• The U.S. Department of Agriculture recognizes 12 major soil classifications, each with many different sub-categories. Of these five are found in the state of Montana. Three are relatively fertile and lend themselves to extensive habitation and agricultural uses. The other types of Montana soil are less useful for human purposes.
  
  

Andisols

• Andisols are soils that have formed from volcanic ash or various other volcanic materials. They are highly fertile soils and are able to retain large amounts of water. Andisols can keep phosophorous in the ground from getting to plants growing in it. Andisols are found only in the extreme western portion of the state.
  
  

Alfisols

• Alfisols are fertile soils with good water retention properties. These soils are primarily established under forest floors and also have layers of clay built up below the surface. These soils have supported agriculture all over the world for thousands of years. Alfisols are scattered all over the state of Montana.
  
  

Entisols

• Entisols are soils of a modern-day creation. All soils which do not fit within any of the 11 other orders are generally classified as entisols. Montana has five different suborders. Entisols are generally on steep rocky slopes and in river valleys and are by far the most widespread soil order in the world. Entisols are found all over Montana but concentrated in the eastern half of the state.
  
  

Mollisols

• Mollisols are often found in grasslands. They are dark brown, almost black in color. This is one of the most fertile types of soil in the entire world. They are rich in calcium and have excellent water retention properties. Mollisols are found mostly in northern and central Montana.
  
  

Vertisols

• Vertisols are clay-rich soils which expand and decrease in size based on how wet they are. Throughout dry cycles, the soil level shrinks and large fractures develop on the land's surface. This can make building on vertisols difficult, or even hazardous. Because of its repeated cycles of cracking and swelling, the soil is constantly mixed and does not form distinctive layers. Vertisols are uncommon in Montana and found mostly near the center of the state.
  
  

Aridisols

• Aridisols are dry soils that are light in color. They are found in arid regions. Aridisols have low levels of organic matter. They also contain accumulations of clay and salts and have an alkaline pH. Aridisols can be used in agriculture if they are properly irrigated. Aridisols are extremely uncommon in Montana but can be found in central southern locations.
  
  

Inceptisols

• Inceptisols are young soils that are found in steep mountainous regions. They do not have well-defined layers, unlike most other types of soil. They are mostly used for non-agricultural purposes such as recreational areas, forest development and watersheds. Inceptisols are the second most common type of soil. Inceptisols are found mostly in western and eastern parts of the state, but not in the northern or central southern parts.