Sinkhole risk in Franklin County, TN: Sinkhole country

Sinkhole country

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

On soluble rock: 66%
At or near the surface: 66%
Buried under cover: 0%

What to do about a house in Franklin County

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

That works out to roughly 368 of Franklin County's 555 square miles on soluble rock, 368 of them with the rock at or near the surface. With about 45,137 residents (81 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 353 map points about 1.3 miles apart, so a pocket smaller than that can be missed or overstated.

Two things to read before deciding: the signs to look for and how an inspection works, and how these percentages are measured.

Counties around Franklin County

The closest county with no soluble rock mapped is Cullman County, AL, about 83 miles southwest. 4 of the 6 closest counties land in the same band, so this is a regional pattern rather than a local quirk.

Moore County, TN 17 mi northwest · 65% at surface
Coffee County, TN 23 mi north · 74% at surface
Marion County, TN 27 mi east · 39% at surface
Grundy County, TN 27 mi northeast · 21% at surface
Jackson County, AL 28 mi south · 60% at surface
Lincoln County, TN 28 mi west · 62% at surface

What Franklin County is built on

The largest mapped soluble unit here is the St. Louis Limestone and Warsaw Limestone (limestone), Mississippian in age, covering about 44% of the county. Next is the Monteagle Limestone at 12%.

Against the rest of Tennessee

Franklin County ranks 35 of 95 in Tennessee for soluble rock at the surface, and sits above 92% of US counties on that measure.