Red Rock River-Medicine Lodge Creek (South) drainage divide area landform origins along the continental divide, Beaverhead County, Montana and Clark County, Idaho, USA

Authors


Abstract:

This essay uses topographic map evidence to interpret landform origins along the continental divide between the Red Rock River in Beaverhead County, Montana and Medicine Lodge Creek in Clark County, Idaho. The continental divide segment investigated in this essay extends from Bannack Pass in the west to Monida Pass in the east and is located on the Beaverhead Mountains eastern end. In addition to Bannack Pass and Monida Pass numerous shallower passes or through valleys link north oriented tributary valleys draining to the west and north-northwest oriented Red Rock River valley with south oriented tributary valleys draining to southeast oriented Medicine Lodge Creek or south-southeast oriented Beaver Creek. These north-to-south oriented passes or through valleys crossing the continental divide provide evidence of what were once diverging and converging south oriented flood flow channels that formed on surface equivalent in elevation to the highest study region elevations today, although regional elevations have probably been significant altered by crustal warping since that time. Floodwaters are interpreted to have been derived from the western margin of a thick North American ice sheet and were flowing from western Canada across western Montana to and across the study region. Crustal warping related to the thick ice sheet presence combined with deep floodwater erosion contributed to the emergence of the Beaverhead Mountains. Headward erosion of a deep southeast oriented flood flow channel from the Monida Pass location along the present day Red Rock River alignment captured south oriented flood flow channels in sequence from east to west. Floodwaters on north ends of beheaded flood flow channels reversed flow direction to form north oriented drainage routes and also captured floodwaters from yet to be beheaded flood flow channels further to the west. The captured flood flow eroded southeast, east, and northeast oriented valleys north of the present day continental divide, but was ultimately beheaded so as to cause flood flow reversals in some of those valleys. Headward erosion of the much deeper Missouri River valley (north and east of the study region) beheaded south oriented flood flow channels supplying floodwaters to the deep southeast oriented flood flow channel on the Red Rock River alignment. The resulting massive reversal of floodwaters created the north oriented Red Rock River drainage system seen today. The much deeper Missouri River valley eroded headward from space being opened up in a deep “hole” the melting ice sheet had occupied. The massive reversal of flood flow in southwest Montana was probably greatly aided by crustal warping that was raising the region.

Preface

The following interpretation of detailed topographic map evidence is one of a series of essays describing similar evidence for all major drainage divides contained within the Missouri River drainage basin and for all major drainage divides with adjacent drainage basins. The research project is interpreting evidence in the context of a previously unexplored deep glacial erosion paradigm, which is fundamentally different from most commonly accepted North American glacial history interpretations. Project essays are listed on the sidebar category list under their appropriate Missouri River tributary drainage basin, Missouri River segment drainage basin (by state), and/or state in which the Missouri River drainage basin is located.

Introduction

The purpose of this essay is to use topographic map interpretation methods to explore the Red Rock River-Medicine Lodge Creek drainage divide area landform origins along the continental divide in Beaverhead County, Montana and Clark County, Idaho 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 Red Rock River-Medicine Lodge Creek drainage divide area landform evidence along the continental divide in Beaverhead County, Montana and Clark County, Idaho will be regarded as evidence supporting the “thick ice sheet that melted fast” paradigm.

Red Rock River-Medicine Lodge Creek drainage divide area location map

Figure 1: Red Rock River-Medicine Lodge Creek drainage divide area location map (select and click on maps to enlarge). National Geographic Society map digitally presented using National Geographic Society TOPO software.

