Missouri River-Smith River drainage divide area landform origins north of Big Belt Mountains, Montana, USA

Authors

Abstract:

Topographic map interpretation methods are used to determine landform origins in the Montana Missouri River-Smith River drainage divide area north of the Big Belt Mountains. The Missouri River flows in a north-northwest and northeast direction west and north of the Big Belt Mountains while the Smith River flows in a north and north-northwest direction from west of the Big Belt Mountain to join the Missouri River near Great Falls, Montana. Missouri and Smith River tributaries in the study region are generally oriented in north directions and at least some valley orientations are related to underlying geologic structures. The north-oriented tributary valleys are linked by through valley eroded across the drainage divides, which provide evidence of previous drainage routes. The study region is interpreted to have been first eroded by massive south oriented floods prior to headward erosion of the deep northeast-oriented Missouri River valley. Headward erosion of the deep Missouri River valley beheaded the south-oriented anastomosing flood flow channels which were crossing the region in sequence from the northeast to the southwest. Flood waters on north ends of the beheaded flood flow channels reversed flow direction to erode what are today north-oriented valleys (including the north-northwest oriented Smith River valley). East-oriented valleys across drainage divides were eroded by south-oriented flood flow captured from yet to be beheaded and reversed flood flow channels west of the actively eroding Missouri River valley head with the flood water moving to the newly beheaded and reversed (and deeper) north-oriented valleys further to the east. Based on evidence from a much larger study region flood waters are interpreted to have been derived from a rapidly melting thick North American ice sheet, which was located in a deep “hole.” The deep Missouri River valley was being eroded headward across massive south- and southeast-oriented ice-marginal melt water flood flow.

Preface

The following interpretation of detailed topographic map evidence is one of a series of essays describing similar evidence for all major drainage divides contained within the Missouri River drainage basin and for all major drainage divides with adjacent drainage basins. The research project is interpreting evidence in the context of a previously unexplored deep glacial erosion paradigm, which is fundamentally different from most commonly accepted North American glacial history interpretations. Project essays 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 Missouri River-Smith River drainage divide area landform origins north of Big Belt Mountains, 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 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 Missouri River-Smith River drainage divide area landform evidence north of the Montana Big Belt Mountains will be regarded as evidence supporting the “thick ice sheet that melted fast” paradigm (see essay listed at header). This essay is included in the Missouri River drainage basin landform origins research project essay collection.

