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A Tertiary mountain-building episode is responsible for the uplift and current topography of the Black Hills region. This uplift was marked by volcanic activity in the northern Black Hills. The southern Black Hills are characterized by Precambrian granite , pegmatite , and metamorphic rocks that comprise the core of the entire Black Hills uplift.
The Laramide orogeny occurred in a series of pulses, with quiescent phases intervening. The major feature that was created by this orogeny was deep-seated, thick-skinned deformation, with evidence of this orogeny found from Canada to northern Mexico, with the easternmost extent of the mountain-building represented by the Black Hills of South ...
The Black Hills are approximately 125 miles (201 km) long and 65 miles (105 km) wide. The Dakota Hogback ridge formed when the resistant sandstones of the Dakota Sandstone and underlying strata were uplifted near the center of the present-day Black Hills because of a granite intrusion , approximately 60 million years ago.
The Laramide orogeny began the uplift of the Rocky Mountains during the Cretaceous. West of the Missouri River, the Niobrara chalk formed in the inland sea during the Cretaceous, which contains mosasaur and plesiosaur bones. Tepee buttes form as small, conical hills in the Pierre shale landscape, from lenses of more erosion resistant limestone.
The rise of the Black Hills uplift on the east and the Hartville uplift on the southeast side of the basin created the present outline of the Powder River Basin. When the coal beds were forming, the climate in the area was subtropical, averaging about 120 inches (3 m) of rainfall a year.
The faster uplift along the Black Mountains formed much smaller alluvial fans because older fans are buried under playa sediments before they can grow too large. Slot canyons are often found at the mouths of the streams that feed the fans, and the slot canyons in turn are topped by V-shaped gorges.
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The Black Hills of South Dakota is one of the few remaining exposed portions of the Trans-Hudson orogenic belt. The peaks of the Black Hills are 3,000–4,000 feet (910–1,220 m) above the surrounding plains, while Black Elk Peak – the highest point in South Dakota – has an altitude of 7,242 feet (2,207 m) above sea level. [4]