In the midst of North Florida's sandy terrain and pine forests, a bowl-shaped cavity 120 feet deep leads down to a miniature rain forest. Devil’s Millhopper is a large, deep, cover-collapse sinkhole. It's called a millhopper because of the hole's shape, which is the same funnel-like shape you would find at the bottom of a grain hopper on a farm.Sinkholes form when limestone is slowly dissolved by acidic groundwater over geologic time. This process of dissolution can create large cavities in limestone. Although sinkholes are common in Florida, Devil’s Millhopper is unique because it is one of the few places in Florida where more than 100 feet of rock layers are exposed. The park is also unique because it is an important and beautiful example of how ecosystems (flora and fauna) develop in response to geological features.
The rocks exposed in the walls of Devil’s Millhopper are older the farther you go. This National Natural Landmark has attracted curious visitors since the 1880s. A thin layer of soil and quartz sand occurs at the top of the sinkhole, overlying the rocks and sediments of the Hawthorn Group. The outcrop of this geological unit in Devil’s Millhopper is composed of dolostone, phosphatic sands and clay that were deposited during the Miocene Epoch between 5.3 and 23 million years ago.
Fossils are commonly seen in the walls and small creeks that flow into the sink. Shark teeth and fossil remains of marine organisms found at Devil’s Millhopper help geologists understand how these geologic units were formed and how old they
The clay-rich layers serve an important role in the protection of groundwater quality in the underlying aquifer, which is a source of drinking water for millions of Floridians. Small streams trickle down the steep slopes of the limestone sinkhole, disappearing through crevices in the ground. Lush vegetation thrives in the shade of the walls even in dry summers.