Sinkhole risk in Collin 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: 47%
At or near the surface: 47%
Buried under cover: 0%

The next step for one property

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 398 of Collin County's 842 square miles on soluble rock, 398 of them with the rock at or near the surface. With about 1,254,658 residents (1,491 per square mile), most of the county is built up, so a mapped unit is likely to sit under somebody's street. The figures come from 387 map points about 1.5 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 Collin County

The nearest county rated sinkhole country is Grady County, OK, about 147 miles northwest. 4 of the 6 closest counties land in the same band, so this is a regional pattern rather than a local quirk.

Rockwall County, TX 23 mi southeast · 0% at surface
Hunt County, TX 29 mi east · 2% at surface
Grayson County, TX 30 mi north · 36% at surface
Denton County, TX 31 mi west · 41% at surface
Dallas County, TX 32 mi south · 39% at surface
Fannin County, TX 39 mi northeast · 25% at surface

The rock underneath

The largest mapped soluble unit here is the Austin Chalk (limestone), Late Cretaceous; Gulfian Series in age, covering about 45% of the county. Next is the Pecan Gap Chalk at 2%.

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

Collin County ranks 54 of 254 in Texas for soluble rock at the surface, and sits above 87% of US counties on that measure.