Boulder River-Missouri River drainage divide area landform origins in Jefferson and Broadwater Counties, Montana, USA

Authors


Abstract:

This essay uses topographic map evidence to interpret landform origins in the region between the Boulder River and the Missouri River in Jefferson and Broadwater Counties, Montana. The Missouri River flows in a north-northwest direction in the study area while the Boulder River flows in a south-southeast and southwest direction. The south oriented Boulder River then joins the east and northeast oriented Jefferson River, which flows to the north oriented Missouri River. The south end of the Elkhorn Mountains is located in the north half of the study area. The north oriented Missouri River has southeast oriented barbed tributaries and the south oriented Boulder River has northwest oriented barbed tributaries. Northwest to southeast and west to east oriented through valleys cross the drainage divide and link Boulder River tributary valleys with Missouri River tributary valleys. The through valleys are interpreted to have been eroded by southeast and south oriented floodwaters, which were derived from a thick North American ice sheet and which were flowing from western Canada across Montana. The thick ice sheet was located in a deep “hole” and the ice sheet weight caused crustal warping that raised Montana and Wyoming mountain ranges. Floodwaters flowed across emerging mountain ranges and carved deep valleys into them. A major south-southeast oriented flood flow channel on what is today the north-northwest oriented Missouri River segment was reversed in flow direction when headward erosion of the much deeper northeast oriented Missouri River valley north of the study area beheaded the south-southeast oriented flood flow channel. The deep northeast oriented Missouri River valley eroded headward from space in the deep “hole” being opened up by ice sheet melting. The flood flow reversal on the Missouri River alignment captured southeast oriented flood flow from the west creating barbed tributaries and significant drainage U-turns. Headward erosion of the Jefferson River valley next captured south oriented flood flow on the Boulder River alignment as the deep north oriented Missouri River valley head eroded headward in a west direction first along the Jefferson River alignment and second in a north direction along what is today the south oriented Boulder River alignment. The massive flood flow reversal responsible for creation of the present day north oriented Missouri River drainage system in the study region was probably greatly aided by ice sheet related crustal warping that raised mountain ranges in the Yellowstone Plateau and Elkhorn Mountains area, which became topographic barriers to the south oriented flood flow.

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 Boulder River-Missouri River drainage divide area landform origins in Jefferson and Broadwater Counties, Montana, USA. Map interpretation methods can be used to unravel many geomorphic events leading up to formation of present-day drainage routes and development of other landform features. While each detailed topographic map feature provides detailed evidence to be explained, the solution must be consistent with explanations for adjacent area map evidence as well as solutions to big picture map evidence puzzles. I invite readers to improve upon my solutions and/or to propose alternate solutions that better explain evidence and are also consistent with adjacent map area and big-picture evidence. Readers may do so either by making comments here or by writing and publishing their own essays and then by leaving a link to those essays in a comment here.

This essay is also exploring a new geomorphology paradigm in which erosional landforms are interpreted as evidence left by immense glacial melt water floods. Implied in that interpretation is the immense floods were derived from a thick North American ice sheet that created a deep “hole” in the North American continent and also melted fast. The previously unexplored paradigm being tested in this and other Missouri River drainage basin landform origins research project essays is a thick North American ice sheet, comparable in thickness to the Antarctic ice sheet, occupied the North American region usually recognized to have been glaciated, and through its weight and erosive actions created a deep North American “hole”. The southwestern rim of that deep “hole” is today preserved in the high Rocky Mountains. The ice sheet through its weight and deep erosion (and perhaps deposition along major south-oriented melt water flow routes) caused significant crustal warping and tectonic change, through its action of melting fast produced immense floods that flowed across the continent, and through its action of melting fast systematically opened up space in the ice sheet created “hole” so headward erosion of newly developed north-oriented drainage systems captured immense south-oriented melt water floods and diverted immense melt water floods north into space the ice sheet had once occupied.

If this previously unexplored paradigm is correct the geographic region explored by this essay should contain evidence of immense floods that were captured by headward erosion of new valley systems so as to cause the floods to flow in a different direction. Ability of this previously unexplored paradigm to explain Boulder River-Missouri River drainage divide area landform evidence in Jefferson and Broadwater Counties, Montana will be regarded as evidence supporting the “thick ice sheet that melted fast” paradigm.

