Sun River-Missouri River drainage divide area landform origins, Cascade County, Montana, USA

Abstract:

Topographic map interpretation methods are used to determine landform origins in the Sun River-Missouri River drainage divide area of Cascade County, Montana. The Missouri River flows in a northeast direction through Cascade County passing the communities of Cascade and Great Falls and is joined by north-northwest oriented tributaries from the south. The Sun River originates along the west-west continental divide and flows in an east direction to join the Missouri River in Cascade County at Great Falls. Isolated buttes, hills, mountains, and other upland areas in the Cascade County Sun River-Missouri River drainage divide area are separated by a maze of through valleys. At the drainage divide east end these through valleys extend in a north-south direction from the Sun River valley to the Missouri River valley. Further west in Cascade County the through valleys link the east-oriented Sun River valley with the northeast and southeast-oriented Little Muddy Creek valley, which drains to the Missouri River or link north-oriented Little Muddy Creek tributary valleys with south and east-oriented Missouri River tributary valleys. The through valleys are interpreted to have been eroded as anastomosing south-oriented flood flow channels into an upland erosion surface as high as the highest Cascade County drainage divide area elevations today. Headward erosion of the deep Little Muddy Creek valley from what was then an actively eroding and deep Missouri River valley first captured the south-oriented flood flow channels with flood waters on north ends of beheaded flood flow routes reversing flow direction to erode north-oriented Little Muddy Creek tributary valleys. Next headward erosion of the deep east-oriented Sun River valley repeated the process. Flood waters were derived from a rapidly melting thick North American ice sheet, which was located in a deep “hole”. The Cascade County, Montana area is interpreted to have been located on the deep “hole’s” southwest and west wall near the deep “hole’s” southwest and west rim.

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-Missouri River drainage divide area landform origins in Cascade 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 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-Missouri River drainage divide area landform evidence in Cascade County, Montana will be regarded as evidence supporting the “thick ice sheet that melted fast” paradigm (see link to thick ice sheet paradigm above title). This essay is included in the Missouri River drainage basin landform origins research project essay collection.

Sun River-Missouri River drainage divide area location map

Figure 1: Sun River-Missouri River drainage divide area location map (select and click on maps to enlarge). National Geographic Society map digitally presented using National Geographic Society TOPO software.

Figure 1 provides a location map for the Sun River-Missouri River drainage divide area in Cascade County, Montana and illustrates a region in north central Montana. The Canadian border is a short distance north of the figure 1 north edge and the southeast tip of Glacier National Park is seen in the figure 1 northwest corner. Great Falls is the major 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 to Wolf Creek where it turns to flow in a northeast direction to Cascade, Great Falls, Fort Benton, and Loma. South of Big Sandy the Missouri River makes a sharp turn to flow in a south-southeast direction and then in an east direction to the figure 1 east edge with water eventually reaching the Gulf of Mexico. The Sun River is an east-oriented tributary joining the Missouri River at Great Falls and originates along the east-west continental divide in the Lewis and Clark Range. The east-west continental divide extends in a south-southeast direction from the figure 1 northwest corner through Marias Pass and along or near the Lewis and Clark Range crest to the figure 1 south edge (west of Helena). All drainage routes west of the continental divide eventually end up in the northwest-oriented Clark Fork, which can be seen in the figure 1 southwest corner flowing from Deer Lodge (near figure 1 south edge) to Drummond and then to the figure 1 west edge, with water eventually reaching the Pacific Ocean. The northwest-oriented Middle Fork Flathead River (south of Glacier National Park) and the north-northwest oriented South Fork Flathead River (between the Lewis and Clark Range and Swan Range) flow to the south-oriented Flathead River (west of figure 1), which is a Clark Fork tributary. North of the east-oriented Sun River is the east-oriented Teton River, which also originates along the continental divide. Essays describing Teton River drainage basin drainage divide areas can be found by selecting the Teton River category (see sidebar). South of the east-oriented Sun River is the east, east-southeast, and southeast oriented Dearborn River, which joins the Missouri River near Craig and which also originates along the continental divide. Note how south of the northeast-oriented Missouri River segment many of the tributaries, including the Missouri River headwaters and the Smith River, are oriented in north-northwest directions. The Sun River-Missouri River drainage divide area in Cascade County illustrated and discussed in this essay is located east of a north-south line through Choteau and Wolf Creek, south of the Sun River, and north of the Missouri River.

