin Bridges, slightly west of center). Note northwest oriented Beaverhead River tributaries from the east and southeast oriented tributaries from the west. The Big Hole River flows in a south direction from the north edge of figure 2 before turning to flow in a northeast direction to join the Beaverhead River to form the Jefferson River. The orientations of the Beaverhead River tributaries provide evidence the Beaverhead River valley eroded headward across south and southeast oriented flood flow channels. Floodwaters on northwest ends of the beheaded flood flow channels reversed flow direction to create what are today northwest oriented Beaverhead River tributary drainage routes. The Ruby River flows in a north, northwest, and north direction from the south edge of figure 2 (east half) to Ruby River Reservoir and then in a north and northwest direction to join the Beaverhead River near the town of Twin Bridges (near north edge of figure 2). Between the Ruby River and the Beaverhead River is the Ruby Range. Note how Beaverhead River tributaries originating in the Ruby Range generally flow in northwest directions while Ruby River tributaries originating in the Ruby Range generally are oriented in southeast directions. The orientations of the tributaries were established by southeast oriented flood flow channels at a time when the Ruby Range did not form a barrier to southeast oriented flood flow. As the Ruby Range emerged headward erosion of a much deeper south oriented valley on the Beaverhead River alignment beheaded the southeast oriented flood flow channels. Floodwaters on northwest ends of the beheaded flood flow channels reversed flow direction to create the northwest oriented Beaverhead River tributaries seen today. These northwest oriented tributaries include Carter Creek, Stone Creek, and McHessor Creek. Southeast oriented Ruby River tributaries are flowing on alignments of the former southeast oriented flood flow channels and include southeast and northeast oriented Sweetwater Creek and southeast oriented Sage Creek.

Carter Creek-Sweetwater Creek drainage divide area

Figure 3: Carter Creek-Sweetwater 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 Carter Creek-Sweetwater Creek drainage divide area. The Ruby Range extends in a southwest-to-northeast direction from the southwest quadrant of figure 3 to the northeast quadrant of figure 3. Carter Creek is a north-northwest and northwest oriented stream flowing from the Ruby Range in the southwest quadrant of figure 3 to near the northwest corner of figure 3 and joins the north-northeast oriented Beaverhead River north and west of figure 3 (the northeast drainage route near the Airway Beacon in the northwest corner of figure 3 is an irrigation canal). Stone Creek is the northwest oriented Beaverhead River tributary flowing to the north center edge of figure 3 and has southwest oriented Left and Middle Forks in the northeast quadrant of figure 3. Winnipeg Creek is a north oriented Stone Creek tributary originating near the center of figure 3. Note how Sweetwater Creek flows in an east direction (near the south center edge of figure 3) and then turns to flow in a southeast direction to the south edge of figure 3. South and east of figure 3 Sweetwater Creek turns again to flow in a northeast direction to join the north and northwest oriented Ruby River. Cottonwood Creek is a south-southeast oriented stream originating in the northeast quadrant of figure 3 and flowing to the east center edge of figure 3. East of figure 3 Cottonwood Creek turns to flow in an east and northeast direction to join the north and northwest oriented Ruby River. The map contour interval for figure 3 is 50 meters. Note how Ruby Range elevations are much lower in the Carter Creek-Sweetwater Creek drainage divide area than they are further to the southwest or to the northeast. The road intersection on the Carter Creek-Sweetwater Creek drainage divide area has an elevation of 2120 meters. The Ruby Range high point near the southwest corner of figure 3 is 2584 meters and the high point near the northeast corner of figure 3 is 2672 meters. These elevations suggest a major northwest-to-southeast oriented through valley has been eroded across the Ruby Range with the Carter Creek-Sweetwater Creek drainage divide area being a deeper channel on the floor of a much broader northwest-to-southeast oriented through valley. The large through valley provides evidence of a major southeast oriented flood flow channel that moved floodwaters across what was probably an emerging Ruby Range. Headward erosion of a deep valley on the present day Beaverhead River alignment captured the southeast oriented flood flow and diverted the water in a south direction. Floodwaters on northwest ends of the beheaded flood flow channels reversed flow direction to create the northwest oriented Beaverhead River tributary drainage routes. Subsequently the south oriented flood flow channel on the Beaverhead River alignment was beheaded and reversed to create the north-northeast oriented Beaverhead River drainage system seen today.