Figure 1 provides a location map for the Red Rock River-Medicine Lodge Creek drainage divide along the continental divide in Beaverhead County, Montana and Clark County, Idaho and illustrates in the north a region in southwestern Montana with Idaho to the south and a thin slice of the northwest corner of Wyoming appearing along the south half of the east edge of figure 1. The Montana-Idaho state line is located on the east-west continental divide from near Lost Trail Pass (near northwest corner of figure 1) to the Wyoming state line (near southeast corner of figure 1) and follows the crest of the Beaverhead and Centennial Mountains. Areas north and east of the continental divide drain to the Missouri River with water eventually reaching the Gulf of Mexico. Areas south of the continental divide drain to the Snake River with water eventually reaching the Pacific Ocean. The Red Rock River originates north of the Centennial Mountains and flows in a west direction to near Lima, Montana and then turns to flow in north-northwest direction to an unlabeled lake (Clark Canyon Reservoir) at the north end of the Tendoy Mountains. At Clark Canyon Reservoir the Red Rock River is joined by north and east oriented streams to form the north-northeast oriented Beaverhead River, which flows to near Twin Bridges, Montana, where it is joined by the south and northeast oriented Big Hole River to form the northeast and east oriented Jefferson River. North of figure 1 the Jefferson River joins the north oriented Madison and Gallatin Rivers to form the north oriented Missouri River, which east of figure 1 eventually turns to become a southeast and south oriented river.

The north and north-northeast oriented unlabeled stream originating near the continental divide and joining the north-northwest oriented Red Rock River near Dell, Montana is Big Sheep Creek and marks the western boundary of the continental divide segment studied in this essay. The highway between Lima, Montana and Spencer, Idaho crosses the continental divide at Monida Pass, which marks the eastern boundary of the continental divide segment studied in this essay and which marks the dividing line between the Beaverhead Mountains to the west and the Centennial Mountains to east. South of Lima, Montana on the south side of the continental divide is an unlabeled southeast oriented stream (Medicine Lodge Creek) flowing to the south center edge of figure 1. Most south oriented drainage seen in the detailed maps illustrated in this essay drain to Medicine Lodge Creek. South of figure 1 Medicine Lodge Creek disappears as a surface stream, but is headed toward the southwest oriented Snake River. The Snake River originates in Wyoming just east of figure 1 as a south oriented stream and then turns to flow in a southwest and northwest direction south of figure 1 before turning to flow in a north direction west of figure 1 to eventually join the west oriented Columbia River. Henrys Fork seen near the southeast corner of figure 1 is a Snake River tributary.

A brief look at the big picture erosion history will help understand detailed maps seen 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 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 north of the continental divide in southwest Montana were initially developed as south and southeast oriented flood flow channels. Initially floodwaters flowed across what are today high mountain ranges including mountain ranges, which today form the east-west continental divide. Bannack Pass at the west end of this essay’s study region and near the Medicine Lodge Creek headwaters is a major north-to-south oriented through valley, which was initially eroded as a deep south oriented flood flow channel. Monida Pass at the east end of this essay’s study region is a deeper through valley eroded across the present day east-west continental divide by a southeast oriented flood flow channel, which beheaded south oriented flood flow channels further to the west with floodwaters on north ends of the beheaded flood flow channels reversing flow direction to create north oriented drainage routes. Often the reversed flood flow channels captured yet to be south oriented flood flow from flood flow channels further to the west.

When floodwaters flowed across the region there was no continental divide and mountain ranges shown in figure 1 were just beginning to emerge. As the mountains emerged floodwaters eroded deep valleys into the emerging mountain masses, with the floodwaters being captured by the most successful of these deep valleys. In time the mountains formed an insurmountable topographic barrier that ended the south oriented flood flow into Idaho. Emergence of the mountain ranges was related to crustal warping caused by the thick ice sheet’s presence north and east of figure 1. The reversal of flood flow that resulted in formation of the north oriented Missouri River drainage basin in western and central Montana occurred when a deep northeast-oriented valley eroded headward into central Montana from space in the deep “hole” the melting ice sheet had once occupied. That deep valley beheaded south oriented flood flow channels supplying floodwaters that were crossing southwest Montana. Floodwaters on north ends of those beheaded flood flow channels reversed flow direction to form the present day north oriented southwest Montana drainage routes, which flow to the Missouri River. Crustal warping that raised mountain ranges and the entire region seen in figure 1 greatly aided in this massive flood flow reversal process.

Detailed location map for Red Rock River-Medicine Lodge Creek drainage divide area

Figure 2: Detailed location map for the Red Rock River-Medicine Lodge Creek drainage divide area. United States Geological Survey map digitally presented using National Geographic Society TOPO software.