Missouri River-Smith River drainage divide area location map

Figure 1: Missouri River-Smith 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 for the Missouri River-Smith River drainage divide area north of the Big Belt Mountains and illustrates a region in central Montana. The green shaded area near the figure 1 northwest corner is the southern tip of Glacier National Park. The east-west continental divide extends from Glacier National Park in a south-southeast direction along or near the Lewis and Clark Range crest and then west of Helena to the figure 1 south edge (east of Butte). The Big Belt Mountains are located in the figure 1 south center region and are labeled. The Missouri River flows in a north and north-northwest direction from Three Forks (along figure 1 south center edge) through Canyon Ferry Lake and Holter Lake along the Big Belt Mountains west side to near the town of Wolf Creek. North of Holter Lake the Missouri River turns to flow in a northeast direction to Great Falls, Fort Benton, and Loma before turning abruptly to flow in a south-southeast and east direction to the figure 1 east edge (north half). The Smith River flows in a north-northwest direction from the east side of the Big Belt Mountains and then between the Big Belt Mountains and Little Belt Mountains to join the Missouri River a short distance upstream from Great Falls. South of the north-northwest oriented Smith River headwaters (near White Sulphur Springs) are headwaters of the south-oriented Shields River, which flows between the Big Belt Mountains and the Crazy Mountains to join the east- and northeast-oriented Yellowstone River (south of the figure 1 map area). Hound Creek is the unlabeled north-northeast oriented Smith River tributary flowing from the Big Belt Mountains north end (north and east of Gates of the Rocky Mountains) and joining the Smith River a short distance upstream from where the Smith River joins the Missouri River. Hound Creek originates in a mountainous region, however this essay focuses on the Missouri River-Smith River and Hound Creek drainage divide north and east of the mountains. Links to essays illustrating and interpreting topographic map evidence for other Smith River drainage divide areas can be found in the Montana Smith River drainage basin landform origins essay. Essays illustrating and describing other Missouri River drainage divide areas available on this site can be found by selecting desired Missouri River tributaries and/or from this essay’s sidebar category list.
  • Based on topographic map evidence illustrated in hundreds of other Missouri River drainage basin landform origins research project essays the figure 1 map area was eroded by immense south and southeast oriented floods, which flowed across the entire figure 1 map area. Flood waters were derived from the western margin of a rapidly melting thick North American ice sheet, which was located in a deep “hole.” The Montana and northern Wyoming Missouri River drainage basin today drains what was the deep “hole’s” southwest wall. The Canadian Rocky Mountains in western Alberta and eastern British Columbia are located along what was the deep “hole’s” western rim. Immense ice-marginal melt water floods flowed along the deep “hole’s” western rim into and across Montana and then further south across Wyoming and Colorado and into New Mexico along routes roughly corresponding with the present day east-west continental divide. Flood waters flowed on a high level erosion surface (at least based on present day elevations) and were captured in sequence (from south to north) by headward erosion of deep valleys from east and west, which created the east-west continental divide. At the same time crustal warping raised the Rocky Mountains and high plateau areas. The crustal warping was probably caused by the ice sheet’s tremendous weight, although once started it was aided by crustal unloading as flood erosion removed bedrock layers from the tops of the rising mountain ranges. In time a combination of Rocky Mountain uplift and of ice sheet melting created a different flood flow pattern as at least some areas on the decaying ice sheet surface (probably near the southern margin) became lower in elevation than the ice-marginal flood flow routes in Montana and northern Wyoming. Of particular importance to the figure 1 map area was a giant southeast and south oriented ice-walled canyon which was carved by a huge supra-glacial melt water river into the ice sheet’s surface in present day Saskatchewan, North Dakota, and South Dakota. In time the giant canyon became an ice-walled and bedrock-floored canyon and detached the ice sheet’s southwest margin. Large and very deep northeast and east-oriented valleys eroded headward from that giant ice-walled canyon into Montana and northern Wyoming to capture the immense south and southeast-oriented ice-marginal melt water floods. The Missouri River valley and its tributary valleys seen in figure 1 eroded headward from that giant canyon to capture east of the present day continental divide the massive south- and southeast-oriented melt water flood flow which was flowing across the figure 1 map area.
  • At the time the deep Missouri River valley eroded headward from the deep ice-walled canyon immense south and southeast-oriented ice-marginal melt water floods were flowing across Montana on an erosion surface equivalent in elevation to some of the highest Montana elevations today (although crustal warping has significantly changed elevations since that time). Prior to headward erosion of the deep Missouri River valley the deep Yellowstone River valley and its tributary valleys had eroded headward across the south and southeast-flood flow and south and southeast-oriented tributary valleys were eroding headward from the newly eroded Yellowstone River valley in a north direction along south and southeast-oriented flood flow routes. At the same time headward erosion of the deep valley beheaded south and southeast-oriented flood flow channels and flood waters on north and northwest ends of those beheaded flood flow channels reversed flow direction to erode north and northwest-oriented tributary valleys. Next headward erosion of the deep Musselshell River valley beheaded south and southeast-oriented flood flow to the newly eroded Yellowstone River valley (Musselshell River valley headward erosion may have begun as an east-oriented Yellowstone River valley tributary, although it was captured when Missouri River valley headward erosion beheaded and reversed a south oriented flood flow channel to the newly eroded Musselshell River valley. Headward erosion of the deep Missouri River valley into and across the figure 1 map area beheaded and reversed other south- and southeast-oriented flood flow channels moving flood waters to the newly eroded Musselshell and Yellowstone River valleys. One south-southeast oriented flood flow channel was on the alignment of the present day north-northwest oriented Smith River. Today, south of the Little Belt Mountains through valleys link Smith River tributary valleys with the Musselshell River headwaters. Also south of White Sulphur Springs the Smith River headwaters are linked by a through valley with headwaters of the south-southeast oriented Shields River, which flows to the Yellowstone River. The Smith River-Hound Creek drainage divide area is a region where headward erosion of the deep Missouri River valley beheaded and reversed south and south-southeast oriented flood flow channels moving large quantities of flood water to what were then the actively eroding Yellowstone River valley and the actively eroding Musselshell River valley.

