Sinkhole risk in Grand County, UT: 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: 7%
At or near the surface: 7%
Buried under cover: 0%

What to do about a house in Grand County

Sinkholes are uncommon here; watch for new depressions after heavy rain or leaking pipes.

That works out to roughly 246 of Grand County's 3,673 square miles on soluble rock, 246 of them with the rock at or near the surface. With about 9,788 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 345 map points about 3.3 miles apart, so a pocket smaller than that can be missed or overstated.

Two things to read before deciding: why gypsum and salt move faster than limestone, and how these percentages are measured.

Counties around Grand County

The nearest county rated sinkhole country is Emery County, UT, about 62 miles west. 2 of the 6 closest counties land in the same band; the ground changes quickly around here.

Mesa County, CO 60 mi east · under 1% at surface
Emery County, UT 62 mi west · 30% at surface
Carbon County, UT 73 mi northwest · 0% at surface
Uintah County, UT 80 mi north · 4% at surface
Montrose County, CO 81 mi southeast · 1% at surface
San Miguel County, CO 91 mi southeast · under 1% at surface

The rock underneath

The largest mapped soluble unit here is the Jurassic (1) sedimentary rocks in southeastern Utah (sandstone), Middle to Late Jurassic in age, covering about 5% of the county. Next is the Jurassic (1) sedimentary rocks in southeastern Utah at 5%.

6% 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 Paradox Basin, 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

Grand County ranks 20 of 29 in Utah for soluble rock at the surface, and sits above 65% of US counties on that measure.