Sinkhole risk in Dallas 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: 27%
At or near the surface: 27%
Buried under cover: 0%

What to do about a house in Dallas 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 260 of Dallas County's 979 square miles on soluble rock, 260 of them with the rock at or near the surface. With about 35,545 residents (36 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 567 map points about 1.3 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 Dallas County

The nearest county rated sinkhole country is Talladega County, AL, about 90 miles northeast. 5 of the 6 closest counties land in the same band, so this is a regional pattern rather than a local quirk.

Perry County, AL 24 mi northwest · 29% at surface
Wilcox County, AL 26 mi southwest · 27% at surface
Lowndes County, AL 30 mi southeast · 49% at surface
Autauga County, AL 31 mi northeast · 2% at surface
Marengo County, AL 40 mi west · 33% at surface
Hale County, AL 41 mi northwest · 20% at surface

Which formation it is

The largest mapped soluble unit here is the Selma Group; Demopolis Chalk (carbonate), Cretaceous in age, covering about 15% of the county. Next is the Selma Group; Mooreville Chalk at 9%.

Against the rest of Alabama

Dallas County ranks 27 of 67 in Alabama for soluble rock at the surface, and sits above 78% of US counties on that measure.