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

Figure 2: Detailed location map for Missouri River-Smith River drainage divide area. United States Geological Survey map digitally presented using National Geographic Society TOPO software. 

  • Focusing now on the Missouri River-Smith River drainage divide area north of the Big Belt Mountains figure 2 provides a more detailed location map. The Missouri River flows in a north-northwest direction through Holter Lake (near figure 2 south edge-west half) to Holter Dam and then turns to flow in a northeast direction to Great Falls (the urban area straddling the figure 2 north edge-east half). The green shaded areas in figure 2 represent National Forest lands and are generally located in mountainous regions. The large green shaded area in the figure 2 southeast corner represents National Forest lands in the Little Belt Mountains. The  green shaded area straddling the figure 2 south center edge is the north end of the Big Belt Mountains region. The Smith River flows in a north direction along the west edge of the Little Belt Mountains National Forest lands and then turns to flow in a north-northwest direction to join the northeast-oriented Missouri River near the town of Ulm. Hound Creek is a labeled northeast and north-northeast oriented tributary flowing from the north edge of the Big Belt Mountains National Forest lands to join the north-northwest oriented Smith River. This essay focuses on the drainage divide between the Missouri River and Smith River north of Hound Creek and between the Missouri River and Hound Creek further to the south (generally north of the east-oriented West Fork Hound Creek). Several unlabeled north-oriented Missouri River and Smith River tributaries are shown in the study region and the general direction of flow for most drainage routes south and east of the Missouri River is north. The north-oriented drainage routes evolved when headward erosion of what was then a very deep northeast-oriented Missouri River valley beheaded a south-oriented anastomosing channel complex one channel at a time from the east to the west. The south-oriented flood waters as seen in figure 1 were moving to what were then deep and actively eroding Yellowstone River and Musselshell River valleys. Flood waters on north ends of the beheaded flood flow channels reversed flow direction to erode north-oriented Missouri River tributary valleys. Because the flood flow channels were beheaded by the deep Missouri River valley headward erosion one channel at a time and because the flood flow channels were anastomosing (diverging and converging) reversed flood flow on a newly beheaded flood flow channel could capture flood flow from channels which had not yet been beheaded by Missouri River valley headward erosion. Such captures of flood flow sometimes resulted in massive flood flow reversals and provided water volumes required to erode significant north-oriented Missouri River tributary valleys (e.g. the north and north-northwest oriented Smith River valley and the north-northwest Missouri River valley upstream from Holter Dam).

Missouri River-Smith River drainage divide area

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

  • Figure 3 illustrates the Missouri River-Smith River drainage divide east of the town of Cascade, Montana. Cascade is the town without a name located near the figure 3 west center edge and is located on the west bank of the northeast-oriented Missouri River. The Missouri River in figure 3 has eroded a broad valley known as the Chestnut Valley. Note near the figure 3 north edge how the bluffs on the northwest side of the Missouri River valley show evidence of what was once a large incised meander. East of the arcuate-shaped bluffs on the east side of the Missouri River valley is a large streamline erosional residual. The large Missouri River valley, incised meander, and streamlined erosional residual all provide evidence the Missouri River valley was eroded by tremendous volumes of northeast-oriented flood flow. The Smith River is the north-northwest and north oriented river near the figure 3 east edge and joins the Missouri River north of the figure 3 map area. Between the northeast-oriented Missouri River and the north oriented Smith River are several other north-oriented streams. Starting in the east the north-northeast oriented Smith River tributary labeled “Coulee” is Spanish Coulee. East of Spanish Coulee is north-oriented Flat Creek which joins north- and northeast-oriented Geyser Creek near Castner Falls to form north-oriented Castner Coulee which drains to the Missouri River north of the figure 3 map area. Bird Creek is the north- and northwest-oriented Missouri River tributary flowing from the figure 3 south center edge and to enter the Missouri River valley east of Cascade. Willow Creek is a north-northeast oriented Bird Creek tributary near the figure 3 south edge. The north-oriented Missouri River tributaries seen in figure 3 are flowing in valleys eroded by reversals of flood flow on north ends of what were once south oriented flood flow channels beheaded by headward erosion of what was then the much deeper northeast-oriented Missouri River valley. At that time the Missouri River valley was eroding headward across massive south- and southeast-oriented flood flow. The broad Missouri River valley (Chestnut Valley) was probably eroded by captured flood flow from south and west of the figure 3 map area and probably is not the valley that initially eroded headward across the south-oriented flood flow channels. The figure 3 map region was deeply eroded by the south-oriented flood flow (before it was beheaded and reversed) and then by massive flood flow reversals caused by the deep Missouri River valley headward erosion.

