Sinkhole risk in Cowlitz County, WA: Not karst, but voids possible

Not karst, but voids possible

No soluble bedrock; some pseudokarst (piping or lava-tube ground).

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

What this means before you buy

Not true karst, but soil piping or lava tubes can still open voids - mention it to an inspector.

Across 1,141 square miles, under one square mile of Cowlitz County maps onto soluble rock. With about 113,982 residents (100 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 280 map points about 2.0 miles apart, so a pocket smaller than that can be missed or overstated.

Worth reading for this county: how ground with no limestone still opens up, and how these percentages are measured.

Counties around Cowlitz County

The nearest county rated sinkhole country is Emery County, UT, about 784 miles southeast. 4 of the 6 closest counties land in the same band, so this is a regional pattern rather than a local quirk.

Columbia County, OR 26 mi southwest · 0% at surface
Lewis County, WA 30 mi northeast · 0% at surface
Clark County, WA 31 mi south · 0% at surface
Wahkiakum County, WA 36 mi west · 0% at surface
Skamania County, WA 37 mi east · 0% at surface
Multnomah County, OR 47 mi south · 0% at surface

Against the rest of Washington

Cowlitz County ranks 16 of 39 in Washington for soluble rock at the surface, and sits above 0% of US counties on that measure.