Fort Drum is located at . In the Pliocene and Pleistocene it was underlain by the now-smaller Lake Okeechobee. Vast limestone deposits containing the remains of large bivalve molluscs developed calcite crystallization while still under water. The gemlike crystals were discovered after the hard limestone deposits came to be excavated for aggregate. In 2008 the quarry known as Ruck's Pit was closed and allowed to flood.