Milk River-Cut Bank Creek drainage divide area landform origins, Glacier County, Montana, USA

Abstract:

Topographic map interpretation methods are used to determine landform origins for the Milk River-Cut Bank Creek drainage divide area located in Glacier County, Montana. The Milk River originates along the east boundary of Glacier National Park and flows generally in a northeast direction across Glacier County before entering southern Alberta and eventually joins the Missouri River in northeast Montana. Cut Bank Creek is located south of the Milk River and also originates on the Glacier National Park east edge and flows in an east and south-southeast direction to join Two Medicine River and to form the Marias River, which then flows to the Missouri River in north central Montana. Cut Bank Creek has multiple south and southeast-oriented tributaries suggesting the deep Cut Bank Creek valley eroded headward across multiple south and southeast-oriented flood flow channels such as might be found in a large-scale anastomosing channel complex. Further supporting this interpretation are numerous through valleys linking south- and southeast-oriented Cut Bank Creek tributary valleys with north-oriented Milk River tributary valleys. These through valleys can be found along the entire Milk River-Cut Bank Creek drainage divide length including the South Fork Milk River-North Fork Cut Bank Creek drainage divide found adjacent to the Glacier National Park eastern boundary. Flood waters responsible for the through valleys are interpreted to have been massive ice-marginal melt water floods during the later melt down stages of a thick North American ice sheet, with the ice sheet having been located in a deep “hole.”

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 Milk River-Cut Bank Creek 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 Milk River-Cut Bank Creek 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.

Milk River-Cut Bank Creek drainage divide area location map

Figure 1: Milk River-Cut Bank Creek 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 Milk River-Cut Bank Creek drainage divide area in Glacier County, Montana and shows a region in northwest Montana with southwest Alberta and southeast British Columbia north of the United States-Canada border. Idaho is located west of Montana near the figure 1 west edge and south of the Canadian border. Glacier National Park is located near the figure 1 center and the Milk River and North Fork Milk River originate in Montana just east of Glacier National Park and then flow in northeast directions into southern Alberta where they join to form the east-oriented Milk River. East of the figure 1 map area the Milk River turns to flow in a southeast direction so as to reenter Montana and eventually join the Missouri River. Cut Bank Creek also originates just east of Glacier National Park and is located south of the northeast-oriented Milk River headwaters. Cut Bank Creek flows in an east direction to north of Cut Bank, Montana and then turns to flow in a south-southeast direction to join east-oriented Two Medicine River and to form the east-southeast oriented Marias River (not labeled, but flows to Lake Elwell along figure 1 east edge). Downstream from Lake Elwell the Marias River flows in an east and south direction to join the Missouri River. The Milk River-Cut Bank Creek drainage divide area in Glacier County investigated in this essay encompasses the entire Milk River-Cut Bank Creek drainage divide area eastward from the Milk River and Cut Bank Creek origin points to south-oriented Rocky Coulee, which drains to the south-southeast oriented Cut Bank Creek segment near Cut Bank, Montana. Note how this Milk River-Cut Bank Creek drainage divide area is located directly east of the Rocky Mountain front, which roughly corresponds with the Glacier National Park eastern boundary. The Milk River-Marias River drainage divide area in Toole County, Montana essay describes the region immediately to the east. Essays for Milk River and Marias River drainage basin areas can be located by selecting the Milk River or Marias River from the sidebar category list.

