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

Authors

Abstract:

Topographic map interpretation methods are used to determine Sun River-Dearborn River drainage divide area landform origins in eastern Lewis and Clark County, Montana. The Sun River originates along the east-west continental divide, which forms the Lewis and Clark County west border, and flows in an east direction to join the northeast-oriented Missouri River at Great Falls. The Dearborn River is located south of the Sun River and also originates along the east-west continental divide and flows in an east and southeast direction to join the Missouri River. Eastern Lewis and Clark County as defined here is the Sun River-Dearborn River drainage divide east of the mountain front. Topographic map evidence shows numerous north-south and northwest-southeast oriented through valleys crossing west to east oriented drainage divides between the Sun River, northeast-oriented Sun River tributaries, east- and southeast-oriented Dearborn River tributaries, and the Dearborn River. These through valleys are interpreted to have been eroded as diverging and converging south and southeast-oriented flood flow channels in a large-scale anastomosing channel complex. Flood waters are interpreted (based on evidence from many similar essays) from a rapidly melting thick North American ice sheet, which was located in a deep “hole”. The Sun River-Dearborn River drainage divide was located near the deep “hole’s” southwest rim and was eroded by immense south and southeast-oriented ice-marginal melt water floods. Flood waters were first captured by Dearborn River headward erosion with headward erosion of east- and south-oriented Dearborn River tributary valleys beheading flood flow to the newly eroded Dearborn River valley. Next headward erosion of northeast-oriented Sun River tributary valleys beheaded flood flow routes to the newly eroded Dearborn River tributary valleys. Finally Sun River valley headward erosion beheaded flood flow to the actively eroding northeast-oriented Sun River tributary valleys. A separate essay describes the Sun River-Dearborn River drainage divide area landform origins in western Lewis and Clark County.

