No limestone, but still holes: pseudokarst explained

The question the numbers raise

A few county pages say there is no soluble bedrock, yet still flag the ground. That is pseudokarst: land that develops holes and underground channels without any rock dissolving. The USGS karst map includes it because the result at the surface can look the same.

The two main kinds

Soil piping happens in fine, loose soils, often silts or dispersive clays in dry country. Water running underground carries soil away and leaves tunnels that can collapse. Lava tubes are hollow channels left when the outside of a lava flow cooled while molten rock drained from inside; their roofs can fail. On this site 108 counties fall in this group, most of them in Texas (36), Oregon (14), Idaho (12), Washington (10). The largest shares are in Lincoln County, ID, Castro County, TX, Lubbock County, TX, Hale County, TX.

What it means for a property

Pseudokarst holes tend to be more local than limestone sinkholes and are often tied to water: irrigation, a leaking line, or drainage pointed at loose soil. Tell an inspector the county has mapped pseudokarst, keep drainage away from the foundation, and treat any new hole as you would a sinkhole. For counties with true soluble rock, the methodology guide explains how the tiers are set.

Where to go next

See how it varies: Izard County, AR, Southampton County, VA, Elmore County, AL.

How SinkholeOdds rates a county · Why "buried" limestone is not automatically safe