Wise River-Big Hole River drainage divide area landform origins, Pioneer Mountains, Beaverhead County, Montana, USA

Authors


Abstract:

This essay uses topographic map evidence to interpret landform origins in the Pioneer Mountains between the north-oriented Wise River and the south-oriented Big Hole River in Beaverhead County, Montana. The Big Hole River flows in a north and northeast direction along the Pioneer Mountains west flank and then makes a U-turn to flow in a southeast and south direction along the Pioneer Mountains north and east flanks before making another U-turn to flow in a northeast direction to join the north-northeast oriented Beaverhead River and to form the Jefferson River. The Wise River originates in the southern Pioneer Mountains and flows in a north-northwest and north-northeast direction and joins the southeast oriented Big Hole River along the Pioneer Mountains north flank. A north-to-south oriented through valley along the west side of the high Pioneer Mountains crest ridge links the north oriented Wise River headwaters area with the south and southeast oriented Grasshopper Creek headwaters, with Grasshopper Creek joining the north oriented Beaverhead River south and east of the Pioneer Mountains. Numerous through valleys in the Pioneer Mountains cross drainage divides between the north-oriented Wise River and north and northeast oriented tributaries to the southeast and south oriented Big Hole River. Many through valleys are oriented in northwest to southeast directions and appear to have been eroded by diverging and converging flood flow channels in what was a large-scale anastomosing channel complex. The highest level through valleys cross what is today the high Pioneer Mountains crest ridge and suggest the floodwaters flowed on a surface equivalent in elevation to the highest Pioneer Mountains elevations today. If correctly interpreted floodwaters crossed the Pioneer Mountains at a time when the deep Wise River valley and the deep Big Hole River valley north and west of the Pioneer Mountains did not exist and when the Pioneer Mountains did not stand high above surrounding regions as they do today. The south oriented Big Hole River valley located east of the Pioneer Mountains was probably eroded by south oriented flood flow, which was captured by headward erosion of the deep Jefferson River valley so as to form the Big Hole River U-turn east of the Pioneer Mountains. Many valleys in the Pioneer Mountains including the north oriented Wise River valley probably were eroded initially as south oriented flood flow channels before being beheaded and reversed so as to create the north oriented drainage routes seen today. The Pioneer Mountains were probably being uplifted as floodwaters flowed across them and this uplift probably contributed to the flood flow reversals. Subsequent to the valley formation and the Pioneer Mountains uplift alpine glaciers further eroded valleys in the high Pioneer Mountains.

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 Wise River-Big Hole River drainage divide area landform origins in the Pioneer Mountains in Beaverhead County, Montana and events leading up to formation of present-day drainage routes and development of other landform features. While each detailed topographic map feature provides detailed evidence to be explained, the solution must be consistent with explanations for adjacent area map evidence as well as solutions to big picture map evidence puzzles. I invite readers to improve upon my solutions and/or to propose alternate solutions that better explain evidence and are also consistent with adjacent map area and big-picture evidence. Readers may do so either by making comments here or by writing and publishing their own essays and then by leaving a link to those essays in a comment here.

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

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

Wise River-Big Hole River drainage divide area location map

Figure 1: Wise 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 Wise River-Big Hole River drainage divide in the Pioneer Mountains in Beaverhead County, Montana and illustrates in the east half a region in southwestern Montana with Idaho west and south of Montana except in the southeast corner of figure 1 where an area in Yellowstone National Park in the northwest corner of Wyoming is visible. The Pioneer Mountains are near the center of figure 1 and the Big Hole River flows in a north direction along the Pioneer Mountains west side then turns and flows in a south direction on the Pioneer Mountains east side before making still another U-turn to flow in a northeast direction to join the north-northeast oriented Beaverhead River and to form the northeast and east oriented Jefferson River. The Missouri River is formed near the town of Three Forks (located near east center edge of figure 1) at the confluence of the Gallatin, Madison, and Jefferson River and flows in a north and north-northwest direction to the north edge of figure 1. North of figure 1 the Missouri River turns to flow in a northeast and then east direction to North Dakota where it turns to flow in a southeast and south direction with water eventually reaching the Gulf of Mexico. The Wise River is shown, but not labeled in figure 1 and flows in a north-northwest and north-northeast direction in the heart of the Pioneer Mountains to join the Big Hole River near the town of Wise River. The Big Hole River-Wise River drainage divide area investigated in this essay is located between the north oriented Wise River in the Pioneer Mountains and the south oriented Big Hole River on the Pioneer Mountains east flank. The Big Hole River-Wise River drainage divide area landform origins in the Pioneer Mountains, Beaverhead County, Montana essay illustrates and interprets landforms between the north oriented Big Hole River on the Pioneer Mountains west flank and the north oriented Wise River in the Pioneer Mountains.