Figure 2 provides a more detailed location map for the Red Rock River-Medicine Lodge Creek drainage divide area along the continental divide in Beaverhead County, Montana and Clark County, Idaho and shows drainage routes not seen in figure 1. The continental divide serves as the Montana-Idaho state line and is shown with a well-marked dashed line extending from the west edge of figure 2 (north half) to the east edge of figure 2 (south of center). Green shaded areas are National Forest lands, which generally are located in mountainous regions. The Red Rock River flows in a west direction from the east edge of figure 2 (south of center) through Lower Red Rock Lake and Lima Reservoir to near the town of Lima, Montana where it turns to flow in north-northwest direction to the north edge of figure 2 (near town of Red Rock in west half). Monida Pass is labeled and is located on the continental divide south of Lima Reservoir. South of Monida Pass is north, east and south-southeast oriented Beaver Creek, which flows to the south edge of figure 2 (east half). South of figure 2 Beaver Creek disappears as a surface stream, but is headed toward the southwest oriented Snake River, which is further to the south. Note the west-northwest oriented stream flowing from near Monida Pass to join the Red Rock River near the town of Lima. Sawmill Creek is a northeast and north oriented tributary to that west-northwest oriented Red Rock River tributary. Just west of Lima is northwest, north-northeast, northwest, and northeast oriented Little Sheep Creek, which originates south of Garfield Mountain and which joins the north-northeast oriented Red Rock River. West of Little Sheep Creek is north and north-northeast oriented (Big) Sheep Creek, which has a north oriented tributary (Deadman Creek) originating near the continental divide to the south and a southeast oriented tributary (Cabin Creek) originating near the continental divide to the west. Just east of Deadman Creek and on the south side of the continental divide is north, east, and southeast oriented Divide Creek, which flows to southeast oriented Medicine Lodge Creek, which in turn flows to the south center edge of figure 2. Bannack Pass is not shown or labeled on figure 2, but is located on the continental divide directly north of the Divide Creek U-turn and south of where Deadman Creek joins north oriented (Big) Sheep Creek. South of figure 2 Medicine Lodge Creek disappears as a surface stream, but is headed toward the southwest oriented Snake River, which is located further to the south.

Cabin Creek-Divide Creek drainage divide area at Bannack Pass

Figure 3: Cabin Creek-Divide Creek drainage divide area at Bannack Pass. United States Geological Survey map digitally presented using National Geographic Society TOPO software.