Boulder River-Missouri River drainage divide area location map

Figure 1: Boulder River-Missouri 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 Boulder River-Missouri River drainage divide area in Jefferson and Broadwater Counties, Montana and illustrates a region in central and western Montana. Helena, Butte, Anaconda, and Bozeman are the major cities in figure 1. The Missouri River is formed at the confluence of east oriented Jefferson River, north oriented Madison River (not labeled in figure 1), and the north and northwest oriented Gallatin River near Three Forks (in southeast quadrant of figure 1-northwest from Bozeman) and flows in a north and north-northwest direction to Holter Lake (along north edge of figure 1). North and east of figure 1 the Missouri River turns to flow in a northeast and then east direction to reach North Dakota where it turns to flow in a southeast and south direction with water eventually reaching the Gulf of Mexico. The unnamed southeast oriented stream flowing to the north-northwest oriented Missouri River (near Toston) as a barbed tributary is Crow Creek. The Boulder River originates north of Butte and flows in a north direction before turning to flow in an east direction to the towns of Basin and Boulder. From the town of Boulder the Boulder River flows in a south-southeast and south-southwest direction to join the east oriented Jefferson River. The Boulder River-Missouri River drainage divide area investigated in this essay is located east of the south-southeast and south-southwest oriented Boulder River and its south oriented tributaries, west of the Missouri River, and north of the Jefferson River, and includes the Crow Creek drainage basin.

Before looking at detailed maps of the Boulder River-Missouri 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. At that time (at least initially) there were no high mountains in western and central Montana and floodwaters could freely flow across locations that are today high mountain ranges. Western Canada, Montana, Wyoming, and other mountain ranges were formed by ice sheet related crustal warping and occurred as floodwaters flowed across what were rising mountain masses. In addition, deep flood water erosion of valleys and basins surrounding the mountain masses contributed to the emergence of present day mountain ranges.

In time the ice sheet related crustal warping combined by deep glacial erosion under the ice sheet created 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’s” southwest rim 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”, which was being opened up by the ice sheet melting, to capture the south and southeast oriented melt water floods in present day Montana. The northeast oriented Missouri River valley segment (north 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 figure 1 were eroded by reversals of flood flow on the north and northwest ends of beheaded south oriented flood flow channels. The present day north oriented Madison River, north and northwest oriented Gallatin River, and north oriented Jefferson River tributaries alignments were established initially as south oriented flood flow channels, which were subsequently reversed and deepened during a massive flood flow reversal that created the present day north oriented Missouri River drainage basin seen in figure 1. Uplift of the Yellowstone Plateau and mountain ranges south of figure 1 probably contributed significantly to the massive flood flow reversal.

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

Figure 2: Detailed location map Boulder River-Missouri 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 Boulder River-Missouri River drainage divide area in Jefferson and Broadwater Counties, Montana. County boundaries are shown and Jefferson and Broadwater Counties are labeled. Green shaded areas are National Forest lands, which generally are located in mountainous regions. Helena is a major city in figure 2 and is located near the north edge of figure 2 (west of center). East of Helena is Canyon Ferry Lake, which floods the north-northwest oriented Missouri River valley with the Missouri River flowing in a north-northwest direction from Three Forks, where the Jefferson, Madison and Gallatin Rivers meet. The Jefferson River flows in a northeast, southeast, and northeast direction along the south edge of Jefferson County from the south edge of figure 2 (west half) to Three Forks. The Madison River flows in a north direction from the south edge of figure 2 (east of center) to Three Forks and the Gallatin River flows in a north and northwest direction from the south edge of figure 2 to join the Jefferson and Madison Rivers at Three Forks and to form the north and north-northwest oriented Missouri River. Butte is a major city located in the southwest quadrant of figure 2 and is located in Silver Bow County. The east-west continental divide is located along the Silver Bow-Jefferson County border just east of Butte. The Boulder River originates north of Butte where the Silver Bow County line turns west (south of Blizzard Hill). After flowing in a north direction along the continental divide to near Blizzard Hill the Boulder River turns to flow in an east direction to the towns of Basin and Boulder and then flows in a south-southeast and south-southwest direction to join the Jefferson River at Cardwell (just west of Lewis and Clark Cavern State Park). Boulder River tributaries of importance in this essay flow in a south direction to the southeast oriented Boulder River segment downstream from the town of Boulder. Muskrat Creek is the unlabeled south oriented tributary joining the Boulder River near the town of Boulder. Elkhorn Creek is the unlabeled south oriented tributary east of Muskrat Creek and Dry Creek is the labeled south oriented tributary east of Elkhorn Creek. Missouri River tributaries of interest in this essay include southeast and northeast oriented Indian Creek, which joins the Missouri River near Townsend (at south end of Canyon Ferry Lake), southeast oriented Crow Creek, which joins the north-northwest oriented Missouri River as a barbed tributary near Toston, and northeast oriented Warm Springs Creek (not labeled in figure 2) which also joins the Missouri River near Toston. Additional streams are seen in the more detailed topographic maps illustrated below.