Before looking at detailed maps of the Wise 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. At that time the high mountain ranges and deep valleys and basins that exist today did not exist and floodwaters formed large anastomosing complexes of diverging and converging south oriented flood flow channels as they flowed freely across the region. The mountains ranges and valleys and valleys and basins emerged as crustal warping related to the presence of a huge continental ice sheet north and east of figure 1 and related to the massive erosion and deposition occurring as floodwaters flowed across the 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 today was formed during massive flood flow reversals that occurred as mountain ranges and high plateaus were uplifted by ice sheet related crustal warping as floodwaters flowed across the region. During these flood flow reversals south oriented flood flow along one route would be captured so as to flow in a north direction along an adjacent route. In addition, deep flood water erosion of valleys and basins surrounding the rising mountain ranges contributed to the emergence of present day mountain ranges.

The south oriented Big Hole River segment east of the Pioneer Mountains is one of the few river segments seen in figure 1 that is still flowing in a south direction. Before being captured by the massive flood flow reversal that took place in the figure 1 region the south oriented flood flow continued in a south direction to what is now the Snake River drainage basin in eastern Idaho and the northwest corner of Wyoming. The north oriented Big Hole River segment west of the Pioneer Mountains and the north oriented Wise River in the Pioneer Mountains flow on the alignments of what began as south oriented flood flow channels, but which were reversed to create the north oriented drainage systems. Reversal of flood flow in the Big Hole River valley west of the Pioneer Mountains and in the Wise River valley in the Pioneer Mountains probably occurred when crustal uplift raised areas in the south relative to areas in the north and as a deep southeast oriented valley eroded headward from the south oriented flood flow channel east of what was then the emerging Pioneer Mountains. The northeast oriented Missouri River valley (north and east of figure 1 and not seen in figure 1) eroded headward from the deep “hole” in which the decaying ice sheet was located. The north-northwest oriented Missouri River valley segment (seen in the figure 1) was eroded by reversals of flood flow on north and northwest ends of beheaded flood flow channels. Reversal of flood flow in the Jefferson River valley captured south oriented flood flow on the present day south oriented Big Hole River alignment (east of the Pioneer Mountains), which created the present day Big Hole River U-turn east of the Pioneer Mountains.

Detailed location map for Wise River-Big Hole River drainage divide area

Figure 2: Detailed location map Wise 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 Wise River-Big Hole River drainage divide area in the Pioneer Mountains in Beaverhead County, Montana and shows drainage routes not seen in figure 1. Green shaded areas are National Forest lands, which generally are located in mountainous regions. The Pioneer Mountains are labeled and are located in Beaverhead County, which is located in the west half of figure 2. The Big Hole River flows in a northeast direction across the northeast corner of figure 2. North of figure 2 the Big Hole River turns to flow in a southeast direction and then flows back into figure 2 to the towns of Wise River, Dewey, and Divide before turning to flow in a south direction to the southeast quadrant of figure 2.  Near the town of Glen in the southeast quadrant of figure 2 the Big Hole River begins to make a large U-turn as it flows around McCartney Mountain to join the north-northeast oriented Beaverhead River near the east edge of figure 2 and to form the north-northeast oriented Jefferson River. Labeled tributaries to the south oriented Big Hole River include northeast and east oriented Canyon Creek, northeast, north, and east-southeast oriented Trapper Creek, southeast, northeast, and east oriented Cherry Creek, and south, southeast, east, and northeast oriented Willow Creek. Torrey Mountain is located in the Pioneer Mountains near the south edge of figure 2 (west of center). The Wise River originates near Torrey Mountain and flows in a north-northwest and north-northeast direction and joins the Big Hole River near the town of Wise River. The Wise River-Big Hole River drainage divide area investigated in this essay is located east of the north oriented Wise River, south and west of the southeast and south oriented Big Hole River, and north of Willow Creek. The Moose Creek-Big Hole River drainage divide area landform origins, Silver Bow and Madison Counties, Montana essay illustrates and interprets landforms in the region between the south oriented and northeast oriented Big Hole River segments in the east half of figure 2.