Figure 3 provides a topographic map of the Cabin Creek-Divide Creek drainage divide area at Bannack Pass and is at the west end of the continental divide segment investigated in this essay. The labeled state and county line in the south half of figure 3 follows the east-west continental divide. Areas north of the continental divide drain to the Red Rock River with water eventually reaching the Gulf of Mexico. Areas south of the continental divide drain to southeast oriented Medicine Lodge Creek, which disappears as a surface stream, but which can be considered to be within the Snake River drainage basin, where water eventually reaches the Pacific Ocean. South of the continental divide near the south center edge of figure 3 is north, east, and southeast oriented Divide Creek, which south of figure 3 flows to southeast oriented Medicine Lodge Creek. Bannack Pass is labeled and is north of Divide Creek where a road crosses the continental divide. North of Bannack Pass is the north oriented Deadman Creek valley, which drains to north oriented Big Sheep Creek (not labeled in figure 3). Big Sheep Creek flows to the north edge of figure 3 and north of figure 3 joins the north-northwest oriented Red Rock River. Note how southeast oriented Cabin Creek flows to the point where Deadman Creek joins north oriented Big Sheep Creek. The map contour interval for figure 3 is 50 meters and the Bannack Pass elevation where the road crosses the continental divide is between 2300 and 2350 meters. Garfield Mountain near the east edge of figure 3 rises to 3841 meters while elevations at Scott Peak near the continental divide south of figure 3 rise to 3473 meters. These elevations suggest Bannack Pass could be as much 1100 meters deep. Bannack Pass is a major through valley linking the southeast oriented Cabin Creek valley with southeast oriented Medicine Lodge Creek valley to the south. The through valley was eroded as a major southeast oriented flood flow channel at a time when the high mountains seen in figure 3 did not exist. Initially floodwaters were flowing in south and southeast directions on a surface equivalent in elevation to some of the highest figure 3 elevations today, although the region has probably been uplifted since that time. Headward erosion of a deep south-southeast oriented flood flow channel on the Red Rock River alignment north of figure 3 beheaded a south oriented flood flow channel on the present day north oriented Big Sheep Creek-Deadman Creek alignment. Floodwaters on the north end of the beheaded flood flow channel reversed flow direction to create the north oriented Big Sheep Creek drainage route and to capture flood flow on the southeast oriented Cabin Creek alignment. Next headward erosion of the deep north-northeast oriented Beaverhead River valley north of this essay’s study region beheaded south oriented flood flow channels moving floodwaters to the south-southeast oriented flood flow channel on the present day Red Rock River alignment and also to the flood flow channel on the present day Cabin Creek alignment. Floodwaters on the north-northwest end of the beheaded Red Rock River flood flow channel reversed flow direction to create the west and north-northwest oriented Red Rock River drainage system and to create the drainage divide at Monida Pass seen in figure 9 and 10 of this essay. Floodwaters on the north end of the flood flow channel on the Cabin Creek alignment reversed flow direction to create a north oriented Medicine Lodge Creek drainage system north of this essay’s study region [see essay titled Red Rock River-Medicine Lodge Creek (North) drainage divide area landform origins, Tendoy Mountains, Beaverhead County, Montana] and to create drainage divide at Bannack Pass seen in figures 3 and 4.

Detailed map of Deadman Creek-Divide Bear Creek drainage divide area at Bannack Pass

Figure 4: Detailed map of Deadman Creek-Divide Creek drainage divide area at Bannack Pass. United States Geological Survey map digitally presented using National Geographic Society TOPO software.

Figure 4 provides a detailed topographic map of the Deadman Creek-Divide Creek drainage divide area at Bannack Pass seen is less detail in figure 3. The continental divide serves as the state and county line and extends from the south edge of figure 4 (near southwest corner) to the east edge of figure 4 (near northeast corner). Bannack Pass is labeled and is located where the road crosses the continental divide slightly south and west of the center of figure 4. South of the continental divide in figure 4 is north-northeast, east, and southeast oriented Divide Creek, which flows from the south edge of figure 4 (near the continental divide) to the east edge of figure 4 (near southeast corner). South and east of figure 4 Divide Creek flows to southeast oriented Medicine Lodge Creek, which disappears as a surface stream, but which is headed toward the Snake River. The north oriented drainage system in the west half of figure 4 (west and north of the continental divide) is the Deadman Creek drainage system with Deadman Creek north of figure 4 flowing to north oriented Big Sheep Creek, which flows to the north-northwest oriented Red Rock River. The map contour interval for figure 4 is 40 feet and the Bannack Pass elevation where the road crosses the continental divide is given as 7679 feet. The continental divide elevation near the northeast corner of figure 4 rises to more than 8760 feet and near the southwest corner the elevation rises to 8494 feet. However, at Italian Peak (south and west of figure 4) the continental divide elevation reaches 10,986 feet and at Garfield Mountain, which is north and east of figure 4 and also slightly north of continental divide the elevation reaches 10,961 feet. Depending on which elevations are used Bannack Pass is from 800 to 3000 feet deep. Regardless of how deep it is Bannack Pass is a major through valley eroded across the present day east-west continental divide and is a water-eroded landform. Converging south and southeast oriented flood flow channels (which converged north of figure 4) supplied the southeast oriented floodwaters that eroded the deep southeast oriented Bannack Pass valley. At that time the surrounding mountains were just beginning to emerge and the flood flow channels were being eroded into a surface as high if not higher than the highest elevations seen in figure 4. The present day Deadman Creek-Divide Creek drainage divide was formed when headward erosion of a much deeper valley on the present day north-northwest oriented Red Rock River alignment north of figure 4 beheaded a south oriented flood flow channel to the Bannack Pass flood flow channel. Floodwaters on the north end of that beheaded flood flow channel reversed flow direction to create the north oriented Deadman Creek-Big Sheep Creek drainage route and to capture southeast oriented flood flow channels, which had been supplying floodwaters to the Bannack Pass through valley. The deep north oriented Deadman Creek-Big Sheep Creek valley was eroded by yet to be beheaded south and southeast oriented flood flow from west of the newly reversed Deadman Creek-Big Sheep Creek drainage route.