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 eastern 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 providing 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 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 eastern Lewis and Clark County, Montana will be regarded as evidence supporting the “thick ice sheet that melted fast” paradigm (see heading for essay related to this). 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 illustrates a location map for the Sun River-Dearborn River drainage divide area in Lewis and Clark County, Montana and shows a region in north central Montana. The Canadian border is a short distance north of the figure 1 north edge. The southeast end of Glacier National Park is located in the figure 1 northwest corner. Great Falls is the largest city shown and 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 abruptly turns to flow in a south-southeast and then east direction to the figure 1 east edge with water eventually reaching the Gulf of Mexico. The east-west continental divide extends in a south-southeast direction from the figure 1 northwest corner through Marias Pass (at south end of Glacier National Park) and then along or near the Lewis and Clark Range crest to the figure 1 south edge (west of Helena). The Sun River originates along the continental divide (south of Marias Pass) 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 along the continental divide in the Lewis and Clark Range and flows in an east and southeast direction to join the northeast-oriented Missouri River near Craig. North of the Sun River is the east-oriented Teton River, which also originates along the continental divide, and which joins the Missouri River near Loma. North of the Teton River is the east- and south-oriented Marias River, tributaries of which originate along the continental divide, and which joins the Teton River to join the Missouri River near Loma. West of the continental divide in the figure 1 southwest corner is north- and northwest-oriented Clark Fork, which flows through Deer Lodge and Drummond, with water eventually reaching the Columbia River and the Pacific Ocean. The west-oriented Blackfoot River is a Clark Fork tributary and the northwest and north-northwest oriented Middle Fork and South Fork Flathead River flow to the south-oriented Flathead River (west of the figure 1 map area), which is also a Clark Fork tributary. Note also the north-northwest oriented Missouri River headwaters valley and tributaries to the northeast-oriented Missouri River segment (including the north-northwest oriented Smith River). The Sun River-Dearborn River drainage divide area in eastern Lewis and Clark County investigated in this essay is located east of the Lewis and Clark Range, north and west of the Missouri River, and south of the Sun River. Essays describing other Dearborn  and Sun River drainage basin drainage divide areas can be found by selecting the Dearborn River or Sun River categories from the sidebar category list.
  • The entire figure 1 map area and a much larger region was eroded during immense south and southeast-oriented melt water floods as a thick North American ice sheet located in a deep “hole” rapidly melted and opened up space in the deep “hole” it had occupied. The Missouri River drainage basin in Montana and northern Wyoming is located on the deeply eroded deep “hole’s” southwest wall and the mountains seen in figure 1 probably developed as the deep “hole” western and southwestern rim was formed. The deep “hole” did not exist when the ice sheet originally developed, but was instead formed by the ice sheet as it deeply eroded bedrock under it and as its weight caused crustal warping elsewhere on the continent. At first as the thick ice sheet began to melt the ice sheet stood high above its western and southwest rim and giant melt water floods from further north in Canada flowed in south and southeast directions along the ice sheet’s western margin into and across Montana to Wyoming, Colorado, and New Mexico along routes which roughly followed the present day east-west continental divide. At that time the Rocky Mountains and high western North American plateau areas were just beginning to be uplifted and the immense south and southeast-oriented floods could freely flow across the region. Uplift of the Rocky Mountains and western North American high plateau areas occurred as the immense melt water floods flowed across them and flood waters were diverted to both the east and the west as deep valleys eroded headward from both directions to carve the east-west continental divide. Rocky Mountain uplift and diversion of flood waters to the east and the west proceeded in sequence from south to north with headward erosion of deep southern valleys capturing the south-oriented flood flow before headward erosion of more northern valleys beheaded flood flow routes to the newly eroded southern valleys. At the same time immense south-oriented melt water floods east of the rising Rocky Mountains deeply eroded the central United States plains region.
  • In time a different melt water flood flow pattern began to develop as the combination of ice sheet melting and of Rocky Mountains uplift created a situation where the ice sheet surface no longer stood high above the developing deep “hole” rim, but instead was beginning to become lower in elevation than the surfaces on which the massive ice-marginal melt water floods were flowing. Huge supra-glacial melt water rivers carved giant south-oriented ice-walled canyons into the decaying ice sheet surface, which evolved into the major regional drainage routes. Of particular significance to the figure 1 map area was a giant southeast and south-oriented ice-walled canyon in 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. The northeast and east-facing Missouri Escarpment in Saskatchewan, North Dakota, and South Dakota is what remains today of that huge ice-walled and bedrock-floored canyon’s southwest and west wall. Deep east and northeast-oriented valleys eroded headward from the large ice-walled canyon into Montana and northern Wyoming to capture the immense southeast oriented ice-marginal melt water floods. These valleys eroded headward in sequence with the northeast-oriented Yellowstone River valley eroding headward in advance of headward erosion of the east-oriented Missouri River valley, which beheaded southeast-oriented flood flow to the newly eroded Yellowstone River valley. [Actually the history was much more complicated as there are dozens of tributary valleys to both rivers and the tributary valleys also headward in sequence with the southern valleys eroding headward in advance of headward erosion of the northern valleys, each of which beheaded flood flow to the newly eroded valley immediately to the south.] North-oriented tributary valleys were eroded by reversals of flood flow on north ends of south-oriented flood flow channels beheaded by headward erosion of much deeper valleys. In figure 1 the north and north-northwest oriented Missouri River headwaters valley and tributary valleys were eroded by such flood flow reversals as deep east- and northeast-oriented Missouri River valley segments eroded headward across the region. Also the north- and northwest-oriented Clark Fork valley was eroded by a massive flood flow reversal when headward erosion of the much deeper Columbia River valley beheaded what was a major southeast- and south-oriented flood flow channel. The northwest and north-northwest oriented Middle and South Forks Flathead River valleys were also eroded by massive flood flow reversals along north ends of southeast and south-southeast oriented flood flow channels, which were beheaded by headward erosion of the much deeper south-oriented Flathead River valley, which had eroded headward from the much deeper northwest-oriented Clark Fork valley (again the history was much more complicated, although this simple description outlines the process).

