The Black Hills are the easternmost uplift in the Laramide province of the Rocky Mountain foreland. In general, the Black Hills uplift is similar in character and origin to the foreland uplifts in Wyoming, but the structural relief is smaller and the associated structures less well developed (Shapiro, 1971; Lisenbee, 1978).
Devils Tower is an erosional remnant of the series of Eocene intrusives that characterize the northern and northwestern parts of the Black Hills. The tower rises vertically for more than 365 m (1,200 ft.). It is composed of phonolite porphyry, an alkaline-rich rock containing soda-rich orthoclase and augite. On a fresh surface the 0.6 to 1.3 cm (¼- to ½- inch) long phenocrysts of white orthoclase stand out against the fine-grained light to dark gray background. The rock weathers light gray or brownish gray.
The eastern flank of the Powder River Basin is dotted with oil fields. Oil was first discovered near Newcastle shortly after the Black Hills gold rush and development continues to this day. Most of the production is from the sands in the Lower Cretaceous Newcastle, Muddy and Fall River sandstones, sandy members of the Carlile and Belle Fourche shales and the Minnelusa Formation.
Few mountain ranges are as “open for view” as the Owl Creeks. Here the huge cleft sawed through the uplift by the Wind River offers a view that is seldom excelled. From classic exposures of Mesozoic sedimentary units on the north flank of the mountains, the highway winds its way through outcrops of thick Paleozoic sandstones, carbonates, and shales until deep within the range the gorge exposes Precambrian igneous and metamorphic rocks.
The Beartooth and Absaroka Ranges were major sources of ice. Ice from the Beartooth and Absaroka centers converged in the northeastern part of Grand Teton National Park and flowed southward along the scarp of the Teton Range. Signal Mountain, Blacktail Butte, and the Gros Ventre Buttes were overridden and shaped by this ice advance.
The dominant structural feature of the range is the Teton fault, a normal fault. Gravity and seismic refraction data suggest the fault dips east at about 40° (Behrendt and others, 1968) Love and others (1973) suggested that movement started after middle Pliocene and continues today, with a total accumulated displacement of nearly 10,000 m (30,000 ft.).
Yellowstone volcanism has been intermittent for 2.2 Ma and the magnitude is impressive when compared to historic eruptions. Volcanic rocks and derivative volcaniclastic deposits are equivalent to more than 6,500 km3 of magma. Perhaps as much as ten times more intrusive material has been produced than the estimated erupted volcanics. Brief episodes of violent and voluminous rhyolitic ash-flow eruption, lasting on the order of hours, days, or at most months, was preceded and followed by quiet intervals lasting sometimes hundreds of thousands of years. Today, magma chambers provide the heat source for the hydrothermal and geothermal features of YNP.
Across Wyoming there are two high-altitude, relatively level erosion surfaces. Remnants of similar surfaces are also found at approximately 10,000 ft. in the Tobacco Root Mountains near the IUGFS. The surfaces, which frequently are referred to as the Summit and Subsummit surfaces, are regional in extent, truncate rocks of varying resistance, and generally slope gently toward intermontane basins or The Great Plains.
Alpine glaciation in northwestern Montana and adjacent Canada occurred repeatedly throughout the Pleistocene, resulting in spectacular erosional features and deposition of drift in Glacier and Waterloo National Parks (Alden, 1953, Horberg, 1954).
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