Sinkhole risk in Polk County, OR: 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: 3%
At or near the surface: 3%
Buried under cover: 0%

What this means before you buy

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

That works out to roughly 23 of Polk County's 741 square miles on soluble rock, 23 of them with the rock at or near the surface. With about 90,549 residents (122 per square mile), homes are spread across towns and farmland, and a mapped unit may or may not reach the developed parts. The figures come from 352 map points about 1.5 miles apart, so a pocket smaller than that can be missed or overstated.

Counties around Polk County

The nearest county rated sinkhole country is Emery County, UT, about 767 miles southeast. None of the 6 closest counties land in the same band, so Polk County stands out from its surroundings.

Yamhill County, OR 24 mi north · 0% at surface
Benton County, OR 28 mi south · 0% at surface
Lincoln County, OR 31 mi southwest · 0% at surface
Marion County, OR 40 mi east · 0% at surface
Tillamook County, OR 42 mi northwest · 0% at surface
Washington County, OR 47 mi north · 0% at surface

What Polk County is built on

The largest mapped soluble unit here is the Yamhill Formation and related rocks (upper and middle Eocene) (siltstone), Middle Eocene to Late Eocene in age, covering about 3% of the county.

Against the rest of Oregon

Polk County ranks 4 of 36 in Oregon for soluble rock at the surface, and sits above 60% of US counties on that measure.