Topographic interpretation methods are used to determine landform origins in the Milk River-Marias River drainage divide area located in Toole County, Montana. Toole County is located in north central Montana and is directly south of the Canadian (Alberta) border. The Milk River originates in Montana on the east edge of Glacier National Park and flows in a northeast direction into southern Alberta. Once in southern Alberta it flows in an east direction north of Toole County, Montana before turning to flow in a southeast direction to reenter Montana and eventually join the Missouri River. The Marias River is formed by east-oriented streams originating along the Montana Rocky Mountain front and flows in an east-southeast and south direction to join the Missouri River near Loma, Montana. Willow Creek is a major south-southeast oriented Marias River tributary originating west of the Sweet Grass Hills in northeast Toole County. The Milk River-Marias River drainage divide area described in this essay is located west of Willow Creek and is a region of deep and sometimes broad north-south oriented dry valleys, which today lack continuous drainage routes. These through valleys provide evidence of massive south-oriented flood flow which stripped at least 100 meters (and probably much more) of bedrock material from most Milk River-Marias River drainage divide areas. Evidence of numerous through valleys, anastomosing channels, beheaded drainage routes, and reversed drainage routes supports this interpretation. Flood waters are interpreted to have been derived from a rapidly melting thick North American ice sheet late during that ice sheet’s rapid melt down history.
- The purpose of this essay is to use topographic map interpretation methods to explore the Milk River-Marias River drainage divide area landform origins in Toole 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 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 Milk River-Marias River drainage divide area landform evidence in Toole County, Montana will be regarded as evidence supporting the “thick ice sheet that melted fast” paradigm (see paradigm related essay on menu at top of page). This essay is included in the Missouri River drainage basin landform origins research project essay collection.
Milk River-Marias River drainage divide area location map
- Figure 1 provides a location map for the Milk River-Marias River drainage divide area in Toole County, Montana and illustrates a region in north central Montana with southern Alberta and the Saskatchewan southwest corner to the north. The Missouri River flows in a northeast direction from Great Falls, Montana (just east of figure 1 south center edge) to Fort Benton and Loma before turning to flow in a south-southeast and east direction to the figure 1 east edge (just north of southeast corner). The Teton River is an east-oriented tributary joining the Missouri River near Loma. The Marias River is formed at the confluence of Cut Bank Creek and the Two Medicine River (south and slightly east of Cut Bank, Montana) and then flows in an east direction to Lake Elwell. From Tiber Dam, which impounds Lake Elwell, the Marias River continues in an east direction before turning to flow in a south direction to also join the Missouri River near Loma. Labeled south-oriented Marias River tributaries seen in figure 1 include Eagle Creek, Willow Creek, and Rocky Coulee. Just north of the headwaters of these south-oriented Marias River tributaries is the United States-Canada border and then the east-oriented Milk River, which flows toward the Alberta southeast corner region before flowing across southern Alberta and then turning to flow in a southeast direction to Havre, Montana. From Havre the Milk River flows in an east and southeast direction and eventually joins the Missouri River with water ending up in the Gulf of Mexico. Milk River headwaters are located on the east edge of Glacier National Park with the North Fork Milk River and the Milk River flowing in northeast directions into Alberta before joining west of Milk River, Alberta. Note how east-oriented Marias River tributaries also begin along the Rocky Mountain front eastern margin. The Milk River-Marias River drainage divide area in Toole County investigated in this essay is north of the Marias River, south of the Milk River, west of Willow Creek, and east of Cut Bank, Montana. The Chin Coulee-Milk River drainage divide landform origins in south central Alberta essay describes the region directly to the north and Milk River-Marias River drainage divide area landform origins in the Sweet Grass Hills, Toole and Liberty Counties, Montana essay describes the region immediately to the east. Marias River and Milk River drainage divide area essays may be found by selecting the Marias River or Milk River from the sidebar category list.
