Soil series profile
Imperial soil series
Imperial is a moderately well drained soil with a silty clay surface, mapped on 236,004 acres in 2 counties in CA. Hydrologic group D.
- Drainage class
- Moderately well drained 50% of mapped acres
- Hydrologic group
- D 52% of mapped acres
- Typical topsoil pH
- 8.2 moderately alkaline · range 8.2–8.4
- Mapped area
- 236k acres in 2 counties, 1 state
Typical Imperial profile
Texture and pH by depth
Show as a table
| Depth | Texture | pH | Clay | Sand | Organic matter |
|---|---|---|---|---|---|
| 0–12 in (H1) | Silty clay | 8.2 | 50% | 5% | 0.5% |
| 12–60 in (H2) | Silty clay loam | 8.2 | 40% | 18% | 0.25% |
What this means
What Imperial soil means for gardens, lawns and septic systems
For gardens
Typical topsoil in Imperial soils is moderately alkaline: pH 8.2 (most land between 8.2 and 8.4). 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).
Clayey topsoil covers 59% of mapped Imperial acres. Clay holds water and nutrients but drains slowly and compacts if worked wet: add compost, avoid tilling soggy soil and consider raised beds. The most common surface texture is silty clay (59% of mapped Imperial acres).
62% of mapped Imperial acres is moderately well to excessively drained, which suits most garden plants.
For lawns and yards
On >99% of mapped acres, rain soaks in slowly (hydrologic groups C and D, including dual groups that are D until drained). Expect runoff and puddles after heavy rain: core-aerate compacted lawns and keep ground sloping away from foundations.
For a septic system
For conventional septic absorption fields, NRCS rates >99% of the acres in mapped Imperial soils very limited, 0% somewhat limited and 0% not limited.
Where the soil is very limited (slow permeability, a high water table, flooding, shallow bedrock or steep slopes), alternative systems such as mound or sand-filter designs are common and cost more.
Only a licensed site evaluation or perc test at the actual lot decides whether a system is allowed and which design.
Where Imperial soil is found
Mapped acres
Imperial is mapped in California.
| County | Acres | Share of county land |
|---|---|---|
| Imperial County, CA | 214,067 | 14.6% |
| Riverside County, CA | 21,375 | 0.7% |
Septic absorption fields
NRCS rating, share of Imperial acres
Show as a table
| Category | Share of acres |
|---|---|
| Not limited | 0.0% |
| Somewhat limited | 0.0% |
| Very limited | 99.6% |
| Not rated | 0.4% |
Drainage, water table and flooding
Share of Imperial acres
- Depth to seasonal high water table
- About 2.9 feet (35 in) (median where reported).
- Flooding
- Not mapped as flooding on most acres.
- Slope
- Typically 1–1% (median 1%).
- Topsoil organic matter
- Median 0.3%.
Drainage class
Show as a table
| Category | Share of acres |
|---|---|
| Excessively drained | 0.0% |
| Somewhat excessively drained | 0.0% |
| Well drained | 12.6% |
| Moderately well drained | 49.5% |
| Somewhat poorly drained | 37.5% |
| Poorly drained | 0.0% |
| Very poorly drained | 0.0% |
| Not rated | 0.4% |
Hydrologic soil group
Show as a table
| Category | Share of acres |
|---|---|
| A: fast infiltration (mostly sandy or gravelly) | 0.0% |
| B: moderate infiltration | 0.0% |
| C: slow infiltration | 47.4% |
| D: very slow infiltration (clayey, shallow or wet) | 52.2% |
| A/D: D as is, A if drained | 0.0% |
| B/D: D as is, B if drained | 0.0% |
| C/D: D as is, C if drained | 0.0% |
| Not rated | 0.4% |
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 Imperial (component kind "Series") in SSURGO: 236,004 acres.
- Method
- Shares are by mapped acres of Imperial components. The profile comes from the single largest Imperial component. Full methodology.