St Mary River-Milk River drainage divide area landform origins, Glacier County, Montana, USA

Authors

Abstract:

Topographic map interpretation methods are used to determine landform origins in the St Mary River-Milk River drainage divide area located in Glacier County, Montana. Glacier County is located immediately south of the Canadian border and east of Glacier National Park. The St Mary River originates in high mountains of eastern Glacier National Park and flows in a north and north-northeast direction into adjacent Alberta with water eventually reaching Hudson Bay. The Milk River originates as several east and northeast oriented streams just east of the deep north and north-northeast oriented St Mary River valley and also flows into southern Alberta. After flowing across southern Alberta the Milk River turns to flow in a southeast direction back into Montana and joins the Missouri River with water eventually reaching the Gulf of Mexico. The St Mary River-Milk River drainage divide in Glacier County, which is the north-south continental divide, is today crossed by numerous through valleys, providing evidence of multiple flood flow routes to what at one time was the actively eroding Milk River valley. At that time the deep St Mary River valley did not exist and flood waters were coming from west and northwest of the Glacier County area. Headward erosion of the deep north and north-northeast oriented St Mary River valley captured the east and southeast oriented flood flow. Flood waters were derived from a rapidly melting thick North American ice sheet, which had been located in a deep “hole.” Present day mountains west and northwest of the north and north-northeast oriented St Mary River valley were located along the deep “hole’s” rim and probably were being uplifted as flood water flowed across them and as the deep St Mary River valley was eroding headward into the Glacier County, Montana region.

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 St Mary River-Milk River drainage divide area landform origins in Glacier 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 St Mary River-Milk River drainage divide area landform evidence in Glacier County, Montana will be regarded as evidence supporting the “thick ice sheet that melted fast” paradigm (see paradigm related essay in menu at top of page). This essay is included in the Missouri River drainage basin landform origins research project essay collection.

