Sinkhole risk in Washington County, UT: Pockets of it

Pockets of it

Soluble rock at the surface or under thin cover in part of the county.

On soluble rock: 16%
At or near the surface: 16%
Buried under cover: 0%

What to do about a house in Washington County

Check the parcel against your state survey sinkhole map, and ask for an inspection if cracks, depressions or sticking doors show up.

That works out to roughly 386 of Washington County's 2,428 square miles on soluble rock, 386 of them with the rock at or near the surface. With about 207,943 residents (86 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 2.6 miles apart, so a pocket smaller than that can be missed or overstated.

Counties around Washington County

The nearest county rated sinkhole country is Emery County, UT, about 193 miles northeast. 3 of the 6 closest counties land in the same band; the ground changes quickly around here.

Iron County, UT 46 mi north · 2% at surface
Beaver County, UT 77 mi north · 8% at surface
Lincoln County, NV 80 mi west · 17% at surface
Kane County, UT 92 mi east · 15% at surface
Piute County, UT 105 mi northeast · 0% at surface
Mohave County, AZ 108 mi south · 32% at surface

Which formation it is

The largest mapped soluble unit here is the Triassic (1) sedimentary rocks in Salt southwestern Utah (mudstone), Early Triassic in age, covering about 7% of the county. Next is the Jurassic (1) sedimentary rocks in southeastern Utah at 3%.

7% of the county sits on gypsum or salt, which dissolves in years rather than millennia. That share matters more than its size suggests.

The county also lies over the Virgina Valley, a deep salt or gypsum basin. Deep beds rarely cause surface collapse on their own, but wells and mining into them have.

Against the rest of Utah

Washington County ranks 7 of 29 in Utah for soluble rock at the surface, and sits above 72% of US counties on that measure.