Sinkhole risk in Allen County, KS: Sinkhole country

Sinkhole country

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

On soluble rock: 90%
At or near the surface: 90%
Buried under cover: 0%

What to do about a house in Allen County

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

That works out to roughly 452 of Allen County's 500 square miles on soluble rock, 452 of them with the rock at or near the surface. With about 12,425 residents (25 per square mile), there is effectively nowhere in the county off the soluble rock, town or country. The figures come from 408 map points about 1.1 miles apart, so a pocket smaller than that can be missed or overstated.

Counties around Allen County

The closest county with no soluble rock mapped is Noble County, OK, about 149 miles southwest. 5 of the 6 closest counties land in the same band, so this is a regional pattern rather than a local quirk.

Neosho County, KS 22 mi south · 78% at surface
Anderson County, KS 23 mi north · 55% at surface
Bourbon County, KS 25 mi east · 68% at surface
Woodson County, KS 25 mi west · 40% at surface
Wilson County, KS 33 mi southwest · 54% at surface
Coffey County, KS 34 mi northwest · 53% at surface

Which formation it is

The largest mapped soluble unit here is the Kansas City Group (limestone), Middle Pennsylvanian- Missourian in age, covering about 77% of the county. Next is the Lansing Group at 14%.

Against the rest of Kansas

Allen County ranks 3 of 105 in Kansas for soluble rock at the surface, and sits above 97% of US counties on that measure.