Sinkhole risk in Alachua County, FL: Sinkhole country

Sinkhole country

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

On soluble rock: 100%
At or near the surface: 78%
Buried under cover: 22%

The next step for one property

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 876 of Alachua County's 876 square miles on soluble rock, 680 of them with the rock at or near the surface. With about 291,782 residents (333 per square mile), there is effectively nowhere in the county off the soluble rock, town or country. The figures come from 291 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 Alachua County

The closest county with no soluble rock mapped is Gulf County, FL, about 175 miles west. 3 of the 6 closest counties land in the same band; the ground changes quickly around here.

Bradford County, FL 22 mi northeast · 20% at surface
Union County, FL 26 mi north · 50% at surface
Gilchrist County, FL 27 mi west · 52% at surface
Clay County, FL 36 mi northeast · 51% at surface
Marion County, FL 38 mi southeast · 46% at surface
Putnam County, FL 38 mi east · 7% at surface

The rock underneath

The largest mapped soluble unit here is the Hawthorn Group, Coosawhatchie Formation (sand), Miocene in age, covering about 44% of the county. Next is the Ocala Limestone 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

Alachua County ranks 13 of 67 in Florida for soluble rock at the surface, and sits above 94% of US counties on that measure.