Sinkhole risk in Montgomery County, VA: Sinkhole country

Sinkhole country

Soluble rock at or near the surface across much of the county.

On soluble rock: 64%
At or near the surface: 64%
Buried under cover: 0%

What to do about a house in Montgomery County

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

That works out to roughly 246 of Montgomery County's 387 square miles on soluble rock, 246 of them with the rock at or near the surface. With about 98,998 residents (256 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 247 map points about 1.3 miles apart, so a pocket smaller than that can be missed or overstated.

Worth reading for this county: the signs to look for and how an inspection works, and how these percentages are measured.

Counties around Montgomery County

The closest county with no soluble rock mapped is Floyd County, VA, about 17 miles south. 4 of the 6 closest counties land in the same band, so this is a regional pattern rather than a local quirk.

Radford city, VA 10 mi west · 84% at surface
Roanoke County, VA 15 mi northeast · 33% at surface
Floyd County, VA 17 mi south · under 1% at surface
Pulaski County, VA 20 mi southwest · 57% at surface
Giles County, VA 20 mi northwest · 65% at surface
Salem city, VA 20 mi northeast · 100% at surface

The rock underneath

The largest mapped soluble unit here is the Rome Formation (shale), Cambrian in age, covering about 22% of the county. Next is the Elbrook Formation at 21%.

Against the rest of Virginia

Montgomery County ranks 17 of 133 in Virginia for soluble rock at the surface, and sits above 91% of US counties on that measure.