St Mary River-Milk River drainage divide area location map

Figure 1: St Mary River-Milk 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 is a location map for the St Mary River-Milk River drainage divide area in Glacier County, Montana and shows a region in northwest Montana with southwest Alberta and the British Columbia southeast corner to the north. The west-east continental divide (not labeled) extends in a south-southeast direction along the British Columbia-Alberta border and then through Glacier National Park (in Montana) to the figure 1 south edge (west of center) and is generally located along the crest of high Rocky Mountain ranges. The St Mary River originates in the St Mary Lakes area of Glacier National Park (just south the Alberta-Montana border on the east side of Glacier National Park) and flows in a north-northeast direction to join the Oldman River near Lethbridge, Alberta. From the Lethbridge region the Oldman River flows in an east-northeast direction to join the northeast-oriented South Saskatchewan River with water eventually reaching Hudson Bay. The Milk River originates on the Glacier National Park east edge, just south of the St Mary Lakes area, and flows in a northeast direction into southern Alberta and then in an east direction across southern Alberta. Just before reaching the figure 1 east edge the Milk River turns to flow in a southeast direction back into Montana. East of the figure 1 map area the Milk River eventually joins the Missouri River in northeast Montana with water eventually reaching the Gulf of Mexico. The St Mary River-Milk River drainage divide area in Glacier County, Montana, which is the north-south continental divide, is located between the north-northeast oriented St Mary River and the northeast-oriented Milk River, south of the Alberta-Montana border, and east of the mountains which form the west-east oriented continental divide. The Milk River-Cut Bank Creek drainage divide area landform origins, Glacier County, Montana essay describes the region directly south of the Milk River in Glacier County while the Chin Coulee-Milk River drainage divide area landform origins south central Alberta essay describes St Mary River-Milk River drainage divide areas in southern Alberta. Milk River drainage basin drainage divide area essays can be found by selecting Milk River from the sidebar category list.
  • The St Mary River-Milk River drainage divide area in Glacier County, Montana is located directly east of the Rocky Mountain front with the St Mary River and to some extent the Milk River headwaters being in high mountain areas and then flowing onto plains east of the mountains. Today it may be difficult to imagine, but the St Mary River-Milk River drainage divide area in Glacier County was eroded by immense south and southeast oriented melt water floods, which were derived from a rapidly melting thick North American ice sheet. The thick ice sheet had been comparable in size (both extent and thickness) to the present day Antarctic Ice Sheet and had been located in a deep “hole.” The deep “hole” had been formed by a combination of crustal warping and of deep glacial erosion. The upper Missouri River drainage basin in Montana and northern Wyoming and the Saskatchewan River drainage basin in southwest Alberta is what remains of the deep “hole’s” deeply eroded southwest wall. At the time the ice sheet originally formed the Rocky Mountains did not stand high like they do today, nor were high western North American plateau areas at the elevations they are today. Uplift of the Rocky Mountains and of western North America plateau areas occurred as the ice sheet was melting and immense south and southeast oriented melt water floods flowed along what are today the crests of high mountain ranges. In fact the west-east continental divide is formed along what was a major south and southeast oriented melt water flood flow river, which was systematically dismembered from south to north, with flood waters diverted both to the east and to the west to erode what are today major river valleys. At first the diversion of flood waters to the east eroded southeast and/or east oriented river valleys, such as the Arkansas River valley. However, in time the ice sheet melting progressed to the point where the ice sheet no longer stood high above the surrounding bedrock surface. At about that time giant southeast and south oriented supra-glacial melt water rivers began to carve deep ice-walled canyons into the decaying ice sheet surface and these canyons became major regional drainage routes from which large east and northeast oriented valleys eroded headward into Montana and northern Wyoming to capture the immense south and southeast oriented ice-marginal melt water floods.
  • Of particular importance to development of the present day Missouri River and Saskatchewan River systems was a giant southeast and south oriented ice-walled canyon in Saskatchewan, North Dakota, and South Dakota (east of the figure 1 map area)., which in time became an ice-walled and bedrock-floored canyon which detached the decaying ice sheet’s southwest margin. 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. East and northeast-oriented valleys eroded headward from that deep southeast and south oriented ice-walled canyon to capture ice-marginal floods south and west of the ice sheet’s southwest margin. The present day Missouri River valley (west of Poplar, Montana) was one such valley, which eroded headward across northern Montana to capture southeast oriented ice-marginal floods and also to capture south and southeast-oriented flood waters that had been trapped by rising Rocky Mountain ranges and then were forced to flow in a north direction toward the deep “hole” melting of the decaying ice sheet was opening up. Headward erosion of the deep Milk River valley from the actively eroding Missouri River valley beheaded south- and southeast-oriented flood flow to the newly eroded Missouri River valley. Subsequently headward erosion of the deep South Saskatchewan River valley and its tributary valleys (e.g. Oldman River valley and St Mary River valley) from the giant ice-walled and bedrock-floored canyon in central Saskatchewan beheaded southeast- and south-oriented flood flow routes to the newly eroded Milk River valley. Headward erosion of the deep east- and northeast-oriented valleys was in sequence from south to north, with headward erosion of each new valley beheading flood flow routes to the newly eroded valley just to the south. Headward erosion of these deep valleys combined with the immense south- and southeast-oriented melt water flood flow deeply eroded the entire region east of the Rocky Mountains. At the same time Rocky Mountain uplift caused by ice sheet related crustal warping, plus crustal unloading triggered by the deep melt water flood erosion, probably was raising the mountains to the west. To what extent present day elevation differences are the result of deep melt water flood water erosion or to continuing uplift of the mountain regions is difficult to determine, although both occurred and contributed to development of landscapes seen today.