Wise River-Canyon Creek drainage divide area

Figure 3: Wise River-Canyon 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 Wise River-Canyon Creek drainage divide area. The Big Hole River serves as the Silver Bow County-Beaverhead County border and extends in an east-southeast direction from the north edge of figure 3 (near town of Wise River) to near the town of Divide (near east edge of figure 3) and then turns to flow in a south-southeast direction to the east edge of figure 3 (near southeast corner). Quartz Hill Gulch originates near the center of figure 3 and flows in a northeast and north direction to join the east-southeast oriented Big Hole River near the town Dewey. Echo Gulch is an east and northeast oriented Quartz Hill Gulch tributary originating south of Quartz Hill. The Wise River flows in a north-northeast direction from the west edge of figure 3 (south half) to the north edge of figure 3 (west half, near town of Wise River) and joins the Big Hole River north of figure 3. Ore Camp Hill is located near the south center edge of figure 3. Canyon Creek flows in a northeast direction from the south edge of figure 3 (west of Ore Camp Hill) and then turns to flow in an east-southeast and northeast direction to join the south-southeast oriented Big Hole River. Vipond Creek is an east, northeast, and southeast oriented Canyon Creek tributary located just north of Canyon Creek in the south center area of figure 3. Adson Creek is a northwest oriented Wise River tributary flowing between Sheep Mountain and Gray Jockey Peak in the southwest quadrant of figure 3. Note how east of Sheep Mountain the northwest oriented Adson Creek valley is linked by a through valley with the Vipond Creek valley. The map contour interval for figure 3 is 50 meters and the through valley floor elevation at the drainage divide is between 2400 and 2450 meters, Sheep Mountain to the west rises to more than 2650 meters and a hill east of the northeast oriented Echo Gulch segment rises also rises to more than 2650 meters suggesting the through valley is at least 200 meters deep. Other northwest-to-southeast oriented through valleys cross the drainage divides between Echo Gulch and Vipond Creek and between Echo Gulch and southeast oriented Big Hole River tributaries. These and many other through valleys crossing drainage divides in figure 3 provide evidence of southeast oriented flood flow channels that once crossed the region. At that time the deep Wise River valley to the west did not exist and floodwaters could freely flow across the region.Headward erosion of the deep north-northeast and north oriented Quartz Hill Gulch and northeast oriented Echo Gulch valley beheaded southeast oriented flood flow channels, which were subsequently beheaded by Wise River valley headward erosion. Floodwaters on north and northwest ends of the beheaded flood flow routes reversed flow direction to erode north and northwest oriented valleys and to create present day drainage divides.

Detailed map of Adson Creek-Vipond Creek drainage divide area

Figure 4: Detailed map of Adson Creek-Vipond 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 Adson Creek-Vipond Creek drainage divide area seen is less detail in figure 3. Canyon Creek flows in a northeast direction across the southeast corner of figure 4. Vipond Creek flows in a southeast direction from the northwest corner of section 10 to the northeast corner of section 14 and then turns to flow in a northeast and east direction to the east center edge of figure 4 and to join Canyon Creek east of figure 4. Adson Creek originates in section 3 and flows in a northwest direction to the northwest corner of figure 4. At the corner of sections 2, 3, 10, and 11 a through valley links the northwest oriented Adson Creek valley with the southeast and northeast oriented Vipond Creek valley. The map contour interval for figure 4 is 40 feet and the through valley floor elevation at the drainage divide is between 7960 and 8000 feet. The hill to the northeast rises to more than 8240 feet and east of figure 4 the ridge rises to 8695 feet. Sheep Mountain, which is west of figure 4, rises to 9578 feet. These elevations suggest the through valley may be as much as 700 feet deep. Another through valley, in the south half of section 31, near the northeast corner of figure 4, links the Echo Gulch valley with the Vipond Creek valley. The floor of the second through valley has an elevation of between 7880 and 7920 feet, which suggests the through valley is also approximately 700 feet deep. The through valleys are water-eroded valleys and were eroded by southeast oriented flood flow, which had been captured by headward erosion of the northeast and east oriented Vipond Creek valley. At that time the deep north-northeast oriented Wise River valley north and west of figure 4 and the high drainage divide seen today did not exist and southeast oriented floodwaters could freely flow into the region shown in figure 4. Crustal warping that raised the Pioneer Mountains and headward erosion of the deep northeast and north Echo Gulch valley and the deep north-northeast oriented Wise River valley captured and beheaded the southeast oriented flood flow channels. Floodwaters on the northwest end of the western flood flow channel reversed flow direction to erode the northwest oriented Adson Creek valley.

