Abstract:

This essay uses topographic map evidence to interpret landform origins along the continental divide between East Fork Bitterroot River and the Big Hole River in Ravalli and Beaverhead Counties, Montana, which is located in the Anaconda Range. The East Fork Bitterroot River is a west and southwest oriented stream flowing roughly parallel to the adjacent continental divide before turning to flow in a northwest direction to join the north-northeast oriented West Fork Bitterroot River and to form the north oriented Bitterroot River with water eventually reaching the Pacific Ocean. The Big Hole River flows in a north, northeast, southeast, and south direction around the Pioneer Mountains in Beaverhead County and then makes a large U-turn to flow in a northeast direction to join the north-northeast oriented Beaverhead River and to form the northeast oriented Jefferson River, which then flows to the north oriented Missouri River with water eventually reaching the Gulf of Mexico. North and northwest oriented East Fork Bitterroot River tributary valleys are linked by through valleys (or mountain passes) across the continental divide with southeast oriented Big Hole River tributary valleys. These through valleys and barbed tributaries provide evidence of southeast and south oriented flood flow channels that crossed the Anaconda Range as the Anaconda Range was being uplifted. Uplift of the Anaconda Range combined with headward erosion of a deeper west and southwest oriented valley on the East Fork Bitterroot River alignment resulted in flood flow reversals that eroded the north and northwest oriented East Fork Bitterroot River tributary valleys and that created the East Fork Bitterroot River-Big Hole River drainage divide. West of the Anaconda Range north oriented Camp Creek flows in a deep valley from Lost Trail Pass to join the East Fork Bitterroot River at the point where the East Fork turns from flowing in a southwest direction to flowing in a northwest direction. South of Lost Trail Pass are headwaters of the south oriented North Fork Salmon River, which flows to Salmon River at the point where the north oriented Salmon River turns to flow in a west direction. While initiated as a south oriented flood flow channel the deep north oriented Camp Creek valley was probably eroded by a reversal of flood flow that moved large volumes of flood water north from the present day Salmon River drainage basin to the present day north oriented Bitterroot River valley. A thick North American ice sheet located in a deep “hole” was the source of the immense floods, which were primarily flowing in a south and southeast direction from the ice sheet’s western margin in Canada. Ice sheet related crustal warping is interpreted  to have been responsible for uplift of mountain ranges, such as the Anaconda Range, as floodwaters flowed across them and also for massive flood flow reversals that eroded present day north oriented valleys.

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 East Fork Bitterroot River-Big Hole River drainage divide area landform origins along the continental divide in Ravalli and Beaverhead Counties, 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 East Fork Bitterroot River-Big Hole River drainage divide area landform evidence along the continental divide in Ravalli and Beaverhead Counties, Montana will be regarded as evidence supporting the “thick ice sheet that melted fast” paradigm.

