Sinkhole risk in Placer County, CA: 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 to do about a house in Placer County

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

Across 1,407 square miles, under one square mile of Placer County maps onto soluble rock. With about 433,822 residents (308 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 455 map points about 1.8 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 Placer County

The nearest county rated sinkhole country is Emery County, UT, about 537 miles east. 1 of the 6 closest counties land in the same band; the ground changes quickly around here.

Nevada County, CA 16 mi north · 0% at surface
El Dorado County, CA 22 mi southeast · 0% at surface
Yuba County, CA 36 mi northwest · 0% at surface
Sierra County, CA 37 mi north · 0% at surface
Amador County, CA 43 mi south · 0% at surface
Carson City, NV 53 mi east · 2% at surface

Against the rest of California

Placer County ranks 45 of 58 in California for soluble rock at the surface, and sits above 0% of US counties on that measure.