Sun River-Dearborn River drainage divide area landform origins, western Lewis and Clark County, Montana, USA

Authors

Abstract:

Topographic map interpretation techniques are used to determine landform origins in the Sun River-Dearborn River drainage divide area located in western Lewis and Clark County, Montana. The Sun River originates in the Lewis and Clark Range along the east-west continental divide and flows in an east direction to join the northeast-oriented Missouri River. The Dearborn River is located south of the Sun River and also originates in the Lewis and Clark Range along the east-west continental divide and flows in a southeast, northeast, and southeast direction to join the northeast-oriented Missouri River. The western Lewis and Clark County region investigated in this essay is located in the Lewis and Clark Range. The southeast-oriented Dearborn River headwaters valley is aligned with and linked by a deep through valley with a northwest-oriented Sun River tributary valley which drains to another south-southeast oriented Sun River tributary valley to form the east-oriented Sun River. Other deep through valleys link north-oriented Sun River tributary valleys with south-oriented Dearborn River tributary valleys and also link northwest-oriented Sun River tributary valleys with southeast-oriented Sun River tributary valleys. These and numerous other through valleys were eroded by south- and southeast-oriented flood flow channels moving immense ice-marginal melt water floods to what was then the actively eroding Dearborn River valley prior to headward erosion of the deep east-oriented Sun River valley. North and northwest-oriented Sun River tributary valleys were eroded by reversals of flood flow on north and northwest-oriented ends of flood flow channels beheaded by headward erosion of the much deeper Sun River valley. Flood waters are interpreted to have been derived from a rapidly melting thick North American ice sheet located in a deep “hole.” The Canadian Rockies, Lewis and Clark Range, and other northern Montana mountain ranges are interpreted to have been located on the deep “hole’s” western rim and was probably uplifted as massive ice-marginal melt water floods flowed from Canada into and across western Montana.

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 available at this site may be found by selecting desired Missouri River tributaries and/or states from this essay’s sidebar category list.

Introduction:

  • The purpose of this essay is to use topographic map interpretation methods to explore the Sun River-Dearborn River drainage divide area landform origins in western Lewis and Clark County, 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 providing 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 essays in the Missouri River drainage basin landform origins research project 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 Sun River-Dearborn River drainage divide area landform evidence in western Lewis and Clark County, Montana will be regarded as evidence supporting the “thick ice sheet that melted fast” paradigm (see heading for link to essay). This essay is included in the Missouri River drainage basin landform origins research project essay collection.