An overview of the regional erosion history is needed before proceeding to more detailed evidence. The Milk River-Cut Bank Creek drainage divide area was eroded during late stages of a thick North American ice sheet’s rapid melt down. The ice sheet had been located in a deep “hole”, which had been formed by a combination of deep glacial erosion and of crustal warping caused by the ice sheet’s great weight. Western North America elevations have changed significantly since the ice sheet formed. At the time the ice sheet originally was formed the Rocky Mountains did not stand high above surrounding regions nor were western North America plateau areas high like they are today. Both the Rocky Mountains and the high western North America plateau areas were uplifted as a result of crustal warping caused by the ice sheet’s great weight. This uplift occurred as immense south and southeast oriented melt water floods were flowing across what are today crests of high Rocky Mountain ranges (and along what is today the east-west continental divide). Rocky Mountain uplift occurred first in the south and diverted the immense south and southeast oriented melt water floods both to the east and west where flood waters eroded what are today major river valley systems. In time ice sheet melting progressed to the point the ice sheet surface was no longer standing higher than the surrounding bedrock surface and uplift of Rocky Mountain ranges was blocking the south and southeast movement of the giant ice-marginal melt water floods. At about the same time deep ice walled canyons formed on the decaying ice sheet surface along routes used 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 Saskatchewan, North Dakota, and South Dakota and which eventually became an ice-walled and bedrock-floored canyon, and 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. This giant southeast- and south-oriented ice walled canyon became the regions major drainage route and large east- and northeast-oriented valleys eroded headward into the surrounding bedrock surface to capture the southeast- and south-oriented melt water floods and also flood waters blocked by the rising Rocky Mountain ranges. The final major east- and northeast-oriented valley to erode headward from this giant ice-walled and bedrock-floored canyon was what is today the Missouri River valley (upstream from Poplar, Montana) with the Milk River valley being a tributary valley that eroded headward from that actively eroding “Missouri River” valley.

Today the Missouri River in Montana and northern Wyoming and the Alberta Saskatchewan River drainage basin represents a segment of what is left of the deep “hole’s” southwest wall with high Rocky Mountain erosion surfaces representing what is left of the deep “hole’s” southwest rim. Repeated erosion by massive ice-marginal melt water floods deeply eroded the deep “hole’s” southwest wall, which as previously stated was also being altered by crustal warping as flood waters flowed across the region. To what extent present day elevation differences are the result of deep erosion or the result of crustal warping is often difficult to determine, although both crustal warping and deep melt water flood erosion played significant roles in producing modern-day landscapes. The Milk River-Cut Bank Creek drainage divide area evidence seen in figure 1 and in the topographic maps illustrated below demonstrates headward erosion of the deep Cut Bank Creek valley occurred in advance of Milk River valley headward erosion. South and southeast-oriented flood flow moving to the newly eroded Cut Bank Creek valley deeply eroded what is now the Milk River-Cut Bank Creek drainage divide area. Headward erosion of the deep Milk River valley then captured the south and southeast-oriented ice-marginal flood flow to the newly eroded Cut Bank Creek valley and beheaded flood routes to actively eroding Cut Bank Creek tributary valleys. Headward erosion of the deep North Fork Milk River valley next beheaded flood flow routes to the newly eroded Milk River valley. And finally headward erosion of the deep northeast-oriented St Mary River valley (from the actively eroding South Saskatchewan River-Oldman River valley) beheaded south and southeast-oriented flood flow routes to the newly eroded North Fork Milk River. Oldman River valley headward erosion next beheaded flood flow routes to the newly eroded St May River and the process was repeated again and again further to north of the figure 1 map area.

Detailed location map for Milk River-Cut Bank drainage divide area

Figure 2: Detailed location for Milk River-Cut Bank 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 Milk River-Cut Bank Creek drainage divide area in Glacier County, Montana. The United States-Canada border is located along the figure 2 north edge. County boundaries and names are shown and Toole County is located east of Glacier County and Flathead County is to the west. Much of Glacier County is shown as being in the Blackfeet Indian Reservation with Glacier National Park being located west of the Blackfeet Indian Reservation. The Glacier County west boundary is located in Glacier National Park and is defined by the east-west continental divide with water in Flathead County flowing to the Flathead River and eventually reaching the Pacific Ocean. Cut Bank is a major town located near the Glacier County east border and Browning is an important town on the railroad and highway west of Cut Bank. Milk River Ridge is a labeled landform north and west of Browning (and east of Glacier National Park). The North Fork Cut Bank Creek flows in an east-northeast direction just south of Milk River Ridge while the South Fork Milk River flows in a northeast direction just north of Milk River Ridge. The North and South Forks Cut Bank Creek join north and east of Browning to form Cut Bank which flows in an east and south-southeast direction to Cut Bank and then joins the east-oriented Two Medicine River so as to form the Marias River, which then flows in an east-southeast direction to the figure 2 east edge (south half). Labeled Cut Bank Creek tributaries from the north (from east to west) are Rocky Coulee, Little Rocky Coulee, Powell Coulee, Cobell Coulee, and Cut Bank John Coulee. Note how these and other unnamed tributaries from the north flow toward Cut Bank Creek in south-southeast directions and suggest the deep Cut Bank Creek valley eroded headward across multiple south-southeast oriented flood flow channels. The northeast-oriented South Fork Milk River joins the northeast and east-northeast oriented Middle Fork Milk River north and west of Red Butte to form the northeast-oriented Milk River, which flows to the figure 2 north center edge and into southern Alberta. In southeast Alberta the Milk River turns to flow back into Montana and eventually joins the Missouri River with water eventually reaching the Gulf of Mexico. North of the Middle Fork Milk River is the northeast-oriented North Fork Milk River, which flows along the labeled Hudson Bay Divide south margin to the figure 2 north edge (west of center) and which joins the Milk River in southern Alberta. Note how west of the North Fork Milk River and Middle Fork Milk River headwaters is Lower St Mary Lake and the north and north-northeast oriented St Mary River, which also flows to the figure 2 north edge (west half). Water in the St Mary River flows to the Oldman River, which flows to the South Saskatchewan River with water eventually reaching Hudson Bay. The St Mary River-Milk River drainage divide seen in figure 2 is the north-south continental divide which follows the ridge labeled as Hudson Bay Divide. The north-south continental divide and the east-west continental divide meet at the Hudson Bay Divide south end.

