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 center, finished in 1957. These structures were part of the Mission 66 effort to improve visitors' facilities at national parks and monuments across the country. On October 15, 1966, Mount Rushmore was listed on the National Register of Historic Places. A 500-word essay giving the history of the United States by Nebraska student William Andrew Burkett was selected as the college-age group winner in a 1934 competition, and that essay was placed on the Entablature on a bronze plate in 1973. In 1991, President George H. W. Bush officially dedicated Mount Rushmore. In a canyon behind the carved faces is