Sinkhole risk in Pima County, AZ: No soluble rock mapped

No soluble rock mapped

No soluble bedrock mapped.

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

The next step for one property

No soluble bedrock is mapped here, so natural sinkholes are unlikely. Collapses from broken pipes or old mines are a separate risk.

That works out to roughly 64 of Pima County's 9,189 square miles on soluble rock, 64 of them with the rock at or near the surface. With about 1,080,149 residents (118 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 290 map points about 5.6 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 Pima County

The nearest county rated sinkhole country is Eddy County, NM, about 437 miles east. None of the 6 closest counties land in the same band, so Pima County stands out from its surroundings.

Pinal County, AZ 60 mi northeast · 3% at surface
Santa Cruz County, AZ 69 mi southeast · 4% at surface
Maricopa County, AZ 94 mi northwest · 0% at surface
Cochise County, AZ 119 mi east · 6% at surface
Graham County, AZ 124 mi northeast · under 1% at surface
Gila County, AZ 128 mi northeast · 35% at surface

Which formation it is

The largest mapped soluble unit here is the Permian to Pennsylvanian sedimentary rocks (sandstone), Pennsylvanian to Permian in age, covering about under 1% of the county.

The county also lies over the Tuscon 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

Pima County ranks 12 of 15 in Arizona for soluble rock at the surface, and sits above 54% of US counties on that measure.