Sinkhole risk in Greer County, OK: Sinkhole country

Sinkhole country

Fast-dissolving gypsum or salt beds under a large part of the county.

On soluble rock: 36%
At or near the surface: 36%
Buried under cover: 0%

The next step for one property

Get a sinkhole or geotechnical inspection before buying, building or adding weight to a foundation.

That works out to roughly 233 of Greer County's 639 square miles on soluble rock, 233 of them with the rock at or near the surface. With about 5,433 residents (8 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 269 map points about 1.5 miles apart, so a pocket smaller than that can be missed or overstated.

Counties around Greer County

The closest county with no soluble rock mapped is Tillman County, OK, about 53 miles southeast. 5 of the 6 closest counties land in the same band, so this is a regional pattern rather than a local quirk.

Harmon County, OK 21 mi southwest · 77% at surface
Beckham County, OK 25 mi north · 32% at surface
Jackson County, OK 25 mi south · 34% at surface
Kiowa County, OK 32 mi east · 4% at surface
Washita County, OK 40 mi northeast · 64% at surface
Collingsworth County, TX 41 mi west · 59% at surface

The rock underneath

The largest mapped soluble unit here is the Flowerpot Shale (shale), Early Permian in age, covering about 17% of the county. Next is the Dog Creek Shale at 6%.

36% 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

Greer County ranks 20 of 77 in Oklahoma for soluble rock at the surface, and sits above 82% of US counties on that measure.