While barrier islands typically are long ridges of sand constantly shifting under the influence of sea level, sand supply, wave energy, and storms, the sea islands have a more complex structure, including an older, Pleistocene age component facing the mainland, and a newer, Holocene age component on the seaward side.

The Pleistocene portion of the island was originally covered by a maritime forest, which produces an abundant mast (primarily acorns and other tree nuts).

Radio-carbon testing of material from the ring yielded median dates of 4,370 and 3,860 years Before Present (BP).

The southern two-thirds of the ring was subject to extensive plowing in the first half of the 19th century, obscuring its surface appearance.

Samples from the central plaza (charcoal and a hickory nut, as shells are absent) yielded a range from 2410 to 2210 BC.

While stone tools are generally rare at archaeological sites in the sea islands and the adjacent coast, they are fairly common at the St. Catherines ring.

Excavators have found 18 projectile points and a drill, as well as very small pieces interpreted as debris from tool reduction or reshaping.

A burial pit containing human and non-human bone fragments was also found in the central plaza.

On the east side of the ring excavations revealed two layers of shell, separated by 3.5 cm of sand.

David Hurst Thomas states that the initial inhabitants settled first in the most productive areas of the Pleistocene core of the island.

[19] As of 2022, excavation of an approximately 4,000-year-old human grave site on St. Catherines Island is spearheaded by David Hurst Thomas and Matthew C. Sanger.

Excavations at the grave site, which is surrounded by a large ring of seashells known as the McQueen shell ring, have uncovered copper objects closely corresponding to those found at hunter-gatherer sites in the Great Lakes region, suggesting that traders may have travelled all the way from the Midwest to St Catherines Island.

They have revealed the remains of the churches, conventos (friars' quarters), a kitchen, wells, the churchyard, and part of the Indian settlement attached to the mission.

Kathleen Deagan writes, "The work has provided detailed information about early Franciscan mission architecture and building construction, organization of space, diet, material culture, and economic strategies.

"[22] A cemetery (campo santo) was found inside the remains of the church of Santa Catalina de Guale, where at least 431 persons were buried beneath the floor.

It contained an assortment of associated grave goods, including crosses, Franciscan medallions, small medals, Jesuit finger rings, a cast figurine of the infant Jesus, and other religious and utilitarian objects.

[23] There was a Guale settlement on St. Catherines Island by 1576, and it was established as the northernmost permanent Spanish outpost on the Atlantic Coast in 1587.

[23] Mary Musgrove, or Coosaponakeesa, daughter of a Muscogee woman and an Indian trader of English descent, obtained a grant for St. Catherines Island from the Spanish crown in 1759.

During the Civil War, the island was granted to the Freedmen's Bureau by Sherman's Special Field Orders No.

On the island, the agent Tunis Campbell, dubbed "the most feared man in Georgia",[25] established a government with schools.

In the autumn of 1865, after the United States Congress repealed Sherman's Orders, African-American Union soldiers were sent to evict Campbell from his island, as he would not fire upon other blacks.

Subsequently, Jacob Waldburg, following his pardon issued by President Andrew Johnson on 29 August, 1865, reclaimed the island and plantation he owned prior to the civil war.

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