The North Sulphur River was channelised a century ago, and the river has been cutting down into Cretaceous chalk ever since, exposing a continuous fossil bed. Ladonia Fossil Park gives free public access to it. Ammonites, shark teeth, mosasaur and plesiosaur material all come out. Walk the riverbed, not the banks, go in dry weather, and be aware it floods fast.
Ammonites, shark teeth, mosasaur · Late Cretaceous, ~80 mya
Open to the public for collecting, and what you find is yours to keep. Check the posted rules before you start: they can change with the season and the landowner.
Other places on the map within a couple of hours.
