Geology and Physiography of the Black Hills
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 metasedimentary rocks that comprise the core of the entire Black Hills uplift. This core is rimmed by Paleozoic, Mesozoic, Cenozoic and sedimentary rocks (Wikipedia (more info) ).
South of the Pine Ridge is a fault which continues Northwest but subsides prior to the immersion of the Black Hills. The presence of the fault is apparent west of Pine Ridge where the southern side of the fault has upsurged (Gries, 1996 ).
The Black Hills are composed of Harney Peak Granite Batholith. The granite contains minerals such as quartz, feldspar, muscovite, and biotite. These minerals formed beneath the surface from molten magma. After the magma cooled and crystallized into solid rock, pegmatite dikes were formed when magma intruded into the granite (Geology Fieldnotes (more info) ).
Show me a stratigraphic column of the Black Hills
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Also found on the Black Hills are Jewel Cave and Mount Rushmore. Jewel Cave was formed by the dissolving action of acidic water. The cave hosts an array of speleothems and crystal formations (Geology of Jewel Cave (more info) ). Mount Rushmore is on the edge on the Harney Peak Granite Batholith (Geology Fieldnotes (more info) ).
