Harney Peak is the highest point within the Black Hills and the highest point within South Dakota. Standing on the bald peak one sees more granite in all directions rising from the dark ponderosa pine forest. To the south, one ridge is named Little Devil's Tower and looks like its namesake in Wyoming. To the east, the prairie and plains stretch to the horizon.
The weathered granite of Harney Peak is very old, dating back 1.7 billion years when magma crystallized miles below the surface. More than 60 million years ago the Black Hills began to rise along with other mountain building going on around Wyoming and Montana. Erosion since then has worn off the covers of sediment from above to reveal the ridges, spires, and pinnacles of this massive body of granite.