Indian Creek-Crow Creek drainage divide area

Figure 3: Indian Creek-Crow 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 Indian Creek-Crow Creek drainage divide area. The Missouri River flows in a north-northwest direction in the east half of figure 3. The lake straddling the north edge of figure 3 north of Townsend is Canyon Ferry Lake, which is impounded behind Canyon Ferry Dam. In spite of what the map shows Canyon Ferry Dam is located at the north end of the lake and is north of figure 3 and is not at the south end of the lake. Indian Creek is a southeast, south, east, northeast, and east-northeast oriented stream joining the Missouri River near the south end of Canyon Ferry Lake and originating near the Park Mines (near north edge of figure 3-west half). Crow Creek flows in a southeast direction from the west edge of figure 3 (north half) to the south center edge of figure 3 and south of figure 3 makes a U-turn to join the north oriented Missouri River. The Indian Creek and Crow Creek U-turns are remarkable landform features and are evidence the region shown by figure 3 was drained by south and southeast oriented flood flow channels prior to the flood flow reversal that resulted in the present day north oriented Missouri River drainage system. Further evidence of south oriented flood flow channels can be found in north to south oriented through valleys linking the Indian Creek valley with the Crow Creek. These through valleys probably follow geologic structures, although the through valleys are water-eroded features. One through valley extends south from the West Fork Indian Creek valley (between Giant Hill and Hassel) to the south oriented Cold Springs Gulch valley, which drains to Crow Creek (just east of Glendale Butte). Slightly to the east another through valley just west of the Limestone Hills is drained by a north oriented Indian Creek tributary. East of the Limestone Hills through valleys can be found on both sides of the Little Hogback ridge. The map contour interval for figure 3 is 50 meters and the through valleys are defined by two to four contour lines on a side. The multiple south oriented flood flow channels were eroded by floodwaters moving to what was then the actively eroding southeast oriented Crow Creek valley, which was eroding headward from a major south oriented flood flow channel on the present day north oriented Missouri River alignment. Headward erosion of the deeper east-northeast and northeast oriented Indian Creek valley (perhaps when flood flow on the Missouri River alignment was being reversed) beheaded the south oriented flood flow channels to the newly eroded Crow Creek valley. Floodwaters on the north end of the flood flow west of the Limestone Hills reversed flow direction to erode the north oriented Indian Creek tributary valley.

Prickly Pear Creek-Crow Creek drainage divide area

Figure 4: Prickly Pear Creek-Crow Creek drainage divide area. United States Geological Survey map digitally presented using National Geographic Society TOPO software.

Figure 4 provides a topographic map of the Prickly Pear Creek-Crow Creek drainage divide area west of figure 3 and includes overlap areas with figure 3. Bullock Hill is located south of the north center edge of figure 4. Prickly Pear Creek originates south of Bullock Hill and flows in a west-northwest direction to the northwest corner of figure 4 where it is joined by north-northeast oriented Beavertown Creek and then turns to flow in a north-northeast direction to join the Missouri River north and east of figure 4.  North of Bullock Hill Wilson Creek flows in an east-southeast direction to join northeast oriented Tizer Creek and to form southeast oriented Crow Creek, which flows to the east edge of figure 4 (south of center). Note how south of Bullock Hill the west-northwest oriented Prickly Pear Creek valley is linked by a through valley with the northeast oriented Tizer Creek valley, which drains to the southeast oriented Crow Creek valley. Also note near the north edge of figure 4 a northwest to southeast oriented through valley just west of the east-oriented Wilson Creek valley. These through valleys provide evidence of converging southeast oriented flood flow channels, which crossed what is today the Elkhorn Mountains upland surface. At that time the Elkhorn Mountains did stand high above the surrounding deep valleys and basins and floodwaters could freely move in a southeast direction across the entire region. Floodwaters initially were flowing to a major south oriented flood flow channel on what is today the  north oriented Missouri River alignment. South of Three Forks at least two major south oriented flood flow channel diverged and continued in south directions along what are today alignments of the north oriented Gallatin and Madison Rivers. Headward erosion of the deep north-northeast oriented Prickly Pear Creek valley, probably when the massive Missouri River flood flow reversal took place then beheaded the southeast oriented flood flow moving across the Elkhorn Mountains regions. Floodwaters on the northwest ends of the beheaded flood flow channels reversed flow direction to erode northwest oriented Prickly Pear Creek tributary valleys including the west-northwest oriented Prickly Pear Creek headwaters valley seen in figure 4. The flood flow reversals were probably greatly aided by ice sheet related crustal warping that was raising the Elkhorn Mountains and the Yellowstone Plateau area where the Gallatin and Madison Rivers originate.

