It was surprisingly difficult to find information about Wilmington's "Rocks" which closed off the New Inlet of the Cape Fear River. This inlet was formed in a huge storm in the 1700s and provided a second inlet to the Cape Fear River in North Carolina.
During the Civil War, this inlet was the one favored by the fleet blockade-runners bringing supplies into the Confederacy and bringing the valuable cotton out. New Inlet was protected by massive Fort Fisher.
After the war, it was decided that New Inlet would have to be closed in order to prevent sanding over of the Cape Fear River Channel. This job was assigned to Henry Bacon, Sr., a civil engineer living in Illinois. In the 1870s, he moved his family to Wilmington, North Carolina where he was assigned to the Wilmington office of the U.S. Engineer Department to take charge of the New Inlet Dam and Swash Defense Dam, two projects that proved to be a major engineering feat.