Sun River-Dearborn River drainage divide area location map

Figure 1: Sun River-Dearborn 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 Sun River-Dearborn River drainage divide area in western Lewis and Clark County, Montana and illustrates a region in northwest and north central Montana. The Canadian border is a short distance north of the figure 1 north edge and the southeast end of Glacier National Park can be seen in the figure 1 northwest corner. Great Falls, Montana is located near the figure 1 center. The Missouri River flows in a north-northwest direction from the figure 1 south center edge through Canyon Ferry Lake to Wolf Creek where it turns to flow in a northeast direction to Great Falls, Fort Benton, and Loma. South of Big Sandy the Missouri River turns abruptly to flow in a south-southeast and east direction to the figure 1 east edge with water eventually reaching the Mississippi River and the Gulf of Mexico. Note how the Missouri River headwaters and tributaries from the south flowing to the northeast-oriented Missouri River segment are oriented in north-northwest directions. The east-west continental divide extends from the figure 1 northwest corner to Marias Pass (on south edge of Glacier Nation Park) and then along or near the crest of the Lewis Clark Range before reaching the figure 1 south edge (west of Helena). Note how west of the continental divide the South Fork Flathead River and the Middle Fork Flathead River are oriented in north-northwest and northwest directions even though they flow to the south-oriented Flathead River (west of the figure 1 map area). Also note in the figure 1 southwest corner north- and northwest-oriented Clark Fork which flows through Deer Lodge and Drummond. The Flathead River is a Clark Fork tributary with water eventually the Columbia River and the Pacific Ocean. The Sun River originates in the Lewis and Clark Range along the continental divide and flows in a south-southeast and east direction to join the Missouri River at Great Falls. The Dearborn River is located south of the Sun River and also originates in the Lewis and Clark Range along the continental divide and flows in an east and southeast direction to join the northeast-oriented Missouri River. The Sun River-Dearborn River drainage divide area in western Lewis and Clark County as defined in this essay is located in the Lewis and Clark Range. The Sun River-Dearborn River drainage divide area landform origins in eastern Lewis and Clark County essay describes the region east of the mountains. Other describing Dearborn River and Sun River drainage basin drainage divide areas can be found by selecting the Dearborn River or Sun River category from the sidebar category list. North of the Sun River drainage basin is the Teton River drainage basin and essays describing Teton River drainage basin drainage divide areas can be found by selecting the Teton River category.
  • Erosional landforms in the figure 1 map area (and a much larger region) were formed during immense south and southeast oriented melt water floods as a thick North American ice sheet rapidly melted. The thick ice sheet was located in a deep “hole” and the figure 1 map area was located near and/or along the deep “hole’s” southwest and west rim. At the time the ice sheet formed there was no deep “hole” and the ice sheet stood high above the surrounding non glaciated continental regions. The deep “hole” evolved as the ice sheet deeply eroded the underlying surface and as the ice sheet’ immense weight caused crustal warping of non glaciated continental regions west and south of the thick ice sheet mass. The crustal warping included uplift of what are today mountain ranges, such as the Rocky Mountains, and of high plateau regions, such as the Colorado Plateau. Uplift of these mountain ranges and high plateau areas occurred as immense melt water floods flowed across them. Initially massive ice-marginal melt water floods from Canada flowed in south and southeast directions along what was the rising deep “hole’s” western rim (which is today the Canadian and northern Montana Rocky Mountains) into the figure 1 map area and then  continued to flow in south and southeast directions along routes roughly corresponding with and paralleling the present day continental divide across Wyoming and Colorado to New Mexico and Texas. Headward erosion of deep southeast- and east-oriented valleys from the Gulf of Mexico and the evolving Mississippi River valley systematically captured the immense south and southeast-oriented floods east of the present day continental divide with southern valleys capturing the flood flow before more northern valleys beheaded flood flow routes to the newly eroded southern valleys. At the same time deep southwest and west-oriented valleys eroded headward from the Pacific Ocean to capture the massive south and southeast-oriented melt water floods west of the present day continental divide. Again these captures occurred in sequence from south to north. The south to north captures on both sides of the evolving continental divide were probably aided by Rocky Mountain uplift, which was occurring as the huge melt water floods flowed across the region. Rocky Mountain uplift may have been aided by crustal unloading which occurred as the massive melt water floods removed great thicknesses of bedrock along what are today crests of high mountain ranges. The east-west continental divide was formed as deep valleys eroded headward from the east and west into rising mountain masses to capture immense south-oriented melt water floods flowing across the rising mountains.
  • In time a combination of mountain and plateau uplift and of ice sheet melting created a different melt water flood flow pattern. As the mountains rose and the ice sheet melted eventually the giant ice-marginal melt water floods from western Canada flowing into Montana along the deep “hole’s” western rim were flowing at elevations greater than at least some elevations on the decaying ice sheet’s surface. Lowest elevations on the ice sheet surface were in giant south oriented ice-walled canyons being carved by gigantic south oriented supra-glacial meltwater rivers. Of particular importance to the figure 1 map area was a large southeast and south-oriented ice-walled canyon crossing present day Saskatchewan, North Dakota, and South Dakota, which eventually became an ice-walled and bedrock-floored canyon and which detached the ice sheet’s southwest margin. Today the northeast and east-facing Missouri Escarpment in Saskatchewan, North Dakota, and South Dakota is what remains of that huge canyon’s southwest and west wall. Deep northeast and east-oriented valleys eroded headward from that large southeast and south-oriented ice-walled canyon into non glaciated regions in Montana and adjacent northern Wyoming to capture the immense south and southeast oriented melt water floods. These deep valleys and their tributary valleys eroded headward in sequence with headward erosion of each valley beheading the southeast- and south-oriented flood flow to the newly eroded valley to the south and/or southeast. For example in figure 1 headward erosion of the deep east-oriented Sun River valley beheaded flood flow channels to what was then the newly eroded Dearborn River valley. Headward erosion of these deep northeast and east-oriented valleys beheaded numerous south- and southeast-oriented flood flow channels and flood waters on the north and northwest ends of the beheaded flood flow channels reversed flow direction to erode north and northwest-oriented tributary valleys. In figure 1 the north-northwest Missouri River tributaries and Missouri River headwaters flow in valleys eroded by such reversal of flood flow on north ends of beheaded flood flow channels. South and southeast-oriented flood flow channels were beheaded in sequence from east to west and often newly reversed flood flow channels could capture significant yet to be beheaded flood flow from west of the actively eroding northeast or east-oriented valley. The evidence for these captures and flood flow reversals is best seen on topographic maps, such as those illustrated in this essay.

