Analysis of Medicine Bow-Laramie River Drainage Divide Using Topographic Map Interpretation Techniques, Southeastern Wyoming, USA

Detailed topographic maps provide much of the information needed to understand how drainage divides like the southeast Wyoming Medicine Bow River-Laramie River drainage divide originated. Topographic map evidence for each Medicine Bow-Laramie River drainage divide segment is here described and analyzed first using a commonly published interpretation (ac-cepted paradigm) in which drainage routes developed on a surface of now mostly absent Oligocene and Miocene sediments that previous investigators have hypothesized to have once filled the Laramie Basin and to have also buried (or partially buried) the surrounding Laramie and Medicine Bow Mountains. 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. Low points along the drainage divide (referred to as divide crossings) are interpreted to be places where water once flowed across the drainage divide with the drainage divide being formed when capture events diverted the water in other directions. Valleys leading away from divide crossings are used to determine the nature of observed capture events, many of which are difficult or impossible to explain from the accepted paradigm perspective, but which are consistent with the mountain uplift, headward erosion of deeper valleys, and/or draining of floodwaters trapped in the Laramie Basin as the new paradigm predicts. However, the new paradigm requires a North American continental ice sheet heavy enough to raise entire regions and mountain ranges as massive and prolonged meltwater floods flowed across them, something the accepted pa-How radigm does not recognize.

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. [4], Pelletier [5], Scherler and Schwanghart [6] and others sometimes suggest. Instead the detailed topographic maps show abandoned valleys cross the Medicine Bow-Laramie River drainage divide not only on the Laramie Basin floor, but also in the mountains at both ends. There is a major disconnect between drainage divides when observed in nature or on the detailed topographic maps and drainage divides when described in laboratory models or in numerical models and simulations. Detailed topographic maps provide what is probably the easiest and most efficient way to investigate actual drainage divides, yet are rarely used to do so.
Detailed topographic maps show drainage divide locations and features, such as low points or abandoned valleys where water once crossed the drainage divides, and topographic map interpretation techniques permit drainage divide origins to be determined. This paper illustrates how detailed topographic maps and topographic map interpretation techniques can be used to determine the Medicine Bow-Laramie River drainage divide origin.

