Soil series profile
Los Osos soil series
Los Osos is a well drained soil with a clay loam surface, mapped on 332,846 acres in 16 counties in CA. Hydrologic group D.
- Drainage class
- Well drained 91% of mapped acres
- Hydrologic group
- D 79% of mapped acres
- Typical topsoil pH
- 6.5 slightly acidic · range 5.8–6.7
- Mapped area
- 333k acres in 16 counties, 1 state
Typical Los Osos profile
Texture and pH by depth
Show as a table
| Depth | Texture | pH | Clay | Sand | Organic matter |
|---|---|---|---|---|---|
| 0–10 in (A) | Clay loam | 6.4 | 35% | 35% | 3% |
| 10–20 in (Bt1) | Clay | 6.4 | 40% | 34% | 0.75% |
| 20–32 in (Bt2) | Clay | 6.4 | 42% | 30% | 0.75% |
| 32–42 in (Cr) | Bedrock | Not reported | Not reported | Not reported | Not reported |

What this means
What Los Osos soil means for gardens, lawns and septic systems
For gardens
Typical topsoil in Los Osos soils is slightly acidic: pH 6.5 (most land between 5.8 and 6.7), the range most vegetables, flowers and lawn grasses prefer.
Loamy topsoil (loam, silt loam and similar) covers 90% of mapped Los Osos acres: generally the easiest soil to garden, holding moisture without staying waterlogged. The most common surface texture is clay loam (59% of mapped Los Osos acres).
92% of mapped Los Osos 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 Los Osos 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 Los Osos soil is found
Mapped acres
Los Osos is mapped in California.
| County | Acres | Share of county land |
|---|---|---|
| San Luis Obispo County, CA | 70,488 | 4.4% |
| Monterey County, CA | 70,126 | 3.2% |
| Contra Costa County, CA | 43,485 | 9.4% |
| Alameda County, CA | 38,020 | 8.1% |
| Santa Clara County, CA | 16,110 | 1.9% |
| Solano County, CA | 15,882 | 3.0% |
| Santa Barbara County, CA | 15,196 | 1.4% |
| Marin County, CA | 15,170 | 4.6% |
| Sonoma County, CA | 15,036 | 1.5% |
| Mendocino County, CA | 11,248 | 0.5% |
| Ventura County, CA | 6,745 | 1.1% |
| Santa Cruz County, CA | 2,728 | 1.0% |
| Los Angeles County, CA | 1,173 | 0.0% |
| Napa County, CA | 231 | 0.1% |
| San Benito County, CA | 96 | 0.0% |
| Glenn County, CA | 63 | 0.0% |
Septic absorption fields
NRCS rating, share of Los Osos 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 Los Osos 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 20–63% (median 40%).
- Topsoil organic matter
- Median 3%.
Drainage class
Show as a table
| Category | Share of acres |
|---|---|
| Excessively drained | 0.0% |
| Somewhat excessively drained | 1.1% |
| Well drained | 91.0% |
| Moderately well drained | 0.0% |
| Somewhat poorly drained | 0.2% |
| Poorly drained | 0.0% |
| Very poorly drained | 0.0% |
| Not rated | 7.6% |
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 | 11.1% |
| D: very slow infiltration (clayey, shallow or wet) | 79.2% |
| 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 | 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 Los Osos (component kind "Series") in SSURGO: 332,846 acres.
- Method
- Shares are by mapped acres of Los Osos components. The profile comes from the single largest Los Osos component. Full methodology.