Sinkhole risk in Butler 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: 44%
At or near the surface: 35%
Buried under cover: 9%

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 347 of Butler County's 789 square miles on soluble rock, 276 of them with the rock at or near the surface. With about 199,341 residents (252 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 367 map points about 1.5 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 why the 9% under cover still counts.

Counties around Butler County

The nearest county rated sinkhole country is Washington County, MD, about 143 miles southeast. 3 of the 6 closest counties land in the same band; the ground changes quickly around here.

Lawrence County, PA 22 mi west · 6% at surface
Armstrong County, PA 25 mi east · 37% at surface
Beaver County, PA 28 mi southwest · 9% at surface
Allegheny County, PA 31 mi south · 28% at surface
Mercer County, PA 32 mi northwest · 0% at surface
Clarion County, PA 33 mi northeast · 36% at surface

What Butler County is built on

The largest mapped soluble unit here is the Allegheny Formation (sandstone), Pennsylvanian in age, covering about 44% 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

Butler County ranks 14 of 67 in Pennsylvania for soluble rock at the surface, and sits above 82% of US counties on that measure.