SinkholeOdds

Sinkhole risk in Navajo County, AZ: Pockets of it

Pockets of it

Soluble rock at the surface or under thin cover in part of the county.

On soluble rock
25%
At or near the surface
25%
Buried under cover
0%

The next step for one property

Check the parcel against your state survey sinkhole map, and ask for an inspection if cracks, depressions or sticking doors show up.

That works out to roughly 2,517 of Navajo County's 9,949 square miles on soluble rock, 2,517 of them with the rock at or near the surface. With about 109,516 residents (11 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 320 map points about 5.6 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 the signs to look for and how an inspection works.

Counties around Navajo County

The nearest county rated sinkhole country is Emery County, UT, about 251 miles north. 3 of the 6 closest counties land in the same band; the ground changes quickly around here.

The rock underneath

The largest mapped soluble unit here is the Permian sedimentary rocks (limestone), Permian in age, covering about 10% of the county. Next is the Moenkopi Formation at 8%.

15% 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 Holbrook 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

Navajo County ranks 4 of 15 in Arizona for soluble rock at the surface, and sits above 77% of US counties on that measure.