The first time I visited Washington Oaks Gardens State Park (Palm Coast, Florida), I didn’t realize that it is divided by Old A1A, the two-lane highway that follows the eastern coastline. I enjoyed the manicured garden and hiking trail, but completely missed the beach and its coquina outcropping, one of the largest in the country.
The coquina at Washington Oaks was formed somewhere between 130,000 to 100,000 years ago, during the early Pleistocene. When mullosks and snails died, their shells were broken by waves and drifted into deposits. When these deposits were exposed to air, by low tides or drying geological events, acid rain dissolved the shell, releasing calcium carbonate. The calcium carbonate then acted as a weak cement, holding one bit of debris to another.
Through the ages, ocean pressure solidified the lightly-cemented debris, creating shelves of porous rock. Thick fields of this porous rock, which we call coquina, can be found throughout Florida. In many parts of the State, sinkholes have formed when extreme rain, exceptional drying, water pumping, or construction causes cracks or shifts in the coquina plates.
As water filters through the rock’s crevices and pores, it is purified and held available underground. Coquina aquifers supply 90% of Florida’s drinking water. The porous nature of coquina also allows it to grasp and hold chemicals, including oil, gas, fertilizers, and pesticides.
While coquina is in the ocean, it is softer and white or tan in color. When exposed to the air, it hardens and becomes gray or brown as it weathers.
Early Florida settlers used coquina to construct buildings, but it is not used now because it eventually crumbles. The Castillo de San Marcos, in St. Augustine, Florida, was constructed of coquina, and it was the stone’s crumbling nature that lent protection. When cannonballs or bullets struck the fort’s walls, the stone wasn’t smashed into flying shrapnel. Instead, incoming rounds were incorporated into the wall, the stone’s porous structure folding around the impacting metal. Visit the fort, and you’ll still see holes left by cannonballs and bullets.
Before you visit the coquina outcroppings at Washington Oaks State Park, check the tides. Formations may be hidden during high tide or severe weather events. The first time I visited the beach, the tide was high and I saw none of its weather-sculpted formations.
Geology of the Coquina Rocks. Florida State Parks.
King Hobart, Coquina. Geology.com.
Scott Thomas M., A Geological Overview of Florida. Florida Geological Survey, 1992.
Florida Geology: Uniquely Beautiful. Florida State Parks.
Brown David, Florida’s Sinkholes. Foundation Professionals of Florida.
General Information. Florida Atlantic University Department of Geosciences.