Detailed map of Carter Creek-Sweetwater Creek drainage divide area

Figure 4: Detailed map of Carter Creek-Sweetwater 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 Carter Creek-Sweetwater Creek drainage divide area seen in less detail in figure 3. Sweetwater Creek flows in an east direction in sections 23, 24, and 19 near the south edge of figure 4 and south of the southeast corner of figure 4 turns to flow in a southeast direction before turning to flow in a northeast direction to the north and northwest oriented Ruby River. The northwest oriented stream in section 11 is Carter Creek, which north of figure 4 flows to the north-northeast oriented Beaverhead River. The Sweetwater Road in section 13 is located in a northwest-to-southeast oriented through valley linking the northwest oriented Carter Creek valley with the southeast oriented Sweetwater Creek valley. The map contour interval for figure 4 is 20 feet and spot elevations in the through valley along the drainage divide read 6955 and 6957 feet. Elevations near the southwest corner of figure 4 rise to 7918 feet and to 8478 feet just a short distance further to the southwest (but not seen in figure 4). Elevations in section 6 in the northeast quadrant of figure 4 rise to more than 7460 feet and to more than 8500 feet north and east of figure 4. Based on evidence seen in figure 4 the through valley is approximately 500 feet deep and based on the more distant elevations (not seen in figure 4) the through valley may be as much as 1500 feet deep. The through valley is a water-eroded feature and was eroded by southeast oriented flood flow moving to a south oriented flood flow channel on the present day north oriented Ruby River alignment. The southeast oriented flood flow was moving across an emerging Ruby Range and eroded a deeper and deeper channel into the emerging mountain mass until headward erosion of a much deeper valley on the Beaverhead River alignment captured the southeast oriented flood flow. Floodwaters on the northwest end of the beheaded flood flow channel reversed flow direction to create the northwest oriented Carter Creek drainage route. Probably the south oriented flood flow on the Ruby River alignment was beheaded and reversed at approximately the same time to create the north and northwest oriented Ruby River drainage system seen today.

Stone Creek-Cottonwood Creek drainage divide area

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

Figure 5 illustrates the Stone Creek-Cottonwood Creek drainage divide area north and east of figure 3 and includes a significant overlap area with figure 3. The Ruby Range extends in a southwest-to-northeast direction from the south edge of figure 5 (west half) to the northeast quadrant of figure 5. The Left Fork Stone Creek originates near the center of figure 5 and flows in a southwest direction to join northwest oriented Stone Creek, which flows to the northwest corner of figure 5 and north and west of figure 5 joins the north-northeast oriented Beaverhead River. Note the southwest and northwest oriented Middle Fork Stone Creek, which is located south and east of the Left Fork. The southeast oriented stream originating just east of the Left Fork Stone Creek headwaters is Cottonwood Creek, which near Table Mountain turns to flow in an east and northeast direction to the east edge of figure 5 and which joins the north oriented Ruby River east of figure 5. The southeast oriented stream in the southeast quadrant of figure 5 flowing to the south edge of figure 5 is Sage Creek, which south and east of figure 5 joins the north oriented Ruby River as a barbed tributary. Note the West Fork Sage Creek, which originates south and east of the Middle Fork Stone Creek and the northwest-to-southeast oriented through valley linking the northwest oriented Stone Creek valley with the southeast oriented (West Fork) Sage Creek valley. The map contour interval for figure 5 is 50 meters and the through valley floor elevation at the drainage divide is between 2100 and 2150 meters (slightly lower than the Carter Creek-Sweetwater Creek through valley seen in figure 3). Elevations seen in figure 5 to the southwest of the through valley rise to more than 2350 meters and to the northeast rise to 2672 meters. Remember the elevation of 2584 meters seen in the southwest corner of figure 3. Based on elevations seen in figure 5 the through valley is at least 200 meters deep and based on elevations seen in figures 3 and 5 the through valley may be as much as 434 meters deep. Again the Stone Creek-West Fork Sage Creek through valley is probably a deep channel eroded into the floor of a much broader northwest-to-southeast oriented through valley carved across the Ruby Range. The through valley was eroded by southeast oriented flood flow moving across the emerging Ruby Range. Flood flow across the Ruby Range ended when headward erosion of a much deeper valley on the Beaverhead River alignment beheaded and reversed the southeast oriented flood flow to create northwest oriented drainage routes seen in figure 5.

