Alameda Area, California
The dominant drainage class is Well drained and the dominant hydrologic group is D (very slow infiltration, high runoff). 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.
| 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 |
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.