- Looking at the larger regional picture Milk River-Marias River drainage divide area erosional landforms were developed during immense south and southeast oriented ice-marginal melt water floods late during the rapid melt down of a thick North American ice sheet. The ice sheet had been located in a deep “hole” and today the upper Missouri River drainage basin in Montana and northern Wyoming is an eroded segment of the deep “hole’s” southwest wall. The ice sheet originally formed on a topographic surface equivalent to or higher than the highest level Rocky Mountain erosion surfaces today. At that time the Rocky Mountains did not stand high as they do today, although uplift occurred as the deep “hole” was formed by a combination of deep glacial erosion and of crustal warping. Melt water floods from the giant ice sheet initially flowed in south and southeast directions across what are today the crests of high Rocky Mountain ranges. Crustal warping caused by ice sheet’s great weight and perhaps aided by deep melt water flood erosion of overlying bedrock materials systematically raised the Rocky Mountains and high plateau areas of western North American from south to north. As uplift occurred the immense south and southeast-oriented melt water floods were diverted to the east and to the west (in other words the melt water floods initially flowed along what is today the east-west continental divide and were diverted to the east and west as the continental divide rose with uplift in the south occurring before uplift in the north). At the same time ice sheet melting was lowering the ice sheet surface and in time the ice sheet surface elevation was less than the elevation of the rising mountains to the west and south. Further giant ice walled canyons were carved into the decaying ice sheet surface by huge supra-glacial melt water rivers. Of particular importance to the Missouri River drainage basin history was a giant southeast- and south-oriented ice walled canyon which extended across present day Saskatchewan, North Dakota, and South Dakota. This ice-walled canyon eventually became an ice walled and bedrock-floored canyon that 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 the giant canyon’s southwest and west wall. However, before becoming a bedrock-floored canyon the canyon floor had already become significantly lower than ice-marginal bedrock surfaces south and west of the ice sheet’s south-west margin. Deep east- and northeast-oriented tributary valleys eroded headward from this giant ice-walled canyon into the adjacent bedrock surface to capture the immense ice-marginal melt water floods and to divert the flood waters onto the ice sheet surface and into the deep ice-walled canyon.
- Erosion of the Milk River-Marias River drainage divide area in northern Montana and southern Alberta occurred very late during the decaying ice sheet’s rapid melt down. At that time a deep east and northeast-oriented valley eroded headward from the floor of the giant ice-walled and bedrock-floored canyon in the North Dakota northwest corner. This deep east and northeast-oriented valley eroded headward across the Medicine Lake area of northeast Montana to near Poplar, Montana and then headward along what is today the Missouri River valley alignment. Headward erosion of this deep “Missouri River” valley and its tributary valleys captured south and southeast-oriented ice-marginal melt water from the north and west and also captured immense south and southeast-oriented ice-marginal floods which were trapped between rising mountain ranges in western Alberta and eastern British Columbia and which flowed into western Montana where rising mountain ranges blocked south and southeast-oriented flood flow routes in southwest Montana and northwest Wyoming. These immense trapped melt water floods were then forced to flow in north and northeast directions into central Montana and toward the ice sheet’s south-west margin. Headward erosion of the deep Missouri River valley was slightly in advance of headward erosion of its deep Milk River tributary valley, which captured south and southeast-oriented flood flow moving to what was then the newly eroded Missouri River valley. In the case of the Milk River-Marias River drainage divide area investigated in this essay headward erosion of the east-oriented Marias River valley in Toole County was in advance of headward erosion of the deep Milk River valley in southern Alberta to the north. Marias River valley headward erosion captured immense southoriented melt water floods, which deeply eroded what is today the Milk River-Marias River drainage divide area in Toole County. Headward erosion of the deep east-oriented Milk River valley across southern Alberta captured the south and southeast-oriented melt water flood flow and beheaded south- and southeast-oriented flood flow routes to the newly eroded Marias River valley
