Santa Monica Mountains National Recreation Area
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 Santa Monica Mountains National Recreation Area.
| Soil Map Unit | Acres | Drainage | Hydro Group | Dwellings | Septic |
|---|---|---|---|---|---|
| Mipolomol-Topanga association, 30 to 75 percent slopes | 31K | Well drained | D | Very limited | Very limited |
| Chumash-Boades-Malibu association, 30 to 75 percent slopes | 23K | Somewhat excessively drained | D | Very limited | Very limited |
| Topanga-Mipolomol-Sapwi association, 30 to 75 percent slopes | 19K | Well drained | D | Very limited | Very limited |
| Cotharin clay loam, 30 to 75 percent slopes | 13K | Well drained | D | Very limited | Very limited |
| Urban land-Xerorthents, landscaped complex, 0 to 5 percent slopes | 12K | D | Not rated | Not rated | |
| Cotharin-Talepop association, 15 to 50 percent slopes, MLRA 20 | 10K | Well drained | D | Very limited | Very limited |
| Linne-Los Osos, warm-Calcic Haploxerepts association, 15 to 65 percent slopes | 7K | Well drained | C | Very limited | Very limited |
| Cotharin-Talepop association, 30 to 75 percent slopes | 7K | Well drained | D | Very limited | Very limited |
| Rock outcrop-Sumiwawa-Hipuk complex, 30 to 75 percent slopes | 7K | D | Not rated | Not rated | |
| Zumaridge-Kawenga association, 30 to 75 percent slopes | 5K | Well drained | D | Very limited | Very limited |
| Cotharin loam-Rock outcrop complex, very bouldery, 30 to 75 percent slopes | 4K | Well drained | D | Very limited | Very limited |
| Gaviota-Rock outcrop association, 50 to 100 percent slopes | 4K | Somewhat excessively drained | D | Very limited | Very limited |
| Xerorthents-Urban land-Balcom complex, 0 to 15 percent slopes | 3K | Well drained | C | Somewhat limited | Very limited |
| Tongva-Cotharin-Rock outcrop complex, 30 to 75 percent slopes | 2K | Well drained | D | Very limited | Very limited |
| Sumiwawa-Hipuk-Rock outcrop complex, 30 to 75 percent slopes | 2K | Somewhat excessively drained | D | Very limited | Very limited |
| Balcom silty clay loam, 30 to 50 percent slopes, MLRA 20 | 2K | Well drained | C | Very limited | Very limited |
| Malibu-Chumash-Boades association, 15 to 50 percent slopes | 2K | Moderately well drained | D | Very limited | Very limited |
| Calcic Haploxerepts-Mollic Haploxeralfs association, 30 to 75 percent slopes | 2K | Well drained | C | Very limited | Very limited |
| Zumaridge-Sapwi-Kawenga association, bouldery, 30 to 75 percent slopes | 2K | Well drained | D | Very limited | Very limited |
| Cotharin loam, 30 to 75 percent slopes, dry | 1K | Well drained | D | Very limited | Very limited |
What This Means
Building & Foundations
About 86% of soils are rated "very limited" for dwellings with basements. Specific challenges include shallow bedrock, steep slopes. A geotechnical assessment is recommended before building.
Septic Systems
About 87% 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.