Physiography, landforms, topography, and surface drainage

The WBRB is bounded by topographic or surface-water divides – and by the Wyoming state line in the northwestern corner of the state and along part of the northern border. The ten segments of the WBRB boundary enumerated below are shown in Figure 3-2 and can be followed on those USGS 1: 500,000-scale maps of Wyoming and Montana that show streams and elevation. Clockwise from the Pryor Mountains in Montana, the boundary runs:

  1. Northward then southeastward along a Pryor mountain ridgeline bordering drainage intoWyoming, to the Wyoming/Montana state line;
  2. Thence eastward along the Wyoming/Montana state line and along a divide in the Bighorn Mountains;
  3. Thence generally south-southeastward along the arcuate ridge of the Bighorn Mountains to T39N, R87W;
  4. Thence generally south-southwestward along a divide on the Casper Arch from T39N, R87W to the northwestern tip of the Rattlesnake Hills, T34N, R89W;
  5. Thence a short distance southeastward along the ridgeline of the Rattlesnake Hills into T33N, R88W;
  6. Thence irregularly west-southwestward along the Beaver Divide (Beaver Rim) – an irregular drainage divide on the Casper arch north and west of the Granite Mountains – to T30N, R101W, where it meets the Continental Divide;
  7. Thence following the Continental Divide northwestward along the ridge of the Wind River Range, past the western end of the Washakie Range, along the southwestern edge of the Absaroka Range, and along a divide on the Yellowstone Plateau to the Wyoming/Idaho/Montana state line intersection;
  8. Thence along the state line northward then eastward around the northwestern corner of Wyoming;
  9. Thence arcing into Montana along a divide bordering drainage into Wyoming in part of the Absaroka Range and continuing generally east-southeastward along a ridge line in the Beartooth Mountains to the Wyoming state line;
  10. Thence eastward along the state line between the eastern edge of the Beartooth Mountains drainage and the western edge of the Pryor Mountain drainage into Wyoming, where the Bighorn structural basin opens north-northwestward into Montana.

In this memorandum, the WBRB comprises four, three, or two areas, according to context. In the context of geography and surface geology the WBRB comprises the four areas shown on Figure 3-2: the Wind River Basin, the Bighorn Basin, the Absaroka Range, and the Yellowstone Plateau. In the context of subsurface geology, Bighorn-basin pre-volcanic stratigraphy extends westward beneath the Absaroka Range volcanics, as shown on Plate VI, sections A-B’ and B-B’. The sub-volcanic structure may be seen as a highly faulted and folded extension of the Bighorn basin on the basis of similar stratigraphy or as a separate basin, the Absaroka Basin of Sundell (1993), separated from the Bighorn Basin by the Cody Arch, on the basis of structure. Under either interpretation, the western and southwestern borders of the Absaroka Basin or extended Bighorn Basin is probably the Washakie Range.

Geographic index map, Wind/Bighorn River Basin.
Geographic index map, Wind/Bighorn River Basin.
Major structural/physiographic features, drainages, and bodies of water
Major structural/physiographic features,
drainages, and bodies of water

In the context of hydrogeology, the Wind River Basin and Bighorn River Basin, having a far higher density of data than the Absaroka and Yellowstone areas, are the two areas of interest; and the Bighorn River Basin may include the eastern drainage of the Absarokas and sub-volcanic units beneath. In detailed hydrogeologic descriptions the Wind River Basin, Bighorn Basin, and Absaroka/Yellowstone areas are treated separately.

The topography of the WBRB is defined by two intermontane basins surrounded and separated by mountain ranges, and the Yellowstone Plateau. Surface elevations within the WBRB drainage basin range from roughly 3,500 feet above sea level where the Bighorn River crosses the Wyoming/Montana state line in the Bighorn Basin to 13,804 feet at the summit of Gannett Peak in the Wind River Range. Within the basin interiors, elevations range from 4,000 to 6,000 feet. The Yellowstone Plateau in the northwestern corner of the WBRB is elevated relative to the basins, with elevations ranging from 7,731 feet at Yellowstone Lake to 12,244 feet at Trout Peak.

The WBRB drainage basin is a headwater of the Missouri River drainage system. Principal rivers include the Wind/Bighorn, Nowood, Greybull, Shoshone, Clark’s Fork (Yellowstone), Yellowstone, Madison, and Gallatin and their tributaries (Figure 3-2). The distal divides of these drainage systems define the limits of the WBRB study area. The Wind River structural basin – the basinal area bordered by uplifts – is drained by the Wind River and its tributaries. The Wind River leaves the Wind River Basin flowing northward through the Wind River Canyon, and becomes the Bighorn River at Wedding of the Waters just into the Bighorn Basin. Most of the Bighorn Basin and the eastern slope of the Absaroka Range is drained by the Bighorn River and its tributaries; a northern part of the eastern slope of the Absarokas and a contiguous southern part of the Beartooth Mountains are drained by the Clarks Fork Yellowstone River. The Bighorn River and Clarks Fork leave the Bighorn Basin flowing northward across the Wyoming/ Montana state line. Much of the Yellowstone Plateau within the WBRB and the western slope of the Absarokas is drained by the Yellowstone River; small areas in the northwestern corner of the state are drained by the Madison River and Gardiner River. The Yellowstone and Gardiner Rivers leave the state flowing northward – the Madison flowing westward – across the Wyoming/Montana state line.

Reference View complete Wind/Bighorn Basin Water Plan