Detailed location map for St Mary River-Milk River drainage divide area

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

 

  • Figure 2 provides a detailed location map for the St Mary River-Milk River drainage divide area in Glacier County, Montana. The United State-Canada border is located along the figure 2 north edge. Glacier County is labeled and the boundaries are shown. Pondera County is south of Glacier County and Flathead County is west of Glacier. The Flathead County-Glacier County border is defined by the west-east continental divide, which with the exception of a few passes, follows the crests of high mountains and runs through Glacier National Park. East of Glacier National Park much of the Glacier County area is included in the Blackfeet Indian Reservation, which is shown and labeled on figure 2. West of the continental divide water flows to the Flathead River with the water eventually reaching the Columbia River and the Pacific Ocean. The St Mary River originates on the east side of the west-east continental divide with water flowing first to St Mary Lake in Glacier National Park and then to Lower St Mary Lake near the Blackfeet Indian Reservation west edge. From Lower St Mary Lake the St Mary River flows in a north and northeast direction to the figure 2 north center edge. Northeast oriented Willow Creek along the figure 2 north edge is a St Mary River tributary. Note how the St Mary River has almost no tributaries from the east and instead east of the St Mary River there is a ridge labeled Hudson Bay Divide. Hudson Bay Divide is the north-south continental divide with water in the St Mary River to the west eventually flowing to Hudson Bay, while drainage east of Hudson Bay Divide flows to the Milk River and eventually reaches the Gulf of Mexico. Emigrant Gap where Hudson Bay Divide crosses the international border is a water eroded through valley crossing the north-south continental divide. The North Fork Milk River originates near Duck Lake in the figure 2 north center region and flows in a northeast direction into Alberta where it joins the main Milk River. The Middle Fork Milk River originates south of Duck Lake and flows in a northeast and east-northeast direction to join the South Fork Milk River in the figure 2 north center region to form the northeast-oriented Milk River. The South Fork Milk River originates between Hudson Bay Divide and Milk River Ridge near the Glacier National Park east boundary and flows in a northeast direction to join the Middle Fork Milk River (Milk River Ridge is the drainage divide between the Milk River and the Marias River, which is a Missouri River tributary south of the figure 2 map area, Cut Bank Creek which originates south of Milk River Ridge is a Marias River tributary). Note in figure 2 how many of the east- and northeast-oriented Milk River tributaries originate just east of the north-oriented St Mary River segment, suggesting St Mary River valley headward erosion beheaded east oriented flood flow to Milk River tributary valleys. Also note how south of the Milk River in the Blackfeet Indian Reservation there are numerous southeast and south-southeast oriented Cut Bank Creek tributaries, suggesting Milk River valley headward erosion captured multiple south-southeast oriented flood flow routes to actively eroding Cut Bank Creek tributary valleys.

North Fork Milk River-Milk River drainage divide area

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

 

  • Figure 3 illustrates the North Fork Milk River-Milk River drainage divide area in Glacier County, Montana and near the Canadian border. The Middle Fork Milk River flows in an east-northeast direction from the figure 3 southwest corner to join the north-northeast oriented South Fork Milk River just north of the figure 3 south center edge and to form the northeast-oriented Milk River which flows to the figure 3 east center edge. The North Fork Milk River flows in a northeast direction from the figure 3 west center edge to the figure 3 north center edge. Squaw Creek is a northeast-oriented North Fork Milk River tributary. Note multiple northwest-oriented Squaw Creek tributaries. What appears to be a northeast-oriented drainage route in the figure 3 northwest corner is the Saint Mary Canal, which is a northeast-oriented irrigation canal. The Saint Mary Canal is located along the southeast margin of a large northeast-oriented valley, with Willow Creek being located along the valley’s northwest margin (north and west of figure 3). Willow Creek as previously noted is a St Mary River tributary so the Saint Mary Canal-North Fork Milk River drainage divide seen in the figure 3 northwest quadrant is the north-south continental divide. Emigrant Gap is located along that north-south continental divide, just north of the figure 3 map area, and is a water eroded northwest-southeast oriented through valley. A somewhat shallower northwest-southeast oriented through valley across the north-south continental divide can be seen north of Hungry Horse Flat and near the figure 3 north edge. The figure 3 contour interval in the west half is 50 meters and the visible through valley is defined by one contour line on each side while the unseen Emigrant Gap through valley is defined by two 50-meter contour lines on a side (the contour interval in the figure 3 east half is 20 meters). Note how in the figure 3 center region there is a large northwest-southeast oriented through valley linking the North Fork Milk River valley with the Milk River valley. The contour lines are somewhat confusing in the figure 3 center region because east of the through valley the contour interval is 20 meters and west of the through valley the contour interval is 50 meters. The through valley floor elevation is less than 1400 meters and elevations to the northeast along the drainage divide rise to at least 1449 meters (based on a spot elevation). Elevations to the southwest of the through valley rise to at least 1550 meters. In other words the through valley is at least 50 meters deep and could be much deeper. These and other northwest-southeast oriented through valleys were eroded as southeast-oriented ice-marginal melt water flood flow channels prior to headward erosion of the deep northeast-oriented Milk River valley, North Fork Milk River valley, and Willow Creek valley. Headward erosion of the deep northeast-oriented Milk River valley captured the southeast-oriented flood flow first. Next North Fork Milk River valley headward erosion beheaded southeast-oriented flood flow to the newly eroded Milk River valley. Flood waters on northwest ends of beheaded flood flow routes reversed flow direction to erode what are today the northwest-oriented Squaw Creek tributary valleys. Subsequently Willow Creek valley headward erosion beheaded southeast-oriented flood flow to the newly eroded North Fork Milk River valley.

