Color is one way geologists classify soil.
Red soil can mean that there are iron oxides present, the case in Alabama and much of the South.
The Cereal Belt in the Tennessee Valley and the counties beyond have the richest soils which are the red clays and dark loams of the river valley.
In places that are hot and wet for much of the year, like Hawaii, red soil can indicate that water has removed much of the nutrients, a process called leaching, leaving behind very infertile soils.
