Sinkhole risk in Madison County, NC: Mostly deep or small

Mostly deep or small

Some soluble rock, mostly deeply buried or in a small share of the county.

On soluble rock: 3%
At or near the surface: 3%
Buried under cover: 0%

What this means before you buy

Sinkholes are uncommon here; watch for new depressions after heavy rain or leaking pipes.

That works out to roughly 15 of Madison County's 450 square miles on soluble rock, 15 of them with the rock at or near the surface. With about 22,352 residents (50 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 549 map points about 0.9 miles apart, so a pocket smaller than that can be missed or overstated.

Two things to read before deciding: how these percentages are measured, and the warning signs that apply anywhere.

Counties around Madison County

The nearest county rated sinkhole country is Cocke County, TN, about 23 miles west, 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.

Buncombe County, NC 20 mi southeast · 3% at surface
Yancey County, NC 23 mi east · 0% at surface
Cocke County, TN 23 mi west · 50% at surface
Greene County, TN 23 mi north · 88% at surface
Unicoi County, TN 23 mi northeast · 11% at surface
Haywood County, NC 26 mi southwest · under 1% at surface

The rock underneath

The largest mapped soluble unit here is the Ocoee Supergroup, Walden Creek Group; Sandsuck Formation (slate), Late Proterozoic in age, covering about 2% of the county. Next is the Ocoee Supergroup, Snowbird Group; Pigeon Siltstone at under 1%.

Against the rest of North Carolina

Madison County ranks 52 of 100 in North Carolina for soluble rock at the surface, and sits above 60% of US counties on that measure.