Detailed location map for Milk River-Marias River drainage divide area
- Figure 2 provides a more detailed location map for the Milk River-Marias River drainage divide area in Toole County, Montana. The United States-Canada border is located near the figure 2 north edge and no map information is shown for Canadian areas. As seen in figure 1 the Milk River flows in an east direction across southern Alberta and north of the figure 2 map area. Montana county boundaries and names are given, with Glacier County being west of Toole County. The Blackfeet Indian Reservation is located in Glacier and Pondera Counties in the figure 2 west half. The Marias River is formed at the confluence of Cut Bank Creek and Two Medicine River near the Blackfeet Indian Reservation east boundary and then flows along or near the Toole-Pondera County border before flowing in an east direction to Lake Elwell (or Tiber Reservoir) and then to the figure 2 east edge (near southeast corner). The major Marias River tributary from the north in Toole County is Willow Creek, which originates near West Butte in the western Sweet Grass Hills and then which flows in a south-southeast direction to enter Lake Elwell. Willow Creek has a number of tributaries and is shown as a continuous drainage route. Most other drainage routes in Toole County are shown as segments of discontinuous drainage routes, which makes determination of drainage history difficult especially on a map which shows no topographic features to identify valley locations. Some clues as to valley locations can perhaps be obtained from other data such as the location of railroad lines (such as figure 2). The railroad line from the Canadian border at Sweetgrass extending south through Sunburst, Kevin, and Shelby appears to be located in what may be a north-south oriented valley. Near Sweetgrass Buckley Coulee and a small lake suggest the presence of a valley. Drainage routes are shown flowing from north of Kevin to Lake Aloe and Virden Lake while a south-oriented Marias River tributary parallels the railroad line south of Shelby. This north-south through valley is quite obvious on topographic maps and is evidence of what was once a major south-oriented flood flow route. Willshaw Flats located between the town of Sweetgrass and the Sweet Grass Hills (near the Canadian border) by its name and the presence of small lakes appears to be another low area, although it will need to be seen on topographic maps to be understood. Generally the discontinuous drainage routes in Toole County are oriented in south and southeast directions and suggest the presence of south- and southeast-oriented valleys. An exception is in the Toole County northwest corner where a short Red “River” (“Creek” on other maps) segment flows in a north and northeast direction to the international border and is a Milk River tributary. South of the Red Creek headwaters are discontinuous south-oriented drainage routes. While the discontinuous drainage routes confuse the picture the figure 2 map area was eroded by immense south-oriented floods moving to what was then the actively eroding Marias River valley. Headward erosion of the east-oriented Milk River valley captured the south-oriented flood flow. The north-oriented Red Creek valley segment was eroded by a reversal of flood flow on the north end of a beheaded flood flow route.
Willshaw Flats-Willow Creek drainage divide area
- Figure 3 illustrates the Willshaw Flats-Willow Creek drainage divide area west of the West Butte of the Sweet Grass Hills. The Canadian border is immediately north of the figure 3 map area. North-northwest and north oriented Police Coulee in the figure 3 northeast quadrant is a Milk River tributary. The West Butte of the Sweet Grass Hills is located along the east edge of the figure 3 northeast quadrant. The highest point in the West Butte area, which is located just east of the figure 3 map area, has an elevation of 2129 meters. Willshaw Flats is labeled in the figure 3 west half and is a broad north-south oriented valley turning to the west in the figure 3 southwest quadrant. The Willshaw Flats valley floor elevation is between 1000 and 1020 meters (the map contour interval is 20 meters). Today no continuous drainage routes are shown on the Willshaw Flats valley floor, although intermittent lakes are shown and several west-oriented streams including Beaupre Coulee drain toward the Willshaw Flat valley. Willshaw Flats appears to have been eroded by south-oriented