Canyon Creek-Big Hole River drainage divide area

Figure 5: Canyon Creek-Big Hole River drainage divide area. United States Geological Survey map digitally presented using National Geographic Society TOPO software.

Figure 5 illustrates the Canyon Creek-Big Hole River drainage divide area south and east of figure 3 and includes an overlap area with figure 3. The Big Hole River flows in a south direction near the east edge of figure 5. Canyon Creek originates near the west edge of figure 5 and flows in a north and northeast direction almost to the north edge of figure 5 before turning to flow in an east-southeast and northeast direction to the north edge of figure 5 (east half) and to join the south oriented Big Hole River as a barbed tributary north of figure 5. The northeast and east-southeast oriented stream located east and south of Canyon Creek is Trapper Creek, which joins the south oriented Big Hole River near the town of Melrose. Southeast and south of Trapper Creek is north, east, and east-northeast oriented Cherry Creek, which also flows to the south oriented Big Hole River. Rock Creek originates north of Mount Tahepia in the southwest corner of figure 5 and flows in an east and southeast direction to the south edge of figure 5 (west of center) and joins the Big Hole River south of figure 5. Note how multiple through valleys cross drainage divides between the north and northeast oriented Canyon Creek, Trapper Creek, and Cherry Creek headwaters. The map contour interval for figure 5 is 50 meters. Some of the through valleys are deep, such as the through between Trapper Creek and Cherry Creek seen just west of Beals Mountain (near center of figure 5), which is more than 300 meters deep. Other through valleys are shallower, although through valleys crossing the Canyon Creek-Trapper Creek drainage divide are shown with two or more contour lines on each side. Today the through valleys stand high above the much deeper north and northeast oriented Big Hole River tributary valleys. However, the through valleys provide evidence of southeast oriented diverging and converging flood flow channels that once crossed the region. At that time the deep north and northeast oriented Big Hole River tributary valleys did not exists and floodwaters could freely flow in a southeast direction across the region. Headward erosion of the deep north and east oriented Cherry Creek valley captured the southeast oriented flood flow first. Next headward erosion of the deep northeast and east-southeast oriented Trapper Creek valley captured the flood flow and beheaded flood flow routes to the newly eroded Cherry Creek valley. Canyon Creek valley headward erosion next captured the southeast oriented flood flow and beheaded flood flow routes to the newly eroded Trapper Creek valley. Vipond Creek headward erosion (from the Canyon Creek valley) next beheaded flood flow routes to the newly eroded Canyon Creek valley and as seen in figures 3 and 4 Echo Gulch and Wise River valley headward erosion beheaded flood flow channels to the newly eroded Vipond Creek valley. Probably Pioneer Mountains uplift was occurring as floodwaters were flowing across the region and as flood flow captures were taking place.

Detailed map of Trapper Creek-Cherry Creek drainage divide area

Figure 6: Detailed map of Trapper Creek-Cherry 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 Trapper Creek-Cherry Creek drainage divide area seen in less detail in figure 5. Cherry Creek originates at Cherry Lake and flows in an east direction to the south center edge of figure 6. South of figure 6 Cherry Creek turns to flow in a north-northeast direction back into figure 6 and in section 8 turns to flow in an east-northeast direction to the east center edge of figure 6. Bear Gulch is a south-southeast oriented tributary draining to the Cherry Creek elbow of capture (where Cherry Creek turns to flow in an east-northeast direction). Trapper Creek flows in a northeast direction from section 11 near the west edge of figure 6 to section 6 and then turns to flow in a north direction to the north center edge of figure 6. Note through valleys linking the Trapper Creek and Cherry Creek valleys. One through valley is located in section 12 and links the northeast oriented Trapper Creek valley with the Cherry Creek headwaters valley. The map contour interval for figure 6 is 40 feet and the through valley floor elevation at the drainage divide is between 8960 and 9000 feet. The hill in the southwest corner of section 7 rises to more than 9280 feet and the mountain peak in section 14 rises to 10, 309 feet suggesting the through valley is at least 220 feet deep. A much deeper through valley is seen in the southwest quadrant of section 5 and links the north oriented Trapper Creek valley segment with the south-southeast oriented Bear Gulch valley and north-northeast oriented Cherry Creek valley segment. This second through valley floor elevation at the drainage divide is between 7920 and 7960 feet. Beals Mountain in section 4 rises to 8965 feet suggesting the through valley is at least 1000 feet deep. A somewhat shallower and more subtle through valley can be seen in the northeast quadrant of section 7. These through valleys provide evidence of southeast oriented flood flow channels that existed prior to headward erosion of the deep Trapper Creek valley. The section 5 through valley to Bear Gulch was probably eroded by flood flow that moved in a south direction along the alignments of the present day north oriented Trapper Creek and Cherry Creek segments. Headward erosion of the deep east oriented Cherry Creek valley from the deep south oriented Big Hole River valley (east of figure 6) captured the south oriented flood flow and floodwaters on the north end of the beheaded flood flow channel reversed flow direction to erode the north oriented Cherry Creek valley segment. Next headward erosion of the deep east oriented Trapper Creek valley north of figure 6 captured the south oriented flood flow and again floodwaters on the north end of the beheaded flood flow channel reversed flow direction to erode the north oriented Trapper Creek valley segment. Uplift of the Pioneer Mountains was probably occurring at the same time as the deep Cherry Creek and Trapper Creek valleys were eroding headward to behead and reverse flood flow routes seen in figure 6.

