Alameda Area, California

Survey Area CA609• 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 Alameda Area, 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
Los Gatos-Los Osos complex, 30 to 75 percent slopes, eroded, MLRA 15	40K	Well drained	C	Very limited	Very limited
Vallecitos loam, 30 to 75 percent slopes, eroded, MLRA 15	27K	Well drained	D	Very limited	Very limited
Vallecitos rocky loam, 30 to 45 percent slopes, eroded	23K	Well drained	D	Very limited	Very limited
Millsholm silt loam, 30 to 45 percent slopes, eroded	11K	Well drained	D	Very limited	Very limited
Millsholm silt loam, 45 to 75 percent slopes, eroded	10K	Somewhat excessively drained	C	Very limited	Very limited
Altamont clay, 15 to 30 percent slopes, MLRA 15	9K	Well drained	C	Very limited	Very limited
Positas gravelly loam, 2 to 20 percent slopes, eroded	9K	Well drained	D	Somewhat limited	Very limited
Rock land	9K			Not rated	Not rated
Altamont clay, moderately deep, 30 to 45 percent slopes, eroded	8K	Well drained	D	Very limited	Very limited
Positas gravelly loam, 20 to 40 percent slopes, eroded	8K	Well drained	D	Very limited	Very limited
Diablo clay, 30 to 45 percent slopes, eroded	8K	Well drained	C	Very limited	Very limited
Los Osos silty clay loam, 30 to 45 percent slopes, eroded	8K	Well drained	C	Very limited	Very limited
Linne clay loam, 15 to 30 percent slopes, MLRA 15	7K	Well drained	D	Very limited	Very limited
Linne clay loam, 3 to 15 percent slopes	7K	Well drained	C	Somewhat limited	Very limited
Henneke rocky loam, eroded	7K	Somewhat excessively drained	D	Very limited	Very limited
Linne clay loam, 30 to 45 percent slopes, eroded	7K	Well drained	C	Very limited	Very limited
Diablo clay, 15 to 30 percent slopes, MLRA 15	6K	Well drained	C	Very limited	Very limited
Altamont rocky clay, moderately deep, 7 to 30 percent slopes	6K	Well drained	D	Very limited	Very limited
Los Osos and Millsholm soils, 30 to 45 percent slopes, eroded	5K	Well drained	C	Very limited	Very limited
Clear Lake clay, drained, 0 to 2 percent slopes, MLRA 14	5K	Poorly 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.

Entisols

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

Inceptisols

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

What This Means

Building & Foundations

About 88% 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.