melt water flood flow which was subsequently beheaded by headward erosion of the deep east-oriented Milk River valley just north of the international border. Willow Creek is labeled and flows to the figure 3 south edge (east half). Timber Coulee and Twomile Coulee are southeast-oriented Willow Creek tributaries. Note how the southeast-oriented Timber Coulee and Twomile Coulee valleys are linked by through valleys with the much larger and deeper Willshaw Flats valley. These northwest-southeast oriented through valleys provide evidence of southeast-oriented flood flow channels to the Willow Creek valley prior to headward erosion of the much larger and deeper Willshaw Flats valley. Valleys in the figure 3 map area appear to have been eroded in sequence from east to west which is consistent with headward erosion of the east-oriented Marias River valley to the south. South and southeast-oriented melt water floods deeply eroded the figure 3 map area as they flowed to the actively eroding Marias River valley. Headward erosion of the large and deep Willshaw Flats valley from the actively eroding Marias River valley (west of the actively eroding Willow Creek tributary valley) captured southeast-oriented flood flow moving to the newly eroded Willow Creek valley. The Timber Coulee and Twomile Coulee through valleys provide evidence of the beheaded flood flow routes. Elevations of those through valley floors at the drainage divide are in the 1160 to 1180 range, indicating that prior to headward erosion of the large and deep Willshaw Flats valley elevations in the figure 3 west half were generally 140 meters or more meters higher than they are today, which gives a measure of erosion that occurred. How much erosion occurred as the higher level Willow Creek valley was eroding headward is not determinable in figure 3, although deep erosion probably occurred at that time as well.
Detailed map of Beaupre Coulee-Willow Creek drainage divide area
- Figure 4 provides a detailed topographic map of the Beaupre Coulee-Willow Creek drainage divide area seen in less detail in figure 3 above. Beaupre Coulee drains in a southwest and west direction in the figure 4 northwest quadrant and west of the figure 4 map area ends as a surface drainage route in the Willshaw Flats area. Willow Creek originates in the east half of section 6 (east of figure 4 center) and flows in a south-southeast direction to the figure 4 south edge (east half). Kicking Horse Creek is the south oriented tributary flowing from the figure 4 north edge (east half) to join Willow Creek in the southeast corner of section 8 (figure 4 southeast quadrant). Timber Coulee drains from sections 12 and 7 (just east of figure 4 south center) in a south-southeast direction to the figure 4 south edge (east of center) and joins Willow Creek south of the figure 4 map area. Note the through valley in section 1 (near figure 4 center) linking the south-southeast oriented Timber Coulee valley with the much deeper Beaupre Coulee valley. Figure 4 elevations are given in feet and the contour interval is ten feet. The through valley floor elevation at its deepest point in section 1 is between 3820 and 3830 feet. Elevations in section 14 near the figure 4 south edge (west of center) rise to more than 3950 feet while elevations in the figure 4 northeast quadrant rise significantly higher. In other words the through valley is at least 170 feet deep. A similar through valley links the Willow Creek headwaters valley with the Beaupre Coulee valley although the floor of this through valley is somewhat higher. These through valleys provide evidence of south- and south-southeast oriented flood flow channels across the figure 4 map region at a time when the deeper Beaupre Coulee valley did not exist. The south- and south-southeast oriented melt water flood flow was moving to what was then the actively eroding Willow Creek valley, which had eroded headward from the newly eroded Marias River valley. Headward erosion of the deep Beaupre Coulee valley from the deeper south-oriented Willshaw Flats valley captured the south and south-southeast oriented flood flow to the Willow Creek valley and diverted the flood flow westward to the newly eroded south-oriented valley, which had eroded headward from the actively eroding Marias River valley (which was eroding headward in west direction). Headward erosion of the deep western south-oriented valley and the Beaupre Coulee valley and associated flood flow movements significantly lowered elevations in the figure 4 northwest quadrant where elevations in the Beaupre Coulee valley are less than 3650 or at least 170 feet lower than the Beaupre Coulee-Timber Coulee through valley floor.