Detailed map of Flat Creek-Spanish Coulee (north) drainage divide area

Figure 4: Detailed map of Flat Creek-Spanish Coulee (north) 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 Flat Creek-Spanish Coulee drainage divide area seen in less detail in figure 3 above. The Smith River meanders in a northwest direction across the figure 4 northeast corner. Spanish Coulee drains in a north-northeast direction from the figure 4 south center edge to join the Smith River near the figure 4 north edge. Flat Creek flows in a north direction from the figure 4 south edge (west half) to the figure 4 north edge (west half). The West Fork Flat Creek flows in an east direction from the figure 4 west edge (south of center) to join north-oriented Flat Creek in section 9. This appears to be a region of dipping strata and the north-oriented Spanish Coulee and Flat Creek valleys appear to be located between hogback ridges. The West Fork Flat Creek has eroded a water gap across the western hogback ridge and in section 10, just east of where the West Fork joins Flat Creek, there is a wind gap eroded across the Flat Creek-Spanish Coulee drainage divide. The figure 4 map contour interval is 20 feet and the floor of the through valley (or wind gap) at the drainage divide has an elevation of between 3760 and 3780 feet. Elevations on the hogback ridge to the north rise to 3882 feet while the 3900 foot contour line can be seen along the figure 4 south edge. In other words the wind gap is at least 100 feet deep and records an east-oriented flood flow channel to the Spanish Coulee valley prior to headward erosion of the deeper north-oriented Flat Creek valley. If West Fork Flat Creek flowed in an east direction to the Spanish Coulee valley then why and how did the north-oriented Flat Creek valley develop? The answer is there had to be water flowing along both routes at the same time as might occur in an anastomosing channel. What we are seeing in figure 4 is evidence of one time diverging and converging flood flow channels. These anastomosing flood flow channels existed in the region just prior to headward erosion of the deep Missouri River valley, which first beheaded and reversed the south-oriented flood flow on the Smith River-Spanish Coulee alignment and next beheaded and reversed flood flow on the Castner Coulee-Flat Creek alignment. A deep knick point eroded headward along the newly reversed Smith River flood flow channel and later along the Castner Coulee-Flat Creek flood flow channel. The deeper Flat Creek valley when it eroded headward into the figure 4 map area beheaded the east-oriented flood flow channel to the Spanish Coulee flood flow channel, which had previously been beheaded and reversed by the Smith River flood flow reversal.

Detailed map of Missouri River-Geyser Creek drainage divide area

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

  • Figure 5 is a reduction of a detailed topographic map of the Missouri River-Geyser Creek drainage divide area east and north of Cascade, Montana. Cascade is the town straddling the figure 5 west edge north of the southwest corner. The Missouri River flows in a northeast direction from Cascade to the figure 5 north edge (west of center). Geyser Creek originates in section 31 in the figure 5 southeast quadrant and flows in a north and northeast direction to the figure 5 east edge (north of center). Note the large streamlined erosional residual located in sections 14, 15, and 22 in the middle of the northeast-oriented Missouri River valley. Bird Creek is the north-oriented stream flowing from the figure 5 south center edge to join the Missouri River east of the erosional residual. Today a well-defined abandoned valley can be seen in section 23 on the east side of the erosional residual. The figure 5 map contour interval is 10 feet and the valley floor at the present day drainage divide is between 3470 and 3480 feet. Elevations along the Missouri River edge in this Chestnut Valley region are generally between 3330 and 3340 feet. Elevations on the erosional residual rise to 3655 feet and elevations in section 19 to the east rise to 3721 feet. In other words the abandoned valley is at least 175 feet deep, but is more than 100 feet higher than the present day Missouri River valley floor. The abandoned valley was eroded by water at a time when there was significantly more water flowing in the Missouri River valley than there is today and also records how the Missouri River valley was eroded as it eroded headward into the figure 5 map area to capture the massive south-oriented flood flow. An equally intriguing but shallower through valley can be seen near the west edge of section 31 (in figure 5 southeast quadrant) and links the north-oriented Geyser Creek headwaters valley with the north-oriented Bird Creek valley and also with the much deeper Missouri River valley. The floor of this Geyser Creek-Bird Creek through valley has an elevation at the drainage divide of between 3710 and 3720 feet. Based on adjacent elevations the valley appears to be at least 30 feet deep. The valley is also a water eroded valley and was probably last eroded by north-oriented flood flow moving from what was then a south-oriented Bird Creek flood flow channel to what was then an actively eroding north-oriented Geyser Creek valley, which was being eroded headward by reversed flood flow on what had been a south-oriented flood flow channel. Remember Geyser Creek flows to north-oriented Castner Coulee, which drains to the Missouri River north and east of figure 5. Headward erosion of the deep northeast-oriented Missouri River valley head would have beheaded and reversed south-oriented flood flow on the Castner Coulee-Geyser Creek alignment before headward erosion of the deep Missouri River valley head would have beheaded and reversed flood flow on the Bird Creek alignment.