St Mary River-Willow Creek drainage divide area

Figure 4: St Mary River-Willow Creek drainage divide area. United States Geological Survey map digitally presented using National Geographic Society TOPO software.

 

  • Figure 4 illustrates the St Mary River-Willow Creek drainage divide area south and west of figure 3 and includes a small overlap area with figure 3. Babb is the small town at the highway intersection near the south edge of the figure 3 southwest quadrant and is located in the valley of the north and north-northeast oriented St Mary River, which flows from the figure 4 south edge (east of Babb) to the figure 4 north center edge. Note relatively short northwest-oriented tributaries flowing into the deep St Mary River valley. Willow Creek originates in the figure 4 north center region and flows in a northeast direction to the figure 4 northeast corner and north and east of figure 4 joins the St Mary River. Note how Hall Coulee is a north-oriented Willow Creek tributary in the figure 4 northeast quadrant. Also note how the northeast-oriented Willow Creek valley is linked by a through valley with the Spider Lake basin and a southwest and northwest oriented St Mary River tributary. The North Fork Milk River originates north of Goose Lake and flows in an east direction (just north of Freezeout Flat) to the figure 4 east center edge. Several prominent through valleys provide evidence of flood flow channels prior to headward erosion of the present day valleys. Starting in the east the north-oriented Hall Coulee valley is linked by a well-defined through valley with the east oriented North Fork Milk River valley. The through valley was eroded by south-oriented flood flow to what was then the newly eroded North Fork Milk River valley prior to headward erosion of the deep Willow Creek valley. Willow Creek valley headward erosion beheaded the south-oriented flood flow and flood waters on the north end of the beheaded flood flow channel reversed flow direction to erode the north-oriented Hall Coulee valley. The Spider Lake-Willow Creek through valley was eroded by flood waters flowing to the actively eroding northeast-oriented Willow Creek valley prior to headward erosion of the deep St Mary River valley. Headward erosion of the St Mary River valley beheaded the southeast and northeast-oriented flood flow channel and flood waters on the west end of the beheaded flood flow channel reversed flow direction to erode the southwest and northwest-oriented Spider Lake outlet channel valley. Goose Lake and Duck Lake are located on floors of through valleys linking east- and northeast-oriented headwaters of the North Fork Milk River with the north-oriented St Mary River valley. These broad west to east-oriented through valleys were eroded by southeast oriented flood water flowing to the what were then actively eroding North Fork Milk River and tributary valleys prior to headward erosion of the much deeper St Mary River valley. Headward erosion of the St Mary River valley captured the southeast- and then east-oriented flood flow and flood waters of northwest ends of the beheaded flood flow routes reversed flow direction to erode northwest-oriented St Mary River tributary valleys.

