Sinkhole risk in Johnston County, NC: Pockets of it

Pockets of it

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

On soluble rock: 38%
At or near the surface: 38%
Buried under cover: 0%

What to do about a house in Johnston County

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 Johnston County's 792 square miles on soluble rock, 303 of them with the rock at or near the surface. With about 249,794 residents (315 per square mile), homes are spread across towns and farmland, and a mapped unit may or may not reach the developed parts. The figures come from 578 map points about 1.2 miles apart, so a pocket smaller than that can be missed or overstated.

Two things to read before deciding: the signs to look for and how an inspection works, and how these percentages are measured.

Counties around Johnston County

The nearest county rated sinkhole country is Wayne County, NC, about 23 miles southeast, close enough that the same rock may run under the county line. 1 of the 6 closest counties land in the same band; the ground changes quickly around here.

Wayne County, NC 23 mi southeast · 84% at surface
Wake County, NC 25 mi northwest · 8% at surface
Wilson County, NC 28 mi northeast · 68% at surface
Harnett County, NC 30 mi west · 60% at surface
Sampson County, NC 36 mi south · 77% at surface
Nash County, NC 38 mi northeast · 16% at surface

Which formation it is

The largest mapped soluble unit here is the Middendorf Formation (sand), Cretaceous in age, covering about 13% of the county. Next is the Black Creek Formation at 13%.

Against the rest of North Carolina

Johnston County ranks 25 of 100 in North Carolina for soluble rock at the surface, and sits above 83% of US counties on that measure.