Present day drainage routes in the entire figure 1 map area were formed during massive south and southeast-oriented melt water floods as a thick North American ice sheet, located in a deep “hole”, rapidly melted. The Missouri River drainage basin in Montana and northern Wyoming is today the deeply eroded deep “hole’s” southwest wall and the Canadian Rocky Mountains and Montana Rocky Mountains (including the Lewis and Clark and Swan Ranges seen in figure 1) at one time formed the deep “hole’s” western rim. The deep “hole” did not exist when the ice sheet was formed, but developed by deep glacial erosion (under the thick ice sheet) and by crustal warping of adjacent and other continental areas. The crustal warping was caused by the ice sheet’s great weight and continued as the thick ice sheet melted, which means immense ice-marginal melt water floods flowed in south and southeast directions along what was at that time a rising western deep “hole” rim from Canada into and across the figure 1 map area. These immense south and southeast-oriented melt water floods deeply eroded regions east of the rising Rocky Mountains, such as the Sun River-Missouri River drainage divide area in Cascade County, while eroding deep southeast and south-southeast oriented flood flow channels into the rising Rocky Mountains. For a time these southeast and south-southeast floods continued to flow along what are now crests of high Rocky Mountain ranges and roughly followed the east-west continental divide into Wyoming, Colorado, and even New Mexico. Headward erosion of deep valleys from both the east and west systematically captured the massive south- and southeast-oriented meltwater floods, proceeding from south to north, as Rocky Mountain uplift, which was occurring as flood waters flowed across the region, systematically blocked the south-oriented flood flow routes. In time the deep west-oriented Columbia River valley eroded headward from the Pacific Ocean to capture the south-oriented meltwater floods and beheaded what had become a major southeast-oriented flood flow channel on the northwest-oriented Clark Fork alignment (actually there were multiple steps involved, but in each step the process was the same). Flood waters on the northwest end of the beheaded flood flow channel reversed flow direction to flow in a northwest direction to the much deeper Columbia River valley and eroded the northwest-oriented Clark Fork valley, which captured south-oriented flood flow on the Flathead River alignment. The much deeper northwest-oriented Clark Fork valley then proceeded to erode headward along the south-oriented Flathead River valley which then beheaded diverging south-southeast and oriented flood flow channels on the present day South Fork Flathead River and Middle Fork Flathead River alignments. Flood waters on the north ends of the beheaded flood flow channels again reversed flow direction to erode the north-northwest and northwest oriented South and Middle Fork Flathead River valleys. Erosion of the much deeper Pacific oriented valley then proceeded headward along the South and Middle Forks Flathead River valleys and captured additional south-oriented flood flow channels along the west side of the present day continental divide and carved deep valleys forming the continental divide west side.

East of the continental divide along the deep “hole” southwest wall a somewhat different process was occurring. For a time the rapidly melting thick ice sheet had stood high above its western rim and ice-marginal floods could only flow in south and southeast directions. However in time the combination of ice sheet melting and of Rocky Mountain uplift, as the deep “hole” western rim began to form, resulted in a situation where elevations on the ice sheet surface were lower than elevations along the deep “hole” rim. This situation developed as giant supra glacial melt water rivers carved huge south oriented ice-walled canyons into the decaying ice sheet surface. Of particular significance to the figure 1 map area was a southeast and south-oriented ice-walled canyon in present day Saskatchewan, North Dakota, and South Dakota, which in time 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 giant canyon’s southwest and west wall. Deep east- and northeast oriented valleys eroded headward from that huge ice-walled canyon into the adjacent non glaciated regions of Montana and Wyoming to capture the massive southeast and south-oriented ice marginal floods. These valleys eroded in sequence from the southeast to the northwest. For example, the northeast oriented Yellowstone River valley eroded headward in advance of the deep northeast- and east-oriented Missouri River valley to the north, which beheaded flood flow routes to the newly eroded Yellowstone River valley (again the process involved multiple steps with headward erosion of many tributary valleys, but each step followed the process). North and northwest-oriented Missouri River tributary valleys and the north-northwest oriented Missouri River headwaters valley were eroded by reversals of flood flow on north ends of south-oriented flood flow channels beheaded by headward erosion of the much deeper northeast- and east-oriented Missouri River valley. East-oriented Missouri River tributary valleys seen in figure 1 eroded headward in sequence from south to north to capture south- and southeast-oriented flood flow (e. g. headward erosion of the Sun River valley was in advance of Teton River valley headward erosion with south-oriented oriented flood flow into the newly eroded and deep Sun River valley deeply eroding what is now the Teton River-Sun River drainage divide area prior to headward erosion of the deep Teton River valley, which beheaded flood flow to the newly eroded Sun River valley). Headward erosion of these deep east-oriented Missouri River tributary valleys and their tributary valleys into the rising mountains along the present day continental divide carved the east side of the mountains and the continental divide east side. While not seen in maps illustrated in this essay significant flood flow responsible for eroding the deep east-oriented Sun River valley came from west of the continental divide along the present day Middle Fork Flathead River alignment and crossed the continental divide at Sun River Pass (see Teton River-Sun River drainage divide landform origins in western Teton County, Montana essay)

