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 Sugarloaf State Reservation Mount Sugarloaf State Reservation Mount Sugarloaf State Reservation is a state-owned, public recreation area managed by the Massachusetts Department of Conservation and Recreation located in South Deerfield, just west of the Connecticut River. The state park includes the summits of North Sugarloaf Mountain and South Sugarloaf Mountain, as well as 1.75 miles of frontage on the Connecticut River and two river islands. The park is part of a larger park designation called the Connecticut River Greenway State Park. Portions of the park property along the river are used by the University of Massachusetts Amherst for agricultural research. The state maintains