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 detailed location map showing Montana county boundaries for the Sun River-Dearborn River drainage divide area in Lewis and Clark County. Lewis and Clark County is labeled as are Teton County to the north and Cascade County to the west. The Lewis and Clark County western boundary follows east-west continental divide north of Twin Peaks (near figure 2 west center) to the figure 2 north edge (note the northwest arm of Lewis and Clark County between the continental divide and the Teton County west border. The Missouri River flows in a northeast direction from the figure 2 south edge (east half) to Great Falls near the figure 2 east center edge. West of the continental divide (in figure 2 north half) is the north-northwest oriented South Fork Flathead River, which north and west of figure 2 flows to the south-oriented Flathead River with water eventually reaching the Pacific Ocean. The North Fork Sun River flows in a south-southeast direction from the figure 2 north edge in the Lewis and County northwest arm to Gibson Reservoir where it turns to flow in more of an east direction along the Teton County-Lewis and Clark County boundary until reaching the Cascade County border where it continues to flow in an east direction to join the northeast-oriented Missouri River at Great Falls. The North Fork Sun River originates south of Sun River Pass (north of figure 2) which is a deep north-south oriented through valley crossing the east-west continental divide and linking the North Fork Sun River valley with the northwest-oriented Middle Fork Flathead River valley. The north-oriented South Fork Sun River joins the south-oriented North Fork Sun River at the west end of Gibson Reservoir providing evidence of what was once a major south-oriented flood flow channel. The South Fork Sun River valley was eroded by a reversal of flood flow after headward erosion of the deep Sun River valley beheaded the flood flow channel. Major Sun River tributaries from the south in eastern Lewis and Clark County shown include northeast-oriented North Fork Simms Creek, Dry Creek, and Elk Creek. Dearborn River headwaters are located near Scapegoat Mountain (north of the Scapegoat Wilderness in figure 2 southwest quadrant) and flows in a southeast, northeast, southeast, east, and southeast direction to follow a segment of the Lewis and Clark County border just before joining the northeast-oriented Missouri River. Major Dearborn River tributaries from the north are northeast, southeast, and south oriented Flat Creek and southeast-oriented Auchard Creek. This essay investigates the Sun River-Dearborn River drainage divide area in eastern Lewis and Clark County, which is the region east of the mountains (green areas on figure 2 are National Forest lands and are generally located in the mountain areas). A separate essay describes Sun River-Dearborn River drainage divide area landform origins in western Lewis and Clark County and another essay describes Flathead River-Sun River drainage divide area landform origins along the east-west continental divide.

North Fork Simms Creek-Flat Creek drainage divide area

Figure 3: North Fork Simms Creek-Flat Creek drainage divide area. United States Geological Survey map digitally presented using National Geographic Society TOPO software. 

 