Detailed location map for Sun River-Dearborn River drainage divide area

Figure 2: Detailed location map for Sun River-Dearborn 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 Sun River-Dearborn River drainage divide area in western Lewis and Clark County, Montana. County boundaries are shown and Lewis and Clark County, Cascade County, and Teton County are labeled. Green areas on figure 2 are National Forest lands and are generally located in the mountain regions. The Sun River-Dearborn River drainage divide area of interest in this essay is located in the green shaded region. The Lewis and Clark County western boundary is defined by the east-west continental divide. The Missouri River flows in a northeast direction from the figure 2 south edge (east of center) to Great Falls and the figure 2 east center edge. Note how a northwest arm of Lewis and Clark County is located west of Teton County in the figure 2 northwest quadrant. The North Fork of the Sun River originates at Sun River Pass, which is located at the north tip of the Lewis and Clark County northwest arm and flows in a south direction along the Teton County-Lewis and Clark County border to join the north-oriented South Fork Sun River just west of Gibson Reservoir and to form the east-oriented Sun River, which flows from Gibson Reservoir in more of an east direction along the Teton-Lewis and Clark County boundary until reaching the Cascade County border where it continues in an east direction to join the Missouri River at Great Falls. Important Sun River tributaries from the south (in this essay) include Straight Creek, which flows in a north-northwest direction to join the north-oriented South Fork Sun River; northeast-oriented Smith Creek which originates near Welcome Pass and which joins northeast-oriented Willow Creek which joins the Sun River near Willow Creek Reservoir; and northeast-oriented Elk Creek, which originates north of Steamboat Mountain and which flows through Augusta and Gilman before joining the Sun River. The Dearborn River originates near Scapegoat Mountain and flows in a southeast and northeast direction to near Welcome Pass before turning to flow in a southeast and northeast direction around the south side of Steamboat Mountain and then turning to flow in a southeast direction to join the northeast-oriented Missouri River.
  • Sun River Pass at the north tip the Lewis Clark County northwest arm is not labeled on figure 2, but is a deep northwest-southeast oriented through valley eroded across the east-west continental divide. The through valley north of Sun River Pass is drained by a northwest-oriented tributary to the northwest-oriented Middle Fork Flathead River. As already noted, south of Sun River Pass drainage flows to the south-oriented North Fork Sun River, which west of Gibson Reservoir joins the north-oriented South Fork Sun River. Also as already noted north-northwest oriented Straight Creek flows to the north-oriented South Fork Sun River and originates near Welcome Pass and the southeast-oriented Dearborn River segment flows near Welcome Pass. As will be seen in the more detailed topographic maps below deep through valleys link the Straight Creek valley and the Dearborn River valley. These through valleys and the Sun River Pass through valley provide evidence of what was once a major southeast-oriented flood flow channel, which was first captured by headward erosion of the deep Dearborn River valley. Next the flood flow channel was further dismembered by headward erosion of the deep Sun River valley with flood waters on the north end of the beheaded flood flow channel reversing flow direction to erode the north-oriented Straight Creek and South Fork Sun River valleys. Finally headward erosion of the deep south-oriented Flathead River valley (west of the figure 2 map area) beheaded the southeast-oriented flood flow channel with flood waters on the northwest end of the beheaded flood flow channel reversing flow direction to erode the northwest-oriented Middle Fork Flathead River valley and to form east-west continental divide at Sun River Pass.

Straight Creek-Dearborn River drainage divide area

Figure 3: Straight Creek-Dearborn River drainage divide area. United States Geological Survey map digitally presented using National Geographic Society TOPO software.