Geographic Setting
Study region geographic features are seen in Figure 1 and include the Medicine Bow (MB in Figure 1) and Laramie Mountains (LM) with the Medicine Bow Mountains extending in a north-northwest direction from northern Colorado into southern Wyoming. Near the Medicine Bow Mountains northern end is a southwest-to-northeast ridge of high peaks known as the Snowy Range. The Laramie Mountains are a northern extension of the Colorado Front Range and extend from northern Colorado in a north direction before turning in a northwestward direction to end in central Wyoming. The Medicine Bow and Laramie Mountains partially enclose the high elevation Laramie Basin (LB), but leave an opening to the northwest and west. All study region drainage flows to the North Platte River (N), which begins in northcentral Colorado in a mountain enclosed basin known as North Park (west of the Medicine Bow Mountains). From North Park the North Platte River flows in a north-northwest direction and south-oriented streams flow as barbed tributaries to it from the Medicine Bow Mountains. Once in Wyoming the North Platte River flows in north and then northeast directions and after cutting across the Laramie Mountains northwest end turns in an east and then southeast direction to flow along the Laramie Mountains northeast flank and into western Nebraska (where it joins the South Platte River to form the Platte River with its water eventually reaching the Missouri and Mississippi Rivers and the Gulf of Mexico). Clausen [7] described north-oriented streams that start as south-oriented streams and then make U-turns to flow across the northern Laramie Mountains to join that east-and southeast-oriented North Platte River segment.
The Laramie River (L) begins in northern Colorado and its headwaters flow northward on the Medicine Bow Mountains east side beginning in what Bolyard [[8], p. 131] refers to as a north-south lineament that crosses the east-west continental divide and that links north-oriented Laramie River headwaters (flowing to the Gulf of Mexico) with south-oriented Colorado River headwaters (flowing to the Pacific Ocean). Clausen [9] suggests that while the region and mountains Today the Laramie River after flowing in a north direction almost to where the Laramie Mountains change from being oriented in a north-to-south to a southeast-to-northwest direction makes an abrupt turn to flow in an east (and later northeast) direction to enter an anastomosing complex of bedrock-walled canyons described by Clausen [11] that cross the Laramie Mountains and to join the southeast-oriented North Platte River. Interestingly the North Laramie River flows in a south direction from the Laramie Mountains toward the Laramie River abrupt turn, but also abruptly turns in a northeast direction to cross the Laramie Mountains in its own canyon before joining the Laramie River. Many previous investigators attribute the Laramie River canyon to superposition (they rarely mention the diverging and converging bedrock-walled canyon complex or the separate North Laramie River canyon The Medicine Bow River (M in Figure 1) begins in the Snowy Range, just to the north of Medicine Bow Peak and flows in a north direction down the Medicine Bow Mountains northern flank before turning in a northeast direction to reach the Laramie Basin western margin where it abruptly turns to flow in a west direction to join the north-oriented North Platte River. Rock Creek is an important Medicine Bow River tributary and begins in the Medicine Bow Mountains (to the east of the Snowy Range) at an abandoned valley's northern end. South-oriented headwaters of the North Fork Little Laramie River drain the abandoned valley's south end and make a U-turn before joining the north-oriented Little Laramie River. Rock Creek flows in north, northwest, and northeast directions as it descends into the northwestern Laramie Basin where it also makes an abrupt turn to flow a northwest direction to join the Medicine Bow River (at the point where the Medicine Bow River turns to flow in a west direction). The west-oriented Medicine Bow River and Rock Creek segments are joined by southwest-and south-oriented tributaries linked by abandoned valleys (referred to as divide crossings) with the south-oriented North Laramie River headwaters valley and with the east-oriented Laramie River (and North Laramie River) anatomizing complex of bedrock-walled canyon complex and also with several north-oriented drainage routes now flowing completely across the northern Laramie Mountains to reach the east-and southeast-oriented North Platte River segment.

