For most of its length it consists of one or more relict beach ridges created when the sea level was about 30 feet (9.1 m) higher than at present.
The Atlantic Coastal Ridge extends from the St. Marys River, which is the boundary between Florida and Georgia, to west of Homestead in southern Miami-Dade County.
The profile of the ridge on the sea-ward side closely resembles the current profile of the nearshore underwater slope along the Atlantic coast of Florida, suggesting that the ridge was formed by the same processes that are currently operating along the Florida coast.
[6] The Anastasia Formation shallowly underlies the Atlantic Coastal Ridge along most of the east coast of Florida.
[7] In southernmost Florida, the Anastasia Formation is deeper, 100 feet (30 m) or more under the surface in Miami-Dade County, where it is overlain by Miami Limestone.
North of Palm Beach County the Atlantic Coastal Ridge is composed of quartz sand, but South of Palm Beach County it is increasingly composed of calcareous oolite, becoming a relict oolite shoal, a few miles wide and 10 to 15 feet (3.0 to 4.6 m) high.
[9] The Miami Rock Ridge formed as a shoal of calcareous oolite, comparable to the ongoing process on the Bahama Banks.