Sinkhole risk in Ferry County, WA: No soluble rock mapped

No soluble rock mapped

No soluble bedrock mapped.

On soluble rock: under 1%
At or near the surface: under 1%
Buried under cover: 0%

What to do about a house in Ferry County

No soluble bedrock is mapped here, so natural sinkholes are unlikely. Collapses from broken pipes or old mines are a separate risk.

That works out to roughly 13 of Ferry County's 2,203 square miles on soluble rock, 13 of them with the rock at or near the surface. With about 7,543 residents (3 per square mile), much of the land is open, and the mapped rock may sit far from where people actually live. The figures come from 314 map points about 2.6 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 Ferry County

The nearest county rated sinkhole country is Emery County, UT, about 760 miles southeast. 4 of the 6 closest counties land in the same band, so this is a regional pattern rather than a local quirk.

Stevens County, WA 32 mi east · 3% at surface
Okanogan County, WA 56 mi west · under 1% at surface
Pend Oreille County, WA 60 mi east · 2% at surface
Lincoln County, WA 62 mi south · 0% at surface
Douglas County, WA 74 mi southwest · 0% at surface
Spokane County, WA 79 mi southeast · 0% at surface

The rock underneath

The largest mapped soluble unit here is the Triassic sedimentary rocks, undivided (limestone), Triassic with some Permian in age, covering about under 1% of the county.

Against the rest of Washington

Ferry County ranks 5 of 39 in Washington for soluble rock at the surface, and sits above 53% of US counties on that measure.