This unique state park in South Carolina is one of the best examples of a large Carolina bay, a mysterious geological oddity found along the Atlantic seaboard. Carolina bays are egg-shaped depressions in the earth filled with shallow freshwater, and to this day their origin is unknown.

There are thousands of these elliptical wetlands scattered across the coastal plains of the Mid-Atlantic. Curiously, they are all oriented in a northwest-southeast direction; looking at an aerial view of the area, it’s truly a bizarre sight. But aside from mystifying geologists, these natural formations also offer a unique habitat for a wonderfully diverse range of wildlife, including rare and endangered plants and animals.

In Olanta, one of the best remaining examples of a large Carolina bay can be found. The natural formation has been preserved as Woods Bay State Park, which stretches 1,590 acres across the coastal plain. More than 200 species of animals (including over 150 bird species) live in the cypress-tupelo swamp, oak-hickory forest, and shrub bog habitats in the park. Visitors can walk the boardwalk or take a canoe through the dark, shallow waters of the Carolina bay. It’s a unique way to experience this enigmatic natural wonder.

Carolina bays vary in depth and range drastically in size, from under an acre to thousands of acres. They number in the thousands, though much fewer remain intact. Interestingly, Carolina bays aren’t technically bays at all. The isolated depressions in the earth fill with freshwater from rain and groundwater, making them more like shallow lakes.

There have been many theories over the years about the origins of these formations. At one point people thought they may have been caused by meteors hitting the Earth, but that is no longer considered likely. Scientists have suggested they were caused by sinkholes, or strong currents following coastal wind patterns, or groundwater springs carrying materials to the surface that dissolved and left behind these peculiar coastal pockmarks.