Data & method

Every figure on this site comes from three public USDA–NRCS databases. Here is what we take from each, what we compute ourselves, and how to read the drawings.

Sources

Soil Survey Staff, Natural Resources Conservation Service, United States Department of Agriculture. Official Soil Series Descriptions; Soil Classification database; Soil Survey Geographic (SSURGO) Database. Accessed October 2026. Extent, ranks and comparisons computed by this site. All are U.S. government works in the public domain. Series descriptions and the classification database were read from the NRCS’s published files; extent was computed from SSURGO through NRCS Soil Data Access.

What is shown

Only structured facts are used: names, taxonomic classes, horizon names and depths, drainage, depth and water-movement classes, parent-material and landform labels, states and MLRAs. No description text is reproduced.

Extent

Acres are current SSURGO mapped acres for map unit components named for the series, summed nationally and by state. They can differ from acreage quoted in a series description. Alaska is only partly mapped. Ranks compare all series with SSURGO extent.

Profiles

Each profile is drawn to scale from the horizon depths of the typical pedon in the official series description. Colors are chosen by horizon type to aid reading; they are not the Munsell colors of the soil. Where the description gives no lower depth for the last horizon, usually bedrock, the drawing fades out. Order pages show a schematic built from the order’s median depth to the first B horizon, median solum thickness and median described depth; it is not a real pedon.

Reading horizon names

The plain-English labels next to each horizon are our own short readings of the standard horizon designations described in the NRCS Soil Survey Manual (USDA Handbook 18) and the Keys to Soil Taxonomy: a capital letter for the master horizon, lower-case suffixes for features, and a leading number for a change in parent material. Trailing numbers only split a horizon into parts. When a designation contains a symbol outside the mapping below, we show the horizon name and depth only.

Master or transition	Our reading
O	Organic layer
A	Topsoil
E	Leached layer
B	Subsoil
C	Parent material
R	Hard bedrock
L	Lake sediment
Cr	Soft bedrock
AB	Topsoil grading to subsoil
BA	Subsoil grading from topsoil
AC	Topsoil grading to parent material
BC	Subsoil grading to parent material
CB	Parent material with subsoil traits
BE	Subsoil with leached traits
EB	Leached layer grading to subsoil
OA	Organic layer grading to topsoil

Suffix	Our reading
jj	Frost-churned
ss	Slickensides (shrink–swell)
kk	Heavy lime build-up
t	Clay build-up
k	Lime (carbonate) build-up
g	Gleyed: gray from wetness
w	Color or structure change
h	Humus build-up
s	Iron and aluminum build-up
x	Fragipan: dense and brittle
y	Gypsum
z	Salts
n	Sodium
o	Residual iron and aluminum oxides
v	Plinthite
q	Silica
m	Cemented
c	Concretions
d	Dense, roots restricted
p	Plowed
b	Buried
f	Frozen
i	Slightly decomposed
e	Moderately decomposed
a	Highly decomposed

Drainage, depth and water classes

Each series’ drainage class, depth class and saturated hydraulic conductivity (Ksat) or permeability class come from its official series description. The classes and their limits are defined in the NRCS Soil Survey Manual (USDA Handbook 18); the one-line explanations on series pages are our own summaries. Depth classes use these limits: very shallow under 25 cm, shallow 25–50 cm, moderately deep 50–100 cm, deep 100–150 cm, very deep over 150 cm.

Order descriptions

The short descriptions of the twelve soil orders are our own summaries of the order definitions in the Keys to Soil Taxonomy.

State soils

State soils follow the NCSS list; some, such as Connecticut’s and Washington’s, are proposed rather than adopted by law.