 

  • Figure 3 illustrates the Straight Creek-Dearborn River drainage divide area in the Lewis and Clark Range. The east-west continental divide crosses Scapegoat Mountain in the figure 3 southwest corner region. The South Fork Sun River originates just north of the continental divide (near figure 3 west edge) and flows in a north and north-northwest direction to the figure 3 northwest corner. Straight Creek originates near Straight Creek Pass (near figure 3 center) and flows in a northwest direction to the figure 3 north edge (west half). Green Fork originates along the continental divide (just west of Scapegoat Mountain) and flows in a north and northeast to join Straight Creek north of Halfmoon Mountain. The Dearborn River originates along the continental divide just east of Scapegoat Mountain and flows in an east-northeast, southeast, and east-northeast direction to join southeast-oriented Welcome Creek and then to flow in a southeast direction to the figure 3 south edge (east half). Welcome Creek originates near Straight Creek Pass and flows in a southeast direction to join the Dearborn River. Note the northwest-southeast oriented through valley at Straight Creek Pass. The figure 3 map contour interval is 50 meters and the through valley floor elevation at Straight Creek Pass is between 2050 and 2100 meters. Immediately to the north is a mountain peak with an elevation of 2574 meters and south of Red Slide Mountain (to the south) is a peak with an elevation of 2440 meters. These adjacent mountain peak elevations suggest the through valley is at least 340 meters lower than the tops of the nearby mountains. This through valley is a water eroded feature and was eroded by southeast-oriented flood flow prior to headward erosion of the much deeper much deeper east-oriented Sun River valley to the north. Sun River valley headward erosion beheaded the southeast-oriented flood flow channel and flood waters on the north end of the beheaded flood flow channel reversed flow direction to erode the northwest-oriented Straight Creek (and South Fork Sun River) valley. Note how west of Red Slide Mountain a north-northeast oriented Straight Creek tributary is linked by a second through valley with a southeast-oriented Dearborn River headwaters valley. This second through valley has a slightly lower valley floor elevation (than Straight Creek Pass) and provides evidence of what were once diverging and converging south and southeast-oriented flood flow channels such as might be found in an anastomosing channel complex. Study of the figure 3 map area reveals many additional through valleys, although most have higher floor elevations. For example a higher level through valley links the north-northeast oriented Green Fork valley with the northeast and north-northeast Straight Creek tributary valley south and east of Halfmoon Peak. These higher level through valleys suggest the entire figure 3 map area was eroded by south and southeast-oriented flood flow, which once flowed on a high level erosion surface at least as high as the present day high mountain ridges.

Detailed map of Straight Creek-Welcome Creek drainage divide area

Figure 4: Detailed map of Straight Creek-Welcome 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 Straight Creek-Welcome Creek drainage divide area seen in less detail in figure 3 above. Straight Creek Pass is labeled and is located a short distance west of the figure 4 center. Straight Creek flows in a west-northwest and northwest direction from Straight Creek Pass to the figure 4 west edge (north half). As previously described Straight Creek flows to the north-oriented South Fork Sun River. Halfmoon Creek is the north-oriented tributary joining Straight Creek west of Red Slide Mountain. Welcome Creek flows in a southeast direction from Straight Creek Pass to join the east-northeast and southeast oriented Dearborn River near the Welcome Creek campground (near the figure 4 south edge, east half). North of the Welcome Creek campground in the section 3 southeast quadrant is Welcome Pass, which links the southeast-oriented Welcome Creek (and Dearborn River valley) with headwaters of north-oriented Moudess Creek, which flows to northeast-oriented Smith Creek, which in turn flows to the east-oriented Sun River. The figure 4 contour interval is 40 feet and the Straight Creek Pass elevation at the Straight Creek-Welcome Creek drainage divide is shown as being 6730 feet. Red Slide Mountain rises to more than 7680 feet while mountains north of Straight Creek Pass rise to more than 8400 feet. In other words the Straight Creek Pass elevation is more than 900 feet lower than the adjacent mountain peaks. Welcome Pass is even deeper with an elevation at the drainage divide of between 6120 and 6160 feet. Elevations along the ridge Welcome Creek Pass crosses rise to more than 7000 feet indicating that Welcome Pass is also at least 800 feet deep. The Straight Creek Pass through valley and the Welcome Pass through valley link north-oriented Sun River tributary valleys with the southeast-oriented Dearborn River valley. These deep passes eroded across high mountain ridges are water eroded features and must be explained. The through valleys were initiated as converging south-oriented flood flow channels moving large quantities of flood water to what was then the actively eroding Dearborn River valley. Headward erosion of deep east-oriented Sun River valley and its northeast-oriented Smith Creek tributary valley north of the figure 4 map area first beheaded the Welcome Pass through valley flood flow channel. Flood waters on the north end of the beheaded flood flow channel reversed flow to erode the north-oriented Moudess Creek valley. For a time southeast-oriented flood flow moving across Straight Creek Pass flowed on the Welcome Creek alignment with some of that flood water probably moving in a north direction to the newly reversed and actively eroding Moudess Creek valley. Headward erosion of the east-oriented Sun River valley north of the figure 4 map area subsequently beheaded the southeast-oriented flood flow route across Straight Creek Pass. Flood waters on the northwest end of the newly beheaded flood flow channel reversed flow direction to erode the northwest and north-oriented Straight Creek and South Fork Sun River valley and to create the Straight Creek Pass drainage divide.

