Sinkhole risk in Franklin 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: 44%
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 340 of Franklin County's 772 square miles on soluble rock, 340 of them with the rock at or near the surface. With about 159,285 residents (206 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 598 map points about 1.1 miles apart, so a pocket smaller than that can be missed or overstated.

Counties around Franklin County

The nearest county rated sinkhole country is Washington County, MD, about 23 miles south, close enough that the same rock may run under the county line. 3 of the 6 closest counties land in the same band; the ground changes quickly around here.

Fulton County, PA 21 mi west · 19% at surface
Washington County, MD 23 mi south · 61% at surface
Adams County, PA 27 mi east · 6% at surface
Cumberland County, PA 29 mi northeast · 48% at surface
Frederick County, MD 36 mi southeast · 13% at surface
Huntingdon County, PA 37 mi north · 35% at surface

The rock underneath

The largest mapped soluble unit here is the Rockdale Run Formation (limestone), Ordovician in age, covering about 8% of the county. Next is the Elbrook Formation at 7%.

Against the rest of Pennsylvania

Franklin County ranks 6 of 67 in Pennsylvania for soluble rock at the surface, and sits above 85% of US counties on that measure.