Sinkhole risk in Pinal 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: 3%
At or near the surface: 3%
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 166 of Pinal County's 5,367 square miles on soluble rock, 166 of them with the rock at or near the surface. With about 513,862 residents (96 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 322 map points about 4.1 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 Pinal County

The nearest county rated sinkhole country is Eddy County, NM, about 412 miles east. 2 of the 6 closest counties land in the same band; the ground changes quickly around here.

Pima County, AZ 60 mi southwest · under 1% at surface
Gila County, AZ 68 mi northeast · 35% at surface
Maricopa County, AZ 72 mi northwest · 0% at surface
Graham County, AZ 86 mi east · under 1% at surface
Santa Cruz County, AZ 101 mi south · 4% at surface
Cochise County, AZ 119 mi southeast · 6% at surface

Which formation it is

The largest mapped soluble unit here is the Middle Proterozoic sedimentary rocks (sandstone), Middle Proterozoic in age, covering about 2% of the county. Next is the Paleozoic sedimentary rocks at under 1%.

The county also lies over the Picacho 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

Pinal County ranks 9 of 15 in Arizona for soluble rock at the surface, and sits above 60% of US counties on that measure.