Sinkhole risk in Washington County, AR: Pockets of it

Pockets of it

Soluble rock at the surface or under thin cover in part of the county.

On soluble rock: 29%
At or near the surface: 29%
Buried under cover: 0%

What to do about a house in Washington County

Check the parcel against your state survey sinkhole map, and ask for an inspection if cracks, depressions or sticking doors show up.

That works out to roughly 277 of Washington County's 941 square miles on soluble rock, 277 of them with the rock at or near the surface. With about 266,184 residents (283 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 299 map points about 1.8 miles apart, so a pocket smaller than that can be missed or overstated.

Counties around Washington County

The nearest county rated sinkhole country is Adair County, OK, about 25 miles west, close enough that the same rock may run under the county line. 1 of the 6 closest counties land in the same band; the ground changes quickly around here.

Adair County, OK 25 mi west · 79% at surface
Benton County, AR 25 mi north · 93% at surface
Crawford County, AR 27 mi south · 0% at surface
Madison County, AR 28 mi east · 27% at surface
Franklin County, AR 37 mi southeast · 0% at surface
Delaware County, OK 44 mi northwest · 94% at surface

What Washington County is built on

The largest mapped soluble unit here is the Boone Formation (limestone), Early Mississippian- Meramecian to Osagean in age, covering about 29% of the county. Next is the Chattanooga Shale (Lower Mississippian and Upper Devonian), Clifty Limestone (Middle Devonian), and Penters Chert (Lower Devonian) at under 1%.

Against the rest of Arkansas

Washington County ranks 17 of 75 in Arkansas for soluble rock at the surface, and sits above 79% of US counties on that measure.