Regosols often form on colluvium parent material associated with steep slopes

Regosols (or Entisols in USDA Soil Taxonomy) are weakly developed soils to meet the classification requirements of other soil orders. They lack a recognizable B horizon (i.e., B horizon is less than 5 cm thick). Soils of the Regosolic order are most commonly associated with landforms where the land surface is (or has recently been) unstable. Because of the unstable surface, the soil has had little time to develop. Consequently, soil horizons are very weakly expressed if present at all.

The two great groups of the Regosolic order are distinguished on the basis of the amount of organic additions to the surface soil layer.

Humic Regosol Great Group

Soils of this great group have an Ah (or Ap) horizon ≥ 10 cm in depth.

Regosol Great Group

Soils of this great group have the C horizon at the surface, or a thin A horizon directly overlies the C horizon or thin B horizon.