claypan

A dense, compacted layer of clay in the subsoil that is nearly impermeable to water and roots — similar to hardpan but distinguished by its high clay content. Water perches on top of a claypan, creating seasonal wetlands in otherwise dry terrain. Trees growing over a claypan are often shallow-rooted and prone to windthrow. A claypan is the soil saying no — no deeper, no drainage, no passage.