Milk River-Big Rock Coulee drainage divide area

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

Figure 3 illustrates the Milk River-Big Rock Coulee drainage divide area near the east end of the Milk River-Cut Bank Creek drainage divide area. The Milk River is located in the figure 3 northwest quadrant and flows in a north, south-southeast, east, southeast, northwest, and north-northeast direction from the figure 3 northwest corner to the figure 3 north edge (west half). As seen in figures 1 and 2 the Milk River is generally flowing in a northeast direction and these jogs in the figure 3 northwest quadrant are somewhat unusual. Note in the figure 3 northeast quadrant how the east-northeast oriented ridge has been cut by several much shallower northwest-southeast oriented through valleys. These northwest-southeast oriented through valleys provide evidence of multiple southeast or south-southeast oriented flood flow routes across the region prior to headward erosion of the deep Milk River valley. These multiple through valleys suggest the presence of a southeast or south-southeast oriented anastomosing channel complex in the region prior to Milk River valley headward erosion. Big Rock Coulee flows in a south direction to the figure 3 south edge (east half) and is joined by its south-southwest oriented East Fork in the figure 3 southeast quadrant. South of the figure 3 map area Big Rock Coulee drains in a south and south-southeast direction to Cut Bank Creek. Note how in the figure 3 center region a well-defined through valley links the Big Rock Coulee valley with the southeast and northwest-oriented Milk River valley segments in the figure 3 northwest quadrant. The map contour interval is 20 meters and the through valley floor elevation at the drainage divide is between 1220 and 1240 meters. Elevations greater than 1320 meters are found on the ridge in the figure 3 northeast quadrant while Landslide Butte in the figure 3 west center region reaches an elevation of 1419 meters. In other words the through valley is at least 80 meters deep and probably is deeper. The through valley was eroded by southeast-oriented flood flow moving to what was then the actively eroding Big Rock Coulee valley, which had eroded headward from what was then the actively eroding Cut Bank Creek valley. Headward erosion of the deep northeast-oriented Milk River valley beheaded the southeast-oriented flood flow (at least on the northeast side of the flood flow channel) and flood waters on the northwest end of the beheaded flood flow channel reversed flow direction to erode the northwest-oriented Milk River valley segment. At the same time the deep northwest-oriented Milk River valley captured the adjacent and parallel southeast-oriented flood flow channel and a deep valley eroded headward along the southwest side of the flood flow channel to erode what is today the southeast-oriented Milk River valley segment. The south-southeast oriented Milk River valley segment probably was eroded headward along the alignment of a south-southeast oriented flood flow channel which continued in a south-southeast and southeast direction east of Landslide Butte to what are now southeast-oriented Big Rock Coulee tributary valleys. Shallow through valleys east of Landslide Butte support this interpretation.

Detailed map of Milk River-Big Rock Coulee drainage divide area

Figure 4: Detailed map of Milk River-Big Rock Coulee drainage divide area. United States Geological Survey map digitally presented using National Geographic Society TOPO software.

