hardpan

Hardpan is a pale, unyielding substratum of soil that is much denser than the horizons above and below. It forms over thousands of years as materials from the upper soil layers dissolve and percolate downward. When the water evaporates within the lower soil layers, these dissolved materials, such as silica, aluminum, iron, and calcium, precipitate onto the surrounding soil particles. The result is a compacted, cemented layer that interferes with the movement of moisture, hinders the growth of plant roots, and is difficult to cultivate. In some regions, this layer is called claypan, and in the desert Southwest, where it occurs at the surface and not just at depth, it’s known as caliche. A hardpan layer can be from a few inches to several feet thick. The shallow soil above the pan dries out quickly but becomes easily saturated, since rainwater cannot drain. Writing about the 1930s Dust Bowl conditions of the Great Plains, poet Archibald MacLeish described “dead quarter sections with the hardpan clean as weathered lime and the four-room flimsy ranch houses two feet deep in sand.”

Charles Frazier