Sinkhole risk in Somerset County, PA: Mostly deep or small

Mostly deep or small

Some soluble rock, mostly deeply buried or in a small share of the county.

On soluble rock: 5%
At or near the surface: 5%
Buried under cover: 0%

What this means before you buy

Sinkholes are uncommon here; watch for new depressions after heavy rain or leaking pipes.

That works out to roughly 55 of Somerset County's 1,075 square miles on soluble rock, 55 of them with the rock at or near the surface. With about 72,134 residents (67 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 272 map points about 2.0 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 how these percentages are measured.

Counties around Somerset County

The nearest county rated sinkhole country is Washington County, MD, about 70 miles east. 2 of the 6 closest counties land in the same band; the ground changes quickly around here.

Bedford County, PA 28 mi east · 26% at surface
Allegany County, MD 31 mi southeast · 24% at surface
Westmoreland County, PA 32 mi northwest · 26% at surface
Fayette County, PA 33 mi west · 23% at surface
Garrett County, MD 33 mi southwest · 8% at surface
Mineral County, WV 40 mi south · 12% at surface

Which formation it is

The largest mapped soluble unit here is the Mauch Chunk Formation (shale), Mississippian in age, covering about 4% of the county. Next is the Monongahela Group at 1%.

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

Somerset County ranks 38 of 67 in Pennsylvania for soluble rock at the surface, and sits above 63% of US counties on that measure.