Sinkhole risk in Snohomish 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%

The next step for one property

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

Across 2,087 square miles, under one square mile of Snohomish County maps onto soluble rock. With about 864,113 residents (414 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 353 map points about 2.4 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 Snohomish County

The nearest county rated sinkhole country is Emery County, UT, about 833 miles southeast. 1 of the 6 closest counties land in the same band; the ground changes quickly around here.

Skagit County, WA 30 mi north · under 1% at surface
King County, WA 39 mi south · 0% at surface
Island County, WA 42 mi west · 0% at surface
Kitsap County, WA 50 mi southwest · 0% at surface
Whatcom County, WA 55 mi north · under 1% at surface
Chelan County, WA 55 mi east · 0% at surface

Against the rest of Washington

Snohomish County ranks 33 of 39 in Washington for soluble rock at the surface, and sits above 0% of US counties on that measure.