Sinkhole risk in Johnston County, OK: Pockets of it

Pockets of it

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

On soluble rock: 33%
At or near the surface: 33%
Buried under cover: 0%

What this means before you buy

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 213 of Johnston County's 643 square miles on soluble rock, 213 of them with the rock at or near the surface. With about 10,293 residents (16 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 325 map points about 1.4 miles apart, so a pocket smaller than that can be missed or overstated.

Counties around Johnston County

The nearest county rated sinkhole country is Grady County, OK, about 85 miles northwest. 4 of the 6 closest counties land in the same band, so this is a regional pattern rather than a local quirk.

Marshall County, OK 21 mi south · 35% at surface
Murray County, OK 27 mi northwest · 49% at surface
Coal County, OK 28 mi northeast · 4% at surface
Pontotoc County, OK 28 mi north · 28% at surface
Bryan County, OK 33 mi southeast · 18% at surface
Atoka County, OK 36 mi east · 5% at surface

What Johnston County is built on

The largest mapped soluble unit here is the West Spring Creek Formation (limestone), Early Ordovician in age, covering about 6% of the county. Next is the Cool Creek and McKenzie Hill Formations at 6%.

Against the rest of Oklahoma

Johnston County ranks 25 of 77 in Oklahoma for soluble rock at the surface, and sits above 81% of US counties on that measure.