Figure 4 provides a detailed topographic map of the Milk River-Big Rock Coulee drainage divide area seen in less detail in figure 3 above. The southeast and northwest-oriented Milk River can be seen in the figure 4 northwest corner. Note how a northwest-oriented tributary flows to the Milk River from the section 29 southwest quadrant and across the section 30 northeast quadrant. An northwest-southeast elongate lake is located in the section 32 northeast corner and section 33 west half and is shown as having an elevation of 4006 feet (the map contour interval is 20 feet). Note how the lake is on the floor of a well-defined dry valley and has an east-southeast oriented outlet leading to an intermittent lake near the south margin of section 33. This intermittent lake in section 33 has no outlet shown although continuing eastward along the dry valley there is a second intermittent lake near the section 34 south margin. This second section 34 intermittent lake is shown as having an east-northeast and east oriented outlet which leads to the south-oriented Big Rock Coulee valley (seen along the figure 4 east edge, although not labeled in figure 4). Elevations on the through valley floor in the section 33 and 34 region are between 4020 and 4040 feet. In section 31 in the figure 4 west center area elevations rise to more than 4300 feet. Elevations greater than 4270 feet can be found near the figure 4 north center edge and elevations rise to more 4300 feet north of the figure 4 map area. These elevations indicate the through valley is at least 160 feet deep and as seen in figure 3 there is evidence the through valley may be even deeper. However deep the through valley is it provides evidence of significant regional erosion feature eroded by the massive southeast-oriented flood flow across the region. Ice-marginal melt water floods at one time flowed across a surface at least as high as the highest point in figure 3 (which is Landslide Butte, not seen in figure 3, but in feet it has an elevation of 4657 feet) which suggests erosion of at least 300-460 feet bedrock material from most figure 4 map areas. How much erosion occurred prior to development of the surface documented today by the Landslide Butte high elevation marker cannot be determined from figure 3 or 4 evidence as there are no nearby higher markers to use for measurements.

Milk River-Little Rock Coulee drainage divide area

Figure 5: Milk River-Little Rock Coulee drainage divide area. United States Geological Survey map digitally presented using National Geographic Society TOPO software.

Figure 5 illustrates the Milk River-Little Rock Coulee drainage divide area south and west of the figure 3 map area and includes overlap areas with figure 3. The Milk River flows in a northeast direction in the figure 5 northwest quadrant. Landslide Butte is located near the figure 5 northeast corner and reaches an elevation 1419 meters. Little Rock Coulee drains in an east-southeast direction in the figure 5 southeast quadrant to the figure 5 east edge. South and east of figure 5 Little Rock Coulee turns to flow in a south-southeast direction and to join Cut Bank Creek. The South Fork Little Rock Coulee drains in a southeast direction near the figure 5 south center edge and joins Little Rock Coulee south and east of the figure 5 map area. Note how between Croffs Lake (near figure 5 north center edge) and Buffalo Lake there is a through valley linking the northeast-oriented Milk River valley with the east-southeast oriented Little Rock Coulee valley. Locally the through valley appears to be shallow with elevations at Eagle Point being between 1300 and 1320 meters while the narrow inner through valley floor at the drainage divide has an elevation of between 1260 and 1280 meters. However continue further in each direction to see how elevations rise. Landslide Butte as mentioned reaches 1419 meters. Elevations greater than 1420 meters can be found at several points in the figure 5 southwest quadrant. In other words the through valley between Croffs Lake and Buffalo Lake is in fact just a deep channel eroded into the floor of a much broader and deeper northwest-southeast oriented through valley which is at least 140 meters deep in the Croffs Lake-Buffalo Lake channel region. This broad northwest-southeast oriented through valley was eroded by massive southeast-oriented melt water flood flow moving to what at that time was the actively eroding Cut Bank Creek valley. At that time the northeast-oriented Milk River valley did not exist and flood waters initially flowed on a surface at least as high as the highest figure 5 elevations today. Headward erosion of the deep northeast-oriented Milk River valley then captured the southeast-oriented flood flow while flood waters on north and northwest ends of beheaded flood flow routes reversed flow direction to erode what are today the short north and north-northwest oriented Milk River tributary valleys seen in figure 5. Note the presence of other northwest-southeast shallow through valleys or channels eroded into the floor of the much broader figure 5 northwest-southeast oriented flood flow channel.

