Sinkhole risk in Decatur County, GA: Sinkhole country

Sinkhole country

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

On soluble rock: 99%
At or near the surface: 55%
Buried under cover: 44%

What this means before you buy

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

That works out to roughly 589 of Decatur County's 597 square miles on soluble rock, 328 of them with the rock at or near the surface. With about 29,391 residents (49 per square mile), there is effectively nowhere in the county off the soluble rock, town or country. The figures come from 315 map points about 1.4 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 44% under cover still counts.

Counties around Decatur County

The closest county with no soluble rock mapped is Randolph County, GA, about 62 miles north. 4 of the 6 closest counties land in the same band, so this is a regional pattern rather than a local quirk.

Seminole County, GA 17 mi west · 86% at surface
Grady County, GA 20 mi east · 29% at surface
Gadsden County, FL 21 mi south · 33% at surface
Miller County, GA 21 mi northwest · 100% at surface
Baker County, GA 31 mi north · 93% at surface
Mitchell County, GA 33 mi northeast · 66% at surface

Which formation it is

The largest mapped soluble unit here is the Ocala Limestone (limestone), Eocene in age, covering about 46% of the county. Next is the "Hawthorn Formation" at 37%.

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

Decatur County ranks 20 of 159 in Georgia for soluble rock at the surface, and sits above 89% of US counties on that measure.