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

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

Figure 2 is a detailed location map for the Sun River-Missouri River drainage divide area in Cascade County, Montana. County boundaries are shown and Cascade County is labeled. Great Falls is the major city in Cascade County. Teton County is located in the figure 2 northwest quadrant and Choutreau County is located in the northeast corner area. Lewis and Clark County is located in the figure 2 southwest corner region. The Missouri River flows in a northeast direction from Holter Lake near the figure 2 south edge (west half) through Great Falls to Fort Benton near the figure 2 northeast corner. The Sun River flows in an east direction from the figure 2 west edge along the Teton-Lewis and Clark County border and then enters Cascade County to join the Missouri River at Great Falls. The Sun River-Missouri River drainage divide area investigated in this essay is south of the Sun River, north of the Missouri River, and east of the north-south Lewis and Clark-Cascade County line. Figure 2 does not show topography, but does identify a number of landscape features including Sun River Bench, Taft Hill, Square Butte, Shaw Butte, Crown Butte, Birdtail Butte, Telegram Mountain, and Mount Cecella. Southeast-oriented Little Muddy Creek is the major Missouri River tributary shown and has northeast-oriented headwaters and tributaries including northeast-oriented Birdtail Creek, which originates north of a south oriented stream flowing to the southeast-oriented Dearborn River, which flows along the Cascade-Lewis and Clark County line to join the northeast-oriented Missouri River. Irrigation canals roughly parallel the east-oriented Sun River, but other than Simms Creek and its north-oriented South Fork figure 2 shows no Sun River tributaries originating in the Cascade County Sun River-Missouri River drainage divide area. Note how south and east of the northeast-oriented Missouri River many tributaries are oriented in north-northwest directions or have significant north-northwest oriented segments. The north-northwest oriented Missouri River tributary valleys were eroded by reversals of flood flow on north and northwest ends of beheaded south- and southeast-oriented flood flow routes. These flood flow reversals were triggered by headward erosion of what was then a much deeper northeast-oriented Missouri River valley. The southeast-oriented Little Muddy Creek and Dearborn River segments seen north and west of the Missouri River flow in valleys eroded by southeast-oriented flood flow moving to the newly eroded and deep northeast-oriented Missouri River valley. Headward erosion of the east-oriented Sun River valley captured flood flow routes to the newly eroded Missouri River valley. Apparently the Sun River valley was not as deep relative to the southeast-oriented flood flow routes it beheaded because any flood flow reversals it triggered did not erode major north- or northwest-oriented Sun River tributary valleys.