East Fork Bitterroot River-Big Hole River drainage divide area location map

Figure 1: East Fork Bitterroot River-Big Hole 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 East Fork Bitterroot River-Big Hole River drainage divide along the continental divide in Ravalli and Beaverhead Counties, Montana and illustrates a region in southwest Montana with Idaho to the west (along west edge of figure 1). The Jefferson River is formed in the southeast quadrant of figure 1 at the confluence of Big Hole and Beaverhead Rivers near Twin Bridges and east of figure 1 joins the north oriented Madison and Gallatin Rivers to form the north and northwest oriented Missouri River (seen crossing the northeast corner of figure 1) with water eventually reaching the Gulf of Mexico. Note how the Big Hole River flows in a north and northeast direction west of the Pioneer Mountains and then turns to flow in an east-southeast direction to the town of Divide. From Divide the Big Hole River flows in a south and northeast direction to join the north-northeast oriented Beaverhead River. North of the south oriented Big Hole River segment are headwaters of north and northwest oriented Clark Fork, which flows from Warm Springs to Deer Lodge and Garrison before turning to flow in a northwest direction to the north edge of figure 1 (near Clinton) with water eventually reaching the Pacific Ocean. The Bitterroot River is a north oriented Clark Fork tributary flowing west of the Sapphire Mountains to join Clark Fork north of figure 1. The unlabeled south, southwest, and northwest oriented Bitterroot River tributary flowing through the town of Sula is the East Fork Bitterroot River. South of the north oriented Bitterroot River headwaters in the state of Idaho is the north and west oriented Salmon River. Lost Trail Pass on the Montana-Idaho state line is located on the drainage divide between a north-oriented East Fork Bitterroot River tributary (not shown) and a south oriented Salmon River tributary. The East Fork Bitterroot River-Big Hole River drainage divide area in Ravalli and Beaverhead Counties and investigated in this essay is located at the southwest end of the Anaconda Range and is south and east of the southwest oriented East Fork Bitterroot River segment and the north oriented tributary flowing to it from Lost Trail Pass and north and west of the northeast oriented Big Hole River segment on the northwest side of the Pioneer Mountains.

Before looking at detailed maps of the East Fork Bitterroot River-Big Hole River drainage divide area a brief look at the big picture erosion history is appropriate. 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 rapidly melting thick North American ice sheet and were flowing in a south and southeast direction from southwest Alberta and southeast British Columbia to and across the figure 1 region. North oriented rivers in figure 1 are generally flowing in valleys that originated as south oriented flood flow channels. The north oriented drainage system seen on both sides of the east-west continental divide developed sequentially during massive flood flow reversals that occurred as mountain ranges and high plateaus were uplifted by ice sheet related crustal warping and occurred as floodwaters flowed across the region. During these flood flow reversals south oriented flood flow along one route would be captured by reversed flow in an adjacent valley and then flow in a north direction along the adjacent valley. In addition, deep flood water erosion of valleys and basins surrounding the rising mountain ranges contributed to the emergence of present day mountain ranges. At the same time ice sheet related crustal warping combined with deep glacial erosion under the ice sheet was creating a deep “hole” in which the ice sheet was located. Eventually as the ice sheet melted there came a time when elevations on the ice sheet surface (at least in the south) were lower than elevations along the deep “hole” southwest rim in Montana where the immense south and southeast oriented ice marginal melt water floods were flowing. Deep northeast oriented valleys then eroded headward from space in the deep “hole” being opened up by the ice sheet melting to capture the south and southeast oriented melt water floods in present day eastern and central Montana. At the same time headward erosion of the south and west oriented Columbia River valley and tributary valleys from the Pacific Ocean beheaded and reversed south and southeast oriented flood flow channels moving floodwaters to western Montana and Idaho.

The northeast oriented Missouri River valley (north and east of figure 1) and its east and northeast oriented tributary valleys eroded headward from the deep “hole” across the south and southeast oriented flood flow. Northwest oriented Missouri River tributary valleys and the north-northwest oriented Missouri River valley segment (seen in the figure 1 northeast corner) were eroded by reversals of flood flow on north and northwest ends of beheaded flood flow channels. North oriented Jefferson River tributary alignments were established initially as south oriented flood flow channels and were reversed and deepened during the massive upper Missouri River drainage basin flood flow reversal. Reversal of flood flow in the Jefferson River valley captured south oriented flood flow on the present day north oriented Clark Fork-Big Hole River alignment, which created the present day Big Hole River U-turn east of the Pioneer Mountains. The north oriented Big Hole River segment west of the Pioneer Mountains flows on the alignments of what began as south oriented flood flow channels, but which were reversed to create the north oriented Big Hole River valley west of the Pioneer Mountains. The north oriented Bitterroot River alignment in western Montana and the north oriented Salmon River alignment in Idaho (south of Lost Trail Pass seen in figure 1) were established by one or more south oriented flood flow channels. Crustal warping that raised mountain ranges and lowered valleys and basins combined with headward erosion of deep valleys from the west systematically dismembered and reversed these earlier south oriented flood flow channel (s) to create the present day north oriented river segments.

