Sinkhole risk in Blair 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: 36%
At or near the surface: 36%
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 187 of Blair County's 525 square miles on soluble rock, 187 of them with the rock at or near the surface. With about 120,269 residents (229 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 596 map points about 0.9 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 Blair County

The nearest county rated sinkhole country is Washington County, MD, about 67 miles southeast. 4 of the 6 closest counties land in the same band, so this is a regional pattern rather than a local quirk.

Huntingdon County, PA 19 mi east · 35% at surface
Cambria County, PA 21 mi west · 2% at surface
Mifflin County, PA 35 mi east · 45% at surface
Bedford County, PA 36 mi south · 26% at surface
Clearfield County, PA 36 mi north · under 1% at surface
Centre County, PA 37 mi northeast · 40% at surface

The rock underneath

The largest mapped soluble unit here is the Bellefonte and Axemann Formations, undivided (dolostone (dolomite)), Ordovician in age, covering about 7% of the county. Next is the Nittany and Stonehenge/Larke Formations, undivided at 6%.

Against the rest of Pennsylvania

Blair County ranks 11 of 67 in Pennsylvania for soluble rock at the surface, and sits above 82% of US counties on that measure.