Research Method
Prior to doing the study reported here many years were spent studying detailed topographic maps in effort to solve unsolved drainage history problems including two multiyear systematic investigations of detailed topographic maps covering the entire Missouri River drainage basin (in which the much smaller Medicine Bow and Laramie River drainage basins are located). More than 500 detailed research notes related to the second Missouri River drainage basin systematic study can be found in blog format at geomorphologyresearch.com. Research related to this paper used detailed topographic maps and tools available at the United States Geological Survey (USGS) National Map website to identify the Medicine Bow-Laramie River drainage divide and low points along the drainage divide (referred as divide crossings) where water could be interpreted to have flowed in one direction or the other across the present-day drainage divide. Each divide crossing was observed to link valleys draining in opposite directions to eventually reach either the Medicine Bow River or the Laramie River. The observed valleys were interpreted to have been used by water that once crossed the drainage divide and the opposing valleys were followed downstream to determine why the flow direction in one of the opposing valleys had been reversed so as to create the drainage divide. Present-day divide crossing elevations were noted and compared with elevations where the opposing valley drainage routes ultimately entered either the Medicine Bow or the Laramie Rivers. Two fundamentally different hypotheses were used to interpret the map observations. The first hypothesis (referred to as the accepted paradigm) as described by Mears [13] begins with greater early Eocene mountain relief than today. During late Eocene, Oligocene, and early Miocene time the mountains were eroded and the intermontane basins (including the Laramie Basin) were filled with volcanic ash and eroded materials from the mountains so as to establish a low relief surface above which present-day mountain peaks stood as residual hills. Evidence supporting the interpretation that Oligocene and Miocene sediments once filled the Laramie Basin include isolated Oligocene deposits described by Evanoff [14] filling some Medicine Bow Mountain and Laramie Mountains valleys. Lillegraven and Ostresh [15] argue that during Oligocene and early Miocene time an east-oriented drainage system flowed across this low relief surface, although Knight [[16], p. 59] includes a diagram showing late Eocene north-oriented drainage in a mountain-surrounded Laramie Basin that turned to flow in a west direction. Regardless, regional uplift during the past 10 million years initiated massive erosion that exhumed what had been the early Eocene topography. Pelletier [17] attributes an increase in the intensity of snowmelt for the deep erosion that removed great thicknesses of the hypothesized Oligocene and early Miocene sediments from the southern Rocky Mountain intermontane basins (such as the Laramie Basin). While investigators disagree about many details the accepted paradigm general outline is commonly used even though geologic maps, such as Love and Christensen [18]  The alternate and fundamentally different hypothesis (referred to as the new paradigm) requires all Missouri River drainage basin valleys (of any size) to have eroded headward across or along immense south-and southeast-oriented floods and forces recognition of a heavy (and probably thick) North American continental ice sheet (located where continental ice sheets are usually thought to have been located) which deeply eroded the underlying bedrock (the accepted paradigm does not recognize deep continental ice sheet erosion) and which caused crustal warping that raised entire regions and mountain ranges as massive melt water floods flowed across them (the accepted paradigm does not see a relationship between continental ice sheets and regional and mountain range uplift). From the new paradigm perspective Clausen [11] used converging north-and south-oriented floods, that spilled from the Laramie Basin across the rising Laramie Mountains to reach what was at the time an actively eroding southeast-oriented North Platte River valley head, to explain the east-oriented diverging and converging bedrock-walled canyon complex where the Laramie and North Laramie Rivers now cross the Laramie Mountains. From the same perspective Clausen [7] used headward erosion of the southeast-oriented North Platte River valley to explain unusual northern Laramie Mountain drainage routes. In addition, Clausen [9] explained how floodwaters that moved south on the present-day north-oriented Laramie and North Platte River alignments eroded what are today mountain passes across the Colorado continental divide before mountain uplift forced a Laramie River flow reversal which captured south-oriented floodwaters still moving on what is today the north-oriented North Platte River alignment.

Medicine Bow Mountains Divide Crossings
Proceeding east and north from its southwest end along the Medicine Bow-Laramie River drainage divide a gap between Medicine Bow Peak and Browns Peak (number 1 in Figure 2) is the first of several divide crossings encountered. The gap floor elevation is about 3360 meters while Brown's Peak (east) rises to 3573 meters and Medicine Bow Peak (west) rises to 3652 meters. In a discussion of Medicine Bow Mountain glaciation Mears [19] points out the high Snowy Range ridge is composed of metasedimentary quartzite while the gap valley has been eroded in less resistant schist. The north-oriented Medicine Bow River begins immediately to the north of the gap and southeast-oriented Libby Creek drains the area to the south to an elevation of about 2530 meters where it joins the southeast-oriented North Fork Little Laramie River, which then makes a U-turn before joining (at an elevation of approximately 2357 meters) the northeast-oriented Little Laramie River (which eventually joins the north-oriented Laramie River at an elevation of about 2153 meters). However, an abandoned Numerous clues on the detailed topographic maps suggest a south-oriented drainage system once flowed across the Medicine Bow Mountains upland surface and to what are today north-oriented rivers. French Creek is one of many south-oriented (and barbed) tributaries flowing from the Medicine Bow Mountains to join the north-oriented North Platte River and the North Fork Little Laramie River U-turn is one of several drainage features suggesting south-oriented drainage from the Medicine Bow Mountains reversed its flow direction to address a Laramie Basin drainage direction reversal. Based on such topographic map evidence a large stream of water flowing in a south direction is interpreted to have eroded the 213-meter deep gap between Medicine Bow and Browns Peaks and to have split into diverging southeast-and southwest-oriented channels to erode the Libby Creek and South Fork French Creek valleys. But where did that water come from? Today the north-oriented Medicine Bow River descends on the Medicine Bow Mountains north slope to enter the Laramie Basin areas where elevations are less than 2100 meters and to have eroded the gap the water would have had to cross a quartzite ridge that today stands almost 1500 meters higher. Obviously when the gap was eroded the Snowy Range crest ridge did not stand higher than Laramie Basin floor as it does today.
A second major Medicine Bow-Laramie River drainage divide crossing is seen at number 2 (in Figure 2)   When trying to interpret the three above described Medicine Bow River-Rock Creek drainage divide crossings regardless of paradigm being used it is assumed running water initially eroded all three divide crossings, although alpine glaciers may have altered some or all of the above described valleys and divide crossings.
Nothing reported in the Mears [19] Medicine Bow Mountains glaciation discussion suggests otherwise. With that assumption from the accepted paradigm perspective the gap between Medicine Bow Peak and Browns Peak (number 1 in

