Sinkhole risk in McLennan County, TX: Pockets of it

Pockets of it

Soluble rock at the surface or under thin cover in part of the county.

On soluble rock: 41%
At or near the surface: 41%
Buried under cover: 0%

What to do about a house in McLennan County

Check the parcel against your state survey sinkhole map, and ask for an inspection if cracks, depressions or sticking doors show up.

That works out to roughly 422 of McLennan County's 1,037 square miles on soluble rock, 422 of them with the rock at or near the surface. With about 270,358 residents (261 per square mile), homes are spread across towns and farmland, and a mapped unit may or may not reach the developed parts. The figures come from 538 map points about 1.4 miles apart, so a pocket smaller than that can be missed or overstated.

Counties around McLennan County

The nearest county rated sinkhole country is Runnels County, TX, about 165 miles west. 4 of the 6 closest counties land in the same band, so this is a regional pattern rather than a local quirk.

Falls County, TX 26 mi southeast · 14% at surface
Hill County, TX 30 mi north · 22% at surface
Bosque County, TX 35 mi northwest · 26% at surface
Limestone County, TX 36 mi east · 4% at surface
Coryell County, TX 37 mi west · 35% at surface
Bell County, TX 39 mi southwest · 32% at surface

Which formation it is

The largest mapped soluble unit here is the Grayson Marl and Main Street Limestone, undivided (mudstone), Early Late Cretaceous and Late Early Cretaceous in age, covering about 16% of the county. Next is the Austin Chalk at 11%.

The county also lies over the Gulf Coast salt domes, 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 Texas

McLennan County ranks 62 of 254 in Texas for soluble rock at the surface, and sits above 84% of US counties on that measure.