Sinkhole risk in Benton County, AR: Sinkhole country

Sinkhole country

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

On soluble rock: 93%
At or near the surface: 93%
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 791 of Benton County's 848 square miles on soluble rock, 791 of them with the rock at or near the surface. With about 321,566 residents (379 per square mile), there is effectively nowhere in the county off the soluble rock, town or country. The figures come from 285 map points about 1.7 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 Benton County

The closest county with no soluble rock mapped is Crawford County, AR, about 52 miles south. 4 of the 6 closest counties land in the same band, so this is a regional pattern rather than a local quirk.

McDonald County, MO 21 mi north · 100% at surface
Washington County, AR 25 mi south · 29% at surface
Delaware County, OK 31 mi west · 94% at surface
Barry County, MO 34 mi northeast · 99% at surface
Madison County, AR 37 mi southeast · 27% at surface
Adair County, OK 38 mi southwest · 79% at surface

Which formation it is

The largest mapped soluble unit here is the Boone Formation (limestone), Early Mississippian- Meramecian to Osagean in age, covering about 89% of the county. Next is the Chattanooga Shale (Lower Mississippian and Upper Devonian), Clifty Limestone (Middle Devonian), and Penters Chert (Lower Devonian) at 3%.

Against the rest of Arkansas

Benton County ranks 6 of 75 in Arkansas for soluble rock at the surface, and sits above 98% of US counties on that measure.