Little Sheep Creek-Irving Creek drainage divide area

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

Figure 5 illustrates the Little Sheep Creek-Irving Creek drainage divide area east and slightly south of figure 3 and includes an overlap area with figure 3. The continental divide serves as the state and county line and extends from Bannack Pass (near west edge of figure 5, south of center) to the east edge of figure 5. South of the continental divide Divide Creek flows in an east and southeast direction from the west edge of figure 5 (south half) to the south edge of figure 5 (west of center). South of figure 5 Divide Creek flows to southeast oriented Medicine Lodge Creek. Red Conglomerate Peaks are a labeled high point on the continental divide near the center of figure 5. Irving Creek is the southeast and south oriented Divide Creek tributary west and south of Red Conglomerate Peaks. North of Red Conglomerate Peaks is Garfield Mountain. Between Garfield Mountain and Red Conglomerate Peaks are headwaters of Little Sheep Creek, which flows in a southwest, northwest, and north-northeast direction to the north edge of figure 5 (west half). East of the Little Sheep Creek headwaters are headwaters of northeast oriented Sawmill Creek, which east of figure 5 flows to north and northwest oriented Junction Creek, which then flows to the north-northwest oriented Red Rock River. Note how the west oriented Little Sheep Creek valley is linked by a through valley with the northeast oriented Sawmill Creek valley. The map contour interval for figure 5 is 50 meters and the through valley floor elevation at the drainage divide is between 2700 and 2750 meters. Garfield Mountain to the north rises to 3841 meters and Red Conglomerate Peaks to the south rises to more than 3100 meters suggesting the through valley may be as much as 350 meters deep. The through valley was eroded by southeast and east oriented flood flow moving to an actively eroding and deep southeast oriented flood flow channel east and north of figure 5. As that deep southeast oriented flood flow channel (on the present day northwest oriented Red Rock River alignment) eroded headward north of figure 5 it beheaded a south oriented flood flow channel, which converged with the southeast oriented flood flow channel supplying floodwaters to erode the through valley. Floodwaters on the beheaded flood flow channel north end then reversed flow direction to create the southwest, northwest, and north oriented Little Sheep Creek drainage route seen today. Also note the through valley or mountain pass west of Red Conglomerate Peaks linking the southeast oriented Irving Creek headwaters valley with the northwest oriented Little Sheep Creek valley to the north. The through valley floor elevation at the drainage divide is also between 2700 and 2750 meters suggesting that prior to the Little Sheep Creek flood flow reversal the southeast oriented flood flow channel split west of Red Conglomerate Peaks with one flood flow channel continuing in an east direction between Garfield Mountain and Red Conglomerate Peaks and the other flood flow channel proceeding in a southeast and south direction on the present day Irving Creek alignment. The flood flow reversal that created the north oriented Little Sheep Creek drainage system ended all south oriented flood flow to the Irving Creek valley.

