Sinkhole risk in Clackamas County, OR: 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 1,871 square miles, under one square mile of Clackamas County maps onto soluble rock. With about 425,857 residents (228 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 324 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 Clackamas County

The nearest county rated sinkhole country is Emery County, UT, about 725 miles southeast. 6 of the 6 closest counties land in the same band, so this is a regional pattern rather than a local quirk.

Marion County, OR 26 mi southwest · 0% at surface
Multnomah County, OR 29 mi north · 0% at surface
Hood River County, OR 36 mi northeast · 0% at surface
Clark County, WA 45 mi north · 0% at surface
Linn County, OR 49 mi south · 0% at surface
Wasco County, OR 50 mi east · 0% at surface

Against the rest of Oregon

Clackamas County ranks 14 of 36 in Oregon for soluble rock at the surface, and sits above 0% of US counties on that measure.