Missouri River-Hound Creek drainage divide area

Figure 6: Missouri River-Hound Creek drainage divide area. United States Geological Survey map digitally presented using National Geographic Society TOPO software. 

  • Figure 6 illustrates the Missouri River-Hound Creek drainage divide area south of the figure 3 map area and includes overlap areas with figure 3. Cascade is the town located near the figure 6 northwest corner. The Missouri River flows in a northeast direction in the large northeast-oriented Chestnut Valley in the region just east and south of Cascade. The Smith River flows in a north-northwest direction in the figure 6 northeast corner. Hound Creek is the north and north-northeast oriented stream flowing from the figure 6 south edge (just west of southeast corner) to the figure 6 east center edge and joins the Smith River east of the figure 6 map area. Spanish Coulee drains in a north-northeast direction to join the Smith River near the figure 6 northeast corner. Bird Creek is located east of Spanish Coulee and flows in a north direction (with some jogs) from the figure 6 south center edge area to the figure 6 north edge (west of center) and joins the Missouri River north of the figure 6 map area. Willow Creek is a northeast, north, and north-northeast oriented Bird Creek tributary located east of Rocky Reef and west of Bird Creek. Other than along its north edge the mountainous region in the figure 6 southwest quadrant is not drained by north-oriented Bird Creek or its north-oriented tributaries. The figure 6 map contour interval is 50 meters and many topography details are lost with this large contour interval. However a close look at the figure 6 map reveals shallow through valleys linking the north-oriented Bird Creek valley with the north-northeast oriented Spanish Coulee valley and also linking the Spanish Coulee valley with the north-oriented Hound Creek valley. Spring Willow Coulee in the figure 6 southeast quadrant is located in the east end of a through valley linking the Spanish Coulee valley with the Hound Creek valley. These through valleys are relics of south-oriented flood flow channels that once crossed the region. Probably the mountainous region in the figure 6 southwest quadrant was being uplifted as flood waters flowed across the region and deep flood water erosion significantly lowered regional elevations both prior to Missouri River valley headward erosion and after the massive flood flow reversals caused by headward erosion of the much deeper Missouri River valley. Figures 7, 8, 9, and 10 below use detailed topographic maps to better illustrate linkages between the present day north-oriented valleys, which were eroded by south-oriented flood flow just prior to the flood flow reversals that eroded the north-oriented valleys.

Detailed map of Cherry Coulee-Willow Creek drainage divide area

Figure 7: Detailed map of Cherry Coulee-Willow Creek drainage divide area. United States Geological Survey map digitally presented using National Geographic Society TOPO software. 

