"C" is for Continental Shelf. The continental shelf that lies off South Carolina’s coast is part of a larger continental shelf that runs from Canada to Mexico. It is formed, in part, by a continuation of the sediments of the coastal plain that are covered by seawater. This continental shelf has been exposed as much as one hundred miles off the present coast during the geologic history of the state. This was due to ancient sea levels rising and falling many times over millions of years. Today’s South Carolina’s continental shelf is a passive margin—meaning that it is not colliding with any other land mass as it did millions of years ago. Instead, the state’s continental shelf is trailing along North America’s active western margin that is presently leading the continent toward Asia.