Sinkhole risk in Marion County, KS: Sinkhole country

Sinkhole country

Fast-dissolving gypsum or salt beds under a large part of the county.

On soluble rock: 80%
At or near the surface: 80%
Buried under cover: 0%

The next step for one property

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

That works out to roughly 754 of Marion County's 944 square miles on soluble rock, 754 of them with the rock at or near the surface. With about 11,670 residents (12 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 344 map points about 1.7 miles apart, so a pocket smaller than that can be missed or overstated.

Two things to read before deciding: why gypsum and salt move faster than limestone, and the signs to look for and how an inspection works.

Counties around Marion County

The closest county with no soluble rock mapped is Stafford County, KS, about 91 miles west. 1 of the 6 closest counties land in the same band; the ground changes quickly around here.

Chase County, KS 28 mi east · 87% at surface
Harvey County, KS 28 mi southwest · 21% at surface
McPherson County, KS 30 mi west · 15% at surface
Morris County, KS 33 mi northeast · 91% at surface
Dickinson County, KS 35 mi north · 79% at surface
Saline County, KS 42 mi northwest · 15% at surface

The rock underneath

The largest mapped soluble unit here is the Sumner Group (shale), Late Permian - Cimarronian in age, covering about 55% of the county. Next is the Chase Group at 24%.

55% of the county sits on gypsum or salt, which dissolves in years rather than millennia. That share matters more than its size suggests.

Against the rest of Kansas

Marion County ranks 6 of 105 in Kansas for soluble rock at the surface, and sits above 95% of US counties on that measure.