Buckley Coulee-Willshaw Flats drainage divide area
- Figure 5 illustrates the Buckley Coulee-Willshaw Flats drainage divide area west of the figure 3 map area and includes overlap areas with figure 3. The United States-Canada border is located along the figure 5 north edge. Sweetgrass is the town located on the United States side of the border and Coutts (not shown) is the Canadian town just north of Sweetgrass. Sunburst is the town located in the figure 5 southeast quadrant on the highway and railroad. The railroad follows a well-defined valley from Sweetgrass to Sunburst and then to the figure 5 south edge. Today there is no continuous drainage route in this valley, although drainage routes flow to the valley and some valley segments have discontinuous drainage routes. Elevations on the floor of this north to south oriented valley vary slightly with a spot elevation of 1054 meters at the south end of the lake near Sweetgrass being a high point and then elevations decrease with some minor ups to the south. There appears to be almost no gradient for much of the figure 5 valley distance. The north to south oriented valley is joined by the Willshaw Flats valley from the east. Elevations in the larger Willshaw Flats area are slightly lower than in the north to south oriented valley the railroad follows. Buckley Coulee is an east, south, east, and southeast-oriented tributary just west of Sweetgrass and has eroded a deep valley. Another shorter and unnamed east-oriented tributary valley can be seen between the Rim Rock Colony and Sunburst. Also west of Sunburst there are dry valleys surrounding erosional remnants suggestive of a former south oriented anastomosing channel complex. Note how elevations in the figure 5 southwest quadrant (west of the east-facing escarpment) are generally greater than 1200 meters while elevations along the railroad are generally in 1020 to 1030 meter range. South-oriented melt water flood flow eroded the region east of the east-facing escarpment and the figure 5 evidence suggests more than 150 meters of bedrock material was stripped from the figure 5 east half at that time. In the figure 5 northwest corner is the Red Creek Oil Field and Red Creek is the northeast-oriented stream flowing through the oil field. North of the figure 5 map area Red Creek flows in a northeast direction to join the east-oriented Milk River. Note how north of the Rim Rock Colony there is a northwest and north-oriented Red Creek tributary. The northwest and north-oriented Red Creek tributary valley is linked by a through valley with an east-oriented valley draining to the much deeper north-south oriented valley to the east. The through valley floor elevation is between 1160 and 1180 meters while elevations greater than 1210 meters can be found on either side. The through valley is evidence of a south- and southeast-oriented flood flow channel that was subsequently beheaded and reversed by headward erosion of the deep northeast-oriented Red Creek valley from what was then the actively eroding Milk River valley. Milk River valley headward erosion (north of figure 5) captured all south-oriented flood flow moving across the figure 5 map area and ended erosion of figure 5 map landforms.
Milk River valley area in southern Alberta (from Atlas of Canada Toporama 1:150,000 scale topographic map)
- Figure 6 is an Atlas of Canada 1:150,000 scale topographic map from the Toporama web site for the region north and west of the figure 5 map area. 82H1 refers to number of the hard copy 1:50,000 scale topographic map published for the indicated region. The west to east oriented Canada-United States border is shown with no data available in the United States region. Coutts near the figure 6 southeast corner is the Alberta town directly across the border from Sweetgrass, Montana (which was seen in figure 5). Red Creek flows in an east-northeast direction in the figure 6 southeast corner region and is just north of Coutts. The Milk River flows in an east direction from near the words North Milk River (west half of map 82H1) to the town of Milk River and then to the figure 6 east edge. East of figure 6 Red Creek joins the Milk River. Labeled names of streams in the west half of map 82H1 are confusing. At the point where the words North Milk River is shown the northeast-oriented stream is the Milk River and the east-oriented stream joining the Milk River is the North Milk River. Mackie Creek is the southeast-oriented stream joining the North Milk River just to the west. The figure 6 contour interval is 20 meters and figure 6 elevations can be compared with figure 5 elevations. Elevations on the Milk River-Red Creek drainage divide in the south half of map 82H1 rise to 1300 meters, which is