Dry Creek-Johnny Gulch drainage divide area

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

Figure 5 illustrates the Dry Creek-Johnny Gulch drainage divide area south and east of figure 4 and includes an overlap area with figure 4. The southeast oriented Boulder River can just barely be seen in the southwest corner of figure 5. The South Fork Crow Creek can be seen flowing in an east direction near the north edge of figure 5 (east half). Elkhorn Creek flows in a south direction along the west margin of figure 5 from the north edge (just east of the northwest corner) to join the Boulder River just west of the west edge of figure 5. Queen Gulch is a southwest oriented Elkhorn Creek tributary in the northwest quadrant of figure 5 (near north edge). Dry Creek originates just west of the north center area of figure 5 and flows in a south-southwest direction to join the Boulder River just south of the south edge of figure 5 (near southwest corner). Note how Dry Creek is formed at the confluence of its south oriented West Fork and its south-southwest oriented East Fork. Also note southwest oriented Sand Creek, which flows to the south-southeast oriented East Fork Dry Creek. Radersburg Pass is one of several through valleys crossing the Queen Gulch-West Fork Dry Creek drainage divide. The through valleys (or mountain passes) provide evidence of former southeast oriented flood flow channels. Johnny Gulch is the southeast oriented stream originating near Sand Creek and flowing to the east edge of figure 5 (south half). East of figure 5 Johnny Gulch drains to the Crow Creek valley near the point where Crow Creek turns to join the north oriented Missouri River (today irrigation canals in that region have altered drainage routes). Note how several northwest to southeast oriented through valleys link the southeast oriented Johnny Gulch valley with the southwest oriented Sand Creek valley. The map contour interval for figure 5 is 50 meters and the through valleys are defined by two or more contour lines on a side. The through valleys are evidence of converging southeast oriented flood flow channels that were beheaded by headward erosion of the deeper southwest oriented Sand Creek valley, which eroded headward from the south-southwest oriented Dry Creek valley. The Dry Creek valley eroded headward from the southeast oriented Boulder River valley, which suggests southeast oriented flood flow to the Johnny Gulch valley may have been beheaded before the flood flow reversal that created the north-oriented Missouri River drainage system.

Detailed map of Sand Creek-Johnny Gulch drainage divide area

Figure 6: Detailed map of Sand Creek-Johnny Gulch 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 Sand Creek-Johnny Gulch drainage divide area seen in less detail in figure 5. Johnny Gulch originates in the southeast corner of section 27 (north center area of figure 6) and drains in a southeast direction to the south edge of figure 6 (near southeast corner). Sand Creek originates in section 22 (just south of the north center edge of figure 6) and flows in a southwest direction to join the East Fork Dry Creek in section 28. A northwest to southeast oriented through valley links the southwest oriented Sand Creek valley with the southeast oriented Johnny Gulch valley. The map contour interval for figure 6 is 40 feet and the through valley at the unimproved road intersection is shown as 6815 feet. Elevations in the southeast corner of section 28 rise to 7280 feet and in the west half of section 26 to 7509 feet suggesting the through valley is at least 450 feet deep. Another northwest to southeast oriented through valley can be seen in the southwest quadrant of section 23 (near north edge of figure 6) and links the southwest oriented Sand Creek headwaters valley with the headwaters valley of southeast and south oriented Dahlman Gulch, which is a Johnny Gulch tributary. This second through valley has an elevation at the drainage divide of 7152 feet. The hill to the north in section 23 rises to 7515 feet and the previously mentioned hill in section 26 rises to 7509 feet suggesting the through valley is also at least 450 feet deep. The through valleys were eroded by southeast flood flow channels, which converged where the Dahlman Gulch and Johnny Gulch valleys meet today. Headward erosion of the deeper southwest oriented Sand Creek valley beheaded the southeast oriented flow channels and diverted the floodwaters to a south oriented flood flow channel on the present day south oriented Boulder River alignment. Study of the figure 6 map area reveals additional through valleys crossing drainage divides and providing further evidence of the southeast oriented flood flow channels and of how those flood flow channels were captured by headward erosion of south and southwest oriented Dry Creek tributary valleys.

