Geologic age: Precambrian

Continue north on route 87 for 1.8 miles. The pegmatites are found at a parking area on the right side of the road with a wayside exhibit titled Ancient Foundations.

Pegmatites are part of the Precambrian core of the Black Hills. They are extremely coarse grained igneous rocks that formed deep within the earth. The large crystals indicate that they cooled very slowly.

Look for three common minerals in pegmatite: quartz (whitish and glassy), feldspar (pink with shiny flat surfaces), and tourmaline (black and long with slender crystals).