Origin of Mountain Passes across Continental Divide Segments Surrounding the Southwest Montana Big Hole and Beaverhead River Drainage Basins, USA

Abstract

The evolution of southwest Montana's Big Hole and Beaverhead River drainage basins is determined from topographic map evidence related to mountain passes crossing what are today high altitude drainage divides including North America's east-west Continental Divide. Map evidence, such as orientations of valleys leading away from mountain passes (and saddles) and barbed tributaries found along the downstream drainage routes, is used to reconstruct flow directions of streams and rivers that once crossed the present-day high mountain divides. Large south-oriented anastomosing complexes of diverging and converging channels are interpreted to have eroded what are today closely spaced passes and saddles now notched into high mountain ridges. Water in those south-oriented channels is interpreted to have flowed across emerging mountains and subsiding basins. Headward erosion of deeper southeast-oriented valleys, assisted by crustal warping, concentrated south-oriented water in fewer and deeper valleys as the water flowed from southwest Montana into what are today Idaho and the Snake River drainage basin. Headward erosion of the Big Hole River valley between the emerging Anaconda and Pioneer Mountains, also assisted by crustal warping, reversed all Big Hole Basin drainage so as to create the north-, east-, and south-oriented Big Hole River drainage route. A final and even more major reversal of flow in the present-day north-oriented Montana Missouri River valley, with the assistance of additional crustal warping, next ended all remaining flow to Idaho and the Snake River drainage basin and reversed and captured all drainage in the present-day north-oriented Big Hole, Beaverhead, and Red Rock River drainage basins. The observed map evidence indicates that prior to the final flow reversal events, large volumes of south-oriented water flowed across southwest Montana's Big Hole and Beaverhead River drainage basins.

Deep Erosion by Continental Ice Sheets: A Northern Missouri River Drainage Basin Perspective: North America

“…An additional paper (Clausen, 2017d) Further evidence for immense south-oriented floods of probable continental ice sheet melt water origin across what must have been emerging mountain ranges, including what are today other segments of North America's east-west Continental Divide, is described by still another paper (Clausen, 2017e). That paper explains the origin of mountain passes notched into drainage divides surrounding the Montana Boulder River drainage basin (in Jefferson County near location 3 in Fig.…”

Yellowstone Region Drainage History as Determined from the 1955 Ashton, Idaho, Montana, and Wyoming 1:250,000 Scale Topographic Map, USA

“…Clausen's book [7] lists published papers which demonstrate the new paradigm's ability to explain detailed topographic map drainage system and erosional landform evidence at more than 40 modest sized continental United States geographic locations. One such paper [24] interprets topographic map evidence to show that immense south-oriented floods carved the mountain passes now crossing continental divide segments surrounding the Beaverhead and Big Hole River drainage basins (see Figure 1). Another paper [25] interprets topographic map evidence to show that immense south-oriented floods eroded mountain passes now crossing continental divide segments surrounding the Boulder River drainage basin (located to the east of the Clark Fork River headwaters seen in Figure 1).…”

Upper Sun River Drainage Basin Origin Determined by Topographic Map Interpretation Techniques: Lewis and Clark and Teton Counties, Montana, USA

“…The presence of south-oriented barbed tributaries to the north-oriented South Fork Sun River suggests a reversal of flow in the South Fork valley is much more likely than a flow reversal in the Dearborn River valley. In addition, two recent papers [22] [23] analyzing mountain passes crossing mountain ranges surrounding the southwest Montana Big Hole, Beaverhead, and Boulder River drainage basins describe considerable geomorphic evidence that suggests immense south-oriented floods once crossed the entire region. Today the Dearborn River after flowing in a northeast direction across the Sawtooth Range turns to flow in more of a southeast direction, however, an abandoned valley where the Dearborn River first flows out onto the plains continues further in a northeast direction.…”