Sinkhole risk in Washington County, AL: Mostly deep or small

Mostly deep or small

Some soluble rock, mostly deeply buried or in a small share of the county.

On soluble rock: 37%
At or near the surface: 3%
Buried under cover: 34%

What to do about a house in Washington County

Sinkholes are uncommon here; watch for new depressions after heavy rain or leaking pipes.

That works out to roughly 396 of Washington County's 1,080 square miles on soluble rock, 27 of them with the rock at or near the surface. With about 15,018 residents (14 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 316 map points about 1.8 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 why the 34% under cover still counts.

Counties around Washington County

The nearest county rated sinkhole country is Noxubee County, MS, about 119 miles north. 1 of the 6 closest counties land in the same band; the ground changes quickly around here.

Greene County, MS 28 mi southwest · 0% at surface
Clarke County, AL 30 mi northeast · 15% at surface
Wayne County, MS 32 mi northwest · 17% at surface
Choctaw County, AL 40 mi north · 5% at surface
George County, MS 46 mi southwest · 0% at surface
Perry County, MS 49 mi west · 0% at surface

What Washington County is built on

The largest mapped soluble unit here is the Oligocene Series undifferentiated (limestone), Oligocene in age, covering about 34% of the county. Next is the Oligocene Series undifferentiated at 1%.

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 Alabama

Washington County ranks 48 of 67 in Alabama for soluble rock at the surface, and sits above 59% of US counties on that measure.