Sinkhole risk in Martin County, IN: Pockets of it

Pockets of it

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

On soluble rock: 30%
At or near the surface: 23%
Buried under cover: 7%

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 101 of Martin County's 336 square miles on soluble rock, 77 of them with the rock at or near the surface. With about 9,864 residents (29 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 363 map points about 1.0 miles apart, so a pocket smaller than that can be missed or overstated.

Counties around Martin County

The nearest county rated sinkhole country is Lawrence County, IN, about 19 miles northeast, 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.

Daviess County, IN 15 mi west · 0% at surface
Lawrence County, IN 19 mi northeast · 71% at surface
Orange County, IN 20 mi southeast · 90% at surface
Dubois County, IN 23 mi south · 5% at surface
Greene County, IN 26 mi northwest · 20% at surface
Pike County, IN 32 mi southwest · 0% at surface

Which formation it is

The largest mapped soluble unit here is the Stephensport Group (sandstone), Mississippian in age, covering about 20% of the county. Next is the West Baden Group at 7%.

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 Indiana

Martin County ranks 9 of 92 in Indiana for soluble rock at the surface, and sits above 76% of US counties on that measure.