Sinkhole risk in Rock County, NE: 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: 5%
At or near the surface: 5%
Buried under cover: 0%

The next step for one property

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

That works out to roughly 47 of Rock County's 1,008 square miles on soluble rock, 47 of them with the rock at or near the surface. With about 1,241 residents (1 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 359 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 how these percentages are measured.

Counties around Rock County

The nearest county rated sinkhole country is Boyd County, NE, about 48 miles northeast. 1 of the 6 closest counties land in the same band; the ground changes quickly around here.

Brown County, NE 26 mi west · under 1% at surface
Holt County, NE 33 mi east · 15% at surface
Loup County, NE 35 mi south · 0% at surface
Keya Paha County, NE 36 mi northwest · 21% at surface
Garfield County, NE 41 mi southeast · 0% at surface
Blaine County, NE 43 mi southwest · 0% at surface

The rock underneath

The largest mapped soluble unit here is the Pierre Shale (shale), Late Cretaceous in age, covering about 5% of the county.

5% 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

Rock County ranks 24 of 93 in Nebraska for soluble rock at the surface, and sits above 62% of US counties on that measure.