East end of Sun River-Missouri River drainage divide area

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

Figure 3 uses a reduced size detailed topographic map to illustrate the Sun River Bench area at the east end of the Sun River-Missouri River drainage divide area. Great Falls is the city located in the figure 3 northeast corner. The Missouri River meanders in an east direction along and across the figure 3 south edge and then flows in a north direction near the figure 3 east edge to Great Falls and the figure 3 north edge. The Sun River is the east-southeast oriented Missouri River tributary north of the Great Falls International Airport. The north-oriented Smith River joins the Missouri River just south of the figure 3 southwest corner. Note in the figure 3 southeast quadrant how the drainage divide between the south-oriented Missouri River segment in section 3 and the north-oriented Missouri River channel along the figure 3 east edge is shown as having many gravel pits, suggesting it is underlain with gravel deposits. Also note southwest-oriented tributaries to the south-oriented Missouri River channel segment and northeast-oriented tributaries to the north-oriented Missouri River channel and how these tributaries are linked by southwest-northeast oriented through valleys. The through valleys were eroded by large northeast-oriented floods which once crossed the present day drainage divide. The gravel deposits suggest flood waters deposited significant debris in the region. Flood waters responsible for eroding this Missouri River valley region were moving from the south and southwest and are probably related to events that occurred after erosion of the Sun River-Missouri River drainage divide area. Sun River Bench is the upland region seen in figure 3 north and west of the Missouri River and south of the Sun River. At first glance Sun River Bench may appear to be a rather unremarkable landform feature, but a closer look reveals a somewhat different picture. The highest elevations on Sun River Bench (seen in figure 3) are located in the figure 3 southeast quadrant at the edge of the Missouri River valley in sections 32 and 33. The map contour interval is 20 feet and those high elevations along the Missouri River valley edge are more than 3740 feet. Sun River Bench elevations gradually become lower both to the north and to the west with elevations along the Missouri River valley north wall at the figure 3 west edge being between 3520 and 3540 feet and in the figure 3 northwest corner being less than 3500 feet. Sun River Bench actually is a shallow and broad north-south oriented through valley linking the present day Sun River valley to the north with the Missouri River valley to the south. This north-south oriented through valley is aligned with the north-oriented Smith River valley (south of the figure 3 southwest corner) and was initiated as a south-oriented flood flow channel, where flood flow was first beheaded and reversed as the deep Missouri River valley eroded headward across it and later as the Sun River valley eroded headward across it. There probably were additional complications, such as uplift in the Smith River headwaters area that also contributed to the flood flow reversals. Figure 4 shows the west wall of the Sun River Bench through valley.

Sun River-Taft Hill escarpment drainage divide area

Figure 4: Sun River-Taft Hill escarpment drainage divide area. United States Geological Survey map digitally presented using National Geographic Society TOPO software.

Figure 4 again uses a reduced size detailed topographic map to illustrate the Sun River-Taft Hill drainage divide area west of the figure 3 map area and includes overlap areas with figure 3. The Sun River can be seen flowing in an east direction along the north edge of the figure 4 northeast quadrant. Sun River Bench is seen in the figure 4 east half south of the visible Sun River channel. Taft Hill is the escarpment surrounded upland west of Sun Bench. Note how just east of Taft Hill on Sun River Bench are north-south oriented through valleys linking north-oriented Sun River tributary valleys with south-oriented Missouri River tributary valleys. Floors of these through valleys at their lowest points along the drainage divide are between 3500 and 3520 feet which is at least 220 feet lower than the 3740 foot elevation at the Missouri River bend seen in figure 3 to the east. Taft Hill elevations in the northwest corner of section 13 (near the east edge of the Taft Hill upland area) are shown as rising to 3769 feet with elevations dropping to the west. In other words Taft Hill is approximately the same elevation as the elevation at the Missouri River bends seen in figure 3 and the north-south oriented Sun River Bench through valley is in between. Also, it appears another broad and shallow through valley has been eroded into the Taft Hill upland surface (elevations rise to more than 3800 feet just west of the figure 4 map area. In other words the Taft Hill upland surface is in reality the floor of what was once a large south-oriented flood flow channel, which was beheaded by headward erosion of the deep east-oriented Sun River valley to the north. North-oriented Fourmile Creek is a Sun River tributary and its valley was eroded by a reversal of flood flow when the deep Sun River valley beheaded and reversed the south-oriented flood waters. The southeast-facing Taft Hill escarpment was probably eroded as a large southeast-oriented headcut by the south-oriented flood waters (prior to being beheaded and reversed by Sun River valley headward erosion) flowing to what at that time was the actively eroding Missouri River valley (or perhaps flowing in a south direction on the south-oriented Smith River flood flow channel prior to it being beheaded and reversed by Missouri River valley headward erosion. A factor contributing to the Smith River flood flow reversal may have been uplift of mountain areas further south which was occurring as flood waters were flowing across the region. The northeast and east-oriented Taft Hill escarpments were probably eroded as headward erosion of the actively eroding and deep Sun River valley captured the south-oriented flood flow and was triggering the flood flow reversal that resulted in the erosion of the north-oriented Fourmile Creek valley.

