Alameda Area, California
The most common soil here is Vallecitos, on about 12% of the land: a gravelly loam, a balanced mix that crumbles in your hand. Los Osos and Altamont come next.
About 90% of the land drains well, and 4% stays wet for long stretches.
USDA rates 94% of the land very limited for a standard septic drain field, and 83% very limited for homes with basements. That means extra cost or special design, not that it can't be done.
Worth knowing: 2% of the land floods occasionally or more, and bedrock lies within 40 inches under 63% of it.
Soils change over short distances, so look up an address below for the soil at that exact spot and the reasons behind each rating.
The soils you're most likely standing on
The biggest named soils in Alameda Area, California, each drawn five feet deep from its official USDA description, in its recorded colors.
Dots mark gravel; white flecks mark lime. Shares are by acres across the survey area, and each mapped patch usually mixes several of these soils.
The biggest mapped areas
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.
What This Means
Building & Foundations
About 83% 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 94% 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.