  • Figure 3 illustrates the North Fork Simms Creek-Flat Creek drainage divide area in eastern Lewis and Clark County. The North Fork Simms Creek flows from the figure 3 center region to the northeast corner with water eventually reaching the east-oriented Sun River (north of figure 3). The South Fork Simms Creek can be seen originating in the figure 3 east center area and flowing in a northeast direction the figure 3 east edge (north half) and joins the North Fork Simms Creek north and east of figure 3 to form northeast-oriented Simms Creek. Dry Creek is the east and north-northeast oriented stream flowing from the figure 3 west edge (north half) to the figure 3 north center edge and north of the figure 3 flows to the Sun River. Flat Creek flows in an east-northeast and east-southeast direction from the figure 3 southwest corner to the Milford Colony and then in an east and southeast direction to the figure 3 south edge (east of center). South and east of the figure 3 map area Flat Creek eventually joins the Dearborn River. The figure 3 map contour interval is 50 meters so only major topographic features can be identified. Note how the north-oriented Dry Creek, North Fork Simms Creek, and South Fork Simms Creek valleys are linked by through valleys with the south-oriented Flat Creek valley. For example, north of the Milford Colony a north-south oriented through valley links the northeast-oriented North Fork Simms Creek headwaters valley with the valley of a south-oriented Flat Creek tributary. The through valley floor elevation at the drainage divide is between 1300 and 1350 meters with low hills on either side rising to more than 1400 meters. Proceeding east along the drainage divide a number of similar through valleys can also be seen. The through valleys are water eroded features and were eroded by diverging and converging south-oriented flood flow channels just prior to headward erosion of the deeper northeast-oriented Simms Creek valley. The south-oriented flood flow was moving to what was then the actively eroding Flat Creek valley which had eroded headward from the newly eroded Dearborn River valley (located south of the figure 3 map area). At that time there was no east-oriented Sun River valley north of the figure 3 map area and south-oriented flood flow could freely move across a surface at least as high as the highest figure 3 elevations to the figure 3 map area. The Simms Creek valley eroded headward from the actively eroding and deeper east-oriented Sun River valley head and reached the figure 3 map area before Sun River valley headward erosion beheaded south-oriented flood flow to the figure 3 east half. The north-northeast oriented Dry Creek valley segment seen in the figure 3 north center area was eroded by a reversal of south-oriented flood flow to what was then the newly eroded Flat Creek valley. The reversal of flood flow occurred when headward erosion of the Sun River valley beheaded the south-oriented flood flow. For a time the reversed flood flow captured south-oriented flood flow from west of the actively eroding Sun River valley head and the captured flood flow moved in an east direction to the newly eroded north-northeast oriented Dry Creek valley and in the process eroded the east-oriented Dry Creek valley segment.

Detailed map of South Fork Simms Creek-Flat Creek drainage divide area

Figure 4: Detailed map of South Fork Simms Creek-Flat Creek drainage divide area. United States Geological Survey map digitally presented using National Geographic Society TOPO software. 

 

  • Figure 4 provides a detailed a topographic map of the South Fork Simms Creek-Flat Creek drainage divide area seen in less detail in figure 3 above. The north-south oriented Lewis and Clark-Cascade County boundary is labeled and can be seen in the figure 4 east half. Milford Colony is located just west of the figure 4 southwest corner. Flat Creek flows in an east and southeast direction in the figure 4 southwest corner region. Hogan Creek is the southeast-oriented tributary flowing from the figure 4 west center edge to join Flat Creek near the figure 4 southwest corner. Myles Creek is a south-oriented stream originating in section 33 and flowing to the figure 4 south edge (just west of center) and joining Flat Creek just south of the figure 4 map area. Henry Creek is an east and south-oriented stream originating just east of the Myles Creek headwaters in the section 33 southeast corner and flowing to the figure 4 south edge (east of center) and joining Flat Creek south of the figure 4 map area. Headwaters of the northeast-oriented South Fork Simms Creek can be seen near the figure 4 north center edge. The North Fork Simms Creek is located immediately to the west and north of the South Fork Simms Creek. Numerous north-south oriented through valleys can be seen linking the north-oriented Simms Creek tributary valleys with the south-oriented Flat Creek tributary valleys. The deepest through valley is located in section 1 just west of the county line and links a north-oriented South Fork Simms Creek tributary valley with the south-oriented Henry Creek valley. The figure 4 contour interval is 20 feet and the through valley floor elevation at the drainage divide is between 4080 and 4100 feet. The high point in section 26 to the west is shown as being 4932 feet and while not seen in figure 4 the high point on Rocky Butte just east of figure 4 is shown as being 4702 feet. In other words the through valley is 500-740 feet lower than the adjacent high points. This deep north-south oriented through valley was eroded as a south-oriented flood flow channel prior to being beheaded by headward erosion of the northeast-oriented South Fork Simms Creek valley. In the section 26, 27, 28, 29, 32, 33, 34, and 35 area there are multiple north-south oriented through valleys linking the south-oriented Flat Creek tributary valleys with north-oriented North and South Forks Simms Creek valleys, although floor elevations of these through valleys are several hundred feet higher than the floor of the section 1 through valley. These higher elevation through valleys were also eroded as south-oriented flow channels located west of the deeper section 1 through valley and suggest flood waters may have been flowing on higher level surfaces in the west than in the east. Again headward erosion of the northeast-oriented South Fork Simms Creek valley and subsequent headward erosion of the northeast-oriented North Fork Simms Creek valley beheaded south-oriented flood flow channels and flood waters on north ends of beheaded flood flow channels reversed flow direction to create the drainage divide.