Milk River-Powell Coulee drainage divide area

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

Figure 6 illustrates the Milk River-Powell Coulee drainage divide area south and west of the figure 5 map area and includes overlap areas with figure 5. The east-oriented Middle Fork Milk River joins the north-northeast oriented South Fork Milk River near the figure 6 northwest corner to form the northeast-oriented Milk River which flows to the figure 6 north edge (just west of center). Labeled drainage routes flowing to the figure 6 south edge (from east to west) are Powell Coulee (draining to near the figure 6 southeast corner), Cobell Coulee, and Cut Bank John Coulee (with its tributary Hoodoo Coulee and its tributary Nightshoot Coulee). All of these drainage routes south and east of the figure 6 map area drain to east-oriented Cut Bank Creek. Note how with the exception of Nightshoot Coulee these and other unnamed drainage routes are oriented in southeast or south directions. Also note how each of these south or southeast oriented Cut Bank Creek tributary valleys is linked by one or more through valleys with valleys of unnamed north-oriented Milk River tributaries. For example in the figure 6 northwest quadrant just west of Red Buttes a through valley links the south-southeast oriented Cut Bank John Coulee valley with the valley of an unnamed north-oriented Milk River tributary valley. Reading elevations on figure 6 is somewhat confusing as the contour interval in the north is 20 meters and in the south is 40 meters. The through valley floor at the drainage divide west of Red Buttes is between 1360 and 1380 meters with elevations in the Red Buttes area reaching at least 1440 meters and elevations in the figure 6 southwest corner rising to more than 1500 meters. In other words based on figure 6 map evidence the through valley is at least 60 meters deep. Just east of Red Buttes is a slightly shallower through valley linking an unnamed north-oriented Milk River tributary valley with the south-southeast oriented Cobell Coulee valley. Continuing further east are more through valleys linking unnamed north-oriented Milk River tributary valleys with the east-southeast oriented valley of a South Fork Little Rock Coulee tributary (unnamed in figure 6) which eroded headward across the southeast-oriented Powell Coulee valley head (and which captured southeast-oriented flood flow which had been moving to the actively eroding Powell Coulee valley). All of these through valleys were eroded by southeast- and south-oriented flood flow moving to the actively eroding Cut Bank Creek valley prior to headward erosion of the deep northeast-oriented Milk River valley. Headward erosion of the deep Milk River valley beheaded the multiple south- and southeast-oriented flood flow channels (in order from east to west) and flood waters on north ends of beheaded flood flow channels reversed flow direction to erode the north-oriented Milk River tributary valleys.

South Fork Milk River-Greasewood Creek drainage divide area

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

Figure 7 illustrates the South Fork Milk River-Greasewood Creek drainage divide area south and west of the figure 6 map area and includes overlap areas with figure 6. The South Fork Milk River flows in a northeast direction from the figure 7 west center edge to the figure 7 north edge (just west of center). Wetzel is the very small town located in the South Fork Milk River valley near the figure 7 west edge. The east-northeast stream joining the South Fork Milk River a short distance downstream from Wetzel is Livermore Creek. Armoux Creek flows in a north-northeast and north direction from the figure 7 west edge (just north of southwest corner) to join the South Fork Milk River near Wetzel. Other north-oriented South Fork Milk River tributaries from west to east are Spring Coulee, Sand Rock Coulee, and Murphy Coulee. The North Fork Greasewood Creek flows in a northeast direction from the figure 7 southwest corner and then turns to flow in a southeast direction to the figure 7 south edge before flowing in an east direction along the figure 7 south edge where it is joined by the South Fork Greasewood Creek (not seen in figure 7) and then joins east-oriented Cut Bank Creek (a short segment of which is seen just south of Sharp Lake). Cut Bank John Coulee can be seen draining in a south and south-southeast direction near the figure 7 east edge and joins Cut Bank Creek east and slightly south of the figure 7 map area. Houseman Hill represents a major ridge along the South Fork Milk River-Cut Bank Creek drainage divide with most elevations along the ridge exceeding 1500 meters, however north-south oriented through valleys cross the ridge at several points. Perhaps the most obvious through valley links the north-oriented Murphy Coulee valley with an unnamed south-southeast oriented Greasewood Creek tributary valley. Note how that south-southeast oriented Greasewood Creek tributary begins as two north-northeast oriented streams on the Houseman Coulee upland surface. The map contour interval is 40 meters and the through valley floor elevation at the drainage divide is between 1460 and 1500 meters. A spot elevation of 1525 meters to the northeast and the 1540 meter contour line to the southwest suggest the through valley is at least 25 meters deep. Another slightly shallower through valley is crossed by the northwest-southeast oriented highway from Wetzel to the figure 7 south edge and has a floor elevation of between 1500 and 1540 meters and is defined by one contour line each side. In the figure 7 north center region a through valley links the north-oriented Murphy Coulee valley with southeast-oriented Hoodoo Creek valley, which drains to the south-oriented Cut Bank John Coulee valley. A spot elevation on the north-south oriented road in the through valley gives an elevation of 1476 meters with a spot elevation of 1494 meters on the hill just to the east and the 1500 meter contour line to west. These through valleys and others provide evidence of multiple south- and southeast-oriented flood flow channels across the figure 7 map area prior to headward erosion of the deep South Fork Milk River valley. Headward erosion of the deep South Fork Milk River valley beheaded the south-oriented flood flow channels in sequence from east to west and flood waters on north ends of beheaded flood flow channels reversed flow direction to erode north-oriented valleys.