  • Starting with the Missouri River valley and working eastward figure 7 begins by using a detailed topographic map to illustrate the Cherry Coulee-Willow Creek drainage divide area. The southeast edge of the northeast-oriented Missouri River valley (Chestnut Valley) can just barely be seen in the figure 7 northwest corner. Cherry Coulee is a short north-oriented Missouri River tributary in the figure 7 northwest quadrant draining to the figure 7 north edge. East of Cherry Coulee is Gollaher Reservoir and Willow Creek is the north-oriented stream flowing from the reservoir to the figure 7 north edge. North of figure 7 Willow Creek flows in a north-northeast direction to join north-oriented Bird Creek. South of Gollaher Reservoir Willow Creek flows in a northeast direction from the figure 7 southwest quadrant. Note how in section 20 the north-oriented Cherry Coulee valley is linked by a through valley with a northeast-oriented Willow Creek tributary valley. The figure 7 map contour interval is 40 feet and the through valley floor elevation is between 3560 and 3600 feet. The hill to the east rises to more than 3640 feet while the hill to the west rises significantly higher. The through valley was eroded by south-oriented flood flow on the yet to be beheaded and reversed Cherry Coulee alignment which was captured by reversed flood flow on the Bird Creek-Willow Creek alignment. Remember, headward erosion of the deep Missouri River valley would have beheaded and reversed south-oriented flood flow on the Bird Creek and Willow Creek alignments before it would have beheaded and reversed south-oriented flood flow on the Cherry Coulee alignment. In other words south-oriented flood flow on the Cherry Coulee alignment was making a U-turn to flow in a north direction to the actively eroding Missouri River valley head. The U-turn was probably aided by uplift of the highlands located south of the figure 7 map area. Bird Creek can be seen flowing in a north and north-northwest direction in the figure 7 east half. Blaine Creek is a north-northeast oriented Bird Creek tributary in the figure 7 southeast quadrant and Huff Creek is a northeast-oriented Blaine Creek tributary. Note how in section 28 there is a through valley linking the north-oriented Willow Creek valley with the Huff Creek valley. Near the southwest corner of section 22 another through valley links the Willow Creek valley with the Bird Creek valley. These through valleys and others were eroded by yet to be beheaded and reversed flood flow on the Willow Creek alignment which was flowing to what was then the newly beheaded and reversed flood flow on the Bird Creek alignment. There probably are other ways to interpret this figure 7 map evidence, but the evidence exists and must be explained.

Detailed map of Bird Creek-Spanish Coulee drainage divide area

Figure 8: Detailed map of Bird Creek-Spanish Coulee drainage divide area. United States Geological Survey map digitally presented using National Geographic Society TOPO software. 

  • Figure 8 provides a detailed topographic map of the Bird Creek-Spanish Coulee drainage divide area east and slightly south of the figure 7 map area and includes overlap areas with figure 7. Bird Creek flows in a north direction in the figure 8 west half. Spanish Coulee drains in a northeast direction from the figure 8 south center edge to the figure 8 east edge (north of center). The figure 8 map contour interval is 40 feet and several northwest-southeast oriented through valleys link the north-oriented Bird Creek valley with the northeast-oriented Spanish Coulee valley. For example in section 1 a through valley used by an unimproved road links the Spanish Coulee valley with the valley of a northwest-oriented Bird Creek tributary. The through valley floor elevation is between 4000 and 4040 feet and the adjacent hill to the east rises to 4162 while the adjacent hill to the west rises to 4174 feet. In other words this through valley is at least 120 feet deep. The through valley is a water eroded feature and was probably eroded by south-oriented flood flow prior to the beheading and reversal of flood flow in the Bird Creek valley. Remember Spanish Coulee drains to the north-northwest oriented Smith River, which would have been beheaded and reversed before south-oriented flood flow on the Bird Creek alignment would have been beheaded and reversed. For a short time south-oriented flood flow on the Bird Creek alignment would have been captured by the reversed flood flow on the Spanish Coulee alignment and this through valley is just one of several used by the captured flood flow to reach the newly reversed Spanish Coulee flood flow channel. Another somewhat higher through valley can be seen in the section 12 northwest corner (directly south of the section 1 southwest corner) and links a north-oriented Bird Creek tributary valley with the northeast-oriented Spanish Coulee valley. Two other through valleys can be seen in sections 31 and 32, although they link north-oriented headwaters of north-oriented Flat Creek with the Spanish Coulee valley. Even more pronounced through valleys link the Flat Creek valley with the Spanish Coulee valley a short distance north and east of the figure 8 map area and are seen in figure 9 below.

