Sinkhole risk in Sierra County, NM: Pockets of it

Pockets of it

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

On soluble rock: 16%
At or near the surface: 16%
Buried under cover: 0%

What to do about a house in Sierra County

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 656 of Sierra County's 4,181 square miles on soluble rock, 656 of them with the rock at or near the surface. With about 11,389 residents (3 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 280 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 the signs to look for and how an inspection works.

Counties around Sierra County

The nearest county rated sinkhole country is Eddy County, NM, about 174 miles east. 2 of the 6 closest counties land in the same band; the ground changes quickly around here.

Doña Ana County, NM 57 mi south · 6% at surface
Socorro County, NM 62 mi north · 23% at surface
Luna County, NM 72 mi southwest · under 1% at surface
Grant County, NM 74 mi west · 2% at surface
Catron County, NM 88 mi northwest · 1% at surface
Otero County, NM 90 mi east · 59% at surface

Which formation it is

The largest mapped soluble unit here is the Pennsylvanian rocks, undivided (sedimentary rock), Pennsylvanian in age, covering about 4% of the county. Next is the San Andres Formation at 3%.

2% of the county sits on gypsum or salt, which dissolves in years rather than millennia. That share matters more than its size suggests.

Against the rest of New Mexico

Sierra County ranks 14 of 33 in New Mexico for soluble rock at the surface, and sits above 72% of US counties on that measure.