The Geology of Fort Caroline National Memorial, Florida

Fort Caroline National Memorial remembers the French colonists who came to North America in the 16th century seeking religious freedom, wealth and new territory. Their colony, Fort de la Caroline, founded in 1564, was one of the earliest European settlements in the New World. It did not last long, but it opened two centuries of French and Spanish rivalry in North America.

The memorial, authorized on September 21, 1950, covers about 55 hectares (138 acres) on the St. Johns River, approximately 10 km (6 mi) upstream from the Atlantic Ocean in Duval County, Florida. It is managed together with the neighboring Timucuan Ecological and Historic Preserve.

Image from NPS’s page.

A plateau that keeps flooding

Fort Caroline, Timucuan and the whole of Florida sit on the Floridian Plateau, a section of land approximately 800 km (500 mi) long and 400–640 km (250–400 mi) wide. The plateau, millions of years old, includes both dry land and submerged continental shelf. Many times over, parts of it have been covered by the sea and then exposed again, so marine and land deposits lie stacked one on top of another.

The plateau belongs to the Coastal Plain physiographic province, so the memorial shares its geologic history and some of its rock formations with a region stretching far beyond the park.

What lies at the surface

The ground at Timucuan and Fort Caroline is made of young sediments:

• beach ridge and dune deposits from the Pleistocene (1.8 million to 10,000 years ago) through the Holocene (the last 10,000 years)
• undifferentiated deposits of Pleistocene to Holocene age
• Holocene sediments laid down in salt marshes, on beaches, in the sea and in lagoons

What lies beneath

To a depth of about 30 m (100 ft), the subsurface holds:

• Quaternary sands, with clay-rich and limestone layers from the Upper Miocene (11.6–5.3 million years ago) or Pliocene (5.3–1.8 million years ago)
• mixed deposits of the Hawthorn Group, from the Upper Oligocene (28.4–23.0 million years ago) to the Miocene

Studying the park’s geology and soils

Geodiversity is the full range of a park’s rocks, minerals, sediments, fossils, landforms, soils and the processes that shape them. This page draws on the NPS Geodiversity Atlas, a product of the Geologic Resources Inventory, which makes digital geologic maps and reports for more than 270 natural resource parks to support education, geoconservation and the joint management of a park’s living and non-living resources. Its products for a park can include scoping summaries, digital geologic maps for GIS, reports, and posters. An NPS Soil Resources Inventory has also been completed for Fort Caroline. Both are available through the NPS DataStore.

Sources

Based on "NPS Geodiversity Atlas—Fort Caroline National Memorial, Florida," National Park Service; a work of the United States government in the public domain. The source once calls the site “Fort Caroline National Monument”; the page uses “National Memorial,” as the rest of the source does.