Santa Monica Mountains National Recreation Area
The most common soil here is Cotharin, on about 16% of the land: a loam, a balanced mix that crumbles in your hand. Topanga and Mipolomol come next.
About 83% of the land drains well.
USDA rates 86% of the land very limited for a standard septic drain field, and 82% very limited for homes with basements. That means extra cost or special design, not that it can't be done.
Worth knowing: 1% of the land floods occasionally or more, and bedrock lies within 40 inches under 86% 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 Santa Monica Mountains National Recreation Area, 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 Santa Monica Mountains National Recreation Area. 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 |
|---|---|---|---|---|---|
| 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 |
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 82% 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 86% 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.