Boulder River-Warm Springs Creek drainage divide area

Figure 7: Boulder River-Warm Springs Creek drainage divide area. United States Geological Survey map digitally presented using National Geographic Society TOPO software.

Figure 7 illustrates the Boulder River-Warm Springs Creek drainage divide area south of figure 5 and includes an overlap area with figure 5. The Boulder River flows in a south-southeast direction from the west edge of figure 7 (north half) to the south edge of figure 7 (west half). Cabin Gulch is the named south-southwest oriented Boulder River tributary in the northwest quadrant of figure 7. Johnny Gulch flows in an east-southeast and east direction across the northeast corner of figure 7 and enters the Crow Creek valley just east of figure 7. Most northeast and east oriented drainage to the figure 7 east edge flows to northeast oriented Warm Springs Creek, which joins Crow Creek shortly before Crow Creek joins the north oriented Missouri River (drainage in the Missouri River valley east of figure 7 has been altered by irrigation ditches so it is difficult to determine original drainage routes in the valley just east of figure 7). Near the center of figure 7 are west to east oriented through valleys linking west oriented Boulder River tributary valleys with east oriented Missouri River tributary valleys. The map contour interval for figure 7 is 50 meters. The floors of the deepest through valleys (south of the Montana Silver Star Mine) have elevations of between 1500 and 1550 meters. Elevations on the forested ridge just east of the Boulder River rise to more than 1700 meters in figure 7 and to more than 1900 meters just south of figure 7. To the north in figure 7 elevations north of the Dandy Mine rise to more than 1800 meters and to more than 2000 meters just north of figure 7. These elevations suggest the through valleys may be at least 350 meters deep, although the deepest through valleys were probably eroded into the floor of what was once a much broader through valley linking the Boulder River valley with the Missouri River valley. The through valleys were eroded by south oriented floodwaters on the Boulder River alignment that were moving in an east direction to the newly reversed Missouri River. In other words the floodwaters were making a big U-turn and were flowing south on the Boulder River alignment, east across figure 7 and then north on the newly reversed Missouri River alignment. Floodwaters also continued to flow further south to other west to east oriented through valleys across the south oriented Boulder River and the north oriented Missouri River drainage divide. Additional through valleys can be seen in figures 9 and 10 and of course the most successful through valley was eroded by the present day east oriented Jefferson River, which ultimately captured the south oriented Boulder River flood flow.

Detailed map of Boulder River-Warm Springs Creek drainage divide area

Figure 8: Detailed map of Boulder River-Warm Springs 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 Boulder River-Warm Springs Creek drainage divide area seen in less detail in figure 7. The south oriented Boulder River can be seen in the southwest corner of figure 8. Meyer Spring is located near the center of figure 8 and is located near the head of a west oriented Boulder River tributary valley. East of Meyer Spring in section 19 are southeast oriented headwaters of an east oriented Missouri River tributary. A west to east oriented through valley in section 24 links the west oriented Boulder River tributary valley with the southeast and east oriented Missouri River tributary valley. The map contour interval for figure 8 is 20 feet and the through valley floor elevation at the drainage divide is between 5040 and 5060 feet. Elevations in section 25 to the south rise to 5604 feet and in the northeast corner of section 13 to the north elevations rise to more than 5480 feet suggesting the through valley is at least 420 feet deep. However, south and west of figure 8 elevations rise to more than 6300 feet and even higher elevations can be found north of figure 8. Based on these higher elevations it is possible the through valley is more than 1200 feet deep. The through valley is a water-eroded feature and was eroded by floodwaters moving in an east direction from a south oriented flood flow channel on the Boulder River alignment to a newly reversed and now north oriented flood flow channel on the Missouri River alignment. Headward erosion of the deep east oriented Jefferson River valley from what was the much deeper deep north oriented Missouri River valley captured the south oriented flood flow on the Boulder River alignment and a deep south oriented Boulder River valley head then eroded headward or northward and beheaded the east oriented flood flow channel across figure 8. Floodwaters on the west end of the beheaded east oriented flood flow channel reversed flow direction and eroded the present day west oriented Boulder River tributary valley. Other through valleys can be seen in figure 8 and they provide evidence of anastomosing east oriented flood flow channels. These flood flow channels were beheaded in sequence from south to north as the much deeper south oriented Boulder valley head eroded headward or northward on the floor of the former south oriented flood flow channel on the Boulder River alignment.

