Sonoma County, California
The dominant drainage class is Well drained and the dominant hydrologic group is B (moderate infiltration). 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 Sonoma County, California.
| Soil Map Unit | Acres | Drainage | Hydro Group | Dwellings | Septic |
|---|---|---|---|---|---|
| Hugo very gravelly loam, 50 to 75 percent slopes | 90K | Well drained | B | Very limited | Very limited |
| Hugo-Josephine complex, 50 to 75 percent slopes | 34K | Well drained | B | Very limited | Very limited |
| Laughlin loam, 50 to 75 percent slopes | 26K | Well drained | C | Very limited | Very limited |
| Hugo loam, 30 to 50 percent slopes | 24K | Well drained | B | Very limited | Very limited |
| Reyes clay, 0 to 2 percent slopes | 24K | Somewhat poorly drained | C | Very limited | Very limited |
| Los Gatos loam, 30 to 75 percent slopes, MLRA 15 | 23K | Well drained | C | Very limited | Very limited |
| Josephine loam, 30 to 50 percent slopes | 23K | Well drained | B | Very limited | Very limited |
| Laughlin loam, 30 to 50 percent slopes | 21K | Well drained | C | Very limited | Very limited |
| Rock land | 19K | Excessively drained | Very limited | Very limited | |
| Clear Lake clay, sandy substratum, 0 to 2 percent slopes | 19K | Poorly drained | C/D | Very limited | Very limited |
| Water | 17K | D | Not rated | Not rated | |
| Josephine loam,50 to 75 percent slopes | 17K | Well drained | C | Very limited | Very limited |
| Suther loam, 30 to 50 percent slopes | 14K | Moderately well drained | D | Very limited | Very limited |
| Stonyford gravelly loam, 50 to 75 percent slopes, eroded | 14K | Well drained | D | Very limited | Very limited |
| Yorkville clay loam, 30 to 50 percent slopes | 14K | Moderately well drained | D | Very limited | Very limited |
| Yorkville-Laughlin complex, 30 to 50 percent slopes | 13K | Moderately well drained | D | Very limited | Very limited |
| Goulding clay loam, 30 to 50 percent slopes | 13K | Well drained | D | Very limited | Very limited |
| Goldridge fine sandy loam, 15 to 30 percent slopes | 12K | Moderately well drained | C | Very limited | Very limited |
| Henneke gravelly loam, 30 to 75 percent slopes, eroded | 12K | Well drained | D | Very limited | Very limited |
| Maymen gravelly sandy loam, 30 to 50 percent slopes | 12K | Well drained | D | Very limited | Very limited |
What This Means
Building & Foundations
About 96% 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.