Black Hills

The geology of the Black Hills is complex. A Tertiary mountain-building episode is responsible for the uplift and current topography of the Black Hills region. This uplift was marked by volcanicactivity 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. This core is rimmed by Paleozoic, Mesozoic, and Cenozoic sedimentary rocks. The stratigraphy of the Black Hills is laid out like a target, as it is an oval dome, with rings of different rock types dipping away from the center.

• http://en.wikipedia.org/wiki/Black Hills