Sonoma County, California
The most common soil here is Hugo, on about 14% of the land: a gravelly sandy clay loam, gritty but holds together. Laughlin and Josephine come next.
About 69% of the land drains well, and 9% stays wet for long stretches; groundwater comes within two feet of the surface under 6% of it.
USDA rates 96% of the land very limited for a standard septic drain field, and 89% very limited for homes with basements. That means extra cost or special design, not that it can't be done.
Worth knowing: 3% of the land floods occasionally or more, and bedrock lies within 40 inches under 44% 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 Sonoma County, 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 B (moderate infiltration). 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 Sonoma County, 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 |
|---|---|---|---|---|---|
| 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 |
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 89% 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.