SinkholeOdds

Sinkhole risk in Putnam County, FL: Pockets of it

Pockets of it

Soluble rock at the surface or under thin cover in part of the county.

On soluble rock
92%
At or near the surface
7%
Buried under cover
85%

The next step for one property

Check the parcel against your state survey sinkhole map, and ask for an inspection if cracks, depressions or sticking doors show up.

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 668 of Putnam County's 728 square miles on soluble rock, 49 of them with the rock at or near the surface. With about 77,301 residents (106 per square mile), there is effectively nowhere in the county off the soluble rock, town or country. The figures come from 254 map points about 1.7 miles apart, so a pocket smaller than that can be missed or overstated.

Worth reading for this county: what Florida insurers have to cover, and why gypsum and salt move faster than limestone.

Counties around Putnam County

The nearest county rated sinkhole country is Clay County, FL, about 28 miles north, close enough that the same rock may run under the county line. 4 of the 6 closest counties land in the same band, so this is a regional pattern rather than a local quirk.

The rock underneath

The largest mapped soluble unit here is the Hawthorn Group, Coosawhatchie Formation (limestone), Eocene in age, covering about 62% of the county. Next is the Shelly sediments of Plio-Pleistocene age at 20%.

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

Putnam County ranks 57 of 67 in Florida for soluble rock at the surface, and sits above 65% of US counties on that measure.