SinkholeOdds

Sinkhole risk in Clay County, FL: Sinkhole country

Sinkhole country

Soluble rock at or near the surface across much of the county.

On soluble rock
96%
At or near the surface
51%
Buried under cover
45%

What this means before you buy

Get a sinkhole or geotechnical inspection before buying, building or adding weight to a foundation.

Standard Florida homeowners policies cover only catastrophic ground cover collapse; full sinkhole coverage is a separately priced option insurers must offer.

That works out to roughly 577 of Clay County's 605 square miles on soluble rock, 308 of them with the rock at or near the surface. With about 236,760 residents (392 per square mile), there is effectively nowhere in the county off the soluble rock, town or country. The figures come from 287 map points about 1.5 miles apart, so a pocket smaller than that can be missed or overstated.

Two things to read before deciding: what Florida insurers have to cover, and why gypsum and salt move faster than limestone.

Counties around Clay County

The closest county with no soluble rock mapped is Gulf County, FL, about 204 miles west. 1 of the 6 closest counties land in the same band; the ground changes quickly around here.

Which formation it is

The largest mapped soluble unit here is the Hawthorn Group, Coosawhatchie Formation, Charlton Member (dolostone (dolomite)), Miocene/Pliocene in age, covering about 51% of the county. Next is the Hawthorn Group, Coosawhatchie Formation at 41%.

The county also lies over the Floridan shelf, a deep salt or gypsum basin. Deep beds rarely cause surface collapse on their own, but wells and mining into them have.

Against the rest of Florida

Clay County ranks 25 of 67 in Florida for soluble rock at the surface, and sits above 88% of US counties on that measure.