Detailed map of Halfmoon Creek-Dearborn River drainage divide area

Figure 5: Detailed map of Halfmoon Creek-Dearborn River drainage divide area. United States Geological Survey map digitally presented using National Geographic Society TOPO software.

 

  • Figure 5 uses a detailed topographic map to illustrate the Halfmoon Creek-Dearborn River drainage divide area south and west of figure 4 and includes overlap areas with figure 4. Red Slide Mountain is labeled and is located near the north edge of the figure 5 northeast quadrant. Scapegoat Mountain is located in the figure 5 southwest quadrant and the east-west continental divide crossing Scapegoat Mountain (the figure 5 southwest corner region drains to the Pacific Ocean while all other figure 5 areas drain to the Gulf of Mexico). Halfmoon Creek originates in Halfmoon Park (north of Scapegoat Mountain) and flows in a north, northeast, and northeast direction to the figure 5 north edge (east half). North of the figure 5 map area Halfmoon Creek joins northwest-oriented Straight Creek with water eventually reaching the east-oriented Sun River. The Dearborn River originates in section 13 (just east of Scapegoat Mountain) and flows in a northeast, southeast, and northeast direction to the figure 5 east edge (south of center). As seen in figures 3 and 4 east of figure 5 the Dearborn River turns to flow in a southeast direction. Note northeast and south-oriented Telephone Creek in section 7 (near figure 5 center), which flows to the Dearborn River. Note how the south-oriented Telephone Creek valley is linked by a deep through valley with a north-oriented Halfmoon Creek tributary. The figure 5 map contour interval is again 40 feet and the through valley floor elevation at the drainage divide is between 6600 and 6640 feet. Red Slide Mountain to the north rises to more than 7680 feet while Scapegoat Mountain to the southwest rises to more than 9000 feet. This Halfmoon Creek-Telephone Creek through valley is more than 1000 feet deep when compared with the adjacent mountain peaks and is a water eroded feature. The through valley was eroded as a diverging and converging flood flow channel west of the Straight Creek Pass through valley. Note how this western through valley is approximately 100 feet deeper than the Straight Creek Pass through valley. Even more intriguing is a higher level through valley in the west half of section 13 linking the north-oriented Halfmoon Creek headwaters valley with the northeast-oriented Dearborn River headwaters valley. The through valley floor elevation at the drainage divide is between 7600 and 7640 feet and is more than 140 feet lower than high point in the section 13 northeast quadrant. This section 13 through valley is also a water eroded feature and provides evidence of a south-oriented flood flow channel adjacent to and almost as high as the present day east-west continental divide. [The north-south oriented through valley crossing the continental divide west of Scapegoat Mountain, which can barely be seen in the figure 5 southwest corner, links north-oriented Green Fork (which flows to the east-oriented Sun River with water eventually reaching the Gulf of Mexico) with a south-oriented Blackfoot River tributary (with water eventually reaching the Pacific Ocean) and provides evidence that flood waters once freely crossed the present day continental divide.]

