The fossils came first and the industry followed. Pleistocene and Miocene material turning up across the Peace River country is what eventually led people to the phosphate underneath it, and most of the river's northern watershed is the ground now called Bone Valley.
The USGS files it as the Land Pebble Phosphate District, and the list of what is in it explains why the name stuck to the fossils rather than the rock. Phosphate is the primary commodity, with fluorine second and uranium, zirconium and titanium behind it. The host rock is phosphorite, in two units: the Hawthorn Formation and the Bone Valley Formation itself. The deposit model the USGS assigns is a mouthful worth knowing, phosphate of the warm current type, and the structural setting is a basin on the flank of a rising dome.
How it formed explains the bone. In the Miocene, phosphate, phosphorite debris and dead marine organisms settled here together. That material was reworked almost as fast as it was laid down, then redeposited with carbonate to build the Hawthorn Formation, and in the late Miocene rivers cut into the whole thing and shuffled it again. Every stage of that mixed skeletal material through the sediment, which is why a phosphate pit is also a fossil bed.
The district is not one mine but dozens, spread across Polk, Hardee, Hillsborough, Manatee and DeSoto counties. The USGS lists the included workings by name, among them Noralyn, Fort Green, Payne Creek, Hooker's Prairie, Kingsford, Saddle Creek and Four Corners, which reads less like a mining district than a gazetteer of central Florida.
Fossils, phosphate
Other places on the map within a couple of hours.