Laramie Mountains Divide Crossings
The Medicine Bow-Laramie River drainage divide northern end is a triple drainage divide (at an elevation of 2631 meters) where it meets the southeast-oriented North Platte River drainage basin and is located in the Laramie Mountains just north of Figure 3 along the south-oriented North Laramie River

Laramie Basin Divide Crossings: Little Medicine Bow-North Laramie River Segment
The Medicine Bow-Laramie River drainage divide in the Laramie Basin can be subdivided into two segments with the first being the between the North Laramie River and the Little Medicine Bow River. As already mentioned, the North Laramie River flows in a south direction to enter the Laramie Basin northeast corner where it turns and crosses the 2100-meter contour line as it enters the northeast-oriented North Laramie River canyon. Perhaps the most intriguing map evidence is at the north end of this drainage divide segment where previously mentioned Rogers Creek (which originated high on the west wall of the south-oriented North Laramie River valley to the south of Figure 3 and which is flowing as an intermittent stream to Sheep Creek, which then flows to the Little Medicine Bow River) and an unnamed southwest-and southeast-oriented intermittent stream (which enters southeast-oriented Twentytwo Mile Draw which drains to the North Laramie River) flow parallel to each other at an elevation of about 2174 meters and about 450 meters apart with the drainage divide between them in places being only about 2 meters high. Such a situation is almost impossible to explain if the North Laramie River route was established on a cover of Oligocene and Miocene sediments that had buried the Laramie Mountains. However the situation is easily explained by headward erosion of a shallow southeast-oriented valley from the actively eroding North Laramie River valley to capture southwest-oriented flood flow that was still moving across what is now the south-oriented North Laramie River headwaters valley just prior to headward erosion of the North Laramie River valley, which captured (and beheaded) the southwest-oriented flood flow. Continuing in a south direction along the Little Medicine Bow-North Laramie River drainage divide a broad (more than 5 kilometers) a shallow divide crossing is just to the southeast of Buck Point and links east-northeast and southeast-oriented Twentytwo Mile Draw drainage to the North Laramie River with southeast-oriented Bone Creek headwaters (which flow to southwest-oriented Greasewood Creek and then to the Little Medicine River). Elevations vary from place to-place along the divide crossing, but are in the 2170-to 2175-meter range. This segment of the drainage divide is asymmetric with a much steeper slopes leading into the Bone Creek drainage basin, which is generally 30-to 40-meters lower than into the Twentytwo Mile Draw drainage area to the northeast. The broad divide crossing and the asymmetric drainage divide suggest large sheets of water flowed in a southwest direction from what is now the North Laramie River valley to reach west-oriented Little Medicine Bow and Medicine Bow River segments. 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). Little Medicine Bow-North Laramie River drainage divide features are difficult to explain from the accepted paradigm perspective but are consistent with new paradigm predictions.

