Index map
Rising topographically from the Great
Plains in eastern Wyoming and western South Dakota, the Black
Hills are conspicuous on the map by the (red) outcrop of Precambrian
rock. The upturned and eroded Paleozoic and Mesozoic strata of
this structural dome surround the ancient granite on which the
four faces of the Mt. Rushmore presidential monument were carved.
Geologically, the Black Hills represent the easternmost outpost
of the Rocky Mountains.
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