The geologic history of Longhorn Cavern is complex, and the theories do not all agree. It is believed that the limestone was deposited roughly 450–500 million years ago on the floor of a shallow tropical sea that covered most of Central Texas. Another 150 million years passed before the cavern itself began forming. Between 280 and 300 million years ago, mountain-building forces shifted under Central Texas in an event called the “Llano Uplift.” During this upheaval, faults and fractures formed in the flat-lying limestone. Water began flowing through the cracks, dissolving the limestone. This downward drainage continued until great underground streambeds were cut out of solid rock. It is this unusual combination of dissolving and cutting by water that makes Longhorn Cavern one of the most unique caves of the world.