Adobe Creek-Dry Fork drainage divide area

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

Figure 5 uses a less detailed topographic map to illustrate the Adobe Creek-Dry Fork drainage divide area west of the figure 5 map area and includes overlap areas with figure 4. The Sun River flows in an east-northeast direction near the north edge of the figure 5 northwest quadrant. Sun River is the small town located where the highway crosses the figure 5 north edge and Fort Shaw is the small town in the figure 5 northwest quadrant. Taft Hill is labeled and can be seen in the figure 5 east half. Shaw Butte is labeled and is the upland near the figure 5 west center edge and Square Butte is also labeled and is located east and slightly south of Shaw Butte. Little Muddy Creek flows in an east-southeast direction across the figure 5 southwest corner region and eventually flows to the northeast-oriented Missouri River. Dry Fork originates between Square Butte and Taft Hill and flows in a south-southeast direction to the figure 5 south edge (east of center) and joins Little Muddy Creek south of the figure 5 map area. Adobe Creek originates north of the Dry Fork headwaters and flows in a west and then north direction to Fort Shaw and then joins the east-oriented Sun River. While the presence of irrigation canals confuses the figure 5 secondary drainage patterns Adobe Creek appears to have north oriented tributaries from the south, especially between Shaw Butte and Square Butte while Little Muddy Creek in the same region appears to have south-oriented tributaries from the north. These north- and south-oriented tributaries are linked by a deep north-south oriented through valley eroded between Shaw Butte and Square Butte. Shallower and broader north-south oriented through valleys can also be seen between Square Butte and Taft Hill. Shaw Butte and Square Butte are erosional residuals and probably are composed and/or capped by erosion resistant bedrock, but they also provide markers for a higher level erosion surface that once existed across the entire figure 5 map area. The figure 5 contour interval is 50 meters and the through valley drainage divide floor elevation between Shaw Butte and Square Butte appears to be slightly over 1100 meters. A spot elevation at the Square Butte top reads 1461 meters while the 1400 meter contour line appears near the top of Shaw Butte. In other words the through valley is approximately 300 meters deep. This 300-meter deep through valley is an erosional landform which was eroded by south-oriented flood flow prior to headward erosion of the east-oriented Sun River valley. The shallower north-south oriented through valleys east of Square Butte are also water eroded features and were eroded by south-oriented flood flow prior to Sun River valley headward erosion. Sun River valley headward erosion captured the south-oriented flood flow and flood waters on the north ends of the beheaded flood flow channels reversed flow direction to erode the north-oriented Adobe Creek valley segment and its tributary valleys.

Sun River-Crown Butte Creek drainage divide area

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

Figure 6 illustrates the Sun River-Crown Butte Creek drainage divide area west of the figure 5 map area and includes significant overlap areas with figure 5. The east-oriented Sun River can be seen flowing near the figure 6 north edge. Square Butte is located near the figure 6 east edge just south of center. Shaw Butte is located just east of the figure 6 north center region. Fort Shaw is the small town located northeast of Shaw Butte and near the figure 6 north edge. Adobe Creek flows in a west and north direction from the figure 6 east edge (north of Square Butte) to Fort Shaw and the Sun River. Simms is a small town located near the Sun River and northwest of Shaw Butte. South of Simms (and southwest of Shaw Butte) is Crown Butte. Little Muddy Creek flows in a northeast direction from the figure 6 southwest corner to the area just south of Crown Butte and then turns to flow in an east and east-southeast direction to the figure 6 southeast corner. Crown Butte Creek originates west of Crown Butte and flows in an east direction to the Crown Butte west margin and then turns to flow in a northeast and south-southeast direction around Crown Butte to join Little Muddy Creek south of Shaw Butte. Note how additional north-south oriented through valleys west of Shaw Butte link the east-oriented Sun River valley with the east-southeast and southeast oriented Little Muddy Creek valley. One of the deeper through valleys is between Simms and Crown Butte and links the east-oriented Sun River valley with the east and south-southeast oriented Crown Butte Creek valley and also with the northeast-oriented Crown Butte Creek headwaters valley, which is linked by a through valley with a south-southeast oriented Little Muddy Creek tributary valley. The figure 6 map contour interval is 50 meters and the through valley floor elevation at the Sun River-Crown Butte Creek drainage divide is between 1100 and 1150 meters. Shaw Butte as previously mentioned rises to more than 1400 meters and Crown Butte also rises to more than 1400 meters. The through valleys describe what was at one time a south-oriented anastomosing channel complex which was eroded into a high level erosion surface at least as high as the tops of Square, Shaw, and Crown Buttes today. The flood flow channels were eroded by massive south-oriented meltwater floods, which flowed across the region prior to headward erosion of the deep east-oriented Sun River valley. Sun River valley headward erosion captured the south-oriented flood flow and beheaded the south-oriented flood flow channels in sequence from the east to the west. This meant flood waters were still flowing south across the figure 6 west half while flood flow routes in the east half had been beheaded. The figure 6 map contour interval is 50 meters and the through valley floor elevation at the Sun River-Crown Butte Creek drainage divide is between 1100 and 1150 meters. Square, Shaw, and Crown Buttes as previously mentioned rise to more than 1400 meters. The through valleys describe what was at one time a south-oriented anastomosing channel complex which was eroded into a high level erosion surface at least as high as the tops of Square, Shaw, and Crown Buttes today. The flood flow channels were eroded by south-oriented meltwater floods, which flowed across the region prior to headward erosion of the deep east-oriented Sun River valley. Sun River valley headward erosion captured the south-oriented flood flow and beheaded south-oriented flood flow channels in sequence from east to west. This meant flood waters were still flowing south across the figure 6 west half while flood flow routes in the east half had been beheaded.

