The second edition of Soil Taxonomy as researched and disseminated by the USDA's soil survey staff in 1999 divides the various soil types of the United States into 12 orders. Arguably, these 12 orders extend to include every part of the planet not covered by water, though this has met with argument from nations that have developed their own soil taxonomies. Though most soils contain a varying percentage of sand, there are only three orders in which sand makes up a major component and is a determinant factor in that soil's classification: entisols, oxisols and spodosols.
Entisols appear in the United States primarily in the flood plains around the Mississippi River and in the foothills surrounding the Rocky Mountains. They are soils that have yet to form stratified layers, known as horizons, from their parent accumulated components. Essentially, they have undergone no change from the state in which they were created, be it by volcanic or tectonic events, thousands if not millions of years ago. As such, they are composed primarily of volcanic sand, ash, silt, mud and other sedimentary debris.
Oxisols are very rare and found only in equatorial tropical regions such as Puerto Rico, Guam and the Hawaiian Islands. These are the exact opposite of entisols. Having been used by so many generations of plant life, they are weathered and leached of most nutrient minerals. No less than 90 percent of their content must be quartz sand and kaolin clay, and with such soft components, any horizons in oxisols are so small and self-contained as to be negligible. Oxisols retain an ochre red color because of high oxidized iron content, which, along with aluminum, make up the majority of the soil's remaining nutrients.
Spodosols appear only in Maine, New Hampshire, Vermont, Central Florida, around the Great Lakes, the southern coast of Alaska and the northern half of Washington. These are highly acidic, highly stratified soils formed as a result of being in areas with high water tables, plenty of sand and variable drainage issues. The parent material, which makes up the lowest layer of soil, was at one time granite or sandstone with a high concentration of quartz. Over time, fluctuations in the water table and natural acidity broke down the granite and sandstone, leaving behind sand granules. Atop this is an accumulated layer of clay and ferrous metals, which makes up the subsurface layer. Spodosols are characterized by a thin layer of decomposing organic matter just beneath the surface layer, making for soil that can be cultivated provided sufficient enriching fertilizers are used to make up for the soil's lack of natural nutrients.