Detailed map of Middle Fork Stone Creek-West Fork Sage Creek drainage divide area

Figure 6: Detailed map of Middle Fork Stone Creek-West Fork Sage 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 Middle Fork Stone Creek-West Fork Sage Creek drainage divide area seen in less detail in figure 5. The Middle Fork Stone Creek flows in a southwest direction from the north center edge of figure 6 into section 27 where it turns to flow in a northwest direction to near the northwest corner of figure 6 and is joined in section 21 by the southwest oriented Left Fork Stone Creek to form northwest oriented Stone Creek. The West Fork Sage Creek flows in a southeast direction to the south edge of figure 6 (south half). Further east the North Fork Sage Creek flows in a south-southeast direction to the south edge of figure 6 (near southeast corner) and still further east Bum Creek flows in a southeast direction to the east edge of figure 6. South and east of figure 6 the West Fork and North Fork join to form southeast oriented Sage Creek, which flows the north oriented Ruby River as a barbed tributary. Bum Creek is a Sage Creek tributary. In the southeast quadrant of section 27 a northwest-to-southeast oriented through valley links the northwest oriented Stone Creek valley with the southeast oriented Sage Creek valley. The map contour interval for figure 6 is 20 feet and the through valley floor elevation at the drainage divide is between 6980 and 7000 feet.  Elevations in section 24 to the northeast rise to 8000 feet while elevations in section 33 to the southwest rise to 7600 feet. North and east of figure 6 elevations rise to 8765 feet and as discussed in the figure 4 elevations south and west of figure 6 rise to 8478 feet. Based on elevations seen in figure 6 the through valley is at least 600 feet deep and based on more distant high points the through valley may be as much 1500 feet deep. The through valley seen in the southeast quadrant of section 27 is a water-eroded feature and was probably eroded as a deeper channel into the floor of a much broader northwest-to-southeast oriented through valley. The through valley was eroded by southeast oriented flood flow prior to the reversal of flood flow that created the northwest oriented Stone Creek drainage route. The southwest oriented Middle Fork and Left Fork valleys were eroded headward from the southeast oriented flood flow channel to capture southeast oriented flood flow channels moving to the actively eroding North Fork Sage Creek and Bum Creek valleys. The southwest oriented Middle Fork valley captured the southeast flood flow to the North Fork Sage  and Bum Creek valleys first and the southwest oriented Left Fork valley then beheaded the southeast flood flow routes to the newly eroded southwest oriented Middle Fork valley.