Negro Hollow-Milligan Canyon drainage divide area

Figure 9: Negro Hollow-Milligan Canyon drainage divide area. United States Geological Survey map digitally presented using National Geographic Society TOPO software.

Figure 9 illustrates the Negro Hollow-Milligan Canyon drainage divide area south of figure 7 and does not include an overlap area with figure 7. The Boulder River flows in a south-southwest direction from the north edge of figure 9 (west half) to the west edge of figure 9 (just north of the southwest corner). Not seen in figure 9 is the east and northeast oriented Jefferson River, which is located south of figure 9. Negro Hollow is northwest oriented drainage route in the west center area of figure 9 and which drains to the south oriented Boulder River as a barbed tributary. Milligan Canyon is located in the southeast quadrant of figure 9 and drains in an east and south direction to the south edge of figure 9 and then to the east oriented Jefferson River. Note the through valley linking northwest oriented Negro Hollow with the east and south oriented Milligan Canyon drainage. The map contour interval for figure 9 is 50 meters and the through valley floor elevation at the drainage divide is between 1500 and 1550 meters. Doherty Mountain near the southwest corner of figure 9 rises to 1949 meters and the forested upland to the north of the through valley rises to more than 1900 meters, which means the through valley is at least 350 meters deep. The through valley was eroded by southeast oriented flood flow moving from a south oriented flood flow channel on the Boulder River alignment to what was then the actively eroding east and northeast oriented Jefferson River valley, which was eroding headward from what was then the newly reversed and actively eroding north oriented Missouri River valley. Enough flood flow was continuing to move south on the Boulder River alignment and then east and northeast on the Jefferson River alignment that the much deeper valley head eroded headward along that more southern flood flow channel route (the Jefferson River route) and not along the Negro Hollow-Milligan Canyon flood flow channel route, which eventually caused the Jefferson River route to capture the south oriented flood flow on the Boulder River alignment. The result was headward erosion of the deep valley on the Boulder River alignment beheaded the southeast oriented Negro Hollow-Milligan Canyon flood flow channel and floodwaters on the northwest end of the beheaded flood flow channel reversed flow direction to erode the northwest oriented Negro Hollow valley. Cottonwood Canyon in the southwest corner of figure 9 has a similar history.

Detailed map of Negro Hollow-Milligan Canyon drainage divide area

Figure 10: Detailed map of Negro Hollow-Milligan 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 Negro Hollow-Milligan Canyon drainage divide area seen in less detail in figure 9. Negro Hollow is labeled and is located in the northwest quadrant of figure 10 and drains in a northwest direction to the west edge of figure 10 (near northwest corner) and then to the south-southwest oriented Boulder River as a barbed tributary. The east oriented streams adjacent to the Milligan Canyon Road in the southeast quadrant of figure 10 drain to the east edge of figure 10 and then to south oriented Milligan Canyon, which drains to the east and northeast oriented Jefferson River. Through valleys (near the center of figure 10) link the northwest oriented Negro Hollow drainage route with the southeast oriented Milligan Canyon drainage route.  The map contour interval for figure 10 is 20 feet and the through valley floor elevations at the drainage divide are between 5060 and 5080 feet. Near the southwest corner of figure 10 elevations rise to more than 5900 feet and south and west of figure 10 Doherty Mountain rises to more than 6200 feet. Elevations near the north center edge of figure 10 rise to 5586 feet and north of figure 10 elevations rise to more than 6300 feet. Depending on which elevations are used the through valleys are between 400 and 1100 feet deep. The through valleys are apparently deeper flood flow channels eroded into the floor of what was once a much broader northwest to southeast oriented flood flow channel. The flood flow channels were eroded by southeast oriented flood flow moving from a south oriented flood flow channel on the Boulder River alignment initially to a south oriented flood flow channel on the Madison River alignment, although that southeast oriented flood flow channel was captured by headward erosion of the much deeper northeast oriented Jefferson River valley from the newly reversed Missouri River valley which was eroding its much deeper north oriented valley along what had been a south oriented flood flow channel. Headward erosion of the deep Jefferson River valley head captured the south and southeast oriented flood flow channels south of figure 10 and then the deep valley head eroded north along the south oriented flood flow channel on the Boulder River alignment and beheaded the southeast oriented flood flow channels crossing figure 10. Floodwaters on the northwest end of the beheaded flood flow channel seen in figure 10 reversed flow direction to erode the northwest oriented Negro Hollow valley.

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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