Stone Mountain

Figure 11. Stone Mountain is a granite intrusion monadnock in Wilkes County. (Photograph by the author. More about the photograph)

Quartzite is not the only erosion-resistant rock that has formed monadnocks on North Carolina’s Piedmont. Another major rock type — granite — has also been responsible for monadnock formation. Granite is a granular rock made primarily of feldspar and quartz, but with a variety of other minerals that alter its color and sparkle. (Sparkle is generally provided by mica incorporated into the matrix.) Granites form deep within the earth’s crust when parent rock or sediments melt and undergo a complete transformation as they recrystallize into a new rock type. Granites formed by this process are the characteristic rock of the earth’s continents. (Sea floors are made of a heavier rock called basalt.)

The abundance of granite has resulted in its presence at the crests of many mountains and hills throughout the Appalachians and the Piedmont. One of the most striking forms that is taken by granite outcrops is a dome structure that results when fracture lines form parallel to the ground surface as the granite intrusion expands upward as overlying rock and soil erodes away. Stone Mountain, Georgia, is such a dome and it is almost vertical flank provides the medium for a gigantic sculptural relief of Civil War heroes.

The most impressive granite dome in North Carolina, despite its lack of artistic expression, is Stone Mountain in Wilkes County, northwest of North Wilkesboro. The dome is visible for miles. The rock that forms it was created in the crust miles below the earth’s surface about 400 million years ago.

Stone Mountain is interesting in many ways. The most spectacular feature is its dramatic size and shape that dominates the surrounding countryside. Also interesting are the examples of soil formation and plant communities found in circular weathering pits that have formed on its surface. In addition, the mountain is tall enough that the vegetation changes from typical Piedmont hardwood forests around the base to scattered patches of pines at the middle levels and to stunted heath-dominated communities on the broad and exposed summit.

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