Sinkhole risk in Calhoun County, AL: Sinkhole country

Sinkhole country

Soluble rock at or near the surface across much of the county.

On soluble rock: 52%
At or near the surface: 52%
Buried under cover: 0%

What this means before you buy

Get a sinkhole or geotechnical inspection before buying, building or adding weight to a foundation.

That works out to roughly 314 of Calhoun County's 606 square miles on soluble rock, 314 of them with the rock at or near the surface. With about 116,427 residents (192 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 243 map points about 1.6 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 Calhoun County

The closest county with no soluble rock mapped is Clay County, AL, about 35 miles south. 2 of the 6 closest counties land in the same band; the ground changes quickly around here.

Cleburne County, AL 19 mi east · 2% at surface
Etowah County, AL 23 mi northwest · 46% at surface
Cherokee County, AL 23 mi northeast · 57% at surface
St. Clair County, AL 28 mi west · 45% at surface
Talladega County, AL 34 mi southwest · 60% at surface
Clay County, AL 35 mi south · 0% at surface

What Calhoun County is built on

The largest mapped soluble unit here is the Knox Group undifferentiated in part (dolostone (dolomite)), Ordovician-Cambrian in age, covering about 23% of the county. Next is the Conasauga Formation at 13%.

Against the rest of Alabama

Calhoun County ranks 9 of 67 in Alabama for soluble rock at the surface, and sits above 88% of US counties on that measure.