What's My Soil

A field guide to the soil under your feet

Soil series profile

Gilman soil series

Gilman is a well drained soil with a loam surface, mapped on 458,718 acres in 9 counties across 2 states. Hydrologic group B.

#647 by mapped area coarse-loamy Typic Torrifluvents (Entisols)

Drainage class
Well drained
92% of mapped acres
Hydrologic group
B
70% of mapped acres
Typical topsoil pH
8.2
moderately alkaline · range 8.0–8.2
Mapped area
459k
acres in 9 counties, 2 states

Typical Gilman profile

Texture and pH by depth

Typical Gilman soil profile by depth 0 in 20 in 40 in 60 in 0–18 in · Ap · pH 8.2 · 24% clay Loam 18–37 in · C1 · pH 8.2 · 13% clay Loam 37–64 in · C2 · pH 8.2 · 13% clay Very fine sandy loam
Depth to scale. More strongly shaded layers hold more clay. Horizon names are the soil survey's (A = topsoil, B = subsoil, C = parent material).
Show as a table
Typical Gilman horizons (representative values)
Depth Texture pH Clay Sand Organic matter
0–18 in (Ap) Loam 8.2 24% 39% 0.25%
18–37 in (C1) Loam 8.2 13% 46% 0.25%
37–64 in (C2) Very fine sandy loam 8.2 13% 64% 0.25%

Representative values from the most extensive Gilman map unit (Gilman loam, 0 to 1 percent slopes, survey area AZ651). Other map units of this series vary within the series range.

Hands holding dark garden soil
Stock photo for illustration, not a sample of this soil series. Credit on the Sources & method page.

What this means

What Gilman soil means for gardens, lawns and septic systems

For gardens

Typical topsoil in Gilman soils is moderately alkaline: pH 8.2 (most land between 8.0 and 8.2). Acid-loving plants such as blueberries and azaleas struggle without amended beds, and some trees and shrubs show iron chlorosis (yellow leaves with green veins).

Loamy topsoil (loam, silt loam and similar) covers 86% of mapped Gilman acres: generally the easiest soil to garden, holding moisture without staying waterlogged. The most common surface texture is loam (52% of mapped Gilman acres).

99% of mapped Gilman acres is moderately well to excessively drained, which suits most garden plants.

For lawns and yards

Most land is in hydrologic groups B and C, where rain soaks in at a moderate pace.

For a septic system

For conventional septic absorption fields, NRCS rates 29% of the acres in mapped Gilman soils very limited, 69% somewhat limited and 1% not limited (1% not rated, such as urban land, pits or water).

Flooding is mapped on 38% of the acres (27% occasional, 0% frequent).

Only a licensed site evaluation or perc test at the actual lot decides whether a system is allowed and which design.

Generated from the mapped numbers above using fixed rules, not a site visit. See how these notes are written.

Where Gilman soil is found

Mapped acres

Gilman is mapped in Arizona and California.

Counties with the most mapped Gilman soil
County Acres Share of county land
Maricopa County, AZ 264,899 4.3%
Riverside County, CA 56,569 1.9%
La Paz County, AZ 37,287 1.3%
Pinal County, AZ 36,339 1.1%
Pima County, AZ 28,471 0.6%
Yuma County, AZ 14,177 0.6%
San Diego County, CA 5,231 0.2%
San Bernardino County, CA 599 0.0%
Imperial County, CA 29 0.0%

Septic absorption fields

NRCS rating, share of Gilman acres

Not limited 1%
Somewhat limited 69%
Very limited 29%
Not rated 1%
Septic tank absorption field rating across mapped Gilman acres. Scale 0 to 100% of mapped land.
Show as a table
Septic tank absorption field rating across mapped Gilman acres.
CategoryShare of acres
Not limited1.3%
Somewhat limited68.5%
Very limited29.2%
Not rated1.0%

Drainage, water table and flooding

Share of Gilman acres

Depth to seasonal high water table
About 3.9 feet (47 in) (median where reported).
Flooding
Mapped as flooding on 38% of acres (27% occasional, 0% frequent).
Slope
Typically 0–2% (median 1%).
Topsoil organic matter
Median 0.2%.

Drainage class

Excessively drained 2%
Somewhat excessively drained 0%
Well drained 92%
Moderately well drained 5%
Somewhat poorly drained 0%
Poorly drained 0%
Very poorly drained 0%
Not rated 1%
Drainage class across mapped Gilman acres. Scale 0 to 100% of mapped land.
Show as a table
Drainage class across mapped Gilman acres.
CategoryShare of acres
Excessively drained2.1%
Somewhat excessively drained0.0%
Well drained92.3%
Moderately well drained4.6%
Somewhat poorly drained0.0%
Poorly drained0.0%
Very poorly drained0.0%
Not rated1.0%

Hydrologic soil group

A: fast infiltration (mostly sandy or gravelly) 18%
B: moderate infiltration 70%
C: slow infiltration 12%
D: very slow infiltration (clayey, shallow or wet) 0%
A/D: D as is, A if drained 0%
B/D: D as is, B if drained 0%
C/D: D as is, C if drained 0%
Not rated 1%
Hydrologic soil group across mapped Gilman acres. Scale 0 to 100% of mapped land.
Show as a table
Hydrologic soil group across mapped Gilman acres.
CategoryShare of acres
A: fast infiltration (mostly sandy or gravelly)17.5%
B: moderate infiltration69.8%
C: slow infiltration11.7%
D: very slow infiltration (clayey, shallow or wet)0.0%
A/D: D as is, A if drained0.0%
B/D: D as is, B if drained0.0%
C/D: D as is, C if drained0.0%
Not rated1.0%

Sources & data dates

Source
USDA NRCS Soil Survey Geographic Database (SSURGO), queried through Soil Data Access. Public domain.
Data date
SSURGO as published on November 3, 2026 (most recent survey area update October 26, 2026). NRCS refreshes SSURGO each October.
Scope
All map unit components named Gilman (component kind "Series") in SSURGO: 458,718 acres.
Method
Shares are by mapped acres of Gilman components. The profile comes from the single largest Gilman component. Full methodology.

Independent reference site. No government affiliation or endorsement.

Full narrative description: USDA Official Soil Series Description for Gilman.