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.

#991 by mapped area fine Typic Argixerolls (Mollisols)

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

Typical Los Osos soil profile by depth 0 in 10 in 20 in 30 in 40 in 0–10 in · A · pH 6.4 · 35% clay Clay loam 10–20 in · Bt1 · pH 6.4 · 40% clay Clay 20–32 in · Bt2 · pH 6.4 · 42% clay Clay 32–42 in · Cr Bedrock
Depth to scale. More strongly shaded layers hold more clay. Horizon names are the soil survey's (A = topsoil, B = subsoil, C = parent material).
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Typical Los Osos horizons (representative values)
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

Representative values from the most extensive Los Osos map unit (Los Osos clay loam, 30 to 50 percent slopes, survey area CA013). 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 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.

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

Where Los Osos soil is found

Mapped acres

Los Osos is mapped in California.

Counties with the most mapped Los Osos soil
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

Not limited 0%
Somewhat limited 0%
Very limited 90%
Not rated 10%
Septic tank absorption field rating across mapped Los Osos acres. Scale 0 to 100% of mapped land.
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Septic tank absorption field rating across mapped Los Osos acres.
CategoryShare of acres
Not limited0.0%
Somewhat limited0.0%
Very limited90.3%
Not rated9.7%

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

Excessively drained 0%
Somewhat excessively drained 1%
Well drained 91%
Moderately well drained 0%
Somewhat poorly drained <1%
Poorly drained 0%
Very poorly drained 0%
Not rated 8%
Drainage class across mapped Los Osos acres. Scale 0 to 100% of mapped land.
Show as a table
Drainage class across mapped Los Osos acres.
CategoryShare of acres
Excessively drained0.0%
Somewhat excessively drained1.1%
Well drained91.0%
Moderately well drained0.0%
Somewhat poorly drained0.2%
Poorly drained0.0%
Very poorly drained0.0%
Not rated7.6%

Hydrologic soil group

A: fast infiltration (mostly sandy or gravelly) 0%
B: moderate infiltration 0%
C: slow infiltration 11%
D: very slow infiltration (clayey, shallow or wet) 79%
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 10%
Hydrologic soil group across mapped Los Osos acres. Scale 0 to 100% of mapped land.
Show as a table
Hydrologic soil group across mapped Los Osos acres.
CategoryShare of acres
A: fast infiltration (mostly sandy or gravelly)0.0%
B: moderate infiltration0.0%
C: slow infiltration11.1%
D: very slow infiltration (clayey, shallow or wet)79.2%
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 rated9.7%

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.

Independent reference site. No government affiliation or endorsement.

Full narrative description: USDA Official Soil Series Description for Los Osos.