(A) Topographic map of Iberia with the main hydrographic divides (thick black lines) and drainage network (thin blue lines).
0000001865 00000 n In a more recent paper [14] Clausen (p. 53) states “south-oriented flood flow moving on what is now the north-oriented North Platte River alignment (which prior to its reversal had been moving water across what are now high mountain passes to the Colorado River drainage basin and to the Laramie and Cache la Poudre Rivers)” and implies huge south-oriented floods flowed around the Medicine Bow Mountains south end on a route that eventually eroded Cameron Pass so as to flow in a north direction and to enter the Laramie Basin area as large north-oriented floods.The study reported here used topographic maps, imagery, and tools available at the USGS National Map website and also the cited geologic maps and literature.
As North Platte River valley headward erosion proceeded along the developing Laramie Mountains northeast flank the south-oriented flood flow channels that had been moving floodwaters across the rising Laramie Mountains to the Laramie Basin were beheaded and reversed in sequence from east to west until south-oriented flood flow on the present-day north-oriented North Platte River segment was beheaded and reversed (regional uplift also greatly aided in that flow reversal process).Before North Platte River valley headwater erosion beheaded and reversed south-oriented flood flow channels being carved into the rising Laramie Mountains the floodwaters had been flowing into the Laramie Basin where they had been met by north-oriented floodwaters that had flowed in a south direction to the west of the rising Medicine Bow Mountains and that had been forced by Colorado mountain uplift to make a U-turn around the Medicine Bow Mountains southern end (after a flow reversal on the Laramie River alignment).
The Medicine Bow-Laramie River drainage divide northeast end is also a hilltop triple drainage divide, but at an elevation of about 2631 meters is just one of many Laramie Range hilltops with similar elevations. The question then arises, how did large east-oriented volumes of water move from the much lower Laramie Basin across what is now a 400-meter or higher mountain range?Any accepted paradigm interpretation of the Laramie Range crest ridge divide crossings must address interpretations such as the Fan et al. [11] state “when and how the central Rocky Mountains (Rockies) of western North America gained modern topography remain controversial questions” and go on to “suggest that the region underwent differential uplift to form relief similar to that of today before earliest Oligocene time”, but do not explain how Colorado late Oligocene volcanic alluvium reached the Cheyenne Tablelands. The elevation of point A is: _____ feet.
Also, such an interpretation does not explain why the south-oriented North Laramie River headwaters valley is much larger than what the North Laramie River would be expected to erode. Second, the same map evidence is analyzed using a recently proposed interpretation (new paradigm) in which massive and prolonged floods flowed across Wyoming as the Laramie and Medicine Bow Mountains began to be uplifted and as the southeast-oriented North Platte River valley eroded headward along the rising Laramie Mountains northeast flank. To the north of the Gangplank divide crossings suggest the Crow and Lodgepole Creek drainage basins were once intertwined and a case can also be made that water once flowed at several localities between the Lodgepole and Horse Creek drainage basins.Lodgepole, Crow, Lone Tree, and Dale Creek flow to the northeast-oriented South Platte River, although at very different locations (see In 1927 J Harlan Bretz [20] used the presence of a large anastomosing channel complex as one line of evidence when he presented his case for flood erosion of the Washington State Channeled Scabland region to what at that time was a skeptical audience and the divide crossings described here (and elsewhere in the Cheyenne Tablelands) are difficult to explain except in the context of a large east-oriented flood formed anastomosing channel complex. Further south the asymmetric drainage divide continues and appears to have been eroded by large sheets of southwest-oriented water moving from the North Laramie River valley across the northeast-oriented Twentymile Draw and Elk Horn Draw drainage basins to reach the southwest-oriented Greasewood Creek drainage basin and Greasewood Flats (which today includes several closed depressions while otherwise being in the Rock Creek drainage basin).
Between the Medicine Bow and Laramie Mountains the Medicine Bow-Laramie River drainage divide crosses Laramie Basin floor regions described by Mears [ [3] , p. 426] as having “a complex history of stream captures involving three streams that formerly flowed northeastward from the Medicine Bow Mountains across the Laramie Basin and Laramie Mountains.”The Medicine Bow-Laramie River drainage divide shows no evidence of ever having migrated as laboratory and numerical landscape evolution models and simulations such as those done by Bonnet [1] , Whipple et al.