Alameda County, California, Western Part
The most common soil here is Novato, on about 9% of the land: a clay, sticky when wet and rock-hard when dry. Danville and Clear Lake come next.
About 22% of the land drains well, and 28% stays wet for long stretches; groundwater comes within two feet of the surface under 10% of it.
USDA rates 52% of the land very limited for a standard septic drain field, and 42% very limited for homes with basements. That means extra cost or special design, not that it can't be done.
Worth knowing: 14% of the land floods occasionally or more, and bedrock lies within 40 inches under 12% 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 County, California, Western Part, 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 County, California, Western Part. 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 |
|---|---|---|---|---|---|
| Water | 52K | D | Not rated | Not rated | |
| Novato clay, ponded | 17K | Very poorly drained | D | Very limited | Very limited |
| Danville silty clay loam, 0 to 2 percent slopes | 12K | Well drained | C | Very limited | Very limited |
| Urban land | 11K | D | Not rated | Not rated | |
| Clear Lake clay, drained, 0 to 2 percent slopes, MLRA 14 | 9K | Poorly drained | D | Very limited | Very limited |
| Yolo silt loam, 0 to 3 percent slopes, dry, MLRA 14 | 6K | Well drained | B | Not limited | Somewhat limited |
| Botella loam, 0 to 2 percent slopes, MLRA 14 | 5K | Well drained | C | Not limited | Very limited |
| Urban land-Tierra complex, 2 to 5 percent slopes | 5K | Moderately well drained | D | Somewhat limited | Very limited |
| Sycamore silt loam, drained, 0 to 2 percent slopes, MLRA 14 | 5K | Poorly drained | B | Not limited | Somewhat limited |
| Xeropsamments, fill | 5K | A | Somewhat limited | Very limited | |
| Urban land-Clear Lake complex | 4K | D | Not rated | Not rated | |
| Urban land-Baywood complex | 4K | D | Not rated | Not rated | |
| Omni silty clay loam, drained | 4K | Poorly drained | C | Very limited | Very limited |
| Reyes clay, 0 to 2 percent slopes | 4K | Somewhat poorly drained | D | Very limited | Very limited |
| Novato clay, tidally flooded | 4K | Very poorly drained | C/D | Very limited | Very limited |
| Marvin silt loam, saline-alkali | 3K | Somewhat poorly drained | C | Very limited | Very limited |
| Xerorthents-Los Osos complex, 30 to 50 percent slopes | 3K | Not rated | Not rated | ||
| Xerorthents-Millsholm complex, 30 to 50 percent slopes | 3K | B | Very limited | Very limited | |
| Maymen loam, 30 to 75 percent slopes | 3K | Somewhat excessively drained | D | Very limited | Very limited |
| Urban land-Danville complex | 3K | D | Not rated | Not rated |
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 42% of soils have significant building limitations, while the rest are generally suitable. Check specific sites carefully — conditions vary across the area.
Septic Systems
About 52% 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.