Sinkhole risk in Pike County, IL: 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: 60%
At or near the surface: 12%
Buried under cover: 48%

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 495 of Pike County's 831 square miles on soluble rock, 99 of them with the rock at or near the surface. With about 14,258 residents (17 per square mile), much of the land is open, and the mapped rock may sit far from where people actually live. The figures come from 252 map points about 1.8 miles apart, so a pocket smaller than that can be missed or overstated.

Two things to read before deciding: why gypsum and salt move faster than limestone, and why the 48% under cover still counts.

Counties around Pike County

The nearest county rated sinkhole country is Calhoun County, IL, about 34 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.

Scott County, IL 22 mi east · 0% at surface
Brown County, IL 24 mi north · 0% at surface
Pike County, MO 25 mi southwest · 0% at surface
Adams County, IL 30 mi northwest · under 1% at surface
Greene County, IL 33 mi southeast · 0% at surface
Calhoun County, IL 34 mi south · 51% at surface

The rock underneath

The largest mapped soluble unit here is the Lower Valmeyeran (Keokuk-Sedalia) Series (limestone), Mississippian in age, covering about 46% of the county. Next is the Kinderhookian Series at 8%.

The county also lies over the Illinois 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 Illinois

Pike County ranks 8 of 102 in Illinois for soluble rock at the surface, and sits above 69% of US counties on that measure.