Sinkhole risk in Shelby County, AL: Pockets of it

Pockets of it

Soluble rock at the surface or under thin cover in part of the county.

On soluble rock: 30%
At or near the surface: 30%
Buried under cover: 0%

What to do about a house in Shelby County

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 239 of Shelby County's 785 square miles on soluble rock, 239 of them with the rock at or near the surface. With about 235,969 residents (300 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 573 map points about 1.2 miles apart, so a pocket smaller than that can be missed or overstated.

Worth reading for this county: the signs to look for and how an inspection works, and how these percentages are measured.

Counties around Shelby County

The nearest county rated sinkhole country is Talladega County, AL, about 29 miles east, close enough that the same rock may run under the county line. 2 of the 6 closest counties land in the same band; the ground changes quickly around here.

Jefferson County, AL 24 mi northwest · 21% at surface
Chilton County, AL 29 mi south · 6% at surface
Talladega County, AL 29 mi east · 60% at surface
Bibb County, AL 32 mi southwest · 12% at surface
Coosa County, AL 33 mi southeast · 3% at surface
St. Clair County, AL 37 mi northeast · 45% at surface

Which formation it is

The largest mapped soluble unit here is the Newala Limestone (limestone), Ordovician in age, covering about 9% of the county. Next is the Knox Group undifferentiated in part at 7%.

Against the rest of Alabama

Shelby County ranks 22 of 67 in Alabama for soluble rock at the surface, and sits above 79% of US counties on that measure.