Pegmatites of the Black Hills, South Dakota
Central to the Black Hills is Harney Peak, the highest point at 7,242 feet above sea level. Harney Peak is comprised of 1.7 billion year old granite and crops out in a roughly circular area of no more than 10 miles in diameter. Flanking the granite are 2.5 billion year old metamorphic rocks in which most of the pegmatites have intruded.