Multnomah County Area, Oregon
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 Multnomah County Area, Oregon.
| Soil Map Unit | Acres | Drainage | Hydro Group | Dwellings | Septic |
|---|---|---|---|---|---|
| Water | 29K | Not rated | Not rated | ||
| Zygore gravelly loam, 5 to 30 percent slopes | 17K | Well drained | B | Very limited | Very limited |
| Urban land-Multnomah complex, 0 to 3 percent slopes | 14K | Not rated | Not rated | ||
| Goble silt loam, 30 to 60 percent slopes | 12K | Well drained | C | Very limited | Very limited |
| Urban land-Latourell complex, 0 to 3 percent slopes | 10K | Not rated | Not rated | ||
| Kinzel-Divers-Goodlow association, moderately steep | 10K | Well drained | B | Very limited | Very limited |
| Aschoff-Rock outcrop-Wahkeena association, very steep | 10K | Well drained | B | Very limited | Very limited |
| Zygore gravelly loam, 30 to 60 percent slopes | 9K | Well drained | B | Very limited | Very limited |
| Kinzel-Divers-Goodlow association, steep | 8K | Well drained | B | Very limited | Very limited |
| Multnomah-Urban land complex, 0 to 3 percent slopes | 7K | Well drained | B | Not limited | Very limited |
| Kinzel-Lastance-Rubble land association, very steep | 7K | Well drained | A | Very limited | Very limited |
| Sauvie silt loam, protected | 7K | Poorly drained | C | Very limited | Very limited |
| Cascade silt loam, 15 to 30 percent slopes | 6K | Somewhat poorly drained | C | Very limited | Very limited |
| Aschoff cobbly loam, 5 to 30 percent slopes | 6K | Well drained | B | Very limited | Very limited |
| Pilchuck-Urban land complex, 0 to 3 percent slopes | 5K | Somewhat excessively drained | A | Very limited | Very limited |
| Urban land, 0 to 3 percent slopes | 5K | Not rated | Not rated | ||
| Cascade silt loam, 8 to 15 percent slopes | 5K | Somewhat poorly drained | C | Very limited | Very limited |
| Cascade silt loam, 30 to 60 percent slopes | 5K | Somewhat poorly drained | C | Very limited | Very limited |
| Sauvie silt loam | 4K | Poorly drained | C/D | Very limited | Very limited |
| Rafton silt loam, protected | 4K | Very poorly drained | B/D | Very limited | Very limited |
What This Means
Building & Foundations
About 63% of soils are rated "very limited" for dwellings with basements. Specific challenges include steep slopes, poor drainage in some areas, flood-prone areas. A geotechnical assessment is recommended before building.
Septic Systems
About 67% 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.