What's Included on the Hydric Soils Lists

National List

"Hydric Soils of the United States" includes at least one phase in the listing that meets the hydric soil criteria. The list does not include soils that are classified at categories higher than the series level in Soil Taxonomy (Soil Survey Staff, 1999) nor does it include map units that may contain these series. The list is useful in identifying map units that may contain hydric soils.

This list includes footnotes for soil series that are known to have nonhydric phases, a temperature column showing the temperature regimes for all taxa, and improved information in the critical phase criteria column. The critical phase criteria column has been misunderstood by many users. This column in some cases determines the capability class and subclass. For some soils not all of the listed critical phases are hydric. For example, it is highly probable that steeply sloping phases of some series may not meet the criteria for hydric soils. For more information, see the hydric soils definition and criteria.

The Natural Resources Conservation Service (NRCS) Hydric Soils Lists, available here, are by soil series. These lists were reviewed and approved by the National Technical Committee for Hydric Soils. More detailed and up-to-date hydric soil lists (e.g. by soil survey area map unit component) are maintained by the NRCS State Offices.

State Lists

The state lists are subsets of the national hydric soils list. For more detailed state lists by mapunit, contact the appropriate NRCS State Office.

County Lists

NRCS has developed local lists of map units that contain hydric soils for each county or parish in the United States. These local lists are available at the NRCS State Offices and are the preferred lists for use in making preliminary wetland determinations. The local lists are developed, using the Map Unit Interpretation Record (MUIR) database and the criteria for hydric soils.