Detailed map of St Mary River-Willow Creek drainage divide area

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

 

  • Figure 5 is a detailed topographic map of the St Mary-Willow Creek drainage divide area near Spider Lake seen in less detail in figure 4 above. The St Mary River flows in a north-northeast direction from the figure 5 southwest corner to the figure 5 north edge (west of center). Spider Lake is located near the figure 5 center and the outlet drains in a southwest and northwest direction to the St Mary River. Willow Creek originates in the section 21 northeast quadrant and flows in a northeast direction to the figure 5 northeast corner and joins the St Mary River north and east of the figure 5 map area. Note how the St Mary Canal moves water in a north-northeast direction along the St Mary River near the figure 5 west edge and then turns to cross the deep St Mary River valley in a southeast direction using a siphon and then drains in a northeast direction in the southwest oriented Spider Lake outlet valley to Spider Lake. From Spider Lake the St Mary Canal continues in a northeast direction across section 21 and then follows the Willow Creek valley. The through valley in section 21 links the northeast-oriented Willow Creek valley with the southwest and northwest-oriented Spider Lake outlet valley and is today used by the northeast-oriented irrigation canal. The figure 5 map contour interval is 20 feet and the through valley floor elevation at the drainage divide is between 4440 and 4460 feet. Elevations rise to more than 4840 on the ridge to the north and to more than 5200 feet on the ridge to the south suggesting the through valley is at least 400 feet deep and may have been deeper when eroded. The through valley was eroded by northeast-oriented flood flow prior to headward erosion of the deep St Mary River valley to the west. Flood waters probably came from the west and northwest of figure 5 map area and evidence of through valleys west of the St Mary River can be seen along the figure 5 west edge. Headward erosion of the deep St Mary River valley captured the east and northeast-oriented flood flow moving to the Willow Creek valley. Flood waters on the west end of the beheaded flood flow channel reversed flow direction to erode the southwest- and northwest-oriented Spider Lake outlet valley. This interpretation requires headward erosion of valleys several hundred feet or more deep into the figure 5 map area in sequence. Further this interpretation also requires that for a time diverging and converging flood waters were flowing in a northeast direction along flood flow channels using both the St Mary River alignment and the Willow Creek alignment as would be expected in an anastomosing channel complex. The North Fork Milk River can be seen flowing in an east direction in the figure 5 southeast quadrant. A prominent through valley can be seen crossing the Willow Creek-North Fork Milk River drainage divide in the northwest quadrant of section 35 (an unimproved road crosses the ridge by using that through valley which might also be called a mountain pass). The through valley floor elevation is between 5060 and 5080 feet and elevations on the ridge to west rise to more than 5300 feet and on the ridge just east of the figure 5 map area to more than 5200 feet. In other words this high level through valley is at least 120 feet deep and is a relic of an earlier south-oriented flood flow channel which was captured by headward erosion of the deep Willow Creek valley.

Detailed map of Hall Coulee-North Fork Milk River drainage divide area

Figure 6: Detailed map of Hall Coulee-North Fork Milk River drainage divide area. United States Geological Survey map digitally presented using National Geographic Society TOPO software.

 

