Sinkhole risk in Venango 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: 9%
At or near the surface: 5%
Buried under cover: 5%

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 62 of Venango County's 674 square miles on soluble rock, 31 of them with the rock at or near the surface. With about 49,476 residents (73 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 325 map points about 1.4 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 Venango County

The nearest county rated sinkhole country is Union County, PA, about 144 miles east. 1 of the 6 closest counties land in the same band; the ground changes quickly around here.

Clarion County, PA 23 mi southeast · 36% at surface
Mercer County, PA 26 mi west · 0% at surface
Crawford County, PA 27 mi northwest · 0% at surface
Forest County, PA 28 mi east · 0% at surface
Butler County, PA 35 mi south · 35% at surface
Warren County, PA 38 mi northeast · 0% at surface

Which formation it is

The largest mapped soluble unit here is the Allegheny Formation (sandstone), Pennsylvanian in age, covering about 9% 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

Venango County ranks 40 of 67 in Pennsylvania for soluble rock at the surface, and sits above 62% of US counties on that measure.