Sinkhole risk in San Juan 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: 3%
At or near the surface: 3%
Buried under cover: 0%

The next step for one property

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

That works out to roughly 154 of San Juan County's 5,517 square miles on soluble rock, 154 of them with the rock at or near the surface. With about 120,817 residents (22 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 360 map points about 3.9 miles apart, so a pocket smaller than that can be missed or overstated.

Two things to read before deciding: why gypsum and salt move faster than limestone, and how these percentages are measured.

Counties around San Juan County

The nearest county rated sinkhole country is Emery County, UT, about 217 miles northwest. 3 of the 6 closest counties land in the same band; the ground changes quickly around here.

Montezuma County, CO 59 mi north · 0% at surface
La Plata County, CO 60 mi northeast · 2% at surface
McKinley County, NM 64 mi south · 13% at surface
Dolores County, CO 85 mi north · 0% at surface
Archuleta County, CO 85 mi northeast · 0% at surface
Rio Arriba County, NM 91 mi east · 6% at surface

What San Juan County is built on

The largest mapped soluble unit here is the Morrison Formation (fine-grained mixed clastic), Jurassic in age, covering about 2% of the county. Next is the San Rafael Group at under 1%.

The county also lies over the Paradox 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

San Juan County ranks 25 of 33 in New Mexico for soluble rock at the surface, and sits above 59% of US counties on that measure.