Barbed tributaries flowing in southeast directions, an asymmetric drainage divide with both the South Fork Grand River and the North Fork Moreau River, and the Jump-off escarpment-surrounded basin (interpreted here to be a large abandoned headcut) are examples of topographic map evidence suggesting the north oriented Little Missouri River valley eroded headward across a large southeast oriented anastomosing complex of ice-marginal melt water flood flow channels that once crossed Harding County, South Dakota. Additional evidence includes southeast oriented tributaries to the northeast oriented South Fork Grand River and multiple divide crossings (e.g. through valleys and wind gaps) on the Boxelder Creek-Little Missouri River divide (in eastern Montana and west of the Little Missouri River) and suggests deep regional erosion occurred as the north oriented Little Missouri River valley eroded headward into and across the region. Harding County is located south and west of the southwest limit of coarse-grained glacial erratic material and icemarginal melt water flow routes logically should have crossed it. Deep melt water erosion of Harding County and adjacent eastern Montana regions to the west is not consistent with many previous drainage history and glacial history interpretations, but is consistent with deep erosion by continental ice sheets.
The Laramie River after flowing in a north direction through southeast Wyoming's Laramie Basin abruptly turns in an east direction to flow across the north-to-south oriented Laramie Range in a bedrock-walled canyon and eventually reaches the lower elevation Great Plains and southeast-oriented North Platte River. The North Laramie River, Bluegrass Creek, and North Sybille/Sybille Creek also flow from the Laramie Basin in separate bedrockwalled valleys into the Laramie Range before eventually joining the Laramie River. Bedrock-walled through valleys link the various Laramie Range stream and river crossing valleys and detailed topographic maps were used to determine how this anastomosing bedrock-walled canyon complex and the large escarpment-surrounded Goshen Hole basin (located just to the east of the anastomosing canyon complex) originated. Map evidence shows multiple streams of water must have diverged in the Laramie Basin from the northoriented Laramie River to enter the Laramie Range before converging in or east of the Laramie Range and also shows how present day through valleys enabled diverging and converging streams of water to cross the Laramie Range. The anastomosing bedrock-walled valley complex studied here extends from north of the North Laramie River valley to south of the North Sybille/ Sybille Creek valley. Large volumes of water flowing from the Laramie Basin to the Great Plains are interpreted to have eroded the anastomosing canyon complex and the "downstream" Goshen Hole escarpment-surrounded basin.
While accepting some erosion by continental ice sheets most geologists reject a previously proposed deep erosion by continental ice sheets hypothesis, yet common sense logic suggests continental ice sheets should have eroded much more than they are usually given credit for. Such situations arise in scientific communities when an accepted paradigm cannot adequately explain significant observable evidence. A new and fundamentally different paradigm, constructed from detailed topographic map evidence, illustrates how deep erosion (and crustal warping) by at least one continental ice sheet explains previously unexplained northern Missouri River drainage basin erosional landform origins. The new paradigm requires at least one North American continental ice sheet to have created (by deep erosion and by ice sheet related crustal warping) a deep "hole" in which the ice sheet was located. Late during that ice sheet's melt history north-and northeast-oriented valleys eroded headward from that deep "hole's" southern end to capture immense southeast-oriented icemarginal melt-water floods and to create what are today north-and northeast-oriented Missouri River headwaters and tributary drainage routes. While successfully explaining numerous previously unexplained erosional landforms the new paradigm challenges a number of commonly accepted middle and late Cenozoic geologic and glacial history interpretations.
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