SinkholeOdds

Sinkhole risk in Collier 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
89%
Buried under cover
7%

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 1,919 of Collier County's 1,997 square miles on soluble rock, 1,781 of them with the rock at or near the surface. With about 416,233 residents (208 per square mile), there is effectively nowhere in the county off the soluble rock, town or country. The figures come from 279 map points about 2.7 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 Collier County

The closest county with no soluble rock mapped is Gulf County, FL, about 350 miles northwest. 5 of the 6 closest counties land in the same band, so this is a regional pattern rather than a local quirk.

What Collier County is built on

The largest mapped soluble unit here is the Tamiami Formation (sand), Pliocene in age, covering about 61% of the county. Next is the Shelly sediments of Plio-Pleistocene age at 22%.

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

Collier County ranks 5 of 67 in Florida for soluble rock at the surface, and sits above 97% of US counties on that measure.