Detailed map of Shaw Butte-Square Butte through valley area

Figure 7: Detailed map of Shaw Butte-Square Butte through valley area. United States Geological Survey map digitally presented using National Geographic Society TOPO software.

Figure 7 uses a detailed topographic map to illustrate the north-south oriented through valley between Shaw Butte and Square Butte. Shaw Butte is the upland region in the figure 7 west half while Square Butte is the upland located in the figure 7 southeast corner region. South-oriented drainage flowing to the figure 7 south edge flows to southeast-oriented Little Muddy Creek, which then flows to the northeast-oriented Missouri River. North-oriented drainage flowing to the figure 7 north edge or to west and north-oriented Adobe Creek (“Creek” on figure 7) flows to the east-oriented Sun River, which joins the Missouri River at Great Falls. The figure 7 contour interval is 20 feet. The elevation at the base of the radio tower on Shaw Butte (east edge of section 27) is 4639 feet. The highest point on Square Butte is shown as being 4792 feet (just east of the section 32 southeast corner). The lowest point on the drainage divide between north-oriented Sun River drainage and the south-oriented Missouri River drainage is between 3600 and 3620 feet meaning the through valley is more than 1000 feet deep. This deep through valley was eroded as a south-oriented flood flow channel prior to headward erosion of the east-oriented Sun River valley to the north. South-oriented flood waters were probably flowing to what was then an actively eroding southeast-oriented Little Muddy Creek valley, which was eroding headward from what was then a newly eroded northeast-oriented Missouri River valley. The deep flood flow channel was eroded into an upland surface at least as high as the Shaw Butte and Square Butte upland surfaces today. In other words the through valley depth provides a minimum measure for the depth of flood water erosion of regions surrounding Shaw and Square Buttes. How much erosion occurred before the upland surface represented by the Shaw Butte and Square Butte upland surfaces today was formed cannot be determined because there are no higher figure 7 markers. It is possible considerable erosion occurred prior to the formation of that Shaw Butte-Square Butte erosion surface. Headward erosion of the east-oriented Sun River valley north of the figure 7 map area beheaded the south-oriented flood flow with flood waters on north ends of the beheaded flood flow route reversing flow direction to erode the north-oriented Sun River tributary valleys. Since that time the figure 7 landscape has not been significantly changed.