Dry Creek-Flat Creek drainage divide area

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

 

  • Figure 5 illustrates the Dry Creek-Flat Creek drainage divide area located west of the figure 3 map area and includes overlap areas with figure 3. Smith Creek is the east-northeast oriented stream located near the north edge of the figure 5 northwest quadrant. Elk Creek is the north-northeast oriented tributary flowing from the figure 5 west edge (near southwest corner) to join Smith Creek near the figure 5 north edge. North of the figure 5 map area Smith Creek joins the Sun River. Flat Creek originates east of the Harrison Basin Ridge in the figure 5 southwest quadrant (just north of the south edge) and flows in an east-northeast and east-southeast direction to the figure 5 east edge (just north of southeast corner). Clemons Creek is the east-northeast and southeast oriented stream south of the Harrison Basin Ridge and flows to the Dearborn River just south of the figure 5 map area. Hay Coulee is a northwest-oriented Elk Creek tributary in the figure 5 southwest quadrant located between Harrison Basin Ridge and Connors Reef. Note how the northwest-oriented Hay Coulee valley is linked by a through valley with the east-oriented Flat Creek valley and also with the southeast-oriented Clemons Creek valley. These through valleys were eroded by diverging south and east-oriented flood flow channels to both the actively eroding Flat Creek valley and the Dearborn River valley (south of figure 5). The south-oriented flood flow ended when headward erosion of the Smith Creek valley beheaded the flood flow channel and flood waters on the north end of the beheaded flood flow routes reversed flow direction to erode the north-northeast Elk Creek valley and its northwest-oriented Hay Coulee tributary valley. Dry Creek originates north of Connors Reef and flows in a northeast and east-northeast direction to the figure 5 east edge (south of northeast corner). Note a northwest-oriented Dry Creek tributary near the figure 5 center, which is linked by a through valley with a southeast-oriented Flat Creek tributary. The through valley is defined by one contour line on each side (the contour interval is 50 meters) and provides evidence of southeast-oriented flood flow prior to headward erosion of the northeast-oriented Dry Creek valley. Headward erosion of the Dry Creek valley beheaded the southeast-oriented flood flow channel and flood waters on the northwest end of the beheaded flood flow channel reversed flow direction to erode the northwest-oriented Dry Creek tributary valley. Other northwest-southeast oriented through valleys can be seen, although the 50-meter contour interval does not include enough topography detail to fully show the extent of figure 5 flood eroded channels.

Detailed map of Dry Creek-Flat Creek drainage divide area

Figure 6: Detailed map of Dry Creek-Flat Creek drainage divide area. United States Geological Survey map digitally presented using National Geographic Society TOPO software. 