Detailed map of Little Sheep Creek-Irving Creek drainage divide area

Figure 6: Detailed map of Little Sheep Creek-Irving 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 Little Sheep Creek-Irving Creek drainage divide area seen in less detail in figure 5. The continental divide is shown and labeled and extends from the west center edge of figure 6 to the east edge of figure 6 (south half). North of the continental divide Little Sheep Creek originates near the north edge of the northeast quadrant of figure 6 and flows in a southwest and west-northwest direction to the north edge of figure 6 (near northwest corner). South of the continental divide Irving Creek originates in section 1 and flows in a southeast direction to the south center edge of figure 6. North of the Irving Creek headwaters a deep through valley or pass crosses the continental divide and links the south oriented Irving Creek valley with the valley of a north oriented Little Sheep Creek tributary. The map contour interval for figure 6 is 40 feet and the through valley floor elevation at the drainage divide is between 8880 and 8920 feet. To the west the continental divide rises to 9641 feet while immediately to the east the continental divide rises to 9201 feet and further east at Red Conglomerate Peaks the continental divide reaches 10,106 feet suggesting the pass or through valley is at least 700 feet deep. While insignificant compared to the much deeper surrounding valleys the through valley or pass is a remnant of a south oriented flood flow channel that once crossed the region. Further east where the continental divide is oriented in a north to south direction a much deeper through valley in Idaho section 6 and Montana section 31 links a south oriented Irving Creek tributary valley with a north oriented Little Sheep Creek tributary valley.  The floor elevation of this second through valley at the continental divide is between 8480 and 8520 feet, which based on nearby high points suggests the pass or through valley is more than 1100 feet deep. This second through valley is also a remnant of a south oriented flood flow channel that once crossed the region and that converged with the first flood flow channel south of the present day continental divide. South oriented flood flow across the continental divide in figure 1 ended when headward erosion of a much deeper southeast oriented flood flow channel on the present day northwest oriented Red Rock River alignment began to behead and reverse the south oriented flood flow channels. These were beheaded and reversed in sequence from east to west, which meant reversed flood flow channels in the east could capture yet to be beheaded south oriented flood flow channels further to the west. The Little Sheep Creek valley north of the continental divide in figure 6 was initiated as an east oriented flood flow channel by such a capture. However, headward erosion of the deep southeast oriented Red Rock River flood flow channel then beheaded and reversed a south oriented flood flow channel supplying floodwaters to the east oriented Little Sheep Creek flood flow channel. Floodwaters on the north and west end of the beheaded flood flow channel reversed flow direction to create the southwest and northwest oriented Little Sheep drainage route seen in figure 6.

Sawmill Creek-East Fork Irving Creek drainage divide area

Figure 7: Sawmill Creek-East Fork Irving Creek drainage divide area. United States Geological Survey map digitally presented using National Geographic Society TOPO software.

Figure 7 illustrates the Sawmill Creek-East Fork Irving Creek drainage divide area east of figure 5 and includes a significant overlap area with figure 5. The continental divide is shown with a labeled dashed line extending from the west edge of figure 7 to the east edge of figure 7. Garfield Mountain is located near the northwest corner of figure 7 and the southwest and northwest oriented headwaters of Little Sheep Creek are located between the continental divide and Garfield Mountain. Sawmill Creek originates east of the Little Sheep Creek headwaters and flows in a northeast direction to join north oriented Little Beaver Creek and to form north-northeast oriented Junction Creek (not labeled in figure 7), which flows to the north center edge of figure 7. North of figure 7 Junction Creek turns to flow in a northwest direction and joins the north-northwest oriented Red Rock River. North oriented streams east of Little Beaver Creek in the northeast quadrant of figure 7 combine north of figure 7 to form north-northwest oriented Big Beaver Creek, which north of figure 7 joins the northwest oriented Junction Creek. South of the continental divide southwest oriented Medicine Lodge Creek can just barely be seen flowing across the southwest corner of figure 7. Irving Creek is the southeast and south-southwest oriented stream joining Medicine Lodge Creek near the southwest corner of figure 7. Other south and south-southwest oriented streams flowing to the south edge of figure 7 join Medicine Lodge Creek south of figure 7. Numerous passes, notches, or through valleys cross the continental divide in figure 7 and link the north oriented valleys with the south oriented valleys. For example, east of Red Conglomerate Peaks is Knob Mountain and just east of Knob Mountain a deep through valley or pass links a north oriented Sawmill Creek headwaters valley with the south oriented East Fork Irving Creek headwaters valley. The map contour interval for figure 7 is 50 meters and the through valley floor elevation at the drainage divide is between 2550 and 2600 meters. Knob Mountain to the west rises to more than 3000 meters, as does an unnamed mountain just to the east. These elevations suggest the through valley is at least 400 meters deep. Similar, although slightly shallower through valleys can be seen linking other north oriented valleys with south oriented valleys. These through valleys provide evidence of multiple diverging and converging flood flow channels that once crossed the region. The flood flow channels were systematically beheaded (one at a time) from east to west by headward erosion of a much deeper southeast oriented flood flow channel on the present day northwest oriented Red Rock River alignment. Floodwaters on north ends of the beheaded flow channels reversed flow direction and captured south oriented flood flow from yet to be beheaded flood flow channels further to the west and in the process eroded what is today the north side of the continental divide seen in figure 7.