  • Figure 6 is a detailed map of the Hall Coulee-North Fork Milk River drainage divide area east of the figure 5 map area and includes an overlap area with figure 5. Willow Creek flows in a northeast direction across the figure 6 northwest corner. The St Mary Canal is labeled drains in a meandering east direction near the 4400 foot contour line from the Willow Creek valley near the figure 6 east edge to the figure 6 northeast corner. The North Fork Milk River flows in an east direction near the figure 6 south edge. Hall Coulee is a north-oriented Willow Creek tributary originating in the section 32 northwest corner (very near the North Fork Milk River) to the figure 6 north edge and joins Willow Creek north of the figure 6 map area. Note the through valley linking the north-oriented Hall Coulee valley with the east-oriented North Fork Milk River valley in section 32. The map contour interval is 20 feet and the through valley floor elevation at the drainage divide is between 4540 and 4560 feet. Elevations in the section 32 northeast corner rise to 4962 feet while elevations in the section 25 south center area rise to more than 5200 feet. Based on these elevations the Hall Coulee-North Fork Milk River through valley is at least 500 feet deep. A much higher level through valley can be seen in the section 30 southwest quadrant and has an elevation of between 4960 and 4980 feet at the drainage divide. Elevations just to the east rise to 5065 feet while elevations in section 25 to west rise to more than 5200 feet. This higher level through valley is also a north-south oriented valley and is at least 100 feet deep. The high level through valley in the section 35 northwest quadrant was discussed in the figure 5 discussion and has a slightly higher floor elevation and is at least 120 feet deep. These north-south oriented through valleys provide evidence of multiple south-oriented flood flow channels, which crossed the region prior to headward erosion of the deep North Fork Milk River valley and subsequently headward erosion of the deep northeast-oriented Willow Creek valley. Headward erosion of the deep North Fork Milk River valley first captured the south-oriented flood flow and the deep Hall Coulee valley eroded headward from the newly eroded North Fork Milk River valley and probably helped erode the figure 6 north half. Headward erosion of the much deeper northeast-oriented oriented Willow Creek valley beheaded what had become a deep south-oriented flood flow channel on the Hall Coulee alignment. Flood waters on the north end of the beheaded flood flow channel reversed flow direction and eroded the north-oriented Hall Coulee valley. Probably for a time significant flood flow was moving east on the North Fork Milk River alignment to section 32 where some flood waters flowed north in the Hall Coulee valley to the Willow Creek valley while the remaining flood flow moved in an east direction along the North Fork Milk River alignment. Ultimately the North Fork Milk River valley captured all of the flood flow and the diverging north-oriented flood flow to the Hall Coulee valley ended.

St Mary River-North Fork Milk River drainage divide area

Figure 7: St Mary River-North Fork Milk River drainage divide area. United States Geological Survey map digitally presented using National Geographic Society TOPO software.

 

  • Figure 7 illustrates the St Mary River-North Fork Milk River drainage divide area south of the figure 4 map area and includes significant overlap areas with figure 4. Babb is the small town at the highway intersection in the figure 7 southwest quadrant. The lake along the figure 7 south edge south of Babb is Lower St Mary Lake and the St Mary River flows in a north and north-northeast direction from the Lower St Mary Lake to the figure 7 north edge (west half). Spider Lake is east of the St Mary River near the figure 7 north edge. The North Fork Milk River flows in an east direction north of Freezeout Flat to the figure 7 east edge (north of center). Goose Lake and Duck Lake are located in what appears to be a poorly drained region along the St Mary River-North Fork Milk River drainage divide. An east-northeast oriented North Fork Milk River tributary is located south of Freezeout Flat and originates just north of the Duck Lake east end. A south and west-oriented St Mary River tributary is located just west of Duck Lake, although no Duck Lake outlet is shown. The numerous small lakes in the Duck and Goose Lake area suggests the possibility of some type of glacial moraine, although whatever covers the surface was not responsible for the broad west to east oriented through valley linking the St Mary River valley with the east-oriented North Fork Milk River valley. The map contour interval is 50 meters and the through valley in the Duck Lake area has an elevation of less than 1550 meters (the Duck Lake elevation is shown as 1530 meters). The “Ridge” south of Duck Lake is St Mary Ridge and is the north-south continental divide and has an elevation of more than 1750 meters at the figure 7 south edge. The ridge north of Goose Lake is lower with an elevation of between 1600 and 1650 meters, however the west to east oriented through valley is at least 50 meters deep. This broad east-oriented through valley was eroded by immense east-oriented flood flow prior to headward erosion of the deep north and north-northeast oriented St Mary River valley. At that time flood waters were probably flowing in a south-southeast direction from the figure 7 northwest corner region to the present day St Mary River valley alignment and then eastward to what was then the actively eroding North Fork Milk River valley. It is also possible some flood waters were also flowing in a north direction into what is now the Lower St Mary Lake basin area and then in an east direction across the present day Duck Lake basin. Headward erosion of the deep St Mary River valley captured these various flood flow routes while perhaps local glaciation further modified the figure 7 landforms. If so the local glaciation occurred after the thick North American ice sheet rapid melt down ended. The rapid melt down ended when the immense south-oriented melt water floods were captured by giant north-oriented ice-walled and bedrock-floored canyons and diverted to the North Atlantic Ocean. This diversion of the immense south-oriented melt water floods changed ocean currents, which in turned changed the North American climate. The result of the climate change was a significant cooling event, which froze the north-oriented flood waters on the former ice sheet floor and which created a thin ice sheet. Any local glaciation in the figure 7 map area would have been associated with the thin ice sheet and not with the earlier thick ice sheet.

