Sinkhole risk in Marion County, IN: 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: 52%
At or near the surface: 0%
Buried under cover: 52%

What this means before you buy

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

That works out to roughly 206 of Marion County's 396 square miles on soluble rock. With about 981,628 residents (2,479 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 375 map points about 1.0 miles apart, so a pocket smaller than that can be missed or overstated.

Worth reading for this county: why the 52% under cover still counts, and how these percentages are measured.

Counties around Marion County

The nearest county rated sinkhole country is Monroe County, IN, about 48 miles southwest. 5 of the 6 closest counties land in the same band, so this is a regional pattern rather than a local quirk.

Hancock County, IN 19 mi east · 0% at surface
Hamilton County, IN 20 mi north · 0% at surface
Hendricks County, IN 20 mi west · 0% at surface
Johnson County, IN 20 mi south · 0% at surface
Shelby County, IN 26 mi southeast · 0% at surface
Boone County, IN 26 mi northwest · 0% at surface

Which formation it is

The largest mapped soluble unit here is the Muscatatuck Group (limestone), Devonian in age, covering about 45% of the county. Next is the Wabash Formation at 6%.

Against the rest of Indiana

Marion County ranks 66 of 92 in Indiana for soluble rock at the surface, and sits above 0% of US counties on that measure.