Sinkhole risk in Marion County, AR: Sinkhole country

Sinkhole country

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

On soluble rock: 94%
At or near the surface: 94%
Buried under cover: 0%

What to do about a house in Marion County

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

That works out to roughly 562 of Marion County's 597 square miles on soluble rock, 562 of them with the rock at or near the surface. With about 17,593 residents (29 per square mile), there is effectively nowhere in the county off the soluble rock, town or country. The figures come from 325 map points about 1.4 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 Marion County

The closest county with no soluble rock mapped is Van Buren County, AR, about 48 miles south. 4 of the 6 closest counties land in the same band, so this is a regional pattern rather than a local quirk.

Baxter County, AR 19 mi east · 96% at surface
Boone County, AR 22 mi west · 83% at surface
Searcy County, AR 26 mi south · 46% at surface
Ozark County, MO 29 mi northeast · 100% at surface
Taney County, MO 33 mi northwest · 100% at surface
Newton County, AR 39 mi southwest · 24% at surface

The rock underneath

The largest mapped soluble unit here is the Cotter and Jefferson City Dolomites (dolostone (dolomite)), Early Ordovician in age, covering about 27% of the county. Next is the St. Peter Sanstone and Everton Formation (Middle Ordovician) at 27%.

Against the rest of Arkansas

Marion County ranks 5 of 75 in Arkansas for soluble rock at the surface, and sits above 98% of US counties on that measure.