The Bone Valley Formation is what geologists have dubbed the ancient fossil bed that now resides 20 to 40 feet below Central Florida. It sits atop the Hawthorne Formation, a layer of clay and sandy limestone deposited long ago when the sea covered the state and the coastline curved around the modern-day Lake Wales Ridge as much as 60 miles inland. The Bone Valley Formation is exposed in the phosphate mines of central Florida (Polk County). It is Miocene in age (10-15 million years ago).
Bone Valley Formation fossils are rare and highly-priced specimens. Due to the unique geological characteristics of the phosphate-rich region, most of the fossils are beautifully preserved with amazing detail and color. Unlike the majority of southeastern U.S. fossils retrieved from rivers and streams, Bone Valley specimens are found in dry earth and are not stained with the typical cruddy black and brown muck from rivers. Because Bone Valley fossils comprise so much variety of both ancient marine and terrestrial creatures, along with their unique and rare beauty of preservation, specimens from this locality are very rare and of great value to any fossil collection.
Fossils found in Bone Valley include many species that came to tropical and sub-tropical frost-free Florida forests to escape the advancing glaciers of the great "Ice Ages." Some of these animals migrated to North America from other parts of the world. For example, some of these animals came across the Bering Strait land bridge from Asia when sea level was lower. Others traveled around the rim of the Gulf of Mexico, when areas that are now submerged were exposed.
Of particular interest to fossil enthusiasts, are the motley colored shark teeth. It is believed that Bone Valley was originally a sort of nursery for young Megalodon sharks, as most C. megalodon teeth found in Bone Valley are less than 3 inches in length. The Bone Valley Formation also has an unusually high abundance of "Hubbel teeth", which are a sort of pathological shark teeth that are heart-shaped, often with root and cusp abnormalities.