Detailed map of South Fork Milk River-Greasewood Creek drainage divide area

Figure 8: Detailed map of South Fork Milk River-Greasewood Creek drainage divide area. United States Geological Survey map digitally presented using National Geographic Society TOPO software.

Figure 8 provides a detailed topographic map of the South Fork Milk River-Greasewood Creek drainage divide area seen in less detail in figure 7 above. The Houseman Hill ridge is labeled and easily identified. Murphy Coulee originates in the section 33 northwest quadrant and drains in a north direction to the figure 8 north edge and then to the north-northeast oriented South Fork Milk River. The north-northeast oriented drainage route from the figure 8 southwest corner to the figure 8 north edge (west half) is Sand Rock Coulee. Note the north-northeast oriented stream originating in section 5 and flowing across the section 32 southeast corner to enter the section 33 southwest quadrant where it turns to flow in south and southeast direction to section 10 in the figure 8 southeast corner. South and east of figure 8 this unnamed stream flows to Greasewood Creek, which then joins Cut Bank Creek. Note how in the section 33 southwest quadrant this south and southeast-oriented stream valley and its north-northeast oriented headwaters valley are linked by a well-defined through valley with the north-oriented Murphy Coulee valley. The map contour interval is 20 feet and the through valley floor at the drainage divide has an elevation of between 4880 and 4900 feet. Elevations in section 33 just to the east of the through valley rise to more than 5080 feet while elevations along Houseman Ridge rise to more than 5060 feet near the figure 8 south edge (and more than 5100 feet just south of figure 8). In other words based on figure 8 map evidence alone the through valley is 80-100 feet deep. This deep north-south oriented through valley was eroded as a south oriented flood flow channel moving flood waters to what at that time was the actively eroding and deep Cut Bank Creek valley. Flood waters at that time had been flowing on a surface at least as high as the highest figure 8 elevations today and the deep south and southeast-oriented flood flow channel eroded headward from the deep Greasewood Creek (and Cut Bank Creek) valley. The north-northeast oriented headwaters valleys of the south and southeast-oriented Greasewood Creek tributary valley were probably eroded by reversals of flood flow on north ends of beheaded flood flow routes and may have been eroded prior to the reversal of flood flow on the north end of the south- and southeast-oriented flood flow channel which was beheaded by headward erosion of the deep north-northeast oriented South Fork Milk River valley, which eroded the north-oriented Murphy Coulee valley.

South Fork Milk River-North Fork Cut Bank Creek drainage divide area

Figure 9: South Fork Milk River-North Fork Cut Bank Creek drainage divide area. United States Geological Survey map digitally presented using National Geographic Society TOPO software.

