Mount Rushmore community. Recent pine beetle infestations have threatened the forest. Mount Rushmore is largely composed of granite. The memorial is carved on the northwest margin of the Black Elk 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 Proterozoic, 1.6 billion years ago. Coarse grained pegmatite dikes are associated with the granite intrusion of Black Elk Peak and are visibly lighter in color, thus explaining the light-colored streaks on the
Mount Rushmore birds, including songbirds, nuthatches, and woodpeckers, inhabit the surrounding pine forests. Terrestrial mammals include the mouse, least chipmunk, red squirrel, skunk, porcupine, raccoon, beaver, badger, coyote, bighorn sheep, bobcat, elk, mule deer, yellow-bellied marmot, and American bison. The striped chorus frog, western chorus frog, and northern leopard frog also inhabit the area, along with several species of snake. Grizzly Bear Brook and Starling Basin Brook, the two streams in the memorial, support fish such as the longnose dace and the brook trout. Mountain goats are not indigenous to the region. Those living near Mount Rushmore are descendants of a tribe