Sinkhole risk in Woodward County, OK: Sinkhole country

Sinkhole country

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

On soluble rock: 46%
At or near the surface: 46%
Buried under cover: 0%

What this means before you buy

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

That works out to roughly 569 of Woodward County's 1,243 square miles on soluble rock, 569 of them with the rock at or near the surface. With about 19,991 residents (16 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 312 map points about 2.0 miles apart, so a pocket smaller than that can be missed or overstated.

Worth reading for this county: why gypsum and salt move faster than limestone, and the signs to look for and how an inspection works.

Counties around Woodward County

The closest county with no soluble rock mapped is Hemphill County, TX, about 70 miles southwest. 5 of the 6 closest counties land in the same band, so this is a regional pattern rather than a local quirk.

Ellis County, OK 30 mi southwest · 14% at surface
Woods County, OK 31 mi northeast · 42% at surface
Harper County, OK 34 mi northwest · 61% at surface
Dewey County, OK 34 mi southeast · 57% at surface
Major County, OK 41 mi east · 39% at surface
Comanche County, KS 52 mi north · 39% at surface

Which formation it is

The largest mapped soluble unit here is the Rush Springs Formation (sandstone), Early Permian in age, covering about 17% of the county. Next is the Blaine Formation at 8%.

46% 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

Woodward County ranks 13 of 77 in Oklahoma for soluble rock at the surface, and sits above 86% of US counties on that measure.