SinkholeOdds

Sinkhole risk in Ellis County, OK: 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 this means before you buy

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

That works out to roughly 167 of Ellis County's 1,231 square miles on soluble rock, 167 of them with the rock at or near the surface. With about 3,601 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 279 map points about 2.1 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 Ellis County

The nearest county rated sinkhole country is Woodward County, OK, about 30 miles northeast, close enough that the same rock may run under the county line. None of the 6 closest counties land in the same band, so Ellis County stands out from its surroundings.

Which formation it is

The largest mapped soluble unit here is the Cloud Chief Formation (shale), Late Permian in age, covering about 10% of the county. Next is the Rush Springs Formation at 4%.

14% 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 Oklahoma

Ellis County ranks 38 of 77 in Oklahoma for soluble rock at the surface, and sits above 70% of US counties on that measure.