  • Figure 6 illustrates a detailed topographic map of the Dry Creek-Flat Creek drainage divide area seen in less detail in figure 5 above. Dry Creek can just barely be seen flowing in a northeast direction across the figure 6 northwest corner. Flat Creek flows in an east-northeast and southeast direction near the south edge of the figure 6 southeast quadrant. Hogan Creek originates in the east half of section 27 and flows in an east-northeast direction to the figure 6 east edge (near northeast corner of section 25). East of figure 6 Hogan Creek joins Flat Creek with water eventually reaching the Dearborn River. North of the Hogan Creek headwaters in section 22 are northwest-oriented headwaters of a north-northeast oriented stream which flows to the figure 6 north edge (east of center) and then to Dry Creek. Note in the section 26 northwest corner a northwest-southeast oriented through valley linking the northwest-oriented Dry Creek tributary headwaters valley with the east-oriented Hogan Creek valley. The figure 6 map contour interval is 20 feet and the through valley floor elevation at the drainage divide is between 4520 and 4540 feet. Hills on either side of the northwest-oriented Dry Creek tributary headwaters valley rise to more than 4740 feet meaning the through valley is at least 200 feet deep. Study of the figure 6 map area reveals numerous other northwest-southeast oriented through valleys crossing the Dry Creek-Flat Creek drainage divide. Elevations of the through valley floors vary as do elevations of the adjacent hills, although each of the through valleys is a water eroded feature. The through valleys were eroded as diverging and converging channels in what was once a large southeast-oriented anastomosing channel complex moving massive amounts of flood water to what at that time was the actively eroding Flat Creek valley. At that time there was no northeast-oriented Dry Creek valley, nor was an east-oriented Sun River valley to the north of the figure 6 map area. Flood waters were free to move in a southeast direction to the figure 6 map area where they were captured by headward erosion of the deeper Flat Creek valley. Hogan Creek valley headward erosion from the newly eroded Flat Creek valley then captured southeast-oriented flood flow channels in the figure 6 east half and beheaded flood flow routes to the newly eroded Flat Creek valley. Headward erosion of the deep northeast-oriented Dry Creek valley next beheaded southeast-oriented flood flow channels to the actively eroding Hogan Creek valley (and to the Flat Creek valley west of the Hogan Creek valley head), with flood waters on north ends of the beheaded flood flow routes reversing flow to erode north- and northwest-oriented Dry Creek tributary valleys.

Sun River-Dry Creek drainage divide area

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

 

  • Figure 7 illustrates the Sun River-Dry Creek drainage divide area north of the figure 5 map area and includes overlap areas with figure 5. Augusta is the small town located in the figure 7 northwest quadrant. The Sun River flows in a southeast and east direction along the north margin of the figure 7 northeast quadrant. Elk Creek is the northeast-oriented tributary flowing from the figure 7 west edge (south half) to Augusta and joining the Sun River near the figure 7 north edge. Dry Creek flows in a northeast, east-northeast, and north-northeast direction from the figure 7 south edge (west half) to join the Sun River near the figure 7 northeast corner. Spring Creek is a northeast and north-northeast Sun River tributary located between Elk Creek and Dry Creek. Note how northwest-southeast oriented through valleys can be seen linking the northeast-oriented Elk Creek valley and the northeast-oriented Spring Creek valley and also linking the Spring Creek valley with the northeast-oriented Dry Creek valley. For example the highway from Augusta to the figure 7 south edge uses a northwest-southeast oriented valley between the Spring Creek valley and the Dry Creek valley which is defined by one 50-meter contour line. To the northeast of the highway a northwest-southeast oriented through valley, defined again by one 50-meter contour line, can be seen southwest of Meyer Hill (where Meyer Lake is located) linking the Elk Creek valley with the Spring Creek valley and then to the southeast a similar through valley links the Spring Creek valley with the Dry Creek valley. In the figure 7 southwest quadrant several northwest-southeast oriented through valleys (defined by one or two 50-meter contour lines) can be seen linking the northeast-oriented Elk Creek valley with the northeast-oriented Dry Creek valley. These northwest-southeast oriented through valleys were eroded as southeast-oriented flood flow channels in the southeast-oriented anastomosing channel complex, which once crossed the figure 7 map area. Headward erosion of the northeast-oriented Dry Creek valley captured the southeast-oriented flood flow first and diverted the flood waters in a northeast direction to what was then the actively eroding Sun River valley (which at that time had not eroded headward far enough to behead southeast-oriented flood flow to the actively eroding Dry Creek valley head). Next Spring Creek valley headward erosion beheaded flood flow routes to the newly eroded Dry Creek valley before headward erosion of the Elk Creek valley beheaded flood flow channels to the actively eroding Spring Creek valley head and then to the actively eroding Dry Creek valley head further to the southwest. Sun River valley headward erosion north and west of the figure 7 map area next beheaded all southeast-oriented flood flow channels to the newly eroded Elk Creek valley in figure 7.