Detailed location map for East Fork Bitterroot River-Big Hole River drainage divide area

Figure 2: Detailed location map East Fork Bitterroot River-Big Hole 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 East Fork Bitterroot River-Big Hole River drainage divide area along the continental divide in Ravalli and Beaverhead Counties, Montana and shows drainage routes not seen in figure 1. County boundaries are shown and Deer Lodge County in the northeast quadrant of figure 2 is labeled. The western tip of Silver Bow County straddles the east center edge area of figure 2. Beaverhead County is the unlabeled county south Deer Lodge and Silver Bow Counties. Ravalli County is the unlabeled county along the west edge of figure 2. The triangular area south of Lost Trail Pass in the southwest quadrant of figure 2 is located in Lemhi County, Idaho. The west-east continental divide extends from the south edge of figure 2 along the Idaho eastern border in a northwest direction to Lost Trail Pass and then in a northeast direction along the Ravalli County-Beaverhead County boundary and the Anaconda Range crest before turning in an east-southeast direction to the east edge of figure 2. Green shaded areas are National Forest lands, which generally are located in mountainous regions. The Pioneer Mountains are located in the southeast corner region of figure 2. The Big Hole River flows in a north direction from the south center edge of figure 2 to the town of Wisdom (west of the Pioneer Mountains) and then gradually turns to flow in a northeast direction to the town of Fishtrap (north of the Pioneer Mountains) and a short distance beyond before turning to flow in a southeast direction to the east edge of figure 2 (south of center). The North Fork Big Hole River flows in a northeast direction from the Big Hole National Battlefield (west of Wisdom) to join the Big Hole River north of Wisdom. Note how there are multiple southeast oriented streams flowing from the continental divide to join the northeast oriented North Fork Big Hole River and Big Hole River segments as barbed tributaries. Joseph Creek is an east-southeast oriented North Fork Big Hole River tributary originating near Lost Trail Pass. Ravalli County as seen in figure 2 is defined by the Bitterroot River drainage basin and the Bitterroot River is formed near the town of Conner (near west edge of figure 2, north of center) at the confluence of its East and West Forks and flows in a north direction to the north edge of figure 2 (near northwest corner). Of interest in this essay is the East Fork Bitterroot River, which originates in the Anaconda Range just north of the continental divide and which flows in roughly a west-southwest direction to the town of Sula before turning to flow in a northwest direction to join the north-northeast oriented West Fork Bitterroot River near Conner. Note how the East Fork Bitterroot River has south and southeast oriented tributaries from the north and north and northwest oriented tributaries from the south. Camp Creek is the north oriented East Fork Bitterroot River tributary originating near Lost Trail Pass.

