Soil series profile

Fallbrook soil series

Fallbrook is a well drained soil with a sandy loam surface, mapped on 209,835 acres in 6 counties in CA. Hydrologic group C.

#1706 by mapped area fine-loamy Typic Haploxeralfs (Alfisols)

Drainage class: Well drained
Hydrologic group: C
Typical topsoil pH: 6.3
Mapped area: 210k

Typical Fallbrook profile

Texture and pH by depth

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 Fallbrook horizons (representative values)
Depth	Texture	pH	Clay	Sand	Organic matter
0–6 in (H1)	Sandy loam	6.3	15%	66%	0.75%
6–24 in (H2)	Sandy clay loam	6.7	23%	60%	0.25%
24–28 in (H3)	Weathered bedrock	Not reported	Not reported	Not reported	Not reported

Representative values from the most extensive Fallbrook map unit (Cieneba-Fallbrook rocky sandy loams, 30 to 65 percent slopes, eroded, survey area CA638). Other map units of this series vary within the series range.

Stock photo for illustration, not a sample of this soil series. Credit on the Sources & method page.

What this means

What Fallbrook soil means for gardens, lawns and septic systems

For gardens

Typical topsoil in Fallbrook soils is slightly acidic: pH 6.3 (most land between 6.1 and 6.7), the range most vegetables, flowers and lawn grasses prefer.

Loamy topsoil (loam, silt loam and similar) covers 98% of mapped Fallbrook acres: generally the easiest soil to garden, holding moisture without staying waterlogged. The most common surface texture is sandy loam (92% of mapped Fallbrook acres).

98% of mapped Fallbrook acres is moderately well to excessively drained, which suits most garden plants.

For lawns and yards

On 96% 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 98% of the acres in mapped Fallbrook soils very limited, 0% somewhat limited and 0% not limited (2% 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 Fallbrook soil is found

Mapped acres

Fallbrook is mapped in California.

Counties with the most mapped Fallbrook soil
County	Acres	Share of county land
San Diego County, CA	152,933	6.6%
Riverside County, CA	30,862	1.0%
Fresno County, CA	17,138	0.4%
Tulare County, CA	5,996	0.2%
Los Angeles County, CA	2,713	0.1%
Orange County, CA	101	0.0%

Septic absorption fields

NRCS rating, share of Fallbrook acres

Not limited 0%

Somewhat limited 0%

Very limited 98%

Not rated 2%

Septic tank absorption field rating across mapped Fallbrook acres. Scale 0 to 100% of mapped land.

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Septic tank absorption field rating across mapped Fallbrook acres.
Category	Share of acres
Not limited	0.0%
Somewhat limited	0.0%
Very limited	97.6%
Not rated	2.4%

Drainage, water table and flooding

Share of Fallbrook 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 7–48% (median 20%).
Topsoil organic matter: Median 0.8%.

Drainage class

Excessively drained 0%

Somewhat excessively drained 0%

Well drained 98%

Moderately well drained 0%

Somewhat poorly drained 0%

Poorly drained 0%

Very poorly drained 0%

Not rated 2%

Drainage class across mapped Fallbrook acres. Scale 0 to 100% of mapped land.

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Drainage class across mapped Fallbrook acres.
Category	Share of acres
Excessively drained	0.0%
Somewhat excessively drained	0.0%
Well drained	98.1%
Moderately well drained	0.0%
Somewhat poorly drained	0.0%
Poorly drained	0.0%
Very poorly drained	0.0%
Not rated	1.9%

Hydrologic soil group

A: fast infiltration (mostly sandy or gravelly) 0%

B: moderate infiltration 1%

C: slow infiltration 88%

D: very slow infiltration (clayey, shallow or wet) 8%

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 2%

Hydrologic soil group across mapped Fallbrook acres. Scale 0 to 100% of mapped land.

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Hydrologic soil group across mapped Fallbrook acres.
Category	Share of acres
A: fast infiltration (mostly sandy or gravelly)	0.0%
B: moderate infiltration	1.2%
C: slow infiltration	88.3%
D: very slow infiltration (clayey, shallow or wet)	8.1%
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	2.4%

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 Fallbrook (component kind "Series") in SSURGO: 209,835 acres.
Method: Shares are by mapped acres of Fallbrook components. The profile comes from the single largest Fallbrook component. Full methodology.

Independent reference site. No government affiliation or endorsement.

Full narrative description: USDA Official Soil Series Description for Fallbrook.