somewhat greater than elevations seen south of the border. Note how southeast oriented streams flow from that drainage divide toward Red Creek (but never reach Red Creek) and northwest oriented streams flow from the drainage divide to the Milk River. Shallow through valleys cross the drainage divide and link the northwest- and southeast-oriented stream valleys. These shallow through valleys provide evidence of southeast-oriented flood flow routes across the region prior to headward erosion of the deep Milk River valley, which is today as much as 200 meters lower than the drainage divide. Also note the north-south oriented through valley north of Coutts linking the Milk River valley with the Red Creek valley and the international border. Remember from figure 5 the through valley continues in a south direction with a valley floor elevation 1054 meters a short distance south of Sweetgrass (and even lower in the Willshaw Flats area to the east). In figure 6 the through valley elevation is between 1040 and 1060 meters, so we are seeing the north end of the large north to south oriented valleys seen in figure 5. The northeast-facing escarpment north of the Milk River in the figure 6 north center area is the northeast edge of the Milk River Ridge upland region. Verdigris Lake is located along the southwest margin of a large northwest-southeast oriented through valley north and east of Milk River Ridge linking the St Mary River valley with the Milk River valley (water in the St Mary River flows to the Oldman River, which flows to the South Saskatchewan River and which eventually reaches Hudson Bay while Milk River water eventually reaches the Gulf of Mexico). Headward erosion of the deep Milk River valley captured the southeast-oriented flood flow moving along the Milk River Ridge northeast margin and beheaded all flood flow routes across figure 5 to the newly eroded Marias River valley. Next headward erosion of the deep South Saskatchewan River-Oldman River-St Mary River valley captured all southeast-oriented flood flow to the newly eroded Milk River valley and ended flood flow in the figure 6 map area.
Rocky Springs Coulee-Fifteenmile Coulee drainage divide area
- Figure 7 illustrates the Rocky Springs Coulee-Fifteenmile Coulee drainage divide area south of the figure 5 map area. Kevin is the town on the railroad west of the figure 7 center. Oilmont is a place-name east of Kevin and Ferdig is another place east and north of Oilmont. Fifteenmile Coulee is a southeast and east-oriented stream originating south of Ferdig and draining to the figure 7 east edge (south half). East of figure 7 Fifteenmile Coulee drains to Willow Creek. Rocky Springs Coulee drains in a south, southeast and south direction from the figure 7 northwest corner region to the figure 7 south edge (west half) and south of figure 7 ends in Aloe Lake (see figure 8). Elevations in the Rocky Springs Coulee headwaters area are greater than 1200 meters and exceed 1300 meters in a few places. Other than in the figure 7 northwest corner region elevations elsewhere in the figure 7 region are less than 1100 meters and often less than 1050 meters. While not visible in figure 7 the south-oriented Rocky Spring Springs headwaters valley is linked by a shallow through valley with a north-oriented Red Creek tributary providing evidence of south-oriented flood flow across the highland area prior to headward erosion of the northeast-oriented Red Creek valley. Red Creek valley headward erosion beheaded the south-oriented flood flow to the actively eroding Rocky Springs Coulee valley and flood waters on the north end of the beheaded flood flow route reversed flow direction to erode the north-oriented Red Creek tributary valley. But, perhaps even more interesting is the evidence that south-oriented flood flow across the figure 7 map area stripped 100 to 150 meters of bedrock material from almost the entire figure 7 map area. Most of the figure 7 area is on the floor of the large north-south oriented valley extending from the Milk River valley in Alberta southward to the Marias River valley. The railroad is following the deepest valley channel eroded into the floor of this huge valley, which has shown a remarkably low gradient in a south direction. Remember north of Sunburst in figure 5 the elevation was 1022 meters and the railroad elevation across the entire 7 map area is between 1000 and 1020 meters. Just south of the figure 7 map area the railroad crosses the 1000 meter contour line and has an elevation of less than 1000 meters. The low gradient may be evidence of massive south-oriented flood flow or it could be the result of subsequent crustal warping that slightly raised or lowered the large valley’s north or south ends.