Detailed map of Spring Creek-Dry Creek drainage divide area

Figure 8: Detailed map of Spring Creek-Dry 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 Spring Creek-Dry Creek drainage divide area seen in less detail in figure 7 above. Spring Creek flows from the east end of Krone Lake (along figure 8 west edge, north of center) in an east and north-northeast direction to the figure 8 north center edge. Dry Creek flows in an east-northeast, east, and east-northeast direction from the figure 8 south edge (west half) to the figure 8 east edge in section 1 (south half). Note how the highway crosses the Spring Creek-Dry Creek drainage divide using a northwest-southeast oriented through valley. The figure 8 contour interval is 20 feet and the through valley floor elevation at the drainage divide is between 4220 and 4240 feet. The hill to the east rises to more than 4380 feet while the hill to west rises to more than 4400 feet meaning the through valley is at least 160 feet deep. Note a northwest-oriented tributary flows from the drainage divide to north-northeast oriented Spring Creek and a southeast-oriented tributary flows from the drainage divide to east-northeast oriented Dry Creek. The through valley was eroded as a southeast-oriented flood flow channel prior to headward erosion of the Spring Creek valley. Flood waters were moving to what was then the actively eroding Dry Creek valley. Headward erosion of the Spring Creek valley captured the southeast-oriented flood flow and diverted the water in a north-northeast direction to the what was then the actively eroding Sun River valley head. Flood waters on the northwest end of the beheaded flood flow channel reversed flow direction to erode the northwest-oriented Spring Creek tributary valley. The north-northeast oriented Spring Creek valley segment was eroded by reversed flood flow on the north end of a beheaded flood flow channel. This reversed flood flow eroded a deep enough valley that it was able to erode headward an east-oriented valley to capture southeast-oriented flood flow moving west of the actively eroding Sun River valley head. Headward erosion of this east-oriented Spring Creek valley segment beheaded additional southeast-oriented flood flow channels, most noticeably in figure 8 a flood flow channel extending across the section 4 southwest quadrant (west half of figure 8). This section 4 through valley is at least 120 feet deep. These former southeast-oriented flood flow channels were eroded into an upland erosion surface at least as high as the highest figure 8 elevations today. How much erosion occurred in the figure 8 map area before that former upland erosion surface was reached cannot be determined from figure 8 map evidence as there are no higher elevations to use as markers.

Flat Creek-Dearborn River drainage divide area

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

 

