Sinkhole risk in Loudoun County, VA: 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: 7%
At or near the surface: 7%
Buried under cover: 0%

The next step for one property

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

That works out to roughly 35 of Loudoun County's 516 square miles on soluble rock, 35 of them with the rock at or near the surface. With about 443,380 residents (860 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 474 map points about 1.0 miles apart, so a pocket smaller than that can be missed or overstated.

Worth reading for this county: how these percentages are measured, and the warning signs that apply anywhere.

Counties around Loudoun County

The nearest county rated sinkhole country is Clarke County, VA, about 19 miles west, close enough that the same rock may run under the county line. None of the 6 closest counties land in the same band, so Loudoun County stands out from its surroundings.

Clarke County, VA 19 mi west · 74% at surface
Jefferson County, WV 20 mi northwest · 84% at surface
Montgomery County, MD 24 mi east · 0% at surface
Manassas Park city, VA 24 mi southeast · 0% at surface
Fairfax city, VA 24 mi southeast · 0% at surface
Manassas city, VA 25 mi south · under 1% at surface

Which formation it is

The largest mapped soluble unit here is the Newark Supergroup; Conglomerate, mixed clasts (conglomerate), Triassic in age, covering about 3% of the county. Next is the Newark Supergroup; Conglomerate, greenstone clasts at 3%.

Against the rest of Virginia

Loudoun County ranks 62 of 133 in Virginia for soluble rock at the surface, and sits above 65% of US counties on that measure.