Soil series profile
Diablo soil series
Diablo is a well drained soil with a clay surface, mapped on 262,711 acres in 14 counties in CA. Hydrologic group C.
- Drainage class
- Well drained 92% of mapped acres
- Hydrologic group
- C 78% of mapped acres
- Typical topsoil pH
- 7.3 neutral · range 7.0–7.5
- Mapped area
- 263k acres in 14 counties, 1 state
Typical Diablo profile
Texture and pH by depth
Show as a table
| Depth | Texture | pH | Clay | Sand | Organic matter |
|---|---|---|---|---|---|
| 0–8 in (A) | Clay | 7.5 | 52% | 23% | 2.5% |
| 8–26 in (Bkss1) | Clay | 7.5 | 52% | 23% | 2.5% |
| 26–38 in (Bkss2) | Clay | 7.9 | 52% | 23% | 2.5% |
| 38–52 in (Bkss3) | Clay | 7.9 | 52% | 23% | 0.5% |
| 52–68 in (Bk) | Clay | 7.9 | 52% | 23% | 0.5% |
| 68–79 in (Cr) | Bedrock | Not reported | 52% | 23% | 0.5% |
What this means
What Diablo soil means for gardens, lawns and septic systems
For gardens
Typical topsoil in Diablo soils is neutral: pH 7.3 (most land between 7.0 and 7.5), the range most vegetables, flowers and lawn grasses prefer.
Clayey topsoil covers 90% of mapped Diablo 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 clay (88% of mapped Diablo acres).
92% of mapped Diablo acres is moderately well to excessively drained, which suits most garden plants.
For lawns and yards
On 90% 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 90% of the acres in mapped Diablo soils very limited, 0% somewhat limited and 0% not limited (10% not rated, such as urban land, pits or water).
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 Diablo soil is found
Mapped acres
Diablo is mapped in California.
| County | Acres | Share of county land |
|---|---|---|
| San Luis Obispo County, CA | 50,459 | 3.1% |
| San Benito County, CA | 37,454 | 4.2% |
| San Diego County, CA | 36,451 | 1.6% |
| Contra Costa County, CA | 31,066 | 6.7% |
| Monterey County, CA | 24,338 | 1.1% |
| Alameda County, CA | 24,207 | 5.1% |
| Solano County, CA | 21,653 | 4.1% |
| Sonoma County, CA | 13,433 | 1.3% |
| Santa Barbara County, CA | 10,043 | 0.9% |
| Ventura County, CA | 5,565 | 0.9% |
| Santa Clara County, CA | 2,535 | 0.3% |
| Napa County, CA | 2,143 | 0.5% |
| Santa Cruz County, CA | 1,371 | 0.5% |
| Yolo County, CA | 6 | 0.0% |
Septic absorption fields
NRCS rating, share of Diablo acres
Show as a table
| Category | Share of acres |
|---|---|
| Not limited | 0.0% |
| Somewhat limited | 0.0% |
| Very limited | 90.3% |
| Not rated | 9.7% |
Drainage, water table and flooding
Share of Diablo acres
- Depth to seasonal high water table
- None reported within about 6.5 feet (median where reported).
- Flooding
- Not mapped as flooding on most acres.
- Slope
- Typically 7–40% (median 23%).
- Topsoil organic matter
- Median 2.5%.
Drainage class
Show as a table
| Category | Share of acres |
|---|---|
| Excessively drained | 0.0% |
| Somewhat excessively drained | 0.0% |
| Well drained | 92.2% |
| Moderately well drained | 0.0% |
| Somewhat poorly drained | 0.0% |
| Poorly drained | 0.0% |
| Very poorly drained | 0.0% |
| Not rated | 7.8% |
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 | 78.3% |
| D: very slow infiltration (clayey, shallow or wet) | 12.0% |
| 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 | 9.7% |
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 Diablo (component kind "Series") in SSURGO: 262,711 acres.
- Method
- Shares are by mapped acres of Diablo components. The profile comes from the single largest Diablo component. Full methodology.