Sinkhole risk in Johnson 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: 0%
Buried under cover: 100%

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 303 of Johnson County's 303 square miles on soluble rock. With about 9,178 residents (30 per square mile), there is effectively nowhere in the county off the soluble rock, town or country. The figures come from 484 map points about 0.8 miles apart, so a pocket smaller than that can be missed or overstated.

Worth reading for this county: why the 100% under cover still counts, and the signs to look for and how an inspection works.

Counties around Johnson County

The nearest county rated sinkhole country is Pulaski County, GA, about 57 miles southwest. 6 of the 6 closest counties land in the same band, so this is a regional pattern rather than a local quirk.

Treutlen County, GA 20 mi south · 0% at surface
Washington County, GA 21 mi north · 10% at surface
Emanuel County, GA 22 mi east · 2% at surface
Laurens County, GA 26 mi southwest · 8% at surface
Jefferson County, GA 29 mi northeast · 8% at surface
Wilkinson County, GA 31 mi west · 44% at surface

Which formation it is

The largest mapped soluble unit here is the Cooper Marl (clay or mud), Eocene in age, covering about 73% of the county. Next is the Suwannee Limestone and its residuum at 23%.

Against the rest of Georgia

Johnson County ranks 116 of 159 in Georgia for soluble rock at the surface, and sits above 0% of US counties on that measure.