Sinkhole risk in Columbia 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: 14%
At or near the surface: 4%
Buried under cover: 10%

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 66 of Columbia County's 483 square miles on soluble rock, 20 of them with the rock at or near the surface. With about 66,012 residents (137 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 242 map points about 1.4 miles apart, so a pocket smaller than that can be missed or overstated.

Two things to read before deciding: why the 10% under cover still counts, and how these percentages are measured.

Counties around Columbia County

The nearest county rated sinkhole country is Union County, PA, about 34 miles west, 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.

Montour County, PA 14 mi west · 40% at surface
Northumberland County, PA 21 mi southwest · 26% at surface
Luzerne County, PA 24 mi east · 0% at surface
Schuylkill County, PA 26 mi south · 2% at surface
Sullivan County, PA 28 mi north · 0% at surface
Union County, PA 34 mi west · 53% at surface

The rock underneath

The largest mapped soluble unit here is the Hamilton Group (shale), Devonian in age, covering about 10% of the county. Next is the Bloomsburg and Mifflintown Formations, undivided at 3%.

Against the rest of Pennsylvania

Columbia County ranks 41 of 67 in Pennsylvania for soluble rock at the surface, and sits above 62% of US counties on that measure.