During the decipherable part of Precambrian history, the Black Hills area was within an undefined geosyncline in which more than 20,000 feet of sediments accumulated. It can be inferred that the axis trended north-northwest, parallel with the isoclinal folding which occurred near the end of Precambrian time. Peneplanation followed the folding.

In early Paleozoic time, the Hills area was part of a stable shelf on the northwest flank of the Sioux arch. Seas encroached from the northwest. Increasing instability in Mississippian time is evidenced by evaporite cycles in upper Mission Canyon and Charles sediments. Post-Madison-pre-Pennsylvanian uplift left the present Hills area as a thumb-like projection extending northward from Siouxia.

With the disappearance of the Central Montana trough at the close of the Mississippian, seas no longer invaded from the northwest.

The Lusk embayment developed in early Pennsylvanian time. Evaporites in the Pennsylvanian sediments testify to instability of the shelf at that time. By late Pennsylvanian or early Permian time, the Black Hills first appeared as a weak but distinct positive element.

Western South Dakota and the surrounding area formed a broad, relatively unstable shelf during the redbed and evaporite deposition of Permian, Triassic, and early Jurassic time. Stable shelf conditions prevailed throughout the upper Jurassic. Local downwarping is indicated by exceptional thicknesses of Jurassic sediments in the southeastern part of the area.

Western South Dakota was near the geographical center of a wide, asymmetrical Cretaceous seaway. The Hills lay along a hingeline, with a wide shelf on the east and a subsiding trough on the west. With brief interruptions, Cretaceous deposition continued over the area through Fox Hills and probably through Hell Creek time.

Laramide doming of the Hills was due primarily to vertical uplift. Folding along the western side, and along the related Old Woman and Cedar Creek trends, suggests some horizontal forces. Effects of primary doming were modified in the Northern Hills by early Tertiary intrusions. By the close of Oligocene time, at least 6,500 feet of sediments had been eroded, and the Hills appeared as a low range of Precambrian rocks nearly engulfed by White River sediments.

Evidence of Miocene and younger folding and faulting occurs south of the Hills. Regional uplifts in the Miocene, Pliocene, and Pleistocene resulted in erosion, reworking, and redeposition of older Tertiary sediments.

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