Detailed map of Sawmill Creek-The Bull Pen drainage divide area

Figure 8: Sawmill Creek-The Bull Pen 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 Sawmill Creek-The Bull Pen Creek drainage divide area seen in less detail in figure 7. The continental divide serves as the state and county line and extends from the west edge of figure 8 (south of center) to the south edge of figure 8 (near southeast corner). Sawmill Creek is located north of the continental divide and flows in a northeast direction to the north edge of figure 8 (east half). North of figure 8 Sawmill Creek joins north and northwest oriented Junction Creek, which then flows to the north-northwest oriented Red Rock River. A north oriented Sawmill Creek tributary is located in sections 34 and 27. South of that north oriented valley and south of the continental divide is a south oriented valley (named on maps south of figure 8 as The Bull Pen), which south of figure 8 turns to flow in a southwest direction to join south oriented Irving Creek, which then flows to southeast oriented Medicine Lodge Creek. Note how the north oriented Sawmill Creek tributary valley and the south oriented The Bull Pen valley are linked by a north-to-south oriented through valley or pass. The map contour interval for figure 8 is 40 feet and the through valley floor elevation at the drainage divide is between 8520 and 8560 feet. The Thumb is the mountain peak to the east and reaches an elevation of 9787 feet while Knob Mountain is directly to the west and reaches an elevation of 9762 feet. These elevations suggest the north-to-south oriented through valley is approximately 1200 feet deep. The through valley was eroded as a south oriented flood flow channel into a surface that was probably equivalent in elevation to the tops of Knob Mountain and The Thumb today (note the similarities of the elevations at the tops of these two mountain peaks). At that time the Beaverhead Mountains (the east end of which is being studied in this essay) did not stand high above surrounding regions as they do today, but were beginning to emerge as floodwaters flowed across and around them. At first floodwaters eroded deep flood flow channels into the rising mountain mass, but in time those south oriented flood flow channels were beheaded by headward erosion of still deeper flood flow channels. A southeast oriented flood flow channel eroded headward from what is today Monida Pass (seen in figures 9 and 10 below) to capture south oriented flood flow channels further to the west, including the south oriented flood flow channel to The Bull Pen valley. Floodwaters on north ends of the beheaded flood flow channels reversed flow direction to create north oriented drainage routes. These north oriented drainage routes captured yet to be beheaded south oriented flood flow from further to the west. This captured flood flow moved in southeast, east, and northeast directions north of the present day continental divide. In the northwest corner of figure 8 are headwaters of southwest, northwest, and north oriented Little Sheep Creek. Note how the southwest Little Sheep Creek headwaters valley is linked by through valleys with east-northeast and east oriented Sawmill Creek tributary valleys.

Junction Creek-Beaver Creek drainage divide area at Monida Pass

Figure 9: Junction Creek-Beaver Creek drainage divide area at Monida Pass. United States Geological Survey map digitally presented using National Geographic Society TOPO software.