Detailed map of Duck Lake-North Fork Milk River drainage divide area

Figure 8: Detailed Map of Duck Lake-North Fork Milk River drainage divide area. United States Geological Survey map digitally presented using National Geographic Society TOPO software.

 

  • Figure 8 is detailed topographic map of the Duck Lake-North Fork Milk River drainage divide area seen in less detail in figure 7 above. The North Fork Milk River originates in section 32 in the figure 8 northwest corner and flows in an east direction near the figure 8 north edge to the figure 8 east edge (just south of northeast corner) and is linked by a through valley with the Goose Lake basin. The through valley floor elevation at the drainage divide is between 5180 and 5200 feet (the map contour interval is 20 feet). Elevations rise to more than 5320 feet in section 32 and in the section 4 southeast quadrant suggesting the through valley is at least 120 feet deep. An east and east-northeast oriented tributary flows across the north halves of section 10 and 11 before flowing to the figure 8 east edge and then to join the North Fork Milk River east of the figure 8 map area. This tributary valley is linked by a through valley in sections 9 and 10 with both the Goose Lake basin and the lower elevation Duck Lake basin (Goose Lake has a surface elevation of 5172 feet while the Duck Lake surface elevation is 5021 feet). The section 9 and 10 through valley floor elevation at the drainage divide is between 5180 and 5200 feet. As already noted elevations in the section 4 southeast quadrant rise to more than 5300 feet and in the section 10 southeast quadrant rise to more than 5240 feet suggesting the through valley is at least 40 feet deep. Still another North Fork Milk River tributary originates in the section 16 northeast corner and flows in an east and east-northeast direction to the figure 8 east edge (south of center) and is linked by a broad through valley with the Duck Lake basin. There appears to be almost no rise between Duck Lake and this east and east-northeast oriented valley so the through valley floor elevation at the drainage divide is between 5020 and 5040 feet. South of Duck Lake the northeast end of Milk River Ridge has elevations greater than 5300 feet, which taper off to the east. Elevations on the ridge north of the North Fork Milk River headwaters (just north of figure 8) rise to more than 5300 feet and also gradually become lower to the east. These elevations suggest there is a broad east-oriented through valley extending across the figure 8 map area with at least three deeper channels eroded onto its floor. The deepest of these three channels is the through valley linking the Duck Lake basin with the east and east-northeast oriented North Fork Milk River tributary in the figure 8 south half. This deepest through valley is at least 300 feet deep and the entire broader east-oriented through valley appears to be at least 4 miles wide. This broader through valley and the deeper channels on its floor were eroded by massive east-oriented flood flow to what was then the actively eroding North Fork Milk River valley prior to headward erosion of the deep St Mary River valley to the west.

Divide Creek-Fox Creek drainage divide area

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

 