East Fork Bitterroot River-Beaver Creek drainage divide area

Figure 3: East Fork Bitterroot River-Beaver 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 East Fork Bitterroot River-Beaver Creek drainage divide area. The continental divide is shown with a dashed line and extends in a northeast and north-northeast direction from the west edge of figure 3 (south of center) to the north edge of figure 3 (west of center) and follows the Anaconda Range crest. The East Fork Bitterroot River originates near Hidden Lake (just west of the continental divide at the north edge of figure 3) and flows in a southwest, south, and west direction to the west edge of figure 3 (north half) with water eventually reaching the Pacific Ocean. Park Creek originates at Park Lake, just north of the continental divide, and flows in a northeast, north, and northwest direction to join the East Fork Bitterroot River at the point where the East Fork turns to flow in a west direction. The northeast oriented Big Hole River crosses the southeast corner of figure 3 with water eventually reaching the Gulf of Mexico. Beaver Creek originates on the east side of the continental divide just east of the south oriented East Fork Bitterroot River segment and flows in a south and southeast direction to join south-southeast oriented Pinter Creek, which then flows to the south edge of figure 3 (east of center) and joins the north oriented Big Hole River as a barbed tributary south of figure 3. Note how the northwest oriented Park Creek valley segment is linked by a through valley (or mountain pass) with the southeast oriented Beaver Creek valley segment. The map contour interval for figure 3 is 50 meters and the through valley floor elevation at the continental divide is between 2400 and 2450 meters. West Pinter Peak at the north edge of figure 3 rises to at least 2850 meters and elevations along the continental divide near the west edge of figure 3 reach 2650 meters (higher elevations can be found west of figure 3), suggesting the through valley is at least 200 meters deep. Other shallower through valleys (or mountain passes) can also be seen crossing the continental divide. These through valleys are water-eroded features and were eroded by southeast oriented flood flow moving from the present day north oriented Bitterroot River drainage basin to the present day north oriented Big Hole River drainage basin (west of Pioneer Mountains). At that time the deep Bitterroot River valley north and west of figure 3 did not exist and the Anaconda Range did not stand high above the surrounding region. Floodwaters could freely flow from the ice sheet western margin in western Canada across western Montana to the region seen in figure 3. Headward erosion of the deep southwest and west oriented East Fork Bitterroot River valley eventually captured the flood flow. Floodwaters on the northwest end of the beheaded flood flow routes reversed flow direction to create the northwest oriented drainage routes such as the Park Creek drainage route.

Detailed map of Park Creek-Beaver Creek drainage divide area

Figure 4: Detailed map of Park Creek-Beaver 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 Park Creek-Beaver Creek drainage divide area seen is less detail in figure 3. The continental divide serves as the county boundary and is labeled and well-marked and extends from the south edge of figure 4 to the north edge of figure 4. East and south of the continental divide water flows to the Big Hole River and eventually reaches the Gulf of Mexico. West and north of the continental divide water flows to the Bitterroot River and eventually reaches the Pacific Ocean. The south and west oriented stream in the northwest quadrant of figure 4 is the East Fork Bitterroot River. Park Lake is located in the southwest quadrant of section 26 and Park Creek flows in a north, east, north, and northwest direction from Park Lake to join the East Fork Bitterroot River in section 22.  Alpine Creek flows from Alpine Lake in section 34 in a west direction to the northeast quadrant of section 33 and then flows in a north-northeast direction to join the East Fork Bitterroot River in section 22 (at almost the same point where Park Creek enters the East Fork). East of the continental divide Pinter Creek flows in a south-southeast direction from the north edge of figure 4 to the east edge of figure 4 (south of center). Beaver Creek headwaters are located along the continental divide in sections 18 and 24 and flow in a south and southeast direction to the east edge of figure 4 (south of Pinter Creek) and join Pinter Creek east of figure 3. Note in section 25 the through valley (or mountain pass) linking the northwest oriented Park Creek valley with the southeast oriented Beaver Creek valley. The map contour interval for figure 4 is 40 feet and the through valley floor elevation at the drainage divide is between 7920 and 7960 feet. Elevations along the continental divide to the north rise to more than 9000 feet near the north edge of figure 4 and to more than 9400 feet north of figure 4. In section 36 elevations rise to more than 8680 feet and south and west of figure 4 the continental divide rises to more than 8800 feet. These elevations suggest the through valley is at least 700 feet deep and may be even deeper. A close look at the continental divide reveals other shallower through valleys. For example, there are north-to-south oriented through valleys south of Alpine Lake and south of the north oriented Park Creek headwaters. These and other through valleys eroded across the continental divide are remnants of south and southeast oriented flood flow channels, which once crossed the region. At that time the Anaconda Range did not form a topographic barrier for south and southeast oriented flood flow as it does today, however the Anaconda Range was probably rising as floodwaters flowed across the region.