Detailed map of Smith Creek-Dearborn River drainage divide area

Figure 6: Detailed map of Smith Creek-Dearborn River 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 Smith Creek-Dearborn River drainage divide area seen in less detail in the figure 3 southeast quadrant. The Dearborn River flows in a southeast direction from the figure 6 west edge (near northwest corner) to the figure 6 south center edge (just west of center). Steamboat Mountain is the high peak located in the figure 6 southeast quadrant. The Wilderness Boundary is conspicuously marked and is located along the Sun River-Dearborn River drainage divide (which was also seen in the east half of figure 4). Smith Creek is the northwest oriented stream in the figure 6 northeast quadrant and north of the figure 6 map area turns to flow in a northeast direction to join the east-oriented Sun River. Named north-oriented Smith Creek tributaries (from east to west) are Bunch Grass Creek (north of Steamboat Mountain), Sixmile Creek, Star Creek, and Weasel Creek. Note how the north-oriented Smith Creek tributary valleys are linked by through valleys across the Sun River-Dearborn River drainage divide with southwest-oriented Dearborn River tributary valleys. For example. the north-oriented Weasel Creek valley is linked by a through valley in section 12 with the northwest- and southwest-oriented Pass Creek valley. The map contour interval is again 40 feet and the through valley floor at its deepest point on the drainage divide is between 6480 and 6520 feet. A high point along the drainage divide to the northwest is shown as being 7292 feet while high points in sections 18, 17, and 20 rise considerably higher. This section 12 through valley is actually a deeper channel eroded into the floor of a much broader through valley with a southeast wall in section 18 (just east of the Elk Pass Trail). This much broader through valley and the deeper channel eroded into its floor were eroded by south-oriented flood flow which was captured by headward erosion of the much deeper southeast-oriented Dearborn River valley. Headward erosion of the deep east-oriented Sun River valley and its northeast-oriented Smith Creek tributary valley beheaded the south-oriented flood flow channel and flood waters on the north end of the beheaded flood flow channel reversed flow direction to erode the northwest-oriented Smith Creek valley and its north-oriented tributary valleys. In actuality the situation was more complicated than described here and involved many steps, although the process in each step was basically as described here. Probably contributing to the flood flow reversals and the headward erosion of the deep valleys was uplift of the mountain region as flood waters flowed across the figure 6 map area.

Elk Creek-Dearborn River drainage divide area

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

 

  • Figure 7 uses a less detailed topographic map to illustrate the Elk Creek-Dearborn River drainage divide area south and east of figure 3 and includes overlap areas with figure 3. The Dearborn River flows in a southeast and east direction from Welcome Pass near the figure 7 northwest corner to Devils Glen and then turns to flow in a northeast direction almost to Bean Lake (near figure 7 east center edge) and then turns to flow in southeast direction to join the northeast-oriented Missouri River east and south of figure 7. Clemons Creek is northeast, southeast, north, east, and south oriented Dearborn River tributary west of Bean Lake and south of Sheep Mountain (in the figure 7 east center area). Smith Creek is the northwest and north-northeast oriented stream in the figure 7 northwest quadrant and as already mentioned north of figure 7 flows in a northeast direction to join the east-oriented Sun River. Smith Creek originates at Elk Pass, which is located north of Steamboat Mountain. Also originating at Elk Pass, but flowing in the other direction, is east-southeast and northeast-oriented Elk Creek, which flows to the figure 7 north edge (east half) and then to the east-oriented Sun River. Elk Pass is a northwest-southeast oriented through valley linking the northwest-oriented Smith Creek headwaters valley with east-southeast oriented Elk Creek headwaters valley. The figure 7 map contour interval is 50 meters and the Elk Pass elevation at the drainage divide is between 1800 and 1850 meters. Elevations north of Elk Pass rise to more than 2250 meters while Steamboat Mountain to the south rises to a much higher elevation. The Elk Pass through valley provides evidence of what was once a southeast-oriented flood flow channel which was at least 400 meters deep. Flood waters were probably flowing to what was then the actively eroding Elk Creek valley, which was eroding headward from the actively eroding Sun River valley. At that time Sun River valley (and Smith Creek valley) headward erosion had not proceeded far enough west to behead south and southeast-oriented flood flow in the figure 7 west half. In time Smith Creek valley headward erosion beheaded the south and southeast-oriented flood flow routes and flood waters on the north ends of the beheaded flood flow channels reversed flow direction to erode the north-northeast and northwest oriented Smith Creek valley and the various north-oriented Smith Creek tributary valleys. Figure 8 below uses a detailed topographic map to illustrate the East Fork Cyanide Creek-Clemons Creek drainage divide area south of the northeast-oriented Elk Creek valley segment (between Lone Chief Mountain and Sheep Mountain, figure 7 east half). Figure 9 uses a detailed topographic map to illustrate the Smith Creek-Elk Creek drainage divide area at Elk Pass. Figure 10 uses a detailed topographic map to illustrate the Clemons Creek-Dearborn River drainage divide area west of Bean Lake (near figure 7 east center edge).

