Sinkhole risk in Cochise County, AZ: 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: 6%
At or near the surface: 6%
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 391 of Cochise County's 6,210 square miles on soluble rock, 391 of them with the rock at or near the surface. With about 125,773 residents (20 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 414 map points about 3.9 miles apart, so a pocket smaller than that can be missed or overstated.

Worth reading for this county: why gypsum and salt move faster than limestone, and how these percentages are measured.

Counties around Cochise County

The nearest county rated sinkhole country is Eddy County, NM, about 323 miles east. 5 of the 6 closest counties land in the same band, so this is a regional pattern rather than a local quirk.

Hidalgo County, NM 60 mi east · 2% at surface
Santa Cruz County, AZ 67 mi west · 4% at surface
Graham County, AZ 76 mi north · under 1% at surface
Greenlee County, AZ 102 mi north · 2% at surface
Grant County, NM 102 mi northeast · 2% at surface
Pinal County, AZ 119 mi northwest · 3% at surface

What Cochise County is built on

The largest mapped soluble unit here is the Mississippian, Devonian, and Cambrian sedimentary rocks (sandstone), Cambrian, Devonian, and Mississippi in age, covering about 2% of the county. Next is the Permian to Pennsylvanian sedimentary rocks at 2%.

2% 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 Elfrida 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

Cochise County ranks 7 of 15 in Arizona for soluble rock at the surface, and sits above 64% of US counties on that measure.