McHessor Creek-Garden Creek drainage divide area

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

Figure 7 illustrates the McHessor Creek-Garden Creek drainage divide area north and east of figure 5 and includes a significant overlap area with figure 5. The towns of Alder and Laurin are located near the northeast corner of figure 7. Ruby River Reservoir is located near the southeast corner of figure 7 and floods the north oriented Ruby River valley. North of Ruby River Reservoir the Ruby River flows in a north-northeast and north-northwest direction near the east edge of figure 7. The Ruby Range extends in a north-northeast direction from the south edge to the north edge of figure 7 and narrows to the north. Garden Creek is a southeast stream originating in the Ruby Range and flows to Ruby River Reservoir. McHessor Creek is the northwest oriented stream originating in the Ruby Range immediately to the northwest of the southeast oriented Garden Creek headwaters and flowing to the north edge of figure 7 (west half) and north of figure 7 joining the north-northeast Beaverhead River. A through valley (or mountain pass) links the northwest oriented McHessor Creek valley with the southeast oriented Garden Creek valley. The map contour interval for figure 7 is 50 meters and the through valley floor elevation at the drainage divide is between 2300 and 2350 meters. Elevations to the southwest rise to 2672 meters while elevations to the northeast rise to 2862 meters suggesting the through valley may be as much 320 meters deep. The through valley is a water-eroded landform and was eroded by a southeast oriented flood flow channel at the time the Ruby Range was emerging as a high mountain range. At first floodwaters eroded a deeper and deeper valley into the emerging mountain mass, which captured southeast oriented flood flow from adjacent flood flow channels. Headward erosion of a much deeper valley on the present day north-northeast oriented Beaverhead River alignment beheaded the southeast oriented flood flow channel. Floodwaters on the northwest end of the beheaded flood flow channel reversed flow direction to create the northwest oriented McHessor Creek drainage route. Much shallower through valleys (some defined by only one or two contour lines on a side) provide evidence that at one time the southeast oriented flood flow moved across the highest Ruby Range regions today. However, at that time the Ruby Range did not stand high above the surrounding valleys as it does today and floodwaters could freely move across it.

Detailed map of McHessor Creek-Garden Creek drainage divide area

Figure 8: Detailed map of McHessor Creek-Garden 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 McHessor Creek-Garden Creek drainage divide area seen in less detail in figure 7. McHessor Creek originates in the north half of section 31 (near center of figure 8) and flows in a north-northwest direction to the north center edge of figure 8. Trout Creek is north-northwest oriented stream flowing to the northwest corner of figure 8. Garden Creek originates near the east center edge of section 31 and flows in a southeast direction to the south edge of figure 8 (near southeast corner). The map contour interval for figure 8 is 40 feet in the east half and 20 feet in the west half. Note the northwest-to-southeast oriented through valley or pass linking the north-northwest oriented McHessor Creek valley with the southeast oriented Garden Creek valley. The through valley floor elevation at the drainage divide is between 7680 and 7700 feet. Elevations in section 29 to the northeast rise to 8778 feet while to the southwest an elevation of 8444 feet can be seen near the west edge of section 1 (near south edge of figure 8). Just south of that 8444-foot elevation and of the south edge of figure 8 elevations rise to 8765 feet. These elevations suggest the McHessor Creek-Garden Creek through valley or pass is approximately 1000 feet deep. The through valley is a water-eroded feature and was eroded as a southeast oriented flood flow channel as the Ruby Range was emerging and prior to the formation of the deep Beaverhead River valley to the northwest. Floodwaters were flowing to a south oriented flood flow channel on the present day north oriented Ruby River alignment. Headward erosion of a deep south-oriented flood flow channel on the present day Beaverhead River alignment beheaded the southeast oriented McHessor Creek-Garden Creek flood flow channel and floodwaters on the northwest end of the beheaded flood flow channel reversed flow direction to create the northwest oriented McHessor Creek drainage route. Prior to the flood flow reversal the southeast oriented flood flow channel had been eroding a deeper and deeper valley into the emerging Ruby Range. Ruby Range emergence was caused by crustal warping related to the thick ice sheet presence north and east of the study region and also by deep erosion of surrounding valleys by the immense south and southeast oriented melt water floods. Ruby Range emergence probably continued after the flood flow reversal that ended southeast oriented flood flow across the region.