Wise River-Rock Creek drainage divide area

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

Figure 7 illustrates the Wise River-Rock Creek drainage divide area south and west of figure 5 and includes an overlap area with figure 5. A high north to south oriented ridge is located near the center of figure 7 and represents the crest of the Pioneer Mountains and appears to have been eroded by alpine glaciers, especially along the east side. While landforms in this region were almost certainly altered by glacial erosion the valleys existed before the glaciation and in this essay our concern is with the valley origins. Sharp Mountain is a labeled mountain peak located just west of the north center region of figure 7. Jacobson Creek originates south of Sharp Mountain and flows in west, southwest and west-southwest to join north and northwest oriented David Creek, north-northwest oriented Elkhorn Creek and northeast oriented Mono Creek and to form the north-northwest and north-northeast oriented Wise River, which is located near the west edge of figure 7 (north half). South oriented drainage in the southwest corner of figure 7 including northwest oriented St. Louis Gulch flows to south and southeast oriented Grasshopper Creek, which south of the Pioneer Mountains joins the north-northeast oriented Beaverhead River (see figure 1). The through valley linking the north oriented Mono Creek headwaters with the south oriented Grasshopper Creek headwaters seen near the west edge of figure 7 (south half) provides evidence the present day north oriented Wise River valley originated as a south oriented flood flow channel that was reversed by Pioneer Mountains uplift and by headward erosion of the much deeper southeast oriented Big Hole River valley along the Pioneer Mountains north flank. East of the Jacobson Creek headwaters are headwaters of east, southeast and northeast oriented Rock Creek, which flows to the east edge of figure 7 (north of center). At first glance the Pioneer Mountains crest ridge does not appear to be crossed by identifiable through valleys, although a closer look reveals numerous notches, mountain passes, or saddles eroded into the ridge, which provide evidence of former water-eroded valleys. One such notch or mountain pass is located between Sharp Mountain and Mount Tahepia and links the west oriented Jacobson Creek headwaters with the east oriented Rock Creek headwaters. The map contour interval for figure 7 is 50 meters and the mountain pass floor elevation, at the drainage divide, is between 2850 and 2900 meters. Sharp Mountain rises to more than 3150 meters while Mount Tahepia to the south rises to more than 3200 meters suggesting the pass is at least 250 meters deep. At the time water flowed in the valley that eroded the present day mountain pass there was no deep Wise River valley to the west and floodwaters were flowing on a surface equivalent in elevation to some of the highest elevations in figure 7 seen today (although the entire Pioneer Mountains region has probably been uplifted since). Headward erosion of a deep south oriented flood flow channel along the present day Grasshopper Creek valley-Wise River valley alignment probably was responsible for much of the erosion west of the Pioneer Mountain crest ridge while headward erosion of a south-oriented flood flow channel on the present day south oriented Big Hole River-north oriented Beaverhead River alignment was probably responsible for much of the erosion east of the Pioneer Mountains crest ridge, although Pioneer Mountain uplift probably also contributed to elevations seen along the Pioneer Mountains crest ridge today. For comparison purposes the Wise River-Grasshopper Creek through valley seen near the southwest corner of figure 7 has an elevation of between 2300 and 2350 meters, or 350 meters lower than the floor of the mountain pass between Sharp Mountain and Mount Tahepia.

