2. Uplift of the Black Hills
Tectonic processes formed the Black Hills about 60 million years ago. The rocks were uplifted, fractured, and faulted. The Black Hills region is an elliptical dome. The higher, central part of the dome has been eroded the most; therefore, the oldest rocks are exposed in the center of the dome. An example of these older rocks is the Precambrian granites at Mount Rushmore National Memorial. The younger rocks—Triassic–Jurassic sedimentary rocks found near Devils Tower—are exposed along the edges of the dome where less erosion has occurred. To create a model of an elliptical dome proceed to the classroom activity.