Sinkhole risk in San Juan County, WA: 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: 4%
At or near the surface: 4%
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 7 of San Juan County's 174 square miles on soluble rock, 7 of them with the rock at or near the surface. With about 18,668 residents (107 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 251 map points about 0.8 miles apart, so a pocket smaller than that can be missed or overstated.

Worth reading for this county: how these percentages are measured, and the warning signs that apply anywhere.

Counties around San Juan County

The nearest county rated sinkhole country is Emery County, UT, about 899 miles southeast. None of the 6 closest counties land in the same band, so San Juan County stands out from its surroundings.

Island County, WA 31 mi southeast · 0% at surface
Clallam County, WA 45 mi southwest · 0% at surface
Jefferson County, WA 52 mi south · 0% at surface
Skagit County, WA 59 mi east · under 1% at surface
Whatcom County, WA 62 mi east · under 1% at surface
Kitsap County, WA 64 mi south · 0% at surface

Which formation it is

The largest mapped soluble unit here is the Triassic sedimentary rocks, undivided (limestone), Triassic with some Permian in age, covering about 4% of the county.

Against the rest of Washington

San Juan County ranks 1 of 39 in Washington for soluble rock at the surface, and sits above 61% of US counties on that measure.