Sometimes “solid rock” turns out to be anything but sturdy stuff.
Limestone and a couple other related sedimentary rocks are common in some parts of the country, including in Florida. The chemistry of limestone and groundwater can combine to make for sinkholes, or vertical holes in bedrock that can open up quickly.
Sinkholes are caused by the fact that groundwater, percolating downward from the land surface, is acidic. And acids eat away at limestone, dissolving it. That means over time limestone bedrock can start to resemble Swiss cheese, with caverns and holes within it. At some point...