Soil series profile

Cohasset soil series

Cohasset is a well drained soil with a stony loam surface, mapped on 281,411 acres in 10 counties in CA. Hydrologic group B.

#1229 by mapped area fine-loamy Ultic Haploxeralfs (Alfisols)

Drainage class: Well drained
Hydrologic group: B
Typical topsoil pH: 5.8
Mapped area: 281k

Typical Cohasset 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 Cohasset horizons (representative values)
Depth	Texture	pH	Clay	Sand	Organic matter
0–18 in (H1)	Stony loam	5.8	20%	42%	6%
18–60 in (H2)	Stony clay loam	5.3	30%	34%	0.75%
60–79 in (H3)	Weathered bedrock	Not reported	Not reported	Not reported	0.75%

Representative values from the most extensive Cohasset map unit (Cohasset stony loam, 0 to 30 percent slopes, survey area CA607). 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 Cohasset soil means for gardens, lawns and septic systems

For gardens

Typical topsoil in Cohasset soils is moderately acidic: pH 5.8 (most land between 5.8 and 6.1). Many vegetables grow well here, and some gardens benefit from a little lime. Test before adding any.

Loamy topsoil (loam, silt loam and similar) covers 98% of mapped Cohasset acres: generally the easiest soil to garden, holding moisture without staying waterlogged. The most common surface texture is loam (38% of mapped Cohasset acres).

99% of mapped Cohasset acres is moderately well to excessively drained, which suits most garden plants.

For lawns and yards

Most land is in hydrologic groups B and C, where rain soaks in at a moderate pace.

For a septic system

For conventional septic absorption fields, NRCS rates 96% of the acres in mapped Cohasset soils very limited, 2% 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 Cohasset soil is found

Mapped acres

Cohasset is mapped in California.

Counties with the most mapped Cohasset soil
County	Acres	Share of county land
Shasta County, CA	102,447	5.7%
Tehama County, CA	78,048	4.2%
El Dorado County, CA	38,442	3.7%
Nevada County, CA	36,001	2.7%
Amador County, CA	13,155	3.6%
Placer County, CA	10,866	2.0%
Sonoma County, CA	1,060	0.1%
Sierra County, CA	38	0.0%
Calaveras County, CA	21	0.0%
Napa County, CA	3	0.0%

Septic absorption fields

NRCS rating, share of Cohasset acres

Not limited 0%

Somewhat limited 2%

Very limited 96%

Not rated 2%

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

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Septic tank absorption field rating across mapped Cohasset acres.
Category	Share of acres
Not limited	0.0%
Somewhat limited	2.1%
Very limited	95.5%
Not rated	2.4%

Drainage, water table and flooding

Share of Cohasset 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 16–33% (median 20%).
Topsoil organic matter: Median 6%.

Drainage class

Excessively drained 0%

Somewhat excessively drained 0%

Well drained 99%

Moderately well drained 0%

Somewhat poorly drained 0%

Poorly drained 0%

Very poorly drained 0%

Not rated 2%

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

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Drainage class across mapped Cohasset acres.
Category	Share of acres
Excessively drained	0.0%
Somewhat excessively drained	0.0%
Well drained	98.5%
Moderately well drained	0.0%
Somewhat poorly drained	0.0%
Poorly drained	0.0%
Very poorly drained	0.0%
Not rated	1.5%

Hydrologic soil group

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

B: moderate infiltration 74%

C: slow infiltration 23%

D: very slow infiltration (clayey, shallow or wet) 0%

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 Cohasset acres. Scale 0 to 100% of mapped land.

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Hydrologic soil group across mapped Cohasset acres.
Category	Share of acres
A: fast infiltration (mostly sandy or gravelly)	0.0%
B: moderate infiltration	74.2%
C: slow infiltration	23.4%
D: very slow infiltration (clayey, shallow or wet)	0.0%
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	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 Cohasset (component kind "Series") in SSURGO: 281,411 acres.
Method: Shares are by mapped acres of Cohasset components. The profile comes from the single largest Cohasset component. Full methodology.

Independent reference site. No government affiliation or endorsement.

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