SinkholeOdds

Sinkhole risk in Washita County, OK: Sinkhole country

Sinkhole country

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

On soluble rock
64%
At or near the surface
64%
Buried under cover
0%

What to do about a house in Washita County

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

That works out to roughly 645 of Washita County's 1,003 square miles on soluble rock, 645 of them with the rock at or near the surface. With about 10,839 residents (11 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 364 map points about 1.7 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 the signs to look for and how an inspection works.

Counties around Washita County

The closest county with no soluble rock mapped is Tillman County, OK, about 64 miles south. 5 of the 6 closest counties land in the same band, so this is a regional pattern rather than a local quirk.

The rock underneath

The largest mapped soluble unit here is the Cloud Chief Formation (shale), Late Permian in age, covering about 45% of the county. Next is the Rush Springs Formation at 16%.

64% 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

Washita County ranks 6 of 77 in Oklahoma for soluble rock at the surface, and sits above 91% of US counties on that measure.