Sinkhole risk in Washington County, PA: Pockets of it

Pockets of it

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

On soluble rock: 31%
At or near the surface: 31%
Buried under cover: 0%

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 269 of Washington County's 857 square miles on soluble rock, 269 of them with the rock at or near the surface. With about 210,434 residents (246 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 264 map points about 1.8 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 Washington County

The nearest county rated sinkhole country is Winchester city, VA, about 131 miles southeast. 4 of the 6 closest counties land in the same band, so this is a regional pattern rather than a local quirk.

Brooke County, WV 18 mi west · 38% at surface
Ohio County, WV 21 mi west · 22% at surface
Allegheny County, PA 23 mi northeast · 28% at surface
Greene County, PA 24 mi south · 8% at surface
Hancock County, WV 28 mi northwest · 2% at surface
Jefferson County, OH 30 mi northwest · 31% at surface

Which formation it is

The largest mapped soluble unit here is the Monongahela Group (limestone), Pennsylvanian in age, covering about 31% of the county.

The county also lies over the Michigan Basin; Ohio Basin; Appalachian 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 Pennsylvania

Washington County ranks 18 of 67 in Pennsylvania for soluble rock at the surface, and sits above 80% of US counties on that measure.