Carmine Creek-Mussigbrod Creek drainage divide area

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

Figure 5 illustrates the Carmine Creek-Mussigbrod Creek drainage divide area south and west of figure 3 and includes a significant overlap area with figure 3. The north and northeast oriented Big Hole River valley is located at the southeast corner of figure 5 although the Big Hole River is located east of figure 5. The continental divide serves as the county line and is shown with a labeled dashed line and extends from the west edge of figure 5 (near southwest corner) in a northeast direction to the north edge of figure 5 (east half). The East Fork Bitterroot River flows in a west direction from near the continental divide to the west edge of figure 5 (near northwest corner). Note the multiple north oriented tributaries flowing from the continental divide to join the west oriented East Fork Bitterroot River. Many of these north oriented East Fork Bitterroot River tributary valleys are linked by through valleys (or mountain passes) across the continental divide with valleys of southeast oriented Big Hole River tributaries. For example, Carmine Creek is a north-northwest oriented East Fork Bitterroot River tributary originating near the continental divide slightly south and west of the center of figure 5 and is linked by a through valley (or mountain pass) with southeast oriented Mussigbrod Creek, which is joined by southeast oriented Hell Roaring Creek and which then flows in a southeast direction to Mussigbrod Lake and the south center edge of figure 5. South of figure 5 Mussigbrod Creek flows to the east-northeast oriented North Fork Big Hole River. The map contour interval for figure 5 is 50 meters and the through valley floor elevation at the drainage divide is between 2250 and 2300 meters. The continental divide near Surprise Lake to the west rises to more than 2700 meters and to the east near Hope Lake the continental divide rises to 2650 meters. These elevations suggest the through valley is at least 350 meters deep. Other similar, but shallower through valleys cross the continental divide in figure 5. These through valleys are more remnants of south oriented flood flow channels that once crossed the region. Floodwaters were flowing to south oriented flood flow channels on the present day north oriented Big Hole River alignment. Headward erosion of the deep west oriented East Fork Bitterroot River valley beheaded the south oriented flood flow channels and floodwaters on north ends of the beheaded flood flow channels reversed flow direction to create the north oriented East Fork Bitterroot River tributaries. Uplift of the Anaconda Range was probably occurring as floodwaters flowed across the region and probably contributed to the flood flow reversal that created the present day East Fork Bitterroot River-Big Hole River drainage divide.

Detailed map of Carmine Creek-Mussigbrod Creek drainage divide area

Figure 6: Detailed map of Carmine Creek-Mussigbrod 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 Carmine Creek-Mussigbrod Creek drainage divide area seen in less detail in figure 5. The continental divide serves as the county boundary and is labeled and marked and extends from near the west edge of figure 6 to near the northeast corner of figure 6. Carmine Creek headwaters are located along the north side of the continental divide and flows in a northwest direction across section 17, the southwest corner of section 1, and the northeast corner of section 2 to the north edge of figure 6 (west half). North of figure 6 Carmine Creek flows to the west oriented East Fork Bitterroot River. Mussigbrod Creek headwaters are located on the south side of the continental divide (south of the Carmine Creek headwaters) and flows in a south-southeast direction through section 19 to the south center edge of figure 6. South of figure 6 Mussigbrod Creek flows to the east-northeast oriented North Fork Big Hole River. Note on the line between sections 13 and 18 the through valley linking the northwest oriented Carmine Creek valley with the south-southeast oriented Mussigbrod Creek valley. The map contour interval for figure 6 is 40 feet and the through valley elevation at the continental divide is shown as 7557 feet. South of Hope Lake in section 9 the continental divide rises to 8694 feet. Near the west edge of figure 6 the continental divide rises to more than 8700 feet. These elevations suggest the Carmine Creek-Mussigbrod Creek through valley is more than 1100 feet deep. The through valley is a water-eroded feature and was eroded by south oriented flood flow moving across the region. Other higher elevation through valleys can also be seen in figure 6 and provide evidence of what were once diverging and converging flood flow channels. Headward erosion of the deeper Carmine Creek-Mussigbrod Creek flood flow channel into what was probably a rising Anaconda Range mountain mass captured flood flow from the adjacent flood flow channels, which resulted in reversals of flood flow north ends of the beheaded flood flow channels. In time Anaconda Range uplift proceeded faster than the Carmine Creek-Mussigbrod Creek flood flow channel could erode its channel floor and headward erosion of the much deeper west oriented East Fork Bitterroot River valley north of figure 6 beheaded and reversed the flood flow channel to create the northwest oriented Carmine Creek drainage system.