  • Figure 9 illustrates the Divide Creek-Fox Creek drainage divide area south of the figure 7 map area (there is no overlap area). The small town of Saint Mary is located in the figure 9 northwest quadrant. North of Saint Mary is Lower St Mary Lake while in the deep valley south of Saint Mary is St Mary Lake. St Mary Lake and Lower St Mary Lake are located in the deep north-northeast oriented St Mary River valley. Divide Creek is a north-oriented tributary flowing from the figure 9 south edge (west half) to the north-oriented St Mary River near the town of Saint Mary. Note how near the figure 9 south edge Divide Creek is flowing between Curly Bear Mountain (west) and Divide Mountain (east). The mountain south of Divide Mountain is White Calf Mountain. The figure 9 contour interval is 50 meters and the Curly Bear Mountain peak elevation is 2469 meters while the White Calf Mountain peak elevation is 2710 meters. The St Mary Lake surface elevation is 1367 meters and the Lower St Mary Lake elevation is 1363 meters. Extending north from Divide Mountain is Saint Mary Ridge, which forms the St Mary River-Milk River drainage divide and is also the north-south drainage divide (water in the St Mary River eventually reaches Hudson Bay while water in the Milk River eventually reaches the Gulf of Mexico). Just north of Divide Mountain (and at the south end of Saint Mary Ridge) are the east-oriented headwaters of Fox Creek, which flows in an east and east-northeast direction to join the north-northeast oriented South Fork Milk River, which flows from the figure 9 south edge (east half) to the figure 9 east edge (north half). Livermore Creek is the east-northeast oriented South Fork Milk River tributary in the figure 9 northeast quadrant. Note the well-defined west to east oriented through valley linking the north-oriented Divide Creek valley with the east-oriented Fox Creek valley. The highway appears to cross the through valley at the west to east drainage divide and a spot elevation of 1749 meters is given. Saint Mary Ridge to the north rise to more than 1850 meters and Divide Mountain is much higher. The through valley is more than 100 meters deep and is a water eroded feature. The through valley was eroded by east-oriented melt water flood flow moving to what was then the actively eroding South Fork Milk River valley prior to headward erosion of the deep north and north-northeast oriented St Mary River valley and also prior to headward erosion of the north-oriented Divide Creek valley. Headward erosion of the deep north-oriented Divide Creek valley beheaded the east-oriented flood flow channel and flood waters on the west end of the beheaded flood flow channel reversed flow direction to erode a west-oriented Divide Creek tributary valley.

Detailed map of Divide Creek-Fox Creek drainage divide area

Figure 10: Detailed map of Divide Creek-Fox 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 Divide Creek-Fox Creek drainage divide area seen in less detail in figure 9 above. Divide Creek flows in a north direction from the figure 10 southwest corner to the figure 10 north edge (near northwest corner). Fox Creek flows from the section 14 east margin into section 13 and then in an east direction across the section 13 and 18 south halves to the section 18 southeast corner and then across the section 20 northeast corner and the section 23 north half to the figure 10 east edge (south of center). The figure 10 map contour interval in the east half is 20 feet while in the west half the contour interval is 40 feet. Note the west to east oriented through valley in the section 14 southeast quadrant and the section 13 southwest quadrant linking a west-oriented Divide Creek tributary valley with the east-oriented Fox Creek valley. The spot elevation at the road intersection on the through valley floor suggests the elevation at the drainage divide is 5742 feet. The spot elevation on Saint Mary Ridge to the north in section 11 gives an elevation of 6154 feet while a spot elevation of 6906 feet can be seen on the side of Divide Mountain to the south (which rises to more than 8600 feet south of the figure 10 map area). The through valley then is more than 400 feet deep and is a water eroded landscape feature. The through valley was eroded by east-oriented melt water flood flow at a time prior to headward erosion of the north-oriented Divide Creek valley (and the subsequent headward erosion of the much deeper St Mary River valley to the west of figure 10). Saint Mary Lake to the west of figure 10 has a surface elevation of 4484 feet, which suggests headward erosion of the deep north-oriented St Mary River valley carved a valley at least 1300 feet deep and which provides a measure of the magnitude of flood erosion that took place. While a 1300 foot deep valley is may seem to be an unreasonably large amount of erosion, the earlier erosion depths reported in this essay did provide evidence for headward erosion of deep valleys that were at least several hundred feet deep (and which could have been much deeper when initially eroded). While erosion of such magnitude is difficult to comprehend based on modern-day flood erosion, volumes of melt water flood flow during the thick North American ice sheet’s rapid melt down greatly exceeded anything seen in recent history. Massive amounts of flood waters reached the figures 9 and 10 map regions from the northwest and west, which means flood waters crossed what are today high mountains. Either the mountains were not high at that time or the flood waters were already flowing on a surface at least as high as the present day mountain ridges. In either case the landscape west of the figures 9 and 10 map area looked very different at that time than it does 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.

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