The Twelve Soil Orders

1. Gelisols: Soils with permafrost within 2 m of the surface.

2. Histosols: Organic Soils

3. Spodosoils: Acid forest soils with a subsurface accumulation of metal-hummus complexions.

4. Andisols: Soils formed from volcanic ash

5. Oxisols: Intensely weathered soils of tropical/subtropical environments

6. Vertisols: Clay soils with high shrink/swell capacity

7. Aridisols: CaCO3 containing soils of arid environment with subsurface horizon development

8. Ultisols: Strongly leached soils with clay accumulation greater than or equal to 35% base saturation.

9. Mollisols: Grassland soils

10. Alfisols: Moderate leached soils with a subsurface zone of clay accumulation and a less than or equal to 35% base saturation

11. Inceptisols: Soils with weakly developed subsurface horizons. 

12. Entisols: Soils with little or no morphological development.