Sinkhole risk in Grady County, GA: Pockets of it

Pockets of it

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

On soluble rock: 100%
At or near the surface: 29%
Buried under cover: 71%

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.

That works out to roughly 454 of Grady County's 454 square miles on soluble rock, 130 of them with the rock at or near the surface. With about 26,271 residents (58 per square mile), there is effectively nowhere in the county off the soluble rock, town or country. The figures come from 371 map points about 1.1 miles apart, so a pocket smaller than that can be missed or overstated.

Worth reading for this county: why gypsum and salt move faster than limestone, and why the 71% under cover still counts.

Counties around Grady County

The nearest county rated sinkhole country is Decatur County, GA, about 20 miles west, close enough that the same rock may run under the county line. 3 of the 6 closest counties land in the same band; the ground changes quickly around here.

Thomas County, GA 19 mi east · 34% at surface
Decatur County, GA 20 mi west · 55% at surface
Mitchell County, GA 25 mi north · 66% at surface
Leon County, FL 29 mi south · 43% at surface
Gadsden County, FL 30 mi southwest · 33% at surface
Baker County, GA 33 mi north · 93% at surface

Which formation it is

The largest mapped soluble unit here is the "Hawthorn Formation" (sand), Miocene in age, covering about 71% of the county. Next is the "Hawthorn Formation" 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 Georgia

Grady County ranks 32 of 159 in Georgia for soluble rock at the surface, and sits above 79% of US counties on that measure.