Figure 9 illustrates the South Fork Milk River-North Fork Cut Bank Creek drainage divide area south and west of the figure 7 map area and includes overlap areas with figure 7. Note the Radio Tower on the southwest end of Houseman Ridge in the figure 9 northeast corner and compare it with figure 7. Milk River Ridge in figure 9 is the ridge located along the Milk River-Cut Bank Creek drainage divide. The North Fork Cut Bank Creek flows in an east-northeast, east-southeast, east-northeast, east-southeast, and northeast direction from the figure 9 southwest corner region to the figure 9 east edge (north of southeast corner). Cut Bank Ridge in the figure 9 southwest quadrant forms the drainage divide between the North Cut Bank Creek drainage basin and the South Fork Cut Bank Creek drainage basin. North of North Fork Cut Bank Creek and originating on the south and southeast side of Milk River Ridge are the South and Middle Forks of Greasewood Creek and then in the figure 9 northeast quadrant the northeast and southeast-oriented North Fork Greasewood Creek, which was seen in figure 7. The South Fork Milk River originates in the basin located north of Milk River Ridge and flows in a north-northeast direction to the figure 9 north center edge. Note how well-defined through valleys have been eroded across Milk River Ridge. Perhaps the best defined through valley is used by the highway to cross Milk River Ridge and the through valley floor elevation at the drainage divide is between 1650-1700 meters (the map contour interval is 50 meters) and elevations east of the through valley rise to more than 1800 meters while elevations to the west rise even higher. Note how that north-south oriented through valley is aligned with a though valley eroded between Cut Bank Ridge and Red Blanket Butte just to the south. That southern through valley has a floor elevation at the drainage divide of between 1600 and 1650 meters and is slightly deeper than the through valley crossing Milk River Ridge. The through valleys are what remain of a dismembered south-oriented flood flow channel which was first captured by headward erosion of the deep South Fork Cut Bank Creek valley. Next headward erosion of the deep North Fork Cut Bank Creek valley captured the south-oriented flood flow and beheaded the flood flow route to the newly eroded South Fork Cut Bank Creek valley. Finally headward erosion of the deep South Fork Milk River valley captured the south-oriented flood flow channel and beheaded the flood flow channel to the newly eroded North Fork Cut Bank Creek valley. Headward erosion of the north-northeast oriented South Fork Milk River valley may have been aided by reversals of flood flow on the north ends of beheaded flood flow routes.

Detailed map of South Fork Milk River-North Fork Cut Bank Creek drainage divide area

Figure 10: Detailed map of South Fork Milk River-North Fork Cut Bank 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 South Fork Milk River-North Fork Cut Bank Creek drainage divide area seen in less detail in figure 9 above. The map contour interval in the sections along the figure 10 south edge is 40 feet while in all other sections the contour interval is 20 feet. The North Fork Cut Bank Creek can be seen flowing in an east-northeast and east-southeast direction in sections 18, 17, and 16 near the figure 10 south edge. Note how elevations in the North Fork Cut Bank Creek valley are lower than 5080 feet. The northeast-oriented stream flowing from section 7 across the section 6 southeast corner and into section 5 before crossing the section 4 northwest corner to flow to the figure 10 north edge is a South Fork Milk River tributary. Note how the northeast oriented South Fork Milk River tributary crosses the 5400 foot contour line in the section 5 northeast quadrant. The well-defined through valley seen in figure 9 linking the South Fork Milk River valley with the North Fork Cut Bank Creek valley is located in the east half of section 9. The through valley floor elevation at the drainage divide is between 5540 and 5560 feet. Elevations rise to more than 6000 feet near the south edge of section 10 to the east and to more than 6180 feet in section 7 to the west. In other words the through valley is at least 440 feet deep and it appears to be almost one mile wide (sections are one mile square). This through valley was eroded by a south-oriented melt water flood flow channel prior to headward erosion of the deep South Fork Milk River valley to the north. Headward erosion of the deep South Fork Milk River valley 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 South Fork Milk River tributary valleys seen in section 4. Another well-defined through valley can be in the southwest quadrant of section 7 (figure 10 southwest quadrant). This through valley is actually two parallel through valleys with elevations at the drainage divide of 5880-5900 feet. Elevations in the section 7 southeast quadrant rise to more than 6180 feet and even higher in the section 13 northeast corner (remember the contour interval in section 13 is 40 feet while in section 7 it is 20 feet). While not seen in figure 10 this western through valley is also aligned with a shallow through valley eroded across Cut Bank Ridge to the south and provides evidence of a dismembered south-oriented melt water flood flow channel. The western through valley history is similar to the eastern through valley history and the two through valleys provide evidence of multiple south-oriented melt water flood flow channels across the figure 10 map area.

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.