Detailed map of Jacobson Creek-Rock Creek drainage divide area

Figure 8: Jacobson Creek-Rock Creek drainage divide area. United States Geological Survey map digitally presented using National Geographic Society TOPO software.

Figure 8 provides a topographic map of the Jacobson Creek-Rock Creek drainage divide area seen in less detail in figure 7. The high Pioneer Mountains crest ridge is seen along the north edge of figure 8 and then extends in a south direction across the center of figure 8. Mount Tahepia is located in section 28 and Sharp Mountain is located to the north near the north edge of figure 8. Rock Creek originates at Waukena Lake in sections 21 and 22 and flows in an east direction to the east edge of figure 8 (north of center). East of figure 8 Rock Creek flows to the south oriented Big Hole River. Jacobson Creek originates at Tahepia Lake in the southwest corner of section 21 and flows in a west and west-southwest direction to the west center edge of figure 8. West of figure 8 Jacobson Creek flows to the north oriented Wise River. The Rock Creek and Jacobson Creek headwaters are located in cirques, which appear to have been carved by alpine glaciers. While glacial erosion has modified the landscape the valleys existed before the glaciers formed and are water-eroded valleys. The through valley or mountain pass linking the east-oriented Rock Creek valley with the west oriented Jacobson Creek valley seen in section 21 probably predates the glaciation and if so was eroded by east oriented flood flow moving to a south oriented flood flow channel on the present day south oriented Big Hole River alignment. At that time the deep valleys west of the Pioneer Mountains crest ridge did not exist and the entire region to the west was at a level comparable in elevation to the Jacobson Creek-Rock Creek pass elevation if not higher in elevation. The map contour interval for figure 8 is 40 feet and the pass elevation (at the drainage divide) is between 8760 and 8800 feet. Mount Tahepia to the south rises to 10,473 feet while the high point in section 21 to the north rises 10,357 feet suggesting the through valley may be more than 1500 feet deep. A close look at the Pioneer Mountains crest ridge in figure 8 reveals other shallower mountain passes or notches in the ridge, which provide evidence of earlier flood flow channels, which flowed on an even higher level surface. While it is difficult to decipher flood flow movements from such limited evidence the multiple mountain passes or through valleys suggest diverging and converging flood flow channels such as are found in an anastomosing channel complex once crossed the region on a former surface as high as the Pioneer Mountain crest ridge, although Pioneer Mountains uplift since that time has probably modified regional elevations. The Pioneer Mountain Mountains crest ridge probably emerged as the drainage divide between a deep south oriented flood flow channel on the present day south oriented Big Hole River-north oriented Beaverhead River alignment east of figure 8 and a deep south oriented flood flow channel on the present day north oriented Wise River-south-oriented Grasshopper Creek alignment west of figure 8. Headward erosion of the deep south oriented flood flow channel west of figure 8 ended all flood flow movements across what is today the Pioneer Mountains crest ridge.

Elkhorn Creek-Birch Creek drainage divide area

Figure 9: Elkhorn Creek-Birch Creek drainage divide area. United States Geological Survey map digitally presented using National Geographic Society TOPO software.