Detailed map of East Fork Cyanide Creek-Clemons Creek drainage divide area

Figure 8: Detailed map of East Fork Cyanide Creek-Clemons Creek drainage divide area. United States Geological Survey map digitally presented using National Geographic Society TOPO software.

 

  • Figure 8 uses a detailed topographic map to illustrate the East Fork Cyanide Creek-Clemons Creek drainage divide area seen in less detail in figure 7 above. Elk Creek flows in a northeast direction across the figure 8 northwest corner and eventually joins the east-oriented Sun River. Cyanide Creek originates near the figure 8 southwest corner and flows in a north-northeast direction to join Elk Creek near the figure 8 north edge. The East Fork Cyanide Creek originates near the figure 8 south edge in the region labeled PB 48 and flows in a north direction to join Cyanide Creek near the east edge of the region labeled PB 46. Clemons Creek originates in the northwest corner of section 20 and flows in a northeast direction across section 17 before turning to flow in an east direction to the figure 8 east center edge. East of figure 8 Clemons Creek eventually turns to flow in a south direction to join the Dearborn River. Note in the section 18 southeast corner a northwest-southeast oriented through valley linking a northwest-oriented East Fork Cyanide Creek tributary valley with the northeast oriented Clemons Creek valley. A higher level northwest-southeast oriented though valley in section 20 links the Clemons Creek valley with headwaters of a southeast-oriented Dearborn River tributary (the tributary headwaters are seen in section 20 along the figure 8 south edge). These through valleys provide evidence of a former southeast-oriented flood flow channel, which moved flood waters to what was at one time the actively eroding Dearborn River valley. At that time the deep Clemons Creek valley had not yet eroded headward to capture the southeast-oriented flood flow nor did the northeast-oriented Elk Creek valley exist and there were no north-oriented Cyanide Creek and East Fork Cyanide Creek valleys. Headward erosion of the deep northeast- and east-oriented Clemons Creek valley first captured the southeast-oriented flood flow channel and flood waters eroded the southeast-oriented flood flow channel to the northwest even deeper. Next headward erosion of the much deeper northeast-oriented Elk Creek valley beheaded the south and southeast-oriented flood flow channel and flood waters on the north end of the beheaded flood flow channel reversed flow direction to erode the north-oriented East Fork Cyanide Creek-Cyanide Creek valley and the northwest-oriented East Fork Cyanide Creek tributary valley. There are many additional through valleys crossing what are today high ridges and these additional through valleys provide evidence flood waters once flowed across a surface as high as the highest figure 8 elevations today. Further these additional through valleys describe a more complicated erosion history than what I have described, although the processes involved were similar to the processes I have described here.

Detailed map of Smith Creek-Elk Creek drainage divide area

Figure 9: Detailed map of Smith Creek-Elk Creek drainage divide area. United States Geological Survey map digitally presented using National Geographic Society TOPO software.

 