Meadow Creek-Schultz Creek drainage divide area

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

Figure 7 illustrates the Meadow Creek-Schultz Creek drainage divide area west and south of figure 5 and includes a significant overlap area with figure 5. The East Fork Bitterroot River flows in a southwest direction in the northwest corner of figure 7. The north and northeast oriented Big Hole River valley can be seen in the southeast corner of figure 7. The continental divide is shown with a labeled dashed line extending from the northeast corner of figure 7 to the west edge of figure 7 (south half). Mussigbrod Lake is located near the east center edge of figure 7 and is drained by southeast oriented Mussigbrod Creek, which flows to the east-northeast oriented North Fork Big Hole River. Other named southeast oriented North Fork Big Hole River tributaries shown (from the northeast to the southwest) include Bender Creek, Schultz Creek, and Tie Creek. Meadow Creek is the north-northwest and northeast oriented stream originating north of the Schultz Creek headwaters on the northwest side of the continental divide. While not seen in figure 7 Meadow Creek flows to the southwest oriented East Fork Bitterroot River as a barbed tributary. West of Meadow Creek is north-northwest and northwest oriented Talon Creek, which flows to the west edge of figure 7 (north half) and then joins the southwest oriented East Fork Bitterroot River west of figure 7. Note how in the continental divide area between the Talon Creek headwaters and the Meadow Creek headwaters there is a mountain pass labeled as the Schultz Saddle, suggesting the continental divide is lower in elevation in that region. In section 36 (near Schultz Saddle) a through valley links the north-northwest oriented Meadow Creek headwaters valley with the southeast oriented Schultz Creek valley. This section 36 through valley is locally defined by 2 contour lines to the west and more to the east. The map contour interval for figure 7 is 50 meters so the through valley based on local elevations is probably about 100 meters deep. To the southwest another through valley links the north-northwest oriented Talon Creek valley with the southeast oriented Tie Creek valley. This second through valley is also defined by two contour lines to the west and more contour lines to the east. These through valleys are remnants of southeast oriented flood flow channels that were eroded into what at that time was a rising Anaconda Range mountain mass. Uplift of the mountain mass combined with headward erosion of the deep southwest oriented East Fork Bitterroot River valley to the north eventually caused flood flow reversals on the northwest ends of the flood flow channels, which resulted in the formation of the north oriented Meadow Creek and north-northwest oriented Talon Creek drainage systems. [Note: I have left out some steps in the flood flow reversal process to simplify the discussion. Missing steps are needed to explain formation of the northeast oriented Meadow Creek valley segment, which probably eroded headward from a south oriented flood flow channel on the North Fork Salmon River alignment seen in figure 9.].