Lepley Creek-Missouri River drainage divide area

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

Figure 8 illustrates the Lepley Creek-Missouri River drainage divide area located south and slightly east of the figure 6 map area. The Missouri River flows in a northeast direction across the figure 8 southeast corner. Cascade is the town located on the Missouri River northwest bank at the southeast end of Cascade Butte. Little Muddy Creek can be seen flowing in an east and southeast direction near the figure 8 northeast corner and east of the figure 8 map area joins the northeast-oriented Missouri River. The figure 8 map area includes numerous buttes and upland regions as high or higher in elevation than the tops of Shaw, Square, and Crown Buttes seen in figure 6 (remember those elevations were in the 1400 to 1500 meter range). The figure 8 map contour interval is again 50 meters and elevations above 1750 meters can be found at Telegraph Mountain (figure 8 southwest quadrant) and Mount Cecelia (just west of figure 8 south center edge area) rises to 1872 meters. South of the figure 8 map area between figure 8 and the northeast-oriented Missouri River are extensive regions with elevations greater than 1750 meters. Lepley Creek originates west of Mount Cecelia at Warner Hill and flows in a northeast and north-northeast direction to join Little Muddy Creek near Rocky Reef Reservoir near the figure 8 north edge. South of Warner Hill are headwaters of south-southeast oriented Hardy Creek which flows to the figure 8 south edge and then to the northeast-oriented Missouri River. Note that at Warner Hill there is a north-south oriented through valley between Telegraph Mountain and Mount Cecelia. The through valley floor elevation where the secondary road crosses the drainage divide is between 1500 and 1550 meters, meaning it is at least 250 meters lower than the “mountains” on either side. This through valley is a water eroded landform and was eroded by south-oriented flood flow at a time when the region north of figure 8 (seen in figure 6) was at least as high as the Warner Hill through valley floor is today. In other words the region north of figure 8 had not yet been eroded. Perhaps an even more remarkable through valley is between Mount Cecelia and Cascade Butte and links the north-northeast Lepley Creek valley with the east and southeast-oriented Knapp Creek valley which drains to the northeast-oriented Missouri River. North Branch is a north-northeast and east oriented Knapp Creek tributary flowing between Lepley Creek and Knapp Creek. The through valley floor elevation at the drainage divide (which is very near Lepley Creek) is between 1200 and 1250 meters. The highest elevation on Cascade Butte is shown as being 1391 meters suggesting the through valley is at least 140 meters deep. This through valley is also a water eroded landform feature and was eroded by south- and southeast-oriented flood flow to what was then the actively eroding northeast-oriented and deep Missouri River valley. Headward erosion of the deep Little Muddy Creek valley beheaded and reversed the south-oriented flood flow to erode the north-oriented Lepley Creek valley. Because Little Muddy Creek valley headward erosion beheaded and reversed flood flow routes in sequence (from east to west) south-oriented flood flow on the present day Smith Creek alignment (Smith Creek originates east of Telegraph Mountain with water eventually reaching Little Muddy Creek) continued to flow to the Lepley Creek headwaters area near Warner Hill and for a time flowed in a northeast and north-northeast direction to the actively eroding Little Muddy Creek valley. Little Muddy Creek valley headward erosion in time beheaded and reversed this western south-oriented flood flow route to erode the north-oriented Smith Creek valley.

Detailed map of Lepley Creek-Knapp Creek drainage divide area

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

Figure 9 provides a detailed topographic map of the Lepley Creek-Knapp Creek and Lepley Creek-North Branch Creek drainage divide areas seen in less detail in figure 8 above. Mount Cecelia is the forested mountain in the figure 9 southwest corner. The figure 9 map contour interval is 20 feet and the Mount Cecelia high point is shown as being 6142 feet. Cascade Butte can be seen in the figure 9 northeast corner and the high point is shown as being 4564 feet. Lepley Creek flows in a northeast direction from the figure 9 west edge (north of Mount Cecelia) to the figure 9 north edge (just west of center) and continues in a north-northeast direction to join southeast-oriented Little Muddy Creek. Knapp Creek originates in sections 2 and 35 east of Mount Cecelia and flows in a northeast and east direction to the figure 9 east edge (south of center) and flows to the northeast-oriented Missouri River. North Branch Creek originates in section 35 northeast quadrant and flows in a north-northeast and east-southeast direction to join Knapp Creek in the section 32 northeast corner. South of Knapp Creek is north-northeast and east-southeast oriented Antelope Creek, which flows from the figure 9 south edge (east of Mount Cecelia) to the figure 9 east edge (near southeast corner). Note how in the section 31 east half Antelope Creek and Knapp Creek almost meet and then diverge to flow along separate routes to the Missouri River (east and south of the figure 9 map area). Converging and diverging channels are characteristics of flood formed anastomosing channel complexes and these converging and diverging stream valleys suggest they were eroded under flood flow conditions. Study of the figure 9 map area reveals several well-defined through valleys linking the northeast and north-northeast oriented Lepley Creek valley with the North Branch Creek valley. These through valleys can be seen sections 26, 25, 30, and 19. Elevations of the through valley floors at the drainage divide are slightly less than 4000 feet, which means the through valleys are at least 550 feet lower than the top of Cascade Butte. The through valleys are in fact flood flow channels eroded into the floor of a much larger through valley or flood flow channel eroded between Mount Cecelia and Cascade Butte and were eroded by south, southeast, and east-oriented flood flow moving to what was at that time the actively eroding and deep Missouri River valley head. Headward erosion of the deep southeast-oriented Little Muddy Creek valley north of the figure 9 map area beheaded and reversed south-oriented flood flow to the figure 9 map area with flood waters on the north end of the beheaded flood flow route reversing flow direction to erode the north-northeast oriented Lepley Creek valley. As seen in figure 8 (and figure 10) yet to be beheaded and reversed south-oriented flood flow continued to move into the Lepley Creek valley west of the figure 9 map area and provided water to erode the deeper Lepley Creek valley seen today.