  • Figure 9 uses a detailed topographic map to illustrate the Smith Creek-Elk Creek drainage divide at Elk Pass seen in less detail in figure 7 above. Steamboat Mountain is the high peak located along the Sun River-Dearborn River drainage divide which also serves as the Wilderness Boundary. Areas south and west of the well-marked drainage divide drain to the Dearborn River while all other figure 9 map areas drain to the Sun River. Elk Pass is located on the line between sections 8 and 9 north of Steamboat Mountain. Smith Creek originates north of the figure 9 north center edge and flows in a southwest direction to the section 8 northeast corner where it is joined by a northwest-oriented tributary originating at Elk Pass and then flows in a northwest direction to the figure 9 north edge (north of section 7). North of figure 9 Smith Creek turns to flow in a northeast direction to join the east-oriented Sun River. Elk Creek originates in section 17 (north of Steamboat Mountain) and flows in a north and northeast direction to Elk Pass and then turns to flow in an east-southeast and northeast direction to the figure 9 east edge (north half). East and north of figure 9 Elk Creek also flows to the east-oriented Sun River. Elk Pass is a well-defined through valley linking the northwest-oriented Smith Creek valley with the east-southeast oriented Elk Creek valley. The figure 9 map contour interval is 40 feet and the Elk Pass elevation at the drainage divide is between 5960 and 6000 feet. Elevations of approximately 6900 feet can be seen along the figure 9 north edge and elevations greater 7600 feet can be found north of the figure 9 map area. Steamboat Mountain rises to 8685 feet and most elevations along the Sun River-Dearborn River drainage divide in figure 9 exceed 7600 feet. In other words the Elk Pass through valley is probably a 1600 foot or more deep erosional landform eroded by southeast-oriented flood flow which was first captured by headward erosion of the deep northeast-oriented Elk Creek valley. At that time headward erosion of the northeast-oriented Smith Creek valley had not yet beheaded the southeast-oriented flood flow and flood waters were free to flow in a southeast direction into and across the figure 9 map area. These southeast-oriented flood waters moving to the actively eroding Elk Creek valley eroded a deep southeast-oriented flood flow channel and beheaded south-oriented flood flow channels to the actively eroding Dearborn River valley south of figure 9. Flood waters on north ends of the beheaded flood routes reversed flow direction to erode north-oriented tributary valleys and to carve what is today the north side of the Sun River-Dearborn River drainage divide. South of the figure 9 map area the actively eroding southeast-oriented  Dearborn River valley captured south-oriented flood flow and eroded the south side of the Sun River-Dearborn River drainage divide until those south-oriented flood flow routes were beheaded and reversed by headward erosion of the deep southeast-oriented Elk Creek flood flow channel. Headward erosion of the deep northeast-oriented Smith Creek valley (north of figure 9) then beheaded the deep southeast-oriented flood flow channel leading to the Elk Creek valley. Flood waters on the northwest end of the beheaded flood flow channel reversed flow direction to erode the northwest-oriented Smith Creek valley segment.

Detailed map of Clemons Creek-Dearborn River drainage divide area

Figure 10: Detailed map of Clemons Creek-Dearborn River drainage divide area.United States Geological Survey map digitally presented using National Geographic Society TOPO software.

 

  • Figure 10 is a detailed topographic map of the Clemons Creek-Dearborn River drainage divide area seen in less detail in figure 7 above. Bean Lake is the lake straddling the figure 10 east center edge. The Dearborn River flows in a northeast direction from the figure 10 south center edge into section 23 and then turns to flow in an east and southeast direction to the figure 10 east edge (south of Bean Lake). Clemons Creek originates near the figure 10 west center edge and flows in a northeast direction to the section 16 north center edge. Clemons Creek then flows in a southeast direction across section 15 to the section 14 southwest quadrant where it jogs to the north and then flows in an east and south direction to join the Dearborn River (it actually looks like most if not all Clemons Creek water is today diverted to an irrigation canal). Note how in the section 14 southwest quadrant there is a large through valley linking the Clemons Creek valley with the Dearborn River valley. The figure 10 map contour interval is 20 feet and the through valley floor elevation at the drainage divide is between 4840 and 4860 feet. The hill to the east, which Clemons Creek flows around, rises to 5106 feet, meaning the through valley is at least 246 feet deep. The through valley is a water eroded feature and was eroded by south-southeast oriented flood flow moving to what was then the actively eroding and deep Dearborn River valley. Rather than proceeding in a south-southeast direction along this convenient through valley Clemons Creek today turns to flow in a north and east direction through a deep water gap before turning to flow in a south direction. What does this unusual Clemons Creek drainage route indicate?
  • First the north-oriented Clemons Creek valley segment was initiated as a south-oriented flood flow channel, which was beheaded by headward erosion of the deep east-oriented Clemons Creek valley segment. Flood waters on the north end of the beheaded flood flow channel then reversed flow direction to erode the north-oriented Clemons Creek valley and to also capture south-southeast oriented flood flow moving in what is now the through valley to the south. Apparently at that time the Dearborn River was not as deep as it is today and headward erosion of its deeper valley occurred slightly faster along the Clemons Creek route than it did along the present day Dearborn River route. Also at that time there apparently enough flood water flowing across the region that water was flowing simultaneously in all of the present day valleys (including the Clemons Creek-Dearborn River through valley route). While this scenario may be difficult to image based on present day topography, most likely the flood waters were carving the landscape features seen today as crustal warping (probably caused by the ice sheet from which the flood flow was derived) was raising the mountains.

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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