Spring Coulee-Marias River drainage divide area
- Figure 8 illustrates the Spring Coulee-Marias River drainage divide area south of the figure 7 map area. Shelby is the town located near the figure 8 southeast corner. Lake Aloe is labeled and is located just east of the figure 8 north center and the south-oriented stream flowing to it is Rocky Springs Coulee seen in figure 7. Note how Lake Aloe, two unnamed intermittent lakes, the town of Shelby, and the railroad are located in a well-defined channel eroded into the floor of what appears to be a much broader north-south oriented valley. The west wall of this broader valley is especially prominent in the figure 8 northwest quadrant. Spring Coulee drains in an east-southeast direction from the highland above this west valley wall onto the broad valley floor and then turns to drain in a northeast direction toward the figure 8 north center edge before turning to drain in an east direction to the Lake Aloe north end. Note how upland elevations for a large region north of the east-southeast oriented Spring Coulee segment are between 1180 and 1200 meters with some elevations exceeding 1200 meters. Note also how elevations on the broader valley floor are less than 1100 meters and decrease as Spring Coulee approaches Lake Aloe, which is shown as having a surface elevation of 997 meters. The Lake Aloe basin appears to be a local basin where elevations are slightly below 1000 meters and with the deeper channel floor rising above 1000 meters just south of the Lake Aloe south end. However the deeper channel floor elevation falls below 1000 meters again to produce another shallow and elongate local basin between the Lake Aloe basin and Shelby. At Shelby the deeper channel floor again rises slightly to over 1000 meters and then begins to decrease more rapidly to the figure 8 southeast corner. South and east of the figure 8 map area the deeper channel drains to the Marias River, which can be seen meandering in an east-southeast direction across the figure 8 southwest corner. The deeper channel extending from Lake Aloe through Shelby to the Marias River valley appears to have been eroded as a deep south-southeast oriented flood flow channel from the actively eroding Marias River valley head. At that time massive south-oriented flood flow was moving across the region on a surface equivalent to the higher elevations in the figure 8 southwest quadrant (greater than 1100 meters). Headward erosion of the deep Marias River valley head captured the south-oriented flood flow by eroding the deep south-southeast oriented Lake Aloe-Shelby-Marias River channel headward into the figure 8 map area. The northeast-oriented Spring Coulee valley segment was eroded by a reversal of flood flow on the north end of a beheaded south-oriented flood route and captured significant south-oriented flood flow from further to the west. The success of the northeast-oriented Spring Coulee valley in capturing south-oriented flood flow may have been aided by bedrock characteristics, although evidence from sources other topographic maps is needed to confirm the hypothesis.