Figure 9 illustrates the Elkhorn Creek-Birch Creek drainage divide area north of figure 7 and includes a significant overlap area with figure 7. Grasshopper Creek flows in a south direction near the southwest corner of figure 9 and south of figure 9 and the Pioneer Mountains flows to the present day north oriented Beaverhead River (see figure 1). Mono Creek near the northwest corner of figure 9 joins west oriented Jacobson Creek and north-northwest oriented Elkhorn Creek near the north edge of figure 9 to form the north oriented Wise River, which flows to the southeast oriented Big Hole River along the Pioneer Mountains north flank. The north and northwest oriented Jacobson Creek tributary east of Elkhorn Creek is David Creek and has a well-marked Pack Trail located in it. The Wise River-Grasshopper Creek drainage divide is located south of Mono Park along the west edge of figure 9 (north half) and has a present day elevation of between 2300 and 2350 meters (the map contour interval for figure 9 is 50 meters). Northwest oriented St Louis Gulch turns to drain in a south direction to Grasshopper Creek while adjacent and parallel northwest oriented Sheldon Creek flows to northeast oriented Mono Creek and then to the Wise River. East of the north to south oriented Pioneer Mountains crest ridge are tributaries to the south oriented Big Hole River on the east side of the Pioneer Mountains. Rock Creek flows in a southeast and northeast direction in the northeast corner of figure 9. Torrey Mountain is located near the center of figure 9 and the southeast, east, and southeast oriented stream originating west of Torrey Mountain and flowing to the southeast corner of figure 9 is Birch Creek. East of figure 9 Birch Creek flows in a southeast direction to the Pioneer Mountains east flank and then turns to flow in a northeast direction to join the south oriented Big Hole River near the point where it begins to make its U-turn so as to flow in a northeast direction (see figure 2). Note how the Birch Creek headwaters valley is on the same alignment as the north oriented David Creek valley and is also linked a mountain pass or through valley with north-northwest oriented Elkhorn Creek valley. The map contour interval for figure 9 is 50 meters and the Elkhorn Creek-Birch Creek mountain pass or through valley elevation at the drainage divide is between 2850 and 2900 meters. Mountain peak elevations to the north and to the south rise to over 3100 meters suggesting the pass or through valley is at least 200 meters deep. Valleys in this region have also been modified by glacial erosion, although the valleys predated the glaciers and the through valley is probably a water-eroded feature. At the time south oriented flood flow moved from the present day north oriented Elkhorn Creek and David Creek alignments to the Birch Creek valley there was no deep Wise River-Grasshopper Creek flood flow channel along the west edge of figure 9. Headward erosion of that deep south oriented flood flow channel or through valley beheaded and reversed the Elkhorn Creek and David Creek flood flow channels and ended flood flow to the Birch Creek valley.

Detailed map of Elkhorn Creek-Birch Creek drainage divide area

Figure 10: Detailed map of Elkhorn Creek-Birch 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 Elkhorn Creek-Birch Creek drainage divide area seen in less detail in figure 9. Torrey Mountain is located in section 28 and Torrey Lake is north of Torrey Mountain in section 21. Glacier Lake is located in the southwest corner of section 20. David Creek headwaters originate at Torrey Lake and Glacier Lakes and join is section 20 to flow in a north direction to the north center edge of figure 10. Elkhorn Creek flows in a north and northwest direction from section 30 or PB 46 to the northwest corner of figure 10. North and west of figure 10 David Creek and Elkhorn Creek eventually reach the north oriented Wise River. Birch Creek originates west of Torrey Mountain and flows in a south-southeast and east-southeast direction to the south edge of figure 10 (east half) and south and east of figure 10 flows to the south-oriented Big Hole River valley east of the Pioneer Mountains. Figure 10 shows a number of excellent glacier formed landform features, however again our interest in showing figure 10 is to demonstrate linkages between the north and south oriented valleys. At first glance an observer might be tempted to say there are no linkages, but a closer look is merited. First the alignments of the northwest oriented Elkhorn Creek valley and the southeast oriented Birch Creek valley suggest a linkage as do the alignments of the north oriented David Creek valley and the south oriented Birch Creek valley. Second in section 30 or PB 46 a deep mountain pass or through valley links the Elkhorn Creek and Birch Creek valleys. The map contour interval for figure 10 is 40 feet and the pass elevation (at the drainage divide) is between 9360 and 9400 feet. Surrounding mountain peaks rise to more than 10,300 feet suggesting the pass or through valley is as much as 900 feet deep. A somewhat shallower pass or through valley can be seen in the southeast corner of section 19 or PB 43 and links the David Creek valley (near Glacier Lake) with the Elkhorn Creek valley. Even more subtle notches in the high mountain ridge link the north oriented David Creek valley and the south oriented Birch Creek valley. These mountain passes are evidence of flood flow that flowed on a surface equivalent in elevation to the high mountain ridges seen in figure 10 today. At that time there was no deep Wise River-Grasshopper Creek valley to the west and the Pioneer Mountains did not stand high above surrounding regions as they do today. Headward erosion of deep south oriented flood flow channels both to the east and west and uplift of the Pioneer Mountains caused the emergence of the Pioneer Mountains crest ridge as seen today. Subsequently headward erosion of the deep southeast oriented Big Hole River valley north of the Pioneer Mountains beheaded and reversed flood flow in the present day Wise River valley. Still later the newly emerged Pioneer Mountains were glaciated with the glaciers further modifying the landscape before the ice melted to produce the spectacular alpine glacial landforms seen today.

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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