Laramie Basin Divide Crossings: Rock Creek-Laramie River Segment
Proceeding from north to south along the Rock Creek-Laramie River drainage Creek (seen in Figure 4). Today Sevenmile Creek joins a northwest-oriented Rock Creek segment flowing to the west-oriented Medicine Bow River. Duck Creek makes a southeast-and then northeast-oriented jog before entering the east-oriented Duck Creek canyon. The Duck Creek canyon is one of many diverging and converging canyons crossing the Laramie Range and within the Laramie Range the east-oriented Laramie River canyon turns in a north direction to join the east-oriented Duck Creek canyon (which then becomes the Laramie River canyon). Other abandoned north-and northeast-oriented canyons link the east-oriented Duck Creek canyon with the northeast-oriented North Laramie River canyon. Orientations of secondary valleys seen in Figure 4 suggest southwest-oriented water eroded the Sevenmile-Duck Creek through valley, which from the accepted paradigm perspective is difficult to explain, but which is consistent with previously described new paradigm interpretations of Little Medicine Bow-North Laramie River drainage divide features. However, the new paradigm interpretation requires at least some of the diverging and converging canyons now crossing the Laramie Range, including the northeast-oriented North Laramie River canyon, to have been initiated by southwest-and south-oriented flood flow channels which headward erosion of much deeper east-oriented valleys then beheaded and reversed. Rock Creek flows a northeast direction where it emerges from the Medicine Bow Mountains onto the Laramie Basin floor and crosses the 2100-meter contour line and enters a narrower valley before continuing to its easternmost point where it makes a U-turn to flow in a northwest direction to join the west-oriented Medicine Bow River (at the point where the Medicine Bow River turns in a west direction). At its easternmost point Rock Creek has an elevation of about 2042 meters and is about 16 kilometers west of the north-oriented Laramie River, which ten kilometers further north turns in an east direction to cross the 2100-meter contour line and enter a canyon to cross the Laramie Mountains. Between the Rock Creek easternmost point and the Laramie River is broad low relief surface (with some shallow closed depressions) where elevations are in the 2100-to 2150-meter range. About 8 kilometers to the east of that broad low relief surface (sometimes referred to as Laramie Flats) is the Laramie Mountains western flank and several entrances to the extensive Laramie Mountains diverging and converging bedrock-walled canyon complex, including the East and West Bluegrass Creek canyons, Halleck Canyon, and the Plumbago Creek valley (leading to the Sybille Creek Canyon) all of which are comparable in elevation to the broad low relief surface's elevation (and not much higher than the Laramie River elevation, which is higher than the Rock Creek elevation). The accepted paradigm provides no way to explain the Laramie Mountains diverging and converging bedrock-walled canyon complex, which may be why many previous investigators fail to mention the North Laramie River and Sybille Creek canyons and even if they do the Duck Creek Canyon, East and West Bluegrass Creek Canyons, and Halleck Canyon are seldom mentioned.

Conclusion
Regardless of the paradigm being used laboratory experiments and numerical models and simulations do not even come close to describing how natural drainage divides such as the Medicine Bow-Laramie River drainage divide originate and evolve. Researchers wanting to understand drainage divide formation need to look at drainage divides as those drainage divides actually exist. To understand actual drainage divides any researcher willing to look can use detailed topographic maps available at the USGS National Map website to analyze drainage divides throughout the United States. The Medicine Bow-Laramie River drainage divide is not unique and is probably typical of many other actual drainage divides. Divide crossings along actual drainage divides are common and record numerous capture events, just as divide crossings along the Medicine Bow-Laramie River drainage divide record capture events. In most cases, just like in the Medicine Bow-Laramie River drainage divide example, the accepted paradigm is unable to explain many of the easy to document capture events that took place. A new and fundamentally different paradigm is needed in which drainage divide formation took place as massive floods flowed across rising regions and mountain ranges and requires recognition of a North American continental ice sheet that not only deeply eroded bedrock underneath it, but that also raised entire regions and mountain ranges as large and prolonged meltwater floods moved across them.