Sinkhole risk in Graham County, AZ: Not karst, but voids possible

Not karst, but voids possible

No soluble bedrock; some pseudokarst (piping or lava-tube ground).

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

The next step for one property

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

That works out to roughly 32 of Graham County's 4,622 square miles on soluble rock, 32 of them with the rock at or near the surface. With about 40,242 residents (9 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 282 map points about 4.0 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 ground with no limestone still opens up.

Counties around Graham County

The nearest county rated sinkhole country is Eddy County, NM, about 326 miles east. None of the 6 closest counties land in the same band, so Graham County stands out from its surroundings.

Greenlee County, AZ 42 mi northeast · 2% at surface
Cochise County, AZ 76 mi south · 6% at surface
Gila County, AZ 80 mi northwest · 35% at surface
Pinal County, AZ 86 mi west · 3% at surface
Grant County, NM 88 mi east · 2% at surface
Hidalgo County, NM 97 mi southeast · 2% at surface

Which formation it is

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

The county also lies over the Safford 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 Arizona

Graham County ranks 11 of 15 in Arizona for soluble rock at the surface, and sits above 54% of US counties on that measure.