Colusa County, California

Survey Area CA011• California

The dominant drainage class is Well drained and the dominant hydrologic group is D (very slow infiltration, high runoff). The most common soil order is Mollisols — grassland soils with a thick, dark, fertile topsoil rich in organic matter. This report summarizes the major soil map units across the survey area to help you understand what to expect when buying, building, or gardening in Colusa County, California. Search your address to find the exact soil composition, drainage, and series details at your specific location.

Soil Map Unit	Acres	Drainage	Hydro Group	Dwellings	Septic
Millsholm-Contra Costa association, 30 to 75 percent slopes	74K	Well drained	D	Very limited	Very limited
Willows silty clay, 0 to 1 percent slopes, occasionally flooded	58K	Poorly drained	D	Very limited	Very limited
Willows silty clay, 0 to 1 percent slopes	37K	Poorly drained	D	Very limited	Very limited
Goldeagle-Positas-Balcom complex, 30 to 75 percent slopes	33K	Well drained	C	Very limited	Very limited
Willows silty clay, 0 to 1 percent slopes, frequently flooded	30K	Poorly drained	D	Very limited	Very limited
Capay clay loam, 0 percent slopes, low precip, MLRA 17	29K	Moderately well drained	D	Very limited	Very limited
Westfan loam, 0 to 2 percent slopes	24K	Well drained	B	Very limited	Very limited
Scribner silt loam, 0 to 1 percent slopes	19K	Poorly drained	C/D	Very limited	Very limited
Etsel-Maymen-Marpa association, 30 to 50 percent slopes	18K	Somewhat excessively drained	D	Very limited	Very limited
Clear Lake clay, 0 to 1 percent slopes, occasionally flooded, MLRA 17	18K	Poorly drained	C/D	Very limited	Very limited
Vina loam, silt loam substratum, 0 to 2 percent slopes, MLRA 17	17K	Well drained	B	Very limited	Somewhat limited
Mallard clay loam, 0 to 1 percent slopes	16K	Somewhat poorly drained	D	Very limited	Very limited
Neuns-Bamtush-Goulding association, 30 to 50 percent slopes	16K	Well drained	C	Very limited	Very limited
Hillgate clay loam, 0 to 2 percent slopes	15K	Well drained	C	Very limited	Very limited
Henneke-Okiota complex, 50 to 75 percent slopes	15K	Well drained	D	Very limited	Very limited
Henneke-Montara-Rock outcrop complex, 10 to 50 percent slopes, MLRA 15	15K	Well drained	D	Very limited	Very limited
Moonbend silt loam, 0 to 2 percent slopes	14K	Moderately well drained	C	Very limited	Very limited
Contra Costa-Millsholm complex, 50 to 75 percent slopes	14K	Well drained	D	Very limited	Very limited
Neuns-Marpa-Goulding complex, 30 to 50 percent slopes	13K	Well drained	C	Very limited	Very limited
Sehorn-Altamont complex, 30 to 50 percent slopes	12K	Well drained	D	Very limited	Very limited

Soil Orders in This Area

The USDA classifies every soil into one of 12 soil orders. Here are the dominant orders found in this survey area.

Mollisols

Fertile grassland soils with thick, dark topsoil. Among the best for agriculture, building, and gardening.

Vertisols

High-clay soils that shrink and swell dramatically. Fertile but challenging for foundations and septic systems.

Alfisols

Moderately weathered forest soils with clay-enriched subsoil. Productive for agriculture, generally good for building and septic.

Inceptisols

Young but developing soils found in mountains and river terraces. Variable properties — check drainage and bedrock depth.

Entisols

Young soils with little development — found on floodplains, dunes, and steep slopes. Properties vary widely by setting.

What This Means

Building & Foundations

About 100% of soils are rated "very limited" for dwellings with basements. Specific challenges include shallow bedrock, steep slopes, poor drainage in some areas, flood-prone areas. A geotechnical assessment is recommended before building.

Septic Systems

About 96% of soils are rated "very limited" for septic absorption fields. Despite good drainage overall, limitations may stem from shallow bedrock, steep slopes, or seasonal conditions. Engineered or alternative systems are frequently required. Always get a professional perc test before purchasing land that needs septic.

Gardening & Agriculture

Well-drained soils on sloped terrain — good for most plants but watch for erosion. Terracing, contour planting, and mulching help retain moisture and topsoil. Drip irrigation is more effective than sprinklers on slopes.