Sinkhole risk in Franklin County, ID: Pockets of it

Pockets of it

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

On soluble rock: 37%
At or near the surface: 37%
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 247 of Franklin County's 663 square miles on soluble rock, 247 of them with the rock at or near the surface. With about 15,638 residents (24 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 284 map points about 1.5 miles apart, so a pocket smaller than that can be missed or overstated.

Two things to read before deciding: the signs to look for and how an inspection works, and how these percentages are measured.

Counties around Franklin County

The nearest county rated sinkhole country is Emery County, UT, about 226 miles south. 5 of the 6 closest counties land in the same band, so this is a regional pattern rather than a local quirk.

Bear Lake County, ID 27 mi east · 45% at surface
Cache County, UT 31 mi south · 41% at surface
Oneida County, ID 36 mi west · 44% at surface
Bannock County, ID 41 mi northwest · 29% at surface
Caribou County, ID 45 mi north · 24% at surface
Rich County, UT 48 mi southeast · 9% at surface

What Franklin County is built on

The largest mapped soluble unit here is the Limestone, arenite, shale, dolostone, and siltstone; Upper Proterozoic to Cambrian marine continental-shelf deposits; southeastern Idaho (limestone), Cambrian in age, covering about 12% of the county. Next is the Arenite, carbonate, conglomerate, and shale; Late Proterozoic rifted continental margin; southeastern Idaho at 10%.

Against the rest of Idaho

Franklin County ranks 3 of 44 in Idaho for soluble rock at the surface, and sits above 83% of US counties on that measure.