Although the high Yellowstone Plateau and Absaroka Range of northwestern Wyoming present a mountainous terrain, these areas are remnants of a plateau that coincided with the top of a vast pile of nearly horizontal sheets of rock materials derived from nearby volcanic vents in the Yellowstone area. Once the pile of volcanic debris had accumulated, the region was subjected to the ever-present forces of erosion, which cut deep valleys. The mountains are those of erosion – the deep dissection of relatively flat lying rock layers – and are a classic example of this type of development.

Even now, the Yellowstone Plateau is a thermally and seismically active area with molten rock perhaps no more than 1.9 miles beneath the surface in some places. While the geysers of Yellowstone also attest to the relatively shallow thermal activity beneath the plateau, researchers have documented recent uplift of portions of the Yellowstone Caldera (remnants of a large volcano), rising at rates up to 15 millimeters per year. The most recent volcanic activity on the plateau, however, has been dated at 600,000 years before the present.

Map of major structural elements in Wyoming.
Map of major structural elements in Wyoming.
(Click image to download PDF)

Scenically, the basins of Wyoming are less satisfying than the other two geologic provinces, and some persons may feel that the long, rather monotonous vistas of low buttes and mesas and sparse vegetation are like a lost world. A trip across the basins during the heat of the day in August can be a less than exciting experience, but if the same trip is made in early morning or early evening, the landscape has a very different appearance. At these times of the day, low-level lighting can accentuate the landscape and make it very beautiful.

Despite the rather limited vegetative cover, the wide lonesome stretches of Wyoming's basins provide pasturage for a large number of cattle, sheep, and wildlife, particularly in the winter months when snowmelt provides water for animals.

Viewed from a geological perspective, these same basins are much more stimulating than some of the uplifts, and are just as profound in terms of the movements of the Earth's crust. In fact, the amount of downfolding of the crust usually exceeds the uplift of the adjacent mountains if sea level is used as a datum. The basins, which are surface topographic depressions, are at the same time compound downfolds in which the layered sedimentary rocks dip toward the lowest point or trough. Many of the exciting aspects of these downwarps are hidden from the eye because they lie at great depths.

In terms of economics and natural resources, Wyoming would not be as prosperous without the raw materials that exist in the rocks of these basins. Along the basin margins, the sedimentary strata often crop out in hogbacks, exposing limestone, gypsum, bentonite, phosphate rock, and building stone. Farther out in the basin, at the surface, one finds some of the great coal fields of Wyoming, and also uranium deposits. The rock units that extend under the basins at depth act as reservoirs for oil and gas accumulations. Trona and oil shale are found in the central part of one of the Green River Basin.

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