Whose faces are carved into Mt Rushmore?

Mount Rushmore is largely composed of granite. The memorial is carved on the northwest margin of the Harney Peak granite batholith in the Black Hills of South Dakota, so the geologic formations of the heart of the Black Hills region are also evident at Mount Rushmore. The batholith magma intruded into the pre-existing mica schist rocks during the Precambrian period about 1.6 billion years ago. However, the uneven cooling of the molten rock caused the formation of both fine and coarse-grained minerals, including quartz, feldspar, muscovite, and biotite. Fractures in the granite were sealed by pegmatite dikes. The light colored streaks in the presidents' foreheads are due to these dikes.