Detailed map of Meadow Creek-Schultz Creek drainage divide area

Figure 8: Detailed map of Meadow Creek-Schultz 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 Meadow Creek-Schultz Creek drainage divide area seen in less detail in figure 7. The continental divide is labeled and extends from the south edge of figure 8 (west half) to the north edge of figure 9 (east half). Schultz Creek originates in the south half of section 36 and flows in southeast direction to the south center edge of figure 8. Meadow Creek originates in the north half of section 36 and flows in a north-northwest direction to the north edge of figure 8 (west half). A through valley in section 36 crosses the continental divide and links the north-northwest oriented Meadow Creek valley with the southeast oriented Schultz Creek valley. The map contour interval for figure 8 is 40 feet and the through valley floor elevation is between 7760 and 7800 feet. To the west in section 36 the continental divide rises to 8152 feet while to the east in section 36 the continental divide rises to 8316 feet suggesting the through valley is at least 350 feet deep. Continental divide elevations in this region are generally decreasing toward Lost Trail Pass (south and west of figure 8 and seen in figure 9) and then rise again west of the Lost Trail Pass area. In other words this 350 foot deep Meadow Creek-Schultz Creek through valley may be a channel eroded into the floor of a much broader and deeper through valley linking the north oriented Bitterroot River valley in Montana with the north and west oriented Salmon River valley in Idaho. The Meadow Creek-Schultz Creek through valley was eroded by southeast oriented flood flow moving across the region to what was probably a south oriented flood flow channel on the present day north oriented Big Hole River alignment (on the west side of Pioneer Mountains). Floodwaters in the Big Hole River valley (south and east of figure 8) reversed flow direction to create the north oriented Big Hole River probably when crustal warping uplifted areas that blocked the south oriented flood flow channel(s) and forced a reversal of floodwaters that created the north oriented Big Hole River segment seen today. That reversal of flood flow was probably aided by headward erosion of a deep southeast oriented flood flow channel on the east side of the Pioneer Mountains.

East Fork Camp Creek-Joseph Creek drainage divide area

Figure 9: East Fork Camp Creek-Joseph Creek drainage divide area. United States Geological Survey map digitally presented using National Geographic Society TOPO software.

Figure 9 illustrates the East Fork Camp Creek-Joseph Creek drainage divide area south and west of figure 7 and includes an overlap area with figure 7. Lost Trail Pass is located near the west edge of figure 9 (south of center) and is not a pass across the continental divide. The north-northeast and north-northwest oriented stream flowing near the west edge to the north edge of figure 9 (near northwest corner) is the East Fork Camp Creek, which  near the northwest corner of figure 9 is joined by the West Fork Camp Creek to form north oriented Camp Creek, which then flows to the East Fork Bitterroot River with water eventually reaching the Pacific Ocean. The south oriented stream flowing from Lost Trail Pass is Moose Creek, which joins the south oriented North Fork Salmon River, which then flows to the southwest corner of figure 9. South of figure 9 the North Fork Salmon River joins the north and west oriented Salmon River at the point where the Salmon River turns to flow in a west direction with water eventually reaching the Pacific Ocean. North of Lost Trail Pass the continental divide serves as the county line while south of Lost Trail Pass the continental divide serves as the Montana-Idaho state line. The continental divide is labeled and is shown with a dashed line and extends from the south edge of figure 9 (west half) to the north edge of figure 9. Chief Joseph Pass, which located near Lost Trail Pass, is where highway 43 crosses the continental divide and is located on the Big Hole River-Salmon River drainage divide. North of Chief Joseph Pass the continental divide is located on the Bitterroot River-Big Hole River drainage divide. Joseph Creek is the east-southeast oriented stream originating near Chief Joseph Pass and flowing to the southeast corner of figure 9. East of figure 9 Joseph Creek joins the east-northeast North Fork Big Hole River with water eventually reaching the Gulf of Mexico. The southwest and southeast oriented stream flowing from the northwest quadrant of figure 9 almost to the edge of the much deeper north oriented East Fork Camp Creek valley and then turning to join Joseph Creek north of the south center edge of figure 9 is Trail Creek. Note how in the west center area of figure 9 the Trail Creek valley is linked by a through valley with the much deeper north oriented East Fork Camp Creek valley. The map contour interval for figure 9 is 50 meters. Elevations along the drainage divide between the two streams flowing in opposite directions are between 2050 and 2100 meters. The East Fork Camp Creek valley at that point is approximately 300 meters deep while the Trail Creek valley is at approximately the same elevation as the drainage divide elevations. The southwest oriented Trail Creek headwaters valley suggests it was eroded by south oriented flood flow moving to a south oriented flood flow channel on the North Fork Salmon River alignment. Headward erosion of what was a deeper southeast oriented valley on the southeast oriented Trail Creek alignment then captured the southwest oriented flood flow channel. The deep north oriented East Fork Camp Creek valley was eroded by flood flow movements not apparent from evidence seen in figure 9, but which may have included significant north oriented flood flow from the present day Salmon River drainage basin in Idaho to the south. Figure 10 below provides a more detailed map of the remarkable East Fork Camp Creek-Trail Creek drainage divide area.

