Sinkhole risk in Putnam County, TN: Sinkhole country

Sinkhole country

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

On soluble rock: 60%
At or near the surface: 60%
Buried under cover: 0%

What to do about a house in Putnam County

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

That works out to roughly 240 of Putnam County's 401 square miles on soluble rock, 240 of them with the rock at or near the surface. With about 84,894 residents (212 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 478 map points about 0.9 miles apart, so a pocket smaller than that can be missed or overstated.

Counties around Putnam County

The closest county with no soluble rock mapped is Morgan County, TN, about 48 miles east. 5 of the 6 closest counties land in the same band, so this is a regional pattern rather than a local quirk.

White County, TN 15 mi south · 74% at surface
Jackson County, TN 18 mi northwest · 58% at surface
Overton County, TN 18 mi northeast · 66% at surface
DeKalb County, TN 22 mi southwest · 61% at surface
Smith County, TN 26 mi west · 87% at surface
Clay County, TN 28 mi north · 39% at surface

The rock underneath

The largest mapped soluble unit here is the St. Louis Limestone and Warsaw Limestone (limestone), Mississippian in age, covering about 32% of the county. Next is the Ordovician [units] including Richmond Group (which includes Mannie Shale, Fernvale Limestone, Sequatchie Formation, and Arnheim Formation), the Maysville Group (which includes Leipers Formation), the Eden Group (which includes Inman Formation), and at 10%.

Against the rest of Tennessee

Putnam County ranks 43 of 95 in Tennessee for soluble rock at the surface, and sits above 90% of US counties on that measure.