County soil summary
Soil types in Riverside County, California
The most widespread soils are Carsitas, Cieneba and Carrizo; the most common drainage class is somewhat excessively drained (29% of the land), and typical topsoil pH is 7.0.
About 80,000 acres of Riverside County lie in multi-county soil survey areas (CA678, CA695, CA698, CA794, CA803, CA804, CA808) that the soil survey does not split by county. Those acres, often public forest or desert land, are counted in the California totals but not in the figures below.
- Well or moderately well drained
- 75% of land · state 81%
- Typical topsoil pH
- 7.0 neutral · state 6.7
- Septic fields very limited
- 77% of land · state 79%
- Subject to flooding
- 13% of land, any frequency · state 11%
Most common soils in Riverside County
Share of mapped land
A county is a patchwork of many soils. These 8 cover 32% of the mapped land; 220 named soil series are mapped here in all.
| Soil | Share of land | Drainage | Topsoil pH |
|---|---|---|---|
| Rock outcropLand type, not a soil series | 11.3% | — | — |
| Carsitas | 4.6% | Somewhat excessively drained | 8.0 |
| Cieneba | 4.1% | Somewhat excessively drained | 6.5 |
| Carrizo | 2.6% | Excessively drained | 7.9 |
| Pintobasin | 2.6% | Somewhat excessively drained | 7.6 |
| Myoma | 2.3% | Somewhat excessively drained | 8.5 |
| Blackeagle | 2.2% | Somewhat excessively drained | 7.2 |
| Gilman | 1.9% | Well drained | 8.2 |
What this means
What the soils in Riverside County mean for gardens, lawns and septic systems
For your garden
Typical topsoil in Riverside County is neutral: pH 7.0 (most land between 6.4 and 8.2), the range most vegetables, flowers and lawn grasses prefer.
Sandy topsoil covers 38% of the land. It drains fast and warms early in spring, but dries out and loses nutrients quickly: mulch, compost and steady watering help. The most common surface texture is sandy loam (13% of the land).
43% of the land is excessively or somewhat excessively drained: water moves through fast, so gardens need more frequent watering in dry spells.
For your lawn and yard
28% of the land is in hydrologic group A, where water soaks in fast. Lawns there dry out quickly; deeper, less frequent watering and organic matter help.
For a septic system
For conventional septic absorption fields, NRCS rates 77% of the land in Riverside County very limited, 5% somewhat limited and 1% not limited (17% not rated, such as urban land, pits or water).
That is close to the state as a whole (79% very 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.
Flooding is mapped on 13% of the land (1% occasional, <1% frequent).
Only a licensed site evaluation or perc test at the actual lot decides whether a system is allowed and which design.
Drainage
How long the soil stays wet
The most common drainage class is somewhat excessively drained (29%). 75% of the land is moderately well drained or better, compared with 81% across California.
Show as a table
| Category | Riverside County | California |
|---|---|---|
| Excessively drained | 13.7% | 7.7% |
| Somewhat excessively drained | 29.0% | 17.6% |
| Well drained | 28.9% | 50.7% |
| Moderately well drained | 3.6% | 4.7% |
| Somewhat poorly drained | 1.2% | 2.5% |
| Poorly drained | 0.5% | 2.0% |
| Very poorly drained | 0.0% | 0.7% |
| Not rated | 23.0% | 14.2% |
Septic absorption fields
NRCS rating for conventional drain fields
The rating looks at the soil from 24 to 60 inches deep: permeability, depth to a seasonal water table or bedrock, flooding and slope. “Very limited” means at least one feature is unfavorable enough that a conventional field is hard to make work.
Show as a table
| Category | Riverside County | California |
|---|---|---|
| Not limited | 1.1% | 4.3% |
| Somewhat limited | 5.1% | 3.6% |
| Very limited | 77.2% | 79.2% |
| Not rated | 16.6% | 12.9% |
Rain, runoff and water table
Hydrologic soil group, flooding, seasonal water table
Hydrologic soil group
How fast rain soaks in when the soil is already wet. Group A soaks in fastest, D slowest.
Show as a table
| Category | Riverside County | California |
|---|---|---|
| A: fast infiltration (mostly sandy or gravelly) | 28.2% | 20.5% |
| B: moderate infiltration | 7.3% | 12.5% |
| C: slow infiltration | 8.6% | 22.7% |
| D: very slow infiltration (clayey, shallow or wet) | 37.9% | 30.3% |
| A/D: D as is, A if drained | 0.6% | 0.3% |
| B/D: D as is, B if drained | 0.1% | 0.3% |
| C/D: D as is, C if drained | 0.8% | 0.9% |
| Not rated | 16.5% | 12.6% |
Flooding
Show as a table
| Category | Riverside County | California |
|---|---|---|
| No flooding | 56.7% | 77.1% |
| Rare or very rare | 10.9% | 8.2% |
| Occasional | 1.2% | 1.6% |
| Frequent or very frequent | 0.9% | 1.0% |
| Not reported | 30.3% | 12.1% |
Seasonal high water table
Show as a table
| Category | Riverside County | California |
|---|---|---|
| Within 18 inches at some time of year | 2.3% | 2.6% |
| 18 inches to 3.3 feet | 0.3% | 1.9% |
| Deeper than 3.3 feet or none reported | 74.6% | 86.9% |
| Not reported | 22.9% | 8.6% |
Topsoil pH and texture
First mineral layer of each soil
Typical topsoil pH is 7.0 (neutral); 80% of rated land falls between 6.4 and 8.2. Median topsoil organic matter is 0.8%.
Show as a table
| Category | Riverside County | California |
|---|---|---|
| Strongly acidic (below 5.5) | 0.0% | 3.1% |
| Moderately to slightly acidic (5.5–6.4) | 9.0% | 22.8% |
| Near neutral (6.5–7.3) | 32.3% | 25.2% |
| Alkaline (7.4 and up) | 32.0% | 30.6% |
| Not reported | 26.7% | 18.2% |
Texture
Show as a table
| Category | Riverside County | California |
|---|---|---|
| Sandy | 38.4% | 21.3% |
| Loamy (loam, silt loam and similar) | 33.7% | 56.7% |
| Clayey (40%+ clay) | 1.7% | 3.9% |
| Organic (muck or peat) | 0.0% | 0.2% |
| Not reported (rock, urban land, etc.) | 26.2% | 18.0% |
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
- Riverside County, California (FIPS 06065): 2,990,683 acres of mapped land, 101,464 acres of open water excluded. State comparisons pool all mapped land in California.
- Method
- Shares are by mapped land area: each map unit’s acres in the county times each soil component’s percentage. Open water is excluded. Topsoil values use the first mineral horizon of each component. Full methodology.