Detailed map of Lepley Creek-Hardy Creek drainage divide area

Figure 10: Detailed map of Lepley Creek-Hardy 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 Lepley Creek-Hardy Creek drainage divide area west of the figure 9 map area and seen in less detail in figure 8. Mount Cecelia is located in section 3 in the figure 10 east half. Lepley Creek originates in the section 33 southwest corner (west of Mount Cecelia) and flows in a northeast direction to the figure 10 northeast corner. North and east of the figure 10 map area Lepley Creek flows in a north-northeast direction to join southeast-oriented Little Muddy Creek. South of the Lepley Creek headwaters in section 4 is a south-oriented stream flowing to southeast and south-southeast oriented Hardy Creek which flows to the figure 10 south edge (east of center) and then to the Missouri River. Warner Hill is a low hill west of Mount Cecelia on the Lepley Creek-Hardy Creek drainage divide. Note how just west of Warner Hill a well-defined north-south oriented through valley links the north-oriented Lepley Creek headwaters with the south-oriented Hardy Creek tributary valley. The figure 10 map contour interval is 20 feet and the through valley floor elevation at the drainage divide is between 4960 and 4980 feet. The high point in section 5 to the west is shown as being 5661 feet while higher elevations (greater than 5800 feet) are found on Telegraph Mountain. Mount Cecelia to the east rises to 6142 feet. In other words the through valley floor is 700 feet or more below the surrounding high elevations. The Lepley Creek valley in section 33 is deeper than the Hardy Creek tributary valley in section 4. Where did the water come from to erode the deeper Lepley Creek valley? In the section 33 northwest corner there is a through valley between the Lepley Creek valley and the north-oriented Smith Creek valley which is located in section 29 (near figure 10 north edge). The elevation of the floor of this section 33 northwest corner through valley at the drainage divide is between 4940 and 4960, which is slightly lower than the floor of the through valley west of Warner Hill. This lower elevation suggests south-oriented flood water continued to the flow from the Smith Creek alignment into the Lepley Creek valley after flood flow to the Hardy Creek tributary valley had ended. However, probably for a long time south-oriented flood flow diverged in section 33 with some flood flow moving in a south direction along the Hardy Creek tributary valley route while other flood flow moved in a northeast direction along the Lepley Creek route to what was at that time the much deeper Little Muddy Creek valley. Headward erosion of the much deeper valley along the Lepley Creek route eventually beheaded the south-oriented flood flow on the Hardy Creek tributary route. The south-oriented stream in the west half of section 5 is Trout Creek which turns to flow in a west direction along the south margin of section 6 to the figure 10 west edge (south half). Note how in section 32 the south-oriented Trout Creek headwaters are linked by a through valley with the north-oriented Smith Creek headwaters, which also originate in section 32. The floor elevation of this through valley at the drainage divide is between 5300 and 5320 feet, but is still almost 500 feet lower than some of the surrounding high points. This and other high level through valleys provide evidence south-oriented flood flow channels were eroded into a high level surface as high as the highest figure 10 elevations today.

Additional information and sources of maps studied

This essay has provided only a sample of the detailed topographic map evidence supporting the flood erosion interpretation. Many additional illustrations could be provided. Readers are encouraged to look at mosaics of detailed topographic maps to see the abundance of available data. Maps used in this study were created and published by the United States Geologic Survey and can be obtained directly from the United States Geological Survey and/or from dealers offering United States Geological Survey maps. Hard copy maps can also be observed at United States Geological Survey map depositories, which are located throughout the United States and elsewhere. Illustrations used here were created using National Geographic Society TOPO software and digital map data. TOPO software and map data can be obtained from the National Geographic Society and/or dealers offering National Geographic Society digital map data.