Beaverhead River-Ruby River drainage divide area

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

Figure 9 illustrates the Beaverhead River-Ruby River drainage divide area north and slightly west of figure 7 and includes an overlap area with figure 7. The north end of the Ruby Range is seen in the east half of figure 9. The Beaverhead River flows in a north-northeast direction across the northwest corner of figure 9. The Ruby River flows in a northwest direction across the northeast corner of figure 9 and joins the Beaverhead River north of figure 9. McHessor Creek flows in a northwest direction from the south center edge of figure 9 to join the north-northeast oriented Beaverhead River. Big Dry Creek flows in a west and northwest direction to join northwest oriented McHessor Creek. Laurin Canyon is a northeast, east, and northeast oriented stream originating in the Ruby Range east of the Big Dry Creek headwaters and drains to the northwest oriented Ruby River. The northwest oriented Big Dry Creek valley is linked by a through valley or mountain pass with the east oriented Laurin Canyon valley. The map contour interval for figure 9 is 50 meters and the through valley floor elevation at the drainage divide is between 2450 and 2500 meters. Ruby Range elevations to the south of the through valley rise to 2862 meters while to the north elevations rise to more than 2800 meters suggesting the through valley is at least 300 meters deep.  The through valley is a water-eroded feature and provides evidence of a southeast and east oriented flood flow channel that once crossed the Ruby Range. At that time the Ruby Range did not stand high above the surrounding region as it does today and the floodwaters could freely flow across what is today a major topographic barrier. The Ruby Range emerged as floodwaters were flowing across it and at first floodwaters eroded a deeper and deeper valley into the emerging mountain range. Eventually the flood flow channel was beheaded west of the emerging mountain range, which caused a reversal of flood flow on the northwest end of southeast oriented flood flow channel to create what is today the Beaverhead River-Ruby River drainage divide.

Detailed map of Big Dry Creek-Larin Canyon drainage divide area

Figure 10:Detailed map of Big Dry Creek-Laurin Canyon drainage divide area. United States Geological Survey map digitally presented using National Geographic Society TOPO software.

Figure 10 provides a detailed topographic map of the Big Dry Creek-Laurin Canyon drainage divide area seen in less detail in figure 9. Big Dry Creek originates in section 17 and flows in a southwest, west-northwest, north, and north-northwest direction to the northwest corner of figure 10. Note also the Big Dry Creek tributary originating in section 8 and flowing in a northwest and west-southwest direction to join Big Dry Creek in section 7. Laurin Canyon originates in the northwest quadrant of section 16 and drains in a north-northeast direction to section 9 where it turns to drain in a northeast and east direction to the east edge of figure 10 (north of center). Two through valleys link the Big Dry Creek valley with the Laurin Canyon valley. The northern through valley is located near the east edge of section 8 and links the west oriented Big Dry Creek tributary valley with the east oriented Laurin Canyon valley. The second through valley is located in the northeast corner of section 17 and links the Big Dry Creek headwaters valley with the north oriented Laurin Canyon valley. The map contour interval for figure 10 is 40 feet and the northern through valley elevation at the drainage divide is between 8400 and 8440 feet while the southern through valley at the drainage divide has an elevation of between 8560 and 8600 feet, which suggests a somewhat different history for the two through valleys. The northern through valley was probably eroded as a southeast and east oriented flood flow channel moving floodwaters to a south oriented flood flow channel on the present day north oriented Ruby River alignment. The southern through valley probably was last eroded by a southwest oriented flood flow channel on the present day southwest oriented Big Dry Creek alignment, which was capturing the southeast oriented flood flow and diverting the floodwaters to south oriented flood flow channels west of the emerging Ruby Range. The north oriented Big Dry Creek segment in sections 18 and 7 was probably initiated as a south oriented valley to capture southeast oriented flood flow on the present day northwest oriented Big Dry Creek alignment. While floodwaters were flowing in anastomosing channels to opposite sides of the emerging Ruby Range the southeast and east oriented flood flow channel using the northern through valley was able to erode a deeper valley and captured the south oriented flood flow using the southern through valley. The result was south oriented flood flow channels on both sides of the present day Ruby Range high crest ridge were beheaded. Floodwaters on north ends of the two beheaded flood flow channels reversed flow direction to create the north oriented Laurin Canyon headwaters drainage route east of crest ridge and the drainage route now used by the north oriented Big Dry Creek segment west of the crest ridge. At the time these flood flow events occurred the Ruby Range was still emerging as a high mountain range and there probably were many additional flood flow movement complexities, which have not been worked out in this essay.

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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