Stoney Ridge Estates and Kingston Ridge.
Sussex County Delaware is distinguished by its flatness. We start at sea-level and rise gently to around 40 feet above sea-level. Gravel Hill itself is one of the few places even close to worthy of the name "hill" (other than the landfill). It goes up to about 50 feet above sea-level for very short stretch.
The nearest "ridge" is a two-hour drive to the north, in northern New Castle County.
By the way, "Stoney" Ridge? This is essentially a large sand-spit of a peninsula. One thing we don't have a whole lot of is stones.