Aloe Lake-Willow Creek drainage divide area
- Figure 9 is a reduced size map illustrating the Lake Aloe-Willow Creek drainage divide area east and slightly south of the figure 8 map area and includes overlap areas with figure 8. Lake Aloe is located at the figure 9 northwest corner. The east-southeast oriented Marias River can be seen in the figure 9 southwest quadrant. Shelby, Montana is the town located at the highway intersection in the figure 9 west center area. The deep south-southeast oriented Lake Aloe-Shelby-Marias River channel can be seen extending from the figure 9 northwest corner to the Marias River south of Shelby. Note how in the region north and slightly west of Shelby there are multiple south-oriented tributary valleys joining this larger south-southeast oriented channel. Mead Coulee just west of the Shelby Airport would be an example of these south-oriented valleys. These south-oriented valleys have isolated a number of erosional remnants to suggest the presence of a south-oriented anastomosing channel complex. The anastomosing channel complex would have been eroded as large volumes of south-oriented flood flow moved into the actively eroding south-southeast oriented Lake Aloe-Shelby-Marias River channel valley. East of Shelby are headwaters of east-oriented Dunkirk Coulee, which are linked by a shallow through valley with the much deeper Lake Aloe-Shelby-Marias River channel. Dunkirk Coulee drains to south-southeast oriented Willow Creek, which can be seen flowing from the figure 9 north edge (near northeast corner) to the figure 9 east edge (south of Mc Carters Lake). The shallow through valley at the Dunkirk Coulee head provides evidence the Dunkirk Coulee valley was eroded headward to capture south- and southeast-oriented flood flow prior to erosion of the deeper Lake Aloe-Shelby-Marias River channel. Also seen in figure 9 is Crooked Coulee which drains in a south-southeast direction to reach the West Fork Willow Creek. South and west of Crooked Coulee is south-southeast oriented Antelope Coulee and an unnamed southeast-oriented stream (West Fork Willow Creek), both of which are joined by Dunkirk Coulee, and the West Fork Willow Creek flows to join Willow Creek near the figure 9 east edge. Note the well-defined erosional remnant north of the town of Devon (on railroad and highway near figure 9 east edge) which provides evidence these Willow Creek tributary valleys are also defining a much larger anastomosing channel complex on the upland surface into which the deeper Lake Aloe-Shelby-Marias River channel was eroded. The figure 9 evidence suggests the upland surface east of the deeper Lake Aloe-Shelby-Marias River channel was sculpted first with the deeper Lake Aloe-Shelby-Marias River channel eroding headward from what was then the actively eroding Marias River valley to define a lower base level and to drain flood flow from the region.
Detailed map of Shelby-Dundirk Coulee drainage divide area
- Figure 10 provides a detailed topographic map of the Shelby-Dunkirk Coulee drainage divide area seen in less detail in figure 9 above. The deep Lake Aloe-Shelby-Marias River channel extends in a south-southeast direction from the figure 10 northwest corner to the figure 10 south center edge. Dunkirk Coulee drains in a south-southeast direction to Summers Reservoir in the figure 10 southeast quadrant and then enters an east-southeast oriented through valley and drains to the figure 10 east edge. The Great Northern Railroad line to the figure 10 east edge is located in the through valley. Elevations on the figure 10 map are given in feet and the spot elevation where the railroad crosses the through valley drainage divide is given as 3374 feet. A spot elevation near the highway on the hill to the south reads 3424 feet while elevations to the north rise to exceed 3480 feet. Note in section 36 how a northeast-southwest oriented through valley also links the Dunkirk Coulee valley with deep Lake Aloe-Shelby-Marias River channel and how in the figure 10 southeast corner there is evidence of still additional through valleys suggesting the low hills in section 31 and 36 are erosional remnants surrounded by what at one time were anastomosing flood flow channels, which were probably eroding headward from the Willow Creek valley. South and west of the deep Lake Aloe-Shelby-Marias River channel evidence for additional south-oriented anastomosing channels can be seen on the upland surface. Directly west of Shelby in section 29 are two north-south oriented through valleys. Elevations in the section 29 region are confusing because in the north of section 29 the contour interval is ten feet and in the south of section 29 the contour interval is 20 feet. The north-south oriented through valleys are eroded into the upland surface and appear to be 30-40 feet deep. Headward erosion of the deep Lake Aloe-Shelby-Marias River channel valley would have captured the south-oriented flood flow and ended flood flow across the upland surface to the south. Evidence presented in this essay has demonstrated massive south-oriented floods across the Milk River-Marias River drainage divide area. These immense south-oriented floods deeply eroded the entire Milk River-Marias River drainage divide area and stripped more than 100 meters of bedrock material from much of the region. South-oriented flood flow across the Milk River-Marias River drainage divide ended when headward erosion of the deep east-oriented Milk River valley captured the south-oriented flood flow.