Sinkhole risk in Grayson County, KY: Sinkhole country

Sinkhole country

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

On soluble rock: 60%
At or near the surface: 60%
Buried under cover: 0%

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 297 of Grayson County's 500 square miles on soluble rock, 297 of them with the rock at or near the surface. With about 27,070 residents (54 per square mile), much of the land is open, and the mapped rock may sit far from where people actually live. The figures come from 274 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 the signs to look for and how an inspection works.

Counties around Grayson County

The closest county with no soluble rock mapped is Daviess County, KY, about 45 miles northwest. 4 of the 6 closest counties land in the same band, so this is a regional pattern rather than a local quirk.

Edmonson County, KY 17 mi southeast · 50% at surface
Breckinridge County, KY 23 mi north · 89% at surface
Butler County, KY 25 mi southwest · 20% at surface
Hardin County, KY 27 mi northeast · 89% at surface
Ohio County, KY 27 mi west · 4% at surface
Hart County, KY 28 mi east · 89% at surface

Which formation it is

The largest mapped soluble unit here is the Rocks of Chesterian age, lower part (limestone), Upper Mississippian in age, covering about 39% of the county. Next is the Rocks of Chesterian age, upper part at 20%.

The county also lies over the Illinois Basin, 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 Kentucky

Grayson County ranks 27 of 120 in Kentucky for soluble rock at the surface, and sits above 90% of US counties on that measure.