Sinkhole risk in Harding County, NM: 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: 12%
At or near the surface: 12%
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 247 of Harding County's 2,125 square miles on soluble rock, 247 of them with the rock at or near the surface. With about 635 residents (0 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 259 map points about 2.9 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 how these percentages are measured.

Counties around Harding County

The nearest county rated sinkhole country is Briscoe County, TX, about 176 miles southeast. 3 of the 6 closest counties land in the same band; the ground changes quickly around here.

Union County, NM 48 mi northeast · 14% at surface
Quay County, NM 55 mi south · 4% at surface
San Miguel County, NM 60 mi southwest · 28% at surface
Mora County, NM 60 mi west · 19% at surface
Colfax County, NM 68 mi northwest · 6% at surface
Hartley County, TX 70 mi east · under 1% at surface

The rock underneath

The largest mapped soluble unit here is the Morrison Formation and upper San Rafael Group (fine-grained mixed clastic), Jurassic in age, covering about 9% of the county. Next is the Greenhorn Formation at 2%.

1% 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 Permian Basin, Anadarko Basin,Dalhart Basin, Palo Duro 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 New Mexico

Harding County ranks 19 of 33 in New Mexico for soluble rock at the surface, and sits above 69% of US counties on that measure.