Detailed map of East Fork Camp Creek-Trail Creek drainage divide area

Figure 10: Detailed map of East Fork Camp Creek-Trail Creek 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 East Fork Camp Creek-Trail Creek drainage divide area seen in less detail in figure 9. The East Fork Camp Creek flows in a north-northeast and north-northwest direction from the south edge of figure 10 (near southwest corner) to the northwest corner of figure 10 with water eventually reaching the Pacific Ocean. The continental divide serves as the Ravalli-Beaverhead County line and extends from the south edge of figure 10 (west half) to the north edge of figure 10 (west of center) and then dips back into figure 10 with the northeast corner of figure 10 north of the continental divide. Trail Creek flows from the section 7 area (near north center edge of figure 10) in a southwest direction to section 14 and then turns to flow in a south-southeast and southeast direction to the south center edge of figure 10 with water eventually reaching the Gulf of Mexico. The East Fork Camp Creek-Trail Creek drainage divide south of Gibbons Pass seen in sections 14, 15 and 23 is remarkable and unique in that Trail Creek is flowing in a south direction on the edge of a 1200-foot deep north oriented canyon (the map contour interval for figure 10 is 40 feet). The Trail Creek valley in sections 14 and 23 (on the west side) is shallow, in some areas of section 23 the south oriented Trail Creek valley on the west is not deep enough to merit a single contour line before reaching the edge of the deep north oriented East Fork Camp Creek canyon. What sequence of events could produce the remarkable drainage arrangement? As seen in previous figures the continental divide east of figure 10 was crossed by southeast and south oriented flood flow channels. The north-northwest oriented East Fork Camp Creek alignment and the southwest oriented Trail Creek headwaters valley were probably initiated as converging flood flow channels while the north-northeast oriented East Fork Camp Creek alignment and southeast oriented Trail Creek valley were probably initiated as diverging flood flow channels in a south oriented anastomosing channel complex. The southeast oriented Trail Creek flood flow channel was captured by headward erosion of the east-southeast oriented Joseph Creek valley, which eroded headward from deeper south oriented flood flow channels on the present day north oriented Big Hole River alignment while the south-southwest oriented flood flow channel on the north-northeast oriented East Fork Camp Creek alignment was captured by headward erosion of south oriented flood flow channels on the alignment of the present day north oriented Salmon River south of Lost Trail Pass. If so, at that time the flood flow channels were all located on a surface higher in elevation than the Lost Trail Pass elevation (all elevations in figure 10 have probably been altered by crustal warping since that time). Crustal warping then raised areas to the south causing massive flood flow reversals that created the north oriented Big Hole River drainage route west of the Pioneer Mountains and that also caused a massive flood flow reversal that created the north oriented Salmon River drainage route south of figure 10 and the north oriented Bitterroot River drainage system north of figure 10. For a time north oriented floodwaters used the flood flow channels on the East Fork Camp Creek alignment to reach the much deeper Bitterroot River valley north of figure 10. Headward erosion of the much deeper west oriented Salmon River valley south of figure 10 then dismembered the north oriented flood flow channel by capturing the north oriented flood flow and diverting the north oriented floodwaters in a west direction. Floodwaters on the north end of the beheaded flood flow channel (south of Lost Trail Pass) reversed flow direction to erode the south oriented Moose Creek and North Fork Salmon River valleys and to create the Bitterroot River-Salmon River drainage divide at Lost Trail Pass.

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.