Sinkhole risk in Harlan County, NE: Sinkhole country

Sinkhole country

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

On soluble rock: 37%
At or near the surface: 37%
Buried under cover: 0%

What this means before you buy

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

That works out to roughly 203 of Harlan County's 553 square miles on soluble rock, 203 of them with the rock at or near the surface. With about 3,018 residents (5 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 414 map points about 1.2 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 Harlan County

The closest county with no soluble rock mapped is Phelps County, NE, about 23 miles north. 2 of the 6 closest counties land in the same band; the ground changes quickly around here.

Franklin County, NE 23 mi east · 78% at surface
Phelps County, NE 23 mi north · 0% at surface
Furnas County, NE 27 mi west · 32% at surface
Phillips County, KS 27 mi south · 32% at surface
Gosper County, NE 32 mi northwest · under 1% at surface
Kearney County, NE 33 mi northeast · 47% at surface

The rock underneath

The largest mapped soluble unit here is the Pierre Shale (shale), Late Cretaceous in age, covering about 33% of the county. Next is the Niobrara Formation at 4%.

33% 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 Nebraska

Harlan County ranks 10 of 93 in Nebraska for soluble rock at the surface, and sits above 82% of US counties on that measure.