• The purpose of this essay is to use topographic map interpretation methods to explore the Shields River-Gallatin River drainage divide area erosional landform origins in Gallatin and Park Counties, 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 erosional 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 by 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 Shields River-Gallatin River drainage divide area landform evidence in Gallatin and Park Counties, Montana will be regarded as evidence supporting the “thick ice sheet that melted fast” paradigm (see essay listed on header). This essay is included in the Missouri River drainage basin landform origins research project essay collection.

• Figure 1 provides a Shields River-Yellowstone River divide area location map and shows a region in southern Montana with a strip from the Wyoming northwest corner seen along the east half of the figure 1 south edge and bits of Idaho seen along the west half of the figure 1 south edge. Yellowstone National Park is located primarily in the Wyoming northwest corner and is labeled near the figure 1 south center edge. The Yellowstone River flows in a northwest direction to Gardiner, Montana (along Yellowstone National Park north edge) and then for a short distance into Montana before turning to flow in a north-northeast direction to near Livingston. Near Livingston the Yellowstone River turns to flow in a northeast direction to Big Timber and then in an east-southeast and east-northeast direction to the figure 1 east center edge. East of figure 1 the Yellowstone River flows in a northeast direction to join the Missouri River near the Montana-North Dakota border. North of Livingston are the Crazy Mountains. The unlabeled stream flowing in a southwest direction from near Loco Mountain to Wilsall and then in a south-southeast direction through Clyde Park to join the Yellowstone River is the Shields River. Flathead Creek is an east-northeast oriented tributary joining the Shields River near Wilsall, but is not shown in figure 1. Note the south-southeast oriented tributary originating near Ringling and joining the Shields River near Wilsall and how north of Ringling there is a north-northwest oriented drainage route between the Big Belt Mountains and the Little Belt Mountains. That north-northwest oriented river is the Smith River, which north of the figure 1 map area joins the Missouri River. Returning to the Yellowstone National Park area the Gallatin River flows in a north-northwest direction between the Gallatin Range and the Madison Range, past the towns of Big Sky and Gallatin Gateway to the town of Three Forks where it joins the north-oriented Madison River and the north-northeast, east, and northeast oriented Jefferson River to form the north and north-northwest oriented Missouri River. North of the figure 1 map area the Missouri River turns to flow in a northeast direction and then after a jog to the south flows in a more of an east direction across Montana. The East Gallatin River flows in a northwest from near Bozeman to join the Gallatin River near Manhattan with only the northwest end shown in figure 1 (a north-northwest and north oriented tributary is shown south Belgrade). East of Bozeman and extending from the Big Belt Mountains south end to the Gallatin Range north end is the Bridger Range, which is not labeled on figure 1, although which is an important mountain range in this essay. The Shields River-Gallatin River drainage divide area investigated in this essay is located south and west of east-northeast oriented Flathead Creek and the south-southeast oriented Shields River and north and east of the East Gallatin River and includes much of the high Bridger Range. The region immediately to the north is described in the Sixteenmile Creek-Shields River drainage divide area landform origins, central Montana essay and the region to the west is described in the Sixteenmile Creek-Gallatin River drainage divide area landform origins Gallatin County, Montana essay.

• Drainage routes in the figure 1 map region (and a much larger region) developed during immense south and southeast-oriented floods which flowed across the entire region. At that time the mountain ranges did not stand high above the surrounding basins and plains and flood waters could freely flow across the region. Flood waters responsible for eroding the Shields River-Gallatin River drainage divide area (and much of the figure 1 map region) were derived from western Alberta and eastern British Columbia, which at time was evolving into western rim of a deep “hole’ in which a rapidly melting thick North American ice sheet was located. The Missouri River drainage basin in Montana and northern Wyoming is the deep “hole’s” deeply eroded southwest wall. The deep “hole” did not exist when the ice sheet first formed, but was created by deep glacial erosion (under the ice sheet) and by crustal warping that raised mountain ranges and high plateau areas along the ice sheet margins and elsewhere on the North American continent. Crustal warping took place as the thick ice sheet melted and mountain ranges were raised as immense south and southeast-oriented melt water floods flowed across them. Massive south and southeast-oriented melt water floods flowed from the ice sheet’s western margin across Montana, Wyoming, and Colorado into New Mexico and Texas along routes roughly corresponding with the present day east-west continental divide while the Rocky Mountains were being uplifted (from south to north). At the same time deep valleys eroded headward from the Gulf of Mexico in the east and the Pacific Ocean in the west to capture the immense south and southeast-oriented melt water floods and to carve the east-west continental divide. In time a combination of deep “hole” formation and of ice sheet melting created a situation where the south and southeast-oriented ice-marginal melt water floods were flowing at elevations higher than deep “hole” space being opened up by the ice sheet melting (especially along the ice sheet’s southern margin). This new situation changed the melt water flood flow directions as deep northeast and east-oriented valleys eroded headward from the newly opened up deep “hole” space into Montana and northern Wyoming to capture the south and southeast-oriented melt water floods. These deep valleys and their tributary valleys eroded headward in sequence from the southeast to the northwest.

