The Piedmont gravity gradient is perhaps the most striking feature of the gravity field of the southeastern United States. It extends more or less linearly through the Piedmont, separating positive gravity values to the southeast from negative gravity values to the northeast.
Analysis of data from a detailed gravity survey in central North Carolina indicates that the source of the anomaly is located within the upper crust. The best model that we were able to obtain consisted of a block 7.6 km thick located at the surface of the ground. The block has a density contrast of +0.213 gm-cm−3 relative to rock to the northwest. The block may be bounded on the northwest by a vertical interface. The higher density rocks causing the anomaly lie within the Carolina Slate Belt.