In looking closer at soils, it is important to understand that there are general regions or horizons of soil development that are usually obvious in an undisturbed area. For example, if we found an undisturbed area, and dug down 3 to 6 feet (1 or 2 meters), we would likely find a soil profile (cross-section of the horizons) of three integrated horizons. The composition and stage of development will obviously vary widely depending on where the soil profile is taken. The top horizon is called the A horizon or topsoil. This horizon is usually 4 to 8 inches on average, again depending on where your sample is from. The A horizon is further subdivided into a darker upper portion, called the A1 horizon and a lighter lower portion A2 horizon. The A1 horizon contains the majority of the organic material out of the three integrated horizons. The next horizon is the B horizon or the subsoil. This is usually 1 or 2 feet deep on average. The subsoil usually contains more clay, so fewer pore spaces, and is lighter in color than the topsoil. The lowest horizon is called the C horizon and it could be 4 inches to 10 feet deep or it may not be present. The C horizon is called the soil parent material and it extends down to bedrock.
