| Soil Type | Description | Most Important Formation Factorsa |
|---|---|---|
| Alfisols | Soils of humid and subhumid climates with a subsurface horizon of clay accumulation, not strongly leached, common in forested areas | Climate, organisms |
| Andisols | Soils that formed in volcanic ash and contain compounds rich in organic matter and aluminum | Parent material |
| Aridisols | Soils formed in dry climates, low in organic matter and often having subsurface horizons with salt accumulation | Climate |
| Entisols | Soils lacking subsurface horizons because the parent material accumulated recently or because of constant erosion; common on floodplains, mountains, and badlands (highly eroded, rocky areas) | Time, topography |
| Gelisols | Weakly weathered soils formed in areas that contain permafrost (frozen soil) within the soil profile | Climate |
| Histosols | Soils with a thick upper layer very rich in organic matter (.25%) and containing relatively little mineral material | Topography |
| Inceptisols | Soils with weakly developed subsurface horizons and little or no subsoil clay accumulation because the soil is young or the climate does not promote rapid weathering | Time, climate |
| Mollisols | Mineral soils of semiarid and subhumid midlatitude grasslands that have a dark, organic-rich A-horizon and are not strongly leached | Climate, organisms |
| Oxisols | Very old, highly leached soils with subsurface accumulations of iron and aluminum oxides, commonly found in humid tropical environments | Climate, time |
| Spodosols | Soils formed in cold, moist climates that have a well-developed B-horizon with accumulation of aluminum and iron oxides, formed under pine vegetation in sandy parent material | Parent material, organisms, climate |
| Ultisols | Soils with a subsurface horizon of clay accumulation, highly leached (but not as highly as oxisols), commonly found in humid tropical and subtropical climates | Climate, time, organisms |
| Vertisols | Soils that develop deep, wide cracks when dry (shrink and swell) due to high clay content (.35%) and are not highly leached | Parent material |
| aAll five soil formation factors (climate, organisms, parent material, topography, time) combine to create these soils, but only the most important factors are listed for each soil type. Source: Adapted from E. C. Brevik, Journal of Geoscience Education 50 (2002): 541. | ||