Look what I just did in Florida
So, how did Florida end up with countless fossils??
Let's start in the Cretaceous around 50 million years ago, when high sea levels caused Florida to be submerged. Florida stayed submerged for many millions of years. During this time at the bottom of the ocean, layers of limestone accumulated on the sea floor, creating the "bed rock" of Florida.
Starting in the Oligocene, about 30 million years ago, the global climate cooled and sea levels began to drop. An island of limestone emerged in north central Florida called Orange Island. This was the first appearance of today's Florida. Rains eroded the porous limestone, creating the cave systems and sink holes common to Florida.
Peace River Formation
Jumping ahead to 20 million years ago, into the next Epoch, the Miocene, sediments coming from the Appalachian mountains further north accumulated around Florida and built up the Orange Island. Although the sea levels were in constant flux during the Miocene, Florida started to get its modern appearance. During this time land animals roamed central Florida, while a very shallow sea covered the coastal areas. At this time nutrient rich deposits washing from the Appalachian mountains created heavy sediment laden and nutrient rich waters. These sediments sank to the bottom entombing dead marine animals, countless teeth from sharks (including the Megalodon Sharks), and also land animals when the sea levels would rise. This trend continued until the Early Pliocene, about 5 million years ago. Today the sediments form the phosphate rich formations, including the Peace River Formation. This formation is mostly underground, but rivers, such as the Peace River, expose this formation. Also just off the beach near Venice, this formation is exposed.
Ice Age Fossils
Besides for the Peace River fossils, there are also fossils from the Pleistocene. During the Pleistocene, from 2.5 million until about 11,000 years ago the Earth was (and still is) in constant glaciations events. During glacial periods, the sea levels would drop, and Florida's land would double in size. Ice Age animals lived here including Mammoths, Dire Wolves, Glyptodonts, Horses, and Giant Ground Sloths. During interglacial periods, the sea levels would rise, covering much of Florida. Sediments would bury and preserve the remains of these Ice Age animals. Today, these fossils erode out of the layers of Pleistocene sands and gravels and wash into rivers.
These Ice Age sand and gravel layers make Florida one of the richest places on Earth to find vertebrate fossils!