Sinkhole risk in Ottawa County, KS: Mostly deep or small

Mostly deep or small

Some soluble rock, mostly deeply buried or in a small share of the county.

On soluble rock: 4%
At or near the surface: 4%
Buried under cover: 0%

What to do about a house in Ottawa County

Sinkholes are uncommon here; watch for new depressions after heavy rain or leaking pipes.

That works out to roughly 25 of Ottawa County's 721 square miles on soluble rock, 25 of them with the rock at or near the surface. With about 5,853 residents (8 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 400 map points about 1.3 miles apart, so a pocket smaller than that can be missed or overstated.

Worth reading for this county: why gypsum and salt move faster than limestone, and how these percentages are measured.

Counties around Ottawa County

The nearest county rated sinkhole country is Dickinson County, KS, about 33 miles southeast, close enough that the same rock may run under the county line. None of the 6 closest counties land in the same band, so Ottawa County stands out from its surroundings.

Saline County, KS 24 mi south · 15% at surface
Cloud County, KS 24 mi north · 22% at surface
Clay County, KS 30 mi northeast · 35% at surface
Lincoln County, KS 31 mi west · 33% at surface
Dickinson County, KS 33 mi southeast · 79% at surface
Mitchell County, KS 34 mi northwest · 38% at surface

Which formation it is

The largest mapped soluble unit here is the Greenhorn Limestone and Graneros Shale (limestone), Late Cretaceous in age, covering about 2% of the county. Next is the Sumner Group at 1%.

1% 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

Ottawa County ranks 83 of 105 in Kansas for soluble rock at the surface, and sits above 61% of US counties on that measure.