Detailed map of Flat Creek-Spanish Coulee (south) drainage divide area

Figure 9: Detailed map of Flat Creek-Spanish Coulee (south) 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 Flat Creek-Spanish Coulee drainage divide area north of the figure 8 map area and south of the figure 4 map area. Spanish Coulee drains in a north-northeast direction in the figure 9 east half. Flat Creek flows in a north-northeast direction from the figure 9 south center region to the figure 9 north edge (east half). West Fork Flat Creek flows in a north-northeast direction from the figure 9 southwest corner to the figure 9 north edge and north of figure 9 turns to flow in an east direction as seen in figure 4. The western two-thirds of figure 9 has a contour interval of 40 feet while the eastern third has a contour interval of 20 feet. Note in section 21 a well-defined northwest-southeast oriented through valley linking a northwest-oriented Flat Creek tributary valley with a east-northeast oriented Spanish Coulee tributary valley. The through valley floor elevation at the drainage divide is between 3800 and 3820 feet. Elevations on the ridge to the north rise to more than 3920 feet while elevations on the ridge to the south rise even higher. The through valley was eroded by southeast-oriented flood flow prior to the reversal of flood flow that eroded the north-northeast oriented Flat Creek valley. Remember Flat Creek flows to Castner Coulee, which enters the northeast-oriented Missouri River upstream from where the Smith River joins the Missouri River. Spanish Coulee drains to the Smith River and south-oriented flood flow on the Smith River-Spanish Coulee alignment would have been beheaded and reversed before Missouri River valley headward erosion would have beheaded and reversed flood flow on the Flat Creek alignment. For a short time at least south-oriented flood flow moving across the present day Flat Creek drainage basin could have been captured by north-oriented flood flow which was then eroding a much deeper valley in the newly reversed Spanish Coulee valley. Headward erosion of the deep northeast-oriented Missouri River valley then beheaded and reversed flood flow in the Flat Creek drainage basin and a deeper north-oriented Flat Creek valley eroded headward into the figure 9 map area and created the present day Flat Creek-Spanish Coulee drainage divide in section 21.

Detailed map of Spanish Coulee-Hound Creek drainage divide area

Figure 10: Detailed map of Spanish Coulee-Hound 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 Spanish Coulee-Hound Creek drainage divide area south and east of the figure 9 map area. Spanish Coulee drains in a north-northeast direction from the figure 10 west center edge to the figure 10 north edge (west half). Hound Creek flows in a north-northeast direction from the figure 10 south edge (east half) to the figure 10 east edge (north of center). Spring Willow Coulee is the labeled east-oriented Hound Creek tributary draining across sections 8, 9, and 10. Note how Spring Willow Coulee has eroded water gaps across the north-northeast oriented hogback ridge. The hogback ridge suggests valley orientations in the figure 10 map area are related to the underlying geologic structures, however the valleys are also water eroded features, which means the through valley seen near the corner of sections 5,6, 7, and 8, which links the Spanish Coulee valley with the Spring Willow Coulee valley (and in turn with the Hound Creek) was eroded by east-oriented flood water at a time when water was also eroding the Spanish Coulee valley. As in previous figures for a short time at least south-oriented flood flow in the Spanish Coulee valley moved in an east direction to the newly beheaded and reversed flood flow in the Hound Creek valley. After north-oriented flood flow in the Spanish Coulee valley was beheaded and reversed a deeper north-oriented Spanish Coulee valley eroded headward into the figure 10 map area and beheaded the east-oriented flood flow channel to the Spring Willow Coulee and Hound Creek valleys. Note also near the figure 10 south edge in the west half of section 16 a north-south oriented through valley linking a north-oriented Spring Willow Coulee tributary valley with a south-oriented Hound Creek tributary valley. This through valley, which is also eroded across the hogback ridge, was eroded by south-oriented flood prior to being beheaded by headward erosion of the deep east-oriented Spring Willow Coulee valley, which was probably eroded by the deep knick point that eroded headward on the Hound Creek valley after flood flow on the Hound Creek alignment had been beheaded and reversed. The interpretations presented in this essay have probably been greatly over simplified and the flood flow movements were probably much more complex than described. Future workers will probably greatly improve on these initial flood flow movement interpretations in ways not considered here. However, the important thing to remember is the Missouri River-Smith River drainage divide area north of the Big Belt Mountains was eroded by massive south-oriented flood flow, which was beheaded and reversed by headward erosion of a much deeper northeast-oriented Missouri River valley at a time when the adjacent mountain regions were being uplifted in ways that aided the flood flow reversal process.

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.

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out /  Change )

Google photo

You are commenting using your Google account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s

%d bloggers like this: