Multnomah County Area, Oregon
The most common soil here is Zygore, on about 7% of the land: a gravelly loam, a balanced mix that crumbles in your hand. Cascade and Aschoff come next.
About 48% of the land drains well, and 22% stays wet for long stretches; groundwater comes within two feet of the surface under 10% of it.
USDA rates 86% of the land very limited for a standard septic drain field, and 65% very limited for homes with basements. That means extra cost or special design, not that it can't be done.
Worth knowing: 4% of the land floods occasionally or more, and bedrock lies within 40 inches under 6% 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 Multnomah County Area, Oregon, 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 Inceptisols — young soils with minimal horizon development but more than Entisols. 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. 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 |
|---|---|---|---|---|---|
| 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 | Very limited | ||
| 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 | Very limited | ||
| 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 |
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 65% 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 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.