Geologically, Windley Key, like the rest of the Florida Keys, dates back to the formation of the southern end of the Appalachian Mountains. More recently, coral reefs were formed during the Sangamon interglacial period, about 100,000 years ago, when the sea level was some 300 feet lower than it is today. The climate pendulum swung to warmer climate and seas begin to rise. In geological time the sea levels are constantly changing. Formed of Key Largo limestone, fossilized coral, this land was sold to the Florida East Coast Railroad, which used the stone to build Henry Flagler's Overseas Railroad in the early 1900s. After the railroad was built, the quarry was used until the 1960s to produce exquisite pieces of decorative stone called Keystone. Today, visitors can walk along eight-foot-high quarry walls to see cross sections of the ancient coral and learn about the quarry and its operation- an important part of Florida's 20th century history. Samples of the quarry machinery have been preserved at the park. Visitors can enjoy the natural attributes of this island while strolling five, short, self-guided trails.