  • Figure 9 illustrates the Flat Creek-Dearborn River drainage divide area south of the figure 5 map area, south and west of the figure 3 map area, and includes overlap areas with figures 3 and 5. Milford Colony is located in the figure 9 northeast quadrant and Bowmans Corner is located at the highway intersection near the figure 9 east edge. Flat Creek originates near Bean Lake in the figure 9 northwest quadrant and flows in a northeast and east-northeast direction almost to the figure 9 north center edge. Near the north center edge Flat Creek turns to flow in a southeast and east direction to Milford Colony and to the figure 9 east edge (north half). Flat Creek eventually joins the Dearborn River, which then flows to the Missouri River. The Dearborn River flows in a northeast direction from the figure 9 west center edge almost to Bean Lake and then turns to flow in an east-southeast, east-northeast, and southeast direction to the figure 9 south edge (east half). South of the figure 9 map area the Dearborn River makes an east-northeast jog  and can just barely be seen in the figure 9 southeast corner. Auchard Creek originates just south and east of Flat Creek in the figure 9 northwest quadrant and then flows in a southeast direction across the figure 9 center to join the Dearborn River near the figure 9 southeast corner. Note how the southeast-oriented Dearborn River valley segment is linked by shallow northwest-southeast oriented through valleys with the northeast-oriented Flat Creek headwaters. Also note how the southeast-oriented Auchard Creek headwaters are also linked by shallow through valleys with the northeast-oriented Flat Creek valley. The southeast-oriented Dearborn River valley, Auchard Creek valley, and Flat Creek valley segments seen in figure 9 were eroded headward along what were  southeast oriented flood flow channels. Headward erosion of the northeast-oriented Flat Creek valley across the flood flow channels captured the southeast-oriented flood flow channel supplying flood waters to what was then the actively eroding Auchard River valley. The northeast-oriented Dearborn River valley in the mountains was probably eroded as an extension of the northeast oriented Flat Creek valley segment, however was captured by headward erosion of the southeast-oriented Dearborn River valley segment. This capture suggests flood flow channels were diverging at the mountain front with one diverging channel using the Flat Creek alignment while another flood flow channel used the present day Dearborn River alignment. Probably at that time the mountains were being uplifted and elevation differences were not as great as they are today. A combination of mountain uplift and deep flood erosion resulted in the topography seen today.

Detailed map of Flat Creek-Dearborn River drainage divide area

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

 

  • Figure 10 uses a detailed topographic map to illustrate the Flat Creek-Dearborn River drainage divide area near Bean Lake seen in less detail in figure 9 above. The Dearborn River flows in an east, southeast, northeast, and southeast direction from the figure 10 west edge (south half) to the figure 10 southeast corner. Note how in section 24 the Dearborn River valley and the Bean Lake basin are linked by a through valley. Flat Creek originates in section 12 (north of Bean Lake) and flows in a southeast and then northeast direction to the figure 10 north edge (east of center). Auchard Creek originates in the section 16 southwest corner and flows in a northeast direction to the section 16 north border and then turns to flow in an east and southeast direction to the figure 10 east edge (just north of center). Note how in section 17 the Auchard Creek headwaters valley is linked by a through valley with the southeast and northeast-oriented Flat Creek valley. Headward erosion of the northeast-oriented Flat Creek valley captured the southeast-oriented flood flow to what was then the actively eroding Auchard Creek valley. The Bean Lake basin is linked to the northeast-oriented Flat Creek valley by a broad southwest-northeast oriented through valley used today by the Dearborn (irrigation) Canal. The through valley floor elevation at the drainage divide is between 4630 and 4640 feet (the map contour interval is 20 feet). Elevations in section 29 to the southeast rise to more than 4900 feet while elevations in the section 12 northeast corner (to the north) rise to more than 4900. These elevations on either side of the through valley suggest the valley at one time may have been at least 260 feet deep. As previously mentioned this through valley suggests for a time flood waters from west of the figure 10 map area flowed from the mountains and diverged with some flood waters flowing in a northeast direction along the present day Flat Creek alignment while other flood waters flowed in more of an east direction along the present day Dearborn River alignment. Headward erosion of a deeper Dearborn River valley eventually beheaded the northeast-oriented flood flow channel to the Flat Creek alignment. However southeast-oriented flood flow moving along what was probably an emerging mountain front continued to flow to the northeast-oriented Flat Creek flood flow channel and also may have deposited flood transported debris to form the drainage divide between Bean Lake and the northeast-oriented Flat Creek valley. This flood deposition interpretation of the Bean Lake northeast margin material is based entirely on flood flow movements suggested by the figure 10 valley patterns and has not been checked to determine the nature of bedrock underlying section 18. Should the material not be flood deposited materials a different origin for the Bean Lake basin may be required.

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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