Sinkhole risk in Union 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: 14%
At or near the surface: 14%
Buried under cover: 0%

What to do about a house in Union County

Sinkholes are uncommon here; watch for new depressions after heavy rain or leaking pipes.

That works out to roughly 547 of Union County's 3,825 square miles on soluble rock, 547 of them with the rock at or near the surface. With about 3,926 residents (1 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 308 map points about 3.5 miles apart, so a pocket smaller than that can be missed or overstated.

Counties around Union County

The nearest county rated sinkhole country is Donley County, TX, about 183 miles southeast. 3 of the 6 closest counties land in the same band; the ground changes quickly around here.

Harding County, NM 48 mi southwest · 12% at surface
Dallam County, TX 51 mi east · 0% at surface
Cimarron County, OK 56 mi east · 7% at surface
Colfax County, NM 65 mi west · 6% at surface
Las Animas County, CO 65 mi northwest · 29% at surface
Hartley County, TX 66 mi southeast · under 1% at surface

Which formation it is

The largest mapped soluble unit here is the Morrison Formation and upper San Rafael Group (fine-grained mixed clastic), Jurassic in age, covering about 8% of the county. Next is the Graneros Shale and Greenhorn Formation at 4%.

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

Union County ranks 15 of 33 in New Mexico for soluble rock at the surface, and sits above 71% of US counties on that measure.