• Headward erosion of the deep northeast-oriented Yellowstone River valley occurred prior to headward erosion of the deep east oriented Missouri River valley, which beheaded the south and southeast-oriented flood flow moving to what was then the newly eroded Yellowstone River valley. Of importance to this essay the deep Yellowstone River eroded headward to the Livingston region and captured a major south-oriented flood flow channel moving flood waters between what were then the emerging Bridger Range and the Crazy Mountains (and between the Big Belt Mountains and Little Belt Mountains further to the north). Prior to being captured much of the south-oriented flood flow was continuing south along a flood flow channel roughly corresponding with the present day northwest, and north-northeast oriented Yellowstone River valley alignment (south of Livingston), although using a much shallower flood flow channel. Headward erosion of the much deeper east and northeast-oriented Yellowstone River valley beheaded the south-oriented flood flow channel near Livingston and flood waters on the north end of the beheaded flood flow channel reversed flow direction to erode the deep northwest and north-northeast oriented Yellowstone River valley seen today. Uplift of the Yellowstone Plateau, which underlies the Yellowstone National Park region, probably greatly aided in this massive flood flow reversal. Headward erosion of the deep Missouri River valley (north of the figure 1 map area) was responsible for even larger flood flow reversals. First deep Missouri River valley headward erosion beheaded and reversed the south-southeast oriented flood flow channel between the Big Belt Mountains and the Little Belt Mountains to erode the north-northwest oriented Smith River valley. Next deep Missouri River valley headward erosion beheaded and reversed a major south-southeast oriented flood flow channel west to the Big Belt Mountains to erode the north and north-northwest oriented Missouri River valley seen in figure 1. Prior to being beheaded and reversed the south-southeast flood flow channel west of the Big Belt Mountains split in the Three Forks region to form three diverging south-oriented flood flow channels moving flood waters to what was probably the actively eroding and deep west-oriented Snake River valley (which at that time may have reached the area south of the figure 1 south center). Reversal of flood flow in the present day north-northwest oriented Missouri River valley also reversed flood flow in each of these diverging flood flow channels so as to erode three north-oriented river valleys, with the north-northwest oriented Gallatin River valley being the easternmost one.

• Figure 2 provides a detailed location map for the Shields River-Gallatin River drainage divide area. Green shaded areas are National Forest lands and are generally located in mountainous regions. County boundaries are shown and Gallatin and Park Counties are labeled. The green shaded area in the figure 2 northeast corner is located in the Crazy Mountains. The green shaded area north of Bozeman is in the Bridger Range. The green shaded area in the figure 2 southeast corner is located in the Absaroka Range and the green shaded area south of Bozeman is in the Gallatin Range. The Yellowstone River flows in a north direction from the figure 2 south edge between the Absaroka Range and Gallatin Range to Livingston and then turns to flow in a northeast direction to Mission and then in an east direction to the figure 2 east edge (south half). The Shields River originates in the Crazy Mountains north of the figure 2 northeast corner and flows in a south-southwest and south direction to Wilsall and then in a south-southeast direction to Clyde Park and then to join the Yellowstone River near Mission. Flathead Creek is an east-northeast oriented tributary originating in the Bridger Ranger Range and joining the Shields River near Wilsall. Other labeled east-oriented Shields River tributaries originating in the Bridger Range include Brackett Creek and Bangtail Creek. The Gallatin River flows in a north direction from the figure 2 south edge (near Spanish Breaks) to Bozeman Hot Springs and then near Manhattan turns to flow in a west-northwest direction to Three Forks where it joins the north-oriented Madison River and northeast-oriented Jefferson River to form the north-northeast oriented Missouri River seen north of Three Forks. The East Gallatin River flows in a northwest and west direction from Bozeman to join the Gallatin River near Logan. Bridger Creek is a south and west oriented tributary flowing from the Bridger Range east side to join the north-northwest oriented East Gallatin River north of Bozeman as a barbed tributary. Jackson Creek is a southwest-oriented East Gallatin River tributary located east of Bridger Creek (more detailed maps show Jackson Creek joining other streams before reaching the East Gallatin River). Between the Bridger Range and the Missouri River in the figure 2 northwest quadrant are the Horseshoe Hills. The lowland between the Horseshoe Hills and the Bridger Range is drained by south-oriented Dry Creek, which flows to the East Gallatin River. Several southwest oriented Dry Creek tributaries originate in the Bridger Range and Bear Creek is the southwest oriented tributary flowing from the Bridger Range to the northwest-oriented East Gallatin River as a barbed tributary. South-oriented streams west of the Bridger Range are flowing to what today is a north-oriented drainage system and provide evidence of a previous south-oriented drainage system that existed prior to the drainage reversal that created the north-oriented Gallatin-Missouri River drainage basin. Note also north-oriented headwaters and tributaries to some of the east-oriented Shields River tributaries. Those north-oriented headwaters and tributaries are flowing in valleys eroded by reversals of flow on the north ends of beheaded south-oriented flood flow channels (with the flood flow reversals probably also aided by Bridger Range uplift, which occurred as flood water flowed in a south direction across the rising mountains).

Additional information and sources of maps studied