Figure 9 illustrates the Junction Creek-Beaver Creek drainage divide area at Monida Pass north and east of figure 7 and includes a small overlap area with figure 7. The continental divide is shown with a dashed line and serves as the state and county line and is seen in the southeast quadrant of figure 9. The town of Monida is located at Monida Pass, which is where the railroad and highway cross the continental divide. South and east of the continental divide drainage flows to east-northeast and south-southeast oriented Beaver Creek, which south of figure 9 disappears as a surface stream, but which is headed toward the southwest-oriented Snake River. Lima Reservoir in the northeast quadrant of figure 9 floods the west and northwest oriented Red Rock River valley, which continues in a west direction just north of the northwest quadrant of figure 9 before turning to drain in a north-northwest direction. Northeast oriented Sawmill Creek (labeled Creek in figure 9) is joined by Spring Creek and Little Beaver Creek in the southwest corner of figure 9 to form north oriented Junction Creek, which near the railroad and highway turns to flow in a west-northwest direction and joins the Red Rock River near the town of Lima, west and north of figure 9.  North oriented streams west of the continental divide in the south half of figure 9 flow to Junction Creek as seen in the figure. Monida Pass is a deep valley crossing the continental divide and marks the boundary between the Beaverhead Mountains to the west and the Centennial Mountains to the east. The map contour interval for figure 9 is 50 meters and the Monida Pass elevation where the railroad crosses the continental divide is between 2050 and 2100 meters. Previous figures have illustrated elevations greater than 3000 meters along the continental divide west of Monida Pass. While this essay does not illustrate regions east of Monida Pass high peaks in the Centennial Mountains to the east exceed 2900 meters in height. Elevations in the Beaverhead Mountains to the west and in the Centennial Mountains to the east suggest Monida Pass is broad through valley crossing the present day east-west continental divide and is more than 800 meters deep. While Monida Pass is probably related to underlying geologic structures it is also a water-eroded landform and was eroded by southeast oriented flood flow, which had been flowing on the present day northwest oriented Red Rock River alignment to what was probably an actively eroding Snake River valley south and east of figure 9. The flood flow direction north of Monida Pass was reversed when headward erosion of the much deeper Missouri River valley (from space in a deep “hole” the melting ice sheet had occupied) beheaded south oriented flood flow channels supplying floodwaters to the southeast oriented Red Rock River flood flow channel. The flood flow reversal was probably greatly aided by ice sheet related crustal warping that was raising the Beaverhead and Centennial Mountains.

Detailed map of Junction Creek-Beaver Creek drainage divide area at Monida Pass

Figure 10:Detailed map of Junction Creek-Beaver Creek drainage divide area at Monida Pass. United States Geological Survey map digitally presented using National Geographic Society TOPO software.

Figure 10 provides a detailed topographic map of the Junction Creek-Beaver Creek drainage divide area at Monida Pass seen in less detail in figure 9. The continental divide is shown with a labeled dashed line extending from near the southwest corner of figure 10 to the east edge of figure 10 (north half) and serves as the state and county line. Beaver Creek is the east-northeast and south-southeast oriented stream south of the continental divide in the southeast quadrant of figure 10 and flows to the southeast corner of figure 10. The west-northwest oriented stream originating near the town of Monida flows to west-northwest oriented Junction Creek, which joins the north-northwest oriented Red Rock River near the town of Lima (west and north of figure 10). The map contour interval for figure 10 is 20 feet and the Monida Pass elevation near where the railroad crosses the continental divide is given as 6820 feet. Just to the north in figure 10 the continental divide rises to 7209 feet while to the south in figure 10 the continental divide rises to 7464 feet. As seen in earlier figures elevations in the Beaverhead Mountains to the west rise to more than 10,000 feet. While not seen in this essay elevations in the Centennial Mountains to the east rise to more than 9800 feet. The local Monida Pass through valley seen in figure 10 is clearly a water-eroded valley approximately 400 feet if not deeper, but the Monida Pass region serves as a major gap between two mountain ranges that is almost 3000 feet deep. To what extent that 3000-foot deep gap is due to crustal warping or to flood flow erosion is difficult to determine, however the magnitude of the Monida Pass gap suggests immense quantities of southeast oriented floodwaters once flowed through the gap as the Beaverhead and Centennial Mountains were emerging on either side. A massive flood flow reversal took place when headward erosion of the much deeper Missouri River valley (from space in the deep “hole” a thick North American had formed and that was being opened up as the ice sheet melted) beheaded south oriented flood channels that were supplying some of the floodwaters that were flowing through this Monida Pass region. The flood flow reversal was probably greatly aided by crustal warping that was raising this entire region. The crustal warping was related to the presence of the thick North American ice sheet north and east of this essay’s study region.

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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